西藏拉康地区南部拆离断层构造变形特征  

TECTONIC DEFORMATION OF DETACHED FAULT IN SOUTHERN LACANG AREA OF TIBET

作　　者：王世龙 米玛旺久 马文成 WANG Shi-ong;MIMA Wang-jiu;MA Wen-cheng(The Second Geological Brigade,Bureau of Geology and Mineral Resources Exploration and Development of Tibet Autonomous Region,Lhasa 850007,China)

机构地区：[1]西藏自治区地质矿产勘查开发局第二地质大队,西藏拉萨850007

出　　处：《甘肃地质》2024年第4期14-25,共12页Gansu Geology

基　　金：中国地质调查局成都地质调查中心地调科研项目(121201010000150014-01、DD20160015-05)。

摘　　要：西藏拉康地区发育的拆离断层叠加在先期逆冲推覆构造之上,在持续挤压作用下,大喜马拉雅基底杂岩带相对向南楔形挤出,同时北侧发生拆离效应,形成研究区内规模较大的北倾韧脆性剪切带。本文通过野外地质调查,根据岩石组合、变形变质、构造层次等,将拉康地区南部拆离断层带进一步划分为上拆离面(F_(18))和下拆离面(F_(20)),厘定出两期主要的构造活动:(1)D_(2)期韧脆性变形;(2)D_(3)期脆性变形。二云二长花岗岩中锆石U-Pb年龄为(19.2±0.1) Ma,代表D_(2)期构造活动的时间下限;白云母二长花岗岩中锆石U-Pb年龄为(13.4±0.1) Ma,代表D_(3)期构造活动发生时间;正断层中石英脉的电子自旋共振(ESR)测年结果:20.43~21.34 Ma和10.64~14.04 Ma,分别与两期构造活动(D_(2)、D_(3))时代相吻合,说明研究区内主要的两期构造活动时代集中在中新世中晚期。The detachment faults developed in the Lhakang area of Tibet are superimposed upon the earlier thrust-nappe structure.Under the continuous compressive effect,the Great Himalayan Basement Complex Zone is extruded relatively southward in a wedge shape,while detachment occurs on the northern side,forming a largescale north-dipping brittle-ductile shear zone within the investigation area.Through field geological investigations and based on rock assemblages,deformation and metamorphism,and structural hierarchies,the southern detachment fault zone in the Lhakang area is further divided into the upper detachment surface(F_(18))and the lower detachment surface(F_(20)),and two phases of tectonic activities are determined:(1)D_(2)phase ductile-brittle deformation;(2)D_(3)phase brittle deformation.The zircon U-Pb age of the two-mica monzogranite is 19.22±0.14Ma,representing the lower limit of the D_(2)phase tectonic activity;the K-Ar age of the muscovite in the muscovite monzogranite is 11.6 Ma,representing the occurrence time of the D_(3)phase tectonic activity;the electron spin resonance(ESR)dating results of quartz veins in the normal faults:20.43~21.34 Ma and 10.64-14.04 Ma are consistent with the two phases of tectonic activities(D_(2),D_(3)),indicating that the two main phases of tectonic activities(D_(2),D_(3))in the study area are concentrated in the middle to late Miocene.

关 键 词：西藏 拉康地区 拆离断层 构造特征 活动时代 

分 类 号：P618.13[天文地球—矿床学] P542[天文地球—地质学]