¹Fei Su et al. (>10)
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008495]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

The Chang’e-5 landing site provides an important window into the Moon’s late Eratosthenian period of volcanism at ∼2 Ga. Clarifying the Moon’s history of volcanic activity using radioisotopic dating assists investigations of the evolution of the lunar surface as well as the Moon’s internal dynamics. Recent chronological investigations of Chang’e-5 basalts produced ages spanning ∼100 Ma, thereby inhibiting interpretation of the duration of volcanism recorded in the returned samples. We used microcomputed tomography and Back-Scatter Electron imaging to characterize the structure and morphology of nine Chang’e-5 basalt clasts. Several basalt clasts lack shock features and are interpreted to have not been significantly thermally disturbed. 40Ar/39Ar incremental heating produced well defined plateaus for four sub-split samples that give a weighted mean age of 2,021 ± 17 Ma (2σ). These are among the youngest mare basalts to be dated thus far by the 40Ar/39Ar method and, when combined with most of the published Pb-Pb ages for Chang’e-5 basalts, define a single episode of mare volcanism at ∼2,021 Ma.

¹Zhongtian Zhang,¹Peter E. Driscoll
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2024JE008671]
¹Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA
Published by arrangement with John Wiley & Sons

Some melted and differentiated planetesimals, such as the parent bodies of angrites and howardite-eucrite-diogenite meteorites, are severely depleted in moderately volatile elements (MVEs). The origins of these depletions are critical for understanding early solar system evolution but remain topics of debate. Numerous previous studies have invoked evaporation from magma oceans as a potential mechanism for producing these depletions, yet this process is poorly explored. In this study, we examine the efficiency of MVE loss from planetesimal magma oceans. Upon heating from short-lived A⁢l26, internal magma oceans can develop beneath insulating crusts. The magma oceans may be exposed to the surface by collisional disruption of the crusts, but would be rapidly cooled by the cold environments. The exposed surface would be quenched to solid/glass; even if the quenched skin can be recycled by convection such that the magma ocean can be continuously resurfaced, only a small portion of the surface can remain molten. In the convection boundary layer, “vertical” advection is suppressed, energy and element transports toward the surface occur via thermal and chemical diffusion (if MVEs do not exsolve as bubbles). As chemical diffusivity is much smaller than thermal diffusivity, MVE transport is much less efficient than heat transport, and MVE loss during magma ocean cooling is likely minimal (≲1% the total inventory). Therefore, MVE depletions may not be easily explained by evaporation from A⁢l26-heated planetesimal magma oceans.