HIGH-PRECISION, IN-SITU OXYGEN-ISOTOPE RATIO MEASUREMENTS OBTAINED FROM GEOLOGICAL AND EXTRATERRESTRIAL MATERIALS USING AN ISOLAB-54 ION MICROPROBE

We have developed an ion probe technique for the in situ measurement o f oxygen isotope ratios, O-18/O-16 and O-17/O-16, with high spatial re solution in polished thin sections of silicate minerals, This techniqu e allo-cvs the isotopic analysis of samples as small as picomoles of m aterial which represents only 10(-7) of the sample size required by co nventional fluorination oxygen isotope measurement methods and thus ha s wide application to the study of many terrestrial and extra-terrestr ial samples that have heterogeneous oxygen isotope compositions on a s cale of tens of micrometres, To illustrate the breadth of studies that are made possible by the ion probe, we report here oxygen isotope mea surements from an authigenic quartz overgrowth obtained from the Penri th sandstone, UK, and measurements of magnetite grains from the Orguei l and Yamato 82162 carbonaceous chondrites which may be used to constr ain possible formation mechanisms of the magnetite.