Argon extraction from geological samples by CO ₂ scanning laser step-heating

Abstract

Abstract Lasers are fundamental tools for sampling in geochemical studies and have found wide application in mass spectrometric sample introduction systems. Here we describe an isotope extraction method for 40 Ar/ 39 Ar geochronology using a new scanning CO 2 laser system. This method can partially un-mix radiogenic ( 40 Ar*) from trapped argon components and provides an alternative to furnace step-heating methods. A key advantage of the laser scanning method developed at the Scottish Universities Environmental Research Centre (SUERC) is the ability to step-heat samples as large as 100 mg to fusion using low raster speeds, although care must be taken to avoid self-shielding of grains and proper laser targeting. The scanning laser extraction system has the potential for lower overall blanks and the ability to run blanks and calibrations between steps of a heating sequence. This provides better control on system performance and characterization during sample measurement and can result in improved data quality. Supplementary material: Ar/Ar data presented in Figures 6a–c and 7 (obsidian) is available at http://www.geolsoc.org.uk/SUP18694 .