STUDIES OF FINE-GRAINED MINERALS: TOCHILINITE.  Meteoritic tochilinite has been widely accepted for almost 20 years as an important mineral in CM chondrites, especially those that have been subjected to aqueous alteration. This presumed identity is important because it has been used, by analogy to its terrestrial counterpart, to interpret the origin of the meteoritic mineral. However, there has not been a thorough chemical and structural study of meteoritic tochilinite that provides definitive information regarding its actual identity or that it is the same as standard tochilinite. Moreover, there are significant differences between terrestrial tochilinite and the mineral in meteorites. We intend to examine these variations and differences. Whatever the outcome of our proposed studies, it is clear that the complexities of tochilinite reflect a range of structural and chemical variations, and these open the possibility that they could provide insights into a range of mechanisms and environments of formation on the meteoritic parent body. We plan to use high-resolution transmission and analytical electron microscopy to study some of these pending issues regarding an important meteoritic mineral.

STUDIES OF Li ISOTOPES.   Large variations in 7Li/6Li of galactic and solar system materials exist as a result of multiple nucleogenic sources of these isotopes. In addition, appreciable fractionation of 7Li/6Li occurs during chemical reactions such as the low-temperature aqueous alteration of planetary materials on their parent bodies. Though currently few in number, the 7Li/6Li data on meteorites indicate substantial variability outside analytical uncertainties, suggesting that 7Li/6Li is a useful tracer of processes in early solar system evolution. We propose to use secondary ion mass spectrometry (SIMS) measurements of 7Li/6Li in various components of meteorites in order to better understand the alteration processes affecting primitive chondritic meteorites. Our SIMS measurements  of 7Li/6Li to olivine from terrestrial mantle xenoliths and pallasites demonstrate the feasibility of the technique, which is uniquely suited to meteorite work where low concentrations of Li are associated with limited quantities of material for analysis, and a high degree of variability exists at small spatial scales. We will study 7Li/6Li variations between chondrules and different generations of secondary phases in chondrules, rims, and matrices of CM and CV chondrites. The goal is to fingerprint different alteration events and place constraints on their origin and physical setting by drawing upon studies of Li isotope behavior in terrestrial alteration systems and laboratory fractionation experiments. We will also determine the degree of primary Li isotope heterogeneity in chondrules, and its relationship to solar system variability as recorded in various types of meteorites.