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

Abstract

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° with respect to each other and separated (on greater extent of their present-day boundary) by an enormous gulf of the Paleopacific called the Mongolia–Okhotsk ocean. Closure of this ocean at the Early/Middle Jurassic boundary led to the complete collision of Siberia and Mongolia, which by then had already become part of the Mongolia–North China continent. This main collisional episode, which lasted through the Middle and Late Jurassic, involved thrusting, folding and magmatism and produced the Mongolia–Okhotsk belt. The Onon island-arc, which was located in the Mongolia–Okhotsk ocean, was squeezed between the two major continents. Inasmuch as the third element (the island arc) was involved in the collision it is reasonable to distinguish two branches of the Mongolia–Okhotsk suture. These branches control the spatial distribution of gold mineralization in the Trans-Baikal region. On the southeastern periphery of Siberia the crust thickened considerably after the collision and a plateau-like uplift formed. In the Early Cretaceous, when compression ceased, the collisional uplift collapsed and the thrusts were transformed into low-angle normal faults, the motions on which were responsible for the formation of rift basins and exhumation of metamorphic core complexes.