喜马拉雅东构造结岩石圈板片深俯冲的地球物理证据  

Geophysical evidence for deep subduction of Indian lithospheric plate beneath Eastern Himalayan Syntaxis

作　　者：姜枚[1] 彭淼[1,2] 王有学[3] 谭捍东[2] 李庆庆[1] 张立树[1] 王伟[1,2] 

机构地区：[1]中国地质科学院地质研究所,大陆构造与动力学国家重点实验室,北京100037 [2]中国地质大学地球物理与信息技术学院,北京100083 [3]桂林理工大学地球科学学院,桂林541004

出　　处：《岩石学报》2012年第6期1755-1764,共10页Acta Petrologica Sinica

基　　金：中国地质调查局项目(1212010918015)资助

摘　　要：2009～2010年在南迦巴瓦地区进行了宽频带地震和大地电磁探测,分别处理获得东构造结及其邻区的地下300km以上的P波速度图像和两条大地电磁电阻率剖面。通过资料的对比和综合解释,发现电阻率分布与地震波速有较好的对应关系。研究结果表明:南迦巴瓦变质体的上地壳部分呈现明显高速高阻特征,为两侧的雅鲁藏布江缝合带所夹持;中下地壳具有不均匀性,且普遍呈低速低阻特征;印度板块在藏东南向欧亚板块的俯冲前缘越过嘉黎断裂,抵达班公湖-怒江缝合带;在拉萨地体的高速俯冲板片以下100km至200km深度范围内存在大规模的低速异常带,其上盘中下地壳也广泛发育低速高导体,指示青藏高原东南缘可能存在韧性易流动的物质向东、东南逃逸的通道,为印度板块在南迦巴瓦的深俯冲动力学模式提供了地球物理证据。We conducted broadband seismic observation and MT detection around the Namche Barwa from 2009 to 2010. P wave velocity perturbations down to 300km were obtained and two electrical models were acquired by 2D inversion. There are similar features between electrical models and the corresponding tomographic images by joint interpretation. Our results show that the upper crust of Namche Barwa is separated by IYS and consists of prominent high-velocity and resistive blocks. The mid-lower crust is inhomogenous and characterized by low-velocity and conductive anomaly. The Indian lithospheric mantle has subducted beneath Eurasian plate and its frontier has passed through the Jiali shear zone and reached the Bangong-Nujiang suture; A large-scale low-velocity anomaly is revealed within the Lhasa block beneath the high-velocity plate from 100km to 200km depth, above which the mid-lower crust is an extensive low-velocity conductor. This suggests that there exist channels beneath southeastern Tibetan Plateau favorable to weak and flowable materials exuding towards east and southeast, which gives geophysical evidence for the dynamics mode of deep-subduction of Indian Plate beneath the Namche Barwa.

关 键 词：宽频地震 大地电磁 板片深俯冲 东构造结 喜马拉雅 

分 类 号：P313[天文地球—固体地球物理学]