东亚西太平洋巨型裂谷体系岩石圈与软流圈结构及动力学

笔者根据地震面波层析成像结果，对欧亚大陆及西太平洋岩石圈和软流圈速度结构进行了研究，发现东亚至西太平洋间存在一巨型低速异常带，结合构造地质学、地幔岩石学、地球化学及其他地球物理特性的研究，确认该区存在巨型裂谷体系。该巨型裂谷体系的岩石圈和软流圈三维Vs速度结构与太平洋洋中脊、大西洋洋中脊和印度洋洋中脊及其邻区的岩石圈和软流圈地震Vs速度结构十分相似，而与东太平洋边缘现代板块俯冲带的岩石圈与软流圈Vs速度结构有显著差异。在进一步论述该区动力学特征后认为，该巨型裂谷体系是中生代中晚期以来岩石圈整体主动伸展变形，大型裂陷盆地形成，岩石圈强烈拆沉减薄，以及软流圈物质上涌加热引起的。边缘海是在大陆裂谷系形成基础上发展起来的，主导扩张期为中渐新世至中中新世（32－13Ma），这些边缘海在17－15Ma后停止扩张，因而未能将所有边缘海和洋中脊联通。据此划分出4期构造变形动力学演化阶段，现今东亚至西太平洋间大陆裂谷、边缘海与沟弧体系是新生代中晚期以来，邻区各板块构造相互作用叠加的结果。

Structure and dynamics of lithosphere and asthenosphere in the gigantic East Asian-West Pacific rift system

Based on the seismic S-wave tomography,the authors carried out a systematic study of the speed structures of the lithosphere and asthenospher e of Eurasia and the West Pacific,and found a gigantic low-velocity anomaly z one between East Asia and the West Pacific.According to this discovery,combine d with the tectonic,mantle petrological and geochemical characteristics,as wel l as other geophysical features,a mega-rift system is defined in the region.T he3D seismic Vs speed structures of the lithosphere and as-thenosphere are v ery similar to those of the Mid-Pacific,Mid-Atlantic,and Mid-Indian ridges and their neighboring regions ,but notably different from those of the pres ent plate subduction zone on the East Pacific margin.On the basis of a furth er discussion on the dynamic characteristics of this re gion,it is con-cluded that the rift system resulted from the massively active extensional deformation and strong delamina-tion and thinning of the lithosphere,formation of large rift basins ,and upwelling and heating of a large amount of the asthenosphe ric substances since the Mid-Late Mesozoic.Marginal seas developed on the basi s of the continental rift system,and the main extension stage is determined to be from the middle Oligocene to middle Miocene(32-13Ma ).The extensions of these marginal seas had ended after the peri-od from17to15Ma ;as a r esult not all of the seas were connected with the mid-ocean ridges.Four sta ges of the tectonic-deformational dynamic evolution may be distinguished,and it is considered that the tectonic superposition of interactions of various neighboring plates resulted in the formation of the continen-tal rifts,margin al seas,and trench-arc-basin systems between present East Asia and the West Pacific since the Mid-Late Cenozoic.