Stratigraphy, major oxide geochemistry, and ⁴⁰Ar/³⁹Ar geochronology of a tephra section near Tok, Alaska

Abstract

Stratigraphy, major oxide geochemistry, and ⁴⁰Ar/³⁹Ar geochronology are used to describe a tephra section near Tok, Alaska, north ofthe Wrangell volcanic field. This tephra section contains seven type II tephras and two type I tephras. Hornblende in a tephra near the base of the section was dated at 627.5 +/- 47.7 ka using the ⁴⁰Ar/³⁹Ar method of single-step total laser fusion. This hornblende-rich tephra is here named the Tetlin Tephra. The age and composition of the Tetlin Tephra indicates that it is likely the product of an explosive phase of activity of Mount Drum volcano, where petrologically similar domes were emplaced 650 to 400 ka. Two widespread tephras, the Old Crow Tephra and the Sheep Creek Tephra are also found at this site. The documentation of these tephras combined with the lithologic descriptions provide valuable information for interpretation of the Pleistocene history of this part of interior Alaska.