EarthRef.org Digital Archive (ERDA) -- Steens Basalts: North Mickey Section

Description
The section at North Mickey (42.8?N, 118.3?) is 25 km east of Steens Mountain at the north end of the Mickey Basin (Figure 4). The section is on a downward dropped block of Steens Basalt as mapped by Hook (1981) and ?correlation is established on the basis of a paleomagnetic reversal observed in the two areas, and supported by petrologic observations and chemical analysis.?(p.2). Hook found two reverse polarity flows below seven normal polarity flows at Mickey Butte 7.5 km southwest of the North Mickey section. 40Ar/39Ar dates from groundmass separates by Brueseke et al. (2007) suggest the reversal at Mickey Butte is the Steens reversal [a reverse lava 16.58 ? 0.18(2Ï¿) Ma, a normal lava 16.48?0.30(2Ï¿) Ma]. On inspection the Mickey Butte section has extensive cover between outcropping flows and few flows are exposed in the 60 m section between the reverse polarity flow at 1470 m and the normal polarity flow at 1530 m. Looking for transitional lavas erupted during the Steens reversal, the better exposed flow-on-flow section at North Mickey was drilled. While only normal polarity lavas were found at the North Mickey location, stratigraphic continuity and the Steens-like character (large 2-4 cm plagioclase crystals) of the lower flows suggest that these lavas erupted soon after the Steens reversal.