滇西崇山剪切带南段左行走滑作用的构造特征及时代约束  

Structural characterization of and geochronological constraints on sinistral strike-slip shearing along the southern segment of Chongshan shear zone, western Yunnan

作　　者：唐渊[1] 尹福光[1] 王立全[1] 王冬兵[1] 廖世勇[1] 孙志明[1] 孙洁[1] 

机构地区：[1]成都地质矿产研究所,成都610081

出　　处：《岩石学报》2013年第4期1311-1324,共14页Acta Petrologica Sinica

基　　金：国家973项目(2009CB421003);中国地质调查局地质矿产调查评价专项项目(1212011220412;1212011085119;212011085147)联合资助

摘　　要：作为保山地块与兰坪-思茅盆地的重要边界,崇山剪切带新生代以来经历了多阶段的构造变形;其中以大规模走滑韧性剪切作用最为明显,表现为北段以右行走滑剪切为主、南段以左行走滑剪切为主。本文通过对崇山剪切带南段永保桥-瓦窑桥剖面出露的崇山群石英片岩、片麻岩及糜棱岩等进行详细露头解析、室内显微构造观察以及变形石英的EBSD组构分析,认为崇山剪切带南段的岩石新生代以来至少经历了两期不同环境下的韧性变形:第一期(D1)为纯剪条件下的收缩变形,发生的温度条件大约在550～650℃(角闪岩相),表现为一些褶皱构造、石香肠或透镜体构造的发育及石英的C轴组构图呈斜方对称式;第二期(D2)为单剪递进条件下的左行走滑剪切变形,表现形式为走滑剪切面理的发育及各类岩石遭受韧性剪切变形从而改造成糜棱岩。此外,在崇山剪切带内发育一套含电气石花岗质脉体,根据详细的露头解析及显微构造分析,本文认为该套含电气石花岗质脉体是左行剪切作用初期阶段伴随的深熔作用的产物,为同剪切花岗岩脉。本文选取了两个含电气石花岗质脉体的样品进行了LA-ICP-MS锆石U-Pb测年,分别得到21.7±0.3Ma和22.7±0.3Ma的锆石U-Pb年龄,进一步表明了崇山剪切带南段的左行剪切作用起始时代在22Ma左右或略早于22Ma。As the important boundary between Baoshan block and Lanping-Simao basin, the Chongshan shear zone has undergone multi-stage tectonic evolution in Cenozoic. The most obvious structural deformation along the shear zone shows large-scale ductile strike-slip shearing, which is characterized by a dextral-dominated strike-slip shearing in northern segment and a sinistral strike-slip shearing in southern segment. Based on macro- and micro-structural observations and fabric analysis of quartz in the deformed rocks, two stages of ductile deformation in the southern segment of Chongshan shear zone have been established in this paper. During the first stage （D1）, the deformation along the Chongshan belt is dominated by contractional deformation under pure shearing at high temperature conditions （550～650℃）, characterized by symmetrical folds, boudinages, tectonic lenses and symmetrical patterns of quartz c-axis fabrics. The second stage deformation （D2） is characterized by sinistral strike-slip shearing along the shear zone under simple shearing, showing highly developed foliation and/or lineation and various mylonites related to the strike-slip shearing. In addition, it can be found that some tourmaline-bearing granitic dykes are intensely developed in the Chongshan shear zone. According to the temporal relationships between granitic dykes and shearing, we interpret such granitic dykes are syn-shearing intrusions which account for crystallization of anatectic magma formed during the early stage of sinistral ductile strike-slip shearing. In this paper, two samples of those granitic dykes in the Chongshan shear zone were chosen for LA-ICP-MS zircon U-Pb dating, giving ages of 21.7±0.3Ma and 22.7±0.3Ma respectively. The zircon U-Pb ages of these syn-shearing granitic dykes reveal that the sinistral ductile strike-slip shearing along the southern segment of Chongshan shear zone started at about （or a little earlier than） 22Ma.

关 键 词：崇山剪切带 构造特征 显微构造分析 石英组构分析 年代学约束 

分 类 号：P542.3[天文地球—构造地质学] P597.3[天文地球—地质学]