See more from this Division: Topical Sessions
See more from this Session: Strengthening Links between Metamorphic Conditions and Time: New Advances in High-Temperature Geochronology and Tracing P-T-t Paths of Metamorphic Terranes
Abstract:
Recent advances in thermal ionization mass spectrometry including the use of NdO+ analysis have improved the precision of 143Nd/144Nd on small samples. Using a Ta2O5 activator slurry, we achieve sub-10ppm internal precision and 13-20ppm long term external precision on 4 nanogram Nd standards and natural samples. The new analytical advances permit high precision analysis of very small garnet separates (>4mg) or microzones within individual garnets depending on garnet Nd concentration, which is often <1ppm . Several studies have shown that with HF-based partial dissolution cleansing of garnets, sufficiently high 147Sm/144Nd ratios (between 1.0 and 5.0) are usually achieved. We have found much greater success in partial dissolution cleansing of crushed separates (100-200 mesh), rather than powdered separates. 13ppm (2sigma) precision on garnet 143Nd/144Nd analysis will produce sub-million year age precision (2sigma) for any garnet whose 147Sm/144Nd exceeds about 1.5. A significant challenge remains in cleanly separating Nd from garnets with Nd concentrations <0.1ppm. For such samples, additional chemical procedures are required to achieve high yields and eliminate ionization inhibiting elements and substances. The ability to achieve sub-million year age precision even on very small garnet samples represents the primary advantage of Sm-Nd garnet geochronology.
See more from this Division: Topical Sessions
See more from this Session: Strengthening Links between Metamorphic Conditions and Time: New Advances in High-Temperature Geochronology and Tracing P-T-t Paths of Metamorphic Terranes