SOUTH CAROLINA RESEARCH FOUNDATION
Grant: $173,958 - National Science Foundation - Jul. 28, 2009
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Award Description: Collaborative Research: Serpentinization and cycling of B, Nd and Sr in submarine hydrothermal systems: An experimental study on the effects of pH and temperature Project Summary Intellectual Merit: The serpentinized ultramafic oceanic lithosphere retains a record of heat and mass transfer between seawater and the earths mantle that takes place during hydrothermal circulation at mid oceanic ridges and subduction zones. In turn, low temperature ultramafic-hosted hydrothermal systems are linked to alkaline fluids enriched in organics and are central to the discussion of energy supply for microbial life at the seafloor. Boron, Sr and Nd isotopes are often used to describe the extent of fluid-rock interaction during serpentinization/hydrothermal alteration. However, little is known on the control of pH, temperature and mineral composition on the boron isotope fractionation and combined B-Sr-Nd mobility and rock-fluid exchange in ultramafic-hosted hydrothermal systems.We propose a collaborative 3-year experimental / geochemical investigation to constrain: - The role of fluid pHT,P and rock composition in sequestrating dissolved B, Sr and Nd released during hydrothermal alteration of ultramafic rocks. What is the role of Mg-bearing secondary phases (e.g. brucite, chrysotile, tremolite, talc) as elemental sinks? - The B isotope fractionation at alkaline pH between tetrahedral dissolved boron (B(OH)4 -) and BO3-bearing minerals (e.g. brucite) as a function of T, pHT,P. Can this explain the low 11B values of the Lost City vent fluids and what is the 11B of the associated ultramafics? - The rate of B, Nd, Sr exchange and B isotope fractionation between mantle peridotite and hydrothermal fluids at low-T/alkaline and high-T/acidic alteration conditions.Our central hypothesis is that precipitation of secondary phases is the main mechanism of B-Sr-Nd peridotite-seawater exchange and boron isotope fractionation, therefore estimates of fluid-rock ratios in hydrothermal systems will strongly depend on T, P, X and pH conditions.This research will ultimately allow to better constrain water/rock ratios and paleo-pHT,P from the B-Sr-Nd isotope compositions of peridotites. We will conduct hydrothermal experiments at the Geophysical Lab between ultramafic mineralogy (peridotite, olivine/diopside, enstatite/diopside and brucite) and Ca-Mg-Na-Clbearing aqueous solutions at 100oC-400oC (@500bars), fluid pH~5-9, and variable water/rock mass ratios (1-100). We will determine the elemental and isotope compositions of fluid and solid products at the Univ. of South Carolina and Dept. of Terrestrial Magnetism, with additional analytical support provided by the Univ. of Leeds (UK). Nuclear Magnetic Resonance data (GL)will be used to constrain the speciation of boron in secondary minerals (e.g. brucite, chysotile,tremolite, talc) and thus better evaluate 11B/10B fractionation between minerals and fluids. Broader Impacts: This research will put constraints on the fundamental process of energy and mass transfer between seawater and ultramafic lithologies during hydrothermal activity and will be of great interest in the broader marine science and bio-geo-chemical community. Proposed research will be part of a graduate students PhD thesis at USC, while undergraduate participation is planned through NSF-REU programs at GL. This project will foster multidisciplinary and international collaboration between researchers with expertise on experimental and isotope geochemistry. The project will support the new geochemical facilities and NSF-funded instrumentation at USC (an EPSCoR state) and expand the hydrothermal lab at GL. This research will support the academic development of Foustoukos and Bizimis, both early career scientists. Both scientists will be involved in advising and training graduate and undergraduate students.
Project Description: As defined in the Award Description field.
Jobs Summary: None to report yet (Total jobs reported: 0)
Project Status: Not Started
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