青藏高原各地体的地壳-上地幔结构及其东西向的变化特征
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摘要
青藏高原是由多个地体拼合而成的,在印度板块向北俯冲的长期作用下,各地体被挤压,地壳缩短,高原隆升。尽管在北北东向挤压作用下发生了高原的近南北向的断裂活动,但各地体本身的结构整体上保持相对稳定,不仅地壳浅部的地层、岩石、古生物保持着各自的特征,而且深部Moho面的变化和岩石圈的特征也是相似的。青藏高原的相距500km以上的2条宽频地震探测剖面的接收函数结果证实:高喜马拉雅地体、特提斯喜马拉雅地体、冈底斯地体、羌塘地体和巴颜喀拉地体在东西方向上保持着相近的速度特征。这充分说明,印度板块向北俯冲与青藏高原碰撞,引发各地体碰撞造山与高原隆升是地壳和岩石圈的整体构造运动,高原各地体,至少高原腹地仍然保持着大致相同的深部结构,Moho面、岩石圈底界面的深度和产状变化不大。
The Qinghai-Tibet Plateau was assembled by many terranes. Under the long-continued action of northward subduction of the Indian plate, the terranes of the plateau were compressed, the crust shortened and the plateau rose. Although nearly N-S-trending fault movement took place on the plateau due to NNE compression, the structure of all the terranes remains relatively stable. Not only the strata, rocks and fossils at the shallow level of the crust retain their own characteristics but also the variation of the Moho and characteristics of the lithosphere below these terranes are also similar. The results of receiver function of two broadband seismic profiles >500 km apart on the Qinghai-Tibet Plateau prove that the Higher Himalaya terrane, Tethys-Himalaya terrane, Gangdise terrane, Qiangtang terrane and Bayan Har terrane maintain similar velocity characteristics in the E-W direction. This fully shows that the collisional orogeny of various terranes and uplift of the plateau caused by northward subduction of the Indian plate and its collision with Qinghai-Tibet Plateau are the holistic tectonic movement of the crust and lithosphere. The terranes of the plateau, at least those in the interior of the plateau, still retain about the same basic deep structure, and the depths and attitudes of the Moho surface and Lithospheric bottom change little.
The Qinghai-Tibet Plateau was assembled by many terranes. Under the long-continued action of northward subduction of the Indian plate, the terranes of the plateau were compressed, the crust shortened and the plateau rose. Although nearly N-S-trending fault movement took place on the plateau due to NNE compression, the structure of all the terranes remains relatively stable. Not only the strata, rocks and fossils at the shallow level of the crust retain their own characteristics but also the variation of the Moho and characteristics of the lithosphere below these terranes are also similar. The results of receiver function of two broadband seismic profiles >500 km apart on the Qinghai-Tibet Plateau prove that the Higher Himalaya terrane, Tethys-Himalaya terrane, Gangdise terrane, Qiangtang terrane and Bayan Har terrane maintain similar velocity characteristics in the E-W direction. This fully shows that the collisional orogeny of various terranes and uplift of the plateau caused by northward subduction of the Indian plate and its collision with Qinghai-Tibet Plateau are the holistic tectonic movement of the crust and lithosphere. The terranes of the plateau, at least those in the interior of the plateau, still retain about the same basic deep structure, and the depths and attitudes of the Moho surface and Lithospheric bottom change little.
引文
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[2]Hirn A,Lépine J C,Jobert G,et al.Crustal structure and variability of the Himalayan boarder of Tibet[J].Nature,1984,307:23-25.
[3]GalvéA,Hirn A,Jiang M,et al.Modes of raising northeastern Tibet probed by explosion seismology[J].Earth Planet.Sci.Lett.,2002,203:35-43.
[4]GalvéA,Sapin M,Hirn A,et al.Complex images of Moho and variation of Vp/Vs across the Himalaya and South Tibet,from a joint receiver-function and wide-angle-reflection approach[J].Geophys.Res.Lett.,2002,29(24):2182,doi:10.1029/2002GL015611.
[5]Hirn A,Jiang M,Sapin M,et al.Seismic anisotropy as an indicator of mantle flow beneath the Himalayas and Tibet[J].Nature,1995,375:571-574.
[6]Hirn A,Sapin M,Lepine J C,et al.Increase in melt fraction along a south-north teaverse below the Tibetan Plateau:Evidence from seis-mology[J].Tectonophys.,1997,273:17-30.
[7]姜枚,吕庆田,史大年.用天然地震探测青藏高原中部地壳、上地幔结构[J].地球物理学报,1996,39(4):470-482.
[8]钱辉,姜枚,薛光琦,等.天然地震接收函数揭示的青藏高原东部地壳结构[J].地震学报,2001,23(1):103-108.
[9]Jiang M,GalvéA,Hirn A,et al.Crustal thickening and variations in architecture from the Qiadam basin to the Qiang Tang(North-Cen-tral Tibet)from wide-angle reflection seismology[J].Tectonophys.,2005,412:121-140.
[10]Kind R,Yuan X,Saul J,et al.Seismic images of crust and upper mantle beneath Tibet:evidence for Eurasian plate subduction[J].Sci-ence,2002,298:1219-1221.
[11]GalvéA,Jiang M,Hirn A,et al.Explosion seismic P and S velocity and attenuation constraints on the lower crust of the North-Central Tibetan Plateau,and comparisom with South Tibet-Himalayas:im-plications on composition,mineralogy,tempera ture,and tectonic evolution[J].Tectonophys.,2006,412:141-157.
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