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Discovery, Nomenclature of the Centimeter Scale Grinding Gravels and the Nanometer Scale Grinding Grains in Fault Shearing Zones and the Significance for Oil-Gas Geology

SUN Yan1, LU Xian-cai1, LIU De-liang2, SHU Liang-shu1, ZHU Wen-bin1, GUO Ji-chun1   

  1. 1. Department of Earth Sciences, Nanjing University, State Key Laboratory of Mineral Deposit, Nanjing 210093, China; 2. Dept. of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
  • Received:2005-12-20 Revised:2005-12-20 Online:2005-12-20 Published:2005-12-20

Abstract: In the early 1970s, the cm-scale grinding gravels were discovered in reverse faults in Jiangning, Jiangsu Province. In general, there grinding gravels can be found in ductile-brittle fault shearing zones. In the end of the 1980s, based on the observation of the deep bore cores from of California, USA using scanning electron microscope the spherical particulate texture with the ultra-size of nm scale was discovered from the slipping lamellae in the granitic mylonite in Late Mesozoic period. The spherical particulates (usually 2-5 nm in diameter) show a close concentration and distinct orientation. It may be the product of the dynamic processes involving tumbling, grinding and shearing functions. Consequently the spherical particulates with ultra-size are called 'grinding grain: Afterwards, a very similar phenomenon ( mostly in um size) was found again from the slipping lamellae in the Carboniferous-Permian mudstone in the deep bore cores from North Shanxi and Yellow Sea. In recent year, the nm scale grinding grain structures were also discovered in Tanlu fault and Middle Tectonic Line gigantic fault zones of Japan as well as various shearing slipping structures in different strata from Cambrian to Triassic system. In the mudstone slipping beds containing grinding grains may possess a sealing effect through systematic analyses of the samples, and it is fully proved in the North Shanxi oil-gas field. The grinding grain textures may contain more detailed geological information in particular the micro-dynamic aspect (including the dynamo-thermal metamorphism, fluid transferring, particulate autorotation and geological catalysis) owing to increasing research.