Title: U‐Pb Geochronological and Thermochronological Time–Temperature Constraints of <sup>40</sup>Ar/<sup>39</sup>Ar Hornblende Reference Material <scp>HB</scp>3gr
Abstract:Hornblende from the Lone Grove Pluton, Llano Uplift, Texas, has served as an irradiation reference material in 40 Ar/ 39 Ar studies for decades. In order to evaluate the apparent age bias that current...Hornblende from the Lone Grove Pluton, Llano Uplift, Texas, has served as an irradiation reference material in 40 Ar/ 39 Ar studies for decades. In order to evaluate the apparent age bias that currently exists between the U‐Pb and 40 Ar/ 39 Ar systems, zircon and titanite were dated by isotope dilution‐thermal ionisation mass spectrometry ( ID ‐ TIMS ) from the same rock from which the hornblende 40 Ar/ 39 Ar reference material HB 3gr is derived. Zircon U‐Pb data indicate initial crystallisation at 1090.10 ± 0.16 Ma (2 s ), a date that is 1.7% older than the accepted K‐Ar date (1072 ± 14 Ma, 2 s ) for HB 3gr; an offset that exceeds the typical 0.5–1% bias between the two systems, though remaining within uncertainty due to the large uncertainties in the 40 K decay constant. Zircon data are presented using both EARTHTIME tracers ET 535 and ET 2535 and are statistically indistinguishable. Single grain titanite analyses range between 1082 ± 0.75 and 1086 ± 0.81 Ma (2 s ) and are interpreted to record the subsequent cooling following crystallisation at rates between 30 and 50 °C Ma −1 . This is supported by the observation that hornblende 40 Ar/ 39 Ar dates corrected for decay constant bias are resolvably younger than the zircon U‐Pb date and in good agreement with titanite U‐Pb dates, permitting the conclusion that both titanite U‐Pb and hornblende 40 Ar/ 39 Ar systems provide a record of cooling.Read More
Publication Year: 2017
Publication Date: 2017-02-06
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 8
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