海洋核杂岩
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摘要
为了解释洋壳中大量铲形正断层及垂直洋中脊的大量线理(如大西洋中脊的巨型窗棱构造)等现象,通过与大陆上变质核杂岩对比,近来提出了一种新的海底构造类型———海洋核杂岩。在洋底深地震剖面上核杂岩结构形态可以分为3部分,其中第1部分为层1和层2,以脆性变形为特征;第2部分为脆-韧性过渡层,拆离带发育其中,由白色结壳式碳酸盐岩和强烈蛇纹石化的橄榄岩或玄武岩、超镁铁质糜棱岩、糜棱状辉长岩等组成。拆离面之上为未变质的薄层海洋沉积层,其下为热洋幔的退变质岩石组成;第3部分为核部,以塑性变形为特征,常被超基性岩体(尤其是辉长岩侵入体)底辟侵入。与大陆变质核杂岩相比,海洋核杂岩具有明显的独特性。海洋核杂岩的拆离断层同样有数十千米的位移量,因而,可能导致出现海底磁条带的局部错位现象,使得洋壳磁条带的平面结构复杂化。
Oceanic core complex,a new structural type,was proposed to explain many listric detachment faults and ridge-perpendicular lineations such as megamullion in the Atlantic by comparison with the metamorphic core complex in the continent.The oceanic core complex consists of three parts based on deep seismic reflection profile.The first part is dominated by brittle deformation in layer 1 and layer 2 of the oceanic crust.The second part is brittle-ductile transition layer dominating the detachment fault.The detachment fault zone is composed of white carbonite,strongly serpentinized peridotite or basalt,ultramafic mylonite and mylonitic gabbro and others,rather than felsic mylonite and chlorinized breccia.The detachment surface is covered with thin,unmetamorphic and oceanic sediments,or directly crops out on oceanic crust.Under the detachment fault is retrograde metamorphic hot oceanic mantle.The third part is the core of oceanic core complex,which is dominated by ductile deformation intruded structurally by diapiric ultramafic plutons,especially gabbro intrusions.The oceanic core complex of the oceanic crust is obviously different from the metamorphic core complex of the continent.The oceanic core complex can result in a displacement of several kilometers along the detachment fault,producing local offsets of seafloor magnetic zones and the complexity of structural pattern in the oceanic crust.
Oceanic core complex,a new structural type,was proposed to explain many listric detachment faults and ridge-perpendicular lineations such as megamullion in the Atlantic by comparison with the metamorphic core complex in the continent.The oceanic core complex consists of three parts based on deep seismic reflection profile.The first part is dominated by brittle deformation in layer 1 and layer 2 of the oceanic crust.The second part is brittle-ductile transition layer dominating the detachment fault.The detachment fault zone is composed of white carbonite,strongly serpentinized peridotite or basalt,ultramafic mylonite and mylonitic gabbro and others,rather than felsic mylonite and chlorinized breccia.The detachment surface is covered with thin,unmetamorphic and oceanic sediments,or directly crops out on oceanic crust.Under the detachment fault is retrograde metamorphic hot oceanic mantle.The third part is the core of oceanic core complex,which is dominated by ductile deformation intruded structurally by diapiric ultramafic plutons,especially gabbro intrusions.The oceanic core complex of the oceanic crust is obviously different from the metamorphic core complex of the continent.The oceanic core complex can result in a displacement of several kilometers along the detachment fault,producing local offsets of seafloor magnetic zones and the complexity of structural pattern in the oceanic crust.
引文
[1]Tucholke B E,Lin J,Kleinrock M C.Megamullions and mul-lion structure defining oceanic metamorphic core complexes onthe Mid-Atlantic Ridge[J].Journal of Geophysical Research,1998,103:9 857-9 866.
[2]Ranero C R,Reston T J.Detachment faulting at ocean corecomplexes[J].Geology,1999,27(11):983-986.
[3]Davis G A,郑亚东.变质核杂岩的定义、类型及构造背景[J].地质通报,2002,21(4-5):185-192.[Davis G A,ZHENG Ya-dong.Definition,classification and tectonic setting of meta-morphic core complex[J].Chinese Geological Bulletin,2002,21(4-5):185-192.]
[4]李学伦.海洋地质学[M].青岛:青岛海洋大学,1997.[LI Xue-lun.Marine Geology[M].Qingdao:Press of Ocean Universityof Qingdao,1997.]
[5]MacLeod C J,Escartin J,Banerji D,et al.Direct geologicalevidence for oceanic detachment faulting:The Mid-AtlanticRidge,15°45′N[J].Geology,2002,30(10):879-882.
[6]Nooner S L,Sasagawa G S,Blackman D K,et al.Structure ofoceanic core complexes:Constraints from seafloor gravitymeasurements made at the Atlantis Massif[J].GeophysicalResearch Letters,2003,30(8):1 446.
[7]Blackman D K,Karson J A,Kelley D S,et al.Geology of theAtlantis Massif(Mid-Atlantic Ridge,30 degrees N):Implica-tions for the evolution of an ultramafic oceanic core complex[J].Marine Geophysical Researches,2002,23(5-6):443-469.
[8]Reston T J,Weinrebe I,Grevemeyer E R F,et al.Partici-pants of Meteor 47/2.A rifted inside corner massif on theMid-Atlantic Ridge at 5°S[J].Earth and Planetary ScienceLetters,2002,200:255-269.
[9]Blackman D K,Cann J R,Janssen B,et al.Origin of exten-sional core complexes:evidence from the Mid-Atlantic Ridge atAtlantis fracture zone[J].Journal of Geophysical Research B:Solid Earth,2001,106(8):16 145-16 161.
[10]Baines A G,Cheadle M J,Dick H J B,et al.Mechanism forgenerating the anomalous uplift of oceanic core complexes:Atlantis Bank,southwest Indian Ridge[J].Geology,2003,31(12):1 105-1 108.
[11]Searle R C,Cannat M,Fujioka K,et al.FUJI Dome:A largedetachment fault near 64 degrees E on the very slow-sprea-ding southwest Indian Ridge[J].Geochemistry GeophysicsGeosystems,2003,4:9 105.
[12]Gao D L,Hurst S D,Karson J A,et al.Computer-aided in-terpretation of side-looking sonar images from the eastern in-tersection of the Mid-Atlantic Ridge with the Kane Transform[J].Journal of Geophysical Research-Solid Earth,1998,103(B9):20 997-21 014.
[13]Kumagai H,Dick H J B,Kaneoka I.Noble gas signatures of a-byssal gabbros and peridotites at an Indian Ocean core complex[J].Geochemistry Geophysics Geosystems,2003,4:9 107.
[2]Ranero C R,Reston T J.Detachment faulting at ocean corecomplexes[J].Geology,1999,27(11):983-986.
[3]Davis G A,郑亚东.变质核杂岩的定义、类型及构造背景[J].地质通报,2002,21(4-5):185-192.[Davis G A,ZHENG Ya-dong.Definition,classification and tectonic setting of meta-morphic core complex[J].Chinese Geological Bulletin,2002,21(4-5):185-192.]
[4]李学伦.海洋地质学[M].青岛:青岛海洋大学,1997.[LI Xue-lun.Marine Geology[M].Qingdao:Press of Ocean Universityof Qingdao,1997.]
[5]MacLeod C J,Escartin J,Banerji D,et al.Direct geologicalevidence for oceanic detachment faulting:The Mid-AtlanticRidge,15°45′N[J].Geology,2002,30(10):879-882.
[6]Nooner S L,Sasagawa G S,Blackman D K,et al.Structure ofoceanic core complexes:Constraints from seafloor gravitymeasurements made at the Atlantis Massif[J].GeophysicalResearch Letters,2003,30(8):1 446.
[7]Blackman D K,Karson J A,Kelley D S,et al.Geology of theAtlantis Massif(Mid-Atlantic Ridge,30 degrees N):Implica-tions for the evolution of an ultramafic oceanic core complex[J].Marine Geophysical Researches,2002,23(5-6):443-469.
[8]Reston T J,Weinrebe I,Grevemeyer E R F,et al.Partici-pants of Meteor 47/2.A rifted inside corner massif on theMid-Atlantic Ridge at 5°S[J].Earth and Planetary ScienceLetters,2002,200:255-269.
[9]Blackman D K,Cann J R,Janssen B,et al.Origin of exten-sional core complexes:evidence from the Mid-Atlantic Ridge atAtlantis fracture zone[J].Journal of Geophysical Research B:Solid Earth,2001,106(8):16 145-16 161.
[10]Baines A G,Cheadle M J,Dick H J B,et al.Mechanism forgenerating the anomalous uplift of oceanic core complexes:Atlantis Bank,southwest Indian Ridge[J].Geology,2003,31(12):1 105-1 108.
[11]Searle R C,Cannat M,Fujioka K,et al.FUJI Dome:A largedetachment fault near 64 degrees E on the very slow-sprea-ding southwest Indian Ridge[J].Geochemistry GeophysicsGeosystems,2003,4:9 105.
[12]Gao D L,Hurst S D,Karson J A,et al.Computer-aided in-terpretation of side-looking sonar images from the eastern in-tersection of the Mid-Atlantic Ridge with the Kane Transform[J].Journal of Geophysical Research-Solid Earth,1998,103(B9):20 997-21 014.
[13]Kumagai H,Dick H J B,Kaneoka I.Noble gas signatures of a-byssal gabbros and peridotites at an Indian Ocean core complex[J].Geochemistry Geophysics Geosystems,2003,4:9 107.
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