投稿时间：2012-07-17
修订日期：2013-05-07
中文摘要:四川省会理菜子园红土型镍矿床中出露较多的基性-超基性岩体,文章系统报道了其中3个橄榄岩体的岩石化学、铂族元素及Re-Os同位素地球化学特征。岩石化学均显示为高MgO及高Mg#值,低SiO2、Al2O3、Na2O、K2O特征,计算显示出主要的标准矿物为橄榄石和紫苏辉石(体积百分数>90%),表明菜子园属镁质方辉橄榄岩。铂族元素总量比世界上大多数地幔橄榄岩低,且Cu/Pd比值大于原始地幔,可能是早期地幔较高部分熔融出的基性岩浆中硫化物的萃取、抽提作用所致。PPGE相对IPGE强烈亏损,与正常蛇绿岩底部的地幔橄榄岩特征类似,向右倾斜的原始地幔标准化配分模式表明菜子园铂族元素体系主要受地幔部分熔融的控制。PPGE中,Pt相对于Pd富集,可能与后期强烈蚀变有关,此外还可能反映了少量Pt以合金形式残留于方辉橄榄岩中,Pd以不相容元素的形式更多被熔体带走。菜子园方辉橄榄岩的Re-Os同位素体系封闭性相对好,γ(Os)值较小。岩石化学、铂族元素及Re-Os同位素地球化学显示,菜子园橄榄岩直接来自地幔,属正常蛇绿岩套底部的方辉橄榄岩,为古小洋盆洋壳的残片。菜子园蛇绿岩反映了中元古代晚期昆阳裂谷在菜子园-踩马水-麻塘断裂带以北演化成小洋盆,于其中沉积会理群,并在中元古代末期与南侧的东川群、汤丹群碰撞、拼贴。菜子园橄榄岩的蛇绿岩属性进一步证明,扬子地台西南缘的基底由不同时代的小陆块碰撞、拼贴导致基底陆壳增生。
Abstract:There exist lots of basic-ultrabasic rock bodies in the Caiziyuan laterite type nickel deposit in Huili County of Sichuan Province. Geochemical characteristics of Platinum group elements(PGEs) and Re-Os isotope of three peridotites rock bodies are reported in this paper. The lithogeochemistry of the Caiziyuan deposit shows high MgO and low SiO2, Al2O3, Na2O and K2O content as well as high Mg# values. CIPW calculation indicates that the main standard minerals of the Caiziyuan deposit are composed of olivines and hypersthenes (the volume fraction is more than 90 percent), showing that the Caiziyuan deposit belongs to magnesia harzburgite type. The ∑PGE of the Caiziyuan deposit is relatively lower than that of most mantle residual peredotites, implying that PGE was extracted by the sulfides in the basic magma resulting from the large melt fractions of mantle at the early stage. The differentiation between PPGE and IPGE in the Caiziyuan deposit is obvious, and is similar to things of mantle residual peridotites at the bottom of normal ophiolite suites reported earlier. The right-oblique mantle normalized PGE patterns are controlled mainly by the high partial melting of the mantle. Pt is concentrated relative to Pd in PPGE, and the differentiation between Pt and Pd might have been caused by obvious hydrothermal alteration; therefore a small amount of Pt probably exists in the form of residue alloy in Caiziyuan peridotites. The small γ(Os) values imply that Caiziyuan peridotites were derived from the mantle with a fine Re-Os isotope sealing system. The petrogeochemistry, platinum group elements and Re-Os isotopic geochemistry suggest that the Caiziyuan deposit was derived directly from the mantle, thus belonging to the residual harzburgite at the bottom of the normal ophiolite suite. Caiziyuan ophiolite may be a part of the relics of ancient ocean floor of small ocean basin, implying that Kunyang rift was evolved into small ocean basin where Huili Group was deposited in the late period of Mesoproterzoic. The ophiolitic characteristics of the Caiziyuan deposit further prove that the Huili Group collided with Dongchuan and Tangdan Group in the south of Caiziyuan-Caimashui-Matang fault belt at the end of Mesoproterozoic, and that the basement in the southwest of Yangtze craton was probably collided and collaged by small continental segments in different periods, resulting in the basal continental crustal accretion.
keywords:geochemistry Caiziyuan peridotites platinum group elements Re-Os isotope ophiolite Kunyang rift Huili Group Dongchuan Group Tangdan Group Huili
文章编号：
中图分类号：P618.63
文献标志码：
基金项目:本文得到国土资源大调查(编号:1212010911064;1212011085162);国家重点基础研究发展规划(973)项目(编号:2009CB421006)和国家自然科学基金(编号:40173025)的联合资助
引用文本：
王生伟,孙晓明,廖震文,屈文俊,杨波,蒋小芳,李超,李永灿.2013.会理菜子园镍矿床方辉橄榄岩铂族元素、Re-Os同位素及其地质意义[J].矿床地质,32(3):515~532WANG ShengWei,SUN XiaoMing,LIAO ZhenWen,QU WenJun,YANG Bo,JIANG XiaoFang,LI Chao,LI YongCan.2013.Platinum group elements and Re-Os isotope geochemistry of harzburgites from Caiziyuan nickel deposit in Huili County of Sichuan Province and its geological significance[J].Mineral Deposits32(3):515~532
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