冈底斯印支晚期后碰撞花岗岩: 锆石U-Pb年代学及岩石地球化学证据

对出露在冈底斯中带的达布拉岩体进行了系统的岩石学研究、LA-ICP-MS锆石U-Pb定年、岩石地球化学分析、Sr-Nd-Pb同位素组成的讨论.结果显示, 达布拉岩体的岩石类型为二长花岗岩, 由中细粒的边缘相和中粗粒的中央相组成, 成岩年龄为230.6±4.3 Ma~228.2±3.5 Ma, 属晚三叠世.岩体具高Si(w(SiO₂)=71.79%~77.27%)、高K(w(K₂O)=4.06%~5.26%)、低Ti(w(TiO₂)=0.06%~0.40%)含量特征, 铝饱和指数(A/CNK)为1.16~1.19, 为强过铝质花岗岩, 负铕异常显著(Eu/Eu*=0.06~0.35), 强烈富集Rb、Th和亏损Ba、Nb、Sr、P、Ti.同位素组成上具高(87Sr/86Sr)_i值(0.712 7~0.720 1)、低ε_Nd(t)值(-10.6)、高放射成因Pb特征.达布拉岩体为澳大利亚大陆北缘与拉萨地块汇聚碰撞触发的班公湖-怒江洋壳岩石圈南向俯冲背景下, 在后碰撞伸展阶段由幔源岩浆底侵引发冈底斯成熟地壳物质部分熔融形成的. 

Post-Collision Related Late Indosinian Granites of Gangdise Terrane:Evidences from Zircon U-Pb Geochronology and Petrogeochemistry

The lithology, LA-ICP-MS zircon U-Pb age, major and trace element geochemistry, Sr-Nd-Pb isotope compositions of Dabula pluton from the middle part of the Gangdise granitoid belt are systematically studied in the paper. Results suggest that the rock type is adamellite, and the pluton is composed of middle-fine grained border facies and middle-coarse grained central facies. The two facies yield weighted mean ages of 230.6±4.3 Ma-228.2±3.5 Ma, with the corresponding age of Late Triassic. The rocks are relatively rich in SiO₂ and kalium, with SiO₂ content between 71.79%-77.27%; relatively high K(w(K₂O)=4.06%-5.26%) and low Ti(w(TiO₂)=0.06%-0.40%) contents; A/CNK varies from 1.16-1.19, displaying strong peraluminous characteristics and sharp negative Eu anomalies (δEu=0.06-0.35). Trace element ratio spider diagram displays apparent enrichments of Rb, Th elements, and marked depletions of Ba, Nb, Sr, P and Ti The Sr-Nd isotopes show the granite bodies have the high initial 87Sr/86Sr ratios (0.712 7-0.720 1) and the negative ε_Nd(t) (-10.6) results. Pb isotope feature shows the enrichment of radiogenic Pb. It is concluded that the Dabula pluton was formed by partial melting of mature crustal materials from Gangdise resulted from the underplating of the subduction-related basaltic magmas during the post-collisional extention in the dynamic background associated with the southward Bangong-Nujiang Tethyan seafloor subduction triggered by the collision between the northern Australia and Lhasa terranes.