冲击变质效应与冲击变质的阶段:兼论岫岩陨石坑的证实

最近辽宁岫岩罗圈里的疑似陨石冲击坑,实施了深达307 m的科学钻探,在107~149 m深度发现一系列冲击波所产生的冲击变质的效应:  含岩石熔体玻璃的多相角砾岩, 石英击变面状页理和陨击玻璃等。从而使岫岩罗圈里陨石坑得到了证实。这是中国冲击变质作用研究方面的一大进展。研究确定陨石坑除了地形地貌特征之外, 主要依靠冲击变质效应的发现。权威性的冲击变质效应是:  震裂锥;高压,超高压矿物多形的出现;石英、长石等矿物中的面状页理以及震击均质体化和冲击玻璃的产生等。冲击波所产生的瞬时高压,不同于常规地质作用,它以应变速率极高并快速高温淬火和一定压力产生的后冲击温度等为特征, 导致不同程度的冲击变质效应,可称为冲击变质阶段 (stage of shock metamorphism), 不同的冲击变质阶段,作为近似的压力计，可以用以衡量冲击变质的强度。

Impact Metamorphic Effects and Stages of Shock Metamorphism:A Special Reference to Identification of Xiuyan Impact Crater

Recently, a scientific drilling of 307 meters deep was penetrated through the previously suspected impact crater located near Luoquanli village of Xiuyan county in Liaoning province. A series of impact metamorphic effects caused by shock wave were found, namely, the melt bearing polymictic breccia, the planar deformation features(PDFs) in quartz grains and impact glasses. From these evidences the Xiuyan impact crater was confirmed. This is a great advance in the study of impact metamorphism in China.
　For the identification of an impact crater besides the crater like topography and geomorphology, the discovery of impact metamorphic effects is more authoritative, i.e., shatter cones, high pressure polymorphs of minerals, the planar deformation features in quartz, feldspar and other minerals, the shock caused isotropization and the forming of diaplectic glass.
　The transient high pressure caused by the shock wave is significantly different from those happened in normal geological processes. It is characterized by extremely high strain rate, rapid and high temperature quenching and 　high pressure post shock temperature which caused various impact metamorphic effects defining different stages of shock metamorphism. These stages are approximate geobarometers and can be used to estimate the intensity of impact metamorphism.