Paper No. 3
Presentation Time: 2:30 PM
BACK-ARC NEIGHBORS: ARC-LIKE FLUID SOURCES
MASSOTH, Gary J.1, BAKER, Edward T.
2, DE RONDE, Cornel E.J.
1, ARCULUS, Richard J.
3, LUPTON, John E.
4, ISHIBASHI, Jun-ichiro
5, RESING, Joseph A.
6, MARTINEZ, Fernando
7, STOFFERS, Peter
8 and WORTHINGTON, Tim J.
8, (1)Institute of Geol and Nuclear Sciences, 30 Gracefield Road, Lower Hutt, (2)Pacific Marine Environmental Lab, National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle, WA 98115-6349, (3)Department of Geology, Australian National Univ, Canberra, ACT 0200, Australia, (4)Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, 2115 Marine Science Drive, Newport, OR 97365, (5)Department of Earth and Planetary Sciences, Faculty of Science, Kyushu Univ, 6-1-10 Hakozaki, Higashi-ku, Fukuoka, Japan, (6)Joint Institute for the Study of the Atmosphere and the Oceans (NOAA-PMEL and Univ. of Washington), 7600 Sand Point Way NE, Seattle, WA 98115-6349, (7)Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Sciences and Technology, University of Hawaii at Manoa, Honolulu, HI 96822, (8)Institute für Geowissenschaften, Christain-Albrechts-Universität zu Kiel, Olshausenstr. 40, D-24118, Kiel, Germany, g.massoth@gns.cri.nz
Back-arc spreading centers that form in oceanic basins near convergent plate margins are recognized sites of ancient and contemporary ore mineralization. While the processes of extension and crustal accretion at many back-arc spreading centers can be similar to those at mid-ocean ridges (MORs), back-arc segments proximal to active arcs may be significantly influenced by the subducting slab. Such is the case at the Valu Fa Ridge, the southern-most section of the Eastern Lau back arc Spreading Center, where high magmatic inflation and lavas with arc-like compositions are manifest along the several ridge segments that most closely neighbor the adjacent S. Tonga (Tofua) active arc front.
Fluids derived and discharged from compositionally-evolved arc volcanics are by definition the most arc-like. To the extent the high concentrations of magmatic volatiles and dissolved ionic species characteristic of these fluids are causal to ore formation (as has been suggested), contemporary magmatic-hydrothermal fluids issuing from arc-corrupted back-arcs, such as the Valu Fa Ridge, may similarly present opportunities for seafloor mineralization.
Here we present the results of a comprehensive and systematic plume reconnaissance along the southern Valu Fa Ridge during TELVE (Tonga-Eastern Lau Vents Expedition, March-April 2003), one of the first surveys of this style along any back arc spreading system. The four overlapping ridge segments that comprise the southern 126 km of the Valu Fa Ridge were surveyed using tow-yo and vertical cast procedures common on MORs. In addition to confirming that two known sites (Hine Hina and Vai Lili) remain actively venting, we newly observed plumes above four other areas along the ridgecrest, each more chemically intense than above the historical sites. We compare the plume chemical results to those now emerging for submarine arcs (e.g., de Ronde et al., this session) and to data for MORs to identify an arc-like chemical signature for hydrothermal plumes, one that we hope eventually will link to arc-like mineralization on the seafloor.
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