Lithium Isotope Studies of Continental Crustal Fluids

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Chan 9506390 The isotope geochemistry of lithium in the continental environments is virtually unknown. The proposed research is intended to examine the behavior of lithium and its two isotopes 6Li and 7Li in brines and waters which reside in a large part of the continental crust. Three major types of crustal fluids will be studied: subsurface brines in sedimentary basins, deep seated brines saturating Archean Shields, and continental geothermal fluids. Representative examples to be included in this project are the Jordon Rift and oil field brines of Israel, saline waters from the Canadian and Fennoscandian shields and the geothermal waters from the Yellowstone system. The objectives are (1) to establish the lithium isotope composition of brines and thermal waters from various environments and of their associated rocks and sediments, (2) to determine element distribution coefficient and isotope fractionation factors by laboratory simulation of water/rock interaction, and (3) to apply the findings to model the origin and evolution of the crustal fluids. Special emphasis will be given to the cause of salinity and the calcium chloridic composition of the brines which remains a subject of considerable debate. Li isotope systematics will be compared to the more established isotope tracers, 87Sr/86Sr and 34S/32S. In addition, all waters will be analyzed for the major and minor constituents (N, K, Ca, Mg, Sr, Li, Cl, SO4, HCO3, and NO3) for an integrated interpretation of the nature of the parent fluid and the effects of interactive processes with the host rock. This work will be in collaboration with Dr. A. Katz of Hebrew University, Jerusalem. The significance of the proposed research lies in the establishment of a new isotope system for the study of continental crustal waters. At the same time, it will leas to a considerable enlargement of reliable lithium isotope data and contribute to the fundamental understanding of the isotope geochemistry of lithium. The study of continental mat erial will complement the recent marine studies to offer a more comprehensive view of the terrestrial variation of lithium isotopes.