藏南定日白垩纪火山岩岩石学与地球化学初步研究

本文描述了西藏定日白垩纪火山岩的地质、岩石学、岩石地球化学特征和构造造背景。该火山岩岩石类型有蚀变英安岩和蚀变安山岩,其岩石化学成分特征表明岩石为二氧化硅过饱、铝过饱和类型,属亚碱性拉斑玄武岩系列。岩石稀土元素配分曲线呈强烈右倾的轻稀土富集型;微量元素配分模式图呈锯齿状“多隆起”型,类似于岛弧火山岩的微量元素配分模式。综合判定该期火山岩形成于大陆边缘造山带岛弧构造环境。

Petrography and geochemistry of the Cretaceous volcanic rocks in Tingri, southern Xizang

The geology, petrography, geochemistry and tectonic settings are described for the Cretaceous (volcanic) rocks in Tingri, southern Xizang. The volcanic rocks consist of altered dacite and andesite, which are assigned to the subalkaline, silica- and aluminum-oversaturated tholeiite series. The REE amounts range (between) (383.17)×(10^-6) and (266.52)×(10^-6). The REE distribution curves display highly right-leaning LREE-enriched patterns, whereas the trace element distribution patterns exhibit zigzag "polydome" patterns, similar to those for island-arc volcanic rocks. The trace element compositions are plotted into the volcanic arc field in the Rb-(Yb+Ta) diagram, and the lithochemical compositions fall into the island-arc orogenic basalt and andesite fields in the ATK diagram. The preceding results of research show that the Cretaceous volcanic rocks in the study area are interpreted to be formed in a continental marginal orogenic island-arc tectonic setting.