大地电磁观测揭示青藏高原东部存在两条地壳物质流
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摘要
本研究通过东喜马拉雅构造结及周围地区连续6年的大地电磁观测,获得了青藏高原东部岩石圈电性结构的初步认识。结果发现,在青藏高原东部存在两条巨大的中下地壳低阻异常带,理论计算显示这是两条中下地壳的弱物质流:一条从拉萨地块沿雅鲁藏布缝合带向东延伸,环绕东喜马拉雅构造结向南转折,最后通过腾冲火山;另一条从羌塘地体沿金沙江-鲜水河断裂带向东延伸,在四川盆地西缘向南转折,最后通过小江断裂和红河断裂之间的川滇菱形块体。本项研究认为,青藏高原深部以两个地壳弱物质流的快速塑性变形为主,上地壳则以块体的走滑变形为主。该模型将有助于对青藏高原动力学的定量研究以及对高原东部和滇川西部地区地震活动机制的分析。
A primary electrical model is suggested by the MT data of 6 years measurements.The model shows two large-scale crustal flow channels in eastern Tibet and southwest China around the eastern Himalayan Syntax(EHS):One flow(A)comes from Lhasa block and extends eastward along the Yalun-Zangbo suture,then turns southward around the EHS,finally goes through the Tengchong volcano.The other flow B.comes from Qiangtang terrain and extends eastward along the Jinshajiang-Xianshuihe fault belt,then turns southeast on the west margin of Sichuan basin,finally goes into the rhombic block confined by the Red River and Xiaojiang faults.It is proposed that the mechanism of the deformation of lithosphere in eastern Tibetan plateau can be described by the slip of rigid blocks in the upper crust and viscous flows in mid-lower crust.These findings can contribute to the quantitative study of uplift of plateaux.The resulted model will also be helpful for explaining the occurrence of earthquakes in eastern Tibet and southwest China.
A primary electrical model is suggested by the MT data of 6 years measurements.The model shows two large-scale crustal flow channels in eastern Tibet and southwest China around the eastern Himalayan Syntax(EHS):One flow(A)comes from Lhasa block and extends eastward along the Yalun-Zangbo suture,then turns southward around the EHS,finally goes through the Tengchong volcano.The other flow B.comes from Qiangtang terrain and extends eastward along the Jinshajiang-Xianshuihe fault belt,then turns southeast on the west margin of Sichuan basin,finally goes into the rhombic block confined by the Red River and Xiaojiang faults.It is proposed that the mechanism of the deformation of lithosphere in eastern Tibetan plateau can be described by the slip of rigid blocks in the upper crust and viscous flows in mid-lower crust.These findings can contribute to the quantitative study of uplift of plateaux.The resulted model will also be helpful for explaining the occurrence of earthquakes in eastern Tibet and southwest China.
引文
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[2]Tapponnier P,Xu Zhiqin,Roger F,Meyer B,arnaud N,Wittlinger G,Yang Jingsui.Oblique stepwise rise and growth of the Tibet Plat-eau.Science,2001,294:1671—1677
[3]England P,Molnar P.Active deformation of Asia:fromkinematics to dynamics.Science,1997,278:647—650
[4]Zhang Peizhen,Shen Zhengkang,Wang Min,Gan Weijun,Burg-mann R,Molnar P,Wang Qi,Niu Zhijun,Sun Jianzhong,Wu Jian-chun,Sun Hanrong,You Xinzhao.Continuous deformation of the Ti-betan Plateau fromglobal positioning systemdata.Geology,2004,32(9):809—812
[5]Royden L H,Burchfiel B C,King R W,Wang E,Chen Zhiliang,Shen Feng,Liu Yuping.Surface deformation and lower crustal flow in eastern Tibet.Science,1997,276:788—790
[6]Clark M K,Royden L H.Topographic ooze:Building the eastern margin of Tibet by lower crustal flow.Geology,2000,28(8):703—706
[7]Beaumont C,Jamieson R A,Nguyen M H,Lee B.Himalayan tec-tonics explained by extrusion of a low-viscosity crustal channel cou-pled to focused surface denudation.Nature,2001.414(13):738—742
[8]Bai Denghai,Unsworth MJ,Meju MA,Ma Xiaobing,Teng Jiwen,Kong Xiangru,Sun Yi,Sun Jie,Wang Lifeng,Jiang Chaosong,Zhao Ciping,Xiao Pengfei,Liu Mei.Crustal deformation of the east-ern Tibetan plateau revealed by magnetotelluric imaging.Nature Geo-science,2010,3(5):358—362
[9]Rippea D,Unsworth M.Quantifying crustal flowin Tibet with magne-totelluric data.Physics of the Earth and Planetary Interiors,2010,179:107—121
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