APPLYING U/TH-PB AND TRACE-ELEMENT LASS PETROCHRONOLOGY TO UNDERSTANDING HIGH-TEMPERATURE METAMORPHISM

LASS (laser-ablation split-stream) petrochronology enables the rapid acquisition of U/Th-Pb dates and trace-element abundances from 10–20 µm spots in accessory minerals using a twin-ICP configuration. This is a useful tool with which to understand high-temperature Earth processes for several reasons. First, the ability to relate dates to elemental abundances allows one to couple time more tightly to petrology--acknowledging the different mobilities of cations of different size and charge. For example, dates combined with quantitative Ti and Zr thermometry, or qualitative Eu/Eu*, Y and HREE barometry can lead to a better understanding of the rates of processes. Second, the rapid throughput opens up many new approaches: entire grains can be mapped with hundreds of spots to discover rich intra-grain histories, and entire orogens can be investigated with campaign-style data acquisition. Finally, the minimal sample preparation means that any grain visible in a clean polished thin section can be analyzed within minutes.