Thermodynamic properties of geikielite (MgTiO3) and ilmenite (FeTiO3) derived from vibrational methods combined with Raman and infrared spectroscopic data

Jacobs, Michael; Berg, A. P. van den; Schmid–Fetzer, Rainer; Vries, J. de; Westrenen, W. van; Zhao, Yue

doi:10.1007/s00269-022-01195-5

“…Focusing now on the elastic properties, we note that the rigidities of olivine (e.g., Mao et al, 2015), ilmenite (Jacobs et al, 2022), and garnetite (Kraettli et al, 2022) are comparable. The temperature has only a limited impact on their value (−0.01 GPa/K for olivine and ilmenite).…”

Section: Highly Dissipative Basal Layermentioning

confidence: 96%

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

Walterová

¹

,

Běhounková

²

,

Efroimsky

³

2023

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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.

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

Walterová

¹

,

Běhounková

²

,

Efroimsky

³

2022

Preprint

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Parameterised by the Love number k 2 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?

Walterová

¹

,

Běhounková

²

,

Efroimsky

³

2022

Preprint

View full text Add to dashboard Cite

Parameterised by the Love number k 2 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

Thermodynamic properties of geikielite (MgTiO3) and ilmenite (FeTiO3) derived from vibrational methods combined with Raman and infrared spectroscopic data

Abstract: Thermodynamic properties of geikielite (MgTiO3) and ilmenite (FeTiO3) derived from vibrational methods combined with Raman and infrared spectroscopic data

Cited by 7 publications

References 76 publications

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?

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?

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