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Argon‐40/argon‐39 analyses of samples from the Gardnos impact structure, Norway
Author(s) -
Grier Jennifer A.,
Swindle Timothy D.,
Kring David A.,
Melosh H. Jay
Publication year - 1999
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.1999.tb01393.x
Subject(s) - impact crater , impact structure , geology , metamorphism , metamorphic rock , devonian , isotopes of argon , geochemistry , orogeny , paleontology , argon , astrobiology , tectonics , physics , atomic physics
— We have conducted 40 Ar/ 39 Ar age dating on a sample of impact melt from the Gardnos impact structure in Norway in an attempt to better constrain the formation age of the crater. Current estimates of the age of the Gardnos crater cover a wide range and are as old as 900 Ma (Dons and Naterstad, 1992; French et al. , 1997). The age spectra that we obtained from three samples are consistent with a thermal event at 385 ± 5 Ma (1σ). Because this differs greatly from the best stratigraphic age of ∼600 Ma, and because the minerals present in the dated sample are a metamorphic assemblage, we believe we have not dated the formation age of the crater. Instead we have probably dated the effect of the early Devonian collapse of the late Caledonian (Scandian) orogeny on these materials (Dons and Naterstad, 1992; French et al. , 1997). Although it may be possible, it will be difficult to determine the age of the impact by isotopic means alone because of this widespread metamorphism. Detailed stratigraphic analyses of the crater fill sediments may be the most promising method for constraining the crater age.