鄂尔多斯及邻区航磁异常特征及其大地构造意义

Aeromagnetic anomaly analysis of Ordos and adjacent regions and its tectonic implications

本文通过对航磁异常资料进行向上解析延拓、垂向不同阶导数及磁性体边界确定新方法等处理,并结合地震震中分布对鄂尔多斯块体及邻区不同深度场源磁异常特征加以分析研究.结果表明,鄂尔多斯块体虽具有整体刚性的特征,但其内部也存在非均质性;块体东缘的华北克拉通地区经后期改造,产生近SN向的基底软弱带;青藏高原地壳缩短增厚的同时,其东北缘下地壳韧性物质分别沿秦岭、祁连两个软弱带向周缘塑性流动,而且青藏高原巨大的NE向挤压应力造成鄂尔多斯块体逆时针旋转;鄂尔多斯块体及其边界多样化的构造特征反映了不同刚性程度的地质体在外部不同应力作用下产生了显著差异的地质构造形态,这种构造形态具有继承性和叠加性.

Affiliated to the North China Craton （NCC）, the Ordos massif contacts with the Qinling-Qilian orogenic belt to the south, with complicated geological features around as a result of episodic tectonics. By applying the upward continuation, vertical derivation of different orders, and a new method for delineating magnetic boundaries to the aeromagnetic data, as well as taking into account the earthquake data, here we present the characteristics of aeromagnetic anomalies of field sources at different depths and their tectonic implications. Our results show that the basement of the Ordos is rigid on the whole but is still heterogeneous. The east of the Ordos massif in NCC is a relatively weak zone with approximately NS trending suffered from subsequent tectonic alternation. The ductile lower crustal material flows along two weak zones of the Qinling and Qilian orogenic belt coevally with the thickening and shortening of the crust in Qinghai-Tibet Plateau, as well as the anticlockwise rotation of the Ordos massif due to the intensive compressional stress in NE direction derived from the India-Eurasia collision. The diverse tectonic features mentioned above in and along the margins of the Ordos massif represent the tectonic responses of the crustal blocks of different rigidity to the boundary forces, that resulted in prominently different geological features. The tectonic deformation in and around the Ordos massif is characterized by inheritance and superimposition.