GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 127-10
Presentation Time: 3:55 PM


MORGAN, Leah E., US Geological Survey, Denver Federal Center, MS 963, Denver, CO 80225, DAVIDHEISER-KROLL, Brett, Department of Geological Sciences, University of Colorado Boulder, 2200 Colorado Ave, Boulder, CO 80309, KUIPER, Klaudia F., Faculty of Earth Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, Amsterdam, 1081 HV, Netherlands, WIJBRANS, Jan R., Faculty of Earth and Life Sciences, Vrije Universiteit, 1085 De Boelelaan, Amsterdam, 1081 HV, Netherlands and MARK, Darren F., Scottish Universities Environmental Research Centre, (SUERC), Rankine Avenue, East Kilbride, G75 0QF, United Kingdom,

The 40Ar/39Ar geochronological method relies on the a priori knowledge of the ages (or, more accurately, the 40Ar/40K ratios) of mineral standards used as neutron flux monitors. These standards are co-irradiated with unknowns and are used to calibrate the neutron flux received by the unknowns. Mineral standard ages have been calibrated in a number of ways, including first principles (e.g. Renne et al., 1998; McDougall and Wellman, 2011), astrochronological calibration (e.g. Kuiper et al., 2008), and an optimization model using known parameters and 40Ar/39Ar – U-Pb data pairs (Renne et al., 2010; Renne et al., 2011).

The approach taken herein applies modern technology and uncertainty propagation to the “first principles” method. We rely on the “Accurate Quantities of Argon” (or “AQuA” pipette system described by Morgan et al. (2011) and valve closing techniques described in Morgan and Davidheiser-Kroll (2015). The AQuA pipette emits metrologically calibrated quantities of high purity 40Ar to allow for high accuracy sensitivity calibration of mass spectrometers. Here we present preliminary metrologically calibrated 40Ar concentration values for biotite standards HDB1 and MD2 (GA1550). Age calculations for these standards are presented by combining 40Ar concentrations with existing 40K concentration data. These and similar data may be used as stand-alone values, and/or they may provide input data for future iterations of the optimization model of Renne et al. (2010, 2011).


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