Density inhomogeneity of the Earth’s crust of the Black Sea and adjacent territories from three dimensional gravity modelling. Part II. Density sections

Abstract

To obtain a more complete picture of the deep structure and density heterogeneity of the main tectonic structures of the Black Sea megadepression and adjacent territories, density sections were constructed that intersect structures along geotraverses, DPS profiles and illustration profiles. Based on the results of three-dimensional gravity modelling, the Scythian plate has a block structure, more complex than the East European platform. It is also characterized by a thick layer of deformed sediments, with the largest compaction of the crust is being in its western and southern parts. The pre-Dobrudzha Trough consists of two parts: the denser one, which adjoins the Serpentine Rise, and the less dense one, adjacent to Zmeiny Uplift. The Karkinitsky Trough is characterized by compaction of the middle and lower parts of the Earth's crust in the south and west, that is associated with tectonic processes during riftogenesis, namely, the introduction of mantle matter into the lower and middle parts of the Earth's crust. There is no «granite» layer under the Black Sea-Kalamitsky Swell, the «basalt» layer is represented by a crust-mantle mixture. The deep domain of the Indolo-Kuban Trough is divided into two blocks along the axis: denser (south, west and southwest) and less dense (northeast, east and north). In Crimea, in all density sections a thick layer of dislocated sediments is observed, the crystalline crust is characterized by significant compaction (especially the southern part), the absence of a «granite» layer, the occurrence of the subsurface «basalt» layer and the presence of the thick crust-mantle mixture. The West Black Sea Depression is characterized by the absence of a granite layer in the central part, the occurrence of sediments on the «basalt» (and sometimes on the «diorite») layer. In this case, the crust is of the oceanic type. In the East Black Sea basin there is a thin layer of dislocated deposits with a density close to the density of crystalline rocks. According to the density value, this layer can be attributed to very compact dislocated deposits that suggests the oceanic or rifted continental crust. The crystalline crust of the Central Black Sea Rise is heterogeneous in composition and structure. The Andrusov and Arkhangelsk Ridges, which echelonedly displaced to each other, have different density characteristics of the crystalline crust, the depth of its bottom and density on it. Collectively, these features give evidence of the heterogeneous history of the formation and development of these structures. The Sinop Depression is a large Neogene graben which is underlain by a crust-mantle mixture of different thickness. The Sorokin Basin is characterized by an increased thickness of the sedimentary cover, the absence of a «granite» layer and a rise in the roof of the «diorite» layer to a depth of 2―3 km in the eastern part, as well as the presence of a «granite» layer with a thickness of over 10 km in the western. The northwestern part of the Shatsky Uplift is characterized by decompression of the entire Earth's crust, and in the southeastern part, decompression is observed only in the middle part of the section.