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Title: Understanding extraneous argon in silicic volcanic products using 4oAr/39Ar laserprobe geochronology
Author: Wilkinson , Camilla M.
Awarding Body: Open University
Current Institution: Open University
Date of Award: 2013
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The Ar-Ar dating technique is one of the most widely applied geochronological techniques to products of silicic volcanism, which represent geologically instantaneous events, and have been used to calibrate the geological timescale, correlate stratigraphy and biostratigraphy over large areas, and assess the impact of explosive volcanic eruptions. Recent advances (e.g., improved instrument precision and recalibration of the K-Ar decay scheme), are now making it possible to obtain increasingly precise and accurate ages for young volcanic eruptions, K-poor minerals, and even discrete parts of single crystals. These advances have highlighted the realisation that relatively small levels of Ar contamination (e.g., extraneous Ar, either excess Ard, or inherited Ar), previously assumed to be minor, may now have a considerable effect on the accuracy of ages detennined using the Ar·Ar technique. To assess the issue of extraneous Ar, this study applied the Ar·Ar technique to a range of minerals (including sanidine, plagioclase and biotite), and glass separated from the products of large volume silicic magma systems, which have undergone repeated cycles of crystallisation and rejuvenation. The in situ Ar·Ar laserprobe technique was applied to dacite of the Fish Canyon magmatic system (erupted at - 28 Ma; Colorado, USA), and the single grain fusion Ar·Ar laser melting technique was applied to rhyolitic pumice (from explosive ignimbrite and ash fall, and effusive dome building events) of the Yellowstone Plateau Volcanic Field (2.1 Ma; Idaho, Wyoming, USA), and the Bishop Tuff (erupted at - 0.76 Ma; California, USA).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available