西南印度洋中脊热液产物稀土元素组成变化及其来源  

Characteristics of composition and source of rare earth elements in the seafloor hydrothermal products from the Southwest Indian Ridge

作　　者：李小虎[1,2] 初凤友[1,2] 张平萍[1,2] 雷吉江[1,2] 余星[1,2] 赵宏樵[1,2] 

机构地区：[1]国家海洋局海底科学重点实验室,浙江杭州310012 [2]国家海洋局第二海洋研究所,浙江杭州310012

出　　处：《海洋学报》2014年第6期33-41,共9页

基　　金：国家自然科学基金项目(40906036;41276055);大洋矿产资源研究协会"十二五"专项项目(DY125-12-R-02;04;06;DY125-11-R-06);海洋公益性行业科研专项(201005003)

摘　　要：对西南印度洋中脊热液区不同热液产物稀土元素（REE）进行了分析，探讨了热液产物形成过程中稀土元素组成变化及其来源。研究结果表明：不同热液产物稀土元素总量变化范围从3．47×10^-7到4．80×10^5，轻重稀土比值（LREE／HREE）从2．06到6．16，表明轻重稀土有较大程度分异，δEu异常（δEu=0．86～3．88）和δCe异常（δCe=0．40～0．86）显示热液产物中REE呈Eu富集δCe亏损特征。稀土元素球粒陨石标准化模式呈现两种类型：（1）呈轻微富集LREE的平坦模式，∑REE大于2×10^-5；（2）呈显著富集LREE和正Eu异常模式，∑REE小于5×10^-7。模式1类似于洋壳火山岩REE配分模式，而模式2与西南印度洋中脊黑烟囱REE模式相似，也与典型洋中脊热液喷口流体和硫化物LREE富集和正Eu异常模式类似。热液产物中稀土元素含量变化和模式特征以及Mg与LREE极强正相关关系可能反映了西南印度洋中脊硫化物形成在热液流体与海水混合沉淀的初始阶段，后期经历了广泛的热液流体再循环和海水蚀变过程。Rare earth element （REE） measurements were carried out on samples from the Southwest Indian Ridge. The results show that the variation range of ∑REE is from 3.47 × 10^-7 to 4.80× 10^-5 with three orders of magnitude which are similar to the difference of ZREE content between hydrothermal fluid and seawater. The ratio of LREE/HREE （from 2.06 to 6. 16） ,δEu value （δEu.0.86 to 3.88） and δCe value （δCe.0. 40 to 0.86） of the hydrothermal products indicate that there are significant differentiation between LREE and HREE, and REE patterns with middle positive Eu abnormal and negative Ce abnormal. There are two different characteristics of REE pattern with chondrite normalization. （1） ∑REE is more than 2 × 10^-5 , which shows slightly enrich LREE with relatively flat pattern; （2） ∑REE is less than 5 × 10^-7 ,which shows significantly enrich LREE with middle positive Eu abnormal pattern. The former pattern is similar to the REE pattern of volcanic rock from the oceanic crust. The latter pattern is similar to REE pattern of black smoker from the Southwest Indian Ridge, which is also similar to REE pattern with LREE enrichment and positive Eu abnormal pattern of the typical hydrothermal fluid and sulfide from mid-ocean ridge. The results of REE composition and REE pattern, as well as the strong positive relationship among Mg concentration and LREE concentration, suggest that the hydrothermal products affected extensively by the recycling of hydrothermal fluid and alteration of seawater, although sulfide precipitating at the initial phase of mixing between hydrothermal fluid and seawater in the Southwest Indian Ridge.

关 键 词：稀土元素 热液产物 源区 热液流体 西南印度洋中脊 

分 类 号：P736.43[天文地球—海洋地质]