Hydrothermal manganese oxide deposits from Baby Bare seamount in the Northeast Pacific Ocean |
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| Institution: | 1. Center for Marine Core Research Institute, Kochi University, Japan;2. Institute for Industrial Science, University of Tokyo, Japan;3. R & D Center for Marine Resources, JAMSTEC, Japan;4. Metals Exploration Dept., JOGMEC, Japan;5. Division of Chemistry, Tsukuba University, Japan;6. Geological Survey of Japan, National Inst. Advanced Industrial Science and Technology (AIST), Japan;7. Tokyo University of Pharmacy and Life Sciences, Japan;8. Emeritus Professor, University of Tokyo, Japan;1. Ministry of Education Key Laboratory for Coast and Island Development, School of Geography and Ocean Science, Nanjing University, Nanjing 210023, China;2. State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China;3. Key Laboratory of Marine Geology and Metallogeny, Ministry of Natural Resources, Qingdao 266061, China;4. Laboratory for Marine Geology, Pilot National Laboratory for Marine Science and Technology, Qingdao 266200, China |
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| Abstract: | Manganese oxide crusts were recovered from Baby Bare seamount in order to investigate the history of off-axis hydrothermal venting. Baby Bare is a small basement high protruding from a regional sediment cover on the eastern flank of the Juan de Fuca Ridge that acts as a focus for discharging crustal fluids. Stratabound Mn-oxide crusts were collected where warm venting has been observed near the seamount summit. Mn-oxide crusts are composed primarily of 10 Å manganate ± pyrolusite, with minor nontronite, saponite, and/or barite. These assemblage and chemical characteristics such as high Mn/Fe ratios and low trace metal and REE concentrations are indicative of a hydrothermal origin. Minimum ages for these deposits, calculated using growth rates (324 to ∼ 1800 mm/Ma) and estimated thicknesses of manganese outcrops, show that Baby Bare has been hydrothermally active for at least 0.5 Myr, and possibly since its formation (1.7–2.7 Ma). Hydrothermal manganese oxide crusts such as these from Baby Bare record interactions between the hydrothermal fluids and seawater and are important tools for estimating the longevity of off-axis hydrothermal activity. |
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