Contraction or expansion of the Moon's crust during magma ocean freezing?

Elkins‐Tanton, L. T.; Bercovici, David

doi:10.1098/rsta.2013.0240

Cited by 18 publications

(13 citation statements)

References 33 publications

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“…This assumption is based on the relatively small abundance of olivine in the vicinity of large impact basins (e.g., the SPA basin) that undoubtedly must have excavated mantle material to the surface, spectral data, lunar samples, seismic, and petrological studies (Lucey et al, ; Melosh et al, ; Melosh et al, ; Wieczorek, ). An orthopyroxene‐rich upper mantle is also supported by modeling of the thermal evolution of the LMO (Elkins‐Tanton & Bercovici, ; Khan et al, ; Kuskov & Kronrod, ). Although the olivine has been observed around the Crisium and Moscoviense basins (Yamamoto et al, ), which may have penetrated through the lunar crust (Miljkovic et al, ; Wieczorek et al, ), the exposures of olivine is thought to originate most likely from the lower crust (Head & Wilson, ; Pieters et al, ).…”

Section: Discussionmentioning

confidence: 74%

Are the Moon's Nearside‐Farside Asymmetries the Result of a Giant Impact?

et al. 2019

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The Moon exhibits striking geological asymmetries in elevation, crustal thickness, and composition between its nearside and farside. Although several scenarios have been proposed to explain these asymmetries, their origin remains debated. Recent remote sensing observations suggest that (1) the crust on the farside highlands consists of two layers: a primary anorthositic layer with thickness of ~30‐50 km and on top a more mafic‐rich layer ~10 km thick and (2) the nearside exhibits a large area of low‐Ca pyroxene that has been interpreted to have an impact origin. These observations support the idea that the lunar nearside‐farside asymmetries may be the result of a giant impact. Here using quantitative numerical modeling, we test the hypothesis that a giant impact on the early Moon can explain the striking differences in elevation, crustal thickness, and composition between the nearside and farside of the Moon. We find that a large impactor, impacting the current nearside with a low velocity, can form a mega‐basin and reproduce the characteristics of the crustal asymmetry and structures comparable to those observed on the current Moon, including the nearside lowlands and the farside's mafic‐rich layer on top of a primordial anorthositic crust. Our model shows that the excavated deep‐seated KREEP (potassium, rare earth elements, and phosphorus) material, deposited close to the basin rim, slumps back into the basin and covers the entire basin floor; subsequent large impacts can transport the shallow KREEP material to the surface, resulting in its observed distribution. In addition, our model suggests that prior to the asymmetry‐forming impact, the Moon may have had an 182W anomaly compared to the immediate post‐giant impact Earth's mantle, as predicted if the Moon was created through a giant collision with the proto‐Earth.

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Section: Discussionmentioning

confidence: 74%

Are the Moon's Nearside‐Farside Asymmetries the Result of a Giant Impact?

et al. 2019

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“…However, partial melting of the earliest olivine and pyroxene LMO cumulates during LMO overturn and adiabatic ascent is also feasible (Joy et al. ; Elkins‐Tanton and Bercovici ).…”

Section: Discussionmentioning

confidence: 99%

“…However, the age overlap between ferroan anorthosite samples, the HMS, and ancient basaltic meteorite ages (Figs. b and c), suggests that the lunar highlands crust may still have been accumulating and was likely warmer and more ductile at ~4300 Ma (Elkins‐Tanton and Bercovici ). Such elevated crustal thermal conditions may have facilitated dissolution (Reiners et al.…”

Section: Discussionmentioning

confidence: 99%

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The early geological history of the Moon inferred from ancient lunar meteorite Miller Range 13317

Curran

Joy

Snape

et al. 2019

Meteorit & Planetary Scien

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Miller Range (MIL) 13317 is a heterogeneous basalt‐bearing lunar regolith breccia that provides insights into the early magmatic history of the Moon. MIL 13317 is formed from a mixture of material with clasts having an affinity to Apollo ferroan anorthosites and basaltic volcanic rocks. Noble gas data indicate that MIL 13317 was consolidated into a breccia between 2610 ± 780 Ma and 1570 ± 470 Ma where it experienced a complex near‐surface irradiation history for ~835 ± 84 Myr, at an average depth of ~30 cm. The fusion crust has an intermediate composition (Al2O3 15.9 wt%; FeO 12.3 wt%) with an added incompatible trace element (Th 5.4 ppm) chemical component. Taking the fusion crust to be indicative of the bulk sample composition, this implies that MIL 13317 originated from a regolith that is associated with a mare‐highland boundary that is KREEP‐rich (i.e., K, rare earth elements, and P). A comparison of bulk chemical data from MIL 13317 with remote sensing data from the Lunar Prospector orbiter suggests that MIL 13317 likely originated from the northwest region of Oceanus Procellarum, east of Mare Nubium, or at the eastern edge of Mare Frigoris. All these potential source areas are on the near side of the Moon, indicating a close association with the Procellarum KREEP Terrane. Basalt clasts in MIL 13317 are from a very low‐Ti to low‐Ti (between 0.14 and 0.32 wt%) source region. The similar mineral fractionation trends of the different basalt clasts in the sample suggest they are comagmatic in origin. Zircon‐bearing phases and Ca‐phosphate grains in basalt clasts and matrix grains yield 207Pb/206Pb ages between 4344 ± 4 and 4333 ± 5 Ma. These ancient 207Pb/206Pb ages indicate that the meteorite has sampled a range of Pre‐Nectarian volcanic rocks that are poorly represented in the Apollo, Luna, and lunar meteorite collections. As such, MIL 13317 adds to the growing evidence that basaltic volcanic activity on the Moon started as early as ~4340 Ma, before the main period of lunar mare basalt volcanism at ~3850 Ma.

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“…These facts suggest that LGAs might be formed by the global expansion due to the remelting of the lunar mantle. Other possible explanations for global expansion include thermal equilibration of a cool interior with the overlying hot LMO cumulates [Solomon, 1977], sinking of KREEP (potassium, rare earth element, and phosphorus)rich material to the core-mantle boundary and subsequent internal heating [Zhang et al, 2013b], and volume changes associated with the crystallization of the LMO [Elkins-Tanton and Bercovici, 2014].…”

Section: Discussionmentioning

confidence: 99%

Constraints on timing and magnitude of early global expansion of the Moon from topographic features in linear gravity anomaly areas

Sawada

Morota

Kato

et al. 2016

Geophysical Research Letters

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Gravity data obtained from the Gravity Recovery and Interior Laboratory have revealed linear gravity anomalies (LGAs) formed by the early global expansion of the Moon and subsequent magma intrusion. In this study, using Lunar Orbiter Laser Altimeter topographic data, we investigated topographic profiles across LGAs to verify that they were formed by extensional tectonics. We found that 17 of the 20 LGAs investigated exhibited a valley structure, suggesting that they were formed by tensile stress. Assuming that these topographic depressions accompanied graben formation, the increase in the lunar radius is estimated to be on the order of several tens of meters. On the other hand, assuming that these topographic depressions accompanied flexure of elastic lithosphere due to the LGA load, the elastic thickness during the LGA formation is estimated as ~10 km. The crater frequencies in the vicinity of LGAs indicate that the peak tectonic activity occurred before the basin‐forming epoch.

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Contraction or expansion of the Moon's crust during magma ocean freezing?

Cited by 18 publications

References 33 publications

Are the Moon's Nearside‐Farside Asymmetries the Result of a Giant Impact?

Are the Moon's Nearside‐Farside Asymmetries the Result of a Giant Impact?

The early geological history of the Moon inferred from ancient lunar meteorite Miller Range 13317

Constraints on timing and magnitude of early global expansion of the Moon from topographic features in linear gravity anomaly areas

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