Ion probe Mg isotopic measurements

Since the IM-20 had not previously been used for high precision isotopic measurements and since previous isotopic measurements with other ion microprobes [24,25] were characterized by percent level relative errors, we carried out an extensive series of Mg isotopic analyses of terrestrial samples. Terrestrial standards were especially emphasized prior to the study of meteoritic samples, but were also periodically interspersed with later meteoritic analyses as a check on the performance of the ion probe. Terrestrial standards included Ceylon spinel (MgAl204), Madagascar hibonite (CaA112019), a suite of olivines (Fo 100 to Fo 5) used in... 

A common feature of anorthite crystals in Allende Type B inclusions is large variations (up to a factor of -v 5) in Mg content on a scale of 10 to 50 pm. (Mg variability and its correlation with Na content and cathodoluminescence color are discussed extensively in [12].) Guided by cathodoluminescence micrographs, we used the microscopic spatial resolution of the ion-probe to measure the Mg isotopic composition at several points with distinct 27Al/24Mg ratios within individual crystals from TS-21 and TS-23. Data from each individual crystal define an... 

The microscopic spatial resolution of the ion probe enabled us to measure the isotopic composition at several points within individual crystals and these ion probe data establish the first single crystal isochron for areas with distinct 27Al/24Mg ratios. The Mg isotopic pattern within each B1 and B2 anorthite is individually consistent with a single (26A1/27A1)q ratio, suggesting... 

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