40Ar/(39Ar) ages of sanidine phenocrysts from Laacher See Tephra (12,900 yr BP): Chronostratigraphic and petrological significance

Single crystal ages of sanidine phenocrysts from pumice lapilli of the Late Glacial phonolitic Laacher See Tephra (East Eifel Volcanic Field, FRG) are determined by laser probe ⁴⁰Ar/ ³⁹Ar analysis. Sanidine megacrysts from the East and West Eifel (SAN6001, 410.4 ± 0.9 kyr; SAN6165, 469.8 ± 1.1 kyr) are applied as irradiation monitors, and their potential as Quaternary interlaboratory single crystal standards assessed. The apparent ages of Laacher See sanidine phenocrysts range from 6.4 ± 3.8 kyr to 127 ± 2 kyr (1σ), comprising up to four distinct subpopulations of crystals with individual ages, weighted mean apparent ages or isochron ages of 127 kyr, 55 kyr, 25 kyr and 12.9 kyr. The Laacher See Tephra ⁴⁰Ar/ ³⁹Ar eruption age is estimated as 12,900 ± 560 yr BP. Older crystals are interpreted as remnants of three earlier magma emplacement and crystallization events in the Laacher See magma system. These recycled, older crystals make up ca. 20% of the apparent juvenile sanidine phenocryst population in the essential phonolite clasts studied.