analyses were done using the USGS/Stanford sensitive high-resolution ion microprobe-reverse geometry (SHRIMP-RG). The primary oxygen-ion beam opereated at about 8 nA and excavated a pit about 25 micron in diameter and 1 micron deep. The magnet was cycled through the mass statations six times per analysis. Elemental fractionation was corrected by analyzing a zircon every fourth analysis of know age standard.