Conditions and extent of volatile loss from the Moon during formation of the Procellarum basin

Rocks from the lunar interior are depleted in moderately volatile elements (MVEs) compared to terrestrial rocks. Most MVEs are also enriched in their heavier isotopes compared to those in terrestrial rocks. Such elemental depletion and heavy isotope enrichments have been attributed to liquid–vapor exchange and vapor loss from the protolunar disk, incomplete accretion of MVEs during condensation of the Moon, and degassing of MVEs during lunar magma ocean crystallization. New Monte Carlo simulation results suggest that the lunar MVE depletion is consistent with evaporative loss at 1,670 ± 129 K and an oxygen fugacity +2.3 ± 2.1 log units above the fayalite-magnetite-quartz buffer. Here, we propose that these chemical and isotopic features could have resulted from the formation of the putative Procellarum basin early in the Moon’s history, during which nearside magma ocean melts would have been exposed at the surface, allowing equilibration with any primitive atmosphere together with MVE loss and isotopic fractionation.

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Volatile loss following cooling and accretion of the Moon revealed by chromium isotopes

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1809060115 ◽

2018 ◽

Vol 115 (43) ◽

pp. 10920-10925 ◽

Cited By ~ 23

Author(s):

Paolo A. Sossi ◽

Frédéric Moynier ◽

Kirsten van Zuilen

Keyword(s):

Atomic Mass Unit ◽

The Moon ◽

Volatile Elements ◽

Mass Unit ◽

Earth’S Mantle ◽

Refractory Elements ◽

Common Precursor ◽

Lunar Rocks ◽

Evaporative Loss ◽

Volatile Loss

Terrestrial and lunar rocks share chemical and isotopic similarities in refractory elements, suggestive of a common precursor. By contrast, the marked depletion of volatile elements in lunar rocks together with their enrichment in heavy isotopes compared with Earth’s mantle suggests that the Moon underwent evaporative loss of volatiles. However, whether equilibrium prevailed during evaporation and, if so, at what conditions (temperature, pressure, and oxygen fugacity) remain unconstrained. Chromium may shed light on this question, as it has several thermodynamically stable, oxidized gas species that can distinguish between kinetic and equilibrium regimes. Here, we present high-precision Cr isotope measurements in terrestrial and lunar rocks that reveal an enrichment in the lighter isotopes of Cr in the Moon compared with Earth’s mantle by 100 ± 40 ppm per atomic mass unit. This observation is consistent with Cr partitioning into an oxygen-rich vapor phase in equilibrium with the proto-Moon, thereby stabilizing the CrO2 species that is isotopically heavy compared with CrO in a lunar melt. Temperatures of 1,600–1,800 K and oxygen fugacities near the fayalite–magnetite–quartz buffer are required to explain the elemental and isotopic difference of Cr between Earth’s mantle and the Moon. These temperatures are far lower than modeled in the aftermath of a giant impact, implying that volatile loss did not occur contemporaneously with impact but following cooling and accretion of the Moon.

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Evaporative fractionation of volatile stable isotopes and their bearing on the origin of the Moon

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2013.0259 ◽

2014 ◽

Vol 372 (2024) ◽

pp. 20130259 ◽

Cited By ~ 61

Author(s):

James M. D. Day ◽

Frederic Moynier

Keyword(s):

Global Scale ◽

Parent Body ◽

The Moon ◽

Magma Ocean ◽

Volatile Elements ◽

Giant Impact ◽

The Earth ◽

Present Distribution ◽

Volatile Loss

The Moon is depleted in volatile elements relative to the Earth and Mars. Low abundances of volatile elements, fractionated stable isotope ratios of S, Cl, K and Zn, high μ ( 238 U/ 204 Pb) and long-term Rb/Sr depletion are distinguishing features of the Moon, relative to the Earth. These geochemical characteristics indicate both inheritance of volatile-depleted materials that formed the Moon and planets and subsequent evaporative loss of volatile elements that occurred during lunar formation and differentiation. Models of volatile loss through localized eruptive degassing are not consistent with the available S, Cl, Zn and K isotopes and abundance data for the Moon. The most probable cause of volatile depletion is global-scale evaporation resulting from a giant impact or a magma ocean phase where inefficient volatile loss during magmatic convection led to the present distribution of volatile elements within mantle and crustal reservoirs. Problems exist for models of planetary volatile depletion following giant impact. Most critically, in this model, the volatile loss requires preferential delivery and retention of late-accreted volatiles to the Earth compared with the Moon. Different proportions of late-accreted mass are computed to explain present-day distributions of volatile and moderately volatile elements (e.g. Pb, Zn; 5 to >10%) relative to highly siderophile elements (approx. 0.5%) for the Earth. Models of early magma ocean phases may be more effective in explaining the volatile loss. Basaltic materials (e.g. eucrites and angrites) from highly differentiated airless asteroids are volatile-depleted, like the Moon, whereas the Earth and Mars have proportionally greater volatile contents. Parent-body size and the existence of early atmospheres are therefore likely to represent fundamental controls on planetary volatile retention or loss.

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Magnesium stable isotopes support the lunar magma ocean cumulate remelting model for mare basalts

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1811377115 ◽

2018 ◽

Vol 116 (1) ◽

pp. 73-78 ◽

Cited By ~ 7

Author(s):

Fatemeh Sedaghatpour ◽

Stein B. Jacobsen

Keyword(s):

Isotopic Composition ◽

Isotopic Fractionation ◽

The Moon ◽

Magma Ocean ◽

Isotopic Analyses ◽

Lunar Samples ◽

Lunar Basalts ◽

Mg Isotopes ◽

Isotopic Variations ◽

Mare Basalts

We report high-precision Mg isotopic analyses of different types of lunar samples including two pristine Mg-suite rocks (72415 and 76535), basalts, anorthosites, breccias, mineral separates, and lunar meteorites. The Mg isotopic composition of the dunite 72415 (δ25Mg = −0.140 ± 0.010‰, δ26Mg = −0.291 ± 0.018‰), the most Mg-rich and possibly the oldest lunar sample, may provide the best estimate of the Mg isotopic composition of the bulk silicate Moon (BSM). This δ26Mg value of the Moon is similar to those of the Earth and chondrites and reflects both the relative homogeneity of Mg isotopes in the solar system and the lack of Mg isotope fractionation by the Moon-forming giant impact. In contrast to the behavior of Mg isotopes in terrestrial basalts and mantle rocks, Mg isotopic data on lunar samples show isotopic variations among the basalts and pristine anorthositic rocks reflecting isotopic fractionation during the early lunar magma ocean (LMO) differentiation. Calculated evolutions of δ26Mg values during the LMO differentiation are consistent with the observed δ26Mg variations in lunar samples, implying that Mg isotope variations in lunar basalts are consistent with their origin by remelting of distinct LMO cumulates.

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Late-stage magmatic outgassing from a volatile-depleted Moon

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1708236114 ◽

2017 ◽

Vol 114 (36) ◽

pp. 9547-9551 ◽

Cited By ~ 22

Author(s):

James M. D. Day ◽

Frédéric Moynier ◽

Charles K. Shearer

Keyword(s):

Lunar Surface ◽

Upper Mantle ◽

Vapor Condensation ◽

Internal Source ◽

The Moon ◽

Volatile Elements ◽

Lunar Interior ◽

Leaching Experiments ◽

Mare Basalts

The abundance of volatile elements and compounds, such as zinc, potassium, chlorine, and water, provide key evidence for how Earth and the Moon formed and evolved. Currently, evidence exists for a Moon depleted in volatile elements, as well as reservoirs within the Moon with volatile abundances like Earth’s depleted upper mantle. Volatile depletion is consistent with catastrophic formation, such as a giant impact, whereas a Moon with Earth-like volatile abundances suggests preservation of these volatiles, or addition through late accretion. We show, using the “Rusty Rock” impact melt breccia, 66095, that volatile enrichment on the lunar surface occurred through vapor condensation. Isotopically light Zn (δ66Zn = −13.7‰), heavy Cl (δ37Cl = +15‰), and high U/Pb supports the origin of condensates from a volatile-poor internal source formed during thermomagmatic evolution of the Moon, with long-term depletion in incompatible Cl and Pb, and lesser depletion of more-compatible Zn. Leaching experiments on mare basalt 14053 demonstrate that isotopically light Zn condensates also occur on some mare basalts after their crystallization, confirming a volatile-depleted lunar interior source with homogeneous δ66Zn ≈ +1.4‰. Our results show that much of the lunar interior must be significantly depleted in volatile elements and compounds and that volatile-rich rocks on the lunar surface formed through vapor condensation. Volatiles detected by remote sensing on the surface of the Moon likely have a partially condensate origin from its interior.

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Remotely distinguishing and mapping endogenic water on the Moon

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2015.0391 ◽

2017 ◽

Vol 375 (2094) ◽

pp. 20150391 ◽

Cited By ~ 4

Author(s):

Rachel L. Klima ◽

Noah E. Petro

Keyword(s):

Solar Wind ◽

Spatial Distribution ◽

Solar System ◽

The Moon ◽

Testing Hypotheses ◽

Origin And Evolution ◽

Lunar Interior ◽

Geological Features ◽

Insight Into

Water and/or hydroxyl detected remotely on the lunar surface originates from several sources: (i) comets and other exogenous debris; (ii) solar-wind implantation; (iii) the lunar interior. While each of these sources is interesting in its own right, distinguishing among them is critical for testing hypotheses for the origin and evolution of the Moon and our Solar System. Existing spacecraft observations are not of high enough spectral resolution to uniquely characterize the bonding energies of the hydroxyl molecules that have been detected. Nevertheless, the spatial distribution and associations of H, OH − or H 2 O with specific lunar lithologies provide some insight into the origin of lunar hydrous materials. The global distribution of OH − /H 2 O as detected using infrared spectroscopic measurements from orbit is here examined, with particular focus on regional geological features that exhibit OH − /H 2 O absorption band strengths that differ from their immediate surroundings. This article is part of the themed issue ‘The origin, history and role of water in the evolution of the inner Solar System’.

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Solid state convection models of the lunar internal temperature

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1977.0096 ◽

1977 ◽

Vol 285 (1327) ◽

pp. 523-536 ◽

Cited By ~ 26

Keyword(s):

Solid State ◽

Creep Behaviour ◽

The Moon ◽

Internal Temperature ◽

Thermal Models ◽

Lunar Interior

Thermal models of the Moon, which include cooling by subsolidus creep and consideration of the creep behaviour of geologic material, provide estimates of 1500- 1600 K for the temperature, and 10 21-1022 cm2/s for the viscosity of the deep lunar interior.

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