青藏高原中段古近纪早期古构造演化

青藏高原古近纪早期发育大量区域逆冲推覆构造系统, 典型实例如冈底斯逆冲断裂系、纳木错西逆冲推覆构造、伦坡拉逆冲推覆构造、唐古拉山北逆冲推覆构造、东昆仑南部左旋斜冲断裂系。古近纪逆冲推覆构造对古新世—始新世沉积盆地具有重要控制和改造作用。冈底斯古新世—始新世早期发育大量中酸性岩浆侵入和多期中酸性火山喷发, 岩石Sr/Y-Y地球化学显示为岛弧岩浆岩, 推断与古近纪早期新特提斯残留古大洋板块俯冲存在成因联系。古近纪早期新特提斯残留大洋板块俯冲向印度大陆板块俯冲的转换时代约为46-45 Ma, 转换期前逆冲推覆构造运动与新特提斯残留古大洋板块俯冲存在密切关系; 转换期后印度大陆板块俯冲导致更为强烈的逆冲推覆构造运动和挤压缩短变形, 不仅使早期很多逆冲推覆构造继续发生构造运动, 还在喜马拉雅、冈底斯、风火山、东昆仑南部形成大量新的逆冲推覆构造系统。

Paleocene-Eocene Tectonic Evolution in Central Tibetan Plateau

Large-scale thrust systems formed in Paleocene-Eocene in central Tibetan Plateau, e.g. Gangdese Thrust System (GTS), West Namco Thrust (WNT), Lunpola Thrust System (LTS), North Tanggula Thrust (NTS) and South Kunlun sinistral-slip thrust faults (SKF), and major thrust systems evidently controlled formation and evolution of Paleocene-Eocene basins. Regional magmatic plutonism and volcanic eruptions occurred in Gangdese areas in Paleocene-Early Eocene, and Sr/Y-Y geochemistry indicates that these magmatic rocks belong to island-arc magma caused by subduction of remained oceanic plate. Paleocene-Early Eocene subduction of remained oceanic plate transferred to subduction of India continental plate in 46-45 Ma. Subduction of remained oceanic plate lead to regional thrusting in Paleocene-Early Eocene, and subduction of India continental plate caused more intense thrusting and crust shortening and formed many new thrust systems as Main Central Thrust (MCT), South Damxiong Thrust (SDT), Fenghuoshan thrust system and South Kunlun Thrust (SKT) since Late Eocene