富钴结壳中的磷酸盐岩及其古环境指示意义  

PHOSPHORITES IN Co-RICH CRUSTS AND THEIR PALAEOOCEANOGRAPHIC SINGIFICANCE

作　　者：武光海[1] 周怀阳[2] 凌洪飞[3] 张文兰[3] 

机构地区：[1]国家海洋局第二海洋研究所国家海洋局海底科学重点实验室,浙江杭州310012 [2]中国科学院广州地球化学研究所,广东广州510640 [3]内生金属矿床成矿机制研究国家重点实验室,江苏南京210008

出　　处：《矿物学报》2005年第1期39-44,共6页Acta Mineralogica Sinica

基　　金：国家自然科学基金(40206010);海洋局青年基金(2002316);南京大学成矿机制研究国家重点实验室开放基金

摘　　要：磷酸盐岩是富钴结壳老壳层的主要组分之一。本文对来自中太平洋海山的三块富钴结壳样品中的磷酸盐岩进行了研究,以期对富钴结壳形成环境的变化有所了解。通过扫描电镜发现结壳中磷酸盐岩的形态有六种,磷酸盐岩主要分布在老壳层,新壳层中偶见。结壳中的磷酸盐岩为碳氟磷灰石(CFA),经成分分析及电镜中反射色的差异可以区分出两种成因的CFA:一种为交代碳酸盐岩型的,相对富Si、Al、Fe;另一种为从结壳孔隙水中直接沉淀而成的,基本不含Si、Al、Fe。对CB12样品中磷酸盐岩脉进行生物地层学鉴定,得出其老壳层下部火焰状磷酸盐岩的形成年代为晚渐新世—早中新世(23.2～29.9Ma),而其上部充填脉状磷酸盐岩的形成年代为中中新世(10.8～16Ma)。老壳层中富集磷酸盐岩说明在结壳形成早期,结壳形成环境条件尚不够稳定,底部存在富磷深层储库,当底流突然增强时,可携带磷在海山上交代结壳中的碳酸盐岩或在结壳内部合适条件下直接沉淀形成磷酸盐岩充填脉。新壳层形成时底流已相对稳定,富磷深层储库已消失,不再有广泛磷酸盐化形成。Phosphorites are the main components in the old layers of the Co-rich crusts. They were studied in three Mid-Pacific seamount Co-rich crusts to probe into changes of the Co-rich crusts' forming environment. The phosphorites in the Co-rich crusts occur in six forms as revealed by scanning electron microscopy. They are distributed mainly in old crust layers, accidentally in younger layers. The phosphorites are all carbonate fluorapatites (CFA) and can be divided into two genetic types as viewed from the differences in their chemical composition and reflection colors under scanning electron microscope. One type was formed by replacement of calcareous (nanno) fossils and the other by direct precipitation from the interstitial (seepage) water in the crust or sediment. The former has relatively high Si, Al, Fe contents and the latter has very low Si, Al, Fe contents.The phosphorites in CB12 are late Oligocene to Early Miocene(29.9-23.2 Ma)and Mid Miocenein age (16-10.8 Ma) in terms of the results of biostratigraphy. The phosphorites are almost all in the old layers, showing that the ore-forming environment wasn't stable in the early period. There was a phosphorus-rich deep sea reservoir and when the bottom flow boost up abruptly, a great deal of phosphorus was carried upward to the surface of the seamount, where the phosphorite veins were formed by replacement of calcareous (nanno) fossils or by direct precipitation from interstitial water in the crust. As to the new layers,their ore-forming environment had been relatively stable, the phosphorus-rich deep sea reservoir had disappeared and almost no phosphorites were formed again.

关 键 词：富钴结壳 磷酸盐岩 古环境指示意义 碳氟磷灰石 CFA 海洋环境 

分 类 号：P744[天文地球—海洋科学]