In this pilot study an extension of whole-rock K-
Ar
dating methods of volcanic rocks is established. Whole-rock sieve fractions 80-250 μm of basaltic rocks were etched for durations up to 20 min in 6% hydrofluoric acid at room temperature and cleaned ultrasonically. Aliquots thereof were further separated into magnetic and nonmagnetic subfractions. Conventional K-
Ar
analyses reveal disturbed K-
Ar
systems in the rocks and nonmagnetic fractions, as both
Ar
loss and extraneous
Ar
are observed.
Ar
loss occurred in high-potassium matrix phases, while olivine- and clinopyroxene-phenocrysts, which are mostly xenocrysts, are carriers of extraneous
Ar
. Magnetic fractions etched for 5 min exhibit no significant
Ar
losses nor extraneous
Ar
and show internally consistent ages or age concordance with minerals of proven suitable quality for K-
Ar
dating. The method is suited for unravelling extrusion ages of volcanic rocks in which the whole-rock K-
Ar
system is disturbed and should be applied whenever adequate minerals cannot be separated for dating purposes. The eight basaltic rocks investigated stem from four localities in the Hocheifel Area, FRG; all of them show significant disturbances in their K-
Ar
system.
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