發(fā)布時間：2018-04-14 19:32

  本文選題：鋯石U-Pb年代學(xué) + 元素地球化學(xué)　； 參考：《中國地質(zhì)大學(xué)(北京)》2015年碩士論文

【摘要】：西秦嶺造山帶出露較多的花崗質(zhì)巖石,其形成和侵位過程是大陸造山帶形成演化中極為重要的問題,記錄著西秦嶺地區(qū)與原特提斯洋和古特提斯洋密切相關(guān)的洋殼俯沖、陸陸(弧)碰撞和碰撞后等構(gòu)造事件,也是長期以來地質(zhì)學(xué)家們研究的重點。本文對西秦嶺西段侵位于中下三疊統(tǒng)隆務(wù)河組的西功卡花崗閃長巖和卡力崗閃長玢巖兩個巖體進行了詳細(xì)的巖石學(xué)、元素地球化學(xué)、鋯石U-Pb同位素年代學(xué)分析研究,以期揭示其巖石成因及構(gòu)造屬性,對恢復(fù)重建西秦嶺造山帶西段印支期構(gòu)造格架及地球動力學(xué)過程均具有重要的理論意義。元素地球化學(xué)特征顯示,兩個巖體具高鉀鈣堿性I型花崗巖特征。西功卡巖體Na2O和K2O的含量分別為1.98~3.4%和3.12~4%,A/CNK值主體小于1.1(0.97~1.2),平均為1.08。稀土總量∑REE=106.69~136.47×10-6,輕稀土LREE=97.84~131.03×10-6,重稀土HREE=5.44~10.07×10-6,LREE/HREE比值介于11~24.1�？�力崗巖體Na2O和K2O的含量分別為2.57%~3.66%和2.3%~3.95%,A/CNK值全部小于1.1(0.85~1),平均為0.92。稀土總量∑REE=117.08~146.42×10-6,輕稀土LREE=104.89~133.27×10-6,重稀土HREE=12.18~13.42×10-6,LREE/HREE比值介于8.5~10.1。兩者在球粒隕石標(biāo)準(zhǔn)化稀土元素配分曲線圖解上也表現(xiàn)出具弱的負(fù)Eu異常、輕稀土富集、重稀土顯著虧損的曲線平滑的右傾特征,在原始地幔標(biāo)準(zhǔn)化微量元素蛛網(wǎng)圖表現(xiàn)出大離子親石元素(Cs、Rb、Ba、Th、U)明顯富集,高場強元素(Nb、Ta、P)明顯虧損的特征。分析認(rèn)為兩者具有同源演化的特征。LA-ICP-MS鋯石U-Pb同位素定年顯示,西功卡花崗閃長巖體的巖漿結(jié)晶年齡為227.2±7.3Ma,形成于晚三疊世卡尼期;卡力崗閃長玢巖體巖漿結(jié)晶年齡為238.7±7Ma,形成于中三疊世拉丁期。由于巖體均侵位于隆務(wù)河組,結(jié)合隆務(wù)河組沉積巖碎屑鋯石測年資料,綜合限定了隆務(wù)河組形成時代為奧倫尼階-拉丁階。通過微量元素組合判別并結(jié)合前人研究資料,認(rèn)為兩個巖體都是在碰撞后環(huán)境下,由于巖石圈拆沉后幔源基性巖漿底侵導(dǎo)致下地殼變基性巖石部分熔融形成的,并可能發(fā)生了一定程度的殼幔巖漿混合作用。
[Abstract]:The formation and emplacement of granitic rocks in the West Qinling orogenic belt are very important problems in the formation and evolution of continental orogenic belts, and record the oceanic crust subduction in the West Qinling region, which is closely related to the original Tethys Ocean and the PaleoTethys Ocean.Continental (arc) collision and post-collision tectonic events have long been the focus of geologists.In this paper, detailed petrology, element geochemistry and zircon U-Pb isotopic chronology of the Xigongka granodiorite and Kaligang diorite porphyrite in the western part of the western Qinling Mountains, located in the middle and lower Triassic Longwuhe formation, have been studied in detail.In order to reveal its petrogenesis and tectonic properties, it is of great theoretical significance to reconstruct the Indosinian tectonic framework and geodynamic process in the western part of the Western Qinling orogenic belt.The geochemical characteristics of elements show that the two rock bodies are characterized by high potassium calc-alkaline I type granite.The contents of Na2O and K _ 2O in Xigongka rock mass are 1.98 ~ 3.4% and 3.12 ~ 4% respectively.The total amount of rare earth 鈭，

本文編號：1750707