Is there a semi-molten layer at the base of the lunar mantle?

Walterová, Michaela; Běhounková, M.; Efroimsky, Michael

doi:10.1002/essoar.10512756.3

Cited by 3 publications

(5 citation statements)

References 77 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…(2007, 2014) and references therein). While alternative rheology models have been showed to also comply with the data without requiring such a layer (Walterová et al., 2023), its existence would place a strong constraint on the present‐day thermal state of the Moon, with which thermal evolution models such as the one presented in this study should comply. The presence of an overturned layer of HTC helps satisfying this constraint as the melting temperature of HTC is significantly lower than that of the lunar mantle (Mallik et al., 2019; Wyatt, 1977).…”

Section: Influence Of the Htc Overturn On The Long‐term Evolution Of ...mentioning

confidence: 80%

See 1 more Smart Citation

Small‐Scale Overturn of High‐Ti Cumulates Promoted by the Long Lifetime of the Lunar Magma Ocean

Maurice,

Tosi,

Hüttig

2024

JGR Planets

View full text Add to dashboard Cite

The fractional crystallization of the lunar magma ocean (LMO) results in a gravitationally unstable layering, with dense Fe‐ and Ti‐oxides overlying lighter mafic cumulates. Due to their high density, these are prone to overturn via Rayleigh‐Taylor instability. However, this instability competes with the downward growth of the cold and stiff stagnant lid, which tends to trap the cumulates preventing their overturn. The fate of high‐Ti cumulates (HTC) plays a major role in several aspects of the Moon's history, including mare volcanism, early magnetism, and the presence of a partially molten layer at the core‐mantle boundary (CMB). To assess the extent of the overturn of HTC, we use 2D simulations of thermo‐chemical mantle convection in the presence of a solidifying LMO. The long lifetime of the magma ocean caused by the insulating effect of the plagioclase crust delays the growth of the stagnant lid and promotes the onset of solid‐state convection during magma ocean solidification. Both phenomena favor a high degree of mobilization of the HTC. Independent of the rheology of the mafic and HTC, the overturn is always characterized by small‐scale instabilities and is completed within ∼300–600 Myr. High‐Ti material accumulates at the CMB where it undergoes partial melting until present‐day, in agreement with the existence of a deep, partially molten layer inferred from geodetic data. Part of the overturned cumulates is entrained by mantle flow and can participate in secondary melting until ∼1 Ga, in agreement with the age of high‐Ti mare basalts.

show abstract

Section: Influence Of the Htc Overturn On The Long‐term Evolution Of ...mentioning

confidence: 80%

“…Finally, overturned HTC remaining at the CMB could lower the melting temperature, and help forming a partially molten layer inferred by geophysical and geodetic data (Briaud et al., 2023; Khan et al., 2007, 2014), although Walterová et al. (2023) recently questioned this conclusion.…”

Section: Introductionmentioning

confidence: 99%

Small‐Scale Overturn of High‐Ti Cumulates Promoted by the Long Lifetime of the Lunar Magma Ocean

Maurice,

Tosi,

Hüttig

2024

JGR Planets

View full text Add to dashboard Cite

show abstract

“…The software developed for the calculation of selenodetic parameters of multi‐layered bodies, the Python interface for running the MCMC inversion, and the plotting tools used for the figures presented in this study are available in Walterová et al. (2023).…”

Section: Data Availability Statementmentioning

confidence: 99%

“…The software developed for the calculation of selenodetic parameters of multi-layered bodies, the Python interface for running the MCMC inversion, and the plotting tools used for the figures presented in this study are available in Walterová et al (2023). We would like to thank the editor Laurent Montési and the two anonymous reviewers for their many constructive comments that were essential in shaping the present manuscript.…”

Section: Data Availability Statementmentioning

confidence: 99%

Is There a Semi‐Molten Layer at the Base of the Lunar Mantle?

2023

Self Cite

View full text Add to dashboard Cite

Fitting of the lunar laser ranging (LLR) data to the quality-factor power scaling law Q ∼ χ p rendered a small negative value of the exponential: p = −0.19 (Williams et al., 2001). Further attempts by the JPL team to reprocess the data led to p = −0.07. According to Williams and Boggs (2009), "Q for rock is expected to have a weak dependence on tidal period, but it is expected to decrease with period rather than increase."The most recent estimates of the tidal contribution to the lunar physical librations (Williams & Boggs, 2015) still predict a mild increase of Q with period: from Q = 38 ± 4 at one month to Q = 41 ± 9 at one year, yielding p = −0.03 ± 0.09. Efroimsky (2012aEfroimsky ( , 2012b suggested that since the frequency-dependence of k 2 /Q always has a kink shape, like in Figure 1, the negative slope found by the LLR measurements could be consistent with the peak of the kink residing between the monthly and annual frequencies. This interpretation entails, for a homogeneous Maxwell or Andrade lunar model, very low values of the mean viscosity, indicating the presence of partial melt.Our goal now is to devise an interpretation based on the Sundberg-Cooper model. Within that model, the kink contains not one but two peaks, and we are considering the possibility that the negative slope of our interest is due to the monthly and annual frequencies bracketing either this peak or the local inter-peak minimum.

show abstract

Section: Open Researchmentioning

confidence: 99%

Is there a semi-molten layer at the base of the lunar mantle?

Walterová

Běhounková

Efroimsky

2023

Preprint

View full text Add to dashboard Cite

Parameterised by the Love number k2 and the tidal quality factor Q, and inferred from lunar laser ranging (LLR), tidal dissipation in the Moon follows an unexpected frequency dependence often interpreted as evidence for a highly dissipative, melt-bearing layer encompassing the core-mantle boundary. Within this, more or less standard interpretation, the basal layer’s viscosity is required to be of order 10^15 to 10^16 Pa.s and its outer radius is predicted to extend to the zone of deep moonquakes. While the reconciliation of those predictions with the mechanical properties of rocks might be challenging, alternative lunar interior models without the basal layer are said to be unable to fit the frequency dependence of tidal Q. The purpose of our paper is to illustrate under what conditions the frequency-dependence of lunar tidal Q can be interpreted without the need for deep-seated partial melt. Devising a simplified lunar model, in which the mantle is described by the Sundberg-Cooper rheology, we predict the relaxation strength and characteristic timescale of elastically-accommodated grain boundary sliding in the mantle that would give rise to the desired frequency dependence. Along with developing this alternative model, we test the traditional model with basal partial melt; and we show that the two models cannot be distinguished from each other by the available selenodetic measurements. Additional insight into the nature of lunar tidal dissipation can be gained either by measurements of higher-degree Love numbers and quality factors or by farside lunar seismology.

show abstract

Is there a semi-molten layer at the base of the lunar mantle?

Cited by 3 publications

References 77 publications

Small‐Scale Overturn of High‐Ti Cumulates Promoted by the Long Lifetime of the Lunar Magma Ocean

Small‐Scale Overturn of High‐Ti Cumulates Promoted by the Long Lifetime of the Lunar Magma Ocean

Is There a Semi‐Molten Layer at the Base of the Lunar Mantle?

Is there a semi-molten layer at the base of the lunar mantle?

Contact Info

Product

Resources

About