摘要
白马寨I号岩体是哀牢山—金沙江构造带白马寨Cu-Ni矿区内最大的一个含矿基性—超基性岩体,从中心向边缘依次由含矿橄榄岩、矿化辉石岩和辉长岩3个相带组成环状体。从中心相到边缘相,岩石中SiO2、TiO2、Al2O3、CaO、Na2O和K2O含量逐渐增加,TFe、MgO含量降低;稀土元素中w（∑REE）、w（LREE）/w（HREE）逐渐增加,δEu由负异常到正异常演变;微量元素具有大离子亲石元素和高场强元素逐渐增加、强亲岩浆元素逐渐降低的演变特征。铂族元素配分模式为Pt-Pd型,w（Pt）/w（Pd）比值为0.32～0.68,介于富硫化物拉斑玄武岩（0.38）和原始上地幔（1.36）之间,以及稀土元素配分模式、微量元素蛛网图和铂族元素配分模式中不同岩石配分曲线的相似性揭示3个相带不同岩石之间的高度一致性,展示基性—超基性岩形成于玄武质岩浆演化、熔离及岩浆一次性侵入、分异成岩成矿的特征。矿区内地层层序稳定,岩体与沉积岩之间的侵入接触关系及w（Zr）-w（Y）-w（Nb）图解说明白马寨岩体形成于陆内环境。岩体的低Ti含量、Th强烈正异常和含矿橄榄岩负Eu异常,以及w（Th）/w（Ta）比值、w（Th）/w（Nb）比值和w（Pd）/w（Pt）比值及Ir族元素配分曲线明显不同于峨眉山玄武岩和典型的地幔柱玄武岩,而与大陆裂谷玄武岩非常相近,说明白马寨I号岩体形成于大陆裂谷环境。
The mafic-ultramafic intrusive rock body I is the largest for Baimazhai Cu-Ni deposit distributed in the Ailaoshan-Jinshajiang tectonic zone.It is a ring-like body consisting of ore-bearing peridotite,mineralized pyroxenite and gabbro phase zones from the center to margin.Accordingly,the contents of SiO2,TiO2,Al2O3,CaO,Na2O and K2O are increasing gradually,and that of TFe and MgO are decreasing as well;the concentrations of ∑REEs,and LREE/HREE ratios are increasing gradually from the central phase to outer phase.Along the same direction,δEu shows negative to positive anomalies;the abundance of the large ion lithophile elements（LILE） and high field strength elements varies increasingly,but the contents of magmatophile elements have a reversal evolutive trend.The PGE distributive patterns are the Pt-Pd type,the Pt/Pd ratios of 0.32-0.68 are between the values of enriched sulfide tholeiite（0.38） and primitive upper mantle（1.36）,and the similarity of partition patterns of chondrite-normalized REE,MORB-normalized trace element and primitive mantle normalized PGE for the rocks of the three phase zones,indicate the Baimazhai intrusive body I formed by the evolution,liquation,intrusion and diagenesis-metallogenesis of basaltic magma.The fact that stable sedimentary succession outcropped in the deposit district,intrusive contact relationships between the sediments and the intrusion and the Zr-Y-Nb diagram of the ring rock body shows the Baimazhai intrusion body formed in an intracontinent.The lower Ti content,strongly Th positive anomaly,and the Th/Ta ratios,Th/Nb ratios,Pd/Pt ratios and the primitive mantle normalized Ir-group patterns for Baimazhai intrusive body I,which are different from those of the Emeishan basalt and typical mantle plume basalts,but similar to those of basalts from a continental rift,suggest that the Baimazhai intrusive body I are probably formed in the tectonic settings of continental rift.
出处
《现代地质》
CAS
CSCD
北大核心
2010年第1期98-106,共9页
Geoscience
基金
中国地质调查局项目(1212010918009)
科技部深部探测技术与实验研究专项(SinoProbe-05-03)
