大陆板内盆山耦合及盆山成因——以青藏高原及周边盆地为例

摘要：大陆造山带与沉积盆地之间具有十分密切的内在联系,空间上相互依存,物质上相互补偿,构造上相互作用,时间上同步演化。这些内在联系体现在统一的形成机制上:大陆造山带和沉积盆地是在大陆边缘俯冲板片脱水熔融和大陆内部地幔柱(枝)上隆的热动力作用下,地壳由盆向山侧向流动,导致盆山地壳物质发生循环运动。青藏高原与周边盆地的耦合作用十分典型。青藏高原不是印度板块与欧亚板块碰撞的结果,而是形成于下地壳流动驱动的板内盆山作用。青藏高原板内盆山耦合可分为两个阶段:(1)板内造山成盆阶段,表现为180～120 Ma→65～30 Ma→23～7 Ma从青藏高原北部和东部盆山系统→青藏高原中部盆山系统→青藏高原南部盆山系统有序迁移,以构造隆升、水平运动、地质作用和大规模板内金属成矿为特征;(2)均衡成山成盆阶段,表现为从36 Ma开始,青藏高原整体快速隆升和周边沉积盆地边缘坳陷带巨厚的磨拉石沉积,以36 Ma B.P.、25 Ma B.P.、18~12 Ma B.P.、 08 Ma B.P.和015 Ma B.P.等一系列脉动式快速隆升、垂直运动、地理作用和水系 环境变化为特征。大陆板内盆山构造演化经历从伸展构造向挤压构造的转换,伴随盆地主动作用转变成造山带主动作用。大陆下地壳流动和盆山耦合形成非安德森式的低角度拆离断层、波状起伏逆冲断层和异常共轭关系走滑断层。

Coupling and formation mechanism of continental intraplate basin and orogen—Examples from the Qinghai Tibet Plateau and adjacent basins

Abstract: There are very close relationship between orogenic belts and sedimentary basins, which show some features including interdependence of their spatial structures, mutual compensation of their materials, interaction of their tectonics, and simultaneity of their tectonic evolutions. A unified formation mechanism of continental orogenic belts and sedimentary basins is presented as follows: The lower crustal ductile flow from basin to orogen driven by thermal energy related to upwelling mantle plume in continental intraplate or vertical diaper movement of dehydration and magma of subduction plate on active continental margin, resulted in the denudation of upper crust and surface in orogenic belt and sediment in basin, and led to a circulative movement of different states of rocks between basin and orogen, and between lower crust and upper crust. The typical coupling between the Qinghai Tibet Plateau and adjacent basins occurred in the intraplate tectonic setting. The formation of the Qinghai Tibet Plateau was not caused by the collision between India Plate and Eurasia Plate, but by intraplate basin mountain coupling driven by lower crustal flow. The intraplate basin mountain coupling process of the Qinghai Tibet Plateau can be divided into two stages: (1)Intraplate orogeny and basin forming stage; (2)Isostatic mountain building and basin margin subsiding stage. The spatial temporal evolution of the intraplate orogeny and basin forming of the Qinghai Tibet Plateau and related basins was shown by the evolution sequence proceeding from the north and east, to the middle, and finally to the south of the Qinghai Tibet Plateau in the corresponding periods from 180120 Ma, 6530 Ma, to 237 Ma, and was represented by extensive intraplate faulting, folding, block movement, magmatism and metallogeny. Rapid uplift and strong erosion of the Qinghai Tibet Plateau as a whole and rapid settlement and molasse formation of the depressions on the margins of the peripheral basins resulting from gravity isostasy since 3.6 Ma, characterized by pulsative uplift and settlement, crust scale vertical movement, integral rapid uplift of the plateau, local subsiding of basin margin, and considerable variations in topography and environment occurring in 3.6 Ma B.P., 2.5 Ma B.P., 1.81.2 Ma B.P., 0.8 Ma B.P., 0.15 Ma B.P., etc. Synchronous evolution of continental intraplate basin orogeny system underwent tectonic transformation from extension to compression, with the transformation from active movement of basin to active movement of orogeny. Non Anderson low angle detachment, wavy thrust fault and abnormal conjugate strike slip fault were formed by lower crustal flow and intraplate basin orogen coupling.