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Anatoli V. Migursky, Siberian Research Institute of Geology, Geophysics and Mineral Resources (Russian Federation)
Aleksandr S. Salnikov, Siberian Research Institute of Geology, Geophysics and Mineral Resources (Russian Federation)
Feliks A. Migursky, Siberian Research Institute of Geology, Geophysics and Mineral Resources (Russian Federation)
Petr N. Sobolev, Siberian Research Institute of Geology, Geophysics and Mineral Resources (Russian Federation)
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Solid geophysical data are first obtained for the northeast of Eurasia. They allow interpreting the depth structure and performing geodynamic constructions and reconstructions to a higher degree of reliability.
The depth of the Earth's crust bottom in section of the 2-DV geotraverse (the Sea of Okhotsk - the Long Strait) is sensibly constant and averages 42 to 47 km. Against the background of the maintained depth of the Earth's crust we distinguish two zones where the Earth's crust grows thicker to 55-60 km. The zones are around the periphery of Early-Mesozoic island arcs, i.e. the Uda-Murgalsk and Oloy ones, respectively.
The Earth's crust grew thicker at areas of junction of the Uda-Murgalsk island-arc terrain with the Arman-Viligin terrain being a part of the Kolyma-Omolon superterrain in Late Jurassic?Early Cretaceous. In Late Cretaceous it became complicated by the formation of the Okhotsk-Chukotsk volcanogenic belt at the same place. According to our interpretation the Uda-Murgalsk terrain splits the crust of the Arman-Viligin terrain forming an indentor more than 80 km in extent. The other anomalous zone of the Earth's crust is confined to the northeastern periphery of the Omolon massif, i.e. to its junction with the Beryozovsk and Oloy terrains. And here the more rigid Omolon massif wedges in the crust of the Oloy folded system. The Beryozovsk terrain is properly an intermediary structure extruded to the upper crust with its collapsing and thrusting over the Omolon massif and Oloy terrain.
The anomalous junction of the terrains is outlined at the boundaries of the Anuy suture zone with the Oloy folded system, the Aluchinsk oceanic block to one side and the Chukotsk microcontinent to the other. The Aluchinsk wedge thrusts over the Oloy terrain and in its turn is overlain by the Uyamkandin shingle-thrust belt which belongs to the Anuy suture zone.
The position of the boundary between the North-Eurasian and North-American plates varied with time. In Devonian the eastern Siberian continent split up as a result of rifting. After that the Omulev, Prikolyma, Omolon and a number of other terrains, between which there occurred water spaces with oceanic and suboceanic crust, separated from it. Until Early Cretaceous those terrains moved rather freely relative to each other and adjacent plates. In Aptian-Albian the Kolyma-Omolon superterrain developed and attached to the Siberian continent. The boundary between the North-Eurasian and North-American plates took shape at areas of the South-Anuy suture. At present ophiolites, glaucophane schists and intense rock deformation prove the existence of the paleoocean there.
In Cenozoic a part of the North-Eurasian plate moved to the Okhotsk plate, and its North-American plate boundary in the vicinity of the line ran along the left shift of Ulukhan. The plates began to part in Miocene 20 Ma back as a maximum, perhaps following the occurrence of Gakkel ridge and initiation of Momsky rift.
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