青藏高原深部热结构模拟的探讨
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摘要
对地幔过渡带的研究表明,410km和660km速度间断界面是由于相变引起的不连续界面.穿越过渡带的深俯冲会引起这2个速度不连续面产生起伏.在中国东北等俯冲带地区,地震层析成像观测到了俯冲板片在660km界面上的平卧滞留,地震接收函数也观测到了这种滞留而产生的相变界面加深.然而在最近青藏高原南部展开的几组研究工作表明,地震接收函数并未在该区域发现不连续面存在明显起伏.为了验证该地区是否不存在穿越不连续面的俯冲,还是俯冲引起的不连续面的起伏没有被观测到,进行了该碰撞区域的热模拟,计算不连续面可能的起伏量.研究大角度俯冲、小角度俯冲和印度岩石层使青藏高原整体加厚等模型.在只考虑橄榄石-尖晶石相变作为410km不连续面产生原因、尖晶石-钙钛矿相变作为660km不连续面产生原因的前提下,计算结果表明,以上模型只要存在穿越以上界面的俯冲,就能够产生比较明显的起伏,这样的起伏应该能被地震接收函数观测到.根据以上的研究结果以及接收函数观测,更倾向于支持藏南区域应该不存在到达地幔过渡带的深俯冲,俯冲带可能向北到达更远的地方.
The study of mantle transition-zone shows that velocity discontinuities of 410km and 660km were caused by phase-change.Subduction through these two discontinuities will change the depth of the discontinuities.A flat subduction slab lying on the 660km was observed in North-East China subduction-zone by seismic imaging,and a deeper 660km discontinuity was reported by receiver function studies.But the receiver function results in Tibetan collocation zone does not show any significant elevation or depression of the discontinuities.To exam whether there is no subduction-slab through the discontinuities in these areas,or we have not observed the discontinuity caused by subduction-slab,we carry out a thermal simulation in the area,and compute the possible elevation and depression of the discontinuities.We have considered subduction models with different angles and a model the whole Tibetan plateau was thicken by Indian lithosphere.When we only consider the Olivine-Spinel phase change as the cause of 410km velocity discontinuity,and Olivine-Perovskite phase change as the cause of the 660km velocity discontinuity,our result shows that the subduction similar to our models will change the depth of discontinuities significantly,and could be observed by seismic receiver function method.According to our results and the receiver function results,we tend to support the opinion that there does not exist deep subduction slab in Southern Tibet,and the subduction may go further north.
The study of mantle transition-zone shows that velocity discontinuities of 410km and 660km were caused by phase-change.Subduction through these two discontinuities will change the depth of the discontinuities.A flat subduction slab lying on the 660km was observed in North-East China subduction-zone by seismic imaging,and a deeper 660km discontinuity was reported by receiver function studies.But the receiver function results in Tibetan collocation zone does not show any significant elevation or depression of the discontinuities.To exam whether there is no subduction-slab through the discontinuities in these areas,or we have not observed the discontinuity caused by subduction-slab,we carry out a thermal simulation in the area,and compute the possible elevation and depression of the discontinuities.We have considered subduction models with different angles and a model the whole Tibetan plateau was thicken by Indian lithosphere.When we only consider the Olivine-Spinel phase change as the cause of 410km velocity discontinuity,and Olivine-Perovskite phase change as the cause of the 660km velocity discontinuity,our result shows that the subduction similar to our models will change the depth of discontinuities significantly,and could be observed by seismic receiver function method.According to our results and the receiver function results,we tend to support the opinion that there does not exist deep subduction slab in Southern Tibet,and the subduction may go further north.
引文
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[2]Tilmann F,Ni J,INDEPTHIII Seismic Team.Seismic imaging of the downwellingindianlithosphere beneath central tibet.Science,2003,300:1424~1427
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[9]Li X,Sobolev SV,Kind R,et al.Adetailedreceiverfunctionimage of the upper mantle discontinuitiesinthe Japansubductionzone.Earth andPlanetary Science Letters,2000,183:527~541
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[11]Ai YS,Zheng TY,Xu WW,et al.Acomplex660 kmdiscontinuity beneath northeast China.Earth and PlanetaryScience Letters,2003,212:63~71
[12]Li XQ,Yuan XH.Receiver functionsin northeast China——implicationsfor slab penetrationintothe lower mantle in northwest Pacific subductionzone,2003,216:679~691
[13]Kind R,Yuan X,Saul J,et al.Seismic images of crust and upper mantle beneath Tibet:evidence for eurasian plate subduction.Science,2002,298:1219~1221
[14]Jin G,Chen J,Sandvol E,et al.Receiver functionimages of the crust and upper mantle structure of southern Tibet in AGUfall meeting.SanFrancisco,2006
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[16]Shi YL,Wang CY.Two-dimensional modeling ofP-T-tpaths of regional metamorphisminsimple overthrust terrains.Geology,1987,15:1048~1051
[17]Zang SX,Ning JY.The negative buoyancy of the subduction zone andits affectingfactors.Acta Geophysica Sinica,1994,37(2):174~183(inChinses)臧绍先,宁杰远.俯冲带的负浮力及其影响因素.地球物理学报,1994,37(2):174~183
[18]Zang SX,Ning JY,Chen YW,et al.Thermal structures of the subduction zones for two types of mantle convection models.Acta GeophysicaSinica,1994,37(4):448~455(in Chinese)臧绍先,宁杰远,陈玉文,等.两种地幔对流模式下俯冲俯冲带的热结构.地球物理学报,1994,37(4):448~455
[19]Zang SX,Song HZ,NingJY.Onthethermal structure of the Japansea subductionzone andthe effect of the heat sources.Acta Geophysica Sinica,1993,36(2):164~173(in Chinese)臧绍先,宋慧真,宁杰远.日本海俯冲带的热结构及热源的影响.地球物理学报,1993,36(2):164~173
[20]Zang SX,Ning JY.Study on the subduction zone in western Pacific and its implication for the geodynamics.Acta Geophysica Sinica,1996,39(2):188~202(in Chinese)臧绍先,宁杰远.西太平洋俯冲带的研究及其动力学意义.地球物理学报,1996,39(2):188~202
[21]Zang SX,Ning JY.The influences of metastable olivine on the negative buoyancy of subduction zones and their geodynamic significance.ActaGeophysica Sinica,2001,44(3):336~345(in Chinese)臧绍先,宁杰远.亚稳态橄榄石对俯冲带负浮力的影响及其动力学意义.地球物理学报,2001,44(3):336~345
[22]Zhu YQ,Shi YL.Shear heating and partial melting of granite——thermal structure at overthrusted terrains in the greater Himalaya.ActaGeophysica Sinica,1990,33(4):408~416(in Chinese)朱元清,石耀霖.剪切生热与花岗岩部分熔融——关于喜马拉雅地区逆冲断层与地壳热结构的分析.地球物理学报,1990,33(4):408~416
[23]Shi YL,Zhu YQ,Shen XJ.Tectonic processes andthermal evolution of the Qinghai-Xizang(Tibetan)Plateau.Acta Geophysica Sinica,1992,35(6):710~720(in Chinese)石耀霖,朱元清,沈显杰.青藏高原构造结构热演化的主要控制因素.地球物理学报,1992,35(6):710~720
[24]Negredo AM,Valera JL,Carminati E.TEMSPOL:a MATLABthermal model for deep subduction zones including major phase transformations.Computers&Geosciences,2004,30:249~258
[25]Turcotte DL,Schubert G.Geodynamics.2nd ed.Cambridge University Press,2002
[2]Tilmann F,Ni J,INDEPTHIII Seismic Team.Seismic imaging of the downwellingindianlithosphere beneath central tibet.Science,2003,300:1424~1427
[3]Zheng HW,Li TD,Gao R,et al.Teleseismic P-wave tomography evidence for the Indianlithospheric mantle subducting northward beneaththeQiangtangterrane.Chinese J Geophys,2007,50(5):1418~1426(in Chinese)郑洪伟,李廷栋,高锐,等.印度板块岩石圈地幔向北俯冲到羌塘地体之下的远震P波层析成像证据.地球物理学报,2007,50(5):1418~1426
[4]Chung SL,Chu MF,Zhang YQ,et al.Tibetan tectonic evolution inferred fromspatial and temporal variations in post-collisional magmatism.Earth-Science Reviews,2005,68:173~196
[5]Zhao ZD,Mo XX,Luo ZH,et al.Subduction of India beneath Tibet magmatismevidence.Earth Science Frontiers,2003,10(3):149~157(inChinese)赵志丹,莫宣学,罗照华,等.印度-亚洲俯冲带结构-岩浆作用证据.地学前缘,2003,10(3):149~157
[6]吕庆田,姜枚,许志琴,等.印度板块俯冲仅到特提斯喜马拉雅之下的地震层析证据.科学通报,1998,43(12):1308~1311
[7]Hou ZQ,Li ZQ.Possible locationfor underthrustingfront of the Indus continent:constraintsfromheliumisotope of the geothermal gasinsouthernTibet and eastern Tibet.Acta Geologica Sinica,2004,78(4):482~493(in Chinese)侯增谦,李振清.印度大陆俯冲前缘的可能位置:来自藏南和藏东活动热泉气体He同位素约束.地质学报,2004,78(4):482~493
[8]Hou ZQ,Zhao ZD,Gao YF,et al.Tearing and dischronal subduction of the Indian continental slab:Evidence fromCenozoic Gangdese volcano-magmatic rocks in south Tibet.Acta Petrologica Sinica,22(4):761~774(in Chinese)侯增谦,赵志丹,高永丰,等.印度大陆板片前缘撕裂与分段俯冲:来自冈底斯新生代火山-岩浆作用证据.岩石学报,2006,22(4):761~774
[9]Li X,Sobolev SV,Kind R,et al.Adetailedreceiverfunctionimage of the upper mantle discontinuitiesinthe Japansubductionzone.Earth andPlanetary Science Letters,2000,183:527~541
[10]赵大鹏,雷建设,唐荣余.中国东北长白山火山的起源:地震层析成像证据.科学通报,2004,49(14):1439~1446
[11]Ai YS,Zheng TY,Xu WW,et al.Acomplex660 kmdiscontinuity beneath northeast China.Earth and PlanetaryScience Letters,2003,212:63~71
[12]Li XQ,Yuan XH.Receiver functionsin northeast China——implicationsfor slab penetrationintothe lower mantle in northwest Pacific subductionzone,2003,216:679~691
[13]Kind R,Yuan X,Saul J,et al.Seismic images of crust and upper mantle beneath Tibet:evidence for eurasian plate subduction.Science,2002,298:1219~1221
[14]Jin G,Chen J,Sandvol E,et al.Receiver functionimages of the crust and upper mantle structure of southern Tibet in AGUfall meeting.SanFrancisco,2006
[15]Shi YL,Wang CY.Thermal structure of the Barbados accretionary complex.PAGEOPH,1988,128(3/4):749~766
[16]Shi YL,Wang CY.Two-dimensional modeling ofP-T-tpaths of regional metamorphisminsimple overthrust terrains.Geology,1987,15:1048~1051
[17]Zang SX,Ning JY.The negative buoyancy of the subduction zone andits affectingfactors.Acta Geophysica Sinica,1994,37(2):174~183(inChinses)臧绍先,宁杰远.俯冲带的负浮力及其影响因素.地球物理学报,1994,37(2):174~183
[18]Zang SX,Ning JY,Chen YW,et al.Thermal structures of the subduction zones for two types of mantle convection models.Acta GeophysicaSinica,1994,37(4):448~455(in Chinese)臧绍先,宁杰远,陈玉文,等.两种地幔对流模式下俯冲俯冲带的热结构.地球物理学报,1994,37(4):448~455
[19]Zang SX,Song HZ,NingJY.Onthethermal structure of the Japansea subductionzone andthe effect of the heat sources.Acta Geophysica Sinica,1993,36(2):164~173(in Chinese)臧绍先,宋慧真,宁杰远.日本海俯冲带的热结构及热源的影响.地球物理学报,1993,36(2):164~173
[20]Zang SX,Ning JY.Study on the subduction zone in western Pacific and its implication for the geodynamics.Acta Geophysica Sinica,1996,39(2):188~202(in Chinese)臧绍先,宁杰远.西太平洋俯冲带的研究及其动力学意义.地球物理学报,1996,39(2):188~202
[21]Zang SX,Ning JY.The influences of metastable olivine on the negative buoyancy of subduction zones and their geodynamic significance.ActaGeophysica Sinica,2001,44(3):336~345(in Chinese)臧绍先,宁杰远.亚稳态橄榄石对俯冲带负浮力的影响及其动力学意义.地球物理学报,2001,44(3):336~345
[22]Zhu YQ,Shi YL.Shear heating and partial melting of granite——thermal structure at overthrusted terrains in the greater Himalaya.ActaGeophysica Sinica,1990,33(4):408~416(in Chinese)朱元清,石耀霖.剪切生热与花岗岩部分熔融——关于喜马拉雅地区逆冲断层与地壳热结构的分析.地球物理学报,1990,33(4):408~416
[23]Shi YL,Zhu YQ,Shen XJ.Tectonic processes andthermal evolution of the Qinghai-Xizang(Tibetan)Plateau.Acta Geophysica Sinica,1992,35(6):710~720(in Chinese)石耀霖,朱元清,沈显杰.青藏高原构造结构热演化的主要控制因素.地球物理学报,1992,35(6):710~720
[24]Negredo AM,Valera JL,Carminati E.TEMSPOL:a MATLABthermal model for deep subduction zones including major phase transformations.Computers&Geosciences,2004,30:249~258
[25]Turcotte DL,Schubert G.Geodynamics.2nd ed.Cambridge University Press,2002
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