南羌塘盆地中-新生代逆冲推覆构造样式及构造应力场特征

An analysis of structure structure and tectonic style of the mega thrust nappe stress fields characterisitics of the southern Qiangtang Basin, Tibet

摘要新生代印度板块与欧亚板块的持续碰撞挤压，造成南羌塘地块向南逆冲于拉萨地块之上，并在南羌塘地块内部形成了一系列的由北往南的逆冲推覆构造。然而，到目前为止，我们对这些逆冲推覆构造及夹持其间的褶皱变形的结构组成、构造样式、形成时代以及缩短量分布等问题仍存在很大的争议。本文在详细的野外调查基础上，对赛布错一扎加藏布断裂（SZT），多玛一其香错断裂（DQT），隆鄂尼褶断带（LF）及南羌塘与中央隆起带分界的肖查卡一双湖断裂（XST）进行了几何学、运动学分析，建立了精细的构造框架。我们认为这些断裂为始新世以来形成的同时期的叠瓦状逆冲推覆；并通过野外褶皱形态，结合层面、节理面、断层面滑动矢量的分析，识别出南羌塘盆地4期构造应力场：1）代表中特提斯俯冲碰撞阶段的近S-N向的挤压；2）中特提斯碰撞后，随着班公湖-怒江缝合带的形成，南羌塘地区构造应力场转为S—N向的伸展；3）新生代印度板块向欧亚板块俯冲碰撞，青藏高原进入陆内变形阶段，南羌塘盆地内表现为NE—SW向的挤压，形成本文提及的一系列逆冲推覆构造；4）随着高原的持续隆升，约14Ma南北向裂谷开始活动，应力场转为NWW．SEE向伸展，形成双湖裂谷系。

Due to the Indian-Eurasian continental sustained collision and the closure of the Neo- Tethys in Cenozoic, The northward subduction of the Lhasa block, and the southern Qiangtang terrane （SQT） thrust southward to the above of the Lhasa block. Thus far, however, the questions about the structure composition, the structure style, the formation age and the structure shorten distribution of the thrusts and the fold deformation which is sandwiched between the mega thrusts are still hotly controversy. Basing on the detailed field investigation, we analysised the Geometry, kinematics feature of the Saibu C oZaga Zangbo thrust fault （SZT）, the Doma-Qixiang Co thrust fault （DQT）, the Longeni thrust-fold belt （LT） and the Xiaochaka- Shuanghu thrust fault （XST）, establishing the tectonic framework in detail. We hold that the thrust faults are the same period imbricated thrust napped structure which formed since Eocene. By analysising the fold feature in the field, combining with the joint surface and fault surface sliding vector analysis, we identified four Periods tectonic stress field of the SQT： 1） The early N-S trending compressive tectonic stress of the subduction collision stage in Meso- Tethys. 2） The N-S trending detaching stress field of the SQT after the form of Bangonghu- Nujiang suture zone. 3） In Cenozoic, the Tibetan Platen entered the stage of intra-continental deformation and the SQT performed a NE-SW trending compressing feature, and then the mega thrust nappe structure of the SQT actived in Late Paleogene, in which a series of north to south exhibition type imbricated thrusts, which thrusted the SQT to the above of the Lhasa, formed. 4） With the continuous uplift of plateau, the north and south rift valley actived in about 14 Ma, and the tectonic stress turned to SE-NW trending detachment in which the Shuanghu-rifts formed.