Geochemical constraints on the origin of the Moon

doi:10.1016/0016-7037(83)90024-8

Geochimica et Cosmochimica Acta

Volume 47, Issue 10, October 1983, Pages 1759-1767

https://doi.org/10.1016/0016-7037(83)90024-8 Get rights and content

Abstract

Hypotheses for the origin of the Moon involve variants on capture, double-planet, and fission processes. Double-planet and fission hypotheses are examined in the light of siderophile trace elements. The siderophile trace elements chosen (W, Re, Mo, P, Ga, Ge) have well understood geochemical behavior such that appropriate metal/silicate partition coefficients are available and their abundances in the lunar and terrestrial mantles 4.4–4.5 × 10⁹ years ago may be reasonably inferred. The fission hypothesis of Ringwood (1979) is not consistent with the behavior of Re, Mo, and P. The hybrid fission hypothesis of Wankeet al. (1983) overcomes many of the deficiencies of ringwood's hypothesis, but is not readily reconcilable with the behavior of Re and Ir. The double-planet hypothesis as most recently advanced by Newsom and Drake (1982, 1983) appears to be consistent with siderophile element behavior in the Moon.

References (62)

E. Anders et al.
Solar system abundances of the elements
Geochim. Cosmochim. Acta
(1982)
R.J. Arculus et al.
Intrinsic oxygen fugacity measurements: techniques and results for spinels from upper mantle peridotites and megacryst assemblages
Geochim. Cosmochim. Acta
(1981)
R. De Argollo et al.
Ge-Si and Ga-Al fractionation in Hawaiian volcanic rocks
Geochim. Cosmochim. Acta
(1978)
J. Hertogen et al.
Trace elements in ocean ridge basalt glasses: implications for fractionations during mantle evolution and petrogenesis
Geochim. Cosmochim. Acta
(1980)
G.W. Kallemeyn et al.
The compositional classification of chondrites—I. The carbonaceous chondrite groups
Geochim. Cosmochim. Acta
(1981)
K. Kimura et al.
Distribution of gold and rhenium between nickel-iron and silicate melts: implications for the abundance of siderophile elements on the Earth and Moon
Geochim. Cosmochim. Acta
(1974)
H.E. Mitler
Formation of an iron-poor Moon by partial capture, or: yet another exotic theory of lunar origin
Icarus
(1975)
J.W. Morgan et al.
A “chondritic” eucrite parent body: inference from trace elements
Geochim. Cosmochim. Acta
(1978)
H.E. Newsom et al.
Experimental investigation of the partitioning of phosphorus between metal and silicate phases: implications for the Earth, Moon and eucrite parent body
Geochim. Cosmochim. Acta
(1983)
H. Palme et al.
A metal particle from a Ca, Al-rich inclusion from the meteorite Allende and the condensation of refractory siderophile elements
Earth Planet. Sci. Lett.
(1976)

T. Staudacher et al.

Terrestrial Xenology

Earth Planet. Sci. Lett.

(1982)

S.J. Weidenschilling

Iron/silicate fractionation and the origin of Mercury

Icarus

(1978)

E. Anders

Procrustean science: indigenous siderophiles in the lunar highlands, according to Delano and Ringwood

E. Anders et al.

Volatile and siderophile elements in lunar rocks: comparison with terrestrial and meteoritic basalts

P.A. Baedecker et al.

Trace element studies of rocks and soils from Oceanus Procellarum and Mare Tranquillitatis

Basaltic Volcanism Study Project

Basaltic Volcanism on the Terrestrial Planets

T.J. Bernatowicz et al.

Noble gas component organization in 14301

A.O. Brunfelt et al.

Determination of 40 elements in Apollo 12 materials by neutron activation analysis

M. Caffee et al.

Troctolite 76535: a study in the preservation of early isotopic records

C.-L. Chou

Comparison of siderophile element fractionation in terrestrial and lunar rocks

Meteoritics

(1982)

C.-L. Chou et al.

Siderophile trace elements in the Earth's oceanic crust and upper mantle

J. Geophys. Res.

(1983)

R.N. Clayton et al.

Genetic relations between the Moon and meteorites

J.W. Delano et al.

Siderophile elements in the lunar highlands: nature of indigenous component and implications for the origin of the Moon

M.J. Drake et al.

Partitioning of Re between metal and silicate phases

Meteoritics

(1983)

M.J. Drake et al.

Experimental determination of the partitioning of gallium between metal and silicate: electron and ion probe study

G. Dreibus et al.

Composition of the Shergotty parent body: further evidence of a two-component model

R. Ganapathy et al.

Trace elements in Apollo 11 lunar rocks: implications for meteorite influx and origin of Moon

P.W. Gast et al.

Chemical composition and petrogenesis of basalts from Tranquility Base

G.G. Goles et al.

Elemental abundances by instrumental activation analyses in chips from 27 lunar rocks

G.G. Goles et al.

Analyses of Apollo 12 specimens: compositional variations, differentiation processes and lunar soil mixing models

L. Grossman et al.

Early chemical history of the solar system

Revs. Geophys. Space Phys.

(1974)

Cited by (15)

Lunar core formation: New constraints from metal-silicate partitioning of siderophile elements
2014, Earth and Planetary Science Letters
Citation Excerpt :
Fig. 1 shows the resulting estimated levels of siderophile element depletion in the lunar mantle due to core formation, based on values from (Walter et al., 2000; Delano, 1986; Righter and Drake, 1996; Newsom and Taylor, 1989; Drake, 1987; Jones and Palme, 2000). In general, the lunar mantle is depleted in siderophile elements relative to the Earthʼs mantle (Drake, 1983; Newsom 1984, 1986). The lunar mantle depletion in the weakly siderophile elements V and Cr is considered to be very similar to the terrestrial mantle depletions of these elements (Dreibus and Wänke, 1979).
Analyses of Apollo era seismograms, lunar laser ranging data and the lunar moment of inertia suggest the presence of a small, at least partially molten Fe-rich metallic core in the Moon, but the chemical composition and formation conditions of this core are not well constrained. Here, we assess whether pressure–temperature conditions can be found at which the lunar silicate mantle equilibrated with a Fe-rich metallic liquid during core formation. To this end, we combine measurements of the metal–silicate partitioning behavior of siderophile elements with the estimated depletion due to core formation in those elements in the silicate mantle of the Moon. We also explore how the presence of the light element sulfur (suggested by seismic models to be present in the core at concentrations of up to 6 wt%) in the lunar core affects core formation models.
We use published metal–silicate partitioning data for Ni, Co, W, Mo, P, V and Cr in the lunar pressure range (1 atm–5 GPa) and characterize the dependence of the metal/silicate partition coefficients (D) on temperature, pressure, oxygen fugacity and composition of the silicate melt and the metal. If the core is assumed to consist of pure iron, core–mantle equilibration conditions that best satisfy lunar mantle depletions of five siderophile elements—Ni, Co, W, Mo and P—are a pressure of $4.5 (\pm 0.5) GPa$ and a temperature of 2200 K. The lunar mantle depletions of Cr and V are also consistent with metal–silicate equilibration in this pressure and temperature range if 6 wt% S is incorporated into the lunar core. Our results therefore suggest that metal–silicate equilibrium during lunar core formation occurred at depths close to the present-day lunar core–mantle boundary. This provides independent support for both the existence of a deep magma ocean in the Moon in its early history and the presence of significant amounts of sulfur in the lunar core.
Comparative geochemistry of basalts from the moon, earth, HED asteroid, and mars: Implications for the origin of the moon
2001, Geochimica et Cosmochimica Acta
Most hypotheses for the origin of the Moon (rotational fission, co-accretion, and collisional ejection from the Earth, including “giant impact”) call for the formation of the Moon in a geocentric environment. However, key geochemical data for basaltic rocks from the Moon, Earth, the howardite-eucrite-diogenite (HED) meteorite parent body (probably asteroid 4-Vesta), and the shergottite-nakhlite-chassignite (SNC) meteorite parent body (likely Mars), provide no evidence that the Moon was derived from the Earth, and suggest that some objects with lunar-like compositions were produced without involvement of the Earth. The source region compositions of basalts produced in the Moon (mare basalts) were similar to those produced in the HED asteroid (eucrites) with regard to volatile-lithophile elements (Na, K, Rb, Cs, and Tl), siderophile elements (Ni, Co, Ga, Ge, Re, and Ir), and ferromagnesian elements (Mg, Fe, Cr, and V), and less similar to those in the Earth or Mars. Mare and eucrite basalts differ in their Mn abundances, Fe/Mn values, and isotopic composition, suggesting that the Moon and HED asteroid formed in different nebular locations. However, previous claims that the Moon and HED parent body differ significantly in the abundances of some elements, such as Ni, Co, Cr, and V, are not supported by the data. Instead, Cr-Mg-Fe-Ni-Co abundance systematics suggest a close similarity between the source region compositions and conditions involved in producing mare and eucrite basalts, and a significant difference from those of terrestrial basalts. The data imply that the Moon and HED asteroid experienced similar volatile-element depletion and similar fractionation of metallic and mafic phases. Among hypotheses of lunar origin, rotational fission, and small-impact collisional ejection seem less tenable than co-accretion, capture, or a variant of giant-impact collisional ejection in which the Moon inherits the composition of the impactor. Both the Moon and HED asteroid may have been derived from a class of objects that were common in the early solar system. “The most plausible model for the origin of the Moon in line with geochemical and cosmochemical constraints is an impact-induced “fission” of the proto-Earth.” —Wänke and Dreibus (1986) “Clearly, the Moon and eucrite parent body resemble each other to a high degree. Nature produced such a composition not once but at least twice. This calls into question an entire class of models that invoke ad hoc processes to explain the Moon by a unique chance event.” —Anders (1977) “The similarity between eucrites and lunar mare basalts are remarkable. Were it not for the differences in age and oxygen-isotope signature, it might be difficult to distinguish them on petrological or geochemical grounds.” —Taylor (1986)
Rubidium and cesium in the Earth and the Moon
1993, Geochimica et Cosmochimica Acta
The volatility of the alkali elements makes them potential tracers of high-temperature geochemical processes. Specifically, the abundances of Rb and Cs in the silicate portions of the Earth and the Moon may be used to evaluate theories of lunar origin which involve energetic events and, hence, high temperatures. In particular, theories which involve derivation of the Moon substantially from the Earth's mantle immediately following terrestrial core formation predict that the Moon would have a higher $Rb Cs$ ratio than the silicate portion of the Earth. Determining $Rb Cs$ ratios existing 4.5 Ga ago is complicated by differentiation and alteration processes. In general, ancient terrestrial “basaltic” rocks have lower $Rb Cs$ ratios than modern MORE and OIB. This apparent secular change is plausibly attributed to low-grade metamorphism and exchange of Rb and Cs with the surrounding crust. An acceptable mass balance for the alkalis appears to be provided by the continental crust ( $Rb Cs ~ 25$ ), MORB mantle ( $Rb Cs ~ 80$ ), and OIB mantle ( $Rb Cs ~ 80$ ). Presently, these are the only major reservoirs of Rb and Cs that have been well characterized. Since only 50% of the Rb resides in the continental crust, the silicate portion of the Earth must have a $Rb Cs$ ratio between 25 and 80. We conclude that the bulk Earth has a $Rb Cs$ ratio 1.5× that of the continental crust, ~ 40. Lunar mare basalts have $Rb Cs$ ratios of about 20, whereas lunar terrae rocks have lower $Rb Cs$ ratios. The Moon appears to have a $Rb Cs$ ratio between 15 and 20. The $Rb Cs$ ratio of the Moon is lower than the silicate portion of the Earth, contrary to the prediction of theories which derive the Moon entirely from the Earth. For the giant impact hypothesis to be correct, there have been alkali element contributions to the Moon from other sources (e.g., the impactor). Depending on the Earth's contribution to the mass of the Moon, these additional sources of alkalis must have had a combined $Rb Cs$ ratio comparable to or lower than that of the Moon.
V, Cr, and Mn in the Earth, Moon, EPB, and SPB and the origin of the Moon: Experimental studies
1989, Geochimica et Cosmochimica Acta
The abundances of V, Cr, and Mn inferred for the mantles of the Earth and Moon decrease in that order and are similar, but are distinct from those inferred for the mantles of the Eucrite Parent Body (EPB) and Shergottite Parent Body (SPB). This similarity between Earth and Moon has been used to suggest that the Moon is derived substantially or entirely from Earth mantle material following terrestrial core formation. To test this hypothesis, we have determined the partitioning of V, Cr, and Mn between solid iron metal, S-rich metallic liquid, and synthetic basaltic silicate liquid at 1260°C and one bar pressure. The sequence of compatibility in the metallic phases is Cr > V > Mn at “high” oxygen fugacity (just below the iron-wüstite buffer) and V > Cr > Mn at low oxygen fugacities. Solubilities in liquid metal always exceed solubilities in solid metal. These partition coefficients suggest that the abundances of V, Cr, and Mn do not reflect core formation in the Earth. Rather, they are consistent with the relative volatilities of these elements. The similarity in the depletion patterns of V, Cr, and Mn inferred for the mantles of the Earth and Moon is a necessary, but not sufficient, condition for the Moon to have been derived wholly or in part from the Earth's mantle.
Experimental determination of crystal/melt partitioning of Ga and Ge in the system forsterite-anorthite-diopside
1987, Geochimica et Cosmochimica Acta
The crystal/liquid partitioning of Ga and Ge has been measured experimentally between forsterite, diopside, anorthite and spinel and melts in the pseudoternary system forsterite-anorthite-diopside at one atmosphere pressure and 1300°C. Gallium is incompatible with forsterite and diopside [D (Ga) = 0.024 and 0.19, respectively], is only slightly incompatible in anorthite [D (Ga) = 0.86] and is highly compatible in spinel [D (Ga) = 4.6]. The partition coefficient for Ge is within a factor of two of unity for forsterite, diopside and anorthite [D (Ge) = 0.62, 1.4 and 0.51, respectively], but Ge is incompatible in spinel [D (Ge) = 0.1]. The coefficients for the exchange of Ga and Al and the exchange of Ge and Si between minerals and melts generally are within a factor of two of unity, as is expected from the geochemical coherence of these element pairs in natural samples. The application of our results to the interpretation of natural basaltic and mantle samples from the Earth and basalts from the Moon and the Shergottite Parent Body demonstrates that it is possible to discriminate between different mantle source compositions using Ga/Al and Ge/Si ratios. The Ge variation among lunar mare basalts may be indicative of a heterogeneous lunar mantle. The substantial depletion of Ge in Chassigny relative to the other SNC meteorites may be evidence of either a heterogeneous Shergottite Parent Body (SPB) mantle, or of different geochemical behavior for Ge in the SPB.
The unique lunar composition and its bearing on the origin of the Moon
1987, Geochimica et Cosmochimica Acta
The noble gas abundance patterns of Earth, Venus and Mars suggest that accretion of the terrestrial planets took place after the loss of H and He from the inner solar nebula. Since most meteorites also have noble gas patterns which differ from “solar” abundances, such dispersal must have occurred close to T₀ (4.55 Ae). An initial depletion of volatile elements, as shown by low $K U$ ratios of the inner planets, is ascribed to the same time. This depletion of volatiles occurred out to a “snow line” around 5 A.U.
Formation of the inner planets, through accretion of planetesimals in a gas-free environment, occurred on timescales of 10⁷–10⁸ years. Large bodies (100 Moon-sized, 10 Mercury-sized and several Mars-sized objects) characterised the later stages of planetesimal sweep-up. Over 50% of the mass of the Earth may have previously existed and have undergone metal-silicate fractionation in these large precursor objects. Evidence for the existence of massive planetesimals comes from the obliquities of the planets and the slow retrograde motion of Venus.
The Moon has a unique composition among satellites and planets. It is strongly depleted in the very volatile elements (e.g. Bi, Tl) by factors of several hundred relative to the solar nebula. FeO values of 13% in the bulk moon contrast with 36% in CI and 8% in the terrestrial mantle. Trace siderophile elements are depleted in order of their metal-silicate partition coefficients, consistent with their removal into a small lunar core. There is a probable enrichment of refractory elements (e.g. Ca, Al, Ti, REE, U, Th) based on geochemical balance considerations, heat flow, the presence of a thick aluminous crust, and the need to satisfy seismic velocity profiles. A major part of the Moon was molten shortly after accretion, followed by extensive differentiation.
Capture, fission or double planet hypotheses for the origin of the Moon all fail to account for the chemical and dynamical problems, including the anomalously high angular momentum of the Earth-Moon system. Only the impact of a massive Mars-sized (>0.1 Earth mass) planetesimal appears adequate to account for both chemical and dynamical aspects. Ejection of a portion of the mantle of the impactor at least partly in a vapor phase accounts for the extreme depletion in volatile elements. The large impactor hypothesis appears to be the only current hypothesis which accounts for the singular composition of the Moon and the unique nature of the Earth-Moon system.

View all citing articles on Scopus

View full text

Geochemical constraints on the origin of the Moon

Abstract

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Icarus

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Icarus

Procrustean science: indigenous siderophiles in the lunar highlands, according to Delano and Ringwood

Volatile and siderophile elements in lunar rocks: comparison with terrestrial and meteoritic basalts

Trace element studies of rocks and soils from Oceanus Procellarum and Mare Tranquillitatis

Basaltic Volcanism on the Terrestrial Planets

Noble gas component organization in 14301

Determination of 40 elements in Apollo 12 materials by neutron activation analysis

Troctolite 76535: a study in the preservation of early isotopic records

Comparison of siderophile element fractionation in terrestrial and lunar rocks

Meteoritics

Siderophile trace elements in the Earth's oceanic crust and upper mantle

J. Geophys. Res.

Genetic relations between the Moon and meteorites

Siderophile elements in the lunar highlands: nature of indigenous component and implications for the origin of the Moon

Partitioning of Re between metal and silicate phases

Meteoritics

Experimental determination of the partitioning of gallium between metal and silicate: electron and ion probe study

Composition of the Shergotty parent body: further evidence of a two-component model

Trace elements in Apollo 11 lunar rocks: implications for meteorite influx and origin of Moon

Chemical composition and petrogenesis of basalts from Tranquility Base

Elemental abundances by instrumental activation analyses in chips from 27 lunar rocks

Analyses of Apollo 12 specimens: compositional variations, differentiation processes and lunar soil mixing models

Early chemical history of the solar system

Revs. Geophys. Space Phys.