Metamorphic Zircons Applied for Dating East African Tectono-Metamorphic Event in Central Mozambique

*Vicente Albino Manjate*

## **Abstract**

The term East African is now used to describe the tectonic, magmatic, and metamorphic activity of Neoproterozoic to earliest Paleozoic age. Metamorphic zircon is the most suitable geochronometer for the determination of both protolithic and metamorphic ages due to its high closure temperature. The study area comprises the Mungari and Macossa-Chimoio nappes (Central Mozambique) tectonically juxtaposed to the Archaean Zimbabwe Craton. We use the metamorphic zircon morphology, Th/U ratios, and U-Pb ages to evaluate the Tectono-Metamorphic Event in central Mozambique. Morphologically, the zircon grains are sub-euhedral to euhedral, prismatic, with dark to gray cores, and narrow dark rims. The cores exhibit homogenous domains and oscillatory zoning. On the other hand, the U-Pb zircon data define Th/U ratios of 0.26–0.66 and 0.06–0.11. Finally, the U-Pb zircon analyses define upper intercept age of 1094 ± 36 Ma and lower intercept age of 498 ± 30 Ma. The zircon grains of the Macossa-Chimoio nappe was metamorphically re-homogenized or recrystallized by East African tectono-metamorphic event from relicts of Mesoproterozoic protolith domains. Thrusting and folding are the main East African reworking mechanisms that generated the metamorphic re-homogenization or recrystallization of the Mesoproterozoic magmatic rocks in the Macossa-Chimoio nappe of Central Mozambique.

**Keywords:** metamorphic zircon, protolith, East African, tectono-metamorphic, Macossa-Chimoio nappe, Mungari nappe

## **1. Introduction**

Zircon is a fundamental secondary mineral of granitic rocks, very unsusceptible to sedimentary and metamorphic processes [1]. The term 'metamorphic zircon' is used to describe zircon that has formed in rocks under system-wide metamorphic conditions by a range of different processes [2]. According to [2], the main processes include precipitation from the melt during anatectic melting, sub-solidus nucleation and crystallization (blastogenesis) by diffusion of Zr and Si released from metamorphic breakdown reactions of major silicates and accessory phases,

#### **Figure 1.**

*Geologic setting of the study area. (a) Regional geologic unities and (b) geology of the Macossa-Chimoio and Mungari nappes. Modified from [5–8].*

precipitation from aqueous metamorphic fluid, and protolith zircon recrystallization. For these authors, knowing which process is responsible for the genesis of 'metamorphic zircon' in a particular sample is crucial for the correct interpretation of U-Pb isotopic data and derived ages, and consequently the interpretations of whole-rock petrogenesis.

**27**

*Metamorphic Zircons Applied for Dating East African Tectono-Metamorphic Event in Central…*

• Accurate with an external error of ~1%; • fast with the time of analyses ~10–15 min; • Primary beam analytical spot size = 30 μm

• High cost partly limits its wide application

• Ultrahigh precision in U-Pb dating

• Requires ultraclean laboratory; • The sample preparation is time-consuming

**Method LA-ICP-MS SHRIMP TIMS** Applicability • U-Pb zircon • U-Pb zircon, titanite • U-Pb zircon

The term East African is applied to illustrate the tectonism, magmatism, and metamorphism that took place on Neoproterozoic to earliest Paleozoic, mainly for a crust that was formally portion of Gondwana [3]. The term 'East African' was suggested by [4] supported on isotopic ages of Africa by Rb-Sr and K-Ar methods. According to [3], the East African was explained as a Neoproterozoic tectono-thermal event (~500 Ma) during which a number of mobile belts produced, bounding older cratons. This tectono-thermal event constitutes the final stage of an orogenic cycle, conducting to orogenic belts presently interpreted as a consequence of the fusion of continental blocks throughout the time interval from ~870 to ~550 Ma [3]. The study area comprises the nappes of Macossa-Chimoio and Mungari [5] (**Figure 1**). According to [5], the northern Mungari nappe is composed of metasedimentary supracrustal rocks intruded by a set of granitoid plutons. On the other hand, the southern Macossa-Chimoio nappe is composed of orthomagmatic rocks covered by medium to high-grade supracrustal rocks. In addition, both nappe

*Summary of the applicability, advantage, and disadvantage of the LA-ICP\_MS, SHRIMP, and TIMS dating* 

complexes include detrital zircon grains with Neoproterozoic age [6].

protoliths from complexly deformed and metamorphosed lithologies.

**2. Geological and tectonic setting**

We use the metamorphic zircon morphology, Th/U ratios, and 207Pb/206Pb ages to evaluate the East African tectono-metamorphic event in Central Mozambique. Although the SHRIMP technique is very expensive, its advantages in comparison to other dating techniques are in favour of the geochronological data determination for this study (**Table 1**). One of the most important legacies of SHRIMP U-Pb dating on zircons is the extraction of crystallization and recrystallization ages of igneous

The study area (**Figure 1**) comprises rocks of the Neoproterozoic Mungari and the Mesoproterozoic Macossa-Chimoio nappes tectonically juxtaposed to the Archaean Zimbabwe Craton [5–7]. The Neoproterozoic Mungari nappe is composed of garnet gneiss-granite plutons of about 850 Ma intruding meta-sedimentary rocks consisting of marbles with calc-silicate interbeds [7]. This nappe is delimited on the west, north and east by Neoproterozoic (~850 Ma) bimodal Guro Suite and on

*DOI: http://dx.doi.org/10.5772/intechopen.88514*

Disadvantage • Does not always produce

error

*Modified from [11, 14, 27].*

**Table 1.**

*techniques.*

• Very quick (~2 min per analysis); • Fairly precise with an internal error of ~1%; • Spot size = 29 μm;

• Excellent sensitivity, precision and good accuracy for isotope ratio measurements

consistent results within

Advantage • Relatively cheap;

*Metamorphic Zircons Applied for Dating East African Tectono-Metamorphic Event in Central… DOI: http://dx.doi.org/10.5772/intechopen.88514*


#### **Table 1.**

*Isotopes Applications in Earth Sciences*

**26**

**Figure 1.**

whole-rock petrogenesis.

*Mungari nappes. Modified from [5–8].*

precipitation from aqueous metamorphic fluid, and protolith zircon recrystallization. For these authors, knowing which process is responsible for the genesis of 'metamorphic zircon' in a particular sample is crucial for the correct interpretation of U-Pb isotopic data and derived ages, and consequently the interpretations of

*Geologic setting of the study area. (a) Regional geologic unities and (b) geology of the Macossa-Chimoio and* 

*Summary of the applicability, advantage, and disadvantage of the LA-ICP\_MS, SHRIMP, and TIMS dating techniques.*

The term East African is applied to illustrate the tectonism, magmatism, and metamorphism that took place on Neoproterozoic to earliest Paleozoic, mainly for a crust that was formally portion of Gondwana [3]. The term 'East African' was suggested by [4] supported on isotopic ages of Africa by Rb-Sr and K-Ar methods. According to [3], the East African was explained as a Neoproterozoic tectono-thermal event (~500 Ma) during which a number of mobile belts produced, bounding older cratons. This tectono-thermal event constitutes the final stage of an orogenic cycle, conducting to orogenic belts presently interpreted as a consequence of the fusion of continental blocks throughout the time interval from ~870 to ~550 Ma [3].

The study area comprises the nappes of Macossa-Chimoio and Mungari [5] (**Figure 1**). According to [5], the northern Mungari nappe is composed of metasedimentary supracrustal rocks intruded by a set of granitoid plutons. On the other hand, the southern Macossa-Chimoio nappe is composed of orthomagmatic rocks covered by medium to high-grade supracrustal rocks. In addition, both nappe complexes include detrital zircon grains with Neoproterozoic age [6].

We use the metamorphic zircon morphology, Th/U ratios, and 207Pb/206Pb ages to evaluate the East African tectono-metamorphic event in Central Mozambique. Although the SHRIMP technique is very expensive, its advantages in comparison to other dating techniques are in favour of the geochronological data determination for this study (**Table 1**). One of the most important legacies of SHRIMP U-Pb dating on zircons is the extraction of crystallization and recrystallization ages of igneous protoliths from complexly deformed and metamorphosed lithologies.

#### **2. Geological and tectonic setting**

The study area (**Figure 1**) comprises rocks of the Neoproterozoic Mungari and the Mesoproterozoic Macossa-Chimoio nappes tectonically juxtaposed to the Archaean Zimbabwe Craton [5–7]. The Neoproterozoic Mungari nappe is composed of garnet gneiss-granite plutons of about 850 Ma intruding meta-sedimentary rocks consisting of marbles with calc-silicate interbeds [7]. This nappe is delimited on the west, north and east by Neoproterozoic (~850 Ma) bimodal Guro Suite and on

the south by the Macossa-Chimoio nappe [7, 8]. The Mesoproterozoic Macossa-Chimoio nappe consists of medium- to high-grade supracrustal rocks composed of quartz-feldspar gneiss, deformed granodiorite, deformed granite, garnetiferous leucocratic gneiss, meta-arkose with amphibolite, calc-silicate gneiss, feldspathic quartzite, and leucocratic gneiss [7, 8]. According to [8], in the north, the Macossa-Chimoio nappe terminates into a northward-directed arcuate thrust (**Figure 1**). For [8], the Macossa-Chimoio nappe consists of supracrustal rocks most likely derived from sedimentary precursors, originally deposited in a shallow marine paleobasin. Although the definitive character and position of all units observed within the supracrustal rocks succession are not fully solved, the overall lithostratigraphy of the paleobasin has been reduced by [8] from several geological sections made in the area [9, 10]. The lowermost rock units of the inferred paleobasin include garnetiferous leucocratic gneisses, quartz-feldspar gneisses, meta-arkoses, and arkosic quartzites. These psammitic metasediments are overlain by more pelitic rocks (metagreywackes, garnet, and sillimanite bearing mica schist and mica gneisses) with thin calc-silicate gneiss and marble interbeds.

The Macossa-Chimoio nappe is delimited by a number of structural domains. According to [8], the eastern margin of the Mesoproterozoic Macossa-Chimoio nappe is bounded by a set of rift faults/dykes 'corridor' against the Karoo and younger formations and partly remains covered by recent sediments, the western margin is a major N-S directed sinistral shear zone along the Archaean cratonic margin, in the north the nappe terminates into a northward-directed thrust, and in the south the rocks of the nappe become covered by Phanerozoic beds. According to [8], the northward thrusting of the northern part of the Macossa-Chimoio nappe over the Mungári nappe gneisses may be attributed to the East African collision, the sinistral shearing is a regional feature in the East Africa orogeny, and the set of rift faults/dykes 'corridor' against the Karoo and younger formations are normal faults with dip values commonly ranging from 45 to 60°.

The granitic pluton (deformed granite) selected for this study is located at the northern end of the Macossa-Chimoio nappe and was emplaced parallel to the foliation of the host gneisses and migmatites. The rock is a pinkish to pinkish gray, medium- to coarse-grained, weakly deformed leucogranite and is mainly composed of quartz, pinkish potassium feldspar, plagioclase, hornblende, and biotite. Accessory minerals include garnet, clinopyroxene, orthopyroxene, zircon, apatite, and opaques.

## **3. Analytical procedures**

Zircon dating analyses by sensitive high-resolution ion microprobe (SHRIMP) U-Pb were performed at the São Paulo University, Brazil. This technique is very important for geochronological studies [11] as it permits *in situ* analyses of complex zircons grains often exhibiting several crystallization phases associated with different geological processes [12]. According to [12], the SHRIMP technique has an improving spatial resolution for dating with precision the different growth episodes on single zircon grains. Zircon crystals were separated utilizing the common manually breaking, crushing and grinding of samples, followed by grain size separation by sieving. The material (100–200 mesh portion) was deposited on a vibrating Wilfley table, and heavy minerals were then densimetrically separated using bromoform (d = 2.89 g/ml; 20°C) and methylene iodide (d = 3.32 g/ml; 20°C). The dense material (density above 3.32 g/ml) was then electromagnetically separated using a Frantz separator. The magnetic minerals were separated using a hand magnet and the paramagnetic minerals were separated by a Frantz

**29**

**Figure 3.**

**Figure 2.**

*Metamorphic Zircons Applied for Dating East African Tectono-Metamorphic Event in Central…*

*Reflected and transmitted light images of the deformed granite zircons. Photograph length of 2.3 mm.*

magnetic separator (amperage variation). Zircon crystals are concentrated in the non-magnetic portion. Zircon crystals along with zircon standards were picked by hand, impregnated in epoxy resin mounts with a diameter of 2.54 cm, ground and polished with diamond compound (1–7 μm) to reveal grain centers and carbon coated as well as cleaned and gold-coated in preparation for the SHRIMP analyses. Reflected and transmitted light images (**Figure 2**) were acquired before the gold coating of 2–3 μm. Zircons internal structures were microphotographed in transmitted and reflected light and characterized by the use of cathodoluminescence (CL) images from scanning electron microscope prior to SHRIMP U-Pb zircon isotopic analyses. CL images of representative zircon crystals can be seen in **Figure 3**. After CL acquisition, the gold was removed and the mount was re-cleaned. The U-Pb zircon dating analyses were made using a SHRIMP IIe/MC mass spectrometer

*CL image of zircons with selected analyses locations (spots) by SHRIMP IIe/MC.*

*DOI: http://dx.doi.org/10.5772/intechopen.88514*

*Metamorphic Zircons Applied for Dating East African Tectono-Metamorphic Event in Central… DOI: http://dx.doi.org/10.5772/intechopen.88514*

#### **Figure 2.**

*Isotopes Applications in Earth Sciences*

with thin calc-silicate gneiss and marble interbeds.

with dip values commonly ranging from 45 to 60°.

the south by the Macossa-Chimoio nappe [7, 8]. The Mesoproterozoic Macossa-Chimoio nappe consists of medium- to high-grade supracrustal rocks composed of quartz-feldspar gneiss, deformed granodiorite, deformed granite, garnetiferous leucocratic gneiss, meta-arkose with amphibolite, calc-silicate gneiss, feldspathic quartzite, and leucocratic gneiss [7, 8]. According to [8], in the north, the Macossa-Chimoio nappe terminates into a northward-directed arcuate thrust (**Figure 1**). For [8], the Macossa-Chimoio nappe consists of supracrustal rocks most likely derived from sedimentary precursors, originally deposited in a shallow marine paleobasin. Although the definitive character and position of all units observed within the supracrustal rocks succession are not fully solved, the overall lithostratigraphy of the paleobasin has been reduced by [8] from several geological sections made in the area [9, 10]. The lowermost rock units of the inferred paleobasin include garnetiferous leucocratic gneisses, quartz-feldspar gneisses, meta-arkoses, and arkosic quartzites. These psammitic metasediments are overlain by more pelitic rocks (metagreywackes, garnet, and sillimanite bearing mica schist and mica gneisses)

The Macossa-Chimoio nappe is delimited by a number of structural domains. According to [8], the eastern margin of the Mesoproterozoic Macossa-Chimoio nappe is bounded by a set of rift faults/dykes 'corridor' against the Karoo and younger formations and partly remains covered by recent sediments, the western margin is a major N-S directed sinistral shear zone along the Archaean cratonic margin, in the north the nappe terminates into a northward-directed thrust, and in the south the rocks of the nappe become covered by Phanerozoic beds. According to [8], the northward thrusting of the northern part of the Macossa-Chimoio nappe over the Mungári nappe gneisses may be attributed to the East African collision, the sinistral shearing is a regional feature in the East Africa orogeny, and the set of rift faults/dykes 'corridor' against the Karoo and younger formations are normal faults

The granitic pluton (deformed granite) selected for this study is located at the northern end of the Macossa-Chimoio nappe and was emplaced parallel to the foliation of the host gneisses and migmatites. The rock is a pinkish to pinkish gray, medium- to coarse-grained, weakly deformed leucogranite and is mainly composed of quartz, pinkish potassium feldspar, plagioclase, hornblende, and biotite. Accessory minerals include garnet, clinopyroxene, orthopyroxene, zircon, apatite,

Zircon dating analyses by sensitive high-resolution ion microprobe (SHRIMP) U-Pb were performed at the São Paulo University, Brazil. This technique is very important for geochronological studies [11] as it permits *in situ* analyses of complex zircons grains often exhibiting several crystallization phases associated with different geological processes [12]. According to [12], the SHRIMP technique has an improving spatial resolution for dating with precision the different growth episodes on single zircon grains. Zircon crystals were separated utilizing the common manually breaking, crushing and grinding of samples, followed by grain size separation by sieving. The material (100–200 mesh portion) was deposited on a vibrating Wilfley table, and heavy minerals were then densimetrically separated using bromoform (d = 2.89 g/ml; 20°C) and methylene iodide (d = 3.32 g/ml; 20°C). The dense material (density above 3.32 g/ml) was then electromagnetically separated using a Frantz separator. The magnetic minerals were separated using a hand magnet and the paramagnetic minerals were separated by a Frantz

**28**

and opaques.

**3. Analytical procedures**

*Reflected and transmitted light images of the deformed granite zircons. Photograph length of 2.3 mm.*

#### **Figure 3.**

*CL image of zircons with selected analyses locations (spots) by SHRIMP IIe/MC.*

magnetic separator (amperage variation). Zircon crystals are concentrated in the non-magnetic portion. Zircon crystals along with zircon standards were picked by hand, impregnated in epoxy resin mounts with a diameter of 2.54 cm, ground and polished with diamond compound (1–7 μm) to reveal grain centers and carbon coated as well as cleaned and gold-coated in preparation for the SHRIMP analyses. Reflected and transmitted light images (**Figure 2**) were acquired before the gold coating of 2–3 μm. Zircons internal structures were microphotographed in transmitted and reflected light and characterized by the use of cathodoluminescence (CL) images from scanning electron microscope prior to SHRIMP U-Pb zircon isotopic analyses. CL images of representative zircon crystals can be seen in **Figure 3**. After CL acquisition, the gold was removed and the mount was re-cleaned. The U-Pb zircon dating analyses were made using a SHRIMP IIe/MC mass spectrometer



**31**

(1

**Figure**

**Figure 4.**

*Macossa-Chimoio nappe.*

**4** are 1

are considered at (1

**4. Results and discussions**

*Metamorphic Zircons Applied for Dating East African Tectono-Metamorphic Event in Central…*

and zircon standards designated Temora 2 [13]. As described in [14], this consisted of measuring U, Pb and Th abundances, and isotopic relationships of these elements in zircon crystals. The precision of the U, Pb and Th zircons analytical data obtained by SHRIMP IIe at São Paulo University Laboratory is of the same standard when compared to the data from leading laboratories worldwide [14]. The reduction of raw data was carried out using SQUID 1.06 [15]. Common lead corrections usually

*Concordia diagram of zircon U-Pb isotope data analyzed by SHRIMP IIe/MC for the deformed granite,* 

inherited cores on CL images. Results from recrystallized domains and inherited cores were not used in the final age determination. Results above 10% discordance

σ) and/or with extremely big errors originated by a correction of common lead were also not used in the final age determination. Age determination and Concordia diagram processed using ISOPLOT of version 4.0 [15]. Errors shown in **Table**

were discarded until obtaining an acceptable mean square of weighted deviations (MSWD). The remaining U-Pb zircon dating results were used to determine the magmatic and metamorphic ages. All age errors in the text and Concordia diagram

Zircon morphology and internal structure provide an important tool for discern

ing their growth stages and genesis. Zircons of our study are products of anatectic melt, altered by metamorphic fluid and hydrothermal alteration. Anatectic melt, metamorphic fluid, and hydrothermal alteration are important factors control

ling the morphology and internal structure of zircons overgrowths [17]. Zircons crystallizing from anatectic melts also have a euhedral shape with no zoning, planar zoning or oscillatory zoning. In addition, zircons altered by the metamorphic fluid

σ levels. In a situation of evident Pb-loss, consecutive younger results

**2** and projected in the

**2** and



**4**). There is evidence of recrystallized domains and

*DOI: http://dx.doi.org/10.5772/intechopen.88514*

use 204Pb according to [16].

Concordia diagram (see **Figure**

σ).

**4.1 Zircon morphology and internal structure**

The U-Pb zircon dating results are shown in **Table**

*Metamorphic Zircons Applied for Dating East African Tectono-Metamorphic Event in Central… DOI: http://dx.doi.org/10.5772/intechopen.88514*

#### **Figure 4.**

*Isotopes Applications in Earth Sciences*

**30**

**Spot**

**206Pbc** 

**U** 

**Th** 

**232Th/238**

**U**

**206Pb\*** 

**Ages (Ma) corrected to 204Pb**

**Disc** 

**Ratios corrected to 204Pb**

**Error** 

**correl**

**(%)**

**(ppm)**

**206P/238**

**U**

**Error** 

**207Pb/206Pb**

**Error** 

**207Pb\*/235**

**U**

**Error (%)**

**206Pb\*/238**

**U**

**Error** 

**(%)**

**(%)**

**(%)**

**(%)**

Amostra 15FR09

**1.1c** **2.1r** **2.2c** **3.1c** **4.1c** **5.1c** **6.1c**

**7.1r** **7.2c** **8.1c** **9.1c** **10.1r** **11.1c** **12.1c** **13.1c** **14.1c** *\*Total radiogenic.*

**Table 2.**

*Analytical data for zircons from the deformed granite, Macossa-Chimoio nappe.*

0.32

110

70

0.66

17.1

1066.0

13.2

1032

35

−3

1.83

2.2

.1798

1.3

.610

0.15

250

145

0.60

34.4

957.5

11.3

1025

23

7

1.62

1.7

.1601

1.3

.751

0.09

288

111

0.40

44.2

1060.1

12.5

1115

16

5

1.89

1.5

.1787

1.3

.847

0.29

238

97

0.42

26.5

782.2

9.5

872

31

11

1.21

2.0

.1290

1.3

.650

0.20

860

95

0.11

59.4

497.7

5.8

510

23

2

0.64

1.6

.0803

1.2

.755

0.05

275

165

0.62

39.7

1000.6

11.6

1057

14

6

1.73

1.4

.1679

1.2

.871

0.06

279

98

0.36

42.6

1056.0

13.9

1136

16

8

1.90

1.6

.1780

1.4

.871

0.07

243

135

0.57

39.9

1127.8

13.1

1114

15

−1

2.02

1.5

.1912

1.3

.856

0.39

942

56

0.06

69.0

525.8

6.2

515

38

−2

0.67

2.1

.0850

1.2

.580

0.05

206

94

0.47

27.6

933.4

11.8

1030

27

10

1.58

1.9

.1558

1.4

.708

0.14

472

133

0.29

65.5

963.1

11.0

971

23

1

1.59

1.7

.1611

1.2

.740

−0.05

210

100

0.49

30.5

1006.4

12.0

1053

30

5

1.73

2.0

.1690

1.3

.656

0.06

175

74

0.43

27.7

1090.8

13.0

1136

19

4

1.97

1.6

.1844

1.3

.804

0.38

275

69

0.26

31.3

799.9

15.9

875

43

9

1.24

3.0

.1321

2.1

.714

0.01

890

88

0.10

61.3

497.0

5.8

542

16

9

0.64

1.4

.0801

1.2

.861

0.19

127

55

0.44

21.6

1159.5

15.0

1102

77

−5

2.07

4.1

.1971

1.4

.346

**(ppm)**

**(ppm)**

*Concordia diagram of zircon U-Pb isotope data analyzed by SHRIMP IIe/MC for the deformed granite, Macossa-Chimoio nappe.*

and zircon standards designated Temora 2 [13]. As described in [14], this consisted of measuring U, Pb and Th abundances, and isotopic relationships of these elements in zircon crystals. The precision of the U, Pb and Th zircons analytical data obtained by SHRIMP IIe at São Paulo University Laboratory is of the same standard when compared to the data from leading laboratories worldwide [14]. The reduction of raw data was carried out using SQUID 1.06 [15]. Common lead corrections usually use 204Pb according to [16].

The U-Pb zircon dating results are shown in **Table 2** and projected in the Concordia diagram (see **Figure 4**). There is evidence of recrystallized domains and inherited cores on CL images. Results from recrystallized domains and inherited cores were not used in the final age determination. Results above 10% discordance (1σ) and/or with extremely big errors originated by a correction of common lead were also not used in the final age determination. Age determination and Concordia diagram processed using ISOPLOT of version 4.0 [15]. Errors shown in **Table 2** and **Figure 4** are 1σ levels. In a situation of evident Pb-loss, consecutive younger results were discarded until obtaining an acceptable mean square of weighted deviations (MSWD). The remaining U-Pb zircon dating results were used to determine the magmatic and metamorphic ages. All age errors in the text and Concordia diagram are considered at (1σ).

#### **4. Results and discussions**

#### **4.1 Zircon morphology and internal structure**

Zircon morphology and internal structure provide an important tool for discerning their growth stages and genesis. Zircons of our study are products of anatectic melt, altered by metamorphic fluid and hydrothermal alteration. Anatectic melt, metamorphic fluid, and hydrothermal alteration are important factors controlling the morphology and internal structure of zircons overgrowths [17]. Zircons crystallizing from anatectic melts also have a euhedral shape with no zoning, planar zoning or oscillatory zoning. In addition, zircons altered by the metamorphic fluid

are usually homogenous with high CL intensity, showing resorption structure. Moreover, zircon domains that lost all radioactive Pb during hydrothermal alteration always show white color in CL image. The study made on deformed granite showed that the zircon grains are inherited from older crustal rocks or metamorphically re-homogenized or recrystallized from relicts of magmatic protolith domains. These zircon grains range in size from 250 to 400 μm of length, and 125 μm of width with length/width ratios of 2:1–3.2:1. In addition, they are colorless and transparent (**Figure 2**), sub-euhedral to euhedral with elongated prismatic shapes. Moreover, these zircon grains exhibit narrow dark rims and dark to gray cores with some homogenous domains and other domains of compositional or oscillatory zoning (**Figure 3**), being thus strongly re-homogenized. Therefore, the zircons of our study are products of anatectic melts or altered by metamorphic and hydrothermal fluids.

#### **4.2 Genesis and recrystallization of the metamorphic zircons**

Sixteen analyses spots (cores and rims) in 14 zircon grains from the deformed granite for Th/U ratios and 207Pb/206Pb ages determinations (**Table 2**). These analyses spots define two groups based on Th/U ratios and apparent 207Pb/206Pb ages. The first group is defined by cores with U grades from 110 to 472 ppm (averaging 242 ppm) and Th ranging from 55 to 165 ppm (averaging 104 ppm). This result in Th/U ratios from 0.26 to 0.66 and 207Pb/206Pb ages varying from 872 ± 31 to 1136 ± 19 Ma. The other group is represented by rims with U grades ranging from 860 to 942 ppm (average of 890 ppm) and Th ranging from 56 to 95 ppm (average of 80 ppm). This result in Th/U ratios from 0.06 to 0.11 (average of 0.09) and 207Pb/206Pb ages varying from 510 ± 23 to 542 ± 16 Ma. The age data follow a regression line (**Figure 4**) that allowed to determine the upper intercept age of 1094 ± 36 Ma and lower intercept age of 498 ± 30 Ma (MSWD = 1.07).

Th/U ratios are used as indicators of zircon types. The Th/U ratios of magmatic zircons are commonly between 0.32 and 0.70, whereas hydrothermal zircons frequently have more extreme values [18–20]. Proposed that Th/U ratios <0.1 are probably a hint for hydrothermal origin. Therefore, the studied zircons are products of metamorphic re-homogenization or recrystallization from relicts of magmatic protoliths.

The studied metamorphic zircons registered two events. The magmatic protolith domains crystalized at ~1094 ± 36 Ma. This was followed by re-homogenization or recrystallization related to northward-directed thrusting and folding at ~498 ± 30 Ma of the Chimoio-Macossa nappe [5]. Using LA-ICP-MS U/Pb zircon for leucocratic gneiss (sample 14FR09, **Figure 1**) of Chimoio-Macossa nappe found 207Pb/206Pb crystallization age of 1067.8 ± 9.0 Ma and a metamorphic age of 504 ± 1.8 Ma. These age determinations are in accordance with that of [21] for the Macossa-Chimoio nappe. According to Yuanbao (2004), the time of metamorphic recrystallization is represented by the age of recrystallized zircon domain with the lowest Th/U ratio and the youngest U-Pb age.

The Cambrian U-Pb ages are found in both cores and rims of the Mesoproterozoic Macossa-Chimoio nappe rocks. Manjate [22] found a Neoproterozoic-Cambrian recrystallization age (498 ± 19–562 ± 14 Ma) on zircon cores of the Dongueni Mount nepheline syenite generated from partial melting of Mesoproterozoic crust, as shown by inherited zircon ages of 1040 ± 14 (15) Ma. The Cambrian magmatism, defined by zircon U-Pb dates of c. 490 Ma, from Dongueni Mount nepheline syenite, southeast of Chimoio village [23], is post-collisional and marks the end stage of East African Orogeny. Therefore, zircons are suitable for dating the tectono-metamorphic Neoproterozoic-Cambrian event that affected the Macossa-Chimoio nappe. The Neoproterozoic-Cambrian recrystallization ages on zircon were the common determinations made by a number of authors [23–26].

**33**

**Author details**

Vicente Albino Manjate

National Institute of Mines, Maputo, Mozambique

provided the original work is properly cited.

\*Address all correspondence to: vmanjate@yahoo.com.br

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*Metamorphic Zircons Applied for Dating East African Tectono-Metamorphic Event in Central…*

Zircons are appropriate for dating the tectono-metamorphic Neoproterozoic-Cambrian event that affected the Macossa-Chimoio nappe. The studied zircon grains exhibit narrow dark rims and dark to gray cores with some homogenous domains and other domains of compositional or oscillatory zoning, as well as, Th/U ratios less than 0.3 which are evidence of metamorphic re-homogenization or

Thrusting and folding are the main East African Neoproterozoic-Cambrian reworking mechanisms (ca. 498 ± 30 Ma) that generated the metamorphic rehomogenization or recrystallization of the Mesoproterozoic magmatic rocks (ca.

This study results from the PhD project involving the cooperation of institutions (CNPQ and PRO-AFRICA, Brazil, and the National Institute of Mines, Mozambique) in the form of financial support and services. The author thanks Centro de Pesquisas Geocronologicas (CPGeo) of IGc/USP for the U-Pb zircon analyses and anonymous reviewers for their careful comments that have improved

recrystallization from relicts of magmatic protolith domains.

The author declares that there is no conflict of interest.

1094 ± 36 Ma) in the Macossa-Chimoio nappe of Central Mozambique.

*DOI: http://dx.doi.org/10.5772/intechopen.88514*

**5. Conclusions**

**Acknowledgements**

the manuscript remarkably.

**Conflict of interest**

*Metamorphic Zircons Applied for Dating East African Tectono-Metamorphic Event in Central… DOI: http://dx.doi.org/10.5772/intechopen.88514*

## **5. Conclusions**

*Isotopes Applications in Earth Sciences*

are usually homogenous with high CL intensity, showing resorption structure. Moreover, zircon domains that lost all radioactive Pb during hydrothermal alteration always show white color in CL image. The study made on deformed granite showed that the zircon grains are inherited from older crustal rocks or metamorphically re-homogenized or recrystallized from relicts of magmatic protolith domains. These zircon grains range in size from 250 to 400 μm of length, and 125 μm of width with length/width ratios of 2:1–3.2:1. In addition, they are colorless and transparent (**Figure 2**), sub-euhedral to euhedral with elongated prismatic shapes. Moreover, these zircon grains exhibit narrow dark rims and dark to gray cores with some homogenous domains and other domains of compositional or oscillatory zoning (**Figure 3**), being thus strongly re-homogenized. Therefore, the zircons of our study are products of anatectic melts or altered by metamorphic and hydrothermal fluids.

**4.2 Genesis and recrystallization of the metamorphic zircons**

1094 ± 36 Ma and lower intercept age of 498 ± 30 Ma (MSWD = 1.07).

re-homogenization or recrystallization from relicts of magmatic protoliths.

The Cambrian U-Pb ages are found in both cores and rims of the Mesoproterozoic Macossa-Chimoio nappe rocks. Manjate [22] found a

Neoproterozoic-Cambrian recrystallization age (498 ± 19–562 ± 14 Ma) on zircon cores of the Dongueni Mount nepheline syenite generated from partial melting of Mesoproterozoic crust, as shown by inherited zircon ages of 1040 ± 14 (15) Ma. The Cambrian magmatism, defined by zircon U-Pb dates of c. 490 Ma, from Dongueni Mount nepheline syenite, southeast of Chimoio village [23], is post-collisional and marks the end stage of East African Orogeny. Therefore, zircons are suitable for dating the tectono-metamorphic Neoproterozoic-Cambrian event that affected the Macossa-Chimoio nappe. The Neoproterozoic-Cambrian recrystallization ages on zircon were the common determinations made by a number of authors [23–26].

lowest Th/U ratio and the youngest U-Pb age.

Sixteen analyses spots (cores and rims) in 14 zircon grains from the deformed granite for Th/U ratios and 207Pb/206Pb ages determinations (**Table 2**). These analyses spots define two groups based on Th/U ratios and apparent 207Pb/206Pb ages. The first group is defined by cores with U grades from 110 to 472 ppm (averaging 242 ppm) and Th ranging from 55 to 165 ppm (averaging 104 ppm). This result in Th/U ratios from 0.26 to 0.66 and 207Pb/206Pb ages varying from 872 ± 31 to 1136 ± 19 Ma. The other group is represented by rims with U grades ranging from 860 to 942 ppm (average of 890 ppm) and Th ranging from 56 to 95 ppm (average of 80 ppm). This result in Th/U ratios from 0.06 to 0.11 (average of 0.09) and 207Pb/206Pb ages varying from 510 ± 23 to 542 ± 16 Ma. The age data follow a regression line (**Figure 4**) that allowed to determine the upper intercept age of

Th/U ratios are used as indicators of zircon types. The Th/U ratios of magmatic zircons are commonly between 0.32 and 0.70, whereas hydrothermal zircons frequently have more extreme values [18–20]. Proposed that Th/U ratios <0.1 are probably a hint for hydrothermal origin. Therefore, the studied zircons are products of metamorphic

The studied metamorphic zircons registered two events. The magmatic protolith

domains crystalized at ~1094 ± 36 Ma. This was followed by re-homogenization or recrystallization related to northward-directed thrusting and folding at ~498 ± 30 Ma of the Chimoio-Macossa nappe [5]. Using LA-ICP-MS U/Pb zircon for leucocratic gneiss (sample 14FR09, **Figure 1**) of Chimoio-Macossa nappe found 207Pb/206Pb crystallization age of 1067.8 ± 9.0 Ma and a metamorphic age of 504 ± 1.8 Ma. These age determinations are in accordance with that of [21] for the Macossa-Chimoio nappe. According to Yuanbao (2004), the time of metamorphic recrystallization is represented by the age of recrystallized zircon domain with the

**32**

Zircons are appropriate for dating the tectono-metamorphic Neoproterozoic-Cambrian event that affected the Macossa-Chimoio nappe. The studied zircon grains exhibit narrow dark rims and dark to gray cores with some homogenous domains and other domains of compositional or oscillatory zoning, as well as, Th/U ratios less than 0.3 which are evidence of metamorphic re-homogenization or recrystallization from relicts of magmatic protolith domains.

Thrusting and folding are the main East African Neoproterozoic-Cambrian reworking mechanisms (ca. 498 ± 30 Ma) that generated the metamorphic rehomogenization or recrystallization of the Mesoproterozoic magmatic rocks (ca. 1094 ± 36 Ma) in the Macossa-Chimoio nappe of Central Mozambique.

## **Acknowledgements**

This study results from the PhD project involving the cooperation of institutions (CNPQ and PRO-AFRICA, Brazil, and the National Institute of Mines, Mozambique) in the form of financial support and services. The author thanks Centro de Pesquisas Geocronologicas (CPGeo) of IGc/USP for the U-Pb zircon analyses and anonymous reviewers for their careful comments that have improved the manuscript remarkably.

## **Conflict of interest**

The author declares that there is no conflict of interest.

## **Author details**

Vicente Albino Manjate National Institute of Mines, Maputo, Mozambique

\*Address all correspondence to: vmanjate@yahoo.com.br

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

## **References**

[1] Martins HCB, Simões PP, Abreu J. Zircon crystal morphology and internal structures as a tool for constraining magma sources: Examples from northern Portugal Variscan biotite-rich granite plutons. Comptes Rendus Geoscience. 2014;**346**:233-243

[2] Hoskin PWO, Black LP. Metamorphic zircon formation by solid-state recrystallization of protolith igneous zircon. Journal of Metamorphic Geology. 2000;**18**:423-439

[3] Kröner A, Stern RJ. Pan-African Orogeny. Africa. Encyclopedia of Geology. Vol. 1. Amsterdam: Elsevier; 2004. pp. 1-12

[4] Stern RJ. ARC assembly and continental collision in the neoproterozoic east african orogen: Implications for the consolidation of gondwanaland. Annual Review of Earth and Planetary Sciences. 1994;**22**:319-351. DOI: 10.1146/annurev. ea.22.050194.001535

[5] Chaúque FR, Cordani UG, Jamal DL. Geochronological systematics for the Chimoio-macossa frontal nappe in Central Mozambique-implications for the tectonic evolution of the southern part of the Mozambique belt. Journal of the African Earth Sciences. 2019;**150**:47-67. DOI: 10.1016/j.jafrearsci.2018.10.013

[6] Chaúque FR, Cordani UG, Jamal DL, Onoe AT. The Zimbabwe craton in Mozambique: A brief review of its geochronological pattern and its relation to the Mozambique belt. Journal of the African Earth Sciences. 2017;**129**:366-379. DOI: 10.1016/J.JAFREARSCI.2017.01.021

[7] Chaúque FR. Contribuição para o conhecimento da evolução tectônica do Cinturão de Moçambique, em Moçambique. Biblioteca Digital de Teses e Dissertações da Universidade de São Paulo; 2012. DOI: 10.11606/T.44.2012. tde-02062015-152355

[8] GTK Volume II. Map explanation: Sheets 1630-1934. Geology of Degree Sheets Mecumbura, Chioco, Tete, Tambara, Guro, Chemba, Manica, Catandica, Gorongosa, Rotanda, Chimoio and Beira; Maputo:vol. 2; 2006

[9] Hunting. Ground geophysics. mineral inventory project in tete province and parts of manica, sofala and zambezia provinces. Report on ground geophysics investigations for the period July to October 1982; Maputo: 1983

[10] Hunting. Mineral inventory project in tete province and parts of manica, sofala and zambezia provinces. Report on ground geophysical investigations for the 1982 and 1983 field season; Maputo: 1984

[11] Sato K, Junior OS, MAS B, CCG T, Onoe AT. SHRIMP U-Th-Pb analyses of titanites: Analytical techniques and examples of terranes of the south-southeast of Brazil: Geoscience Institute of the University of São Paulo. Geologia USP. Série Científica. 2016;**16**:3-18. DOI: 10.11606/issn. 2316-9095.v16i2p3-18

[12] Chemale F Jr, Kawashita K, Dussin IA, Ávila JN, Justino D, Bertotti A. U-Pb zircon in situ dating with LA-MC-ICP-MS using a mixed detector configuration. Annals of the Brazilian Academy of Sciences. 2012;**84**:275-295

[13] Black LP, Kamo SL, Allen CM, Davis DW, Aleinikoff JN, Valley JW, et al. Improved 206Pb/238U microprobe geochronology by the monitoring of a trace-element-related matrix effect; SHRIMP, ID–TIMS, ELA–ICP–MS and oxygen isotope documentation for a series of zircon standards. Chemical Geology. 2004;**205**:115-140. DOI: 10.1016/j.chemgeo.2004.01.003

[14] Sato K, Tassinari CCG, Basei MAS, Siga Júnior O, Onoe AT, de

**35**

*Metamorphic Zircons Applied for Dating East African Tectono-Metamorphic Event in Central…*

to Cambrian tectonic evolution. Journal of the African Earth Sciences. 2013;**86**:65-106. DOI: 10.1016/j.

jafrearsci.2013.06.004

[22] Manjate VA. Whole-rock

DOI: 10.1016/j.gsf.2016.10.009

[24] Manjate VA. Caracterização geocronológica dos granitóides do complexo de bárue e da suíte de guro, centro-oeste de moçambique: Iplicações tectônicas e metalogenéticas.

Biblioteca Digital de Teses e

[25] Manjate VA. U-Pb zircon geochronology and Sr-Nd isotopic composition of the Inchope orthogneiss in Mozambique: Age constraints and petrogenetic implications. Journal of the African Earth Sciences. 2017;**131**:98-104. DOI: 10.1016/j.jafrearsci.2017.03.027

tde-22122015-143300

jafrearsci.2018.05.012

B203028B

Dissertações da Universidade de São Paulo; 2015. DOI: 10.11606/T.44.2015.

[26] Manjate VA, Tassinari CCG. Zircon U-Pb geochronology and Nd isotope systematics of the Guro suite

granitoids, Mozambique: Implications for Neoproterozoic crust reworking events. Journal of the African Earth Sciences. 2018;**148**:69-79. DOI: 10.1016/j.

[27] Becker JS. State-of-the-art and progress in precise and accurate isotope ratio measurements by ICP-MS and LA-ICP-MS: Plenary lecture. Journal of Analytical Atomic Spectrometry. 2002;**17**:1172-1185. DOI: 10.1039/

tde-21122012-085416

geochemical, U-Pb and Sm-Nd isotope characteristics of the Dongueni Mont nepheline syenite intrusion, Mozambique. Geoscience Frontiers. 2015;**8**:1063-1071.

[23] Manjate VA. Geocronologia da região de Gondola-Nhamatanda (Centro de Moçambique). Biblioteca Digital de Teses e Dissertações da Universidade de São Paulo; 2012. DOI: 10.11606/D.44.2012.

*DOI: http://dx.doi.org/10.5772/intechopen.88514*

Souza MD. Sensitive high resolution ion microprobe (SHRIMP IIe/MC) of the institute of geosciences of the University of São Paulo, Brazil: Analytical method and first results. Geologia USP. Série Científica. 2014;**14**:3-18. DOI: 10.5327/

Z1519-874X201400030001

[16] Stacey JS, Kramers JD. Approximation of terrestrial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters. 1975;**26**:207-221. DOI: 10.1016/0012-821X(75)90088-6

10.1360/04wd0130

[15] Ludwig KR. User's Manual for Isoplot 3.00: A Geochronological Toolkit for Microsoft Excel. Berkeley CA: Special publication/Berkeley Geochronology Center; 2003

[17] Yuambao W, Yongfei Z. Genesis of zircon and its constraints on the interpretation of U-Pb age. Chinese Science Bulletin. 2004;**49**:1554. DOI:

[18] Fu B, Mernagh TP, Kita NT, Kemp AIS, Valley JW. Distinguishing magmatic zircon from hydrothermal

zircon: A case study from the Gidginbung high-sulphidation Au– Ag–(Cu) deposit, SE Australia. Chemical Geology. 2009;**259**:131-142. DOI: 10.1016/J.CHEMGEO.2008.10.035

S0009-2541(01)00355-2

[19] Rubatto D. Zircon trace element geochemistry: Partitioning with garnet and the link between U-Pb ages and metamorphism. Chemical Geology. 2002;**184**:123-138. DOI: 10.1016/

[20] Hoskin PWO, Schaltegger U. The composition of zircon and igneous and metamorphic petrogenesis. Reviews in Mineralogy and Geochemistry. 2003;**53**:27-62. DOI: 10.2113/0530027.

[21] Fritz H, Abdelsalam M, Ali KA, Bingen B, Collins AS, Fowler AR, et al. Orogen styles in the east African orogen: A review of the Neoproterozoic *Metamorphic Zircons Applied for Dating East African Tectono-Metamorphic Event in Central… DOI: http://dx.doi.org/10.5772/intechopen.88514*

Souza MD. Sensitive high resolution ion microprobe (SHRIMP IIe/MC) of the institute of geosciences of the University of São Paulo, Brazil: Analytical method and first results. Geologia USP. Série Científica. 2014;**14**:3-18. DOI: 10.5327/ Z1519-874X201400030001

[15] Ludwig KR. User's Manual for Isoplot 3.00: A Geochronological Toolkit for Microsoft Excel. Berkeley CA: Special publication/Berkeley Geochronology Center; 2003

[16] Stacey JS, Kramers JD. Approximation of terrestrial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters. 1975;**26**:207-221. DOI: 10.1016/0012-821X(75)90088-6

[17] Yuambao W, Yongfei Z. Genesis of zircon and its constraints on the interpretation of U-Pb age. Chinese Science Bulletin. 2004;**49**:1554. DOI: 10.1360/04wd0130

[18] Fu B, Mernagh TP, Kita NT, Kemp AIS, Valley JW. Distinguishing magmatic zircon from hydrothermal zircon: A case study from the Gidginbung high-sulphidation Au– Ag–(Cu) deposit, SE Australia. Chemical Geology. 2009;**259**:131-142. DOI: 10.1016/J.CHEMGEO.2008.10.035

[19] Rubatto D. Zircon trace element geochemistry: Partitioning with garnet and the link between U-Pb ages and metamorphism. Chemical Geology. 2002;**184**:123-138. DOI: 10.1016/ S0009-2541(01)00355-2

[20] Hoskin PWO, Schaltegger U. The composition of zircon and igneous and metamorphic petrogenesis. Reviews in Mineralogy and Geochemistry. 2003;**53**:27-62. DOI: 10.2113/0530027.

[21] Fritz H, Abdelsalam M, Ali KA, Bingen B, Collins AS, Fowler AR, et al. Orogen styles in the east African orogen: A review of the Neoproterozoic to Cambrian tectonic evolution. Journal of the African Earth Sciences. 2013;**86**:65-106. DOI: 10.1016/j. jafrearsci.2013.06.004

[22] Manjate VA. Whole-rock geochemical, U-Pb and Sm-Nd isotope characteristics of the Dongueni Mont nepheline syenite intrusion, Mozambique. Geoscience Frontiers. 2015;**8**:1063-1071. DOI: 10.1016/j.gsf.2016.10.009

[23] Manjate VA. Geocronologia da região de Gondola-Nhamatanda (Centro de Moçambique). Biblioteca Digital de Teses e Dissertações da Universidade de São Paulo; 2012. DOI: 10.11606/D.44.2012. tde-21122012-085416

[24] Manjate VA. Caracterização geocronológica dos granitóides do complexo de bárue e da suíte de guro, centro-oeste de moçambique: Iplicações tectônicas e metalogenéticas. Biblioteca Digital de Teses e Dissertações da Universidade de São Paulo; 2015. DOI: 10.11606/T.44.2015. tde-22122015-143300

[25] Manjate VA. U-Pb zircon geochronology and Sr-Nd isotopic composition of the Inchope orthogneiss in Mozambique: Age constraints and petrogenetic implications. Journal of the African Earth Sciences. 2017;**131**:98-104. DOI: 10.1016/j.jafrearsci.2017.03.027

[26] Manjate VA, Tassinari CCG. Zircon U-Pb geochronology and Nd isotope systematics of the Guro suite granitoids, Mozambique: Implications for Neoproterozoic crust reworking events. Journal of the African Earth Sciences. 2018;**148**:69-79. DOI: 10.1016/j. jafrearsci.2018.05.012

[27] Becker JS. State-of-the-art and progress in precise and accurate isotope ratio measurements by ICP-MS and LA-ICP-MS: Plenary lecture. Journal of Analytical Atomic Spectrometry. 2002;**17**:1172-1185. DOI: 10.1039/ B203028B

**34**

tde-02062015-152355

*Isotopes Applications in Earth Sciences*

[1] Martins HCB, Simões PP, Abreu J. Zircon crystal morphology and internal structures as a tool for constraining magma sources: Examples from northern Portugal Variscan biotite-rich granite plutons. Comptes Rendus Geoscience. 2014;**346**:233-243

[2] Hoskin PWO, Black LP. Metamorphic

[8] GTK Volume II. Map explanation: Sheets 1630-1934. Geology of Degree Sheets Mecumbura, Chioco, Tete, Tambara, Guro, Chemba, Manica, Catandica, Gorongosa, Rotanda, Chimoio and Beira; Maputo:vol. 2; 2006

[9] Hunting. Ground geophysics. mineral inventory project in tete

province and parts of manica, sofala and zambezia provinces. Report on ground geophysics investigations for the period July to October 1982; Maputo: 1983

[10] Hunting. Mineral inventory project in tete province and parts of manica, sofala and zambezia provinces. Report on ground geophysical investigations for the 1982 and 1983 field season; Maputo: 1984

[11] Sato K, Junior OS, MAS B, CCG T, Onoe AT. SHRIMP U-Th-Pb analyses of titanites: Analytical techniques and examples of terranes of the south-southeast of Brazil: Geoscience Institute of the University of São Paulo. Geologia USP. Série Científica. 2016;**16**:3-18. DOI: 10.11606/issn.

2316-9095.v16i2p3-18

2012;**84**:275-295

[12] Chemale F Jr, Kawashita K, Dussin IA, Ávila JN, Justino D, Bertotti A. U-Pb zircon in situ dating with LA-MC-ICP-MS using a mixed detector configuration. Annals of the Brazilian Academy of Sciences.

[13] Black LP, Kamo SL, Allen CM, Davis DW, Aleinikoff JN, Valley JW, et al. Improved 206Pb/238U microprobe geochronology by the monitoring of a trace-element-related matrix effect; SHRIMP, ID–TIMS, ELA–ICP–MS and oxygen isotope documentation for a series of zircon standards. Chemical Geology. 2004;**205**:115-140. DOI: 10.1016/j.chemgeo.2004.01.003

[14] Sato K, Tassinari CCG,

Basei MAS, Siga Júnior O, Onoe AT, de

zircon formation by solid-state recrystallization of protolith igneous zircon. Journal of Metamorphic Geology. 2000;**18**:423-439

[3] Kröner A, Stern RJ. Pan-African Orogeny. Africa. Encyclopedia of Geology. Vol. 1. Amsterdam: Elsevier;

[4] Stern RJ. ARC assembly and

continental collision in the neoproterozoic east african orogen: Implications for the consolidation of gondwanaland. Annual Review of Earth and Planetary Sciences. 1994;**22**:319-351. DOI: 10.1146/annurev.

[5] Chaúque FR, Cordani UG, Jamal DL. Geochronological systematics for the Chimoio-macossa frontal nappe in Central Mozambique-implications for the tectonic evolution of the southern part of the Mozambique belt. Journal of the African Earth Sciences. 2019;**150**:47-67. DOI: 10.1016/j.jafrearsci.2018.10.013

[6] Chaúque FR, Cordani UG, Jamal DL, Onoe AT. The Zimbabwe craton in Mozambique: A brief review of its geochronological pattern and its relation to the Mozambique belt. Journal of the African Earth Sciences. 2017;**129**:366-379. DOI: 10.1016/J.JAFREARSCI.2017.01.021

[7] Chaúque FR. Contribuição para o conhecimento da evolução tectônica do Cinturão de Moçambique, em

Moçambique. Biblioteca Digital de Teses e Dissertações da Universidade de São Paulo; 2012. DOI: 10.11606/T.44.2012.

**References**

2004. pp. 1-12

ea.22.050194.001535

**37**

Section 2

Applications in

Hydrosphere

Section 2

Applications in Hydrosphere

**39**

**Chapter 3**

Conditions

This will include the following: the δ

and Yunnan and their application in the origins of brine.

vironmental evolution, and tectonic uplift [1–3].

the 87Sr/86Sr, δ34S, and δ

salt minerals

**1. Introduction**

*and Liping Zhu*

**Abstract**

Isotopic Application in High Saline

*Minghui Li, Xiaomin Fang, Jiao Li, Maodu Yan, Shurui Sun* 

Evaporite minerals record the hydrogeochemical conditions in which they precipitated. And therefore they can be used to reconstruct the paleoclimate and paleoenvironments. Evaporite minerals are also major sources of industrial minerals including gypsum, halite, borates, lithium concentrates, and others. Because of their scientific significance and economic importance, evaporite minerals and their isotopic hydrochemical processes linked to their formation have been the focus of many geologists and paleoclimatologists. This chapter will discuss the application of isotopes of hydrogen, oxygen, sulfur, strontium, and boron in saline conditions.

their paleoclimate since 2.2 Ma in the Qaidam Basin, NE Tibetan Plateau; the δ18O and δD of the interlayer water of clay minerals in salar lacustrine sediments; and

Evaporite minerals record the hydrogeochemical conditions in which they precipitated. And therefore they can be used to reconstruct the paleoclimate and paleoenvironments. Evaporite minerals are also major sources of industrial minerals including gypsum, halite, borates, lithium concentrates, and others. Given their scientific significance and economic importance, evaporite minerals and their isotopic hydrochemical processes linked to their formation have become the focus of many geologists and paleoclimatologists. The Qaidam Basin and Lanping-Simao Basin (LSB) in China and Khorat Basin (KB) and Sakhon Nakhon Basin (SNB) in Thailand and Laos, which have thick sequences of evaporites, have been the focus of study by researcher concerned with its mineral resources, geochemistry, paleoen-

Water is nearly ubiquitously in nature. Its isotopic compositions also were recorded in many minerals. In order to identify the past conditions at which sediments formed, many studies focused on the stable isotopes of carbon and oxygen as tracers of environmental conditions. However, we know little about the δ

δD in saline conditions. On the other hand, halite and gypsum are two common minerals in evaporite deposits. Today, exploited evaporite deposits are most found

**Keywords:** oxygen and hydrogen, Sr isotope, sulfur isotope, boron isotope,

18O and δD of hydrated water of gypsum and

18O and

11B of halite from evaporite deposits in Khorat Plateau, Laos,

## **Chapter 3**

## Isotopic Application in High Saline Conditions

*Minghui Li, Xiaomin Fang, Jiao Li, Maodu Yan, Shurui Sun and Liping Zhu*

### **Abstract**

Evaporite minerals record the hydrogeochemical conditions in which they precipitated. And therefore they can be used to reconstruct the paleoclimate and paleoenvironments. Evaporite minerals are also major sources of industrial minerals including gypsum, halite, borates, lithium concentrates, and others. Because of their scientific significance and economic importance, evaporite minerals and their isotopic hydrochemical processes linked to their formation have been the focus of many geologists and paleoclimatologists. This chapter will discuss the application of isotopes of hydrogen, oxygen, sulfur, strontium, and boron in saline conditions. This will include the following: the δ 18O and δD of hydrated water of gypsum and their paleoclimate since 2.2 Ma in the Qaidam Basin, NE Tibetan Plateau; the δ18O and δD of the interlayer water of clay minerals in salar lacustrine sediments; and the 87Sr/86Sr, δ34S, and δ 11B of halite from evaporite deposits in Khorat Plateau, Laos, and Yunnan and their application in the origins of brine.

**Keywords:** oxygen and hydrogen, Sr isotope, sulfur isotope, boron isotope, salt minerals

### **1. Introduction**

Evaporite minerals record the hydrogeochemical conditions in which they precipitated. And therefore they can be used to reconstruct the paleoclimate and paleoenvironments. Evaporite minerals are also major sources of industrial minerals including gypsum, halite, borates, lithium concentrates, and others. Given their scientific significance and economic importance, evaporite minerals and their isotopic hydrochemical processes linked to their formation have become the focus of many geologists and paleoclimatologists. The Qaidam Basin and Lanping-Simao Basin (LSB) in China and Khorat Basin (KB) and Sakhon Nakhon Basin (SNB) in Thailand and Laos, which have thick sequences of evaporites, have been the focus of study by researcher concerned with its mineral resources, geochemistry, paleoenvironmental evolution, and tectonic uplift [1–3].

Water is nearly ubiquitously in nature. Its isotopic compositions also were recorded in many minerals. In order to identify the past conditions at which sediments formed, many studies focused on the stable isotopes of carbon and oxygen as tracers of environmental conditions. However, we know little about the δ 18O and δD in saline conditions. On the other hand, halite and gypsum are two common minerals in evaporite deposits. Today, exploited evaporite deposits are most found

in the arid and semiarid deserts of the world (the areas between latitudes 15° and 45° both north and south of the equator). Tectonics, climate, and origins of brine are the prime controls on most evaporite deposits. However, the origins of brine was a big topic for some giant evaporite deposits, for example, the evaporite deposit in Khorat Basin (KB) in Thailand, Sakhon Nakhon Basin (SNB) in Laos, and Lanping-Simao Basin (LSB) in China. Almost all large potash deposits are associated with marine fluids (such as the deposits in Thailand, the United States, Germany, Russia, France, and Brazil), whereas some small potash deposits are with fluids of continental source (such as deposits in the Qaidam Basin, Western Tibet, China) [1, 2]. The isotopes of S, Sr, and B of halite could be very useful in determining the origins of brine. So this chapter will use well-known accepted methods to analyze minerals (halite, gypsum, and clay minerals) and stable isotopes (δ 18O and δD, 87Sr/86Sr, δ34S, and δ 11B) to discuss their application in paleoclimate and origins of brine.

## **2. The δ18O and δD in saline conditions**

## **2.1 Geological setting and the Core SG-1 in the Qaidam Basin, NE Tibetan Plateau**

The Qaidam Basin is a Mesozoic-Cenozoic sedimentary basin located on the northern margin of the Tibetan Plateau in China (**Figure 1**). The Asian inland drought basin was formed as the result of intracontinental deformation and plateau uplift due to the collision of the Indian and Eurasian Plates. It is bordered by the Kunlun Mountains to the south, the Qilian Mountains to the northeast, and the Arjin Mountains to the northwest, which have altitudes ranging from 4000 to 4500 m asl to over 5000 m asl. A network of faults exists within the basin [3]. The Paleogene and Neogene strata are widespread and include intrusive rocks. From the Middle Oligocene to the Upper Pliocene, the strata consist of mudstones, calcareous mudstones and marls, intercalating siltstone, very thick gypsum, and rock salt beds in the western basin [4]. Some secondary or subsidiary basins have become well developed since the Middle Pleistocene as a result of slow uplift [1]. Lacustrine sediments in

**41**

**Figure 2.**

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

the basin cover an area of 30,000 km2

tion of inland Asia since 2.8 Ma.

*2.2.1 Clay minerals*

with strata up to 700 m thick [4]. Abundant

records of palaeo-lake level and paleoclimatic changes are indicated by various proxies, such as pollen, ostracods, evaporite minerals, and isotopic geochemistry [5, 6]. Studies on evaporite minerals and hydrochemistry and geochemistry of salt lakes have been ongoing for about 50 years because of great economic significance [1, 2, 5, 7]. However, no two drainage basins have identical climatic and hydrologic conditions, and even adjacent basins can show striking variations in evaporite mineralogy [8]. The Core SG-1 (38°24'35.3" N, 92°30'32.7" E, 2900 m asl) was located in a playa in the Qahansilatu sub-basin, western Qaidam Basin (**Figure 1**). The core spanned from 2.77 to 0.1 Ma, dated by paleomagnetism and optically stimulated luminescence (OSL) with a sedimentary rate of 26.1–51.5 cm/ka [9]. The sedimentary sequence is composed of clay, clay-silt, and siltstone intercalated with salt layers (mainly halite), marl beds, and thin and/or scattered gypsum crystals, indicating clay-silt and halitemarl depositional cycles (**Figure 2**). The fluctuation between evaporite minerals and carbonaceous clay strata indicates a shift between dry and wet climates. Gypsum and halite make up the majority of the evaporite minerals in the core [11, 12]. During the last ~2.8 Ma, the lake basin evolved from a semi-deep fresh lake to a semi-brackish lake (2.8–2.2 Ma), to a perennial saline lake (2.2–2.0 Ma), to a shallow brackish lake

(1.8–1.6 Ma), to a perennial saline lake (1.2–0.6 Ma), to a playa saline lake

**2.2 Clay minerals and the δ18O and δD of their interlayer water**

(0.9–0.6 Ma), and to a saline mudflat (0.6–0.1 Ma) [10] (**Figure 2**). Multi-proxies, such as sedimentary features [10], salt minerals [11], isotope records [13, 14], and rare earth elements [15] of the study area, indicate the long-term persistent aridifica-

Clay minerals have been used to reconstruct paleoclimates and environments since Singer's review in 1984 [16]. It is common that the clay minerals undergo

*Lithology, sedimentary environment, sediment accumulation rates (SAR), and magnetostratigraphic ages of the Core SG-1 (after Zhang et al. [9] and Wang et al. [10]). DL, semi-deep fresh to semi-brackish lake; BL, shallow brackish lake; SL, perennial saline lake; PL, playa saline lake; and MF, playa saline mudflat.*

**Figure 1.** *Map of the Qaidam Basin showing the core site.*

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

*Isotopes Applications in Earth Sciences*

and δ

**Plateau**

in the arid and semiarid deserts of the world (the areas between latitudes 15° and 45° both north and south of the equator). Tectonics, climate, and origins of brine are the prime controls on most evaporite deposits. However, the origins of brine was a big topic for some giant evaporite deposits, for example, the evaporite deposit in Khorat Basin (KB) in Thailand, Sakhon Nakhon Basin (SNB) in Laos, and Lanping-Simao Basin (LSB) in China. Almost all large potash deposits are associated with marine fluids (such as the deposits in Thailand, the United States, Germany, Russia, France, and Brazil), whereas some small potash deposits are with fluids of continental source (such as deposits in the Qaidam Basin, Western Tibet, China) [1, 2]. The isotopes of S, Sr, and B of halite could be very useful in determining the origins of brine. So this chapter will use well-known accepted methods to analyze minerals

11B) to discuss their application in paleoclimate and origins of brine.

**2.1 Geological setting and the Core SG-1 in the Qaidam Basin, NE Tibetan** 

The Qaidam Basin is a Mesozoic-Cenozoic sedimentary basin located on the northern margin of the Tibetan Plateau in China (**Figure 1**). The Asian inland drought basin was formed as the result of intracontinental deformation and plateau uplift due to the collision of the Indian and Eurasian Plates. It is bordered by the Kunlun Mountains to the south, the Qilian Mountains to the northeast, and the Arjin Mountains to the northwest, which have altitudes ranging from 4000 to 4500 m asl to over 5000 m asl. A network of faults exists within the basin [3]. The Paleogene and Neogene strata are widespread and include intrusive rocks. From the Middle Oligocene to the Upper Pliocene, the strata consist of mudstones, calcareous mudstones and marls, intercalating siltstone, very thick gypsum, and rock salt beds in the western basin [4]. Some secondary or subsidiary basins have become well developed since the Middle Pleistocene as a result of slow uplift [1]. Lacustrine sediments in

18O and δD, 87Sr/86Sr, δ34S,

(halite, gypsum, and clay minerals) and stable isotopes (δ

**2. The δ18O and δD in saline conditions**

**40**

**Figure 1.**

*Map of the Qaidam Basin showing the core site.*

the basin cover an area of 30,000 km2 with strata up to 700 m thick [4]. Abundant records of palaeo-lake level and paleoclimatic changes are indicated by various proxies, such as pollen, ostracods, evaporite minerals, and isotopic geochemistry [5, 6]. Studies on evaporite minerals and hydrochemistry and geochemistry of salt lakes have been ongoing for about 50 years because of great economic significance [1, 2, 5, 7]. However, no two drainage basins have identical climatic and hydrologic conditions, and even adjacent basins can show striking variations in evaporite mineralogy [8].

The Core SG-1 (38°24'35.3" N, 92°30'32.7" E, 2900 m asl) was located in a playa in the Qahansilatu sub-basin, western Qaidam Basin (**Figure 1**). The core spanned from 2.77 to 0.1 Ma, dated by paleomagnetism and optically stimulated luminescence (OSL) with a sedimentary rate of 26.1–51.5 cm/ka [9]. The sedimentary sequence is composed of clay, clay-silt, and siltstone intercalated with salt layers (mainly halite), marl beds, and thin and/or scattered gypsum crystals, indicating clay-silt and halitemarl depositional cycles (**Figure 2**). The fluctuation between evaporite minerals and carbonaceous clay strata indicates a shift between dry and wet climates. Gypsum and halite make up the majority of the evaporite minerals in the core [11, 12]. During the last ~2.8 Ma, the lake basin evolved from a semi-deep fresh lake to a semi-brackish lake (2.8–2.2 Ma), to a perennial saline lake (2.2–2.0 Ma), to a shallow brackish lake (1.8–1.6 Ma), to a perennial saline lake (1.2–0.6 Ma), to a playa saline lake (0.9–0.6 Ma), and to a saline mudflat (0.6–0.1 Ma) [10] (**Figure 2**). Multi-proxies, such as sedimentary features [10], salt minerals [11], isotope records [13, 14], and rare earth elements [15] of the study area, indicate the long-term persistent aridification of inland Asia since 2.8 Ma.

## **2.2 Clay minerals and the δ18O and δD of their interlayer water**

## *2.2.1 Clay minerals*

Clay minerals have been used to reconstruct paleoclimates and environments since Singer's review in 1984 [16]. It is common that the clay minerals undergo

#### **Figure 2.**

*Lithology, sedimentary environment, sediment accumulation rates (SAR), and magnetostratigraphic ages of the Core SG-1 (after Zhang et al. [9] and Wang et al. [10]). DL, semi-deep fresh to semi-brackish lake; BL, shallow brackish lake; SL, perennial saline lake; PL, playa saline lake; and MF, playa saline mudflat.*

diagenetic transformations or postdepositional diagenetic changes, and as a result, some paleoclimate information of clays will be overprinted or changed. However, there are still lots of studies to use clay minerals to reconstruct paleoenvironments and paleoclimates. The isotopic exchange rates between the interlayer water of clay minerals and the ambient water are very fast and, in general, are less than a few days. However, in saline conditions, we know little about the isotopic exchange between them.

The clay mineral assemblages in the Core SG-1 are shown in **Figure 3**. The curves of chlorite and illite abundances are similar, but they are different with those of the kaolinite, smectite, and I/Sm (**Figure 3**). The curve of smectite content shows a decreasing trend with decreasing depth, and that of the illite content shows an increasing trend slightly (**Figure 3**). The XRD analyses suggest that the I/Sm in the core exhibits order (R3 I/Sm) (mixed layer of I/Sm > 80%). R1 I/Sm is more stable than any other mixed layer I/Sm phase because it has a unique structure, composition, and order [17]. The clay minerals that were identified as R3 I/Sm by XRD analyses are possible to be mixtures of discrete smectite and R1 I/Sm [17].

The diagenesis of clay minerals in lacustrine sediments is a disputed topic. The clays in Core SG-1 in the Qaidam Basin probably underwent early diagenesis based on their curves and relationship between them (**Figures 4** and **5**) [18]. Climate changes, to some extent, control on the degree of alteration of the primary minerals and the composition of the secondary products. In the clay minerals, the exchange between the interlayer water and the ambient water recorded the diagenetic information. For instance, the **δ** 18O and **δ**D of the different clays and interlayer water record temperatures that range from surface temperatures to hydrothermal temperatures of about 150–200°C [19]. In situ precipitation of I/Sm minerals may take place in chemical and isotopic equilibrium with the reacting solution [20, 21]. However, in high saline conditions, the reaction or the above exchange may be extremely slowly.

#### *2.2.2 The δ 18O and δD of the interlayer water*

The δ18O of the interlayer water ranged from −11.8 to 82.95% with the average of 20.8%, and the δD ranged from −114.3 to 165.5% with the average of −35.6%

#### **Figure 3.**

*Variations in the amount of illite, chlorite, kaolinite, smectite, and illite/smectite (I/Sm) and in the chemistry of illite (I5Å/I10Å ratios) and chlorite (I7Å/I14Å ratios). Colored lines represent a five-point running average. Sedimentary environments are from Wang et al. [10]; ages are from Zhang et al. [9].*

**43**

**Figure 5.**

**Figure 4.**

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

*Correlations between the abundances (%) of (a) illite and I/Sm, (b) chlorite and kaolinite, (c) illite and* 

*Relationship between the δ18O and δD of the interlayer water of the clay minerals and different types of water from the Qaidam Basin. The global and modern local meteoric water lines are from Craig [22] and Li et al. [23], respectively. The present-day precipitation and hot spring data are from Zhang [24]. Gypsum hydration water data are from Li et al. [14], deep brine water data are from Fan et al. [25], and surface water and pore water data are from Xiao [26] and Fan et al. [25]. The large differences in the δ18O and δD of the pure water and the interlayer water of the clay minerals suggest that the interlayer water did not exchange with the pure* 

*water and other water used during the processing and pretreatment.*

*chlorite, (d) smectite and kaolinite, (e) KI (Kübler index), and AI (Árkai index).*

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

**Figure 4.**

*Isotopes Applications in Earth Sciences*

between them.

mation. For instance, the **δ**

*18O and δD of the interlayer water*

*2.2.2 The δ*

diagenetic transformations or postdepositional diagenetic changes, and as a result, some paleoclimate information of clays will be overprinted or changed. However, there are still lots of studies to use clay minerals to reconstruct paleoenvironments and paleoclimates. The isotopic exchange rates between the interlayer water of clay minerals and the ambient water are very fast and, in general, are less than a few days. However, in saline conditions, we know little about the isotopic exchange

The clay mineral assemblages in the Core SG-1 are shown in **Figure 3**. The curves of chlorite and illite abundances are similar, but they are different with those of the kaolinite, smectite, and I/Sm (**Figure 3**). The curve of smectite content shows a decreasing trend with decreasing depth, and that of the illite content shows an increasing trend slightly (**Figure 3**). The XRD analyses suggest that the I/Sm in the core exhibits order (R3 I/Sm) (mixed layer of I/Sm > 80%). R1 I/Sm is more stable than any other mixed layer I/Sm phase because it has a unique structure, composition, and order [17]. The clay minerals that were identified as R3 I/Sm by XRD analyses are possible to be mixtures of discrete smectite and R1 I/Sm [17].

The diagenesis of clay minerals in lacustrine sediments is a disputed topic. The clays in Core SG-1 in the Qaidam Basin probably underwent early diagenesis based on their curves and relationship between them (**Figures 4** and **5**) [18]. Climate changes, to some extent, control on the degree of alteration of the primary minerals and the composition of the secondary products. In the clay minerals, the exchange between the interlayer water and the ambient water recorded the diagenetic infor-

record temperatures that range from surface temperatures to hydrothermal temperatures of about 150–200°C [19]. In situ precipitation of I/Sm minerals may take place in chemical and isotopic equilibrium with the reacting solution [20, 21]. However, in high saline conditions, the reaction or the above exchange may be extremely slowly.

The δ18O of the interlayer water ranged from −11.8 to 82.95% with the average of 20.8%, and the δD ranged from −114.3 to 165.5% with the average of −35.6%

*Variations in the amount of illite, chlorite, kaolinite, smectite, and illite/smectite (I/Sm) and in the chemistry of illite (I5Å/I10Å ratios) and chlorite (I7Å/I14Å ratios). Colored lines represent a five-point running average.* 

*Sedimentary environments are from Wang et al. [10]; ages are from Zhang et al. [9].*

18O and **δ**D of the different clays and interlayer water

**42**

**Figure 3.**

*Correlations between the abundances (%) of (a) illite and I/Sm, (b) chlorite and kaolinite, (c) illite and chlorite, (d) smectite and kaolinite, (e) KI (Kübler index), and AI (Árkai index).*

#### **Figure 5.**

*Relationship between the δ18O and δD of the interlayer water of the clay minerals and different types of water from the Qaidam Basin. The global and modern local meteoric water lines are from Craig [22] and Li et al. [23], respectively. The present-day precipitation and hot spring data are from Zhang [24]. Gypsum hydration water data are from Li et al. [14], deep brine water data are from Fan et al. [25], and surface water and pore water data are from Xiao [26] and Fan et al. [25]. The large differences in the δ18O and δD of the pure water and the interlayer water of the clay minerals suggest that the interlayer water did not exchange with the pure water and other water used during the processing and pretreatment.*

(**Figure 5**). They exhibit a roughly linear relationship and are significantly correlated (*R* = 0.96), indicating that these isotopes share the same sources. The isotopes of the interlayer water possibly recorded the brine composition which contained interstitial water or pore water derived from lake water and underwent strong evaporation. This could be understood as the following. (a) Some of the **δ**18O and **δ**D of the interlayer water are close to those of surface water, deep brine, and pore water. (b) The rates of isotopic exchange between the interlayer water and the ambient water are very fast and, sometimes, are less than a few days. Therefore, the exchange rate between the structural oxygen of the clay minerals and that of the ambient water could be insignificant over a 2.8 Ma time span at a temperature of ≤100°C [27, 28]. (c) The slopes of the **δ**18O and **δ**D of the interlayer water are smaller than that of the gypsum hydrated water that recorded the evolution of lake water or subsurface water (**Figure 5**), suggesting the interlayer water underwent more stronger evaporation than gypsum hydrated water. (d) The **δ**18O and **δ**D of the interlayer water of clay minerals are very different with those of pure water (**Figure 5**), which was used to treat the clay minerals.

Independent of the oxygen isotopic exchange, the hydrogen isotopic exchange occurs by a proton exchange mechanism [28, 29]. The hydrogen isotopic exchange between smectite and its ambient water is very fast and significantly relative to that between illite and kaolinite with their ambient water [28].

## **2.3 Gypsum and the δ18O and δD of hydrated water**

#### *2.3.1 Gypsum*

Gypsum (CaSO4·2H2O), one of the most abundant evaporite minerals occurring as a syndepositional evaporite, carries information about brines from which they precipitate. There are several shapes of gypsum crystals (**Figure 6**). These prismatic and tabular gypsum layers were vertically aligned, indicating primary subaqueous precipitates and with bottom nucleation [31, 32]. Some euhedral gypsum crystals were scattered in the mudstone-siltstone layers, which are possibly formed by evaporation of pore water or interstitial brine and regarded as diagenetic gypsum. Based solely on their morphology, it is not easy to confirm gypsum to be synsedimentary or diagenetic, because there is no diagnostic relationship between crystal morphology and depositional environment [33]. Besides the aligned gypsum, scattered euhedral crystals may be significant for understanding the evolution of lake water, because pore water or interstitial brine may have originated from infiltration of lake water. The Core SG-1 showed an increase of evaporite mineral contents upward, and the strata were mainly horizontal and not affected by tectonic deformation [10]. Therefore, these selected gypsums may have been primary in origin in arid, or aqueous, young lacustrine. These environments contain deposits that have never been exposed or deeply buried and may also retain their original isotopic compositions [34–36].

Minor cations such as Sr2+, K+ , and Mg2+ may be incorporated into gypsum lattice via substitution for Ca2+ during the coprecipitation process because they have similar ionic radii. Different cations are selectively attracted to particular faces [37, 38]. For example, the (1 1 1) face is covered by either calcium ions or sulfate clusters and the (1 1 0) and (0 1 0) faces by both calcium and sulfate clusters [39]. Na<sup>+</sup> is preferentially adsorbed on (1 1 1) surface of sulfate salts that is dominantly occupied by Ca2+ [39, 40]. However, the presence of Na+ also impedes the (1 1 1) face growth and, as a result, minimizes parallel to its c axis [36, 39]. K<sup>+</sup> has a similar inhibitory effect [40]. Because of the difference in coordination number between Ca2+ (eight in gypsum) and Mg2+ (six in most minerals), Mg2+ will disturb gypsum

**45**

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

growth along c axis [41]. Preferentially adsorbed on the (1 1 0) face, Sr2+ forms

*The monoclinic gypsum exhibits four principal forms in the Core SG-1 [30]: prismatic crystals, lenticular crystals, and tabular crystals. The tabular and prismatic crystals tend to increase with decreasing depth. The red numbers mean that the same kind of crystal morphology can appear in different environments and* 

c value smaller, while Sr2+ reduces a and b values. As a result, there have different

The δ18O of gypsum hydrated water ranged from −4.21 to 8.69%, with average of 5.74%; and the δD was from −72.77 to 49.73%, with average of −28.09%. They exhibit a roughly linear relationship with the slope of 5.39, and its mother water-

those of today's mean precipitation (δ18O = −9.25% and δD = −41.3%) [14]. This indicated a slightly weaker evaporation and/or colder climate than today [36, 43]. On the other hand, the δ18O and δD are close to those of the Altyn Tagh Mountain groundwater that sourced from meteoric water (**Figure 7**). It is therefore likely that meteoric water was the main source of hydration water during gypsum formation. In general, gypsum could be formed in the following ways: in situ formation (e.g., resulting from the oxidation of sulfide minerals); hydration of anhydrite; and direct deposition from an evaporating solution saturated with gypsum [44]. If gypsum was formed in situ formation, the δ18O and δD of hydrated water would reflect those of meteoric and/or surface waters [44, 45]. If it is formed from the hydration of anhydrite, which is assumed to be a Rayleigh process, both the hydration water and its mother water would be expected to move along a line with a negative ΔδD/Δδ18O [46, 47]. In this study, the ΔδD/Δδ18O value was 5.39 [14], suggesting evaporation to be the major geochemical process for gypsum deposition, that is, the gypsum in the Core SG-1 was likely to deposit directly from brines. The degree

, Na+

18O and δD appear to be much lower than

, and Mg2+ make the

epitaxial deposits of strontium sulfate [39]. Therefore, K<sup>+</sup>

*different crystal morphologies can also occur in the same depositional environment.*

*18O and δD of hydrated water*

line has a slope of 5.52 (**Figure 7**). The δ

gypsum morphologies.

*2.3.2 The δ*

**Figure 6.**

#### *Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

#### **Figure 6.**

*Isotopes Applications in Earth Sciences*

was used to treat the clay minerals.

*2.3.1 Gypsum*

compositions [34–36].

Minor cations such as Sr2+, K+

occupied by Ca2+ [39, 40]. However, the presence of Na+

face growth and, as a result, minimizes parallel to its c axis [36, 39]. K<sup>+</sup>

between illite and kaolinite with their ambient water [28].

**2.3 Gypsum and the δ18O and δD of hydrated water**

(**Figure 5**). They exhibit a roughly linear relationship and are significantly correlated (*R* = 0.96), indicating that these isotopes share the same sources. The isotopes of the interlayer water possibly recorded the brine composition which contained interstitial water or pore water derived from lake water and underwent strong evaporation. This could be understood as the following. (a) Some of the **δ**18O and **δ**D of the interlayer water are close to those of surface water, deep brine, and pore water. (b) The rates of isotopic exchange between the interlayer water and the ambient water are very fast and, sometimes, are less than a few days. Therefore, the exchange rate between the structural oxygen of the clay minerals and that of the ambient water could be insignificant over a 2.8 Ma time span at a temperature of ≤100°C [27, 28]. (c) The slopes of the **δ**18O and **δ**D of the interlayer water are smaller than that of the gypsum hydrated water that recorded the evolution of lake water or subsurface water (**Figure 5**), suggesting the interlayer water underwent more stronger evaporation than gypsum hydrated water. (d) The **δ**18O and **δ**D of the interlayer water of clay minerals are very different with those of pure water (**Figure 5**), which

Independent of the oxygen isotopic exchange, the hydrogen isotopic exchange occurs by a proton exchange mechanism [28, 29]. The hydrogen isotopic exchange between smectite and its ambient water is very fast and significantly relative to that

Gypsum (CaSO4·2H2O), one of the most abundant evaporite minerals occurring as a syndepositional evaporite, carries information about brines from which they precipitate. There are several shapes of gypsum crystals (**Figure 6**). These prismatic and tabular gypsum layers were vertically aligned, indicating primary subaqueous precipitates and with bottom nucleation [31, 32]. Some euhedral gypsum crystals were scattered in the mudstone-siltstone layers, which are possibly formed by evaporation of pore water or interstitial brine and regarded as diagenetic gypsum. Based solely on their morphology, it is not easy to confirm gypsum to be synsedimentary or diagenetic, because there is no diagnostic relationship between crystal morphology and depositional environment [33]. Besides the aligned gypsum, scattered euhedral crystals may be significant for understanding the evolution of lake water, because pore water or interstitial brine may have originated from infiltration of lake water. The Core SG-1 showed an increase of evaporite mineral contents upward, and the strata were mainly horizontal and not affected by tectonic deformation [10]. Therefore, these selected gypsums may have been primary in origin in arid, or aqueous, young lacustrine. These environments contain deposits that have never been exposed or deeply buried and may also retain their original isotopic

lattice via substitution for Ca2+ during the coprecipitation process because they have similar ionic radii. Different cations are selectively attracted to particular faces [37, 38]. For example, the (1 1 1) face is covered by either calcium ions or sulfate clusters and the (1 1 0) and (0 1 0) faces by both calcium and sulfate clusters [39].

is preferentially adsorbed on (1 1 1) surface of sulfate salts that is dominantly

inhibitory effect [40]. Because of the difference in coordination number between Ca2+ (eight in gypsum) and Mg2+ (six in most minerals), Mg2+ will disturb gypsum

, and Mg2+ may be incorporated into gypsum

also impedes the (1 1 1)

has a similar

**44**

Na<sup>+</sup>

*The monoclinic gypsum exhibits four principal forms in the Core SG-1 [30]: prismatic crystals, lenticular crystals, and tabular crystals. The tabular and prismatic crystals tend to increase with decreasing depth. The red numbers mean that the same kind of crystal morphology can appear in different environments and different crystal morphologies can also occur in the same depositional environment.*

growth along c axis [41]. Preferentially adsorbed on the (1 1 0) face, Sr2+ forms epitaxial deposits of strontium sulfate [39]. Therefore, K<sup>+</sup> , Na+ , and Mg2+ make the c value smaller, while Sr2+ reduces a and b values. As a result, there have different gypsum morphologies.

#### *2.3.2 The δ 18O and δD of hydrated water*

The δ18O of gypsum hydrated water ranged from −4.21 to 8.69%, with average of 5.74%; and the δD was from −72.77 to 49.73%, with average of −28.09%. They exhibit a roughly linear relationship with the slope of 5.39, and its mother waterline has a slope of 5.52 (**Figure 7**). The δ 18O and δD appear to be much lower than those of today's mean precipitation (δ18O = −9.25% and δD = −41.3%) [14]. This indicated a slightly weaker evaporation and/or colder climate than today [36, 43]. On the other hand, the δ18O and δD are close to those of the Altyn Tagh Mountain groundwater that sourced from meteoric water (**Figure 7**). It is therefore likely that meteoric water was the main source of hydration water during gypsum formation.

In general, gypsum could be formed in the following ways: in situ formation (e.g., resulting from the oxidation of sulfide minerals); hydration of anhydrite; and direct deposition from an evaporating solution saturated with gypsum [44]. If gypsum was formed in situ formation, the δ18O and δD of hydrated water would reflect those of meteoric and/or surface waters [44, 45]. If it is formed from the hydration of anhydrite, which is assumed to be a Rayleigh process, both the hydration water and its mother water would be expected to move along a line with a negative ΔδD/Δδ18O [46, 47]. In this study, the ΔδD/Δδ18O value was 5.39 [14], suggesting evaporation to be the major geochemical process for gypsum deposition, that is, the gypsum in the Core SG-1 was likely to deposit directly from brines. The degree

#### **Figure 7.**

*Relationship between δ18O and δD of gypsum hydration water and mother water as compared to meteoric water and different types of water from the Qaidam Basin. The global and modern local meteoric waterlines are from Craig [22] and Li et al. [23], respectively. The present-day precipitation and Dachaidan geothermal water are from Zhang [24]. Altyn Tagh Mountain groundwater data are from Wang et al. [42].*

of evaporation depends upon the salinity and atmospheric humidity [22, 48]. In humid conditions, ΔδD/Δδ18O gradients are usually between ~5 and ~6, whereas the gradient can be low as 2.5–4 in arid regions. The evaporation line gradient for present-day Qaidam Basin meteoric water is lower 4.4 [24], which is less than that of gypsum hydration water in Core SG-1. This suggested that brine in the 2.2–0.1 Ma had lighter isotopes than today's local meteoric water and that evaporation was weaker than today's.

#### **2.4 Paleoclimatic implications**

The climate in the area indicates a long-term persistent aridification event in inland Asia, which is supported by several climate proxies [10–15]. The δ 18O and δD of the clay interlayer water and gypsum hydrated water both reflect the compositional variations of the lake water or pore water and record changes in environment [14, 18]. According to the significant positive relationship between δ 18O and δD and their low slope (2.933, **Figure 7**), most of the interlayer water could be from pore water and lake water in an evaporative environment. The main factor contributing to the variations in the δ 18O and δD water was probably E/P value oscillations, which were linked to the climate changes.

Both the lake water and gypsum hydrated water, their curves of the δ18O and δD, display a stepwise increasing trend (**Figure 8**), indicating a drying trend from 2.2 to 0.1 Ma. This is consistent with the global cooling trend, which is also recorded by the δ18O of marine sediments (**Figure 8**). The lower values of δ 18O and δD in 1.2–0.1 Ma than in 2.77–1.2 Ma (**Figure 8**) agreed with the sedimentary changes from brackish lakes to saline and playa lakes [10]. Compared with brackish lakes, it is harder for brines in mudflat and playa lakes to lose water. The occurrence of Na2SO4-bearing salt minerals such as glauberite, thenardite, mirabilite, and bloedite [11] and the high δ 18O of carbonates [13] also suggest the climate to be extremely

**47**

[10–13, 49–51].

*paleomagnetic results of Zhang et al. [9].*

**Figure 8.**

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

arid in 1.2–0.1 Ma. At about 1.2–1.1 Ma, the low value was likely due to the MPT cold event, which was also recorded in other places in the Qaidam Basin [49]. This is also consistent with other proxies in Central Asia such as lithological and sedimentary records, evaporative minerals, pollen records, grain size, and trace elements

*Hydrogen and oxygen isotopes of gypsum hydrated water and interlayer water of clay minerals vs. depth. The lithologic column and sedimentary environment are from Wang et al. [10]. The ages were based on* 

In summary, δ18O and δD of the gypsum hydrated water, and interlay water of

Halite is common in evaporite deposits. Today, exploited evaporite deposits are most found in the arid and semiarid deserts of the world (the areas between latitudes 15° and 45° both north and south of the equator). Tectonics, climate, and origins of brine are the prime controls on most evaporite deposits. However, the origins of brine were a big topic. Giant evaporite deposits typically originate from brines with a marine or/and land origin(s), along with varying inputs from deeply circulated meteoric, basinal, and hydrothermal fluids [52]. The isotopes of S, Sr, and B of halite could be very useful in determining the origins of brine. We used well-known accepted methods to analyze halite and the isotopes to distinguish

Southeast Asia is composed of a series of Gondwana-derived continental blocks which experienced heterogeneous collision with the closure of multiple Tethyan Ocean branches (see reviews in Metcalfe [53, 54]). The Khorat Basin (KB) in Thailand and Sakhon Nakhon Basin (SNB) and the Lanping-Simao Basin (LSB) in Southwest China belong to the Indochina Block (**Figure 9**). The central part of the

clay in high saline conditions, both have recorded environmental signals.

**3. The isotopes of Sr, S, and B of halite in saline conditions**

origins of brine for the evaporite deposits in Laos and Southern China.

**3.1 Geological setting and the Core ZK2893**

*3.1.1 Geological setting in Laos and Southern China*

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

#### **Figure 8.**

*Isotopes Applications in Earth Sciences*

of evaporation depends upon the salinity and atmospheric humidity [22, 48]. In humid conditions, ΔδD/Δδ18O gradients are usually between ~5 and ~6, whereas the gradient can be low as 2.5–4 in arid regions. The evaporation line gradient for present-day Qaidam Basin meteoric water is lower 4.4 [24], which is less than that of gypsum hydration water in Core SG-1. This suggested that brine in the 2.2–0.1 Ma had lighter isotopes than today's local meteoric water and that evaporation was

*water are from Zhang [24]. Altyn Tagh Mountain groundwater data are from Wang et al. [42].*

*Relationship between δ18O and δD of gypsum hydration water and mother water as compared to meteoric water and different types of water from the Qaidam Basin. The global and modern local meteoric waterlines are from Craig [22] and Li et al. [23], respectively. The present-day precipitation and Dachaidan geothermal* 

The climate in the area indicates a long-term persistent aridification event in

of the clay interlayer water and gypsum hydrated water both reflect the compositional variations of the lake water or pore water and record changes in environment

their low slope (2.933, **Figure 7**), most of the interlayer water could be from pore water and lake water in an evaporative environment. The main factor contribut-

1.2–0.1 Ma than in 2.77–1.2 Ma (**Figure 8**) agreed with the sedimentary changes from brackish lakes to saline and playa lakes [10]. Compared with brackish lakes, it is harder for brines in mudflat and playa lakes to lose water. The occurrence of Na2SO4-bearing salt minerals such as glauberite, thenardite, mirabilite, and bloedite

Both the lake water and gypsum hydrated water, their curves of the δ18O and δD, display a stepwise increasing trend (**Figure 8**), indicating a drying trend from 2.2 to 0.1 Ma. This is consistent with the global cooling trend, which is also recorded

18O of carbonates [13] also suggest the climate to be extremely

18O and δD water was probably E/P value oscillations,

18O and δD

18O and δD and

18O and δD in

inland Asia, which is supported by several climate proxies [10–15]. The δ

[14, 18]. According to the significant positive relationship between δ

by the δ18O of marine sediments (**Figure 8**). The lower values of δ

**46**

[11] and the high δ

weaker than today's.

**Figure 7.**

**2.4 Paleoclimatic implications**

ing to the variations in the δ

which were linked to the climate changes.

*Hydrogen and oxygen isotopes of gypsum hydrated water and interlayer water of clay minerals vs. depth. The lithologic column and sedimentary environment are from Wang et al. [10]. The ages were based on paleomagnetic results of Zhang et al. [9].*

arid in 1.2–0.1 Ma. At about 1.2–1.1 Ma, the low value was likely due to the MPT cold event, which was also recorded in other places in the Qaidam Basin [49]. This is also consistent with other proxies in Central Asia such as lithological and sedimentary records, evaporative minerals, pollen records, grain size, and trace elements [10–13, 49–51].

In summary, δ18O and δD of the gypsum hydrated water, and interlay water of clay in high saline conditions, both have recorded environmental signals.

## **3. The isotopes of Sr, S, and B of halite in saline conditions**

Halite is common in evaporite deposits. Today, exploited evaporite deposits are most found in the arid and semiarid deserts of the world (the areas between latitudes 15° and 45° both north and south of the equator). Tectonics, climate, and origins of brine are the prime controls on most evaporite deposits. However, the origins of brine were a big topic. Giant evaporite deposits typically originate from brines with a marine or/and land origin(s), along with varying inputs from deeply circulated meteoric, basinal, and hydrothermal fluids [52]. The isotopes of S, Sr, and B of halite could be very useful in determining the origins of brine. We used well-known accepted methods to analyze halite and the isotopes to distinguish origins of brine for the evaporite deposits in Laos and Southern China.

#### **3.1 Geological setting and the Core ZK2893**

#### *3.1.1 Geological setting in Laos and Southern China*

Southeast Asia is composed of a series of Gondwana-derived continental blocks which experienced heterogeneous collision with the closure of multiple Tethyan Ocean branches (see reviews in Metcalfe [53, 54]). The Khorat Basin (KB) in Thailand and Sakhon Nakhon Basin (SNB) and the Lanping-Simao Basin (LSB) in Southwest China belong to the Indochina Block (**Figure 9**). The central part of the

#### **Figure 9.**

*(a) Google Earth map showing the locations of the Sakhon Nakhon Basin and the Khorat Basin; (b) tectonic map modified from Sone and Metcalfe [55] and El Tabakh et al. [56]; (c) location of Khorat Basin and Sakhon Nakhon Basin, in the Middle and Late Cretaceous (after El Tabakh et al. [56]); (d) geological map showing the general distribution of sediments in the study region (after Zhang et al. [57]).*

Indochina Block (the Khorat Plateau) is relatively rigid with respect to the Simao Terrane (including the LSB) and has been experiencing clockwise rotation of about 15° up to the present day [58, 59]. The location of LSB changed from 25.7° N in Cretaceous to 18.6°N in Paleocene and Eocene [60]. This suggested that the LSB was gradually southward approaching the KB and SNB.

During the Middle and Late Cretaceous, salts formed; however, these salt formations lie atop thick nonmarine sediments of the Mesozoic Khorat Group. The nonmarine sediments were more than 5 km thick, which were deposited in the Late Triassic [56, 61, 62]. From the very Late Triassic to the Early Cretaceous, the KB and SNB were filled with fluvial and lacustrine facies [56]. Due to the occurrence of similar salt minerals within the same tectonic belt in KB and the LSB, they have formed in brines from similar sources [63].

In the mid-Cretaceous, the basins (LSB, KB, and SNB) were within the subtropical high-pressure belt [64]. However, the scale of the Mengye potash deposit in the LSB is much smaller than those in the KB and SNB of Thailand and Laos [63]. This surprising contrast drove many scientists to explore it in the area for ~50 years. But no consensus has therefore been reached regarding their fluid origins [56, 65, 66].

**49**

**Figure 10.**

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

The lithostratigraphy contained three evaporite-clastic cycles, upper member (148.4 m to top), middle member (299.2–148.4 m), and lower member cycles (595.4– 299.2 m), which are composed of evaporite unit and red-colored siliciclastic unit (**Figure 10**). The lithostratigraphy of the core could match with a reviewed section by El Tabakh et al. [56]. Blocky halite beds were only present in the lower and middle members (**Figure 11**). Chevron or cumulate crystals were well developed. Some thin salt units are observed (**Figure 10**), suggesting salt dissolution to be happened and their dissolved solutes to be mixed with their adjacent mudstone. Salt dissolution resulted in a lack of salts in many cores and the deposition of anhydrite [56].

The evaporite minerals in the halite beds are pure, massive red halite in ZK2893 (**Figure 11**). Some samples have trace or minor anhydrite content [60]. Compared with gypsum, the crystal shapes of halite seldom vary. But halite is much easier to be dissolved and recrystallized than gypsum. The halite crystals in the Core ZK2893 were primary, because (a) the primary fluid inclusions were developed (**Figure 12**), suggesting the halite was not dissolved; (b) the curve of Br in the core changed with depth (**Figure 13C**), consistent with the Br curve of primary halite (**Figure 13A**) and very different with the Br curve of secondary halite (**Figure 13B**); and (c) the Br of basal halite was the lowest in the core, suggesting the primary halite to have been preserved. Basal halite is defined as the first Cl mineral to be precipitated during the evaporation of seawater/lake water. During syndepositional and early diagenetic processes, Br content of basal halite is stable [69, 71], and the initial compositions of

*Left: lithostratigraphical review of the evaporite formation of the Khorat basin and Sakhon Nakhon Basins, after El Tabakh et al. [56]. Right: lithostratigraphy of Core ZK2893 (this study). The paleomagnetic ages are from Zhang [67]; the pollen ages are from Zhong et al. [62]; the isotopic ages are from Hansen et al. [68].*

*3.1.2 The Core ZK2893 in Laos*

**3.2 Halite**

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

## *3.1.2 The Core ZK2893 in Laos*

The lithostratigraphy contained three evaporite-clastic cycles, upper member (148.4 m to top), middle member (299.2–148.4 m), and lower member cycles (595.4– 299.2 m), which are composed of evaporite unit and red-colored siliciclastic unit (**Figure 10**). The lithostratigraphy of the core could match with a reviewed section by El Tabakh et al. [56]. Blocky halite beds were only present in the lower and middle members (**Figure 11**). Chevron or cumulate crystals were well developed. Some thin salt units are observed (**Figure 10**), suggesting salt dissolution to be happened and their dissolved solutes to be mixed with their adjacent mudstone. Salt dissolution resulted in a lack of salts in many cores and the deposition of anhydrite [56].

#### **3.2 Halite**

*Isotopes Applications in Earth Sciences*

Indochina Block (the Khorat Plateau) is relatively rigid with respect to the Simao Terrane (including the LSB) and has been experiencing clockwise rotation of about 15° up to the present day [58, 59]. The location of LSB changed from 25.7° N in Cretaceous to 18.6°N in Paleocene and Eocene [60]. This suggested that the LSB was

*showing the general distribution of sediments in the study region (after Zhang et al. [57]).*

*(a) Google Earth map showing the locations of the Sakhon Nakhon Basin and the Khorat Basin; (b) tectonic map modified from Sone and Metcalfe [55] and El Tabakh et al. [56]; (c) location of Khorat Basin and Sakhon Nakhon Basin, in the Middle and Late Cretaceous (after El Tabakh et al. [56]); (d) geological map* 

During the Middle and Late Cretaceous, salts formed; however, these salt formations lie atop thick nonmarine sediments of the Mesozoic Khorat Group. The nonmarine sediments were more than 5 km thick, which were deposited in the Late Triassic [56, 61, 62]. From the very Late Triassic to the Early Cretaceous, the KB and SNB were filled with fluvial and lacustrine facies [56]. Due to the occurrence of similar salt minerals within the same tectonic belt in KB and the LSB, they have

In the mid-Cretaceous, the basins (LSB, KB, and SNB) were within the subtropical high-pressure belt [64]. However, the scale of the Mengye potash deposit in the LSB is much smaller than those in the KB and SNB of Thailand and Laos [63]. This surprising contrast drove many scientists to explore it in the area for ~50 years. But no consensus has therefore been reached regarding their fluid

gradually southward approaching the KB and SNB.

formed in brines from similar sources [63].

**48**

**Figure 9.**

origins [56, 65, 66].

The evaporite minerals in the halite beds are pure, massive red halite in ZK2893 (**Figure 11**). Some samples have trace or minor anhydrite content [60]. Compared with gypsum, the crystal shapes of halite seldom vary. But halite is much easier to be dissolved and recrystallized than gypsum. The halite crystals in the Core ZK2893 were primary, because (a) the primary fluid inclusions were developed (**Figure 12**), suggesting the halite was not dissolved; (b) the curve of Br in the core changed with depth (**Figure 13C**), consistent with the Br curve of primary halite (**Figure 13A**) and very different with the Br curve of secondary halite (**Figure 13B**); and (c) the Br of basal halite was the lowest in the core, suggesting the primary halite to have been preserved.

Basal halite is defined as the first Cl mineral to be precipitated during the evaporation of seawater/lake water. During syndepositional and early diagenetic processes, Br content of basal halite is stable [69, 71], and the initial compositions of

#### **Figure 10.**

*Left: lithostratigraphical review of the evaporite formation of the Khorat basin and Sakhon Nakhon Basins, after El Tabakh et al. [56]. Right: lithostratigraphy of Core ZK2893 (this study). The paleomagnetic ages are from Zhang [67]; the pollen ages are from Zhong et al. [62]; the isotopic ages are from Hansen et al. [68].*

**Figure 11.** *Photos of halite in Core ZK2893 (after Li et al. [60]).*

**Figure 12.** *Photomicrographs showing primary fluid inclusion banding in chevron halite.*

brine are well-preserved in basal halite [60, 71]. Therefore, the Br content of basal halite can be used to reconstruct the composition and origins of paleo-water. For example, Siemann [71] used the Br content of primary basal halite to reconstruct the Br variations in seawater over the past 500 Ma.

## **3.3 The isotopes of sulfur, strontium, and boron**

Isotopic compositions of sulfur, boron, and strontium could be more robust indicators of the origins of evaporites (marine vs. continental origins).

## *3.3.1 Sulfur isotope*

Waters from continental sources in general have lower δ34S values than those from contemporary seawater. The 34S values of freshwater usually range from −5 to 5%, while that of recent seawater is globally uniform with value being 20 ± 0.5% [72]. Sulfate minerals (such as gypsum and anhydrite) have stable δ34S values and are typically resistant to diagenetic alteration [72–74]. Factors influencing the δ34S values of evaporative sulfates are marine and nonmarine contributions, reservoirs, and redox [72, 74]. For example, bacterial-facilitated sulfate reduction is preferentially enriched in lighter 32S isotope, and therefore, the residual sulfate minerals

**51**

*3.3.2 Strontium isotope*

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

abovementioned basins (**Figure 14**).

**Figure 13.**

*halite in the core to be primary.*

paleo-lake water possible to be mixed with freshwater.

(such as gypsum) will enrich heavy 34S [72, 73]. In contrast, reservoir effects can decrease δ34S values of the subsequently precipitated gypsum. If sulfate evaporites precipitated in a closed system, the δ34S values expectedly display a gradual decrease upward in a vertical stratigraphic sequence. The reservoir effect played an active role influencing the δ34S values of gypsum, anhydrite, and halite in the

*(A) Curves of Br in primary halite in KB, after Hite and Japakasetr [69]. (B) Curves of Br in secondary halite, after Hite and Japakasetr [69]. (C) Curves of Br in the Core ZK2893 in SNB, Laos [70], suggesting the* 

The average of δ34S values increase from the lower to the upper member, which indicates an evaporation effect. Microbial effect on the core's δ34S-SO4 values may be insignificant. This could be understood in the following. (a) There is no relationship between sulfate concentrations and the δ34S-SO4 values of halite (**Figure 14**). Generally, microbial sulfate reduction can result in an inverse correlation of them [78]. And (b) the δ34S values observed in the halite and anhydrite are very similar. Redox recycling of bacterial reduction can result in the enrichment of δ34S values and significant difference within evaporites [72, 73]. Therefore, δ34S in this study could be used to identify the origins of brine. In the Core ZK2893, all of δ34S values are lower than, or similar to, those of contemporary seawater (**Figure 14**), suggesting a possible continental origin. Both the δ34S and δ18O-SO4 values of halite are lower than those of Middle Cretaceous seawater (**Figure 14**) with a short range dispersion, shorter than that between δ34S and SO4 values (**Figure 14**), suggesting that

Strontium is a divalent alkaline earth element. Its isotope composition is almost homogeneous with modern seawater with 87Sr/86Sr values of 0.709175–0.709235 [79, 80]. Because the Sr composition/isotope ratios for the weathering and erosion of rocks are high [81], the 87Sr/86Sr ratios for river water evince a large range

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

**Figure 13.**

*Isotopes Applications in Earth Sciences*

*Photos of halite in Core ZK2893 (after Li et al. [60]).*

brine are well-preserved in basal halite [60, 71]. Therefore, the Br content of basal halite can be used to reconstruct the composition and origins of paleo-water. For example, Siemann [71] used the Br content of primary basal halite to reconstruct

Isotopic compositions of sulfur, boron, and strontium could be more robust

Waters from continental sources in general have lower δ34S values than those from contemporary seawater. The 34S values of freshwater usually range from −5 to 5%, while that of recent seawater is globally uniform with value being 20 ± 0.5% [72]. Sulfate minerals (such as gypsum and anhydrite) have stable δ34S values and are typically resistant to diagenetic alteration [72–74]. Factors influencing the δ34S values of evaporative sulfates are marine and nonmarine contributions, reservoirs, and redox [72, 74]. For example, bacterial-facilitated sulfate reduction is preferentially enriched in lighter 32S isotope, and therefore, the residual sulfate minerals

indicators of the origins of evaporites (marine vs. continental origins).

the Br variations in seawater over the past 500 Ma.

*Photomicrographs showing primary fluid inclusion banding in chevron halite.*

**3.3 The isotopes of sulfur, strontium, and boron**

**50**

*3.3.1 Sulfur isotope*

**Figure 11.**

**Figure 12.**

*(A) Curves of Br in primary halite in KB, after Hite and Japakasetr [69]. (B) Curves of Br in secondary halite, after Hite and Japakasetr [69]. (C) Curves of Br in the Core ZK2893 in SNB, Laos [70], suggesting the halite in the core to be primary.*

(such as gypsum) will enrich heavy 34S [72, 73]. In contrast, reservoir effects can decrease δ34S values of the subsequently precipitated gypsum. If sulfate evaporites precipitated in a closed system, the δ34S values expectedly display a gradual decrease upward in a vertical stratigraphic sequence. The reservoir effect played an active role influencing the δ34S values of gypsum, anhydrite, and halite in the abovementioned basins (**Figure 14**).

The average of δ34S values increase from the lower to the upper member, which indicates an evaporation effect. Microbial effect on the core's δ34S-SO4 values may be insignificant. This could be understood in the following. (a) There is no relationship between sulfate concentrations and the δ34S-SO4 values of halite (**Figure 14**). Generally, microbial sulfate reduction can result in an inverse correlation of them [78]. And (b) the δ34S values observed in the halite and anhydrite are very similar. Redox recycling of bacterial reduction can result in the enrichment of δ34S values and significant difference within evaporites [72, 73]. Therefore, δ34S in this study could be used to identify the origins of brine. In the Core ZK2893, all of δ34S values are lower than, or similar to, those of contemporary seawater (**Figure 14**), suggesting a possible continental origin. Both the δ34S and δ 18O-SO4 values of halite are lower than those of Middle Cretaceous seawater (**Figure 14**) with a short range dispersion, shorter than that between δ34S and SO4 values (**Figure 14**), suggesting that paleo-lake water possible to be mixed with freshwater.

#### *3.3.2 Strontium isotope*

Strontium is a divalent alkaline earth element. Its isotope composition is almost homogeneous with modern seawater with 87Sr/86Sr values of 0.709175–0.709235 [79, 80]. Because the Sr composition/isotope ratios for the weathering and erosion of rocks are high [81], the 87Sr/86Sr ratios for river water evince a large range

#### **Figure 14.**

*(a) δ34S values of halite for Core ZK2893 and anhydrite. Anhydrite data are from El Tabakh et al. [58] and Xu [75]. (b) Plot of δ34S-δ18O-SO4 of halite and Mid-Cretaceous seawater. Mid-Cretaceous seawater data are from Claypool et al. [76]. (c) Comparison of δ34S values between halite in this study and seawater. The δ34S curve of seawater from Paytan et al. [77].*

from 0.7074 to 0.803 (**Figure 15**). In a continental setting, the 87Sr/86Sr ratio for continental waters is almost always higher than that for marine waters (**Figure 15**). The 87Sr/86Sr values of Paleocene halite in the Qaidam Basin (a continental basin), for example, were higher than those of Paleocene seawater (**Figure 9**). Thus, the 87Sr/86Sr values of authigenic minerals are very variable and higher than those of seawater when the minerals are precipitated from a solution.

As no fractionation of Sr isotopes occurs during halite precipitation, the measured halite 87Sr/86Sr ratios for Core ZK2893 (ranging from 0.707443 to 0.708587) could represent those of the parent solution. 87Sr/86Sr ratios for the lower member ranged from 0.707443 to 0.708587, averaging 0.707693, while those for the middle member ranged from 0.70752 to 0.708105, averaging 0.70764. There was only one 87Sr/86Sr ratio value in the upper member, of 0.708163. In the lower member, the possible reasons for the high 87Sr/86Sr ratios in the upper part (**Figure 15**) are (a) the permeation of continental waters from the middle clastic unit into the halite layers and (b) an inflow of continental waters into the Sakhon Nakhon Basin during the shrinkage process of the basin. However, the 87Sr/86Sr ratios exhibit no significant variability in the middle member [83], suggesting no, or little, penetration of continental waters into the halite layers. The 87Sr/86Sr and 1/Sr halite ratios in Core ZK2893 do not show a linear relation but rather a weak positive relation (**Figure 15a**). Some 87Sr/86Sr ratios are far higher than those of contemporary seawater, indicating the possible input of continental waters into these evaporite basins; these 87Sr/86Sr ratios in the lower member are lower than, or similar to, those of Cretaceous seawater; further, mean Middle Cretaceous 87Sr/86Sr ratios are similar to those of paleo-seawater (**Figure 15b**), suggesting a marine remnant origin.

#### *3.3.3 Boron isotope*

Natural boron, a highly soluble element, has two stable isotopes (l0B and l1B) with approximate abundances of 20 and 80%, respectively. Boron isotope

**53**

**Figure 15.**

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

fractionation is dependent upon the distribution of boron species, temperature, and pH, but pH is the key factor [84–89]. Dissolved boron exists mainly in the form of B(OH)3 and B(OH)4, which are dominantly present as 11B(OH)3 at low pH values and as 10B(OH)4 at high pH values [85–88]. Because pH values increased with the increasing extent of evaporation, the minerals precipitated in early stages have higher δ11B values than those of minerals precipitated in later stages. Generally, the sequence of δ11B values of different minerals is following as: carbonate > gypsum > borate > halite > sylvite. As boron was present in inclusion [90], the δ11B values of halite and sylvite are exactly representative of those for contemporary paleo-brines. Therefore, the δ11B values of halite and sylvite are higher than those in carbonates and borate minerals, and all of minerals have lower δ11B than those of brine. In the Core ZK2893, however, the δ11B values of halite and sylvite were lower than those of borate minerals (**Figure 16**). One possible reason is that there have different sources of brines, such as continental, marine residue and groundwater/hydrothermal brine. In the LSB, China, most of δ11B values of

*for Yunnan Province in China, and for Laos, are from Bo et al. [82].*

*(a) Plot of 87Sr/86Sr and 1/Sr of halite and hot spring water; and (b) 87Sr/86Sr ratios in halite, gypsum, hot spring water and saline lake water: A dot indicates a mean value. Gypsum data are from Tan et al. [66], hot spring data*  *Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

*Isotopes Applications in Earth Sciences*

from 0.7074 to 0.803 (**Figure 15**). In a continental setting, the 87Sr/86Sr ratio for continental waters is almost always higher than that for marine waters (**Figure 15**). The 87Sr/86Sr values of Paleocene halite in the Qaidam Basin (a continental basin), for example, were higher than those of Paleocene seawater (**Figure 9**). Thus, the 87Sr/86Sr values of authigenic minerals are very variable and higher than those of

*(a) δ34S values of halite for Core ZK2893 and anhydrite. Anhydrite data are from El Tabakh et al. [58] and Xu [75]. (b) Plot of δ34S-δ18O-SO4 of halite and Mid-Cretaceous seawater. Mid-Cretaceous seawater data are from Claypool et al. [76]. (c) Comparison of δ34S values between halite in this study and seawater. The δ34S curve of* 

As no fractionation of Sr isotopes occurs during halite precipitation, the measured halite 87Sr/86Sr ratios for Core ZK2893 (ranging from 0.707443 to 0.708587) could represent those of the parent solution. 87Sr/86Sr ratios for the lower member ranged from 0.707443 to 0.708587, averaging 0.707693, while those for the middle member ranged from 0.70752 to 0.708105, averaging 0.70764. There was only one 87Sr/86Sr ratio value in the upper member, of 0.708163. In the lower member, the possible reasons for the high 87Sr/86Sr ratios in the upper part (**Figure 15**) are (a) the permeation of continental waters from the middle clastic unit into the halite layers and (b) an inflow of continental waters into the Sakhon Nakhon Basin during the shrinkage process of the basin. However, the 87Sr/86Sr ratios exhibit no significant variability in the middle member [83], suggesting no, or little, penetration of continental waters into the halite layers. The 87Sr/86Sr and 1/Sr halite ratios in Core ZK2893 do not show a linear relation but rather a weak positive relation (**Figure 15a**). Some 87Sr/86Sr ratios are far higher than those of contemporary seawater, indicating the possible input of continental waters into these evaporite basins; these 87Sr/86Sr ratios in the lower member are lower than, or similar to, those of Cretaceous seawater; further, mean Middle Cretaceous 87Sr/86Sr ratios are similar to those of paleo-seawater (**Figure 15b**), suggesting a marine remnant origin.

Natural boron, a highly soluble element, has two stable isotopes (l0B and l1B) with approximate abundances of 20 and 80%, respectively. Boron isotope

seawater when the minerals are precipitated from a solution.

**52**

*3.3.3 Boron isotope*

**Figure 14.**

*seawater from Paytan et al. [77].*

**Figure 15.**

*(a) Plot of 87Sr/86Sr and 1/Sr of halite and hot spring water; and (b) 87Sr/86Sr ratios in halite, gypsum, hot spring water and saline lake water: A dot indicates a mean value. Gypsum data are from Tan et al. [66], hot spring data for Yunnan Province in China, and for Laos, are from Bo et al. [82].*

fractionation is dependent upon the distribution of boron species, temperature, and pH, but pH is the key factor [84–89]. Dissolved boron exists mainly in the form of B(OH)3 and B(OH)4, which are dominantly present as 11B(OH)3 at low pH values and as 10B(OH)4 at high pH values [85–88]. Because pH values increased with the increasing extent of evaporation, the minerals precipitated in early stages have higher δ11B values than those of minerals precipitated in later stages. Generally, the sequence of δ11B values of different minerals is following as: carbonate > gypsum > borate > halite > sylvite. As boron was present in inclusion [90], the δ11B values of halite and sylvite are exactly representative of those for contemporary paleo-brines. Therefore, the δ11B values of halite and sylvite are higher than those in carbonates and borate minerals, and all of minerals have lower δ11B than those of brine. In the Core ZK2893, however, the δ11B values of halite and sylvite were lower than those of borate minerals (**Figure 16**). One possible reason is that there have different sources of brines, such as continental, marine residue and groundwater/hydrothermal brine. In the LSB, China, most of δ11B values of

#### **Figure 16.**

*δ11B values from published papers. Marine and nonmarine borates after Swihart et al. [91], Xiao et al. [90], and Palmer and Helvaci [85]. Seawater after Vengosh et al. [86] and Foster et al. [89]. River water after Vengosh et al. [7]; Rose et al. [92]; and Lemarchand et al. [93]. Halite after from Vengosh et al. [86]; Liu et al. [94]; and Kloppmann et al. [95]. Borate minerals in SNB after Zhang et al. [96]. Halite and sylvite in SNB after Tan et al. [66]). Halite and sylvite in LSB after Zhang et al. [97]. Curve of seawater after Lemarchand et al. [98].*

halite and sylvite ranged from −1.54 to 19.1%, which are lower than those in Laos (19.9–31.1‰) (**Figure 16**). This suggested the paleo-brines in LSB, China, are from Laos and diluted during the flow process.

Comparison of δ11B values between known marine minerals and unknown minerals is a useful way to distinguish marine and continental origin. In nonmarine setting, some δ11B values of hydrothermal fluid, saline lake water and river water, are higher than those of seawater (**Figure 16**), that is, lower δ11B values of minerals than that of seawater are not indicate continental origin. The comparison of δ11B between salt minerals is valid. Although the δ11B values of halite in Laos were lower than those of seawater, they were near to those of marine borates (**Figure 16**). This suggested minor or trace marine origin. The δ11B values of the evaporite in LSB in China are lower than, but some are near to, those of halite and sylvite in SNB, Laos, also suggesting continental origin with minor residual seawater.

In summary, halite isotopic compositions (in the form of δ34S-δ18O-SO4 values, 87Sr/86Sr and δ 11B) appear to represent an original composition associated with brine. These isotopic proxies indicate that continental and hydrothermal origins are likely to be more important sources of evaporite deposits than marine origins for these Laotian evaporite deposits.

#### **4. Summary**

The gypsum in the Core SG-1 was deposited directly from brines and was stable after deposition. The δ 18O and δD curves of hydrated water in gypsum record the evolution of paelo-lake in Qaidam Basin, Western Tibetan Plateau since 2.2 Ma, including the famous cold event, mid-Pleistocene event.

**55**

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

environment.

ing δ34S-δ18O-SO4, 87Sr/86Sr, and δ

**Acknowledgements**

**Author details**

and Liping Zhu1,2,4

Beijing, China

China

between the interlayer water and the ambient water. The δ

origins are likely to be more important than marine origins.

Foundation of China (Grant No. 41620104002).

Minghui Li1,2\*, Xiaomin Fang2,3,4, Jiao Li1

In high saline conditions, the clay minerals from Core SG-1 may have undergone early diagenesis. The primary illite and chlorite contents in Core SG-1 were lower than those observed, while the primary smectite and kaolinite contents were higher than those observed. After early diagenesis, there were no isotopic exchange

cated the interlayer water of clay minerals to be more concentrated than those of hydrated water. The isotopic composition of the interlayer water reflects variations in the pore water/lake water or in the reacting solutions and also records changes in

Using isotopic compositions of salt minerals to identify origins of brine is a complex topic. It should be careful to use sole isotope to identify the origins. For the evaporite deposits in LSB in China and NSB, in Laos, these isotopic proxies, includ-

This study was supported by the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDA20070201, XDA20070101), the National Basic Research Program of China (Grant No. 2017YFC0602803), the International Cooperation Project of the Chinese Academy of Sciences (Grant No. 131C11KYSB20160072), the Second Tibetan Plateau Scientific Expedition and Research (Grant No. 2019QZKK0202), and the National Natural Science

1 Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences (ITPCAS),

2 CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing, China

3 Key Laboratory of Continental Collision and Plateau Uplift, ITPCAS, Beijing,

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

4 University of Chinese Academy of Sciences, Beijing, China

\*Address all correspondence to: liminghui@itpcas.ac.cn

provided the original work is properly cited.

11B, indicate that continental and hydrothermal

, Maodu Yan2,3, Shurui Sun1

18O and δD values indi-

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

*Isotopes Applications in Earth Sciences*

halite and sylvite ranged from −1.54 to 19.1%, which are lower than those in Laos (19.9–31.1‰) (**Figure 16**). This suggested the paleo-brines in LSB, China, are from

*δ11B values from published papers. Marine and nonmarine borates after Swihart et al. [91], Xiao et al. [90], and Palmer and Helvaci [85]. Seawater after Vengosh et al. [86] and Foster et al. [89]. River water after Vengosh et al. [7]; Rose et al. [92]; and Lemarchand et al. [93]. Halite after from Vengosh et al. [86]; Liu et al. [94]; and Kloppmann et al. [95]. Borate minerals in SNB after Zhang et al. [96]. Halite and sylvite in SNB after Tan et al. [66]). Halite and sylvite in LSB after Zhang et al. [97]. Curve of seawater after Lemarchand et al. [98].*

Comparison of δ11B values between known marine minerals and unknown minerals is a useful way to distinguish marine and continental origin. In nonmarine setting, some δ11B values of hydrothermal fluid, saline lake water and river water, are higher than those of seawater (**Figure 16**), that is, lower δ11B values of minerals than that of seawater are not indicate continental origin. The comparison of δ11B between salt minerals is valid. Although the δ11B values of halite in Laos were lower than those of seawater, they were near to those of marine borates (**Figure 16**). This suggested minor or trace marine origin. The δ11B values of the evaporite in LSB in China are lower than, but some are near to, those of halite and sylvite in SNB, Laos, also suggesting continental origin with minor residual

In summary, halite isotopic compositions (in the form of δ34S-δ18O-SO4 values,

brine. These isotopic proxies indicate that continental and hydrothermal origins are likely to be more important sources of evaporite deposits than marine origins for

The gypsum in the Core SG-1 was deposited directly from brines and was stable

evolution of paelo-lake in Qaidam Basin, Western Tibetan Plateau since 2.2 Ma,

including the famous cold event, mid-Pleistocene event.

18O and δD curves of hydrated water in gypsum record the

11B) appear to represent an original composition associated with

Laos and diluted during the flow process.

**54**

seawater.

**Figure 16.**

87Sr/86Sr and δ

**4. Summary**

after deposition. The δ

these Laotian evaporite deposits.

In high saline conditions, the clay minerals from Core SG-1 may have undergone early diagenesis. The primary illite and chlorite contents in Core SG-1 were lower than those observed, while the primary smectite and kaolinite contents were higher than those observed. After early diagenesis, there were no isotopic exchange between the interlayer water and the ambient water. The δ 18O and δD values indicated the interlayer water of clay minerals to be more concentrated than those of hydrated water. The isotopic composition of the interlayer water reflects variations in the pore water/lake water or in the reacting solutions and also records changes in environment.

Using isotopic compositions of salt minerals to identify origins of brine is a complex topic. It should be careful to use sole isotope to identify the origins. For the evaporite deposits in LSB in China and NSB, in Laos, these isotopic proxies, including δ34S-δ18O-SO4, 87Sr/86Sr, and δ 11B, indicate that continental and hydrothermal origins are likely to be more important than marine origins.

## **Acknowledgements**

This study was supported by the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDA20070201, XDA20070101), the National Basic Research Program of China (Grant No. 2017YFC0602803), the International Cooperation Project of the Chinese Academy of Sciences (Grant No. 131C11KYSB20160072), the Second Tibetan Plateau Scientific Expedition and Research (Grant No. 2019QZKK0202), and the National Natural Science Foundation of China (Grant No. 41620104002).

## **Author details**

Minghui Li1,2\*, Xiaomin Fang2,3,4, Jiao Li1 , Maodu Yan2,3, Shurui Sun1 and Liping Zhu1,2,4

1 Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences (ITPCAS), Beijing, China

2 CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing, China

3 Key Laboratory of Continental Collision and Plateau Uplift, ITPCAS, Beijing, China

4 University of Chinese Academy of Sciences, Beijing, China

\*Address all correspondence to: liminghui@itpcas.ac.cn

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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*Isotopes Applications in Earth Sciences*

[1] Chen K, Bowler JM. Late Pleistocene evolution of salt lakes in the Qaidam basin, Qinghai province, China. Palaeogeography, Palaeoclimatology, Palaeoecology. 1986;**54**:87-104

Review of Earth and Planetary Sciences.

[9] Zhang WL, Appel E, Fang XM, Song CH, Cirpka O. Magnetostratigraphy of deep drilling core SG-1 in the western Qaidam Basin (NE Tibetan Plateau) and its tectonic implications. Quaternary

Research. 2012;**78**(1):139-148

[10] Wang JY, Fang XM, Appel E, Song CH. Pliocene-Pleistocene climate change at the NE Tibetan Plateau deduced from lithofacies variation in the drill Core SG-1, western Qaidam basin, China. Journal of Sedimentary Research. 2012;**82**(12):933-952

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[12] Li MH, Fang XM, Yi CL, Gao SP, Zhang WL, Galy A. Evaporite minerals and geochemistry of the upper 400 m sediments in a core from the Western Qaidam Basin, Tibet. Quaternary International. 2010;**218**(1-2):176-189

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Change. 2014;**116**:68-75

Zhang WL, Liu XM. Isotopic composition of gypsum hydration water in deep Core SG-1, western Qaidam basin (NE Tibetan Plateau), implications for paleoclimatic evolution.

Global and Planetary Change.

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2013;**298**:123-133

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[3] Fang X, Zhang W, Meng X, Gao J, Wang X, King J, et al. High-resolution magnetostratigraphy of the Neogene Huaitoutala section in the eastern Qaidam Basin on the NE Tibetan

Plateau, Qinghai Province, China and its implication on tectonic uplift of the NE Tibetan Plateau. Earth and Planetary Science Letters. 2007;**258**(1-2):293-306

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2008;**27**:867-879

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[6] Mischke S, Sun Z, Herzschuh U, Qiao Z, Sun N. An ostracod-inferred large Middle Pleistocene freshwater lake in the presently hyper-arid Qaidam

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[45] Dowuona GN, Mermut AR, Krouse HR. Isotopic composition of hydration water in gypsum and hydroxyl in jarosite. Soil Science Society of America Journal. 1992;**56**(1):309-313

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[59] Yang W, Spencer RJ, Roy Krouse H, Lowenstein TK, Casas E. Stable isotopes of lake and fluid inclusion brines, Dabusun Lake, Qaidam Basin, western China: Hydrology and paleoclimatology in arid environments. Palaeogeography Palaeoclimatology Palaeoecology.

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[61] Timofeeff MN, Lowenstein TK, Da Silva MAM, Harris NB. Secular variation in the major-ion chemistry of seawater: Evidence from fluid inclusions in cretaceous halites. Geochimica et Cosmochimica Acta.

[62] Zhong XY, Yuan Q, Qin ZJ, Wei HC, Shan FS. The sporo-pollen analyses and ore-forming age of Nong Bok formation in Khammouane, Laos. Acta Geoscientica Sinica. 2012;**33**(3):323-330 (in Chinese with English abstract)

[63] Qu YH, Yuan PQ, Shuai KY, Zhang Y, Cai KQ, Jia SY, et al. Potash Forming Rules and Prospects of Lower Tertiary in Lanping-Simao Basin,

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[54] Metcalfe I. Gondwana dispersion and Asian accretion: Tectonic and palaeogeographic evolution of eastern Tethys. Journal of Asian Earth Sciences.

[55] Sone M, Metcalfe I. Parallel Tethyan sutures in mainland Southeast Asia: New insights for Palaeo-Tethys closure and implications for the Indosinian orogeny. Comptes Rendus Geoscience.

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[40] Zhang J, Nancollas GH. Influence of calcium/sulfate molar ratio on the growth rate of calcium sulfate dihydrate at constant supersaturation. Journal of Crystal Growth. 1992;**118**:287-294

[41] Franchini-Angela M, Rinaudo C. Influence of sodium and magnesium on the growth-morphology of

gypsum, CaSO4. 2H2O. Neues Jahrbuch Fur Mineralogie Abhandlungen.

[42] Wang ML, Yang ZC, Liu CL, Xie ZC, Jiao PC, Li CH. Potash Deposits and Their Exploitation Prospects of Saline Lakes of the Northern Qaidam Basin. Beijing: Geological Publishing House;

[43] Farpoor MH, Khademi H, Eghbal MK, Krouse HR. Mode of gypsum deposition

1996. pp. 33-51 (in Chinese)

in southeastern Iranian soils as revealed by isotopic composition of crystallization water. Geoderma.

[44] Sofer Z. Isotopic composition of hydration water in gypsum. Geochimica et Cosmochimica Acta.

[45] Dowuona GN, Mermut AR, Krouse HR. Isotopic composition of hydration water in gypsum and hydroxyl in jarosite. Soil Science Society of America Journal. 1992;**56**(1):309-313

[46] Matsubaya O, Sakai H. Oxygen and hydrogen isotopic study on the water of crystallization of gypsum from the Kuroko type mineralization. Geochemical Journal. 1973;**7**(3):153-165

[47] Chen F, Turchyn AV, Kampman N, Hodell D, Gázquez F, Maskell A, et al. Isotopic analysis of sulfur cycling and gypsum vein formation in a natural CO2 reservoir. Chemical Geology.

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[48] Sofer Z, Gat JR. The isotope composition of evaporating brines: Effect of the isotopic activity ratio in saline solutions. Earth and Planetary Science Letters. 1975;**26**(2):179-186

[49] Cai MT, Fang XM, Wu FL, Miao YF, Appel E. Pliocene-Pleistocene stepwise drying of Central Asia: Evidence from paleomagnetism and sporopollen record of the deep borehole SG-3 in the western Qaidam Basin, NE Tibetan Plateau. Global and Planetary Change. 2012;**94-95**:72-81

[50] Wu FL, Fang XM, Ma YZ, Herrmann M, Mosbrugger V, An ZS, et al. Plio–Quaternary stepwise drying of Asia: Evidence from a 3-Ma pollen record from the Chinese Loess Plateau. Earth Planetary Science Letters. 2007;**257**(1-2):160-169

[51] Ding ZL, Sun JM, Liu DS. Stepwise advance of the Mu Us desert since late Pliocene: Evidence from a red clayloess record. Chinese Science Bulletin. 1999;**44**:1211-1214

[52] Warren JK. Evaporites: Sediments, Resources and Hydrocarbons. Berlin: Springer; 2006

[53] Metcalfe I. Tectonic framework and Phanerozoic evolution of Sundaland. Gondwana Research. 2011;**19**:3-21

[54] Metcalfe I. Gondwana dispersion and Asian accretion: Tectonic and palaeogeographic evolution of eastern Tethys. Journal of Asian Earth Sciences. 2013;**66**:1-33

[55] Sone M, Metcalfe I. Parallel Tethyan sutures in mainland Southeast Asia: New insights for Palaeo-Tethys closure and implications for the Indosinian orogeny. Comptes Rendus Geoscience. 2008;**340**(2-3):166-179

[56] El Tabakh M, Utha-Aroon C, Schreiber BC. Sedimentology of the Cretaceous Maha Sarakham evaporites in the Khorat Plateau of northeastern Thailand. Sedimentary Geology. 1999;**123**(1-2):31-62

[57] Zhang XY, Ma HZ, Tan HB, Gao DL, Li BK, Wang MX, et al. Preliminary studies of on geochemistry and postdepositional change of Dong Tai potash deposit in Laos. Mineral Deposits. 2010;**4**:713-721

[58] Yang ZY, Besse J. Paleomagnetic study of Permian and Mesozoic sedimentary rocks from Northern Thailand supports the extrusion model for Indochina. Earth and Planetary Science Letters. 1993;**117**:525-552

[59] Yang W, Spencer RJ, Roy Krouse H, Lowenstein TK, Casas E. Stable isotopes of lake and fluid inclusion brines, Dabusun Lake, Qaidam Basin, western China: Hydrology and paleoclimatology in arid environments. Palaeogeography Palaeoclimatology Palaeoecology. 1995;**117**:279-290

[60] Li MH, Yan MD, Wang ZR, Liu XM, Fang XM, Li J. The origins of the Mengye potash deposit in the Lanping-Simao Basin, Yunnan Province, Western China. Ore Geology Reviews. 2015;**69**:174-186

[61] Timofeeff MN, Lowenstein TK, Da Silva MAM, Harris NB. Secular variation in the major-ion chemistry of seawater: Evidence from fluid inclusions in cretaceous halites. Geochimica et Cosmochimica Acta. 2006;**70**(8):1977-1994

[62] Zhong XY, Yuan Q, Qin ZJ, Wei HC, Shan FS. The sporo-pollen analyses and ore-forming age of Nong Bok formation in Khammouane, Laos. Acta Geoscientica Sinica. 2012;**33**(3):323-330 (in Chinese with English abstract)

[63] Qu YH, Yuan PQ, Shuai KY, Zhang Y, Cai KQ, Jia SY, et al. Potash Forming Rules and Prospects of Lower Tertiary in Lanping-Simao Basin,

Yunnan. Beijing: Geological Press; 1998 (in Chinese with English abstract)

[64] Hasegawa H, Imsamut S, et al. Thailand was a desert' during the mid-Cretaceous: Equatorward shift of the subtropical high-pressure belt indicated by Eolian deposits (Phu Thok Formation) in the Khorat Basin, northeastern Thailand. Island Arc. 2010;**19**(4):605-621

[65] Utha-Aroon C. Continental origin of the Maha Sarakham evaporites, northeastern Thailand. Journal of Southeast Asian Earth Sciences. 1993;**8**(1-4):193-203

[66] Tan H, Ma H, Li BK, Zhang XY, Xiao YK. Strontium and boron isotopic constraint on the marine origin of the Khammouane potash deposits in southeastern Laos. Chinese Science Bulletin. 2010;**55**(27):3181-3188

[67] Zhang DW. Magnetostratigraphic studies of the Potash-bearing strata of the Lanping-Simao and the Vientiane Basins and their tectonic implications [thesis]. University of Chinese Academy of Sciences; 2016 (in Chinese with English abstract)

[68] Hansen BT, Wemmer K, Pawlig S, et al. Isotopic evidence for a Late Cretaceous age of the potash and rock salt deposit at Bamnet Narong, NE Thailand. In: Symposium on the Geology of Thailand, Bangkok; August 2002; Extended Abstract; 2002. pp. 26-31

[69] Hite RJ, Japakasetr T. Potash deposits of the khorat plateau, Thailand and Laos. Economic Geology. 1979;**74**(2):448-458

[70] Sun SR, Li MH, Yan MD, Fang XM, Zhang GX, Liu XM. et al. Bromine content and Br/Cl molar ratio of halite in a core from Laos: Implications for origin and environmental changes. Carbonates and Evaporites. 2019. DOI: 10.1007/s13146-019-00508-0

[71] Siemann MG. Extensive and rapid changes in seawater chemistry during the Phanerozoic: Evidence from Br contents in basal halite. Terra Nova. 2003;**15**(4):243-248

[72] Lu FH, Meyers WJ, Schoonen MA. S and O (SO4) isotopes, simultaneous modeling, and environmental significance of the Nijar Messinian gypsum, Spain. Geochimica et Cosmochimica Acta. 2001;**65**(18):3081-3092

[73] Pierre C. Isotopic evidence for the dynamic redox cycle of dissolved sulphur compounds between free and interstitial solutions in marine salts pans. Chemical Geology. 1985;**53**:191-196

[74] Bottrell SH, Newton RJ. Reconstruction of changes in global sulfur cycling from marine sulfate isotopes. Earth Science Reviews. 2006;**75**:59-83

[75] Xu JX. Geochemistry and genesis of Mengyejing potash deposits [thesis]. Yunnan: Chinese Academy Science; 2008 (in Chinese with English abstract)

[76] Claypool GE, Holser WT, Kaplan IR, Sakai H, Zak I. The age curves of sulfur and oxygen isotopes in marine sulfate and their mutual interpretation. Chemical Geology. 1980;**28**:199-260

[77] Paytan A, Kastner M, Campbell D, Thiemens MH. Seawater sulfur isotope fluctuations in the Cretaceous. Science. 2004;**304**:1663-1665

[78] Hurtgen MT, Suits NS, Kaufman AJ. The sulfur isotopic composition of Neoproterozoic seawater sulfate: Implications for a snowball earth? Earth and Planetary Science Letters. 2002;**203**(1):413-429

[79] Hess J, Bender ML, Schilling JG. Evolution of ratio of strontium 87 to strontium 86 in seawater from

**61**

*Isotopic Application in High Saline Conditions DOI: http://dx.doi.org/10.5772/intechopen.88532*

marine vs. nonmarine debate. Geology.

[87] Pagani M, Lemarchand D, Spivack A, Gaillardet J. A critical evaluation of the boron isotope-pH proxy: The accuracy of ancient ocean pH estimates. Geochimica et Cosmochimica

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2010;**38**(11):1035-1038

1992;**56**:1561-1568

1986;**50**(6):1297-1301

2000;**64**(3):397-408

[92] Rose EF, Chaussidon M, France-Lanord C. Fractionation of boron isotopes during erosion processes: The example of Himalayan rivers. Geochimica et Cosmochimica Acta.

[93] Lemarchand D, Gaillardet J, Lewin E. Boron isotope systematics in large rivers: Implications for the marine boron budget and paleo-pH reconstruction over the Cenozoic. Chemical Geology. 2002;**190**(1):123-140

[94] Liu WG, Xiao YK, Peng ZC, An ZS, He XX. Boron concentration

and isotopic composition of halite from experiments and

[89] Foster GL, Pogge von

[88] Paris G, Gaillardet J, Louvat P. Geological evolution of seawater boron isotopic composition recorded in evaporites. Geology.

Strandmann PAE, et al. Boron and magnesium isotopic composition of seawater. Geochemistry, Geophysics, Geosystems. 2010;**11**(8):Q08015

[90] Xiao Y, Sun D, Wang YH, Qi HP, Jin L. Boron isotopic compositions of brine, sediments, and source water in Da Qaidam Lake, Qinghai, China. Geochimica et Cosmochimica Acta.

[91] Swihart GH, Moore PB. Boron isotopic composition of marine and nonmarine evaporite borates. Geochimica et Cosmochimica Acta.

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*Isotopes Applications in Earth Sciences*

Yunnan. Beijing: Geological Press; 1998 (in Chinese with English abstract)

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[72] Lu FH, Meyers WJ, Schoonen MA. S and O (SO4) isotopes, simultaneous modeling, and environmental significance of the Nijar Messinian gypsum, Spain. Geochimica et Cosmochimica Acta. 2001;**65**(18):3081-3092

[73] Pierre C. Isotopic evidence for the dynamic redox cycle of dissolved sulphur compounds between free and interstitial solutions in marine salts pans. Chemical Geology.

[74] Bottrell SH, Newton RJ.

Reconstruction of changes in global sulfur cycling from marine sulfate isotopes. Earth Science Reviews.

[75] Xu JX. Geochemistry and genesis of Mengyejing potash deposits [thesis]. Yunnan: Chinese Academy Science; 2008 (in Chinese with English abstract)

[76] Claypool GE, Holser WT, Kaplan IR, Sakai H, Zak I. The age curves of sulfur and oxygen isotopes in marine sulfate and their mutual interpretation. Chemical Geology. 1980;**28**:199-260

[77] Paytan A, Kastner M, Campbell D, Thiemens MH. Seawater sulfur isotope fluctuations in the Cretaceous. Science.

[78] Hurtgen MT, Suits NS, Kaufman AJ. The sulfur isotopic composition of Neoproterozoic seawater sulfate: Implications for a snowball earth? Earth and Planetary Science Letters.

[79] Hess J, Bender ML, Schilling JG. Evolution of ratio of strontium 87 to strontium 86 in seawater from

2004;**304**:1663-1665

2002;**203**(1):413-429

2003;**15**(4):243-248

1985;**53**:191-196

2006;**75**:59-83

[64] Hasegawa H, Imsamut S, et al. Thailand was a desert' during the mid-Cretaceous: Equatorward shift of the subtropical high-pressure belt indicated by Eolian deposits (Phu Thok Formation) in the Khorat Basin, northeastern Thailand. Island Arc.

[65] Utha-Aroon C. Continental origin of the Maha Sarakham evaporites, northeastern Thailand. Journal of Southeast Asian Earth Sciences.

[66] Tan H, Ma H, Li BK, Zhang XY, Xiao YK. Strontium and boron isotopic constraint on the marine origin of the Khammouane potash deposits in southeastern Laos. Chinese Science Bulletin. 2010;**55**(27):3181-3188

[67] Zhang DW. Magnetostratigraphic studies of the Potash-bearing strata of the Lanping-Simao and the Vientiane Basins and their tectonic implications [thesis]. University of Chinese Academy of Sciences; 2016 (in Chinese with

2010;**19**(4):605-621

1993;**8**(1-4):193-203

English abstract)

[68] Hansen BT, Wemmer K,

Pawlig S, et al. Isotopic evidence for a Late Cretaceous age of the potash and rock salt deposit at Bamnet Narong, NE Thailand. In: Symposium on the Geology of Thailand, Bangkok; August 2002; Extended Abstract; 2002. pp. 26-31

[69] Hite RJ, Japakasetr T. Potash deposits of the khorat plateau,

10.1007/s13146-019-00508-0

1979;**74**(2):448-458

Thailand and Laos. Economic Geology.

[70] Sun SR, Li MH, Yan MD, Fang XM, Zhang GX, Liu XM. et al. Bromine content and Br/Cl molar ratio of halite in a core from Laos: Implications for origin and environmental changes. Carbonates and Evaporites. 2019. DOI:

**60**

[80] Krabbenhöft A, Eisenhauer A, Böhm F, Vollstaedt H, Fietzke J, Liebetrau V, et al. Constraining the marine strontium budget with natural strontium isotope fractionations (87Sr/86Sr, δ88/86Sr) of carbonates, hydrothermal solutions and river waters. Geochimica et Cosmochimica Acta. 2010;**74**:4097-4109

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[82] Bo Y, Liu CL, Zhao YJ, Wang LC. Chemical and isotopic characteristics and origin of spring waters in the Lanping-Simao Basin, Yunnan, Southwestern China. Chemie der Erde-Geochemistry. 2015;**75**:287-300

[83] Li MH, Yan MD, Fang XM, Zhang ZJ, Wang ZR, Sun SR, et al. Origins of the Mid-Cretaceous evaporite deposits of the Sakhon Nakhon Basin in Laos: Evidence from the stable isotopes of halite. Journal of Geochemical Exploration. 2018;**184**:209-222

[84] Spivack AJ, Edmond JM. Boron isotope exchange between seawater and the oceanic-crust. Geochimica et Cosmochimica Acta. 1987;**51**(5):1033-1043

[85] Palmer MR, Helvaci C. The boron isotope geochemistry of the neogene borate deposits of western Turkey. Geochimica et Cosmochimica Acta. 1997;**61**(15):3161-3169

[86] Vengosh A, Starinsky A, Kolodny Y, Chivas AR, Raab M. Boron isotope variations during fractional evaporation of sea water: New constraints on the

marine vs. nonmarine debate. Geology. 1992;**20**:799-802

[87] Pagani M, Lemarchand D, Spivack A, Gaillardet J. A critical evaluation of the boron isotope-pH proxy: The accuracy of ancient ocean pH estimates. Geochimica et Cosmochimica Acta. 2005;**69**(4):953-961

[88] Paris G, Gaillardet J, Louvat P. Geological evolution of seawater boron isotopic composition recorded in evaporites. Geology. 2010;**38**(11):1035-1038

[89] Foster GL, Pogge von Strandmann PAE, et al. Boron and magnesium isotopic composition of seawater. Geochemistry, Geophysics, Geosystems. 2010;**11**(8):Q08015

[90] Xiao Y, Sun D, Wang YH, Qi HP, Jin L. Boron isotopic compositions of brine, sediments, and source water in Da Qaidam Lake, Qinghai, China. Geochimica et Cosmochimica Acta. 1992;**56**:1561-1568

[91] Swihart GH, Moore PB. Boron isotopic composition of marine and nonmarine evaporite borates. Geochimica et Cosmochimica Acta. 1986;**50**(6):1297-1301

[92] Rose EF, Chaussidon M, France-Lanord C. Fractionation of boron isotopes during erosion processes: The example of Himalayan rivers. Geochimica et Cosmochimica Acta. 2000;**64**(3):397-408

[93] Lemarchand D, Gaillardet J, Lewin E. Boron isotope systematics in large rivers: Implications for the marine boron budget and paleo-pH reconstruction over the Cenozoic. Chemical Geology. 2002;**190**(1):123-140

[94] Liu WG, Xiao YK, Peng ZC, An ZS, He XX. Boron concentration and isotopic composition of halite from experiments and

salt lakes in the Qaidam Basin. Geochimica et Cosmochimica Acta. 2000;**64**(13):2177-2183

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[98] Lemarchand D, Gaillardet J, Lewin EÂ, AlleÁgre CJ. The influence of rivers on marine boron isotopes and implications for reconstructing past ocean pH. Nature. 2000;**408**:951-954

**63**

**Chapter 4**

**Abstract**

groundwater salinity

**1. Introduction**

the West Bank)

Mapping the Stable Isotopes to

Understand the Geo-Structural

From the Northeastern Basin of

*Saed Khayat, Amer Marei and Zaher Barghouthi*

Control of Groundwater Recharge

and Flow Mechanisms (Case Study

Conventional stable isotopic technique was used to differentiate between the potential recharge sources and mixing and flow mechanisms in the Northeastern basin of the West Bank. The isotopic signatures from deep wells show two main fingerprints with respect to recharge sources and mechanisms. These are wells located in the upper part of the Faria fault system and along the Rujeib Moncline which are fed by triggered water in-line the fault system in the south and deep wells surrounded by the Anabta anticline to the west which are fed by the exposed Jerusalem-Hebron formations. This suggests a mixing process with freshwater sources that mainly flow to the system from southern mountains. The isotopic signatures from the shallow well in Marj Sanoor wells and Nassariyeh in the upper Faria well suggest a kind of partial recharge from the Marj Sanoor Lake leaking to the upper Faria Graben area and participating in the recharge process of these wells. The whole finding out of this project might be used for tuning and revision of the groundwater model that has been built by the Palestinian Water Authority.

**Keywords:** isotope hydrology, Palestine, Northeastern aquifer, recharge mechanism,

Providing the Palestinian people with their water needs is the main concern for the Palestinian Water Authority, Ministry of Agriculture, as well as for water service providers. During the last 20 years, the annual average water consumption from the Northeastern aquifer reached 25 MCM [1]; this is due to improvement of water infrastructure including drilling new domestic deep wells, improvement of

Tapping of groundwater, using spring water, purchase of water from Mekerot Israeli Company, and collection of rainwater are the sources for domestic and agricultural water in the West Bank. In this context, groundwater is the main one which

water institutions, and increase in the public awareness.

## **Chapter 4**

*Isotopes Applications in Earth Sciences*

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**62**
