A diode laser system for heating minerals for (U-Th)/He chronometry

Abstract

We have developed a diode laser (25 W 808 nm) system for He extraction from minerals for (U-Th)/He chronometry. The laser beam is delivered via a 600 μm fiber cable and focused using a binocular microscope. Temperatures necessary for He release from apatite (500-600°C) and zircon (1100-1300°C) encapsulated in Pt-foil tubes are attained by heating to 0.5 W for 30 s and 1.25-2.5 W for 20 min, respectively, using a defocused beam. Heating at these powers does not result in measurable U and/or Th loss from apatite, as noted by the preservation of the distinct Th/U in multiple splits of two different Durango apatite crystals. Analyses of Durango and the California Institute of Technology internal standard apatite 97MR22 yield (U-Th)/He ages of 32.8 ± 1.8 Ma (1