菲律宾海中部铁锰结核地球化学特征与成矿环境约束

Geochemical characteristics and metallogenic environmental constraints of ferromanganese nodules in the central Philippine Sea

  • 摘要: 阐明菲律宾海中部铁锰结核的地球化学特征、成因类型及成矿环境主控因素,可为西太平洋边缘海结核资源评价提供科学依据。本文依托“海洋地质九号”科考船在菲律宾海中部九州-帕劳海脊南段采集的铁锰结核样品,系统分析了铁锰结核的微观结构与元素地球化学特征。结果表明,结核显微构造显示混杂状纹层→水平纹层→叠层状的圈层序列,指示水动力环境由弱渐强。地球化学指标(Mn/Fe均值为0.95,δCe均值为1.7,Co/(Ni+Cu)均值为0.5)明确指示水成成因占主导;Ti异常富集(均值为0.93%)揭示亚洲风尘物质输入,而Co+Ni+Cu总量(0.74%)偏低反映强底流限制金属长期富集。结核空间分布受控于南极底层水路径与海底地形。南极底层水流经的九州-帕劳海脊及帕里西维拉海盆区域,结核发育较为显著;而地形封闭的西菲律宾海盆南部,由于缺氧环境,铁锰结核的发育受到明显限制。菲律宾海中部水成结核形成于强氧化、低沉积速率环境,其资源潜力受深部环流与构造地貌协同制约。研究结果对深化西太平洋边缘海成矿机制认知及资源勘探工作具有一定的参考意义。

     

    Abstract: Understanding the geochemical characteristics, genetic types, and key controls on ferromanganese nodule (FMN) formation in the Central Philippine Sea is essential to assess the nodule resources across the Western Pacific marginal seas. We examined the microstructure and elemental geochemistry of FMNs collected from the southern Kyushu-Palau Ridge (KPR). Results indicate that the microstructure of FMN displays a distinct micro-laminae sequence transitioning from mixed to parallel or laminated structures, reflecting a progressive increase in bottom current energy. Diagnostic geochemical signatures—Mn/Fe ratios averaging 0.95, positive δCe anomalies (mean ~1.7), and high Co/(Ni+Cu) values (mean ~0.5)—confirmed collectively a predominantly hydrogenetic origin. The pronounced Ti enrichment (mean 0.93%) indicated significant aeolian input from Asian sources. Conversely, the relatively low combined content of Co, Ni, and Cu (0.74%) reflected existence of strong bottom current that restricted long-term metal accumulation. The spatial distribution of the FMN was controlled by the Antarctic Bottom Water (AABW) flow paths and seafloor topography. Abundant FMN occurred along the AABW-influenced KPR and Parece Vela Basin, while the nodule growth in the topographically enclosed southern West Philippine Basin was obviously very limited due to oxygen-deficient conditions. Therefore, hydrogenetic FMNs in the central Philippine Sea were formed in a strongly oxidizing and low sedimentation rate environment, and their resource potential was constrained by the synergy of deep-ocean circulation and tectonic geomorphology. This research improved our understanding of FMN genesis and provided valuable insights for resource exploration strategies in the Western Pacific marginal seas.

     

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