Experimental constraints on the long-lived radiogenic isotope evolution of the Moon

Snape JF, Nemchin AA, Johnson T, Luginbühl S, Berndt J, Klemme S, Morrissey LJ, van Westrenen W

Research article (journal)

Abstract

This study presents the results of high pressure and temperature experiments toinvestigate the mineral–melt trace element partitioning behaviour for minerals predictedto have formed during the crystallisation of the Lunar Magma Ocean (LMO). The focusof this work has been particularly on determining partition coefficients forparent–daughter pairs of radiogenic elements, for LMO-relevant temperatures,pressures and compositions. The new experimental data are compared with previousstudies for the same minerals and elements in order to establish best estimates for thepartition coefficient of each element for evolving compositions of minerals as predictedin recent studies modelling LMO crystallisation. These estimates are used to calculateevolving parent–daughter ratios in the LMO residual melt and crystallising minerals forthe four main long-lived radiogenic isotope systems that have been studied in lunarsamples (Rb–Sr, Sm–Nd, Lu–Hf and U–Pb). The calculated 87 Rb/ 86 Sr, 147 Sm/144 Nd, and 176 Lu/ 177 Hf ratios are consistent with predictions for the mantlesources of lunar basalts and evolved lithologies. In contrast, it is difficult to explain thewide range of 238 U/ 204 Pb source ratios predicted from the Pb isotopiccompositions of basaltic lunar samples. Potential explanations for this observation arediscussed, with the conclusion that the Moon most likely experienced a significant lossof volatiles (including Pb), towards the end of LMO crystallisation, resulting in thedramatic U–Pb fractionation evidenced by recent sample analyses.

Details zur Publikation

Release year: 2022
Language in which the publication is written: English