摘要
应用超高压电子显微镜对太湖及其附近的五通组石英岩中的石英晶粒进行研究,发现它们在自由位错密度、位错壁、亚晶粒和出熔构造等特征上存在着明显差别。据此推论,太湖和其附近地区的五通组石英岩曾遭受过不同的应力作用历史,太湖的标本曾受到高应力的瞬时高压影响。因此,太湖环形构造可能与小天体的撞击有关。
A detail study of the Wutong quartzite from Taihu Lake region, China, was undertaken using High-voltage (1000 kV) Transmission Electron Microscopy to investigate the supermicro-structures in quartz grains. The rock samples have been collected either from the inner islands in the Taihu Lake, Jiangsu Province, or from its outer part, for examples, its west edge and also as far as Hangzhou City, Zhejiang Province.In the studied quartzite, many grains are altered by fractures and planar lamellae. In strongly fractured rocks from the inner part of the Taihu Lake, quartz grains exhibit abundant fractures, and free dislocations are generally preserved. The quartz is fragmented by numerous sets of irregular partings, many partings or planar features are open, and some are filled with , amorphous or aphanitic materials. The free dislocation density can be reached as High as 1.2×1010cm-2, and regions of relatively undeformed quartz show low density of free dislocations (only 4.7×107cm-2). On the contrary in the rocks from the outer part of the Taihu Lake, distribution of the density of free dislocation in the quartz is more and less homogeneous and it varites in a range of 108-9cm-2.Some of the quartz contain irregular dark lamellae, which show weak crystal orientation, and may be the aggregated matters of non-crystalline and cryptolcrystalline substances. Three tpyes of exsolution textures are observed: parallel bands or lamellae, fractural dislocation and dislocation bunch. The diffraction patterns taken for the parallel bands show nearly who'e destruction of the crystallographic structure.The occurrence of the exsolution textures indicates that the Wutong quartzite in the Taihu Lake has suffered instantaneous high pressure earlier. Therefore, it is suggested that the circular structure of Taihu Lake may be formed as a result of impact of small astronomical body (such as asteroid or comet) sometimes ago.
出处
《地质科学》
CAS
CSCD
北大核心
1993年第2期161-166,T002,共7页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
国家自然科学基金(4880076项目)资助成果
关键词
超微构造
石英
太湖地区
晶粒
成因
Super-microstructure, Quartz, Dislocation, Transmission electron microscopy, Exsolution strip, Impact metamorphism, Taihu area.
