NJG65-4-03
1985
K/Ar ages from the Basal Gneiss Region, Stadlandet area, Western Norway
65
4
277-286

K/Ar and 40Ar/39Ar geochronology of minerals from the Stadlandet region, Norway, is complicated by the presence of excess 40Ar in many samples. There is a correlation between excess 40Ar concentration and textural occurrence of samples. Amphiboles and micas closely associated with eclogite pods are likely
to contain significant concentrations of excess 40Ar while samples from the country rocks are not. K/Ar and 40Ar/39Ar ages for horn blende from the country rocks suggest that post-metamorphic cooling through 500°C occurred about 410 Ma ago, shortly after eclogite formation. Biotites containing no excess 40Ar cooled through 300°C about 370 Ma ago. A post-metamorphic cooling rate of about 5°C/Ma can be inferred.

0029-196X
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