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  

Hotspot-ridge interaction for the evolution of Neo-Tethys: insights from the Late Jurassic-Early Cretaceous magnatism in southern Tibet.

作　　者：朱弟成[1,2] 莫宣学[1] 王立全[2] 赵志丹[1] 廖忠礼[2] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,中国地质大学地球科学与资源学院,北京100083 [2]成都地质矿产研究所,成都610082

出　　处：《岩石学报》2008年第2期225-237,共13页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(编号：2002CB412603);国家自然科学基金(40503005，40572051，40473020);国土资源部百名优秀青年科技人才计划、地质过程与矿产资源国家重点实验室开放课题(GPMR0539);中国地质调查局青藏高原基础地质综合研究项目(1212010610101)资助

摘　　要：雅鲁藏布蛇绿混杂岩代表了新特提斯洋盆闭合的地表残余。本文在测试数据基础上,综合分析了目前雅鲁藏布江蛇绿混杂岩研究中取得的比较可信的晚侏罗世-早白垩世玄武岩的地球化学数据,并对其进行了较为详细的区域对比分析以讨论涉及新特提斯演化的地球动力学过程。结果表明:(1)雅鲁藏布蛇绿混杂岩带吉定洞拉村玄武岩、错拉山口北部玄武岩为大洋中脊玄武岩(MORB)型,错拉山口南部玄武岩为洋岛玄武岩(OIB)型,萨嘎桑单林玄武岩既包括OIB型,又包括MORB型;(2)在东西延伸约1500km的雅鲁藏布蛇绿混杂岩带中,至少可能存在OIB、MORB(包括N-MORB、E-MORB)和岛弧玄武岩IAB三种类型的晚侏罗世-早白垩世玄武岩。不活动的高场强元素比值(如Nb/Y,Zr/Y等)指示雅鲁藏布蛇绿混杂岩带中部仁布、杯玛让、吉定洞拉村和错拉山口北部地区以及中西部萨嘎地区的MORB型玄武岩中的亏损组分很可能来源于深部亏损的地幔柱源区。微量元素地球化学模拟表明,雅鲁藏布蛇绿混杂岩带OIB型玄武岩可能主要来源于石榴石二辉橄榄岩源区中等程度(10%～20%)的部分熔融,而MORB型玄武岩主要来源于尖晶石二辉橄榄岩源区中等程度(7%～25%)的部分熔融,IAB型玄武岩所代表的源区熔融深度以中部较浅而东西两端较深为特点,其中中部得几、杯玛让、吉定等地的IAB很可能与尖晶石二辉橄榄岩源区的部分熔融有关,而东部和西部达几翁IAB的熔融源区可能残留有石榴石。结合该带报道的He同位素数据和矿物学观察,以及在喜马拉雅带新获得的古地磁数据,可以认为热点与洋脊的相互作用是对晚侏罗世-早白垩世新特提斯演化的一种很可能的地球动力学解释。需要强调,虽然该模式可以较好地解释目前在藏南观察到的晚侏罗世-早白垩世岩浆作用特点和性质,但因资料有限,还需要做许多非常细致的工作�The Yarlung Zangbo Ophiolitic M lange Zone （YZOMZ） is generally accepted as the surface relic of the Neo-Tethys. Combined our data with previously available data, we synthesize the distribution and geochemistry of Late Jurassic Early Cretaceous basalts from the YZOMZ in order to test the geodynamic process involved in the evolution of the Neo-Tethys by regional comparison in detail. The results indicate that： （1） basalts from Dongla village, and northern Cuolashankou have closely geochemical affinities with MORB, basalts from southern Cuolashankou are resembled with OIB-type basalts, and basalts from Sangdanlin near Saga are composed of OIB- and MORB-type basalt ; （2） at least OIB-, MORB- （ include N-MORB and E-MORB）, and IAB-type Late Jurassic Early Cretaceous basalt are probably coexisted in the YZOMZ, stretching E-W about 1500 km in south Tibet. Ratios of immobile high-field strength elements （e. g. , Nb/Y, Zr/Y ratios） indicate that the depleted components observed in MORB-type basalts from the central YZOMZ （include Renbu, Beimarang, Dongla village, and northern Cuolashankou） and the central-western YZOMZ （e. g. , Saga） may be originated from a deep depleted source of hotspot activities, Trace elemental modeling results suggest that （ 1 ） OIB-type basalts from the YZOMZ may be derived primarily from moderate partial melting （10% -20% ） of garnet lherzolite; （2） MORB-type basalts may be originated predominantly from moderate partial melting （7% - 25% ） of spinel lherzolite; and （3） IAB-type basalt from the central YZOMZ （e. g. , Deji, Beimarang, and Dongla village） may be generated by partial melting of spinel lherzolite, while garnet would be left as a residual mineral in the mantle source of IAB-type basalts from the eastern and western YZOMZ （e, g. , Dajiweng）. Combined our results with He isotopic data, mineralogical observations reported previously in the YZOMZ, and newly palaeomagnetic studies in Himalayas, we propose a probable model of hotspot-

关 键 词：新特提斯 热点与洋脊相互作用 晚侏罗世-早白垩世玄武岩 雅鲁藏布蛇绿混杂岩 藏南 

分 类 号：P588.111[天文地球—岩石学]