柴达木北缘超高压变质带形成与折返的时限及机制  

Timing and Machanism of Formation and Exhumation of the Qaidam Ultra-Pressure Metamorphic Belt

作　　者：许志琴[1] 杨经缓 吴才来[1] 李海兵[1] 张建新[1] 戚学祥[1] 宋述光[1] 万渝生[1] 陈文[1] 邱海峻[1] 

机构地区：[1]中国地质科学院地质研究所大陆动力学实验室,北京100037

出　　处：《地质学报》2003年第2期163-176,共14页Acta Geologica Sinica

基　　金：国家自然科学基金重点项目(编号49732070)

摘　　要：位于青藏高原北缘的祁连山加里东造山带的形成是阿拉善板块、祁连微板块及柴达木—东昆仑板块在加里东期间汇聚和碰撞的结果。祁连微板块和柴达木—东昆仑板块之间的柴(达木)北缘超高压变质带形成于495～440 Ma,是继南祁连洋壳向北俯冲于祁连微板块下形成增生的柴北缘火山岛弧带之后,陆壳深俯冲的产物。柴北缘超高压变质带是在祁连微板块及柴达木—东昆仑板块之间的“正向陆内俯冲”向“斜向陆内俯冲”转化过程中“斜向挤出”机制下折返的,开始折返年龄为470～460 Ma,最后的折返时间为400～406 Ma。折返构造很好地保存在超高压变质岩石中,并且记录了广泛的退变质作用。The Qilian Caledonides on the north margin of the Qinghai-Xinjiang (Tibet) Plateau were formed by convergence and collision of the Alxa plate, Qilian microplate and Qaidam-East Kunlun microplate. The North Qaidam ultrahigh-pressure (UHP) metamorphic belt, lying between the Qilian and Qaidam-East Kunlun plates was formed between 495 and 440 Ma by deep subduction of the Qaidam-East Kunlun continental crust after the South Qilian oceanic subduction beneath the Qilian microplate and formation of the North Qaidam arc volcanic belt. The UHP belt was exhumed by a process of 'oblique extrusion' during transformation from 'normal' to 'oblique' intracontinental subduction between the Qiliabn microplate and Qaidam-East Kunlun plates. Exhumation began at 470 ~ 460 Ma and was completed by 406 ~ 400 Ma. Exhumation structures are well-preserved in the UHP rocks and record extensive retrograde metamorphism.

关 键 词：超高压变质带 折返构造 退变质作用 俯冲 碰撞 柴达木北缘 造山带 

分 类 号：P542[天文地球—构造地质学]