Abstract:

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 km2. Northern and north-western parts of the pluton intruded into the middle segment of the Late Proterozoic 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 lithofacies, 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 Sr, 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.

Key words: alkaline rocks, Indosinian period, geochemistry, western-Kuoktagh, Xinjiang