TRIASSIC PALEOMAGNETIC DATA FROM SOUTH CHINA AND THEIR BEARING ON THE TECTONIC EVOLUTION OF THE WESTERN CIRCUM-PACIFIC REGION

We report Early and Middle Triassic paleomagnetic data from the south Chinese provinces of Fujian and Guangxi. The characteristic magnetization of the rocks in each case is concluded to be a primary remanence that passes the fold test. The Triassic pole from western Guangxi and four other Triassic and Late Permian poles from three provinces that lie on undisputed parts of the Yangtze craton are well clustered. This suggests that Guangxi (except the southeast part) was also a part of the Yangtze craton, at least since the Triassic and probably since the Late Permian. With respect to the Yangtze craton, between the Early Triassic and the Late Cretaceous, Fujian may have been rotated 121 +/- 9 degrees counterclockwise and displaced 22 +/- 9 degrees north, or rotated 59 +/- 9 degrees clockwise and displaced 3 +/- 9 degrees south, depending on the hemisphere in which the magnetization was acquired. Based on consistency with other paleomagnetic results, and in accordance with the geologic data from the area, the former interpretation is preferred. A remarkable coincidence of Mesozoic poles for south China and south Korea is observed which, if true, implies that the South China Block (except for the displaced terranes in the coastal provinces) and Korea may have been part of the same continental landmass from the Triassic onwards. This is consistent with some geologic observations suggesting affinities between the two places. It also implies that the major fault zones in north China (e.g., the Tan-Lu fault) are unrelated to major fault zones in southeast China (e.g., the Changle-Nanao fault), with the former probably associated with the suturing of north and south China and the latter influenced by proto-Pacific plate motion.