GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 259-12
Presentation Time: 9:00 AM-6:30 PM


PRAVDIVTSEVA, Olga and MESHIK, Alex, Physics, Washington University, 1 Brookings Dr., CB1105, Saint Louis, MO 63130,

Xenon has nine stable isotopes and is the least abundant terrestrial noble gas. Yet heavy Xe isotopes have high fission yields. Xe is also retained by minerals much better than other noble gases. These properties led to development of several dating schemes utilizing Xe isotopes. (i) U-Xe chronometer and its neutron activation version, Xes-Xen isochron chronometer, are used for dating of pitchblends [1], zircons [2] and other U-bearing minerals [3]. (ii) The decay of 129I formed during neutron induced fission of 235U to 129Xe provides the age of neutron exposure and, in conjunction with Xes-Xen isochron dating, can be used to estimate the time required to grow cm-size U-bearing veins. (iii) Double beta decay of 130Te to 130Xe allows dating gold deposits using associated Te minerals like calaverite [5]. This technique also has a neutron activation version where 130Xe is converted to 131Xe, and then natural diffusional losses of radiogenic 130Xe could be estimated by analyses of 130Xe/131Xe in step-wise heating experiments. (iv) I-Xe dating is successfully used for study of early Solar system events. It is based on decay of primordial 129I (T1/2=15.7Ma) to 129Xe. After neutron irradiation stable 127I is converted to 128Xe. An analysis of radiogenic 129Xe/128Xe ratio in the course of step-wise pyrolysis provides the mean to account for natural losses of 129Xe and evaluate the thermal history of host meteorite. I-Xe is a relative chronometer and is anchored to an absolute time-scale through the standard of known Pb-Pb age. Finally light Xe isotopes can be used to estimate cosmic ray exposure ages.

Supported by NASA grant NNX14A124G. [1] Meshik et al. 2000. Mineralum Deposita 35, 190-205. [2] Shukolyukov et al. 2009. Petrology 17, 1-24. [3] Teitsma and Clarke. 1978. J. Geophys. Res. 83, 5443-5453. [4] Meshik et al. 1988. PhD Thesis. [5] Meshik et al. 2008. Nuclear Phys. A 809, 275-289. [6] Hohenberg and Pravdivtseva. 2008. Chemie der Erde 68, 339-351.