青藏高原中部麻米地区晚侏罗世火山岩岩石成因及其地质意义

在青藏高原中部中拉萨地块之上新识别了一套晚侏罗世-早白垩世早期岩浆岩，本次对其中麻米地区出露的火山岩进行了锆石U-Pb定年与全岩主微量元素分析研究工作.测年结果显示麻米火山岩形成于晚侏罗世（152~150 Ma），岩石地球化学具有高SiO₂、高全碱含量（Na₂O+K₂O）、低MgO、低P₂O₅的特征，并显示明显的Eu、Sr、Ba等元素的亏损，具有高分异I型花岗质岩石的特征.结合区域上报道的同期中酸性侵入岩资料，麻米酸性火山岩起源于古老地壳物质重熔并经历了广泛的结晶分异作用.本文研究表明中拉萨地块上晚侏罗世-早白垩世早期岩浆作用形成于洋壳俯冲背景，应该是新特提斯洋北向俯冲过程中引发的弧型岩浆事件. 

Petrogenesis and Geological Significance of Late Jurassic Volcanic Rocks in Mami Area,Central Tibetan Plateau

A new Late Jurassic-Early Cretaceous magmatic belt has been identified in the central Tibetan Plateau. This paper reports two zircon U-Pb ages and also new whole-rock major and trace element data of the newly discovered volcanic rocks in Mami area. These volcanic rocks were dated as Late Jurassic (152-150 Ma). The studied samples are characterized by high SiO₂ content, high alkali, low MgO, and low P₂O₅ abundances, with significant depletion in Eu, Sr, and Ba, suggesting a geochemical affinity with highly fractionated I-type granites. It is concluded that the volcanic rocks were derived by partial melting of ancient mafic lower crust, followed by fractional crystallization. Our research propose that Late Jurassic-Early Cretaceous magmatic magmatism occurred in an oceanic subduction setting, likely related to the northward subduction of the Neo-Tethys oceanic lithosphere.