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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.

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 reflection, 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.

76 Since 1992, project INDEPTH (International Deep Profiling of Tibet and the Himalaya) geoscientists from Chinese, American, British, German, and Canadian institutions have collaborated to collect high-quality seismic, MT, and geologic data along a roughly north–south transect from the Himalaya to northern Tibet. The current field effort from 2007–2009, INDEPTH IV, targets the NE margin of the plateau, with goals of testing models of subduction (relict and current) near the Kunlun and Jinsha sutures and probing the deep geometry of key features such as the Kunlun and Altyn Tagh Faults. Our new datasets are intended to shed light on the possible existence of a lower-crustal flow channel beneath northern Tibet, analogous to the weak (and flowing?) lower crust evidenced by INDEPTH observations of mid-crustal low seismic velocities, seismic bright spots and high electrical conductivities (Nelson et al. 1996) in southern Tibet. INDEPTH IV further aims to evaluate the possible subduction of Asian crust from the north beneath the Kunlun suture (Kind et al. 2002) and to probe whether the Kunlun and Jinsha sutures act as crustal-scale faults. Active seismic experiment, summer 2007