(U-Th)/He dating of volcanic phenocrysts with high-U-Th inclusions, Jemez Volcanic Field, New Mexico

Kyoungwon Min, Peter W Reiners, John A. Wolff, Roland Mundil, R. Lee Winters

Research output: Contribution to journalArticle

21 Scopus citations

Abstract

We measured (U-Th)/He ages of fayalite and hedenbergite phenocrysts with britholite and chevkinite inclusions from the ∼1.6 Ma Otowi (Lower) Member of the Bandelier Tuff, Jemez Volcanic Field. U and Th, the major parent nuclides of radiogenic 4He, are concentrated in britholite and chevkinite inclusions and are essentially absent from the host grains. We analyzed 36 fayalite (21 non-abraded + 15 abraded) and 13 hedenbergite (7 non-abraded + 6 abraded) phenocrysts, and applied alpha-ejection corrections assuming uniform intracrystalline distributions of inclusions and parent nuclides in the phenocrysts. A subset of phenocrysts was subjected to abrasion to remove the alpha-ejection affected regions. The alpha-ejection correction factors (FT) of the non-abraded samples range between 0.90 and 0.96, whereas those of the abraded samples are virtually unity. The fayalite and hedenbergite crystals yield mean ages of 1.60 ± 0.10 Ma (S.D.) and 1.69 ± 0.13 Ma, respectively. The overall mean age of 1.62 ± 0.11 Ma (S.D.) is indistinguishable from previously published 40Ar/39Ar ages of 1.61 ± 0.01 Ma (1σ). Our results suggest that other inclusion-bearing volcanic phenocrysts and their host units may be dateable by the (U-Th)/He method.

Original languageEnglish (US)
Pages (from-to)223-235
Number of pages13
JournalChemical Geology
Volume227
Issue number3-4
DOIs
Publication statusPublished - Apr 5 2006
Externally publishedYes

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Keywords

  • (U-Th)/He dating
  • Bandelier Tuff
  • Britholite inclusion
  • Chevkinite inclusion
  • Fayalite
  • Hedenbergite

ASJC Scopus subject areas

  • Geochemistry and Petrology

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