【摘要】 对西藏错那洞穹隆核部的一套动力变质花岗片麻岩(正片麻岩)开展年代学及岩石地球化学研究,探讨其成因机制。结果显示,花岗片麻岩锆石具有显著的岩浆锆石形态学特征及Th和U含量,年龄谐和度较高,加权平均年龄为(809.4±3.1)Ma,代表了花岗片麻岩的结晶时间;花岗片麻岩为一套富硅、富碱、过铝质的花岗岩,轻重稀土元素分馏强烈,稀土配分曲线为轻稀土富集、重稀土亏损的右倾式,有显著的负Eu异常,亏损Ti、Nb、Ta,具低Ba、Sr和高Rb的特征,Nb/Ta比值低,远低于幔源岩浆,显示了典型的壳源特征。结合全球构造岩浆演化,认为喜马拉雅造山带中存在广泛的新元古代岩浆活动。新元古代花岗岩类岩石是沿Rodinia超大陆西北缘发育的安第斯型造山作用的产物,随后在喜马拉雅造山运动时期经历了新生代变质作用。更多还原

【Abstract】 The petrogeochemistry and chronology of Neoproterozoic granitic gneiss in the Cuonadong dome are studied and its genetic mechanism is discussed. It shows that the morphological features and Th and U contents of the zircon grains in the granitic gneiss are similar to the characteristics of igneous rocks. Zircon U-Pb dating for the gneiss yields a 809.4±3.1 Ma age with high concorde degrees, which represents the crystallization age of granitic gneiss. Geochemical analysis indicates that the granitic gneiss is characterized by high-K, high-Si and alkali, and belongs to peraluminous granite series with strong HREE and LREE fractionation. Right inclined pattern indicates LREE enrichment and HREE depletion with obvious negative Eu anomalies. The rocks are depleted in Ti, Nb and Ta with low content of Ba and Sr, and high content of Rb. And the value of Nb/Ta is much lower than the mantle source magma, characteristic of typical earth crust source. In consideration of the global magmatic evolution, an extensive Neoproterozoic magmatic event may have occurred in the Himalayan orogen. The Neoproterozoic granitoids were resulted from the Andean-type orogeny and formed along the northwestern margin of Rodinia supercontinent. These granites experienced the Cenozoic high-grade metamorphism during the Himalayan orogeny.更多还原