摘要
锡铁山地区位于柴北缘超高压变质构造带上,该构造带内发育多处金矿床。对锡铁山地区的二长花岗岩进行了锆石U-Pb年代学、全岩地球化学和Hf同位素测试分析。其中:锆石定年获得的二长花岗岩的成岩年龄为370.8 Ma±1.8 Ma(MSWD=0.34),属于晚泥盆世。岩石地球化学分析表明,二长花岗岩具有高SiO_2、Al_2O_3,富碱,低CaO、MgO的特征,属于弱过铝质高钾钙碱性花岗岩;微量元素原始地幔标准化蛛网图上显示,相对富集大离子亲石元素(Rb、Th、U、K),相对亏损高场强元素(Nb、Ta、P、Ti)。锆石Hf同位素分析结果表明,二长花岗岩锆石的εHf(t)值均为正值,且变化范围较小,对应的二阶段模式年龄为1 005~1 298 Ma,岩浆主要来源于新生基性地壳的部分熔融。综合区域岩石构造背景的研究,认为锡铁山地区二长花岗岩形成于南祁连向柴达木板块俯冲碰撞后伸展的环境,该期花岗岩与区域上热液脉型金矿床关系密切。
Xitieshan area sits in the ultra high pressure alteration tectonic belt of northern Qaidam,where there are a great number of gold deposits.In this paper,the monzogranite exposed in Xitieshan area was analyzed using zircon U-Pb dating,whole-rock geochemistry and Hf isotopes.Zircon dating yields an age of 370.8 Ma±1.8 Ma(MSWD=0.34)for the monzogranite,suggesting its emplacement in Late Devonian.The rock geochemistry indicates that the monzogranite has the characteristics of high SiO2 and Al2O3,rich alkali and low CaO and MgO,and belongs to the weak peraluminous high-K calc-alkaline granite.Primitive mantle-normalized trace element spider diagrams show relative enrichment of LILE(Rb,Th,U,K),and relative depletion of HFSE(Nb,Ta,P,Ti).Zircon Hf isotope analysis shows that the monzogranite has depleted Hf isotopic compositions with positiveεHf(t)values with narrow range of variation and the corresponding two-stage model age is 1 005 to 1 298 Ma.Magma mainly comes from partial melting of the new crust.Taking a study on the tectonic setting of rock structure into consideration,it can be concluded that the monzogranite from the Xitieshan intrusion formed in an extensional structure setting,which could be related to the subduction of the south Qilian orogenic belt beneath the Qaidam block.The granite in this period is closely related to the hydrothermal vein type gold deposit in the region.
作者
杨佰慧
李碧乐
金烨
高歌悦
张俊怡
孙景
廖宇斌
Yang Baihui;Li Bile;Jin Ye;Gao Geyue;Zhang Junyi;Sun Jing;Liao Yubin(College of Earth Sciences,Jilin University)
出处
《黄金》
CAS
2018年第4期7-14,共8页
Gold
基金
中国地质调查局整装勘查项目(121201004000150017)
