INDEPTH-Ⅲ地震层析成像--藏北印度岩石圈俯冲断落的证据

德庆-龙尾错剖面层析速度结构剖面揭示了在高原地壳发生缩短与增厚后,高速的印度大陆地幔岩石圈分为两层以不同角度向北伸展到(美)塘盆地的中部(33°N～34°N之间).上层在拉萨地块岩石圈(速度为7.9～8.0 km/s)之下向北伸展过程中发生断裂,形成若T断块,并下沉;下层以较大角度向北俯冲下去,并在32°N之下进人软流圈;发现北部有一浅一深2条低速带,可能代表地幔内温度较高的热流体的流动通道,并产生强烈的各向异性.浅处低速带与深部低速带有联系;此低速带与东部Wittlinger发现的34.5°N深部的高温低速体没有直接联系,后者呈NV-SE走向.

Seismic Imaging of the Subducting Indian Lithosphere beneath North Tibet

A tomographic image of the upper mantle beneath Central Tibet from INDEPTH III seismic data has revealed two high velocity layers in the Lower Velocity Zone of the Upper Mantle. It is referred that these two layers are the northward continuation of Indian high velocity lithosphere. While the upper layer was broken down and subsided in its northward extending process beneath the Lhasa Block Lithosphere, the other layer was subducting gently into the asthenosphere under 32°N. It is suggested that the two lo wer velocity belts, located just north of 33°N at different depths, are not related to the deep Lower Velocity Body at 35.5°N disco vered by Wittlinger in 1996, and that they might have originated from another thermo fluid source at 32°N,91°E.