An anorthositic meteorite supporting an ancient magma ocean on Vesta
Shijie Li, Dongliang Zhang, Qiao Shu, Huiming Bao, Xiaobin Cao, Jia Liu, Liping Qin, Yan Fan, Shenghua Zhou, Dehan Shen & Mingbao Li
Nature Astronomy
“The widespread occurrence of ferroan anorthosites and other magmatic rock types in Apollo lunar samples directly contributed to the construction and development of modern planetary formation models. If the Vesta magma ocean (VMO) model is analogous to the lunar magma ocean model, anorthosites should be present as a late crystallization product of the Vesta magma ocean. However, the lack of anorthositic meteorites unequivocally linked to Vesta or its parent body casts doubts on the existence of a past VMO and to our knowledge of Vesta’s formation and early evolution. Here, we report a newly discovered ferroan anorthosite, Northwest Africa 15118, consisting entirely of anorthite (~94 vol%) and orthopyroxene (~6 vol%). We show that the mineral chemical compositions, whole-rock oxygen isotope composition (Δ17O = −0.243 ± 0.014‰), as well as chromium isotope composition in chromite (ε54Cr = −0.74 ± 0.14), of Northwest Africa 15118 overlaps with howardite–eucrite–diogenite meteorites, indicating a Vestan origin for this meteorite. The occurrence of ferroan anorthosite with prominent positive Eu anomalies supports a primary anorthositic crust layer in Vesta, thus validating the VMO model.”
