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Underplating in the middle-lower yangtze Valley and model of geodynamic evolution:Constraints from geophysical data

Science china Earth sciences 2005年第7期48卷 985-999页

作者： lü qingtian, hou zengqian, yang zhusen & shi danian institute of mineral resources,chinese academy of geological sciences,beijing 100037,china institute of mineral resources Chinese Academy of Geoloqical Sciences Beijina 100037 China

The lower crust and Moho are the most active boundary layers in the process of continental evolution, in which marks left by tectonic and magmatic activities during the process are preserved. The evolutionary process of the continental lithosphere may be reconstructed by exploring the structures of the lower crust and Moho. According to a study of the deep seismic reflection data obtained from the middle-lower yangtze Valley, the authors find bright layered reflections ubiquitous in the lower crust and think that the bright reflections are caused by un-derplating of basic or ultrabasic magmas, which might be related to delamination of the lithosphere. On the basis of an integrated analysis of the geophysical and geological data of the region, the authors propose a model for geodynamic evolution of the middle-lower yangtze Valley. This model suggests that the middle-lower yangtze Valley had undergone such geodynamic processes as collision-compression, delamination-extension and underplating-melting since the end of the Permian, finally forming the gigantic middle-lower yangtze Valley metallogenic belt.

关键词： lower crust deep seismic reflection underplating tectonic evolution.

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Deep seismic reflection profiling revealing the complex crustal structure of the Tongling ore district

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Science china Earth sciences 2004年第3期47卷 193-200页

作者： l5 qingtian1, hou zengqian1, ZHAO Jinhua1, shi danian1, WU Xuanzhi1, CHANG Yinfo1, PEI Rongfu1,HUANG Dongding2 & KUANG Chaoyang2 1. institute of mineral resources, chinese academy of geological sciences, beijing 100037, china 2. The Sixth Geophysical Exploration Brigade, Petroleum Bureau of East china, Nanjing 210009, china institute of mineral resources Chinese Academy of Geological Sci. Beijing 100037 China The Sixth Geophys. Explor. Brigade Petroleum Bureau of East China Nanjing 210009 China

The deep seismic profiling across the Tongling ore district reveals a complex crustal structure. Strong contrasting dipping layered reflections (4—11 s, TWT),which dominate the lower crust of the northern part of the profile, are interpreted as the underplating of the basalt related to extensional tectonism. In the south of the profile, the yangtze craton is characterized by strong reflections in the middle crust, showing a distinct two-layer crustal structure. Over the region of the Tongling uplift, there appear the complex arc shape reflections, suggesting folded, faulted and intruded structures, and the transparent zone below them reveals the existence of batholith. The south dipping strong reflections between the upper crust and lower crust (4—7 s, TWT) suggest a detachment between them. The detachment provided space for the magma intrusion, and caused the formation of the batholith. The yangtze craton has a clear Moho re-flection, while the Tongling uplift has a weak Moho, whereas below the reflective lower crust in the northern part of the profile, there are sub-Moho reflections. The abrupt variation of the Moho characteristics within a short distance indicates the complexity of magmatic activity.

关键词： metallogenic belt, ore district, deep seismic profiling, crustal structure.

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