Geological Society of America

261 D29. Petrology, Metamorphic (Posters)

Wednesday, 7 November 2018
9:00 AM - 6:30 PM
Halls J-K

DEVELOPMENT OF A ~3.3 MA SANIDINE STANDARD FOR 40AR/39AR DATING

Paper number: 261-9
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Alan L. Deino Presenting Author
Berkeley Geochronology Center, Berkeley, CA
Jeffrey R. Knott
California State Univ, Fullerton, Fullerton, CA
P.R. Renne
Berkeley Geochronolgy Ctr, Berkeley, CA
Sidney Hemming
LDEO, Columbia University, Palisades, NY
Brent Turrin
Rutgers University, Piscataway, NJ

Abstract

Deino et al. (2015AGUFM.V51A3029D) discussed the merits of developing a set of intercalibrated mineral standards for ⁴⁰Ar/³⁹Ar dating, noting that the ⁴⁰Ar*/³⁹Ar_Kratio 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.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-318767

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