Lu-Hf sysematics and the early silicate differentiation of the Moon

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The Earth's Moon is an invaluable archive for investigating the earliest differentiation history of the Earth and Moon, providing information that is inaccessible from studies on even the oldest terrestrial samples. Combined Lu–Hf and Sm–Nd studies on lunar samples provide key information on the timing and nature of the early differentiation of the Moon, and are essential for distinguishing between a chondritic and non-chondritic composition of the Earth and Moon. For instance, the lunar Hf-Nd isotopic record has been used to argue for non-chondritic relative abundances of refractory lithophile elements in the Earth and Moon. If true, all geochemical models for the differentiation of the Earth need to be revised entirely. However, cosmic-ray induced Hf isotope shifts can significantly bias the Lu-Hf record of lunar samples, a phenomenon that has not been accounted for in previous studies. This proposal aims to (1) evaluate the influence of neutron-capture reactions on the Lu-Hf system in lunar rocks, and (2) to comprehensively assess the Lu–Hf record of all known major silicate reservoirs of the Moon (including the first study of the Lu–Hf system in lunar highland rocks). Based on our results, we will revisit and discuss the current concept of the lunar Lu-Hf systematics, will constrain the timing and nature of the lunar differentiation, and (in conjunction with Sm–Nd data) will constrain the bulk budget of refractory lithophile elements in the Earth and Moon.