本文選題：巖漿巖 + 鋯石U-Pb年齡��； 參考：《中國(guó)地質(zhì)大學(xué)(北京)》2017年碩士論文

【摘要】：近年來(lái),許多學(xué)者對(duì)特提斯喜馬拉雅帶白堊紀(jì)火山巖非常關(guān)注。研究區(qū)位于特提斯喜馬拉雅帶中東部,古地理上屬大印度北緣,也位于措美殘余大火成巖省范圍內(nèi)。本論文擬通過(guò)對(duì)巖漿巖地球化學(xué)及年代學(xué)的研究,分析其成因、構(gòu)造環(huán)境,為新特提斯洋擴(kuò)張及措美大火成巖東延提供證據(jù),也為進(jìn)一步找礦指明方向。西藏夏瓦地區(qū)火山巖的巖石類型主要為英安巖、粗面玄武巖、安山質(zhì)玄武巖。獲得英安巖鋯石U-Pb年齡為142±1.0Ma,其形成時(shí)代為早白堊世。元素地球化學(xué)研究表明,玄武巖是富Ti、Fe、P、Mg過(guò)鋁質(zhì)堿性玄武巖,與OIB特征相似;稀土元素總量∑REE=270.01-311.19ppm,LREE略富集,大離子親石元素中相對(duì)富集Ba,貧K、Sr;在高場(chǎng)強(qiáng)元素中相對(duì)富集Th、U、Zr、Hf,貧Nb;Eu異常不明顯。英安巖是富Si、Al、K、Ca,貧Mg、Fe的過(guò)鋁質(zhì)鈣堿性酸性巖;稀土元素總量∑REE=266.20-555.8ppm,富集LREE,在大離子親石元素中相對(duì)富集Rb、Ba,虧損Sr、K、Eu;在高場(chǎng)強(qiáng)元素相對(duì)富集Th、U,虧損Nb、Ti、Zr、Hf;具有明顯Sr負(fù)異常,可能與低壓條件下的斜長(zhǎng)石分離結(jié)晶有關(guān);Th豐度高(平均為40.1ppm),Nb/La平均為0.29,暗示與硅鋁質(zhì)地殼的深熔作用有關(guān)。西藏夏瓦地區(qū)基性脈巖的巖石類型主要為輝長(zhǎng)巖、輝綠巖,近東西向展布。獲得2個(gè)輝長(zhǎng)巖鋯石U-Pb年齡分別為145.99±0.98Ma和146.12±0.72Ma,其結(jié)晶時(shí)代均為早白堊世。元素地球化學(xué)研究表明,輝長(zhǎng)巖、輝綠巖富集全堿、Ti、Fe、P、Mg,屬鈣堿性系列,與OIB特征相似;稀土元素總量ΣREE=897-1121ppm,LREE略富集,在大離子親石元素中相對(duì)富集Ba、虧損K、Pb、Sr;在高場(chǎng)強(qiáng)元素中相對(duì)富集Nb、Ta、Zr、Hf、Th,虧損U、Ti;Eu弱富集。巖漿巖形成于大陸邊緣初始裂谷的環(huán)境下,其中輝綠巖、輝長(zhǎng)巖、玄武巖可能是Kerguelen地幔柱與巖石圈地幔相互作用的產(chǎn)物;英安巖的形成與硅鋁質(zhì)地殼的重熔有關(guān)。早白堊世巖漿巖為研究區(qū)初始礦源層的富集提供了成礦物質(zhì)來(lái)源,古近紀(jì)和新近紀(jì)酸性侵入巖為研究區(qū)成礦提供了物質(zhì)來(lái)源和熱動(dòng)力,在中基性侵入巖發(fā)育地區(qū)和酸性巖體周邊構(gòu)造發(fā)育區(qū)是找礦有利部位。
[Abstract]:In recent years, many scholars have paid close attention to the Cretaceous volcanic rocks in the Tethys Himalayan belt. The study area is located in the central and eastern part of the Tethys Himalayan belt. It belongs to the northern margin of Great India and is also located in the province of residual igneous rocks in Tethys. Through the study of geochemistry and geochronology of magmatic rocks, this paper analyzes its genesis and tectonic environment, which provides evidence for the Neo-Tethys Ocean expansion and the eastward extension of Tethys igneous rocks, and also points out the direction for further prospecting. The volcanic rocks in Xiawa area, Tibet are mainly composed of dolomite, trachyte and anshanian basalt. The zircon U-Pb age is 142 鹵1.0 Ma.The zircon was formed in early Cretaceous. Elemental geochemistry shows that basalts are rich in Tianfeipeng mg peraluminous alkaline basalts, which are similar to OIB, and the total amount of rare earth elements 鈭，

本文編號(hào)：2115122