日喀则雄玛岩浆岩岩石学与年代学特征

发布时间：2018-02-06 05:57

本文关键词： 西藏日喀则锆石U-Pb年龄地球化学　出处：《中国地质大学(北京)》2017年硕士论文　论文类型：学位论文

【摘要】：日喀则雄玛中-基性岩位于雅鲁藏布江蛇绿岩中段吉定蛇绿岩南侧,出露于日喀则市吉定县雄玛乡,侵入于套三叠纪的复理石中。雄玛岩体由细粒辉绿岩、中粒辉长岩、石英闪长岩组成。具有高铝富钛贫镁的特点(Al2O3=11.81%-14.96%,平均14.1%;TiO2=1.64%-3.64%,平均2.2%;MgO=1.73%-7.93%,平均5.2%)。大离子亲石元素(LILE)(Rb、Ba、Th、U、Pb)强烈富集,Pb具有显著的正异常,Nb、Ta富集显示了岩石具有大陆裂谷玄武岩特征。稀土元素球粒陨石标准化图解总体表现为右倾模式,轻稀土元素富集的特征。轻重稀土元素强烈分馏,LREE/HREE=5.29-7.87,(La/Yb)N=6.39-10.49,平均值为8.3,(La/Sm)N=2.17-3.26,平均值为2.7。存在Eu负异常,σEu=0.69-0.94,平均值为0.80,指示可能存在斜长石的分离结晶。锆石U-Pb定年结果显示,细粒辉绿岩、粗粒辉长岩、石英闪长岩形成的时代分别为136.4±2.2 Ma(MSWD=0.40)、133.8±2.7 Ma(MSWD=1.4)、138.8±1.5 Ma(MSWD=1.07),表明雄玛中-基性岩浆岩形成于早白垩世。雄玛中-基性岩矿物学、岩石学及地球化学特征显示雄玛岩浆岩地幔源区可能存在石榴石和尖晶石,指示了岩石可能由较深的富集地幔(含石榴子石相)发生10%的部分熔融形成。3种岩性的Mg#均明显低于原生岩浆(Mg#=68-72),指示了岩浆演化的早期阶段发生了橄榄石、单斜辉石等镁铁矿物的结晶分离,稀土微量元素特征暗示雄玛岩浆岩可能还遭受了地壳物质的混染,细粒辉绿岩、粗粒辉长岩、石英闪长岩可能代表了同一源区不同程度的部分熔融作用。雄玛中-基性岩浆岩的主量元素、微量元素地球化学研究表明具有陆内裂谷玄武岩的地球化学特征,初步认为形成于陆内裂谷环境。雄玛中-基性岩浆岩代表的可能是早于雅鲁藏布江蛇绿岩带形成,且略早于措美大火成岩省地幔柱岩浆活动的一次小规模板内拉张活动。
[Abstract]:Shigatse Xiongma - basite is located in the middle of the Yarlung Zangbo River ophiolite yoshisada ophiolite outcropped in the south, Shigatse Ji Ding County Xiong Ma Xiang, into the set of Triassic flysch. Xiongma rock consisting of fine grain gabbro, diabase, quartz diorite. Gao Lvfu has the characteristics of titanium magnesium poor (Al2O3=11.81%-14.96% the average, 14.1%; TiO2=1.64%-3.64%, an average of 2.2%; MgO=1.73%-7.93%, 5.2%). The average large ion lithophile elements (LILE) (Rb, Ba, Th, U, Pb) strong enrichment, Pb has significant positive anomaly, Nb, enrichment of Ta show that the rock has the characteristics of continental rift basalt. The chondrite normalized REE graphic overall performance for the right mode, enrichment of light rare earth elements. REE elements strongly fractionated, LREE/HREE=5.29-7.87, (La/Yb) N=6.39-10.49, the average value is 8.3, N=2.17-3.26 (La/Sm), the average value of 2.7. is negative anomaly of Eu, Eu=0.69-0.94, The average value is 0.80, indicating there may be fractional crystallization of plagioclase. Zircon U-Pb dating results show that fine coarse grained gabbro, diabase, quartz diorite formed times were 136.4 + 2.2 Ma (MSWD=0.40), Ma (MSWD=1.4) 133.8 + 2.7, 138.8 + 1.5 Ma (MSWD=1.07), show that the magma Xiongma in rock formed in Early Cretaceous. Xiongma - mafic mineralogy, petrology and geochemical characteristics show that Xiongma magmatite mantle may exist in garnet and spinel, indicating the rock from deep enriched mantle (Garnet phase) partial melting occurred 10%.3 formation lithology of Mg# was significantly lower than that of the primary magma (Mg#=68-72), indicating the occurrence of early stage of magmatic evolution of olivine, clinopyroxene and crystallization of mafic minerals, trace element characteristics suggest that Xiongma magmatite might suffer the crustal contamination, Fine grained coarse grained gabbro, diabase, quartz diorite may represent partial melting of the same source region in different degrees. The main elements of magmatite - based Xiongma, trace element geochemical study shows geochemical characteristics of continental rift basalt has the preliminary thought formed in the continental rift environment. In Xiongma - Basic magmatite representatives may be earlier than the Yarlung Zangbo ophiolites formation, and slightly earlier than the comai Large Igneous Province, mantle plume magmatism in a small scale template extension activities.

【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P597.3;P588.1

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