Initial argon in amphiboles from the Chugach Mountains, southern Alaska

Tullis C. Onstott, V. B. Sisson, D. L. Turner

Research output: Contribution to journalArticle

22 Scopus citations

Abstract

The 40Ar/39Ar step-heating analyses of three hornblende samples from the Border Ranges ultramafic-mafic assemblage yield plateaus with slightly discordant dates of 180.2 ± 0.7, 177.5 ± 0.7, and 181.1 ± 1.7 Ma. A plot of the plateau temperature data for all three hornblende samples on an 36Ar/40Ar versus 39Ar/40Ar diagram reveals the presence of a non-atmospheric "initial' argon component with an apparent 40Ar/36Ar versus 39Ar/40Ar diagram reveals the presence of a non-atmospheric "initial' argon comonent with an apparent 40Ar/36Ar of 379 ± 16 and yields a date of 175.7 ± 1.0 Ma. A potassium-poor hastingsite from the same complex yields a complicated spectra with dates as high as ~900 Ma. These older dates reflect contamination by argon with an isotopic composition similar to that found for the initial argon in the hornblende and do not record a Paleozoic component in the age of the Border Ranges ultramafic-mafic complex. -from Authors

Original languageEnglish (US)
Pages (from-to)4361-4372
Number of pages12
JournalJournal of Geophysical Research
Volume94
Issue numberB4
DOIs
StatePublished - Jan 1 1989

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

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