西太平洋Lamont海山中新世以来富钴结壳成矿环境的演化

Evolution of Ore-forming Condition of Co-rich Crusts From Lamont Guyot in the Western Pacific Since the Miocene

分析了西太平洋Lamont海山12个站位33个富钴结壳样品的主元素和稀土元素，结果表明，该海山富钴结壳成因类型属于水成成因，并且在形成过程中基本未受到磷酸盐化作用的影响。Lamont海山的一个富钴结壳样品剖面的电子探针数据显示，该海山富钴结壳的成矿环境在新第三纪以来至少存在2个演化阶段：第1阶段，23～15Ma，富钴结壳中Mn相对富集，成矿环境以富氧贫硅为特征；第2阶段，15～0 Ma，富钴结壳中Fe相对富集，成矿环境以贫氧富硅为特征。成矿环境的氧化能力总体上呈现下降的趋势。联系新生代世界大洋，尤其是西太平洋的地质演化背景，认为引起成矿环境演变的原因主要是西太平洋大洋板块的WNW向漂移和新第三纪以来全球水道开合，造成了Lamont海山所处海区最低含氧带逐渐减薄。

The major elements and REEs in 33 Co-rich crust samples from Lamont Guryot in the western Pacific were analyzed,and it is shown from the analysis results that the Co-rich crusts are hydrogenetic in origin,and were basically not affected by phosphatization. It is shown from the analysis data of a crust sample profile that the ore-forming conditions of Co-rich crusts since the Neogene have at least two evolutional stages, namaly,stage 1 （23 to 15 Ma BP） is characteristic of a rich oxygen and poor silicon condition with relatively enriched Mn in the Co-rich crusts, and stage 2 （15 Ma BP to present） is characteristic of a poor oxygen and rich silicon condition with relatively enriched Fe in the Co-rich crusts. The oxidation capacity of ore-forming condition of the crusts generally shows a decreasing trend. In consideration of the geologic evolution background of the world ocean, especially the western Pacific in the Cenozoic, it is suggested that the Western Pacific Plate drift to the WNW and the closure of global seaways resulted in the thinning of the oxygen minimum zone in the sea area near Lamont Guyot, which is the main reason for the evOlution of ore-forming conditions of the Co-rich crusts.