A Review and Analysis of Dating Techniques for Neogene and Quaternary Volcanic Rocks

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Technical Report

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The large uncertainties in many of the published dates for volcanic rocks in the Yucca Mountain region (YMR) strongly affect probability and consequence models of volcanism, especially models focusing on Quaternary volcanism. Dating techniques for post-10 Ma basaltic rocks in the YMR have inherent limitations and uncertainties, which are rarely discussed in detail. Dates produced from the most widely available techniques have uncertainties that generally increase with decreasing age of the rock. Independent evaluation of most published dates is difficult due to a lack of information on analytical techniques, sample characteristics, and sources of error. Neogene basaltic volcanoes in the YMR have reported dates that generally reflect the precision and accuracy of the analytical technique, although the number of samples dated for each volcanic center only ranges from one to three. Dates for Quaternary volcanoes in the YMR have relatively large reported uncertainties and yield averages with large errors when reported uncertainty is propagated through statistical calculations. Using available data, estimates of the average ages of the Quaternary YMR volcanoes are 1.2±0.4 Ma for Crater Flat, 0.3±0.2 Ma for Sleeping Butte, and 0.1+0.05 Ma for Lathrop Wells. These dates generally do not represent the best dates possible with currently available geochronological techniques. Uncertainty in the age of Lathrop Wells is relatively small and does not affect current probability models significantly. However, the relatively large uncertainties in the ages of Crater Flat volcanoes strongly affect probability models.

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Citation / Publisher Attribution

A Review and Analysis of Dating Techniques for Neogene and Quaternary Volcanic Rocks, Nuclear Regulatory Commission Contract NRC-02-88-005, CNWRA 93-018