Meteoritics & Planetary Science 48, Nr 11, 2105–2134 (2013)
doi: 10.1111/maps.12182
Composition and petrology of HED polymict breccias: The regolith of (4) Vesta†
David W. MITTLEFEHLDT1*, Jason S. HERRIN2,5, Julie E. QUINN2,6, Stanley A. MERTZMAN3,
Julia A. CARTWRIGHT4,7, Karen R. MERTZMAN3, and Zhan X. PENG2
1
KR/Astromaterials Research Office, Astromaterials Research and Exploration Sciences Directorate,
NASA/Johnson Space Center, 2101 NASA Parkway, Houston, Texas 77058, USA
2
Science Analysis and Research Development, Engineering and Science Contract Group, Houston, Texas 77258, USA
3
Department of Geosciences, Franklin & Marshall College, Lancaster, Pennsylvania 17604, USA
4
Max-Planck-Institut f€
ur Chemie, Hahn-Meitner-Weg 1, Mainz 55128, Germany
5
Present address: Facility for Analysis, Characterization, Testing and Simulation, School of Materials Science and Engineering,
and Earth Observatory of Singapore, Nanyang Technological University, 50 Nanyang Avenue 639798, Singapore
6
Present address: PANalytical, Inc., 117 Flanders Rd., Westborough, Massachusetts 01581, USA
7
Present address: Division of Geological and Planetary Sciences, California Institute of Technology, MC 100-23,
1200 E. California Blvd., Pasadena, California 91125, USA
*
Corresponding author: E-mail: [email protected]
(Received 15 April 2013; revision accepted 06 July 2013)
†
This study is dedicated to the memory of friend and colleague David S. McKay, who taught us much about the regoliths of airless bodies.
Abstract–We have done petrologic and compositional studies on a suite of polymict eucrites
and howardites to better understand regolith processes on their parent asteroid, which we
accept is (4) Vesta. Taking into account noble gas results from companion studies, we
interpret five howardites to represent breccias assembled from the true regolith: Elephant
Moraine (EET) 87513, Grosvenor Mountains (GRO) 95535, GRO 95602, Lewis Cliff
(LEW) 85313, and Meteorite Hills (MET) 00423. We suggest that EET 87503 is paired with
EET 87513, and thus is also regolithic. Pecora Escarpment (PCA) 02066 is dominated by
melt-matrix clasts, which may have been formed from true regolith by impact melting.
These meteorites display a range in eucrite:diogenite mixing ratio from 55:45 to 76:24. There
is no correlation between degree of regolith character and Ni content. The Ni contents of
howardite, eucrite, and diogenites (HEDs) are mostly controlled by the distribution of
coarse chondritic clasts and metal grains, which in some cases resulted from individual, lowvelocity accretion events, rather than extensive regolith gardening. Trace element
compositions indicate that the mafic component of HED polymict breccias is mostly basalt
similar to main-group eucrites; Stannern-trend basaltic debris is less common. Pyroxene
compositions show that some trace element-rich howardites contain abundant debris from
evolved basalts, and that cumulate gabbro debris is present in some breccias. The scale of
heterogeneity varies considerably; regolithic howardite EET 87513 is more homogeneous
than fragmental howardite Queen Alexandra Range (QUE) 97001. Individual samples of a
given howardite can have different compositions even at roughly 5 g masses, indicating that
obtaining representative meteorite compositions requires multiple or large samples.
INTRODUCTION
The howardite, eucrite, and diogenite (HED) clan
of meteorites is the largest suite of rocks from a
differentiated asteroid. As such, these meteorites provide
an extensive set of magmatic lithologies with which to
decipher the geologic evolution of smaller bodies during
the early stages of solar system history (see Mittlefehldt
et al. 1998a). Eucrites are basaltic composition rocks
from flows and shallow to deep intrusive bodies. Most
are fine- to medium-grained basalts and diabases that
represent melt compositions. Some are coarse-grained
2105
© Published 2013. This article is a U.S. Government work
and is in the public domain in the USA.
D. W. Mittlefehldt et al.
HED
polymict
breccias
0 100
vol
%)
40
polymict
basaltic
eucrites
fragmental
& regolitic
howardites
80
100
0
40
20
polymict
cumulate
eucrites
polymict
diogenites
20
60
c
60
80
l%)
(vo
ite
ucr
ic e
s
alt
it e
bas
ucr
te
20
i
lym
po
gabbroic cumulates. Diogenites are very coarse-grained
cumulate orthopyroxenites, harzburgites (Beck and
McSween 2010), and rare dunites (Beck et al. 2011)
thought to have formed deep in the crust. Thermal
metamorphism, brecciation, and impact-induced shockmodification have affected most of the rocks (e.g., Duke
and Silver 1967; Takeda and Graham 1991).
Nevertheless, the petrology and composition of eucrites
and diogenites permit development of detailed models
for melting and crystallization on their parent asteroid
(e.g., Righter and Drake 1997; Ruzicka et al. 1997;
Treiman 1997; Warren 1997; Barrat et al. 2000, 2007,
2010; Barrat 2004; Shearer et al. 2010).
Within the HED clan is a subset of samples formed
by impact fragmentation and mixing of the primary
crustal lithologies, the polymict breccias. Howardites are
polymict breccias composed mostly of clasts and mineral
fragments of eucritic and diogenitic parentage (Wahl
1952; Duke and Silver 1967). Importantly, some
howardites contain chondritic or other exogenous clasts
derived from impactors (Zolensky et al. 1996; Gounelle
et al. 2003; Lorenz et al. 2007; Beck et al. 2012). Early
work interpreted howardites as representing the lithified
regolith of their parent asteroid in analogy to lunar
regolith breccias (e.g., see Duke and Silver 1967; Bunch
1975; Chou et al. 1976; Prinz et al. 1977). With the
recovery and study of numerous Antarctic HEDs, it was
recognized that there are polymict breccias consisting
only of debris from different types of eucrites
(Miyamoto et al. 1978), and that some polymict breccias
have eucrite:diogenite mixing ratios outside the range
typical of howardites (Mason et al. 1979). This led to
revision of the HED classification system (Fig. 1).
Polymict eucrites are defined as eucrite-rich breccias
containing <10% diogenitic material, and conversely,
polymict diogenites contain <10% eucritic material
(Delaney et al. 1983). Note that these definitions imply
that monomict breccias must be 100% pure. The suite of
HED polymict breccias thus forms a continuum from
monomict basaltic eucrite to monomict diogenite
breccias. Even some traditional monomict breccias are
now known to contain small amounts of extraneous
lithologic material indicating polymict character
(Pasamonte—Metzler et al. 1995; Ellemeet—Mittlefehldt
1994; Sioux County—Yamaguchi et al. 1997). There are
very few polymict breccias composed only of mixtures of
cumulate and basaltic eucrites, or only of diogenites and
cumulate eucrites. At present, there is no breccia term
specific for mixtures of HED lithologies and exogenous
material. Indeed, Wahl (1952) included Cumberland
Falls, a breccia of aubrite with exogenic chondritic
material, as one of his examples of polymict breccia.
Recently, howardites have been divided into two
subtypes: regolithic howardites, the lithified remnants of
dio
gen
ite
(
2106
40
60
80
0
100
cumulate eucrite (vol%)
Fig. 1. Nomenclature of howardite, eucrite, and diogenite
polymict breccias based on recommendations in Delaney et al.
(1983) and Miyamoto et al. (1978). Although based on modal
abundances (vol%), the nomenclature boundaries on the
polymict eucrite–polymict diogenite join can be directly related to
the mass-based percentage of eucritic material used here (see text).
the active regolith of Vesta; and nonregolithic
howardites, simpler polymict breccias (Warren et al.
2009). Following Bischoff et al. (2006), we refer to the
latter
as
fragmental
howardites.
Furthermore,
Cartwright et al. (2013) have suggested that there are
two different endmember types of regolithic howardites:
(1) those dominated by trapped solar wind gases
indicative of irradiation on the vestan surface, and (2)
those dominated by planetary-type noble gases derived
from chondritic clasts indicative of mixing with
impactor debris, but also containing a component of
solar wind noble gases associated with vestan materials.
Thus, our understanding of HED polymict breccias is in
flux, and this influences how we interpret impact mixing
and gardening processes on Vesta, and on larger
asteroids in general.
The Dawn spacecraft spent 14 months in orbit
about Vesta (July 2011 to September 2012) remotely
sensing the surface. The Framing Camera and VisibleInfrared Mapping Spectrometer studied the optical
surface, imaged the morphology and geology, and
mapped mineralogical variations (De Sanctis et al.
2012a, 2012b; Denevi et al. 2012a; Reddy et al. 2012;
Ammannito et al. 2013). The Gamma-Ray and Neutron
Detector mapped variations in neutron leakage and
gamma-ray emission from roughly the upper meter of
the vestan surface (Prettyman et al. 2012, 2013;
Lawrence et al. 2013; Yamashita et al. 2013). Thus, the
Dawn spacecraft mostly observed the regolith, and for
HED polymict breccias
this reason, an improved understanding of regolith
development derived from studying HED polymict
breccias will aid in interpreting the returned data.
We are doing a collaborative investigation of HED
polymict breccias to improve our understanding of the
vestan regolith. Here, we present our results on the
mineralogy, petrology, and bulk rock compositions of a
suite of polymict eucrites and howardites. Companion
studies report on the noble gas contents and isotopic
ratios of a subset of these samples (Cartwright et al.
2012a, 2012b, 2013) and reflectance spectrometry of all
of them (Mittlefehldt et al. 2013). One goal of our
investigation is to test the hypothesis that some
howardites represent breccias formed from an ancient,
well-mixed vestan regolith (Warren et al. 2009).
Another is to use our results to further understand
regolith processing on large asteroids as compared to
what has been learned from the Moon.
REGOLITHS OF AIRLESS BODIES
The polymict breccias of the HED clan of
meteorites—howardites, polymict eucrites, and polymict
diogenites—preserve records of regolith processes that
occur on Vesta. Early petrologic work recognized that
the howardites contain a mixture of rock types (Wahl
1952), and that they represent fragmental debris from
impacts on their parent body (Duke and Silver 1967).
With the return of documented samples from the
Moon, breccias were found to come in several varieties.
Some had petrologic characteristics that indicated that
they were formed by fusing lunar soil. Early on, these
lunar regolith breccias invited comparison to the
howardites (e.g., Mason and Melson 1970; Mason et al.
1970), but important distinctions were noted (e.g.,
Bunch 1975; Chou et al. 1976). On the Moon, the true
regolith1 is generally 4–15 m thick (McKay et al. 1991).
This true regolith overlies a debris layer of large-scale
crater ejecta and fractured bedrock, referred to as the
megaregolith zone (McKay et al. 1991). Theoretical
modeling indicated that the regolith on medium-sized
asteroids (100–300 km in diameter) would differ from
that on the Moon, being much thicker (Housen and
Wilkening 1982). Observations by the Dawn spacecraft
show that ejecta deposits from individual craters can be
hundreds of meters thick (Denevi et al. 2012b; Jaumann
et al. 2012). However, the thick ejecta deposits on Vesta
1
We follow the terminology of McKay et al. (1991) and use “true
regolith” to describe the soil layer that is being churned by smaller
impacts that periodically bring the lithic, glass, and mineral fragments
to the surface where exposure to solar wind, galactic cosmic rays, and
micrometeorites occurs. This is an inexact definition because there is
no definition of the minimum time scale for grain exposure required to
be considered true regolith.
2107
from the younger craters are analogous to the largescale ejecta deposits overlying the fractured bedrock on
the Moon, such as the Fra Mauro Fm. and Descartes
Fm. at the Apollo 14 and 16 landing sites (Swann et al.
1977; Spudis 1984), and are not true vestan regolith.
Modeling suggests that because of the higher impact
rate in the asteroid belt and the lower gravity of
asteroids that allows for a greater ballistic range, a
packet of fragmental debris on Vesta will spend less time
exposed to the space environment than the equivalent
debris on the Moon (Housen and Wilkening 1982).
Thus, modeling of the physics of asteroidal regolith
formation indicates that the maturity of vestan true
regolith will be generally lower than that on the Moon.
Regolithic howardites are a subset of howardites
that were previously characterized by high 20Ne contents,
elevated Ni contents, and a higher abundance of glass—
especially brown, turbid glass (Warren et al. 2009).
Based on a general concordance of these characteristics
with a narrow range in Al contents for bulk samples,
Warren et al. (2009) posited that such regolithic
howardites may represent lithified, ancient, well-mixed
true regolith. However, there are few characterized
examples of regolithic howardite (Warren et al. 2009),
which reduces the confidence one can have in defining a
characteristic mixing ratio for well-mixed vestan regolith.
Kapoeta, the prototypical example of a regolithic
howardite, contains petrologic and chemical indicators
that some of its constituents were exposed as part of the
active surface of the vestan regolith. Particle track
studies show that track-rich grains occur in Kapoeta
(Lal and Rajan 1969; Pellas et al. 1969), and that these
are preferentially within the dark portion of the breccia
(Wilkening et al. 1971). Caffee et al. (1983)
demonstrated a direct relationship between track-rich
pyroxene grains and implanted Ne with a solar
20
Ne/22Ne ratio in Kapoeta. Glassy spherules containing
microcraters caused by hypervelocity impacts of
micrometeorites have been found in Kapoeta (Brownlee
and Rajan 1973). Agglutinates are present in Kapoeta,
although they are rare, while nanophase Fe0-bearing
grain rims and amorphous grain rims are very rare
(Noble et al. 2010). Fused-soil components in Kapoeta
make up a much smaller fraction of the rock than
observed for lunar soils (Fuhrman and Papike 1981).
Microporphyritic
spheres
with
microcrystalline
groundmass that are thought to have been formed by
impact occur in Kapoeta (Olsen et al. 1990).
M€
uller and Z€ahringer (1966) demonstrated that the
dark portion of Kapoeta, in addition to having an
elevated 20Ne/22Ne like that of solar Ne, is enriched in
C. They interpreted this to indicate that the dark
portion of Kapoeta contained carbonaceous chondrite
material. Wilkening (1973) documented the presence of
2108
D. W. Mittlefehldt et al.
carbonaceous chondrite clasts in Kapoeta. Planetarytype noble gases in carbonaceous chondrites have
elevated 20Ne/22Ne, but with ratios somewhat lower
than that of the solar wind (see for example, Ott 2002).
Thus, high trapped 20Ne contents alone need not
indicate exposure to the solar wind.
Noble gas analyses have been done on a subset of
the HED polymict breccia suite studied here. Cartwright
et al. (2013) found two distinct Ne release profiles for
samples showing elevated 20Ne/22Ne. One shows the
highest 20Ne/22Ne in the lowest temperature fraction,
and the other shows the highest 20Ne/22Ne ratio in the
intermediate temperature step. The latter release pattern
was prominent for those samples that contained a high
proportion of CM-like material, and was also found for
a CM chondrite clast separated from PRA 04401. The
heavier noble gases indicate mixing between planetarytype noble gases (especially Q) and solar wind gases, and
some with added contamination by Earth’s atmosphere
(Cartwright et al. 2013). Thus, gas-rich howardites with
elevated 20Ne/22Ne likely acquired their noble gases by
some combination of solar irradiation in the true vestan
regolith and low-velocity accretion of chondritic
material. Note that the latter component can include
planetary-type and solar wind–implanted gases (cf. the
Murchison results of Caffee et al. 1983). Elevated 20Ne
contents determined on bulk howardite samples do not
uniquely identify breccias formed from true regolith.
SAMPLES AND ANALYTICAL METHODS
This study includes whole rock and matrix samples,
mostly from the U.S. Antarctic Meteorite Collection,
which were acquired over time as part of general studies
of HED petrology and composition. We will refer to
these as the general set. Samples of the general set
varied from 0.13 to 0.94 g in mass, and were used in
instrumental neutron activation analysis (INAA) work
at Johnson Space Center (JSC).
We subsequently acquired a set of samples
specifically for an investigation of the petrologic,
compositional, and noble gas diversity of HED
polymict breccias. We will refer to these as the targeted
set. Samples from the targeted set were requested from
the larger meteorites in the U.S. Antarctic Meteorite
Collection, and varied from 4.83 to 5.78 g in mass. One
purpose of the study is to understand the heterogeneity
of polymict breccias. Thus, the large sample mass is an
attempt to ensure as representative sampling as possible
at the roughly cm-scale (Fig. 2a). However, limitations
in meteorite size preclude the possibility of obtaining
truly representative samples (cf. Vander Voet and
Riddle 1993, p. 31; see Appendix S1). Duplicate samples
of some meteorites and samples from allegedly paired
a
b
Fig. 2. Sample processing photos of a) EET 87513, and b)
QUE 97001. Cubes are 1 cm; images are to the same scale.
EET 87513,136 is a targeted set sample. Images courtesy of
NASA-Johnson Space Center.
meteorites were requested to evaluate decimeter-scale
variations and to test pairing suggestions. The samples
from the targeted set were used in x-ray fluorescence
spectrometry (XRF) work at Franklin & Marshall
College and in solution aspiration inductively coupled
plasma mass spectrometry (ICP-MS) work at JSC.
Splits of the samples were used for noble gas analysis at
the Max-Planck-Institut f€
ur Chemie, and for reflectance
spectroscopy at the spectroscopy laboratory of Istituto
di Astrofisica e Planetologia Spaziali and Istituto
Nazionale di Astrofisica and at the Reflectance
Experiment Laboratory (RELAB) of Brown University
(Mittlefehldt et al. 2013). Companion thin sections were
studied at JSC for petrologic characterization; for EET
87510, EET 87512, and LEW 87002, only thin sections
were studied. Mineral compositions were determined by
electron microprobe analysis (EMPA) at JSC.
Details of the samples studied are given in Table 1;
analytical methods are described in Appendix S1.
Classifications of the samples taken from the online
Meteoritical Bulletin Database are given in Table 1. For
two meteorites, we recommend reclassification, with our
reasons for this given in Appendix S1. In this study, we
use our recommended classifications for these. We have
indicated in Table 1 those samples that contain solar
HED polymict breccias
2109
Table 1. Details of samples studied.
Pairinga
Meteorite
Split
Sample
Sample type mass (g) Class
CRE 01400
EET 83376
EET 87503
–
–
EET 87509
–
–
–
–
EET 87510
EET 87512
EET 87513
–
–
–
–
–
–
,12
,16
,24
,54
,166
,31
,37
,81
,90
,109
n/a
n/a
,48
,50
,56
,86
,101
,102
,134
Whole rock
Whole rock
Matrixc
Matrix
Whole rock
Matrix
Matrix
Matrix
Matrix
Whole rock
n/a
n/a
Matrix
Matrix
Matrix
Matrix
Matrix
Matrix
Whole rock
5.32
5.73
0.940
0.618
5.46
0.340
0.190
0.207
0.315
5.04
n/a
n/a
0.264
0.151
0.165
0.151
0.287
0.362
5.08
Howardite
Howardite
Howardite
–
–
Howardite
–
–
–
–
Howardite
Howardite
Howardite
–
–
–
–
–
–
n/p
n/p
EET
–
–
EET
–
–
–
–
EET
EET
n/p
–
–
–
–
–
–
–
EET 87518
EET 87531
–
–
–
–
EET 87532
EET 99400
EET 99408
Erevan
GRO 95535
GRO 95574
GRO 95581
GRO 95602
LAP 04838
–
LEW 85313
LEW 86001
,136
,10
,35
,52
,103
,104
,135
,16
,11
,12
ER-1,3
,13
,14
,11
,7
,8
,9
,39
,21
Whole rock
Whole rock
Matrix
Matrix
Matrix
Matrix
Whole rock
Whole rock
Whole rock
Whole rock
Matrix
Whole rock
Whole rock
whole rock
Whole rock
Whole rock
Whole rock
Whole rock
Whole rock
5.62
5.36
0.153
0.130
0.221
0.338
5.57
4.95
5.00
4.94
lostd
5.03
5.00
5.15
5.76
5.38
5.78
4.91
5.51
–
EET 87503
EET 87503
–
–
–
–
n/p
EET 99400
EET 99400
n/p
GRO 95534
GRO 95534
GRO 95534
GRO 95534
n/p
–
LEW 85441
n/p
–
EET 87509
EET 87509
–
–
–
–
EET 87509
EET 87509
EET 87509
n/p
GRO 95534
GRO 95534
GRO 95534
n/p
n/p
–
LEW 85441
n/p
XRF, ICP-MS
XRF, ICP-MS
INAA
INAA
INAA
INAA
XRF, ICP-MS
XRF, ICP-MS
XRF, ICP-MS
XRF, ICP-MS
INAA
XRF, ICP-MS
XRF, ICP-MS
XRF, ICP-MS
XRF, ICP-MS
XRF, ICP-MS
XRF, ICP-MS
XRF, ICP-MS
XRF, ICP-MS
LEW 87002
LEW 87004
n/a
,25
n/a
Whole rock
n/a
4.96
n/p
n/p
n/p
n/p
n/a
,3
XRF, ICP-MS ,5
MET 00423
MET 96500
–
Mundrabilla
020
PCA 02066
PRA 04401
QUE 94200
–
,7
,17
,19
NP-1
Whole
Whole
Whole
Whole
5.46
5.44
5.11
lostd
–
Howardite
Howardite
–
–
–
–
Polymict eucrite
Howardite
Howardite
Howardite
Howardite
Howardite
Howardite
Howardite
Howardite
–
Howardite
Polymict
eucrite
Howarditee
Polymict
eucrite
Howardite
Howardite
–
Howardite
n/p
n/p
XRF, ICP-MS
MET 96500 MET 96500 XRF, ICP-MS
–
–
XRF, ICP-MS
n/p
n/p
INAA
,10
,26
–
NP-1
SW
nd
CG
nd
,8
,7
,8
,29
Whole rock
Whole rock
Matrix
Whole rock
5.45
5.17
0.280
5.61
Howardite
Howardite
Howardite
–
PCA 02009
PRA 04401
n/p
–
,11
,10
,6
CG+
PG
nd
CG
rock
rock
rock
rock
Initial
Suggested
Analysis
Thin
Noble
section gasesb
n/p
EET
EET
–
–
EET
–
–
–
–
EET
n/p
EET
–
–
–
–
–
–
XRF, ICP-MS
XRF, ICP-MS
INAA
INAA
XRF, ICP-MS
INAA
INAA
INAA
INAA
XRF, ICP-MS
n/a
n/a
INAA
INAA
INAA
INAA
INAA
INAA
XRF, ICP-MS
,17
,5
–
–
,6
–
–
–
–
,10
,8
,20
–
–
–
–
–
–
,7
–
,9
–
–
–
–
,7
,14
,15
,14
–
,6
,4
,14
,10
,14
–
,19
,7
87503
87503
87503
87503
87509
87503
87509
87509
87503
PCA 02009
PRA 04401
QUE 99033
–
XRF, ICP-MS
XRF, ICP-MS
INAA
XRF, ICP-MS
CG
CG
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
SW &
PG
nd
CG
nd
nd
nd
nd
nd
nd
CG
CG
nd
SW
nd
nd
SW
nd
nd
SW
nd
nd
nd
2110
D. W. Mittlefehldt et al.
Table 1. Continued. Details of samples studied.
QUE 97001
–
–
–
QUE 97002
–
–
–
–
QUE 99033
SAN 03472
SCO 06040
Yurtuk
Zmenj
,9
,10
,39
,40
,7
,9
,11
,28
,29
,14
,9
,8
YU-1081,0
ZH-782
Whole rock
Whole rock
Whole rock
Whole rock
Whole rock
Whole rock
Whole rock
Whole rock
Whole rock
Whole rock
Whole rock
Whole rock
Matrix
Matrix
0.604
0.532
4.83
5.07
0.465
0.653
0.475
4.92
5.19
5.08
5.27
5.40
lostd
lostd
Howardite
–
–
–
Polymict eucritee
–
–
–
–
Howardite
Howardite
Howardite
Howardite
Howardite
n/p
QUE 99033 INAA
–
–
–
INAA
–
–
–
XRF, ICP-MS ,6
–
–
XRF, ICP-MS –
n/p
n/p
INAA
–
–
–
INAA
–
–
–
INAA
–
–
–
XRF, ICP-MS ,34
–
–
XRF, ICP-MS –
QUE 99033 QUE 99033 XRF, ICP-MS ,18
n/p
n/p
XRF, ICP-MS ,12
n/p
n/p
XRF, ICP-MS ,11
n/p
n/p
INAA
–
n/p
n/p
INAA
–
nd
nd
nd
nd
nd
nd
nd
CG
nd
nd
CG+
PG
nd
nd
CG = cosmogenic-dominated; CG+ = cosmogenic-dominated, but with slightly elevated 20/22 Ne; PG = planetary gases; SW = solar wind
gases; nd = not determined; n/p = not paired.
a
Initial pairing—proposed at initial processing as given in the Antarctic Meteorite Newsletter; suggested pairing—revisions to pairing suggested
here and in Cartwright et al. (2012a, 2012b).
b
Noble gas information from Cartwright et al. (2012a, 2012b, 2013).
c
Matrix samples were selected to avoid larger clastic material.
d
Samples acquired by M. Lindstrom; information lost upon her retirement.
e
LEW 87002: official classification—Mg-rich eucrite; QUE 97002: official classification—howardite
wind and/or planetary noble gases or are dominated by
cosmogenic noble gases (Cartwright et al. 2012a, 2012b,
2013).
PETROLOGY
The basic petrologic characteristics of many
howardites and polymict eucrites have been described
(e.g., Delaney et al. 1984; Duke and Silver 1967;
Fuhrman and Papike 1981; Labotka and Papike 1980;
Miyamoto et al. 1978; Takeda et al. 1983) and will not
be repeated here. Our main interest is in trying to
understand how petrologic features correlate (or do not)
with chemical characteristics inferred for regolithic
howardites (Warren et al. 2009) and noble gas evidence
for exposure in the regolith (Cartwright et al. 2012a,
2012b, 2013). For this reason, we focused on the
petrographic characteristics of “reworked” clasts; those
clasts that have been texturally modified from igneous
protoliths. We have done reconnaissance electron
microprobe analyses of pyroxene and olivine to evaluate
variations in the ultramafic (diogenetic) component, and
done more targeted analyses to address specific
questions raised for some meteorites.
We have attempted to evaluate the extent of regolith
gardening represented by the samples through
comparison with textural features used for this purpose
on lunar soils and breccias. We have made qualitative
visual estimates of the abundances of glass clasts, meltmatrix breccia clasts, dark-matrix breccia clasts,
chondritic clasts, clast size, and clast rounding. We
assume that these characteristics will correlate with the
length of time the debris was gardened in the regolith.
This assumption is based on analogy with the lunar
regolith, where maturation by meteoroid impacts causes
diminution of particle sizes, rounding of mineral and clast
fragments, the development of soil aggregates welded by
impact glass (agglutinates), and elevated contents of
siderophile elements derived from the impactors (McKay
et al. 1991). The abundance of impact glass and
siderophile element contents are two characteristics used
to define regolithic howardites (Warren et al. 2009).
Agglutinates are particles of fused soil and are
characteristic of mature lunar soils (McKay et al. 1991).
True agglutinates are rarely found in HED polymict
breccias (Noble et al. 2010). Dark-matrix breccias are
considered to represent fused soil of the HED regolith in
analogy to lunar agglutinates (Labotka and Papike 1980).
Initially, we used the abundance of breccia clasts, lumped
with impact–melt-matrix breccia clasts as “reworked”
clasts as part of our regolith index (Mittlefehldt et al.
2010). However, breccia clasts, including polymict breccia
clasts, can be produced in a single impact event, as
observed for the Bunte Breccia and suevite of the Ries
crater (H€
orz 1982; St€
offler et al. 2013). For this reason,
we no longer use the presence of breccia clasts as a
regolith criterion. We now use the descriptive terms
dark-matrix breccias and melt-matrix breccias instead of
the process-oriented term impact–melt-matrix breccias
for these clasts. Examples of the hand sample textures
and petrographic characteristics used here to evaluate
regolith maturity are shown in Figs. 1 and 2. The
petrographic characteristics of each meteorite and their
regolith indexes are summarized in Table 2.
HED polymict breccias
2111
Table 2. Petrographic characteristics of the targeted set samples.
Melt-matrix
clasts
Dark-matrix
clasts
Glass clasts
Chondritic
clasts
Euc:dio
Regolith
index
No
Few
Abundant
Abundant
Moderate
No
Few
Abundant
Abundant
Moderate
No
Few
Abundant
Abundant
Moderate
No
No
No
No
No
20:80
65:35
75:25
75:25
50:50
Low
Moderate
High
High
Moderate
Moderate
Moderate
Moderate
No
35:65
Moderate
Few
Few
Few
Yesa
65:35
Moderate
Abundant
Abundant
Abundant
Abundant
Abundant
Abundant
No
No
40:60
70:30
Moderate
Moderate
Abundant
Abundant
Abundant
No
50:50
High
Angular
Rounded
Abundant
Abundant
Abundant
Abundant
Abundant
Few
No
No
80:20
80:20
Moderate
High
Angular
Subrounded
Subangular/
subrounded
Subangular/
subrounded
Subangular/
subrounded
Subrounded
Moderate
Moderate
Moderate
Moderate
Moderate
Moderate
Few
Few
No
Yesb
Yes
Yesb
65:35
40:60
50:50
Moderate
High
Moderate
Few
Few
No
No
70:30
Moderate
Abundant
Moderate
Few
No
85:15
Moderate
No
No
No
Yes
80:20
Moderate
Angular/
subangular
Subrounded
No
No
No
No
95:5
Low
Moderate
Few
No
No
95:5
Moderate
Meteorite
Class
Clast size
Clast shape
CRE 01400
EET 83376
EET 87503
EET 87509
EET 87510
Howardite
Howardite
Howardite
Howardite
Howardite
Coarse
Coarse
Coarse
Medium
Variable
EET 87512
Howardite
EET 87513
Howardite
EET 87518
EET 87531
Howardite
Howardite
Coarse/
medium
Medium/
fine
Coarse
Coarse
EET 87532
EET 99400
EET 99408
Polymict
eucrite
Howardite
Howardite
Subangular
Rounded
Rounded
Rounded
Angular to
subrounded
Subangular/
subrounded
Angular/
subangular
Angular
Angular/
subangular
Subrounded
GRO 95535
GRO 95574
GRO 95581
Howardite
Howardite
Howardite
GRO 95602
Howardite
LAP 04838
Howardite
LEW 85313
Howardite
LEW 86001
MET 00423
Polymict
eucrite
Polymict
eucrite
Howardite
MET 96500
Howardite
PCA 02066
Howardite
PRA 04401
QUE 94200
Howardite
Howardite
QUE 97001
Howardite
QUE 97002
QUE 99033
Polymict
eucrite
Howardite
SAN 03472
Howardite
SCO 06040
Howardite
LEW 87004
a
Coarse
Coarse
Medium/
fine
Medium
Medium
Coarse/
medium
Medium/
fine
Coarse/
medium
Coarse/
medium
Coarse
Medium
Coarse
Coarse/
medium
Coarse/
medium
Coarse
Coarse
Coarse/
medium
Coarse/
medium
Coarse/
medium
Coarse/
medium
Coarse/
medium
Subangular/
subrounded
Subangular
No
No
No
Yes
65:35
Low
Moderate
Few
No
No
60:40
Low
Rounded
Abundant
No
No
No
30:70
High
Angular
Subangular/
subrounded
Subangular/
subrounded
Subrounded
Abundant
Abundant
No
Abundant
No
Few
Yes
No
50:50c
30:70
Moderate
Moderate
Moderate
Abundant
Few
No
20:80
Moderate
No
No
No
Yes
98:2
Low
Angular/
subangular
Angular
Moderate
Moderate
No
No
50:50
Moderate
Moderate
Moderate
No
No
65:35
Low
Subrounded
Few
No
No
Yes
80:20
Moderate
Carbonaceous chondrite clasts are reported (Buchanan and Mittlefehldt, 2003; Buchanan et al. 1993; Mittlefehldt, unpublished data), but none
were found in our thin section.
b
Carbonaceous chondrite clasts are reported in paired meteorites GRO 95534 (Prettyman et al. 2012) and GRO 95574 (this study).
c
Approximately 60% of this thin section is carbonaceous chondrite clasts; euc:dio ratio uncertain.
2112
D. W. Mittlefehldt et al.
a
b
c
d
e
Fig. 3. Plane polarized light photomicrographs (a–d) and backscattered electron (e) image of regolithic characteristics of
howardite, eucrite, and diogenite polymict breccias. a) Rounded mafic clast in EET 87503,6. b) Dark-matrix breccia clast in EET
87503,6. c) Brown glass fragments in EET 87518,9. d) Dark-matrix breccia clast and glass sphere in EET 87532,14. e) Chondritic
clast in LEW 85313,19. Scale bars: a, b: 0.5 mm, c, d: 1 mm, e, 100 lm.
The hand sample of EET 87513 shows a more
homogeneous texture with fewer and smaller clasts than
does QUE 97001 (Fig. 2). These characteristics suggest
that the former was formed from regolith that was more
extensively gardened—is more mature—than the latter.
EET 87503 has a high proportion of rounded mafic
lithic clasts (Fig. 3a) and dark-matrix breccia (Fig. 3b;
Table 2) suggesting working by meteoroid impacts and
a more mature regolith. Several of the Elephant
Moraine polymict breccias have a higher abundance of
brown turbid glass used by Warren et al. (2009) as one
indicator of regolithic character (Table 2). Turbid
brown glass and cryptocrystalline material is especially
common in EET 87518 where it has a typically angular
HED polymict breccias
morphology, and larger fragments include fragmental
debris (Fig. 2c). Several of the Queen Alexandra Range
howardites contain abundant black clasts up to
approximately cm size (Fig. 2b) that include darkmatrix breccia clasts, and porphyricitc glassy spherules
and fragments. Polymict eucrite EET 87532 also
contains abundant dark-matrix breccia clasts and
porphyricitc glassy spherules (Fig. 3d). Singerling et al.
(2013) describe glassy materials in several howardites
studied here and found no convincing evidence that any
of them are pyroclastic, even for microporphyritic
glassy spherules such as shown in Fig. 3d.
Carbonaceous chondrite clasts are found in several of
our meteorites (Table 2) and vary in size from <10 lm
to several mm. Most are a few hundred microns in size
(Fig. 3e). Low analysis totals for EMPA of matrix
indicates that they contain hydrous phases (Herrin et al.
2011). Accretion to Vesta and lithification of the
breccias did not engender dewatering of the clasts.
Thermal metamorphism has affected the polymict
breccias to varying degrees (e.g., Labotka and Papike
1980). LEW 87002 shows the most extreme degree of
Fe-Mg homogenization of any of our samples, with
evidence for Fe-Mg exchange on an mm-scale (see
Appendix S1). All other polymict breccias show only
narrow rims on pyroxene grain fragments, and typically
these rims are only a few tens of microns wide.
Magnesian pyroxenes have more ferroan rims and
ferroan pyroxenes have more magnesian rims. Rims on
pyroxenes demonstrate localized Fe-Mg exchange in the
breccias, possibly at the time of lithification. However,
there is no evidence that large-scale element migration
occurred that would compromise our ability to interpret
bulk major and trace element compositions for the
samples.
BULK COMPOSITION RESULTS
The results of individual measurements are
presented in Appendix S1, INAA results in Table S1,
XRF results in Table S2, ICP-MS results in Table S3,
and CIPW normative mineralogy in Table S4. Each of
the five polymict breccias contained a small metallic
nugget that was discovered during grinding (see
Appendix S1). These were removed from the samples
and analyzed separately by ICP-MS; the results are
given in Table S5. The composition of USGS standard
rock BHVO-1 determined by INAA and ICP-MS is
compared to the preferred values from the GeoReM
website in Table S6. A quality-control comparison on
USGS standard rock BHVO-2 analyzed by XRF is
discussed in Appendix S1. The main focus of this study
is the chemistry of the targeted set samples; Table 3
presents the averaged data for them. We have calculated
2113
Ce/Ce* and Eu/Eu* ratios (Table 3), where Ce* and
Eu* are the concentrations calculated by interpolation
of CI-normalized rare earth element (REE) diagrams.
The Ce/Ce* ratio gives an indication of possible
Antarctic alteration of the REE contents of the
meteorites (Mittlefehldt and Lindstrom 1991, 2003).
Given a precision of 5% on the ICP-MS analyses
(Appendix S1), we calculate 2r uncertainty limits on the
Ce/Ce* and use a ratio of 12r as indicating unaltered
REE contents. We flag those samples in Table 3 that we
think have had their REE contents altered while in
Antarctica. Table 3 also gives the mg# (molar
100*MgO/(MgO+FeO)).
A major concern here is the mixing ratio of eucrite
to diogenite in the breccias. We give the percentage of
eucritic material (POEM) by mass for each meteorite in
Table 3. The POEM is calculated following Jerome and
Goles (1971) using Al and Ca; the listed POEM is the
average of these two calculations. The POEM index
assumes that polymict breccias are two component
mixtures, basaltic eucrite and diogenite, which is a good
assumption to first order. The Al and Ca contents of
endmember basaltic eucrites and diogenites used in the
calculation were derived from an extensive database of
literature analyses maintained by the senior author, and
are virtually identical to those given by Warren et al.
(2009). Details of the POEM calculation are given in
Appendix S1. We directly equate the mass-based POEM
of ≥90 with the ≥90 vol% eucritic material limit used to
define polymict eucrites, and similarly for the polymict
diogenite limits. Grain densities of eucrites and
diogenites differ by <9% (Consolmagno et al. 2008).
A 10 vol% eucrite mixture (polymict diogenite)
corresponds to POEM 9.3, and a 90 vol% eucrite
mixture (polymict eucrite) corresponds to POEM 89.2.
Given uncertainties in modes and POEM, equating the
two does not introduce significant error.
Figure 4 shows major element compositions of our
samples, along with literature data on basaltic eucrites,
cumulate eucrites, and diogenites determined by wet
chemistry or XRF, where similarly sized or larger
samples were analyzed. The polymict breccias studied
here range from Mg-poor compositions with POEM
97—essentially basaltic eucrite in composition—to
Mg-rich compositions with POEM 32. This represents
most of the range of mixing ratios observed for
howardites and polymict eucrites. The eucrite-poor
howardite, Y-7308, has a POEM of 29 based on
literature data (W€anke et al. 1977; Yagi et al. 1978;
Jochum et al. 1980; Yanai et al. 1995; Warren et al.
2009). Some of the Pecora Escarpment (PCA) 2002
polymict HED breccias are classified as howardites, but
are paired with others that are classified as polymict
diogenites (Beck et al. 2012). The bulk compositions of
6.39
224
2.42
74.4
50.4
230
210
200
55.5
3.16
94.6
4.24
4.23
142
19.4
167
2.32
1.24
267
58.6
12.9
30.7
2.95
178
8.08
23.7
2.06
5.5
0.804
4.08
1.34
0.446
1.78
0.335
2.18
0.475
1.36
0.21
1.35
6.38
233
2.61
58.1
57.3
226
460
200
59
3.47
75.8
2.91
4.11
138
8.3
24.2
2.18
1.27
310
65.8
17.9
39.7
3.45
244
8.45
26.2
3.58
7.75
1.53
7.56
2.36
0.575
2.92
0.526
3.34
0.706
2.01
0.298
1.84
6.63
183
2.21
76.7
48.3
228
270
170
53.6
3.13
105
4.63
4.25
143
23.8
224
1.91
1.18
271
59.4
12.6
27.3
2.82
283
7.25
21
2.38
5.74
0.941
4.78
1.52
0.431
1.94
0.345
2.27
0.482
1.4
0.21
1.3
6.55
177
2.47
76.9
46.7
231
250
210
56
3.1
102
4.44
4.46
148
31.3
279
2.12
1.42
248
56
12.4
29.2
2.62
169
6.34
21.9
2.1
5.4
0.805
4.14
1.36
0.429
1.77
0.327
2.14
0.462
1.35
0.206
1.29
7.37
265
2.69
54.6
59.8
222
310
260
63.3
3.73
76.6
2.94
4.11
142
33.2
153
6.96
1.60
324
70.1
13.7
43.7
3.71
258
10.6
27.2
2.21
7.07
1.01
5.1
1.69
0.527
2.13
0.405
2.63
0.57
1.66
0.257
1.61
6.49
278
2.86
53.1
61.1
223
300
210
63.3
3.62
76.8
3.01
4.1
137
8.2
27.8
1.85
1.36
276
66.7
14.3
43.5
3.46
137
6.8
25.9
2.1
8
0.939
4.73
1.64
0.51
2.06
0.396
2.64
0.57
1.67
0.265
1.66
6.94
311
3.59
45.5
65.2
216
360
500
72.9
4.05
76.4
2.72
3.99
137
3.4
10
2.75
1.57
415
79.8
13.2
43.8
4.21
141
7.82
30.8
2.19
7.2
0.962
4.94
1.63
0.582
1.99
0.374
2.44
0.52
1.53
0.236
1.52
4.05
214
2.45
64
53.8
228
310
170
59.2
3.58
86.9
3.6
4.2
141
8.28
25.9
1.74
1.24
310
65.2
12.4
37.8
3.42
249
9
25.3
2.62
6.25
1.09
5.53
1.75
0.5
2.18
0.397
2.58
0.546
1.58
0.235
1.46
6.89
259
2.96
55.5
60.9
224
300
240
64.2
3.62
81.9
3.19
4.24
141
9
23.3
1.24
1.56
267
68.1
15.3
40.9
3.33
140
7.73
25.6
2.31
7
1
5.08
1.74
0.538
2.23
0.424
2.79
0.6
1.77
0.272
1.71
8.01
115
1.46
116
26.8
235
120
83
29.8
1.65
131
6.68
4.18
134
19.9
31.9
2.13
0.597
155
27.4
6.96
17.1
1.52
124
3.65
11
1.25
3.38
0.497
2.49
0.81
0.207
1.01
0.186
1.22
0.262
0.751
0.117
0.726
Li (lg g 1)
Be (ng g 1)
Na (mg g 1)
Mg (mg g 1)
Al (mg g 1)
Si (mg g 1)
P (lg g 1)
K (lg g 1)
Ca (mg g 1)
Ti (mg g 1)
V (lg g 1)
Cr (mg g 1)
Mn (mg g 1)
Fe (mg g 1)
Co (lg g 1)
Ni (lg g 1)
Zn (lg g 1)
Ga (lg g 1)
Rb (ng g 1)
Sr (lg g 1)
Y (lg g 1)
Zr (lg g 1)
Nb (lg g 1)
Mo (ng g 1)
Cs (ng g 1)
Ba (lg g 1)
La (lg g 1)
Ce (lg g 1)
Pr (lg g 1)
Nd (lg g 1)
Sm (lg g 1)
Eu (lg g 1)
Gd (lg g 1)
Tb (lg g 1)
Dy (lg g 1)
Ho (lg g 1)
Er (lg g 1)
Tm (lg g 1)
Yb (lg g 1)
6.98
211
2.47
72.6
50.5
228
330
140
54.1
3.4
78.5
3.31
4.21
141
12.4
33.2
1.52
1.26
234
56.4
15.2
36.4
3.17
141
6.21
24.2
2.66
7.36
1.1
5.55
1.81
0.488
2.26
0.418
2.7
0.577
1.66
0.251
1.57
CRE 01400 EET 83376 EET 87503 EET 87509 EET 87513
EET 87518 EET 87531 EET 87532
EET 99400 EET 99408
,12
,16
,166
,109
,134
,136
,10
,135
,16
,11
,12
Howardite Howardite Howardite Howardite Howardite Howardite Howardite Howardite Polymict eucrite Howardite Howardite
Meteorite
Split
Class
Table 3. Means of x-ray fluorescence spectrometry and inductively coupled plasma mass spectrometry data for the targeted set samples.
2114
D. W. Mittlefehldt et al.
Li (lg g )
Be (ng g 1)
Na (mg g 1)
Mg (mg g 1)
Al (mg g 1)
Si (mg g 1)
P (lg g 1)
K (lg g 1)
Ca (mg g 1)
Ti (mg g 1)
V (lg g 1)
Cr (mg g 1)
Mn (mg g 1)
Fe (mg g 1)
Co (lg g 1)
Ni (lg g 1)
Zn (lg g 1)
Ga (lg g 1)
Rb (ng g 1)
Sr (lg g 1)
Y (lg g 1)
Zr (lg g 1)
5.8
146
1.81
91.7
40.1
232
190
110
44.1
2.4
114
5.27
4.14
134
18.1
117
1.09
0.986
209
45.6
9.45
23
6.5
137
2.11
88.7
42.7
230
230
150
47.8
2.63
113
5.19
4.33
141
17.8
120
1.06
1.3
284
48.5
11.4
25.3
Howardite
5.98
162
1.93
89
40
238
190
120
45
2.35
110
5.12
4.12
135
23.3
236
1.99
1.03
204
45.5
9.24
22.8
Howardite
6.03
184
2.21
78.4
44.8
231
270
150
52.5
3.1
100
4.53
4.19
143
22.9
258
1.72
1.18
273
56.1
11.6
40.9
Howardite
0.249
1.2
186
50.5
325
119
1.35a
0.861
47.1
86
9.36
265
3.21
53.4
58.9
224
320
390
65.7
4.23
78.4
2.95
4.21
144
9.68
40
1.86
1.48
731
76.1
15.4
55.4
9.61
281
3.29
58.4
56.5
226
330
370
64.7
3.98
82
3.39
4.33
148
7.7
33.4
1.25
1.63
792
70.3
12.6
48.2
6.52
179
2.49
71.9
48.8
220
280
220
53.6
2.8
86.1
3.77
4.1
147
56.2
1270
10.1
1.49
365
54.9
10.2
31.2
11.3
443
3.95
41.6
62.2
224
460
620
74
5.82
67.6
2.53
4.32
153
7.54
0.783
2.37
1.72
740
94.3
19.5
83.7
0.215
1.07
171
69.2
170
94.1
0.874
0.794
51.1
77
0.253
1.14
180
40.2
306
119
1.09
0.848
47.5
87
9.16
303
3.39
48.7
62
224
320
360
72.1
4.07
80.2
2.93
4.33
147
9.5
35.1
1.54
1.69
480
76.8
15.4
46
6.2
208
2.28
81.3
47.5
225
230
120
51.9
3.11
85
3.61
4.24
144
44.7
556
0.998
1.16
188
54.7
12.4
37.6
6.07
226
2.24
79.7
44.9
224
300
150
49.1
2.97
98.4
4.14
4.14
140
21.8
238
1.7
1.24
194
50
11.6
29.6
MET
LEW 87004 MET 96500 96500
,25
,17
,19
Polymict
eucrite
Howardite
Howardite
0.226
1.2
212
32.4
337
134
1.17
1.00
43.3
97
Howardite
1
0.243
1.25
197
103
262
110
1.12
0.862
46.9
85
Class
0.191
0.824
135
51.2
222
72.9
0.981
0.858
54.4
69
LEW 85313 LEW 86001
,39
,21
Polymict
Howardite Howardite Howardite
eucrite
0.193
0.792
139
51.9
190
67.5
0.906
0.779
55.2
69
GRO 95535 GRO 95574 GRO 95581 GRO 95602 LAP 04838
,13
,14
,11
,7
,8
,9
0.271
1.13
180
49.2
305
111
0.782a
0.680
49.2
80
Meteorite
Split
0.199
0.849
160
233
228
73.3
1.01
0.896
54.6
72
0.11
0.476
74.9
24.9
152
39.8
1.01
0.710
66.5
33
Lu (lg g 1)
Hf (lg g 1)
Ta (ng g 1)
W (ng g 1)
Th (ng g 1)
U (ng g 1)
Ce/Ce*
Eu/Eu*
mg# (molar)
POEM (%)
0.232
1.01
169
58.2
290
100
1.02
0.749
54.2
71
CRE 01400 EET 83376 EET 87503 EET 87509 EET 87513
EET 87518 EET 87531 EET 87532
EET 99400 EET 99408
,12
,16
,166
,109
,134
,136
,10
,135
,16
,11
,12
Howardite Howardite Howardite Howardite Howardite Howardite Howardite Howardite Polymict eucrite Howardite Howardite
Meteorite
Split
Class
Table 3. Continued. Means of x-ray fluorescence spectrometry and inductively coupled plasma mass spectrometry data for the targeted set
samples.
HED polymict breccias
2115
Howardite
Class
Li (lg g )
Be (ng g 1)
Na (mg g 1)
Mg (mg g 1)
7.35
198
2.41
69.5
MET 00423
,7
Meteorite
Split
1
1.94
241
7.5
17.6
1.53
3.94
0.596
3.04
0.997
0.342
1.27
0.238
1.61
0.346
1.02
0.158
1
0.155
0.655
88.5
258
191
52.8
0.975
0.943
61.1
55
Nb (lg g )
Mo (ng g 1)
Cs (ng g 1)
Ba (lg g 1)
La (lg g 1)
Ce (lg g 1)
Pr (lg g 1)
Nd (lg g 1)
Sm (lg g 1)
Eu (lg g 1)
Gd (lg g 1)
Tb (lg g 1)
Dy (lg g 1)
Ho (lg g 1)
Er (lg g 1)
Tm (lg g 1)
Yb (lg g 1)
Lu (lg g 1)
Hf (lg g 1)
Ta (ng g 1)
W (ng g 1)
Th (ng g 1)
U (ng g 1)
Ce/Ce*
Eu/Eu*
mg# (molar)
POEM (%)
5.14
123
2.39
87.3
Howardite
PCA 02066
,8
2.21
145
11.5
18.2
2.02
5.22
0.763
3.9
1.26
0.371
1.61
0.297
1.93
0.414
1.21
0.185
1.17
0.176
0.714
114
65.3
243
59.3
0.993
0.808
59.1
60
Howardite
3.18
59.6
2.47
108
Howardite
PRA 04401
,7
2.02
160
5.95
16.8
1.51
3.92
0.573
2.93
0.981
0.335
1.28
0.239
1.6
0.345
1.01
0.16
0.993
0.152
0.642
105
265
189
54.2
1.00
0.928
60.2
55
Howardite
5.54
125
1.48
112
Howardite
QUE 94200
,29
2.79
284
7
21.5
2.01
5.32
0.816
4.11
1.33
0.421
1.7
0.315
2.1
0.449
1.31
0.199
1.26
0.184
0.935
138
40.2
200
69.4
0.982
0.869
55.7
65
Howardite
Howardite
1
Class
5.63
121
1.57
110
Howardite
5.46
97.6
1.43
116
Howardite
8.99
281
3.36
43.7
8.13
268
3.19
45.4
,29
Polymict
eucrite
QUE 97002
7.06
278
10.3
53.3
3.34
10.4
1.34
6.81
2.31
0.713
2.96
0.567
3.81
0.821
2.43
0.381
2.45
0.365
2.2
356
184
382
194
1.16
0.846
38.5
96
,28
Polymict
eucrite
,40
2.14
355
11.4
18.5
1.58
4.27
0.666
3.42
1.15
0.401
1.48
0.276
1.86
0.401
1.17
0.178
1.15
0.169
0.657
106
59.4
138
75.2
0.984
0.954
52.9
69
QUE 97001
3.82
169
22.5
31.8
1.52
5.56
0.667
3.49
1.26
0.544
1.69
0.331
2.23
0.494
1.48
0.234
1.53
0.232
1.34
199
60.8
356
109
1.30a
1.16
47.6
84
,39
4.32
262
19.4
32.7
2.32
6.92
0.971
5
1.68
0.555
2.18
0.412
2.73
0.599
1.76
0.267
1.71
0.257
1.37
219
67.9
316
108
1.09
0.900
46.0
87
LEW 85313 LEW 86001
,39
,21
Polymict
Howardite Howardite Howardite
eucrite
GRO 95535 GRO 95574 GRO 95581 GRO 95602 LAP 04838
,13
,14
,11
,7
,8
,9
Meteorite
Split
6.08
160
1.53
112
Howardite
QUE 99033
,14
3.67
157
14.6
29.5
2.35
7.05
1.01
5.21
1.76
0.567
2.25
0.431
2.85
0.615
1.81
0.277
1.77
0.264
1.28
190
61
273
118
1.08
0.884
43.2
94
3.1
251
2.85
66.3
Howardite
SAN 03472
,9
2.79
282
4.7
21.8
1.87
6.62
0.822
4.13
1.38
0.444
1.76
0.325
2.15
0.459
1.34
0.206
1.33
0.197
0.845
135
46.7
246
78.7
1.26a
0.884
56.5
67
7.21
193
2.52
70.4
Howardite
SCO 06040
,8
2.73
167
6.08
22.7
1.6
7.33
0.736
3.82
1.26
0.405
1.63
0.311
2.04
0.447
1.31
0.211
1.34
0.198
0.871
148
67.6
286
93.1
1.60a
0.877
56.7
62
MET
LEW 87004 MET 96500 96500
,25
,17
,19
Polymict
eucrite
Howardite
Howardite
Table 3. Continued. Means of x-ray fluorescence spectrometry and inductively coupled plasma mass spectrometry data for the targeted set
samples.
2116
D. W. Mittlefehldt et al.
Howardite
Howardite
52.2
226
230
210
59.3
3.13
90.3
3.73
4.19
142
18.2
221
6.41
1.37
311
61.5
12.9
36.1
2.62
285
9.35
21.5
2.23
5.87
0.894
4.46
1.44
0.453
1.84
0.336
2.22
0.477
1.39
0.211
1.35
0.201
0.837
Class
Al (mg g 1)
Si (mg g 1)
P (lg g 1)
K (lg g 1)
Ca (mg g 1)
Ti (mg g 1)
V (lg g 1)
Cr (mg g 1)
Mn (mg g 1)
Fe (mg g 1)
Co (lg g 1)
Ni (lg g 1)
Zn (lg g 1)
Ga (lg g 1)
Rb (ng g 1)
Sr (lg g 1)
Y (lg g 1)
Zr (lg g 1)
Nb (lg g 1)
Mo (ng g 1)
Cs (ng g 1)
Ba (lg g 1)
La (lg g 1)
Ce (lg g 1)
Pr (lg g 1)
Nd (lg g 1)
Sm (lg g 1)
Eu (lg g 1)
Gd (lg g 1)
Tb (lg g 1)
Dy (lg g 1)
Ho (lg g 1)
Er (lg g 1)
Tm (lg g 1)
Yb (lg g 1)
Lu (lg g 1)
Hf (lg g 1)
42.5
219
470
170
46
2.36
94.6
4.21
3.82
154
116
2140
5.68
1.67
428
45.5
9.64
32.1
1.95
582
11.9
15.4
1.62
4.02
0.63
3.2
1.05
0.337
1.37
0.249
1.64
0.356
1.04
0.156
1
0.149
0.723
PCA 02066
,8
MET 00423
,7
Meteorite
Split
22.5
177
700
280
24.6
1.46
84.8
4.16
2.79
181
332
6840
114
5.25
1000
23.9
4.79
18.6
1.03
803
82.5
8.29
0.775
1.98
0.301
1.54
0.509
0.174
0.641
0.122
0.823
0.176
0.531
0.081
0.535
0.081
0.338
Howardite
PRA 04401
,7
29.5
237
200
91
32.6
2.09
110
5.45
4
131
44
188
1.65
1.01
176
36
8.77
22.9
2.17
133
6.43
16
1.55
4.01
0.608
3.07
0.994
0.285
1.3
0.236
1.53
0.326
0.946
0.145
0.912
0.135
0.636
Howardite
QUE 94200
,29
30.9
236
190
91
34.5
2.12
104
5.4
3.9
126
15.3
58.8
1.7
0.749
211
36.9
9
30.8
1.94
210
7.7
17.1
1.64
4.1
0.622
3.15
1.01
0.289
1.25
0.232
1.52
0.324
0.949
0.146
0.917
0.136
0.646
Howardite
27.5
239
190
91
30
1.96
111
5.79
3.94
125
20
67.2
2.03
0.979
160
31.6
9.01
23.4
1.74
135
5.43
14.3
1.54
3.66
0.612
3.15
1.01
0.254
1.29
0.236
1.52
0.325
0.947
0.143
0.889
0.135
0.635
Howardite
65.5
222
320
370
72.6
4.09
75.8
2.49
4.27
147
20.1
246
4.88
1.77
396
79.8
16.8
52.5
4.15
292
12.3
34.4
2.33
6.51
1.11
5.65
1.94
0.6
2.51
0.47
3.16
0.665
2
0.296
1.91
0.277
1.25
62.8
219
360
230
70.9
3.78
74.2
2.54
4.28
149
34.8
513
8.7
1.85
306
73.8
19.2
39.1
3.33
190
15.4
27
2.96
6.29
1.32
6.78
2.24
0.578
2.91
0.518
3.4
0.751
2.12
0.315
1.96
0.29
1.13
,29
Polymict
eucrite
,28
Polymict
eucrite
,39
,40
QUE 97002
QUE 97001
29.2
239
140
91
33.2
2.06
107
5.56
3.98
127
13.9
31.9
2.96
0.767
160
34.4
7.31
24.4
2.03
125
4.93
15.3
1.02
3.88
0.433
2.18
0.76
0.263
0.976
0.186
1.26
0.271
0.805
0.131
0.831
0.126
0.665
Howardite
QUE 99033
,14
54.2
226
260
280
61.3
3.2
92.4
3.99
4.24
137
9.3
14.4
1.9
1.22
515
65.3
9.56
32.8
3.01
162
15
25.2
1.06
2.91
0.465
2.45
0.883
0.484
1.19
0.234
1.63
0.365
1.11
0.182
1.2
0.184
0.945
Howardite
SAN 03472
,9
50.6
225
280
190
57.4
3.23
87.4
3.69
4.13
147
41
740
8.43
1.56
365
61.2
12
22.2
2.9
431
12.2
21.1
1.97
5.16
0.792
3.99
1.3
0.436
1.69
0.312
2.07
0.439
1.3
0.194
1.26
0.182
0.654
Howardite
SCO 06040
,8
Table 3. Continued. Means of x-ray fluorescence spectrometry and inductively coupled plasma mass spectrometry data for the targeted set
samples.
HED polymict breccias
2117
131
38.2
266
68.3
0.982
0.864
52.9
76
99.5
48
184
53.4
0.940
0.872
56.6
58
Howardite
PCA 02066
,8
54.5
994
81.6
26.1
0.969
0.945
57.8
47b
Howardite
PRA 04401
,7
100
34
192
59
0.976
0.778
66.3
37
Howardite
QUE 94200
,29
75.4
43.4
199
54.4
0.959
0.798
66.7
40
Howardite
89.4
34.6
167
55.5
0.891
0.691
68.1
33
Howardite
200
110
266
123
0.956
0.844
40.6
97
175
59.4
245
119
0.752a
0.703
41.2
94
,29
Polymict
eucrite
,28
Polymict
eucrite
,39
,40
QUE 97002
QUE 97001
Ce* and Eu* are the the concentrations of these elements calculated by interpolation of rare earth element diagrams (see text).
a
Samples considered to have suffered REE mobilization while in Antarctica based on Ce/Ce* outside 2r uncertainty limts of 1.
b
POEM for PRA 04401 is calculated after correcting the bulk composition for an estimated 55% CM clast component.
Ta (ng g )
W (ng g 1)
Th (ng g 1)
U (ng g 1)
Ce/Ce*
Eu/Eu*
mg# (molar)
POEM (%)
Howardite
Class
1
MET 00423
,7
Meteorite
Split
102
41.4
189
58.3
1.38a
0.948
67.0
37
Howardite
QUE 99033
,14
160
67.8
289
90
0.979
1.47
52.7
79
Howardite
SAN 03472
,9
142
55.5
187
65.8
0.976
0.913
52.4
73
Howardite
SCO 06040
,8
Table 3. Continued. Means of x-ray fluorescence spectrometry and inductively coupled plasma mass spectrometry data for the targeted set
samples.
2118
D. W. Mittlefehldt et al.
HED polymict breccias
basaltic eucrite
100
cumulate eucrite
diogenite
Yamato Type B diogenite
80
Al (mg/g)
howardite
PRA 04401
60
polymict eucrite
polymict diogenite
40
PCA 2002
20
0
30
60
90
120
150
Mg (mg/g)
180
210
30
60
90
120
150
Mg (mg/g)
180
210
100
Ca (mg/g)
80
60
40
20
0
Fig. 4. Plots of Al-Mg and Ca-Mg for the targeted set
samples compared with basaltic and cumulate eucrites, and
diogenites, and analyses of individual samples of Pecora
Escarpment 2002 paired polymict breccias (see text). PRA
04401 is plotted as measured (low Al, Ca) and after correction
for approximately 55% CM clast content (see text). Howardite
and polymict eucrite data are from this study; literature data
are from Allen and Mason (1973), Cleverly et al. (1986), Duke
and Silver (1967), Fitzgerald (1980), Ghosh et al. (2000),
Jarosewich (1990), Jerome (1970), Kharitonova & Barsukova
(1982), Kolesov & Hernandez (1984), Lovering (1975), Marvin
and Mason (1980), Mason (1974), Mason and Jarosewich
(1971), Mason et al. (1979), McCarthy et al. (1972, 1973,
1974), von Michaelis et al. (1969), Mittlefehldt et al. (2012),
Shima (1974), Shukla et al. (1997), Simpson (1982), Symes and
Hutchison (1970), Takeda (1979), Takeda et al. (1978, 1979,
1984), Yanai et al. (1995).
2119
content. We have corrected the bulk composition for
CM material and plot the measured and corrected data
in Fig. 4. The corrected data have a POEM of 47.
Basaltic eucrites are the major lithologic repository
of incompatible trace lithophile elements in HED
polymict breccias. Figure 5 shows the refractory
elements Zr-Al, Nb-Al, and Ba-Al for our analyses of
HED polymict breccias compared to literature data for
diogenites, cumulate eucrites, and basaltic eucrites. The
refractory incompatible trace lithophile elements are
correlated with Al, as expected for physical mixtures of
basaltic eucrites with incompatible trace element- and
Al-poor diogenitic material. The polymict breccias have
element/Al ratios greater than the CI ratio, as do
basaltic eucrites for the most part. The tight linear
arrays bespeak either (1) a limited range in basaltic
eucrite components in the breccias; or (2) thorough
blending of the basaltic component on an
approximately cm-scale in the breccias. This will be
discussed in more detail later.
The HED suite is noted for having low moderately
volatile lithophile element contents (e.g., see Mittlefehldt
1987; Mittlefehldt et al. 1998a). Excluding PRA 04401,
our data yield median Na/Ba, Rb/Ba, and Cs/Ba CInormalized ratios of 0.0480, 0.0132, and 0.0044 (Fig. 6).
The data for alkali elements are not as well correlated
with Ba as the refractory incompatible trace lithophile
elements (cf. Mittlefehldt 1987). The R2 values for Na,
Rb, and Cs correlations with Ba are 0.79, 0.56, and
0.22, respectively, compared to values between 0.94 and
0.98 for correlations of Zr, Nb, Hf, and Ta with Ba. A
stronger correlation exists between Cs and Rb
(R2 = 0.70) than between either of these and a
refractory incompatible trace lithophile element (Fig. 6).
The Ni contents of the polymict breccias studied
here are plotted versus their POEM in Fig. 7. A high
siderophile element content was one of the indicators
used to identify potential regolithic howardites by
Warren et al. (2009), and they suggested that
≥300 lg g 1 Ni might indicate regolithic character.
Several of the howardites studied here exceed that limit,
as do polymict diogenite ALH 85015 (Mittlefehldt et al.
2012), and paired howardites PCA 02013 and PCA
02015 (Beck et al. 2012).
DISCUSSION
these span the range POEM 58 down to POEM 9 (this
study; Warren et al. 2009; Beck et al. 2012; Mittlefehldt
et al. 2012). The PCA 2002 polymict breccias will be
discussed in more detail later. Howardite PRA 04401 is
very rich in CM chondrite clasts, with one thin section
containing an estimated 60 vol% of such clasts (Herrin
et al. 2011). We estimate that the bulk sample contains
approximately 55 wt% CM material based on its Ni
Our primary focus is identifying and characterizing
howardites composed of material from the true regolith,
contrasting these with fragmental howardites, and
understanding how regolith processes on Vesta differ
from those on the Moon. We will start the discussion
by evaluating those meteorites with noble gas evidence
for exposure to the solar wind.
2120
D. W. Mittlefehldt et al.
howardite
100
PRA04401
SB
polymict eucrite
80
LEW
basaltic eucrite
Zr (µg/g)
cumulate eucrite
NL
diogenite
60
LAP
polymict diogenite
40
J
6
Q
SC
G
CI
20
0
0
20
40
Al (mg/g)
60
80
8
SB
LEW
Nb (µg/g)
6
NL
J
LAP
4
6
Q
G
2
SC
CI
0
0
20
40
Al (mg/g)
60
80
60
SB
LEW
NL
40
Ba (µg/g)
LAP
20
Q
6
G
J
SC
CI
0
0
20
40
Al (mg/g)
60
80
Fig. 5. Plots of Zr-Al, Nb-Al, and Ba-Al for the targeted set
samples compared with basaltic and cumulate eucrites, and
diogenites. Tie line connects measured PRA 04401 (low Al)
with values corrected for approximately 55% included CM
clasts (see text). Labeled meteorites are LAP 04838 and LEW
86001. Ellipse Q encloses QUE 94200, QUE 97001, and QUE
99033, and ellipse G encloses GRO 95535, GRO 95574, and
GRO 95581; GRO 95602 indicated by 6. SB, NL, J, and SC
indicate Stannern and Bouvante, Nuevo Laredo and
Lakangaon, Juvinas, and Sioux County. The dashed line is a
regression through the polymict breccias, excluding meteorites
discussed in the text. CI chondrite ratios are shown for
comparison. Howardite and polymict eucrite data are from
this study; literature data are from Barrat et al. (2000, 2003,
2007), Cleverly et al. (1986), Mittlefehldt et al. (2012), and
Palme et al. (1978).
Five of the samples of the targeted set are
confirmed to contain solar wind gases, EET 87513,
GRO 95535, GRO 95602, LEW 85313, and MET 00423
(Cartwright et al. 2012a, 2012b, 2013; summarized in
Table 1). LEW 85313 and MET 00423 are not
considered to be paired with any of the other polymict
breccias studied here, while GRO 95535 and GRO
95602 are thought to be paired with GRO 95534 (not
studied here), GRO 95574, and GRO 95581. EET 87513
is not thought to be paired with any other meteorite,
but we suggest that it is paired with EET 87503 (see
below, and Appendix S1). Most of these meteorites
have some petrographic characteristics associated with
true regolith. Glass clasts are abundant in EET 87503,
present, but not abundant, in EET 87513, GRO 95535,
and GRO 95574, but they are absent in GRO 95581,
GRO 95602, and LEW 85313. Dark-matrix and meltmatrix breccia clasts are present in all of these
meteorites except for LEW 85313 (Table 2). Based on
petrologic criteria, we considered GRO 95574 to have
high regolithic character and the others to have
moderate regolithic character. MET 00423 contains few
petrologic indicators of regolith maturity and we gave it
a low regolith index (Table 2). In addition to the
samples with clear solar wind noble gas components,
PCA 02066 shows a slight elevation in 20Ne/22Ne in the
highest temperature fraction, but this is of uncertain
origin (Cartwright et al. 2013). The thin section of this
sample is dominated by melt-matrix breccia clasts
(Fig. 8a), and we judged it to have high regolithic
character based on petrologic criteria (Table 2).
We considered the paired howardites EET 99400
and EET 99408 to have moderate-to-high regolithic
character based on an abundance of melt-matrix
breccia, dark-matrix breccia, and glass clasts. However,
Ne in these samples is dominated by cosmogenic gases
and there is no indication of implanted solar wind Ne
(Cartwright et al. 2012a, 2013). Some of the melt-matrix
breccias in the EET 99400 and EET 99408 are
petrologically distinct from those in PCA 02066 (Fig. 8)
in that the former are simple impact melts of basaltic
eucrite material, not melt-matrix breccias formed from
polymict debris.
Regolithic Howardites: Identification and
Characterization
Warren et al. (2009) made the important distinction
between regolithic and fragmental howardites.
Cartwright et al. (2013) suggested further dividing
regolithic howardites into two subtypes, one in which
the noble gases are dominated by implanted solar wind
and the other in which the noble gases are dominated
by a mixture of planetary-type gases and fractionated
HED polymict breccias
5
0.0480*CI
NL
J
SC
3
LEW
800
howardite
PRA 04401
polymict eucrite
basaltic eucrite
cumulate eucrite
diogenite
polymict diogenite
6
Q
1
1000
LAP
G
2
SB
Rb (ng/g)
4
Na (mg/g)
2121
LAP
600
0.0132*CI
400
NL
SB
6
G
Q
200
SC
0
J
0
0
20
40
60
0
20
40
Ba (µg/g)
80
80
60
60
40
SC
20
6
G
60
Ba (µg/g)
Cs (ng/g)
Cs (ng/g)
LEW
LAP
0.0044*CI
NL
40
J
SB
SC
NL
LAP
Q
LEW
LEW
J
0.336*CI
SB
20
0
0
0
20
40
60
Ba (µg/g)
0
200
400
600
Rb (ng/g)
800
1000
Fig. 6. Plots of Na-Ba, Rb-Ba, Cs-Ba, and Cs-Rb for the targeted set of samples compared with basaltic and cumulate eucrites,
and diogenites. Tie line connects measured PRA 04401 (high alkali) with values corrected for approximately 55% included CM
clasts (see text). CI chondrite ratios multiplied by median alkali element/Ba and Cs/Rb ratios are shown for comparison. Labels
as in Fig. 5. Howardite and polymict eucrite data are from this study; literature data are from sources listed in Fig. 5 plus Tera
et al. (1970).
solar wind associated with carbonaceous chondrite
clastic debris, with some contribution from implanted
solar wind in the host HED material. Although most
regolithic howardites show dominance to one subtype
compared to the other, some regolithic howardites have
characteristics of both subtypes, as demonstrated by
EET 87513, which contains some solar wind–dominant
features and some planetary-type noble gases gas
features (Cartwright et al. 2013; see also Table 1). The
main focus of the following discussion is on solar wind–
dominated howardites, which we consider to have
formed from true regolith. We will consider the second
subtype at the end of this section.
Warren et al. (2009) noted that the howardites they
considered to be regolithic tended to have Al contents
indicating a eucrite:diogenite mixing ratio of roughly
2:1, and Ni contents of ≥300 lg g 1 due to admixture
of impactor debris. High Ni (and other siderophile
element) contents are not likely to be from vestan
lithologies as Ni-rich HEDs are rare. The unbrecciated
cumulate eucrite EET 92023 contains an average of
1160 lg g 1 Ni (Mittlefehldt and Lindstrom 2003;
Warren et al. 2009), approximately eight times higher
than in any other HED igneous lithology, but is an
anomaly in the HED suite. Eight of our howardites
have POEM of 59–74 (Al and Ca contents within
10% of POEM 67), and of these, three also have Ni
contents ≥300 lg g 1—LEW 85313, MET 96500, and
Scott Glaciers (SCO) 06040 (Fig. 7). These potentially
represent ancient, well-mixed vestan regolith a la
Warren et al. (2009). Of these, only LEW 85313
contains noble gases dominated by an implanted solar
wind component (Cartwright et al. 2012a, 2012b, 2013)
and thus meets our criterion for having been assembled
from true regolith. SCO 06040 contains noble gases
dominated by planetary-type gases (Cartwright et al.
2122
D. W. Mittlefehldt et al.
poly
dio
10000
poly
euc
howardites
P
e:d 2:1
±10%
Ni (µg/g)
1000
Q
100
E3
6
G
E9
10
E0
SW howardite
GCR howardite
polymict eucrite
1
P howardite
nd howardite
polymict diogenite
0.1
0
20
40
60
80
100
POEM
Fig. 7. Plot of Ni versus percentage of eucritic material for
the targeted set samples, plus two polymict diogenites taken
from Mittlefehldt et al. (2012). Howardite symbols summarize
noble gas results from Cartwright et al. (2012a, 2012b, 2013):
SW = solar wind–dominated, P = planetary gas–dominated,
GCR = galactic cosmic ray–dominated, nd = not determined.
Asterisks indicate meteorites with carbonaceous chondrite
clasts reported. Tie lines join duplicate samples of a meteorite
except for PRA 04401 (P), which joins measured value (high
Ni) with that corrected for 55% CM clast content (see text).
Solid-line fields enclose members of the initially proposed EET
87503 (E3), EET 99400 (E0), and GRO 95534 (G) pairing
groups. The latter is suggested to include GRO 95602 (6), but
it cannot be part of the group (see text). Dotted-line fields
enclose members of our suggested revised EET 87503 (E3)
pairing group and the EET 87509 (E9) pairing group. The
solid and dashed lines show the 2:1 eucrite:diogenite mixing
ratio with 10% limits. Horizontal line is suggested to
separate the Ni contents of regolithic (above) from fragmental
howardites (Warren et al. 2009).
2013) and is rich in carbonaceous chondritic clasts
(Herrin et al. 2011). The high Ni content of this
howardite, 740 lg g 1, thus reflects incorporation of
approximately 6% CM chondritic debris. The Ne in
MET 96500 is dominated by galactic cosmic ray–
produced Ne (Cartwright et al. 2013). Chondritic clasts
have not been identified in this howardite, but its high
Ni content (this study; Warren et al. 2009) suggests that
either such clasts are present but not included in our
thin section, or chondritic debris is finely dispersed in
the matrix. Metal nuggets are a potential cause of high
Ni content (cf. Beck et al. 2012), but none was present
in our samples of MET 96500.
Four other howardites studied by our collaboration
have Ne dominated by solar wind–implanted gases:
EET 87513, GRO 95535, GRO 95602, and MET 00423
(Cartwright et al. 2012a, 2012b, 2013). GRO 95535 and
GRO 95602 are suggested to be members of the GRO
95534 pairing group (Table 1). We have bulk rock
compositions, but not noble gas analyses for two
additional members, GRO 95574 and GRO 95581.
These four meteorites are similar in bulk major and
trace element composition, which supports pairing,
although GRO 95602 is moderately distinct from the
other three (Figs. 3–6). More significantly, the contents
of cosmogenic noble gases in GRO 95535 and GRO
95602 are very different, demonstrating that they are
not paired (Cartwright et al. 2012b). The GRO
howardites straddle the POEM 59-74 region, with GRO
95602 having a POEM very near the eucrite:diogenite
mixing ratio of 2:1 (Fig. 7). The Ni contents of the
GRO howardites varies from 117 to 258 lg g 1, with
GRO 95602 having the highest content (Fig. 7), which
is below the limit suggested as indicative of regolithic
howardites. However, the noble gas data indicate that
the GRO howardites are regolithic, having been
assembled from true regolith.
Our two samples of EET 87513 from the targeted
set have an average POEM of 69 and Ni of 252 lg g 1.
Matrix samples from our general set range in Ni from
110 to 1150 lg g 1. Splits of the same matrix samples
studied by Buchanan and Mittlefehldt (2003) range in
Ni from 145 to 403 lg g 1. The average Ni content
weighted by mass for EET 87513 is 345 lg/g. The wide
range in Ni determinations indicates a heterogeneous
distribution for the CM chondrite clasts that occur in
this meteorite (Buchanan et al. 1993; Buchanan and
Mittlefehldt 2003). The range in POEM for the general
set samples and those of Buchanan and Mittlefehldt
(2003) is 58–75. The noble gas contents and isotopic
compositions indicate that EET 87513 is a breccia
formed from true regolith (Cartwright et al. 2012a,
2012b, 2013). The eucrite:diogenite mixing ratio and Ni
content for this meteorite is consistent with the
hypothesized ancient, well-mixed vestan regolith
(Warren et al. 2009).
MET 00423 has a POEM of 76 and a Ni content of
221 lg g 1 (Table 3), similar to the results of Warren
et al. (2009)—POEM 77, Ni 228 lg g 1. MET 00423
contains chondritic clasts (Table 2), but the noble gas
signature is dominated by solar wind gases, not
planetary-type gases (Cartwright et al. 2013). Thus, the
noble gas data indicate that MET 00423 represents true
regolith, but compositionally, it falls just outside the
range of the posited ancient, well-mixed regolith
(Warren et al. 2009). We consider MET 00423 to be a
breccia formed from true regolith.
Three meteorites have Ni contents above the
300 lg g 1 threshold, but have POEM outside our
admittedly arbitrary 10% limits on the 2:1 mixing
ratio: PCA 02066, PRA 04401, and one of two samples
of QUE 97002. PCA 02066, with a POEM of 58, is only
marginally outside the 10% POEM limit. This sample
HED polymict breccias
c
a
b
2123
di
d
hd
di
hd
host
melt-matrix clast
ophitic clast
host
melt-matrix clast
en
fs
en
fs
Fig. 8. Backscattered electron image of a melt-matrix breccia clast in PCA 02066 (a), and pyroxene quadrilateral for the host
breccia and melt-matrix clast (b). Backscattered electron image of a melt-matrix breccia clast in EET 99400 (c), and pyroxene
quadrilateral for the host breccia, melt-matrix clast, and a basalt clast (d). Scale bars are 1 mm.
is dominated by melt-matrix clasts of polymict
parentage (Fig. 8) and petrologically could be a regolith
breccia. The Ne isotopic data are dominated by galactic
cosmic ray–produced Ne, although there is a small 20Ne
excess in the highest temperature fraction (Cartwright
et al. 2013). As most of the thin section contained meltmatrix clasts and the bulk rock is Ni-rich, the minor
20
Ne excess in the highest temperature release step could
be a memory of largely digested chondritic clasts that
were almost entirely degassed during impact melting.
Olivine is present in melt-matrix clasts in PCA 02066
and this meteorite has a much higher normative olivine
content (approximately 12 wt%) than any other sample
studied here (<5 wt%), excluding PRA 04401 (Table
S4). This suggests that chondritic clasts may have been
a significant component in the precursors to the meltmatrix clasts. However, based on the presence of
magnesian olivine and metal nuggets, Beck et al. (2012)
suggested that the xenolithic component in polymict
breccias paired with PCA 02066 was from a pallasitic,
not a chondritic, source. Our sample of PCA 02066
contained one small (approximately 1 mg) metal nugget
(Table S5). Regardless, we suggest that the melt-matrix
clasts in PCA 02066 may have been assembled from
true regolith. Any solar wind gases in precursor grains
would have been effectively degassed during melting
because such gases are implanted only in grain rims,
which would have been melted. The non–melt-matrix
fraction of PCA 02066 is likely fragmental howardite
material because of the lack of solar wind gases in the
bulk sample (Cartwright et al. 2013). (See additional
discussion of PCA 2002 polymict breccias, below.)
The noble gases of PRA 04401 are dominated by
planetary-type gases and our sample contains
approximately 55% CM clasts as estimated from the
bulk rock Ni content. The chondritic clasts are
heterogeneously distributed as evidenced by differences
in modal abundance in thin sections. A maximum is
estimated at 60% for section 10, while paired howardite
PRA 04402 only contains an estimated 3–5% CM clasts
in sections 6 and 7 (Herrin et al. 2011). We find only
moderate petrologic evidence for material from the true
regolith in PRA 04401 in the form of melt-matrix
breccia clasts (Table 2). If present, it is obscured by the
large content of chondritic debris.
QUE 97002 likewise is not regolithic, and is clearly
misclassified (see Appendix S1). All of our samples have
POEM of 90–99 (Fig. 7; Tables 3 and S1) and are
therefore polymict eucrites (Table 1). All samples have
high Ni contents, 246–834 lg g 1 (Tables 3 and S1),
and chondritic clasts are present (Table 2). Noble gas
analysis of a targeted set sample shows only galactic
2124
D. W. Mittlefehldt et al.
cosmic ray–produced Ne (Cartwright et al. 2013). QUE
97002 is a fragmental polymict eucrite uncommonly rich
in carbonaceous chondrite clasts.
Several of our meteorites or their pairs contain
carbonaceous chondrite clasts (Table 2). Of these, PRA
04401 and SCO 06040 are considered to be a subtype of
regolithic howardites by Cartwright et al. (2013)
because their noble gas contents are dominated by a
mixture of planetary-type/fractionated solar wind gases
from CM material, and solar wind/fractionated solar
wind from the vestan regolith. By assessing the
petrology alone, it is not clear that these samples have
been subjected to long exposure as part of the true
regolith. Individual low-velocity accretion events have
the potential to locally add a substantial amount of
impactor material to the ejecta (Yue et al. 2013). Thus,
the very high modal abundance of clasts in PRA 04401
suggests that this meteorite is an exceptionally xenolithrich howardite, and may have been formed by a single
low-velocity accretion event. One further key to
ascertaining whether a howardite rich in carbonaceous
chondrite clasts is regolithic is to establish whether the
chondritic clasts are of one or multiple types. Bholghati,
Jodzie, Kapoeta, and Y-793497 contain CM and CR
clasts (Bunch et al. 1979; Buchanan et al. 1993;
Zolensky
et al.
1996;
Gounelle
et al.
2003)
demonstrating that they contain debris from multiple
impactors. This favors an origin in more extensively
gardened regolith and the first three are indeed
regolithic (Warren et al. 2009).
Mafic Component of the Vestan Crust
Diogenites are poor in incompatible lithophile
elements and thus act as a dilutant in the polymict
breccias for most such elements. Because they are
coarse-grained cumulates, variations in V and Cr that
are primarily hosted in chromite reflect sample
heterogeneity, not diversity of the parent lithologies
mixed into the polymict breccias. The tight linear
relationships between Al-Mg and Ca-Mg (Fig. 4) show
that there is little variation in the olivine/orthopyroxene
ratio of the ultramafic component.
On the other hand, the lithophile element
characteristics of the polymict breccias do afford us the
opportunity to constrain the type of mafic component
mixed with the ultramafic component. Studies of HEDs
show that vestan mafic rocks include cumulate eucrites,
main-group eucrites, Stannern-trend eucrites, and
Nuevo Laredo–trend eucrites (e.g., Stolper 1977;
Mittlefehldt et al. 1998a; McSween et al. 2011). The
main-group and Nuevo Laredo–trend eucrites are meltcomposition basalts with a continuum of compositions
formed by fractional crystallization; main-group eucrites
represent the most primitive melts of the sequence
(Stolper
1977).
Stannern-trend
eucrites
are
compositionally distinct melts (Barrat et al. 2007;
McSween et al. 2011). Other igneous lithologies are
present as clasts in polymict breccias (see, for example,
Barrat et al. 2009, 2012), but they are not represented
as individual meteorites. The evidence suggests that they
are minor components of the vestan crust.
Some cumulate eucrites have high Al contents
caused by a higher plagioclase/pyroxene ratio in the
crystallizing assemblage than in their basaltic parent
melts. Our polymict breccia data have very strongly
anticorrelated Al-Mg contents that show no evidence
for a significant component of Al-rich cumulates in the
mix (Fig. 4). However, not all cumulate eucrites are
Al-rich. Cumulate eucrites have low contents of
incompatible trace lithophile elements (Mittlefehldt
et al. 1998a), although some contain a significant
trapped-melt component that obscures this distinction
(Treiman 1997; Mittlefehldt and Lindstrom 2003). None
of the polymict breccias studied here is distinctly low in
Rb, Zr, Nb, Cs, and Ba, as would be expected if the
mafic components were dominated by cumulate eucrites
(Figs. 5 and 6). Two howardites, LEW 85313 and SCO
06040, have somewhat lower Zr, but not Nb or Ba,
contents for their Al, compared with the other polymict
breccias (Fig. 5). These two rocks also have somewhat
lower Hf contents, but not Ta contents. This suggests
slight undersampling of baddeleyite and/or zircon rather
than their having a higher cumulate eucrite component.
Although cumulate eucrites are not a major mafic
component of the breccias, pyroxene compositions and
textures show that such material is present (Fig. 9).
Trace incompatible lithophile element contents of
polymict breccias demonstrate that main-group eucrites
dominate as the basaltic component. With the exception
of LEW 86001, mixing diagrams of Zr, Nb, Ba, with Al
show no evidence for a significant contribution from
Stannern-trend eucrites (Fig. 5). LEW 86001 (POEM
92) has Zr, Nb, Ba, Hf, and Ta contents higher than
the most trace element–rich evolved basalts of the
Nuevo Laredo–trend (Lakangaon, Nuevo Laredo;
Warren and Jerde 1987), but similar to Bouvante and
Stannern (Barrat et al. 2007). LEW 86001 is a polymict
eucrite formed mostly of Stannern-trend basalts with a
minor diogenitic component.
Howardite LaPaz Ice Field (LAP) 04838 (POEM
84) has higher trace refractory incompatible lithophile
element concentrations than other polymict breccias,
excluding LEW 86001 (Fig. 5), and has high alkali
element contents (Fig. 6). This rock either contains a
slight Stannern-trend basaltic component, or has a
significant contribution from evolved basalts such as
Lakangaon and Nuevo Laredo. Patzer and McSween
HED polymict breccias
a
b
Fig. 9. a) Pyroxene quadrilateral diagram for howardites EET
83376, EET 87509, and LAP 04838 showing the presence of
pyroxenes with compositions like those of cumulate eucrites
Binda (B), Moama (M), Moore County (MC), and Serra de
Mage (SM). LAP 04838 contains many grains more ferroan
than those in main-group eucrite Sioux County (SC) or a
Nuevo Laredo-trend eucrite basalt clast from Y-793164 (Y).
Eucrite data are from Harlow et al. (1979), Lovering (1975),
Mittlefehldt (1990), Mittlefehldt and Lindstrom (1993),
Mittlefehldt et al. (1998b), and Pun and Papike (1995). b)
Backscattered electron image showing pyroxene grain in EET
83376 (labeled 6 in a) with a blebby augite exsolution texture
like those of some cumulate eucrites. Scale bar is 200 lm.
(2012) documented three phase (ferroan augite-fayalitesilica) symplectite assemblages in LAP 04838 and noted
that they were more abundant in this howardite than
the others they had studied. These authors interpreted
the ferroan symplectites to be breakdown products of
iron-rich metastable pyroxene or pyroxferroite.
Pyroxene compositions that we have determined for
LAP 04838 show a population of ferroan augites that
are more Fe-rich than pyroxenes in Nuevo Laredo–
trend basalts (Fig. 9). We conclude that the mafic
component of LAP 04838 is a mixture of basalts from a
main
group—Nuevo
Laredo–trend
fractionation
sequence and based on pyroxene compositions and the
abundance of ferroan symplectites (Patzer and
McSween 2012), includes primitive and highly evolved
members of the fractionation sequence. Highly evolved
mafic clasts are also found in the howardites Northwest
Africa (NWA) 1664 and NWA 1769 (Barrat et al.
2125
2012). The howardites QUE 94200, QUE 97001, and
QUE 99033 may also contain a significant component
of fractionated basalts, but because of their lower mafic
component (POEM approximately 37), their trace
incompatible lithophile element signature is not as clear
(Fig. 5). Patzer and McSween (2012) studied QUE
94200, but did not find any ferroan symplectite clasts
in it.
All other howardites and polymict eucrites studied
here are dominated by a mafic component like that of
main-group eucrites such as Juvinas and Sioux County.
Shown in Fig. 5 are lines regressed only through the
howardite and polymict eucrite data from this study,
and two polymict diogenites from Mittlefehldt et al.
(2012). We have excluded from the regressions: LEW
86001 and LAP 04838 for the reasons discussed above,
PRA 04401 because of its high CM chondrite
component, and LEW 85313 and SCO 06040 from the
Zr versus Al regression only for the reason given above.
The regressions pass through the diogenite field, and
pass through (or nearly through) the Juvinas data
(Fig. 5). The same is observed for plots of Hf-Al and
Ta-Al (not shown). The regressions are more distant
from the Sioux County data in Nb-Al and Ba-Al.
However, the analysis shown has an unusually lower Al
content compared with other Sioux County analyses or
for basaltic eucrites in general. Sioux county is very
coarse grained (Duke and Silver 1967) and contains a
small amount of other lithologic components, which
indicate some polymict character (Yamaguchi et al.
1997; Mittlefehldt et al. 1998b). The position of Sioux
County on Fig. 4 is probably related to the aliquot
being nonrepresentative of the bulk sample, and/or
possibly by the presence of extraneous materials. The
positions of the Juvinas data near the regression lines
make a compelling case: the mafic component of the
howardites and polymict eucrites studied here is
dominantly main-group eucrites, with much lesser
contributions from Stannern-trend basalts, evolved
basalts (like Nuevo Laredo and Lakangaon), or
cumulate eucrites.
The paucity of evolved basalts in the polymict
breccias immediately suggests that the complementary
fractionated solids—cumulate eucrites—might also be a
minor component, as we observe. Thus, it is not
necessary to invoke poor sampling of deeper plutons by
the impacts that add material to the regolith, although
this could also have contributed to the general low
abundance of cumulate eucrites in HED polymict
breccias. However, the fact that many howardites
contain >30% diogenite component indicates that poor
sampling of deep cumulate gabbros is not the likely
explanation of their low abundance in the vestan
regolith. Petrologic models uniformly place cumulate
D. W. Mittlefehldt et al.
eucrites at higher levels in the crust than diogenites
(e.g., see Shearer et al. 2010). The dearth of Stannerntrend basaltic debris in the polymict breccias suggests
that they may also represent a minor component in the
vestan crust. This is what their low abundance among
basaltic eucrites (e.g., McSween et al. 2011) would
suggest. Models for the formation of Stannern-trend
basalts via an assimilation/fractional crystallization
interaction of main-group eucrite-like magmas with
basaltic crust (Barrat et al. 2007) imply that Stannerntrend basalts should be a minor component of the
vestan crust. The polymict breccia data are consistent
with this model for formation of Stannern-trend basalts,
but cannot be used to verify it. We suggest that the
majority of the vestan crust is composed of basalts
similar in composition to main-group eucrites.
Cumulate gabbros, complementary evolved basalts, and
Stannern-trend basalts make up smaller proportions of
the crust.
Scale of Mixing in HED Polymict Breccias
The varied compositions of HED polymict breccias
allow us to investigate the small-scale mixing efficiency
on Vesta. We will first consider the compositional
variations determined for multiple samples of individual
meteorites. We will then use this information to
compare the compositions of allegedly paired meteorites
to help evaluate pairing suggestions. PCA polymict
breccias are paired based on petrologic and cosmogenic
nuclide data and are postulated to be fragments of a
meter-sized bolide (Beck et al. 2012). We will compare
the compositional variation in this suite with other
allegedly paired samples. Fragmental polymict breccias
will be less thoroughly blended than those formed from
material that had been churned in the true regolith.
Comparison of data from multiple samples of regolithic
vs. fragmental howardites will also inform us of the
relative efficiency of mixing on Vesta.
From the targeted set, we have duplicate samples of
EET 87513, LAP 04838, MET 96500, QUE 97001, and
QUE 97002 (Table 3). From the general set, we have
multiple samples (n) of EET 87509 (4), EET 87531 (4),
EET 87503 (2), EET 87513 (6), QUE 97001 (2), and
QUE 97002 (3) (Table S1). For EET 87503, EET 87513,
MET 96500, and QUE 97001, additional data are
available in Buchanan and Mittlefehldt (2003),
Jarosewich (1990), and Warren et al. (2009). The bulk
analyses reported in Buchanan and Mittlefehldt (2003)
are on splits of EET 87513 samples analyzed here
(Table S1). The duplicate analyses for these were
averaged and weighted by mass analyzed. For the
general set samples, our INAA procedure did not allow
determination of Mg or Al. Chromium has higher
8
d
polymict
breccias
POEM10
6
Cr (mg/m)
2126
0
EET87503
EET87509
EET87513
EET87531
LAP 04838
MET 96500
QUE 97001
QUE 97002
4
2
2
6
e
8, 18
POEM90
0
0
20
40
Ca (mg/g)
60
80
Fig. 10. Cr versus Ca for multiple samples. Large symbols are
for samples ≥5 g in mass from this study, plus an
approximately 30 g sample of EET 87503 (Jarosewich 1990).
Field encompasses >90 of the howardite, eucrite, and diogenite
polymict breccia analyses available in the literature. Dotted
lines mark the Ca limits for percentage of eucritic material 10
and 90, based on the diogenite (d) and basaltic eucrite (e)
endmembers shown (asterisks). Small circles showed targeted
set samples of EET 83376 (6), EET 87518 (18), EET 87532
(2), EET 99400 (0), and EET 99408 (8).
concentrations in diogenites compared with basaltic
eucrites, and we use Cr vs. Ca to evaluate
heterogeneous mixing in duplicate samples.
Figure 10 shows all available data on the multiple
samples compared to a field encompassing most of the
data (90%) for other polymict breccias. The average
diogenite and basaltic eucrite endmember compositions
are also shown. (The minor phase chromite is
heterogeneously distributed in diogenites, and thus
potential diogenite endmembers are not as uniform in
Cr as they are in Mg. The diogenitic component of a
polymict breccia may also have under- or oversampled
coarse-grained chromite, adding to scatter.) EET 87509,
EET 87531, and QUE 97002 show tight clusters on this
diagram, while EET 87503, EET 87513, MET 96500,
and QUE 97001 do not. One individual sample of each
of EET 87503 and MET 96500 is much richer in
basaltic material compared with the others. For EET
87503, the discrepant sample is from a chip that was
0.94 g in mass (Table S1), whereas the mass of the
discrepant MET 96500 sample was 0.54 g (Warren et al.
2009). This suggests that howardite sample masses of
<1 g can yield material that is significantly biased by
inclusion of nonrepresentative proportions of coarse
clasts.
Howardites vary widely in hand sample texture,
with some showing abundant coarse clasts while others
show relatively few. Figure 2 compares hand samples of
two of the howardites—EET 87513 and QUE 97001—
HED polymict breccias
which show moderate dispersion in bulk compositional
analyses. EET 87513 is fairly uniform in texture, with a
fine- to medium-grained matrix supporting relatively
few clasts >1 mm in size. In contrast, QUE 97001 is
heterogeneous in texture and contains abundant clasts
up to roughly cm size set in a fine- to medium-grained
matrix. Analyses of EET 87513 and QUE 97001 show
modest variations, with relative standard deviations in
Ca of 12% versus 16% and in Cr of 12% versus 16%,
respectively, indicating that EET 87513 is more
homogeneous as the texture suggests. In fact, the
difference is even more impressive when sample mass is
considered. All of the QUE 97001 samples are >0.49 g
in mass, and excluding the targeted set samples, all of
the EET 87513 samples are <0.36 g in mass.
Considering only the duplicate analyses done here by
XRF, all major and minor elements in EET 87513 agree
to within ≤3.3%, while the differences in QUE 97001
are up to approximately 11% for Al and Ca (see
Appendix S1). EET 87513 displays a mixture of both
solar wind and planetary noble gas components
indicating exposure in the true regolith (Cartwright
et al. 2012a, 2012b). The more homogeneous texture of
this howardite is also suggestive of a longer residence in
the true regolith. We do not have noble gas data on
QUE 97001, but we argue below that it is likely paired
with QUE 94200, which contains only cosmogenic Ne
(Cartwright et al. 2013).
The cautionary tale of Fig. 10 is that individual
samples of even roughly gram-sized pieces of HED
polymict breccias can be grossly nonrepresentative.
Nevertheless, averaging multiple sample analyses, and/
or analyzing ≥5 g samples yields bulk compositions that
we suggest are suitably representative to infer eucrite:
diogenite mixing ratios and to test for pairing in most
cases. However, consideration of Fig. 2 indicates that
gross textural heterogeneity will have to be factored into
decisions regarding sampling and the reliability of the
resulting data as representing the true composition of
the breccia.
Five of the six GRO howardites were suggested to
be paired based on petrologic observations during initial
classification (Table 1). (The sixth, GRO 95633, was
originally classified as a brecciated eucrite, but
Mittlefehldt and Lindstrom [2003] showed that its
composition
is
howarditic
and
recommended
reclassification.) The four GRO howardites studied here
have a narrow range of POEM (55–65, Table 3).
However, GRO 95602 is considerably outside the range
of the other three on compositional plots (Figs. 5–7).
Nevertheless, we would not argue on this basis alone
that it should be separated from the pairing group.
However, noble gas data demonstrate that GRO 95602
had a different cosmic ray irradiation history than GRO
2127
95535 and thus cannot be paired with it (Cartwright
et al. 2012a, 2012b). The very close compositional
similarity of GRO 95535, GRO 95574, and GRO 95581
argues for pairing of these. Whether they or GRO
95602 is paired with GRO 95534 remains unknown.
The composition of GRO 95633 (Mittlefehldt and
Lindstrom 2003; Okamoto et al. 2004) shows that it has
a moderately higher eucritic component than any of the
four analyzed here and may not be paired with any of
them.
Mindful of these cautions, there are several
howardites and polymict eucrites from individual
icefields that are close in composition and likely paired.
Earlier, we mentioned that QUE 94200, QUE 97001,
and QUE 99033 are likely paired. These have narrow
ranges in trace refractory incompatible lithophile
element contents (Fig. 5), alkali element contents
(Fig. 6), POEM, and Ni contents (Fig. 7). These
howardites are rich in microphenocryst-bearing glass
spheres and fragments (Figs. 2b and 3d). We think it
likely that they are paired. Only one of them was
analyzed for noble gases in our collaboration, so we
cannot further test our conclusion.
Thirty-five HED polymict breccias have been
recovered from the Elephant Moraine icefields. We have
bulk compositions for nine of them and petrographic
data for two others. In Appendix S1, we discuss
pairings among our samples. Our suggested pairings for
these meteorites are given in Table 1. In Fig. 10, the
targeted set samples for each of our suggested pairing
groups are enclosed. The field for EET 87503 pairing
group includes the wet chemistry analysis by Jarosewich
(1990) of an approximately 30 g sample. On a ≥5 g
sampling scale, EET 87503 and EET 87513 are very
similar in composition (e.g., POEM 69-72), which is
consistent with them being well-blended regolithic
howardites. However, this observation is weakened
when noting that while four of the meteorites of the
EET 87509 pairing group of fragmental howardites are
close in composition at large sample sizes (e.g., POEM
80-87), when considering all members of the pairing
group, significant heterogeneity is present (POEM 7187). The recovered masses of the meteorites in our EET
87509 pairing group are from 79 to 584 g. If our
pairing suggestions are correct and if our samples are
representative, this implies heterogeneity on the severalhundred-gram mass level.
Pairing of Antarctic meteorites from a given
location is first suggested based on similarity in
petrology; petrologically dissimilar meteorites are not
suggested to be paired. Two diogenites and nine
howardites recovered in 2002–2003 from the PCA
Icefield were initially considered to be two pairing
groups. Subsequently, cosmogenic nuclide analyses and
2128
D. W. Mittlefehldt et al.
petrologic studies have shown that all 11 are paired and
resulted from the fall of a heterogeneous, roughly 1 m
diameter bolide (Beck et al. 2012). These meteorites
cover more than half the mixing range of HED
polymict breccias (Fig. 4), from POEM 10-11 (PCA
02008 and PCA 02009, Warren et al. 2009; Beck et al.
2012; Mittlefehldt et al. 2012) to POEM 58 (PCA
02066, this study). Beck et al. (2012) determined the
modal abundance of eucritic material (including eucritic
breccia clasts) in six of the PCA 2002 polymict breccias
and found a range from approximately 17 vol% for
PCA 02009 to approximately 50 vol% for PCA 02013.
(The difference in grain density for eucrites and
diogenites is only approximately 9% [Consolmagno
et al. 2008] and directly comparing wt% eucritic
component [POEM] with vol% eucritic component
[mode] does not introduce significant additional error.)
Orthopyroxene fragments in the breccias are typically
very coarse grained while the eucritic material is finer
grained (Beck et al. 2012). This drives the compositional
heterogeneity in these small meteorites (2.4–57 g
recovered mass). Beck et al. (2012) noted that the PCA
2002 polymict breccias contain mineral fragments with
compositions that cover nearly the range of all HED
lithologies. The evidence for sampling diverse lithologies
indicates widespread sampling of the vestan surface.
The current PCA 2002 breccias are very heterogeneous
and immature (Beck et al. 2012). Beck et al. (2012)
interpreted the melt-matrix clasts in the PCA 2002
polymict breccias they studied to be impact melts of
targets rich in harzburgitic/dunitic material. PCA 02066,
which is dominated by melt-matrix breccia clasts, has a
higher eucritic component than any of the meteorites
studied by Beck et al. (2012). Ultimately, the whole
ejecta layer was lithified as a very heterogeneous
fragmental howardite.
Regolith Processes—Lunar-Vestan Comparison
It has long been appreciated that the analogy
between howardites and lunar regolith breccias is
imperfect (e.g., Chou et al. 1976). Petrologically,
Apollo 11 regolith breccias are dominated by fused-soil
components plus lithic clasts, while howardites are
dominated by mineral fragments (Simon et al. 1984).
Agglutinates,
solar
wind–irradiated
rims
and
nanophase Fe0-bearing rims are extremely rare in
howardites (Noble et al. 2010). Even correcting for
diminished solar wind flux at Vesta compared with the
Moon, the trapped 20Ne content of regolithic
howardites is lower than found for mature lunar
regolith breccias, but the siderophile element contents
are as high or higher than in those breccias (Warren
et al. 2009). Chondritic clasts are rare and typically
small (<250 lm) in lunar breccias (Joy et al. 2012), but
are often found in HED polymict breccias (see
Prettyman et al. [2012] supplementary material for a
compilation) where they can be large and abundant
(e.g., Herrin et al. 2011).
Environmental factors have conspired to weaken
the analogy between lunar and vestan regolith
development, where the impact environment is the
controlling factor. The cratering rate in the asteroid belt
is higher, causing more rapid turn-over of the surface,
and thus a shorter residence time in the true regolith
affected by solar wind, micrometeoroid, and cosmic ray
exposure (Housen and Wilkening 1982). The amount of
regolith developed is also different: for equivalent time
periods, it is estimated that a Vesta-sized body at 3 AU
would develop a regolith that is 50 times thicker than a
regolith developed on a similar sized body at 1 AU
(Housen and Wilkening 1982). The gravity of the target
body is also an important factor. It is estimated that a
Vesta-sized body at 1 AU would develop a four times
thicker regolith than that of the Moon (Housen and
Wilkening 1982). Another parameter is the collisional
velocity for impactors on Vesta, compared with those
on the Moon. The median impact velocity for Vesta is
4.6 km/s, with 64% of impacts occurring at <5.5 km s 1
(Rivkin and Bottke 1996), which contrasts with the
average impact velocity for near-Earth objects on the
Moon of approximately 22 km s 1 (Ito and Malhotra
2010). Micrometeoroids also impact the Moon at much
higher velocities, ≥11 km/s, compared with asteroidal
dust impacting Vesta, of which approximately 75% are
modeled to impact at <5 km s 1 (Gounelle et al. 2003).
These disparities in impact velocities mean that the
production of fused-soil clasts—agglutinates and darkmatrix breccias—will be much less efficient on Vesta
than on the Moon.
Due to the larger semimajor axis of the vestan
orbit, the intensity of the solar wind and solar flare
irradiation will be diminished to about 0.18 times that
at the lunar surface. Thus, the abundance of implanted
solar wind atoms and formation of amorphous grain
rims would be correspondingly lower than for lunar
materials exposed for similar time intervals. Such a
difference would be exacerbated by the shorter average
surface exposure time expected for vestan regolith.
Characterization of the solar wind–implanted noble gas
content of vestan regolith is further complicated by the
survival of chondritic clasts, which contain planetarytype noble gases (Cartwright et al. 2013). These may
also contain their own component of implanted solar
wind (Caffee et al. 1983; Cartwright et al. 2012a, 2012b,
2013). Thus, bulk sample trapped 20Ne contents do not
uniquely identify vestan materials that had been in the
true regolith (cf. Warren et al. 2009).
HED polymict breccias
Densities of energetic particle tracks in mineral
grains offer the surest way to directly compare the levels
of maturity between lunar soils and regolith breccias
and howardites. Solar flare tracks can be scaled for the
difference in distance from the Sun. The mineral grains
can be identified unambiguously as vestan in origin
(e.g., Wilkening et al. 1971), thus establishing their bona
fides. We have identified a number of howardites
containing material that was in the true regolith of
Vesta, and have suggested others that are possibly
regolithic. Energetic particle track studies of these
would reveal greater details of the level of regolith
maturity represented by each.
CONCLUSIONS
By combining our petrologic and compositional
studies with companion studies on the noble gas
chemistry of HED polymict breccias (Cartwright et al.
2012a, 2012b, 2013), the nature of the true regolith of
Vesta is coming into sharper focus.
1. Based on noble gas results (Cartwright et al. 2012a,
2012b, 2013), five additional regolithic howardites
are identified: EET 87513, GRO 95535, GRO
95602, LEW 85313, and MET 00423. PCA 02066 is
dominated by melt-matrix clasts, which we infer
may have been formed from true regolith by impact
melting, although no solar wind gases are contained
in it (Cartwright et al. 2013).
2. We find that petrologic characteristics suggesting
residence in the true regolith (dark-matrix breccia
clasts, melt-matrix breccia clasts, glass clasts) do not
correlate with noble gas evidence demonstrating
material derived from the true regolith.
3. These regolithic howardites range in percentage of
eucritic material (POEM) from 55 to 76 and
modestly broaden the compositional range inferred
for well-mixed regolith on Vesta. Nevertheless,
they are still roughly centered on a 2:1 eucrite:
diogenite mixing ratio, which then plausibly
represents the relative proportions of upper and
lower crustal debris resident in the ejecta that
could be gardened and blended by small impacts
(Warren et al. 2009).
4. There is no correlation between degree of regolith
character and Ni content. On the Moon, the
siderophile content of the regolith is largely a
cryptic component because the impactors are
efficiently destroyed at their high impact velocities.
On Vesta, the much lower average collision velocity
allows a much higher survival rate for the
impactors. Thus, the siderophile element contents of
HEDs are controlled by the distribution of coarse
chondritic clasts. These can result from individual,
2129
low-velocity accretion events (Yue et al. 2013), as is
inferred for the PRA 04401 CM-clast–rich
howardite (Herrin et al. 2011). Extensive regolith
gardening and maturity are not needed on Vesta to
engender high siderophile element contents.
5. Trace element compositions indicate that the mafic
component of HED polymict breccias is
dominated by basalts similar to main-group
eucrites. Stannern-trend basaltic debris is much less
common: only one of our samples, polymict
eucrite LEW 86001, is composed largely of
Stannern-trend type basalts. Trace element–rich
evolved basalts like Nuevo Laredo and Lakangaon
are present in LAP 04838 as suggested by its bulk
rock composition. Pyroxene compositions and the
presence of ferroan symplectite clasts (Patzer and
McSween 2012) show that debris from evolved
basalts is more common in this howardite than in
most.
6. The scale of heterogeneity varies considerably:
regolithic howardite EET 87513 is more
homogeneous than fragmental howardite QUE
97001. Individual samples of a given howardite can
have very different compositions, even at roughly
gram sizes. This indicates that obtaining
representative meteorite compositions requires
multiple or large samples. Due to this, pairings by
composition are suggestive, not definitive.
7. Even with the preceding caution, we suggest that
the howardites QUE 94200, QUE 97001, and QUE
99033 are likely paired. Our data support pairing of
GRO 95535, GRO 95574, and GRO 95581 as
suggested during initial processing. Noble gas data
show that GRO 95602 has had a different
irradiation history, precluding pairing of it with the
GRO pairing group (Cartwright et al. 2012a,
2012b). Compositionally, GRO 95602 is only
slightly different from the other three GRO
howardites. Finally, we suggest that EET 87503 is
paired with regolithic howardite EET 87513, but
not with the other Elephant Moraine howardites
with which it was initially paired. Our
compositional and petrologic data favor pairing
EET 87509 with EET 83376, EET 87510, EET
87531, EET 99400, and EET 99408.
Due to the environmental difference between the
asteroid belt and the Earth–Moon system, features used
to define regolith maturity for the Moon have to be
applied cautiously to vestan polymict breccias.
Properties that depend on irradiation by the solar wind
and solar flares—implanted solar wind and solar flare
tracks on documented vestan materials—are needed to
establish the bona fides of HED polymict breccias as
being derived from the true regolith.
2130
D. W. Mittlefehldt et al.
Acknowledgments—We thank the National Science
Foundation for funding the ANSMET collecting teams
that brought back the Antarctic samples studied here,
and the Meteorite Working Group, NASA-Johnson
Space Center and the National Museum of Natural
History (Smithsonian Institution) for allocation of the
samples. We thank K. M. McBride and C. E.
Satterwhite for providing photodocumentation and
details of sample allocations for select howardites, J.
Schutt for providing the map of Elephant Moraine
polymict breccia to find locations (Fig. S3), and D. K.
Ross for help acquiring all BSE images except for Fig.
S5a. Editorial handling by H. Y. McSween Jr., and
reviews by A. W. Beck, J. S. Delaney, and R. G. Mayne
resulted in considerable improvement in the article; we
thank them for their efforts. Funding for this research
was
provided
to
DWM
from
the
NASA
Cosmochemistry Program.
Editorial Handling—Dr. Harry Y. McSween Jr.
REFERENCES
Allen R. O. Jr. and Mason B. 1973. Minor and trace elements
in some meteoritic minerals. Geochimica et Cosmochimica
Acta 37:1435–1456.
Ammannito E., De Sanctis M. C., Capaccioni F., Capria M.
T., Carraro F., Combe J.-P., Fonte S., Frigeri A., Joy S.,
Longobardo A., Magni G., Marchi S., McCord T. B.,
McFadden L. A., McSween H. Y., Palomba E., Pieters C.
M., Polanskey C., Raymond C. A., Sunshine J., Tosi F.,
Zambon F., and Russell C. T. 2013. Vestan lithologies
mapped by the visual and infrared spectrometer on Dawn.
Meteoritics & Planetary Science, doi:10.1111/maps.12192.
Barrat J.-A. 2004. Determination of parental magmas of HED
cumulates: The effects of interstitial melts. Meteoritics &
Planetary Science 39:1767–1779.
Barrat J.-A., Blichert-Toft J., Gillet P. H., and Keller F. 2000.
The differentiation of eucrites: The role of in situ
crystallization.
Meteoritics
&
Planetary
Science
35:1087–1100.
Barrat J.-A., Jambon A., Bohn M., Blichert-Toft J., Sautter
V., Gopel C., Gillet P., Boudouma O., and Keller F. 2003.
Petrology and geochemistry of the unbrecciated achondrite
Northwest Africa 1240 (NWA 1240): An HED parent
body impact melt. Geochimica et Cosmochimica Acta
67:3959–3970.
Barrat J.-A., Yamaguchi A., Greenwood R. C., Bohn M.,
Cotten J., Benoit M., and Franchi I. A. 2007. The
Stannern trend eucrites: Contamination of main group
eucritic magmas by crustal partial melts. Geochimica et
Cosmochimica Acta 71:4108–4124.
Barrat J.-A., Bohn M., Gillet P., and Yamaguchi A. 2009.
Evidence for K-rich terranes on Vesta from impact
spherules. Meteoritics & Planetary Science 44:359–374.
Barrat J.-A., Yamaguchi A., Zanda B., Bollinger C., and
Bohn M. 2010. Relative chronology of crust formation on
asteroid Vesta: Insights from the geochemistry of
diogenites.
Geochimica
et
Cosmochimica
Acta
74:6218–6231.
Barrat J.-A., Yamaguchi A., Jambon A., Bollinger C., and
Boudouma O. 2012. Low-Mg rock debris in howardites:
Evidence for KREEPy lithologies on Vesta? Geochimica et
Cosmochimica Acta 99:193–205.
Beck A. W. and McSween H. Y. Jr. 2010. Diogenites as
polymict breccias composed of orthopyroxenite and
harzburgite. Meteoritics & Planetary Science 45:850–872.
Beck A. W., Mittlefehldt D. W., McSween H. Y. Jr., Rumble
D. III, Lee C.-T. A., and Bodnar R. J. 2011. MIL 03443,
a dunite from asteroid 4 Vesta: Evidence for its
classification and cumulate origin. Meteoritics & Planetary
Science 46:1133–1151.
Beck A. W., Welten K. C., McSween H. Y., Viviano C. E., and
Caffee M. W. 2012. Petrologic and textural diversity among
the PCA 02 howardite group, one of the largest pieces of the
Vestan surface. Meteoritics & Planetary Science 47:947–969.
Bischoff A., Scott E. R. D., Metzler K., and Goodrich C. A.
2006. Nature and origins of meteoritic breccias. In
Meteorites and the early solar system II, edited by Lauretta
D. S. and McSween H. Y. Jr. Tucson, Arizona: University
of Arizona Press, pp. 679–712.
Brownlee D. E. and Rajan R. S. 1973. Micrometeorite craters
discovered on chondrule-like objects from Kapoeta
meteorite. Science 182:1341–1344.
Buchanan P. C. and Mittlefehldt D. W. 2003. Lithic
components in the paired howardites EET 87503 and EET
87513: Characterization of the regolith of 4 Vesta.
Antarctic Meteorite Research 16:128–151.
Buchanan P. C., Zolensky M. E., and Reid A. M. 1993.
Carbonaceous chondrite clasts in the howardites Bholghati
and EET 87513. Meteoritics 28:659–682.
Bunch T. E. 1975. Petrography and petrology of basaltic
achondrite polymict breccias (howardites). Proceedings,
6th Lunar Science Conference. pp. 469–492.
Bunch T. E., Chang S., Frick U., Neil J., and Moreland G.
1979. Carbonaceous chondrites; I, Characterization and
significance of carbonaceous chondrite (CM) xenoliths in
the Jodzie howardite. Geochimica et Cosmochimica Acta
43:1727–1742.
Caffee M. W., Goswami J. N., Hohenberg C. M., and Swindle
T. D. 1983. Cosmogenic neon from precompaction
irradiation of Kapoeta and Murchison. Proceedings, 14th
Lunar and Planetary Science Conference. pp. B267–B273.
Cartwright J. A., Mittlefehldt D. W., Quinn J. E., and Ott U.
2012a. The continuing quest for “regolithic” howardites
(abstract #1211). 43rd Lunar and Planetary Science
Conference. CD-ROM.
Cartwright J. A., Ott U., Mittlefehldt D. W., Herrin J. S.,
Mertzman K. R., Mertzman S. A., Peng Z. X., and Quinn J.
E. 2012b. In the pursuit of regolithic howardites (abstract
#5057). In 75th Annual Meeting of the Meteoritical Society.
Houston, Texas: Lunar and Planetary Institute.
Cartwright J. A., Ott U., Mittlefehldt D. W., Herrin J. S.,
Herrmann S., Mertzman S. A., Mertzman K. R., Peng Z.
X., and Quinn J. E. 2013. The quest for regolithic
howardites. Part 1: Two trends uncovered using noble
gases. Geochimica et Cosmochimica Acta 105:395–421.
Chou C.-L., Boynton W. V., Bild R. W., Kimberlin J., and
Wasson J. T. 1976. Trace element evidence regarding a
chondritic component in howardite meteorites. Proceedings,
7th Lunar Science Conference. pp. 3501–3518.
Cleverly W. H., Jarosewich E., and Mason B. 1986. Camel
Donga meteorite, a new eucrite from the Nullarbor Plain,
Western Australia. Meteoritics 21:263–269.
HED polymict breccias
Consolmagno G. J., Britt D. T., and Macke R. J. 2008. The
significance of meteorite density and porosity. Chemie der
Erde—Geochemistry 68:1–29.
Delaney J. S., Takeda H., Prinz M., Nehru C. E., and Harlow
G. E. 1983. The nomenclature of polymict basaltic
achondrites. Meteoritics 18:103–111.
Delaney J. S., Prinz M., and Takeda H. 1984. The polymict
eucrites. Proceedings, 15th Lunar and Planetary Science
Conference, Part 1. Journal of Geophysical Research
89(S01):C251–C288.
Denevi B. W., Blewett D. T., Buczkowski D. L., Capaccioni
F., Capria M. T., De Sanctis M. C., Garry W. B., Gaskell
R. W., Le Corre L., Li J.-Y., Marchi S., McCoy T. J.,
Nathues A., O’Brien D. P., Petro N. E., Pieters C. M.,
Preusker F., Raymond C. A., Reddy V., Russell C. T.,
Schenk P., Scully J. E. C., Sunshine J. M., Tosi F.,
Williams D. A., and Wyrick D. 2012a. Pitted terrain on
Vesta and implications for the presence of volatiles.
Science 338:246–249.
Denevi B. W., Coman E. I., Blewett D. T., Mittlefehldt D. W.,
Buczkowski D. L., Combe J.-P., De Sanctis M. C., Jaumann
R., Li J. Y., Marchi S., Nathues A., Petro N. E., Pieters C.
M., Schenk P., Schmedemann N., Schr€
oder S., Sunshine J.
M., Williams D. A., Raymond C. A., and Russell C. T.
2012b. Regolith depth, mobility, and variability on Vesta
from Dawn’s low altitude mapping orbit (abstract #1943).
43rd Lunar and Planetary Science Conference. CD-ROM.
De Sanctis M. C., Ammannito E., Capria M. T., Tosi F.,
Capaccioni F., Zambon F., Carraro F., Fonte S., Frigeri
A., Jaumann R., Magni G., Marchi S., McCord T. B.,
McFadden L. A., McSween H. Y., Mittlefehldt D. W.,
Nathues A., Palomba E., Pieters C. M., Raymond C. A.,
Russell C. T., Toplis M. J., and Turrini D. 2012a.
Spectroscopic characterization of mineralogy and its
diversity across Vesta. Science 336:697–700.
De Sanctis M. C., Combe J.-P., Ammannito E., Palomba E.,
Longobardo A., McCord T. B., Marchi S., Capaccioni F.,
Capria M. T., Mittlefehldt D. W., Pieters C. M., Sunshine
J., Tosi F., Zambon F., Carraro F., Fonte S., Frigeri A.,
Magni G., Raymond C. A., Russell C. T., and Turrini D.
2012b. Detection of widespread hydratred materials on
Vesta by the VIR imaging spectrometer on board the
Dawn mission. The Astrophysical Journal Letters
758:L36–L40.
Duke M. B. and Silver L. T. 1967. Petrology of eucrites,
howardites and mesosiderites. Geochimica et Cosmochimica
Acta 31:1637–1665.
Fitzgerald M. J. 1980. Muckera and Millbillillie-Australian
achondritic meteorites. Transactions of the Royal Society
of South Australia 104:201–209.
Fuhrman M. and Papike J. J. 1981. Howardites and polymict
eucrites: Regolith samples from the eucrite parent body.
Petrology of Bholgati, Bununu: Kapoeta and ALHA76005
(abstract). 12th Lunar and Planetary Science Conference.
p. 1257.
Ghosh S., Pant N. C., Rao T. K., Mohana C. R., Ghosh J.
B., Shome S., Bhandari N., Shukla A. D., and Suthar K.
M. 2000. The Vissannapeta eucrite. Meteoritics &
Planetary Science 35:913–917.
Gounelle M., Zolensky M. E., Liou J.-C., Bland P. A., and
Alard O. 2003. Mineralogy of carbonaceous chondritic
microclasts in howardites: Identification of C2 fossil
micrometeorites. Geochimica et Cosmochimica Acta
67:507–527.
2131
Harlow G. E., Nehru C. E., Prinz M., Taylor G. J., and Keil
K. 1979. Pyroxenes in Serra de Mage; Cooling history in
comparison with Moama and Moore County. Earth and
Planetary Science Letters 43:173–181.
Herrin J. S., Zolensky M. E., Cartwright J. A., Mittlefehldt D.
W., and Ross D. K. 2011. Carbonaceous chondrite-rich
howardites; The potential for hydrous lithologies on the
HED parent (abstract #2806). 42nd Lunar and Planetary
Science Conference. CD-ROM.
H€
orz F. 1982. Ejecta of the Ries crater, Germany. In
Geological Implications of Impacts of Large Asteroids and
Comets on the Earth, edited by Silver L. T. and Schultz P.
H. GSA Special Paper 190. Boulder, Colorado: Geological
Society of America. pp. 39–55.
Housen K. and Wilkening L. L. 1982. Regoliths on small
bodies in the solar system. Annual Review of Earth and
Planetary Sciences 10:355–376.
Ito T. and Malhotra R. 2010. Asymmetric impacts of nearEarth asteroids on the Moon. Astronomy & Astrophysics
519:A63.
Jarosewich E. 1990. Chemical analyses of meteorites: A
compilation of stony and iron meteorite analyses.
Meteoritics 25:323–337.
Jaumann R., Williams D. A., Buczkowski D. L., Yingst R. A.,
Preusker F., Hiesinger H., Schmedemann N., Kneissl T.,
Vincent J. B., Blewett D. T., Buratti B. J., Carsenty U.,
Denevi B. W., De Sanctis M. C., Garry W. B., Keller H.
U., Kersten E., Krohn K., Li J.-Y., Marchi S., Matz K.
D., McCord T. B., McSween H. Y., Mest S. C.,
Mittlefehldt D. W., Mottola S., Nathues A., Neukum G.,
O’Brien D. P., Pieters C. M., Prettyman T. H., Raymond
C. A., Roatsch T., Russell C. T., Schenk P., Schmidt B.
E., Scholten F., Stephan K., Sykes M. V., Tricarico P.,
Wagner R., Zuber M. T., and Sierks H. 2012. Vesta’s
shape and morphology. Science 336:687–690.
Jerome D. Y. 1970. Composition and origin of some
achondritic meteorites. Ph.D. dissertation, University of
Oregon, Eugene, Oregon. 166 p.
Jerome D. Y. and Goles G. G. 1971. A re-examination of
relationships among pyroxene=plagioclase achondrites. In
Activation analysis in geochemistry and cosmochemistry,
edited by Brunfelt A. O. and Steinnes E. Oslo:
Universitetsforlaget. pp. 261–266.
Jochum K. P., Grais K. I., and Hintenberger H. 1980.
Chemical composition and classification of 19 Yamato
meteorites. Meteoritics 15:31–39.
Joy K. H., Zolensky M. E., Nagashima K., Huss G. R., Ross
D. K., McKay D. S., and Kring D. A. 2012. Direct
detection of projectile relics from the end of the lunar
basin–forming epoch. Science 336:1426–1429.
Kharitonova V. Y. and Barsukova L. D. 1982. Chemical
composition of the Aliskerovo, Aprel’skii, Vetluga, and
Kuleshovka meteorites (in Russian). Meteoritika 40:41–44.
Kolesov G. M. and Hernandez A. 1984. Investigation of the
chemical composition of meteorites by an activation method
using a microtron (in Russian). Meteoritika 43:106–113.
Labotka T. C. and Papike J. J. 1980. Howardites; samples of
the regolith of the eucrite parent-body; petrology of
Frankfort, Pavlovka, Yurtuk, Malvern, and ALHA77302.
Proceedings, 2nd Lunar Science Conference. pp.
1103–1130.
Lal D. and Rajan R. S. 1969. Observations on space
irradiation of individual crystals of gas-rich meteorites.
Nature 223:269–271.
2132
D. W. Mittlefehldt et al.
Lawrence D. J., Peplowski P. N., Prettyman T. H., Feldman
W. C., Bazell D., Mittlefehldt D. W., Reedy R. C., and
Yamashita N. 2013. Constraints on Vesta’s elemental
composition: Fast neutron measurements by Dawn’s
gamma ray and neutron detector. Meteoritics & Planetary
Science, doi:10.1111/maps.12187.
Lorenz K., Nazarov M., Kurat G., Brandstaetter F., and
Ntaflos T. 2007. Foreign meteoritic material of howardites
and polymict eucrites. Petrology 15:109–125.
Lovering J. F. 1975. The Moama eucrite—A pyroxeneplagioclase adcumulate. Meteoritics 10:101–114.
Marvin U. B. and Mason B. 1980. Catalog of Antarctic
meteorites, 1977-1978. Smithsonian Contributions to the
Earth Sciences 23:48.
Mason B. 1974. Notes on Australian meteorites. Records of
the Australian Museum 29:169–186.
Mason B. and Jarosewich E. 1971. The composition of the
Johnstown meteorite. Meteoritics 6:241–245.
Mason B. and Melson W. G. 1970. Comparison of lunar
rocks with basalts and stony meteorites. Proceedings,
Apollo 11 Lunar Science Conference. pp. 661–671.
Mason B., Fredriksson K., Henderson E., Jarosewich E.,
Melson W., Towe K., and White J., Jr. 1970. Mineralogy
and petrography of lunar samples. Proceedings, Apollo 11
Lunar Science Conference. pp. 655–660.
Mason B., Jarosewich E., and Nelen J. A. 1979. The
pyroxene-plagioclase
achondrites.
Smithsonian
Contributions to the Earth Sciences 22:27–43.
McCarthy T. S., Ahrens L. H., and Erlank A. J. 1972.
Further evidence in support of the mixing model for
howardite origin. Earth and Planetary Science Letters
15:86–93.
McCarthy T. S., Erlank A. J., and Willis J. P. 1973. On the
origin of eucrites and diogenites. Earth and Planetary
Science Letters 18:433–442.
McCarthy T. S., Erlank A. J., Willis J. P., and Ahrens L. H.
1974. New chemical analyses of six achondrites and one
chondrite. Meteoritics 9:215–221.
McKay D. S., Heiken G., Basu A., Blanford G., Simon S., Reedy
R., French B. M., and Papike J. 1991. The lunar regolith. In
Lunar sourcebook: A user’s Guide to the Moon, edited by
Heiken G., Vaniman D., and French B. M. Cambridge, UK:
Cambridge University Press. pp. 285–356.
McSween H. Y. Jr., Mittlefehldt D. W., Beck A. W., Mayne
R. G., and McCoy T. J. 2011. HED meteorites and their
relationship to the geology of Vesta and the Dawn
mission. Space Science Reviews 163:141–174.
Metzler K., Bobe K. D., Palme H., Spettel B., and St€
offler D.
1995. Thermal and impact metamorphism on the HED
parent asteroid. Planetary and Space Science 43:499–525.
Michaelis H. von, Ahrens L. H., and Willis J. P. 1969. The
composition of stony meteorites II. The analytical data
and an assessment of their quality. Earth and Planetary
Science Letters 5:387–394.
Mittlefehldt D. W. 1987. Volatile degassing of basaltic
achondrite parent bodies: Evidence from alkali elements and
phosphorus. Geochimica et Cosmochimica Acta 51:267–278.
Mittlefehldt D. W. 1990. Petrogenesis of mesosiderites: I.
Origin of mafic lithologies and comparison with basaltic
achondrites.
Geochimica
et
Cosmochimica
Acta
54:1165–1173.
Mittlefehldt D. W. 1994. The genesis of diogenites and HED
parent body petrogenesis. Geochimica et Cosmochimica
Acta 58:1537–1552.
Mittlefehldt D. W. and Lindstrom M. M. 1991. Generation of
abnormal trace element abundances in Antarctic eucrites
by weathering processes. Geochimica et Cosmochimica Acta
55:77–87.
Mittlefehldt D. W. and Lindstrom M. M. 1993. Geochemistry
and petrology of a suite of ten Yamato HED meteorites.
Proceedings of the NIPR Symposium on Antarctic
Meteorites 6:268–292.
Mittlefehldt D. W. and Lindstrom M. M. 2003. Geochemistry
of eucrites: Genesis of basaltic eucrites, and Hf and Ta as
petrogenetic indicators for altered Antarctic eucrites.
Geochimica et Cosmochimica Acta 67:1911–1934.
Mittlefehldt D. W., McCoy T. J., Goodrich C. A., and
Kracher A. 1998a. Non-chondritic meteorites from
asteroidal bodies. In Planetary materials, edited by Papike
J. J. Washington, D.C.: Mineralogical Society of America.
pp. 1–195.
Mittlefehldt D. W., Jones J. H., Palme H., Jarosewich E., and
Grady M. M. 1998b. Sioux County: A study in why
sleeping dogs are best left alone (abstract #1220). 29th
Lunar and Planetary Science Conference. CD-ROM.
Mittlefehldt D. W., Herrin J. S., Mertzman S. A., and
Mertzman K. R. 2010. Petrology and composition of
HED polymict breccias (abstract #2655). 41st Lunar and
Planetary Science Conference. CD-ROM.
Mittlefehldt D. W., Beck A. W., Lee C.-T. A., McSween H.
Y., and Buchanan P. C. 2012. Compositional constraints
on the genesis of diogenites. Meteoritics & Planetary
Science 47:72–98.
Mittlefehldt D. W., Ammannito E., Hiroi T., De Angelis S.,
Di Iorio T., Pieters C. M., and De Sanctis M. C. 2013.
Towards calibrating the vestan regolith: Correlating the
petrology, chemistry and spectroscopy of howardites
(abstract #5333). Meteoritics & Planetary Science 48.
Miyamoto M., Takeda H., and Yanai K. 1978. Yamato
achondrite polymict breccias. Memoirs of the National
Institute of Polar Research, Special Issue 8:185–197.
M€
uller H. W. and Z€
ahringer J. 1966. Chemische Unterschiede
bei Uredelgashaltigen Steinmeteoriten. Earth and Planetary
Science Letters 1:25–29.
Noble S. K., Keller L. P., and Pieters C. M. 2010. Evidence of
space weathering in regolith breccias II: Asteroidal regolith
breccias. Meteoritics & Planetary Science 45:2007–2015.
Okamoto C., Ebihara M., and Yamaguchi A. 2004.
Geochemical study of metal-rich eucrites from Antarctica.
Antarctic Meteorites XXVIII:68–69.
Olsen E., Fredriksson K., Rajan S., and Noonan A. 1990.
Chondrule-like objects and brown glasses in howardites.
Meteoritics 25:187–194.
Ott U. 2002. Noble gases in meteorites—Trapped components.
In Noble gases in geochemistry and cosmochemistry, edited
by Porcelli D., Ballentine C. J., and Wieler R. Washington,
DC: Mineralogical Society of America. pp. 71–100.
Palme H., Baddenhausen H., Blum K., Cendales M., Dreibus
G., Hofmeister H., Kruse H., Palme C., Spettel B., Vilcsek
E., W€
anke H., and Kurat G. 1978. New data on lunar
samples and achondrites and a comparison of the least
fractionated samples from the Earth, the Moon and the
eucrite parent body. Proceedings, 9th Lunar and Planetary
Science Conference. pp. 25–57.
Patzer A. and McSween H. Y. Jr 2012. Ordinary (mesostasis)
and not-so-ordinary (symplectites) late-stage assemblages
in howardites. Meteoritics & Planetary Science
47:1475–1490.
HED polymict breccias
Pellas P., Poupeau G., Lorin J. C., Reeves H., and Audouze J.
1969. Primitive low-energy particle irradiation of
meteoritic crystals. Nature 223:272–274.
Prettyman T. H., Mittlefehldt D. W., Yamashita N., Lawrence
D. J., Beck A. W., Feldman W. C., McCoy T. J.,
McSween H. Y., Toplis M. J., Titus T. N., Tricarico P.,
Reedy R. C., Hendricks J. S., Forni O., Le Corre L., Li
J.-Y., Mizzon H., Reddy V., Raymond C. A., and Russell
C. T. 2012. Elemental mapping by Dawn reveals exogenic
H in Vesta’s regolith. Science 338:242–246.
Prettyman T. H., Mittlefehldt D. W., Yamashita N., Beck A.
W., Feldman W. C., Hendricks J. S., Lawrence D. J.,
McCoy T. J., McSween H. Y., Peplowski P. N., Reedy R.
C., Toplis M. J., Le Corre L., Mizzon H., Reddy V., Titus
T. N., Raymond C. A., and Russell C. T. 2013. Neutron
absorption constraints on the composition of 4 Vesta.
Meteoritics & Planetary Science, doi:10.1111/maps.12244.
Prinz M. Fodor R., and Keil K. 1977. Comparison of lunar
rocks and meteorites: Implications to histories of the
moon and parent meteorite bodies. NASA Special
Publication 370:183–199.
Pun A. and Papike J. J. 1995. Ion microprobe investigation of
exsolved pyroxenes in cumulate encrites: Determination of
selected trace-element partition coefficients. Geochimica et
Cosmochimica Acta 59:2279–2289.
Reddy V., Nathues A., Le Corre L., Sierks H., Li J.-Y.,
Gaskell R., McCoy T., Beck A. W., Schr€
oder S. E.,
Pieters C. M., Becker K. J., Buratti B. J., Denevi B.,
Blewett D. T., Christensen U., Gaffey M. J., GutierrezMarques P., Hicks M., Keller H. U., Maue T., Mottola
S., McFadden L. A., McSween H. Y., Mittlefehldt D.,
O’Brien D. P., Raymond C., and Russell C. 2012. Color
and albedo heterogeneity of Vesta from Dawn. Science
336:700–704.
Righter K. and Drake M. J. 1997. A magma ocean on Vesta:
Core formation and petrogenesis of eucrites and
diogenites. Meteoritics & Planetary Science 32:929–944.
Rivkin A. S. and Bottke W. F. 1996. Hypovelocity impacts in
the asteroid belt (abstract #1539). 27th Lunar and
Planetary Science Conference. CD-ROM.
Ruzicka A., Snyder G. A., and Taylor L. A. 1997. Vesta as
the howardite, eucrite and diogenite parent body:
Implications for the size of a core and for large-scale
differentiation.
Meteoritics
&
Planetary
Science
32:825–840.
Shearer C. K., Burger P., and Papike J. J. 2010. Petrogenetic
relationships between diogenites and olivine diogenites:
Implications for magmatism on the HED parent body.
Geochimica et Cosmochimica Acta 74:4865–4880.
Shima M. 1974. The chemical compositions of the stone
meteorites Yamato (a), (b), (c) and (d), and Numakai.
Meteoritics 9:123–135.
Shukla A. D., Shukla P. N., Suthar K. M., Bhandari N., Vaya
V. K., Sisodia M. S., Roy S. S., Rao K. N., and Rajawat
R. S. 1997. Piplia Kalan eucrite: Fall, petrography and
chemical characteristics. Meteoritics & Planetary Science
32:611–615.
Simon S. B., Papike J. J., and Shearer C. K. 1984. Petrology
of Apollo 11 regolith breccias. Proceedings of the 15th
Lunar and Planetary Science Conference, Part 1. Journal
of Geophysical Research 89(Suppl.):C109–C132.
Simpson A. B. 1982. Aspects of the composition and origin of
achondrites and mesosiderites. Ph.D. dissertation,
University of Cape Town, Cape Town, South Africa. 629 p.
2133
Singerling S. A., McSween H. Y., and Taylor L. A. 2013.
Glasses in howardites: Impact melts or pyroclasts?
Meteoritics & Planetary Science 48:715–729.
Spudis P. D. 1984. Apollo 16 site geology and impact melts—
Implications for the geologic history of the lunar highlands.
Proceedings, 15th Lunar and Planetary Science Conference,
Part 1. Journal of Geophysical Research 89(S01):C95–C107.
St€
offler D., Artemieva N. A., W€
unnemann K., Reimold W.
U., Jacob J., Hansen B. K., and Summerson I. A. T. 2013.
Ries crater and suevite revisited—Observations and
modeling Part I: Observations. Meteoritics & Planetary
Science 48:515–589.
Stolper E. 1977. Experimental petrology of eucritic meteorites.
Geochimica et Cosmochimica Acta 41:587–611.
Swann G. A., Bailey N. G., Batson R. M., Eggleton R. E.,
Hait M. H., Holt H. E., Larson K. B., Reed V. S.,
Schaber G. G., Sutton R. L., Trask N. I., Ulrich G. E.,
and Wilshire H. G. 1977. Geology of the Apollo 14
landing site in the Fra Mauro Highlands. U. S. Geological
Survey Professional Paper 800:103.
Symes R. F. and Hutchison R. 1970. Medanitos and Putinga,
two South American meteorites. Mineralogical Magazine
37:721–723.
Takeda H. 1979. A layered-crust model of a howardite parent
body. Icarus 40:455–470.
Takeda H. and Graham A. L. 1991. Degree of equilibration
of eucritic pyroxenes and thermal metamorphism of the
earliest planetary crust. Meteoritics 26:129–134.
Takeda H., Miyamoto M., Yanai K., and Haramura H. 1978.
A preliminary mineralogical examination of the Yamato74 achondrites. Memoirs of the National Institute of Polar
Research, Special Issue 8:170–184.
Takeda H., Duke M. B., Ishii T., Haramura H., and Yanai K.
1979. Some unique meteorites found in Antarctica and
their relation to asteroids. Memoirs of the National
Institute of Polar Research, Special Issue 15:54–76.
Takeda H., Wooden J. L., Mori H., Delaney J. S., Prinz M.,
and Nyquist L. E. 1983. Comparison of Yamato and
Victoria Land polymict eucrites: A view from
mineralogical and isotopic studies. Proceedings, 14th
Lunar and Planetary Science Conference, Part 1. Journal
of Geophysical Research 88(S01):B245–B256.
Takeda H., Mori H., Ikeda Y., Ishii T., and Yanai K. 1984.
Antarctic howardites and their primitive crust. Memoirs of
National Institute of Polar Research, Special Issue
35:81–101.
Tera F., Eugster O., Burnett D. S., and Wasserburg G. J.
1970. Comparative study of Li, Na, K, Rb, Cs, Ca, Sr,
and Ba abundances in achondrites and in Apollo 11 lunar
samples. Proceedings, Apollo 11 Lunar Science
Conference. pp. 1637–1657.
Treiman A. H. 1997. The parent magmas of the cumulate
eucrites: A mass balance approach. Meteoritics &
Planetary Science 32:217–230.
Vander Voet A. H. M. and Riddle C. 1993. The analysis of
geological materials, volume I: A practical guide. Toronto,
Ontario: Ontario Geological Survey. Miscellaneous Paper
149. 415 p.
Wahl W. 1952. The brecciated stony meteorites and meteorites
containing foreign fragments. Geochimica et Cosmochimica
Acta 2:91–117.
W€
anke H., Baddenhausen H., Blum K., Cendales M., Dreibus
G., Hofmeister H., Kruse H., Jagoutz E., Palme C., Spettel
B., Thacker R., and Vilcsek E. 1977. On the chemistry of
2134
D. W. Mittlefehldt et al.
lunar samples and achondrites. Primary matter in the lunar
highlands: A re-evaluation. Proceedings, 8th Lunar Science
Conference. pp. 2191–2213.
Warren P. H. 1997. Magnesium oxide-iron oxide mass balance
constraints and a more detailed model for the relationship
between eucrites and diogenites. Meteoritics & Planetary
Science 32:945–963.
Warren P. H. and Jerde E. A. 1987. Composition and origin
of Nuevo Laredo Trend eucrites. Geochimica et
Cosmochimica Acta 51:713–725.
Warren P. H., Kallemeyn G. W., Huber H., Ulff-Møller F.,
and Choe W. 2009. Siderophile and other geochemical
constraints on mixing relationships among HED-meteoritic
breccias. Geochimica et Cosmochimica Acta 73:5918–5943.
Wilkening L. L. 1973. Foreign inclusions in stony meteorites—I.
Carbonaceous chondritic xenoliths in the Kapoeta
howardite. Geochimica et Cosmochimica Acta 37:1985–1989.
Wilkening L., Lal D., and Reid A. M. 1971. The evolution of
the Kapoeta howardite based on fossil track studies. Earth
and Planetary Science Letters 10:334–340.
Yagi K., Lovering J. F., Shima M., and Okada A. 1978.
Mineralogical and petrographical studies of the Yamato
meteorites, Yamato-7301(j), -7305(k), -7308(l) and -7303(m)
from Antarctica. Memoirs of the National Institute of Polar
Research, Special Issue 8:121–141.
Yamaguchi A., Taylor G. J., and Keil K. 1997. Not all
eucrites are monomict breccias (abstract #1360). 28th
Lunar and Planetary Science Conference. CD-ROM.
Yamashita N., Prettyman T. H., Mittlefehldt D. W., Toplis M.
J., McCoy T. J., Beck A. W., Reedy R. C., Feldman W. C.,
Lawrence D. J., Peplowski P. N., Forni O., Mizzon H.,
Raymond C. A., and Russell C. T. 2013. Distribution of
iron on Vesta. Meteoritics & Planetary Science, doi:
10.1111/maps.12139.
Yanai K., Kojima H., and Haramura H. 1995. Catalog of the
Antarctic meteorites. Tokyo, Japan: National Institute of
Polar Research.
Yue Z., Johnson B. C., Minton D. A., Melosh H. J., Di K., Hu
W., and Liu Y. 2013. Projectile remnants in central peaks
of lunar impact craters. Nature Geosciences 6:435–437.
Zolensky M. E., Weisberg M. K., Buchanan P. C., and
Mittlefehldt D. W. 1996. Mineralogy of carbonaceous
chondrite clasts in HED achondrites and the Moon.
Meteoritics & Planetary Science 31:518–537.
SUPPORTING INFORMATION
Additional supporting information may be found in
the online version of this article:
Appendix S1: Details of samples, analytical
methods, data tables (S1 through S6b), pairing and
nomenclature issues, and other supporting discussion.