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

地球的月球是研究地球和月球最早分化历史的宝贵档案，提供了即使是最古老的陆地样本研究也无法获得的信息。对月球样品的Lu-Hf和Sm-Nd联合研究提供了关于月球早期分化的时间和性质的关键信息，对于区分地球和月球的南极和非南极成分至关重要。例如，月球Hf-Nd同位素记录已被用于论证地球和月球中难熔亲石元素的非亲石相对丰度。如果属实，那么所有关于地球分化的地球化学模型都需要彻底修改。然而，宇宙射线引起的Hf同位素位移可以显着偏置的Lu-Hf记录的月球样品，在以前的研究中没有考虑的现象。该建议旨在（1）评估中子俘获反应对月球岩石中Lu-Hf系统的影响，以及（2）全面评估月球所有已知主要硅酸盐储层的Lu-Hf记录（包括首次对月球高地岩石中Lu-Hf系统的研究）。根据我们的研究结果，我们将重新审视和讨论目前的概念，月球的Lu-Hf系统，将限制的时间和性质的月球分化，并（结合Sm-Nd数据）将限制批量预算难熔亲石元素在地球和月球。

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.