Anorthite isotope correlation

Figure 7. Three-isotope correlation diagram for Mg using 0-notation for unnormalized data from Allende anorthite.

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... 

Three distinct nebular phenomena can in principle contribute to the discordant Mg isotopic systematics late formation of individual anorthites followed by gentle compaction of B2 inclusions, selective secondary alteration of anorthites after inclusion formation, and initial heterogeneities in 26A1 similar to those observed in stable isotopes. The fact that data from anorthites in both B2 inclusions are used to construct the two new Al-Mg correlation lines suggests that whatever processes(es) or... 

---