| 中国西部及邻区岩石圈S波速度结构面波层析成像 |
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| 引用本文： | 黄忠贤,李红谊,胥颐.中国西部及邻区岩石圈S波速度结构面波层析成像[J].地球物理学报,2014,57(12):3994-4004. |
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| 作者姓名： | 黄忠贤 李红谊 胥颐 |
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| 作者单位： | 1. 中国地震局地壳应力研究所, 北京 100085;2. 中国地质大学地球物理与信息技术学院, 北京 100083;3. 中国科学院地质与地球物理研究所, 北京 100029 |
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| 基金项目： | 国家自然科学基金(41174050)和中国地质调查局科研项目(GZH200900504)资助. |
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| 摘 要： | 本文利用瑞利波群速度频散资料和层析成像方法,研究了中国西部及邻近区域(20°N—55°N,65°E—110°E)的岩石圈S波速度结构.结果表明这一地区存在三个以低速地壳/上地幔为特征的构造活动区域:西蒙古高原—贝加尔地区,青藏高原,印支地区.西蒙古高原岩石圈厚度约为80 km,上地幔低速层向下延伸至300 km深度,说明存在源自地幔深部的热流活动.缅甸弧后的上地幔低速层下至200 km深度,显然与印度板块向东俯冲引起俯冲板片上方的热/化学活动有关.青藏高原地壳厚达70 km,边缘地区厚度也在50 km以上并且具有很大的水平变化梯度,与高原平顶陡边的地形特征一致.中下地壳的平均S波速度明显低于正常大陆地壳,在中地壳20~40 km深度范围广泛存在速度逆转的低速层,这一低速层的展布范围与高原的范围相符.这些特征说明青藏高原中下地壳的变形是在印度板块的北向挤压下发生塑性增厚和侧向流动.地幔的速度结构呈现与地壳显著不同的特点.在高原主体和川滇西部地区上地幔顶部存在较大范围的低速,低速区范围随深度迅速减小;100 km以下滇西低速消失,150 km以下基本完全消失.青藏高原上地幔速度结构沿东西方向表现出显著的分段变化.在大约84°E以西的喀喇昆仑—帕米尔—兴都库什地区,印度板块的北向和亚洲板块的南向俯冲造成上地幔显著高速;84°E—94°E之间上地幔顶部速度较低,在大约150~220 km深度范围存在高速板片,有可能是俯冲的印度岩石圈,其前缘到达昆仑—巴颜喀拉之下;在喜马拉雅东构造结以北区域,存在显著的上地幔高速区,可能阻碍上地幔物质的东向运动.川滇西部岩石圈底界深度与扬子克拉通相似,约为180 km,但上地幔顶部速度较低.这些现象表明青藏高原岩石圈地幔的变形/运动方式可能与地壳有本质的区别.
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| 关 键 词： | 中国西部 岩石圈 速度结构 面波 层析成像 |
| 收稿时间： | 2013-08-16 |
Lithospheric S-wave velocity structure of west China and neighboring areas from surface wave tomography |
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| HUANG Zhong-Xian,LI Hong-Yi,XU Yi.Lithospheric S-wave velocity structure of west China and neighboring areas from surface wave tomography[J].Chinese Journal of Geophysics,2014,57(12):3994-4004. |
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| Authors: | HUANG Zhong-Xian LI Hong-Yi XU Yi |
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| Institution: | 1. Institute of Crustal Dynamics, China Earthquake Administration, Beijing 100085, China;2. School of Geophysics and Information Technology, China University of Geosciences, Beijing 100083, China;3. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China |
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| Abstract: | We used Rayleigh wave dispersion data and the tomographic method to study the lithospheric S-wave structure in west China and neighboring areas (20°N—55°N,65°E—110°E). The results indicate three active tectonic regions characterized by low crust/upper mantle velocities, i.e., the west Mongolia-Baikal region, Tibetan plateau, and Indo-China region. The lithosphere beneath west Mongolia is about 80 km thick, where the low velocity layer in upper mantle extends down to 300 km depth, indicating the existence of thermal activity originating from deep mantle. The upper mantle low velocity zone in the Myanmar back-arc region reaches 200 km depth, which is apparently related to the thermal/chemical activities above the eastward subducting India plate. The crust of the Tibetan plateau is as thick as 70 km; in its marginal area the thickness exceeds 50 km and varies rapidly across the plateau margin, which accords with the flat top and steep edge character of the plateau landform. The average mid-lower crust velocity of the Tibetan plateau is remarkably lower than normal continental crust; in the middle crust (depth 20~40 km) a low velocity layer with velocity reversal exists in the entire plateau. These characteristics indicate that the mid-lower crust deformation of the plateau is mainly plastic thickening and lateral flow under the northward compression of India plate. On the other hand the upper mantle structure shows distinctly different characteristics from the crust. Low velocity exists in the top of upper mantle beneath the plateau proper and the west Sichuan—Yunnan region, and the scope of this low velocity diminishes rapidly with depth: it vanishes below 100 km in west Sichuan-Yunnan, and is basically absent below 150 km in the entire plateau. The upper mantle structure of the Tibetan plateau varies significantly in EW direction. In the Karakorum-Pamir-Hindu Kush region west of 84°E the northward subduction of India and the southward subduction of Asia caused magnificent high velocities in the upper mantle. Between 84°E and 94°E the velocity at the top of upper mantle is low, and a slab-like high velocity exists in the depth range 150~220 km, which probably is the subducting India lithosphere with its front reaching beneath the Kunlun-Bayankala mountains. In the region north of the eastern Himalayan syntaxis the velocity in upper mantle is obviously high, which may hamper the eastward movement of upper mantle material. In the west Sichuan-Yunnan region the lithosphere thickness is similar to that of the Yangtze craton, about 180 km, but the velocity in the top of upper mantle is low. These phenomena indicate that the deformation/tectonic movement of the lithospheric mantle in the Tibetan plateau is fundamentally different from its crust. |
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| Keywords: | West China Lithosphere Velocity structure Surface wave Tomography |
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