The formation of pure anorthosite on the Moon

Piskorz, Danielle; Stevenson, D. J.

doi:10.1016/j.icarus.2014.06.015

Cited by 23 publications

(23 citation statements)

References 18 publications

(6 reference statements)

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“…Furthermore, this may be consistent with an existence of PAN‐bearing farside lunar meteorites, such as the Dhofar 489 group [ Nagaoka et al , ]. Although Parmentier and Liang [], Piskorz and Stevenson [], and Yamamoto et al [] proposed the possibility that there is an interstitial mafic melt layer at the thin, top layer of the crust, such a small amount of mafic does not affect this scenario.…”

Section: Discussionsupporting

confidence: 57%

Featureless spectra on the Moon as evidence of residual lunar primordial crust

et al. 2015

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We report the global distribution of areas exhibiting no absorption features (featureless or FL) on the lunar surface, based on the reflectance spectral data set obtained by the Spectral Profiler onboard Kaguya/SELENE. We found that FL sites are located in impact basins and large impact craters in the Feldspathic Highlands Terrane, while there are no FL sites in the Procellarum regions nor the South Pole‐Aitken basin. FL sites in each impact basin/crater are mainly found at the peak rings or rims, where the purest anorthosite (PAN) sites are also found. At the local scale, most of the FL and PAN points are associated with impact craters and peaks. Most of the FL spectra show a steeper (redder) continuum than the PAN spectra, suggesting the occurrence of space weathering effects. We propose that most of the material exhibiting a FL spectrum originate from space weathered PAN. Taking into account all the occurrence trends of FL sites on the Moon, we propose that both the FL and PAN materials were excavated from the primordial lunar crust during ancient basin formations below the megaregolith in the highlands. Since the FL and PAN sites are widely distributed over the lunar surface, our new data may support the existence of a massive PAN layer below the lunar surface.

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Section: Discussionsupporting

confidence: 57%

Featureless spectra on the Moon as evidence of residual lunar primordial crust

et al. 2015

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“…This problem is similar to the accumulation of the anorthositic crust on the Moon and the potential trapping of interstitial melt in the crust (Piskorz & Stevenson, 2014). We consider an idealized scenario where the ice shell is initially 1 km thick and cools by conduction.…”

Section: Methodsmentioning

confidence: 99%

Compaction and Melt Transport in Ammonia‐Rich Ice Shells: Implications for the Evolution of Triton

2018

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Ammonia, if present in the ice shells of icy satellites, could lower the temperature for the onset of melting to 176 K and create a large temperature range where partial melt is thermally stable. The evolution of regions of ammonia‐rich partial melt could strongly influence the geological and thermal evolution of icy bodies. For melt to be extracted from partially molten regions, the surrounding solid matrix must deform and compact. Whether ammonia‐rich melts sink to the subsurface ocean or become frozen into the ice shell depends on the compaction rate and thermal evolution. Here we construct a model for the compaction and thermal evolution of a partially molten, ammonia‐rich ice shell in a one‐dimensional geometry. We model the thickening of an initially thin ice shell above an ocean with 10% ammonia. We find that ammonia‐rich melts can freeze into the upper 5 to 10 km of the ice shell, when ice shell thickening is rapid compared to the compaction rate. The trapping of near‐surface volatiles suggests that, upon reheating of the ice shell, eutectic melting events are possible. However, as the ice shell thickening rate decreases, ammonia‐rich melt is efficiently excluded from the ice shell and the bulk of the ice shell is pure water ice. We apply our results to the thermal evolution of Neptune's moon Triton. As Triton's ice shell thickens, the gradual increase of ammonia concentration in Triton's subsurface ocean helps to prevent freezing and increases the predicted final ocean thickness by up to 50 km.

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“…Colors indicate the assumed compaction viscosity. The model is not sensitive to melt viscosity within LMO‐relevant bounds; cases that produce melt fractions consistent with the observed crustal purity have compaction viscosities ⪅10 20 Pa s. The density difference between plagioclase and melt was assumed to be 200 kg/m 3 , and other parameters are assumed by Piskorz and Stevenson ().…”

Section: Purity Of An Anorthositic Flotation Crustmentioning

confidence: 99%

“…To form a pure flotation crust, the rate of compaction or squeezing of trapped liquid out of the accumulating crust must exceed the propagation rate of the solidification front. Piskorz and Stevenson () developed a compaction‐solidification model to estimate the amount of trapped liquid frozen into the flotation crust. Assuming conductive cooling, they argue the solidification front propagates downward at a rate proportional to the square root of inverse time, and that melt escapes the crust by Darcy flow facilitated by compaction.…”

Section: Purity Of An Anorthositic Flotation Crustmentioning

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%

See 1 more Smart Citation

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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The formation of pure anorthosite on the Moon

Cited by 23 publications

References 18 publications

Featureless spectra on the Moon as evidence of residual lunar primordial crust

Featureless spectra on the Moon as evidence of residual lunar primordial crust

Compaction and Melt Transport in Ammonia‐Rich Ice Shells: Implications for the Evolution of Triton

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

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