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Project Progress

We have advanced the research on five fronts. (1) Our work in collaboration with the Dietrich group reached fruition as high-quality He-3 exposure ages were determined for the Box Canyon basalts of south central Idaho. A paper on the geochronology has been submitted to EPSL. This is the first demonstration of the combined U-Th-⁴He-³He approach to simultaneously dating the eruption age and exposure age of lava flows. The data place strong constraints on the possible origins of the Canyon by sapping processes. (2) Ca isotopic analyses have been completed on a sediment core from Badwater dry lake in Death Valley, which we are using as an analogue for early Mars surface conditions to assess the role of non-biological processes in fractionating Ca isotopes. To complete this part of the study, new samples of stream waters, lake waters, and bedrock have been collected in Death Valley. (3) We have also completed analyses of Ca in a soil section from the Atacama desert, another Mars analogue site. In this case we have observed considerable Ca isotope fractionation, unlike any we have found elsewhere in terrestrial materials, which we believe is due to kinetic effects in the dissolution and reprecipitation of calcium carbonate and sulfate in the soil over millions of years. (4) Measurements and modeling of an 800 meter-long deep-sea carbonate core, and the associated pore fluids, have been done as a means of further evaluating the equilibrium fractionation factor for 44Ca/40Ca between calcite and aqueous solution. The results show that slow inorganic precipitation of calcite results in no fractionation of Ca isotopes. A paper on this work will be submitted in late summer 2006. (5) We have begun analytical work on a larger sample of the Martian meteorite ALH84001 to better constrain the Ca and Fe isotopic composition of the igneous and secondary minerals, and thereby assess whether there is evidence that the precipitation of carbonate was biologically mediated. We have also spent substantial effort in further refining the analytical techniques for Ca isotopic measurements, and we have established methods for investigating variations of radiogenic 40Ca in meteorites, which could provide insights into the early formation and bulk composition of Mars.

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