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Project Progress

Over the course of the past year, the aqueous alteration project has sustained substantial progress. We have requested and received meteorite thin sections from the Johnson Space Center through the Meteorite Working Group, including some rare samples of type CR1 (GRO95577) and CR3 (MET00426 and QUE99177). Through the use of various micro-analytical tools (such as the Scanning Electron Microscope and Electron Microprobe) we have located areas of secondary (aqueous) alteration in our sample thin sections. False-color elemental X-ray maps have been useful in identification of distinct lithologies, which likely were formed under various conditions on the CR parent body. Quantitative elemental analysis of minerals has helped to identify phase assemblages that formed under distinct aqueous environments. To gain further understanding of the CR aqueous alteration environment, we have utilized Geochemist Workbench software for fluid chemistry modeling. These models have helped to constrain parameters such as pH and oxygen fugacity during fluid events that led to secondary mineral formation. Progress in this modeling work was presented in a talk at the 75^th Annual Meeting of the Meteoritical Society in August 2012.

Secondary carbonates have been identified in the CR thin sections, and are excellent candidates for manganese-chromium radiometric dating using Secondary Ion Mass Spectrometry (SIMS). The Mn-Cr radiochronometer system can resolve aqueous events occurring up to around 20Myr after the formation of CAIs. However, a historic problem with measurements has been finding appropriate standards. Current progress is being made on the development/acquisition of carbonate mineral standards so that anticipated measurements yield valid isochrons.

In our studies of organic compounds, we are working on a suite of techniques that will allow us to more easily detect organic molecules in situ in aqueously altered carbonaceous meteorites. With the help of our collaborators Shiv Sharma and Anupam Misra, we are developing a time-resolved laser-induced fluorescence instrument dubbed “biofinder.” The biofinder instrument uses a pulsed green or UV laser and an intensified CCD camera designed to separate the short-lived fluorescence, usually attributable to bio-organic molecules or biosignatures, from long-lived fluorescence, attributable to minerals. The fluorescence images are collected in real time. Hence, the biofinder can be used as a field instrument to find interesting targets for closer study. Unfortunately, the biofinder cannot directly measure another very important class of organic materials in meteorites, macromolecular kerogen-like material known as insoluble organic material (IOM). We are developing a technique called Imaging Raman Microscopy to quickly map parts of our meteorite samples that we suspect contain IOM. Imaging Raman Microscopy is an established technique that uses a laser and a microscope with a moving stage to collect high spatial resolution spectral images of samples. We use a computer program to process the raw data and give us a set of spectral parameters that can describe the IOM. Using a combination of the biofinder and the Raman Imager, we can get a full picture of the distribution of organic molecules present in our meteorite samples. Initial results were presented in a talk at the 75^th Annual Meeting of the Meteoritical Society in August 2012 and a poster at the 43^rd Lunar and Planetary Science Conference in March 2012.