滇西三江地区西盟群的再认识——来自构造变形特征及锆石U-Pb年代学的证据
发布时间：2019-03-06 08:25
【摘要】：位于保山-掸泰地块东缘的西盟群,长期以来被认为是该地块在我国境内唯一出露的"前寒武纪"基底变质岩系,但其缺乏可靠的年代学数据和化石支持。本文基于详细地野外考察和显微构造分析认为,西盟群变质岩系可解体为花岗质糜棱岩和浅变质岩。前者主要出露于西盟穹形隆起的核部,遭受了强烈的韧性剪切变形;后者分布于隆起的边缘及东西两侧,归属为帕克组、王雅-允沟组。通过变形岩石的石英EBSD组构分析,揭示出位于西盟隆起核部的岩石经历了中等温度条件(550~650℃,角闪岩相)下的变形作用,并叠加了较低温度条件(400~550℃,绿片岩相)下的变形作用;而靠近西盟隆起边部的岩石仅经历了较低温度条件(400~550℃,绿片岩相)下的变形作用。本文还对西盟群变质岩中的3个花岗质糜棱岩样品进行了LA-ICP-MS锆石U-Pb测年,得到的锆石U-Pb年龄分别为455±3Ma、456±3Ma和454±3Ma。结合前人获得的年代学数据和化石资料,认为西盟群变质岩系的原岩主要由两个不同时期的物质组成,即中-晚奥陶世(~460Ma)侵入的花岗岩及寒武纪的碳酸盐岩和碎屑岩夹少量基性火山岩等;前者遭受强烈变质变形作用的改造,形成花岗质糜棱岩;后者遭受低级变质作用形成千枚岩、片岩、大理岩等浅变质岩。进而表明,前人将西盟群作为保山地块的"前寒武系"结晶基底变质岩系是不合理的。
[Abstract]:Ximeng Group, located in the eastern margin of Baoshan-Shantai massif, has long been regarded as the only "Precambrian" basement metamorphic series of this massif in China, but it lacks reliable chronological data and fossil support. Based on the detailed field investigation and microstructural analysis, it is considered that the metamorphic rock series of Ximeng Group can be disintegrated into granitic mylonite and shallow metamorphic rock. The former is mainly exposed to the nucleus of the Ximeng dome and suffers strong ductile shear deformation, while the latter is distributed on the margin and east-west sides of the uplift, belonging to the Parke formation and Wangya-Yungou formation. By means of quartz EBSD fabric analysis of deformed rocks, it is revealed that the rocks located in Ximeng uplift underwent deformation under medium temperature conditions (550 鈩，
本文编号：2435363
[Abstract]:Ximeng Group, located in the eastern margin of Baoshan-Shantai massif, has long been regarded as the only "Precambrian" basement metamorphic series of this massif in China, but it lacks reliable chronological data and fossil support. Based on the detailed field investigation and microstructural analysis, it is considered that the metamorphic rock series of Ximeng Group can be disintegrated into granitic mylonite and shallow metamorphic rock. The former is mainly exposed to the nucleus of the Ximeng dome and suffers strong ductile shear deformation, while the latter is distributed on the margin and east-west sides of the uplift, belonging to the Parke formation and Wangya-Yungou formation. By means of quartz EBSD fabric analysis of deformed rocks, it is revealed that the rocks located in Ximeng uplift underwent deformation under medium temperature conditions (550 鈩，
本文编号：2435363
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