摘要
中国东北地区处于古亚洲构造域、蒙古—鄂霍茨克构造域和环太平洋构造域叠加作用最为显著的地区,是地学研究的热点区域.为了探析欧亚大陆下西太平洋板片的俯冲形态以及揭示该区域深部地球动力学机制,利用卫星重力数据通过预处理共轭梯度快速密度反演算法获得了包含东北地区、华北部分地区及日本海海域在内的研究区域上地幔三维密度结构,结合天然地震三维层析成像结果共同揭示太平洋板片的俯冲形态和深部动力机制.俯冲的太平洋板片在日本海沟处呈高密度异常,向西横向持续扩张,深度方向上有逐渐增加趋势.不连续的高密度体俯冲至地幔转换带(410～660km)后继续水平西向俯冲,部分滞留板片可能进入下地幔;在大兴安岭断裂带下面转换带中同样发现水平分布的高密度体,推断是大兴安岭断裂带下方地幔岩石圈拆沉的结果,横向不均匀分布的俯冲板片边缘已抵至大兴安岭造山带附近,这对于研究东北地区深部动力学机制具有重要的意义.
Northeast China is the most prominent region of structural superposition in the PaleoAsian ocean,Mongol-Okhotsk Ocean and Pacific ocean tectonic domains,and has long been a focused area for geoscience research.In order to study the shape of the subduction slab of the West Pacific plate beneath the Eurasian continent and to reveal the deep geodynamics of the region,three-dimensional density distribution of upper mantle is obtained by using a fast preconditionedconjugated gradient density inversion algorithm to process satellite gravity data over Northeast China,part of North China and the sea of Japan.Combined with the three-dimensional velocity structure from seismic data,this density structure permits to reveal the shape of the subduction slab and deep dynamics of the Pacific plate.The results show that the Pacific subduction slab exhibits high density anomalies at the Japan trench,moves westward with continuous expansion and a gradual increasing trend in the depth direction.The high-density body subducting to the mantle transition zone(410～660 km)continues to move westward horizontally,and the stagnant slab partly may have penetrated into the lower mantle.Also we found high density in the transition zone below the Da Hinggan Mountains fault zone which is presumably the result of lithosphere detachment of mantle beneath thisDa Hinggan Mountains fault zone.The edge of the subduction slab that is laterally unevenly distributed has arrived near the DaHinggan Mountainsorogenic belt.These are of great significance for studying the deep dynamic mechanism in Northeast China.