Date of Award

2001

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology and Geophysics

First Advisor

Lui-Heung Chan

Abstract

While the isotope geochemistry of lithium in the marine environment is increasingly known, there are still outstanding problems concerning its oceanic budget and mantle-crust recycling that remain to be resolved. To evaluate the role of marine sediments in the oceanic budget, laboratory experiments were conducted to determine the extent of lithium adsorption on marine sediments and the magnitude of isotopic fractionation. Sediments from the Greenland margin were studied to gain further understanding of the sediment-water interaction. The isotopic compositions of the major types of marine sediments were characterized to understand the sedimentary cycle of lithium. The enhanced database permits a re-evaluation of the oceanic lithium budget. In the adsorption experiments, greater magnitude of adsorption was observed in river water than seawater demonstrating the effect of competition of major ions for sorption sites. The isotopic fractionation factors for adsorption on kaolinite, vermiculite, and Mississippi River suspended sediment are similar within uncertainty, giving a mean value of 1.024 +/- 0.003. In the comprehensive study of the sediments from the Greenland margin, the similarity between solid and pore water concentration profiles suggests that the sediments largely control the distribution of lithium in pore water. The isotopic compositions of the sediments are well correlated with source material as defined by lithology and bulk chemistry. Based on the isotopic data of various types of marine sediments, it is concluded that lithium isotopic compositions of marine sediments are dominated by terrigenous components and reflect local source. Most pelagic and hemipelagic sediments studied have isotopic compositions that are distinct from the mantle, making lithium isotopic ratio a valuable tracer for the subducted component in arc magmas. Among the sedimentary sinks evaluated in this study, namely incorporation in marine carbonates and biogenic silica, diffusion into sediments, and adsorption on marine sediments, only adsorption appears to be a significant sink for lithium in the oceans. The importance of the oceanic crust alteration at low and moderate temperatures as a lithium sink may be underestimated. Further insight into the lithium balance in the oceans depends on the characterization of water flux on the ocean ridge flank.

ISBN

9780493213989

Pages

142

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