¹Jennifer L. Claydon,¹Sarah A. Crowther,^1,2,3Vera A. Fernandes,¹Jamie D. Gilmour
¹School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
²Museum für Naturkunde- Berlin, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstrasse 43, 10115 Berlin, Germany
³UNINOVA, Universidade Nova de Lisboa, Quinta da Torre, 2829-516 Monte de Caparica, Portugal
⁴The Centre for Earth Evolution and Dynamics, Univ. of Oslo, PO Box 1048 Blindern 0316 Oslo, Norway

The meteorite Graves Nunataks 06128/06129 is the only known example of felsic asteroidal crust. Knowledge of its history can help shed light on the evolution processes of planetesimals. The noble gases can be used to constrain both the chronology of meteorites and the processes that result in movements of volatile elements on asteroidal bodies. We have examined the I-Xe and Ar-Ar systems of the plagioclase-rich achondrite, Graves Nunataks 06129 by high-resolution laser step-heating of irradiated samples. Iodine and 129Xe∗ are both present but are released at different temperatures and do not show a correlation, therefore the I-Xe system in GRA 06129 has no chronological significance. We propose that radiogenic 129Xe∗ was lost from primary phases and parentless 129Xe∗ was later introduced into the rock by interaction with a fluid sourced from a reservoir that evolved with a high I/Xe ratio. This could have been the same halogen-rich fluid that induced the conversion of merrillite and pyroxene into chlorapatite. Inherited 40Ar (i.e. not generated by in situ decay of 40K) is also present in one of three fragments studied here and may have been introduced at the same time as parentless 129Xe∗.

Reference
Claydon CK, Crowther SA, Fernandes VA, Gilmour JD (2015) Noble gases and halogens in Graves Nunataks 06129: the complex thermal history of a felsic asteroid crust. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.03.01]

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