藏北银顶山地区中新世高镁-超钾质火山岩成因研究

The volcanic rocks of the Cenozoic in North Tibet Plateau have important implications for crust-mantle material composition as well as growth process of the plateau. At present, the intermediate to acidic volcanics of studied area have been paid more attention to, while the magma system from lithospheric mantle and asthenosphere has been weakly researched. There develop High Magnesium-Ultrapotassic Volcanic Rocks in the Miocene in the Yinding mountain area of the Hoh Xil, North Tibetan Plateau. They contain several type of phenocrysts such as phlogopite, leucite, nepheline and olivine. Thus, high magnesium-ultrapotassic volcanic rocks have been selected to do researches on in this project. The age of volcano eruption could be relatively accurately measured on potassium-rich minerals such as phlogopite and leucite by the laser microprobe 40Ar/39Ar isotope dating technique. Where the olivines come from could be answered according to Mg brand (phenocrysts and xenocrysts) by the electron probe analysis of single mineral. We intend to do experiments of micro-zone Li and O isotopic analysis on the olivines by SIMS, in order to reveal the petrogenesis of high Mg-ultrapotassic volcanics and discuss the effect of intracontinental subduction on the lithospheric mantle.

青藏高原北部新生代火山岩对于揭示高原壳-幔物质组成与探讨高原生长过程具有重要的指示作用。目前的研究主要针对中酸性火山岩，但对于来自于岩石圈地幔甚至软流圈的岩浆系统研究非常薄弱。青藏高原可可西里北缘银顶山地区中新世高镁-超钾质火山岩含有金云母、白榴石，橄榄石、霞石等斑晶。本项目选取高镁-超钾质火山岩为研究对象，针对金云母或白榴石等富钾矿物，利用激光显微探针40Ar/39Ar同位素定年技术，精确限定新生代火山岩喷发时代；借助电子探针单矿物分析结果，根据Mg牌号识别橄榄石的来源（斑晶或捕掳晶）；并利用SIMS对橄榄石进行微区Li和O同位素分析，揭示高镁-超钾质火山岩的成因，探讨陆内俯冲对藏北岩石圈地幔的影响作用。