Asteroid (4) Vesta: I. the Howardite-Eucrite-Diogenite (HED) Clan of Meteorites

Home , Angrite, Diogenite, Eucrite, HED meteorite, Howardite, Jodzie

Chemie der Erde 75 (2015) 155–183

Contents lists available at ScienceDirect

Chemie der Erde

j ournal homepage: www.elsevier.de/chemer

Invited Review

Asteroid (4) Vesta: I. The howardite-eucrite-diogenite (HED) clan of meteorites

∗

David W. Mittlefehldt

XI3/Astromaterials Research Ofﬁce, Astromaterials Research and Exploration Sciences Division, NASA/Johnson Space Center, 2101 NASA Parkway, Houston,

TX 77058, USA

a r a

t b

i c s t

l e i n f o r a c t

Article history: The howardite, eucrite and diogenite (HED) clan of meteorites are ultramaﬁc and maﬁc igneous rocks

Received 23 November 2013

and impact-engendered fragmental debris derived from a thoroughly differentiated asteroid. Earth-based

Accepted 21 August 2014

telescopic observation and data returned from vestan orbit by the Dawn spacecraft make a compelling

Editorial handling – K. Keil

case that the asteroid (4) Vesta is the parent asteroid of HEDs, although this is not universally accepted.

Diogenites are petrologically diverse and include dunitic, harzburgitic and noritic lithologic types in addi-

Keywords:

tion to the traditional orthopyroxenites. Diogenites form the lower crust of Vesta. Cumulate eucrites are

Howardites

gabbroic rocks formed by accumulation of pigeonite and plagioclase from a maﬁc magma at depth within

Eucrites

Diogenites the crust, while basaltic eucrites are melt compositions that likely represent shallow-level dikes and sills,

Vesta and ﬂows. Some basaltic eucrites are richer in incompatible trace elements compared to most eucrites,

Basaltic achondrites and these may represent mixed melts contaminated by partial melts of the maﬁc crust. Differentiation

Differentiated asteroids occurred within a few Myr of formation of the earliest solids in the Solar System. Evidence from oxy-

gen isotope compositions and siderophile element contents favor a model of extensive melting of Vesta

forming a global magma ocean that rapidly (period of a few Myr) segregated and crystallized to yield a

metallic core, olivine-rich mantle, orthopyroxene-rich lower crust and basaltic upper crust. The igneous

lithologies were subjected to post-crystallization thermal processing, and most eucrites show textural

and mineral-compositional evidence for metamorphism. The cause of this common metamorphism is

unclear, but may have resulted from rapid burial of early basalts by later ﬂows caused by high effusion

rates on Vesta. The observed surface of Vesta is covered by fragmental debris resulting from impacts,

and most HEDs are brecciated. Many eucrites and diogenites are monomict breccias indicating a lack of

mixing. However, many HEDs are polymict breccias. Howardites are the most thoroughly mixed polymict

breccias, yet only some of them contain evidence for residence in the true regolith. Based on the numbers

of meteorites, compositions of howardites, and models of magma ocean solidiﬁcation, cumulate eucrites

and their residual ferroan maﬁc melts are minor components of the vestan crust.

Contents

1. Introduction ...... 156

2. Lithologies ...... 156

3. Mineralogy and petrology...... 157

3.1. Diogenites...... 157

3.2. Cumulate eucrites ...... 162

3.3. Basaltic eucrites...... 164

3.4. Petrologically anomalous eucrites ...... 165

3.5. HED polymict breccias ...... 166

∗

Tel.: +1 281 483 5043; fax: +1 281 483 1573.

E-mail address: [email protected]

http://dx.doi.org/10.1016/j.chemer.2014.08.002

156 D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183

4. HED compositions ...... 167

4.1. Oxygen isotopic composition...... 167

4.2. Lithophile element compositions ...... 169

4.3. Siderophile element compositions ...... 171

4.4. Noble gas contents...... 172

5. HED ages...... 172

6. HED meteorite petrogenesis ...... 174

7. Thermal metamorphism of the HED parent body crust ...... 175

8. Fluid-mediated metasomatism? ...... 176

9. Mixing of the vestan crust ...... 176

10. Ungrouped basaltic achondrites ...... 178

11. The future ...... 178

Acknowledgments ...... 179

Appendix A. Supplementary data ...... 179

References ...... 179

1. Introduction geological, mineralogical, compositional and geophysical informa-

tion on Vesta. The returned data are consistent with the identity

Meteorites of the howardite, eucrite and diogenite (HED) clan of Vesta as the HED parent asteroid (McSween et al., 2013). Never-

make up the largest suite of crustal igneous rocks available for study theless, there continues to be a minority view that Vesta is not the

from any solar system body, baring the Earth and Moon. As of July HED parent. Wasson (2013) contends that the numerous V-type

2014, there were over 1450 named HED meteorites with 270 new asteroids in the inner main belt are debris from the disruption of

HED meteorites announced during the previous year. Because most several differentiated asteroids, and that these are more probable

are from collection ﬁelds in Antarctica and northern Africa, pairings as sources for HEDS than debris knocked off Vesta by the impact

greatly reduces the number of individual fall events represented. that formed the Rheasilvia basin. He argues that the isotopic simi-

HEDs include basalts, cumulate gabbros, norites, orthopyroxenites, larity of IIIAB irons and HEDs indicates that they were derived from

harzburgites and rare dunites, plus brecciated mixtures of these the same asteroid, and that asteroid must have been completely

igneous lithologies. The HED clan provides an unmatched look at disrupted in order to liberate IIIAB irons from the core. Although

differentiation processes that occurred on asteroidal-sized bodies Wasson (2013) argues against Vesta being the parent asteroid of

early in the history of the solar system. HEDs, none of his arguments requires that this be true. The evi-

Aside from lunar and martian meteorites, the HED meteorite dence outlined by McSween et al. (2013) in favor of Vesta as the HED

clan is the only group for which we have a strong candidate for the parent asteroid is more compelling in my opinion, but again, does

parent body, the asteroid (4) Vesta. McCord et al. (1970) showed not require that this be true. We could only be certain by returning

that the visible and infrared reﬂectance spectrum of Vesta is closely samples from Vesta so that the rocks and soils could be studied in

matched by the laboratory spectrum of the basaltic eucrite Nuevo laboratories for direct comparison with HEDs.

Laredo. Subsequently, Consolmagno and Drake (1977) argued that This article will cover the mineralogy, petrology, chemistry and

Vesta was indeed the parent body of the HED meteorites. How- petrogenesis of HED meteorites, and is an updated and expanded

ever, there appeared to be severe dynamical problems with moving version of the material covered in Mittlefehldt et al. (1998). Since

material from Vesta to Earth-crossing orbits and this cast doubt on the publication of that paper, several basaltic achondrites that are

a vestan origin for HEDs (Wasson and Wetherill, 1979). Vesta is compositionally, mineralogically and petrographically very similar

far from orbital resonances such that only energetic events could to HED meteorites, but demonstrably distinct, have been iden-

propel material into regions where they would have a reasonable tiﬁed (Bland et al., 2009; Mittlefehldt, 2005; Scott et al., 2009;

probability of evolving into Earth-crossing orbits. Cruikshank et al. Yamaguchi et al., 2002). These are classiﬁed here as ungrouped

(1991) showed that three near-Earth asteroids (NEAs) ∼1–3 km in basaltic achondrites. The silicates of mesosiderites are also petro-

diameter have spectral characteristics like those of Vesta and the logically similar to HEDs, but are distinct (Mittlefehldt, 1990; Rubin

HED meteorites. They suggested that these asteroids are the imme- and Mittlefehldt, 1992). All of these basaltic materials are thought

diate sources of many of the HED meteorites, but Cruikshank et al. to have been derived from different parent asteroids based on

(1991) did not favor Vesta as the ultimate source for the Earth- isotopic and/or petrologic differences. I will brieﬂy discuss the

approaching asteroids. Binzel and Xu (1993) found 20 asteroids ungrouped basaltic achondrites as they provide important infor-

with diameters in the range of 4–10 km in orbits similar to Vesta’s mation that may help constrain the nature of vestan differentiation.

that have Vesta-like spectra. These vestoids form a “trail” in orbital Mesosiderite silicates are too complex a topic to be included in this

element space from near Vesta to near the 3:1 resonance from review.

which material can be perturbed into NEA orbits. Binzel and Xu

(1993) proposed that these vestoids are blocks spalled off Vesta 2. Lithologies

by impacts, and that some spalls reached the 3:1 resonance and

evolved into NEAs, ultimately delivering HED meteorites to the The lithologic diversity of the HED clan is greater than can be

Earth. Thomas et al. (1997) determined the shape of Vesta to have a inferred from classiﬁcation designations. This has largely resulted

ﬂattened southern hemisphere, which they interpreted as indicat- from the explosive growth in meteorite recoveries beginning with

ing that a large impact basin was located approximately coincident the systematic harvesting of meteorites from Antarctica and later

with the southern rotation axis. Asphaug (1997) modeled an impact by the retrieval of meteorites from desert regions of the temperate

by a moderate-sized asteroid onto Vesta and showed that Vesta zones. With greater numbers of rocks available, the chance of rare

could have survived such an impact, forming the southern basin lithologic types being in collections increases. One side effect has

and the family of vestoids identiﬁed by Binzel and Xu (1993). been that some unique lithologies have been shoehorned into an

The Dawn mission to Vesta, the subject of a forthcoming existing classiﬁcation, and that can result in obscuring important

review (McCoy et al., 2014), has provided a wealth of detailed petrogenetic information.

D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183 157

There are three general types of lithologic diversity in the

HED clan; one engendered by igneous fractionation processes, one

resulting from thermal metamorphism, and one caused by impact

processing of the vestan crust. Of primary concern for decipher-

ing the geological evolution of Vesta is the diversity of igneous

rock types, the major focus of this paper. Metamorphic grade is

an important indicator of the thermal evolution of the crust and

is brieﬂy considered here. Most HEDs are breccias, but the brec-

ciation process is not a major focus of this paper. The terminology

for breccias used here follows Bischoff et al. (2006), and the clas-

siﬁcation of HED polymict breccias largely follows that of Delaney

et al. (1983) and Miyamoto et al. (1978). Fig. 1 graphically shows

the igneous and breccia lithologic types; modal mineralogy used in

Fig. 1a, b are given in Table S1. This paper is structured around the

major lithologic types given in the ﬁgure.

3. Mineralogy and petrology

3.1. Diogenites

The majority of diogenites are coarse-grained ultramaﬁc rocks

dominated for the most part by magnesian orthopyroxene. Most are

orthopyroxenites but several are harzburgites (Beck and McSween,

2010; Beck et al., 2013; Mason, 1963; Mittlefehldt et al., 1998).

Wittke et al. (2011) suggest that meteoriticists follow IUGS nomen-

clature for terrestrial ultramaﬁc rocks and thus diogenites with

between 10 and 40 vol% olivine should be referred to as olivine-

orthopyroxenitic diogenites rather than harzburgitic diogenites. I

will follow the Beck and McSween (2010) system here (Fig. 1a).

A few dunites seem related to diogenites. Beck et al. (2011) pre-

sented petrologic, compositional and oxygen isotopic data on Miller

Range (MIL) 03443 and concluded that it is related to HEDs (cf.

Krawczynski et al., 2008; Mittlefehldt, 2008). They argued that it

should be classiﬁed as a dunitic diogenite. Several other ultramaﬁc

meteorites have been suggested to be dunites from Vesta (North-

west Africa (NWA) 2968, NWA 5784, NWA 5968), but they are only

documented in abstracts (Bunch et al., 2006, 2010); their pedi-

gree remains to be veriﬁed. Some diogenites that contain more

ferroan orthopyroxene, pigeonite and plagioclase are transitional

to cumulate eucrites. Meteorites paired with Yamato (Y-) 75032

were originally classiﬁed as Yamato Type B or Y-75032-type dio-

genites (e.g., Takeda and Mori, 1985; Takeda et al., 1979) or as

pigeonite cumulate eucrites (Delaney et al., 1984a,b). An average

mode weighted by area of seven of these meteorites (Delaney et al.,

1984a,b) has 85 vol% total pyroxene (opx:pig:aug ∼ 62:17:6) and

12 vol% plagioclase. In terrestrial plutonic rock nomenclature, these

would be referred to as clinopyroxene norites or possibly gab-

bronorites (Streckeisen, 1976). Following Wittke et al. (2011), I

recommend classifying these and similar plagioclase-rich, ferroan

diogenites (e.g., Queen Alexandra Range (QUE) 93009, Mittlefehldt

et al., 2012a) as noritic diogenites (Fig. 1b). A caveat is that diogen-

ites that are plagioclase-rich by virtue of admixed eucritic debris

are polymict diogenites, not noritic diogenites.

Most diogenites are breccias (Fig. 2a and b), and some are

polymict breccias. An important type of diogenitic breccia is dimict

breccia composed of orthopyroxenitic and harzburgitic lithologies

(Beck and McSween, 2010; Mittlefehldt et al., 2012a) (Fig. 2c). The

original grain sizes of the diogenite protoliths are not well known.

The typical brecciated orthopyroxenitic diogenite is composed of

coarse orthopyroxene clasts up to 5 cm in size set in a ﬁne-grained

fragmental matrix of orthopyroxene (Mason, 1963). Dunitic dio-

genite MIL 03443 has a similar texture but with olivine as the Fig. 1. Modal mineralogy and classiﬁcation of diogenites (a) and diogenites and

eucrites (b). Modal mineralogy data taken from Table S1. Classiﬁcation of HED brec-

major mineral (Fig. 2e); olivine clasts up to 2.5 mm in size are

cia types (c) after Delaney et al. (1983) and Miyamoto et al. (1978).

present (Beck et al., 2013). Dimict orthopyroxenitic-harzburgitic

diogenites are composed of fragmental breccias of more magnesian

158 D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183

Fig. 2. Diogenite images. (a) Photomicrograph in plane polarized light of orthopyroxenitic diogenite LaPaz Ice Field (LAP) 91900. (b) X-ray elemental map of brecciated

orthopyroxenitic diogenite MET 01084 colorized using red = Mg, green = Ca, blue = Al. (c) Backscattered electron (BSE) image of dimict diogenite LEW 88679, showing a

triangular magnesian harzburgitic clast contained within less magnesian orthopyroxenite. (d) BSE image of unbrecciated harzburgitic diogenite GRA 98108. (e) BSE image of

brecciated dunitic diogenite MIL 03443.

harzburgite and more ferroan orthopyroxenite that are moderately indicating the meteorite broke up late during entry. Pyroxenes

intermingled (Beck and McSween, 2010). The Yamato Type B noritic in Tatahouine show patchy extinction under crossed polars indi-

diogenites are brecciated rocks composed of subangular mineral cating shock damage. Two unbrecciated harzburgitic diogenites

and lithic clasts in a black, glassy matrix containing ﬁne-grained, have quite different textures. Graves Nunataks (GRA) 98108 has

clastic debris (Mittlefehldt and Lindstrom, 1993; Takeda and Mori, an allotriomorphic-granular texture composed of orthopyroxene

1985; Takeda et al., 1979). and olivine grains up to mm size, with smaller grains of plagioclase

Some diogenites are unbrecciated but the abundance of them and diopside (Fig. 2d). MIL 07001 has a poikilitic texture in which

is not well documented; “unbrecciated” is not a descriptor used numerous olivine grains a few hundred ␮m in size are enclosed

for diogenites in the Meteoritical Bulletin Database. Three unbrec- in mm-sized orthopyroxene, and olivine-free zones contain sub-

ciated orthopyroxenitic diogenites, Grosvenor Mountains (GRO) hedral orthopyroxene grains with interstitial groundmass rich in

95555, Tatahouine and Y-74013 and pairs, have metamorphic or tridymite (Mittlefehldt and Peng, 2013). Unbrecciated orthopyrox-

shock textures. GRO 95555 has a polygonal-granular texture of enitic diogenite NWA 4215 has an unusual medium-grained texture

anhedral orthopyroxene grains up to 2.4 mm in size (Antarctic composed of zoned xenomorphic orthopyroxene grains ∼0.5 mm

Meteorite Newsletter, 19(2), 1996; Papike et al., 2000). The Yamato in size, and larger, irregularly shaped chromite grains (Barrat et al.,

Type A, or Y-74013-type, diogenites have a granoblastic texture 2006). Dhofar (Dho) 700 is a medium-grained unbrecciated rock

composed of equant, rounded orthopyroxene grains a few tens of composed of ∼99% slightly zoned orthopyroxene (mg# from 68 to

␮

m to mm in size, containing inclusions dominantly of chromite 71) with interstitial plagioclase and silica phases (Yamaguchi et al.,

and troilite (Mittlefehldt and Lindstrom, 1993; Takeda et al., 1978, 2011).

1981). Tatahouine is composed of numerous individual orthopy- Orthopyroxene is the major phase of most diogenites. Harzbur-

roxene fragments of cm size that are generally free of fusion crust gitic and orthopyroxenitic diogenites contain from ∼64 to

D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183 159

Fig. 3. Pyroxene quadrilateral diagrams for diogenites (a), cumulate eucrites (b), basaltic eucrites (c) and ungrouped basaltic achondrites (d). The ﬁeld for primary pyroxenes

in unmetamorphosed basaltic clasts from polymict eucrite Y-75001 is taken from Barrat et al. (2011). Representative tie lines between low-Ca pyroxene hosts and high-Ca

pyroxene exsolutions are shown in panels a-c. Data plotted are from Table S2. Pasamonte zoning trends (arrows) are from Schwartz and McCallum (2005).

∼

100 vol% orthopyroxene (Beck and McSween, 2010; Beck et al., Some diogenites contain orthopyroxene grains with varying

2013; Bowman et al., 1997; Sack et al., 1991, 1994) (Fig. 1a). Asuka Fe/Mg. Fowler et al. (1994) showed that individual grains in Garland

(A-) 881548 contains ∼37 vol% orthopyroxene (Yamaguchi et al., have higher Ti, Mn and Fe and lower Mg, Si and Cr in rims compared

2011) but these authors note that because of the small sample to cores. They concluded that this is a record of original igneous

size, coarse grain size and heterogeneous distribution of olivine, zoning and rejected the hypotheses that the compositional varia-

this mode might not be accurate. Dunitic diogenite MIL 03443 con- tions were caused by either interaction of pyroxene grains with a

tains only ∼5 vol% orthopyroxene (Beck et al., 2011). The pyroxene

mode of Yamato Type B noritic diogenites is given above. Different

sections of individual diogenites can have widely different orthopy-

roxene contents (Beck et al., 2013; Bowman et al., 1997; Yamaguchi

et al., 2011), demonstrating that modal abundances determined on

a single thin section can have low ﬁdelity.

The compositions of pyroxenes in many diogenites are well

characterized; Table S2 gives representative pyroxene com-

positions. For diogenites that contain distinct sub-lithologies,

such as Elephant Moraine (EETA) 79002 (Mittlefehldt, 2000)

and the dimict orthopyroxenite-harzburgite diogenites (Beck

and McSween, 2010), representative compositions for distinct

lithologies are presented. Fig. 3a shows pyroxene composi-

tions for diogenites. Orthopyroxenitic and harzburgitic diogenites

generally contain orthopyroxene of uniform major element

composition of ∼Wo2±1En74±2Fs24±1 (Fig. 3a) and mg# (molar

100 × MgO/(MgO + FeO)) of 74–77 (Fig. 4). Orthopyroxenes in MIL

03443 are at the magnesian edge of the range typical of orthopy-

roxenitic and harzburgitic diogenites: Wo3.0En75.3Fs31.7, mg# 78

(Fig. 3a, Fig. 4). Some diogenites are exceptionally magnesian or

ferroan. The diogenites with the most magnesian orthopyrox-

ene are NWA 1461 with orthopyroxene mg# of 86 (Bunch et al.,

2007; Barrat et al., 2010) and Meteorite Hills (MET) 00425 with an

orthopyroxene mg# of 84 (Mittlefehldt, 2012; Table S2); both are

orthopyroxenitic diogenites. Noritic diogenites are more ferroan

than typical diogenites; QUE 93009 contains orthopyroxene with

mg# of 70 (Mittlefehldt et al., 2012a; Table S2) and Yamato Type

B diogenites contain orthopyroxene with mg# of 66 (Fowler et al.,

1994; Mittlefehldt and Lindstrom, 1993; Table S2). Dimict diogen-

ite Lewis Cliff (LEW) 88008 is composed of two orthopyroxenitic

diogenite lithologies and the more ferroan contains orthopyroxene

Fig. 4. Histograms of low-Ca pyroxene mg#s in diogenites, cumulate eucrites and

with mg# 68 (Beck and McSween, 2010).

basaltic eucrites. Data plotted are from Table S2.

160 D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183

trapped melt phase or metamorphic equilibration between more

magnesian and more ferroan lithologies in this polymict breccia.

However, details of the textural context were not provided that

would allow full evaluation of the hypothesis. Fowler et al. (1994)

did note that some fractured grains show zoning only on a portion

of the grain margin and thus that compositional zonation occurred

prior to the ﬁnal brecciation and assembly. Fine-grained NWA 4215

contains orthopyroxene grains that are zoned in Fe/Mg, Ca, Al and

Ti that is thought to have resulted from interaction between cumu-

lus crystals and an interstitial melt that was ultimately expelled

from the rock (Barrat et al., 2006). Yamaguchi et al. (2011) stud-

ied a suite of diogenites and showed that compositional variations

within orthopyroxene grains are present in three. Two (Dhofar 700

and the Yamato Type A diogenite Y-74097) have variations in Fe/Mg

while A-881377 has variation in Ca content. These authors refer to

diogenites having compositional variations within orthopyroxene

grains as unequilibrated; those that do not are equilibrated in their

parlance.

Minor and trace element contents of diogenite orthopyroxenes

show considerable variation (Barrat et al., 2006; Fowler et al., 1994,

1995; Mittlefehldt, 1994; Shearer et al., 1997, 2010). The average

orthopyroxene Al and Cr within the diogenite group vary by factors

of 5 and Ti by a factor of 17 (Table S2). Fowler et al. (1994, 1995)

showed that minor and trace incompatible element contents for

different grains within individual diogenites can be quite variable.

Barrat et al. (2006) showed that within zoned ﬁne-grained orthopy-

roxenes there is a strong Ti–Al correlation. Mittlefehldt and Peng

(2013) demonstrated substantial Al and Ti variations on the scale of

a few hundred microns in orthopyroxene in unbrecciated harzbur-

gitic diogenite MIL 07001. Minor and trace incompatible elements

are decoupled from orthopyroxene mg# (Fowler et al., 1994, 1995;

Mittlefehldt, 1994). Incompatible element contents of diogenite

orthopyroxenes are positively correlated in general (Fowler et al.,

1994, 1995; Mittlefehldt, 1994), although some diogenites are

anomalous. For example, Al and Ti are positively correlated for

the most part, although some diogenites have anomalously high or

low Ti/Al ratios (Fig. 5a). Pyroxenes in the noritic diogenites have

very high Ti/Al ratios, consistent with co-crystallization with pla-

gioclase. Individual diogenites can show a weak positive correlation

between orthopyroxene Cr content and mg# (Berkley and Boynton,

1992), but this is not evident when considering the diogenite group

as a whole (Fig. 5b).

Olivine is a minor to major mineral making up between 0 and

33 vol% of orthopyroxenitic and harzburgitic diogenites (Beck and Fig. 5. (a) Ti (apfu) vs. Al (apfu) for diogenite orthopyroxenes. (b) Cr (apfu) vs. mg#

for diogenite orthopyroxenes. Data plotted are from Table S2.

McSween, 2010; Beck et al., 2013; Bowman et al., 1997; Sack

et al., 1991, 1994), and ∼91 vol% of MIL 03443 (Beck et al., 2011).

A-881548 contains ∼63 vol% olivine but this mode might not be

accurate (Yamaguchi et al., 2011). Again, different sections of indi- diogenites. Table S3 summarizes representative olivine composi-

vidual diogenites can have very different olivine contents (Beck tions for diogenites, and Fig. 6 gives a histogram of olivine mg#.

et al., 2013; Bowman et al., 1997; Yamaguchi et al., 2011). Olivine When multiple lithologies are present in a diogenite, olivine is

grains are commonly a few hundred ␮m to ∼mm in size, but they usually associated with the more magnesian lithology and this

are often crystal fragments as clasts and matrix grains. Olivine has is independent of the mg# of the rock. Mittlefehldt (2000) con-

been found with its original textural context with orthopyroxene cluded that olivine in EETA79002 was in equilibrium with the most

partially or completely preserved in only a few diogenites – Allan magnesian orthopyroxenes in this genomict breccia, and suggested

Hills (ALHA) 77256, Dhofar 700, GRA 98108, LEW 88679, MIL 03443, the parent lithology was a harzburgite more magnesian than the

MIL 07001, NWA 4215 and Roda (Barrat et al., 2006; Beck and orthopyroxenite that constituted the bulk of the breccia. Beck and

McSween, 2010; Mittlefehldt, 1994, 2008; Mittlefehldt and Peng, McSween (2010) documented that for a set of orthopyroxenite-

2013; Sack et al., 1991; Yamaguchi et al., 2011) (Fig. 2c–e). Olivine harzburgite dimict breccias, the harzburgite lithology is always the

in harzburgitic diogenites MIL 07001 and NWA 5480 and in dunitic more magnesian. Further, some of the harzburgite lithologies are

diogenite NWA 5784 show lattice-preferred orientations similar to more ferroan than some olivine-free orthopyroxenite lithologies

those observed in olivine from terrestrial mantle peridotites that in different meteorites (Beck and McSween, 2010). This is one of

were affected by high-temperature solid-state plastic deformation the most signiﬁcant new ﬁndings in diogenite petrology because it

(Tkalcec and Brenker, 2014; Tkalcec et al., 2013). suggests that the rocks were not formed as a single, continuously

Olivine compositions have been determined for many dio- evolving magmatic sequence. This had previously been inferred

genites, although mostly for diogenites containing olivine-rich from trace element distributions in orthopyroxene separates of dio-

lithologies; few analyses exist for olivine in orthopyroxenitic genites (Mittlefehldt, 1994). Olivine is present in the anomalous

D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183 161

Fig. 6. Histogram of olivine mg#s for diogenites. Data represent either a single mete-

orite for unbrecciated and monomict diogenites, or each distinct lithology in the rock

for dimict and polymict rocks. Data plotted are from Table S3.

diogenites Dhofar 700 and NWA 4215; in the latter the grains have

modest Fe/Mg zoning (Barrat et al., 2006; Yamaguchi et al., 2011)

Chromite is a ubiquitous minor mineral making up from a trace

to 5 vol% (Beck and McSween, 2010; Bowman et al., 1997). It occurs

as mm-sized equant grains in igneous contact with orthopyrox-

ene, as clasts in the breccia and as grains a few tens to hundreds of

␮

m in size poikilitically enclosed in orthopyroxene. Table S4 gives

average chromite compositions for diogenites. Chromite grains in

typical diogenites are variable in Cr/Al and mg# but have a limited

variation in Ti contents (Fig. 7). Sack et al. (1991, 1994) show a range

in mg# for EETA79002 chromites from ∼14 to 32. This is most of

the range found for the averages of chromites for all diogenites. The

range in Al2O3 contents of average chromites is considerable, from

5.5 to 21.8 wt%, (Beck and McSween, 2010; Bowman et al., 1999;

Domanik et al., 2004; Mittlefehldt, 1994; Yamaguchi et al., 2011). Fig. 7. Compositions of chromites and ulvöspinels in HEDs. Data plotted are from

Within individual diogenites, chromite grains can also be variable Table S4.

in Al2O3 composition. Chromite grains in Roda range in Al2O3 from

8.6 to 18.6 wt%, although most grains contain between 8.6 and give an analysis. High-Ca pyroxene is often present as thin lamel-

10.2 wt% (Gooley, 1972). Small grains are often of different com- lae or blebs in orthopyroxene, but discrete grains in the matrix

position than large grains, but the differences are not systematic or interstitial to orthopyroxene grains are also found (Beck and

(Mittlefehldt, 1994; Mittlefehldt and Lindstrom, 1993). Chromite McSween, 2010; Domanik et al., 2004; Mittlefehldt, 1994, 2000).

grains in NWA 4215 show substantial variations in composition The lamellae are the products of subsolidus exsolution from the

(Barrat et al., 2006) but this is a very unusual diogenite and its orthopyroxene and can have sub-micron widths; these are iden-

properties were established by processes not common to diogenite tiﬁed as augite (Mori and Takeda, 1981a). Lamellae and discrete

petrogenesis. grains large enough for electron microprobe analysis include augite

Other minor silicate minerals include plagioclase (≤5 vol%), and diopside; representative compositions are given in Table S2.

high-Ca pyroxene (≤12 vol%) and a silica phase (≤2 vol%) (Beck Note that low-Ca clinopyroxene is also present in some diogen-

et al., 2010; Bowman et al., 1997; Domanik et al., 2004, 2005; ites were it was formed by shock deformation of orthopyroxene

Mittlefehldt, 1994). The Yamato Type B noritic diogenites also con- (Mori and Takeda, 1981a). A silica phase can occur as equant grains

tain on average ∼17 vol% inverted pigeonite, which has exsolved a few tens of ␮m in size, but the textural setting has not been

augite as lamellae and blebs (Delaney et al., 1984a,b; Mittlefehldt well described. In MIL 07001 silica is an interstitial phase between

and Lindstrom, 1993; Takeda and Mori, 1985; Takeda et al., orthopyroxene grains (Mittlefehldt and Peng, 2013).

1979). Plagioclase is often found as crystal fragments in the Troilite (≤3 vol%) and metal (≤1 vol%) are common minor phases

matrix (Fig. 2b), but does occur in primary textural context in (Beck et al., 2010; Bowman et al., 1997; Domanik et al., 2004).

some diogenites (Fig. 2d). Plagioclase is usually anorthitic in the Troilite occurs as equant grains or polycrystalline aggregates sev-

range An82–96, but grains as sodic as An73–77 are found in some eral hundred microns in size in the matrix, or as small grains less

(Beck and McSween, 2010; Domanik et al., 2004; Floran et al., than a few microns in size included within orthopyroxene. The lat-

1981; Fredriksson, 1982; Gooley, 1972; Mittlefehldt, 1979, 1994; ter often form inclusion curtains within orthopyroxene along with

Mittlefehldt et al., 2012a; Table S5, Fig. 8). Domanik et al. (2004) some combination of metal, chromite and silica (Domanik et al.,

report plagioclases as sodic as An46 in Bilanga, but they do not 2004; Gooley and Moore, 1976; Mori and Takeda, 1981a). The metal

162 D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183

Henderson, 1949; Lovering, 1975; Mayne et al., 2009; Mittlefehldt

and Lindstrom, 1993), for example, Moore County and Moama

(Fig. 9). The cumulate eucrites have been subdivided into the

feldspar- and orthopyroxene-cumulate eucrites based on modal

abundances (Delaney et al., 1984a,b), but this terminology is not

widely used. Binda is the only orthopyroxene-cumulate eucrite

identiﬁed by Delaney et al. (1984a). However, Takeda et al. (1976)

had previously demonstrated that the primary igneous pyroxene in

Binda is a low-Ca pigeonite that had exsolved augite and inverted

to hypersthene.

The original igneous pyroxene of most cumulate eucrites was

pigeonite, which subsequently underwent subsolidus exsolution

of augite and for some the pigeonite inverted to orthopyroxene

accompanied by additional augite exsolution (Hess and Henderson,

1949; Harlow et al., 1979; Lovering, 1975; Mori and Takeda, 1981b;

Takeda et al., 1976). The result is a complex pyroxene texture that

can involve as many as seven distinct phases (Mori and Takeda,

1981b). These exsolution textures can be used to model cooling

rates for the cumulate eucrites (e.g., Miyamoto and Takeda, 1977).

Table S2 gives representative low-Ca and high-Ca pyroxene analy-

ses for several cumulate eucrites, and pyroxene compositions are

shown in Fig. 3b. ALH 85001 and Binda are the most magnesian

of the cumulate eucrites, with low-Ca pyroxene mg# of 66.1 and

64.6 (this work; Pun and Papike, 1995). These cumulate eucrites

merge into the pyroxene compositional range of diogenites: Yam-

ato Type B diogenites, 66.5 (Mittlefehldt and Lindstrom, 1993); MIL

07613, 62.7 (Mittlefehldt et al., 2013a). The most ferroan cumu-

late eucrite, Y-791195, contains low-Ca pyroxene with mg# of 42.6

(Mittlefehldt and Lindstrom, 1993).

Cumulate eucrites contain plagioclase with compositions in

the range An91–95 and with very low K2O contents, mostly

<0.05 wt% (Lovering, 1975; Mayne et al., 2009; Mittlefehldt, 1990;

Fig. 8. Histograms of plagioclase An contents in diogenites, cumulate eucrites and Mittlefehldt and Lindstrom, 1993; Treiman et al., 2004). These com-

basaltic eucrites. Data plotted are from Table S5.

positions are on average more calcic than those of basaltic eucrite

plagioclases. Cumulate eucrite plagioclase compositions are shown

in Fig. 8 and representative compositions are given in Table S5.

phases are kamacite, taenite and tetrataenite that occur as grains

Chromite/ulvöspinel is a minor mineral in all cumulate eucrites

in the matrix and as inclusions in orthopyroxene (Domanik et al.,

(Delaney et al., 1984a,b). It occurs in a variety of textures, includ-

2004; Gooley and Moore, 1976; Mittlefehldt, 2000). Kamacite and

ing discrete gains interstitial to pyroxene and plagioclase, elongate

taenite grains have wide ranges in Co and Ni contents and Ni/Co

grains intergrown with tridymite and as inclusions in pyrox-

ratios, even within a given diogenite (Gooley and Moore, 1976;

ene (Ghosh et al., 2000; Hostetler and Drake, 1978; Kaneda

Mittlefehldt, 2000).

et al., 2000; Lovering, 1975; Mittlefehldt and Lindstrom, 1993).

Trace phases include Ca-phosphates, K-feldspar, pentlandite

Chromite/ulvöspinel grains in cumulate eucrites typically have

and native copper (Domanik et al., 2004, 2005; Mittlefehldt, 1994;

higher TiO2 contents and lower mg# than those in diogenites

Mittlefehldt and Peng, 2013). The phosphates in Bilanga and

(Fig. 7), but the Al2O3 contents overlap (e.g., Bunch and Keil,

Roda are rich in light rare earth elements with wt% quantities of

1971; Ghosh, 2000; Hostetler and Drake, 1978; Lovering, 1975;

La O and Ce O (Domanik et al., 2004, 2005; Mittlefehldt, 1994).

2 3 2 3 Mayne et al., 2009; Mittlefehldt and Lindstrom, 1993). In many

Ilmenite is a trace phase in some nortitic diogenites (Delaney

cases, the compositional variability of chromite/ulvöspinel grains

et al., 1984a,b; Mittlefehldt and Lindstrom, 1993; Mittlefehldt et al.,

within cumulate eucrites is not well documented because average

2012a).

analyses are often presented. Ferroan cumulate eucrite Y-791195

contains chromite/ulvöspinel grains that vary from 8.6 to 15.7 wt%

3.2. Cumulate eucrites in TiO2, which is negatively correlated with Al2O3 and Cr2O3

contents (Mittlefehldt and Lindstrom, 1993). Average or represen-

Cumulate eucrites are medium- to coarse-grained gabbros tative chromite/ulvöspinel compositions for cumulate eucrites are

composed principally of low-Ca clinopyroxene and calcic pla- given in Table S4.

gioclase with minor chromite and accessory silica, phosphate, Ilmenite occurs in many cumulate eucrites but it has not

ilmenite, metal, troilite and zircon (e.g. Delaney et al., 1984a,b; been reported in ALHA81313, Moama or Vissannapeta (Delaney

Gomes and Keil, 1980). Several cumulate eucrites are unbrec- et al., 1984a,b; Ghosh et al., 2000; Lovering, 1975; Mayne et al.,

ciated but many are breccias. Binda is a polymict breccia (Delaney 2009). Ilmenite occurs as individual grains, composite grains with

et al., 1983; Garcia and Prinz, 1978; Yanai and Haramura, 1993) chromite and as exsolution lamellae in chromite (Bunch and Keil,

and some polymict eucrites and howardites contain abundant 1971; Hostetler and Drake, 1978; Mittlefehldt and Lindstrom,

cumulate eucrite material (e.g., Gardner and Mittlefehldt, 2004; 1993). Minor constituents of ilmenite – MgO, MnO and Cr2O3 –

Mittlefehldt and Lindstrom, 1993; Saiki et al., 2001; Takeda, 1986, usually are at <3 wt%, and mg# varies from 9 to 5 (Bunch and Keil,

1991). The typical texture of unbrecciated cumulate eucrites is 1971; Mayne et al., 2009; Mittlefehldt and Lindstrom, 1993). Aver-

equigranular with subequal amounts of pyroxene and plagio- age or representative ilmenite compositions for cumulate eucrites

clase grains 0.5–5 mm across (Duke and Silver, 1967; Hess and are given in Table S6.

D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183 163

Fig. 9. Colorized mineralogy maps for select unbrecciated cumulate eucrites (Moore County and Moama) and basaltic eucrites (all others), showing the range of textures and

grain sizes.

Modiﬁed from Mayne et al. (2009).

A silica polymorph is commonly present but the speciﬁc poly- in terrestrial rocks. These authors conclude the quartz veins were

morph is often not identiﬁed. Tridymite is present in Moama, precipitated from aqueous ﬂuids (see Section 8).

Moore County and Serra de Magé (Duke and Silver, 1967; Hess and Metal in several unbrecciated cumulate eucrites has low Ni

Henderson, 1949; Lovering, 1975; Treiman et al., 2004). Treiman contents, ≤0.5 wt% (Duke, 1965; Lovering, 1964, 1975; Mayne et al.,

et al. (2004) document the presence of quartz veinlets in Serra 2009). Polymict cumulate eucrite Binda contains some metal grains

de Magé in a textural context similar to that of antitaxial veinlets with ∼2 wt% Ni (Lovering, 1964). The textural setting of this metal

164 D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183

Fig. 10. Basaltic eucrite images. (a) Photomicrograph in plane polarized light of brecciated eucrite QUE 97430. (b) Photomicrograph in plane polarized light of unbrecciated,

porphyritic basaltic eucrite LEW 88009. (c) BSE image of anomalous unbrecciated, metamorphose basaltic eucrite EET 90020. (d) Initial processing image of unbrecciated

metamorphosed basaltic eucrite GRA 98098. The light-toned “veins” contain long, tridymite needles. (e) Photomicrograph in crossed polarized light of unbrecciated meta-

morphosed basaltic eucrite GRA 98098. The medium-gray cracked grain is coarse tridymite from one of the light-toned “veins.” (f) BSE image of unbrecciated metamorphosed

basaltic eucrite GRA 98098 showing a portion of one of the plagioclase-tridymite light-toned “veins.”.

was not given, and possibly the high-Ni metal is not innate to the from very ﬁne-grained vitrophyric texture consisting of pyroxene

cumulate gabbro lithology of this polymict breccia. microphenocrysts set in a groundmass of pyroxene microcrysts

and glass of mixed plagioclase-silica composition (ALHA81001) to

3.3. Basaltic eucrites coarse-grained subophitic texture with ﬁne-grained, recrystallized

mesostasis (paired Pecora Escarpment (PCA) 91078, PCA 91245)

Basaltic eucrites are pigeonite-plagioclase rocks with ﬁne to (Howard et al., 2002; Mayne et al., 2009) (Fig. 9). NWA 5073 is a

medium grain size. Most are brecciated, composed of mineral rare, unbrecciated and almost unmetamorphosed basaltic eucrite

and lithic fragments set in a ﬁne-grained, generally fragmen- composed of coarse-grained zoned pyroxenes, skeletal plagioclase

tal matrix (Fig. 10a). Original igneous textures are preserved in grains, dendritic chromite grains and a ﬁne-grained mesostasis

lithic clasts in brecciated eucrites and are generally subophitic (Roszjar et al., 2011).

to ophitic (Duke and Silver, 1967). A few basaltic eucrites are The original igneous pyroxene in basaltic eucrites was fer-

unbrecciated (Figs. 9 and 10b), but some of these have been roan pigeonite, but some original pyroxene in Sioux County

highly metamorphosed, resulting in recrystallized, granoblastic was orthopyroxene (Takeda et al., 1978a). Most eucrites have

textures (Fig. 10c–f) (Mayne et al., 2009). Two of these, A- been metamorphosed and the original pigeonite underwent sub-

881388 and A-881467, are interpreted to be granulitic breccias solidus exsolution of augite and homogenization of original Fe/Mg

- brecciated eucrites that were highly metamorphosed to yield zonation. Inversion of pigeonite to orthopyroxene is uncommon.

an overall granulitic textured rock (Yamaguchi et al., 1997a). Metamorphism also engendered clouding of pyroxene and pla-

Unbrecciated, igneous-textured basaltic eucrites vary in texture gioclase through exsolution and/or redox of minor elements into

D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183 165

accessory phases (Harlow and Klimentidis, 1980; Schwartz and (Harlow and Klimentidis, 1980; Schwartz and McCallum, 2005).

McCallum, 2005). Takeda and Graham (1991) described the min- Olivine in basaltic eucrites is rare and very iron-rich. It occurs

eralogic characteristics of basaltic eucrite pyroxenes, and related in the most ferroan rocks and in the mesostasis of the least-

them to a metamorphic sequence of types from 1 to 6. The least metamorphosed basalts (e.g. Mittlefehldt and Lindstrom, 1993;

metamorphosed, type 1, basaltic eucrites contain pigeonite with Takeda et al., 1994). Ferroan olivine is also present in late-stage

only very narrow, <0.1 ␮m thick, augite exsolution lamellae, the veins transecting pyroxenes in some basaltic eucrites (e.g., Barrat

pyroxenes are not cloudy, and the original igneous Fe/Mg/Ca zon- et al., 2011); these are discussed in Section 8.

ing is preserved. The type 1 pyroxenes have cores of magnesian Calcium-phosphate phases are apatite and merrillite, and both

pigeonite with low Ca contents and are zoned to ferroaugite or phases can occur in a given eucrite. Merrilite is rich in rare earth ele-

subcalcic ferroaugite compositions. Type 6 basaltic eucrites, the ments (REE) while apatite contains lower concentrations of them

highest metamorphic grade, contain pigeonite with augite lamel- (e.g., Hsu and Crozaz, 1996). Eucrites are generally considered to

lae several ␮m thick and exhibit partial inversion of pigeonite to be volatile-poor igneous rocks, but the apatites in them contain

orthopyroxene. The grains are cloudy and homogeneous in Fe/Mg volatile elements in the structural X site. Saraﬁan et al. (2013) have

composition. Preservation of original Ca zoning is evident in some shown that apatite grains in basaltic and cumulate eucrites have

basaltic eucrites where grain rims contain higher densities of augite mostly F in the X sites, but some grains in Juvinas contain up to

lamellae than do cores. Note that Takeda and Graham (1991) used about 25% OH in the X sites. The apatite grains in eucrites are poor

preservation of chemical zoning of the pyroxene as one of the meta- in Cl, with <3% of the X site ﬁlled by it. However, unbrecciated, meta-

morphic type criteria. Basaltic eucrites exhibit a range of original morphosed basaltic eucrite GRA 98098 contains apatite grains with

grain sizes indicating differences in cooling rates; quite likely not ∼11% of the X sites ﬁlled by Cl (Saraﬁan et al., 2013).

all had the same original igneous zoning. Yamaguchi et al. (1996)

added a type 7 metamorphic grade containing pyroxenes with a 3.4. Petrologically anomalous eucrites

mixture of characteristics from types 4 and 6. The exsolution tex-

tures of basaltic eucrite pyroxenes have been used to quantify the A few eucrites have anomalous textures and compositions that

cooling rates for the rocks (e.g., Miyamoto and Takeda, 1977). Rep- cannot be easily ﬁt into the cumulate gabbro or basalt/metabasalt

resentative analyses for low-Ca and high-Ca pyroxenes are given in categories. Magnesian eucrite Pomozdino is an orthocumulate –

Table S2, and are shown in Fig. 3c. a rock consisting of a mixture of 30 ± 10% cumulus crystals with

Plagioclase in basaltic eucrites is calcic, in the range of bytownite a solidiﬁed melt (Warren et al., 1990). It is a monomict breccia

to anorthite (Table S5). Unlike cumulate eucrites where plagioclase but contains two distinctly different types of maﬁc clasts; coarse-

grains are typically homogeneous, plagioclase grains in individ- grained ophitic-poikilophitic and ﬁne-grained, anhedral-granular

ual basaltic eucrites can show considerable range in composition. clasts. Two distinct primary pyroxenes are present, one is composi-

Plagioclase compositions in Chervony Kut span the range An75–94 tionally similar to the primary pigeonite of cumulate eucrite Moore

(Mayne et al., 2009), while those in Nuevo Laredo span the range County, and the other shows Ca zoning similar to that documented

An74–92 (Warren and Jerde, 1987). These represent most of the in pyroxenes of the basaltic eucrites Bouvante and Stannern (Table

range observed for all HEDs (cf. Fig. 25 of Delaney et al., 1984a,b). S2). Both of these pyroxene types are magnesian, with mg# of ∼47

The K2O contents are low, usually ≤0.2 wt% (e.g., Mayne et al., and ∼52, quite different from pyroxenes from basaltic eucrites such

2009; and see Mittlefehldt et al., 1998), although some basaltic as Bouvante, which have mg#s of ∼38 (Christophe-Michel-Levy

eucrites contain plagioclase with K2O contents of ∼0.5 wt% (Mayne et al., 1987). Chromite and ilmenite in Pomozdino are similar to

et al., 2009; Mittlefehldt and Lindstrom, 1993). The An contents of those in Moore County and more magnesian than those of basaltic

basaltic eucrite primary plagioclases are shown in Fig. 8. Secondary eucrites (Tables S4, S6). Plagioclase is more sodic than those in

plagioclase is present in late-stage veins transecting pyroxenes in cumulate eucrites, An81–87 vs. An91–95 (Table S5).

some basaltic eucrites (Barrat et al., 2011); these are discussed in EET 90020 is an unusual unbrecciated, metamorphosed eucrite

Section 8. containing two distinct lithologies, one coarse-grained (Fig. 10c),

Chromite/ulvöspinel is a common minor mineral in basaltic one ﬁne-grained (Yamaguchi et al., 2001). The coarse-grained

eucrites. Chromite/ulvöspinel grains show wide ranges in com- lithology shows a REE pattern similar to those of cumulate eucrites,

positions, with TiO2 ranging between ∼1 and 23 wt%, Al2O3 but other incompatible lithophile element (Hf and Ta) contents

between ∼3 and 18 wt% and Cr2O3 between ∼18–59 wt%; rep- are typical of basaltic eucrites (Mittlefehldt and Lindstrom, 2003;

resentative compositions are given in Table S4 (Bunch and Keil, Warren et al., 2009). Pyroxene and spinel compositions are fer-

1971; Christophe-Michel-Levy et al., 1987; Mayne et al., 2009; roan, like those of basaltic eucrites (Mayne et al., 2009; Yamaguchi

Warren et al., 1990; Yamaguchi et al., 1994, 2009; this work). et al., 2001; this study). It seems clear that EET 90020 is a meta-

While in diogenites the major substitution is Al ↔ Cr, in basaltic morphosed basaltic eucrite, but the process that engendered its

eucrite it is Ti ↔ (Al + Cr), with a fairly constant Cr/Al (Fig. 7a). anomalous REE pattern is obscure. Yamaguchi et al. (2001) con-

Chromite/ulvöspinel compositions in basaltic eucrites completely cluded that the rock was heated to the point of partial melting and

overlap the range for cumulate eucrites in molar Al–Cr–Ti, but are loss of some of the melt engendered the cumulate eucrite-like REE

more ferroan (Fig. 7). pattern. In contrast, Mittlefehldt and Lindstrom (2003) concluded

Ilmenite grains are mostly ilmenite-picroilmenite solid solu- that the depletion of light REE but not of other highly incompati-

tions; representative compositions are given in Table S6. The minor ble elements (Hf, Ta) reﬂected subsolidus REE exchange between

element contents of MgO, Al2O3, Cr2O3 and MnO are <1.4 wt%, and the Ca-phosphates in the coarse- and ﬁne-grained lithologies cou-

mg# varies from 1.6 to 5.3. pled with non-representative sampling of this heterogeneous rock.

Other minor and accessory phases are the silica polymorphs Rare-earth-element-rich merrillite is present only in the ﬁne-

tridymite and quartz, ferroan olivine, metal, troilite, whitlock- grained lithology (Saraﬁan et al., 2013; Yamaguchi et al., 2001).

ite, apatite, zircon and baddeleyite (e.g., Delaney et al., 1984a,b; Several other basaltic eucrites with granulitic texture (Agoult, A-

Haba et al., 2014; Mayne et al., 2009; Saiki et al., 1991). These 87272, DaG 945, and NWA 2362) have REE patterns with some

phases typically occur interstitial to pyroxene and plagioclase, or similarities to that of EET 90020, and these have again been inter-

in mesostasis if present. Zircon is often intergrown with ilmenite preted to be restites (Yamaguchi et al., 2009). As was the case for

(e.g., Misawa et al., 2005). Cloudy pyroxene and plagioclase grains EET 90020, these other granulitic-textured basaltic eucrites do not

contain inclusions of silica, metal, troilite and phosphate phases have depletions in other highly incompatible elements (Yamaguchi

166 D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183

et al., 2009). Y-86763 is described as having a texture like that of evidence for Fe-Mg exchange among pyroxenes on a mm-scale

EET 90020, and the trace element compositions of pyroxenes are (Mittlefehldt et al., 2013b). Some polymict breccias contain glassy

like those of pyroxenes from the coarse-grained lithology of EET or glass-rich matrices. Paired polymict eucrites LEW 85300, LEW

90020 (Floss et al., 2000; Yamaguchi et al., 2001). 85302, LEW 85303 and LEW 88005 have matrices rich in dense,

ALHA81001 is a ﬁne-grained, quench-textured unbrecciated dark brown glass (Kozul and Hewins, 1988). Polymict diogenite Y-

basalt unlike any other eucrite (Mayne et al., 2009; Mittlefehldt 791073 is heavily shocked with a vesicular glassy matrix (Takeda,

and Lindstrom, 2003; Warren and Jerde, 1987). The mg# of the 1986). However, there has been no systematic study of matrix types

low-Ca pyroxene is higher than typical for basaltic eucrites, and in the polymict breccias and an evaluation of the degree of meta-

the feldspar component occurs as a glass with the composition of a morphism and the fraction of melt-matrix types are unknown.

plagioclase–silica mixture (Mayne et al., 2009). The bulk rock com- The polymict breccias, especially the howardites and polymict

position is also at the high end of the basaltic eucrite mg# range, eucrites, contain lithic components formed during gardening on

the Na content is anomalously low, and refractory incompatible ele- the surface of Vesta. Bunch (1975) recognized three types of brec-

ment contents are higher than typical for eucrites (Mittlefehldt and cia clasts: crystalline matrix breccias with ﬁne-grained fragmental

Lindstrom, 2003; Warren and Jerde, 1987). Warren and Jerde (1987) matrix, glassy matrix breccias having glassy or devitriﬁed matrix,

noted compositional similarities between ALHA81001 and Ibitira, and sulﬁde matrix breccias having troilite matrix. Labotka and

while Mittlefehldt and Lindstrom (2003) considered it an anoma- Papike (1980) and Fuhrman and Papike (1981) recognized sul-

lous member of the Stannern-trend eucrites. Delaney et al. (1984b) ﬁde matrix breccias as an important clast type, but they combined

considered an impact-melt origin as one possible explanation for crystalline and glassy matrix breccias and melt rocks into their

the petrologic characteristics of ALHA81001, but Warren and Jerde dark-matrix breccia type. Labotka and Papike (1980) considered

(1987) cited low upper limits for Ni and Au contents as making the dark-matrix breccia clasts to be fused soil and thus vestan

an impact-melt origin unlikely (see Warren, 1999; Warren et al., analogs of lunar agglutinates. However, true agglutinates are rare

1996, for published siderophile element data on this meteorite). in howardites (Noble et al., 2010). The matrices of melt rocks vary

ALHA81001 holds remanent magnetization that was acquired by from glassy to cryptocrystalline to ﬁne-grained quench-textured

cooling in a ﬁeld of crustal remanent magnetization formed by an (Bunch, 1975; Delaney et al., 1984a,b; Hewins and Klein, 1978;

early vestan core dynamo (Fu et al., 2012). The remanent magneti- Klein and Hewins, 1979; Mittlefehldt and Lindstrom, 1997, 1998).

zation was acquired 3.69 Gyr ago based on Ar-Ar chronometry (Fu Mittlefehldt et al. (2013b) distinguished between melt-matrix and

et al., 2012). dark-matrix breccias, with the difference being the grain size of the

matrix, but did not set rigorous limits for separating the two types.

3.5. HED polymict breccias Glassy spheres and irregularly shaped particles are commonly

found in howardites and can be composed of glass sensu stricto or

Airless rocky bodies in the Solar System are covered with a devitriﬁed glass (e.g., Barrat et al., 2009a; Bunch, 1975; Hewins and

layer composed of fragmental debris, lithiﬁed breccias and solidi- Klein, 1978; Labotka and Papike, 1980; Olsen et al., 1990). Warren

ﬁed melt particles formed by hypervelocity meteoroid impacts onto et al. (2009) used the abundance of glass particles, especially brown,

the surface (McKay et al., 1991). Howardites are polymict brec- turbid glass, as one indicator that a howardite might be regolithic.

cias, the lithiﬁed remnants of that debris layer from Vesta, and are Glassy particles may contain microphenocrysts of olivine and/or

mostly composed of diogenitic and eucritic debris (Duke and Silver, low-Ca pyroxene (Barrat et al., 2009a; Bunch, 1975; Hewins and

1967). There are also polymict breccias consisting only of debris Klein, 1978; Labotka and Papike, 1980; Mittlefehldt and Lindstrom,

from different types of eucrites (Miyamoto et al., 1978; Olsen et al., 1998; Olsen et al., 1990; Singerling et al., 2013). Most glassy par-

1978; Takeda et al., 1978b), and a few diogenites contain basaltic ticles in HED polymict breccias have petrologic characteristics and

eucritic clasts (e.g., Lomena et al., 1976). Thus, the suite of polymict compositions indicating that they are impact-melt particles of the

breccias includes rocks with eucrite:diogenite-mixing ratios out- vestan regolith (e.g., Olsen et al., 1990; Singerling et al., 2013).

side the range of “traditional” howardites (Mason et al., 1979). The However, some have unusual compositions suggestive of formation

HED classiﬁcation system now recognizes a continuum of brec- from speciﬁc lithologic components, such as evolved mesostasis

cia types from monomict basaltic eucrite to monomict diogenite (Singerling et al., 2013), or distinctly different lithologic terrains

breccias (Fig. 1c). Polymict eucrites are eucrite-rich breccias con- (Barrat et al., 2009a,b).

taining <10% diogenitic material, and polymict diogenites contain Most igneous clasts in polymict breccias are very similar or

<10% eucritic material (Delaney et al., 1983). Very few polymict identical to the lithologies found as basaltic eucrites, cumulate

breccias are composed only of mixtures of cumulate and basaltic eucrites and diogenites. However, some unusual lithologies are

eucrite materials. Binda is one (Yanai and Haramura, 1993), and is found only as clasts. Fine-grained porphyritic or microporphyritic

classiﬁed as a polymict cumulate eucrite (Delaney et al., 1983). Sim- clasts composed of pyroxene phenocrysts or microphenocrysts in

ilarly, polymict breccias composed only of diogenites and cumulate holocrystalline or variolitic groundmass of acicular plagioclase and

eucrites seem very rare; Y-791073 is an example (Takeda, 1986). pyroxene have been described in few howardites (Dymek et al.,

Howardites fall into two subtypes: regolithic howardites, the lithi- 1976; Mittlefehldt and Lindstrom, 1997), but these seem likely to

ﬁed remnants of the active regolith of Vesta; and fragmental be impact-melt clasts of howarditic composition (Mittlefehldt and

howardites, simpler polymict breccias (Mittlefehldt et al., 2013b; Lindstrom, 1997). Texturally and mineralogically, they are similar

Warren et al., 2009). Most of the material in the polymict brec- to microporphyritic glassy spherules and fragments (Barrat et al.,

cias is essentially the same as basaltic eucrites, cumulate eucrites 2009a; Olsen et al., 1990; Singerling et al., 2013). Howardite Y-

or diogenites, and their descriptions need not be repeated. Here I 7308 contains olivine-orthopyroxene clasts with variable amounts

will focus on material formed by regolith gardening and on unusual of plagioclase, chromite and high-Ca clinopyroxene (Ikeda and

lithologic components. Takeda, 1985). The olivine is euhedral to anhedral with mg# of

Many polymict breccias have fragmental matrixes that have 65–73; the orthopyroxene is similar in composition to those in the

been little modiﬁed by metamorphism, for example the howardites Yamato Type B noritic diogenites with mg# 69–74.

Bholghati, Kapoeta and Frankfort (Mason and Wiik, 1966a,b; Reid Numerous clasts of material as ferroan as or more so than

et al., 1990). Some polymict breccias have metamorphosed matri- the most evolved eucrites – Lakangaon and Nuevo Laredo, low-

ces. Polymict eucrite Y-792769 has a ﬁne-grained, sintered matrix Ca pyroxene mg# of 28–32 (Mason et al., 1979; Warren and

(Takeda et al., 1994), while howardite LEW 87002 shows petrologic Jerde, 1987) – have been described from howardites and polymict

D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183 167

eucrites. Ikeda and Takeda (1985) described a clast in Y-7308

composed of fayalitic olivine (mg# 10–14), hedenbergitic pyrox-

ene (mg# 27–32), tridymite, plagioclase (An78–85) and minor

ilmenite, chromite, troilite, Fe-metal and whitlockite. Mittlefehldt

and Killgore (2003) describe a cm-sized ferroan clast composed

of euhedral to subhedral plagioclase grains (An83–86) poikilitically

enclosed in a framework consisting of a single ferroan augite grain

(mg# 21); ﬁne-grained accessory silica, chromite, ilmenite, troilite

and metal decorate the boundaries between plagioclase and augite.

Several polymict breccias contain ferroan clasts consisting of pla-

gioclase and iron-rich pyroxenes, some with an assemblage of a

silica, fayalitic olivine and hedenbergite in symplectitic texture that

are likely breakdown products of pyroxferroite or metastable fer-

roan pyroxene (Barrat et al., 2012; Buchanan et al., 2000, 2005;

Patzer and McSween, 2012). The olivine in these has mg# in the

range 5–19, and high-Ca pyroxene has mg# as low as ∼3 (Barrat

et al., 2012; Buchanan et al., 2000; Patzer and McSween, 2012).

Accessory phases in these clasts include ilmenite, merrillite, apatite,

hyalophane, troilite, zircon and baddeleyite (Barrat et al., 2012).

Chondritic clasts were inferred to occur in the dark portion of

Kapoeta based on higher C content of this material compared to the

light portion (Müller and Zähringer, 1966), and were subsequently

identiﬁed in thin section (Wilkening, 1973). Since then, chondritic

clasts have been identiﬁed as a minor component of many HED

meteorites, especially the polymict breccias. Zolensky et al. (1996)

and Gounelle et al. (2003) found that most chondritic clasts in HEDs

are CM2 materials, with CR2 chondritic materials being less abun-

dant. Some clasts appear to be thermally processed CI chondrites

(Buchanan et al., 1993), and some clasts are closest to CV3 chon-

drites in mineralogy and petrology (Zolensky et al., 1992). Recent

surveys of exogeneous materials in HEDs have shown that ordinary

chondrite, mesosiderite and possibly pallasite clasts are present

(Beck et al., 2012; Lorenz et al., 2007; Prettyman et al., 2012).

4. HED compositions

Fig. 11. Oxygen isotope compositions of HEDs, other basaltic achondrites,

Basaltic eucrites show very limited ranges in major and minor

mesosiderites and pallasites. Data are from Bland et al. (2009), Floss et al. (2005),

element composition, while cumulate eucrites and diogenites are

Greenwood et al. (2005, 2006), Scott et al. (2009), Wiechert et al. (2004).

more diverse. The polymict breccias, to ﬁrst order, are simple mix-

tures of basaltic eucrites and orthopyroxenitic diogenites (e.g.,

High precision O isotopic analyses for IIIAB irons are reported

Jérome and Goles, 1971; Dreibus et al., 1977). Trace lithophile ele- 17

to have a mean O identical to that of main-group pallasites

ment and siderophile element contents show much wider ranges.

(Franchi et al., 2013).

I have maintained a database of achondrite compositions for 17

There is a systematic bias in O between data from the

decades. Whole rock and separated clast major, minor and trace

Carnegie Institution of Washington (Day et al., 2012; Wiechert et al.,

element compositions for HED meteorites and ungrouped basaltic

2004) and the Open University (Greenwood et al., 2005, 2014; Scott

achondrites are given in Table S7, a version of my current database

et al., 2009). I have adjusted data from the former institution so that

including only published data. Note that this database always lags

the mean values from the two laboratories agree; see discussion in

behind the publication rate to some extent so some data, especially

Scott et al. (2009). For the remainder of this paper, only data from

the most recent, may not be included.

Greenwood and colleagues at the Open University will be used.

Scott et al. (2009) calculated a 2× standard error of the mean

4.1. Oxygen isotopic composition (SEM) on O for eucrites and diogenites they measured of

±0.004‰, although they preselected the data to exclude analy-

With the advent of the laser-assisted ﬂuorination technique ses that are more than 3 standard deviations from a penultimate

for oxygen isotope analysis, HED meteorites have been shown mean. Using the same methodology, they calculated essentially

to be uniform in oxygen isotopic composition to high precision identical 2 SEM for the data from Greenwood et al. (2005) and

(Day et al., 2012; Greenwood et al., 2005, 2014; Scott et al., Wiechert et al. (2004). Using the same procedures, I calculate a 2

‰

2009; Wiechert et al., 2004). Fig. 11a shows the oxygen isotopic SEM for non-polymict HEDs of 0.0022 for Open University data

‰

compositions of HEDs, petrologically similar meteorites, and the (Greenwood et al., 2005, 2014; Scott et al., 2009) and of 0.0072 for

isotopically similar angrites and main-group pallasites in Clayton- Carnegie Institution of Washington data (Day et al., 2012; Wiechert

Mayeda oxygen-isotope space, and Fig. 11b focuses in on the region et al., 2004). In spite of the greater SEM for the latter dataset,

occupied by HEDs. The narrow range shown in Fig. 11b is crowded an important conclusion of these studies is that the HED igneous

with material derived from numerous differentiated asteroids, all of lithologies point to an isotopically uniform system. This was taken

which may have been formed in the same general region of the solar as evidence for isotopic homogenization by the magmatic processes

nebula. The IIIAB iron data are not shown in Fig. 11 because only operating on Vesta, and it was concluded that >50% melting of the

lower precision data are published (Clayton and Mayeda, 1996). asteroid occurred (Greenwood et al., 2005).

168 D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183

Fig. 12. Select element-element diagrams for HED meteorites showing distinct compositional ranges for diogenites, cumulate eucrites and basaltic eucrites, and mixing

ranges for polymict breccias. Data shown are averages calculated from the analyses given in Table S7. The ﬁeld “Sg” encloses the data for Stannern group of basaltic eucrites.

Mittlefehldt (2005) noted that the unbrecciated eucrite Ibitira Scott et al. (2009) describe other “eucrites” that are discrepant by

has a O that is 16 outside the mean of other HEDs (Wiechert >4 from the mean of other HED data, and ascribe them as hav-

et al., 2004), and demonstrated that signiﬁcant petrologic and trace ing been derived from distinct parent asteroids. Note that there

element differences are also observed. I concluded that Ibitira is is circularity in the logic here; Scott et al. (2009) ﬁrst excluded

an ungrouped basaltic achondrite from a distinct parent asteroid. outliers from calculation of the mean, and then concluded that

D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183 169

discrepant meteorites are likely from distinct parents. Some sup-

port for this conclusion is derived from recent Cr isotopic studies.

Benedix et al. (2014) and Sanborn and Yin (2014) showed that sev-

eral basaltic achondrites that have O isotopic compositions distinct

from eucrites also have ␧ Cr that is resolved from eucrites. These

include Pasamonte and PCA 91007 that have O displaced only

∼5 above the HED mean (Scott et al., 2009). However, Trinquier

et al. (2007) determined that the Cr isotopic composition of Pasa-

monte is identical to those of eucrites and diogenites, a discrepancy

that requires resolution. The alternative scenario is that Vesta is iso-

topically heterogeneous. The implications of this will be discussed

in the section on vestan geologic evolution.

4.2. Lithophile element compositions

The HED meteorites have several distinctive compositional

characteristics. Among these is a general paucity of moderately

volatile and volatile lithophile elements. The Na/Al ratios of basaltic

eucrites is roughly a factor of 10 lower than that of solar abundances

and of ordinary chondrite abundances, and a factor of ∼3 lower than

for CV and CK chondrites (McSween et al., 2011). The latter are the

most volatile-depleted chondrite groups (see Lodders and Fegley,

1998). The more volatile alkali elements (Rb, Cs) are at much lower

abundances relative to refractory elements (Mittlefehldt, 1987).

Estimates of the bulk composition of the HED parent asteroid have

abundances of moderately volatile and volatile elements similar to

those of the Moon (e.g., Anders, 1977; Dreibus and Wänke, 1980).

Other distinctive characteristics of eucrites and diogenites are their

very low abundances of siderophile elements. For example, typical

−2

CI-normalized abundances for basaltic eucrites are Co ∼10 , Ni

∼ −3 −6 −4 −7

10 to 10 , and Ir ∼10 to 10 (Warren et al., 2009). Cumu-

late eucrites and diogenites have on average higher siderophile

element abundances than basaltic eucrites, but their abundances

are low (Warren et al., 2009). In spite of their very low siderophile

element abundances, basaltic eucrites are rich in FeO, with the most

primitive basalts having mg#s of ∼40–42.

The compositions for select major and minor elements on HEDs

are shown in Fig. 12. Basaltic eucrites show very little variation in

bulk rock Mg, Al, Si, Ca and Fe; the most ferroan basaltic eucrites

have only ∼15% more Fe than the group average, and Mg-rich

basaltic eucrite EET 87520 has ∼12% less Fe (Fig. 12a). Cumulate

eucrites show greater variations in all but Si, in part due to vari-

ations in the mg# of their pyroxene (Fig. 3b) and in part due to

variations in modal pyroxene/plagioclase ratio (Fig. 1b; cf. Table

Fig. 13. Ti and Hf vs. mg# and Hf vs. Sc for basaltic eucrites showing the distinct

3c of Delaney et al., 1984a,b). Among igneous lithologies, diogen-

groupings of main-group, Stannern-group and Nuevo-Laredo-group eucrites. Data

ites show the widest ranges in major element composition. This is

shown are averages calculated from the analyses given in Table S7.

mostly a reﬂection of their lithologic diversity including dunites,

harzburgites, orthopyroxenites and norites (Beck and McSween,

2010; Beck et al., 2011; this work). Dunitic diogenite MIL 03443 has closest Sc contents to Dho 700 are all breccias, and their Sc contents

the highest Mg and Fe contents and lowest Al, Si and Ca (Fig. 12). might have been enhanced by basaltic components in the breccia.

However, some orthopyroxenitic diogenites contain exceptionally The basaltic eucrites were subdivided based on mg# and Ti

magnesian pyroxenes; these diogenites have higher bulk Mg and Si contents into the main-group, the Nuevo Laredo-trend and the

coupled with lower Fe. Diogenites include coarse-grained chromite Stannern-trend (Stolper, 1977). With the availability of a much

as a ubiquitous minor phase and bulk rock diogenites show a wide larger database, trends among basaltic eucrites have become more

range in Cr contents. This reﬂects a combination of the difﬁculty complex (McSween et al., 2011). Fig. 13a, is a Ti vs. mg# plot for

in obtaining a representative sample of coarse-grained cumulates basaltic eucrites, a variant of the diagram used by Stolper (1977)

and real heterogeneity in the diogenite suite. Bulk rock analyses to discuss basaltic eucrite petrogenesis. Most basaltic eucrites plot

∼ ∼

for Cr in some diogenites are always higher than typical for the within a region of mg# 36–42, Ti 2.3–4.9 mg/g; I will refer to

group indicating a more chromite-rich lithology rather than simple these as the main group as is common practice. Some eucrites plot

intra-sample heterogeneity (Mittlefehldt et al., 1998). Unbrecciated within this same mg# band, but at higher Ti contents; I will refer

orthopyroxenitic diogenite Dhofar 700 stands out as being mod- to these as the Stannern group. These equate with the Stannern-

estly anomalous in composition. Its Sc content (29.4 ␮g/g; Barrat trend of Stolper (1977), but with the discovery of new members

et al., 2008) is higher than for any other orthopyroxenitic diogenite and the redeﬁnition of Ibitira as an ungrouped basaltic achondrite

(5.6–21.6 ␮g/g; Table S7), and overlaps the range for main-group (Mittlefehldt, 2005), a “trend” from Ti-rich Stannern-group eucrites

eucrites (∼27–36; Table S7). Orthopyroxenitic diogenites with the to high mg# main-group eucrites no longer exists. The Stannern

170 D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183

group shows less dispersion on a Hf vs. mg# plot and is well-

resolved from the main group (Fig. 13b). A ferroan group of three

eucrites – Igdi, Lakangaon and Nuevo Laredo – is separated from

the main group with mg# ∼33, Ti ∼5.4 mg/g, Hf ∼1.7 ␮g/g. The cur-

rent population of basaltic eucrites shows a signiﬁcant gap in mg#

between the main group and the trio of ferroan eucrites. The data

form separate groups, rather than trends. Unless the gap is closed

through discovery of new basaltic eucrites, I recommend abandon-

ing the term “trend” to describe these eucrites and instead refer to

them as the Nuevo Laredo group. The Nuevo Laredo group is tightly

clustered in Fig. 13a and b, while the main group is not. There is

a crystal fractionation sequence between main-group and Nuevo-

Laredo-group eucrites (cf. Stolper, 1977), but there might be two or

more fractionation sequences represented by main-group eucrites

(McSween et al., 2011). Pomozdino has a higher mg#, and high

Ti and Hf contents. It is characterized as an orthocumulate from

an Stannern-group parent magma (Warren et al., 1990). McSween

et al. (2011) used a plot of Hf vs. Sc to distinguish the main group

from the Stannern group. On this plot (Fig. 13c), the Stannern group

is cleanly separated from the main group, while the Nuevo Laredo

group is on the edge of the ﬁeld of main-group eucrite data.

Yamaguchi et al. (2009) have proposed that eucrites like EET

90020 are a distinct compositional group, which they refer to as

“residual” eucrites. (Restitic eucrites would be a better term as the

hypothesis is that these eucrites are anatectic residues. This would

avoid confusing them with residual melts like Nuevo Laredo.)

Yamaguchi et al. (2013) have done melting experiments on a main-

Fig. 14. (a) Plagioclase An vs. low-Ca pyroxene En for basaltic eucrites and basaltic

group eucrite at temperatures just bracketing the solidus. They

clasts in polymict breccias, modiﬁed after Delaney et al. (1981) and Ikeda and Takeda

ﬁnd that at small degrees of melting, the mesostasis-rich regions

(1985). Fields “p” and “e” are peritectic and evolved basalt groups of Delaney et al.

melt, leaving the pyroxene-plagioclase framework largely intact.

(1981), and trends “A” and “B” are from Ikeda and Takeda (1985). (b) An equivalent

The minor/accessory phases apatite and ilmenite and by inference diagram based on bulk compositions shows that the main-group is equivalent to

zircon, enter the melt phase (Yamaguchi et al., 2013), which then Trend A while the Stannern group is equivalent to Trend B. Data shown are averages

calculated from the analyses given in Table S7.

should carry the bulk of the Zr, Nb, REE exclusive of Eu, Hf and Ta.

Zirconium, Nb, Hf, Ta in the alleged restitic eucrites are sometimes

at basaltic eucrite abundances, and sometimes abundances equal

to those of La and Ce (Mittlefehldt and Lindstrom, 2003; Warren They noted that the two new eucrites with trace element charac-

et al., 2009; Yamaguchi et al., 2009). The formation scenario pro- teristics similar to Stannern (Bouvante and Y-74450) plot on trend B

posed by Yamaguchi et al. (2001; 2009) does not address these of Ikeda and Takeda (1985), presaging the equivalence of the min-

inconsistencies, and because of this, the “restitic” eucrite group is eralogical groups and compositional groups argued for here and

not considered here. in McSween et al. (2011). Hewins and Newsom (1988) favored

Petrologic study of basaltic eucrites and clasts in polymict fractional crystallization of distinct parent magmas as the origin

breccias suggested that there are two groups of basalts – called peri- of the two mineralogical/compositional (trend A/main group and

tectic and evolved basalts – deﬁned by differences in plagioclase trend B/Stannern group) sequences. However, they noted a poten-

vs. orthopyroxene compositional trends (Delaney et al., 1981). The tial problem with modeling the trace element contents of trend B

peritectic group has petrologic similarities to main-group eucrites, basalts, and suggested that trend B magmas may have resulted from

while the evolved group shows similarities to Stannern (Delaney contamination or magma mixing with incompatible-element-rich

et al., 1981). Ikeda and Takeda (1985) extended this observation residual melts, presaging the model for Stannern-group formation

to clasts in howardite Y-7308, gave the trends the neutral desig- presented by Barrat et al. (2007).

nations A and B, equivalent to the peritectic, and evolved trends The polymict breccias show extreme heterogeneity in bulk

of Delaney et al. (1981). Fig. 14a is a schematic plot of plagioclase major and minor element composition, and span the ranges from

anorthite content vs. low-Ca pyroxene enstatite content showing basaltic eucrites to diogenites (Fig. 12). The linear relationships in

the mineralogical differences between trends A and B. Fig. 14b is Fig. 12 are consistent with the petrographic evidence that basalt

an equivalent bulk compositional plot of Na/Al vs. mg# for basaltic clasts are similar to basaltic eucrites and that orthopyroxene clasts

eucrites. In basaltic eucrites, most of the Na and Al are contained in are similar to diogenites (e.g., Bunch, 1975; Duke and Silver, 1967;

plagioclase, and the Na/Al ratio thus tracks the plagioclase compo- Mason et al., 1979). Note that on Al vs. Mg and Ti vs. Mg dia-

sition. Because the mineralogical basalt groups are deﬁned based on grams (Fig. 12c, e) the polymict breccia data do not show evidence

plagioclase anorthite content, Fig. 14b plots Na/Al in reverse order. for mixing with a substantial cumulate eucrite component (cf.,

The Stannern-group basalts generally have higher Na/Al, consis- Jérome and Goles, 1971; Dreibus et al., 1977; McSween et al.,

tent with trend B basalts. Thus the bulk compositional data are 2011; Mittlefehldt et al., 2013b). Some polymict breccias con-

consistent with the Delaney et al. (1981) supposition that trend tain Stannern-group basalts as their dominate maﬁc component

A (peritectic) basalts are equivalent to main-group eucrites, while (Fig. 12e), but the majority have compositions consistent with mix-

trend B (evolved) basalts included Stannern (cf. McSween et al., tures of main-group eucrites and diogenites (Mittlefehldt et al.,

2011). 2013b). Note that on an Hf vs. Mg diagram there is less evidence

Hewins and Newsom (1988) noted that the compositions of new for involvement of Stannern-group basalts in the polymict breccias

members of the Stannern group demonstrated that a single partial (Fig. 12f). (Many of the Ti data are from wet chemistry analyses that

melting trend as originally deﬁned (Stolper, 1977) was incorrect. can be inaccurate and/or imprecise for minor elements like Ti.)

D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183 171

Fig. 15. Incompatible lithophile trace element diagrams for HEDs showing good correlations and chondritic ratios for refractory elements (a), poorer correlations for

moderately volatile-refractory data (b) and volatile-refractory data (c) with decreasing element/refractory ratio for increasingly volatile elements, and moderately well

correlated volatile/moderately volatile element ratios (d) that are lower than the CI ratio. Data shown are averages calculated from the analyses given in Table S7.

The contents of incompatible trace lithophile elements gener- 4.3. Siderophile element compositions

ally increase in the sequence diogenite, cumulate eucrite, basaltic

eucrite, but there are overlaps of the ranges for cumulate eucrites Siderophile elements are at low to very low abundances

and diogenites for some elements (Fig. 15). For refractory highly in HED igneous lithologies, and are generally highest in the

incompatible elements, element-element ratios are generally polymict breccias. Chondritic debris is found even in supposedly

equivalent to CI ratios (Fig. 15a). For moderately volatile incompati- monomict breccias (e.g., Mittlefehldt, 1994), and for this reason, the

ble elements such as K, the correlation with refractory incompatible siderophile element contents of HED igneous lithologies need to be

elements breaks down for diogenites, and basaltic and cumulate evaluated cautiously. Cobalt is a moderately siderophile element

∼

eucrites have moderately-volatile/refractory incompatible element and HED igneous lithologies show ranges in Co contents from 3

␮ ∼ ␮

ratios much lower than CI (Fig. 15b). For volatile incompatible ele- to 9 g/g for basaltic eucrites and up to 11–30 g/g for diogenites.

␮

ments such as Cs or Tl, the correlation with refractory incompatible Nickel contents show much wider ranges: 0.1–50 g/g for basaltic

␮

elements completely breaks down and volatile/refractory incom- eucrites, 1–150 g/g for diogenites (Fig. 16). Carbonaceous chon-

patible element ratios are again much lower than CI (Fig. 15c). drites have about 20–200 times as much Co, but 80 to 123,000 times

Volatile element Cs is generally correlated with moderately the Ni. Contamination by chondritic debris in monomict breccias

volatile Rb, but with a ratio lower than that of CI chondrites is therefore much less a problem for Co. A mixing model between

(Fig. 15d). the most Ni-poor basaltic eucrite and CM chondrites shows that the

The contents of refractory incompatible lithophile elements in entire Ni range can be explained by as little as 0.5% chondritic debris

diogenites show wide ranges compared to those of basaltic or in the breccias (Fig. 16), but this engenders only a modest increase

cumulate eucrites (Fig. 15a). Part of this variation is due to varying in the Co content. For the most part, the ranges in Co contents

mixtures of a trapped-melt component in the cumulate rocks (cf., of basaltic eucrites, cumulate eucrites and diogenites likely reﬂect

Barrat et al., 2010; Mittlefehldt, 1994). However, even after consid- those of pristine igneous lithologies.

ering the potential effects of included trapped melt on diogenite The highly siderophile element contents will be similarly very

compositions, wide ranges in refractory incompatible lithophile susceptible to chondritic contamination. Warren et al. (2009)

element contents remain (Mittlefehldt, 1994). These ranges cannot demonstrated that the polymict breccias have Ir/Ni ratios that

be explained by simple models for HED petrogenesis that invoke almost exactly match the CM chondrite ratio, while some basaltic

crystallization of a global magma ocean (Barrat et al., 2008, 2010; eucrites, cumulate eucrites and diogenites have Ir/Ni ratios that are

∼

Mittlefehldt, 1994; Shearer et al., 1997, 2010). This topic will be consistently 0.4 times lower. These igneous HEDs have Ni and Ir

∼

explored in more detail in Section 6. concentrations that span a range of 600 times (lowest to highest)

172 D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183

This is a relatively metal-rich basaltic eucrite (Cleverly et al., 1986;

Palme et al., 1988) that also has a high Ni content (Barrat et al.,

2007). Béréba and Juvinas have generally increasing abundances

of highly siderophile elements from Os, the most compatible, to

Re, the least compatible. Stannern generally shows this same trend

except that Os is at a higher abundance than Ir and Ru (Fig. 17).

4.4. Noble gas contents

The noble gas contents of HED igneous lithologies are generally

quite low (e.g., Eugster and Michel, 1995), but some howardites are

rich in noble gases compared to other HED meteorites. Howardites

with higher noble gas contents contain two components, planetary-

and solar-type gases (e.g., Mazor and Anders, 1967). These authors

thought that these gases were added to the regolith by a single

carrier phase because the planetary- and solar-type gas contents

were correlated. Characterization of carbonaceous chondrite frag-

Fig. 16. Ni vs. Co for HEDs showing asymptotic approach to CM chondrite ratio with

ments in howardites (Wilkening, 1973) led to the identiﬁcation of

increasing siderophile element contents in polymict breccias. Small amounts of CM

chondrite contamination causes substantial increase in Ni with little change in Co as these clasts as the carriers of the planetary-type gases (Wilkening,

shown by the mixing model. Data shown are averages calculated from the analyses

1976). Experiments have shown that the solar-type gases are a sur-

given in Table S7.

face correlated component in mineral and glass fragments of HED

parentage, not just of the chondritic materials (Black, 1972; Caffee

et al., 1983; Padia and Rao, 1989; Rao et al., 1991). These solar-type

and includes monomict breccias and unbrecciated rocks, provid-

gases represent solar wind and fractionated solar wind implanted

ing good evidence that these are endogenous siderophile element

in the outer few ␮m of grains in the breccias. (The fractionated

contents. Within this subset, diogenites have the highest Ni and Ir

solar wind component was formerly referred to as a solar energetic

contents and basaltic eucrites have the lowest. Dale et al. (2012) and

particle component and thought to be derived from solar ﬂares,

Day et al. (2012) determined highly siderophile element (Ru, Pd, Re,

cf. Grimberg et al., 2006.) The solar wind component shows that

Os, Ir, and Pt) contents for suites of eucrites and diogenites. These

some howardites were part of the true regolith of their parent body

authors found ranges in concentrations spanning nearly 4 orders

(see discussion in Cartwright et al., 2013, 2014; Mittlefehldt et al.,

of magnitude, and most of the eucrites and diogenites have nearly

2013b).

chondritic patterns for highly siderophile elements (Fig. 17). The

unbrecciated harzburgitic diogenite MIL 07001 has the highest con-

−2

centrations, with abundances at ∼10 times CI for these elements

5. HED ages

(Day et al., 2012). Unbrecciated harzburgitic diogenite NWA 5480

−3

has ∼10 times CI abundances of the elements, and unbrecciated

The crystallization ages of HED igneous lithologies as deter-

−5 −4

orthopyroxenitic diogenite Tatahouine has ∼4 × 10 to 10 times

mined by long-lived chronometer systems – Rb-Sr, Sm-Nd, Pb-Pb

CI abundances. Some of the brecciated diogenites have lower abun-

– demonstrate that magmatism on Vesta occurred very early in

dances. Brecciated diogenite MET 00424 has lower abundances of

Solar System history (e.g., Allègre et al., 1975; Birck and Allègre,

highly siderophile elements than any of the unbrecciated diogen-

1978; Nyquist et al., 1986; Papanastassiou and Wasserburg, 1969;

ites (Fig. 17), while brecciated AHLA77256 and LAP 91900 have

Smoliar, 1993; Tera et al., 1997). However, almost all eucrites and

abundances lower than those of NWA 5480.

diogenites have been brecciated and/or thermally metamorphosed,

Basaltic eucrites have abundances of highly siderophile ele-

and the different geochronometers have responded differently to

−4 −5

ments typically between 10 and 10 (Dale et al., 2012) (Fig. 17).

these post-crystallization perturbations depending on the relative

Camel Donga has among the highest siderophile element contents.

diffusivities of the parent and daughter elements. The unbrecciated

cumulate eucrites Moore County and Serra de Magé yield Pb-Pb

model ages (Tera et al., 1997) that are resolvably lower than the best

estimate of the age of magmatism for the basaltic eucrites based on

Rb-Sr data (Smoliar, 1993). The cumulate eucrites have textures

and pyroxene exsolution characteristics that indicate they were

formed deep in the vestan crust and cooled slowly (e.g., Miyamoto

and Takeda, 1977; Takeda, 1979). Similarly, a Rb-Sr isochron age

for diogenites Johnstown and Tatahouine (Takahashi and Masuda,

1990) is resolvably lower than the estimate age of basaltic eucrite

magmatism. Johnstown is a breccia and Tatahouine suffered shock

damage, potentially resetting the Rb-Sr chronometer. Thus, while

long-lived chronometer systems provide evidence that magmatism

occurred very early on Vesta, the derived ages are neither robust

enough nor precise enough to detail the ﬁne-scale history of vestan

global igneous evolution.

Fine-scale interrogation of the relative ages of events in the dif-

ferentiation history of Vesta is provided by an array of short-lived

chronometers. These short-lived chronometers can be tied into an

Fig. 17. CI-normalized abundances of highly siderophile elements for select basaltic

absolute age scale if an accurate, precise, long-lived chronometer

eucrites (diamonds) and diogenites (circles) plotted in order of decreasing compat-

system can be applied to a milestone meteorite. Precise long-lived

ibility in silicate systems. Shown are averages of data from Dale et al. (2012), Day

et al. (2012) and Warren et al. (2009). chronometry is achievable with the Pb-Pb model age system that

D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183 173

can yield ages with uncertainties on the order of 120–200 Kyr for of the earliest diogenite cumulates at 0.6 Myr after CAI formation

igneous meteorites that are ∼4565 Myr old (Amelin, 2008; Wadhwa derived from the Al-Mg system (Schiller et al., 2011). Schiller et al.

26 26

et al., 2009). The short-lived chronometer systems Al- Mg (t½ (2011) concluded that the very short time interval between CAI and

53 53 182 182

0.73 Ma), Mn- Cr (t½ 3.7 Ma) and Hf- W (t½ 8.9 Ma) are diogenite formation is inconsistent with derivation of HEDs from

important ﬁne-scale chronometers for probing the timing of dif- an asteroid as large as Vesta because a large magma ocean could not

60 60

ferentiation of Vesta. The Fe- Ni system (t½ 2.62 Ma) appears reach the point where diogenites were crystallizing in only 600,000

to have suffered late-stage disturbance, possibly related to the Fe- years.

Mg exchange documented in pyroxenes, and has not yet provided Metamorphic and impact ages are best determined using the

39 40

chronological constraints on HED formation (Quitté et al., 2011). Ar- Ar method, and Bogard (2011) has summarized these stud-

The Al–Mg offers ﬁne-scale temporal resolution by virtue of ies for eucrites and howardites. The data show that the HED suite

the very short half-life of the parent nuclide. Because they are contains evidence for signiﬁcant Ar degassing in the period of about

an incompatible-compatible lithophile element pair, the system is 4.1 to 3.3 Ga ago. The broad age probability spectrum in this time

well ﬁtted for dating mantle differentiation events. Bizzarro et al. range shows highs and lows that are interpreted to indicate group-

26 26

(2005) determined that Mg* anomalies (radiogenic Mg) com- ings of ages that may be related to different large impact events

pared to the Earth, Moon, Mars and chondrites are present in on Vesta (Bogard, 2011). Relatively few HED samples have Ar-Ar

cumulate and basaltic eucrites. This demonstrated that Al was ages older than 4.1 Ga. Bogard and Garrison (2003) showed that a

live during magmatism on Vesta. The data were conﬁrmed by suite of unbrecciated, metamorphosed basaltic eucrites and cumu-

Schiller et al. (2010) who calculated that magmatism occurred on late eucrites have Ar-Ar ages consistent with a single thermal event

Vesta 2.6–3.2 Myr after formation of CAIs. Study of an extensive at 4.48 Gyr ago. They interpreted this result as indicating that the

suite of diogenites shows that they exhibit a range in Mg* that rocks had resided at depth where temperatures were sufﬁcient to

correlates with the contents of Ca, Ti and Yb in the orthopyroxene, keep the K-Ar system open until a large impact excavated them

and that are lower than the Mg* of basaltic eucrites (Schiller et al., and allowed rapid cooling and K-Ar closure to occur. Cohen (2013)

2011). These authors conclude that the data are consistent with the determined Ar-Ar ages for impact-melt clasts from the howardites

ingrowth of radiogenic Mg while the HED suite was forming via EET 87513, QUE 94200 and QUE 97001, and compared her results

solidiﬁcation of a global magma ocean. Schiller et al. (2011) calcu- with literature data from several howardites. She concluded that

late that diogenites crystallized from 0.6 to 2.5 Myr after formation the impact-melt clasts may indicate that impacts occurred at atyp-

of CAIs, and that the cumulate and basaltic eucrite reservoirs were ically high velocities during the time period 3.3–3.8 Ga, and that

formed between 2.1 and 2.8 Myr after CAI formation. As mentioned a greater number of impacts may not be the cause. In cases where

in Section 4.2, the variations in refractory incompatible lithophile multiple samples have been analyzed from the same meteorite, the

element contents of diogenites cannot be explained by simple Ar-Ar ages are not always concordant. For example, the results com-

global magma ocean models. Thus, the interpretation of the Mg* piled by Bogard (1995) show that Ar-Ar ages of different samples of

variations in diogenites espoused by Schiller et al. (2011) cannot Kapoeta vary from ∼3.44 to 4.48 Ga, and Cohen (2013) found ages

be correct in detail. Nevertheless, the correlations of Mg* with of 3.37 to 3.73 for impact-melt clasts from QUE 94200. This indi-

incompatible lithophile elements in diogenites does support the cates that the Ar-Ar ages of howardite clasts predate the assembly

general conclusion of ingrowth of radiogenic Mg with increasing of the breccias.

fractionation. This is explored in more detail in Section 6. Ages of thermal metamorphis can also be determined using the

Lugmair and Shukolyukov (1998) determined that diogenites, Hf-W system applied to metal and pyroxene. Under the tempera-

182

cumulate eucrites and basaltic eucrites deﬁne an isochron in the ture conditions of eucrite metamorphism, radiogenic W diffuses

53 53

Mn- Cr system. They indexed a precise Pb-Pb absolute age and out of pyroxene (high Hf/W) and is sequestered in metal (Hf/W ∼

53 53

Mn- Cr isotopic systematics for the angrite LEW 86010 to the 0) allowing computation of the timing of thermal metamorphism if

182 180

HED Mn-Cr isochron to derive an estimate for the time of differ- the Hf/ Hf ratio at the time of formation of the eucrite can be

entiation of the HED parent body at 7.1 ± 0.8 Myr before formation determined (Kleine et al., 2005, 2009). Using this technique, Kleine

of angrite LEW 86010, or an absolute age of 4564.8 ± 0.9 Ma. LEW et al. (2005) determined that the thermal metamorphism recorded

86010 is a plutonic and metamorphosed angrite (see Keil, 2012), in a suite of three main-group eucrites occurred 13–18 Myr after

and volcanic, unmetamorphosed angrite D’Orbigny is 5.9 Myr older crystallization.

than LEW 86010 (Amelin, 2008), indicating that HED parent body Cosmic ray exposure ages for HED meteorites range from ∼3

differentiation occurred roughly 1 Myr before magmatism on the Ma for the howardite Kapoeta (Wieler et al., 2000) to 110 Ma for

angrite parent asteroid. Trinquier et al. (2008) conﬁrmed this abso- the howardite Lohawat (Sisodia et al., 2001). Eugster and Michel

lute age for HED parent body differentiation, and pegged this event (1995), Herzog (2007), Shukolyukov and Begemann (1996) and

to 2.3 Myr after CAI formation. Welten et al. (1997) synthesized the cosmic ray exposure data that

182 182

The Hf– W system is uniquely able to constrain the timing were available. Eugster and Michel (1995) found that 80% of the 67

of core-mantle separation on differentiated asteroids because W HED meteorites studied fell into ﬁve exposure age clusters of 6 ± 1,

is a moderately siderophile element while Hf is lithophile. At the 12 ± 2, 21 ± 4, 38 ± 8 and 73 ± 3 Ma. Shukolyukov and Begemann

low oxygen fugacity conditions of vestan petrogenesis, a signiﬁcant (1996) found ﬁve CRE age clusters for eucrites. Three correlate with

fractionation of W from Hf occurred during metal-silicate separa- the Eugster and Michel (1995) clusters at 6, 21 and 38 Ma, but

tion (Newsom and Drake, 1982). In the silicate phase, both elements Shukolyukov and Begemann (1996) concluded that there are two

are incompatible and thus not very sensitive to mantle-crust frac- clusters at 10 ± 1 and 14 ± 1 Ma instead of a single cluster at 12

tionation. Early work in the W-Hf system suggested ages for vestan Ma. Welten et al. (1997) calculated exposure ages for the diogen-

differentiation of a few million years after formation of ordinary ites they analyzed, and combined their data with literature data to

chondrites (e.g., Quitté et al., 2000), but these analyses may have reevaluate the clustering of HED exposure ages. They parsed the

been compromised by contamination with terrestrial W (Kleine dataset differently than did Eugster and Michel (1995), and use 63

et al., 2009; Touboul et al., 2008). At present, the best estimate for HEDs for their analysis. They found only two statistically signiﬁcant

core-mantle differentiation of Vesta is 2.5 ± 1.2 Myr after CAI for- age clusters in the data, 22 ± 2 and 39 ± 5 Ma. The other age clus-

mation (Touboul et al., 2008), which is consistent with estimates ters identiﬁed by Eugster and Michel (1995) were not statistically

of HED parent asteroid differentiation from Mn-Cr (Trinquier et al., robust. Herzog (2007) also concluded that two impacts at ∼20 and

2008). However, these estimates are inconsistent with formation ∼40 Myr could have ejected most HEDs from their parent object.

174 D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183

The 22 and the 39 Ma age clusters each contain eucrites, polymict basaltic eucrite melts did not equilibrate with metal (McSween

eucrites, diogenites and howardites demonstrating the individual et al., 2011; Newsom, 1985; Palme and Rammensee, 1981), con-

impact events can liberate the range of petrologic types. Many cos- trary to the inference from melting experiments (Stolper, 1977).

mic ray exposure ages have been published since Herzog (2007) The abundances of P, Co, Ni, Mo and W in basaltic eucrites are best

(see for example Cartwright et al., 2013, 2014), and a reevaluation ﬁt by a model in which metal and silicate are totally molten (Righter

of HED exposure age clusters would be timely given that the Dawn and Drake, 1996); a Mason-type petrogenetic model.

mission has provided a detailed record of cratering on Vesta (e.g., High precision oxygen isotope measurements have shown that

Marchi et al., 2012). HEDs are very uniform in O (Greenwood et al., 2005, 2014;

Scott et al., 2009; Wiechert et al., 2004). Greenwood et al. (2005)

cited models that match the bulk composition of the HED parent

6. HED meteorite petrogenesis asteroid by mixing known chondrite types as indicating that prior

to differentiation Vesta would have been heterogeneous in O iso-

The earliest petrogenetic model for asteroidal differentiation tope composition on a many-km scale. They then concluded that

was based on the petrology and mineralogy of HED meteorites, the extreme uniformity in O isotopic composition of HEDs ( O

pallasites and iron meteorites and envisioned total melting and within ±3% of the mean) indicated homogenization via a magma

crystallization to produce a suite of igneous rocks. Mason (1962) ocean stage, which they calculated must have been formed by >50%

observed that the lithologies of the HED clan could represent a melting. Note that this conclusion stands on the assumption that

fractional crystallization sequence from early magnesian orthopy- because the bulk composition of Vesta can be modeled as a mixture

roxenites, through a series of rocks with increasing plagioclase of known chondrite types, the post-accretion interior was com-

content and Fe-enrichment of pyroxene, ending with basaltic posed of large-scale disparate compositional regions. As mentioned

eucrites as residual melts. He inferred that an iron core and dunitic above, the uniformity in O inferred for HEDs is partially because

mantle would occur in the deep interior. (Note that at this time, outliers were excluded from calculations of the means.

Mason thought howardites were a brecciated igneous rock type, Partly because of these problems with the Stolper (1977) petro-

and not an impact-engendered mixture of distinct lithologies.) genetic scheme, Mason-type magma ocean models have regained

The Mason model was the standard until Stolper (1977) pre- favor. Righter and Drake (1997) and Ruzicka et al. (1997) made

sented the alternative anatexis model. He did a series of melting detailed calculations of major and trace element fractionation

experiments on basaltic eucrites and found conditions of temper- during crystallization of a magma ocean, while Warren (1997) pre-

ature and oxygen fugacity at which some eucrites are saturated sented a more conceptualized view of vestan petrologic evolution

with pyroxene, plagioclase, olivine, metal and spinel, a mineral by magma ocean crystallization. Ruzicka et al. (1997) modeled

assemblage like that of ordinary chondrites. Thus he concluded that basaltic eucrites, excluding Stannern-group basalts, as having

some eucrites are primary partial melts of their parent body. Some formed in a magma ocean that ﬁrst fractionally crystallized dunites

eucrites are more Fe-rich, and he noted that these follow major and orthopyroxenites, and then crystallized under conditions

element trends of glasses produced in his experiments at differing approaching equilibrium to produce the suite of basaltic eucrites. In

degrees of crystallization. He interpreted the more ferroan eucrites contrast, Righter and Drake (1997) modeled the early stage of pet-

to be residual melts from differing degrees of crystallization of pri- rogenesis as equilibrium crystallization forming harzburgites, with

mary partial melts. The partial melting/fractional crystallization the basaltic residual liquid then undergoing fractional crystalliza-

model can successfully explain trace incompatible lithophile ele- tion to form the main-group basaltic eucrite suite. Stannern-group

ment contents of basaltic eucrites (e.g., Consolmagno and Drake, basalts represent other residual melts. Ruzicka et al. (1997) and

1977; Mittlefehldt and Lindstrom, 2003). Melting experiments on Righter and Drake (1997) come to opposite conclusions as to which

chondritic meteorites at the oxygen fugacity inferred for eucrite lithologies require equilibrium vs. fractional crystallization for their

petrogenesis yield melts from some chondrite types with compo- formation. The Righter and Drake (1997) model is more ﬁrmly

sitional characteristics similar to basaltic eucrites (Jurewicz et al., grounded in magma physics; they computed that a vestan magma

1993, 1995). In these experiments, moderately volatile elements ocean would undergo vigorous convection until sufﬁcient crystals

like Na were allowed to escape from the system and the resulting were present to cause convective lockup, and this informed their

melts had eucrite-like Na contents. modeling of the early stage as an equilibrium process.

However, details of eucrite and diogenite compositions have However, there are problems with these simple magma ocean

revealed several problems with the Stolper (1977) petrogenesis models in that they do not obviously describe the ranges of incom-

scheme. Warren (1985, 1997) used mass-balance constraints from patible trace element variations observed for diogenites. Bulk

major and trace elements to conclude that the maﬁc fraction of samples and pyroxene separates of diogenites show wide ranges in

howardites was mostly residual after crystallization of diogenites, incompatible element contents, which would imply a wide range

and by extension, most eucrites must also be. This contradicts the in fractional crystallization, but they have restricted ranges in mg#

conclusion based on the eucrite melting experiments that basaltic and mineralogy, suggesting a very narrow range in degree of crys-

eucrites are unlikely to be residual melts after extensive crystalliza- tallization (Mittlefehldt, 1994). In situ measurements of minor and

tion of more magnesian magmas (Stolper, 1977). A related problem trace elements in diogenite pyroxenes support this general conclu-

is that although experimental melts of a Na-poor CM chondrite sion (Fowler et al., 1994, 1995; Shearer et al., 1997). Fowler et al.

are similar to basaltic eucrites in composition, there is insufﬁcient (1995) and Shearer et al. (1997) concluded that the diogenite suite

pyroxene in the restite to produce abundant orthopyroxene cumu- can be modeled as cumulates arising via small amounts (10–20%)

lates from higher temperature partial melts (Jurewicz et al., 1993). of fractional crystallization of a suite of distinct basaltic magmas

Contrarily, high temperature melts in experiments on Na-poor LL formed either by fractional melting of a homogeneous source, or

chondrites do contain sufﬁcient normative pyroxene to explain dio- equilibrium melting of heterogeneous sources. This scenario is at

genites, but the low temperature melts produced are not a good odds with magma ocean models.

match for eucrite compositions (Jurewicz et al., 1995). The most recent magma ocean model incorporates polybaric

The siderophile element contents of basaltic eucrites also sug- crystallization and periodic tapping of a deep magma layer, and

gest that a primary partial melt model for basaltic eucrites is may have achieved resolution of this conundrum. The concep-

incorrect. Calculations using metal/silicate partition coefﬁcients for tualized model is shown in Fig. 18. Mandler and Elkins-Tanton

the moderately siderophile elements Co, Mo and W indicate that (2013) propose a model that includes an early stage of equilibrium

D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183 175

processes. Future extensions of the model will determine whether

the shortcoming identiﬁed by Barrat and Yamaguchi (2104) repre-

sents a fatal ﬂaw.

The petrologic and compositional characteristics of diogenites

do seem inconsistent with magma ocean models for vestan petro-

genesis (e.g., Barrat, 2004; Fowler et al., 1995; Mittlefehldt, 1994;

Shearer et al., 1997). Barrat et al. (2008, 2010) and Yamaguchi

et al. (2011) have concluded that the trace element characteristics

of diogenites are explained by a complex petrogenetic scheme in

which olivine- and pyroxene-rich magma ocean cumulates were

remelted, some were contaminated with melts derived from the

basaltic crust, and some were formed as shallow intrusions or even

surface ﬂows. At present, the energy source for this process has

not been identiﬁed. The heat engine powering vestan petrogene-

sis is thought to be primarily the decay of short-lived Al with a

lesser contribution from Fe (for example, Formisano et al., 2013).

Olivine-pyroxene-rich cumulates will have low contents of Al. Their

solidus temperature will also be higher than the temperature at

Fig. 18. Conceptualized differentiation model for Vesta, after Mandler and Elkins-

which they crystallized from the magma ocean because of their

Tanton (2013). Vestan structure: 1. metallic core; 2. possible restitic dunite lower

separation from the more felsic magma of their formation. Thus,

mantle if melting <100%; 3. cumulate harzburgite mantle; 4. possible minor cumu-

late dunitic diogenite layer; 5. diogenite lower crust; 6. minor cumulate eucrite a plausible scenario that allows this refractory cumulate to remelt

layer; 7. basaltic eucrite upper crust.

will be challenging to develop for Vesta.

The calculations of Wilson and Keil (2012, 2013) have chal-

crystallization à la Righter and Drake (1997). With an increasing lenged the magma ocean concept altogether. They argue that the

abundance of crystals, convective lockup occurs and the melt is fast melt production and easy melt migration in differentiated

essentially ﬁlter-pressed to the top of the mush where crystal- asteroids, including those of the size of 4 Vesta, imply formation

lization becomes non-equilibrium (fractional). An initial thermal of giant sills, not magma oceans. Thus, large-scale “magma oceans”

boundary layer of primitive chondritic material is gradually in asteroid mantles should not form.

replaced by a maﬁc crust through impact disruption, foundering The cumulate eucrites are accumulations of plagioclase and

and magma extrusion/intrusion; the maﬁc crust thickens over time. pyroxene from a crystallizing maﬁc melt. Cumulate eucrites are too

Melt from the residual magma ocean intrudes into the maﬁc crust iron-rich to be adcumulates from basaltic eucrites (Stolper, 1977).

and crystallizes a sequence of diogenitic and eucritic cumulates. However, Barrat et al. (2000) and Treiman (1997) showed that the

Periodic recharge of these crustal plutons from the residual magma major and trace element compositions of Binda, Moore County and

ocean melt buffers the major element composition of the magma Serra de Magé can be modeled as mixtures of cumulus minerals

but allows for increases in the incompatible lithophile trace ele- and trapped melt from magmas similar to basaltic eucrites. Barrat

ment contents. This causes decoupling major elements from trace (2004) and Mittlefehldt and Lindstrom (2003) showed that the

elements in the cumulate diogenites and restricts the evolution of trace element contents of many cumulate eucrites are consistent

basaltic eucrite compositions. Eruption of the maﬁc magmas forms with mixtures of cumulus pyroxene and plagioclase mixed with

basaltic eucrites. trapped melt, and that the parent magmas were similar to basaltic

The Mandler and Elkins-Tanton (2013) model is more detailed eucrites in trace element composition.

and dynamic than previous magma ocean models, but is still broad- Trace element data from mineral separates and in situ anal-

brush and does not treat the differences between the main-group yses on cumulate eucrites have been taken to indicate that the

and Stannern-group basalts. Barrat et al. (2007) put forth a crustal- parent magmas of cumulate eucrites were richer in REE than

contamination model to explain the genesis of Stannern-group basaltic eucrites and had unusual light REE-enriched patterns (Hsu

basalts. They showed that small degrees of partial melting of a and Crozaz, 1997; Ma and Schmitt, 1979; Ma et al., 1977). Pun

crust with the composition of main-group eucrites, and mixing and Papike (1995) also calculated nominal equilibrium melt REE

of this crustal melt with main-group basaltic eucrite magmas, contents from their in situ analyses of cumulate eucrites, but cau-

could replicate the trace element compositions of Stannern-group tioned that unusual parent melt compositions provided only one

basalts. Stannern-group basalts have higher Na/Al than main-group possible explanation of the result. They noted that subsolidus

basalts (Fig. 14b, and see McSween et al., 2011), and higher average redistribution of the REE or inappropriate partition coefﬁcients

modal tridymite/quartz (Delaney et al., 1984a,b), consistent with could be the cause of the unusual calculated patterns. Treiman

the crustal contamination model of Barrat et al. (2007). Yamaguchi (1996, 1997) showed that subsolidus redistribution of the REE

et al. (2009) have concluded that eucrites with light REE-depleted in cumulate eucrites and diogenites causes parent melts calcu-

patterns are restites from the process that formed Stannern-group lated by inversion of ion microprobe data to have unusual REE

basalts. However, when other refractory incompatible elements patterns that have no bearing on the original parent melt composi-

(Zr, Nb, Hf, Ta) are considered, these rocks do not match the mod- tion. There is no compelling evidence that magmas with very high

eling of Barrat et al. (2007). Thus, there is not a compelling reason light REE/heavy REE ratios existed during formation of the vestan

to connect EET 90020 and similar eucrites with the formation of crust.

Stannern-group eucrites.

Barrat and Yamaguchi (2014) contend that the Mandler and

Elkins-Tanton (2013) model is incapable of explaining some of the 7. Thermal metamorphism of the HED parent body crust

incompatible trace element characteristics of the diogenite suite,

for example the Dy/Yb ratios. But again, even though the Mandler- Most HED igneous lithologies show textural evidence for ther-

Elkins-Tanton is a great improvement over older magma ocean mal annealing expressed as variable degrees of Fe-Mg equilibration,

models (Righter and Drake, 1997; Ruzicka et al., 1997), the model exsolution of augite from pigeonite sometimes accompanied

is still of necessity rather simplistic in the way it treats geological by inversion of pigeonite to orthopyroxene, and mineral grain

176 D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183

recrystallization and clouding (Harlow and Klimentidis, 1980; 8. Fluid-mediated metasomatism?

Mayne et al., 2009; Metzler et al., 1995; Schwartz and McCallum,

2005; Takeda and Graham, 1991; Yamaguchi et al., 1996). Pyroxene Historically, HEDs have been considered to have formed on a

textures are generally correlated with mg#; pyroxenes in cumu- volatile-depleted asteroid and that ﬂuid phases were not involved

late eucrites (magnesian lithologies) have coarser exsolutions than in melting, magma crystallization or subsolidus processing.

those in basaltic eucrites (ferroan lithologies). These pyroxene tex- Mittlefehldt and Lindstrom (1997) presented evidence from an

tures can be used to model quantitatively the cooling rates of the impact-melt clast in the EET 92014 howardite that ﬂuid-mediated

rocks, which inform estimates of the depth of formation. These metasomatism occurred. Magnesian orthopyroxene phenocrysts in

observations led to development of a layered-crust model for Vesta the clast contained veins of Fe-rich pyroxene that have anoma-

(e.g., Miyamoto and Takeda, 1977; Takeda, 1979; Takeda et al., lously high Fe/Mn ratios, precluding igneous fractionation as the

1976). The pyroxene textures were interpreted to be caused largely cause of Fe enrichment. Similar Fe-rich, high Fe/Mn veining is

by slow cooling from the magmatic stage and hence the extent of found in numerous magnesian orthopyroxene clasts in several

pyroxene exsolution and inversion is related to the depth of forma- Elephant Morraine howardites (Mittlefehldt et al., 2011, 2013b)

tion of the rock (Takeda, 1979). Some eucrites do not ﬁt the general suggesting that a metasomatized orthopyroxenite protolith was

trend, suggesting that later metamorphism was an important pro- the source. These studies did not attempt to characterize the nature

cess in speciﬁc cases (e.g., Takeda and Graham, 1991). Possible of the ﬂuid agent. Treiman et al. (2004) concluded that the quartz

mechanisms for later metamorphism include impact heating and veinlets in Serra de Magé are the result of precipitation from aque-

heating by subsequent ﬂows or intrusions (contact metamorphism) ous solutions. The water was exogenic in origin, and aqueous

(e.g., Nyquist et al., 1986; Takeda and Graham, 1991). Impact mobilization of SiO2 in Serra de Magé was engendered sometime

heating was invoked to explain the pyroxene textural differences after formation of eucritic basalts and gabbros (Treiman et al.,

between monomict eucrites and basalt clasts in polymict breccias. 2004).

Monomict basaltic eucrites were thought to represent material Some Fe-enrichment zoning patterns in Pasamonte pyroxenes

from crater ﬂoors where impact energy is deposited and heat is are interpreted to have resulted from post-magmatic metasoma-

retained for longer times, while the basaltic clasts were ballisti- tism by a dry Fe-rich vapor (Schwartz and McCallum, 2005). In

cally dispersed in the polymict ejecta that was cooler (e.g., Nyquist contrast, Barrat et al. (2011), documented a variety of composi-

et al., 1986; Takeda and Graham, 1991). Impact heating, not global tional and mineralogical changes crosscutting pyroxenes in several

crustal metamorphism, was considered to be the cause of thermal eucrites, which they concluded were cause by interaction with late-

metamorphism recorded in the Hf-W systematics of basaltic eucrite stage aqueous ﬂuids. The veins included simple Fe-enrichment in

metal (Kleine et al., 2005, 2009). However, impact heating and con- Pasamonte, Fe-enrichment coupled with formation of ﬁne-grained

tact metamorphism by later intrusions/extrusions seem incapable ferroan olivine and sometimes very calcic plagioclase (An97–99)

of explaining the great preponderance of metamorphosed igneous in several eucrites, and this same assemblage but on wider scale

lithologies in the HED suite (Keil et al., 1997; Yamaguchi et al., and with development of Al-depletions (Barrat et al., 2011). These

1996). authors conclude that aqueous solutions were plausible agent of

Yamaguchi et al. (1996, 1997b) developed a model to explain the metasomatism based on terrestrial hydrothermal analogs, but they

prevalence of thermally metamorphosed basaltic eucrites, which did not discuss at what point in the post-magmatic-crystallization

likely were extrusive ﬂows, shallow dikes and/or shallow sill-like stage the metasomatism occurred.

intrusions on Vesta. These authors posit that eruption rates were Warren et al. (2014) described a set of late-stage alteration fea-

very high, resulting in rapid burial of early formed basalts. In their tures in brecciated and metamorphosed Stannern-group eucrite

model, heat conducted from the mantle through the crust would NWA 5738. They document two types of microveins: one dom-

∼

be sufﬁcient to anneal eucrites. Thus, reestablishment of the par- inantly of calcic plagioclase (An∼95), ferroan olivine (mg# 14)

ent body thermal gradient causes global thermal metamorphism in and Cr-spinels containing Fe (from stoichiometry); one domi-

the crust. The least metamorphosed basaltic eucrites would be the nantly composed of very pure Fe-metal. These authors conclude

latest extrusions. The maximum eruption rates used by Yamaguchi that the two types of veins were formed at distinct times, and that

et al. (1996, 1997b) are consistent with the maximum magma vol- thermal metamorphism did not postdate vein formation. Warren

ume ﬂuxes calculated by Wilson and Keil (2012) based on magma et al. (2014) conclude that the veins were formed from aqueous-

physics for asteroids of the size of Vesta. Haraiya is one of the rich ﬂuids derived from carbonaceous chondrite impactor debris on

metamorphic type 7 basaltic eucrites of Yamaguchi et al. (1996) Vesta.

and thus represents a deeply buried rock in their model. However, Zhang et al. (2013) have documented ferroan pyroxenes as

Schwartz and McCallum (2005) found that exsolution textures of mineral fragments and in lithic clasts that are partially replaced

Haraiya are inconsistent with simple burial metamorphism. Rather, by ﬁne-grained troilite, magnesian augite or hedenbergite, and a

they concluded that a short-lived thermal pulse provided the peak silica phase in melt-breccia eucrite NWA 2339. They concluded

metamorphic temperature. that the primary grains suffered sulfurization likely the result of

Bogard and Garrison (2003) determined that a number of impact heating mobilizing S-rich vapors. This is essentially the

unbrecciated cumulate and metamorphosed basaltic eucrites have same scenario as invoked by Palme et al. (1988) for the formation

Ar-Ar ages of 4.48 Ga which they interpreted as indicating that the of abundant Fe metal in brecciated eucrite Camel Donga.

rocks were at depth at temperatures above Ar diffusion closure until At present, evidence for metasomatism is not widespread,

a large, basin scale impact excavated them, promoting rapid cooling documents different types of processes, and appears to indi-

to below the Ar closure temperature. One of these is the anoma- cate late-stage, post-magmatic processes unrelated to formation

lous basaltic eucrite EET 90020. Yamaguchi et al. (2001) presented of primary lithologies on Vesta. The evidence for aqueous-based

evidence that they interpret as indicating that EET 90020 was at metasomatism points to an exogenous source for the water.

∼ ◦

870 C at the time of excavation, and was brieﬂy heated to above

◦

the solidus (∼1060 C) by this process, resulting in partial melting

and melt migration. The scenario developed by Yamaguchi et al. 9. Mixing of the vestan crust

(2001) implies that at depth but within the crust of Vesta, temper-

◦

atures of ∼870 C were maintained (or achieved) for ∼80 Myr after The Dawn spacecraft has returned images, visible and infrared

global differentiation. reﬂectance spectra, and gamma ray and neutron spectra of the

D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183 177

regolith surface of Vesta. Howardites, polymict eucrites and

polymict diogenites preserve records of regolith processes that

occur on Vesta but at smaller spatial scales. Most HED polymict

breccias are fragmental breccias that do not contain material that

spent signiﬁcant time in the actively gardened soil at the top of

the debris layer, the true regolith (McKay et al., 1991). Bischoff

et al. (2006) suggest that ∼38% of howardites are gas-rich, and

thus regolith breccias, but the details behind this census have not

been published. Warren et al. (2009) determined that ∼12% of

the howardites they discussed are regolithic. However, subsequent

noble gas analyses have shown that several howardites studied

by Warren et al. (2009) contain implanted solar wind gases and

thus are regolithic (Cartwright et al., 2013, 2014). Adding these

to the list and correcting for pairings, ∼21% of the howardites

discussed in Warren et al. (2009) are regolithic. Cartwright et al.

(2013, 2014) found that 33% of the howardites they studied con-

tain solar wind implanted Ne. Based on these observations, roughly

one quarter to one third of howardites contain material exposed in

the true regolith. Considering that howardites make up roughly

half of all HED polymict breccias listed in the Meteoritical Bulletin

Database, the abundance of regolithic howardites may be ∼15% of

HED polymict breccias. This estimate is consistent with theoretical

modeling of asteroidal regoliths that shows that a packet of frag-

mental debris on Vesta will spend less time exposed to the space

environment than the equivalent debris on the Moon (Housen and

Wilkening, 1982).

Warren et al. (2009) noted that the few regolithic howardites

identiﬁed by them tended to have a narrower range in composition

than shown by the suite as a whole. Their Al contents suggested

eucrite:diogenite-mixing ratios of ∼2:1, which they posited was

that of ancient, well-mixed vestan regolith. Mittlefehldt et al.

(2013b) found that the additional regolithic howardites identi-

ﬁed by Cartwright et al. (2013, 2014) have a range of mixing

ratios of ∼1:1 to ∼3:1. Fig. 19 is a histogram of the percentage

of eucritic material (POEM) in HED polymict breccias highlight-

ing those that are regolithic. The POEM index, ﬁrst introduced by

Jérome and Goles (1971), is calculated as described in Mittlefehldt

et al. (2013b). Ignoring MacAlpine Hills (MAC) 02666 (POEM

88) which is only possibly regolithic (Warren et al., 2009), Fig. 19. Variation in calculated percentage of eucrite material (POEM) in HED

polymict breccias estimated from data averages calculated from the analyses given

eucrite:diogenite mixing for regolithic howardites covers ∼40%

in Table S7. Howardites with “?” in the symbol are only possibly regolithic. Excluding

of the range observed for howardites generally. About a third of

those, regolithic howardites range in POEM from about 50 to 80.

the howardites shown have not had noble gas analyses published

on them, and thus cannot be subtyped with certainty. Comparing

only those that have been characterized, there are numerous frag-

This is also the conclusion reached through qualitative evaluation

mental howardites with POEM <50 but no regolithic howardites

of mixing diagrams. McSween et al. (2011) used averages of litera-

in this range; the average POEM for fragmental howardites is 55

ture data and showed that most polymict eucrites and howardites

and for regolithic howardites is 63. The data are suggestive that

are consistent with simple main-group eucrite-diogenite mixtures;

regolithic howardites generally have a more restricted mixing ratio,

only a few contain a signiﬁcant Stannern-group basalt component,

but there are too few well-characterized howardites to allow ﬁrm

conclusions. and only a few contain a signiﬁcant cumulate eucrite compo-

nent. Mittlefehldt et al. (2013b) similarly found that of the 29

The compositions of howardites also inform us of the nature

HED polymict breccias they analyzed, only one was dominated

of the maﬁc end member of the mixtures. An early study focused

by a Stannern-group basaltic component, one contained substan-

on quantitative modeling using linear regression analysis by pair-

tial Nuevo-Laredo-group basalt debris, and none were dominated

wise mixing of speciﬁc basaltic eucrites and diogenites to yield

by cumulate eucrite material. They ran linear regressions on dif-

a best ﬁt for a suite of major and trace elements in individ-

ferent incompatible refractory lithophile elements vs. Al, which

ual howardites (Fukuoka et al., 1977). These authors found that

consistently passed through the composition of main-group eucrite

howardite compositions were generally well matched by combi-

Juvinas. Mittlefehldt et al. (2013b) concluded that because diogen-

nations of main-group eucrites and orthopyroxenitic diogenites.

ites are a major component of HED polymict breccias yet were

Mässing was the only howardite that was better ﬁt using a Nuevo-

formed lower in the crust than cumulate eucrites (Takeda, 1979),

Laredo-group eucrite (Fukuoka et al., 1977). They did not test

the paucity of cumulate eucrites and their complementary fer-

cumulate eucrite-diogenite mixtures, or ternary mixtures of cumu-

roan basalts is plausibly an indication that they are truly rare

late and basaltic eucrites with diogenites. Usui and Iwamori (2013)

in the vestan crust, not just under sampled. The petrogenetic

have modeled the entire HED suite using independent component

model of Mandler and Elkins-Tanton (2013) predicts that cumu-

analysis to ferret-out mixing and fractionation trends. They con-

late eucrites should be much less common than basaltic eucrites or

ﬁrmed that mixing of the HED polymict breccias is dominantly

diogenites.

between main-group eucrites and orthopyroxenitic diogenites.

178 D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183

10. Ungrouped basaltic achondrites 11. The future

Northwest Africa 011 was the ﬁrst basaltic achondrite described There are several areas where our current knowledge of HEDs

that is petrologically very similar to eucrites but demonstrably and vestan geologic evolution is lacking, and research directed into

from a different parent asteroid (Yamaguchi et al., 2002). It and its these areas could help us more fully understand differentiation of

pairs remain the most distinct from HEDs in O isotope composition asteroids.

(Fig. 11a). Subsequently, I argued that the unusual basaltic eucrite

•

Ibitira was also unrelated to HEDs. This rock is one of a very few How many parent asteroids? The very large difference in oxygen

meteoritic basalts to have vesicles (Wilkening and Anders, 1975) isotope composition between HEDs and NWA 011 et al. make a

and has unusually low alkali element contents (Stolper, 1977). It strong case that a distinct parent asteroid is required (Yamaguchi

has an O isotope composition like angrites and very different from et al., 2002). Ibitira is substantially different in O isotopes, and

HEDs (Greenwood et al., 2005; Wiechert et al., 2004), an Fe/Mn has additional compositional differences that also favor a dis-

ratio in pyroxenes signiﬁcantly higher than for basaltic eucrites, tinct parent asteroid (Mittlefehldt, 2005). However, some basaltic

and ratios for some incompatible trace element that are different achondrites are less distinct, Pasamonte for example, which nev-

from those of basaltic eucrites (Mittlefehldt, 2005). Subsequently, ertheless are purported to be from different asteroids than HEDs

high precision O isotope analyses have shown that A-881394 and (Scott et al., 2009). My sense is that some of these noted distinc-

Bunburra Rockhole have similar O isotope compositions with O tions are not robust, and the number of differentiated asteroids

that lie ∼15 away from the HED mean composition (Benedix et al., represented might be less than thought. If true, the oxygen

2014; Bland et al., 2009; Scott et al., 2009). Preliminary data on isotopic composition of Vesta is not as uniform as thought. Addi-

unbrecciated cumulate gabbro EET 92023 and basaltic achondrite tional high precision O isotopic work, especially on HEDs that

Emmaville, both classiﬁed as eucrites, show that they have O iso- have petrologic and/or compositional anomalies ought to be done

tope compositions that are close to those of A-881394 and Bunburra to evaluate this issue further. In particular, O isotope analyses of

Rockhole (Greenwood et al., 2012, 2013). Dhofar 007 is a polymict diogenitic and eucritic clasts separated from howardites could

breccia composed mostly of cumulate gabbro debris and is rich in provide strong tests. Oxygen isotopic variations (or uniformity)

metal and siderophile elements (Dale et al., 2012; Yamaguchi et al., within an individual polymict breccias would allow for more

2006). It contains materials with differing O within the range muscular conclusions.

•

found for Bunburra Rockhole (Greenwood et al., 2012). NWA 2824 The unusual Mg isotopic result on diogenites that suggests they

has rare-earth-element contents like those of basaltic eucrites, but were formed only 0.6 Myr after CAIs (Schiller et al., 2011) should

is more Mg-rich than eucrites (Bunch et al., 2009). Its O-isotopic be revisited. These authors conclude that the time scale is too

composition is very similar to Ibitira. Pasamonte and PCA 91007 lie short to ﬁt thermal models for the differentiation of a Vesta-

∼

5 from the HED mean, and NWA 1240 lies ∼4 from the mean sized asteroid. If this result stands up upon further testing, then

(Scott et al., 2009) (Fig. 11b). we would have to conclude that HEDs do not come from Vesta

Sayh al Uhaymir (SaU) 493 is truly anomalous (Irving et al., after all. Additional isotopic work and more sophisticated aster-

2011). It is composed of exsolved pigeonitic pyroxene and calcic oid thermal models are required to investigate this issue.

•

plagioclase with an annealed igneous texture, and has a rare- A related but separate issue is whether diogenite petrogenesis

earth-element pattern like that of cumulate eucrites. Other highly occurred as part of magma ocean solidiﬁcation (Mandler and

incompatible elements (Zr, Nb, Hf, Th) are at abundance levels Elkins-Tanton, 2013), or via remelting of magma ocean cumulates

like those of basaltic eucrites. SaU 493 contains substantial Fe with or without contamination by basaltic-crust-melts (Barrat

in pyroxene and as hematite, indicating formation at higher oxy- et al., 2008; 2010). The trace element and mineralogic character-

gen fugacity conditions than those of any other maﬁc achondrite istics of diogenites remain difﬁcult to factor into magma ocean

(Irving et al., 2011). models (e.g., Barrat and Yamaguchi, 2014; Mittlefehldt et al.,

All of these maﬁc rocks have broadly eucrite-like mineralogy: 2014). Further petrologic/compositional study of diogenites and

calcic plagioclase and pyroxene compositions like those of cumu- continuing efforts to increase the sophistication of petrogenetic

late (A-881394) or basaltic eucrites (Fig. 3d) (see discussion in Scott models are needed to close this gap.

•

et al., 2009). NWA 1240 is unusual in that it has highly zoned pyrox- The evidence that ﬂuid phases might have metasomatized mate-

enes but a trace element signature of a cumulate gabbro (Barrat rials on Vesta is poorly understood. The timing of metasomatic

et al., 2003). This rock is interpreted to be an impact melt. The events with respect to the history of the rocks has not been well

extreme view based on O isotope compositions is that six parent deﬁned, but is certainly post-brecciation in some cases (Warren

asteroids are represented by the basaltic achondrites: HEDs, NWA et al., 2014; Zhang et al., 2013). The source of the ﬂuid phase

011 and pairs, Ibitira (and possibly NWA 2824), A-881394 and Bun- (endogenic vs. exogenic) is unknown, but has been inferred to

burra Rockhole (and possibly EET 92023, Emmaville and Dhofar be exogenic in some cases (Treiman et al., 2004; Warren et al.,

007), Pasamonte and PCA 91007, and NWA 1240 (Scott et al., 2009). 2014). Several types of ﬂuids have been suggested, including hot

Mittlefehldt (1990) and Rubin and Mittlefehldt (1992) have argued dry vapors (Schwartz and McCallum, 2005), aqueous-based ﬂu-

that mesosiderite silicates cannot be from the same parent asteroid ids (Barrat et al., 2011; Treiman et al., 2004; Warren et al., 2014)

as HEDs, and this is supported by an evaluation of the preliminary and S-rich ﬂuids (Palme et al., 1988; Zhang et al., 2013). A more

Fe composition of the vestan surface determined by the Gamma systematic study of metasomatic effects in HEDs would allow for

Ray and Neutron Detector on the Dawn spacecraft (Mittlefehldt greater understanding of the role of ﬂuids on Vesta.

•

et al., 2012b). The implication is that generally similar asteroids in The cosmic ray exposure ages show that substantial numbers of

terms of low moderately volatile element contents (Na, K), oxy- HEDs were excavated from their immediate parent object, pre-

gen isotope composition (except for NWA 011 and pairs), and with sumably a vestoid, by only two impacts (e.g., Herzog, 2007). Thus,

an oxygen fugacity near that of the iron-wüstite buffer (except many HEDs sample the same limited region of Vesta. Has this

for SaU 493) differentiated to produce basaltic crusts. These par- limited sampling biased our view of vestan differentiation? A

ent asteroids are low in moderately volatile elements compared casual glance comparing cosmic ray exposure ages with mete-

to all chondrites (McSween et al., 2011). There is no obvious rea- orite petrology and compositions does not suggest any bias, but a

son why basaltic meteorites should be dominated by Na,K-poor more rigorous petrologic and compositional comparison of HEDs

compositions. that are not members of the 22 or 39 Myr age groups with those

D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183 179

that are should be done to ascertain the representativeness of Barrat, J.-A., Yamaguchi, A., Zanda, B., Bollinger, C., Bohn, M., 2010. Relative chronol-

ogy of crust formation on asteroid Vesta: insights from the geochemistry of

our sampling of the vestan crust. Further study of the lithologic

diogenites. Geochim. Cosmochim. Acta 74, 6218–6231.

diversity of igneous clasts in HED polymict breccias would also

Barrat, J.A., Yamaguchi, A., Bunch, T.E., Bohn, M., Bollinger, C., Ceuleneer, G., 2011.

help in addressing this issue. Possible ﬂuid-rock interactions on differentiated asteroids recorded in eucritic

meteorites. Geochim. Cosmochim. Acta 75, 3839–3852.

Barrat, J.A., Yamaguchi, A., Jambon, A., Bollinger, C., Boudouma, O., 2012. Low-Mg

rock debris in howardites: evidence for KREEPy lithologies on Vesta? Geochim.

Acknowledgments

Cosmochim. Acta 99, 193–205.

Beck, A.W., McSween Jr., H.Y., 2010. Diogenites as polymict breccias composed of

orthopyroxenite and harzburgite. Meteorit. Planet. Sci. 45, 850–872.

My career-long infatuation with HEDs and mesosiderites began

Beck, A.W., Mittlefehldt, D.W., McSween Jr., H.Y., Rumble III, D., Lee, C.-T.A., Bodnar,

as a graduate student at UCLA working under John T. Wasson.

R.J., 2011. MIL 03443, a dunite from asteroid 4 Vesta: evidence for its classiﬁca-

Regardless of the fact that we did not (and still do not) see eye- tion and cumulate origin. Meteorit. Planet. Sci. 46, 1133–1151.

Beck, A.W., Welten, K.C., McSween, H.Y., Viviano, C.E., Caffee, M.W., 2012. Petrologic

to-eye on several aspects of HEDs and mesosiderites, this review

and textural diversity among the PCA 02 howardite group, one of the largest

would not have been possible without his mentoring; special

pieces of the Vestan surface. Meteorit. Planet. Sci. 47, 947–969.

thanks to him. Collaborations and discussions with several col- Beck, A.W., McCoy, T.J., Sunshine, J.M., Viviano, C.E., Corrigan, C.M., Hiroi, T., Mayne,

R.G., 2013. Challenges in detecting olivine on the surface of 4 Vesta. Meteorit.

leagues over the years have helped me reﬁne my thinking on HED

Planet. Sci. 48, 2155–2165.

genesis: A.W. Beck, D.D. Bogard, P.C. Buchanan, J.S. Delaney, R.

Benedix, G.K., Bland, P.A., Friedrich, J.M., Mittlefehldt, D.W., Sanborn, M.E., Yin, Q.-Z.,

Greenwood, R.H. Hewins, J.H. Jones, A.G.J. Jurewicz, K. Keil, M.M. Greenwood, R.C., Franchi, I.A., Bevan, A.W.R., Towner, M.C., Perotta, G.C.,2014.

Lindstrom, H.Y. McSween, Jr., L.E. Nyquist, H. Palme, J.J. Papike, R.G. Bunburra Rockhole: exploring the geology of a new differentiated basaltic aster-

oid, 45th Lunar and Planetary Science Conference. Lunar and Planetary Institute,

Mayne, C.H. Shearer, H. Takeda, P.H. Warren. Seminal papers by

Houston, Abstract #1650.

J.-A. Barrat and A. Yamaguchi have had considerable inﬂuence on

Berkley, J.L., Boynton, N.J., 1992. Minor/major element variation within and among

my understanding of HED meteorites. I thank these individuals for diogenite and howardite orthopyroxenite groups. Meteoritics, 387–394.

Binzel, R.P., Xu, S., 1993. Chips off of asteroid 4 Vesta: evidence for the parent body

their insights. I thank B. Mandler and R. Mayne for some of the

of basaltic achondrite meteorites. Science 260, 186–191.

graphics used here, and K. Ross for some of the SEM BSE images

Birck, J.L., Allègre, C.J., 1978. Chronology and chemical history of the parent body of

87 87

used. I thank Associate Editor K. Keil for inviting me to write this basaltic achondrites studied by the Rb- Sr method. Earth Planet. Sci. Lett. 39,

37–51.

review and for his handling of the manuscript. Journal reviews by

Bischoff, A., Scott, E.R.D., Metzler, K., Goodrich, C.A., 2006. Nature and origins

J.-A. Barrat and A. Yamaguchi resulted in substantial improvements

of meteoritic breccias. In: Lauretta, D.S., McSween Jr., H.Y. (Eds.), Meteorites

in the manuscript. Support for this work came from the NASA Cos- and the Early Solar System II. University of Arizona Press, Tucson, pp. 679– 712.

mochemistry Program.

Bizzarro, M., Baker, J.A., Haack, H., Lundgaard, K.L., 2005. Rapid timescales for

26 26

accretion and melting of differentiated planetesimals inferred from Al- Mg

chronometry. Astrophys. J. Lett. 632, L41.

Appendix A. Supplementary data Black, D.C., 1972. On the origins of trapped helium, neon and argon isotopic vari-

ations in meteorites—I. Gas-rich meteorites, lunar soil and breccia. Geochim.

Cosmochim. Acta 36, 347–375.

Supplementary data associated with this article can be

Bland, P.A., Spurny, P., Towner, M.C., Bevan, A.W.R., Singleton, A.T., Bottke Jr., W.F.,

found, in the online version, at http://dx.doi.org/10.1016/j.chemer. Greenwood, R.C., Chesley, S.R., Shrbeny, L., Borovicka, J., Ceplecha, Z., McClaf-

2014.08.002. ferty, T.P., Vaughan, D., Benedix, G.K., Deacon, G., Howard, K.T., Franchi, I.A.,

Hough, R.M., 2009. An anomalous basaltic meteorite from the innermost main

belt. Science 325, 1525–1527.

Bogard, D.D., 1995. Impact ages of meteorites: a synthesis. Meteoritics 30, 244–268.

References Bogard, D.D., 2011. K-Ar ages of meteorites: clues to parent-body thermal histories.

Chemie der Erde - Geochemistry 71, 207–304.

39 40

Allègre, C.J., Birck, J.L., Fourcade, S., Semet, M.P., 1975. Rubidium-87/Strontium-87 Bogard, D.D., Garrison, D.H., 2003. Ar- Ar ages of eucrites and thermal history of

age of Juvinas basaltic achondrite and early igneous activity in the solar system. asteroid 4 Vesta. Meteorit. Planet. Sci. 38, 669–710.

Science 187, 436–438. Bowman, L.E., Spilde, M.N., Papike, J.J., 1997. Automated energy dispersive spec-

Amelin, Y., 2008. The U-Pb systematics of angrite Sahara 99555. Geochim. Cos- trometer modal analysis applied to the diogenites. Meteorit. Planet. Sci. 32,

mochim. Acta 72, 4874–4885. 869–875.

Anders, E., 1977. Chemical compositions of the Moon, Earth and eucrite parent body. Bowman, L.E., Spilde, M.N., Papike, J.J., 1999. Diogenites as asteroidal cumulates:

Philos. Trans. Roy. Soc. London Ser. A: Math. Phys. Sci. 285, 23–40. insights from spinel chemistry. Am. Mineral. 84, 1020–1026.

Antarctic Meteorite Newsletter, 1996. vol. 19, #2. Buchanan, P.C., Zolensky, M.E., Reid, A.M., 1993. Carbonaceous chondrite clasts in

Asphaug, E., 1997. Impact origin of the Vesta family. Meteorit. Planet. Sci. 32, the howardites Bholghati and EET87513. Meteoritics 28, 659–682.

965–980. Buchanan, P.C., Lindstrom, D.J., Mittlefehldt, D.W., 2000. Pairing among the

Barrat, J.-A., 2004. Determination of parental magmas of HED cumulates: the effects EET87503 group of howardites and polymict eucrites. In: Schultz, L., Franchi,

of interstitial melts. Meteorit. Planet. Sci. 39, 1767–1779. I.A., Reid, A.M., Zolensky, M.E. (Eds.), Workshop on Extraterrestrial Mate-

Barrat, J.-A., Yamaguchi, A., 2014. Comment on The origin of eucrites, diogenites, rials from Cold and Hot Deserts. Lunar and Planetary Institute, Houston,

and olivine diogenites: magma ocean crystallization and shallow magma pro- pp. 21–24.

cesses on Vesta by B. E. Mandler and L. T. Elkins-Tanton. Meteorit. Planet. Sci. Buchanan, P.C., Noguchi, T., Bogard, D.D., Ebihara, M., Katayama, I., 2005. Glass veins

49, 468–472. in the unequilibrated eucrite Yamato 82202. Geochim. Cosmochim. Acta 69,

Barrat, J.A., Blichert-Toft, J., Gillet, P.H., Keller, F., 2000. The differentiation of eucrites: 1883–1898.

the role of in situ crystallization. Meteorit. Planet. Sci. 35, 1087–1100. Bunch, T.E., 1975. Petrography and petrology of basaltic achondrite polymict brec-

Barrat, J.A., Jambon, A., Bohn, M., Blichert-Toft, J., Sautter, V., Gopel, C., Gillet, P., cias (howardites). In: Proceedings of the Lunar Science Conference, 6th, pp.

Boudouma, O., Keller, F., 2003. Petrology and geochemistry of the unbrecciated 469–492.

achondrite Northwest Africa 1240 (NWA 1240): an HED parent body impact Bunch, T.E., Keil, K., 1971. Chromite and ilmenite in non-chondritic meteorites. Am.

melt. Geochim. Cosmochim. Acta 67, 3959–3970. Mineral. 56, 146–157.

Barrat, J.A., Beck, P., Bohn, M., Cotten, J., Gillet, P., Greenwood, R.C., Franchi, I.A., Bunch, T.E., Wittke, J.H., Rumble, D.I., Irving, A.J., Reed, B.,2006. Northwest Africa

2006. Petrology and geochemistry of the ﬁne-grained, unbrecciated diogenite 2968: a Dunite from 4Vesta 69th Annual Meeting of the Meteoritical Society.

Northwest Africa 4215. Meteorit. Planet. Sci. 41, 1045–1057. Lunar and Planetary Institute, Houston, Abstract #5252.

Barrat, J.A., Yamaguchi, A., Greenwood, R.C., Bohn, M., Cotten, J., Benoit, M., Franchi, Bunch, T., Irving, A., Wittke, J., Kuehner, S., Rumble, D., 2007. Distinctive magne-

I.A., 2007. The Stannern trend eucrites: contamination of main group eucritic sian, protogranular, and polymict diogenites from Northwest Africa, Oman, and

magmas by crustal partial melts. Geochim. Cosmochim. Acta 71, 4108–4124. United Arab Emirates. Meteorit. Planet. Sci. 42, A27.

Barrat, J.A., Yamaguchi, A., Greenwood, R.C., Benoit, M., Cotten, J., Bohn, M., Franchi, Bunch, T.E., Irving, A.J., Rumble III, D., Korotev, R.L., Wittke, J.H., Sipiera, P.P.,2009.

I.A., 2008. Geochemistry of diogenites: still more diversity in their parental Northwest Africa 2824: another eucrite-like sample from the Ibitira parent

melts. Meteorit. Planet. Sci. 43, 1759–1775. body? 72nd Annual Meeting of the Meteoritical Society. Lunar and Planetary

Barrat, J.A., Bohn, M., Gillet, P., Yamaguchi, A., 2009a. Evidence for K-rich terranes Institute, Houston, Abstract #5367.

on Vesta from impact spherules. Meteorit. Planet. Sci. 44, 359–374. Bunch, T.E., Irving, A.J., Wittke, J.H., Kuehner, S.M., Rumble, D.I., Sipiera, P.P.,2010.

Barrat, J.-A., Yamaguchi, A., Greenwood, R.C., Bollinger, C., Bohn, M., Franchi, I.A., Northwest Africa 5784, Northwest Africa 5968 and Northwest Africa 6157: More

2009b. Trace element geochemistry of K-rich impact spherules from howardites. Vestan Dunites and Olivine Diogenites 73rd Annual Meeting of the Meteoritical

Geochim. Cosmochim. Acta 73, 5944–5958. Society. Lunar and Planetary Institute, Houston, Abstract #5315.

180 D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183

Caffee, M.W., Goswami, J.N., Hohenberg, C.M., Swindle, T.D., 1983. Cosmogenic neon Fu, R.R., Weiss, B.P., Shuster, D.L., Gattacceca, J., Grove, T.L., Suavet, C., Lima, E.A.,

from precompaction irradiation of Kapoeta and Murchison. In: Proceedings of Li, L., Kuan, A.T., 2012. An ancient core dynamo in asteroid vesta. Science 338,

the Lunar and Planetary Science Conference, 14th, pp. B267–B273. 238–241.

Cartwright, J.A., Ott, U., Mittlefehldt, D.W., Herrin, J.S., Herrmann, S., Mertzman, S.A., Fuhrman, M., Papike, J.J., 1981. Howardites and polymict eucrites: regolith sam-

Mertzman, K.R., Peng, Z.X., Quinn, J.E., 2013. The quest for regolithic howardites ples from the eucrite parent body. Petrology of Bholgati, Bununu: Kapoeta and

Part 1: two trends uncovered using noble gases. Geochim. Cosmochim. Acta 105, ALHA76005. Proceedings of the Lunar and Planetary Science Conference 12th B

395–421. , pp. 1257–1279.

Cartwright, J.A., Ott, U., Mittlefehldt, D.W., 2014. The quest for regolithic howardites Fukuoka, T., Boynton, W.V., Ma, M.-S., Schmitt, R.A., 1977. Genesis of howardites, dio-

Part 2: surface origins highlighted by noble gases. Geochim. Cosmochim. Acta, genites, and eucrites. Proceedings of the 8th Lunar Science Conference, 187–210.

http://dx.doi.org/10.1016/j.gca.2014.05.033. Garcia, D.J., Prinz, M., 1978. The Binda orthopyroxene cumulate eucrite. Meteoritics

Christophe-Michel-Levy, M., Bourot-Denise, M., Palme, H., Spettel, B., Wänke, H., 13.

1987. L’eucrite de Bouvante: chimie, petrologie et mineralogie. Bull. Minerol. Gardner, K.G., Mittlefehldt, D.W.,2004. Petrology of New Stannern-trend Eucrites

110, 449–458. and Eucrite Genesis 35th Lunar and Planetary Science Conference. Lunar and

Clayton, R.N., Mayeda, T.K., 1996. Oxygen isotope studies of achondrites. Geochim. Planetary Institute, Houston, Abstract #1349.

Cosmochim. Acta 60, 1999–2017. Ghosh, S., Pant, N.C., Rao, T.K., Mohana, C.R., Ghosh, J.B., Shome, S., Bhandari, N.,

Cleverly, W.H., Jarosewich, E., Mason, B., 1986. Camel Donga meteorite, a new eucrite Shukla, A.D., Suthar, K.M., 2000. The Vissannapeta eucrite. Meteorit. Planet. Sci.

from the Nullarbor Plain, Western Australia. Meteoritics 21, 263–269. 35, 913–917.

Cohen, B.A., 2013. The Vestan cataclysm: impact-melt clasts in howardites and the Gomes, C.B., Keil, K., 1980. Brazilian Stone Meteorites. University of New Mexico

bombardment history of 4 Vesta. Meteorit. Planet. Sci. 48, 771–785. Press, Albuquerque, NM.

Consolmagno, G.J., Drake, M.J., 1977. Composition and evolution of the eucrite par- Gooley, R.C., (Ph.D. dissertation) 1972. The chemistry and mineralogy of the diogen-

ent body; evidence from rare earth elements. Geochim. Cosmochim. Acta 41, ites. Arizona State University, Tempe, Arizona, USA.

1271–1282. Gooley, R., Moore, C.B., 1976. Native metal in diogenite meteorites. Am. Mineral. 61,

Cruikshank, D.P., Tholen, D.J., Hartmann, W.K., Bell, J.F., Brown, R.H., 1991. Three 5–6.

basaltic earth-approaching asteroids and the source of the basaltic meteorites. Gounelle, M., Zolensky, M.E., Liou, J.-C., Bland, P.A., Alard, O., 2003. Mineralogy of

Icarus 89, 1–13. carbonaceous chondritic microclasts in howardites: identiﬁcation of C2 fossil

Dale, C.W., Burton, K.W., Greenwood, R.C., Gannoun, A., Wade, J., Wood, B.J., Pearson, micrometeorites. Geochim. Cosmochim. Acta 67, 507–527.

D.G., 2012. Late accretion on the earliest planetesimals revealed by the highly Greenwood, R.C., Franchi, I.A., Jambon, A., Buchanan, P.C., 2005. Widespread magma

siderophile elements. Science 336, 72–75. oceans on asteroidal bodies in the early Solar System. Nature 435, 916–

Day, J.M., Walker, R.J., Qin, L., Rumble III, D., 2012. Late accretion as a natural conse- 918.

quence of planetary growth. Nat Geosci 5, 614–617. Greenwood, R.C., Franchi, I.A., Jambon, A., Barrat, J.A., Burbine, T.H., 2006. Oxygen

Delaney, J.S., Prinz, M., Nehru, C.E., Harlow, G.E.,1981. A New Basalt Group from isotope variation in stony-iron meteorites. Science 313, 1763–1765.

Howardites: Mineral Chemistry and Relationships with Basaltic Achondrites Greenwood, R.C., Barrat, J.-A., Scott, E.R.D., Janots, E., Franchi, I.A., Hoffman, B., Yam-

Twelfth Lunar and Planetary Science Conference. Lunar and Planetary Institute, aguchi, A., Gibson, J.M.,2012. Has Dawn gone to the wrong asteroid? Oxygen

Houston, Abstract #1075. isotope constraints on the nature and composition of the HED parent body 43rd

Delaney, J.S., Takeda, H., Prinz, M., Nehru, C.E., Harlow, G.E., 1983. The nomenclature Lunar and Planetary Science Conference. Lunar and Planetary Institute, Houston,

of polymict basaltic achondrites. Meteoritics 18, 103–111. Abstract #2711.

Delaney, J.S., Prinz, M., Takeda, H., 1984a. The polymict eucrites. J. Geophys. Res. 89, Greenwood, R.C., Barrat, J.A., Scott, E.R.D., Franchi, I.A., Yamaguchi, A., Gibson, J.M.,

C251–C288. Haack, H., Lorenz, C.A., Ivanova, M.A., Bevan, A.,2013. Large-scale melting and

Delaney, J.S., Prinz, M., Nehru, C.E., Stokes, C.P.,1984b. Allan Hills A81001 Cumulate impact mixing on early-formed asteroids: evidence from high-precision oxy-

Eucrites and Black Clasts from Polymict Eucrites Fifteenth Lunar and Planetary gen isotope studies 44th Lunar and Planetary Science Conference. Lunar and

Science Conference. Lunar and Planetary Institute, Houston, Abstract #1108. Planetary Institute, Houston, Abstract #3048.

Domanik, K., Kolar, S., Musselwhite, D., Drake, M.J., 2004. Accessory silicate mineral Greenwood, R.C., Barrat, J.-A., Yamaguchi, A., Franchi, I.A., Scott, E.R.D., Bottke, W.F.,

assemblages in the Bilanga diogenite: a petrographic study. Meteorit. Planet. Sci. Gibson, J.M., 2014. The oxygen isotope composition of diogenites: evidence for

39, 567–579. early global melting on a single, compositionally diverse, HED parent body. Earth

Domanik, K., Sideras, L., Drake, M., 2005. Olivine and Ca-phosphates in the diogenites Planet. Sci. Lett. 390, 165–174.

Manegaon and Roda 36th Lunar and Planetary Science Conference , Abstract# Grimberg, A., Baur, H., Bochsler, P., Bühler, F., Burnett, D.S., Hays, C.C., Heber, V.S.,

2128. Jurewicz, A.J.G., Wieler, R., 2006. Solar Wind Neon from Genesis: implications

Dreibus, G., Wänke, H., 1980. The bulk composition of the eucrite parent asteroid for the Lunar Noble Gas Record. Science 314, 1133–1135.

and its bearing on planetary evolution. Zeitschrift fuer Naturforschung. Teil A: Haba, M.K., Yamaguchi, A., Horie, K., Hidaka, H., 2014. Major and trace elements of

Physik, Physikalische Chemie, Kosmophysik, 204–216. zircons from basaltic eucrites: implications for the formation of zircons on the

Dreibus, G., Kruse, H., Spettel, B., Wänke, H., 1977. The bulk composition of the eucrite parent body. Earth Planet. Sci. Lett. 387, 10–21.

moon and the eucrite parent body. In: Lunar and Planetary Science Conference Harlow, G.E., Klimentidis, R., 1980. Clouding of pyroxene and plagioclase in eucrites;

Proceedings, pp. 211–227. implications for post-crystallization processing. Proceedings of the Lunar and

Duke, M.B., 1965. Metallic iron in basaltic achondrites. J. Geophys. Res. 70, Planetary Science Conference no 2 , pp. 1131–1143.

1523–1527. Harlow, G.E., Nehru, C.E., Prinz, M., Taylor, G.J., Keil, K., 1979. Pyroxenes in Serra

Duke, M.B., Silver, L.T., 1967. Petrology of eucrites, howardites and mesosiderites. de Magé; cooling history in comparison with Moama and Moore County. Earth

Geochim. Cosmochim. Acta 31, 1637–1665. Planet. Sci. Lett. 43, 173–181.

Dymek, R.F., Albee, A.L., Chodos, A.A., Wasserburg, G.J., 1976. Petrography of Herzog, G.F., 2007. 1.13-Cosmic-Ray Exposure Ages of Meteorites I: Editors-in-Chief.

isotopically-dated clasts in the Kapoeta howardite and petrologic constraints In: Heinrich, D.H., Karl, K.T. (Eds.), Treatise on Geochemistry. Pergamon, Oxford,

on the evolution of its parent body. Geochim. Cosmochim. Acta 40, 1115– pp. 1–36.

1130. Hess, H.H., Henderson, E.P., 1949. The Moore County meteorite: a further study with

Eugster, O., Michel, T., 1995. Common asteroid break-up events of eucrites, dio- comment on its primordial environment. Am. Mineral. 34, 494–507.

genites, and howardites and cosmic-ray production rates for noble gases in Hewins, R.H., Klein, L.C., 1978. Provenance of metal and melt rock textures in the

achondrites. Geochim. Cosmochim. Acta 59, 177–199. Malvern howardite. Proceedings of the Lunar and Planetary Science Conference

Floran, R.J., Prinz, M., Hlava, P.F., Keil, K., Spettel, B., Wänke, H., 1981. Mineralogy, no 1 , pp. 1137–1156.

petrology, and trace element geochemistry of the Johnstown meteorite: a brec- Hewins, R., Newsom, H., 1988. Igneous activity in the early solar system. In: Kerridge,

ciated orthopyroxenite with siderophile and REE-rich components. Geochim. J.F., Matthews, M.S. (Eds.), Meteorites and the early solar system. University of

Cosmochim. Acta 45, 2385–2391. Arizona Press, Tucson, AZ, USA, pp. 73–101.

Floss, C., Crozaz, G., Yamaguchi, A., Keil, K., 2000. Trace element constraints on the Hostetler, C.J., Drake, M.J., 1978. Quench temperatures of Moore County and other

origins of highly metamorphosed Antarctic eucrites. Antarctic Meteorite Res. 13, eucrites; residence time on eucrite parent body. Geochim. Cosmochim. Acta 42,

222–237. 517–522.

Floss, C., Taylor, L.A., Promprated, P., Rumble, D., 2005. Northwest Africa 011: a Housen, K., Wilkening, L.L., 1982. Regoliths on small bodies in the solar system. Annu.

eucritic basalt from a non-eucrite parent body. Meteorit. Planet. Sci. 40, 343–360. Rev. Earth Planet. Sci. 10, 355–376.

Formisano, M., Federico, C., Turrini, D., Coradini, A., Capaccioni, F., De Sanctis, M.C., Howard, L.M., Domanik, K.J., Drake, M.J., Mittlefehldt, D.W.,2002. Petrology of

Pauselli, C., 2013. The heating history of Vesta and the onset of differentiation. Antarctic Eucrites PCA 91078 and PCA 91245 33rd Lunar and Planetary Science

Meteorit. Planet. Sci. 48, 2316–2332. Conference. Lunar and Planetary Institute, Houston, Abstract #1331.

Fowler, G.W., Papike, J.J., Spilde, M.N., Shearer, C.K., 1994. Diogenites as asteroidal Hsu, W., Crozaz, G., 1996. Mineral chemistry and the petrogenesis of eucrites: I.

cumulates: insights from orthopyroxene major and minor element chemistry. Noncumulate eucrites. Geochim. Cosmochim. Acta 60, 4571–4591.

Geochim. Cosmochim. Acta 58, 3921–3929. Hsu, W., Crozaz, G., 1997. Mineral chemistry and the petrogenesis of eucrites: II.

Fowler, G.W., Shearer, C.K., Papike, J.J., Layne, G.D., 1995. Diogenites as asteroidal Cumulate eucrites. Geochim. Cosmochim. Acta 61, 1293–1302.

cumulates: insights from orthopyroxene trace element chemistry. Geochim. Ikeda, Y., Takeda, H., 1985. A model for the origin of basaltic achondrites based on

Cosmochim. Acta 59, 3071–3084. the Yamato 7308 howardite. J. Geophys. Res.: Solid Earth 90, C649–C663.

Franchi, I.A., Greenwood, R.C., Scott, E.R.D.,2013. The IIIAB-Pallasite Relationship Irving, A.J., Kuehner, S.M., Seda, T., Herd, C.D.K., Gellissen, M., Rumble III, D.,2011.

Revisited: The Oxygen Isotope Perspective 76th Annual Meeting of the Mete- Sayh al Uhaymir 493: an unusual hematite-bearing, eucrite-like maﬁc achon-

oritical Society. Lunar and Planetary Institute, Houston, Abstract #5326. drite with ferrian pyroxenes 42nd Lunar and Planetary Science Conference.

Fredriksson, K., 1982. The Manegaon diogenite. Meteoritics 17, 141–144. Lunar and Planetary Institute, Houston, Abstract #1614.

D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183 181

Jérome, D.Y., Goles, G.G., 1971. A re-examination of relationships among pyrox- McSween Jr., H.Y., Binzel, R.P., De Sanctis, M.C., Ammannito, E., Prettyman, T.H., Beck,

ene = plagioclase achondrites. In: Brunfelt, A.O., Steinnes, E. (Eds.), Activation A.W., Reddy, V., Le Corre, L., Gaffey, M., McCord, T.B., Raymond, C.A., Russell, C.T.,

Analysis in Geochemistry and Cosmochemistry. Universitetsforlaget, Oslo, pp. 2013. Dawn, the Vesta–HED connection, and the geologic context for eucrites,

261–266. diogenites, and howardites. Meteorit. Planet. Sci. 48, 2090–2104.

Jurewicz, A.J.G., Mittlefehldt, D.W., Jones, J.H., 1993. Experimental partial melting Metzler, K., Bobe, K.D., Palme, H., Spettel, B., Stöfﬂer, D., 1995. Thermal and

of the Allende (CV) and Murchison (CM) chondrites and the origin of asteroidal impact metamorphism on the HED parent asteroid. Planet. Space Sci. 43, 499–

basalts. Geochim. Cosmochim. Acta 57, 2123–2139. 525.

Jurewicz, A.J.G., Mittlefehldt, D.W., Jones, J.H., 1995. Experimental partial melting of Misawa, K., Yamaguchi, A., Kaiden, H., 2005. U-Pb and 207Pb-206Pb ages of zircons

the St, Severin (LL) and Lost City (H) chondrites. Geochim. Cosmochim. Acta 59, from basaltic eucrites: implications for early basaltic volcanism on the eucrite

391–408. parent body. Geochim. Cosmochim. Acta 69, 5847–5861.

Kaneda, K., Warren, P.H., Miyamoto, M.,2000. Petrology and Thermal History of Mg- Mittlefehldt, D.W., 1979. Petrographic and chemical characterization of igneous

rich Pyroxene Bearing Cumulate Eucrite, Talampaya 31st Lunar and Planetary lithic clasts from mesosiderites and howardites and comparison with eucrites

Science Conference. Lunar and Planetary Institute, Houston, Abstract #2069. and diogenites. Geochim. Cosmochim. Acta 43, 1917–1936.

Keil, K., 2012. Angrites, a small but diverse suite of ancient, silica-undersaturated Mittlefehldt, D.W., 1987. Volatile degassing of basaltic achondrite parent bodies:

volcanic-plutonic maﬁc meteorites, and the history of their parent asteroid. evidence from alkali elements and phosphorus. Geochim. Cosmochim. Acta 51,

Chemie der Erde - Geochemistry 72, 191–218. 267–278.

Keil, K., Stoefﬂer, D., Love, S., Scott, E., 1997. Constraints on the role of impact heating Mittlefehldt, D.W., 1990. Petrogenesis of mesosiderites: I. origin of maﬁc litholo-

and melting in asteroids. Meteorit. Planet. Sci. 32, 349–363. gies and comparison with basaltic achondrites. Geochim. Cosmochim. Acta 54,

Klein, L.C., Hewins, R.H., 1979. Origin of impact melt rocks in the Bununu howardite. 1165–1173.

Proceedings of the Lunar and Planetary Science Conference no 1 , pp. 1127–1140. Mittlefehldt, D.W., 1994. The genesis of diogenites and HED parent body petrogen-

Kleine, T., Mezger, K., Palme, H., Scherer, E., Münker, C., 2005. The W isotope com- esis. Geochim. Cosmochim. Acta 58, 1537–1552.

position of eucrite metals: constraints on the timing and cause of the thermal Mittlefehldt, D.W., 2000. Petrology and geochemistry of the Elephant Moraine

metamorphism of basaltic eucrites. Earth Planet. Sci. Lett. 231, 41–52. A79002 diogenite: a genomict breccia containing a magnesian harzburgite com-

Kleine, T., Touboul, M., Bourdon, B., Nimmo, F., Mezger, K., Palme, H., Jacobsen, S.B., ponent. Meteorit. Planet. Sci. 35, 901–912.

Yin, Q.-Z., Halliday, A.N., 2009. Hf–W chronology of the accretion and early Mittlefehldt, D.W., 2005. Ibitira: A basaltic achondrite from a distinct parent aster-

evolution of asteroids and terrestrial planets. Geochim. Cosmochim. Acta 73, oid and implications for the Dawn mission. Meteorit. Planet. Sci. 40, 665–

5150–5188. 677.

Kozul, J., Hewins, R.H.,1988. LEW 85300,02,03 Polymict Eucrites Consortium–II: Mittlefehldt, D.W.,2008. Meteorite Dunite Breccia MIL 03443: A Probable Crustal

Breccia Clasts, CM, Inclusion, Glassy Matrix and Assembly History Ninteenth Cumulate Closely Related to Diogenites from the HED Parent Asteroid 39th

Lunar and Planetary Science Conference. Lunar and Planetary Institute, Houston, Lunar and Planetary Science Conference. Lunar and Planetary Institute, Houston,

Abstract #1325. Abstract #1919.

Krawczynski, M.J., Elkins-Tanton, L.T., Grove, T.L.,2008. Petrology of Olivine- Mittlefehldt, D.W., Lindstrom, M.M., 1993. Geochemistry and petrology of a suite of

Diogenite MIL03443, 9: Constraints on Eucrite Parent Body Bulk Composition ten Yamato HED meteorites. Antarctic Meteorite Res. 6, 268.

and Magmatic Processes 39th Lunar and Planetary Science Conference. Lunar Mittlefehldt, D.W., Lindstrom, M.M., 1997. Magnesian basalt clasts from the EET

and Planetary Institute, Houston, Abstract #1229. 92014 and Kapoeta howardites and a discussion of alleged primary magnesian

Labotka, T.C., Papike, J.J., 1980. Howardites; samples of the regolith of the eucrite HED basalts. Geochim. Cosmochim. Acta 61, 453–462.

parent-body; petrology of Frankfort, Pavlovka, Yurtuk, Malvern, and ALHA Mittlefehldt, D.W., Lindstrom, M.M.,1998. Black Clasts from Howardite QUE 94200

77302. Proceedings of the Lunar and Planetary Science Conference, no. 2 , pp. Impacts Melts Not Primary Magnesian Basalts 29th Lunar and Planetary Science

1103–1130. Conference. Lunar and Planetary Institute, Houston, Abstract #1832.

Lodders, K., Fegley Jr., B., 1998. The Planetary Scientist’s Companion. Oxford Univer- Mittlefehldt, D.W., Lindstrom, M.M., 2003. Geochemistry of eucrites: genesis of

sity Press, New York. basaltic eucrites, and Hf and Ta as petrogenetic indicators for altered antarctic

Lomena, I.S.M., Touré, F., Gibson, E.K., Clanton, U.S., Reid, A.M., 1976. Aïoun el eucrites. Geochim. Cosmochim. Acta 67, 1911–1934.

Atrouss: a new hypersthene achondrite with eucritic inclusions. Meteoritics 11, Mittlefehldt, D.W., Killgore, M.,2003. Northwest Africa 1401: A Polymict Cumulate

51–57. Eucrite with a Unique Ferroan Heteradcumulate Maﬁc Clast 34th Lunar and

Lorenz, K., Nazarov, M., Kurat, G., Brandstaetter, F., Ntaﬂos, T., 2007. Foreign mete- Planetary Science Conference. Lunar and Planetary Institute, Houston, Abstract

oritic material of howardites and polymict eucrites. Petrology 15, 109–125. #1251.

Lovering, J.F., 1964. Electron microprobe analysis of the metallic phase in basic Mittlefehldt, D.W., Peng, Z.X., 2013. Petrologic and In-Situ Geochemical Constraints

achondrites. Nature, 203. on Diogenite Genesis, 44th Lunar and Planetary Science Conference. Lunar and

Lovering, J.F., 1975. The Moama eucrite - a pyroxene-plagioclase adcumulate. Mete- Planetary Institute, Houston, Abstract #1285.

oritics 10, 101–114. Mittlefehldt, D.W., McCoy, T.J., Goodrich, C.A., Kracher, A., 1998. Non-chondritic

Lugmair, G.W., Shukolyukov, A., 1998. Early solar system timescales according to meteorites from asteroidal bodies. In: Papike, J.J. (Ed.), Planetary Materials. Min-

53 53

Mn- Cr systematics. Geochim. Cosmochim. Acta 62, 2863–2886. eralogical Society of America, Washington, DC, USA, pp. 1–195.

Ma, M.S., Schmitt, R.A., 1979. Genesis of the cumulate eucrites Serra de Mage and Mittlefehldt, D.W., Johnson, K.N., Herrin, J.S., 2011. Fluid-Mediated Alteration on

Moore County; a geochemical study. Meteoritics 14, 81–88. 4 Vesta Evidence from Orthopyroxene Clasts in Howardites, 42nd Lunar and

Ma, M.S., Murali, A.V., Schmitt, R.A., 1977. Genesis of the Angra dos Reis and other Planetary Science Conference. Lunar and Planetary Institute, Houston, Abstract

achondritic meteorites. Earth Planet. Sci. Lett. 35, 331–346. #1834.

Mandler, B.E., Elkins-Tanton, L.T., 2013. The origin of eucrites, diogenites, and olivine Mittlefehldt, D.W., Beck, A.W., Lee, C.-T.A., McSween, H.Y., Buchanan, P.C., 2012a.

diogenites: Magma ocean crystallization and shallow magma chamber pro- Compositional constraints on the genesis of diogenites. Meteorit. Planet. Sci. 47,

cesses on Vesta. Meteorit. Planet. Sci., http://dx.doi.org/10.1111/maps.12135 72–98.

Marchi, S., McSween, H.Y., O’Brien, D.P., Schenk, P., De Sanctis, M.C., Gaskell, R., Jau- Mittlefehldt, D.W., Prettyman, T.H., Reedy, R.C., Beck, A.W., Blewett, D.T., Gaffey, M.J.,

mann, R., Mottola, S., Preusker, F., Raymond, C.A., Roatsch, T., Russell, C.T., 2012. Lawrence, D.J., McCoy, T.J., McSween, H.Y.J., Toplis, M.J., Team, D.S., 2012. Do

The Violent Collisional History of Asteroid 4 Vesta. Science 336, 690–694. Mesosiderites Reside on 4 Vesta? An Assessment Based on Dawn GRaND Data,

Mason, B., 1962. Meteorites. Wiley, New York. 43rd Lunar and Planetary Science Conference. Lunar and Planetary Institute,

Mason, B., 1963. The hypersthene achondrites. Am. Museum Novitates 2155, 1–13. Houston, Abstract #1655.

Mason, B., Jarosewich, E., Nelen, J.A., 1979. The pyroxene-plagioclase achondrites. Mittlefehldt, D.W., Mertzman, S.A., Peng, Z.X., Mertzman, K.R., 2013. Petrologic and

In: Smithsonian Contributions to the Earth Sciences, no. 22, pp. 27–43. Chemical Characterization of a Suite of Antarctic Diogenites, 76th Annual Meet-

Mason, B., Wiik, H.B., 1966a. The composition of the Bath, Frankfort, Kakangari, Rose ing of the Meteoritical Society. Lunar and Planetary Institute, Houston, Abstract

City, and Tadjera meteorites. Am Museum Novitates 2272, 1–24. #5337.

Mason, B., Wiik, H.B., 1966b. The composition of the Barratta, Carraweena, Kapoeta, Mittlefehldt, D.W., Herrin, J.S., Quinn, J.E., Mertzman, S.A., Cartwright, J.A., Mertzman,

Mooresfort, and Ngawi meteorites. Am. Museum Novitates 2273, 1–25. K.R., Peng, Z.X., 2013b. Composition and petrology of HED polymict breccias: the

Mayne, R.G., McSween Jr., H.Y., McCoy, T.J., Gale, A., 2009. Petrology of the unbrec- regolith of (4) Vesta. Meteorit. Planet. Sci. 48, 2105–2134.

ciated eucrites. Geochim. Cosmochim. Acta 73, 794–819. Mittlefehldt, D.W., Peng, Z.X., Mertzman, S.A., Mertzman, K.R., 2014. Petrology and

Mazor, E., Anders, E., 1967. Primordial gases in the Jodzie howardite and the origin geochemistry of unbrecciated harzburgitic diogenite MIL 07001: A window into

of gas-rich meteorites. Geochim. Cosmochim. Acta 31, 1441–1456. vestan geological evolution, 45th Lunar and Planetary Science Conference. Lunar

McCord, T.B., Adams, J.B., Johnson, T.V., 1970. Asteroid Vesta: Spectral Reﬂectivity and Planetary Institute, Houston, Abstract #1613.

and Compositional Implications. Science 168, 1445–1447. Miyamoto, M., Takeda, H., 1977. Evaluation of a crust model of eucrites from the

McCoy, T.J., Beck, A.W., Mittlefehdt, D.W., 2014. Dawn’s mission to asteroid 4Vesta: width of exsolved pyroxene. Geochem. J. 11, 161–169.

exploring a geologically and geochemically complex world. Chemie der Erde- Miyamoto, M., Takeda, H., Yanai, K., 1978. Yamato achondrite polymict breccias.

Geochemistry, in press. Memoirs of the National Institute of Polar Research, 185–197, Special Issue, No.

McKay, D.S., Heiken, G., Basu, A., Blanford, G., Simon, S., Reedy, R., French, B.M., 8.

Papike, J., 1991. The lunar regolith. In: Heiken, G., Vaniman, D., French, B.M. Mori, H., Takeda, H., 1981a. Thermal and deformational histories of diogenites as

(Eds.), Lunar sourcebook A User’s Guide to the Moon. Cambridge University inferred from their microtextures of orthopyroxene. Earth Planet. Sci. Lett. 53,

Press, Cambridge, UK, pp. 285–356. 266–274.

McSween Jr., H.Y., Mittlefehldt, D.W., Beck, A.W., Mayne, R.G., McCoy, T.J., 2011. HED Mori, H., Takeda, H., 1981b. Evolution of the Moore County pyroxenes as viewed

meteorites and their relationship to the geology of vesta and the dawn mission. by an analytical transmission electron microprobe (ATEM). Meteoritics 16,

Space Sci. Rev. 163, 141–174. 362–363.

182 D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183

Müller, H.W., Zähringer, J., 1966. Chemische Unterschiede bei Uredelgashaltigen Schiller, M., Baker, J., Creech, J., Paton, C., Millet, M.-A., Irving, A., Bizzarro, M., 2011.

Steinmeteoriten. Earth Planet. Sci. Lett. 1, 25–29. Rapid timescales for magma ocean crystallization on the howardite-eucrite-

Newsom, H.E., 1985. Molybdenum in eucrites: evidence for a metal core in the diogenite parent body. Astrophys. J. Lett. 740, L22.

eucrite parent body. J. Geophys. Res.: Solid Earth 90, C613–C617. Schwartz, J.M., McCallum, I.S., 2005. Comparative study of equilibrated and unequi-

Newsom, H.E., Drake, M.J., 1982. The metal content of the eucrite parent body: con- librated eucrites: subsolidus thermal histories of Haraiya and Pasamonte. Am.

straints from the partitioning behavior of tungsten. Geochim. Cosmochim. Acta Mineral. 90, 1871–1886.

46, 2483–2489. Scott, E.R.D., Greenwood, R.C., Franchi, I.A., Sanders, I.S., 2009. Oxygen isotopic con-

Noble, S.K., Keller, L.P., Pieters, C.M., 2010. Evidence of space weathering in straints on the origin and parent bodies of eucrites, diogenites, and howardites.

regolith breccias II: asteroidal regolith breccias. Meteorit. Planet. Sci. 45, 2007– Geochim. Cosmochim. Acta 73, 5835–5853.

2015. Shearer, C.K., Fowler, G.W., Papike, J.J., 1997. Petrogenetic models for magmatism on

Nyquist, L.E., Takeda, H., Bansal, B.M., Shih, C.-Y., Wiesmann, H., Wooden, J.L., 1986. the eucrite parent body: evidence from orthopyroxene in diogenites. Meteorit.

Rb-Sr and Sm-Nd internal isochron ages of a subophitic basalt clast and a matrix Planet. Sci. 32, 877–889.

sample from the Y75011 eucrite. J. Geophys. Res. 91, 8137–8150. Shearer, C.K., Burger, P., Papike, J.J., 2010. Petrogenetic relationships between dio-

Olsen, E., Noonan, A., Fredriksson, K., Jarosewich, E., Moreland, G., 1978. Eleven new genites and olivine diogenites: implications for magmatism on the HED parent

meteorites from Antarctica, 1976–1977. Meteoritics 13, 209–225. body. Geochim. Cosmochim. Acta 74, 4865–4880.

Olsen, E.J., Fredriksson, K., Rajan, S., Noonan, A., 1990. Chondrule-like objects and Shukolyukov, A., Begemann, F., 1996. Cosmogenic and ﬁssiogenic noble gases and

brown glasses in howardites. Meteoritics 25 (3), 187–194. Kr-Kr exposure age clusters of eucrites. Meteorit. Planet. Sci. 31, 60–72.

Padia, J.T., Rao, M.N., 1989. Neon isotope studies of Fayetteville and Kapoeta Singerling, S.A., McSween, H.Y., Taylor, L.A., 2013. Glasses in howardites: impact

meteorites and clues to ancient solar activity. Geochim. Cosmochim. Acta 53, melts or pyroclasts? Meteorit. Planet. Sci. 48, 715–729.

1461–1467. Sisodia, M.S., Shukla, A.D., Suthar, K.M., Mahajan, R.R., Murty, S.V.S., Shukla, P.N.,

Palme, H., Rammensee, W., 1981. The signiﬁcance of W in planetary differentiation Bhandari, N., Natarajan, R., 2001. The Lohawat howardite: mineralogy, chemistry

processes: evidence from new data on eucrites. Proceedings of the 12th Lunar and cosmogenic effects. Meteorit. Planet. Sci. 36, 1457–1466.

and Planetary Science Conference 12B , pp. 949–964. Smoliar, M.I., 1993. A survey of Rb-Sr systematics of eucrites. Meteoritics 28,

Palme, H., Wlotzka, F., Spettel, B., Dreibus, G., Weber, H., 1988. Camel Donga: a eucrite 105–113.

with high metal content. Meteoritics 23, 49–57. Stolper, E., 1977. Experimental petrology of eucritic meteorites. Geochim. Cos-

Papanastassiou, D.A., Wasserburg, G.J., 1969. Initial strontium isotopic abundances mochim. Acta 41, 587–611.

and the resolution of small time differences in the formation of planetary objects. Streckeisen, A., 1976. To each plutonic rock its proper name. Earth-science Rev. 12,

Earth Planet. Sci. Lett. 5, 361–376. 1–33.

Papike, J.J., Shearer, C.K., Spilde, M.N., Karner, J.M., 2000. Metamorphic diogenite Takahashi, K., Masuda, A., 1990. Young ages of two diogenites and their genetic

Grosvenor Mountains 95555: mineral chemistry of orthopyroxene and spinel implications. Nature 343, 540–542.

and comparisons to the diogenite suite. Meteorit. Planet. Sci. 35, 875–879. Takeda, H., 1979. A layered-crust model of a howardite parent body. Icarus 40,

Patzer, A., McSween Jr., H.Y., 2012. Ordinary (mesostasis) and not-so-ordinary 455–470.

(symplectites) late-stage assemblages in howardites. Meteorit. Planet. Sci. 47, Takeda, H., 1986. Mineralogy of Yamato 791073 with reference to crystal fraction-

1475–1490. ation of the Howardite parent body. J. Geophys. Res.: Solid Earth 91, 355–363.

Prettyman, T.H., Mittlefehldt, D.W., Yamashita, N., Lawrence, D.J., Beck, A.W., Feld- Takeda, H., 1991. Comparisons of Antarctic and non-Antarctic achondrites and pos-

man, W.C., McCoy, T.J., McSween, H.Y., Toplis, M.J., Titus, T.N., Tricarico, P., Reedy, sible origin of the differences. Geochim. Cosmochim. Acta 55, 35–47.

R.C., Hendricks, J.S., Forni, O., Le Corre, L., Li, J.-Y., Mizzon, H., Reddy, V., Ray- Takeda, H., Graham, A.L., 1991. Degree of equilibration of eucritic pyroxenes and

mond, C.A., Russell, C.T., 2012. Elemental Mapping by Dawn Reveals Exogenic H thermal metamorphism of the earliest planetary crust. Meteoritics 26, 129–134.

in Vesta’s Regolith. Science 338, 242–246. Takeda, H., Mori, H., 1985. The diogenite-eucrite links and the crystallization history

Pun, A., Papike, J.J., 1995. Ion microprobe investigation of exsolved pyrox- of a crust of their parent body. J. Geophys. Res.: Solid Earth 90, C636–C648.

enes in cumulate encrites: determination of selected trace-element partition Takeda, H., Miyamoto, M., Ishii, T., Reid, A., 1976. Characterization of crust formation

coefﬁcients. Geochim. Cosmochim. Acta 59, 2279–2289. on a parent body of achondrites and the moon by pyroxene crystallogra-

Quitté, G., Birck, J.-L., Allègre, C.J., 2000. 182Hf-182W systematics in eucrites: the phy and chemistry, Lunar and Planetary Science Conference Proceedings , pp.

puzzle of iron segregation in the early solar system. Earth Planet. Sci. Lett. 184, 3535–3548.

83–94. Takeda, H., Miyamoto, M., Yanai, K., Haramura, H., 1978a. A preliminary mineralogi-

Quitté, G., Latkoczy, C., Schönbächler, M., Halliday, A.N., Günther, D., 2011. cal examination of the Yamato-74 achondrites. Memoirs of the National Institute

60Fe–60Ni systematics in the eucrite parent body: a case study of Bouvante of Polar Research, pp. 170–184, Special Issue, No. 8.

and Juvinas. Geochim. Cosmochim. Acta 75, 7698–7706. Takeda, H., Ishii, T., Miyamoto, M., Duke, M., 1978b. Crystallization of pyroxenes in

Rao, M., Garrison, D., Bogard, D., Badhwar, G., Murali, A., 1991. Composition of solar lunar KREEP basalt 15386 and meteoritic basalts Lunar and Planetary Science

ﬂare noble gases preserved in meteorite parent body regolith. J. Geophys. Res.: Conference Proceedings , pp. 1157–1171.

Space Physics 96, 19321–19330. Takeda, H., Miyamoto, M., Ishii, T., Yanai, K., Matsumoto, Y., 1979. Mineralogical

Reid, A.M., Buchanan, P., Zolensky, M.E., Barrett, R.A., 1990. The Bholghati howardite: examination of the Yamato-75 Achondrites and their layered crust model. Mem-

petrography and mineral chemistry. Geochim. Cosmochim. Acta 54, 2161–2166. oirs of National Institute of Polar Research. Special issue, 12, pp. 82–108.

Righter, K., Drake, M.J., 1996. Core Formation in Earth’s Moon, Mars, and Vesta. Icarus Takeda, H., Mori, H., Yanai, K., 1981. Mineralogy of the Yamato diogenites as possible

124, 513–529. pieces of a single fall. Memoirs of National Institute of Polar Research. Special

Righter, K., Drake, M.J., 1997. A magma ocean on Vesta: core formation and petro- issue, 20, pp. 81–99.

genesis of eucrites and diogenites. Meteorit. Planet. Sci. 32, 929–944. Takeda, H., Yamaguchi, A., Nyquist, L., Bogard, D., 1994. A mineralogical study of the

Roszjar, J., Metzler, K., Bischoff, A., Barrat, J.-A., Geisler, T., Greenwood, R.C., Franchi, proposed paired eucrites Y-792769 and Y-793164 with reference to cratering

I.A., Klemme, S., 2011. Thermal history of Northwest Africa 5073––A coarse- events on their parent body. Antarctic Meteorite Res. 7, 73.

grained Stannern-trend eucrite containing cm-sized pyroxenes and large zircon Tera, F., Carlson, R.W., Boctor, N.Z., 1997. Radiometric ages of basaltic achondrites

grains. Meteorit. Planet. Sci. 46, 1754–1773. and their relation to the early history of the solar system. Geochim. Cosmochim.

Rubin, A.E., Mittlefehldt, D.W., 1992. Classiﬁcation of maﬁc clasts from Acta 61, 1713–1731.

mesosiderites: implications for endogenous igneous processes. Geochim. Cos- Thomas, P.C., Binzel, R.P., Gaffey, M.J., Storrs, A.D., Wells, E.N., Zellner, B.H., 1997.

mochim. Acta 56, 827–840. Impact excavation on asteroid 4 Vesta: Hubble Space Telescope results. Science

Ruzicka, A., Snyder, G.A., Taylor, L.A., 1997. Vesta as the howardite, eucrite and 277, 1492–1495.

diogenite parent body: implications for the size of a core and for large-scale Tkalcec, B.J., Brenker, F.E., 2014. Plastic deformation of olivine-rich diogenites and

differentiation. Meteorit. Planet. Sci. 32, 825–840. implications for mantle processes on the diogenite parent body. Meteorit. Planet.

Sack, R.O., Azaredo, W.J., Lipschutz, M.E., 1994. Erratum to R. O. Sack, W. J. Azaredo, Sci., http://dx.doi.org/10.1111/maps.12324.

and M. E. Lipschutz (1991) Olivine diogenites: the mantle of the eucrite parent Tkalcec, B.J., Golabek, G.J., Brenker, F.E., 2013. Solid-state plastic deformation in the

body. Geochem. Cosmochim. Acta 55, 1111–1120. dynamic interior of a differentiated asteroid. Nat. Geosci. 6, 93–97.

Sack, R.O., Azeredo, W.J., Lipschutz, M.E., 1991. Olivine diogenites: the mantle of the Touboul, M., Kleine, T., Bourdon, B.,2008. Hf-W Systematics of Cumulate Eucrites

eucrite parent body. Geochim. Cosmochim. Acta 55, 1111–1120. and the Chronology of the Eucrite Parent Body 39th Lunar and Planetary Science

Saiki, K., Takeda, H., Tagai, T., 1991. Zircon in magnesian, basaltic eucrite Yam- Conference. Lunar and Planetary Institute, Houston, Abstract #2336.

ato 791438 and its possible origin Lunar and Planetary Science Conference Treiman, A.H., 1996. The perils of partition: difﬁculties in retrieving magma compo-

Proceedings , pp. 341–349. sitions from chemically equilibrated basaltic meteorites. Geochim. Cosmochim.

Saiki, K., Takeda, H., Ishii, T., 2001. Mineralogy of Yamato-791192, HED breccia Acta 60, 147–155.

and relationship between cumulate eucrites and ordinary eucrites. Antarctic Treiman, A.H., 1997. The parent magmas of the cumulate eucrites: a mass balance

Meteorite Res. 14, 28. approach. Meteorit. Planet. Sci. 32, 217–230.

Sanborn, M.E., Yin, Q.-Z.,2014. Chromium isotopic composition of the anomalous Treiman, A.H., Lanzirotti, A., Xirouchakis, D., 2004. Ancient water on asteroid 4 Vesta:

eucrites: an additional geochemical parameter for evaluating their origin 45th evidence from a quartz veinlet in the Serra de Magé eucrite meteorite. Earth

Lunar and Planetary Science Conference. Lunar and Planetary Institute, Houston, Planet. Sci. Lett. 219, 189–199.

Abstract #2018. Trinquier, A., Birck, J.-L., Allègre, C.J., 2007. Widespread Cr heterogeneity in the

Saraﬁan, A.R., Roden, M.F., Patino-Douce,˜ A.E., 2013. The volatile content of Vesta: inner Solar System. Astrophys. J. 655, 1179.

clues from apatite in eucrites. Meteorit. Planet. Sci. 48, 2135–2154. Trinquier, A., Birck, J.L., Allègre, C.J., Göpel, C., Ulfbeck, D., 2008. 53Mn-53Cr sys-

Schiller, M., Baker, J.A., Bizzarro, M., 2010. 26Al–26Mg dating of asteroidal magma- tematics of the early Solar System revisited. Geochim. Cosmochim. Acta 72,

tism in the young Solar System. Geochim. Cosmochim. Acta 74, 4844–4864. 5146–5163.

D.W. Mittlefehldt / Chemie der Erde 75 (2015) 155–183 183

Usui, T., Iwamori, H., 2013. Mixing relations of the howardite-eucrite-diogenite Wilson, L., Keil, K., 2012. Volcanic activity on differentiated asteroids: a review and

suite: a new statistical approach of Independent Component Analysis for the analysis. Chemie der Erde-Geochemistry 72, 289–321.

Dawn mission. Meteorit. Planet. Sci. 48, 2289–2299. Wilson, L., Keil, K.,2013. Fast melt production and easy melt migration in differenti-

Wadhwa, M., Amelin, Y., Bogdanovski, O., Shukolyukov, A., Lugmair, G.W., Janney, P., ated asteroids implies giant sills not magma oceans. Workshop on Planetesimal

2009. Ancient relative and absolute ages for a basaltic meteorite: implications for Formation and Differentiation. Lunar and Planetary Institute, Houston, Abstract

timescales of planetesimal accretion and differentiation. Geochim. Cosmochim. #8004.

Acta 73, 5189–5201. Wittke, J.H., Irving, A.J., Bunch, T.E., Kuehner, S.M.,2011. A Nomenclature System for

Warren, P.H., 1985. Origin of howardites, diogenites and eucrites: a mass balance Diogenites Consistent with the IUGS System for Naming Terrestrial Ultramaﬁc

constraint. Geochim. Cosmochim. Acta 49, 577–586. Rocks 74th Annual Meteoritical Society Meeting. Lunar and Planetary Institute,

Warren, P.H., 1997. Magnesium oxide-iron oxide mass balance constraints and a Houston, Abstract #5223.

more detailed model for the relationship between eucrites and diogenites. Mete- Yamaguchi, A., Takeda, H., Bogard, D.D., Garrison, D., 1994. Textural variations and

orit. Planet. Sci. 32, 945–963. impact history of the Millbillillie eucrite. Meteoritics 29, 237–245.

Warren, P.H., 1999. Differentiation of siderophile elements in the Moon and the HED Yamaguchi, A., Taylor, G.J., Keil, K., 1996. Global crustal metamorphism of the eucrite

parent asteroid. Antarctic Meteorites XXIV, 185–186. parent body. Icarus 124, 97–112.

Warren, P.H., Jerde, E.A., 1987. Composition and origin of Nuevo Laredo Trend Yamaguchi, A., Taylor, G.J., Keil, K., 1997a. Shock and thermal history of equilibrated

eucrites. Geochim. Cosmochim. Acta 51, 713–725. eucrites from Antarctica. Antarctic Meteorite Res. 10, 415–436.

Warren, P.H., Jerde, E.A., Migdisova, L.F., Yaroshevsky, A.A., 1990. Pomozdino: an Yamaguchi, A., Taylor, G.J., Keil, K., 1997b. Metamorphic history of the eucritic crust

anomalous, high-MgO/FeO, yet REE-rich eucrite, Proceedings of the 20th Lunar of 4 Vesta. J. Geophys. Res. 102, 13381–13386.

and Planetary Science Conference , pp. 281–297. Yamaguchi, A., Taylor, G.J., Keil, K., Floss, C., Crozaz, G., Nyquist, L.E., Bogard, D.D.,

Warren, P.H., Kallemeyn, G.W., Arai, T., Kaneda, K., 1996. Compositional-petrologic Garrison, D.H., Reese, Y.D., Wiesmann, H., Shih, C.-Y., 2001. Post-crystallization

investigation of eucrites and the QUE94201 shergottite. Antarctic Meteorites reheating and partial melting of eucrite EET90020 by impact into the hot crust

XXI, 195–197. of asteroid 4Vesta ∼4.50 Ga ago. Geochim. Cosmochim. Acta 65, 3577–3599.

Warren, P.H., Kallemeyn, G.W., Huber, H., Ulff-Møller, F., Choe, W., 2009. Siderophile Yamaguchi, A., Clayton, R.N., Mayeda, T.K., Ebihara, M., Oura, Y., Miura, Y.N.,

and other geochemical constraints on mixing relationships among HED- Haramura, H., Misawa, K., Kojima, H., Nagao, K., 2002. A new source of

meteoritic breccias. Geochim. Cosmochim. Acta 73, 5918–5943. basaltic meteorites inferred from Northwest Africa 011. Science 296, 334–

Warren, P.H., Rubin, A.E., Isa, J., Gessler, N., Ahn, I., Choi, B.-G., 2014. Northwest 336.

Africa 5738: multistage ﬂuid-driven secondary alteration in an extraordi- Yamaguchi, A., Setoyanagi, T., Ebihara, M., 2006. An anomalous eucrite, Dhofar 007,

narily evolved eucrite. Geochim. Cosmochim. Acta, http://dx.doi.org/10.1016/ and a possible genetic relationship with mesosiderites. Meteorit. Planet. Sci. 41,

j.gca.2014.06.008. 863–874.

Wasson, J., Wetherill, G., 1979. Dynamical chemical and isotopic evidence regarding Yamaguchi, A., Barrat, J.A., Greenwood, R.C., Shirai, N., Okamoto, C., Setoyanagi,

the formation locations of asteroids and meteorites. Asteroids 1, 926–974. T., Ebihara, M., Franchi, I.A., Bohn, M., 2009. Crustal partial melting on Vesta:

Wasson, J.T., 2013. Vesta and extensively melted asteroids: why HED meteorites are evidence from highly metamorphosed eucrites. Geochim. Cosmochim. Acta 73,

probably not from Vesta. Earth Planet. Sci. Lett. 381, 138–146. 7162–7182.

Welten, K.C., Lindner, L., Van Der Borg, K., Loeken, T., Scherer, P., Schultz, L., 1997. Yamaguchi, A., Barrat, J.-A., Ito, M., Bohn, M., 2011. Posteucritic magmatism on Vesta:

Cosmic-ray exposure ages of diogenites and the recent collisional history of the evidence from the petrology and thermal history of diogenites. J. Geophys. Res.:

howardite, eucrite and diogenite parent body/bodies. Meteorit. Planet. Sci. 32, Planets 116, E08009.

891–902. Yamaguchi, A., Mikouchi, T., Ito, M., Shirai, N., Barrat, J.A., Messenger, S., Ebihara,

Wiechert, U.H., Halliday, A.N., Palme, H., Rumble, D., 2004. Oxygen isotope evidence M., 2013. Experimental evidence of fast transport of trace elements in planetary

for rapid mixing of the HED meteorite parent body. Earth Planet. Sci. Lett. 221, basaltic crusts by high temperature metamorphism. Earth Planet. Sci. Lett. 368,

373–382. 101–109.

Wieler, R., Pedroni, A., Leya, I., 2000. Cosmogenic neon in mineral separates from Yanai, K., Haramura, H., 1993. Achondrite Binda: Re-examination as a common type

Kapoeta: no evidence for an irradiation of its parent body regolith by an early eucrite, Antarctic Meteorites XVIII, pp. 7-8.

active Sun. Meteorit. Planet. Sci. 35, 251–257. Zhang, A.-C., Wang, R.-C., Hsu, W.-B., Bartoschewitz, R., 2013. Record of S-rich vapors

Wilkening, L.L., 1973. Foreign inclusions in stony meteorites. I. Carbonaceous chon- on asteroid 4 Vesta: sulfurization in the Northwest Africa 2339 eucrite. Geochim.

dritic xenoliths in the Kapoeta howardite. Geochim. Cosmochim. Acta 37, Cosmochim. Acta 109, 1–13.

1985–1989. Zolensky, M.E., Hewins, R.H., Mittlefehldt, D.W., Lindstrom, M.M., Xiao, X., Lipschutz,

Wilkening, L., 1976. Carbonaceous chondritic xenoliths and planetary-type M.E., 1992. Mineralogy, petrology and geochemistry of carbonaceous chondritic

noble gases in gas-rich meteorites, Lunar and Planetary Science Conference clasts in the LEW 85300 polymict eucrite. Meteoritics 27, 596–604.

Proceedings , pp. 3549–3559. Zolensky, M.E., Weisberg, M.K., Buchanan, P.C., Mittlefehldt, D.W., 1996. Mineralogy

Wilkening, L.L., Anders, E., 1975. Some studies of an unusual eucrite: Ibitira. of carbonaceous chondrite clasts in HED achondrites and the Moon. Meteorit.

Geochim. Cosmochim. Acta 39, 1205–1210. Planet. Sci. 31, 518–537.