青海共和盆地东部曲乃亥花岗闪长岩锆石U-Pb定年及地球化学特征

文章对青海共和盆地东部曲乃亥花岗闪长岩体的岩石学、岩石地球化学、年代进行了研究,其结果表明：曲乃亥花岗闪长岩LA-ICP-MS锆石U-Pb定年239.4 Ma±2.8 Ma（n=16,MSWD=0.29）,表示该岩体形成于中三叠世;岩石的主量元素地球化学特征值反映曲乃亥花岗闪长岩（体）具富硅、富钾、准铝质-过铝质等特征,属于高钾钙碱性花岗岩;岩石的微量元素地球化学分析显示,富集大离子亲石元素（如Rb、Th、K、U）,亏损高场强元素（如Nb、Ta、Ti）,在稀土配分图上呈现轻稀土元素富集、重稀土元素亏损的右倾曲线特征;岩石构造环境判别图解反映曲乃亥花岗闪长岩（体）为Ⅰ型花岗岩,属于俯冲环境下活动大陆边缘构造作用所形成的产物,其可能主要来自于地壳物质的部分熔融。

Zircon U-Pb dating and geochemical characteristics of the Qunaihai granodiorite in the eastern part of the Gonghe Basin, Qinghai province

This paper studied petrology, chronology and rock geochemistry of Qunaihai granodiorite in the eastern part of the Gonghe Basin. The LA-ICP-MS zircon U-Pb dating of the granodiorite is 239.4 Ma±2.8 Ma (n=16, MSWD=0.29) indicating that the rock mass was formed in the Middle Triassic Epoch. Major elements of the granodiorite are characteristic of silicon-rich, potassium-rich, metaluminous to weak peraluminous material thus it belongs to high-potassium-calcium-alkaline granite; trace elements characteristic of enrichment of large-ionic lithophile elements (Rb, Th, K, U) and depletion of high-field strength elements (Nb, Ta, Ti) LREE enrichment and HREE depletion pattern. In the geotectonic environment discremination plot it is identified as I-type granite, the product of active continental marginal structural activity under subduction environment derived mainly from partial melting of the crustal material.