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All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

The origin of KREEP

KREEP is a lunar material having very high concentrations of incompatible elements; its name is an acronym for the incompatibles K, rare-earth elements (REE), and P. Although a few pristine (endogenously igneous) KREEPy samples were returned from the Apollo 15 and 17 sites, most KREEPy samples are polymict breccias. Most models of KREEP petrogenesis have been based on partial melting of a variety of sources. Such models fail to explain the veritable absence of variations in incompatible element patterns over the sampled portion of the moon. We have defined a KREEP component based on the average composition of Apollo 14 breccias having extremely high concentrations of incompatible elements. Normalization of accurate incompatible data for KREEPy samples from the Apollo 12, 14, 15, 16, and 17 sites to this component virtually always shows no resolvable fractionation (e.g., <10% variation in the La/Lu ratio), whereas partial melting models typically produce larger fractionations (±20–25% in La/Lu) from a factor of 2 difference in degree of partial melting. Required is a single major source that could provide KREEP to widely separated locations on the nearside of the moon. The anorthositic crust of the moon is commonly attributed to the flotation of plagioclase on a deep, moon-wide magma ocean. Fractional crystallization of this magma ocean would have produced large enrichments of incompatibles in a residual liquid. No other plausible major source of incompatibles has been proposed. We borrow the German prefix ur—meaning primeval and designate this residual liquid ‘urKREEP.’ We propose that all KREEPy rocks originated by dilution of urKREEP with crustal or mantle materials during assimilation, or zone-refining (pristine samples), or impact-induced brecciation (breccias and melt rocks). The formation of urKREEP cannot be dated precisely. Correction of breccia Rb-Sr model ages for Rb loss or gain during the early intense bombardments yields ages that cluster in the range 4.4–4.5 Gy. This implies that crystallization of the magma ocean was essentially complete at this time and is in general agreement with U-Pb evidence indicating crustal formation at 4.4 Gy. Assuming that the moon had the composition of an H-group chondrite depleted in Fe-Ni and FeS and that half the incompatibles fractionated into materials other than urKREEP, the thickness of a moon-wide urKREEP layer was <2 km. Thorium concentrations determined by gamma ray spectroscopy indicate that about 4% of the incompatibles in an H chondritic moon are now in the outermost kilometer.

Paul H. Warren↗
NASA NTRS1985

Implications of Convection in the Moon and the Terrestrial Planets

The early evolution of the Moon and its implications for the early evolution of the Earth was studied. The study is divided into two parts: (1) studies of core formation. Cosmochemical studies strongly favor a near-homogeneous accretion of the Earth. It is shown that core segregation probably occurred within the first 10,000 years of Earth history. It is found that dissipative heating may be a viable mechanism for core segregation if sufficiently large bodies of liquid iron can form; (2) early thermal evolution of the Earth and Moon. The energy associated with the accretion of the Earth and the segregation of the core is more than sufficient to melt the entire Earth. The increase in the mantle liquidus with depth (pressure) is the dominant effect influencing heat transfer through the magma ocean. It is found that a magma ocean with a depth of 100 km would have existed as the Earth accreted. It is concluded that this magma ocean zone refined the earth resulting in the simultaneous formation of the core and the atmosphere during accretion. The resulting mantle was a well-mixed solid with a near pyrolite composition.

Turcotte, D. L.↗
NASA NTRS1995

A Model for the Thermal and Chemical Evolution of the Moon's Interior: Implications for the Onset of Mare Volcanism

Crystallization of the lunar magma ocean creates a chemically stratified Moon consisting of an anorthositic crust and magma ocean cumulates overlying the primitive lunar interior. Within the magma ocean cumulates the last liquids to crystallize form dense, ilmenite-rich cumulates that contain high concentrations of incompatible radioactive elements. The underlying olivine-orthopyroxene cumulates are also stratified with later crystallized, denser, more Fe-rich compositions at the top. This paper explores the chemical and thermal consequences of an internal evolution model accounting for the possible role of these sources of chemical buoyancy. Rayleigh-Taylor instability causes the dense ilmenite-rich cumulate layer and underlying Fe-rich cumulates to sink toward the center of the Moon, forming a dense lunar core. After this overturn, radioactive heating within the ilmenite-rich cumulate core heats the overlying mantle, causing it to melt. In this model, the source region for high-TiO2 mare basalts is a convectively mixed layer above the core-mantle boundary which would contain small and variable amounts of admixed ilmenite and KREEP. This deep high-pressure melting, as required for mare basalts, occurs after a reasonable time interval to explain the onset of mare basalt volcanism if the content of radioactive elements in the core and the chemical density gradients above the core are sufficiently high but within a range of values that might have been present in the Moon. Regardless of details implied by particular model parameters, gravitational overturn driven by the high density of magma ocean Fe-rich cumulates should concentrate high-TiO2 mare basalt sources, and probably a significant fraction of radioactive heating, toward the center of the Moon. This will have important implications for both the thermal evolution of the Moon and for mare basalt genesis.

Hess, Paul C.↗
NASA NTRS1979

Complex igneous processes and the formation of the primitive lunar crustal rocks

Crystallization of a magma ocean with initial chondritic Ca/Al and REE ratios such as proposed by Taylor and Bence (TB, 1975), is capable of producing the suite of primitive crustal rocks if the magma ocean underwent locally extensive assimilation and mixing in its upper layers as preliminary steps in formation of an anorthositic crust. Lunar anorthosites were the earliest permanent crustal rocks to form the result of multiple cycles of suspension and assimilation of plagioclase in liquids fractionating olivine and pyroxene. There may be two series of Mg-rich cumulate rocks: one which developed as a result of the equilibration of anorthositic crust with the magma ocean; the other which formed in the later stages of the magma ocean during an epoch of magma mixing and ilmenite crystallization. This second series may be related to KREEP genesis. It is noted that crystallization of the magma ocean had two components: a low pressure component which produced a highly fractionated and heterogeneous crust growing downward and a high pressure component which filled in the ocean from the bottom up, mostly with olivine and low-Ca pyroxene.

Longhi, J.↗
NASA NTRS2007

Liquidus Phases of the Richardson H5 Chondrite at High Pressures and Temperatures

Part of early mantle evolution may include a magma ocean, where core formation began before the proto-Earth reached half of its present radius. Temperatures were high and bombardment and accretion were still occurring, suggesting that the proto-Earth consisted of a core and an at least partially liquid mantle, the magma ocean. As the Earth accreted, pressure near the core increased and the magma ocean decreased in volume and became shallower as it began to cool and solidify. As crystals settled, or floated, the composition of the magma ocean could change significantly and begin to crystallize different minerals from the residual liquid. Therefore, the mantle may be stratified following the P-T phase diagram for the bulk silicate Earth. To understand mantle evolution, it is necessary to know liquidus phase relations at high pressures and temperatures. In order to model the evolution of the magma ocean, high pressure and temperature experiments have been conducted to simulate the crystallization process using a range of materials that most likely resemble the bulk composition of the early Earth.

Channon, M.↗
NASA NTRS1980

Early lunar petrogenesis, oceanic and extraoceanic

An attempt is made to ascertain which (if any) pristine nonmare rocks, other than KREEPy ones, are not cumulates from the magma ocean. It is noted that the only pristine rocks having bulk densities low enough to have formed by floating above the magma ocean are the ferroan anorthosites, which are easily recognizable as a discrete subset of pristine rocks in general, on the basis of mineral composition relationships. The other class of pristine nonmare rocks, the Mg-rich rocks, did not form from the same magma that produced the ferroan anorthosites. It is suggested that they were formed in layered noritic-troctolitic plutons. These plutons, it is noted, were apparently intruded at, or slightly above, the boundary between the floated ferroan anorthosite crust and the underlying complementary mafic cumulates. It is thought that the parental magmas of the plutons may have arisen by partial melting of either deep mafic cumulates from the magma ocean or a still deeper, undifferentiated primordial layer that was not molten during the magma ocean period.

Warren, P. H.↗
NASA NTRS1994

Petrogenesis of lunar troctolites

Models of petrogenesis for lunar troctolites are severely constrained by the high Mg(*) (greater than 88) values of the most primitive members of the Mg-rich suite. Melts derived by partial melting of olivine cumulates to the lunar magma ocean have high Mg(*) but are strongly undersaturated with respect to plagioclase. Assimilation of lunar crust cannot bring these melts to the plagioclase liquious without unduly reducing the Mg(*) values of olivine. Partial melts derived by melting a lherzolite primitive interior have higher normative plagioclase contents but require sources with Mg(*) greater than 90. More terrestrial-like Mg(*) (approximately 88) values are permitted if rising thermal plumes are capable of entraining the most Mg-rich cumulates of the magma ocean. The Mg(*) values of lunar troctolites may, therfore, reflect a hybrid source composed of primitive mantle and Mr-rich cumulates of the magma ocean. Higher Mg(*) values may also arise from the reducction of small amounts of FeO to Fe. Alternatively, the parent magmas to lunar troctolites may be impact melts of the anorthositic crust and the Mg-rich dunites cumulates of the magma ocean; the latter were brought to the upper mantle during the overturn of the unstable cumulate pile of the magma ocean.

Hess, Paul C.↗
NASA NTRS2004

Core Formation in the Earth: Constraints from Ni and Co

Due to their metal-loving nature, Ni and Co were strongly partitioned into the metallic core and were left depleted in the silicate mantle during core formation in the Earth. Based on experimental liquid metal- liquid silicate partition coefficients (D), studies have suggested that core formation in an early magma Ocean can explain the observed mantle depletions of Ni and Co [l-51. However, the conditions proposed by the magma ocean models have ranged from pressures of 24 to 59 GPa and temperatures of 2200 to < 4000 K. Furthermore, the proposed magma Ocean oxygen fugacities have differed by nearly two orders of magnitude.Chabot and Agee noted that the different models predicted contradictory behaviors for D(Ni) and D(Co) as a function of temperature. With the hope of resolving the discrepancies between the magma ocean models, we conducted a systematic experimental study to constrain the effects of temperature on D(Ni) and D(Co).

Chabot, N. L.↗
NASA NTRS1985

Thermal structure of the accreting earth

The energy associated with the accretion of the earth and the segregation of the core is more than sufficient to melt the entire earth. In order to understand the thermal evolution of the early earth it is necessary to study the relevant heat transfer mechanisms. In this paper the existence of a global magma ocean is postulated and calculations are carried out of the heat flux through it in order to determine its depth. In the solid mantle heat is transferred by the upward migration of magma. This magma supplies the magma ocean. The increase in the mantle liquidus with depth (pressure) is the dominant effect influencing heat transfer through the magma ocean. It is found that a magma ocean with a depth of the order of 20 km would have existed as the earth accreted. It is concluded that the core segregated and an atmosphere was formed during accretion.

Turcotte, D. L.↗
DOE OSTI2022

The Evolving Chronology of Moon Formation

Defining the age of the Moon has proven to be an elusive task because it requires reliably dating lunar samples using radiometric isotopic systems that record fractionation of parent and daughter elements during events that are petrologically associated with planet formation. Crystallization of the magma ocean is the only event that unambiguously meets this criterion because it probably occurred within tens of millions of years of Moon formation. There are three dateable crystallization products of the magma ocean: mafic mantle cumulates, felsic crustal cumulates, and late-stage crystallization products known as urKREEP (uniform residuum K, rare earth elements, and P). Although ages for these materials in the literature span 200 million years, there is a preponderance of reliable ages around 4.35 billion years recorded in all three lunar rock types. This age is also observed in many secondary crustal rocks, indicating that they were produced contemporaneously (within uncertainty of the ages), possibly during crystallization and overturn of the magma ocean. •The duration of planet formation is key information in understanding the mechanisms by which the terrestrial planets formed. •Ages of the oldest lunar rocks range widely, reflecting either the duration of Moon formation or disturbed ages caused by impact metamorphism. •Ages determined for compositionally distinct crust and mantle materials produced by lunar magma ocean differentiation cluster near 4.35 Gyr. •The repeated occurrence of 4.35 Gyr ages implies that Moon formation occurred late in Solar System history, likely by giant impact into Earth.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2015

Are the Clast Lithologies Contained in Lunar Breccia 64435 Mixtures of Anorthositic Magmas

The anorthositic crust of the Moon is often used as the archtypical example of a primary planetary crust. The abundance and purity of anorthosite in the Apollo sample collection and remote sensing data are generally attributed to an early global magma ocean which produced widespread floating plagioclase cumulates (the ferroan anorthosites; FANs. Recent geochronology studies report evidence of young (less than 4.4 Ga) FAN ages, which suggest that either some may not be directly produced from the magma ocean or that the final solidification age of the magma ocean was younger than previous estimates. A greater diversity of anorthositic rocks have been identified among lunar meteorites as compared to returned lunar samples. Granted that these lithologies are often based on small clasts in lunar breccias and therefore may not represent their actual whole rock composition. Nevertheless, as suggested by the abundance of anorthositic clasts with Mg# [Mg/(Mg+Fe)] less than 0.80 and the difficulty of producing the extremely high plagioclase contents observed in Apollo samples and the remote sensing data, modification of the standard Lunar Magma Ocean (LMO) model may be in order. To ground truth mission science and to further test the LMO and other hypotheses for the formation of the lunar crust, additional coordinated petrology and geochronology studies of lunar anorthosites would be informative. Here we report new mineral chemistry and trace element geochemistry studies of thick sections of a composite of FAN-suite igneous clasts contained in the lunar breccia 64435 in order to assess the significance of this type of sample for petrogenetic studies of the Moon. This work follows recent isotopic studies of the lithologies in 64435 focusing on the same sample materials and expands on previous petrology studies who identified three lithologies in this sample and worked on thin sections.

Simon, J. I.↗
NASA NTRS2010

Conditions of Core Formation in the Early Earth: Single Stage or Heterogeneous Accretion?

Since approx.1990 high pressure and temperature (PT) experiments on metal-silicate systems have showed that partition coefficients [D(met/sil)] for siderophile (iron-loving) elements are much different than those measured at low PT conditions [1,2]. The high PT data have been used to argue for a magma ocean during growth of the early Earth [3,4]. In the ensuing decades there have been hundreds of new experiments carried out and published on a wide range of siderophile elements (> 80 experiments published for Ni, Co, Mo, W, P, Mn, V, Cr, Ga, Cu and Pd). At the same time several different models have been advanced to explain the siderophile elements in Earth's mantle: a) shallow depth magma ocean 25-30 GPa [3,5]; b) deep magma ocean; up to 50 GPa [6,7], and c) early reduced and later oxidized magma ocean [8,9]. Some studies have drawn conclusions based on a small subset of siderophile elements, or a set of elements that provides little leverage on the big picture (like slightly siderophile elements), and no single study has attempted to quantitatively explain more than 5 elements at a time. The purpose of this abstract is to identify issues that have lead to a difference in interpretation, and to present updated predictive expressions based on new experimental data. The resulting expressions will be applied to the siderophile element depletions in Earth's upper mantle.

Righter, Kevin↗
NASA NTRS2022

A Primordial Atmospheric Origin of Hydrospheric Deuterium Enrichment on Mars

The deuterium-to-hydrogen (D/H or 2H/1H) ratio of Martian atmospheric water (~6× standard mean ocean water, SMOW) is higher than that of known sources, requiring planetary enrichment. A recent measurement by NASA’s Mars Science Laboratory rover Curiosity of Hesperian-era (>3 Ga) clays yields a D/H ratio ~3×SMOW, demonstrating that most of the enrichment occurs early in Mars’s history, reinforcing the conclusions of Martian meteorite studies. As on Venus, Mars’s D/H enrichment is widely thought to reflect preferential loss to space of 1H (protium) relative to 2H (deuterium), but both the cause and the global environmental context of large and early hydrogen losses remain to be determined. Here, we apply a recent model of primordial atmosphere evolution to Mars, link the magma ocean of the accretion epoch with a subsequent water-ocean epoch, and calculate the behavior of deuterium for comparison with the observed record. In contrast to earlier works that consider Martian D/H fractionation in atmospheres in which hydrogen reservoirs are present exclusively as H2O or H2, here we consider 2-component (H2O-H2) outgassed atmospheres in which both condensed (H2O) and escaping (H2) components – and their interaction – are explicitly calculated. We find that a a ≈2-3× hydrospheric deuterium-enrichment is produced rapidly if the Martian magma ocean is chemically reducing at last equilibration with the primordial atmosphere, making H2 and CO the initially dominant species, with minor abundances of H2O and CO2. Reducing gases – in particular H2 – can cause substantial greenhouse warming and prevent a water ocean from freezing immediately after the magma ocean epoch. We find that greenhouse warming due to plausible H2 inventories (pH2=1-102 bars) yields surface temperatures high enough (Ts=290-560 K) to stabilize a water ocean and produce an early hydrological cycle through which surface water can be circulated. Moreover, the pressure-temperature conditions are high enough to produce ocean-atmosphere H2O-H2 isotopic equilibrium through gas-phase deuterium exchange such that surface H2O strongly concentrates deuterium relative to H2, which preferentially takes up protium and escapes from the primordial atmosphere. The efficient physical separation of deuterium-rich (H2O) and deuterium-poor (H2) species via condensation permits equilibrium isotopic partitioning and early atmospheric escape to be recorded in modern crustal reservoirs. The proposed scenario of primordial H2-CO-rich outgassing and escape suggests significant durations (>Myr) of chemical conditions on the Martian surface conducive to prebiotic chemistry immediately following magma ocean crystallization.

Mars↗
NASA NTRS2021

The abundances of F, Cl, and H2O in eucrites: Implications for the origin of volatile depletion in the asteroid 4 Vesta

We conducted a petrologic study of apatite within eight unbrecciated, non-cumulate eucrites and two monomict, non-cumulate eucrites. These data were combined with previously published data to quantify the abundances of F, Cl, and H2O in the bulk silicate portion of asteroid 4 Vesta (BSV). Using a combination of apatite-based melt hygrometry/chlorometry and appropriately paired volatile/refractory element ratios, we determined that BSV has 3.0–7.2 ppm F, 0.39–1.8 ppm Cl, and 3.6–22 ppm H2O. The abundances of F and H2O are depleted in BSV relative to CI chondrites to a similar degree as F and H2O in the bulk silicate portion of the Moon. This degree of volatile depletion in BSV is similar to what has been determined previously for many moderately volatile elements in 4 Vesta (e.g., Na, K, Zn, Rb, Cs, and Pb). In contrast, Cl is depleted in 4 Vesta by a greater degree than what is recorded in samples from Earth or the Moon. Based on the Cl-isotopic compositions of eucrites and the bulk rock Cl/F ratios determined in this study, the eucrites likely formed through serial magmatism of a mantle with heterogeneous δ37Cl and Cl/F, not as extracts from a partially crystallized global magma ocean. Furthermore, the volatile depletion and Cl-isotopic heterogeneity recorded in eucrites is likely inherited, at least in part, from the precursor materials that accreted to form 4 Vesta and is unlikely to have resulted solely from degassing of a global magma ocean, magmatic degassing of eucrite melts, and/or volatile loss during thermal metamorphism. Although our results can be reconciled with the past presence of wide-scale melting on 4 Vesta (i.e., a partial magma ocean), any future models for eucrite petrogenesis involving a global magma ocean would need to account for the preservation of a heterogeneous eucrite source with respect to Cl/F ratios and Cl isotopes.

Francis M. Mccubbin↗
NASA NTRS2017

A Model of the Primordial Lunar Atmosphere

We create the first quantitative model for the early lunar atmosphere, coupled with a magma ocean crystallization model. Immediately after formation, the moon's surface was subject to a radiative environment that included contributions from the early Sun, a post-impact Earth that radiated like a mid-type M dwarf star, and a cooling global magma ocean. This radiative environment resulted in a largely Earth-side atmosphere on the Moon, ranging from approximately 10(exp 4) to approximately 10(exp 2) pascals, composed of heavy volatiles (Na and SiO). This atmosphere persisted through lid formation and was additionally characterized by supersonic winds that transported significant quantities of moderate volatiles and likely generated magma ocean waves. The existence of this atmosphere may have influenced the distribution of some moderate volatiles and created temperature asymmetries which influenced ocean flow and cooling. Such asymmetries may characterize young, tidally locked rocky bodies with global magma oceans and subject to intense irradiation.

Moo↗
NASA NTRS2002

Re-Os Isotopic Constraints on the Chemical Evolution and Differentiation of the Martian Mantle

The (187)Re-187Os isotopic systematics of SNC meteorites, thought to be from Mars, provide valuable information regarding the chemical processes that affected the Martian mantle, particularly with regard to the relative abundances of highly siderophile elements (HSE). Previously published data (Birck and Allegre 1994, Brandon et al. 2000), and new data obtained since these studies, indicate that the HSE and Os isotopic composition of the Martian mantle was primarily set in its earliest differentiation history. If so, then these meteorites provide key constraints on the processes that lead to variation in HSE observed in not only Mars, but also Earth, the Moon and other rocky bodies in the Solar System. Processes that likely have an effect on the HSE budgets of terrestrial mantles include core formation, magma ocean crystallization, development of juvenile crust, and the addition of a late veneer. Each of these processes will result in different HSE variation and the isotopic composition of mantle materials and mantle derived lavas. Two observations on the SNC data to present provide a framework for which to test the importance of each of these processes. First, the concentrations of Re and Os in SNC meteorites indicate that they are derived from a mantle that has similar concentrations to the Earth's mantle. Such an observation is consistent with a model where a chondritic late veneer replenished the Earth and Martian mantles subsequent to core formation on each planet. Alternative models to explain this observation do exist, but will require additional data to test the limitations of each. Second, Re-Os isotopic results from Brandon et al. (2000) and new data presented here, show that initial yos correlates with variations in the short-lived systems of (182)Hf- (182)W and (142)Sm-142Nd in the SNC meteorites (epsilon(sub W) and epsilon(sub 142Nd)). These systematics require an isolation of mantle reservoirs during the earliest differentiation history of Mars, and subsequent inefficient mixing between these reservoirs. These data show that models for the origin of isotopic variation for SNC meteorites require at least two long-lived mantle reservoirs, and possibly three. The range in the projected present day gamma(sub Os) of these reservoirs is from -5.4+/-2.6, to +4+/-1. The isotopic systematics of these reservoirs may be linked to development of cumulate crystal piles in a Martian magma ocean and variable amounts of late stage intercumulus melt. In this model, fractional crystallization of olivine and possibly other phases with slightly subchondritic Re/Os, from a solidifying magma ocean, resulted in a lower Re/Os ratio early cumulates, and a resultant low gamma(sub Os). Later cumulates or evolved melts crystallized with higher Re/Os ratios to produce the mantle reservoir(s) with consequent higher gamma(sub Os). Crystallization of the Martian magma ocean followed earliest core formation, as indicated by the correlation of epsilon(sub W) with epsilon(sub 142Nd) and initial gamma(sub Os).

Brandon, Alan D.↗
NASA NTRS2022

Global Hydrogen Abundances on the Lunar Surface

A global map of bulk hydrogen abundances on the Moon is presented. This map was generated using data from the Lunar Prospector Neutron Spectrometer. This map required corrections for variations due to rare-earth elements, and was calibrated to Apollo sample hydrogen abundances. Since neutron-derived measurements sample hydrogen content to a depth of tens of cm, these results provide complementary insights to those provided by studies using spectral reflectance data, which sample depths of order μm. Comparison of these abundances to Apollo sample values suggest that the samples reflect actual hydrogen content on the lunar surface, not dominantly from non-lunar contamination. The average lunar hydrogen abundance is 47 ppm with a systematic uncertainty of ∼10 ppm. This is consistent with bulk hydrogen from solar wind emplacement. A bulk hydrogen enhancement (50–68 ppm) has been identified at the Moon's largest pyroclastic deposit (Aristarchus Plateau), which corroborates prior observations that hydrogen and/or water plays a role in lunar magmatic events. Global data show a correlation between hydrogen and evolved materials rich in incompatible trace elements (i.e., KREEP type rocks), with a hydrogen excess of 14–36 ppm in these materials. Based on this hydrogen enhancement, we estimate a lower-limit water abundance within urKREEP materials (i.e., the final ∼2% of the lunar magma ocean) of 320–820 ppm H2O. This observation implies that water played a role in the original magma-ocean formation and solidification with a lower-limit water content in the original lunar magma ocean of 7–16 ppm or higher.

David J. Lawrence↗
NASA NTRS1991

Lunar ferroan anorthosites and mare basalt sources - The mixed connection

Global overturn of a hot, gravitationally unstable lunar mantle immediately following the solidification of a magma ocean explains several characteristics of lunar petrology. Lunar mare basalt sources are inferred to be depleted in europium and alumina. These depletions are consensually attributed to complementary plagioclase floating from a magma ocean. However, in contrast to the mare basalt source parent magma, the ferroan anorthosite parent magma was more evolved by virtue of its lower Mg/Fe ratio and Ni abundances, although less evolved in its poverty of clinopyroxene constituents, flat rare earth pattern, and lower incompatible element abundances. The europium anomaly in mare sources is inferred to be present at 400 km depth, too deep to have been directly influenced by plagioclase crystallization. Massive overturning of the post-magma ocean mantle would have carried down clinopyroxene, ilmenite, and phases containing fractionated rare earths, europium anomalies, and some heat-producing radionuclides.

Ryder, Graham↗