用多层变密度直接反演法研究下扬子地区的岩石圈构造

本文用多层变密度直接反演方法研究下扬子地区的岩石圈结构,并讨论其大地构造涵义及演化问题。文中给出了三次样条密度-深度函数的重力正演公式,采用非线性最小二乘优化算法,得到岩石圈内G_5、G_6、G_7三个主要密度界面,它们分别相应于中地壳低密度层底面、Moho面和上地幔顶部低密度层上界面。通过岩石圈结构分析,得到以下结果:杭州湾—海盐—嘉兴—长兴—高淳—芜湖隐伏深断裂是一条北西向的一级构造边界,它对下扬子区的大地构造发展和地壳演化有重要影响。

A STUDY OF THE LITHOSPHERIC STRUCTURE BENEATH THE LOWER YANGZI VALLEY BY USING THE DIRECTLY INVERSING METHOD OF MULTI-LAYERED VARIABLE DENSITY

This paper deals with the lithospheric structure beneath the Lower Yangzi Valley as derived from invesing the multi-layered variable density, and also discusses its geotectonic significances, and its connection with the evolution. The gravity formula in the form of cubic-spline function of density contrast with depth was induced, and the main density interfaces G5, G6, and G7, which are respectively corresponding to the bottom surface of the low-density layer in the mid-crust, the Moho discontinuity, and the upper surface of low-density layer in the top part of the upper mantle, were found by using the optimization algorithm of nonlinear least squares. Based on the analyses of the lithospheric structure, it is concluded that a hidden deep fault of the bay of Hangzhou-Haiyan-Jiaxing-Changxing-Gaochun-Wuhu, which takes an important part in the tectonic development and crustal evolution in the area, is a main tectonic boundary characterised by NW trend.