中国蛇绿岩中变质橄榄岩的稀土元素地球化学  

Rare Earth Elements Geochemistry of the MantlePeridotite in the Ophiolite Suites of China

作　　者：王希斌[1] 鲍佩声[1] 戌合 

机构地区：[1]中国地质科学院地质研究所

出　　处：《岩石学报》1995年第S1期24-41,共18页Acta Petrologica Sinica

基　　金：国家自然科学基金

摘　　要：中国蛇绿岩中变质橄榄岩（方辉橄榄岩、纯橄岩、二辉橄榄岩及其蚀变岩石）的ＲＥＥ丰度范围很宽，其∑ＲＥＥ变化于０．１４８～＞７μｇ／ｇ，为球粒陨石丰度的０．０１～５．６倍。其ＲＥＥ特征表现为五种分布型式即：（１）Ｖ或Ｕ型，（２）烟斗型（本文提出的），（３）ＬＲＥＥ富集型，（４）ＬＲＥＥ亏损型和（５）平坦型．其中以前三种ＲＥＥ型式为主，后两种型式则不多见。中国造山带橄榄岩以其强烈的ＬＲＥＥ富集为主要特征区别于现代洋底橄榄岩和国外某些阿尔卑斯橄榄岩。三种主要ＲＥＥ型式有相似的成因机制，可用Ｓｏｎｇ和Ｆｒｅｙ的混合模式得到统一解释：三者差异的原因是由不同熔融程度的地幔残余与不同数量比例和不同熔融程度的熔体混合的结果引起的。含豆荚状铬铁矿的方辉橄榄岩和纯橄岩是各类变质橄榄岩中ＲＥＥ丰度最低，多属强烈亏损和超强烈亏损（其∑ＲＥＥ多在０．８μｇ／ｇ以下）的地幔橄榄岩类，为豆荚状铬铁矿的地幔高度熔融富集的成因提供了证据。The available analytic data of rare earth elements (REE) indicate that REE abundances ofmantle Peridotites (harzburgite, dunite, lherzolite and their altered rocks) in the ophiolite of China range from0. 148 to values higher than 7 μg/g, i. e., 0. 01 to 5. 6 times of those of chondrite. Their chondrite-normalizedREE patterns are divided into five types: (1 ) V (or U)-shaped pattern, (2) tobacco pipe-shaped pattern, (3)LREE-enriched pattern, (4) LREE-depleted pattern and (5) flat pattern. The former three patterns aredominated, while the latter two patterns are less imPOrtant. The majority of Peridotites in the OPhiolites of Chinais characterized by enrichment in LREE, which differs from ocean-floor peridotites and some Alpine peridotitesabroad. The three main REE patterns have a similar genetic mechanism and can be explained identically with amixing model of Song and Frey: The differences between the V(or U)-shaped, tobacco pipe-shaped and enriched patterns result from mixing of mantle residues formed by melting in varying degree with melts invarying proportions.A comprehensive comparison of REE data indicates that the pediform chromite-beating peridotites(harzburgites and dunnes) from the orogenic belts of China have the lowest REE in Alpine peridotites. Most ofthem belong to strongly and extremely depleted mantle peridotite separately (with REE abundances lower than0. 8μg/g). Therefore, it could be an evidence that the podiform chromite deposits are products formed by highdegree melting of mantle peridotites.

关 键 词：中国 蛇绿岩 变质橄榄岩 稀土元素 地球化学 

分 类 号：P585[天文地球—岩石学]