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Main Title: Overturn of ilmenite‐bearing cumulates in a rheologically weak lunar mantle
Author(s): Yu, Shuoran
Tosi, Nicola
Schwinger, Sabrina
Maurice, Maxime
Breuer, Doris
Xiao, Long
Type: Article
Language Code: en
Abstract: The crystallization of the lunar magma ocean (LMO) determines the initial structure of the solid Moon. Near the end of the LMO crystallization, ilmenite‐bearing cumulates (IBC) form beneath the plagioclase crust. Being denser than the underlying mantle, IBC are prone to overturn, a hypothesis that explains several aspects of the Moon's evolution. Yet the formation of stagnant lid due to the temperature dependence of viscosity can easily prevent IBC from sinking. To infer the rheological conditions allowing IBC to sink, we calculated the LMO crystallization sequence and performed high‐resolution numerical simulations of the overturn dynamics. We assumed a diffusion creep rheology and tested the effects of reference viscosity, activation energy, and compositional viscosity contrast between IBC and mantle. The overturn strongly depends on reference viscosity and activation energy and is facilitated by a low IBC viscosity. For a reference viscosity of 1021 Pa s, characteristic of a dry rheology, IBC overturn cannot take place. For a reference viscosity of 1020 Pa s, the overturn is possible if the activation energy is a factor of 2–3 lower than the values typically assumed for dry olivine. These low activation energies suggest a role for dislocation creep. For lower‐reference viscosities associated with the presence of water or trapped melt, more than 95% IBC can sink regardless of the activation energy. Scaling laws for Rayleigh‐Taylor instability confirmed these results but also showed the need of numerical simulations to accurately quantify the overturn dynamics. Whenever IBC sink, the overturn occurs via small‐scale diapirs.
Issue Date: 31-Jan-2019
Date Available: 27-Jan-2020
DDC Class: 550 Geowissenschaften
Subject(s): Moon
magma ocean
mantle rheology
Journal Title: Journal of Geophysical Research: Planets
Publisher: Wiley ; American Geophysical Union (AGU)
Publisher Place: Hoboken, NJ
Volume: 124
Issue: 2
Publisher DOI: 10.1029/2018JE005739
Page Start: 418
Page End: 436
EISSN: 2169-9100
ISSN: 2169-9097
Notes: ©2019. American Geophysical Union
Appears in Collections:Zentrum für Astronomie und Astrophysik » Publications

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