HR: 1340h
AN: B13A-0188    [Abstracts]
TI: Geophysical and Hydrothermal Survey of the Lau Basin Integrated Studies Site
AU: * Martinez, F
EM: fernando@hawaii.edu
AF: University of Hawaii, SOEST, 1680 East West Rd., Honolulu, HI 96822 United States
AU: Taylor, B
EM: taylorb@hawaii.edu
AF: University of Hawaii, SOEST, 1680 East West Rd., Honolulu, HI 96822 United States
AU: Resing, J A
EM: joseph.resing@noaa.gov
AF: JIASO, University of Washington, 7600 Sand Point Way NE, Seattle, WA 98115 United States
AU: Baker, E
EM: edward.baker@noaa.gov
AF: NOAA/PMEL, 7600 Sand Point Way NE, Seattle, WA 98115 United States
AU: Walker, S L
EM: sharon.l.walker@noaa.gov
AF: NOAA/PMEL, 7600 Sand Point Way NE, Seattle, WA 98115 United States
AU: Massoth, G J
EM: g.massoth@gns.cri.nz
AF: Inst. Geologic and Nuclear Sciences, 30 Gracefield Road, Lower Hut, 00000 New Zealand
AB: In April-May 2004 we conducted the first combined geophysical and hydrothermal survey of the entire backarc Eastern Lau Spreading Center (ELSC) and Valu Fa Ridge (VFR) on R/V Kilo Moana as part of the Ridge 2000 Lau Integrated Studies. Backarc crustal accretion differs in systematic ways from that at mid-ocean ridges (MORs) because of mantle wedge compositional variations including hydration and depletion effects with distance from the arc volcanic front that respectively increase and decrease melt production relative to MORs. This effect decouples melt production from spreading rate and allows crustal accretion and hydrothermal activity to be investigated under different parameters than commonly prevail at MORs. To study these effects the length of the ELSC/VFR was surveyed with nested shipboard multibeam and two deep-towed sonars (DSL120A and IMI30) and concurrent MAPR/Chemical Scanner and CTD/rosette tow-yos and vertical casts. The spreading center can be divided into three geophysically and morphologically distinct segments each with smaller overlapping sub-segments. The southernmost segment and closest to the volcanic front is the VFR ($22\deg45'-21\deg26'$S). It is volcanically robust, spreads at 39-61 mm/yr, forms a narrow peaked ridge capped by multiple small volcanic cones and is underlain by a deep axial magma lens reflector. Sonar backscatter on the VFR suggests that volcaniclastics debris mantles the ridge flanks in places, probably resulting from high volatile contents of erupted lavas and shallow (1600-2000 m) axial depths. Areas of numerous but small relief faults can be found in this area. The next segment to the north ($21\deg26'-20\deg32'$S), referred to here as the southern ELSC (S-ELSC) increases in spreading rate to 61-76 mm/yr, but abruptly deepens to 2000-2500 m and looses its axial high morphology and axial volcanic cones although it is also underlain by a magma lens reflector. Backscatter intensities increase somewhat and longer and larger faults develop. The northern ELSC (N-ELSC) ($20\deg32'-19\deg20'$S) spreads at 76-96 mm/yr but deepens to 2500-3000 m and has no magma lens reflector. It has higher near-axis backscatter than the S-ELSC with greater coverage by volcanic flows and pillow mounds and fewer large faults evident within the 1-2 km near-axis deep-towed sonar coverage. However, overall along the length of the ELSC/VFR broader coverage from the shipboard multibeam system shows greater faulting and larger flanking abyssal hills from south to north, indicating greater tectonism northward as spreading rates increase but magmatic robustness decreases. Hydrothermal activity was measured by the percentage of ridge length covered by all distinct plume signatures identified. This activity increases to the north with spreading rate as at MORs but is counter to the trend with magmatic robustness found at MORs, as these indicators decrease northward along the ELSC/VFR. We hypothesize that total mantle heat input, as parameterized by spreading rate, and permeability of crustal structure, as indicated by faulting, are stronger controls on hydrothermal activity than magmatic budget.
DE: 4832 Hydrothermal systems
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3045 Seafloor morphology and bottom photography
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting