苏州西山震裂锥:太湖冲击坑又一新证据  

Shatter Cones in Xishan, Suzhou: A New Evidence for Taihu Lake Impact Crater

作　　者：王鹤年 钱汉东[1,2] 陈旸[1] 周丽娅[3] WANG Henian;QIAN Handong;CHEN Yang;ZHOU Liya(School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China;State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing 210023, China;School of Geography and Ocean Sciences, Nanjing University, Nanjing 210023, China)

机构地区：[1]南京大学地球科学与工程学院,南京210023 [2]南京大学内生金属矿床成矿机制研究国家重点实验室,南京210023 [3]南京大学地理与海洋科学学院,南京210023

出　　处：《高校地质学报》2019年第1期58-67,共10页Geological Journal of China Universities

基　　金：南京大学内生金属矿床成矿机制研究国家重点实验室自主研究课题(2008-Ⅱ-15;2008-Ⅱ-04);国家自然科学基金(40972031)联合资助

摘　　要：震裂锥已被公认为陨石冲击地球表面遗留的标志。研究及统计资料表明,震裂锥与陨石冲击形成的中、大型冲击坑有关。太湖西山震裂锥呈圆锥形,锥体表面有自锥顶向下辐射的锥纹,锥纹具有分叉的特征,这些特征与震裂锥的国际公认的定义和标准相符。此外,西山震裂锥还具有其特有的其他特征:碎裂岩化显著;气化—熔融现象发育;锥体表面具网状构造及波纹状、蜂窝状等多种气印。岩相学研究显示,震裂锥及含锥岩石中冲击变质现象明显,微页理(PDFs)、微裂隙(PFs)以及靶岩熔融现象发育。以上这些冲击变质的标志,可证明西山震裂锥是冲击成因,而非地表水风化淋溶石灰岩的喀斯特或风蚀成因的凤稜石。西山震裂锥的发现、太湖湖底冲击击变角砾岩"太湖石"的确定,为太湖冲击坑的研究增添了新的诊断性证据;加上早期研究确定的、冲击回落至太湖湖底淤泥层中的冲击溅射物,这些众多证据为确定"太湖冲击坑"或"太湖冲击事件"展示了美好前景。但是,要确定太湖冲击坑的具体位置、大小及构造模式等,尚需更多的深入研究。The shatter cones have been recognized as a sign of meteorite impact on the earth's surface. Research and statistical data show that shatter cones are related to medium-or larger-scale impact craters. The shatter cones found in Xishan, Suzhou provides a diagnostic evidence for the existence of impact crater happened in Taihu Lake. The shatter cones are characterized by the conical shapes and coved with conical striations radiating downward from the top of the cones. The striation has been shown as the feature of bifurcation. The evidences are consistent with the international definition and standard for the shatter cone. In addition, special characteristics are also found in shatter cones in Xishan: remarkable cataclasis and the obvious melt-gasification phenomenon. On surface of cones, there are mesh-structure and the ripples-like, honeycomb-like gas imprint developed. Results of petrographic study show that shatter cones and cone-contained target rocks have visible impact metamorphism. Planar Deformation Features [PDFs], Planar Features [PFs] and target rock melting indicate the impact metamorphism happened. All of these show that shatter cones in Xishan are distinctly different from cone-sharp karst limestone formed by the surface water dissolution or ventifacts formed by eolian erosive action. The discovery of Xishan shatter cones and the breccias“Taihu stone” occurring at the bottom of the Taihu Lake has provided the new diagnostic evidence for the Taihu impact crater. There are also existed impact ejecta identified in earlier studies which fallen back into the silt layers under the Taihu Lake. Numerous evidences show a beautiful prospect for the determination of “Taihu impact crater” or “Taihu impact event”. However, there is still much work to be done to determine the detailed locations, size and structural model of the impact crater in Taihu Lake.

关 键 词：太湖 震裂锥 冲击坑 冲击角砾岩 熔融-气化作用 

分 类 号：P588.3[天文地球—岩石学]