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Direct comparison of astronomical and 40 Ar/ 39 Ar ages of ash beds: Potential implications for the age of mineral dating standards
Author(s) -
Hilgen F. J.,
Krijgsman W.,
Wijbrans J. R.
Publication year - 1997
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/97gl02029
Subject(s) - sanidine , biotite , geology , isotopes of argon , volcanic ash , radiometric dating , mineralogy , geochemistry , volcano , argon , chemistry , paleontology , quartz , organic chemistry
We present first results of 40 Ar/ 39 Ar multiple single fusion datings on biotites and feldspars from two volcanic ash beds found on Crete, Gavdos and Koufonisi (Greece). Preferred 40 Ar/ 39 Ar ages—calculated against TCR sanidine with an age of 27.92 Ma, intercalibrated to an age of 28.09 ± 0.10 Ma (1σ) for FCT‐3 biotite and an age of 24.99 ± 0.07 Ma for DRA sanidine—are slightly but consistently younger than astronomical ages obtained independently for the same ash beds. The best fit to the astronomical ages is obtained when the age of TCR sanidine is increased slightly to 27.98 ± 0.19 Ma, the age of FCT‐3 biotite to 28.15 ± 0.19 Ma and the age of DRA sanidine to 25.05 ± 0.17 Ma. The ages for the standards arrive slightly younger if the 40 Ar/ 39 Ar age ‐ of 6.936 ± 0.006 Ma (1σ)—for a single pure sanidine separate of the lower ash—dated astronomically at 6.941 Ma—is considered most reliable.