Internal features, mineralogy and geochemistry of ferromanganese nodules from the Gulf of Cadiz: The role of the Mediterranean Outflow Water undercurrent
Internal features, mineralogy and geochemistry of ferromanganese nodules from the Gulf of Cadiz: The role of the Mediterranean Outflow Water undercurrent
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DOI：
10.1016/j.jmarsys.2009.10.010
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发表时间：
2010-03-01
影响因子：
2.8
通讯作者：
Diaz-del-Rio, V.
中科院分区：
文献类型：
--
作者：
Gonzalez, F. J.;Somoza, L.;Diaz-del-Rio, V.
2001 年阿纳斯塔西亚号航行（TASYO 项目）期间，沿地中海与大西洋交汇处的加的斯湾（中东部大西洋）大陆边缘回收了大量铁锰结核（561 个样本），在那里发现了大片结核区。根据先前的广泛研究，包括条带测深、多通道和超高分辨率地震反射、重力测量、磁力、热流探测器和水下摄影勘测，在850至1000 m的水深收集了结核，这些结核与碳氢化合物衍生的镁方解石、铁白云石和白云石烟囱和结壳有关。从各种形态类型中选出的 46 个样品用于物理性质（形态、颜色、表面纹理、球形度、重量和尺寸）、矿物学（XRD、光学和电子显微镜）、地球化学（XRF、AAS、ICP-MS、ICP-AES、EPMA 和 GC-MS）和稳定同位素的实验室分析。结节的尺寸、密度、重量和形态各不相同。它们是由围绕核心的多个毫米厚的 Fe 和 Mn 羟基氧化物层形成的，该核心由早中中新世塑料泥灰和沉积物组成，这些沉积物是通过流体喷发从底层单元中衍生出来的。 Fe 和 Mn 的羟基氧化物层形成了块状、层状、碎屑状和斑驳的树枝状结构特征。主要成分为针铁矿、纤铁矿、锰氧化物（7埃锰酸盐和10埃锰酸盐）、石英、层状硅酸盐。副矿物有方解石、白云石、菱铁矿、菱锰矿、球霍石、黄铁矿、黄铜矿、钾长石、锆石、金红石、钛铁矿和绿泥石。来自菱铁矿-菱锰矿连续系列的铁锰碳酸盐是晶核的主要成分。在铁锰氧化物和黄铁矿中观察到草莓状、丝状和球状结构，表明生物起源。与其他洋区深海海底多金属结核的平均含量相比，这些结核的铁平均丰度较高（38.6%），锰平均丰度较高（6.0%），微量金属和稀土元素含量较低。 Mn/Fe比率范围为0.07至0.25。研究的结核在其氧化层中含有源自海洋细菌活动的碳氢化合物（正烷烃），还存在菲等芳香烃，这是成熟石油的特征。研究的结核的结构、矿物学和化学成分更类似于成岩-水成岩大陆边缘结核，而不是深海结核。我们认为，此类结核的形成可能响应于成岩-水力生长的综合过程，其中深层油气藏的流体排出、生物矿化过程以及底部水流侵蚀和化学可能发挥了重要作用。 (C) 2009 Elsevier B.V. 保留所有权利。
A large suite of Fe-Mn nodules (561 samples) were recovered during the Anastasya 2001 cruise (TASYO project) along the continental margin of the Gulf of Cadiz (Eastern Central Atlantic), at the confluence of the Mediterranean Sea with the Atlantic Ocean, where extensive nodule fields were discovered. Based on wide previous Studies that included swath bathymetry, multi-channel and very high-resolution seismic reflection, gravimetry, magnetism, heat flow probes and underwater photography surveys, nodules were collected at water depths ranging from 850 to 1000 m, associated with hydrocarbon-derived Mg-calcite, ankerite and dolomite chimneys and crusts. Forty-six selected samples among the various morphological types were used for the laboratory analysis of physical properties (morphology, color, surface texture, sphericity, weight and size), mineralogy (XRD, optical and electronic microscopy), geochemistry (XRF, AAS, ICP-MS, ICP-AES, EPMA, and GC-MS) and stable isotopes. The nodules show a wide range of sizes, densities, weights and morphologies. They are formed by multiple millimeter-thick layers of Fe and Mn oxyhydroxides surrounding the nucleus composed of Early-Middle Miocene plastic marl and sediment, which were derived from underlying units by fluid venting. Massive, laminated, detrital and mottled to dendritic textural features were developed by the Fe and Mn oxyhydroxide layers. The main components are Goethite, lepidocrocite, Mn oxides (7 angstrom manganates and 10 angstrom manganates), quartz, and phyllosilicates. Accessory minerals are calcite, dolomite, siderite, rhodochrosite, kumahorite, pyrite, chalcopyrite, potassium feldspar, zircon, rutile, ilmenite and chlorite. Fe-Mn carbonates from the siderite-rhodochrosite continuous series are the principal constituent of the nuclei. Framboidal, filamentous and globular textures are observed in Fe-Mn oxides and pyrite, suggesting biogenic origin. The nodules show a high mean abundance of Fe (38.6%), moderate Mn (6.0%) and low contents of trace metals and REEs compared to the average content of deep-seabed polymetallic nodules from other oceanic areas. The Mn/Fe ratio ranges from 0.07 to 0.25. The studied nodules hold hydrocarbons (n-alkanes) derived from marine bacterial activity in their oxide layers, with the presence of aromatic hydrocarbons as phenanthrene as well, characteristic of mature petroleum. The structure, mineralogy and chemical composition in the studied nodules are more similar to those of diagenetic-hydrogenetic continental margin nodules rather than deep-sea nodules. We Suggest that the formation of this type of nodule could respond to a combined diagenetic-hydrogenetic growth process, where the fluid venting from deep-seated hydrocarbon reservoirs, the bio-mineralization processes and the bottom currents erosion and chemistry could have played an important role. (C) 2009 Elsevier B.V. All rights reserved.