The East Siberia Transect

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Abstract
The new East Siberia transect, constructed by synthesizing recently analyzed geological and geophysical data, runs in a broken line through the vicinities of the towns of Nizhneangarsk, Chita, and Borzya, traversing the Siberian Platform margin and the Baikal and Mongolia-Okhotsk fold areas. The transected region encompasses a number of terranes, most of which once were arc-trench systems with fore-arc and back-arc basins. The island arcs involved Early Precambrian blocks that were sialic cores of some of their islands. The terranes have complex spatial relations in the present tectonic framework, with most of the rocks belonging to magmatic arcs, whereas the associated basins comprise allochthons thrust over continental margins. Accretion of the terranes to the Siberian continent occurred in two stages, the Early Proterozoic and the Early Paleozoic. Middle Paleozoic and Late Paleozoic–Early Mesozoic subduction on the periphery of the Mongolia-Okhotsk ocean, which actually was an enormous guK of the Pacific separating the Siberian and Mongolian (Amurian) continents, was not accompanied by accretion. In the Middle Jurassic, a major part of Siberia collided with Amuria, which at that time already represented a portion of the Mongolia-China continent. As a result of the collision, the southern margin of Siberia, together with the adjacent Onon island arc, were thrust over the passive margin of Mongolia-China. In the Early Cretaceous, neighboring southern Siberia and northern Mongolia-China were involved in rifting accompanied by “exhumation” of mylonitegneiss domes classified as metamorphic core complexes.