台西南盆地岩石圈伸展及裂后沉降特征分析

Analysis of Lithospheric Extension and Post-rift Subsidence in Taixinan Basin

计算有效弹性厚度和不同尺度的拉张因子,并结合裂后的沉积记录可以反映一个伸展性盆地的形成演化特征.运用基于弹性梁模型和挠曲均衡原理的二维构造模拟软件重点对横穿台西南盆地的一条地震地质剖面进行模拟.分析结果表明:1.5km为台西南盆地最合适的有效弹性厚度;岩石圈尺度的拉张因子在1.2～4.8之间,上地壳尺度的拉张因子在1.0～1.2之间,全地壳尺度的拉张因子在1.1～3.0之间,岩石圈伸展具有横向的非均质性和深度的依赖性;台西南盆地裂后阶段受陆架坡折形成、东沙运动两期构造运动影响较大,不同于典型伸展性盆地裂后沉降模式,沉降特征无明显规律性.

The effective elastic thickness,different scales of extension factors and post-rift subsidence are important in reflecting characteristics of an extensional basin.2D structural simulation softwares based on the flexure isostasy model and the flexural cantilever mode were employed to model the interpreted seismic profiles across Taixinan Basin.Results show that the appropriate effective elastic thickness value in Taixinan basin is 1.5 km.The extension is characterized by the lateral heterogeneity and depth-dependence of lithospheric extension in Taixinan Basin,the extension factor changing between 1.2 and 4.8 in lithosphere,between 1.2 and 2.9 in the whole crust,and between 1.0 and 1.2 in the upper crust.Being different from subsidence characteristics of a classical extensional basin,the post-rift subsidence rate in Taixinan Basin is not of obvious regularity,which is mainly affected by the formation of slope and Dongsha tectonic movement.