Genetic Mechanism of Inversion Anticline Structure at the End of Miocene in Xihu Sag, East China Sea: A New Understanding of Basement Structure Difference

Large inversion anticlines formed at the end of the Miocene are widely developed in Xihu Sag in the East China Sea,which have generally attributed to external forces,ignoring the influence of the internal structure of the sag. Based on the comprehensive interpretation and analysis of gravity and magnetic seismic data,this paper systematically sorts out the relationship between the distribution of inversion anticlines at the end of Miocene and the basement structure,and discusses the influence of basement structure difference on the development of inversion anticlines in Xihu Sag by combining with structural physical simulation experimental methods. The research results show that there is a clear correlation between the inversion anticline at the end of Miocene and the distribution of high magnetic igneous rock basement,and it shows South-North segments. The igneous rock basement in the northern part of the sag is distributed in the central sag-inversion zone,and the inversion anticline is mainly developed on the eastern edge of the igneous rock basement. The igneous rock basement in the southern part of the sag is distributed on the eastern and western edges,and the inversion anticline is mainly developed on the inner side of the distribution area of the igneous rock basement on the edge. Structural physical simulation results show that under the compression background,the compressive stress is released through the edge of rigid silica gel to control the formation of compression anticline folds. The results reflect the difference in compressive strength caused by different lithological basement and can significantly affect the strength distribution of inversion anticlines. Finally,this paper proposes that the change of regional tectonic stress caused by igneous rock basement with high magnetic and high compressive strength is the key to control the strength distribution of the inversion anticline at the end of Miocene.