西太平洋海山磷酸盐的常量、微量和稀土元素地球化学研究  

Research on Geochemical Characteristics of Major, Trace and Rare-Earth Elements in Phosphates from the West Pacific Seamounts

作　　者：潘家华[1] 刘淑琴[1] 杨忆[2] 刘学清 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]中国科学院研究生院,北京100039 [3]北京市地质矿产勘探开发局,100050

出　　处：《地质论评》2002年第5期534-541,共8页Geological Review

基　　金：中国大洋矿产资源研究和开发协会(COMRA)"大洋富钴结壳形成富集的地球化学限制"(编号 DY95-08-05)资助的成果

摘　　要：本文对主要取自于西太平洋我国调查区内不同海山、不同水深、不同产状的13个磷酸盐样品进行了常量、微量和稀土元素测定,以探讨与大洋富钴结壳密切伴生的磷酸盐的常、微量和稀土元素地球化学的特征。分析结果表明,调查区磷酸盐中主要氧化物的平均值与赤道太平洋的相近,暗示两者可能有相似的形成环境和形成机制。磷酸盐中微量元素Sr、Ba、Co、Cu、Ni及U丰度分别变化于862×10^(-6)～2181×10^(-6)、29×10^(-6)～3429×10^(-6)、6.3×10^(-6)～115×10^(-6)、23×10^(-6)～263×10^(-6)、12×10^(-6)～825×10^(-6)及4×10^(-6)～11×10^(-6),丰度多数低于泥质岩平均值,其CaO/P_2O_5、F/CO_2、Sr/P_2O_5值及常量、微量元素间的相关关系,清晰地显示了磷酸盐的种类、成分与结构、形成的地质背景和元素的主要组合特征。磷酸盐的稀土丰度为136.50×10^(-6)～853.70×10^(-6);Ce~*变化于0.01～0.18之间;(Ce/Yb)_N值变化于0.01～0.21之间。研究证实,不同产状磷酸盐的稀土元素配分模式基本一致,曲线相互平行,基本不呈现交叉现象,均呈Ce强烈亏损,轻、重稀土分馏程度大及重稀土富集的型式。调查区、赤道太平洋、中太平洋磷酸盐的稀土元素丰度、Ce~*、Ce/Yb值以及它们与海水稀土元素配分模式相似的特征,也进一步显?This paper presents our first researches on the major and trace elements and REE geochemistry of seamount phosphates closely associated with cobalt-rich crusts mainly from the western Pacific. We have measured the major and trace elements and REE contents in 13 phosphate samples dredged from different seamounts, different water depths and different occurrences in the study area. The results show that the average values of main oxides of phosphates from the study area are close to those from the tropic Pacific, which suggests that they are probably formed in similar environments with a similar formation mechanism. The Sr, Ba, Co, Cu, Ni and U abundances of phosphates vary from 862 × 10-6- 2181 × 10-6 29 × 10-6-3429 × 10-6, 6. 3×10-6-115×-6, 23 × 10-6-263× 10-6, 12 × 10-6-825 × 10-6 and 4× 10-6-11 × 10-6 respectively, most of which are lower than the average values of argillaceous rocks. The ratios of CaO/P2O5, F/ CO2, Sr/ P2O5, and the relationship between the major and trace elements of phosphates reflect the characteristics of the variety, composition and structure of phosphates, the geological settings of their formation and the main element association of the phosphates in the study area. Their REE, Ce and(Ce/Yb)N vary from 136. 50× 10-6-853. 70 × 10-6, 0. 01 - 0. 18 and 0. 01 -0. 21 respectively. The studies verify that phosphates of different occurrences show similar REE patterns of fractional distillation with strong negative Ce anomalies, obvious difference of fractional distillation in light and heavy REEs as well as enrichment of HREE. The authors consider that the similar REE features of phosphates from the study area, the Tropic and the Central Pacific and their REE patterns of fractional distillation with those of seawater also indicate that seamount phosphates have derived mainly from seawater and probably have the same formation mechanism of the latter. Besides, the formation environment of phosphates is also discussed.

关 键 词：海山磷酸盐 微量元素 稀土元素 地球化学 西太平洋 富钴结壳 形成机制 

分 类 号：P59[天文地球—地球化学]