伊豆-小笠原和汤加地区中地幔多层速度结构差异性研究
摘要
中部地幔间断面的存在及其性质对于理解地球内部对流过程并对地球化学和矿物物理学的约束均具有重要意义.本文通过利用美国西部高密度短周期地震台网记录的汤加和伊豆-小笠原地区的深震波形资料的倾斜叠加处理,进而从中提取离源下行的次生转换震相SdP,据此分析两个俯冲区域的中部地幔速度界面的差异性存在:(1)伊豆-小笠原地区对应于"920km"间断面的深度应该位于910km,而汤加地区则存在着两个速度跃变面,分别位于850和950km处;(2)两个地区均存在着1000和1050km深度附近一定的转换点集中;(3)两个地区在1100km深度处都存在着比较明确的转换点集中,同时伊豆-小笠原地区在更深处的1168km附近存在转换点集中,而汤加地区相应的界面则存在于1200km深度附近.这样的复杂结构与铁在地幔主要岩石组分铁-镁钙钛矿和铁-镁方铁矿的配比不同造成的密度异常有关,同时汤加和伊豆-小笠原两个俯冲区间存在的差异性速度结构与两者不同的俯冲板片形态和残留有很密切的关联.
引文
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31Irifune T,Shinmei T,McCammon C A,et al.Iron partitioning and density changes of pyrolite in earth’s lower mantle.Science,2010,327:193–195
32Hirose K.Deep mantle properties.Science,2010,327:151–152
2Kennett B L N,Engdahl E R.Travel times for global earthquake location and phase association.Geophys J Int,1991,105:429–465
3Kennett B L N.Engdahl E R,Buland R.Constraints on seismic velocities in the Earth from travel times.Geophys J Int,1995,122:108–124
4Kárason H,van der Hilst R D.Constraints on mantle convection from seismic tomography.In:Richards M R,Gordon R,Van der Hilst R D,eds.The History and Dynamics of Global Plate Motion.Washington DC:American Geophysical Union.Geophy Monograph,2000,121:277–288
5Gorbatov A,Fukao Y,Widiyantoro S.Application of a three-dimensional ray-tracing technique to global P,PP and Pdiff traveltime tomography.Geophys J Inter,2001,146:583–593
6Hager B H,Clayton R W,Richards M A,et al.Lower mantle heterogeneity,dynamic topography and the geoid.Nature,1985,313:541–545
7Tanimoto T.Predominance of large-scale heterogeneity and the shift of velocity anomalies between the upper and the lower mantle.J Phys Earth,1990,38:493–509
8Wen L,Anderson D L.The fate of the slabs inferred from seismic tomography and130Ma subduction.Earth Planet Sci Lett,1995,133:185–198
9Anderson D L.New Theory of the Earth.Cambridge:Cambridge University Press,2007
10Kellogg L H,Hager B H,Van Der Hilst R D.Compositional stratification in the deep mantle.Science,1999,283:1881–1884
11Huang J,Zhao D.High-resolution mantle tomography of China and surrounding regions.J Geophys Res,2006,111:B09305,doi:10.1029/2005JB004066
12Niu F,Kawakatsu H,Fukao Y.Seismic evidence for a chemical heterogeneity in the midmantle:A strong and slightly dipping seismic reflector beneath the Mariana subduction zone.J Geophys Res,2003,108:2419,doi:10.1029/2002JB002384
13Castle J C,van der Hilst R D.Searching for seismic scattering off mantle interfaces between800km and2000km depth.J Geophys Res,2003,108(B2):2095,doi:10.1029/2001JB000286
14Courtier A M,Revenaugh J.Slab and shear wave reflectors in the midmantle.J Geophy Res,2008,113:B08312,doi:10.1029/2007JB005261
15Shen Y,Wolfe C J,Solomon S C.Seismic evidence for a lower mantle discontinuity beneath Hawaii and Iceland.Earth Planet Sci Lett,2003,214:143–151
16Kawakatsu H,Niu F.Seismic evidence for a920-km discontinuity.Nature,1994,371:301–305
17Wicks C W,Richards M A.Seismic evidence for1200km discontinuity.EOS Trans Am Geophys Un,1993,43(Suppl):550
18Niu F,Kawakatsu H.Depth variation of the mid-mantle seismic discontinuity.Geophys Res Lett,1997,24:429–432
19Vanacore E,Niu F,Kawakatsu H.Observations of the mid-mantle discontinuity beneath Indonesia from S to P converted waveforms.Geophys Res Lett,2006,33,doi:10.1029/2005GL025106
20Van der Meijde M,Marone F,Giardini D,et al.Seismic evidence for water deep in earth’s upper mantle.Science,2003,300:1556–1558
21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,2010,53:86–93,doi:10.3969/j.issn.0001-5733.2010.01.009
22臧绍先,宁杰远.西太平洋俯冲带研究及其动力学意义.地球物理学报,1996,39:188–202
23Fukao Y,Widiyantoro S,Obayashi M.Stagnant slabs in the upper and lower mantle transition region.Rev Geophys,2001,39:291–323
24Helffrich G.Topography of the transition zone seismic discontinuities.Rev Geophys,2000,38:141–158
25Collier J D,Helffrich G R,Wood B J.Seismic discontinuities and subduction zones.Phys Earth Planet Inter,2001,127:35–49
26Tibi R,Wiens D A.Detailed structure and sharpness of upper mantle discontinuities in the Tonga subduction zone from regional broadband arrays.J Geophys Res,2005,110,doi:10.1029/2004JB003433
27Zang S X,Zhou Y Z,Ning J Y,et al.Multiple discontinuities near660km beneath Tonga area.Geophys Res Lett,2006,33,doi:10.1029/2006GL027262
28Vinnik L,Kato M,Kawakatsu H.Search for seismic discontinuities in the lower mantle.Geophys J Int,2001,147:41–56
29Castle J C,Creager K C.Local sharpness and shear wave speed jump across the660-km discontinuity.J Geophys Res,2000,105:6191–6200
30Wen L,Anderson D L.Layered mantle convection:A model for geoid and topography.Earth Planet Sci Lett,1997,146:367–377
31Irifune T,Shinmei T,McCammon C A,et al.Iron partitioning and density changes of pyrolite in earth’s lower mantle.Science,2010,327:193–195
32Hirose K.Deep mantle properties.Science,2010,327:151–152
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