Evolution of hydrogen in the inner solar system: volatile abundances and isotopic compositions in CAIs and chondrules from primitive carbonaceous chondrites

The abundances and isotopic composition of hydrogen and other volatiles in CAIs and chondrule glasses & minerals can potentially provide information on the immediate environment surrounding their formation, including the vapor pressure of various volatiles in environments ranging from the proto-solar nebula to impacts to post-accretion interactions with ices and H2O-rich fluids during the processes of parent body assembly, heating & metamorphism. In the inner solar system, end member volatile sources include the solar nebula gas and low-temperature water ice; these two sources have D/H ratios that differ by orders of magnitude, and are also characterized by very different oxygen isotope compositions. Additionally, coupled data on hydration and oxygen isotope composition of CAIs and chondrules can provide important information that can potentially identify open-system behavior in phases that are used for Al-Mg, Pb-Pb, Sm-Nd and Hf-W chronometry. Objectives: We will examine CAIs and chondrules in the most primitive CO, CM, CR and CV carbonaceous chondrites of lowest metamorphic and aqueously altered petrologic types, to determine if they (A) preserve evidence for volatiles incorporated from the solar nebula, potentially recording the partial pressure of hydrogen during their formation; and (B) record open-system behavior for H and O. Nebular signatures can be overprinted by later interactions with low-temperature, H2O-rich fluids in chondrite parent bodies, accompanied by hydration and formation of molecular H2O in glass that is far in excess of the H2O/OH ratio typical of quenched high-temperature melts (cf. Stolper, 1982). This excess molecular H2O is readily observed by FTIR, so much so that it has formed the foundation of a crude dating method for obsidian stone tools in archaeology (Stevenson, 1993; Liritzis, 2006). We will use SIMS and FTIR methods to focus on documenting the relationship between concentrations and isotopic compositions of hydrogen and oxygen in CAIs and chondrules, and the H2O/OH ratio in chondrule glasses, in the least altered and metamorphosed chondrites, in order to determine the sources of hydrogen and other volatiles present in the earliest inner solar system. Detection of hydrogen in CAIs and chondrules is challenging, but within the detection limits of our instruments (~0.1 ppm H on the NanoSIMS) our study will provide constraints on the various models that exist to explain their formation. We will also examine the abundances and isotopic compositions of other volatile elements (C, Na, K, S, Cl) in the same objects, and evaluate them in the context of geochemical models (e.g., MELTS) and experiments, and modeling of conditions and outcomes associated with the processes of impact, evaporation, condensation and fluid-rock interaction. Relevance: This study will address several objectives of the Emerging Worlds program, including: (1) protoplanetary disk formation and evolution, (2) nebular transport mechanisms, (3) large-scale chemical and isotopic fractionation processes, (4) chemical processing of gas, dust and ice, (5) the chemical properties of ancient materials (CAIs, chondrules), (6) early thermal and chemical processes occurring on small bodies, and (7) processes that occur on solar-system bodies during the period of global differentiation. The project will support a postdoc at the Carnegie Institution of Washington and provide analytical support for a graduate student at Northwestern University.