核幔边界D″区的地震学研究进展
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摘要
核幔边界层在地球演化过程中扮演着极为重要的作用,是人们认识地球的主要研究对象之一。文中综述了近十多年来对核幔边界D″区开展地震学研究的主要方法及成果,内容涵盖了核幔边界D″区上部间断面、不均匀性、各向异性和超低速层等4个主要研究对象。结合多个相关学科的研究进展,从对热-化学-动力学三方面的耦合作用的分析,来探讨形成D″区各种观测现象的原因和机制,以及在此基础上提出的动力学演化模型。最后简要叙述了有关核幔边界研究的地震学、矿物实验、理论分析及计算科学的发展方向和挑战。随着对D″区认识的不断更新,逐步揭示地表观测到的可能受核幔边界因素控制的多种地质及地球物理现象。
The core-mantle boundary(CMB) layer plays a significant role in the evolution of both the Earth's mantle and core. This paper outlines the generally used methods and vigorously debated results in seismological measurement about the core-mantle boundary and the D double prime region (or the Earth's lowermost mantle) during the last decades. The heterogeneity and anisotropy of the D″ discontinuity are discussed in detail, as well as those of the ultra-low velocity zones just above the core-mantle boundary. Mechanisms of observations in the D″ region are discussed using the coupling of thermal, chemical and dynamical factors, combining the research progresses of other disciplines; two dynamic models are proposed based on their coupling mechanism. The challenges for future research in seismological, mineral experiments, theoretical and computational geophysics have emerged. A reasonable model is necessary and expected to explain various Earth's surface observed geological, geochemical, and geophysical phenomena controlled by the lowermost mantle.
The core-mantle boundary(CMB) layer plays a significant role in the evolution of both the Earth's mantle and core. This paper outlines the generally used methods and vigorously debated results in seismological measurement about the core-mantle boundary and the D double prime region (or the Earth's lowermost mantle) during the last decades. The heterogeneity and anisotropy of the D″ discontinuity are discussed in detail, as well as those of the ultra-low velocity zones just above the core-mantle boundary. Mechanisms of observations in the D″ region are discussed using the coupling of thermal, chemical and dynamical factors, combining the research progresses of other disciplines; two dynamic models are proposed based on their coupling mechanism. The challenges for future research in seismological, mineral experiments, theoretical and computational geophysics have emerged. A reasonable model is necessary and expected to explain various Earth's surface observed geological, geochemical, and geophysical phenomena controlled by the lowermost mantle.
引文
[1]LAY T,WILLI AMS Q,GARNERO E J.The core-mantle boundary layer and deep Earth dynamics[J].Nature,1998,392:461-468.
[2]LAY T,GARNERO E J.Core-mantle boundary structures and processes[M]//SPARKS R S J,HAWKESWORTH C J.The state of the planet:frontiers and challenges in geo-physics.Geophysical Monograph150,I UGG Volume19,2004,doi:10.1029/150GM04.
[3]GARNERO EJ.The structure of Earth s dynamic deep man-tle and core-mantle boundary region[J].Global Tectonics Metallogeny,June2003,8(1-4).
[4]GARNERO E J,MAUPI N V,LAY T,et al.Variable azi-muthal anisotropy in Earth s lowermost mantle[J].Science,2004,306(5694).
[5]RUSSELL S,LAY T,GARNERO E J.Small scale lateral shear velocity and anisotropy heterogeneity near the core-mantle boundary beneath the central Pacific i maged using broadband ScS waves[J].J Geophys Res,1999,104(13):183-199.
[6]GARNERO E J,LAY T.D″Shear velocity heterogeneity,anisotropy and discontinuity structure beneath the Caribbean and Central America[J].Phys Earth Planet Int,2003,140:219-242.
[7]WYSESSION M E,LAY T,REVENAUGHJ S,et al.The D″discontinuity andits i mplications[M]//GURNIS M,WY-SESSION ME,KNITTLE E,et al.The core-mantle bound-ary region.Washington,DC:AGU,1998:273-297.
[8]KENDALL J M,SHEARER P M.Lateral variations in D″thickness fromlong-period shear wave data[J].J Geophys Res,1994,99(B6):11575-11590.
[9]TROMP J,DZIEWONSKI A M.Two views of the deep mantle[J].Science,1998,281:655-656.
[10]LAY T,GARNERO E J,YOUNG C J.Scale-lengths of het-erogeneity at the base of the mantle from S-wave differentialtravel ti mes[J].J Geophys Res,1997,102:9887-9909.
[11]KITO T,KR GER F,NEGISHI H.Seismic heterogeneous structure in the lowermost mantle beneath the southwestern Pacific[J].J Geophys Res,2004,109:B09304,doi:10.1029/2003JB002677.
[12]YAMADA A,NAKANISHI I.Detection of P wave reflec-tionin D″beneath the southwestern Pacific using double-ar-ray stacking[J].Geophys Res Lett,1996,23:1553-1556.
[13]RUSSELL S A,REASONER C,LAY T,et al.Coexisting shear-and compressional-wave seismic velocity discontinuities beneath the central Pacific[J].Geophys Res Lett,2001,28:2281-2284.
[14]ROST S,REVENAUGHJ S.Detection of a D″discontinuity in the south Atlantic using PKKP[J].Geophys Res Lett,2003,30(16),1840,doi:10.1029/2003GL017585.
[15]EDMOND K MS,van der HILST R D.Core mantle bounda-ry topography fromshort period PcP,PKP,and PKKP data[J].Physics of the Earth and Planetary Interiors,2003,135:27-46.
[16]ROST S,REVENAUGHJ S.Small-scale changes of core-mantle boundary reflectivity studied using core reflected PcP[J].Physics of the Earth and Planetary Interiors,2004,145:19-36.
[17]LOPER D E,LAY T.The core-mantle boundary region[J].J Geophys Res,1995,100(B4):6397-6420.
[18]EARLE P S,SHEARER P M.Observations of PKKP pre-cursors used to esti mate small-scale topography on the core-mantle boundary[J].Science,1997,227.
[19]MURPHY F E,NEUBERGJ W,JACOB A WB.Alterna-tives to core-mantle boundary topography[J].Physics of the Earth and Planetary Interiors,1997,103:349-364.
[20]WYSESSION M E,BARTKO L,WILSON J B.Mapping the lowermost mantle using core-reflected shear waves[J].J Geophys Res,1994,99:13667-13684.
[21]GARNERO E J.Lower mantle heterogeneity[J].Ann Rev Earth Planetary Sci,2000,28:509-537.
[22]WYSESSION M E.Large-scale structure at the core-mantle boundary fromcore-diffracted waves[J].Nature,1996,382:244-248.
[23]ZHAO D.Global tomographic i mages of mantle plumes and subducting slabs:insight into deep Earth dynamic[J].Phys-ics of the Earth and Planetary Interiors,2004,146:3-34.
[24]GRAND S P.Mantle shear-wave tomography and the fate of subducted slabs[J].Phil Trans R Soc Lond A,2002,360:2475-2491.
[25]GARNERO E J,LAY T.D″shear velocity heterogeneity,anisotropy and discontinuity structure beneath the Caribbean and Central America[J].Physics of the Earth and Planetary Interiors,2003,140:219-242.
[26]RITSEMA J,GARNERO E,LAY T.A strong negative shear velocity gradient andlateral variabilityinthelowermost mantle beneath the Pacific[J].J Geophys Res,1997,102(B9):20395-20411.
[27]WEN L,HELMBERGER D V.A2-D P-SV hybrid method and its application to modeling localized structures near the core-mantle boundary[J].J Geophys Res,1998,103:17901-17918.
[28]WEN L.An SHhybrid method and shear velocity structures in thelowermost mantle beneaththe central Pacific and South Atlantic oceans[J].J Geophys Res,2002,107:10.1029/2001JB000499.
[29]WEN L,HELMBERGER D V.Ultra lowvelocity zones near the core-mantle boundary from broadband PKP precursors[J].Science,1998,279:1701-1703.
[30]WEN L.Seismic evidence for a rapidly varying compositional anomaly at the base of the Earth s mantle beneath the Indian ocean[J].Earth Planet Sci Lett,2001,194:83-95.
[31]WEN L,SILVER P,JAMES D.Seismic evidence for a ther-mo-chemical boundary layer at the base of the Earth s mantle[J].Earth Planet Sci Lett,2001,189:141-153.
[32]WANG YI,WEN Lianxing.Mapping the geometry and geo-graphic distribution of a verylowvelocity province at the base of the Earth s mantle[J].J Geophys Res,2004,109:B10305,doi:10.1029/2003JB002674.
[33]LAY T,WILLI AMS Q,GARNERO EJ,et al.Seismic wave anisotropyin the D″region and its i mplications[M]//GUR-NIS M,WYSESSION M,KNITTLE E,et al.The core-mantle boundary region.AGU,Washington,D.C:1998:229-318.
[34]NI U F,PEREZ A M.Seismic anisotropy in the lower man-tle:a comparison of waveform splitting of SKS and SKKS[J].Geophys Res Lett,2004,31:10.1029/2004GL021196.
[35]GARNERO E J,LAY T.Lateral variations in lowermost mantle shear wave anisotropy beneath the north Pacific and Alaska[J].J Geophys Res,1997,102,8121-8135.
[36]RUSSELL S A,LAY T,GARNERO E J.Seismic evidence for small-scale dynamics in the lowermost mantle at the root of the Hawaiian hotspot[J].Nature,1998,369:255-257.
[37]MEADE C,SILVER P G,KANESHI MAS.Laboratory and seismological observations of lower mantle isotropy[J].Geo-phys Res Lett,1995,22:1293-1296.
[38]GARNERO EJ,THORNE M.Earth s ULVZ:ultra-lowve-locity zone[M]//Encyclopedia of geomagnetism and paleo-magnetism.The Netherlands:Kluwer Publishing,2005(in press).
[39]WILLI AMS Q,GARNERO EJ.Seismic evidence for partial melt at the base of Earth s mantle[J].Science,1996,273:1528-1530.
[40]GARNERO E J,GRAND S P,HELMBERGER D V.Low P-wave velocity at the base of the mantle[J].Geophys Res Lett,1993,20:1843-1846.
[41]GARNERO E J,VIDALE J E.ScP:a probe of ultralow ve-locity zones at the base of the mantle[J].Geophys Res Lett,1999,26:377-380.
[42]CASTLE J C,van der HILST R D.The core-mantle bounda-ry under the Gulf of Alaska:no ULVZ for shear waves[J].Earth Planet Sci Lett,2000,176,311-321.
[43]ROST S,REVENAUGHJ S.Small scale ultralow-velocity zone structurei maged by ScP[J].J Geophys Res,2003,108:B1,2056,doi:10.1029/2001JB001627.
[44]ROST S,REVENAUGHJ S.Lateral variation of the small-scale structure at the CMB west of Tonga-Fiji[C].AGUFall Meeting San Francisco,2001.
[45]VIDALE J E,HEDLI N M.Evidence for partial melt at the core mantle boundary north of Tonga fromthe strong scatter-ing of seismic waves[J].Nature,1998,391:682-685.
[46]WEN L.Intense seismic scattering near the Earth s core-mantle boundary beneath the Comoros hotspot[J].Geophys Res Lett,2000,27:3627-3630.
[47]GARNERO E J,HELMBERGER D V.Further structural constraints and uncertainties of a thin laterally varying ul-tralow-velocity layer at the base of the mantle[J].J Geophys Res,1998,103:12495-12509.
[48]HELMBERGER D V,WEN L,DI NG X.Seismic evidence that the source of Iceland hotspot lies at the core-mantle boundary[J].Nature,1998,396:251-255.
[49]GARNERO E J,HELMBERGER D V.Seismic detection of a thinlaterally varying boundarylayer at the base of the man-tle beneath the central-Pacific[J].Geophys Res Lett,1996,23:977-980.
[50]HELMBERGER D V,GARNERO E J,DI NG X.Modeling two-di mensional structure at the core-mantle boundary[J].J Geophys Res,1999,101:13963-13972.
[51]GARNERO E J,REVENAUGHJ S,WILLI AMS Q,LAY T,et al.Ultralowvelocity zone at the core-mantle boundary[M]//GURNIS M,WYSESSION M,KNITTLE E,et al.The core-mantle boundary.Washington,D.C:American Ge-ophysical Union,1998:319-334
[52]ROST S,REVENAUGH J S.Seismic detection of rigid zones at the top of the core[J].Science,2001,294:1911-1914.
[53]BUFFETT B A,GARNERO E J,JEANLOZ R.Sedi ments at the top of the Earth s core[J].Science,2000,290:1338-1342.
[54]GARNERO EJ,JEANLOZ R.Fuzzy patches on the Earth s core-mantle boundary[J]?Geophys Res Lett,2000,27:2777-2780.
[55]SIDORI N I,GURNIS M,HELMBERGER D V.Evidence for a ubiquitous seismic discontinuity at the base of the man-tle[J].Science,1999,286:1326-1331.
[56]MAUPI N V,GARNERO EJ,LAY T,et al.Azi muthal ani-sotropy in the D″layer beneath the Caribbean[J].J Geophys Res,2005(in review).
[57]DOBSON D P,BRODHOLTJ P.Subducted bandedironfor-mations as a source of ultralow-velocity zones at the core?mantle boundary[J].Nature,2005,434:371-374.
[58]WILLI AMS Q,REVENAUGHJ S,GARNERO EJ.Acor-relation between ultralow basal velocities in the mantle and hotspots[J].Science,1998,281:546-549.
[59]MURAKAMI M,HIROSE K,SATA N,et al.Post-perovs-kite phase transition and mineral chemistry in the pyrolitic lowermost mantle[J].Geophys Res Lett,2005,32:L03304,doi:10.1029/2004GL021956.
[2]LAY T,GARNERO E J.Core-mantle boundary structures and processes[M]//SPARKS R S J,HAWKESWORTH C J.The state of the planet:frontiers and challenges in geo-physics.Geophysical Monograph150,I UGG Volume19,2004,doi:10.1029/150GM04.
[3]GARNERO EJ.The structure of Earth s dynamic deep man-tle and core-mantle boundary region[J].Global Tectonics Metallogeny,June2003,8(1-4).
[4]GARNERO E J,MAUPI N V,LAY T,et al.Variable azi-muthal anisotropy in Earth s lowermost mantle[J].Science,2004,306(5694).
[5]RUSSELL S,LAY T,GARNERO E J.Small scale lateral shear velocity and anisotropy heterogeneity near the core-mantle boundary beneath the central Pacific i maged using broadband ScS waves[J].J Geophys Res,1999,104(13):183-199.
[6]GARNERO E J,LAY T.D″Shear velocity heterogeneity,anisotropy and discontinuity structure beneath the Caribbean and Central America[J].Phys Earth Planet Int,2003,140:219-242.
[7]WYSESSION M E,LAY T,REVENAUGHJ S,et al.The D″discontinuity andits i mplications[M]//GURNIS M,WY-SESSION ME,KNITTLE E,et al.The core-mantle bound-ary region.Washington,DC:AGU,1998:273-297.
[8]KENDALL J M,SHEARER P M.Lateral variations in D″thickness fromlong-period shear wave data[J].J Geophys Res,1994,99(B6):11575-11590.
[9]TROMP J,DZIEWONSKI A M.Two views of the deep mantle[J].Science,1998,281:655-656.
[10]LAY T,GARNERO E J,YOUNG C J.Scale-lengths of het-erogeneity at the base of the mantle from S-wave differentialtravel ti mes[J].J Geophys Res,1997,102:9887-9909.
[11]KITO T,KR GER F,NEGISHI H.Seismic heterogeneous structure in the lowermost mantle beneath the southwestern Pacific[J].J Geophys Res,2004,109:B09304,doi:10.1029/2003JB002677.
[12]YAMADA A,NAKANISHI I.Detection of P wave reflec-tionin D″beneath the southwestern Pacific using double-ar-ray stacking[J].Geophys Res Lett,1996,23:1553-1556.
[13]RUSSELL S A,REASONER C,LAY T,et al.Coexisting shear-and compressional-wave seismic velocity discontinuities beneath the central Pacific[J].Geophys Res Lett,2001,28:2281-2284.
[14]ROST S,REVENAUGHJ S.Detection of a D″discontinuity in the south Atlantic using PKKP[J].Geophys Res Lett,2003,30(16),1840,doi:10.1029/2003GL017585.
[15]EDMOND K MS,van der HILST R D.Core mantle bounda-ry topography fromshort period PcP,PKP,and PKKP data[J].Physics of the Earth and Planetary Interiors,2003,135:27-46.
[16]ROST S,REVENAUGHJ S.Small-scale changes of core-mantle boundary reflectivity studied using core reflected PcP[J].Physics of the Earth and Planetary Interiors,2004,145:19-36.
[17]LOPER D E,LAY T.The core-mantle boundary region[J].J Geophys Res,1995,100(B4):6397-6420.
[18]EARLE P S,SHEARER P M.Observations of PKKP pre-cursors used to esti mate small-scale topography on the core-mantle boundary[J].Science,1997,227.
[19]MURPHY F E,NEUBERGJ W,JACOB A WB.Alterna-tives to core-mantle boundary topography[J].Physics of the Earth and Planetary Interiors,1997,103:349-364.
[20]WYSESSION M E,BARTKO L,WILSON J B.Mapping the lowermost mantle using core-reflected shear waves[J].J Geophys Res,1994,99:13667-13684.
[21]GARNERO E J.Lower mantle heterogeneity[J].Ann Rev Earth Planetary Sci,2000,28:509-537.
[22]WYSESSION M E.Large-scale structure at the core-mantle boundary fromcore-diffracted waves[J].Nature,1996,382:244-248.
[23]ZHAO D.Global tomographic i mages of mantle plumes and subducting slabs:insight into deep Earth dynamic[J].Phys-ics of the Earth and Planetary Interiors,2004,146:3-34.
[24]GRAND S P.Mantle shear-wave tomography and the fate of subducted slabs[J].Phil Trans R Soc Lond A,2002,360:2475-2491.
[25]GARNERO E J,LAY T.D″shear velocity heterogeneity,anisotropy and discontinuity structure beneath the Caribbean and Central America[J].Physics of the Earth and Planetary Interiors,2003,140:219-242.
[26]RITSEMA J,GARNERO E,LAY T.A strong negative shear velocity gradient andlateral variabilityinthelowermost mantle beneath the Pacific[J].J Geophys Res,1997,102(B9):20395-20411.
[27]WEN L,HELMBERGER D V.A2-D P-SV hybrid method and its application to modeling localized structures near the core-mantle boundary[J].J Geophys Res,1998,103:17901-17918.
[28]WEN L.An SHhybrid method and shear velocity structures in thelowermost mantle beneaththe central Pacific and South Atlantic oceans[J].J Geophys Res,2002,107:10.1029/2001JB000499.
[29]WEN L,HELMBERGER D V.Ultra lowvelocity zones near the core-mantle boundary from broadband PKP precursors[J].Science,1998,279:1701-1703.
[30]WEN L.Seismic evidence for a rapidly varying compositional anomaly at the base of the Earth s mantle beneath the Indian ocean[J].Earth Planet Sci Lett,2001,194:83-95.
[31]WEN L,SILVER P,JAMES D.Seismic evidence for a ther-mo-chemical boundary layer at the base of the Earth s mantle[J].Earth Planet Sci Lett,2001,189:141-153.
[32]WANG YI,WEN Lianxing.Mapping the geometry and geo-graphic distribution of a verylowvelocity province at the base of the Earth s mantle[J].J Geophys Res,2004,109:B10305,doi:10.1029/2003JB002674.
[33]LAY T,WILLI AMS Q,GARNERO EJ,et al.Seismic wave anisotropyin the D″region and its i mplications[M]//GUR-NIS M,WYSESSION M,KNITTLE E,et al.The core-mantle boundary region.AGU,Washington,D.C:1998:229-318.
[34]NI U F,PEREZ A M.Seismic anisotropy in the lower man-tle:a comparison of waveform splitting of SKS and SKKS[J].Geophys Res Lett,2004,31:10.1029/2004GL021196.
[35]GARNERO E J,LAY T.Lateral variations in lowermost mantle shear wave anisotropy beneath the north Pacific and Alaska[J].J Geophys Res,1997,102,8121-8135.
[36]RUSSELL S A,LAY T,GARNERO E J.Seismic evidence for small-scale dynamics in the lowermost mantle at the root of the Hawaiian hotspot[J].Nature,1998,369:255-257.
[37]MEADE C,SILVER P G,KANESHI MAS.Laboratory and seismological observations of lower mantle isotropy[J].Geo-phys Res Lett,1995,22:1293-1296.
[38]GARNERO EJ,THORNE M.Earth s ULVZ:ultra-lowve-locity zone[M]//Encyclopedia of geomagnetism and paleo-magnetism.The Netherlands:Kluwer Publishing,2005(in press).
[39]WILLI AMS Q,GARNERO EJ.Seismic evidence for partial melt at the base of Earth s mantle[J].Science,1996,273:1528-1530.
[40]GARNERO E J,GRAND S P,HELMBERGER D V.Low P-wave velocity at the base of the mantle[J].Geophys Res Lett,1993,20:1843-1846.
[41]GARNERO E J,VIDALE J E.ScP:a probe of ultralow ve-locity zones at the base of the mantle[J].Geophys Res Lett,1999,26:377-380.
[42]CASTLE J C,van der HILST R D.The core-mantle bounda-ry under the Gulf of Alaska:no ULVZ for shear waves[J].Earth Planet Sci Lett,2000,176,311-321.
[43]ROST S,REVENAUGHJ S.Small scale ultralow-velocity zone structurei maged by ScP[J].J Geophys Res,2003,108:B1,2056,doi:10.1029/2001JB001627.
[44]ROST S,REVENAUGHJ S.Lateral variation of the small-scale structure at the CMB west of Tonga-Fiji[C].AGUFall Meeting San Francisco,2001.
[45]VIDALE J E,HEDLI N M.Evidence for partial melt at the core mantle boundary north of Tonga fromthe strong scatter-ing of seismic waves[J].Nature,1998,391:682-685.
[46]WEN L.Intense seismic scattering near the Earth s core-mantle boundary beneath the Comoros hotspot[J].Geophys Res Lett,2000,27:3627-3630.
[47]GARNERO E J,HELMBERGER D V.Further structural constraints and uncertainties of a thin laterally varying ul-tralow-velocity layer at the base of the mantle[J].J Geophys Res,1998,103:12495-12509.
[48]HELMBERGER D V,WEN L,DI NG X.Seismic evidence that the source of Iceland hotspot lies at the core-mantle boundary[J].Nature,1998,396:251-255.
[49]GARNERO E J,HELMBERGER D V.Seismic detection of a thinlaterally varying boundarylayer at the base of the man-tle beneath the central-Pacific[J].Geophys Res Lett,1996,23:977-980.
[50]HELMBERGER D V,GARNERO E J,DI NG X.Modeling two-di mensional structure at the core-mantle boundary[J].J Geophys Res,1999,101:13963-13972.
[51]GARNERO E J,REVENAUGHJ S,WILLI AMS Q,LAY T,et al.Ultralowvelocity zone at the core-mantle boundary[M]//GURNIS M,WYSESSION M,KNITTLE E,et al.The core-mantle boundary.Washington,D.C:American Ge-ophysical Union,1998:319-334
[52]ROST S,REVENAUGH J S.Seismic detection of rigid zones at the top of the core[J].Science,2001,294:1911-1914.
[53]BUFFETT B A,GARNERO E J,JEANLOZ R.Sedi ments at the top of the Earth s core[J].Science,2000,290:1338-1342.
[54]GARNERO EJ,JEANLOZ R.Fuzzy patches on the Earth s core-mantle boundary[J]?Geophys Res Lett,2000,27:2777-2780.
[55]SIDORI N I,GURNIS M,HELMBERGER D V.Evidence for a ubiquitous seismic discontinuity at the base of the man-tle[J].Science,1999,286:1326-1331.
[56]MAUPI N V,GARNERO EJ,LAY T,et al.Azi muthal ani-sotropy in the D″layer beneath the Caribbean[J].J Geophys Res,2005(in review).
[57]DOBSON D P,BRODHOLTJ P.Subducted bandedironfor-mations as a source of ultralow-velocity zones at the core?mantle boundary[J].Nature,2005,434:371-374.
[58]WILLI AMS Q,REVENAUGHJ S,GARNERO EJ.Acor-relation between ultralow basal velocities in the mantle and hotspots[J].Science,1998,281:546-549.
[59]MURAKAMI M,HIROSE K,SATA N,et al.Post-perovs-kite phase transition and mineral chemistry in the pyrolitic lowermost mantle[J].Geophys Res Lett,2005,32:L03304,doi:10.1029/2004GL021956.
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