HR: 0800h
AN: V41D-1476    [Abstracts]
TI: A Diode Laser gas Extraction System for Heating Minerals for Geochronology
AU: * Foeken, J P
EM: j.foeken@suerc.gla.ac.uk
AF: Scottish Universities Environmental Reserach Centre, Rankine Avenue Scottish Enterprise and Technology Park, East Kilbride, G75 0QF United Kingdom
AU: * Foeken, J P
EM: j.foeken@suerc.gla.ac.uk
AF: Department of Geographical and Earth Sciences, University Avenue, Glasgow, G12 8QQ United Kingdom
AU: Stuart, F M
EM: f.stuart@suerc.gla.ac.uk
AF: Scottish Universities Environmental Reserach Centre, Rankine Avenue Scottish Enterprise and Technology Park, East Kilbride, G75 0QF United Kingdom
AU: Persano, C
EM: cpersano@ges.gla.ac.uk
AF: Department of Geographical and Earth Sciences, University Avenue, Glasgow, G12 8QQ United Kingdom
AU: Vilbert, D
EM: d.vilbert@suerc.gla.ac.uk
AF: Scottish Universities Environmental Reserach Centre, Rankine Avenue Scottish Enterprise and Technology Park, East Kilbride, G75 0QF United Kingdom
AB: Diode lasers, in comparison to Ar ion and Nd:YAG lasers, are compact, and cheap to purchase and maintain. We have developed a 25 W diode laser (808 nm) system for He extraction from minerals primarily for (U-Th)/He chronometry. The laser beam is delivered via a 600 æm fibre cable and focused using a binocular microscope. Temperatures necessary for He release from apatite and zircon encapsulated in Pt foil are attained by heating to 0.5 W and 1-1.5 W using a defocused beam. Analysis of 11 fragments from two different Durango apatite crystals yield (U-Th)/He ages of 32.8 ñ 0.7 Ma (1s). Five aliquots of apatite grains from 97MR22 (California Institute of Technology internal standard) yields ages of 4.5 ñ 0.5 Ma. The (U-Th)/He ages, and U/Th ratios are well within the published ages for these minerals. In order to test the diode laser for other geochronological and isotope applications we have heated various un-encapsulated crystals. The diode laser couples well with optically opaque minerals (e.g. hornblende, biotite, muscovite, garnet) and basalt groundmass. Heating and partial melting typically occurs at less than 4 W using a defocused beam. Coupling with muscovite, plagioclase, and semi-transparent sanidine required laser power of 5-10 W to initiate melting. Heating of near-transparent sanidine did not produce partial melting even at laser power in excess of 20 W. These results are consistent with other visible/near-infra red lasers and suggests that diode lasers offer a cheap, small, low-maintenance alternative for 40Ar/39Ar chronology and stable isotope studies.
DE: 1040 Radiogenic isotope geochemistry
DE: 1130 Geomorphological geochronology
DE: 1140 Thermochronology
DE: 1194 Instruments and techniques
DE: 8175 Tectonics and landscape evolution
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005