Lithium systematics in howardite–eucrite–diogenite meteorites: Implications for crust–mantle evolution of planetary embryos

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ScienceDirect Geochimica et Cosmochimica Acta 125 (2014) 131–145 www.elsevier.com/locate/gca

Lithium systematics in howardite–eucrite–diogenite meteorites: Implications for crust–mantle evolution of planetary embryos Toma´sˇ Magna a,⇑, Magdalena Sˇimcˇ´ıkova´ a, Fre´de´ric Moynier b a

Czech Geological Survey, Kla´rov 3, CZ-118 21 Prague 1, Czech Republic Universite´ Paris Diderot, 1 rue Jussieu, F-75238 Paris Cedex 05, France

b

Received 12 July 2013; accepted in revised form 8 October 2013; available online 22 October 2013

Abstract We present lithium (Li) abundances and isotope compositions in a suite of howardites, eucrites and diogenites (HEDs). These meteorites most likely originated from asteroid Vesta and were delivered to Earth by a series of independent impact events. The Li concentrations show striking differences between Li-poor diogenites plus cumulate eucrites and Li-enriched eucrites whilst howardites have Li abundances intermediate between eucrites and diogenites. Contrary to Li elemental inter-group differences, Li isotope compositions are irresolvable among these individual groups of HED meteorites despite their wildly distinct petrography, attesting to insignificant Li isotope fractionation during formation of a thick basaltic crust by melting of the Vestan mantle. The mean Li isotope composition of Bulk Silicate Vesta is estimated at 3.7 ± 0.6& (1r), intermediate to that of the Earth versus Mars and Moon but identical with these terrestrial bodies within uncertainty. This further validates largely homogeneous inner Solar System solids from the Li isotope perspective and supports the lack of loss of moderately volatile elements from planetary embryos during their magmatic histories because Li does not follow depletion trends inferred from more volatile elements. Pasamonte eucrite has the same Li isotope composition as other eucrites although it may not be directly linked to Vesta. These observations are also important for generating Li elemental and isotope signatures in juvenile basaltic crusts of large terrestrial planets and numerous planetary embryos in the early Solar System. A combination of CV + L chondrites may be less suitable for building Vesta from Li perspective but this may face sampling bias of available data and only further analyses may resolve this issue. Alternatively, significant shift of 1& towards heavier Li isotope compositions must have occurred during thermal processing of CV + L (2.2–2.8&) mixture in order to account for the observed Li isotope systematics in HED meteorites. No correlation is observed between Li versus Zn, Fe or Si isotopes, respectively, implying unrelated processes of forming stable isotope variations observed in HED meteorites. Ó 2013 Elsevier Ltd. All rights reserved.

1. INTRODUCTION The howardites–eucrites–diogenites (HEDs) are differentiated meteorites (achondrites) which are thought to originate from the asteroid Vesta, based on spectroscopic data (e.g., Consolmagno and Drake, 1977; Stolper, 1977; Binzel and Xu, 1993; De Sanctis et al., 2012). HEDs have very ⇑ Corresponding author. Tel.: +420 2 5108 5331; fax: +420 2 5181 8748. E-mail address: [email protected] (T. Magna).

0016-7037/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.gca.2013.10.015

ancient ages that are close to the age of the Solar System at 4.568 Ga (Bouvier and Wadhwa, 2010). The antiquity of HED meteorites has independently been confirmed by several different extinct chronometers such as Hf–W, Al– Mg or Mn–Cr (Trinquier et al., 2008; Kleine et al., 2009; Schiller et al., 2011; Day et al., 2012). The HEDs have distinctive O isotope systematics that distinguishes them from the Earth–Moon, Mars, and other meteorites (Clayton and Mayeda, 1996; Wiechert et al., 2004; Greenwood et al., 2005; Scott et al., 2009), as well as a characteristic Si isotope composition that suggests highly reducing conditions

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during formation of a small metallic core (Pringle et al., 2013). Several petrogenetic models have been proposed in order to explain the complexity of HED petrology and geochemistry, such as partial melting (e.g., Stolper, 1977), fractional crystallization (Mason, 1967; Warren, 1985), or magma ocean coupled with either fractional (Ruzicka et al., 1997) or equilibrium crystallization (Righter and Drake, 1997). Lithium (Li) is a moderately volatile element with a 50% condensation temperature (50% Tc) of 1140 K, similar to those of Mn and P, and higher than those of other alkali metals (Lodders, 2003). Contrary to more volatile elements such as Zn, Li is not volatilized significantly during impact events (cf. Moynier et al., 2009; Magna et al., 2011b) and may thus preserve isotope signatures of precursor materials. This, in turn, can be used to deconvolve magmatic histories of celestial bodies provided that secondary processes such as fluid percolation and/or terrestrial contamination did not modify the original samples. Cumulative data indicates that Li isotope compositions of differentiated planetary bodies is very homogeneous with a range of mean d7Li (per mil deviation from the L-SVEC standard) between 3& and 4& (Magna et al., 2006; Jeffcoate et al., 2007; Seitz et al., 2006; Pogge von Strandmann et al., 2011) although modest variations within individual bodies exist that may reflect largely anhydrous magmatic fractionation (Moon), interaction with hydrously altered surface lithologies (Mars) and/or long-term magmatic evolution coupled with large-scale interactions with the hydrosphere (Earth). A few analyzed bulk eucrites show broadly invariant d7Li values (Magna et al., 2006; Seitz et al., 2007; Pogge von Strandmann et al., 2011) whilst intra-mineral variations reported for clinopyroxene crystals in eucrites may indicate a complex history of chemical and thermal disequilibrium and diffusive within-crystal re-distribution of Li isotopes upon cooling (Herd et al., 2004; Rieck et al., 2008). Stannerntrend eucrites (e.g., Bouvante, Stannern) do not show distinctive Li isotope composition from the main group eucrites (Magna et al., 2006; Pogge von Strandmann et al., 2011) although they carry peculiar elemental (e.g., Stolper, 1977; Barrat et al., 2007; Yamaguchi et al., 2009) and stable as well as radiogenic isotope signatures (e.g., Blichert-Toft et al., 2002; Kleine et al., 2005; Wang et al., 2012). No particular difference exists between Li isotope data for wholerock diogenites and orthopyroxene (Seitz et al., 2007) which may attest to insignificant disequilibrium and/or minimal post-magmatic disturbance (Jeffcoate et al., 2007). The Li isotope homogeneity of the bulk terrestrial mantle contrasts strongly with fractionated Li isotope signature in evolved continental rocks (Bryant et al., 2004; Teng et al., 2004, 2008; Magna et al., 2010a) which reflects long-term processes of weathering, 7Li loss into oceans and re-melting of such 7Li-depleted reservoirs. Contrary to this, juvenile oceanic crust (e.g., mid-ocean ridge basalts or ocean island basalts) formed by melting of the upper mantle carries Li isotope compositions that are largely indistinguishable from the precursor mantle assemblage (Elliott et al., 2006; Tomascak et al., 2008) attesting to limited or absent Li isotope fractionation during such large-scale mantle melting events.

Here, we aim at characterizing in more detail the Li elemental and isotope signature of HED meteorites that may help clarify the magmatic evolution of Vesta – a planetary embryo. Whether or not planetary embryos with clear magmatic differentiation retain lack of Li isotope stratification, paralleled by Li enrichments such as observed in juvenile basaltic settings on Earth, remains unclear. This could have important consequences for large terrestrial planets such as the Earth and Mars where similar process formed early crust developed on a slowly cooling residual magma ocean. Whilst formation and subsequent magmatic and thermal metamorphic history of Vesta was accompanied by volatile element depletions (e.g., Paniello et al., 2012), Li might have escaped such processes and its isotope compositions could instead record planetary processes. Based on petrologic arguments it has been proposed that HED meteorites have recorded pre-terrestrial aqueous alteration (Barrat et al., 2011). Lithium isotopes are fractionated to a measurable extent during mineral/fluid interactions (Tomascak, 2004) and we tested whether Li isotopes have recorded such event. 2. SAMPLES AND ANALYTICAL METHODS Four main groups of HED meteorites are distinguished. Non-cumulate eucrites are mostly basalts that have magmatic textures and were probably formed as surface flows or shallow intrusions with not yet completely clear nature but it appears that they originated from a magma ocean (Ruzicka et al., 1997). They typically are composed of orthopyroxene, clinopyroxene (pigeonite + augite) and Ca-plagioclase with accessory silica, chromite, ilmenite, troilite and metal (Duke and Silver, 1967). Original igneous pyroxene (pigeonite) commonly underwent exsolution of augite; pigeonite in highly metamorphosed eucrites has partially been inverted into orthopyroxene. Metamorphic eucrite types were defined based on degree of preservation of primary pyroxene zoning (Takeda and Graham, 1991). In particular, Fe/Mn ratios of pyroxene distinguish HEDs from lunar and martian pyroxene–plagioclase basalts (Goodrich and Delaney, 2000; Karner et al., 2006). Olivine is rare and usually high in Fe, and can mostly be found in more ferroan samples or, rarely, in very little metamorphosed basaltic eucrites (Mittlefehldt and Lindstrom, 1993). Cumulate eucrites are coarse-grained gabbros formed by gravitational settling of Mg-rich pyroxene and plagioclase within a shallow mantle magma chamber beneath the basaltic crust of Vesta. Plagioclase is more calcic (An91–98) than that in basaltic eucrites (Takeda et al., 1997). Polymict eucrites are composed of eucritic clasts and less than 10% diogenite (orthopyroxenite) material. Diogenites are orthopyroxene cumulates essentially composed of 90 modal% coarsegrained orthopyroxene (En72–76), with accessory olivine, plagioclase, spinel and metal (Mittlefehldt et al., 1998), and they are commonly brecciated. Peculiar olivine-rich diogenites contain up to 50 modal% olivine; this group may indeed provide insights into the evolution of Vesta’s mantle or final stages of magmatic evolution when olivine and orthopyroxene co-crystallized (Hewins and Newsom, 1988; Bartels and Grove, 1991) because they are thought to come from deeper crustal/shallow mantle levels of Vesta,

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likely excavated by large impacts (e.g., Takeda, 1997). Howardites represent physical mixtures of diogenite and eucrite clasts, sometimes with an additive of foreign material – mostly carbonaceous chondrite clasts (Buchanan et al., 1993). Many howardites such as Kapoeta and Frankfort have fragmented matrices only little affected by metamorphism (e.g., Reid et al., 1990) whilst some have metamorphosed (sintered) matrix. Petersburg was classified as polymict eucrite/regolith breccia (Buchanan and Reid, 1994) with pyroxenes similar to, but more magnesian than, Stannern-trend eucrites, although Grady (2000) described it as howardite. The presence of mesosiderite clasts enclosed in howardites (Rosing and Haack, 2004) and similarity in O isotope compositions (Greenwood et al., 2006) may imply that siderites (stony–iron meteorites) could originate from the same parent body as HEDs. We have analyzed 22 HED meteorites (13 eucrites – seven non-cumulate monomict, three non-cumulate polymict and three cumulate eucrites, four howardites and five diogenites) for Li abundances and isotope compositions. Falls and hot/cold desert finds were included in order to compare the effects of possible terrestrial contamination through secondary processes, such as weathering and fluid infiltration, on Li isotope distribution (Fehr et al., 2009). A subset of HED samples was previously characterized for Zn, Fe, and Si isotope compositions (Paniello et al., 2012; Wang et al., 2012; Pringle et al., 2013). Analytical protocols for Li isolation and mass spectrometry techniques were described elsewhere (Magna et al., 2004, 2006). Briefly, bulk sample powders were dissolved using a mixture of ultra-pure concentrated HNO3 and HF (1:6 v/v) in screw-top TeflonÒ vials; dried residues were re-fluxed repeatedly with concentrated HNO3 and finally equilibrated in 6 M HCl. The dissolved samples were loaded onto the cation-exchange resin BioRad AG50WX8 (mesh 200–400) and Li was eluted by using 1 M HNO3–80% methanol mixture. The second step employed cation-exchange resin BioRad AG50W-X12 (mesh 200– 400) and 0.5 M HNO3 as elution media. Lithium concentrations and isotope compositions in HED meteorites were measured using a Neptune MC-ICPMS housed at the Czech Geological Survey. Lithium concentrations were determined by measuring Li beam intensities in clean fractions against 1-, 10-, 20- and 30-ppb Li reference solutions. Sample solutions for Li isotope measurements were matched with 10-ppb L-SVEC solution in order to avoid instrumental mass bias (Magna et al., 2004). The Li isotope results are reported in per mil units relative to the L-SVEC reference material (Flesch et al., 1973) and calculated as d7Li (&) = [(7Li/6Li)sample/(7Li/6Li)L-SVEC  1]  1000. The external reproducibility of Li isotope measurements was better than ±0.4& (2r; calculated from two to four individual runs) from measurements of international reference rocks. See Table 1 footnote for results of reference rocks and further information. 3. RESULTS The Li contents and isotope compositions of HED meteorites measured during this study are shown in Fig. 1 and

133

listed in Table 1 together with published data. The newly obtained Li abundances for eucrites are in accord with those given elsewhere (Tera et al., 1970; Kitts and Lodders, 1998; Barrat et al., 2007). The basaltic eucrites have higher Li abundances (7.2–14.6 ppm) than cumulate eucrites (3.0– 7.7 ppm). There is no apparent difference in Li contents between monomict (7.3–14.6 ppm) and polymict (7.2– 11.2 ppm) eucrites. Howardites have lower Li contents compared to basaltic eucrites (4.0–6.2 ppm). Low Li concentrations were found for diogenites (0.5–3.2 ppm), with the exception of Aioun El-Atrouss (6.0 ppm). The new data is consistent with Li abundances reported for LaPaz Icefield (LAP) 03569 and LAP 91900 (Day et al., 2012) and for a larger suite of diogenites in general (Mittlefehldt et al., 2012). Lithium contents anti-correlate with magnesium number (Mg#; molar Mg/molar Mg + Fetot) as well as modal orthopyroxene in the whole suite whereas they correlate with modal plagioclase, excluding Serra de Mage´ which is exceptionally rich in modal plagioclase (Fig. 2). Lithium contents correlate negatively with modal pigeonite plus augite in eucrites but there is an overall positive correlation with Li contents in the whole suite when solely modal augite is considered. These findings indicate strong control of both plagioclase and augite on Li distribution in eucrites (and likely in howardites) whereas orthopyroxene carries Li in diogenites. The d7Li values in non-cumulate eucrites are surprisingly uniform (2.9–4.4&; see Fig. 1), with the exception of Cachari (d7Li > 5.2&; see also Magna et al., 2006). Hammadah alHamra (HaH) 286 has been suggested to belong to Nuevo Laredo-trend eucrites (Szurgot and Polan´ski, 2011). Its d7Li of 2.9& is identical within error to the Li isotope composition of other eucrites, suggesting that Nuevo Laredo-trend eucrites may have similar d7Li as main group eucrites. Compared to previous studies, our Li isotope composition of Camel Donga differs by 1& whereas Stannern is identical within error (cf. this study; Pogge von Strandmann et al., 2011) and consistent with d7Li value found for Bouvante, another Stannern-trend eucrite (Magna et al., 2006). Cumulate eucrites have a spread in d7Li values (2.2–4.2&) which largely mimics that found for non-cumulate eucrites. The slightly lower d7Li of 2.2& in Northwest Africa (NWA) 2650 is paralleled by higher Li abundance of 7.7 ppm and could be indicative of terrestrial hot desert residence although no significant alteration products were observed in NWA 2650. Alternatively, it could entrap locally altered lithologies on Vesta. The d7Li values of howardites (3.1– 3.8&) are in the range of eucritic meteorites but Petersburg has somewhat distinctive d7Li of 4.9& which could possibly reflect its intermediate classification between howardites and polymict eucrites. Diogenites have d7Li values (3.0–4.5&) in the range of eucrites and howardites with the exception of LAP 03569 that has distinctively light Li isotope signature (4.3&), perhaps reflecting terrestrial alteration/contamination as indicated by slightly elevated Pb contents and Ba/La ratios (Day et al., 2012). However, an exact evaluation of such effects would require more detailed investigation (e.g., Sephton et al., 2013). Alternatively, such a low value could hint to metasomatic modification of a cumulate pile from which LAP 03569 originated. Except for this latter

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Table 1 Lithium concentrations and isotope composition in eucrites, howardites and diogenites.

Eucrites Berebaa Berebac Cachari Cacharia Camel Donga Camel Dongab HaH 286 Juvinasa Juvinasa NWA 3152 NWA 4536 NWA 5235

Locality; year of fall/find

Classification

Li (ppm)

Burkina Faso; fall 1924

Non-cumulate, monomict, brecciated

Argentina; find 1916

Non-cumulate, monomict, brecciated

Australia; find 1984

Non-cumulate, monomict, brecciated

Libya; find 2000

Non-cumulate, monomict, brecciated (NL?) Non-cumulate, monomict, brecciated

10.6 11.7 9.0 10.5 7.3 7.2 9.0 9.0

France; fall 1821

Bouvantea

Morocco; find 2005 Western Sahara; find 2006 Northwest Africa; find 2008 France; find 1978

Stannern

Czech Republic; fall 1808

d7Li (&)

2r

Yb (ppm)d

4.23 3.9 5.15 5.75 3.87 2.8 2.90

0.22 0.9 0.25 0.89 0.21 0.1 0.06

1.9

0.29 0.34 0.22 0.15 0.32

1.5 1.8 1.8

2.3 2.0 1.5

Non-cumulate, monomict, brecciated Non-cumulate, monomict, brecciated Non-cumulate, monomict, brecciated

14.6 8.3 8.5

3.65 3.61 4.00 3.12 2.99

Non-cumulate, monomict, brecciated (ST) Non-cumulate, monomict, brecciated (ST)

13.1

3.84

0.48

3.0

10.9

3.85

0.35

2.7

8.3 7.2 7.5 11.2 10.1 12.2 3.3 7.7 3.0

3.4 3.04 3.64 3.68 4.38 3.65 3.7 3.81 2.22 4.18

0.2 0.24 0.33 0.22 0.24 0.20 0.1 0.15 0.19 0.04

3.80 3.73 3.05 4.90

0.22 0.17 0.10 0.24

1.0

4.49 3.5 4.7 4.25 3.03 3.15 3.7 2.6 3.93

0.31 0.5 0.3 0.27 0.16 0.41 0.2 0.9 0.09

0.06 0.22

Stannernb ALHA 78132a EETA 79006 EET 83227 NWA 1109 Pasamontea Pasamonteb EET 87548 NWA 2650 Serra de Mage´

Antarctica; find 1978 Antarctica; find 1979 Antarctica; find 1983 Morocco; find 2001 New Mexico; fall 1933

Non-cumulate, Non-cumulate, Non-cumulate, Non-cumulate, Non-cumulate,

Antarctica; find 1987 Morocco; find 2004 Brazil; fall 1923

Cumulate, Mg-rich Cumulate, unbrecciated Cumulate, unbrecciated

Howardites EET 87503 Frankfort Kapoeta Petersburg

Antarctica; find 1987 USA; fall 1868 Sudan; fall 1942 USA; fall 1855

Fragmental breccia Fragmental breccia Regolith breccia Howardite/polymict eucrite(?)

6.2 4.0 4.6 5.7

Diogenites Tatahouine Johnstownc

Tunisia; fall 1931 USA; fall 1924

LAP 03569 LAP 91900 MET 00436 Bilangac

Antarctica; find 2003 Antarctica; find 1991 Antarctica; find 2000 Burkina Faso; fall 1999

Aioun ElAtrouss

Mauritania; fall 1974

Monomict, unbrecciated Monomict, brecciated Orthopyroxene Monomict, brecciated, olivine-rich Monomict, brecciated Monomict, brecciated Monomict, brecciated, Mg-rich Orthopyroxene Polymict, brecciated

1.2 3.3 3.6 3.2 1.8 0.48 2.9 1.9 6.0

polymict, brecciated polymict, brecciated polymict, brecciated polymict, brecciated polymict (reclassified)

1.8

1.7

1.8 1.8 0.37 1.4 0.51

0.89

0.15 0.08 0.02 0.13 1.9

The results obtained for USGS and GSJ reference materials BHVO-2 ([Li] = 4.2 ppm; d7Li = 4.62 ± 0.38&), BIR-1 ([Li] = 3.1 ppm; d7Li = 3.87 ± 0.22&) and JGb-1 ([Li] = 4.4 ppm; d7Li = 4.13 ± 0.22&) as well as internal eclogite standard OK-1 ([Li] = 9.5 ppm; d7Li = 8.48 ± 0.30&) are in excellent agreement with published data (e.g., Tomascak et al., 1999; Magna et al., 2004, 2006; Rudnick et al., 2004; Seitz et al., 2004; Schuessler et al., 2009; Pogge von Strandmann et al., 2011). NL and ST designate the Nuevo Laredo and Stannern trend, respectively, as defined in Barrat et al. (2000). A preliminary association of HaH 286 with NL-trend has been suggested by Szurgot and Polan´ski (2011). a Li data from Magna et al. (2006). b Li data from Pogge von Strandmann et al. (2011). c Li data from Seitz et al. (2007). d See Fig. 6 caption for [Yb] references.

meteorite, there is no resolved d7Li difference between falls and hot/cold desert meteorites and therefore, we do not consider the issue of terrestrial contamination further. No correlation is observed between d7Li and either modal pyroxene

or plagioclase although increasing augite proportion appears to have minor positive effect on Li isotope systematics in howardites. Also, Li isotope compositions do not correlate with either O, Si, Fe, or Zn isotopes in HEDs (Fig. 3)

T. Magna et al. / Geochimica et Cosmochimica Acta 125 (2014) 131–145

135

7.0

6.0

Cachari MARS

δ7Li (‰)

5.0

4.0

Stannern trend

3.0

Nuevo Laredo trend?

EARTH 2.0

1.0

LAP 03569

eucrites (this study) howardites (this study) eucrites (Magna et al. 2006) diogenites (this study) eucrites (Seitz et al. 2007) diogenites (Seitz et al. 2007) eucrites (Pogge von Strandmann et al. 2011)

0.0 0

4

8

12

16

20

Li (ppm) Fig. 1. Lithium isotope compositions versus Li abundances in howardites–eucrites–diogenites. LAP 03569 is not plotted for clarity and its position is only marked with an arrow. Previous analyses are also plotted (Magna et al., 2006; Seitz et al., 2007; Pogge von Strandmann et al., 2011). The Li abundance and isotope composition of the Earth and Mars is from Elliott et al. (2006) and Magna et al. (2010b), respectively, with 1r error bars, clearly attesting to limited Li isotope fractionation at planetary scale. Cachari plots clearly off the main trend, perhaps reflecting secondary effects, whilst Stannern-trend eucrites do not posses distinguished Li systematics. Nuevo Laredo-trend eucrites appear to have been formed through fractional crystallization of residual liquids (Warren and Jerde, 1987) but no representative Li data exists for this latter group in order to quantify the effects of such processes on Li systematics.

which implies that d7Li is driven by processes different to those exerting control on the other stable isotope systems, such as volatilization (Zn; Paniello et al., 2012), re-melting of Fe–Ti oxides (Fe; Wang et al., 2012), or metal/silicate segregation (Si; Pringle et al., 2013). 4. DISCUSSION 4.1. Assessment of Li isotope composition of Vesta Virtually all HED meteorites from this study coupled with few other published bulk rock Li data (Magna et al., 2006; Seitz et al., 2007; Pogge von Strandmann et al., 2011) form an extremely narrow range of d7Li values between 2.9& and 4.9&, excluding anomalously light diogenite LAP 03569, isotopically slightly lighter eucrite NWA 2650 and isotopically heavy eucrite Cachari (Fig. 1). The latter meteorite also has distinctive O isotope composition (Wiechert et al., 2004) and the present study confirms the isotopically heavy Li in another Cachari aliquot (Magna et al., 2006). Overall, such Li isotope homogeneity comprising virtually the bulk celestial body is somewhat surprising

provided that Vesta experienced the existence of a magma ocean, core segregation, solidification through crystallization and later period of thermal metamorphism (e.g., Takeda and Graham, 1991; Righter and Drake, 1997; Kleine et al., 2005; Elkins-Tanton, 2012; Pringle et al., 2013) some of which could have modified Li contents and isotope compositions to a resolved extent. This Li isotope homogeneity of HEDs contrasts with >5& span in d7Li of martian meteorites, >7& variation found for lunar mantle-derived and crustal rocks and with even larger variability of d7Li in terrestrial magmatic lithologies (Tomascak, 2004). The bulk mean d7Li of all samples (excluding Cachari, NWA 2650 and LAP 03569) is 3.7 ± 0.6& (1r) which is extremely narrow considering that HEDs sample most of the Vestan silicate reservoirs. Here, we adopt this value as a d7Li estimate for the bulk silicate Vesta (BSV). This is in between the mean d7Li values derived for the Earth (3.3&; Elliott et al., 2006), Mars (4.0&; Magna et al., 2010b) and the Moon (4.1&; Magna et al., 2009) while it largely overlaps within the errors estimated for bulk silicate mantle of these planetary bodies. This derived d7Li value of BSV is also identical to that found for Juvinas (Magna et al., 2006)

T. Magna et al. / Geochimica et Cosmochimica Acta 125 (2014) 131–145 16

16

12

12

Li (ppm)

Li (ppm)

136

8 Aioun El-Atrouss

4

8

4 Serra de Magé

Serra de Magé

0

0 30

40

50

60

70

80

0

40

60

80

100

Orthopyroxene (modal %)

16

16

12

12

Li (ppm)

Li (ppm)

Mg number

20

8

8

4

4

Serra de Magé

Serra de Magé

0

0 0

20

40

60

80

0

20

40

60

80

Pigeonite+augite (modal %)

Plagioclase (modal %) 16

Li (ppm)

12

8

4 Serra de Magé

0 0

5

10

15

20

25

Augite (modal %) Fig. 2. Bulk rock Li abundances versus modal compositions in howardites–eucrites–diogenites. The cumulate eucrite Serra de Mage´ is highlighted due to its peculiar mineralogy, in particular unusually high modal plagioclase, paralleled by low modal abundance of both clinopyroxene and orthopyroxene. Also, Aioun El-Atrouss diogenite has a very low Mg number. Mineral modes: Delaney et al. (1984), Bowman et al. (1997), Domanik et al. (2004), Weisberg et al. (2008) and Szurgot and Polan´ski (2011). Symbols are as in Fig. 1.

considered to represent near-primary signature of eucritic liquids as evidenced by its near-flat rare earth element pattern with no apparent Eu anomaly and rather magnesian nature of its phases (Consolmagno and Drake, 1977; Stolper, 1977). 4.2. A difficulty in search for chondritic precursors of Vesta? Righter and Drake (1997) and Gupta and Sahijpal (2010) suggested that Vesta was assembled from broadly chondritic material (CV + L) but the inferred bulk d7Li of silicate Vesta does not correspond well to this view because available data for these two chondrite classes show somewhat lower

d7Li values below 3&, paralleled by <2 ppm Li (Seitz et al., 2007; Pogge von Strandmann et al., 2011). In fact, no chondrite class mimics closely the Li isotope composition of Vesta apart from carbonaceous chondrites whilst ordinary chondrites are lighter by 1& (Seitz et al., 2007; Pogge von Strandmann et al., 2011). However, it must be stressed that the number of analyzed meteorites of various classes is too limited in order to place stringent constraints on end member compositions that could have mixed into final composition of (not only) Vesta. It is important to note that high Li abundances found for basaltic eucrites are not common in melt derivatives from terrestrial mantle, such as MORBs and OIBs (e.g., Ryan and Langmuir, 1987; Chan and

T. Magna et al. / Geochimica et Cosmochimica Acta 125 (2014) 131–145 6.0 Stannern trend

δ7Li (‰)

5.0 4.0

Pasamonte

3.0

ilmenite crystallization

-0.05

0.00

δ57Fe

0.05

0.10

(‰)

6.0

δ7Li (‰)

5.0 4.0 3.0 2.0 core segregation 1.0 -0.6

at the time of magma ocean or bulk water content of the respective planetary body. We note that Vesta is presumably dry on a global scale whilst the Earth and Mars contained significant water quantities (McCubbin et al., 2012). Indigenous water content in the Moon is still debated (cf. Saal et al., 2008; Sharp et al., 2010; Hauri et al., 2011; Albare`de et al., 2013; Hui et al., 2013). 4.3. Pasamonte eucrite – a distinct asteroid from Li perspective

2.0 1.0 -0.10

137

-0.5

-0.4

-0.3

δ30Si

-0.2

-0.1

0.0

(‰)

Fig. 3. Lithium isotopes versus iron and silicon isotope compositions in howardites–eucrites–diogenites. Iron isotope data are from Poitrasson et al. (2004) and Wang et al. (2012), Si isotope data are from Armytage et al. (2011) and Pringle et al. (2013), Li isotope data for Johnstown is from Seitz et al. (2007). The uncertainties of Fe and Si isotope compositions are plotted as two standard errors of the mean. No clear relationship exists between d7Li versus d57Fe and d30Si in the whole suite or within individual groups of HED meteorites. Symbols are as in Fig. 1.

An important aspect of the data set is the observation that Pasamonte has exactly the same Li content and isotope composition (Magna et al., 2006; Pogge von Strandmann et al., 2011) as the other eucrites (Fig. 1 and Table 1). Although Wiechert et al. (2004) advocated for an isotopically heterogeneous source of Pasamonte located in Vesta, more recently it has been suggested based on distinctive O isotope signature (Greenwood et al., 2005; Scott et al., 2009) that Pasamonte may originate from another parent body with similar, though not identical, chemical properties [note discussion in Barrat et al. (2011) for Pasamonte]. If, therefore, the nature and magmatic history of Pasamonte are not strictly linked with Vesta, then the Li systematics of Pasamonte, and its Li abundance in particular, provide strong evidence (i) for rapid magmatic fractionation of other bodies akin to Vesta that too must have developed basaltic crust with elevated Li concentrations despite the likelihood that all these bodies formed during the first few millions of years after the start of the Solar System and (ii) that they formed from (chondritic) sources which, however, do not have Li contents high enough by themselves (Sephton et al., 2006; Maruyama et al., 2009; Seitz et al., 2012). This implies the existence of chemically evolved planetary embryos in the infancy of the Solar System that were large enough to sustain large-scale magmatic differentiation for protracted period of time (Blichert-Toft et al., 2002; Kleine et al., 2005; Srinivasan et al., 2007; Zhou et al., 2013) and yet preserving Li isotope compositions intact 100 evaporation of Li evaporation of LiO evaporation of LiCl

80

δ7Li (‰)

Frey, 2003; Elliott et al., 2006; Tomascak et al., 2008; Krienitz et al., 2012), nor are they found in martian basalts (Magna et al., 2006; Seitz et al., 2006; Magna et al., 2010b). These Li contents are more typical of arc and continental alkaline basalts (e.g., Ryan and Langmuir, 1987; Ryan and Kyle, 2004) and also are common in lunar lowTi and high-Ti mare basalts (Magna et al., 2006; Seitz et al., 2006; Magna et al., 2009), thought to have formed at later stages (>82% percent solid) of the lunar magma ocean crystallization (e.g., Snyder et al., 1992; Elkins-Tanton et al., 2011). This would require substantial Li enrichment during the ephemeral existence of a magma ocean, or at any later stage prior to solidification, coupled with preferential incorporation of 7Li into the eucrite source melts provided that subsequent bombardment history, remelting and thermal metamorphism imparted little modification to Li isotope systematics in Vesta. It is unclear, however, if this observation may relate to the size of the body, depth of a magma ocean, p–T and redox conditions existing

60

40

20

0 1

3

5

7

9

11

13

15

Li in residuum (ppm) Fig. 4. The evolution of the d7Li as a function of Li remaining in the residuum. Different Li species in vapor are plotted (Li, LiO and LiCl; after Schaefer and Fegley, 2005); starting Li abundance was set to 15 ppm, close to the Li-richest NWA 3152 eucrite. Lithium apparently does not follow Rayleigh distillation and other processes are thus required for the observed (though minor) Li isotope variations. Symbols are as in Fig. 1.

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throughout their apparently ephemeral active magmatic histories. These inferences are in accord with the existence of other basaltic achondrites (e.g., angrites) that have distinctive O isotope compositions, attesting to multiple differentiated parent asteroidal bodies (e.g., Yamaguchi et al., 2002). 4.4. Evidence for limited loss of moderately volatile elements from Vesta The new and published data show that there is no particular elemental depletion of Li in HEDs relative to chondrites which is different from more volatile elements such as Zn or Cd (Scho¨nba¨chler et al., 2008; Paniello et al., 2012). These elements underwent significant depletion in large planetary bodies when compared with chondrites (e.g., Lodders and Fegley, 1998; Wolf et al., 2009; Paniello et al., 2012), paralleled by no resolved Cd and Zn isotope differences, respectively. It was suggested that Zn isotopes can fractionate during volatilization caused by impacts or ion sputtering (e.g., Moynier et al., 2006; Moynier et al., 2009; Moynier et al., 2010b) while they are not fractionated during hightemperature processes in the Earth’s mantle (Chen et al., 2013). Paniello et al. (2012) suggested that most Zn could have been lost during the accretion of Vesta. In order to constrain volatility of Li during the accretion we assume that evaporation follows a Rayleigh distillation processes: 7

d Liresidue ¼ 1000  ð½Li=½Li0 Þ

a1

 1000

ð1Þ

where [Li]0 is the concentration of Li prior to evaporation (we used 15 ppm Li as starting abundance, which is the closest to NWA 3152 eucrite, HED meteorite with the highest Li content), and a is the kinetic fractionation factor that is assumed to be equal to the square root of the ratio of the mass of the species which are evaporated (Li, LiO and LiCl). If the Li elemental and isotope variations observed in HEDs would follow a volatile origin, much larger Li isotope fractionations were expected (Fig. 4). Therefore, our data suggest that Li was effectively retained in the accreted matter of Vesta which is compatible with moderately volatile behavior of Li at high temperatures and/or during planetary melting (Brenan et al., 1998). It provides further evidence that Li is not volatile enough to experience massive loss through planetary-scale thermal events (Magna et al., 2011b) such as has been found for Zn, for example (Moynier et al., 2009). These results are also supported by experimental study of Herd et al. (2004) who did not observe any loss of Li from a silicate melt at temperatures up to 1300 °C. Alternatively, Li could perhaps be lost from a silicate melt at far higher temperatures of 1900 K (Le Gac et al., 2008) as has been modeled for other alkali elements (Na, K) between the melt and vapor for conditions at Io (Schaefer and Fegley, 2004) but we emphasize that Li behaves differently compared to major alkali elements in silicate systems. 4.5. Comparison of lithium with other stable isotope systems in HED meteorites The lack of correlation between Li (this study), Fe (Wang et al., 2012), and Si (Pringle et al., 2013) isotope

compositions in HEDs (Fig. 3) suggests that Li isotopes are not re-distributed by any process involving metal (core segregation) or metallic oxides (late-stage ilmenite crystallization). Therefore, elevated d57Fe values found in Stannern-trend eucrites (Wang et al., 2012) that were probably result of re-melting of a former asteroidal crust with abundant modal ilmenite do not find its counterpart in different d7Li. Interestingly, Pasamonte shares similar d57Fe with Stannern-trend eucrites. It is important to note that the Stannern parent melt might have been located elsewhere on Vesta when compared to other Stannern-trend eucrites (Kleine et al., 2005) with similarly elevated incompatible element abundances (Barrat et al., 2007). However, from the Li perspective basaltic melts will likely be very similar at asteroidal level, considering strictly uniform d7Li values of Bouvante and Stannern, paralleled by moderate to high Li abundances. These inferences may be compared with lunar mare basalts whose minor Li isotope fractionation has been explained in the framework of distinct mantle sources for low-Ti and high-Ti mare basalts (olivine–orthopyroxene cumulates vs. predominantly clinopyroxene cumulates, respectively; Magna et al., 2006) but without any effect of late-stage ilmenite-rich cumulates on Li systematics [cf. Liu et al. (2010) for Fe]. 4.6. Basaltic versus late-stage cumulate eucrites The late-stage cumulate eucrites have substantially lower Li abundances than basaltic eucrites. This is somewhat surprising considering that (i) chronology of formation of cumulate eucrites implies their rather late origin compared to basaltic eucrites (Blichert-Toft et al., 2002) and (ii) Li is moderately incompatible during mantle melting (Ryan and Langmuir, 1987; Brenan et al., 1998). This would effectively mean that Li becomes depleted as crystallization of magma ocean proceeds which is rather unlikely from general geochemical characteristics of Li and by juxtaposing these rather depleted Li patterns recorded in cumulate eucrites with large Li enrichments in late-stage residual melts of the lunar magma ocean (Warren and Wasson, 1979). Indeed, similarly low Li abundances were also found for diogenites (Table 1) but chronologies of diogenites and cumulate eucrites remain vastly different (cf. McSween et al., 2011; Day et al., 2012). Whether or not these low Li contents are intrinsic to the parent source of cumulate eucrites remains to be tested although Barrat et al. (2000) suggested some entrapment of residual melt during accumulation process. Wolf et al. (2009) noted that cumulate eucrites could be mantle-derived in origin based on cluster analysis of labile elements (e.g., Sb, Se). In this respect, it is interesting to note that the cumulate character differs in terms of modal phases for Serra de Mage´ and Elephant Moraine (EET) 87548 with the former rich in plagioclase and the latter exceptionally rich in pyroxene (Warren et al., 1996) but that this difference is not reflected in distinctive Li systematics. Following the approach of Treiman (1997), the low Li content of Serra de Mage´ can be successfully modelled from a cumulus pigeonite plus plagioclase, and small amounts of melt (10%) with eucrite-like Li contents (8 ppm). The assessment of parent magma of

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Li (ppm)

cumulate eucrites being similar to Nuevo Laredo (Treiman, 1997) cannot be tested based on the current data set but genetic relationship between cumulate and non-cumulate eucrites appears to be likely (Barrat, 2004). Collectively, even if cumulate eucrites represent a closer look into the mantle of Vesta, their d7Li values, identical within analytical error, may be taken to further confirm the bulk estimated d7Li which is well constrained (see above). 4.7. Juvenile versus mature planetary crust from Li perspective

30 20 10 0 0

10

20

30

MgO (wt.%) 10.0

hydrothermal alteration

8.0

δ7Li (‰)

The terrestrial felsic continental crust is rich in Li, paralleled by fractionated d7Li relative to upper mantle estimates (Ryan and Langmuir, 1987; Rudnick and Gao, 2003; Seitz et al., 2004; Teng et al., 2004; Magna et al., 2006; Jeffcoate et al., 2007). This is the result of long-term secondary processes that also develop distinctive signatures between the hydrosphere and magmatic residues in other stable isotope systems, such as B (Spivack and Edmond, 1987; Chaussidon and Albare`de, 1992). On the other hand, low-degree partial melting of variably enriched/depleted mantle components with modest addition of recycled crust may result in a range of elemental and radiogenic isotope compositions found in juvenile basaltic crust exposed in ocean island locations (e.g., Prytulak and Elliott, 2007; Sobolev et al., 2007; Stracke and Bourdon, 2009). Therefore, the non-existence of mature (‘evolved’) crustal rocks and prevalence of juvenile lavas may generally be discerned with Li elemental and isotope systematics. This is apparent by comparing Li contents and isotope compositions in continental crustal rocks (in general >15 ppm Li and d7Li 0&; Bryant et al., 2004; Teng et al., 2004, 2008; Magna et al., 2010a) with those in melt derivatives from the mantle. The latter mainly are manifested by MORBs and OIBs having low Li contents (<6 ppm) and d7Li values that largely mimic Li isotope compositions found in pristine peridotites and/ or are displaced toward slightly higher d7Li. This may, in part, be due to mixing of isotopically distinctive reservoirs which may introduce complex Li isotope variations observed in several OIB localities such as Hawaii, Iceland and Polynesia (Chan et al., 1992; Chan and Frey, 2003; Ryan and Kyle, 2004; Elliott et al., 2006; Tomascak et al., 2008; Schuessler et al., 2009; Vlaste´lic et al., 2009; Magna et al., 2011a). This suggests that melt extraction itself from the mantle does not impart significantly different Li fingerprint to the newly formed basalts, irrespective of the degree of melting. The latter observation is confirmed by experiments in which possible parent source of eucrites were melted (Stolper, 1977). These experiments resulted in slightly elevated Li abundances in eucrites but would not be capable to shift d7Li. For example, similar enrichments in Li contents (up to 42 ppm) without paralleled shifts toward lower d7Li (>3.8&) were observed independently for several suites of effusive lavas in Iceland that show a large range in silica contents from basaltic through andesitic to rhyolitic compositions (Fig. 5). Such evolved lithologies are missing on Vesta at global scale (De Sanctis et al., 2012) although silica-evolved compositions were rarely found in HED meteorites (Barrat et al., 2009). It is also

139

6.0 4.0 2.0

magmatic differentiation 0.0 0

10

20

30

40

50

Li (ppm) Fig. 5. Lithium abundances versus MgO contents and d7Li values in HEDs compared with fresh lavas from Iceland (grey circles). HEDs follow a general negative trend in [Li] vs. MgO space with progressive Li depletion in high-MgO rocks. Incorporation of highd7Li lithologies into the source of some Icelandic basalts through recycling of oceanic lithosphere cannot be envisaged for Vesta and hydrothermally altered lithologies may in general be missing on Vesta or were not sampled by currently available meteorite collection. Data for Iceland: Pistiner and Henderson (2003), Ryan and Kyle (2004), Jeffcoate et al. (2007), Schuessler et al. (2009), Hansen et al. (2011) and Magna et al. (2011a). Symbols are as in Fig. 1.

apparent from comparison with fresh lavas from Iceland that any fluid percolation during magmatic activity on Vesta must have been ephemeral which did not impart resolved low or high d7Li signatures although it could act locally as we may speculate in case of Cachari (note also higher Sr, Ba and Rb contents relative to other eucrites; e.g., Magna et al., 2006). Collectively, the data suggests that Li systematics in basalts may provide important insights into the history of crustal segregation from mantle source regions and that juvenile, newly formed crust is largely homogeneous at asteroidal level irrespective of its trace element leverage. It further shows that spatially extensive lavas (comprising in fact bulk planetary embryo) may be homogeneous at Li isotope level to within ±1&, attesting to limited volume of remelting of chemically distinct lithologies. These inferences may be underscored by analyses of chemically evolved martian basaltic meteorites (Magna et al., 2006, 2010b; Seitz

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et al., 2006) that also show d7Li values not differing significantly from the estimated martian mantle value. On the contrary, lunar anorthositic crust reveals Li systematics opposite to other terrestrial planets, i.e., extreme depletion in Li and heavy Li isotope signature (Magna et al., 2006; Magna and Neal, 2011) that may bear on differences in development of crustal Li signatures. 4.8. Diogenites – a probe into the mantle of Vesta? No or limited amounts of water were present during the epoch of melting and magmatic fractionation because most water detected by remote sensing (Prettyman et al., 2012) is supposed to originate from extraneous sources (Treiman et al., 2004). This may be consistent with important delivery of highly siderophile elements (HSE) within a short time as found for diogenites (Day et al., 2012). Considering generally low Li contents in primitive meteorites (e.g., Nichiporuk and Moore, 1970; Murty et al., 1983; Seitz et al., 2007; Pogge von Strandmann et al., 2011), the very low addition (<1.5% estimated from HSE abundances; Day et al., 2012) of any meteorite class can be regarded as insignificant in possibly altering the intrinsic Li contents and isotope compositions of diogenites and we can thus interpret the Li systematics in a magmatic context. One possible exception may be Aioun El-Atrouss, representative of

16

polymict diogenites from polymict eucrites–howardites– polymict diogenites sequence (Delaney et al., 1984). Its Li content (6.0 ppm) is nearly twice as high as Li contents found for other diogenites (Table 1), paralleled by elevated incompatible element abundances, all of which suggest large eucritic clast component inherited from brecciation (Lomena et al., 1976). Therefore, we omit this meteorite from further discussion of intrinsic isotope signatures in diogenites although we are cautious that our results may be particular to a specific Aioun El-Atrouss aliquot, potentially rich in eucrite clasts. There is an extremely well defined co-variation of Li and Yb for diogenites (Fig. 6), with the exception of Aioun ElAtrouss with higher [Yb] at given [Li] which broadly follows eucrites and howardites (see above). All other diogenites display a far steeper trend compared to the rest of HEDs (Fig. 6). Orthopyroxene/low-Ca pyroxene belongs to important carriers of heavy rare earth elements although partition coefficient of Yb is smaller than that of Li. van Kan Parker et al. (2011) found DLi/Ybopx  5–6 for high p–T and dry (‘lunar’) conditions whereas anhydrous experiments at ambient pressures gave DLi/Ybopx  1–2 (van Kan Parker et al., 2010). Eucrites display homogeneous Li/Yb ratios, mostly between 4 and 6 whereas high Li/Yb ratios in diogenites (up to 25) may imply derivation of orthopyroxene-rich cumulates at greater depths, supporting

diogenites ~20

‘S E THNTL R EA MA ~4.5

Li (ppm)

12

nakhlites chassignites ALH 84001 8 30 KREEP-rich

20

4

low-Ti mare

B

MOR ~1.7

10

high-Ti mare HED

cumulate eucrites

shergottites

0

0

10

20

30

0 0

1

2 Yb (ppm)

3

4

Fig. 6. Lithium versus Yb in HEDs. Lithium/Yb ratios in eucrites and howardites largely follow common planetary trend illustrated by the Earth and Mars whilst lunar maria basalts have much lower Li/Yb (Neal, 2001). Steep trend recorded in diogenites likely reflects the incompatibility of Yb and modest Li enrichment in orthopyroxene. No enrichments in incompatible trace elements such as for lunar KREEP are observed for HEDs. Lithium abundances are from this study, Magna et al. (2006, 2009) and Seitz et al. (2006, 2007), Yb abundances are from Wa¨nke et al. (1972), Duke (1978), Metzler et al. (1995), Kitts and Lodders (1998), Barrat et al. (2000, 2008), Mittlefehldt and Lindstrom (2003), Magna et al. (2006) and Day et al. (2012). Symbols are as in Fig. 1.

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tentatively a deep mantle origin for diogenites and shallower depths of origin for eucritic melts. Papike (1996) found that orthopyroxenes from diogenites have much lower concentrations of incompatible trace elements compared to terrestrial Stillwater bronzitites which is consistent with the idea of diogenite parental melts being depleted in these elements due to prior removal of eucritic basalts (Stolper, 1977). However, a genetic relationship between diogenites and eucrites still remains unclear (e.g. Consolmagno and Drake, 1977; Stolper, 1977; Grove and Bartels, 1992) and it may well be that these two HED groups are genetically unrelated (Barrat, 2004; Barrat et al., 2008). These latter authors invoke heterogeneous parental melts of diogenites being unrelated to eucritic sources by any simple genetic relationship. The source heterogeneity of diogenites is exemplified by highly variable REE patterns (Barrat et al., 2008) but this diversity is not directly reflected in Li isotope systematics. Contrary to this, variability in elemental Li distribution appears to reflect variously depleted sources of diogenites. This is particularly apparent for Meteorite Hills (MET) 00436 (0.5 ppm Li) that also caries very depleted incompatible trace element signature (Barrat et al., 2008), yet its d7Li converges around a singular value akin to d7Li of other diogenites and eucrites. The negative d7Li of 4.3& found for LAP 03569 contrasts strongly with limited total d7Li variation (1.5&) for other diogenites and cannot be easily reconciled with its rather low terrestrial exposure age (Welten et al., 2007) although low-temperature alteration can severely modify the intrinsic Li isotope composition at very short time scales (Pistiner and Henderson, 2003). Moreover, Antarctic meteorites may undergo multiple repeated ice cover freeze–thaw cycles through receiving solar radiation on exposed dark surfaces which would facilitate penetration of ice-melted water into the meteorite interiors and, by inference, could impose further complexities to the intrinsic Li signatures. No modal analysis is available for LAP 03569 and we thus cannot quantify whether this low value may eventually be related to higher modal olivine that would carry low to negative d7Li signature, or reflect open and closed system effects. Even if the dominant Li carrier would be orthopyroxene, its low d7Li would suggest non-magmatic nature of this signature. This would attest to the existence of active metasomatic events shortly after the earliest magmatic activity on Vesta ceased as suggested by Barrat et al. (2011) and/or sub-solidus kinetic effects via diffusive isotope fractionation (Seitz et al., 2004; Jeffcoate et al., 2007). Low d7Li was also reported for martian orthopyroxenite Allan Hills (ALH) 84001 that could reflect metamorphic and hydrothermal history (Seitz et al., 2006) or could perhaps invoke assimilation of hydrously altered surface lithologies. Contrary to this, Li isotope compositions of orthopyroxene from Johnstown and Bilanga largely mimic the respective bulk rocks (Seitz et al., 2007) which may suggest distinct processes for source regions of these diogenites compared with that of LAP 03569. Further work is thus required to solve this issue, also by considering other cumulate lithologies such as dunites, assigned to be derived from Vesta (e.g., Beck et al., 2011).

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5. CONCLUDING REMARKS Vesta represents a unique look into an embryonal stage of a terrestrial planet with a core and silicate envelope. Although mixture of CV + L chondrites most closely resembles some properties of Vesta, it may not mean that Vesta accreted from such a mixture. The Li elemental and isotope systematics of these two meteorite classes are somewhat different to intrinsic Li signature of Vestan lithologies. From new and published data for eucrites, howardites and diogenites, d7LiBSV = 3.7 ± 0.6& (1r) is derived which is essentially identical to the mean Li isotope composition of the Earth, Mars, and the Moon, respectively. This is similar to stable Sr isotopes (Moynier et al., 2010a) although Vesta appears to have resolved 84Sr enrichments relative to the Earth, Moon, and the Mars (Moynier et al., 2012). Neither residual liquids, likely represented by the Stannern-trend eucrites, nor cumulate eucrites carry distinctly different Li isotope compositions, implying limited Li isotope fractionation during segregation of late-stage melts. Considering the ancient nature of HED meteorites, it is notable that magmatic differentiation imparted substantial Li enrichments in eucrites within a very short time after the onset and rapid solidification of a magma ocean on Vesta. Indices of possible fluid activity on Vesta are missing from the Li elemental and isotope perspective but we do not preclude such lithologies to be present and/or sampled by fortuitous coincidence. Variations in other stable isotope systems, such as Zn, Fe and Si, are not clearly related to variations in Li isotopes and explanations must be considered other than core segregation, late-stage ilmenite cumulate melting or impact-assisted volatilization. In any case, juvenile basaltic crust of Vesta appears to carry similar elemental and isotope load of Li as fresh basaltic derivatives of mantle on Earth. ACKNOWLEDGEMENTS We thank Cecilia Satterwhite and Kevin Righter (NASA, Houston), Brigitte Zanda (MNHN Paris), Laurence Garvie and Meenakshi Wadhwa (ASU, Tempe), Ludovic Ferrie`re and Franz Brandsta¨tter (NMV Vienna), Caroline Smith (NHM London), Philip Heck and James Holstein (Field Museum, Chicago), Alex Bevan (W. Australian Museum, Perth), Tim McCoy (SI, Washington, DC) and Guy Consolmagno (Vatican Observatory) who generously supplied most of the meteorite samples. We are grateful to J. Mı´kova´ and V. Chrastny´ for the maintenance of the clean lab and mass spectrometry facility at the Czech Geological Survey. Insightful reviews by H.-M. Seitz, two anonymous reviewers and comments and editorial handling by Maud Boyet clarified the manuscript. We acknowledge partial support from the Czech Science Foundation grant P210/12/1990 to TM and the internal project 328600 at the Czech Geological Survey.

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