Experimental constraints on the solidification of a nominally dry lunar magma ocean

Lin, Yanhao; Tronche, E. J.; Steenstra, E. S.; Westrenen, W. van

doi:10.1016/j.epsl.2017.04.045

Cited by 62 publications

(137 citation statements)

References 76 publications

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“…According to the LMO crystallization experiments and our MAGFOX models, the Mg# of the mafic component in impure crustal units should be ≲80 (e.g., Lin et al, 2017b), in agreement with pristine Apollo samples (Papike et al, 1998). Our analysis suggests that the most important remaining uncertainties in predicting the mafic fraction in a lunar flotation crust are the evolution of the LMO heat flux (Figure 4a) and the crustal compaction viscosity (Figure 4b).…”

Section: Discussionsupporting

confidence: 82%

“…LMO liquid viscosity and density can be estimated using composition and temperature output from MAGFOX (Longhi, ), an experimentally calibrated fractional crystallization program developed to predict LMO liquid and cumulate compositions throughout LMO solidification for an assumed LMO bulk composition. Fractional crystallization experiments evaluating LMO cumulate and liquid compositions as a function of the degree of LMO solidification were also recently published (Lin et al, , ). Liquid compositions from plagioclase saturated experiments and two MAGFOX models (run assuming two different LMO bulk compositions) were input into predictive viscosity models to estimate reasonable bounds on LMO viscosity (dry and with 0.5 wt % H 2 O) and are presented in Figure a as a function of Mg# (100×Mg/Mg+Fe, in moles) and Figure b as a function of temperature.…”

Section: The Evolving Viscosity and Density Of The Lmomentioning

confidence: 99%

“…Fractional crystallization experiments evaluating LMO cumulate and liquid compositions as a function of the degree of LMO solidification were also recently published (Lin et al, 2017a(Lin et al, , 2017b. Liquid compositions from plagioclase saturated experiments and two MAGFOX models (run assuming two different LMO bulk compositions) were input into predictive viscosity models to estimate reasonable bounds on LMO viscosity (dry and with 0.5 wt % H 2 O) and are presented in Figure 2a as a function of Mg# (100×Mg/Mg+Fe, in moles) and Figure 2b as a function of temperature.…”

Section: The Evolving Viscosity and Density Of The Lmomentioning

confidence: 99%

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A Low Viscosity Lunar Magma Ocean Forms a Stratified Anorthitic Flotation Crust With Mafic Poor and Rich Units

Dygert

Lin

Marshall

et al. 2017

Geophysical Research Letters

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Much of the lunar crust is monomineralic, comprising >98% plagioclase. The prevailing model argues the crust accumulated as plagioclase floated to the surface of a solidifying lunar magma ocean (LMO). Whether >98% pure anorthosites can form in a flotation scenario is debated. An important determinant of the efficiency of plagioclase fractionation is the viscosity of the LMO liquid, which was unconstrained. Here we present results from new experiments conducted on a late LMO‐relevant ferrobasaltic melt. The liquid has an exceptionally low viscosity of 0.22−0.19+0.11 to 1.45−0.82+0.46 Pa s at experimental conditions (1,300–1,600°C; 0.1–4.4 GPa) and can be modeled by an Arrhenius relation. Extrapolating to LMO‐relevant temperatures, our analysis suggests a low viscosity LMO would form a stratified flotation crust, with the oldest units containing a mafic component and with very pure younger units. Old, impure crust may have been buried by lower crustal diapirs of pure anorthosite in a serial magmatism scenario.

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Section: Discussionsupporting

confidence: 82%

Section: The Evolving Viscosity and Density Of The Lmomentioning

confidence: 99%

Section: The Evolving Viscosity and Density Of The Lmomentioning

confidence: 99%

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A Low Viscosity Lunar Magma Ocean Forms a Stratified Anorthitic Flotation Crust With Mafic Poor and Rich Units

Dygert

Lin

Marshall

et al. 2017

Geophysical Research Letters

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“…For example, according to dislocation creep flow laws, olivine with 10-ppm H 2 O deforms at a strain rate approximately a factor of 30 faster of dry olivine (at 1 MPa and 1100°C; Hirth & Kohlstedt, 2003). The water abundance in the early LMO is suggested to be a few hundred parts per million, corresponding to concentrations in the last dregs of the magma ocean >10,000 ppm, depending on the initial bulk water content Hauri et al, 2017;Hui et al, 2013;Lin et al, 2017;Saal et al, 2008Saal et al, , 2013. A fractionally crystalized IBC layer would be enriched in water (Elkins-Tanton & Grove, 2011), but ilmenite deformation experiments were run at nominally dry conditions and the effect of water on the rheology of the IBC is unknown.…”

Section: Generation and Timescale Of Overturn: Importance Of Ibc Viscmentioning

confidence: 99%

Lunar Cumulate Mantle Overturn: A Model Constrained by Ilmenite Rheology

Zhang

Liang

et al. 2019

JGR Planets

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Lunar cumulate mantle overturn has been proposed to explain the abundances of TiO2 and heat‐producing elements (U, Th, and K) in the source region of lunar basalts. Ilmenite‐bearing cumulates (IBCs) that were formed near the end of lunar magma ocean solidification are the driving force for overturn. IBCs are enriched with dense TiO2 and FeO contents and have lower viscosity and solidus than those of the underlying lunar cumulate mantle. We investigate the effects of temperature‐ and ilmenite‐dependent mantle rheology on the dynamic process of lunar cumulate mantle overturn and conditions for long‐wavelength downwellings of an IBC layer in a 3‐D spherical geometry. Our results show that the ilmenite‐induced rheological weakening is necessary to decouple the IBC layer from the top stagnant lid and facilitate overturn. Models with IBC viscosity derived from the experimental scaling can only produce short‐wavelength downwellings (spherical harmonic degree >3) and show an overturn timescale more than 100 Ma. A viscosity of the IBC layer at least 10−4 lower than that of the ambient mantle can produce the long‐wavelength (spherical harmonic degree ≤3) downwellings in ~10 Ma and even a hemispheric downwelling. Such low IBC viscosity requires additional weakening mechanisms, such as remelting or/and water enrichment. During the overturn, the cold downwellings displace upward the materials from hot lower mantle and produce partial melting in upper mantle, which may serve as a viable mechanism for early lunar magmatisms. The settling of cold downwellings on the core‐mantle boundary stimulates a transient high heat flux, which may contribute to generating an early lunar dynamo event.

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“…LMO that has to be solidified prior to plagioclase stability vary from 60% to 80% (Elkins-Tanton et al, 2011;Lin et al, 2017a;Longhi, 1980;Snyder et al, 1992). Thus, it is important to evaluate the sensitivity of output parameters, particularly the solidification time of the LMO, to variability of input parameters.…”

Section: Discussionmentioning

confidence: 99%

Effect of Reimpacting Debris on the Solidification of the Lunar Magma Ocean

et al. 2018

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Anorthosites that comprise the bulk of the lunar crust are believed to have formed during solidification of a lunar magma ocean (LMO) in which these rocks would have floated to the surface. This early flotation crust would have formed a thermal blanket over the remaining LMO, prolonging solidification. Geochronology of lunar anorthosites indicates a long timescale of LMO cooling, or remelting and recrystallization in one or more late events. To better interpret this geochronology, we model LMO solidification in a scenario where the Moon is being continuously bombarded by returning projectiles released from the Moon‐forming giant impact. More than one lunar mass of material escaped the Earth‐Moon system onto heliocentric orbits following the giant impact, much of it to come back on returning orbits for a period of 100 Myr. If large enough, these projectiles would have punctured holes in the nascent floatation crust of the Moon, exposing the LMO to space and causing more rapid cooling. We model these scenarios using a thermal evolution model of the Moon that allows for production (by cratering) and evolution (solidification and infill) of holes in the flotation crust that insulates the LMO. For effective hole production, solidification of the magma ocean can be significantly expedited, decreasing the cooling time by more than a factor of 5. If hole production is inefficient, but shock conversion of projectile kinetic energy to thermal energy is efficient, then LMO solidification can be somewhat prolonged, lengthening the cooling time by 50% or more.

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Experimental constraints on the solidification of a nominally dry lunar magma ocean

Cited by 62 publications

References 76 publications

A Low Viscosity Lunar Magma Ocean Forms a Stratified Anorthitic Flotation Crust With Mafic Poor and Rich Units

A Low Viscosity Lunar Magma Ocean Forms a Stratified Anorthitic Flotation Crust With Mafic Poor and Rich Units

Lunar Cumulate Mantle Overturn: A Model Constrained by Ilmenite Rheology

Effect of Reimpacting Debris on the Solidification of the Lunar Magma Ocean

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