Characterization of Six Vent Fields Within the Lau Basin

Six active vent fields on the Valu Fa Ridge and Eastern Lau Spreading Center were successfully characterized on R/V Melville cruise TUIM05MV. The Kilo Moana (20deg3.2'S), Tow Cam (20deg19'S), and ABE (20deg45.6-46'S) vent fields were first noted during two R/V Kilo Moana cruises (in April (F. Martinez, Chief Scientist) and Sept (C. Langmuir, Chief Scientist) 2004). A fourth vent field, Mariner at 22deg10.8'S, was located Sept 2004 during the Shinkai 6500 program (K. Takai, Chief Scientist) using data from previous cruises. The fifth vent field examined was the Vai Lili vent field at 22deg12.95'S (Fouquet et al., 1991, Nature 349). On the TUIM05MV cruise, a sixth large active vent field was found at 21deg59.4'S using Jason2 and data from multiple CTD tow-yos, following up on plume observations provided by the Martinez et al. cruise. Tasks conducted to characterize each vent field included 1) detailed SM2000 bathymetric surveys; 2) down-looking and/or forward-looking camera surveys to create photomosaics of megafauna distributions; 3) recovery of biological, rock (basalt and sulfide), and fluid samples, and microbiological sampling of sulfide and diffuse fluid samples; 4) MOCNESS tows to recover larval plankton from plumes; 5) CTD casts to collect plume particles. At the Kilo Moana, Tow Cam, ABE and Tui Malila vent fields, hydrothermal activity occurs in proximity to major faults. At Kilo Moana, active venting occurs in three areas from ~5m tall, branched structures as focused, high temperature flow (to 333C) through chalcopyrite (Cp)- and/or wurtzite (Zn)- lined conduits and as diffuse flow through beehive-type structures. At Tow Cam high temperature (to 330C) active venting occurs in two areas at the base of a western fault from Cp- and/or Zn-lined conduits; diffuse flow exits basalt east of the black smoker areas. Within the ABE vent field there are three large areas of active venting spaced 150 to 300 m apart along NNE trending faults and benches; fluid exits from Cp- and/or Zn - lined conduits (at temperatures to 309C), diffuse spires, and beneath flanges; low to moderate temperature diffuse flow is also observed. At Tui Malila fluids exit tall structures through Cp- and Zn-lined conduits (at temperatures to 312C), and from beneath flanges, and directly from andesite; hydrothermal breccias are also present. Within the Mariner and Vai Lili vent fields, hydrothermal activity is not related to faulting, but may be concurrent with magmatic processes. At Mariner, venting occurs from the base and sides of 10 to 25 m tall narrow structures. Fluids exit as vigorous, high temperature (to 363C) black smoker fluids through Cp-lined conduits and less focused flow from porous beehive structures. Inactive structures are friable, composed of Fe- and Cu-oxides. At Vai Lili, the highest temperature fluids observed (121C) exit from beneath marcasite-lined flanges, and 70C clear fluids exit from an Fe-oxide chimney. The geochemistry and mineralogy of deposits from these six vent fields, and their relation to vent chemistry and biology, will be presented.