西太平洋海山富钴结壳的稀土和铂族元素特征及其意义  

Geochemistry and Significance of REE and PGE of the Cobalt-Rich Crusts from West Pacific Ocean Seamounts

作　　者：任江波[1,2] 何高文[1,2] 姚会强[1,2] 张伙带[1,2] 杨胜雄[1,2] 邓希光[1,2] 朱克超[1,2] 

机构地区：[1]国土资源部海底矿产资源重点实验室,广东广州510075 [2]中国地质调查局广州海洋地质调查局,广东广州510640

出　　处：《地球科学（中国地质大学学报）》2016年第10期1745-1757,共13页Earth Science-Journal of China University of Geosciences

基　　金：国际海域资源调查与开发"十二五"课题项目(Nos.DY125-13-R-01;DY125-13-R-05;DY125-13-R-08;DY125-13-R-09);国家自然科学基金项目(No.91428207);国土资源部海底矿产资源重点实验室开放基金课题项目(No.KLMMR-2013-A-05)

摘　　要：为了探讨富钴结壳的稀土和铂族元素是否有相似的形成机制,对西太平洋海山富钴结壳稀土和铂族元素进行了类比研究.结果表明：富钴结壳的∑REY范围为1 433.7×10-6~2 888.0×10-6,其中Ce占到近50%,北美页岩标准化后显示较平坦的稀土模式和显著的Ce正异常特征.根据稀土配分模式及已有的Nd同位素结果,富钴结壳具有亲陆壳属性.富钴结壳具有极高的Pt（115.5×10-9~1 132.0×10-9）、（Pt/Pd）N和（Pt/Os）N值,Ir与Pt及Rh与Pt显示良好相关性.经球粒陨石标准化后显示较一致PGE（platinum-group elements）配分模式,从Os到Pt逐渐富集,Pd元素强烈亏损.已有的Os同位素研究结果显示物源在地质历史时期从幔源属性向陆源属性变化,但富钴结壳PGE元素内部相对含量仍在一定程度上保持稳定.研究认为：富钴结壳对海水中的稀土清扫具有选择性,Ce的正异常恰恰是结壳对海水稀土中Ce的优先选择造成的,从而导致海水亏损Ce.然而海水中Ce的亏损并未改变新形成富钴结壳的稀土模式,原因是在海洋中存在适量的具有亏损Ce特征的磷酸盐等组分,理论上只需要氧化物类稀土与磷酸盐类稀土消耗的稀土与海水中的补给平衡即可.只是在相关过程中,海洋中氧化物类对稀土的选择更具有主动性,而磷酸盐类表现更多的继承关系.尽管Os同位素显示物源供给发生变化,然而富钴结壳PGE模式相对稳定.因此富钴结壳PGE模式同样可以用富钴结壳对PGE的选择性吸收解释,因富钴结壳优先选择Pt与Ir以及相对排斥Pd和Os,形成了现有独特的PGE模式.In order to discuss the differences of the formation mechanism between REE and PGE of the Co-rich Crust, in this study, rare earth elements （REE） and platinum-group elements （PGE） of the Co-rich Crusts from West Pacific Ocean Seamounts are compared and analyzed. The results show that EREY of Co-rich crusts ranges from 1 433.7×10-6 to 2 888.0×10-6 , in which Ce accounts for nearly 50%. After being shale-normalized, REE patterns display relatively flat models but significant positive Ce anomalies. According to REE patterns and previous Nd isotope results, REE of Co-rich crusts have an affinity with continental crust attribution. Co-rich Crusts are also enriched in PGE and have rather high Pt content （115.5× 10-9-1132.0×10-9）, high （Pt/Pd）N and （Pt/Os）N ratios, with good correlation between Ir and Pt, Rh and Pt. After being ehondrite- normalized, PGE patterns show relatively consistent models characterized by Os to Pt gradual enrichment and Pd element strong loss. Previous Os isotope of Co-rich crusts studies indicate provenance supply changes from mantle source to continental crust source, but the relative amounts of PGE internal elements remain stable in a certain extent. Our studies suggest that Corich crusts are selective when enriching rare earth. Ce positive anomaly in Co-rich crusts and Ce loss in seawater is probably due to the fact that Ce in seawater is favored by Co-rich crusts. Ce loss in seawater doesn＇t change REE patterns of the newly formed Co-rich crusts, and the reason is probably that there is large number of authigenic phosphates characterized by negative anomaly of Ce, which are similar to seawater. In theory, the supply of rare earth in seawater should reach equilibrium with consumption of rare earth in seawater by oxides and phosphates. Importantly in this reaction, the choice of oxides of REE is more active, and phosphates show more inheritance. Despite the provenance supply changing, PGE patterns of Co rich crusts are still stable. So the fractionation of PGE from

关 键 词：稀土元素 铂族元素 富钴结壳 西太平洋海山 地球化学 

分 类 号：P736.4[天文地球—海洋地质]