太湖地区砂岩中石英变形特征:太湖冲击假说探讨  

The Deformation Features of Quartz grains In the Sandstone of Taihu Area:Taihu Impact Origin Controversy

作　　者：董宇婕[1] 谢志东[1] 左书豪[1] 

机构地区：[1]内生金属矿床成矿机制研究国家重点实验室,南京大学地球科学与工程学院,南京210093

出　　处：《高校地质学报》2012年第2期395-403,共9页Geological Journal of China Universities

基　　金：国家自然科学基金项目(40972031);成矿机制研究国家重点实验室自主基金项目(2008-II-15)联合资助

摘　　要：太湖冲击成因假说作为众多太湖成因说之一,于20多年前被提出至2009年的再次复兴,颇受争议。本文从冲击的关键证据之一石英变形特征入手,以新的实证研究重新审视前人的工作,并对太湖冲击假说展开探讨。主要通过光学显微镜观察太湖地区泥盆系砂岩中石英受应力而致的不均匀消光、碎裂、变形纹等变形特征;利用费氏台测量石英变形纹的定向特征,研究薄片中大量的人字形微裂隙现象;同时对比分析了九江地区同类砂岩及太湖地区菱铁矿结核体中石英碎屑的变形特征。研究显示太湖地区砂岩中发育的石英变形纹并非典型的击变页理纹(PDF),石英变形特征主要为较低应力下的变形特征,其成因具有多解性。因此太湖冲击成因假说以及太湖的形成机制值得多角度进一步研究。The hypothesis of impact origin is one of many origin hypotheses of Tai Lake basin, which were proposed in twenty years ago and revived in 2009 with many opposite arguments. The goal of this paper is to review and check the similar previous work having been done in twenty years ago based on current observation of the deformation features in quartz grains, and to discuss the Taihu impact hypothesis. Various deformation features of quartz grains in Devonian sandstone of Taihu area, including uneven extinction, fractures, and deformed lamella, are observed under optical microscopy. The preferred orientations of quartz deformed lamella were measured by using the universal stage. The well developed braided micro-fractures and artificial network fractures in the sandstone samples were observed. We also compare the quartz deformation features from sandstone of Taihu area to that from similar formation sandstone from Jiujiang area 300 km away from Taihu, and similar deformed features in quartz debris in the siderite concretions of Taihu area. The results show that the quartz deformed lamella of sandstone of Taihu area are not typical impact-induced planar deformation features （PDF）. Most of the deformation features are caused by relatively lower pressure, the origin of these deformation features can be explained by multiple forces. Therefore, the hypothesis of impact origin of Taihu lake is not mature yet, it is rewarded and valuable to intensively study the origin mechanism of Taihu lake basin by multiple approaches.

关 键 词：太湖 石英 冲击变质 变形特征 撞击 

分 类 号：P574.1[天文地球—矿物学]