Lunar Magma Ocean crystallization revisited: Bulk composition, early cumulate mineralogy, and the source regions of the highlands Mg-suite
By S. Elardo, D. Draper, C. Shearer. 2011
256 citations recorded by the source corpus.
Abstract Crystallization of the Lunar Magma Ocean (LMO) has been numerically modeled and its products inferred from sample observations, but it has never been fully tested experimentally. This study is a reexamination of the LMO hypothesis by means of the first experimental simulation of lunar differentiation. Two end-member bulk Moon compositions are considered: one enriched in refractory lithophile elements relative to Earth and one with no such enrichment. A “two-stage” model of magma ocean crystallization based on geophysical constraints is simulated and features early crystal suspension and equilibrium crystallization followed by fractional crystallization of the residual magma ocean. An initially entirely molten Moon is assumed. Part 1 of this study, presented here, focuses on stage 1 of this model and considers the early cumulates formed by equilibrium crystallization, differences in mantle mineralogy resulting from different bulk Moon compositions, and implications for the source regions of the highlands Mg-suite. Refractory element enriched bulk Moon compositions produce a deep mantle that contains garnet and trace Cr-spinel in addition to low-Ca pyroxene and olivine. In contrast, compositions without refractory element enrichment produce a deep dunitic mantle with low-Ca pyroxene but without an aluminous phase. The differences in bulk composition are magnified in the residual melt; the residual LMO from the refractory element enriched composition will likely produce plagioclase and ilmenite earlier and in greater quantities. Both compositions produce Mg-rich early cumulate piles that extend from the core-mantle boundary to ∼355 km depth, if 50% equilibrium crystallization and whole Moon melting are assumed. These early LMO cumulates provide good fits for the source regions for a component of the high-Mg ∗ , Ni- and Co-poor parental magmas of the Mg-suite cumulates, if certain conditions are called upon. The olivine in early LMO cumulates produced by either bulk Moon composition is far too rich in Cr to be reasonable for the source regions of the Mg-suite, meaning either core formation in the presence of S and/or C must be invoked to deplete the LMO and the crystallizing olivine in Cr, or that current estimates of the bulk lunar Cr content are too high. We infer that melts meeting the criteria of the Mg-suite parents could be produced from early LMO cumulates by solid state KREEP and plagioclase hybridization near the base of the crust and subsequent partial melting. Additionally, we propose a revised model for Mg-suite petrogenesis.
Subfields: Aerospace Engineering, Astronomy and Astrophysics
View Paper: https://www.semanticscholar.org/paper/e48840ceefe347ad7c4b3e10205988b628bd97af
How researchers see this paper
The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.
In Astronomy and Astrophysics
Citations in the corpus
- The origin of water in the primitive Moon as revealed by the lunar highlands samples (2014, background): “…and crystallisation ages (∼4.44 to 4.29 Ga), these rocks are considered to represent mixtures of some of the most primitive magmas that formed from the partial-melting of early LMO cumulates, which then assimilated urKREEP and crustal components (Shearer and Papike, 2005; Elardo et al., 2011).”
- Crustal evolution and the temporality of anorthosites (2017, background): “Mg-suite magmas are thought to have originated by partial melting of ultramafic magma ocean cumulates, perhaps induced by gravitational overturn during tidal heating (e.g. Elardo et al., 2011; Elkins-Tanton et al., 2011); many appear to have assimilated a KREEP component during ascent.”