新疆库鲁克塔格阔克塔格西碱性岩年代学、岩石地球化学特征及其地质意义

Geochronology,Petrogeochemistry of Western-Kuoktagh Alkaline Rocks in Quruqtagh Area in Xinjiang and Its Geological Implications

阔克塔格西碱性岩体出露于库鲁克塔格地块东段,兴地断裂南0.5km,呈椭圆状岩株产出,出露面积约17.5km2。岩体北部和西北部侵入于古元古界兴地塔格群中亚群大理岩、片岩及片麻岩之中,南部和东南部分别侵入于中元古代黑云母石英正长岩和黑云母角闪二长岩中。岩体从边部至中心可分为霓石钠长岩、霓石角闪正长岩和角闪正长岩3个岩相带。岩体边部内接触带形成ERR-Nb-Ta-Zr中型矿床。岩体锆石U-Pb年龄(LA-ICP-MS方法)为(224±2)Ma。岩石主要矿物为微斜长石和条纹长石,暗色矿物主要为钠铁闪石,具有碱性岩典型的富碱、低硅的特点。此外,富集轻稀土元素,负Eu异常,富集Nb、Ta、Th及Hf等高场强元素,亏损Sr、P及Ti不相容元素。Hf同位素特征显示岩浆源于富集岩石圈地幔。地球动力学背景属造山后的板内演化阶段。

The western-Kuoktagh alkaline pluton is located in eastern part of Quruqtagh area, 0.5 km to the Xingdi fault. It＇s an over-shape stock with the outcrop area of 17.5 km2. Northern and north- western parts of the pluton intruded into the middle segment of the Late Proterozoie Xingditage Group composed of marble, schist and gneiss. Southern and southeastern parts of the pluton intruded into the Middle Proterozoic biotite quartz syenite and biotite hornblende monzonite, respectively. The pluton could be divided into three lithofacies belts, from edge to center, i.e. aegirin albitite lithofaeies, aegirine hornblende syenite lithofacies and amphibolite hornblende syenite lithofacies. A medium-sized REE - Nb - Ta - Zr deposit occurs in inner contact zone of the pluton. LA - ICP - MS zircon U - Pb dating of the pluton obtains an age of （224_--＋-2） Ma. Major minerals in the rock include microcline, perthite and arfvedsonite. The rock is of typical characters of alkaline rocks： high alkali and low silicate. Geochemically, the alkaline rock is characterized by enrichment of Nb, Ta, Th, Hf, LREE and depletion of St, P, Ti as well as negative Eu anomalies. Hf isotopic characteristics in the zircon indicate that the magma derived from enriched lithospheric mantle. Its geodynamic setting belonged to the inner plate evolution stage post orogenic process.