Lau Basin Vent Deposit Morphology and Composition: Links to Geologic Setting and Vent Fluid Chemistry
Intellectual merit - Vent deposits are intimately linked within paths of energy and mass transport from the mantle and crust to the oceans and provide habitats for biota. Deposit composition and morphology are linked to the composition and temperature of vent fluids, and to structural aspects of the geologic setting that control the delivery of fluids to the seafloor. In some deposits, incorporation of organisms and/or their products affects deposit evolution. Through their mineral compositions and textures the deposits, which range in age from days to hundreds of years, serve as recorders of past geologic, hydrothermal and biological activity. The goal of this proposal is to use detailed mineralogical data and textural observations combined with geochemical data (from both deposits and fluids) and geochemical modeling of transport and reaction, to determine the formation and evolution of deposits at 6 vent fields along the East Lau Spreading Center/Valu Fa Ridge. It builds on recent published work for the Lau Integrated Study Site (ISS), including information about along-axis trends in composition of the igneous substrate, vent fluid chemistry, and relationships between tectonics, volcanism and hydrothermal activity (Ferrini et al., 2008; Bezos et al., 2009; Escrig et al., 2009; Mottl et al., accepted). Initial characterization of deposits recovered in 2005 has been done, with deposit descriptions and locations relative to geologic features in Ferrini et al. (2008), and with geochemical and XRD analyses released and available through the Marine Geosciences Data System (MGDS). In 2009, additional samples were recovered (including from the recently discovered Tahi Moana vent field), filling gaps in the sample set collected in 2005, resulting in an excellent full suite of representative vent deposit samples from each vent field. Study of this sample set, and integration and synthesis of resultant data with information on geologic settings and vent fluid chemistry, will allow testing of a number of hypotheses that have been developed over the years about seafloor vent deposit formation. The gradient in the composition of the volcanic substrate and vent fluid chemistry from north to south, combined with the pronounced differences in vent fluid chemistry at the southernmost Mariner vent field, allows testing of hypotheses about extents to which deposit composition, morphology, and evolution are affected by 1) volcanic substrate composition, and 2) input of magmatic volatiles (which can result in very low pH vent fluids). Resulting models of vent deposit formation at Lau vent fields will be compared to models developed for other well-described seafloor vent deposits. Of particular interest is that the study of the vent deposits along the Lau ISS, given the range in geologic settings and vent fluid chemistry, will allow comparisons to be made globally between vent fields that exhibit many similarities, and that differ mainly with respect to a single parameter (e.g., depth or volcanic substrate composition or fluid pH or fauna). In addition to testing specific hypotheses, results of this proposal will provide important information on conditions within and on surfaces of deposits, relative fluxes of low temperature vs high temperature flow, extents to which biological activity affects deposit growth, and extents to which biological activity is recorded in the deposits. Broader Impact -This project will provide training and support for a graduate student, and opportunities for undergraduate students through the WHOI summer student fellow program. The PI will continue the types of outreach she has done in the past, including writing papers for and giving lectures to general audiences. The results of the project will be made available to the community through conferences, workshops and publications, and by submitting data and model results to the MGDS/Ridge2000 Data Portal.