中国东部新生代岩石圈构造滑脱、岩浆活动和地震

Cenozoic Lithosphere Tectonic Detachments,Magmatism and Earthquake in Eastern China

在岩浆活动比较发育的中国东部地区,通过研究岩浆起源深度来大致判断岩石圈底部和内部是否存在局部构造滑脱面是一种可行的研究方法。华北期(始新世—渐新世)的构造滑脱主要局限在岩石圈底面与先存的NW或E—W向与NNE向岩石圈断裂的交点附近。喜马拉雅期(中新世—早更新世)在先存的NNE和NE向3条岩石圈断裂(太行山断裂,郯庐断裂和东南沿海断裂)与岩石圈底面相交部位发生较强烈的滑脱。根据地震资料分析,新构造期(中更新世以来)的构造滑脱主要发生在莫霍面和中地壳附近,局部呈面状分布,但华南地区则不发育构造滑脱。现代的重力梯度带就是大陆岩石圈地幔与大洋岩石圈地幔的分界线,也是岩浆作用强烈与微弱区的分界,此界线从白垩纪到现代最大向东移动了大约200 km。作者认为,主干断层是造成岩石圈内构造滑脱的主导因素。中国东部新生代岩石圈内部不同圈层之间的构造滑脱作用与断层控制了板内岩浆活动和地震的性质、强度及空间分布。研究结果不支持在中国东部新生代岩石圈深部存在广泛的地幔羽和热地幔上隆作用,也不支持中国东部在新生代发生大规模的岩石圈拉张减薄作用的假说。

It is a suitable method to roughly determine partial detachment in lithosphere or at the bottom of lithosphere,used by data of magmatic source depth at strong magmatism areas in eastern China.In the North Sinian stage（Eocene-Oligocene）,partial tectonic detachments mainly occurred at the intersection among the bottom of lithosphere and pre-existing NW or N-E and NNE striking lithospheric faults.In the Himalayan stage（Miocene-Early Pleistocene）,detachments widely occurred at the intersection among the bottom of lithosphere and three NE and NNE trending lithospheric faults（Taihangshan,Tan-Lu and southeast coastal of China）.In the Neotectonic stage（since Middle Pleistocene） according to the seismic data,detachments mainly occurred near Moho discontinuity and intermediate crust,with sheety-like,but not in south China.The recent gravity gradient zone is the division line between continental and oceanic lithosphere mantle,also indicates the division of the strong and weak area of magmatism,migrating eastwards at most about 200 km,compared with that from Cretaceous to present.Therefore,the authors suggested that tectonic detachment was occurred by main brench faults,and the type,characteristics and distribution of magmatic rocks and earthquakes were controlled by the detachments,occurred at the intersection area of the faults and different tectono-spheres in the lithosphere.Neither mantle plume nor hot magma uplifting widely existed,and no large-scale extension-thinning process occurred in eastern China lithosphere during Cenozoic.