HR: 17:30h
AN: V54A-07    [Abstracts]
TI: Hydrothermal Plume Distributions Along the Valu Fa Ridge and East Lau Spreading Center, Lau Backarc Basin
AU: * Baker, E T
EM: edward.baker@noaa.gov
AF: NOAA/PMEL, 7600 Sand Point Wy NE, Seattle, WA 98115 United States
AU: Walker, S L
EM: sharon.l.walker@noaa.gov
AF: NOAA/PMEL, 7600 Sand Point Wy NE, Seattle, WA 98115 United States
AU: Resing, J A
EM: joseph.resing@noaa.gov
AF: JIASO/University of Washington, 7600 Sand Point Wy NE, Seattle, WA 98115 United States
AU: Massoth, G J
EM: g.massoth@gns.cri.nz
AF: Institute of Geological & Nuclear Sciences, 30 Gracefield Road, Lower Hutt, 00000 New Zealand
AU: Martinez, F
EM: fernando@hawaii.edu
AF: Hawaii Institute of Geophys. and Planetol., University of Hawaii 1680 East-West Road, Honolulu, HI 96822 United States
AU: Taylor, B
EM: taylorb@hawaii.edu
AF: Dept. of Geology and Geophysics, University of Hawaii 1680 East-West Road, Honolulu, HI 96822 United States
AU: de Ronde, C E
EM: cornel.deRonde@gns.cri.nz
AF: Institute of Geological & Nuclear Sciences, 30 Gracefield Road, Lower Hutt, 00000 New Zealand
AB: Extensive studies along midocean ridges (MORs) from ultraslow- to superfast-spreading find a robust correlation, at the multi-segment scale, between the incidence of hydrothermal plumes (p$_{h}$) and the spreading rate, a proxy for the long-term melt supply. On the segment and sub-segment scales, these studies likewise find a good correlation between p$_{h}$ and cross-axial inflation, a proxy for higher frequency variability in the melt supply. To test the validity of these correlations in a backarc setting, where complex tectonics may weaken the connection between spreading rate and melt supply, we conducted multiple surveys of the hydrothermal plume distribution along three geophysically and morphologically distinct ridge sections in the Lau backarc basin: Valu Fa Ridge (VFR, 22.7-21.43$\deg$S), southern East Lau Spreading Center (S-ELSC, 21.43-20.53$\deg$S), and N-ELSC (20.53-19.3$\deg$S). On the TELVE cruise in March 2003 we used an optical sensor on CTDO tow-yos to map plumes on the southern 88 km of the VFR. In April 2004, on the initial cruise of the RIDGE ISS Lau project, we used both CTDO tow-yos and a vertical array of optical/temperature sensors (MAPRs) on the DSL-120 sidescan vehicle to conduct multiple surveys of the entire VFR/ELSC. The VFR/ELSC complex is distinctly different than typical MORs in several ways: (1) spreading rate more than doubles from 39 to 96 mm/yr over just 400 km between the southern end of the VFR and the northern end of the ELSC; (2) cross-axial inflation and axial depth are inversely correlated with spreading rate, decreasing northward from +5 km$^{2}$ and $\sim$1800 m, respectively, to -5 km$^{2}$ and $\sim$3000 m; and (3) geophysical studies suggest that melt production is also inversely correlated with spreading rate, owing to increasing distance from the melt-rich arc front from south to north along the ridge complex. Our surveys found $>$20 hydrothermal plume areas, ranging from $<$1 km to $>$20 km in axial extent, and rising as high as 500 m above the seafloor. The p$_{h}$ (fraction of axis overlain by a plume) increases northward as spreading rate increases, from $<$0.3 along the VFR (39-61 mm/yr) to $>$0.4 along the N-ELSC (76-96 mm/yr). This trend is reasonably consistent with the global MOR trend of spreading rate vs. p$_{h}$, though the relatively short length of these segments (100-150 km) makes comparisons tentative. On the subsegment scale, the lack of any consistent correlation between axial inflation and p$_{h}$ is strikingly different than most MORs. We speculate that despite a northward diminishment of melt supply, resulting in a thinner crust and deeper seafloor, hydrothermal discharge is enhanced by heat from mantle rocks accessed by the pervasive faulting and fracturing that increases northward with spreading rate. Forthcoming data from the chemical analyses of the plumes and the fine-scale sidescan imagery will provide further evidence to support or reject this hypothesis.
DE: 8424 Hydrothermal systems (8135)
DE: 8135 Hydrothermal systems (8424)
DE: 3035 Midocean ridge processes
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting