羌塘盆地中央隆起性质与成因

NATURE AND ORIGIN OF THE CENTRAL UPLIFT IN THE QIANGTANG BASIN

羌塘盆地夹持于可可西里-金沙江缝合带和班公-怒江缝合带之间,未出露中生界地层的中央隆起将盆地分为南北两部分。在金沙江关闭时,俯冲板块向南俯冲。而在羌塘的中部一带由于软流圈的垫托作用,使地幔热隆,导致大规模重熔。地幔和重熔物向上加入中地壳,使中地壳增厚,同时使中上地壳受热弱化,导致快速变形(拆离)和构造剥蚀,产生均衡隆升,形成变质核杂岩。重熔物质的上升进一步加强浮力反弹,加之侵位的侧向应力,形成拉伸应力场。在失稳的重力作用下,促使伸展构造和拆离断层的形成。上下部变形范围形成拉张沉积区-新盆成生。中央隆起的变质核杂岩体为片麻岩,上覆层为以断层分割的未变质、弱变质的盖层岩石。

The Qiangtang basin is between the Kokoxili Jingshajiang suture belt and Banggong Lujing suture belt. The basin is divided into two section: the south and north by the central uplift that the Mesozoic is not outcropped. The blue schists have been discovered in the Gangmaco, Guanganjianianshan, Mayigangri, Jiomuri, Shuhu regions. Their range is about 500 km2. It is a elliptic, linear and insular vault uplift that is make up of intensly metamorphosed metamorphites, which form the metamorphic core complex. The metamorphic core complex and the blue schists are formed during the low angle normal fault detaches in the central uplift area. The top layer of no or light metamorphism is intersected by faults. When the Jingshajiang suture belt subducts southward, the asthenosphere of the suture plate underplates, and mantle heat uplift takes place. When the mantle and remelting material adds to crust,the middle crust becomes thick, and the upper middle crust is heated and weaken and the lower crust is exhumed by low angle normal faults. The rising of the remelting material further enhances the buoyancy rebounds. The extensional stresses occur while the lateral stress invades. The new basin is formed in extentional metamorphosed scope.