LATE CARBONIFEROUS TO PERMIAN SEDIMENTATION IN INNER-MONGOLIA, CHINA, AND TECTONIC RELATIONSHIPS BETWEEN NORTH CHINA AND SIBERIA

A belt of deformed Permo-Carboniferous sedimentary rocks in Inner Mongolia represents an orogenic zone between the North China and Siberian blocks. The belt apparently contains accretionary terranes thrust onto the margins of both blocks, with scattered ophiolite/blueschist suites indicating the consumption of oceanic crust at least slightly older than the age of deformation. Upper Carboniferous to Lower Permian strata in central Inner Mongolia show both sedimentological and paleontological differences from Middle and Upper Permian rocks. In comparison with pre-Middle Permian rocks, younger Permian strata: (1) contain less laterally extensive limestone and more lensoidal carbonate in clastic sections; (2) contain a higher percentage of coarse clastic material; (3) grade upward from marine to terrestrial deposits; (4) contain fauna indicating more restricted circulation, particularly toward the western part of the belt; and (5) contain fauna that are consistent with, but do not require, northward movement of the North China block during the Permian. These differences indicate continued compression and progressive shallowing, and ultimate destruction, of the ocean basin between North China and Siberia. The lithologic and paleontologic similarity of Upper Carboniferous strata on both sides of proposed suture zones, however, is consistent with the possibility that virtually all Permo-Carboniferous sediments in central Inner Mongolia were deposited along the margin of the North China block, possibly on continental crust above an older suture zone. Thus, closure of an ocean basin by subduction of oceanic lithosphere in the Permo-Carboniferous may have been north of Inner Mongolia.