西藏安多纳茸矿区石英闪长玢岩成因及地质意义  

Petrogenesis and Geological Significance of Quartz Diorite Porphyry in Narong Mining Area, Tibet

作　　者：刘海永[1,2] 唐菊兴 王雨[2] 曾庆高 赵洪飞 央宗 华康 张鹏 Liu Haiyong;Tang Juxing;Wang Yu;Zeng Qinggao;Zhao Hongfei;Yang Zong;Hua Kang;Zhang Peng(College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,China;Tibet Institute of Geological Survey,Lhasa 850000,China;Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;Tibet Bureau of Geological and Mineral Exploration and Development,Lhasa 850000,China;The Second Geological Party,Tibet Bureau of Geological and Mineral Exploration and Development,Lhasa 850000,China;Sichuan Institute of Land Science and Technology,Chengdu 610045,China)

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]西藏自治区地质调查院,西藏拉萨850000 [3]中国地质科学院矿产资源研究所,北京100037 [4]西藏自治区地质矿产勘查开发局,西藏拉萨850000 [5]西藏地勘局第二地质大队,西藏拉萨850000 [6]四川省国土科学技术研究院,四川成都610045

出　　处：《地球科学》2022年第3期1059-1077,共19页Earth Science

基　　金：中国地质调查项目(No.DD20190167);第二次青藏高原综合科学考察研究典型地区岩石圈组成、演化与深部过程专题(No.2019QZKK0702)。

摘　　要：纳茸矿区位于南羌塘南缘东段,是认识班公湖‒怒江成矿带构造‒岩浆‒成矿作用的理想窗口.以纳茸矿区内出露的石英闪长玢岩为研究对象,对其进行了系统的锆石U-Pb定年、全岩地球化学、锆石原位Hf同位素及全岩Sr-Nd同位素研究.结果显示纳茸矿区石英闪长玢岩形成于晚侏罗世(158~155 Ma),属于钙碱性系列,具有高Sr(178×10^(-6)~1086×10^(-6))含量以及高Sr/Y(15~82)和(La/Yb)^(N)(17~34)比值,亏损重稀土元素(如Yb=1.05×10^(-6)~1.45×10^(-6),Y=10.50×10^(-6)~14.78×10^(-6)),整体呈现出与埃达克质岩石相似的地球化学特征.石英闪长玢岩样品低MgO、Cr、Ni,高Th和Th/U,锆石ε_(Hf)(t)值在-1.7~4.3之间,(^(87)Sr/^(86)Sr)i比值为0.70593~0.70681,ε_(Nd)(t)值在-2.67~-0.49之间.结合区域地质资料,指示其是俯冲背景下加厚下地壳部分熔融的产物.将本文研究结果与南羌塘中西段的同期岩浆作用相结合,表明班公湖‒怒江洋向北俯冲至羌塘地体之下,在晚侏罗世形成了超过1200 km的近东西向岩浆弧.纳茸矿区与多龙矿集区内成矿岩体具有相似的锆石Hf同位素组成,锆石微量元素具有高Ce/Ce^(*)、Eu/Eu^(*)比值,全岩微量元素具有较高的Sr/Y、V/Sc比值,显示纳茸矿区具有较好的成矿潜力.Narong mining area is located in the southern margin of southern Qiangtang Block,providing an ideal window for understanding the tectonic-magmatic activities and mineralization of Bangong Co-Nujiang metallogenic belt.In this case study,we focus on the quartz diorite porphyries in the Narong mining area and report new zircon U-Pb ages,geochemical,zircon Hf and whole-rock Sr-Nd isotopic data.The results show that the Narong quartz diorite porphyries were emplaced during the Late Jurassic(158-155 Ma).Geochemically,the quartz diorite porphyry samples belong to calc-alkaline series.They are characterized by high Sr(178×10^(-6)-1086×10^(-6))contents,and high Sr/Y(15-82),(La/Yb)N(17-34)ratios with depletions of heavy rare earth elements(such as Yb=1.05×10^(-6)-1.45×10^(-6),Y=10.50×10^(-6)-14.78×10^(-6)).These geochemical features are generally consistent with those of typical adakitic rocks.Additionally,the studied samples have lower MgO,Cr,Ni but higher Th and Th/U.Their zirconε_(Hf)(t)values are between-1.7 to+4.3,initial(^(87)Sr/^(86)Sr)i values are between 0.70593-0.70681 and theε_(Nd)(t)are between-2.67 to-0.49.These features,along with regional geological information,indicate that they are products of partial melting of thickened lower crust during slab subduction process.In combination with data from the middle and western segments of South Qiangtang,we infer that the Bangong Co-Nujiang Ocean subducted northward beneath the Qiangtang Block,forming a nearly E-W direction magma arc(>1200 km)during the Late Jurassic.The ore-forming intrusions in the Narong mining area and the Duolong ore concentration area have similar zircon Hf isotopic compositions,and zircon trace elements have high Ce/Ce*and Eu/Eu*ratios,and whole rock trace elements have high Sr/Y and V/Sc ratios,showing positive mineralization potential.

关 键 词：青藏高原 纳茸矿区 晚侏罗世 岩石成因 成矿潜力 地球化学 

分 类 号：P581[天文地球—岩石学]