马里亚纳海槽扩张轴(中心)玄武岩铂族元素特征  

Characteristics of platinum-group elements in Mariana Trough basalts

作　　者：曹志敏[1] 安伟 周美夫[3] 郑建斌[1] 漆亮[3] 

机构地区：[1]中国海洋大学海洋地球科学学院,山东青岛266003 [2]中海石油环保服务有限公司,天津塘沽300452 [3]香港大学地球科学系,香港999077

出　　处：《海洋学报》2006年第5期69-75,共7页

基　　金：国家自然科学基金(40273025);国家重点基础研究973项目(G2000078503)

摘　　要：马里亚纳海槽扩张轴中心玄武岩铂族元素（PGE）总量变化范围为0．418×10^-9～1．022×10^-9，其原始地幔标准化配分模式呈正倾斜型，表现出PPGE（包括Pt，Pd，Rh）和金的相对富集．与其他幔源岩石相比，该区玄武岩PGE总量较低，（Pd／Ir）N，（Pd／Pt）N，（Pd／Ru）N变化较大，表现出铂、铱的相对亏损和明显的铂负异常（Pt／Pt^＋=0．01～0．15）．PGE的分布特征一方面反映了该区地幔熔融度不高，另一方面，大离子亲石元素LILE（铷、锶、钾等）、铅和轻稀土LREE略富集，暗示扩张中心之下的软流圈地幔源受到了岛弧地幔的混染．上述特征反映了马里亚纳海槽玄武岩是MORB型与岛弧型地幔源不同程度混合后部分融熔的产物．Total platinum-group elements concentrations （Σ PGE） from Mariana Trough basalts ranged from 0. 418 to 1. 022 ng/g, and primitive mantle-normalized PGE concentration patterns are of positive slope with a clear Pt negative anomaly （Pt/Pt^＋ =0. 01-0. 15）, showing the relative enrichment of PPGE and Au relative to IPGE. Compared with other mantle-originated rocks, Mariana Trough basalts have lower PGE contents and wider ranges of （Pd/Ir）N, （Pd/Pt）N, （Pd/Ru）N. On the other hand, Mariana Trough basalts exhibited a relative Pt and Ir depletion. Characteristics of PGE patterns indicated that the studied Mariana Trough basalts were originated from low partial melting, and the MORB mantle beneath the spreading center had been contaminated by arc-island mantle. In the aspect of trace elements, Mariana Trough basalts showed the enrichment of LILE, Pb and LREE, indicating that they had been influenced by subduction compositions. All these demonstrated that Mariana Trough basalts are products of partial melting from a mixed mantle （the contamination of MORE mantle by arc-island mantle）.

关 键 词：弧后盆地玄武岩 铂族元素(PGE) 铂负异常 俯冲带 

分 类 号：P574.2[天文地球—矿物学]