Abstract:

       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.

Key words: Taihu, Quartz, shock metamorphism, deformation feature, impact