Geodynamics of the western part of the Mongolia-Okhotsk collisional belt, Trans-Baikal region (Russia) and Mongolia

After the western edge of the Mongolian microcontinent joined the Siberian continent in the region of Central Mongolia in the earliest Permian, these two continental blocks remained turned at an angle of about 120 degrees wit h respect to each other and separated (on greater extent of their present-d ay boundary) by an enormous gulf of the Paleopacific called the Mongolia-Ok hotsk ocean. Closure of this ocean at the Early/Middle Jurassic boundary le d to the complete collision of Siberia and Mongolia, which by then had alre ady become part of the Mongolia-North China continent. This main collisiona l episode, which lasted through the Middle and Late Jurassic, involved thru sting, folding and magmatism and produced the Mongolia-Okhotsk belt. The On on island-are, which was located in the Mongolia-Okhotsk ocean, was squeeze d between the two major continents. Inasmuch as the third element (the isla nd are) was involved in the collision it is reasonable to distinguish two b ranches of the Mongolia-Okhotsk suture. These branches control the spatial distribution of gold mineralization in the Trans-Baikal region. On the sout heastern periphery of Siberia the crust thickened considerably after the co llision and a plateau-like uplift formed. In the Early Cretaceous, when com pression ceased, the collisional uplift collapsed and the thrusts were tran sformed into low-angle normal faults, the motions on which were responsible for the formation of lift basins and exhumation of metamorphic core comple xes. (C) 1999 Elsevier Science B.V. All rights reserved.