**3. Correlation between heat flow, seismicity, and deep structure**

The time of thermal relaxation of the Earth (~1.5 × 109 years) makes it possible to consider the Earth's thermal component as constant [25]. There are two main heat sources: that supplied from the mantle (~60%) and that formed by radioactive decay in crustal rocks (~40%). In the sedimentary cover, the majority of radioactive elements are hosted in clay rocks, whereas intrusive bodies are the local heat sources. Based on the data from different sources [14–17], we complied a database of heat flow values. The summary data on seismicity and heat flow within the distinguished tectonic structures (cratonic and oceanic) of the studied region are presented in **Table 2**.

The seismic activity correlates with heat flow values in middle ocean ridge (MOR) areas. In the northern East European Craton, there was no clear relationship between these parameters, except for the North Barents Rise. Let us consider


#### **Table 2.**

*Seismicity parameters and heat flow in distinguished tectonic structures of studied region of the Arctic.*

**47**

**Figure 5.**

*generation is possible.*

*Recent Geodynamics and Seismicity of the European Arctic DOI: http://dx.doi.org/10.5772/10.5772/intechopen.80800*

Kvarts, 1-AR, 2-AR, 3-AR, 4-AR, DSS-82, etc. [10–13, 26].

reflection CMP method) [2, 11, 13].

sections (**Figure 1**).

the distribution of these parameters in more detail, with knowledge about the structure of the lithosphere along the composite geological and geophysical cross

Profile A–B (**Figure 5**) crosses such morphostructures as the MOR (Gakkel Ridge), the abyssal plain (Nansen Basin), the Barents Sea shelf, the eastern Baltic Shield, the White Sea shelf, and the continental rise of the East European Craton. To construct the model for the lithosphere structure on Р-wave velocities, we used data from deep geological and geophysical cross sections along such profiles as

Profile C–D (**Figure 6**) crosses such morphostructures as the Svalbard anteclise, North Barents Basin, North Kara syneclise, and the Taimyr-Severnaya Zemlya fold system. The majority of it is overlapped by the 4-AR deep seismic profile (seismic

*Distribution of heat flow (I) and seismicity (II) and geological and geophysical cross section along profile A–B (III) (with data from [10, 13, 26]). Notation: M, Moho; K, middle boundary in crust; F0, top of upper Proterozoic basement; and F1, top of Archean-Proterozoic crust (PR1-AR). Arbitrary notes:* 

*1995–2015, (3) crossing points of geotraverses, (4)* Р*-wave velocities, (5) faults, (6) sedimentary cover and its age, (7) acoustic basement of oceanic crust, (8) upper Proterozoic basement (PR2), (9) upper sialic part of consolidated crust (PR1-AR), (10) basite part of consolidated crust, (11) upper mantle, (12) basite massif, and (13) fluid-saturated decompacted zones in sedimentary cover where hydrocarbon* 

*, (2) epicenters of earthquakes in* 

*(1) heat flow values (including averaged ones) along profile, mW/m<sup>2</sup>*

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presented in **Table 2**.

**structures**

Novaya Zemlya microplate

Eurasian and North Atlantic Basins

decay in crustal rocks (~40%). In the sedimentary cover, the majority of radioactive elements are hosted in clay rocks, whereas intrusive bodies are the local heat sources. Based on the data from different sources [14–17], we complied a database of heat flow values. The summary data on seismicity and heat flow within the distinguished tectonic structures (cratonic and oceanic) of the studied region are

The seismic activity correlates with heat flow values in middle ocean ridge (MOR) areas. In the northern East European Craton, there was no clear relationship between these parameters, except for the North Barents Rise. Let us consider

**Structures Earthquakes Average** 

**mW/m2 Superorder** 

Barents plate Central Barents Basin (1a) 23 3.6 2.48 60–70

Timan-Pechora plate Pechora plate (2b) - - - 40–50

North Barents Rise (2a) Orly trough (exclusion)

Kos'yu-Rogovskaya Basin (3c)

monocline (4d)

East Novaya Zemlya step zone (4e)

North Siberian step zone (4f)

Early Cimmerian folding of Novaya Zemlya (9)

(2c)

structures of Scandinavian Peninsula (7)

*Seismicity parameters and heat flow in distinguished tectonic structures of studied region of the Arctic.*

West Siberian plate East Novaya Zemlya

North Kara plate North Siberian threshold

Baltic Shield Caledonian folding

**First and second orders Number MLmax MLav**

North Barents Basin (1b) 3 2.7 2.4 60–80

Sedov trough (3a) 2 2.3 2.25 50–80 East Barents step zone (4a) 1 2.7 2.7 70 Luninskaya saddle (8) - - - 70 South Barents step zone (4b) 9 3.7 2.37 60–70 Kola monocline (4c) 2 1.6 1.35 50–60

Korotaikha Basin (3b) - - - 40

Timan Range (5a) - - - 50

Pai-Khoy Range (5b) - - - 60

North Kara syneclise (6) - - - 70

Nansen Basin 135 4.3 2.5 60–80 MOR 3224 6.6 2.83 >100

1758 5.9 2.5 60–80,





5 4.5 3.24 60


33 2.8 1.9 40–50

**heat flow,** 

100–300

**46**

**Table 2.**

the distribution of these parameters in more detail, with knowledge about the structure of the lithosphere along the composite geological and geophysical cross sections (**Figure 1**).

Profile A–B (**Figure 5**) crosses such morphostructures as the MOR (Gakkel Ridge), the abyssal plain (Nansen Basin), the Barents Sea shelf, the eastern Baltic Shield, the White Sea shelf, and the continental rise of the East European Craton. To construct the model for the lithosphere structure on Р-wave velocities, we used data from deep geological and geophysical cross sections along such profiles as Kvarts, 1-AR, 2-AR, 3-AR, 4-AR, DSS-82, etc. [10–13, 26].

Profile C–D (**Figure 6**) crosses such morphostructures as the Svalbard anteclise, North Barents Basin, North Kara syneclise, and the Taimyr-Severnaya Zemlya fold system. The majority of it is overlapped by the 4-AR deep seismic profile (seismic reflection CMP method) [2, 11, 13].

#### **Figure 5.**

*Distribution of heat flow (I) and seismicity (II) and geological and geophysical cross section along profile A–B (III) (with data from [10, 13, 26]). Notation: M, Moho; K, middle boundary in crust; F0, top of upper Proterozoic basement; and F1, top of Archean-Proterozoic crust (PR1-AR). Arbitrary notes: (1) heat flow values (including averaged ones) along profile, mW/m<sup>2</sup> , (2) epicenters of earthquakes in 1995–2015, (3) crossing points of geotraverses, (4)* Р*-wave velocities, (5) faults, (6) sedimentary cover and its age, (7) acoustic basement of oceanic crust, (8) upper Proterozoic basement (PR2), (9) upper sialic part of consolidated crust (PR1-AR), (10) basite part of consolidated crust, (11) upper mantle, (12) basite massif, and (13) fluid-saturated decompacted zones in sedimentary cover where hydrocarbon generation is possible.*

#### **Figure 6.**

*Distribution of heat flow (I) and seismicity (II) and geological and geophysical cross section along profile C-D (III) (with data from [10, 13, 26]). Notations are shown in* **Figure 5***.*

The heat flow values and earthquake epicenters are drawn along the composite lithosphere cross sections. Below are the results of comparison of the geological and geophysical fields.

#### **3.1 Profile A–B**

The oceanic lithosphere is sharply distinguishable from the continental crust, and the oceanic Moho is located at a depth of 12–13 km (**Figure 5**). The seismic velocities in the upper oceanic crust are from 4.5 to 6 km/s, whereas they are from 6.8 to 7.3 km/s in the lower part. The rift valley of the Gakkel Ridge is formed by rocks from the oceanic basement, which supposedly had velocities of more than 7.5 km/s [26]. In the sedimentary cover above the basement of the oceanic crust, we can distinguish several stratigraphic complexes, whose thicknesses increase toward

**49**

*Recent Geodynamics and Seismicity of the European Arctic DOI: http://dx.doi.org/10.5772/10.5772/intechopen.80800*

cally detected at 10–12 km depth [26].

sinking zone [10, 11].

the heat flow values are 98 mW/m<sup>2</sup>

heat flow values (60–80 mW/m2

of large tectonic structures [29].

peak values of ≈500 mW/m2

North Kara Basin [6].

**3.2 Profile C–D**

average heat flow decreases to 70 mW/m<sup>2</sup>

gradual metamorphic transition of gabbroids to eclogite.

m2

the Barents-Kara continental margin. In the Nansen Basin, the Moho was acousti-

Seismic activity has been recorded in the zone where the continental and oceanic lithosphere joins. Single seismic events in this area are supposedly caused by the removal of sedimentary masses from the continent [2] or by transform fault activity. The lithosphere is the continental type. The surface of the mantle (Р-wave velocities from 8.0 to 8.5 km/s) is at 34–36 km in the Barents Sea Basin, 35–40 km in the Kola monocline, and 44–46 km in the Baltic Shield. The consolidated crust can be roughly subdivided into two layers. The upper one has velocities of 5.6–6.5 km/s and the lower 6.6–7.2 km/s. The thickness of the upper layer of the consolidated crust changes from 8 km in the basin to 15–25 km in the areas of the Voronin, Albanov, and Fedynsky rises, as well as beneath the Baltic Shield [8]. The thickness of the basite part of the consolidated crust in this area ranges from 10 to 20 km in the zone of the rise, whereas it thins to 5–16 km in the

For the oceanic lithosphere with thinned crust, heat flow increases to 200 mW/

. Based on the seismic data, the upper layer of the consolidated crust beneath the South Barents Basin contains local velocity inhomogeneities. It is assumed that the upper crust contains abundant plateau basalts and is close to oceanic crust in its physical properties. Such thinning and transformation of the continental crust, coupled with its sinking, were probably caused by phase transitions of rocks [1, 27]. **Figures 5** and **6** schematically show fluid-saturated decompaction zones in the sedimentary cover, where subsequent generation of hydrocarbons is possible. In the North Barents Basin, the lower crustal layer contains high-velocity inhomogeneities with values of 7.1 km/s. According to [1, 28], their compactions were the result of

In the Barents Sea Basin, singular earthquakes have been recorded in zones where rock transformation takes place (**Figure 4**). These areas are remarkable for higher

crustal structure; it is thermally cold (heat flow values from 30 to 50 mW/m2

a thin, up to wedging, sedimentary layer in the southwestern part of the continental rise of the East European Craton. It can be assumed that this structure limits shortening from the Middle Arctic Ridge and tectonic deformations from the fold units of the Polar Urals, Novaya Zemlya, Taimyr Peninsula, and Caledonides of the North Atlantic, which is manifested as single relatively weak earthquakes at the boundaries

High seismic activity has been recorded in the area of collisional dislocations at

the mean ones for the Barents Sea Rise, and in the area of Orly Trough, they reach

the Barents Sea plate to an almost horizontal plane resulted in the formation of the

Seismic data suggest that the crust is continental type, which is supported by low seismic wave velocities (5.6–6.0 km/s) in the granitic-gneissic layer.

According to [8, 11], thinning of the crust and the influence of small flows of deep mantle fluids (compared to those that affected the South Barents Basin) gave rise

the Svalbard plate margin (**Figure 6**). Heat flow values of about 80 mW/m<sup>2</sup>

, and seismic activity is higher, especially in the Gakkel Ridge area. In the Nansen Basin, where single earthquakes have been recorded closer to the transform zones,

. Toward the ledge of the continental shelf, the

). The last zone along profile A–B is a thick mantle-

. The slow and gentle downwarping of this part of

) and has

exceed

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The heat flow values and earthquake epicenters are drawn along the composite lithosphere cross sections. Below are the results of comparison of the geological and

*Distribution of heat flow (I) and seismicity (II) and geological and geophysical cross section along profile C-D* 

*(III) (with data from [10, 13, 26]). Notations are shown in* **Figure 5***.*

The oceanic lithosphere is sharply distinguishable from the continental crust, and the oceanic Moho is located at a depth of 12–13 km (**Figure 5**). The seismic velocities in the upper oceanic crust are from 4.5 to 6 km/s, whereas they are from 6.8 to 7.3 km/s in the lower part. The rift valley of the Gakkel Ridge is formed by rocks from the oceanic basement, which supposedly had velocities of more than 7.5 km/s [26]. In the sedimentary cover above the basement of the oceanic crust, we can distinguish several stratigraphic complexes, whose thicknesses increase toward

**48**

geophysical fields.

**3.1 Profile A–B**

**Figure 6.**

the Barents-Kara continental margin. In the Nansen Basin, the Moho was acoustically detected at 10–12 km depth [26].

Seismic activity has been recorded in the zone where the continental and oceanic lithosphere joins. Single seismic events in this area are supposedly caused by the removal of sedimentary masses from the continent [2] or by transform fault activity. The lithosphere is the continental type. The surface of the mantle (Р-wave velocities from 8.0 to 8.5 km/s) is at 34–36 km in the Barents Sea Basin, 35–40 km in the Kola monocline, and 44–46 km in the Baltic Shield. The consolidated crust can be roughly subdivided into two layers. The upper one has velocities of 5.6–6.5 km/s and the lower 6.6–7.2 km/s. The thickness of the upper layer of the consolidated crust changes from 8 km in the basin to 15–25 km in the areas of the Voronin, Albanov, and Fedynsky rises, as well as beneath the Baltic Shield [8]. The thickness of the basite part of the consolidated crust in this area ranges from 10 to 20 km in the zone of the rise, whereas it thins to 5–16 km in the sinking zone [10, 11].

For the oceanic lithosphere with thinned crust, heat flow increases to 200 mW/ m2 , and seismic activity is higher, especially in the Gakkel Ridge area. In the Nansen Basin, where single earthquakes have been recorded closer to the transform zones, the heat flow values are 98 mW/m<sup>2</sup> . Toward the ledge of the continental shelf, the average heat flow decreases to 70 mW/m<sup>2</sup> .

Based on the seismic data, the upper layer of the consolidated crust beneath the South Barents Basin contains local velocity inhomogeneities. It is assumed that the upper crust contains abundant plateau basalts and is close to oceanic crust in its physical properties. Such thinning and transformation of the continental crust, coupled with its sinking, were probably caused by phase transitions of rocks [1, 27]. **Figures 5** and **6** schematically show fluid-saturated decompaction zones in the sedimentary cover, where subsequent generation of hydrocarbons is possible. In the North Barents Basin, the lower crustal layer contains high-velocity inhomogeneities with values of 7.1 km/s. According to [1, 28], their compactions were the result of gradual metamorphic transition of gabbroids to eclogite.

In the Barents Sea Basin, singular earthquakes have been recorded in zones where rock transformation takes place (**Figure 4**). These areas are remarkable for higher heat flow values (60–80 mW/m2 ). The last zone along profile A–B is a thick mantlecrustal structure; it is thermally cold (heat flow values from 30 to 50 mW/m2 ) and has a thin, up to wedging, sedimentary layer in the southwestern part of the continental rise of the East European Craton. It can be assumed that this structure limits shortening from the Middle Arctic Ridge and tectonic deformations from the fold units of the Polar Urals, Novaya Zemlya, Taimyr Peninsula, and Caledonides of the North Atlantic, which is manifested as single relatively weak earthquakes at the boundaries of large tectonic structures [29].
