南北构造带及邻域地壳、岩石层速度结构特征研究

本文利用重力数据采用Parker-Oldenburg方法反演了南北构造带及邻域地区的地壳厚度,同时采用体波地震层析成像方法反演了研究区的地壳至上地幔的三维速度结构.根据计算结果对研究区的地壳及岩石层结构进行了探讨,力图揭示南北构造带及邻域地壳、岩石层变形特征,并且对青藏高原边缘活动带壳幔构造演化的深部成因、研究区的上地幔流变性及其动力学意义进行了相应的讨论.通过分析研究表明南北构造带地区为地壳厚度剧变区,西侧为地壳增厚区,东侧的鄂尔多斯、四川盆地为地壳稳定区,而再向东为地壳逐渐减薄区.中国岩石层减薄与增厚的边界基本被限定在大兴安岭—太行山—秦岭—大巴山—武陵山一带,这也是东部陆缘带和中部扬子、鄂尔多斯克拉通地区深部构造边界的分界线,其两侧不仅浅层地质构造存在较大的差异,上地幔深部的物性状态和热活动也明显不同,这说明研究区的岩石层和软流层结构以及深部物质的分布存在横向非均匀性.中部地区和青藏高原深部构造边界的分界线位于东经100°—102°左右.

Features of crust and lithosphere velocity structures along the north-south tectonic belt and adjacent regions in China

We conduct gravity data inversion using the Parker-Oldenburg method to calculate crustal thickness, and employ seismic tomography to research the three-dimensional velocity structure of the crust and mantle along the north-south tectonic zone in central China. According to results of calculation we attempt to reveal the crust and lithosphere structures and the deformation characteristics in the study area. Then we further discuss the deep causes of crust-mantle tectonic evolution in the Tibetan Plateau active zones, the upper mantle rheological property in the study area and its dynamics significance. Studies show that crustal thickness of the north-south tectonic belt is highly variable, with thickening crust in west, stable crust of Ordos Basin and Sichuan Basin in east, and thinning crust farther east. The boundary between thinning and thickening lithosphere is along the Da Hinggan Ling Mountains—Taihang Mountains—Qinling Mountains—Daba Mountains—Wuling Mountains. It is also the deep tectonic boundary between the eastern continental margin zone and central Yangzi—Ordos Craton regions. Not only are the shallow geological structures different on both sides, but alos the physical properties and thermal activity in deep upper mantle are distinctly different. It indicates that, in the study area, the structure of lithosphere and asthenosphere and the distribution of deep material have lateral heterogeneity. The deep tectonic boundary between central regions and the Tibetan Plateau is roughly along 100—102°E.