| 滇西地区壳幔解耦与腾冲火山区岩浆活动的深部构造研究 |
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| 引用本文： | 胥颐,钟大赉,刘建华.滇西地区壳幔解耦与腾冲火山区岩浆活动的深部构造研究[J].地球物理学进展,2012,27(3):846-855. |
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| 作者姓名： | 胥颐 钟大赉 刘建华 |
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| 作者单位： | 中国科学院地质与地球物理研究所,中国科学院油气资源研究重点试验室,北京100029 |
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| 基金项目： | 国家自然科学基金，中国地质调查局项目 |
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| 摘 要： | 根据青藏东部边缘的深部地球物理资料,分析了滇西地区壳幔耦合和腾冲火山区岩浆活动的深部构造特征,确认了地幔各向异性与上地幔速度结构(包括P波速度和S波速度)的内在联系,指出产生这一结果的原因与以腾冲火山区为中心的地幔热物质上涌有关:上地幔顶部平均温度升高导致介质强度降低,在印支块体的侧向挤压或印缅块体的向东俯冲作用下发生韧性变形,造成滇西地区地幔各向异性的快波方向与青藏东部地壳块体的旋转方向不一致.此外,鉴于中下地壳低速层的横向非均匀性,估计韧性流动并非贯通青藏高原的东部边缘,而是被不同的构造块体和边界断裂限定在局部地区.总体而言,滇西地区下地壳的地震波速度和电阻率偏低,具备发生韧性变形的构造条件.作为地壳和上地幔之间的解耦层,它使得青藏东部地壳块体旋转产生的构造应力未能传输至上地幔.腾冲火山区的地壳结构与不同时期的岩浆活动有关,火山区东侧的高速结构代表了上新世时期火山通道内冷凝固结的岩浆侵入体或难以挥发的高密度残留物质,火山区西侧的低速结构反映了更新世以来持续至今的岩浆活动,壳内岩浆源主要分布在10～20km的深度范围内,横向尺度约为15～20km,有可能通过地壳深部的断裂与上地幔岩浆源区相连,估计腾冲火山区下方的岩浆活动将持续进行.
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| 关 键 词： | 滇西地区 壳幔解耦 腾冲火山区 岩浆活动 |
Constraints of deep structures on the crust-mantle decoupling in the western Yunnan and the magma activity in the Tengchong volcanic area |
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| XU Yi
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ZHONG Da-lai
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LIU Jian-hua.Constraints of deep structures on the crust-mantle decoupling in the western Yunnan and the magma activity in the Tengchong volcanic area[J].Progress in Geophysics,2012,27(3):846-855. |
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| Authors: | XU Yi ZHONG Da-lai LIU Jian-hua |
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| Institution: | (Key Laboratory of Petroleum Resource Research,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China) |
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| Abstract: | Based on deep geophysical data in the eastern Tibetan margin,we analyzed the deep structure characters of the crust-mantle coupling in the western Yunnan and the magma activities in the Tengchong volcanic area.We found that the mantle anisotropy in the western Yunnan is well correlated to the velocity structure in the uppere mantle.This is attributed to the upwelling of hot mantle materials beneath the Tengchong volcanic area:higher temperatures lead to a strength decrease in the uppermost mantle and made it easy to produce ductile deformation when affected by the lateral penetration of the Indo-China block and the eastward subduction of the Indo-Burma micro-plate,leading to that the fast direction of the mantle anisotropy in the western Yunnan differs from the crustal rotation in the eastern Tibetan plateau.Besides,owing to a lateral variation of the low-velocity zone in the mid-lower crust,we estimate that ductile flows would not happen throughout the eastern Tibetan margin,are restricted in local regions by different blocks and fault boundaries.Generally,the western Yunnan is underlain by a weak lower crust that has lower seismic velocity and lower electric resistivity.It provides a tectonic condition for ductile deformation and appears as a decoupling zone between the crust and the upper mantle.Thus,the stress caused by the rotation of the eastern Tibetan crust could not be transmitted into the upper mantle.The crustal structure of the Tengchong volcanic area is related to volcanic activities in different periods.A high-velocity zone in the east represent cooled and solidified magma intrusions or high density remnants within the cooled volcanic channels during Pliocene;the lower seismic velocity zone in the west reflects magma activities from Pleistocene to present time.The magma source within the crust is centered at 10～20 km depths,with a lateral extent of 15～20 km.It is probably linked with mantle magma chambers through fault systems in the Tengchong basin.We estimate that magma activities will be continuously happening beneath the volcanic area. |
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| Keywords: | Western Yunnan crust-mantle decoupling Tengchong volcanic area magma source |
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