云南马关新生代钾玄质玄武岩的岩石学与地球化学特征及构造环境  

Petro-Geochemical Characteristics and Tectonic Setting of Cenozoic Shoshonitic Basalts from Maguan,Yunnan Province

作　　者：黄行凯[1] 莫宣学[1] 喻学惠[1] 李勇[1] 和文言[1] 李小伟[2] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,中国地质大学地球科学与资源学院,北京100083 [2]北京大学地球空间与科学学院,北京100871

出　　处：《地球科学（中国地质大学学报）》2012年第3期463-474,共12页Earth Science-Journal of China University of Geosciences

基　　金：国家重点基础研究"973"项目(No.2009CB421000)

摘　　要：云南马关地区广泛出露了一套富含大量幔源包体和捕掳晶的新生代玄武岩.对该地区的新生代玄武岩进行了岩石学和地球化学方面的研究,为该地区自新生代印度-欧亚大陆碰撞以来发生的岩浆活动及壳幔物质交换等问题提供重要的信息和岩浆岩约束.研究表明:该区玄武岩具有富碱且富钾的特征,其中全碱含量w(K2O+Na2O)变化在2.94%～8.23%之间、K2O/Na2O在0.44～6.72之间,21个样品平均的K2O/Na2O比值为1.26.采用火山岩类型系列与划分方法,确定本区多数岩石属于钾玄岩类的玄武岩或碧玄岩.岩石具有富集LREE和LILE的特征,经球粒陨石/原始地幔标准化后的稀土元素配分形式和微量元素蜘蛛图均具有与OIB相似的特征.岩石中含有大量深源岩石包体,斑晶含量少且结晶程度低,相容元素Ni含量较高等特点,符合原生岩浆的基本特征;唯有Mg#(0.49～0.72)偏低,可能与源区本身的性质或者源区发生的壳幔混合作用等因素有关.根据钾质岩石构造环境判别标准,显示岩石形成于板内环境,其成因与印度-欧亚大陆的碰撞诱发的软流圈物质向高原东南方向侧向挤出有关.A suite of Cenozoic shoshonitic basalts bearing abundant mantle-derived xenoliths and xenocrysts outcropped in Maguan area, Yunnan Province. This study provides results of petrological and geochemical characteristics of the Cenozoic shoshonitic volcanic rocks, aiming to offer some food to thoughts related to volcanism and mantle-crust interation induced by to the continental collision between India and Asia plates. Results showed that Cenozoic shoshonitic basalts from this area have relatively high and variable alkali contents （2.94%-8. 23%）, and are rich in potassium （average K2O/Na2O of 2] samples is 1.26）. They are classified as shoshonitie basalts or basanite. They are enriched in both light rare earth elements （LREE） and large ion lithophile elements （LILE）, and distribution patterns in the chondrite-normalized diagram and primitive-normalized spidergram collectively resemble the pattern of OIB. The shoshonitic basalts contain abundant mantle-derived xenoliths and xenocrysts, and are poorly crystallized with very low contents of phenocrysts, and have considerably high abundance of compatible elements such as Ni, implying that the Cenozoic basaltic rocks of Maguan area are representatives of primary magma derived from mantle sources. The relatively low Mg# of rocks, ranging from 0. 49 to 0. 72, can either be ascribed to the intrinsic characteristics of the source region or to the mixing of crust and mantle materials in the source region, which needs to be further studied. The Cenozoic shoshonitic basalts formed in a within-plate tectonic setting, the petrogenesis of which is related to the lateral extrusion of asthenospheric mantle along the southeastern of Tibetan plateau induced by the Indo-Asia collision.

关 键 词：云南马关 新生代钾玄岩 岩石学 地球化学 构造环境 

分 类 号：P584[天文地球—岩石学]