华南早三叠世的古地磁学与大地构造

PALEOMAGNETIC CONSTRAINTS ON EARLY TRIASSIC TECTONICS OF SOUTH CHINA

从华南几个具代表性地点的下三叠统灰岩中，获得了有意义的古地磁学初步结果．这些结果支持华南存在分离板块的设想．根据新近获得的地质与古地磁学证据，推断华南存在４个岩石图板块．它们是扬子（Ｄ＝２３２．４°，Ｉ＝－１１．８°，Ｋ＝２８．２，α９５＝５．５°），湘桂（Ｄ＝１９８．０°，Ｉ＝３２．２°，α９５＝１２．９°），华夏（Ｄ＝８８．０°，Ｉ＝１３．０°，Ｋ＝２０．１，α９５＝９．１°）和海南（上二叠统Ｄ＝３３８．２°，Ｉ＝１５．９°，Ｋ＝１０．２，α９５＝１４．３°）板块．４个板块的古地磁极位分散，纬度差明显，并存在碰撞后的局部与区域性的旋转作用，尤其是顺时针旋转．华南早中生代的大地构造可理解为４个来自古特提斯和冈瓦纳的岩石圈碎块与欧亚大陆聚合作用的产物．

New preliminary paleomagnetic results from the Lower Triassic limestones in several representative localities of South China support the suggestion of the existence ofdisplaced blocks proposed by Hsu et al.(1987;1990).Four continental fragments havebeen recognized based on the geological and paleom3gnetic evidences.They are the Yangtze (D = 232.4°,I =- 11.8°,K= 28.2,a95=5.5°),Xianggui (D=198.0°,I =-32.2°,a95= 12.9°), Cathaysia (D= 88.0°,I=- 13.0°, K= 20.1,a95=9.1°) and Hainan(late Permian data D=338.2°,I= - 15.9°,K=10.2,a95=14.3°) blocks.The paleopole positions of the four blocks are scarttered and latitudinal discrepancies are apparent. This may be due to the separations and displacements of the blocks instead ofcrustal shortening.Differential post-collision rotations, especially clockwise rotationscan be seen in the blocks,which may be the product of regional and local rotations.The early Mesozoic tectonics of South China can be interpreted in terms of amalgamation of the four continental blocks from the Paleotethys and Gandwanaland towards the Eurasia continent.