The Cause of Anomalous Potassium-Argon "Ages" for Recent Andesite Flows at Mt. Ngauruhoe, New Zealand, and the Implications for Potassium-Argon "Dating"

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Presented at the Fourth International Conference on Creationism, Pittsburgh, Pennsylvania, August 3–8, 1998. Published in: Proceedings of the Fourth International Conference on Creationism, R. E. Walsh (editor), pp. 503–525.

© 1998 Creation Science Fellowship, Inc., Pittsburgh, Pennsylvania, USA. All Rights Reserved.

Abstract

New Zealand’s newest and most active volcano, Mt. Ngauruhoe in the Taupo Volcanic Zone, produced andesite flows in 1949 and 1954, and avalanche deposits in 1975. Potassium-argon “dating” of five of these flows and deposits yielded K-Ar model “ages” from <0.27Ma to 3.5±0.2 Ma. “Dates” could not be reproduced, even from splits of the same samples from the same flow, the explanation being variations in excess 40Ar* content. A survey of anomalous K-Ar “dates” indicates they are common, particularly in basalts, xenoliths, and xenocrysts such as diamonds that are regarded as coming from the upper mantle. In fact, it is now well established that there are large quantities of excess 40Ar* in the mantle, which in part represent primordial argon not produced by in situ radioactive decay of 40K and not yet outgassed. And there are mantle-crust domains between, and within, which argon circulates during global tectonic processes, magma genesis, and mixing of crustal materials. This has significant implications for the validity of K-Ar and 40Ar/39Ar “dating.”

Keywords

Andesite, 1949–1975 Flows, Mt. Ngauruhoe, New Zealand, Potassium-Argon Dating, Anomalous Model “Ages,” Excess 40Ar*, Excess 40Ar* in Rocks and Minerals, Upper Mantle, Geochemical Reservoirs, Mantle-Crust Domains, Crustal Mixing, Magma Genesis

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