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.

[1]  C. Bacon,et al.  Origin of phenocrysts and compositional diversity in pre-Mazama rhyodacite lavas, Crater Lake, Oregon. , 1994 .

[2]  G. Wörner,et al.  Gradients in physical parameters in zoned felsic magma bodies: Implications for evolution and eruptive withdrawal , 1990 .

[3]  E. Alexander,et al.  Calibration of the interlaboratory 40Ar39Ar dating standard, MMhb-1 , 1987 .

[4]  Derek York,et al.  Least squares fitting of a straight line with correlated errors , 1968 .

[5]  G. Wörner,et al.  Evolution of the Laacher See magma chamber: Evidence from SIMS and TIMS measurements of UTh disequilibria in minerals and glasses , 1994 .

[6]  W. Schirmer.  Rheingeschichte zwischen Mosel und Maas , 1990 .

[7]  K. Foland.  Ar40 diffusion in homogenous orthoclase and an interpretation of Ar diffusion in K-feldspars , 1974 .

[8]  D. York,et al.  Precise single-grain 40Ar/39 Ar dating of a cold to warm climate transition in Central Europe , 1989, Nature.

[9]  G. B. Dalrymple,et al.  High precision 40Ar/39Ar dating of Oligocene rhyolites from the Mogollon-Datil Volcanic Field using a continuous laser system , 1988 .

[10]  D. York,et al.  40Ar/39Ar laser dating of single grains: Ages of Quaternary tephra from the East Eifel Volcanic Field, FRG , 1987 .

[11]  Hans-Ulrich Schmincke,et al.  Petrogenesis of the Zoned Laacher See Tephra , 1984 .

[12]  M. Suter,et al.  AMS radiocarbon dating and varve chronology of Lake Soppensee: 6000 to 12000 14C years BP , 1993 .

[13]  G. Mahood,et al.  Evidence for long residence times of rhyolitic magma in the Long Valley magmatic system: the isotopic record in precaldera lavas of Glass Mountain , 1989 .

[14]  G. Mahood,et al.  Isotopic constraints on the production rates, crystallisation histories and residence times of pre-caldera silicic magmas, Long Valley, California , 1994 .

[15]  B. Houghton,et al.  40Ar/39Ar dating of Quaternary feldspar: Examples from the Taupo Volcanic Zone, New Zealand , 1992 .

[16]  Hans-Ulrich Schmincke,et al.  The eruptive center of the late quaternary Laacher see tephra , 1984 .

[17]  Hans-Ulrich Schmincke,et al.  Evolution of complex plinian eruptions: The Late Quaternary Laacher See case history , 1990 .

[18]  Hans-Ulrich Schmincke,et al.  Laacher See Tephra: A widespread isochronous late Quaternary tephra layer in central and northern Europe , 1985 .

[19]  W. F. Libby.  Radiocarbon dates, II. , 1951, Science.

[20]  E. Bard,et al.  Calibration of the 14C timescale over the past 30,000 years using mass spectrometric U–Th ages from Barbados corals , 1990, Nature.

[21]  Lasing in the Holocene: extending the 40Ar39Ar laser probe method into the 14C age range , 1994 .