Geological Society of America

T2 Modern and Ancient Mineralizing Seafloor Hydrothermal Systems II

Saturday, 1 November 2003
1:30 PM - 5:30 PM

BACK-ARC NEIGHBORS: ARC-LIKE FLUID SOURCES

Paper number: T2-3
Program: Technical Sessions
Time: 2:30 PM – 3:00 PM

Authors

Gary J. Massoth Presenting Author
Institute of Geol and Nuclear Sciences, Lower Hutt, N/A
Tim J. Worthington
Christain-Albrechts-Universität zu Kiel, Kiel, N/A
Edward T. Baker
Pacific Marine Environmental Lab, National Oceanic and Atmospheric Administration, Seattle, WA
Cornel E.J. de Ronde
Institute of Geol and Nuclear Sciences, Lower Hutt, N/A
Richard J. Arculus
Australian National Univ, Canberra, N/A
John E. Lupton
National Oceanic and Atmospheric Administration, Newport, OR
Jun-ichiro Ishibashi
Kyushu Univ, Fukuoka, N/A
Joseph A. Resing
Joint Institute for the Study of the Atmosphere and the Oceans (NOAA-PMEL and Univ. of Washington), Seattle, WA
Fernando Martinez
School of Ocean and Earth Sciences and Technology, Honolulu, HI
Peter Stoffers
Christain-Albrechts-Universität zu Kiel, Kiel, N/A

Abstract

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.