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Evidence of extensive lunar crust formation in impact melt sheets 4,330 Myr ago


Accurately constraining the formation and evolution of the lunar magnesian suite is key to understanding the earliest periods of magmatic crustal building that followed accretion and primordial differentiation of the Moon. However, the origin and evolution of these unique rocks is highly debated. Here, we report on the microstructural characterization of a large (~250-μm) baddeleyite (monoclinic-ZrO2) grain in Apollo troctolite 76535 that preserves quantifiable crystallographic relationships indicative of reversion from a precursor cubic-ZrO2 phase. This observation places important constraints on the formation temperature of the grain (>2,300 °C), which endogenic processes alone fail to reconcile. We conclude that the troctolite crystallized directly from a large, differentiated impact melt sheet 4,328 ± 8 Myr ago. These results suggest that impact bombardment would have played a critical role in the evolution of the earliest planetary crusts.

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Fig. 1: Phase diagram of the ZrO2 system.
Fig. 2: Optical imaging, EBSD data and parent-grain reconstruction for the large baddeleyite grain in Apollo sample 76535.
Fig. 3: Pb–Pb data generated by SIMS analysis of the large reversion twinned baddeleyite grain in troctolite 76535, and comparison with published Sm–Nd7, Rb–Sr7 and Ar–Ar43 chronology for the same rock.

Data availability

The authors declare that data supporting the findings in this study are available within the paper and its Supplementary Information files. All other data are available from the corresponding author upon request.

Code availability

The code that was used for the U–Pb analysis is available from the corresponding author upon request.


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L.F.W. and A.C. are funded by a Hatch postdoctoral fellowship. A.C. has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 704696 RESOLVE, and M.A.’s contribution to this work was partly funded by the UK Science and Technology Facilities Council (ST/L000776/1 and ST/P000657/1). The NordSIMS facility is supported by Swedish Research Council infrastructure grant 2017-00671 and the Swedish Museum of Natural History; this is NordSIMS publication 609. K.H.J. acknowledges STFC grant ST/M001253 and Royal Society grant UF140190. J.R.D. acknowledges STFC grant ST/S000291/1 and Royal Society Research Grant RG160237. We thank G. Long for conducting colloidal silica polishing of the thin section to facilitate EBSD analysis of the target grain. M.A. thanks NASA CAPTEM for the allocation of polished thin section 76535, 51.

Author information




L.F.W., A.C., J.R.D. and M.A. designed the initial study. L.F.W., A.C., J.R.D. and J.D. conducted EBSD analysis of the baddeleyite grain. C.C. conducted phase reconstruction using the ARPGE and GenOVa software packages. A.C. and M.J.W. conducted SIMS analysis on the baddeleyite grain. All authors discussed the results and interpretation, and commented on the manuscript at all stages.

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Correspondence to L. F. White.

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The authors declare no competing interests.

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Peer review information Nature Astronomy thanks Marc Norman and Jennifer Whitten for their contribution to the peer review of this work.

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Supplementary Information

Supplementary Figs. 1–3 and Tables 1–4.

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White, L.F., Černok, A., Darling, J.R. et al. Evidence of extensive lunar crust formation in impact melt sheets 4,330 Myr ago. Nat Astron 4, 974–978 (2020).

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