The abundances and isotopic signatures of volatile elements provide critical information for understanding the delivery of water and other essential life-giving compounds to planets. It has been demonstrated that the Moon is depleted in moderately volatile elements (MVE), such as Zn, Cl, S, K and Rb, relative to the Earth. The isotopic compositions of these MVE in lunar rocks suggest loss of volatile elements during the formation of the Moon, as well as their modification during later differentiation and impact processes. Due to its moderately volatile and strongly chalcophile behaviour, copper (Cu) provides a distinct record of planetary accretion and differentiation processes relative to Cl, Rb, Zn or K. Here we present Cu isotopic compositions of Apollo 11, 12, 14 and 15 mare basalts and lunar basaltic meteorites, which range from delta 65Cu of +0.55 +/- 0.01 %o to +3.94 +/- 0.04 %o (per mil deviation of the 65Cu/63Cu from the NIST SRM 976 standard), independent of mare basalt Ti content. The delta 65Cu values of the basalts are negatively correlated with their Cu contents, which is interpreted as evidence for volatile loss upon mare basalt emplacement, plausibly related to the presence Cl- and S-bearing ligands in the vapour phase. This relationship can be used to determine the Cu isotopic composition of the lunar mantle to a delta 65Cu of +0.57 +/- 0.15 %o. The bulk silicate Moon (BSM) is 0.5%o heavier than the bulk silicate Earth (+0.07 +/- 0.10 %o) or chondritic materials (from -1.45 +/- 0.08 %o to 0.07 +/- 0.06 %o). Owing to the ineffectiveness of sulfide segregation and lunar core formation in inducing Cu isotopic fractionation, the isotopic difference between the Moon and the Earth is attributed to volatile loss during the Moon-forming event, which must have occurred at- or nearequilibrium.

Space weathering alters the surface materials of airless planetary bodies; however, the effects on moderately volatile elements in the lunar regolith are not well constrained. For the first time, we provide depth profiles for stable K and Fe isotopes in a continuous lunar regolith core, Apollo 17 double drive tube 73001/2. The top of the core is enriched in heavy K isotopes (delta 41K = 3.48 +/- 0.05 parts per thousand) with a significant trend toward lighter K isotopes to a depth of 7 cm; while the lower 44 cm has only slight variation with an average delta 41K value of 0.15 +/- 0.05 parts per thousand. Iron, which is more refractory, shows only minor variation; the delta 56Fe value at the top of the core is 0.16 +/- 0.02 parts per thousand while the average bottom 44 cm is 0.11 +/- 0.03 parts per thousand. The isotopic fractionation in the top 7 cm of the core, especially the K isotopes, correlates with soil maturity as measured by ferromagnetic resonance. Kinetic fractionation from volatilization by micrometeoroid impacts is modeled in the double drive tube 73001/2 using Rayleigh fractionation and can explain the observed K and Fe isotopic fractionation. Effects from cosmogenic 41K (from decay of 41Ca) were calculated and found to be negligible in 73001/2. In future sample return missions, researchers can use heavy K isotope signatures as tracers of space weathering effects.

Volcanic products returned from the Apollo missions over 50 years ago provide a unique perspective into the magmatic evolution of the Moon. However, questions remain regarding the volatile loss, crystallization, and emplacement histories of lunar lavas. To address gaps in our understanding of the eruptive histories of lunar lavas, we investigate phase chemistry and 3D morphologies of low-titanium Apollo 15 basalts belonging to the olivine-normative and quartz-normative suites. We report the 2D and 3D petrography, mineral chemistry, and 3D void space morphologies of 15499, 15555, 15556, and the lesser studied 15495 and 15608 basalts. Quantitative apatite chemistry shows a wide range of apatite volatile compositions and that low-Ti basalt 15495 may contain the most OH-rich compositions measured from the Moon. Analyses of metal grains within the low-Ti basalts have expanded the field of expected Ni and Co metal concentrations for Apollo 15 mare basalts and are used to determine the petrogenesis of two of the studied samples. Coupling 2D chemistry with nondestructive 3D morphologic analyses provides critical insights on the relative timing of volatile exsolution in low-titanium lavas. Through the analysis of vesicles and vugs from X-ray computed tomographic data, we report the first 3D void space volume percentages for a suite of low-Ti basalts and show that these basalts degassed before the onset of mesostasis (e.g., apatite) crystallization. We use calculated cooling rates and 3D morphologic analyses to show that the studied basalts crystallized at various depths in separate lava flows, and 15608 represents the quenched margin of a mare flow. Our work highlights the value of combining 2D and 3D analytical techniques to study the emplacement history of basalts that lack geological context.

The lunar surface exhibits an absorption band near 3 mu m due to hydration, either water or hydroxyl. In most analyses, the band is variable at least in latitude and temperature. Hypotheses for the variability include infilling of the band by thermal emission, migration of molecular water along temperature gradients, and formation and destruction of metastable hydroxyl as solar wind hydrogen diffuses through lunar surface grains. The degree to which lunar soil exhibits an inherent hydration feature in the absence of environmental influences is an open question. The recent opening of Apollo core sample 73001 that was sealed in vacuum on the lunar surface and curated in dry nitrogen since its return from the Moon affords an opportunity to determine if lunar soil exhibits a spectral feature due to hydration isolated from the lunar environment. To that end, near the close of dis of the core into samples for allocation to the lunar science community, we introduced an infrared spectrometer into the nitrogen purged curation cabinet and collected reflectance spectra of portions of the core between 2 and 4 mu m. We found no evidence of absorption due to hydration to 1.1% band depth uncertainty. The measurements were relative to a diffuse aluminum standard, which itself could possibly absorb light at 3 mu m due to a thin film of water; we estimate a possible negative bias of about 50 mu g/g equivalent water absorption, leading to a final estimate of core water abundance of 50 mu g/g +/- 50 mu g/g. This finding does not contradict prior estimates of lunar surface hydration as core sample 73001 is immature and may not have had sufficient opportunity to gather enough hydrogen from the solar wind or water from micrometeorites to form detectable hydration. After exposure of the core to laboratory atmosphere, a strong 3 mu m absorption developed, equivalent to over 1,000 mu g/g at a rate of about 5 mu g/g per minute, illustrating the sensitivity of lunar materials to water contamination, and the effectiveness of curation of the sample.

We report the occurrence of a previously unidentified mineral in lunar samples: a Cl-,F-,REE-rich silico-phosphate identified as Cl-bearing fluorcalciobritholite. This mineral is found in late-stage crystallization assemblages of slowly cooled high-Ti basalts 10044, 10047, 75035, and 75055. It occurs as rims on fluorapatite or as a solid-solution between fluorapatite and Cl-fluorcalciobritholite. The Cl-fluorcalciobritholite appears to be nominally anhydrous. The Cl and Fe2+ of the lunar Cl-fluorcalciobritholite distinguishes it from its terrestrial analog. The textures and chemistry of the Cl-fluorcalciobritholite argue for growth during the last stages of igneous crystallization, rather than by later alteration/replacement by Cl-, REE-bearing metasomatic agents in the lunar crust. The igneous growth of this Cl- and F-bearing and OH-poor mineral after apatite in the samples we have studied suggests that the Lunar Apatite Paradox model (Boyce et al. 2014) may be inapplicable for high-Ti lunar magmas. This new volatile-bearing mineral has important potential as a geochemical tool for understanding Cl isotopes and REE chemistry of lunar samples.

The isotopes of chlorine (Cl-37 and Cl-35) are highly fractionated in lunar samples compared to most other Solar System materials. Recently, the chlorine isotope signatures of lunar rocks have been attributed to large-scale degassing processes that occurred during the existence of a magma ocean. In this study we investigated how well a suite of lunar basalts, most of which have not previously been analyzed, conform to previous models. The Cl isotope compositions (delta Cl-37 (parts per thousand) = [(Cl-37/Cl-35(sample)/Cl-37/Cl-35(SMOC)) - 1] x 1000, where SMOC refers to standard mean ocean chloride) recorded range from similar to+7 to +14 parts per thousand (Apollo 15), +10 to +19 parts per thousand (Apollo 12), +9 to +15 parts per thousand (70017), +4 to +8 parts per thousand (MIL 05035), and +15 to +22 parts per thousand (Kalahari 009). The Cl isotopic data from the present study support the mixing trends previously reported by Boyce et al. (2015) and Barnes et al. (2016), as the Cl isotopic composition of apatites are positively correlated with bulk-rock incompatible trace element abundances in the low-Ti basalts, inclusive of low-Ti and KREEP basalts. This trend has been interpreted as evidence that incompatible trace elements, including Cl, were concentrated in the urKREEP residual liquid of the lunar magma ocean, rather than the mantle cumulates, and that urKREEP Cl had a highly fractionated isotopic composition. The source regions for the basalts were thus created by variable mixing between the mantle (Cl-poor and relatively unfractionated) and urKREEP. The high-Ti basalts show much more variability in measured Cl isotope ratios and scatter around the trend formed by the low-Ti basalts. Most of the data for lunar meteorites also fits the mixing of volatiles in their sources, but Kalahari 009, which is highly depleted in incompatible trace elements, contains apatites with heavily fractionated Cl isotopic compositions. Given that Kalahari 009 is one of the oldest lunar basalts and ought to have been derived from very early-formed mantle cumulates, a heavy Cl isotopic signature is likely not related to its mantle source, but more likely to magmatic or secondary alteration processes, perhaps via impact-driven vapor metasomatism of the lunar crust. (C) 2019 The Authors. Published by Elsevier Ltd.

We present reaction balancing and thermodynamic modeling based on microtextural observations and mineral chemistry, to constrain the history of phosphate crystallization within two lunar mare basalts, 10003 and 14053. Phosphates are typically found within intercumulus melt pockets (mesostasis), representing the final stages of basaltic crystallization. In addition to phosphates, these pockets typically consist of Fe-rich clinopyroxene, fayalite, plagioclase, ilmenite, SiO2, and a residual K-rich glass. Some pockets also display evidence for unmixing into two immiscible melts: A Si-K-rich and an Fe-rich liquid. In these cases, the crystallization sequence is not always clear. Despite petrologic complications associated with mesostasis pockets (e.g., unmixing), the phosphates (apatite and merrillite) within these areas have been recently used for constraining the water content in the lunar mantle. We compute mineral reaction balancing for mesostasis pockets from Apollo high-Ti basalt 10003 and high-Al basalt 14053 to suggest that their parental magmas have an H2O content of 25 +/- 10 ppm, consistent with reported estimates based on directly measured H2O abundances from these samples. Our results permit to constrain in which immiscible liquid a phosphate of interest crystallizes, and allows us to estimate the extent to which volatiles may have partitioned into other phases such as K-rich glass or surrounding clinopyroxene and plagioclase using a non-destructive method.

Compared to most other planetary materials in the Solar System, some lunar rocks display high delta Cl-37 signatures. Loss of Cl in a H << Cl environment has been invoked to explain the heavy signatures observed in lunar samples, either during volcanic eruptions onto the lunar surface or during large scale degassing of the lunar magma ocean. To explore the conditions under which Cl isotope fractionation occurred in lunar basaltic melts, five Apollo 14 crystalline samples were selected (14053,19, 14072,13, 14073,9, 14310,171 along with basaltic clast 14321,1482) for in situ analysis of Cl isotopes using secondary ion mass spectrometry. Cl isotopes were measured within the mineral apatite, with delta Cl-37 values ranging from +14.6 +/- 1.6 parts per thousand to +40.0 +/- 2.9 parts per thousand. These values expand the range previously reported for apatite in lunar rocks, and include some of the heaviest Cl isotope compositions measured in lunar samples to date. The data here do not display a trend between increasing rare earth elements contents and delta Cl-37 values, reported in previous studies. Other processes that can explain the wide inter- and intra-sample variability of delta Cl-37 values are explored. Magmatic degassing is suggested to have potentially played a role in fractionating Cl isotope in these samples. Degassing alone, however, could not create the wide variability in isotopic signatures. Our favored hypothesis, to explain small scale heterogeneity, is late-stage interaction with a volatile-rich gas phase, originating from devolatilization of lunar surface regolith rocks similar to 4 billion years ago. This period coincides with vapor-induced metasomastism recorded in other lunar samples collected at the Apollo 16 and 17 landing sites, pointing to the possibility of widespread volatile-induced metasomatism on the lunar nearside at that time, potentially attributed to the Imbrium formation event. (C) 2018 Elsevier Ltd. All rights reserved.

Recent geochemical and geophysical data from the Moon enable a revision of earlier interpretations regarding lunar origin, structure and bulk composition. Earth and Moon show many similarities among their isotopic compositions, but they have evolved in totally dissimilar ways, probably related to the deficiency of water and volatile elements in the Moon as well as the vast differences in size and internal pressure. Some global geochemical differences from the Earth such as volatile depletion based on K/U ratios have been established. However, all current lunar samples come from differentiated regions, making the establishment of a bulk composition more reliant on bulk geophysical properties or isotopic similarities; it remains unclear how the latter arose or relate to whole Moon composition. The lack of fractionation effects among the refractory and super-refractory elements indicates that the proto-lunar material seems unlikely to have been vaporized while the presence of volatile elements may place lower limits on proto-lunar temperatures. The apparent lack of geochemical evidence of an impacting body enables other possible impactors, such as comets, to be considered. Although the origin of the Moon remains currently unknown, it is generally believed that the Moon originated as the result of a giant impact on the Earth.

In the last decade, it has been recognized that the Moon contains significant proportions of volatile elements (H, F, Cl), and that they are transported through the lunar crust and across its surface. Here, we document a significant segment of that volatile cycle in lunar granulite breccia 79215: impact-induced remobilization of volatiles, and vapor-phase transport with extreme elemental fractionation. 79215 contains similar to 1% volume of fluorapatite, Ca-5(PO4)(3)(F,Cl,OH), in crystals to 1 mm long, which is reflected in its analyzed abundances of F, Cl, and P. The apatite has a molar F/Cl ratio of similar to 10, and contains only 25 ppm OH and low abundances of the rare earth elements (REE). The chlorine in the apatite is isotopically heavy, at delta Cl-37 = +32.7 +/- 1.6 parts per thousand. Hydrogen in the apatite is heavy at delta D = +1060 +/- 180 parts per thousand.; much of that D came from spallogenic nuclear reactions, and the original delta D was lower, between +350 parts per thousand and +700 parts per thousand. Unlike other P-rich lunar rocks (e.g., 65015), 79215 lacks abundant K and REE, and other igneous incompatible elements characteristic of the lunar KREEP component. Here, we show that the P and halogens in 79215 were added to an otherwise normal granulite by vapor-phase metasomatism, similar to rock alteration by fumarolic exhalations as observed on Earth. The ultimate source of the P and halogens was most likely KREEP, it being the richest reservoir of P on the Moon, and 79215 having H and Cl isotopic compositions consistent with KREEP. A KREEP-rich rock was heated and devolatilized by an impact event. This vapor was fractionated by interaction with solid phases, including merrillite (a volatile-free phosphate mineral), a Fe-Ti oxide, and a Zr-bearing phase. These solids removed REE, Th, Zr, Hf, etc., from the vapor, and allowed the vapor to transport primarily P, F, and Cl, with lesser proportions of Ba and U into 79215. Vapor-deposited crystals of apatite (to 30 mu m) are known in some lunar regolith samples, but lunar vapor has not (before this) been implicated in significant mass transfer. It seems unlikely, however, that phosphate-halogen metasomatism is related to the high-Th/Sm abundance ratios of this and other lunar magnesian granulites. The metasomatism of 79215 emphasizes the importance of impact heating in the lunar volatile cycle, both in mobilizing volatile components into vapor and in generating strong elemental fractionations.