内蒙古西北部望湖山韧性剪切带构造特征及其地质意义  

Structural characteristics of the Wanghushan ductile shear zone in northwestern Inner Mongolia and its geological significance

作　　者：王文宝 雷聪聪 李刚[2] 李卫星 丁海生 马军 闫振军 WANG Wenbao;LEI Congcong;LI Gang;LI Weixing;DING Haisheng;MA Jun;YAN Zhenjun(Hohhot Natural Resources Com prehensive Survey Center,China Geological Survey,Hohhot,Inner Mongolia 010020,China;College of Earth Sciences,Jilin University,Changchun,Jilin 130061,China)

机构地区：[1]中国地质调查局呼和浩特自然资源综合调查中心,内蒙古呼和浩特010020 [2]吉林大学地球科学学院,吉林长春130061

出　　处：《地质学报》2023年第7期2141-2156,共16页Acta Geologica Sinica

基　　金：中国地质调查局项目(编号DD20208005)资助的成果。

摘　　要：望湖山韧性剪切带位于中亚造山带中段南缘的雅干断裂带内。本文应用野外和显微构造解析、^(40)Ar/^(39)Ar和U-Pb同位素地质年代学手段来恢复该剪切带的构造演化史,并探讨了其与中亚造山带碰撞造山的关系。望湖山韧性剪切带走向近东西,具右行走滑性质。糜棱岩中长石和石英的动态重结晶方式限定了其变形温度在400~500℃,属高绿片岩相—低角闪岩相动力变质带。剪切带内岩株状产出的糜棱岩化闪长岩结晶年龄为331.3±5.7 Ma,侵入其中的同构造花岗岩脉结晶年龄为304.8±2.3 Ma。咸水湖组中同构造糜棱岩化黑云母二长花岗岩脉结晶年龄为308.9±2.0 Ma。侵入剪切带且未变形正长花岗岩结晶年龄为288.4±1.3 Ma。以上限定了该期韧性剪切变形时代在331~288 Ma之间。剪切带中糜棱岩的黑(白)云母^(40)Ar/^(39)Ar同位素测年获得了253~237 Ma坪年龄,与侵入剪切带的三叠纪花岗岩年龄近一致,为晚期岩浆热事件的记录。综合分析,望湖山韧性剪切带应为中亚造山带在晚石炭世—早二叠世碰撞造山的直接记录,并在早二叠世晚期本区域碰撞造山结束。The Wanghushan ductile shear zone(WHSSZ)is located in the Yagan fault zone in Southernmost Central Asian Orogenic Belt(CAOB).In this study,we applied structural,microstructural and ^(40)Ar/^(39)Ar thermochronology,and U-Pb zircon geochronology to constrain the tectonic evolution of WHSSZ,and discussed its relations with subduction/collision dynamics in the Central Asian Orogenic Belt(CAOB).The WHSSZ is a nearly E-W striking ductile strike-slip shear zone,and various kinematic indicators indicate dextral shearing.The dynamic recrystallization characteristics of quartz and plagioclase indicate that the dextral ductile shearing belt is a high greenschist facies to low amphibolite facies dynamical metamorphism belt and the deformation temperature is approximately 400~500℃.LA-ICP-MS U-Pb dating were conducted on zircons from the mylonitized diorite,granite dikes,and undeformed syenogranite The weighted mean ages of diorite and syntectonic granitic vein are 331.3±5.7 Ma and 304.8±2.3 Ma.The crystallization ages of syntectonic mylonitized granite dikes and undeformed syenogranite are 308.9±2.0 Ma and 288.4±1.3 Ma,suggesting that the dextral shearing took place after 331 Ma and before 288 Ma.^(40)Ar/^(39)Ar plateau age of muscovite and biotite samples from metamorphic-deformed rocks of the WHSSZ range from 253 Ma to 237 Ma,which are consistent with the age of the Triassic magmatic rocks intrusive in the WHSSZ,and should be the record of that magmatic thermal event.We infer that the WHSSZ should be the direct record of the assembly of the middle segment of the southern CAOB during Late Carboniferous to Early Permian,and probably ended in Late Early Permian.

关 键 词：韧性剪切带 晚石炭世—早二叠世 阿拉善 U-PB测年 中亚造山带 

分 类 号：P534.4[天文地球—古生物学与地层学] P542[天文地球—地质学] P597.3