本文基于跨越华夏块体至四川盆地西部的130个线性流动地震台站及其附近90个固定台网台站的观测资料,采用S波接收函数波动方程叠后偏移方法,开展了华南大陆岩石圈结构研究.成像结果显示,研究区岩石圈结构复杂,不同构造单元之间差异显著,构造边界带附近小尺度变化强烈.150 km以上的厚岩石圈主要位于四川盆地,不足100 km的薄岩石圈主要分布于川东褶皱带和华夏块体.雪峰山下方岩石圈厚度显著增加,且以雪峰山为界岩石圈结构和性质存在着显著的东西差异.结合其它地球物理观测得到的地壳-上地幔结构信息,我们提出:(1)四川盆地还保留着厚而冷的克拉通岩石圈根,且岩石圈地幔具有结构分层特征;(2)雪峰山可能是扬子克拉通与华夏块体在西南部的边界;(3)雪峰山以东区域可能经历了岩石圈的减薄和改造,且华南岩石圈的减薄与华北相似,都主体发生在东部地区,造成现今南北重力梯度带两侧强烈的结构差异.研究结果为认识华南大陆的构造演化及其深部动力学提供了地震学约束.%A ～2500 km broadband digital seismic array was deployed in the South China Block and the northeastern Tibetan Plateau,from December 2009 to September 2013.Based on the teleseismic data from 130 portable stations in the South China Block of this array and 90 nearby national permanent stations,we utilize the wave equation-based migration technique on S-receiver functions (RF) to image the lithospheric structure.Our imaging results show that the lithospheric structure is dramatically distinct for different tectonic units and there are very local variations of the lithospheric structure near the tectonic boundaries.Thick lithosphere is mainly distributed beneath the Sichuan Basin.Thin lithosphere is mainly imaged beneath the Eastern Sichuan Fold Belt and the Cathaysia Block.The lithosphere is obviously thickened beneath the Xuefeng Mountain,and the lithospheric structure and feature show significant E-W difference separated by this mountain along the profile.Combining with other geophysical observations on the crust and the upper mantle,several conclusions are achieved as below:(1) The Sichuan Basin has preserved a thick and cold cratonic lithospheric root and the mid-lithospheric structure is characterized by obvious stratification.(2) The Xuefeng Mountain may be the tectonic boundary of the Yangtze Craton and the Cathaysia Block in the southwest.(3) The region to the east of the Xuefeng Mountain may have experienced lithospheric modification and thinning since Phanerozoic.The pattern of the modification is similar to that in the North China Craton,which shows different lithospheric structure on the opposite sides of the North-South Gravity Lineament.Our results could provide new insights into the tectonic evolution and dynamic process of the South China Block.
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