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Discovery of Impact Ejecta from Taihu Lake Impact Crater

WANG He-nian, XIE Zhi-dong*, QIAN Han-dong   

  1. State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering,Nanjing University, Nanjing 210093, China
  • Received:2009-12-20 Revised:2009-12-20 Online:2009-12-20 Published:2009-12-20

Abstract: The hypothesis of impact origin of the Taihu Lake was proposed about twenty years ago, but never confirmed.Recently some weird-shaped concretions were found embedded in the mud layer in the vicinity of the Taihu Lake, which might be impact ejecta from the Taihu impact crater. These new samples comprise two categories. One is rich in iron with fine siderite as concretion matrix, including abundant small spheroid concretions, stick-shaped concretions, and irregular shaped concretions.The other one is poor in iron with calcite as concretion matrix, including twisted-shaped concretions. The fragments embedded in matrix mainly consist of angular-sharp-edged quartz grains, and minor fragments of clay and plagioclase minerals. The sizes of the ejected materials range from centimeters of massive rocks to millimeters even to micrometers of the spheroids. Most hand samples show abundant semi-plastic features, such as twisted shape and molten crust, which might be caused by their flying in the air in the molten or semi-molten status. All these features suggest that these new samples once experienced a series of the impact cratering processes, such as the shock-induced fragmentation, shock-induced melting, ejection into the air, flying in the air, and falling in and around the impact crater. The components of the ejected materials are consistent with the target rocks in the Taihu Lake area. The confirmation of impact ejecta is another important discovery after the discovery of the shock-induced microfeatures in deformed quartz in the sandstone of islands in the Taihu Lake. The discovery of the ejection materials, combining with other features, confirmed the impact origin of the Taihu Lake.