青藏高原北部黑石北湖新生代钾质火山岩的成因

昆仑岩带新生代钾质火山活动是青藏高原北缘深部动力学过程的重要记录。有关岩浆源区的性质和岩浆产生的机制一直存在较大的认识分歧。阐述了昆仑岩带黑石北湖钾质火山岩的岩石学和地球化学特征，并与西昆仑康西瓦和泉水沟新生代火山岩进行了成因对比分析。研究表明，昆仑火山岩带玄武质岩石的K2O和Na2O含量变化较大，从钠质过渡到钾质，硅碱图显示玄武质初始岩浆向钾质安粗岩方向演化。黑石北湖火山岩的高场强元素和Sr、Nd同位素组成显示岩浆源区具有EMⅡ的性质。岩石LREE的强烈富集和HREE的强烈分馏指示岩浆来自富集型含石榴子石地幔源区。不相容元素K/Nb、Ba/La等比值具有岛弧火山岩与OIB型玄武岩的过渡特征，指示源区为曾遭受软流圈流（熔）体交代的古俯冲地幔楔。

Genesis of Heishibeihu Cenozoic potassic volcanic rocks from northern Qinghai-Tibet Plateau,China

Cenozoic potassic volcanism of Kunlun area recorded the deep geodynamic processes of northern Qinghai-Tibet Plateau. There have always been major cognitive divergences about the source characteristics and generation mechanism of Cenozoic magma of Kunlun volcanic belt. In this paper, petrological and geochemical characteristics of Heishibeihu potassic volcanic rocks in Kunlun volcanic belt are discussed, and further genesis comparison of the Cenozoic volcanic rocks among Heishibeihu, Kangxiwa and Quanshuigou of west-Kunlun area are made. According to research, the K2O and Na2O contents of basaltic rocks of Kunlun volcanic belt vary largely, from sodic to potassic, and all the basaltic magma displays an evolution tendency of potassic latite in TAS diagram. Magmatic source of Heishibeihu volcanic rocks display EMⅡ characteristics in the composition of high field-strength element (HFSE) and Sr, Nd isotopic system. The Cenozoic volcanic rocks are intensively enriched in LREE and have strong differentiation in HREE, which indicates the magma was originated form garnet-bearing enriched mantle. The ratios of incompatible elements, such as K/Nb and Ba/La, show transitional features between island arc volcanic rocks and OIB (ocean island basalt), which indicates the magmatic source is an ancient subduction mantle wedge undergone metasomatism of asthenosphere fluid.