RECOGNITION OF THE SUTURE BETWEEN THE SINO-KOREAN AND SIBERIAN PALEOPLATES IN THE MIDDLE PART OF INNER MONGOLIA
Wang Quan (Institute of Geology, Chinese Academy of Geological Science)
Based on a recent study, the author suggests that the final collision zone between the Sino-Korean and Siberian paleoplates is not situated in the Xar Moron River valley, as was previously presumed, but lies about 60 km north of the valley, along the line from the Baleng Mountain of Linxi county to Huanggang Liang of the Hexigten Banner, extending westwards as far as to the Solid Right Banner. The suture is coincident with the axial region of an anticlinorium in this area. Along the suture there occur two parallel ophiohte belts, 500 m apart only, which have been emplaced into the flysch formation of late Early Permian age. The strata and ophiolites of the southern, belt dip southwards, while those of the northern belt northwestwards. The ophiolite suites are both composed of mafic and ultramafic cumulates, sheeted diabasic dikes and basic pillow lavas, with an apparent thickness of over 1,000 m. Both limbs of the anticlinorium are structurally symmetrical, but have notable differences in respects of their stratigraphic sequence, lithologic character and Paleozoic floras and faunas. To the south of the suture there is a 180-km-wide Permian island arc-type magmatic rock belt, extending from the Xianghuan Banner westwards through Huade County to the Aohan Banner. Likewise, to the north of the suture, there is also a magmatic rock belt of similar type and age, which, over 240 km wide, is distributed in a northeast direction. The plate suture just coincides with the boundary of the late Paleozoic biogeographic provinces. South of the suture, the continental strata yield fossils of the Cathaysian flora, while the marine strata are abundant in fossils of warm-water faunas. North of the suture is the cold-water fauna province, which also contains the Angara flora. Between the northern margin of the Sino-Korean Platform and the plate suture, there are two accretion complex zones, the early Paleozoic Ongniud Banner accretion complex zone and the late Paleozaic Linxi accretion complex zone. From the China-Mongolian border southwards, there are aligned successively the Devanian Dang Ujimqin Banner accretion complex zone, the Carboniferous-Permian Xi Ujimqin Banner accretion complex zone and the Permian Haortumiao accretion complex zone. The presence of these accretion complex zones and the ophiolite suites in the eastern part af Inner Mongolia indicates that there had been an open ocean between the Siberian and Sino-Korean platforms in Paieozoic time and that the ancient oceanic crust of the latter had been stbducted repeatedly along both of the continental margins. In the Late Permian, there occurred final collision of the Cathaysia oldland and the Angara oldland, thus forming an integrted continent in the northern hemisphere.