摘要
东昆仑造山带出露大量花岗质岩浆岩,岩石中广泛发育暗色微粒包体,是研究岩浆混合作用的天然场所。本文以东昆仑东段香加南山花岗岩基为研究对象,对暗色微粒包体的野外地质特征进行研究,探讨岩浆混合作用和岩浆动力过程。暗色微粒包体具细粒-中粗粒结构,含有斜长石、角闪石、石英、暗色环边石英和钾长石等斑晶,偶见斑晶横跨寄主岩和包体,常发育反向脉,包体与寄主岩接触关系呈截然型或过渡型,这些特征说明暗色微粒包体为岩浆混合作用的产物,混合过程存在着物质交换。包体从细粒-粗粒-弥散状-完全混合岩浆说明岩浆混合的比例越来越大,温差越来越小,两种岩浆温度差对包体的形成具有很大影响。对包体的形态研究显示,包体不同拉伸程度是岩浆黏度、温度、流动速度等因素共同作用的结果,拉伸程度越大塑性变形程度越大。包体的长轴方向主要分为两类:一类与包体的整体方向近似,代表岩浆的流动方向;另一类要么没有固定方向,要么同一露头有几种不同方向,为岩浆局部搅动、对流的结果。包体进入寄主岩自身的旋转、流动和岩浆的局部搅动,使少量包体边部矿物和寄主岩矿物具有定向性。暗色微粒包体相互包裹和同一露头不同类型的暗色微粒包体说明岩浆混合具有多期次性。香加南山花岗岩基暗色微粒包体的野外地质特征为岩浆混合作用以及岩浆动力学过程提供了重要佐证。
East Kunlun Orogen is a natural site to study the magma mixing and mingling,where a lot of granitic magmatic rocks outcropped with widely developed mafic microgranular enclaves in it. Taking the Xiangjiananshan granitic batholith in eastern section of East Kunlun Orogen as the object,the paper has studied the field geological characteristics of mafic microgranular enclaves developed in the batholith,in order to research the magma mixing and mingling and the magma dynamics process.The enclaves have fine grained to medium-coarse grained texture,and contain phenocrysts like plagioclase,amphibole,quartz,mafic minerals edged quartz,and K-feldspar,which stretch across the host rocks and enclaves occasionally.The enclaves often contain back veins,and the contact boundaries between the enclaves and host rocks are sharp or transitional.The above characteristics suggest that the mafic microgranular enclaves are the products of magma mixing and mingling,in which an interchange of material have taken place in the processes.The textures of enclaves vary from fine grain to coarse grain,and dispersive to completely mixed,indicating that the proportions of magma mixing become bigger and the temperature differences between the two magmas become smaller.The temperature differences between the two magmas have a great influence on the formation of enclaves.Research on the morphology of enclaves shows that they have different stretch degrees,resulting from interactions among viscosity,temperature,flow rate,etc.The plastic deformation degree increases with the stretch degree of the enclaves.The enclaves have different long-axis directions,mainly divided into two categories,one with approximately directions representing the magma flow direction,one with no fixed direction or with several different directions at the same outcrop representing the magma partial stirring and convection.When injected into the acidic magma represented by the host rocks,the basic magma represented by the enclaves came into rotating and flowing,and partial sti
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2016年第4期226-240,共15页
Earth Science Frontiers
基金
国家自然科学基金项目(41472191
41502191
41172186
40972136)
高等学校博士学科点专项科研基金项目(20110205110004)
中央高校基本科研业务费专项资金项目(CHD2011TD020
2013G1271091
2013G1271092)
青海省国土资源厅-中国铝业公司公益性区域地质矿产调查基金项目(中铝基金200801)