• journal_title：Geological Society of America Bulletin
• Contributor：Brent D. Turrin ; Robert L. Christiansen ; Michael A. Clynne ; Duane E. Champion ; Wendy J. Gerstel ; L. J. Patrick Muffler ; Deborah A. Trimble
• Publisher：Geological Society of America
• Date：1998-
• Format：text/html
• Language：en
• Identifier：10.1130/0016-7606(1998)110<0931:AOLPCA>2.3.CO;2
• journal_abbrev：Geological Society of America Bulletin
• issn：0016-7606
• volume：110
• issue：7
• firstpage：931

Lassen Peak is a large volcanic dome of late Pleistocene age at the southern end of the Cascades arc. This dacitic dome has a complex phenocryst assemblage of mixed-magma origin and has been effectively dated for the first time using the ⁴⁰Ar/³⁹Ar technique. Emplacement of the dome occurred after an advance of late Pleistocene glaciers from an older volcanic cone to the southwest and from a large volcanic plateau to the east. Emplacement of the Lassen Peak dome before the latest major Pleistocene glaciation—correlated by previous workers with the Tioga glaciation of the Sierra Nevada—formed a high peak that intercepted some of the precipitation that previously had fed the plateau ice cap, forming a 10-km-long glacier from a cirque on the northeast side of the peak. The weighted mean ⁴⁰Ar/³⁹Ar age of the dacite of Lassen Peak is 28.3 ± 2.7 ka. Comparison of its remanent magnetic direction to that of sedimentary deposits at Mono Lake, California, indicates a correlation to strata of 27 ± 1 ka. The dacite of Kings Creek, which erupted from the site of Lassen Peak before a glacial advance that predated the Lassen Peak dome, overlies peat that has a U-Th-calibrated ¹⁴C age of 37.6 ± 0.2 ka. The dacite of Kings Creek yielded a ⁴⁰Ar/³⁹Ar age of 32 ± 17 ka. The paleomagnetism of this dacite is similar to that of Mono Lake sediments of 35 ± 1 ka age. Thus, a late Pleistocene glacial advance probably began in the Lassen region between about 35 and 27 ka.