No 1 (2024)

The article summarizes paleomagnetic data for Tuva, Mongolia and Eastern China, which showed that in the central part of the Central Asian fold belt, areas with different paleomagnetic characteristics are distinguished, these are areas located north of the Mongol-Okhotsk mobile belt, the western and eastern parts of the South Mongolia and Eastern China. The areas located north of the Mongol-Okhotsk mobile belt were part of the structure of the Siberian continent from the Ordovician and experienced movement similar to the Siberian continent. The regions of the western part of Southern Mongolia have been part of the structure of the Siberian continent since the late Carboniferous. The geological complexes of the eastern part of Southern Mongolia and the blocks of Eastern China in the Middle Paleozoic and Early Mesozoic were located in a latitudinal interval close to the North China block and experienced similar latitudinal movements and similar rotations. The large difference between the paleolatitudes of coeval strata in western and eastern Mongolia and Eastern China south of the Mongol-Okhotsk mobile belt suggests the existence of a tectonic boundary that separated blocks formed at paleolatitudes along the 107E meridian, close to Siberia and Northern China. To the west of the 107° longitude meridian, the paleolatitudes of formation of the Late Carboniferous–Permian strata are close to the paleolatitudes of Siberia, and to the east of the meridian — to the paleolatitudes of Northern China. The width of the Mongol-Okhotsk Ocean in the late Paleozoic–early Mesozoic was 30°–40° latitude (~3000–4000 km). The southern limit of the Mongol-Okhotsk Ocean was segmented and consisted of terranes of various genesis and structure. The closure of segments of the Mongol-Okhotsk Ocean occurred as a result of the collision of terranes with the Siberian continent during the period from the Late Carboniferous (in the west) to the Jurassic (in the east).

Based on the method of gravity modeling, taking into account the accumulated geophysical data on the Eurasian Basin of the Arctic Ocean, the authors have developed digital models of the deep structure of the Earth’s crust. The digital models of the basement relief and sedimentary cover thickness in the Eurasia Basin are calculated on the basis of reinterpretation of depth multi-channel seismic cross-sections and 2D gravity modeling. The digital models of the Mohorovichich surface relief and the earth’s crust thickness were calculated using the improved 3D gravity modeling method. It is shown that the reason for the deepening of the basement in the Nansen Basin by 1‒1.5 km in comparison with the Amundsen Basin is a larger volume of accumulated sedimentary cover in the Nansen Basin, with a similar thickness of the crust ~4.8 km in both basins. The characteristics of the oceanic crust studied on the basis of the obtained digital models reveal a complex, three-dimensional variability characteristic of ultra-slow spreading ridges. In the region of the Gakkel Ridge, which was formed at full spreading rates of less than 12 mm/year, the maximum spread of crust thickness is observed, as well as the predominance of the role of the tectonic factor over the magmatic one during the accretion of oceanic crust. Latter fact is expressed in the formation of extended subsea ridges parallel to the amagmatic segments of the ridge.

The geodynamic features of the Fergana intermountain depression are the presence of a rift during meridional compression of the region and the discrepancy between the location of earthquake sources and the boundaries of heterogeneities in the layers of the earth’s crust. The first feature is solved using the ideas of multi-stage plate tectonics, which provides an additional opportunity to assess the oil and gas content of the basin. However, existing hypothetical tectonic schemes are not supported by mathematical calculations. To clarify these features, we have developed a mathematical model of the stress-strain state in relation to one of the cross sections of the Earth’s crust in the Fergana depression, which has a zonally inhomogeneous density structure. The results of the mathematical model show that the presence of blocks of different densities creates displacements under the influence of horizontal compressive stresses. It is also shown that the isolines of maximum tangential stresses are located close to the boundaries of inhomogeneous zones, which indicates the presence of large errors in determining earthquake hypocenters.