Andrew T. Calvert
Matthew Coble
Joseph L. Wooden
Kip V. Hodges
Leslie A. Hayden
Matthijs C. van Soest
Edward A. du Bray
David A. John
Robert J. Fleck
2019
<div id="sp0110" class="u-margin-s-bottom"><span>The rhyolite of Bodie Hills (California) is characterized compositionally and the geochronology of selected phases is studied. Sanidine (BHs) from the rhyolite is well suited as a </span><sup>40</sup>Ar/<sup>39</sup><span>Ar reference material with high K/Ca and radiogenic yield. Intercalibration with GA1550 biotite from the Dromedary igneous complex (New South Wales, Australia) yields an age of 9.7946 ± 0.0031 Ma for BHs relative to an age of 98.79 ± 0.54 Ma for GA1550 and a calibration factor (</span><i>R</i><sub>BHs/GA1550</sub>) of 0.096719 ± 0.000032. BHs is also intercalibrated with sanidines of the Taylor Creek Rhyolite (TCs;<span> </span><i>R</i><sub>TCs/BHs</sub><span> </span>of 2.90874 ± 0.00067), Fish Canyon Tuff (FCs;<span> </span><i>R</i><sub>FCs/BHs</sub><span> </span>of 2.88339 ± 0.00088), and rhyolite of Alder Creek (ACs;<span> </span><i>R</i><sub>ACs/BHs</sub><span> </span>of 0.12028 ± 0.00024). These calibration factors yield ages of 28.344 ± 0.011 Ma, 28.099 ± 0.013 Ma, and 1.1809 ± 0.0024 Ma for TCs, FCs, and ACs, respectively, relative to GA1550. Full propagation of errors increases these uncertainties and that of BHs to ±0.9% of their ages. Calibration of BHs using the astronomically tuned age of FCs determined by Kuiper et al. (2008) yields an age of 9.8295 ± 0.0036 Ma. Stepwise heating of BHs reveals the same small, progressive increase in age across the age spectrum reported for FCs, ACs, and other potassium feldspars (e.g., Foland and Xu, 1990; Phillips et al., 2017). This increase is consistent with mass fractionation of argon during step heating and favors use of single-step fusion ages of all sanidines for monitor and calibration purposes.</div>
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10.1016/j.chemgeo.2019.07.022
en
Elsevier
Characterization of the rhyolite of Bodie Hills and 40Ar/39Ar intercalibration with Ar mineral standards
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