东南印度洋中脊(108°—134°E区域)断层构造与岩浆活动关系
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摘要
东南印度洋脊(SoutheastIndianRidge,简称SEIR)是中速扩张洋中脊,在其中的108°—134°E区域的全扩张速率为72～76 mm·a–1。但在接近澳大利亚-南极洲不整合带(Australian-Antarctic Discordance,简称AAD)区内,海底地貌沿洋中脊的变化强烈,其变化范围涵盖了从慢速到快速扩张洋中脊上常见的例子,且出现了明显的地球物理与地球化学异常,说明洋中脊在AAD区附近的岩浆供应量极不均匀。文章定量分析了高精度多波束测深数据,计算了洋中脊不同段的地形坡度、断层比例以及平面与剖面的岩浆参数M值,结合研究区内剩余地幔布格重力异常以及洋中脊轴部地球化学指标Na8.0、Fe8.0等资料,分析与讨论了研究区的断层构造与岩浆活动特征的关系。研究发现,东南印度洋脊108°—134°E区域的B区(在AAD区内)及C5段(在AAD区外西侧)发育有大量的海洋核杂岩,而且B区的海洋核杂岩单体规模更大,其中最大的位于B3区,沿洋中脊扩张方向延伸约50km。研究结果首次系统性地显示,相比东南印度洋的其他区域, B和C5异常区具有偏低的平面与剖面M值、偏高的断层比例、偏正的地幔布格重力异常以及偏高的Na8.0值与偏低的Fe8.0值,这些异常特征可能反映了B区和C5段的岩浆初始熔融深度较浅以及岩浆熔融程度较低,因此导致其岩浆供应量异常少,形成较薄的地壳。研究结果同时表明,在岩浆供应量极少的洋中脊,构造伸展作用有利于海洋核杂岩的发育,导致地壳进一步减薄。
The Southeast Indian Ridge(SEIR) at 108°-134°E has a relatively constant intermediate full spreading rate of72-76 mm·a-1 but exhibits significant variations in seafloor tectonic faulting and magmatism. This section of the SEIR encompasses the Australian-Antarctic Discordance(AAD), shows a wide range of seafloor morphology similar to the diverse examples from slow-to fast-spreading ridges, and is associated with significant geophysical and geochemical anomalies. We used high-resolution multi-beam bathymetry data to calculate seafloor topographic slopes, ratio of fault scarp areas, map view and profile M factors. Combining residual mantle Bouguer anomaly and geochemical factors of Na8.0 and Fe8.0, we analyzed the fault tectonics and magmatic characteristics in our study area. A large number of Oceanic Core Complexes(OCC) zones are observed in Zone B within the AAD and Segment C5 immediately to the west of the AAD. The OCC features in Zone B are in general larger in size than those of Segment C5. The largest OCC is located in Segment B3, which extends～50 km along the SEIR spreading direction. In comparison to other segments, Zone B and Segment C5 have more negative residual mantle Bouguer anomalies, higher Na8.0 and lower Fe8.0, more fault scarp areas, and lower plane and profile M factors. These anomalies may reflect shallower initial mantle melting and lower degree of partial melting in Zone B and Segment C5,resulting in anomalously low magma supply, thin crust, and the development of OCC features when the magma supply is severely limited.
The Southeast Indian Ridge(SEIR) at 108°-134°E has a relatively constant intermediate full spreading rate of72-76 mm·a-1 but exhibits significant variations in seafloor tectonic faulting and magmatism. This section of the SEIR encompasses the Australian-Antarctic Discordance(AAD), shows a wide range of seafloor morphology similar to the diverse examples from slow-to fast-spreading ridges, and is associated with significant geophysical and geochemical anomalies. We used high-resolution multi-beam bathymetry data to calculate seafloor topographic slopes, ratio of fault scarp areas, map view and profile M factors. Combining residual mantle Bouguer anomaly and geochemical factors of Na8.0 and Fe8.0, we analyzed the fault tectonics and magmatic characteristics in our study area. A large number of Oceanic Core Complexes(OCC) zones are observed in Zone B within the AAD and Segment C5 immediately to the west of the AAD. The OCC features in Zone B are in general larger in size than those of Segment C5. The largest OCC is located in Segment B3, which extends～50 km along the SEIR spreading direction. In comparison to other segments, Zone B and Segment C5 have more negative residual mantle Bouguer anomalies, higher Na8.0 and lower Fe8.0, more fault scarp areas, and lower plane and profile M factors. These anomalies may reflect shallower initial mantle melting and lower degree of partial melting in Zone B and Segment C5,resulting in anomalously low magma supply, thin crust, and the development of OCC features when the magma supply is severely limited.
引文
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CHRISTIE D M,WEST B P,PYLE D G,et al,1998.Chaotic topography,mantle flow and migration in the Australian Antarctic Discordance[J].Nature,394(6694):637-644.
CIAZELA J,KOEPKE J,DICK H J B,et al,2015.Mantle rock exposures at oceanic core complexes along mid-ocean ridges[J].Geologos,21(4):207-231.
COWIE P A,KARNER G D,1990.Gravity effect of sediment compaction:examples from the North Sea and the Rhine Graben[J]Earth and Planetary Science Letters,99(1-2):141-153.
DICK H J B,LIN JIAN,SCHOUTEN H,2003.An ultraslowspreading class of ocean ridge[J].Nature,426(6965):405-412.
DIVINS D L,2003.Total sediment thickness of the World’s oceans and marginal seas[R].Boulder,CO:NOAA National Geophysical Data Center.
ESCARTíN J,MéVEL C,MACLEOD C J,et al,2003.Constraints on deformation conditions and the origin of oceanic detachments:the Mid-Atlantic Ridge core complex at 15°45'N[J].Geochemistry,Geophysics,Geosystems,4(8):1067.
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GURNIS M,MüLLER R D,MORESI L,1998.Cretaceous vertical motion of Australia and the Australian-Antarctic discordance[J].Science,279(5356):1499-1504.
HAYES D E,1976.Nature and implications of asymmetric sea-floor spreading-“different rates for different plates”[J].GSA Bulletin,87(7):994-1002.
KLEIN E M,LANGMUIR C H,1987.Global correlations of ocean ridge basalt chemistry with axial depth and crustal thickness[J].Journal of Geophysical Research:Solid Earth,92(B8):8089-8115.
KLEIN E M,LANGMUIR C H,ZINDLER A,et al,1988.Isotope evidence of a mantle convection boundary at the AustralianAntarctic discordance[J].Nature,333(6174):623-629.
KLEIN E M,LANGMUIR C H,STAUDIGEL H,1991.Geochemistry of basalts from the Southeast Indian Ridge,115°E-138°E[J].Journal of Geophysical Research:Solid Earth,96(B2):2089-2107.
KOJIMA,Y,SHINOHARA M,MOCHIZUKI K,et al,2003.Seismic velocity structure in the Australian-Antarctic Discordance,Segment B4 revealed by airgun-OBSexperiment[J].EOS Transactions,American Geophysical Union 2003 AGU Fall Meeting,84(46):F1060.
LAVIER L L,BUCK W R,2002.Half graben versus large-offset low-angle normal fault:importance of keeping cool during normal faulting[J].Journal of Geophysical Research:Solid Earth,107(B6):2122.
LIN J,PURDY G M,SCHOUTEN H,et al,1990.Evidence from gravity data for focused magmatic accretion along the Mid-Atlantic Ridge[J].Nature,344(6267):627-632.
MACDONALD K C,1990.A slow but restless ridge[J].Nature,348(6297):108-109.
MüLLER R D,ROEST W R,ROYER J Y,et al,1997.Digital isochrons of the world's ocean floor[J].Journal of Geophysical Research:Solid Earth,102(B2):3211-3214.
MüLLER R D,SDROLIAS M,GAINA C,et al,2008.Age,spreading rates,and spreading asymmetry of the world's ocean crust[J].Geochemistry,Geophysics,Geosystems,9(4):Q04006.
NEUMANN G A,FORSYTH D W,SANDWELL D,1993.Comparison of marine gravity from shipboard and highdensity satellite altimetry along the Mid-Atlantic Ridge,30.5°-35.5°S[J].Geophysical Research Letters,20(15):1639-1642.
OHARA Y,YOSHIDA T,KATO Y,et al,2001.Giant megamullion in the Parece Vela backarc basin[J].Marine Geophysical Researches,22(1):47-61.
OKINO K,MATSUDA K,CHRISTIE D M,et al,2004.Development of oceanic detachment and asymmetric spreading at the Australian-Antarctic discordance[J].Geochemistry,Geophysics,Geosystems,5(12):Q12012.
OLIVE J A,BEHN M D,TUCHOLKE B E,2010.The structure of oceanic core complexes controlled by the depth distribution of magma emplacement[J].Nature Geoscience,3(7):491-495.
PARKER R L,1973.The rapid calculation of potential anomalies[J].Geophysical Journal International,31(4):447-455.
SANDWELL D T,MüLLER R D,SMITH W H F,et al,2014.New global marine gravity model from CryoSat-2 and Jason-1reveals buried tectonic structure[J].Science,346(6205):65-67.
SHAW W J,LIN JIAN,1996.Models of ocean ridge lithospheric deformation:dependence on crustal thickness,spreading rate,and segmentation[J].Journal of Geophysical Research:Solid Earth,101(B8):17977-17993.
SMITH D,2013.Mantle spread across the sea floor[J].Nature Geoscience,6(4):247-248.
TUCHOLKE B E,LIN JIAN,KLEINROCK M C et al,1997.Segmentation and crustal structure of the western Mid-Atlantic Ridge flank,25°25’-27°10’N and 0-29 m.y.[J].Journal of Geophysical Research:Solid Earth,102(B5):10203-10223.
TUCHOLKE B E,LIN JIAN,KLEINROCK M C,1998.Megamullions and mullion structure defining oceanic metamorphic core complexes on the Mid-Atlantic Ridge[J].Journal of Geophysical Research:Solid Earth,103(B5):9857-9866.
TUCHOLKE B E,BEHN M D,BUCK W R,et al,2008.Role of melt supply in oceanic detachment faulting and formation of megamullions[J].Geology,36(6):455-458.
TURCOTTE D L,SCHUBERT G,2014.Geodynamics[M].Cambridge:Cambridge University Press:848.
WANG TINGTING,LIN JIAN,TUCHOLKE B,et al,2011.Crustal thickness anomalies in the North Atlantic Ocean basin from gravity analysis[J].Geochemistry,Geophysics,Geosystems,12(3):Q0AE02,doi:10.1029/2010GC003402.
WEISSEL J K,HAYES D E,1971.Asymmetric seafloor spreading south of Australia[J].Nature,231(5304):518-522.
YOUNG M,1978.Statistical characterization of altitude matrices by computer.Report 5.Terrain analysis:program documentation[R].Durham:Durham University.
BONATTI E,LIGI M,BRUNELLI D,et al,2003.Mantle thermal pulses below the Mid-Atlantic Ridge and temporal variations in the formation of oceanic lithosphere[J].Nature,423(6939):499-505.
BUCK W R,LAVIER L L,POLIAKOV A N B,2005.Modes of faulting at mid-ocean ridges[J].Nature,434(7034):719-723.
CHRISTIE D M,WEST B P,PYLE D G,et al,1998.Chaotic topography,mantle flow and migration in the Australian Antarctic Discordance[J].Nature,394(6694):637-644.
CIAZELA J,KOEPKE J,DICK H J B,et al,2015.Mantle rock exposures at oceanic core complexes along mid-ocean ridges[J].Geologos,21(4):207-231.
COWIE P A,KARNER G D,1990.Gravity effect of sediment compaction:examples from the North Sea and the Rhine Graben[J]Earth and Planetary Science Letters,99(1-2):141-153.
DICK H J B,LIN JIAN,SCHOUTEN H,2003.An ultraslowspreading class of ocean ridge[J].Nature,426(6965):405-412.
DIVINS D L,2003.Total sediment thickness of the World’s oceans and marginal seas[R].Boulder,CO:NOAA National Geophysical Data Center.
ESCARTíN J,MéVEL C,MACLEOD C J,et al,2003.Constraints on deformation conditions and the origin of oceanic detachments:the Mid-Atlantic Ridge core complex at 15°45'N[J].Geochemistry,Geophysics,Geosystems,4(8):1067.
GéLI L,COCHRAN J R,LEE T C,et al,2007.Thermal regime of the Southeast Indian Ridge between 88°E and 140°E:remarks on the subsidence of the ridge flanks[J].Journal of Geophysical Research:Solid Earth,112(B10):B10101.
GURNIS M,MüLLER R D,MORESI L,1998.Cretaceous vertical motion of Australia and the Australian-Antarctic discordance[J].Science,279(5356):1499-1504.
HAYES D E,1976.Nature and implications of asymmetric sea-floor spreading-“different rates for different plates”[J].GSA Bulletin,87(7):994-1002.
KLEIN E M,LANGMUIR C H,1987.Global correlations of ocean ridge basalt chemistry with axial depth and crustal thickness[J].Journal of Geophysical Research:Solid Earth,92(B8):8089-8115.
KLEIN E M,LANGMUIR C H,ZINDLER A,et al,1988.Isotope evidence of a mantle convection boundary at the AustralianAntarctic discordance[J].Nature,333(6174):623-629.
KLEIN E M,LANGMUIR C H,STAUDIGEL H,1991.Geochemistry of basalts from the Southeast Indian Ridge,115°E-138°E[J].Journal of Geophysical Research:Solid Earth,96(B2):2089-2107.
KOJIMA,Y,SHINOHARA M,MOCHIZUKI K,et al,2003.Seismic velocity structure in the Australian-Antarctic Discordance,Segment B4 revealed by airgun-OBSexperiment[J].EOS Transactions,American Geophysical Union 2003 AGU Fall Meeting,84(46):F1060.
LAVIER L L,BUCK W R,2002.Half graben versus large-offset low-angle normal fault:importance of keeping cool during normal faulting[J].Journal of Geophysical Research:Solid Earth,107(B6):2122.
LIN J,PURDY G M,SCHOUTEN H,et al,1990.Evidence from gravity data for focused magmatic accretion along the Mid-Atlantic Ridge[J].Nature,344(6267):627-632.
MACDONALD K C,1990.A slow but restless ridge[J].Nature,348(6297):108-109.
MüLLER R D,ROEST W R,ROYER J Y,et al,1997.Digital isochrons of the world's ocean floor[J].Journal of Geophysical Research:Solid Earth,102(B2):3211-3214.
MüLLER R D,SDROLIAS M,GAINA C,et al,2008.Age,spreading rates,and spreading asymmetry of the world's ocean crust[J].Geochemistry,Geophysics,Geosystems,9(4):Q04006.
NEUMANN G A,FORSYTH D W,SANDWELL D,1993.Comparison of marine gravity from shipboard and highdensity satellite altimetry along the Mid-Atlantic Ridge,30.5°-35.5°S[J].Geophysical Research Letters,20(15):1639-1642.
OHARA Y,YOSHIDA T,KATO Y,et al,2001.Giant megamullion in the Parece Vela backarc basin[J].Marine Geophysical Researches,22(1):47-61.
OKINO K,MATSUDA K,CHRISTIE D M,et al,2004.Development of oceanic detachment and asymmetric spreading at the Australian-Antarctic discordance[J].Geochemistry,Geophysics,Geosystems,5(12):Q12012.
OLIVE J A,BEHN M D,TUCHOLKE B E,2010.The structure of oceanic core complexes controlled by the depth distribution of magma emplacement[J].Nature Geoscience,3(7):491-495.
PARKER R L,1973.The rapid calculation of potential anomalies[J].Geophysical Journal International,31(4):447-455.
SANDWELL D T,MüLLER R D,SMITH W H F,et al,2014.New global marine gravity model from CryoSat-2 and Jason-1reveals buried tectonic structure[J].Science,346(6205):65-67.
SHAW W J,LIN JIAN,1996.Models of ocean ridge lithospheric deformation:dependence on crustal thickness,spreading rate,and segmentation[J].Journal of Geophysical Research:Solid Earth,101(B8):17977-17993.
SMITH D,2013.Mantle spread across the sea floor[J].Nature Geoscience,6(4):247-248.
TUCHOLKE B E,LIN JIAN,KLEINROCK M C et al,1997.Segmentation and crustal structure of the western Mid-Atlantic Ridge flank,25°25’-27°10’N and 0-29 m.y.[J].Journal of Geophysical Research:Solid Earth,102(B5):10203-10223.
TUCHOLKE B E,LIN JIAN,KLEINROCK M C,1998.Megamullions and mullion structure defining oceanic metamorphic core complexes on the Mid-Atlantic Ridge[J].Journal of Geophysical Research:Solid Earth,103(B5):9857-9866.
TUCHOLKE B E,BEHN M D,BUCK W R,et al,2008.Role of melt supply in oceanic detachment faulting and formation of megamullions[J].Geology,36(6):455-458.
TURCOTTE D L,SCHUBERT G,2014.Geodynamics[M].Cambridge:Cambridge University Press:848.
WANG TINGTING,LIN JIAN,TUCHOLKE B,et al,2011.Crustal thickness anomalies in the North Atlantic Ocean basin from gravity analysis[J].Geochemistry,Geophysics,Geosystems,12(3):Q0AE02,doi:10.1029/2010GC003402.
WEISSEL J K,HAYES D E,1971.Asymmetric seafloor spreading south of Australia[J].Nature,231(5304):518-522.
YOUNG M,1978.Statistical characterization of altitude matrices by computer.Report 5.Terrain analysis:program documentation[R].Durham:Durham University.