西藏安多纳茸矿区石英闪长玢岩成因及地质意义

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（178×10-6~1 086×10-6）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，（87Sr/86Sr）_i比值为0.705 93~0.706 81，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1 200 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. 

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

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 (178×10-6-1 086×10-6) 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 zircon ε_Hf(t) values are between -1.7 to +4.3, initial (87Sr/86Sr)_i values are between 0.705 93-0.706 81 and the ε_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 (> 1 200 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.