穿越冈底斯地体的宽频地震探测研究

A Tomography Study of the Broad-band Seismic Profiling across Gangdise Block

青藏高原是大约60 Ma以来印度次大陆与欧亚大陆直接碰撞形成的,是研究大陆碰撞过程和发展板块构造理论的最佳场所。冈底斯构造带位于印度次大陆与欧亚大陆碰撞的前沿地带,对冈底斯构造带的探测结果将直接影响到对大陆碰撞过程和整个青藏高原地壳变形过程的认识。2011年9月至2012年9月一条穿越冈底斯(GDS)地体的地震深部探测剖面始于班公怒江断裂带北缘,向南穿越了崩错—嘉黎断裂带、冈底斯地体、雅鲁藏布缝合线并跨过藏南拆离断层系(STD),终止于喜马拉雅山南坡。本文作者利用天然地震体波完成了该条剖面的二维走时残差反演,展现出了该地段深部构造格局。首先验证了冈底斯地体浅部存在大面积部分熔融层的研究结论;支持甲玛大型斑岩铜矿为大陆碰撞挤压条件下岩浆上侵的成矿模式;PKP曲线描绘出了本次研究区间内Moho界面的形态,确定地壳最厚处在雅江缝合线南北两侧约50 km区间。这些推论和发现为青藏高原深部的结构研究提供了重要信息。

As the Tibetan Plateau resulted from the direct collision between Indian and Eurasian continents which started about 60 Ma ago, it is regarded as the best stage for studying the continental collision process and perfecting the theory of plate tectonics. As the Gangdise Block （GDS） lies in the frontier of the collision zone, the research on the GDS would be greatly helpful to the understanding of the whole process of the collision and the derived crustal deformation evolution of the Tibetan Plateau. A seismic profiling stretching from the north of Bangong–Nujiang faulted zone to southern Himalayas was performed from September 2011 to September 2012. This profile ran across Bengcuo–Jiali faulted zone, Gangdise Block （GDS）, Yarlung Zangbo suture zone and South Tibetan De-collaboration （STD） system. The authors conducted the 2D travel-time residual inversion of the profile using the body wave of natural earthquakes, revealed the deep structural geometry of the study region, and for the first time verified the conclusion about the existence of massive partial-melting layer in the shallow part of GDS. The results obtained by the authors support the metallogenic model that the Jiama porphyry Cu deposit was derived from the magma intrusion in a continental collision environment. The PKP curves depict the Moho pattern of the study area, and determine that the thickest crust lies within 50 km from the north and south sides of the Yarlung Zangbo suture zone. The authors hold that these discoveries and inferences would provide significant information for the study of deep structures of the Tibetan Plateau.