Meteoritics 27,596-604 (1992)
© Meteoritical Society, 1992. Printed in USA
Mineralogy, petrology and geochemistry of carbonaceous chondritic
clasts in the LEW 85300 polymict eucrite
M. E. ZoLENSKY,' R. H. HEWINS,2 D. w. MITTLEFEHLDT/ M. M. LINDSTROM,!
X. XIAo· AND M. E. LIPSCHUTz'
'SN2/So1ar System Exploration Division, NASA/Johnson Space Center, Houston Texas 77058 USA
. -Dept. of Geological Sciences, Rutgers University, New Brunswick, New Jersey 08903, USA
'Mall Code C23, Lockheed Engineering & Sciences Co., 2400 NASA Rd. 1, Houston, Texas 77058, USA
'Dept. of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA
(Received 1992 April 2; acceptedin revisedform 1992 September 25)
Abs~act:- We
have performed a detailed petro.logic and mineralogic study of two chondritic clasts from the polymict eucrite
LeWiS Chff(LEW) 85300, and performed chemical analyses by INAA and RNAA on one of these. Petrologically the clasts are
identical and are composed of dis~~sed aggregates, chondrules and chondrule fragments supported by matrix. ,he aggregates
an~ chon~~les are composed of olivine (Fo",o.,')' orthopyroxene (Wo,.2En.8.60), plus some diopside. The matrix consists of finegrained olivine (~?66'53)' and lesse~ o~h?pyr<?xen~ and augite. Fine-~ined saponite is common in the matrix. The bulk major
element. ~ompositiOn of th~ matnx IS identical in both clasts and SImilar to that of CM, CO and CV chondrites. The bulk
composition ~fthe ~last studied ~y.INAA and RNAA shows unusual abundance patterns for lithophile, siderophile and chalcophile
elements but is basically chondritic, Th~ INAAIRNAA data preclude assignment of the LEW 85300,15 clast to any commonly
accepted group of carbonaceous chondnte. The unusual rare earth element abundance pattern may, in part, be due to terrestrial
alteration.
4) by geochemical techniques (Laul and Gosselin, 1990; Wang
et
al., 1990). The petrologic investigations suggested that three
EARLY RARE GAS AND TRACE ELEMENT MEASUREMENTS of the
Jodzie and Kapoeta howardites showed that primordial rare of the Bholghati chondritic clasts are similar to CM and one to
gases, C, Bi, and Ni are enriched in the dark portion of the CI chondrites (Reid et al., 1990). However, additional petrologic
breccia compared to the light portion (Mazor and Anders, 1967; work has suggested that the Bholghati chondritic clasts are not
Muller and Zahringer, 1966). These authors concluded that the CM material (Zolensky and Buchanan, unpublished data). Clast
enrichments can most easily be explained by assuming that BH-4 is similar to CM chondrites in bulk chemical charactercarbonaceous chondrite material was mixed into the dark por- istics (Laul and Gosselin 1990), but unlike any chondrite type
tion of the breccias (Mazor and Anders, 1967; Muller and Zah- in volatile/mobile element abundance pattern (Wang et al., 1990).
We present here the detailed results of consortium study of
ringer, 1966). Subsequently, Wilkening (1973) first identified
the
LEW 85300 chondritic clast cited above, with additional
carbonaceous chondrite clasts in the Kapoeta howardite which
she showed were mineralogically most similar to CM or CV3 mineralogic and volatile/mobile trace element study, plus petchondrites. Further work on siderophile element contents of rologic and mineralogic study of a second chondritic clast from
diogenites, eucrites and howardites showed that the howarditic this meteorite. The purpose ofthis study was to obtain as much
breccias contained 2-3% chondritic contamination and that the detailed information as possible on these clasts in order to fasiderophile element signature was most similar to CM chon- cilitate comparison with clasts from other basaltic achondrites
and chondritic meteorites, and to attempt classification of the
drites (Chou et al., 1976).
chondritic
debris. The ultimate goal ofthese studies is to identify
Study ofseparated chondritic clasts from basaltic achondrites
the
types
of
impactors responsible for formation of basaltic
was undertaken by Bunch et al. (1979), who performed a detailed
achondrite
regoliths,
and to compare these clasts with similar
petrologic study and analyses of light elements, organic compounds and rare gases of several chondritic clasts from the Jod- material from lunar and other meteoritic breccias. If the effects
zie howardite. They concluded that the Jodzie clasts were most of processing on the eucrite parent body are well understood, it
similar to CM chondrites. Later, Smith (1982) analyzed four may be possible to determine whether any of the clasts were
chondritic clasts from Kapoeta by INAA but did not perform derived from parent bodies other than those of the well known
petrologic characterization. On the basis of his interpretation of carbonaceous chondrite groups.
analyses for siderophile elements and Zn, Smith (1982) conSAMPLING AND EXPERIMENTAL PROCEDURE
cluded that the chondritic clasts were most similar to either CI
One
of
us (RHH) selected clast and matrix material for petrologic
or.CM ch~ndrites. As part of a consortium study of three polymict eucntes, KozuI and Hewins (1988) and Hewins (1990) examination from three paired polymict eucrites: LEW 85300, 85302
and 85303. After preliminary petrologic examination, several clast and
repo:ted a dark, possible CM chondritic clast from the polymict matrix samples were selected for detailed geochemical and petrologic
eucnte Lewis Cliff (LEW) 85300. Mittlefehldt and Lindstrom study. Thin section LEW 85300,40 contained a relatively large chon(1988~ reported INAA data for this clast and showed that it was dritic clast and a sample for geochemical analyses, LEW 85300,15, was
:~sentlallY chondritic, although with a strange REE pattern un- removed from an adjacent chip containing more of this clast. Thin
section LEW 85300,39 contained a small chondritic clast that was studBhel:o~ of chondrites. A consortium organized to study the ied
by petrologic techniques only.
. 0 I a!1 howardite has characterized four chondri tic clasts by
Thin sections LEW 85300,40 LEW 85300,39 and LEW 85300,15
petro ogle techniques (Reid et al., 1990) and one of these (BH- (made from the INAA sample, see below) were examined by standard
INTRODUCTION
596
597
Carbonaceous clasts in LEW 85300
petrographic techniques. Mineral analyses were performed on ,39 and
,40 at Rutgers University using a JEOL JXA-8600 microprobe. Bulk
matrix and mineral grain analyses were performed on sections ,39 and
,15 at Johnson Space Center (JSC) using a CAMECA CAMEBAX microprobe using a focussed beam. Selected matrix samples from each of
'these two thin sections were then removed, impregnated with MBED812 low-viscosity epoxy, microtomed and examined using a JEOL
2oo0FX STEM equipped with a LINK EXL EDX analysis system.
Microprobe analyses reported are considered to be accurate to within
5% relative. STEM EDX analyses are no more accurate than 10% relative. In all analyses, natural mineral standards were used.
Geochemical analyses were performed by INAA at JSC and RNAA
at Purdue University. A 36-mg sample ofchondrite clast LEW 85300,15
was prepared, irradiated and counted according to standard JSC procedures (Mittlefehldt and Lindstrom, 1991). After data reduction, the
REE pattern proved to be highly unusual for either chondritic or achondritic material. In order to verify that this pattern was not due to foreign
contamination, the sample vial was opened, the sample cleaned in alcohol in an ultrasonic bath and counted for the long-lived nuclides. The
results agreed with analysis of the bulk sample and indicated that contamination was unlikely. The sample was then split into three portions.
One portion was thin sectioned so that petrologic comparison with the
other thin section of this clast (40) could be made. A second portion
was destroyed while attempting to prepare it for major element analysis.
The third portion of the sample was sent to Purdue University for
reactivation and RNAA.
The four-mg portion of clast LEW 85300,15 received at Purdue was
removed from its irradiation vial, weighed and re-sealed in a quartz
irradiation vial in standard use at Purdue. Since the portion of clast
LEW 85300,15 for RNAA was so much smaller than the 100-200 mg
sample usually analyzed at Purdue University, it was decided to investigate the extent to which chemical heterogeneity of elements in the
RNAA suite could affect interpretation of the RNAA data. Therefore,
four samples each of 5, 32 and 200 mg were prepared and analyzed
from specimen Me-2641 of the Murchison CM2 chondrite. Sample
preparation for the Murchison replicates, irradiation conditions (thermal neutron fiuenceof 1.4 x 101• /cm- for the larger Murchison samples,
3.5 x IOI'fern2 for LEW 85300,15 and the smaller Murchison samples),
monitors, chemical yields, counting methods and data reduction were
similar to those used previously at Purdue (e.g., Xiao, 1992). Average
chemical yields for both samples and monitors were similar to those
reported by Xiao and Lipschutz (1991).
is extremely fine-grained and reddish-brown (probably due to
rust) in ultra-thin section. Olivine compositions for aggregates
and chondrules from section,40 are FOlOo-4s and pyroxene compositions range from W0 37En6 1 to WolOEn so' Analyses of similar
materials from section ,39 were olivine FO••.s4 and pyroxene
WoIEn" to W0 2En6o ' One pyroxene of composition W04 1EnS8
was found in ,39. Olivine compositions for ,15 are FO"-62' consistent with the results from section ,40. Representative mineral
analyses are presented in Fig. 2. Olivines in ,39 show abundant
evidence of shock: undulatory extinction, pronounced mosaicism and planar fractures in multiple directions. Olivines in
,15 are less abundant, and show only weak undulatory extinction.
Matrix Mineralogy
The matrix of both clasts, 15 and ,39 is dominantly composed
of fine-grained « 1 /lm-diameter) irregularly-shaped grains of
olivine and lesser orthopyroxene and augite. Analytical electron
microscope analyses of matrix olivine grains yielded the compositional range Fo 66• s3 ; i.e., at the Fe-rich end ofthe range found
for coarser-grained olivines present in the chondrules and aggregates. However, these analyses could have been compromised by the presence of ubiquitous rust, yielding analyses with
incorrectly high Fe-contents. Grains of pyrrhotite, with intergrown pentlandite, and Fe-Ni metal were also noted in the matrix. The sulfide grains generally measure <um in size and are
scattered throughout the matrix, in some instances rimming
larger bodies.
Fine-grained flakes (up to 30 nm thick) of saponite are common, but dispersed, throughout the matrix of both clasts (see
Fig. I b). We cannot positively rule out the possibility that this
phyllosilicate is terrestrial in origin. But from the amount present, and lack of saponite reported among terrestrial weathering
products ofAntarctic meteorites (Zolensky and Gooding, 1986),
we suggest that this mineral is preterrestrial in origin.
PETROGRAPHY AND MINERALOGY
GEOCHEMISTRY
Eucritic Matrix
A portion of the matrix of LEW 85300 is typical of eucrites,
consisting of fine-grained crystal debris. More generally, however, the matrix consists ofdark glasscontaining vugs and charged
with lithic and crystal fragments. Glass veins transect some lithic
inclusions, and glass patches occur in the interiors ofsome clasts.
Textures of mineral fragments range from pristine, unshocked
igneous grains to recrystallized grains to melted grains. Many
small, cryptocrystalline plagioclase patches enclosed in the dark
glass have very irregular forms, suggesting that they may have
originally been melted plagioclase rather than maskelynite. The
bulk composition ofthe glass is very similar to that of common
eucrites. Glass of pyroxene composition is also present.
Bulk Clast
The bulk composition of dark clast, 15 determined by INAA
presented in Table 1 and shown in Fig. 3 is normalized to a
moderately volatile lithophile element, Cr and to CI chondrites.
The clast is compared with Bholghati clast BH-4 (Laul and
Gosselin, 1990), four chondritic clasts from Kapoeta (Smith,
1982) and average eucritic matrix from LEW 85300, 85302 and
85303 (Mittlefehldt and Lindstrom, unpublished). LEW 85300,
85302, and 85303 are petrologically identical and are almost
certainly fragments ofthe same fall. Also shown are mean values
for CM, CO, CV, CK and CR chondrites from Kallemeyn and
Wasson (1981; 1982) and Kallemeyn et al. (1991). The CR
chondrite mean is an average of Al Rais and Renazzo, which
Bulk Clast
have similar refractory element abundances but distinct volatile
As previously noted (Kozul and Hewins, 1988; Hewins, 1990), element abundances (Kallemeyn and Wasson, 1982).
the dark clasts within LEW 85300 generally have sharp boundClast, 15 has a bulk composition unlike chondritic clasts from
aries with the enclosing eucrite matrix. However, a 5-micron other basaltic achondrites, any carbonaceous chondrite type or
wide vein ofeucritic matrix glass penetrates -100 microns into the eucritic matrix. This is clearly shown by the refractory liththe dark clast in ,39 (Hewins, 1990).The clasts contain abundant; ophile elements, Hfthrough Lu in Fig. 3. Hafnium, Sc and Ca
but dispersed, aggregates, chondrules, and possible chondrule have abundance levels in ,15 similar to those of the various
fragments resembling those encountered in carbonaceous chon- carbonaceous chondrite classes, especially CM and CO, while
drites (Fig. la). These bodies are matrix supported. The matrix Ba and the REE are highly enriched, with the REE showing an
598
M. E. Zolensky et al.
FIG. 1. Textures of the LEW 85300 dark clast. a) BSE photomicrograph of LEW 85300,39. b) TEM image of saponite flakes from LEW
85300,39 dark clast matrix.
unusual M-shaped pattern (Fig. 3). Europium is the only REE
with an abundance similar to other chondritic clasts from basaltic achondrites. Among the siderophile, chalcophile and volatile/mobile elements determined by INAA, clast, IS is most
similar to CM chondrites in its abundance of the most volatile
elements, except for Br. However, there is a large depletion in
the siderophile elements Ni and Co which distinguishes this
clast from any carbonaceous chondrite type.
In Table 2, we list RNAA data for clast LEW 85300,15 and
a number of different size samples of Murchison. The CI-nor-
Carbonaceous clasts in LEW 85300
o
_
,40
,15
_
,39
Fs
Ln
--J..JII,
~ ~
~
olivine
n
(l1Y)
m
I
m
I
~
~
ro
n 40
FIG. 2. Pyroxene quadrilateral and olivine Mg# histogram for aggregates and chondrules from ,40, ,IS and ,39.
TABLE 1. Major and trace element compositions of LEW 85300,15
determined by INAA.Split 15+
Na
K
Ca
Sc
Cr
Fe
Co
Ni
As
Se
Br
Sb
Cs
Ba
malized volatile/mobile element concentrations for LEW
85300,15 are shown in Fig. 4. For five elements-Au, Co, Sb,
Se and Cs- INAA data for the entire 36-mg clast sample are
available for comparison (Table I). Concentrations of Au, Se
and Cs determined by RNAA in the 4.16-mg aliquot agree
reasonably well (i.e., within 20-40%) with the INAA data and
are lower than those determined by INAA for the larger sample.
For the siderophiles Co and Sb, the differences are larger (6080%) and the RNAA results are higher than those determined
by INAA. We suspect that the Co and Sb differences reflect the
heterogeneous distribution of metal. However, Au is also a siderophile element and should show similar differences.
To put the results on LEW 85300,15 into perspective, we
have analyzed four samples each ofMurchison in the size ranges
._---
100
C
.....
-------00
--cv
-----cz;:
I
-g
I:.
S2 10
.. I:.
~Rrt
---(2.
!
{J
-
--
lithophile
0.1
-
..
siderophile,
chalcophile
andothers
I ohkLpLJl-,
'C'
La
Ce
Nd
Sm
Eu
Th
Yb
Lu
Hf
Ir
Au
4.34 :t: 0.06 mrlg
3.0 :t: 0.9 mrlg
16:t: 3mglg
9.1 :t: 0.1 p.glg
3.66 :t: 0.05 mrlg
252:t: 3mrlg
350 ± 4p.rlg
5.4 :t: 0.1 mglg
2.6 :t: 0.3 p.glg
23.4 :t: 0.8 p.rlg
760 :t: 120 nrlg
13O:t: 14nrlg
190:t: 60nrlg
58:t: 11 p.rlg
2.07 ± 0.04 p.rlg
4.1 :t: 0.4 p.rlg
11 :t: 2p.rlg
2.42 :t: 0.04 p.rlg
0.184 :t: 0.006 p.rlg
0.59 :t:0.02 p.rlg
1.67 :t: 0.04 p.rlg
0.241 :t: 0.007 p.rlg
200 ± 30nrlg
600:t: 20nrlg
171 :t: 3 nrlg
-Mass of the sample was 35.74 mg.
+Uncertainties are 1 sigma.
----(SI
UlWU3OO,lS
LJ..,... ....
'C'
599
8
Il:.
c.--c
c
~
I
~
lI:;jfiB
If t,l,~ 7\.0
~~.
)IE
'~.
C o
,\, -.
.
'
.
I
.. +++ + 't/1
Hf Ca La Nd Eu Vb Cr Na
Sc Ba Ce SmTb Lu K Cs
Ir
Ni
Co Au Sb Se
Fe As Br
FIG. 3. INAA data for LEW 85300,15 normalized to Cr and CI
chondrites (Anders and Grevesse, 1989). For comparison, the range for
four chondritic clasts from Kapoeta (Smith, 1982), Bholghati BH-4
(Laul and Gosselin, 1990) and various carbonaceous chondrite types
are shown. Also shown is the average eucritic matrix for the paired
meteorites LEW 85300, 85302 and 85303 (Mittlefehldt and Lindstrom,
unpublished).
of200 mg (our typical sample size), 5-6 mg (similar to our split
of LEW 85300) and 32 mg (geometric mean of200 and 5, also
similar to the LEW 85300 sample mass analyzed by INAA)
(Table 2). As can be seen in Table 2, replicates of the 200-mg
samples are quite homogeneous; relative standard deviations
are 10% or less for all elements but Rb (13%). For the 32-mg
samples, the relative standard deviations of Ga, Sb, Ag and In
are more than twice the relative standard deviations for the 200mg samples. For the 5-mg chips, all elements except for Rb, Cs
and Zn have relative standard deviations more than twice the
values for the 200-mg samples. Clearly, Murchison chips are
chemically heterogeneous at the 5-mg level. However, means
of only 2 of 14 elements differ significantly between the 200mg and 5-mg suites. Differences of this order could well reflect
chance, so a 5-mg chip of Murchison should be identifiable as
compositionally consistent with its parent.
Another way to consider these data is to take advantage of
the fact that is most carbonaceous chondrites, CI-normalized
concentrations of the nine most volatile elements in Table 2
(Ag-In), vary relatively little (Xiao and Lipschutz, 1992). The
LEW 85300 clast is very unusual, having a mean concentration
and associated standard deviation of0.94 ± 0.55 x CIfor these
elements. Of 61 carbonaceous chondrites for which data are
M. E. Zolensky et al.
600
3+---+---+---+---+----+---+---+-----<-+--+---+----+---+---+---t
-~~
~~~~
~~~~~~
~~~~o~o~~o~~~~ciciN~
•
~~~~~~~~~N~-~~~~~
~N
~
N-~~OO-~-MN~
~~~~~N~~~~~~NN~~d~
~~~~=~~~~~~
~~~~~
~
~~~~~N
~~
~-~~
~~~~~~~~~~~~g~;~~~
-
--u
2
l r'l
1
~
0.8
0.6
~O~O~~~ON~~~~OO-~~
~~~~~
~~~~~
~~~~~
----- ----- -----
-~N~~-N~~~~~~~~~~~
~-~~~~~~~~~O~~~~~O
~N~N~O~~~~~o~~~~~d
~~-~~~~M~~O~~N~V-O
----- ----- -----
N~NNN
-MNMM
~--NN-
N~
O\Q\Q~~- ~-~~~~ ON~~\Q~
~~r-:C"'iC"'i~
C"'i~~C"'iC"'ici
C"'iNNNNO
NN
--
-----
-----
oC"'i
--
-N~~~~~-MMV~VV~~~­
MMOO--v~~~~
NNNNN
----- -----
~
~~
----~
N~~~OO~~~~~N~~~N~­
--N-- --- -
~O~~~~-~ON~V-O-~O-
v
--
~~~-~~~--~NO~~~~~~
MV--N-OOVMNN~OO--­
~~~~~d~~~~~d~~~~~d
N~--
~~MV
v~~VMV
~~\Q~~O~~~~~~~\Q~~~~
~~C"'i~~N~~~~~~~~r-:r-:r-:ci
0.4
•
•
•
•
.---------------•
•
• • •
•
•
•
Au Co Ga Rb Sb Ag Se Cs Te Zn Cd Bi T1 In
FIo.4. Concentrations of 14 trace elementsdeterminedby RNAA
in the LEW 85300,15 carbonaceous chondrite clast normalized to CI
chondrites (Anders and Grevesse, 1989). Elements are ordered by increasing volatilityduringnebularcondensation. Concentrations of the
nine most volatileelements (Ag-In) in typicalcarbonaceous chondrites
define horizontallines at levels between 0.2~.6 x CI (Xiaoand Lipschutz,1992). Data for LEW 85300, 15areclearly veryscattered, unlike
the casefor typical carbonaceous chondrites. The dashedlinerepresents
the mean CI-normalized abundance (0.97)for the 14 elements in LEW
85300,15.
available (Xiao and Lipschutz, 1992), only three petrologic grade
2 carbonaceous chondrites have similarly high Cl-normalized
values: Haripura, 0.92 ± 0.53; Erakot, 0.81 ± 0.40 (Wolf et al.,
1980); and LEW 87148, 0.98 ± 1.0 (Xiao and Lipschutz, 1992).
The four 5-mg sized replicates of Murchison have CI-normalized means and associated standard deviations for Ag through
In of 0.75 ± 0.34,0.81 ± 0.24,0.68 ± 0.30 and 0.66 ± 0.22.
The relative standard deviations of these samples, 30-45%, are
well below the 60% value for LEW 85300,15.
All information from the volatile trace elements argues for
compositional differences between LEW 85300,15 clast and generally accepted chondrite groups such as CM. As noted by Xiao
and Lipschutz (1992), those four carbonaceous chondrites (including LEW 85300, 15) with volatile trace element means >0.7
x CI have very large standard deviations, hinting at nebular
condensation and/or accretion conditions that are unusual compared with those under which other carbonaceous chondrites
formed. Nothing peculiar is evident in the Au/Co or Ga/Co
ratios of the LEW 85300,15 clast compared with other carbonaceous chondrites, suggesting that unusual redox conditions
during formation of its parent materials are not the cause.
Matrix
The dark clasts in all sections, but particularly LEW 85300,15,
were discolored with rust, probably from terrestrial alteration.
The effects of this rust on bulk matrix major element compositions are unclear, although experience with other Antarctic
meteorites suggests that chemical mobilization does not significantly affect bulk matrix major element analyses (McSween,
1987; Zolensky et al., 1992). Individual focussed electron microprobe analyses of matrix from sections, 15 and ,39 are presented in Table 3 and Fig. 5, on a reduced area Fe-Si-Mg ternary
plot. It is clear that the bulk matrix major element compositions
Carbonaceous clasts in LEW 85300
601
Table 3. Average major element oomposition (wt%) of LEW 85300
clast matrices. INAA data on bulk clast shownfor comparison.
Samples LEW
No. analyses
Na;zO
MgO
Defocussed EMPA
85300,39 85300,15
13
INAA
85300,15
9
0.39
17.1
4.2
30.2
0.29
3.0
0.31
203
4.1
35.8
032
1.58
0.59
0.15
0.72
0.13
0.36
0.52
0.20
053
MnO
FeOI
NiO
0.47
2.8
0.12
0.41
0.26
36.8
0.97
33.7
0.68
TOTAL
97.1
98.5
AI203
Si02
P205
S
K20
Cao
Ti02
Cr203
23
Fe
32.4
0.69
•••....• - CM MATRIX
- - CO AND CY MATRIX
".. A
1All Fe as FeO
of the dark clasts in the two sections are identical with respect
to the three elements presented here (Fig. 5a). Because, 15 was
more highly discolored than ,39 these results support our belief
that weathering has not affected the hulk matrix major element
composition. Figure 5b compares the average matrix composition of these clasts to the fields occupied by average matrix
and chondrule rims (all called "matrix" in the figure) from 20
CM and 6 CO and CV chondrites (Zolensky et al., 1992). Considered on the basis of element ratios, the matrix compositions
of the LEW 85300 dark clasts are truly compatible with either
CM, CO or CV materials. P 20S content is most compatible with
CM and CV matrix (Zolensky et al.• 1992). However, the analysis totals of -97-98% (Table 3) are more typical of those of
CV3 (87-99%) and C04 (one measured, 99%) chondrites, and
much higher than the totals of 79-89% typical of C03, and 7185% typical ofCM chondrites (McSweenand Richardson, 1977;
Zolensky et al., 1992). CI matrix (not shown) is iron-depleted
relative to LEW 85300 dark clast matrix and yields low totals
as well (McSween and Richardson, 1977).
DISCUSSION
The LEW 85300 clasts have apparently experienced variable
shock histories. Clast, 15shows only weak undulatory extinction
of olivines, indicating peak shock pressures < 5 GPa (Steffler et
al., 1991). Clast ,39 shows evidence ofa peak shock pressure
in the range 30-35 GPa (Steffler et al. 1991). Experimental
studies indicate that smectites (of which saponite is a member)
can survive shock to these pressures, although dehydration is
extreme (Boslough et al., 1980).
Fe
51
Mg
~EW85300 ::'
C~ASTS
.
20
55
25
45 45
25
55
Mg
51
b
FIG. 5. Bulk matrix composition for elemental Fe-Si-Mg in wt%. a)
Individual focussed electron microprobe analyses of matrix from both
LEW 85300 thin sections presented on a reduced area Fe-Si-Mg ternary
plot. b) Comparison of the average matrix composition of the LEW
85300 dark clast to the fields ofaverage matrix and chondrule rims (all
called "matrix" in the figure) from 20 CM and six CO and CV chondrites
(Zolensky et al., 1992).
The bulk matrix compositions of LEW 85300 dark clasts are
most consistent with either CM, CO or CV matrix, although
the analyses totals favor CV3 or C04 matrix. The matrix contains dominantly olivine with minor pyroxene, pyrrhotite, pentlandite, metal and saponite. The mineralogy of these clasts'
matrix is, therefore, most similar to CV3s and unequilibrated
ordinary chondrites and to smectite class chondritic interplanetary dust particles (Zolensky and McSween, 1988; Zolensky
and Lindstrom, 1992). The observed compositional range of
large olivine grains in chondrules and aggregates(Fig. 2) is consistent with CM, CO or CV chondrites (Mason, 1963; McSween,
1977). The observed compositional range offine-grained matrix
olivines (F066_s 3) is consistent with either CO or CV matrix (Scott
et al., 1988). Considering both bulk matrix composition and
mineralogy, the presence of chondrules and anhydrous silicate
602
M. E. Zolensky et al.
clasts, we suggest that these LEW 85300 clasts are petrologically
most similar to altered CV3 meteorites and not to CMs.
The bulk compositional information does not obviously agree
with the assessment made on petrological grounds. As discussed
above, the detailed trace element abundance patterns (Figs. 3,
4) do not match any of the carbonaceous chondrite types. However, because LEW 85300 is a find, alteration while on earth
might conceivably have affected the trace element contents. Clast
,15 was obtained from near the surface of the LEW 85300.
Mittlefehldt and Lindstrom (1991) have shown that the REE,
with the exception ofEu, have been leached out of many of the
basaltic clasts in LEW 85300, 85302 and 85303, and that differential mobility of Ce compared to the other trivalent REE
occurred. In addition, the LREE are more susceptible to leaching
than are the HREE. Mittlefehldt and Lindstrom (1991) posit
that Antarctic weathering preferentially dissolves LREE-rich
phosphates in the mesostasis, mobilizing the REE. Europium,
which is primarily contained in plagioclase, is not affected. Oxidation of Ce+3 to Ce+4 allows differential mobility of Ce from
the other REE. Hence, the unusual REE abundance pattern of
,15 could possibly be due to precipitation of REE from weathering solutions onto the fine-grained matrix phases, The weathering solutions are expected to have high LREE/HREE ratios,
and be depleted in Eu and Ceo Except for La, this-is qualitatively
the pattern observed for, 15. Mittlefehldt and Lindstrom (1991)
also showed that Se and K enrichments are sometimes observed
in weathered samples of Antarctic eucrites. We have no a priori
reason to suspect our Se data. However, Ar release data on
samples of LEW 85300, LEW 85302 and LEW 85303 indicate
very strong mobilization of K by weathering (Bogard, pers.
comm.). The K concentration of ,15 is high, but poorly determined, at 5.4 ± 1.6 x CI, well above the range for any carbonaceous chondrite type (Kallemeyn and Wasson, 1981; 1982;
Kallemeyn et al., 1991). On the other hand, Rb and Cs, elements
that should be easily transported by the action of water, do not
have unusual Cl-normalized concentrations in LEW 85300,15.
Hafnium, Sc, Ca and Cr (the normalizing element) are less
affected by weathering in Antarctic eucrites because they are not
concentrated in the phosphates. Their abundances in clast, 15
are within the range of various carbonaceous chondrites. Scandium is the most precisely determined of these three elements,
and its abundance in ,15 closely matches that of either CM or
CO chondrites. The volatile/mobile elements determined by
INAA are more compatible with CM chondrite abundances,
except for Br, which is anomalously low. The siderophile elements Ni and Co are depleted when compared to any carbonaceous chondrite group and do not support classification of
clast, 15 with any carbonaceous chondrite group.
The RNAA data presented in Table 2 and Fig. 4 similarly do
not match those of any known carbonaceous chondrite group.
Previous work on non-Antarctic carbonaceous chondrites has
suggested that the CI-normalized concentrations of volatile elements systematically varied with petrologictype. For example,
Anders et al. (1976) and Wolf et al. (1980) reported data indicating Cl-normalized concentrations of the volatile elements of
0.61, 0.44 and 0.36 in CM, CV and CO chondrites, respectively.
However, more recent study of Antarctic carbonaceous chondrites has indicated that these samples form a continuum in
volatile/mobile element concentrations that do not vary systematically with chemical or petrologic type (Xiao and Lipschutz,
1992). The results of our RNAA study of LEW 85300,15 then
are in accord with the conclusions ofXiao and Lipschutz (1992);
clast ,15 cannot be classified with any of the traditional carbonaceous chondrite groups.
Data for other putative CM inclusions in the Bholghati howardite are instructive in this connection. Concentrations of II
elements (Au, Co, Ga, Rb, Ag, Se, Cs, Te, Zn, Cd and Bi) in a
3-mg sample of Bholghati clast BH-4 (Wang et al., 1990) yield
a pattern broadly parallel to those of the LEW 85300,15 but
displaced to lower values, the mean Bholghati BH-4/Lew
85300,15 ratio being 0.44 ± 0.18. Data for TI and In in Bholghati clast BH-4 are comparable to or somewhat higher than
those in LEW 85300,15, while Sb is an order of magnitude
higher in the Bholghati clast. But, as noted earlier, Sb is uniquely
variable among the RNAA suite of elements. In view of the
small masses ofthe two clasts, it is not the Tl and In agreements
that are surprising, but the systematic difference of a factor of
2 in their contents ofthe other II trace elements of the RNAA
suite. Neither of these inclusions appears to have the properties
ofa CM chondrite (Wang et al., 1990; Zolensky and Buchanan,
unpublished data).
Eucrites have experienced metamorphism, largely through
impact. Therefore thermal metamorphism might conceivably
have affected the more volatile/mobile element abundances of
clast ,15. The matrix of LEW 85300 is rich in impact glass,
which is unusual for polymict eucrites, and howardites, which
are generally fragmental breccias. This indicates a higher temperature of final assembly for LEW 85300 than was typical for
polymict eucrites and howardites. Argon-Ar age dating of a
eucritic clast from LEW 85300 and two eucritic clasts from LEW
85302 (paired with LEW 85300) yielded plateau ages of 3.03.5 Ga (Bogard and Garrison, 1989). Argon redistribution experiments suggest that the eucritic clasts were heated to 800 "C
beneath -I meter of overburden (Nyquist et al., 1991). The
eucritic feldspars in LEW 85303 (also paired with LEW 85300)
have unusual thermoluminescence (TL) properties that have
been experimentally duplicated by heating for four days at 1000
°C (Batchelor and Sears, 1991). Hence, there is abundant evidence that LEW 85300 was metamorphosed after original igneous formation of the eucritic clasts. Perhaps carbonaceous
chondrite clasts were mixed cold with eucritic material and melt
excavated from the crater during the impact process.
We have no specific way of assessing the detailed thermal
history of clast, 15, but the presence of saponite in the matrix
does place limits on the maximum sustained temperature. Heating experiments on Orgueil show that saponite is stable up to
-600°C at 10- 4 bars H 2 , and up to 800°C in vacuum (Akai,
1990; Zolensky et al., 1991). The presence of isolated saponite
within LEW 85300,15 and ,39 indicates that any heating above
600-800 °C (depending on f0 2) was not pervasive. Loss of the
more volatile/mobile elements in Allende and Murchison heated under 10- 5 b H 2 pressure was noted by Ikramuddin and
Lipschutz (1975) and Matza and Lipschutz (1977). At 600 "C,
Murchison lost 60-80% of its initial Bi, In and TI and 95% of
its initial Cd (Matza and Lipschutz, 1977) and Allende lost 7080% of its initial Bi and TI (Ikramuddin and Lipschutz, 1975).
Cadmium and In are present in clast ,15 at 0.5 x CI concentrations, while Bi is - 2.3 x CI and Tl is - 1.1 x CI concentrations (Fig. 4). These are not the compositional characteristics
of a CI, CM, CV or CO chondrite thermally metamorphosed
Carbonaceous clasts in LEW 85300
in an open system (Paul and Lipschutz, 1989). We therefore,
find no evidence that heating significantly affected the volatile/
mobile element abundances in the carbonaceous chondrite clast.
We believe that the chondritic clasts were either mixed into the
. breccia after the metamorphic event that reset the 40 Ar_39Ar ages
of the eucritic clasts at 3.5 Ga and generated the unusual TL
properties, or were mixed into the breccia colder than the eucritic debris and never reached the peak temperatures indicated
by the 4OAr_39Ar ages and TL. We prefer the latter interpretation
because the petrology of LEW 85300 suggeststhat finalassembly
ofthe breccia involved intrusion of dark glass into and between
eucrite and carbonaceous chondrite clasts (Kozul and Hewins,
1988) which might be beneath an impact melt sheet. The large
amount of melting suggests that this process was an unusually
high temperature event for eucrites.
CONCLUSIONS
Two chondritic clasts in LEW 85300 have identical matrix
mineralogies and bulk major element compositions and are most
similar to CV3 chondrites. Bulk clast trace and major element
abundances do not match any type of chondritic material. Except perhaps for REE and K, compositional data do not indicate
significant alteration of LEW 85300,15 by weathering; neither
do we find compositional effects of open-system thermal metamorphism for LEW 85300,15. Refractory lithophile elements
least affected by weathering support either CM or CO classification. Volatile/mobile element concentrations are similar to
those of some unusual CM chondrites (Haripura, Erakot and
LEW 87148), but Ni and Co are depleted relative to any carbonaceous chondrite type. We conclude that if the composition
of LEW 85300,15 clast was not affected by thermal metamorphism or terrestrial alteration, except as noted above, then this
clast represents carbonaceous chondrite material of unique origin. We caution, however, that pervasive rust in the clasts
indicates alteration has occurred, and that we have no information on what affect heating to 600 °C in a eucritic melt sheet
will have on the volatile/mobile elements in small carbonaceous
chondrite clasts.
Acknowledgements- This work was supported by NASA through RTOP
#452-12-92-02 (M. Zolensky), grant NSG 9-35 (R. Hewins), RTOP
#152-13-40-21 (M. Lindstrom) and grant NAG 9-48 (M. Lipschutz).
We appreciate helpful reviews by H. Y. McSween, Jr., S. Richardson
and G. Kallemeyn.
Editorial handling: H. Y. McSween.
REFERENCES
ANDERS E. AND GREVESSE N. (1989) Abundances of the elements:
Meteoritic and solar. Geochim. Cosmochim. Acta 53, 197-214.
ANDERS E., Hroucm H., GANAPATHY R. AND MORGAN J. W. (1976)
Chemical fractionations in meteorites - IX. C3 chondrites. Geochim.
Cosmochim. Acta 40, 1131-1139.
AxAI J. (1990) Mineralogical evidence of heating events in Antarctic
carbonaceous chondrites Y-86720 and Y-82162. Proc. NIPR Symp.
Antarctic Meteorites 3, 55-68.
BATCHELOR J. D. AND SEARS D. W. G. (1991) Thermoluminescence
constraints on the metamorphic, shock, and brecciation history of
basaltic meteorites. Geochim. Cosmochim. Acta 55, 3831-3844. .
BOGARD D. D. AND GARRISON D. H. (1989) 39Ar_4 °Ar ages ofeucrites:
Did the HED parent body experience a long period of thermal events
due to major impacts? (abstr.). Lunar Planet. Sci. 20, 90-91.
603
BOSLOUGH M. B., WELDON R. J. AND AHRENs T. J. (1980) Impactinduced water loss from serpentine, nontronite and kemite. Proc.
Lunar Planet. Sci. Con! 11th, 2145-2158.
BUNCH T. E., CHANG S., FRICK D., NEILJ. AND MORELAND G. (1979)
carbonaceous chondrites-I. Characterization and significance of carbonaceous chondrite (CM) xenoliths in the Jodzie howardite. Geochim. Cosmochim. Acta 43, 1727-1742.
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. Proc. Lunar Sci. Con/7th, 35013518.
HEWINS R. H. (1990) Geologic history of LEW 85300, 85302 and
85303 polymict eucrites (abstr.). Lunar and Planetary Science 21,
509-510.
IKRAMUDDIN M. AND LIPscHurz M. E. (1975) Thermal metamorphism
of primitive meteorites-I. Variation of six trace elements in Allende
carbonaceous chondrite heated at 400-1000 OC. Geochim. Cosmochim. Acta 39, 363-375.
KA1.I.EMEYNG. W.ANDWASSONJ.T. (1981) Thecompositionalclassification ofchondrites- I. The carbonaceous chondrite groups. Geochim. Cosmochim. Acta 45, 1217-1230.
KA1.I.EMEYNG. W. AND WASSON J. T. (1982) The compositional classification of chondrites: III. Ungrouped carbonaceous chondrites.
Geochim. Cosmochim. Acta 46, 2217-2228.
KA1.I.EMEYN G. W., RUBIN A. E. AND WASSON J. T. (1991) The compositional classification of chondrites: V. The Karoonda (CK) group
ofcarbonaceous chondrites. Geochim. Cosmochim. Acta 55,881-892.
KOZUL J. AND HEWINS R. H. (1988) LEW 85300,02,03 polymict eucrites consortium - II: Breccia clasts, CM inclusion, glassy matrix and
assembly history (abstr.). Lunar and Planetary Science 19, 647-648.
LAUL J. C. AND GossELIN D. C. (1990) The Bholghati howardite:
Chemical Study. Geochim. Cosmochim. Acta 54,2167-2175.
MASON B. (1963) Olivine composition in chondrites. Geochim. Cosmochim. Acta 27, 1011-1023.
MATZA S. D. AND LIPSCHUTZ M. E. (1977) Thermal metamorphism
of primitive meteorites-VI. Eleven trace elements in Murchison C2
chondrite heated at 400-1000 OC. Proc. Lunar Sci. Con! 8th, 161176.
MAzoR E. AND ANDERS E. (1967) Primordial gases in the Jodzie howardite and the origin of gas-rich meteorites. Geochim. Cosmochim.
Acta 31, 1441-1456.
McSWEEN H. Y., JR. (1977) On the nature of isolated olivine grains
in carbonaceous chondrites. Geochim. Cosmochim. Acta 41, 411-418.
McSWEEN H. Y., JR. (1987) Aqueous alteration in carbonaceous chondrites: Mass balance constraints on matrix mineralogy. Geochim. Cosmochim. Acta 51, 2469-2477.
McSWEEN H. Y., JR. AND RICHARDSON S. M. (1977) The composition
of carbonaceous chondrite matrix. Geochim. Cosmochim. Acta 41,
1145-1161.
MfITLEFEHLDT D. W. AND LINDSTROM M. M. (1988) Geochemistry
of diverse lithologies in Antarctic eucrites (abstr.). Lunar Planet. Sci.
19, 790-791.
MIlTLEfEHLDT D. W. AND LINDSTROM M. M. (1991) Generation of
abnormal trace element abundances in Antarctic eucrites by weathering processes. Geochim. Cosmochim. Acta 55,77-87.
MULLER O. AND ZAHRINGER J. (1966) Chemische Unterschiede bei
uredelgashaltigen Steinmeteoriten. Earth Planet. Sci. Lett. 1, 25-29.
NYQUIST L. E., BOGARD D. D., GARRISON D. H., BANSAL B. M., WIESMANN H. AND SHIH Cr-Y. (1991) Thermal resetting of radiometric
ages. II: Modeling and applications (abstr.). Lunar Planet. Sci. 22,
987-988.
PAUL R. L. AND LIPSCHUTZ M. E. (1989) Labile trace elements in some
Antarctic carbonaceous chondrites: Antarctic and non-Antarctic meteorite comparisons. Zeitschr. Naturforsch. 44A, 979-987.
REIDA. M., BUCHANAN P., ZoLENSKY M. E. AND BARRETT R. A. (1990)
The Bholghati howardite: Petrography and mineral chemistry. Geochim. Cosmochim. Acta 54, 2161-2166.
Soon E. R. D., BARBER D. J., ALExANoER C. M., HUTCHISON R. AND
PECK J. A. (1988) Primitive materials surviving in chondrites: Matrix. In Meteorites and the Early Solar System (eds. J. F. Kerridge
and M. S. Matthews), pp. 718-745. Univ, Arizona Press, Tucson,
Arizona.
SMITH M. R. (1982) A chemical and petrologic study ofigneous lithic
604
M. E. Zolensky et al.
clasts from the Kapoeta howardite. Ph.D. dissertation, University of
Oregon. 193 pp.
STOFFLER D., KEn. K. AND Scorr E. R. D. (1991) Shock metamorphism of ordinary chondrites. Geochim. Cosmochim. Acta 55, 38453867.
Wang M.-S., Paul R. L. and Lipschutz M. E. (1990) Volatile/mobile
trace elements in Bholghati howardite. Geochim. Cosmochim. Acta
54,2177-2181.
WILKENING L. L. (1973) Foreign inclusions in stony meteorites-I.
Carbonaceous chondritic xenoliths in the Kapoeta howardite. Geochim. Cosmochim. Acta 37, 1985-1989.
Wou R., RICHTER G., WOODROW A. B. AND ANDERS E. (1980) Chemical fractionations in meteorites. XI. C2 chondrites. Geochim. Cosmochim. Acta 44, 711-717.
XIAO X. (1992) Trace element study of formation processes of carbonaceous chondrites and regolith processes on Fayetteville parent
body. Ph.D. dissertation, Purdue University. 176 pp.
XIAO X. AND LIPSCHUTZ M. E. (1991) Chemical studies ofH chondrites- III. Regolith evolution of the Fayetteville chondrite parent.
Geochim. Cosmochim. Acta 55,3407-3415.
XIAO X. AND LIPSCHUTZ M. E. (1992) Labile trace elements in carbonaceous chondrites: A survey. J. Geophys. Res. Planets, submitted.
ZoLENSKY M. E. AND GooDING J. L. (1986) Aqueous alteration on
carbonaceous chondrite parent bodies as inferred from weathering of
meteorites in Antarctica (abstr.). Meteoritics 21, 548-549.
ZoLENSKY M. E. AND LINDSTROM D. (1992) Mineralogy of 12 large
"chondritic" interplanetary dust particles. Proc. Lunar Planet. Sci.
Conf. 22nd, 161-169.
ZoLENSKY M. E. AND McSWEEN H. Y., JR. (1988) Aqueous alteration.
In Meteorites and the Early Solar System (eds. J. F. Kerridge and M.
S. Matthews), pp. 114-143. University of Arizona Press, Tucson,
Arizona.
ZoLENSKY M. E., PRINz M. AND LIPSCHUTZ M. E. (1991) Mineralogy
and thermal history ofY-82162, Y-86720 and B-7904 (abstr.). Symp.
Antarctic Meteorites 16th, 195-196.
ZoLENSKY M. E., BARRETI'R. A. AND BROWNING L. (1992) Mineralogy
and composition ofmatrix and chondrule rims in carbonaceous chondrites. Geochim. Cosmochim. Acta, submitted.