揭开南岭地壳形成演化之谜

Raise the Curtain on Formation and Evolution of Nanling Mountains

南岭的形成演化目前尚不清楚,作为板内造山的一个典型,研究南岭地区的地壳构造对大陆动力学有重要意义。本文对南岭地区重力异常进行了多尺度密度反演,首先利用小波变换对重力异常进行多尺度分解,接着利用功率谱分析方法估算各等效层场源的平均深度,然后利用广义线性反演方法进行各层密度反演,取得区域地壳多个深度上的密度扰动图像。用小波变换多尺度分析和三维密度结构反演确定了南岭中上地壳存在独立的构造单元,它具有低密度性质,反映区域规模的大花岗岩基。南岭中上地壳的构造单元位于北纬24°～26°,东经100°～116°,深达22 km左右。深度22 km以下南岭地壳低密度带与武夷低密度带连通为武夷—云开构造带。南岭最终形成与100 Ma以前特提斯洋俯冲和亚欧板块与加里曼丹地体的陆岛碰撞直接有关。同期发生的区域规模的燕山晚期南岭花岗岩基对应特提斯洋向华南俯冲的第二岩浆带。基于地球物理资料提出的这个陆岛俯冲碰撞假说能否成立,还需要更多岩石学的直接证据证实。

The crust structures of Nanling Mountains has to be revealed for identifying its tectonic characteristics and formation processes. This paper presents 3D crustal density disturbance maps of the studied area, and finds information corresponding to the upper, middle and lower crustal structures respectively. Writer use a method called the multi-scale analysis for delineating density disturbances of the crust at different depths. This method of regional gravity data processing combines theories based on multi-scale wavelet analysis, spectral analysis of potential fields and geophysical inversions. Density disturbance maps corresponding to depths from 1.5 kin to 48.6 km are obtained, showing that the Nanling Mountains is an independent tectonic unit of low density in the upper and middle crust. Writer suggest that subduction of the Tethys ocean and collision between the Eurasia plate and the Kalimantan Terrane completes the formation of the Nanling Mountains in about 100 Ma ago, and the late magma chambers of low density in the upper and middle crust represents the second magma belt of the subduction of the Tethys. The method of multi-scale analysis demonstrates its power for delineation of crustal structures and 3D locations of tectonic units of the Nanling Mountains, providing new evidences for understanding corresponding intraplate mountain-building processes.