Crystals stirred up: 2. Numerical insights into the formation of the earliest crust on the Moon

Suckale, Jenny; Elkins-Tanton, Linda T.; Sethian, James A.

doi:10.1029/2012je004067

Cited by 50 publications

(45 citation statements)

References 43 publications

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“…Second, as demonstrated by simulation B, the geochemical evolution of the suspension may have important dynamic ramifications when the coupling of the solid phase on the ambient flow field is taken into account. We explore both observations in more detail in the companion paper [ Suckale et al , 2012].…”

Section: Resultsmentioning

confidence: 99%

“…Third, direct numerical simulations can incorporate observational data at the microscopic scale, such as crystal‐size distributions derived from thin section analysis, and explore ramifications for large‐scale dynamics, thus contributing to bridge petrological data and geodynamic modeling. The complementary nature of simulations at the small and large scale indicates that except in rare case where scale separation is limited [ Verhoeven and Schmalzl , 2009], the best way forward might be the combination of small‐ and large‐scale code as attempted for the Moon in the companion paper [ Suckale et al , 2012].…”

Section: Introductionmentioning

confidence: 99%

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Crystals stirred up: 1. Direct numerical simulations of crystal settling in nondilute magmatic suspensions

Suckale¹,

Sethian²,

Yu³

et al. 2012

J. Geophys. Res.

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[1] This is the first paper in a two-part series examining the fluid dynamics of crystal settling and flotation in the lunar magma ocean. A key challenge in constraining solidification processes is determining the ability of individual crystals to decouple from vigorous thermal convection and settle out or float. The goal of this paper is to develop a computational methodology capable of capturing the complex solid-fluid interactions that determine settling and flotation. In the second paper, we use this computational approach to explore the conditions under which plagioclase feldspar would be able to buoyantly float and form the earliest crust on the Moon. The direct numerical method described in this paper relies on a fictitious domain approach and captures solid-body motion in 2D and 3D with little overhead beyond single fluid calculations. The two main innovations of our numerical implementation of a fictitious domain approach are an analytical quadrature scheme, which increases accuracy and reduces computational expense, and the derivation of a multibody collision scheme. Advantages of this approach over previous simulations of crystal-bearing magmatic suspensions include the following: (1) we fully resolve the two-way interaction between fluid and solid phases, implying that crystals are not only passively advected in an ambient flow field but are also actively driving flow, and (2) we resolve the flow around each individual crystal without assuming specific settling speeds or drag coefficients. We present several benchmark problems and convergence tests to validate our approach.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Crystals stirred up: 1. Direct numerical simulations of crystal settling in nondilute magmatic suspensions

Suckale¹,

Sethian²,

Yu³

et al. 2012

J. Geophys. Res.

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“…Because Stokes' settling rates, particle entrainment in convecting magma ocean liquids, and interactions among suspended particles depend on the viscosity of the magma ocean liquid (e.g., Elkins‐Tanton, ; Solomatov et al, ; Suckale et al, ), the purity of the ferroan anorthositic crust largely depends on the viscosity of the LMO, which evolved throughout plagioclase crystallization. Our Arrhenius relation places an important bound on the viscosity of the LMO at end‐stage (~95%) solidification.…”

Section: The Evolving Viscosity and Density Of The Lmomentioning

confidence: 99%

“…Additionally, melt viscosity plays a critical role in determining rates of melt percolation through a crystalline matrix and the characteristic compaction length of a cumulate pile (e.g., McKenzie, ). Estimates for LMO viscosities differ by as much as 2 orders of magnitude (1–100 Pa s, Piskorz & Stevenson, ; Suckale et al, ). Here we present new experimental measurements that constrain viscosity of the plagioclase‐saturated LMO.…”

Section: Introductionmentioning

confidence: 99%

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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“…Previous numerical models of crystals segregation in convecting systems were generally based on tracers, representing solid particles [e.g., Suckale et al ., ; Verhoeven and Schmalzl , ; Höink et al ., ]. This strategy suffers from two main limitations.…”

Section: Introductionmentioning

confidence: 99%

Modeling phase separation and phase change for magma ocean solidification dynamics

Boukaré

Ricard

2017

Geochem Geophys Geosyst

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Just after accretion, the Earth's mantle was significantly molten by the heat dissipation due to large impacts and to the segregation of the core. The mineralogical observations and thermodynamics models of solid‐liquid equilibrium of silicates show that several types of crystallization may have happened at different depths in the mantle. Solids were probably formed first at the bottom of the lower mantle or at midmantle leaving two possible magma oceans, a shallow one and an abyssal one. Near the bottom of the mantle, the liquid phase might become denser than solids due to iron enrichment. In the shallow magma ocean, the crystallizing solid phase was denser and sank through the magma to settle and compact at depth. To understand these complex dynamics, we develop a two‐phase numerical code that can handle simultaneously convection in each phase and in the slurry, and the compaction or decompaction of the two phases. Although our code can only run in a parameter range (Rayleigh number, viscosity contrast between phases, Prandlt number) far from what would be realistic, we think it already provides a rich dynamics that illustrates what could have happened. We show situations in which the crystallization front is gravitationally stable and situations where the newly formed solids are gravitationally unstable and can snow across the magma. Our study suggests that the location of a density contrast between solid and magma must be considered of equal importance with that of the intersection between liquidus and isentrope for what concerns mantle solidification.

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Crystals stirred up: 2. Numerical insights into the formation of the earliest crust on the Moon

Cited by 50 publications

References 43 publications

Crystals stirred up: 1. Direct numerical simulations of crystal settling in nondilute magmatic suspensions

Crystals stirred up: 1. Direct numerical simulations of crystal settling in nondilute magmatic suspensions

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

Modeling phase separation and phase change for magma ocean solidification dynamics

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