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报道了西藏自治区拉萨地块中部仁错地区的念青唐古拉岩群中变质辉长岩的锆石U-Pb定年结果和岩石地球化学资料以及锆石Hf同位素组成.LA-ICP-MS和SIMS锆石U-Pb定年结果表明,变质辉长岩原岩形成于新元古代早期(约925 Ma),这是目前拉萨地块乃至整个青藏高原内部最古老的基性岩浆记录.全岩地球化学资料显示,变质辉长岩具有类似典型大洋中脊玄武岩(N-MORB)的地球化学特征,并有部分岛弧拉斑玄武岩(IAT)的亲缘性.变质辉长岩锆石具有明显正的?Hf(t)值(8.26~13.7)和年轻的Hf模式年龄(TDM=933~1205 Ma),表明变质辉长岩原岩的岩浆来自于亏损的地幔源区.综合这些资料可知,变质辉长岩可能代表了新元古代早期的洋壳残片,这为深入理解青藏高原前寒武纪的构造演化的研究提供了重要信息.
This paper reports the zircon U-Pb dating and geochemical data of zircons and the zircon Hf isotopic compositions of metamorphic gabbro from the Nyainqentanglt group in the central part of the Lhasa massif in the Tibet Autonomous Region The results of U-Pb dating indicate that the metamorphic gabbro protolith was formed in the early Neoproterozoic (about 925 Ma), which is the oldest basic magma record in Lhasa block and the entire Qinghai-Tibet Plateau. , Metamorphic gabbro has geochemical characteristics similar to those of typical mid-ocean ridge basalts (N-MORB) and is associated with some island arc tholeiitic basalts (IATs). The metamorphic gabbro zircons have a significantly positive Hf (8.26 ~ 13.7) and young age of Hf (TDM = 933 ~ 1205 Ma), indicating that the magma in the metamorphic gabbro originates from a depleted mantle source.According to these data, the metamorphic gabbro may represent The early Neoproterozoic oceanic crust fragments, which provide in-depth understanding of the Precambrian tectonic evolution of the Qinghai-Tibet Plateau provides important information.