In the last decade, several studies have reported enrichments of the heavy isotopes of moderately volatile elements in lunar mare basalts. However, the mechanisms controlling the isotope fractionation are still debated and may differ for elements with variable geochemical behaviour. Here, we present a new comprehensive dataset of mass-dependent copper isotope compositions (delta 65Cu) of 30 mare basalts sampled during the Apollo missions. The new delta 65Cu data range from +0.14 %o to +1.28 %o (with the exception of two samples at 0.01 %o and -1.42 %o), significantly heavier than chondrites and the bulk silicate Earth. A comparison with mass fractions of major and trace elements and thermodynamic constraints reveals that Cu isotopic variations within different mare basalt suites are mostly unrelated to fractional crystallisation of silicates or oxides and late-stage magmatic degassing. Instead, we propose that the delta 65Cu average of each suite is representative of the composition of its respective mantle source. The observed differences across geographically and temporally distinct mare basalt suites, suggest that this variation relates to large-scale processes that formed isotopically distinct mantle sources. Based on a Cu isotope fractionation model during metal melt saturation in crystal mush zones of the lunar magma ocean, we propose that distinct delta 65Cu compositions and Cu abundances of mare basalt mantle sources reflect local metal melt-silicate melt equilibration and trapping of metal in mantle cumulates during lunar magma ocean solidification. Differences in delta 65Cu and mass fractions and ratios of siderophile elements between low- and high-Ti mare basalt sources reflect the evolving compositions of both metal and silicate melt during the late cooling stages of the lunar magma ocean.

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.

Elevated water contents in various lunar materials have invigorated the discussion on the volatile content of the lunar interior and on the extent to which the volatile element inventory of lunar magmatic rocks is controlled by volatility and degassing. Abundances of moderately volatile and siderophile elements can reveal insights into lunar processes such as core formation, late accretion and volatile depletion. However, previous assessments relied on incomplete data sets and data of variable quality. Here we report mass fractions of the siderophile volatile elements Cu, Se, Ag, S, Te, Cd, In, and Tl in lunar magmatic rocks, analyzed by state-of-the-art isotope dilution-inductively coupled plasma mass spectrometry. The new data enable us to disentangle distribution processes during the formation of different magmatic rock suites and to constrain mantle source compositions. Mass fractions of Cu, S, and Se in mare basalts and magnesian suite norites clearly correlate with indicators of fractional crystallization. Similar mass fractions and fractional crystallization trends in mafic volcanic and plutonic rocks indicate that the latter elements are less prone to degassing during magma ascent and effusion than proposed previously. The latter processes predominate only for specific elements (e.g., Tl, Cd) and complementary enrichments of these elements also occur in some brecciated highland rocks. A detailed comparison of elements with different affinities to metal or sulfide and gas phase reveals systematic differences between lunar magmatic rock suites. The latter observation suggests a predominant control of the variations of S, Se, Cu, and Ag by mantle source composition instead of late-stage magmatic degassing. New estimates of mantle source compositions of two low-Ti mare basalt suites support the notion of a lunar mantle that is strongly depleted in siderophile volatile elements compared to the terrestrial mantle.(C) 2022 Elsevier B.V. All rights reserved.

The origin of volatile species such as water in the Earth-Moon system is a subject of intense debate but is obfuscated by the poten-tial for volatile loss during the Giant Impact that resulted in the formation of these bodies. One way to address these topics and place constraints on the temporal evolution of volatile components in planetary bodies is by using the observed decay of Rb-87 to Sr-87 because Rb is a moderately volatile element, whereas Sr is much more refractory. Here, we show that lunar highland rocks that crystallized similar to 4.35 billion years ago exhibit very limited ingrowth of Sr-87, indicating that prior to the Moon-forming impact, the impactor commonly referred to as Theia and the proto-Earth both must have already been strongly depleted in volatile elements relative to primitive meteorites. These results imply that 1) the volatile element depletion of the Moon did not arise from the Giant Impact, 2) volatile element distributions on the Moon and Earth were principally inherited from their precursors, 3) both Theia and the proto-Earth probably formed in the inner solar system, and 4) the Giant Impact occurred relatively late in solar system history.

The chemical and isotopic signatures of moderately volatile elements are useful for understanding processes of volatile depletion in planetary formation and differentiation. However, the fractionation factors between gas and melt phases during evaporation that are required to model these planetary volatile depletion processes are still sparse. In this study, twenty heating experiments were conducted in 1 atm gas-mixing furnaces to constrain the behavior of K, Cu, and Zn evaporation and isotopic fractionation from basaltic melts at high temperatures. The temperatures range from 1300 degrees C to 1400 degrees C, and durations are from 2 to 8 days. Oxygen fugacities (fO(2)) range from one log unit below to ten log units above that of the ironwu.stite buffer (IW-1 to IW + 10, corresponding to logfO(2) of -10.7 to -0.68 at 1400 degrees C). The conditions were selected to achieve an evaporation-dominated regime (where timescales of diffusion << evaporation for trace elements) in order to avoid diffusion-limited evaporation. Our results show during evaporation Zn behaved as the most volatile, followed by Cu and then K, regardless of temperature and oxygen fugacity. Partitioning of Zn into spinel layers within experimental capsules, however, has been observed, which has substantial effects on the Zn isotope fractionation factor. Therefore, Zn results are presented but further discussion is excluded. Element loss depends on both temperature and oxygen fugacity, where higher temperatures and lower oxygen fugacities promote evaporation. However, with varying temperature and oxygen fugacity, the kinetic isotopic fractionation factors, a (where, R/R-0 = f(alpha-) (1)), for K and Cu remain constant, thus these factors can be applied to a wider range of conditions than those in this study. The experimentally determined fractionation factors for K, and Cu during evaporation from basaltic melts are 0.9944, and 0.9961, respectively. The fractionation factors for these elements with varying volatilities are significantly larger than the apparent observed fractionation factors, which approach one and are inferred from lunar basalts relative to the Bulk Silicate Earth. This observation suggests near-equilibrium conditions during volatile-element loss from the Moon as the apparent observed fractionation factors of lunar basalts are similar for all three elements. (C) 2021 Elsevier Ltd. All rights reserved.

Eucrite meteorites are early-formed (>4.5 Ga) basaltic rocks that are likely to derive from the asteroid 4 Vesta, or a similarly differentiated planetesimal. To understand trace element and moderately volatile element (MVE) behavior more fully within and between eucrites, a laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) study is reported for plagioclase and pyroxene, as well as fusion crust and vitrophyric materials for ten eucrites. These eucrites span from a cumulate eucrite (Northwest Africa [NWA] 1923) to samples corresponding to Main Group (Queen Alexandra Range 97053, Pecora Escarpment 91245, Cumulus Hills 04049, Bates Nunatak 00300, Lewis Cliff 85305, Graves Nunataks 98098) and Stannern Group (Allan Hills 81001, NWA 1000) compositions, in addition to Elephant Moraine 90020. Along with a range of refractory trace elements, focus was given to abundances of five MVE (K, Zn, Rb, Cs, Pb) to interrogate the volatile abundance distributions in eucrite mineral phases. Modal recombination analyses of the eucrites reveals the important role of accessory phases (zircon, apatite) in some of the incompatible trace element (ITE) distributions, but not for the MVE which, for the phases that were analyzed, are mostly sited within plagioclase (Cs, Rb, K) and pyroxene (Zn, Pb), and are in equilibrium with a parental melt composition for Main Group eucrites. The new data reveal a possible relationship with total refractory ITE enrichment and texture, with the most ITE enriched Stannern Group eucrites examined (NWA 1000, ALHA 81001) having acicular textures and, in the case of ALHA 81001 a young degassing age (-3.7 Ga). Collectively the results suggest that Stannern Group eucrites may be related to anatexis of the eucritic crust by thermal metamorphism, with the heat source possibly coming from impacts. Impact processes do not have a pronounced effect on the abundances of the MVE, where plagioclase, pyroxene, fusion crust, and whole rock compositions of eucrites are all significantly depleted in the MVE, with Zn/Fe, Rb/Ba and K/U similar to lunar rocks. Assessment of eucrite compositions, however, suggests that Vesta has a more heterogeneous distribution of volatile elements and is similarly to slightly less volatile-depleted than the Moon. Phase dependence of the MVE (e.g., Cl in apatite, Zn primarily into spinel and early formed phases, including pyroxene) is likely to influence comparison diagrams where MVE stable isotopes are shown. In the case of delta Cl-37 versus delta Zn-66, metamorphism and impact processes may lead to a decrease in the delta Cl-37 value for a given delta Zn-66 value in eucrites, raising the possibility that late-stage impact and metamorphism had a profound effect on volatile distributions in early planetesimal crusts.(C) 2021 Elsevier Ltd. All rights reserved.

The Apollo 16 'Rusty Rock' impact melt breccia 66095 is a volatile-rich sample, with the volatiles inherited through vapor condensation from an internal lunar source formed during thermo-magmatic evolution of the Moon. We report Cu and Fe isotope data for 66095 and find that bulk-rocks, residues and acid leaches span a relatively limited range of compositions (3.0 +/- 1.3 wt.% FeO [range = 2.0-4.8 wt.%], 5.4 +/- 3.1 ppm Cu [range = 3-12 ppm], average delta Fe-56 of 0.15 +/- 0.05 parts per thousand [weighted mean = 0.156 parts per thousand] and delta Cu-65 of 0.72 +/- 0.14 parts per thousand[weighted mean = 0.78 parts per thousand]). In contrast to the extreme enrichment of the light isotopes of Zn and heavy isotopes of Cl in 66095, delta Fe-56 and delta Fe-56 in the sample lie within the previously reported range for lunar mare basalts (0.92 +/- 0.16 parts per thousand and 0.12 +/- 0.02 parts per thousand, respectively). The lack of extreme isotopic fractionation for Cu and Fe isotopes reflects compositions inherent to 66095, with condensation of a cooling gas from impact-generated fumarolic activity at temperatures too low to lead to the condensation of Cu and Fe in the sample, but higher than required to condense Zn. Together with thermodynamic models, these constraints suggest that the gas condensed within 66095 between 700 and 900 degrees C (assuming a pressure of 10(-6) and an fO(2) of IW-2). That the Cu and Fe isotopic compositions of sample 66095 are within the range of mare basalts removes the need for an exotic, volatile-enriched source. The enrichment in Tl, Br, Cd, Sn, Zn, Pb, Rb, Cs, Ga, B, Cl, Li relative to Bi, Se, Te, Ge, Cu, Ag, Sb, Mn, P, Cr and Fe in the 'Rusty Rock' is consistent with volcanic outgassing models and indicates that 66095 likely formed distal from the original source of the gas. The volatile-rich character of 66095 is consistent with impact-generated fumarolic activity in the region of the Cayley Plains, demonstrating that volatile-rich rocks can occur on the lunar surface from outgassing of a volatile-poor lunar interior. The 'Rusty Rock' indicates that the lunar interior is significantly depleted in volatile elements and compounds and that volatile-rich surface rocks likely formed through vapor condensation. Remote sensing studies have detected volatiles on the lunar surface, attributing them dominantly to solar wind. Based on the 'Rusty Rock', some of these surface volatiles may also originate from the Moon's interior. (C) 2019 Elsevier Ltd. All rights reserved.

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 mu (U-238/Pb-204) 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.