CRETACEOUS AND TERTIARY PALEOMAGNETIC RESULTS FROM SOUTHEAST CHINA AND THEIR TECTONIC IMPLICATIONS

We report Cretaceous and Tertiary paleomagnetic data from Fujian, Guangxi and Guangdong provinces in south China. In Guangxi Province we sampled Early Cretaceous redbeds of the Xinlong Formation at eight localities separated by up to 100 km. The high-temperature component obtained by thermal demagnetization is of dual polarity and passes the fold test, and implies 18-degrees +/- 8-degrees counterclockwise rotation and insignificant poleward displacement with respect to cratonic localities in Sichuan Province. A Tertiary basin lying in a southeast-trending fault zone is also rotated counterclockwise by 40-degrees +/- 8-degrees. Both results can be explained very well by a simple block rotation model for the Cenozoic tectonic evolution of western Guangxi Province that is driven by left-lateral shear on southeast-trending faults. The timing and sense of shear are the same as for India-Asia collision models involving the extrusion of Indochina along the Red River fault zone, which lies several hundred kilometers to the southwest, but the magnitude of fault displacement in Guangxi is much less. In the coastal provinces of Fujian and Guangdong we find Late Cretaceous directions that are rotated clockwise with respect to Sichuan Province. Combined with similar clockwise rotations found by two other studies of coeval rocks from the same region, the mean rotation for the coastal provinces is 12-degrees +/- 8-degrees; this could indicate a coherent block rotation of the region driven by extrusion tectonics. However, the limited number of sampling localities also allows the possibility that the directions reflect local rotations due to dextral shearing driven by circum-Pacific tectonics.