哈山冲断带构造变形数值模拟

岩石圈流变结构是控制大陆碰撞造山的重要因素.哈山冲断带的构造变形、地表地形与青藏高原周缘冲断带差异较大,指示需要开展地壳流变学研究.本研究采用二维数值模拟,设计了盆山上地壳强度横向差异的单因素实验,模拟结果分析表明：若上地壳强度山弱盆强,构造变形集中于造山带,断块垂向叠置造成造山带隆升,使地表地形的构造高点位于造山带;若上地壳强度山强盆弱,构造变形集中于冲断带和盆地,盆山相互作用造成地表地形的构造高点位于冲断带,而非后陆.本文基于此单因素实验,模拟了哈山冲断带构造演化,发现哈山冲断带晚二叠世发育推覆构造后,构造变形逐渐减弱,扩展方式由前展式变为后展式,基底倾向由向后陆变为向前陆.结合哈山及龙门山的多学科观测资料,本文认为哈山和龙门山冲断带的构造变形、地表地形分别符合地壳强度山强盆弱模式和山弱盆强模式.研究成果可以为中西部冲断带的地球动力学模型和实验模型的搭建提供一定启示,同时对研究区内构造控藏分析和油气勘探具有指导意义.

Horizontal differentiation of crustal rheology control the deformation of Haraarat thrust belt: insight from numerical modelling

The rheological structure of the lithosphere is an essential factor controlling continental collision. The structural deformation and topography of the Haraarat Thrust Belt are pretty different from those of the thrust belts around the Tibet Plateau, indicating that a crustal rheology study is needed. In this paper, we conducted seven single-factor experiments using two-dimensional numerical simulation to explore the horizontal differentiation of the upper crust strength beneath the basin and the mountain. The results show that: the structural deformation would concentrate on orogen if the upper crust strength is in the 'weak orogen and strong basin' pattern, and the vertical superposition of fault blocks would cause the orogen uplift, leaving structural highs of the topography developed mainly in the orogenic belt. The structural deformation would concentrate in both basin and thrust belts if the upper crust strength is in 'strong orogen and weak basin' pattern, and the structural highs mainly appeared in the thrust belt instead of the hinterland owing to the orogen-basin interaction. Based on these single-factor experiments, we simulate the tectonic evolution of the Haraarat Thrust Belt and found that after the development of the nappe structure in the Late Permian, the tectonic deformation weakened gradually in the Haraarat Thrust Belt, where the propagating mode changed from forward to backward, and the basement dip reversed from hinterland to foreland. Combined with the geophysical data of the Haraarat and Longmenshan thrust belts, we found that the structural deformation and topography of the Haraarat Thrust Belt and the Longmenshan Thrust Belt conform to the 'strong mountain and weak basin' and the 'weak mountain and strong basin' patterns, respectively. These results could provide important insights into establishing geodynamic and experimental models of thrust belts in Central-Western China and have guiding significance for reservoir-controlling analysis and oil-gas exploration in the study area.