【作者】 孙挪亚；

【导师】 李亚林；

【作者基本信息】 中国地质大学(北京) ， 地质工程， 2012， 硕士

【摘要】 西藏仲巴地处世界屋脊-青藏高原的西南边，大地构造位置上属于冈底斯-念青唐古拉构造带的冈底斯岩浆岩带南带，自中生代以来，该带发育有多期次、大规模的中酸性侵入岩及火山岩。本文在前人的研究基础上，以仲巴始新世花岗岩为研究对象，进行了岩石学、地球化学、SHRIMP锆石U-Pb年代学、矿相学以及光谱等综合研究，并分析了岩石成因、形成的构造环境，评价了岩石成矿潜力，探讨了仲巴始新世花岗岩所代表的壳幔物质演化与深部作用过程。仲巴始新世花岗岩主要岩性为石英二长岩、二长花岗岩、黑云母二长花岗岩、石英闪长岩、钾长花岗岩，中到粗粒结构，发生不同程度的发生碎裂，这可能与本区多次的构造运动有关。通过岩石地球化学分析，发现所测样品中，SiO₂含量64.76%-76.96%，平均在69.82%，K₂O含量为3.82%-5.83%，平均在4.83%，同时具有高的K₂O/Na₂O比值（1.21-2.43）和低P₂O₅含量（0.02%-0.27%）；里特曼指数（δ）介于1.79-4.00之间，为钙碱性岩类；铝饱和指数A/CNK介于0.86-1.03之间，平均0.95<1.1，为I型花岗岩；CaO、Fe₂O₃、TiO₂、Al₂O₃、MgO、P₂O₅与SiO₂呈现较明显的负相关关系；微量元素含量明显偏高，标准化值多大于1，标准化曲线向右倾斜，表现出相对富集U，而强烈亏损Ba、Nb、Sr、Ti；稀土元素总量∑REE＝（84.94-304.51）μg/g，平均211.91μg/g；强烈富集轻稀土元素，LREE/HREE＝13.95-20.00，平均17.32；具较强烈的Eu负异常；以上这些数据显示，这可能是壳幔岩浆混合的产物，是地壳不同深度源岩重熔的结果。仲巴始新世花岗岩SHRIMP锆石U-Pb测年结果表明，该花岗岩形成于38.25Ma，处于青藏高原的后碰撞阶段，是青藏高原后碰撞阶段的产物。通过矿相学发现，本区部分岩石中含有较多的蓝铜矿、黄铜矿、黄铁矿、闪锌矿，通过光谱数据发现，本区个别岩石中Ag、Cu、Sb含量较高，这表明本区有可能存在与碰撞作用相关的矿床。更多还原

【Abstract】 Zhongba area,located in the southwest of Tibet plateau-the roof of the world，isgeotectonically included to the south belt of Gangdise compound magmatic belts ofGangdise-Nyainqentanglha tectonic zone,where develops of multi-periods, large-scaleintermediate-acidic intrusive rocks and volcanic rocks since Mesozoic time.Based on the previous studies,this thesis takes the Cenozoic granites as researchobject,by means of petrology, geochemistry， Zircon SHRIMP U-Pb Geochronology,mineralogy， spectrum analysis,analyzing the petrogenesis and tectonicenvironment,evaluating the mineralization potentiality,discussing the evolution anddeep action processes of crust-mantle materials that they represent.The Cenozoic granites are mainly composed of medium-coarse grained quartzmonzonite, monzonitic granite, biotite monzogranite, quartz diorite and potassiumgranite.They contains varied fractures,which may related to multiple tectonicmovements occurring in this area.Through geochemical analysis, we find that the SiO₂content is64.76%-76.96%（average,69.82%）, the K₂O content is3.82%-5.83%（average,4.83%）,with highK₂O/Na₂O ratio（1.21².43） and low P₂O₅content（0.02%⁰.27%）;δ=1.79-4.00,calc-alkaline series； A/CNK=0.86-1.03（average,0.95<1.1）, I type granite;CaO,Fe₂O₃,TiO₂,Al₂O₃,MgO,P₂O₅shows obvious negative correlation with SiO₂; thecontents of trace elements,whose standardized values are more often than1,aresignificantly higher,with normalized curves skewing to the right,presenting relativelyhigher U concertration,strongly lossing Ba,Nb,Sr,Ti;∑REE=84.94-304.51μg/g（average,211.91μg/g）; intensely enriched in LREE, LREE/HREE=13.95-20.00（average,17.32）; strong negative Eu anomalies.The refered datas reveal that thegranites are probably the mixtures of crust-mantle magmas and the results of theremelting of crust-derived rocks from different depths.The datas of SHRIMP U–Pb dating of zircon from Mesozoic Zhongba granitesindicate that this granites,which were formed at38.25Ma, were the consequences ofthe post-collisional stage of Tibet plateau.The mineralogy shows that some granites contain higher grade of Azurite,chalcopyrite, pyrite and sphalerite. According to spectroscopic datas,we find thatthere are higher grade of Ag,Cu,Sb in several collected samples, it indicates that theremay exist relative deposits.更多还原