西藏日喀则地区雅鲁藏布蛇绿岩地球化学特征及其源区性质
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摘要
日喀则地区的蛇绿岩是西藏南部雅鲁藏布蛇绿岩带出露较好的蛇绿岩之一。对日喀则地区白朗蛇绿岩的主量、微量元素及Sr-Nd同位素研究表明,其基性岩石为钙碱性系列,主要氧化物具有低钛(0.6%~1.1%)和富镁(6.6%~8.7%)、高铝(15.3%~16.0%),以及烧失量普遍较高(2.8%~4.6%)的特征。岩石微量元素配分型式与N-MORB类似,又具有岛弧玄武岩的地球化学特征,表明蛇绿岩受到了俯冲作用的影响。Sr-Nd同位素特征表明源区为略富集的MORB型地幔。白朗蛇绿岩所代表的特提斯地幔域与印度洋地幔域具有相似的地球化学性质,进一步证实了现今的印度洋继承了特提斯地幔域的地球化学特征。
Ophiolite from Xigaze is one of well-outcropped rocks in the Yalung Zangpo ophiolite,southern Tibet. Elemental and Sr-Nd isotopic compositions of the basaltic rocks from Bainang ophiolite in Xigaze were studied in this paper. The rocks are calc alkalic series,with low Ti O2( 0. 6%- 1. 1%),high Mg O( 6. 6%-8. 7%),Al2O3( 15. 3%- 16. 0%) and LOI( 2. 8%- 4. 6%). The primitive mantle-normalized multi-element pattern of basaltic rocks is similar to that of the normal Mid-Ocean Ridge Basalt( N-MORB) with the characteristics of island arc,which suggests that the rocks are related to subduction processes. The geochemical characteristics of Sr-Nd reflect that mantle source of Bainang ophiolite is a little enriched MORB mantle. The geochemical characteristics of Tethyan Ocean are similar to those of the Indian sub-oceanic mantle,which further confirms that the Indian sub-oceanic mantle is inherited from the Tethyan Ocean geochemical domain.
Ophiolite from Xigaze is one of well-outcropped rocks in the Yalung Zangpo ophiolite,southern Tibet. Elemental and Sr-Nd isotopic compositions of the basaltic rocks from Bainang ophiolite in Xigaze were studied in this paper. The rocks are calc alkalic series,with low Ti O2( 0. 6%- 1. 1%),high Mg O( 6. 6%-8. 7%),Al2O3( 15. 3%- 16. 0%) and LOI( 2. 8%- 4. 6%). The primitive mantle-normalized multi-element pattern of basaltic rocks is similar to that of the normal Mid-Ocean Ridge Basalt( N-MORB) with the characteristics of island arc,which suggests that the rocks are related to subduction processes. The geochemical characteristics of Sr-Nd reflect that mantle source of Bainang ophiolite is a little enriched MORB mantle. The geochemical characteristics of Tethyan Ocean are similar to those of the Indian sub-oceanic mantle,which further confirms that the Indian sub-oceanic mantle is inherited from the Tethyan Ocean geochemical domain.
引文
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[2]张旗,周德进.一种新的洋壳类型及其动力学意义[J].科学通报,1996,41(11):1025-1027.
[3]白文吉,杨经绥,施倪承,等.西藏罗布莎蛇绿岩地幔岩中首次发现超高压矿物方铁矿和自然铁[J].地质论评,2004,50(2):184-188.
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[5]DILEK Y,FURNES H.Ophiolite genesis and global tectonics:Geochemical and tectonic fingerprinting of ancient oceanic lithosphere[J].Geological Society of America Bulletin,2011,123(3/4):387-411.
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[8]朱弟成,莫宣学,王立全,等.新特提斯演化的热点与洋脊相互作用:西藏南部晚侏罗世—早白垩世岩浆作用推论[J].岩石学报,2008,24(2):225-237.
[9]H BERT R,BEZARD R,GUILMETTE C,et al.The IndusYarlung Zangbo ophiolites from Nanga Parbat to Namche Barwa syntaxes,southern Tibet:First synthesis of petrology,geochemistry,and geochronology with incidences on geodynamic reconstructions of Neo-Tethys[J].Gondwana Research,2012,22(2):377-397.
[10]DAI J G,WANG C S,H BERT R,et al.Late Devonian OIB alkaline gabbro in the Yarlung Zangbo Suture Zone:Remnants of the Paleo-Tethys?[J].Gondwana Research,2011,19(1):232-243.
[11]ZHU D C,MO X X,PAN G T,et al.Petrogenesis of the earliest Early Cretaceous basalts and associated diabases from Cona area,eastern Tethyan Himalaya in south Tibet:Interaction between the incubating Kerguelen plume and eastern Greater India lithosphere?[J].Lithos,2008,100:147-173.
[12]ZHU D C,ZHAO Z D,NIU Y L,et al.Lhasa Terrane in southern Tibet came from Australia[J].Geology,2011,39:727-730.
[13]ZHU D C,ZHAO Z D,NIU Y L,et al.The origin and preCenozoic evolution of the Tibetan Plateau[J].Gondwana Research,2013,23(4):1429-1454.
[14]MAHONEY J J,FREI R,TEJADA M L G,et al.Tracing the Indian Ocean mantle domain through time:isotope results from old west Indian,East Tethyan,and South Pacific seafloor[J].Journal of Petrology,1998,39(7):1285-1306.
[15]XU J F,CASTILLO P R.Geochemical and Nd-Pb isotopic characteristics of the Tethyan asthenosphere:implications for the origin of the Indian Ocean mantle domain[J].Tectonophysics,393(1):9-27.
[16]牛晓露,赵志丹,莫宣学,等.西藏日喀则地区德村—昂仁蛇绿岩内基性岩的元素与Sr-Nd-Pb同位素地球化学及其揭示的特提斯地幔域特征[J].岩石学报,2006,22(12):2875-2888.
[17]潘桂棠,丁俊.青藏高原及邻区地质图(1∶1 500 000)[M].成都:成都地图出版社,2004.
[18]张浩勇,巴登珠,郭铁鹰,等.西藏自治区曲松县罗布莎铬铁矿床研究[M].拉萨:西藏人民出版社,1996:1-181.
[19]王希斌,鲍佩声,邓万明.西藏蛇绿岩[M].北京:地质出版社,1987:1-137.
[20]ZHOU S,MO X X,MAHONEY J J,et al.Geochronology and Nd and Pb isotopic characteristics of gabbro dikes in the Luobusha ophiolite,Tibet[J].Chinese Science Bulletin,2002,47(2):143-146.
[21]钟立峰,夏斌,周国庆,等.藏南罗布莎蛇绿岩辉绿岩中锆石SHRIMP测年[J].地质论评,2006,52(2):224-229.
[22]MCDERMID I R C,AITCHISON J C,DAVIS A M,et al.The Zedong terrane:a Late Jurassic intra-oceanic magmatic arc within the Yarlung-Tsangpo suture zone,southeastern Tibet[J].Chemical Geology,2002,187(3):267-277.
[23]王冉,夏斌,周国庆,等.西藏吉定蛇绿岩中辉长岩SHRIMP锆石U-Pb年龄[J].科学通报,2006,51(1):114-117.
[24]GUILMETTE C,H BERT R,WANG C S,et al.Geochemistry and geochronology of the metamorphic sole underlying the Xigaze Ophiolite,Yarlung Zangbo Suture Zone,South Tibet[J].Lithos,2009,112(1):149-162.
[25]李建峰,夏斌,刘立文,等.西藏群让蛇绿岩辉长岩SHRIMP锆石U-Pb年龄及地质意义[J].大地构造与成矿学,2009,33(2):294-298.
[26]夏斌,李建峰,刘立文,等.西藏桑桑蛇绿岩辉绿岩SHRIMP锆石U-Pb年龄:对特提斯洋盆发育的年代学制约[J].地球化学,2008,37(4):399-403.
[27]韦振权,夏斌,张玉泉,等.西藏休古嘎布蛇绿岩中辉绿岩锆石SHRIMP U-Pb定年及其地质意义[J].大地构造与成矿学,2006,30(1):93-97.
[28]刘钊,李源,熊发挥,等.西藏西部普兰蛇绿岩中的MOR型辉长岩:岩石学和年代学[J].岩石学报,2011,27(11):3269-3279.
[29]G PEL C,ALLGRE C J,XU R H.Lead isotopic study of the Xigaze ophiolite(Tibet):the problem of the relationship between magmatites(gabbros,dolerites,lavas),and tectonites(harzburgites)[J].Earth and Planetary Science Letters,1984,69(2):301-310.
[30]吴浩若.西藏南部下鲁硅质岩晚侏罗世罩笼虫(放射虫)新材料[J].现代地质,2000,14(3):301-306.
[31]GAO S,LIU X M,YUAN H L,et al.Determination of forty two major and trace elements in USGS and NISTSRM glasses by laser ablation inductively coupled plasma mass spectrometrygeostandards[J].News letter Journal of Geostandards and Geoanalysis,2002,26(2):191-196.
[32]ZHANG H F,GAO S,ZHONG Z Q,et al.Geochemical and Sr-Nd-Pb isotopic compositions of Cretaceous granitoids:constraints on tectonic framework and crustal structure of the Dabieshan ultrahigh-pressure metamorphic belt,China[J].Chemical Geology,2002,186(3/4):281-299.
[33]邓晋福,肖庆辉,苏尚国,等.火成岩组合与构造环境:讨论[J].高校地质学报,2007,13(3):392-402.
[34]LE MAITRE R W.Igneous Rocks:A Classification and Glossary of Terms:Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks[M].Cambridge:Cambridge University Press,2002:33-39.
[35]Miyashiro A.Volcanic rock series in island arcs and active continental margins[J].American Journal of Science,1974,274(4):321-355.
[36]李文霞,赵志丹,朱弟成,等.西藏雅鲁藏布蛇绿岩形成构造环境的地球化学鉴别[J].岩石学报,2012,28(5):1663-1673.
[37]BOYNTON W V.Geochemistry of the rare earth elements:Meteorite studies[M]//HENDERSON P.Rare Earth Element Geochemistry[J].Amsterdam:Elsevier,1984:63-114.
[38]SUN S S,MCDONOUGH W F.Chemical and isotopic systematics of oceanic basalts:implications for mantle composition and processes[J].Geological Society of London Special Publications,1989,42(1):313-345.
[39]沈渭洲.同位素地质学教程[M].北京:原子能出版社,1997:1-287.
[40]FAURE G.Origin of Igneous Rocks:the Isotope Evidence[M].Heidelberg:Springer-Verlag,2001:1-495.
[41]SAUNDERS A D,NORRY M J,TAMEY J.Origin of MORB and chemically depleted mantle reservoirs:trace element constraints[J].Journal of Petrology,1988,29:415-445.
[42]钟立峰,夏斌,周国庆,等.藏南罗布莎蛇绿岩成因:壳层熔岩的Sr-Nb-Pb同位素制约[J].矿物岩石,2006,26(1):57-63.
[43]DUPR B,ALLGRE C J.Pb-Sr isotope variation in Indian Ocean basalts and mixing phenomena[J].Nature,1983,303:142-146.
[44]JACOBSEN S B,WASSERBURG G J.Nd and Sr isotopic study of Bay of Islands Ophiolite Complex and the evolution of the source of mid-ocean ridge basalt[J].Journal of Geophysical Research,1979,84(B13):7429-7445.
[45]EISELE J,SHARMA M,GALER S J G,et al.The role of sediment recycling in EM-I inferred from Os,Pb,Hf,Nd,Sr isotope and trace element systematics of the Pitcairn hotspot[J].Earth and Planetary Science Letters,2002,196(3):197-212.
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