下扬子北缘和华北南缘地壳上地幔结构研究

Formed by the contiental collision between the South China and North China plates in the late Triassic, the Dabie-Sulu orogen experienced significant back-arc extension, lithospheric thinning and magmatism by subduction of the Pacific plate in the late Mesozoic in regions of northern Lower Yangtze and southern North China. Hence the regions are not only important for studying continental collision and ultrahigh-pressure meatamorphism, but also critical for our understanding about the tectonic transition from the north-south collision in the early Mesozoic to east-west extension in the late Mesozoic-Cenozoic in eastern China. In order to investigate the mantle dynamcis and evolution in plate convergent boundary, this project will perform an integreted study of seismic observations. We will deploy three portable broadband three-component digital seismic arrays in the adjacent regions of Anhui and Jiangsu provinces. After 2 to 3 years observation, we will obtain the crust-upper mantle structure characterized by the lateral variations of Vp, Vs, Poisson's ratio and seismic anisotropy. Combined with results from thermal structure and effective elastic thickness of lithosphere, we will have more detailes about the rheological hetrogeneity of the lithosphere. The results will provide new insights into some important issues, such as boundary bwteen the South China and North China plates, distribution of the subducted Yangtze plate, formation of the Dabie-Sulu ultrahigh-pressure metamorphic terrane, magmatism and lithospheric extension in eastern China, evolution of the Tanlu fault, etc., and give new constraints on natural resources exploration and seismicity in this region.

下扬子北缘和华北南缘地区晚三叠纪发生了陆-陆碰撞造山，形成举世瞩目大别-苏鲁造山带和郯庐断裂带，保存了世界上规模最大的超高压变质带，中、新生代岩浆作用强烈，并发育了蕴含丰富油气资源的盆地和成矿带。该区是揭示我国大陆南北碰撞缝合过程和动力学的关键地区。在江苏和安徽交接地区布设宽频带三分量数字地震台阵，进行2－3年观测，利用远震和近震的数字地震记录，以及中国和全球 地震台网记录，进行该区地壳上地幔结构研究，获得包括Vp、Vs和泊松比等参数横向变化，以及上地幔各向异性特征；进一步结合岩石圈热结构和深部物质组成，以及地质、地球物理综合研究结果，分析该区岩石圈流变学横向不均一性特性及其所反映的深部过程和地球动力学；为探索中新生代期间扬子与华北碰撞及碰撞后的构造演化与大陆动力学，以及该区自然资源的勘探评价和地震灾害预防提供深部依据。

下扬子北缘和华北南缘地区晚三叠纪发生了陆-陆碰撞造山，形成举世瞩目大别-苏鲁造山带和郯庐断裂带，保存了世界上规模最大的超高压变质带，中、新生代岩浆作用强烈，并发育了蕴含丰富油气资源的盆地和成矿带。该区是揭示我国大陆南北碰撞缝合过程和动力学的关键地区。.项目通过宽频地震流动观测获得第1手观测数据，并收集固定台站等相关观测，采用接收函数、S波分裂和各向异性、P和S波层析成像等方法研究，获得了下扬子北缘和华北南缘地壳上地幔结构横向差异特征。S波分裂的快波方向是扬子与华北克拉通碰撞和太平洋板块俯冲及俯冲弧后扩张3期地球动力学过程中形成的，下扬子块体上地幔过渡带厚度与华夏块体有明显差异，表明下扬子块体和华夏块体有不同的深部热状态，且华夏块体地壳上地幔相对较热。P波层析成像结果表明，下扬子北缘和华北南缘上地幔存在北东方向低速带和高速体。高速体可能是残留的扬子板块的俯冲板片，低速带可能是中生代广泛的岩浆作用的深部背景。这些成果丰富了对下扬子北缘和华北南缘地壳上地幔结构的认识，为揭示该地区早中生代以来盆地和造山带形成演化、岩浆作用的地球动力学过程提供了深部依据，为该区矿产和油气资源勘探和评价以及地震和地质灾害评价预防等方面提供基础依据。.项目研究成果发表了6篇期刊论文，其中5篇发表在JGR、EPSL和Tectonophysics等国外SCI期刊上，1篇发表在国内核心期刊上，1篇国际会议（AGU会议）论文。发表的论文已被引用43次，单篇引用23次。