DIFFUSION OF HELIUM IN CALCITE, ARAGONITE, AND DOLOMITE

Many modern cosmogenic dating techniques are limited by time-consuming and labor intensive mineral or chemical purification procedures which are required to ensure reliable and repeatable age determinations. ³He cosmogenic dating of calcite, aragonite, and dolomite has the potential to provide cosmogenic ages relatively quickly and easily in a range of field environments. However, the primary limitation to applying cosmogenic ³He dating is the poor helium retention observed in many natural carbonates and the lack of understanding regarding helium diffusion behavior in these minerals. More knowledge of what controls He retention in calcite, dolomite, and aragonite is required to identify types of natural samples which are reliably retentive and therefore useful for geochronology. One of the first steps to improving our understanding of helium diffusion in these minerals is to determine the basic trends in diffusion behavior, such as anisotropic diffusion. To test for anisotropy, slabs of gem-quality calcite, aragonite, and dolomite were prepared in two orientations: parallel to cleavage and perpendicular to the c-axis. These faces were implanted with a narrow plane of ³He using the Extrion ion implanter at the Ion Beam Laboratory at the University of Albany. Implanted specimens were then subjected to step heating in 1 atm furnaces, followed by set of profiling experiments using Nuclear Reaction Analysis via ³He(d,p)⁴He.