汤加—斐济地区300km间断面的SdP转换波证据
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摘要
上地幔速度间断面的存在形态及其性质的研究对于理解地球构造运动以及地球内部物质运移过程具有重要意义.针对上地幔中可能存在的300km速度间断面,本文收集日本Hi-net地震台网所记录的2004年以来、震源深度在145～219km之间、且震级为mb5.0～6.0之间的6个汤加—斐济地区地震的波形资料.利用4次根倾斜叠加方法对收集到的波形资料进行叠加处理,获得了相应的叠加灰度图,从中提取的离源下行的SdP次生转换震相,进而据此确认了汤加—斐济地区下方的300km深度附近的速度界面.因该界面起伏较小,更倾向于该界面为辉石的斜方到高压单斜相变面;同时基于转换震相的强度差异,我们发现该界面速度跃变量要大于410km间断面,因而俯冲带的化学分异和脱水过程产生的较轻物质可能在该界面处形成一定的聚集,使得汤加—斐济地区的该界面更容易被观测到.
The upper-mantle discontinuities are important for understanding the tectonics and the material transportation in the Earth′s interior.In order to retrieve the SdP conversion phases from the possible 300 km discontinuity,the waveform data of six earthquakes with focal depths between 145 and 219 km and mb5.0~6.0 since 2004 are collected from Hi-net of Japan.The data are processed by 4-th root slant stack method to get the vespegrams which are used to pick the SdP phases based on the theoretical differential times and slownesses.The conversion points related to the SdP phases show that there is a clear and flat velocity interface around 300 km which means the interface is preferred as the orthorhombic to high-pressure monoclinic phase transition of(Mg,Fe)SiO3 pyroxene.What′s more,the velocity contrast of the interface is larger than the 410 km discontinuity,which means that the light chemical differentiation or slab dehydration from the subduction zone accumulated at the interface and makes the interface beneath the Tonga-Fiji more detectable.
The upper-mantle discontinuities are important for understanding the tectonics and the material transportation in the Earth′s interior.In order to retrieve the SdP conversion phases from the possible 300 km discontinuity,the waveform data of six earthquakes with focal depths between 145 and 219 km and mb5.0~6.0 since 2004 are collected from Hi-net of Japan.The data are processed by 4-th root slant stack method to get the vespegrams which are used to pick the SdP phases based on the theoretical differential times and slownesses.The conversion points related to the SdP phases show that there is a clear and flat velocity interface around 300 km which means the interface is preferred as the orthorhombic to high-pressure monoclinic phase transition of(Mg,Fe)SiO3 pyroxene.What′s more,the velocity contrast of the interface is larger than the 410 km discontinuity,which means that the light chemical differentiation or slab dehydration from the subduction zone accumulated at the interface and makes the interface beneath the Tonga-Fiji more detectable.
引文
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[6]Thybo H,Perc'h ucE.The seismic 8°discontinuity andpartial melting in continental mantle.Science,1997,275(5306):1626-1629.
[7]Revenaugh J,Jordan T H.Mantle layering from SCSreverberations 3.The upper mantle.J.Geophys.Res.,1991,96(B12):19781-19810.
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[14]Matsukage K N,Nishihara Y,Karato S I.Seismologicalsignature of chemical differentiation of Earth′s upper mantle.J.Geophys.Res.,2005,110:B12305,doi:10.1029/2004JB003504.
[15]Helffrich G.Topography of the transition zone seismicdiscontinuities.Rev.Geophys.,2000,38(1):141-158.
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[22]Dziewonski A M,Anderson D L.Preliminary reference Earthmodel.Phys.Earth Planet.Inter.,1981,25(4):297-356.
[23]Kennett B L N,Engdahl E R.Traveltimes for globalearthquake location and phase identification.Geophys.J.Int.,1991,105(2):429-465.
[24]Kennett B L N,Engdahl E R,Buland R.Constraints onseismic velocities in the Earth from traveltimes.Geophys J.Int.,1995,122(1):108-124.
[25]Kanasewich E R,Hemmings C D,Alpaslan T.Nth-rootstack nonlinear multichannel filter.Geophysics,1973,38(2):327-338.
[26]McFadden P L,Drummond B J,Karvis S.The Nth-rootstack:theory,applications,and examples.Geophysics,1986,51(10):1879-1892.
[27]臧绍先,周元泽.N次根倾斜叠加方法在间断面研究中的应用.地球物理学报,2002,45(3):407-415.Zang S X,Zhou Y Z.N-th root slant stack and its applicationin study of mantle discontinuities.Chinese J.Geophys.(inChinese),2002,45(3):407-415.
[28]Rost S,Thomas C.Array seismology:methods andapplications.Rev.Geophys.,2002,40:1008,doi:10.1029/2000RG000100.
[29]Niu F L,Kawakatsu H.Direct evidence for the undulation ofthe 660-km discontinuity beneath Tonga:comparison ofJapan and California array data.Geophys.Res.Lett.,1995,22(5):531-534.
[30]周元泽,臧绍先.牡丹江和海拉尔台下方地幔间断面结构及推论.地球物理学报,2001,44(6):761-773.Zhou Y Z,Zang S X.Mantle discontinuities beneath thestations MDJ and HIA and its implications.Chinese J.Geophys.(in Chinese),2001,46(1):761-773.
[31]Gudmundsson,Sambridge M.A regionalized upper mantle(RUM)seismic model.J.Geophys.Res.,1998,103(B4):7121-7136.
[32]Shearer P M.Upper mantle seismic discontinuities.∥Earth′sDeep Interior:Mineral Physics and Tomography from theAtomic to the Global Scale.AGU Geophysical Monograph,2000,117:115-131.
[33]Collier J D,Helffrich G R,Wood B J.Seismic discontinuitiesand subduction zones.Phys.Earth Planet.Inter.,2001,127(1-4):35-49.
[34]周元泽,眭怡.南美地区下地幔速度界面结构研究.地球物理学报,2010,53(1):86-93.Zhou Y Z,Sui Y.On the velocity interfaces in the lowermantle beneath South America.Chinese J.Geophys.(inChinese),2010,53(1):86-93.
[35]van Keken P E,Hacker B R,Syracuse E M,et al.Subduction factory:4.Depth-dependent flux of H2O fromsubducting slabs worldwide.J.Geophys.Res.,2011,116:B01401,doi:10.1029/2010JB007922.
[36]Akaogi M,Yusa H,Shiraishi K,et al.Thermodynamicproperties ofα-quartz,coesite,and stishovite and equilibriumphase relations at high pressures and high temperatures.J.Geophys.Res.,1995,100(B11):22337-22347.
[37]Liu J,Topor L,Zhang J Z,et al.Calorimetric study of thecoesite-stishovite transformation and calculation of the phaseboundary.Phys.Chem.Miner.,1996,23(1):11-16.
[38]Zhang J Z,Li B S,Utsumi W,et al.In situ X-rayobservations of the coesite-stishovite transition:reversedphase boundary and kinetics.Phys.Chem.Miner.,1996,23(1):1-10.
[39]Angel R J,Chopelas A,Ross N L.Stability of high-densityclinoenstatite at upper-mantle pressures.Nature,1992,358(6384):322-324.
[40]Mendelssohn M J,Price G D.Computer modelling of apressure induced phase change in clinoenstatite pyroxenes.Phys.Chem.Miner.,1997,25(1):55-62.
[41]Woodland A B.The orthorhombic to high-P monoclinic phasetransition in Mg-Fe pyroxenes:can it produce a seismicdiscontinuity?Geophys.Res.Lett.,1998,25(8):1241-1244.
[42]Tibi R,Wiens D A.Detailed structure and sharpness ofupper mantle discontinuities in the Tonga subduction zonefrom regional broadband arrays.J.Geophys.Res.,2005,110:B06313,doi:10.1029/2004JB003433.
[43]刘良,杨家喜,章军锋等.超高压岩石中矿物显微出溶结构研究进展、面临问题与挑战.科学通报,2009,54(10):1387-1400.Liu L,Yang J X,Zhang J F,et al.Exsolution microstructuresin ultrahigh-pressure rocks:Progress,controversies and challenges.Chinese Sci.Bull.,2009,54(12):1983-1995,doi:10.1007/s11434-009-0204-5.
[44]Mibe K,Kawamoto T,Matsukage K N,et al.Slab meltingversus slab dehydration in subduction-zone magmatism.Proc.Natl.Acad.Sci.USA,2011,108(20):8177-8182.
[2]Ai Y S,Zheng T Y.The upper mantle discontinuitystructure beneath eastern China.Geophys.Res.Lett.,2003,30(21):2089,doi:10.1029/2003GL017678.
[3]许卫卫,郑天愉,赵亮.华北地区410km间断面和660km间断面结构——克拉通活化的地幔动力学状态探测.中国科学:地球科学,2011,41(5):678-685.Xu W W,Zheng T Y,Zhao L.Mantle dynamics of thereactivating North China Craton:Constraints from thetopographies of the 410-km and 660-km discontinuities.Sci.China Ser.D:Earth Sci.,2011,54(6):881-887,doi:10.1007/s11430-010-4163-0.
[4]Lehmann I.S and the structure of the upper mantle.Geophys.J.R.Astron.Soc.,1961,4:124-138.
[5]Vidale J E,Benz H M.Upper-mantle seismic discontinuitiesand the thermal structure of subduction zones.Nature,1992,356(6371):678-683.
[6]Thybo H,Perc'h ucE.The seismic 8°discontinuity andpartial melting in continental mantle.Science,1997,275(5306):1626-1629.
[7]Revenaugh J,Jordan T H.Mantle layering from SCSreverberations 3.The upper mantle.J.Geophys.Res.,1991,96(B12):19781-19810.
[8]Xu F,Vidale J E,Earle P S,et al.Mantle discontinuitiesunder southern Africa from precursors to P′P′df.Geophys.Res.Lett.,1998,25(4):571-574.
[9]Deuss A,Woodhouse J H.The nature of the Lehmanndiscontinuity from its seismological Clapeyron slopes.EarthPlanet.Sci.Lett.,2004,225(3-4):295-304.
[10]Zheng Y C,Lay T,Flanagan M P,et al.Pervasive seismicwave reflectivity and metasomatism of the Tonga mantlewedge.Science,2007,316(5826):855-859.doi:10.1126/science.1138074.
[11]Deuss A.Global observations of mantle discontinuities usingSS and PP precursors.Surv.Geophys.,2009,30(4-5):301-326.doi:10.1007/s10712-009-9078-y.
[12]Deuss A,Woodhouse J H.A systematic search for mantlediscontinuities using SS-precursors.Geophys.Res.Lett.,2002,29(8):1249,doi:1029/2002GL014768.
[13]Williams Q,Revenaugh J.Ancient subduction,mantleeclogite,and the 300 km seismic discontinuity.Geology,2005,33(1):1-4.
[14]Matsukage K N,Nishihara Y,Karato S I.Seismologicalsignature of chemical differentiation of Earth′s upper mantle.J.Geophys.Res.,2005,110:B12305,doi:10.1029/2004JB003504.
[15]Helffrich G.Topography of the transition zone seismicdiscontinuities.Rev.Geophys.,2000,38(1):141-158.
[16]Zang S X,Zhou Y Z,Ning J Y,et al.Multiplediscontinuities near 660km beneath Tonga area.Geophys.Res.Lett.,2006,33:L20312.doi:10.1029/2006GL027262.
[17]Obara K.Hi-net:high sensitivity seismograph network,Japan.//Takanami T,Kitagawa G eds.Lecture Notes inEarth Sciences.Methods and Applications of Signal Processing inSeismic Network Operations.Berlin:Springer,2003,98:79-88.
[18]Kawakatsu H,Watada S.Seismic evidence for deep-watertransportation in the mantle.Science,2007,316(5830):1468-1471.
[19]Zhao D P,Wang Z,Umino N,et al.Tomographic imagingoutside a seismic network:application to the northeast Japanarc.Bull.Seism.Soc.Am.,2007,97(4):1121-1132,doi:10.1785/0120050256.
[20]Engdahl E R,van der Hilst R,Buland R.Global teleseismicearthquake relocation with improved travel times andprocedures for depth determination.Bull.Seism.Soc.Am.,1998,88(3):722-743.
[21]Castle J C,Creager K C.Local sharpness and shear wavespeed jump across the 660-km discontinuity.J.Geophys.Res.,2000,105(B3):6191-6200.
[22]Dziewonski A M,Anderson D L.Preliminary reference Earthmodel.Phys.Earth Planet.Inter.,1981,25(4):297-356.
[23]Kennett B L N,Engdahl E R.Traveltimes for globalearthquake location and phase identification.Geophys.J.Int.,1991,105(2):429-465.
[24]Kennett B L N,Engdahl E R,Buland R.Constraints onseismic velocities in the Earth from traveltimes.Geophys J.Int.,1995,122(1):108-124.
[25]Kanasewich E R,Hemmings C D,Alpaslan T.Nth-rootstack nonlinear multichannel filter.Geophysics,1973,38(2):327-338.
[26]McFadden P L,Drummond B J,Karvis S.The Nth-rootstack:theory,applications,and examples.Geophysics,1986,51(10):1879-1892.
[27]臧绍先,周元泽.N次根倾斜叠加方法在间断面研究中的应用.地球物理学报,2002,45(3):407-415.Zang S X,Zhou Y Z.N-th root slant stack and its applicationin study of mantle discontinuities.Chinese J.Geophys.(inChinese),2002,45(3):407-415.
[28]Rost S,Thomas C.Array seismology:methods andapplications.Rev.Geophys.,2002,40:1008,doi:10.1029/2000RG000100.
[29]Niu F L,Kawakatsu H.Direct evidence for the undulation ofthe 660-km discontinuity beneath Tonga:comparison ofJapan and California array data.Geophys.Res.Lett.,1995,22(5):531-534.
[30]周元泽,臧绍先.牡丹江和海拉尔台下方地幔间断面结构及推论.地球物理学报,2001,44(6):761-773.Zhou Y Z,Zang S X.Mantle discontinuities beneath thestations MDJ and HIA and its implications.Chinese J.Geophys.(in Chinese),2001,46(1):761-773.
[31]Gudmundsson,Sambridge M.A regionalized upper mantle(RUM)seismic model.J.Geophys.Res.,1998,103(B4):7121-7136.
[32]Shearer P M.Upper mantle seismic discontinuities.∥Earth′sDeep Interior:Mineral Physics and Tomography from theAtomic to the Global Scale.AGU Geophysical Monograph,2000,117:115-131.
[33]Collier J D,Helffrich G R,Wood B J.Seismic discontinuitiesand subduction zones.Phys.Earth Planet.Inter.,2001,127(1-4):35-49.
[34]周元泽,眭怡.南美地区下地幔速度界面结构研究.地球物理学报,2010,53(1):86-93.Zhou Y Z,Sui Y.On the velocity interfaces in the lowermantle beneath South America.Chinese J.Geophys.(inChinese),2010,53(1):86-93.
[35]van Keken P E,Hacker B R,Syracuse E M,et al.Subduction factory:4.Depth-dependent flux of H2O fromsubducting slabs worldwide.J.Geophys.Res.,2011,116:B01401,doi:10.1029/2010JB007922.
[36]Akaogi M,Yusa H,Shiraishi K,et al.Thermodynamicproperties ofα-quartz,coesite,and stishovite and equilibriumphase relations at high pressures and high temperatures.J.Geophys.Res.,1995,100(B11):22337-22347.
[37]Liu J,Topor L,Zhang J Z,et al.Calorimetric study of thecoesite-stishovite transformation and calculation of the phaseboundary.Phys.Chem.Miner.,1996,23(1):11-16.
[38]Zhang J Z,Li B S,Utsumi W,et al.In situ X-rayobservations of the coesite-stishovite transition:reversedphase boundary and kinetics.Phys.Chem.Miner.,1996,23(1):1-10.
[39]Angel R J,Chopelas A,Ross N L.Stability of high-densityclinoenstatite at upper-mantle pressures.Nature,1992,358(6384):322-324.
[40]Mendelssohn M J,Price G D.Computer modelling of apressure induced phase change in clinoenstatite pyroxenes.Phys.Chem.Miner.,1997,25(1):55-62.
[41]Woodland A B.The orthorhombic to high-P monoclinic phasetransition in Mg-Fe pyroxenes:can it produce a seismicdiscontinuity?Geophys.Res.Lett.,1998,25(8):1241-1244.
[42]Tibi R,Wiens D A.Detailed structure and sharpness ofupper mantle discontinuities in the Tonga subduction zonefrom regional broadband arrays.J.Geophys.Res.,2005,110:B06313,doi:10.1029/2004JB003433.
[43]刘良,杨家喜,章军锋等.超高压岩石中矿物显微出溶结构研究进展、面临问题与挑战.科学通报,2009,54(10):1387-1400.Liu L,Yang J X,Zhang J F,et al.Exsolution microstructuresin ultrahigh-pressure rocks:Progress,controversies and challenges.Chinese Sci.Bull.,2009,54(12):1983-1995,doi:10.1007/s11434-009-0204-5.
[44]Mibe K,Kawamoto T,Matsukage K N,et al.Slab meltingversus slab dehydration in subduction-zone magmatism.Proc.Natl.Acad.Sci.USA,2011,108(20):8177-8182.
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