HR: 0800h
AN: V41F-1533    [Abstracts]
TI: Li Concentration and Isotope Cycling In The Ocean, An Experimental Study
AU: Kastner, M
EM: mkastner@ucsd.edu
AF: Scripps Institution of Oceanography, SIO 0212, UCSD, La Jolla, CA 92037 United States
AU: * Wei, W
EM: wewei@ucsd.edu
AF: Scripps Institution of Oceanography, SIO 0212, UCSD, La Jolla, CA 92037 United States
AU: Chan, L H
EM: lchan@geol.lsu.edu
AF: Louisiana State Univ., Dept. of Geology and Geophysics, Baton Rouge, LA 70803 United States
AU: Rosenbauer, R
EM: brosenbauer@usgs.gov
AF: U.S. Geological Survey, 349 Middlefield Road, Menlo Park, CA 94025 United States
AU: Weinstein, Y
EM: weinsty@mail.biu.ac.il
AF: Bar Ilan University, Dept. of Geography, Ramat Gan, 52900 Israel
AB: Hydrothermal experiments of basaltic ash-seawater and smectite-seawater exchange reactions, were conducted from 35 to 350°C, with 25 or 50°C increments, at 600 bar pressure. The water/rock mass ratios evolve from 5.2 at the beginning of the experiment to 2.6 at 350°C in the basalt-seawater experiment, and 6.5 to 4.5, respectively, in the smectite-seawater experiment. Li concentration in the fluid was analyzed at each temperature and δ⁷Li was analyzed at 50, 75, 100, 150, 200, 300, and 350°C. In both basalt and smectite experiments, δ⁷Li is lower at 50°C than in starting seawater and 75°C experimental fluid. From 100 to 200°C, Li concentration gradually increases from 59 to 84 μM in the basalt experiment, with δ⁷Li decreasing from 19.66 to 14.40 ‰. In the smectite experiment, Li concentration increases from 125 to 400 μM, and δ⁷Li decreases from 15.80 to 11.34‰. The nonlinear δ⁷Li and 1/Li relationship in 35 to 200°C fluids in both experiments confirms that both Li leaching from the solids and uptake into alteration phases are occurring simultaneously. Similar results were obtained by James et al. (2003). From 250 to 350°C, Li is leached from the solid to the fluid. At 350°C, the Li concentration and δ⁷Li value of the fluid in the basalt-seawater experiment are within the range of the corresponding values in hydrothermal fluids at ridge crests (Chan et al., 1992). Based on known water/rock ratio at each temperature, analyzed Li concentration and δ⁷Li in the initial fluids and solids, as well as in the reacted fluids, the fractionation factor of Li isotopes and distribution coefficient of Li between fluid and alteration products, are estimated as a function of temperature. With Li mass fluxes and assumption of steady state, the Li isotope balance in the ocean is estimated. Based on input fluxes (river + hydrothermal vents + subduction zone refluxes), the calculated isotopic fractionation factor α is 19.1‰, the same as the empirical value estimated from altered basalt from mid-Atlantic Ridge (Chan and Edmond, 1988). This implies that the main mechanism of Li removal from the ocean, that keeps the Li isotopes in balance in the ocean, is low temperature (2-5°C) diagenetic reactions.
DE: 1000 GEOCHEMISTRY
DE: 1039 Alteration and weathering processes (3617)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
DE: 4832 Hydrothermal systems (0450, 1034, 3017, 3616, 8135, 8424)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005