丽江—攀枝花—者海地带二维地壳结构及其构造意义

THE 2-D STRUCTURE AND IT'S TECTONIC IMPLICATIONS OF THE CRUST IN THE LIJIANG-PAN- ZHIHUA-ZHEHAI REGION

本文利用攀西地区通过攀枝花的东西向剖面爆炸地震资料,进行了震相的重新识别和二维射线追踪与理论图计算.结果表明,沿剖面地表附近有4个低速区和若干高速带,它们与地质和构造有很好的对应关系.渡口附近的高速岩体一直延伸到了上地壳的底部,形成一个统一的地垒状构造,该高速体与攀枝花成矿岩体相关,并推断华坪及其以西地带也是找矿的有利地区.中地壳下部有一厚度约9km的低速层,它可能是壳内的韧性剪切带.低速层顶部深度为27.0—29.5km,与研究地区的居里面深度及天然地震震源深度的分布基本符合.剖面东段中地壳顶部还有一层很薄的低速层,反映了构造带两侧运动的不对称性.地壳厚度为53—56km,构造带中部的Moho界面没有明显的上隆.

A reconfirmation of the seismic phases and computations of 2-D ray tracing and synthetic seismograms are completed in this paper for the explosion seismological data along profile WE in the Panzhihua-Xichang region Seven seismic phases Pg,P1,P2,P3,P4, Pm and Pn have been confirmed, the P1 and P3 are neglected in 1-D explanation in the past.The result shows that: There are four low- and several high-velocity zones near the surface and they are well related to the geology and tectonics. A high-velocity body near Panzhihua extends downwards from surface to the bottom of upper crust and forms a shape out horst structure which are seemly deeper tectonic background from whole structure of the crust. This high-velocity body is related to the Panzhihua mineralization and it is thought that to the west from Huaping is also a favorable zone for looking for mineral deposit. There is a low-velocity zone about 9km thick and it is possible a tenacity shear zone in the crust. The top of this zone is located at 27.0-29.5km deep which is in keeping with the lower depth of earthquake focusi and to the Curie deep in the region. There is another small low-velocity zone at the upper part of the middle crust, and it is reflecting tectonized inhomogeneity in different parts of the tectonic belt-The crust is 53.0-56.0 km thick and the Moho is not obvious uplift in the middle part of the tectonic belt.