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

Dygert, Nick; Lin, Jung‐Fu; Marshall, Edward W.; Kono, Yoshio; Gardner, James E.

doi:10.1002/2017gl075703

Cited by 42 publications

(32 citation statements)

References 47 publications

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“…The corrected Uhlmann et al (1974) viscosity η = 0.54 Pa-s is higher than the one derived from our data η = 0.33 Pa-s; however the difference is not unacceptable considering experimental uncertainties. Recently, Sehlke and Whittington (2016) measured the 1 atm viscosity of a synthetic high-Ti lunar basalt (LM sample, 9.52 wt% TiO 2 ), and obtained η = 0.19 Pa-s at 1850 K, which extrapolates to η = 0.14 Pa-s at 1906 K. This value is again close to our present estimate for black glass composition η = 0.15 Pa-s at 1 atm -1906 K. Dygert et al (2017) reported a viscosity of η = 0.22-1.45 Pa-s at experimental conditions, 1573-1873 K and 0.1-4.4 GPa, for a late Lunar Magma Ocean (LMO) analog. Although a direct comparison cannot be made because the composition of the late LMO (Fe-and Ti-rich ferrobasalt) is quite different from the present primitive lunar melts, both studies point to very low viscosities for these lunar melts.…”

Section: Comparison With Previous Work and Model Predictionssupporting

confidence: 89%

“…For example, Liebske et al (2005) measured an activation energy E a = 197 kJ/mol for a peridotite liquid. For Ti-bearing ferrobasaltic melts, Chevrel et al (2014) reported E a = 179 kJ/mol for a 1.1 wt% TiO 2 and 20.36 wt% FeO composition, and Dygert et al (2017) derived E a = 153 kJ/mol for a 4.1 wt% TiO 2 and 29,9% FeO liquid. For lunar mare basalt compositions, the high-temperature data of Uhlmann et al (1974) on a synthetic Apollo15 green glass showed E a = 167 kJ/mol, and the more recent experimental measurements by Sehlke and Whittington (2016) on a high-Ti (9.54 wt% TiO 2 ) sample produced E a = 165 kJ/mol.…”

Section: Effects Of Temperature Pressure and Compositionmentioning

confidence: 99%

“…4. Experimental data fromDygert et al (2017) for a Fe-Ti lunar basalt are also shown, as well as the models ofDufils et al (2018) for green and black glasses compositions.…”

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confidence: 99%

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In situ Viscometry of Primitive Lunar Magmas at High Pressure and High Temperature

et al. 2019

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Understanding the dynamics of the magmatic evolution of the interior of the Moon requires accurate knowledge of the viscosity (η) of lunar magmas at high pressure (P) and high temperature (T) conditions. Although the viscosities of terrestrial magmas are relatively well-documented, and their relation to magma composition well-studied, the viscosities of lunar titano-silicate melts are not well-known. Here, we present an experimentally measured viscosity dataset for three end member compositions, characterized by a wide range of titanium contents, at lunar-relevant pressuretemperature range of ∼1.1-2.4 GPa and 1830-2090 K. In situ viscometry using the falling sphere technique shows that the viscosity of lunar melts varies between ∼0.13 and 0.87 Pa-s depending on temperature, pressure and composition. Viscosity decreases with increasing temperature with activation energies for viscous flow of E a = 201 kJ/mol and E a = 106 kJ/mol for low-titanium (Ti) and high-Ti melts, respectively. Pressure is found to mildly increase the viscosity of these intermediate polymerized melts by a factor of ∼1.5 between 1.1 and 2.4 GPa. Viscosities of low-Ti and high-Ti magmas at their respective melting temperatures are very close. However at identical P-T conditions (∼1.3 GPa, ∼1840 K) low-Ti magmas are about a factor of three more viscous than high-Ti magmas, reflecting structural effects of Si and Ti on melt viscosity. Measured viscosities differ significantly from empirical models based on measurements of the viscosity of terrestrial basalts, with largest deviations observed for the most Tirich and Si-poor composition. Viscosity coefficients for these primitive lunar melts are found to be lower than those of common terrestrial basalts, giving them a high mobility throughout the lunar mantle and onto the surface of the Moon despite their Fe and Ti-rich compositions.

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Section: Comparison With Previous Work and Model Predictionssupporting

confidence: 89%

Section: Effects Of Temperature Pressure and Compositionmentioning

confidence: 99%

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In situ Viscometry of Primitive Lunar Magmas at High Pressure and High Temperature

et al. 2019

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“…However, HCP, pyroxene-dominated mixture spectra, spinel, or olivine were also detected in most of the surveyed central peaks where purest anorthosite was detected in previous studies (Donaldson Hanna et al, 2014;Yamamoto et al, 2010Yamamoto et al, , 2012. Head and Wilson (1992) proposed that as much as 50% of the lower crust is intruded by plutons; and Dygert et al (2017) proposed that the present-day lunar crust is composed of a relatively impure, old crust, later intruded by pure anorthositic diapirs. Alternatively, the anorthositic crust may be intruded later by more mafic plutons.…”

Section: Plagioclase Detectionsmentioning

confidence: 72%

“…Alternatively, the anorthositic crust may be intruded later by more mafic plutons. Head and Wilson (1992) proposed that as much as 50% of the lower crust is intruded by plutons; and Dygert et al (2017) proposed that the present-day lunar crust is composed of a relatively impure, old crust, later intruded by pure anorthositic diapirs. Both processes are consistent with the observation of PAN occurrences juxtaposed to mafic detections.…”

Section: Plagioclase Detectionsmentioning

confidence: 99%

Compositional Variations in the Vicinity of the Lunar Crust‐Mantle Interface From Moon Mineralogy Mapper Data

et al. 2018

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Moon Mineralogy Mapper spectroscopic data were used to investigate the mineralogy of a selection of impact craters' central peaks or peak rings, in order to characterize the lunar crust‐mantle interface, and assess its lateral and vertical heterogeneity. The depth of origin of the craters' central peaks or peak rings was calculated using empirical equations, and compared to Gravity Recovery and Interior Laboratory crustal thickness models to select craters tapping within +10/−20 km of the crust‐mantle interface. Our results show that plagioclase is widely detected, including in craters allegedly sampling lower crustal to mantle material, except in central peaks where Low‐Calcium Pyroxene was detected. Olivine detections are scarce, and identified in material assumed to be derived from both above and below the crust‐mantle interface. Mineralogical detections in central peaks show that there is an evolution of the pyroxene composition with depth, that may correspond to the transition from the crust to the mantle. The correlation between High‐Calcium Pyroxene and some pyroxene‐dominated mixture spectra with the location of maria and cryptomaria hints at the existence of lateral heterogeneities as deep as the crust‐mantle interface.

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A Long-Lived Lunar Magnetic Field Powered by Convection in the Core and a Basal Magma Ocean

Hamid

O’Rourke

Soderlund

2022

Preprint

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An internally generated magnetic field once existed on the Moon. This field reached high intensities (~10-100 μT, perhaps intermittently) from ~4.3-3.6Gyr ago and then weakened to ≲ 5 μT before dissipating by ~1.9-0.8 Gyr ago.While the Moon's metallic core could have generated a magnetic field via a dynamo powered by vigorous convection, models of a core dynamo often fail to explain the observed characteristics of the lunar magnetic field. In particular, the core alone likely may not contain sufficient thermal, chemical, or radiogenic energy to sustain the high-intensity fields for >100 Myr. A recent study by Scheinberg et al. suggested that a dynamo hosted in electrically conductive, molten silicates in a basal magma ocean (BMO) may have produced a strong early field. However, that study did not fully explore the BMO's coupled evolution with the core. Here we show that a coupled BMOcore dynamo driven primarily by inner core growth can explain the timing and staged decline of the lunar magnetic field. We compute the thermochemical evolution of the lunar core with a 1-D, parameterized model tied to extant simulations of mantle evolution and BMO solidification. Our models are most sensitive to four parameters: the abundances of sulfur and potassium in the core, the core's thermal conductivity, and the present-day heat flow across the core-mantle boundary. Our models best match the Moon's magnetic history if the bulk core contains ~6.5-8.5 wt% sulfur, in agreement with seismic structure models.

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

Cited by 42 publications

References 47 publications

In situ Viscometry of Primitive Lunar Magmas at High Pressure and High Temperature

In situ Viscometry of Primitive Lunar Magmas at High Pressure and High Temperature

Compositional Variations in the Vicinity of the Lunar Crust‐Mantle Interface From Moon Mineralogy Mapper Data

A Long-Lived Lunar Magnetic Field Powered by Convection in the Core and a Basal Magma Ocean

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