Argon extraction from geological samples by CO<sub>2</sub> scanning laser step-heating

<p>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 <sup>40</sup>Ar/<sup>39</sup>Ar geochronology using a new scanning CO<sub>2</sub> laser system. This method can partially un-mix radiogenic (<sup>40</sup>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. </p>