Seismic tomography of Tianshan-Junggar region and its lithospheric structure
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摘要: 通过对东西天山两条天然地震剖面的远震P波与近震P波走时资料以及2001——2007年新疆地方台网的近震走时资料分析，获得了天山——准噶尔地区的三维地震层析图像.层析反演使用的台站数140个，地震事件1132个，P波走时数24904条.检测板试验结果指出,东西天山剖面、天山轴部和东准噶尔地区P波速度扰动恢复能力相对高.纵波波速反演扰动结果能明确区分天山内部的高速体和两侧盆地的低速体，同时也可以分辨天山内部的山间盆地及深部的低速体.而且发现东西天山地壳上地幔结构存在较大差异.西天山地壳内部呈现南北向中间拼贴的构造样式，而东天山则主要表现为天山与准噶尔盆地强烈的耦合作用；地幔深度两个区域都出现的中天山低速体，在西天山表现为上涌，而在东天山则卷入俯冲过程.天山准噶尔接触带的两个切片表现为西陡东缓,这可能是由于西部帕米尔阻挡造成天山地区中部活化断裂存在走滑分量，使塔里木盆地地壳与地幔内的高低速体分布倾向或倾角不一致.阿尔泰地区地幔深度发现大规模高速体分布，可能与地幔中基性岩浆上升侵入有关，地壳浅部再分异混染成矿.Abstract: Based on 24 904 P-wave arrival time data from 1132 events recorded at 140 stations in two seismic profiles across Tianshan mountain and in Xinjiang regional seismic network, tomographic images of P-wave velocity are achieved beneath Tianshan-Junggar region by travel time inversion. Result of checkboard tests indicates that the reliability of velocity perturbation recovering is relatively high for the region beneath the two profiles themselves, along Tianshan and eastern Junggar. The inversion result of P-wave velocity perturbations clearly tells the boundary between the high velocity zone in Tianshan terrane and low velocity zone in the basins on both sides of Tianshan. Moreover, the result also reveals the low velocity beneath inner-Tianshan basin and in the upper mantle. On the tomographic image we can see distinguished difference between eastern and western Tianshan. In the crust beneath western Tianshan a typical structure of knocking together from both northern and southern part towards central can be found, while beneath eastern Tianshan the structure shows strong coupling between Tianshan mountain and Junggar basin. Nevertheless at the depth in top mantle both areas display a low velocity zone named as Central Tianshan LVZ, behaving as medium upgoing flow in the west and as block subducting in the east. At the depth of upper mantle in Altai area there is a large size high velocity zone, which may be attributed to the intruding of intermediate-basaltic magma.The magmatic differentiation in shallow crust may form hybrid deposits.
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