PROBLEMS OF TECTONICS OF THE MONGOL-OKHOTSK OROGENIC BELT

Abstract

The Mongol-Okhotsk orogenic belt occupies a pivotal position among the Paleozoic orogenic belts of Central Asia, and at the same time is closely linked to the Mesozoic orogenic belts of the western Pacific framing. Recognition of its nature is of key import in specifying interaction between plates of contiguous regions of the paleo-Pacific and paleo-Asian Oceans and interpretation of the history of formation of different-age orogenic belts of Asia. The former models of formation of the Mongol-Okhotsk belt do not explain its characteristic features, such as 1) linear ribbon-like form; 2) discontinuance in extension; 3) "blind" termination in Central Mongolia; 4) absence of associated, fully developed passive continental margins and fold-and-thrust belts emerging in their place; 5) absence of marginal troughs and typical collisional granites; 6) wide distribution of extensive (hundreds of kilometers) longitudinal sinistral strike-slip motions determining deformational style; and 7) distribution of faunas belonging to different paleobiogeographic realms. The characteristic features of the Mongol-Okhotsk belt are probably conditioned by oblique convergence of the Amur terrane (microcontinent) with the Siberian continent. In the Early and Middle Paleozoic the superterrane adjoined the Altai-Sayans area, and this accounts for similarity in their Cambrian, Silurian, Devonian, and Early Carboniferous faunas. In the Late Paleozoic and Early Mesozoic the Amur superterrane (microcontinent) was moving along the southern margin of the Siberian continent from southwest to northeast (in the modern coordinates), successively being accreted to the continent.