PALEOMAGNETIC CONSTRAINTS ON THE PALEOGEOGRAPHY OF CHINA - IMPLICATIONS FOR GONDWANALAND

Published palaeomagnetic results for China unequivocally show that the three major blocks of China-North and South China Blocks and Tarim-we re at or near equatorial latitudes in the Early and Middle Palaeozoic, although they certainly did not have their present relative configura tion during that time. These Chinese blocks may have been an ancient e quatorial archipelago lying between a northerly Siberia continent and a southerly Gondwanaland continent throughout the Palaeozoic. Palaeoma gnetic evidence from Chinese blocks appear not to be consistent in det ail with various speculations on rapid true polar wander during Early and Middle Palaeozoic. Late Palaeozoic palaeomagnetic data suggest tha t the various blocks of China were too far north to have attached to G ondwanaland and suggest that they rifted from Gondwanaland during the Late Devonian and Carboniferous. Studies of Late Permian palaeomagneti c data for the major blocks of China demonstrate major diachronous clo sures between the Chinese blocks themselves and with Eurasia. They con tradict the widely held view that the Central Asian Fold Belt, which r uns across North China just north of the 40 degrees N, is the zone whe re China was sutured to Siberia in Permian time, and suggest a composi te Mongolia-North China plate that became sutured to Siberia in Mesozo ic time by anticlockwise relative rotation about a point of initial co llision (50 degrees N, 75 degrees E) near the western end of the South Siberian Fold Belt. The westward disappearance of Jurassic marine sed iments on the northern margin of the Mongolia-North China plate indica tes that suturing and rotation were essentially complete by the end of the Jurassic. The amalgamation of North and South China appears to ha ve taken place over a similar time span and by a similar but antitheti c mechanism, with collision first occurring near the eastern end of th e Qinling Fold Belt in the Permo-Triassic, and suturing progressing we stward due to clockwise rotation of South China relative to North Chin a. The accretion of the North and South China Blocks probably was fini shed in Middle Jurassic, a little earlier than their final suturing wi th Eurasia. A left-lateral strike-slip displacement of 1400 km for Tar im, parallel to the southeast boundary of the Kazakhstan Block, can ac count for the discrepancy in Early Triassic poles for Tarim and Siberi a and there is an indication that Tarim may have moved northeastward w ith respect to Eurasia even after the Cretaceous as a result of the In dia-Eurasia collision. This event appears to have affected a region mu ch larger than the Tibetan plateau, perhaps reaching as far north as t he Altai fold belt in Central Asia.