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 of oxygen isotope ratios, O-18/O-16 and O-17/O-16, with high spatial resolution in polished thin sections of silicate minerals, This technique allo-cvs the isotopic analysis of samples as small as picomoles of material which represents only 10(-7) of the sample size required by conventional fluorination oxygen isotope measurement methods and thus has wide application to the study of many terrestrial and extra-terrestrial samples that have heterogeneous oxygen isotope compositions on a scale of tens of micrometres, To illustrate the breadth of studies that are made possible by the ion probe, we report here oxygen isotope measurements from an authigenic quartz overgrowth obtained from the Penrith sandstone, UK, and measurements of magnetite grains from the Orgueil and Yamato 82162 carbonaceous chondrites which may be used to constrain possible formation mechanisms of the magnetite.