Distribution and geochronology of Oregon Plateau (U.S.A.) flood basaltvolcanism; the Steens Basalt revisited

Abstract

The timing and petrogenesis of mid-Miocene flood basalt volcanism inthe northwest United States has been extensively addressed, yet thechemical characteristics and temporal details of the Steens Basalt,exposed on the Oregon Plateau, are poorly defined. Steens Basaltvolcanism has generally been accepted to have occurred atapproximately 16.6 Ma, coeval and/or just prior to the onset ofColumbia River Basalt Group volcanism to the north. New major andtrace element analyses and nine (super 40) Ar/ (super 39) Ar agesranging from 15.51+ or -0.28 to 16.58+ or -0.18 Ma were obtained onOregon Plateau flood basalt lava flows from stratigraphic sections inclose proximity to Steens Mountain. Additionally, new (super 40) Ar/(super 39) Ar ages were obtained on the uppermost and thirty-firstlava flow down from the top of the approximately 1 km section ofSteens Basalt exposed at Steens Mountain and yield eruption ages of16.59+ or -0.10 and 16.55+ or -0.10 Ma, respectively. Field relation!

115 samples from this reference