3.1 Granite gneisses and migmatites

The Hafafit granitic gneisses are enriched in REE, whereas the Um Baanib orthogneiss presents alkaline granite Rear Earth Elements (REE) pattern (Figure 2a and b). Um Baanib deformed granites (granite gneisses) are enriched in High Field Strength Elements (HFSE) (Zr, Nb, Y, Th), Rb, Ga, and total REE and depleted in MgO, CaO, and V, showing alkaline and A-type characters, whereas Hafafit granitic gneisses are calcalkaline and of I-type granites [34, 35]. In terms of the Nb, Y, and Rb contents, the Hafafit granite gneisses plot in the field of volcanic arc granites [36], whereas the Um Baanib granite gneisses plot within the field of anorogenic or within-plate A-type granites. Aswan orthogneisses are clacalkaline I-type granitoids [37] that are generally described as subduction-related granitoids [38].

(BAB) magmas or similar to fore arc, boninites and SSZ basalts. Immobile traceelement abundances, together with significant Light Rear Earth Elements (LREE) depletion to almost flat REE patterns for pillow lavas and sheeted dykes of Gerf ophiolite, are compatible with the N-MORB distribution patterns [39]. Volcanic rocks of Fawakhir (El Sid) SSZ ophiolites display moderately depleted to slightly enriched LREE patterns (Figure 3a), whereas pillow lavas of Ghadir MORB ophiolites have similar chondrite-normalized REE patterns (Figure 3b) [40, 41]. They are enriched in LREE. Most Gerf gabbros have REE patterns with a slight LREE enrichment and a small positive Eu anomaly, whereas the Gerf serpentinized peridotites have Large Ion Lithophile Elements (LILE)-depleted patterns. The Abu Dahr metagabbro and metabasalt have enrichment LILE and LREE enrichment, whereas serpentinized harzburgite and dunite are characterized by enrichment of LILE and nearly flat and unfractionated chondrite-normalized pattern indicating they originated by up to 30% partial melting of a spinel lherzolite mantle in a

Geochemistry and Tectonic Setting of Neoproterozoic Rocks from the Arabian-Nubian Shield…

Generally, most samples of ophiolitic lavas are subalkaline and reveal tholeiitic

The serpentinites and serpentinized peridotite ophiolites display a diverse suite of geochemical signatures, which make their origin or tectonic setting controversial.

Geochemical characteristics of ophiolites. (a) Chondrite-normalized REE patterns for Fawakhir (El Sid) ophiolitic pillow lavas, (b) Ghadir pillow lavas [40, 41], (c) Ti/1000 vs. V diagram [20], and (d) chrome

spinels from ophiolitic blocks of metamorphosed ultramafics in mélanges [20].

affinities, together with minor calcalkaline characters, although subordinate, amount of boninites have been identified as in El Sid ophiolite. On the Ti-V tectonic setting discrimination diagram (Figure 3c), generally, ophiolitic metavolcanics and metagabbros of the ED of Egypt fall into two groups: (i) MORB ophiolites and (ii) fore arc or suprasubduction zone (SSZ) ophiolites (e.g., [20, 25, 39, 40–46]). The MORB affinity of metagabbros from Muweilih is documented for the first time by El Bahariya [43], and the whole Muweilih ophiolite sequence is mapped and recorded for the first time as MORB intact ophiolite by El Bahariya [20].

subarc setting [25].

DOI: http://dx.doi.org/10.5772/intechopen.82519

Figure 3.

7

Thermobarometry based on composition of coexisting mineral pairs for granite gneisses indicates that peak metamorphism and partial melting occurred at 750°C and 5 kb at high H2O activity for the metatexite. The granite gneiss in the core of Hafafit dome is suggested to have been formed by syntectonic partial melting of lower to middle crustal protoliths [14]. Plagioclase, clinopyroxene, hornblende, garnet, and biotite show compositional variability as a consequence of the composition of protoliths and prevailing P-T conditions of metamorphism (Figure 2c–e). Migmatitic rocks provide an example of the close relation among metamorphism, deformation, and melt generation and emplacement. This migmatitic rock association is interpreted as syntectonic anatectic migmatites formed during compressional phase in an Andean-type continental margin tectonic setting.

### 3.2 Ophiolite-island arc assemblages

#### 3.2.1 Ophiolite geochemistry

The HFSE and (REE) of Neoproterozoic ophiolites of ED of Egypt suggest either similarities with normal-type mid-ocean ridge basalts (N-MORB) or back-arc basin

#### Figure 2.

Rare earth element abundances in the infrastructural rocks from Meatiq (a) and Hafafit core complexes (b) normalized to primitive mantle from [35] and (c–e) compositional variations of plagioclase, amphibole, and garnet in Hafafit migmatitic rocks from [14].

## Geochemistry and Tectonic Setting of Neoproterozoic Rocks from the Arabian-Nubian Shield… DOI: http://dx.doi.org/10.5772/intechopen.82519

(BAB) magmas or similar to fore arc, boninites and SSZ basalts. Immobile traceelement abundances, together with significant Light Rear Earth Elements (LREE) depletion to almost flat REE patterns for pillow lavas and sheeted dykes of Gerf ophiolite, are compatible with the N-MORB distribution patterns [39]. Volcanic rocks of Fawakhir (El Sid) SSZ ophiolites display moderately depleted to slightly enriched LREE patterns (Figure 3a), whereas pillow lavas of Ghadir MORB ophiolites have similar chondrite-normalized REE patterns (Figure 3b) [40, 41]. They are enriched in LREE. Most Gerf gabbros have REE patterns with a slight LREE enrichment and a small positive Eu anomaly, whereas the Gerf serpentinized peridotites have Large Ion Lithophile Elements (LILE)-depleted patterns. The Abu Dahr metagabbro and metabasalt have enrichment LILE and LREE enrichment, whereas serpentinized harzburgite and dunite are characterized by enrichment of LILE and nearly flat and unfractionated chondrite-normalized pattern indicating they originated by up to 30% partial melting of a spinel lherzolite mantle in a subarc setting [25].

Generally, most samples of ophiolitic lavas are subalkaline and reveal tholeiitic affinities, together with minor calcalkaline characters, although subordinate, amount of boninites have been identified as in El Sid ophiolite. On the Ti-V tectonic setting discrimination diagram (Figure 3c), generally, ophiolitic metavolcanics and metagabbros of the ED of Egypt fall into two groups: (i) MORB ophiolites and (ii) fore arc or suprasubduction zone (SSZ) ophiolites (e.g., [20, 25, 39, 40–46]). The MORB affinity of metagabbros from Muweilih is documented for the first time by El Bahariya [43], and the whole Muweilih ophiolite sequence is mapped and recorded for the first time as MORB intact ophiolite by El Bahariya [20].

The serpentinites and serpentinized peridotite ophiolites display a diverse suite of geochemical signatures, which make their origin or tectonic setting controversial.

#### Figure 3.

Geochemical characteristics of ophiolites. (a) Chondrite-normalized REE patterns for Fawakhir (El Sid) ophiolitic pillow lavas, (b) Ghadir pillow lavas [40, 41], (c) Ti/1000 vs. V diagram [20], and (d) chrome spinels from ophiolitic blocks of metamorphosed ultramafics in mélanges [20].

3.1 Granite gneisses and migmatites

The Hafafit granitic gneisses are enriched in REE, whereas the Um Baanib orthogneiss presents alkaline granite Rear Earth Elements (REE) pattern (Figure 2a and b). Um Baanib deformed granites (granite gneisses) are enriched in High Field Strength Elements (HFSE) (Zr, Nb, Y, Th), Rb, Ga, and total REE and depleted in MgO, CaO, and V, showing alkaline and A-type characters, whereas Hafafit granitic gneisses are calcalkaline and of I-type granites [34, 35]. In terms of the Nb, Y, and Rb contents, the Hafafit granite gneisses plot in the field of volcanic arc granites [36], whereas the Um Baanib granite gneisses plot within the field of anorogenic or within-plate A-type granites. Aswan orthogneisses are clacalkaline I-type granitoids

Applied Geochemistry with Case Studies on Geological Formations, Exploration Techniques…

Thermobarometry based on composition of coexisting mineral pairs for granite gneisses indicates that peak metamorphism and partial melting occurred at 750°C and 5 kb at high H2O activity for the metatexite. The granite gneiss in the core of Hafafit dome is suggested to have been formed by syntectonic partial melting of lower to middle crustal protoliths [14]. Plagioclase, clinopyroxene, hornblende, garnet, and biotite show compositional variability as a consequence of the composition of protoliths and prevailing P-T conditions of metamorphism (Figure 2c–e). Migmatitic rocks provide an example of the close relation among metamorphism, deformation, and melt generation and emplacement. This migmatitic rock association is interpreted as syntectonic anatectic migmatites formed during compressional

The HFSE and (REE) of Neoproterozoic ophiolites of ED of Egypt suggest either similarities with normal-type mid-ocean ridge basalts (N-MORB) or back-arc basin

Rare earth element abundances in the infrastructural rocks from Meatiq (a) and Hafafit core complexes (b) normalized to primitive mantle from [35] and (c–e) compositional variations of plagioclase, amphibole,

[37] that are generally described as subduction-related granitoids [38].

phase in an Andean-type continental margin tectonic setting.

3.2 Ophiolite-island arc assemblages

and garnet in Hafafit migmatitic rocks from [14].

3.2.1 Ophiolite geochemistry

Figure 2.

6

Generally, the chrome spinels from the serpentinites and metamorphosed ultramafic ophiolites have a wide range of Cr#, where the Cr# ranges from 0.3 to 0.85 and display both MORB and SSZ affinities [45]. They are classified into three groups (G1, G2, and G3) according to their Cr# (Figure 3d). Most serpentinized peridotites of the ED show significantly more Mg-rich olivine and chrome spinel with high Cr# (G1 and G2), suggesting a forearc or SSZ environment [42, 45, 47, 48]. Only, data of Cr-spinel from the serpentinized peridotite blocks of Esel olistostrome commonly show low Cr# (G1), and accordingly, they show MORB affinity similar to abyssal peridotites [45]. Moreover, the previous studies dealt collectively with the ophiolitic serpentinites of the ED to be of fore arc or SSZ geochemical signature. However, El Bahariya [20, 47] reported the presence of both SSZ and MORB ophiolitic serpentinized peridotites.

#### 3.2.2 Geochemistry of island arc assemblages

Geochemistry of intermediate and acidic island arc metavolcanics, together with the native intermediate and acidic metavolcanic clasts of the ophiolitic mélanges, is presented. The metavolcanic rocks at Wadi E Dabbah show slightly fractionated REE patterns (Figure 4a) and negative Eu and Ce anomalies [49]. The island arc metavolcanics are of oceanic island arc affinity (Figure 4d) [23, 24]. The intermediate and acidic island-arc rocks at Gebel Zabara area are calcalkaline and of continental island-arc setting, representing an intermediate maturity stage between the primitive arc and the mature active continental margin [50]. Um Anab metaandesites, metafelsites, and metarhyolites varieties are predominantly of calcalkaline nature, enriched in LILE and depleted in HFSE, with a pronounced negative Nb anomaly [51]. These rocks are most probably derived from a mantle source produced in an island arc environment where fall in the plate margin field confirming the orogenic nature of these rocks.

The REE patterns of bimodal Um Samiuki metavolcanics rhyodacites are very nearly flat (Figure 4b) [28]. Also, the REE patterns of the felsic lavas are slightly LREE-depleted, whereas basalt is slightly LREE-enriched and characterized by negative Eu anomalies. The trace element characteristics of both mafic and felsic members of the Shadli Metavolcanics indicate that these rocks were originated in a magmatic rift. The bimodal metavolcanics at Wadi Sodmien show mafic tholeiitic character and felsic rocks calcalkaline affinity (Figure 4c) [52]. They have transitional tectonic setting between island arc/active continental margin and within plate (extensional environment) tectonic setting (Figure 4d). Their petrogenesis can be attributed to partial melting of continental crust, and they suggested to be formed in ensialic back arc basin due to extensional rifting. Major trace elements and REE indicate that Igla Eliswid-Um Khariga bimodal mafic and felsic metavolcanic assemblages [53] are clearly tholeiitic in character and share a large number of geochemical features of island-arc tholeiites. The geochemical data are most consistent with the hypothesis that these rocks originated in a magmatic rift. The REE concentrations of Gebel El Hadid banded iron formation (BIF) have LREE depleted and HREE enriched patterns [54] and are characterized by low ΣREE contents (13.7–77.5 ppm) with an average of 45.2 ppm.

The intra-arc metagreywackes of Alam volcaniclastic metasediments show variable abundances of Zr, Cr, Ni, and V. Their provenance components are mainly of evolved felsic and mafic (bimodal) island arcs and show oceanic arc tectonic

(a) Rare earth element (REE) and trace element diagrams for the analyzed metavolcanic samples from Wadi El Dabbah from [49]; (b) REE patterns for Um Samiuki Volcanics, normalized to chondritic meteorites from [28]; (c) AFM diagram of Sodmien bimodal metavolcanics, fields based on data from [52]; (d) Sodmien bimodal metavolcanics, data for field of Zabara metavolcanics from [50] and field of Hammariya metavolcanics from [24]; and (e and f) tectonic setting of metagreywackes from matrix of mélanges and from

Geochemistry and Tectonic Setting of Neoproterozoic Rocks from the Arabian-Nubian Shield…

DOI: http://dx.doi.org/10.5772/intechopen.82519

metagreywackes derived from a mixed provenance consisting of mafic and felsic source rocks (e.g., [26, 55]). The rocks are suggested to be deposited in a localized intra-arc basin. The clasts and grains constituting the sediments simulate the principal bimodal volcanic rocks of both the Sukkari metavolcanics and Um Khariga

setting (Figure 4e). They are comparable with Archaean Ranebennur

bimodal intra-arc volcaniclastic metasediments, data from [23, 24, 26].

metapyroclastics in the near area [26].

Figure 4.

9

On the other hand, the geochemistry of arc-related volcaniclastic metagreywackes constituting the matrix of the mélange indicates that they are chemically similar to quartz-poor oceanic island arc sandstones and were derived mainly from intermediate and felsic volcanic igneous provenances [19, 23, 24]. They are of oceanic island arc tectonic setting (Figure 4e and f) and appear to be deposited in back-arc basins or interarc basins.

Geochemistry and Tectonic Setting of Neoproterozoic Rocks from the Arabian-Nubian Shield… DOI: http://dx.doi.org/10.5772/intechopen.82519

#### Figure 4.

Generally, the chrome spinels from the serpentinites and metamorphosed ultramafic ophiolites have a wide range of Cr#, where the Cr# ranges from 0.3 to 0.85 and display both MORB and SSZ affinities [45]. They are classified into three groups (G1, G2, and G3) according to their Cr# (Figure 3d). Most serpentinized peridotites of the ED show significantly more Mg-rich olivine and chrome spinel with high Cr# (G1 and G2), suggesting a forearc or SSZ environment [42, 45, 47, 48]. Only, data of Cr-spinel from the serpentinized peridotite blocks of Esel olistostrome commonly show low Cr# (G1), and accordingly, they show MORB affinity similar to abyssal peridotites [45]. Moreover, the previous studies dealt collectively with the ophiolitic serpentinites of the ED to be of fore arc or SSZ geochemical signature. However, El

Applied Geochemistry with Case Studies on Geological Formations, Exploration Techniques…

Bahariya [20, 47] reported the presence of both SSZ and MORB ophiolitic

Geochemistry of intermediate and acidic island arc metavolcanics, together with the native intermediate and acidic metavolcanic clasts of the ophiolitic mélanges, is presented. The metavolcanic rocks at Wadi E Dabbah show slightly fractionated REE patterns (Figure 4a) and negative Eu and Ce anomalies [49]. The island arc metavolcanics are of oceanic island arc affinity (Figure 4d) [23, 24]. The intermediate and acidic island-arc rocks at Gebel Zabara area are calcalkaline and of continental island-arc setting, representing an intermediate maturity stage between the primitive arc and the mature active continental margin [50]. Um Anab metaandesites, metafelsites, and metarhyolites varieties are predominantly of calcalkaline nature, enriched in LILE and depleted in HFSE, with a pronounced negative Nb anomaly [51]. These rocks are most probably derived from a mantle source produced in an island arc environment where fall in the plate margin field

The REE patterns of bimodal Um Samiuki metavolcanics rhyodacites are very nearly flat (Figure 4b) [28]. Also, the REE patterns of the felsic lavas are slightly LREE-depleted, whereas basalt is slightly LREE-enriched and characterized by negative Eu anomalies. The trace element characteristics of both mafic and felsic members of the Shadli Metavolcanics indicate that these rocks were originated in a magmatic rift. The bimodal metavolcanics at Wadi Sodmien show mafic tholeiitic character and felsic rocks calcalkaline affinity (Figure 4c) [52]. They have transitional tectonic setting between island arc/active continental margin and within plate (extensional environment) tectonic setting (Figure 4d). Their petrogenesis can be attributed to partial melting of continental crust, and they suggested to be formed in ensialic back arc basin due to extensional rifting. Major trace elements and REE indicate that Igla Eliswid-Um Khariga bimodal mafic and felsic metavolcanic assemblages [53] are clearly tholeiitic in character and share a large number of geochemical features of island-arc tholeiites. The geochemical data are most consistent with the hypothesis that these rocks originated in a magmatic rift. The REE concentrations of Gebel El Hadid banded iron formation (BIF) have LREE depleted and HREE enriched patterns [54] and are characterized by low ΣREE contents (13.7–77.5 ppm) with an

On the other hand, the geochemistry of arc-related volcaniclastic metagreywackes constituting the matrix of the mélange indicates that they are chemically similar to quartz-poor oceanic island arc sandstones and were derived mainly from intermediate and felsic volcanic igneous provenances [19, 23, 24]. They are of oceanic island arc tectonic setting (Figure 4e and f) and appear to be

serpentinized peridotites.

average of 45.2 ppm.

8

3.2.2 Geochemistry of island arc assemblages

confirming the orogenic nature of these rocks.

deposited in back-arc basins or interarc basins.

(a) Rare earth element (REE) and trace element diagrams for the analyzed metavolcanic samples from Wadi El Dabbah from [49]; (b) REE patterns for Um Samiuki Volcanics, normalized to chondritic meteorites from [28]; (c) AFM diagram of Sodmien bimodal metavolcanics, fields based on data from [52]; (d) Sodmien bimodal metavolcanics, data for field of Zabara metavolcanics from [50] and field of Hammariya metavolcanics from [24]; and (e and f) tectonic setting of metagreywackes from matrix of mélanges and from bimodal intra-arc volcaniclastic metasediments, data from [23, 24, 26].

The intra-arc metagreywackes of Alam volcaniclastic metasediments show variable abundances of Zr, Cr, Ni, and V. Their provenance components are mainly of evolved felsic and mafic (bimodal) island arcs and show oceanic arc tectonic setting (Figure 4e). They are comparable with Archaean Ranebennur metagreywackes derived from a mixed provenance consisting of mafic and felsic source rocks (e.g., [26, 55]). The rocks are suggested to be deposited in a localized intra-arc basin. The clasts and grains constituting the sediments simulate the principal bimodal volcanic rocks of both the Sukkari metavolcanics and Um Khariga metapyroclastics in the near area [26].
