Plutonium-Xenon systematics of Angrites

Introduction: Angrites are igneous meteorites that crystallized very early in the solar system, ~10 Ma after CAIs, as also implied by the presence of now extinct short-lived radionuclides such as Mn, Sm and Pu [1]. Fission Xe was used to calculate Pu-Xeretention ages of eucrites, relative to that of Angra dos Reis (AdoR) [2]. AdoR has an absolute Pb-Pb age of 4557.8 Ma [see 1 for ref.]. Most eucrites, being as old as angrites, experienced various parent body processes leading to ages ranging from ~20 Ma before, to ~100 Ma after AdoR [2]. Angrites, however, remained largely unaltered after differentiation. Here, we examine whether Xe isotopic characteristics allow determining an age sequence for angrites. Experiment: We measured the Xe isotopic composition for the recent finds Sahara 99555 and D’Orbigny (details in [3]) and reexamined data for other angrites [4-8]. Two methods are used to obtain Pu-Xe-ages: method 1 assumes Pu/Nd to be constant in the early solar system [9]. However, LEW 86010 implied some variations [5]. We thus also applied method 2 using spallogenic Xe as a proxy for Nd, thus reducing distribution effects of Nd [2].