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 language | English (US) |
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Pages (from-to) | 4361-4372 |
Number of pages | 12 |
Journal | Journal of Geophysical Research |
Volume | 94 |
Issue number | B4 |
DOIs | |
State | Published - 1989 |
All Science Journal Classification (ASJC) codes
- Forestry
- Aquatic Science
- Soil Science
- Water Science and Technology
- Earth-Surface Processes
- Geochemistry and Petrology
- Geophysics
- Oceanography
- Palaeontology
- Ecology
- Space and Planetary Science
- Earth and Planetary Sciences (miscellaneous)
- Atmospheric Science