GENESIS AND ORE-FORMING STAGES OF CO-RICH FERROMANGANESE CRUSTS FROM SEAMOUNT M OF MAGELLAN SEAMOUNTS: EVIDENCE FROM GEOCHEMISTRY AND CO CHRONOLOGY
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摘要: 利用电感耦合等离子体原子发射光谱仪(ICP-AES)和重量法,对麦哲伦海山链西北端M海山9个站位、17个富钴结壳样品的主要元素和稀土元素进行了分析,分析结果显示,该海山富钴结壳是水成成因的,且多数富钴结壳在生长过程中没有受到磷酸盐化作用的影响。推广富钴结壳Co地层学年代计算公式的应用范围,并基于此建立了研究区富钴结壳的年代学框架。研究区富钴结壳的Co地层学年代计算公式的计算结果显示,中新世以来的地质时代是M海山富钴结壳的主成矿期,并且大约在15 Ma发生了一次磷酸盐化事件,推测当时导致磷酸盐化发生的最低含氧带(OMZ)的深度下降到相当于现今2 000~2 700 m水深之间。Abstract: 17 Co-rich ferromanganese crusts from 9 sites at the Seamount M in the northwest of Magellan Seamounts were investigated geochemically with inductively coupled plasma atomic emission spectroscopy (ICP-AES) and weight method. Geochemical composition of those samples suggests that those Co-rich Fe-Mn crusts are hydrogenetic in origin and most of them were not phosphatized during formation. This paper extends the usage of Co chronology to bulk samples. The ages dated by the Co chronology suggest that those Co-rich Fe-Mn crusts mainly formed since Miocene, and one of them were phosphatized around 15 Ma when the oxygen minimum zone (OMZ), where the Co-rich Fe-Mn crust formed, immerged to the present water depth of 2 000~2 700 m.
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Key words:
- Co-rich ferromanganese crust /
- metallogeny /
- ore-forming epoch /
- Magellan Seamounts
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