GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 261-9
Presentation Time: 9:00 AM-6:30 PM


DEINO, Alan L., Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, KNOTT, Jeffrey R., Department of Geological Sciences, California State Univ, Fullerton, Box 6850, Fullerton, CA 92834, RENNE, P.R., Berkeley Geochronolgy Ctr, 2455 Ridge Road, Berkeley, CA 94709, HEMMING, Sidney, LDEO, Columbia University, Palisades, NY 10964 and TURRIN, Brent, Department of Earth & Planetary Sciences, Rutgers University, 610 Taylor Rd, Piscataway, NJ 08854, United States, Piscataway, NJ 08854

Deino et al. (2015AGUFM.V51A3029D) discussed the merits of developing a set of intercalibrated mineral standards for 40Ar/39Ar dating, noting that the 40Ar*/39ArKratio of geological unknowns should be as close as practical to those of co-irradiated mineral standards in order to achieve best analytical practices. A scheme involving an approximately factor-of-three age progression of geological materials was proposed (0.4, 1.2, 3.3, 9.4, 28.2, 95, 320, and 1080 Ma). Here we report on initial testing of a potentially suitable sanidine separated from a ~3.3 Ma tuff (sample EV-1) from Eureka Valley on the northern edge of Death Valley National Park, California. Single-grain incremental heating 40Ar/39Ar dating of this material using the BGC Noblessemulti-collector mass spectrometer yielded an age of 3.3032 ± 0.0025 Ma (± 1stotal error = 0.07%, n= 32), using sanidine from the Alder Creek Rhyolite of California as the neutron fluence monitor with a reference age of 1.1848 ± 0.0006 Ma (Niespolo et al., 2016). All 32 sanidine grains yield apparent-age plateaus, typically across the entire gas release. The Ca/K of these analyses range from ~ 0.010 – 0.015. Thus this material passes initial examination as an age standard, to be followed by further evaluation.