Petrographic investigations of seafloor sediments from the Kita-Bayonnaise submarine caldera, Shichito-Iwojima Ridge, Izu-Ogasawara Arc, northwestern Pacific
Petrographic investigations of seafloor sediments from the Kita-Bayonnaise submarine caldera, Shichito-Iwojima Ridge, Izu-Ogasawara Arc, northwestern Pacific
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西北太平洋伊豆-小笠原弧七刀-硫磺岛海脊北贝永海底破火山口海底沉积物的岩相学研究
DOI：
10.1016/0025-3227(93)90173-s
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
K. Iizasa
中科院分区：
文献类型：
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作者：
K. Iizasa
海底沉积物样品是通过箱式和重力取样器从西北太平洋伊豆-小笠原弧的七户-岩岛海岭的北-巴永奈斯海底破火山口中采集的。通过显微镜、SEM-EDX和XRD分析，将样品分为重、轻和粘土级3个组分，重组分主要由磁性矿物、硅酸盐和硫化物组成，其次为硫酸盐、金红石、磷酸盐、碳酸盐和锰的氢氧化物。原生热液物相主要由重晶石、黄铁矿、闪锌矿、黄铜矿、方铅矿、红铁矿、白铁矿和金红石组成。次生矿物组合通常存在于方铅矿和黄铜矿颗粒周围。重晶石-球粒型黄铁矿-黄铜矿-闪锌矿和闪锌矿-黄铜矿-黄铁矿与方铅矿或红柱石的组合表明热液成矿作用发生在破火山口，重透明组分中绿帘石-碳酸盐或碳酸盐和轻组分中绢云母-石英-长石的组合表明热液蚀变成因，因为破火山口中只有英安岩样品。粘土粒级中的蒙脱石、绢云母、绢云母和库纳霍里石也支持热液活动的存在。由紫苏辉石、普通辉石、角闪石、石英、长石和黑云母组成的其他矿物在重馏分和轻馏分中作为破火山口中英安岩的碎屑被观察到。重力岩心样品中Ag、Th的含量（0.063- 0.25mm）表明破火山口曾发生过多次热液成矿作用，许多证据表明Kita-Bayonnaise海底破火山口存在与Ag、Th有关的热液成矿作用。这些矿物学分析对于探索海底破火山口过去或现在的热液成矿迹象具有重要意义。
Seafloor sediment samples were recovered by box and gravity corers from the Kita-Bayonnaise submarine caldera, Shichito-Iwojima Ridge, Izu-Ogasawara Arc, northwestern Pacific. The samples were separated into heavy, light, and claysized fractions for assessment of the hydrothermal contribution to the sediments of the submarine caldera, and have been determined by microscopy, SEM-EDX, and XRD.Heavy fractions are composed of predominant magnetic minerals, dominant silicates and common sulfides and sulfate, minor sulfosalt, rutile, phosphates, carbonates and Mn-oxyhydroxides. Primary hydrothermal phases are composed of barite, pyrite, sphalerite, chalcopyrite, galena, fahlore, marcasite and rutile. Secondary mineral associations are usually present around galena and chalcopyrite grains. The assemblages of barite-pellet type pyrite-chalcopyrite-sphalerite and sphalerite-chalcopyrite-pyrite with galena or fahlore suggest that hydrothermal mineralization took place in the caldera.The assemblages of epidote-carbonate or chlorite in heavy transparent fractions and of sericite-quartz-feldspar in light fractions are indicative of hydrothermal alteration origin because of only dacite sampled from the caldera. Some of the smectite, chlorite, sericite and kutnahorite in clay-sized fractions could also support the existence of hydrothermal activity. Other minerals consisting of hypersthene, augite, hornblende, quartz, feldspar and biotite are observed in heavy and light fractions as detritus of dacite in the caldera.Significant amounts of sulfides and barite mixtures (ranging from about 1.0 to 3.5 wt.% in treated fractions, 0.063–0.25 mm) in gravity core samples suggest that hydrothermal mineralization took place several times in the caldera.Many lines of evidence indicate the presence of hydrothermal mineralizations associated with Ag and Th in the Kita-Bayonnaise submarine caldera. The mineralogical analyses are powerful for exploring signs of past or present hydrothermal mineralization in submarine calderas.