Groundmass microsampling using laser ablation time-of-flight inductively coupled plasma mass spectrometry (LA–TOF–ICP–MS): potential for rhyolite provenance research

Provenance research using rhyolite formations that cooled too slowly to form obsidian has proven difficult for geochemical researchers to date. Uncertainties about the temperature regimes within the parent magma chamber and subsequently of the eruption process itself yield highly divergent phenocryst compositions and quantities. Variable and uncertain phenocryst composition and content make bulk and surface compositional analysis techniques (e.g., INAA, XRF) ineffectual without efforts to homogenise or render samples into solutions. This is frequently not a viable option for archaeological materials, thus rendering provenance research on rhyolite artifacts impractical using traditional techniques.One hundred and fifty-one source samples from five rhyolite sources in the western Mojave Desert, California were used to conduct a pilot study on the potential for using LA–TOF–ICP–MS to pursue provenance research using rhyolite. To test this methodological question, an archaeological case study using fifty-one rhyolite artifacts collected from the western Mojave Desert region was sampled. Analysis of samples indicates that using LA–TOF–ICP–MS to microsample the rock's groundmass coupled with multivariate statistics can confidently distinguish rhyolite sources in geochemical space. Results indicate that geochemical survey and analyses of rhyolite sources should be undertaken to provide a database for archaeological provenance studies in the region.