本文關(guān)鍵詞： 西藏日喀則 鋯石U-Pb年齡 地球化學(xué)　出處：《中國地質(zhì)大學(xué)(北京)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：日喀則雄瑪中-基性巖位于雅魯藏布江蛇綠巖中段吉定蛇綠巖南側(cè),出露于日喀則市吉定縣雄瑪鄉(xiāng),侵入于套三疊紀(jì)的復(fù)理石中。雄瑪巖體由細(xì)粒輝綠巖、中粒輝長巖、石英閃長巖組成。具有高鋁富鈦貧鎂的特點(diǎn)(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%)。大離子親石元素(LILE)(Rb、Ba、Th、U、Pb)強(qiáng)烈富集,Pb具有顯著的正異常,Nb、Ta富集顯示了巖石具有大陸裂谷玄武巖特征。稀土元素球粒隕石標(biāo)準(zhǔn)化圖解總體表現(xiàn)為右傾模式,輕稀土元素富集的特征。輕重稀土元素強(qiáng)烈分餾,LREE/HREE=5.29-7.87,(La/Yb)N=6.39-10.49,平均值為8.3,(La/Sm)N=2.17-3.26,平均值為2.7。存在Eu負(fù)異常,σEu=0.69-0.94,平均值為0.80,指示可能存在斜長石的分離結(jié)晶。鋯石U-Pb定年結(jié)果顯示,細(xì)粒輝綠巖、粗粒輝長巖、石英閃長巖形成的時(shí)代分別為136.4±2.2 Ma(MSWD=0.40)、133.8±2.7 Ma(MSWD=1.4)、138.8±1.5 Ma(MSWD=1.07),表明雄瑪中-基性巖漿巖形成于早白堊世。雄瑪中-基性巖礦物學(xué)、巖石學(xué)及地球化學(xué)特征顯示雄瑪巖漿巖地幔源區(qū)可能存在石榴石和尖晶石,指示了巖石可能由較深的富集地幔(含石榴子石相)發(fā)生10%的部分熔融形成。3種巖性的Mg#均明顯低于原生巖漿(Mg#=68-72),指示了巖漿演化的早期階段發(fā)生了橄欖石、單斜輝石等鎂鐵礦物的結(jié)晶分離,稀土微量元素特征暗示雄瑪巖漿巖可能還遭受了地殼物質(zhì)的混染,細(xì)粒輝綠巖、粗粒輝長巖、石英閃長巖可能代表了同一源區(qū)不同程度的部分熔融作用。雄瑪中-基性巖漿巖的主量元素、微量元素地球化學(xué)研究表明具有陸內(nèi)裂谷玄武巖的地球化學(xué)特征,初步認(rèn)為形成于陸內(nèi)裂谷環(huán)境。雄瑪中-基性巖漿巖代表的可能是早于雅魯藏布江蛇綠巖帶形成,且略早于措美大火成巖省地幔柱巖漿活動(dòng)的一次小規(guī)模板內(nèi)拉張活動(dòng)。
[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.

【學(xué)位授予單位】：中國地質(zhì)大學(xué)(北京)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：P597.3;P588.1

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