摘要
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。
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.
出处
《中国地质》
CAS
CSCD
2002年第3期234-245,共12页
Geology in China
基金
国家自然科学基金重点项目(49734150)
国土资源部专项计划(20001010)
关键词
巨型裂谷体系
巨型地震低速异常带
地震层析成像
岩石圈
软流圈
地幔岩
东亚大陆
太平洋
地球动力学
gigantic longitudinal extensi onal rift system
giant longitudinal seismic low-velocity zone
seis-mic tomo graphy
lithosphere
asthenosphere
pyrolite
East Asian continent
West Pacifi c
