HR: 1330h
AN: T32A-0915    [PDF]
TI: Geochemical Characterization of Hydrothermal Plumes Above Hydrothermally Active Volcanos on the Mariana Arc
AU: * Resing, J A
EM: resing@u.washington.edu
AF: Joint Institute for the Study of the Atmosphere and the Oceans, University of Washington Box 357941, Seattle, WA 98195 United States
AU: Lebon, G
AF: Joint Institute for the Study of the Atmosphere and the Oceans, University of Washington Box 357941, Seattle, WA 98195 United States
AU: Baker, E
AF: NOAA PMEL, 7600 Sand Point Way NE, Seattle, WA 98115 United States
AU: Lupton, J
AF: NOAA PMEL, Hatfield Marine Science Center 2115 SE Oregon State University Way, Newport, OR 97365 United States
AU: Nakamura, K
AF: National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba Ibaraki, 305-8567 Japan
AU: Massoth, G
AF: Inst.Geological and Nuclear Sciences, 30 Gracefield Road, Lower Hutt,, Lower Hutt, 1 New Zealand
AU: Embley, R
AF: NOAA PMEL, Hatfield Marine Science Center 2115 SE Oregon State University Way, Newport, OR 97365 United States
AB: During February-March, 2003, a comprehensive survey of hydrothermal plumes and their geochemistry was made along 1200 km of the Mariana Arc from $13.5\deg$N to $22.5\deg$N. Eight of the 50 submarine volcanoes surveyed had intense hydrothermal emissions indicated by extremely elevated levels of Fe, Mn, $\Sigma$CO$_{2}$, H$_{2}$S, particulate sulfur, particulate Fe, and/or particulate Al (PAl). The geochemical signature in the plumes above each of the eight volcanos was distinctly different, with elevated levels of Fe being the most common feature. Hydrothermal activity was found at another three volcanos but the chemical anomalies at these sites were much smaller. Of particular geochemical interest were elevated levels of PAl that were observed at three sites of intense activity with the NW Rota site having PAl $>$ 1100nM. SEM-IXRF analysis of the particles found in the plumes revealed them to be Natroalunite, (K,Na)Al$_{2}$(SO$_{4}$)$_{3}$OH$_{6}$. Elevated Al levels have been observed only rarely in hydrothermal systems and their plumes (e.g., in the Manus Basin by Gamo et al., 1993) and have never been observed along the mid ocean ridges. The elevated Al must arise from SO$_{2}$- or sulfuric acid-rich hydrothermal fluids stripping Al from the host rocks resulting in the pervasive argillic alteration found in various arc and back arc settings. This interpretation is supported by elevated Fe:Mn ratios which are closer to those found in the host rocks than those found in MOR hydrothermal fluids. End member hydrothermal fluids that might support the Al levels found in the plumes have never been found, suggesting that the fluids producing this type of alteration are rare. The total Fe concentrations above the eight most active volcanos ranged from 90 to 2300 nM Fe, averaging $>$ 700nM. Of these volcanos, two are within 200 m of the surface of the ocean while another four were within 450m, thereby making these volcanos potentially large sources of the trace nutrient Fe to the surface oceans. The elevated levels of Fe also have important implications for the geo-chemical cycle of other elements (e.g., P) that are scavenged from the oceans during Fe oxidation and particle formation. Scavenging may be the ultimate removal mechanism for these elements from the oceans, suggesting that arc hydrothermalism may provide an important sink for these elements in their oceanic geochemical cycles.
DE: 4805 Biogeochemical cycles (1615)
DE: 4832 Hydrothermal systems
DE: 8419 Eruption monitoring (7280)
DE: 8424 Hydrothermal systems (8135)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting