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Eruption age of an approximately 100,000-year-old basalt from Ar-40/Ar-39 analysis of partially degassed xenolithsEleven samples from five partially degassed Mesozoic granitic xenoliths and two late Pleistocene host basalt samples from Sawmill Canyon in Sierra Nevada, California, have been analyzed using stepwise Ar-40/Ar-39 dating techniques. The petrography and analytic techniques are described and the results are presented. Isotopic compositions of Ar released from the xenoliths in several extraction steps at temperatures below about 900 C were colinear in Ar-36/Ar-40 versus Ar-39/Ar-40 diagrams and defined isochrons, giving a mean age of degassing of 119,000 + or - 7000 yr. Ar-40 extracted at higher temperatures included ancient radiogenic Ar-40 that never diffused from the xenoliths during immersion in the magma. This Ar-40 caused an increase in the apparent age for the high-temperature extractions. The high precision of the eruption age determined by this method is comparable to that obtained elsewhere by conventional K/Ar dating of sanidine.
Document ID
19840040889
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Gillespie, A. R.
(California Institute of Technology, Jet Propulsion Laboratory; California Institute of Technology, Pasadena CA, United States)
Huneke, J. C.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Wasserburg, G. J.
(California Institute of Technology Pasadena, CA, United States)
Date Acquired
August 12, 2013
Publication Date
February 10, 1984
Publication Information
Publication: Journal of Geophysical Research
Volume: 89
ISSN: 0148-0227
Subject Category
Geophysics
Accession Number
84A23676
Funding Number(s)
CONTRACT_GRANT: NSF EAR-79-19997
CONTRACT_GRANT: NSF EAR-78-01717
Distribution Limits
Public
Copyright
Other

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