西昆仑康西瓦韧性走滑剪切带的两类剪切指向、形成时限及其构造意义  

Senses and timings of two kinds of shear in the Kangxiwar strike-slip shear zone, West Kunlun, and their tectonic significance. Geological Bulletin of China.

作　　者：许志琴[1] 戚学祥[1] 杨经绥[1] 嵇少丞 李海兵[1] 陈方远[1] 

机构地区：[1]中国地质科学院地质研究所,国土资源部大陆动力学重点实验室,北京100037 [2]加拿大蒙特利尔综合工学院民用,地质,采矿工程系

出　　处：《地质通报》2007年第10期1252-1261,共10页Geological Bulletin of China

基　　金：中国地质调查局项目(编号:12010610105)

摘　　要：详细的野外观察和显微构造研究表明,西昆仑南缘康西瓦韧性走滑剪切带主要由宽7km的孔兹岩质糜棱岩组成,具有早期自西向东的右行走滑剪切、后期自东向西的左行走滑剪切的剪切应变特征。韧性剪切带孔兹岩质糜棱岩中典型造岩矿物的晶格优选方位的电子背散射(EBSD)测量结果表明,钠长石具(010)[001]或(100)[001]滑移系,矽线石具{hk0}[001]滑移系,均反映了高温(>650℃)和中—高温(650～550℃)的应变特征。差应力作用下的变质生长与剪切所致的刚性旋转进一步增加了矽线石的组构强度。然而,石英却具形成于中温→中低温→低温环境(<550℃)的{10ī0}<a>→{10ī1}<a>→{0001}<a>3组滑移系,均指示自东向西的左行剪切指向,EBSD组构的结果与野外剪切应变的判断一致。Ar/Ar同位素年代学及锆石SHRIMPU-Pb同位素定年结果表明,右行韧性走滑作用形成于加里东期(445～428Ma),继后的左行走滑作用主要经历了3次明显的构造热事件(250Ma、203Ma和101～125Ma)。在白垩纪时期,阿尔金左行走滑断裂和康西瓦左行走滑断裂连接成一条连续的巨型(长度2200km)走滑构造带,同时康西瓦走滑断裂和铁克里克逆冲断裂之间的挤压转换域的形成制约了青藏高原西北缘塔里木南部前陆盆地的发育。Detailed field observations and microstructural studies indicate two opposite shear senses in the Kangxiwar strike-slip shear zone on the southern margin of the West Kunlun. The shear zone, consisting predominantly of khondalitic mylonite 7 km wide, shows the features of east-directed dextral strike-slip shear in the early stage and west-directed sinistral strike-slip shear in the late stage. Measurements of lattice preferred orientations （LPOs） of typical rock-forming minerals in the khondalitic mylonite in the ductile shear zone using the EBSD techniques demonstrate a （010）[001] or （100） [001] slip system for albite and a {hk0} [001] slip system for sillimanite, indicating a dextral strike-slip shear at high temperatures （〉650℃） and high-middle temperatures （650-550℃）. The sillimanite LPO was most probably enhanced by metamorphic growth under differential stresses and shear-induced rigid rotation. However, LPOs of quartz exhibit {10i0}〈a〉, {10i1}〈a〉 and {0001}〈a〉 slip systems, indicating a west-directed sinistral shear at middle-low temperatures （〈550℃ to 〈350℃）. ^39Ar/^40Ar and zircon SHRIMP U-Pb dating shows that the dextral ductile strike-slip shear took place in the Early Paleozoic （-445 - 428 Ma） whereas the sinistral shear occurred in 3 tectonothermal events （250, 203 and 101-125 Ma）. In the Cretaceous, the Kangxiwar sinistral strike-slip fault joined with the Altyn Tagh sinistral fault to form a continuous huge shear zone with a length of approximately 2200 km. In addition, the fomlation of the transpressional domain between the Tekilik ductile thrust and the Kangxiwar strike-slip shear zone since the Cretaceous controlled the uplift of the NW margin of the Qinghai-Tibet Plateau and development of a foreland basin in the south of Tarim.

关 键 词：西昆仑山 康西瓦韧性走滑剪切带 两类剪切指向 EBSD组构 构造事件年代学 

分 类 号：P542.3[天文地球—构造地质学] P542.4[天文地球—地质学]