摘要
老挝NM矿区位于中北部长山(Truong Son)岩浆-构造内。在二叠-三叠纪的印支运动期间,Sibumasu板块沿Nan-Uttaradit缝合线与印支板块拼接后,在印支板块的东部形成了北西向右旋的长山(Truong Son)岩浆-构造剪切带。NM矿区的花岗岩可分为中粗粒花岗岩、斑状花岗岩和细粒花岗岩。本区不同类型花岗岩的地球化学特征显示其ACNK值多介于0.9～1.1之间,为高钾钙碱性花岗岩;微量元素中多富集Cs,Rb,Th,U,K而相对亏损Ba,Sr等大离子亲石元素,高场强元素分异明显,Nb,P,Ti表现出明显的负异常;稀土元素相对富集轻稀土,轻稀土元素分馏程度高而重稀土元素分馏程度不明显,铕具中等或明显的负异常,上述特征表明本区不同类型花岗岩的物质来源相似。结合本区的大地构造特征和花岗岩的地球化学特征来看,本区花岗岩可能形成于印支碰撞造山后期的挤压-剪切环境。同时岩浆在从中粗粒花岗岩向斑状花岗岩和细粒花岗岩的结晶演化过程中,TFe,TiO2,MgO,CaO,Na2O的含量逐渐降低,而SiO2和K2O的含量相对增加,Fe,Cu,Zn(Pb)等矿化主要与其中的斑状花岗岩的关系较为密切。
The NM deposit is located in the northwest trending magmatic-tectonic belt, northcentral part of Truong Son, which was subjected to right-lateral shearing due to the collision of Sibumasu micro-continent with Indo-China micro-continent along Nan-Uttaradit suture during Permian-Triassic Period. Based on the grain size and spatial distribution,the granites in NM deposit can be classified into medium-coarse grained granite, porphyritic granite and fine grained granite respectively. The geochemical characteristics of different types of granite show that they are high-potassium, calc-alkaline granitoids with the ACNK ratios mostly ranging from 0.9 to 1.1. Trace elements of the granites show that the variety of LILE enriches in Cs,Rb,Th,U,K, while depletes in Ba and Sr,distinct fractionation of HFSE with clearly negative anomaly of Nb,P and Ti. REE analysis reveals relative high content and distinct fractionation of LREE in contrast to HREE,and moderate to sharp negative Eu anomaly. All of the geochemical features indicate that these different types of granites in NM deposit were derived from the same origin related to the special tectonic setting of post-collision volcanic arc. During the magmatic evolution process from early stage represented by medium-coarse grained granite to last stage represented by fine grained granite,the TFe, TiO2, MgO, CaO and Na2O contents in magma tend to decrease, while the SiO2 and K2O contents increase gradually, and the Fe,Cu and Zn （Ph） mineralization is mainly related to the porphyritic granite.
出处
《矿物岩石》
CAS
CSCD
北大核心
2011年第3期82-89,共8页
Mineralogy and Petrology
基金
中国科学院地球化学研究所资助项目
有色金属矿产地质调查研究中心创新项目
关键词
地球化学
花岗岩
印支运动
老挝
geochemistry
granite
Indo-China movement
Laos
