Ten volatile elements (and non-volatile Co) in co-existing light and dark portions of 5 gas-rich chondrites were studied. Patterns of distinct but non-uniform enrichment by dark admixing material are revealed. The dark admixing material is enriched in Cs; Bi and Tl covary in it. It is compositionally unique from known types of primitive materials and is apparently not derived by secondary processes from such materials

Bart, G.

Lipschutz, M. E.

English

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Can Volatile Elftment Trends in
Gas-Rich Meteorites
(NASA-CR- 157E1 7 )	 ON V(:LNTILE FLCMFNT TRENES
IN GAS-RICH F.EIMFITES (Purlu r- Univ.)	 18 F
HC A02/MF A01	 CSCL 03P
Gerhard Bartt
and
Michael E. Lipschutz*
Departmr.nt of Chemistry
Purdue University
W. Lafayette, IN 47907
Submitted to
Geochim!.ca at Cosmochimica Act&
January, 1979
e
N79- 1398 1
Ui1clas
G3/91 40698
s
tNow aL Eidg. Inatitut fur Reaktorfors4-hung, 5303 Wirenlingen, Switzerland.
*Author to whom correspondence should be addressed.
04
rI
Abstract - Study of 10 volatile elenente (and non-volatile Co) in co-existing;
light and dark portions of 5 gas-rich chondrites indicates patterns of distinct
M g t non-uniform enrichment by dark admixing material (DAM). DAM is enriched
in Cs;	 Ri and Tl covary in it. It is compositionally unique from known
types of primitive materials and is apparently not derived Ly secondary
processes frim such materials.
I
2INTRODUCTION
Gas-rich meteorites exhibit unusual features of genetic interest in
addition to the ones encountered in otherwise - similar chondrites and
achondrites containing "normal" gas amounts and composition. From the
major element standpoint, these meteorites consist of compositionally -
similar light and dark portions in sharply - defined contact; large differences
for some major elements are seen in achondrites and more subtle ones in the
chondrites (Muller and Zahringer, 1966). In some instances, clasts of
distinctly different composition are present (e.g. Schultz and Signer, 1977)
cf. Motylewski, 1978) 30 that the breccia is more obviously polymict than
monomict. Numerous studies (e.g. Schultz and Signer, 1977) demonstrate
^hat the 12rge amounts of :rapped gas present in the dark portions of such
meteorites was introduced during exposure of fine-grained regolithic
material to corpuscular radiation on the surface of parent bodies. This
portion, possibly light material darkened during irradiatlon, was then
compacted with unirradiated light material and subsequently ejected as
meteoroids by impacts (Ashworth and Barber, 1976) on parent bodies (e.g.
Schultz and Signer, 1977 and studies cited therein).
The gas-containing portions of such meteorites apparently acquired
their dark color by admixture of volatile-rich dust. The nearly-ubiquitous
C- enrichment in such meteorites (e.g. Muller and Zahringer, 1966; cf.
Begemann and Heinzinger, 1969) and very scattered data for a few volatile
trace elements led Muller and Zahringer (1966) and Mazor and Anders (1967)
to suggest that the adulterant dark ad?"txing material (DAM) was carbonaceous
chondrite-like, in at least one howardite, Jodzie. From additional trace
l
IL1
3element data, Hertogen et al. (1978) re-stated this conclusion for Jcdzie but
suggested that several meteoritic classes constituted DAM in the Kapoeta
howardite while DAM in the Khor Temiki aubrite was E-chondrite dust. On the
other hand, the He, B, C and In enrichment pattern mis-match for five H-
group chondrites with Murray (C2) led Rieder and Wanke (1969) to state that
DAM could be carbonaceous chondrite only if t , nreasonable fractionation processes
are invoked.
To study this question further we determ-.ned volatile Ag, Ca, Se, Cs, Te,
Zn, Cd, B1, T1 and In (and non-volatile Co) in co-existing light and dark
portions of five gas-rich chondrites. These ten volatile elements are known
to be uniformly depleted in carbonaceous chondrites (relative to Cl chondrites)
and have characteristic abundance patterns in primitive ordinary and enstatite
chondrites (cf. Bint et al., 1974, 1976). Thus, their relative enrichment
patterns in the dark/light portions of gas-rich meteorites should "fingerprint"
the nature of DAM in these chondrites.
Experimental
We chipped samples from co-existing light and dark portions of the 114
chondrites Tysnes Island (Me 1719) and Weston (2419 L1), the H5 chondrites
Cangas de Onis (987M) and Leighton (Me 768) and the LL6 chondrite St. Me:.min
(368); regions sampled seemed free of obvious clasts. The dark portions of
the chondrites obtained from the Field Museum of Natural History (Tysnes Island
and Leighton) were considerably darker than corresponding portions of the three
obtained from the Museum National d'Histoire Naturelle in Paris. All samples
were irradiated in the CP5 reactor, processed chemically and counted as described
by Ikramuddin et al. (1976); chemir_al yields were at least as high as reported
there. In that study ar_d subsequent ones by several members of our group, replicate
analyses of homogc:aeous chondrite powders yielded estimated relative standard
deviations from the mean of <10%, typi.cally 3-5X. We assume these precisions
e
k
4to hold in this study since they represent the limitations of our techniques
at the ppm-ppb level.
RESULTS AND DISCUSSION
There exist few published data with which our results (Table 1) can be
compared. The Te ebtimates of Clark et al.. (1967) for Leighton are so uncertain
that little can be made of their being considerably higher than our own.
Published Ga data for the light and dark portions of Leighton, Tysnes Island
and Weston are systematically lower than ours (Table 1) by 0-302 (Rieder and
Wanke, 1969). We have no reason to doubt our data but, a9 we show below, the
systematic difference is unimportant since dark/light Ga patterns for these
chondrites in our study and that of Rieder and Wanke (1969) are identical.
Indium is another matter. In three cases (Leighton dark, Tysnes Island dark
and Weston light) our data (Table 1) and those of Rieder and Wanke (1969)
agree well. However, their data for Leighton light and Weston dark are factors
of 18 and 2, respectively, higher than ours while our datum for Tysnes Island
light is 33 times theirs; we cannot reconcile this difference. We note
however that Rieder and Wanke's datum for Leighton light falls outside the
range reported for In in H5-6 chondrites while our result is within the
range in H3-4 chondrites (cf. Binz et al., 1976). Fortunately, our conclusions
are unaffected by these discrepancies.
5The tabulated data for 11 elements in 5 gas-rich chondrites reveal
numerous instances of significant volatile enrichment by DAM. (In view of
the experimental precision established for our techniques, we take a 10%
enrichment or depletion in dsrk relative to co-existing light material as
signaling significant differences.) Only Cs is enriched in all cases; other
elements are enriched in dark portions of som, meteorites while being depleted
in others (e.g. Tl) or are uniformly concentrated in both portions (e.g. Te).
Furthermore, in no case are all volatile elements enriched in the dark portion
of a given meteorite. Tysnes Island and Leighton exhibit the largest degree and
number of such enrichments but two elements in each are exceptions: In in Tvsnes,
Island is significantly depleted while Cd in that meteorite anu Ga and Se in
Leighton are uniform (as is Co which, being non-volatile, is present in equal
concentration in both portions of all chondrites studied here).
The data of Table 1 are depicted in Fig. 1 in the usual manner (e.g.
Rieder and Wanke, 1969; Hertogen et al., 1978), i.e. as the (dark-light) atomic
abundance relative to that in C1 chondrites. Rieder and Wanke's observation
is confirmed by additional data: volatile elements are not enriched by
addition of DAM similar in composition to carbonaceous chondrites since the
10 volatile elements are not enriched to an equal extent in any chondrite.
For example, while Ca and In in Leighton are at near-C1 levels, Ga, Se and
Cd are a hundred-fold less (fig. 1). The other chondrites exhibit similar
trends.
We attemped to match the observed enrichment patterns to those of E4
and unequilibrated ordinary chondrites (B ing et al., 1974, 1976) and ureili:es,
which also seem to reflect admixture by a volatile-rich component( Bin7
 et al., 1975);
no suitable match was found in any case. The zompositions of all light and dark
portions as well as the DAM enrichments (Table 1, Fig.l) do not correspond to
those of "mysterite," hypothesized late nebular condensates (Higuchi et al.,
1977). In short, we are unable to identify any known meteorite or meteoritic
constituent with compositions similar to those of either part of light-dark
chondrites or DAM.
There is no evidence that the DAM composition is a unique one. Table 2
summarizes all enrichment/uniformity/depletion trends for the 10 volatile
elements studied here in all gals-rich meteorites for which data are available.
In seven instances, duplicate sets of results exist and, except for In in
Tysnes Island, all duplicate data - sets agree. All elements are enriched
in the dark portion of at least two meteorites; Cs is the only element of
those studied here which is enriched in the dark-portion of all gas-rich
chondrites (Table 2).
Apart from the prominence of the Cs - enrichment, no DAM feature
in any chondrite is reproduced in another (Fig. 1). ► eighton and, to a
lesser extent, Tysnes Island (the chondrites with the most pronounced dark
portion) are richest in volatiles; thus, as noted for C (Begemann and
Heinzinger, 1%9)  darkening and volatile -enrichment go hand-in-hand.
While we recognize that DAM may not be a single constituent in all
meteorites we treated it as such to determine whether any pairs of elements
correlate significantly in DAM from the chondrites we studied. A surprisingly
large number of element-pairs exhibited high correlation coefficients but we
could establish only four statistically-significant correlations in which
DAM enrichments occur in at least four chondrites [Fisher'sL-transformation
involves n-3 degrees of freedom.] The linear correlations of Cs with Bi. and
T1 (r - 0.97 and 0.99, respectively) are heavily-weighted by Leighton.
Linear and exponential correlations of Bi and T1 (r - 0.998 and 0.996,
7respectively) sera well-established and Indicate a coherent trend of slope 1.6
between these elements in DAM from all chondrites (Fig. 2). Measurement of
these elements in additional meteorites should clarify whether additional
elements, e. g. Ag. In, vary coherently in DAM.
CONCLUSIONS
In contradistinction from the situation in achondrites, DAM in gas-rich
chondrites does not correspond compositionally to any known primitive meteorite.
It is difficult to imagine a secondary fractionation process that could transform
such a known composition to those observed in the dark portions of such chondrites.
DAM is not compositionally constant but it is enriched in Cs; B1 and T1 (and
perhaps other elements) covary in this material. While it is disappointing
that DAM in gas-rich chondrites remains unidentified, it is exciting that such
chondrites constitute a source for yet another and hitherto - unknown sort of
primitive nebular material.
Acknowledgements - We thank Drs. E. Olsen of the Field Museum and P. Pellas
of the Paris Museum for providing material for this study which was supported
by the National Aeronautics and Space Administration under grant NGL 15-005-140.
a.
8REFERENCES
ASHWORTH J. R. and BARBER D. J. (1976) Lithification of gas-rich meteorites.
Earth Planet. Sci. Lett. 30, 222-233.
.w
BEGEMANN F. and HEINZINGER K. (1969) Content and isotopic composition of
carbon in the light and dark portions of gas-rich chondrites. In
Meteorite Research (ed. P. M. Millman), ;,p. 87-92. Jtaidel.
BINZ C. M., KURIMOTO R. K. and LIPSCHUTZ M. E. (1974) Trace elements in
primitive meteorites-V. Abundance patterns of thirteen trace elements
and interelement relationships in enstatite chondrites. Geochim. Cosmochim.
Acta 38, 1579-1606.
BINZ C. M., IKRAMUDUIN M. and LIPSCHUTZ M. E. (1975) Contents of eleven trace
elements in ureilite achondrites. Geochim. Cosmochim. Acts 39, 1576-1579.
._..
HINZ C. M., IKRAMUDDIN M., REY P. and LIPSCHUTZ M. E. (1976) Trace elements in
primitive meteorites-VI. Abundance patterns of thirteen trace elements and
interelement relationships in unequilibrated ordinary chondrites. Geochim.
Cosmochim. Act& 40, 59-71.
'-wV.
CLARK R. S., ROWE M. W., GANAPATHY R. and '^URODA P. K. (1967) Iodine, uranium
and tellurium ►
 contents in meteorites. Geochim. Cosmochim. Acts 31, 1605-1613.w
HERTOGEN J. 0
 JANSSENS M. J., PALME H. and ANDERS E. (1978) Late nebular condensates
and other materials collected by the meteorite parent bodies. In Lunar and
Planetary Science IX, pp.497--499. Lunar and Planetary InsL.
HIGUCHI H., GANAPATHY R., MORGAN J. W. and ANDERS E. (1977) "Myttorite" : a late
condensate from the solar nebula. Geochim. Cosmochim. Acts 41, 843-852.
IKRAKUDDIN M., BINZ C. M. and LIPSCHUTZ M. E. (1976) Thermal metamorphism of
primitive meteorites-II. Ten trace elements in Abee enstatite chondr!.te
heated at 400-1000°C. Geochim. Cosmochim. Acta 40, 133-142.
"'wN
9MAZOK E. and AIQ)ERS E. (1967) Primordial gases in the Jodzic hovardite an^ the
origin of gas-rich meteorites, Geochim. Cosmochim. Acta 31, 1441-:456.
MOTYLEWSKI K. (1978) The revised Cambridge Chondrite Compendium. Preprint.
MULLER 0. and ZAHRINGER J. (1966) Chemische l,nterschlede bei Uredelgastaltigen
Steinmeteoriten. Eartn Plane , Sci. Lett. 1, 25-29.N
RIEDER R. and WANKS H. (1969) Study of trace elwnent abundances in meteorites
by neutron activation. In Meteorite Research (ed. P. M. Millman),
pp. 75-86. Reidei.
SCHULTZ L. and SIGNER P. (1977) Noble gase6 in the St. Mesmin chondrite:
Implications to the irradiation history of a brecciated meteorite.
Earth Planet. Sci. Lett. 36, 363-371.
w.
16
10
Table 1. Trace element concentrations in coexisting light and dark portions
of gas-rich chondrites.
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Table 2. Truth table for volatile element enrichments in dark portion relative
to light in gas-rich meteorites.
r 13 Table T.
Elements*
Meteorite	 Ag	 Ga	 Se	 Cs	 Te	 Zn	 Cd	 Bi	 T1	 In
Cangas de Onts - 0 0 + 0 + 0 + + +
Fayetteville Ob Od +c +d +d +d +b
Jodzle +e +e -e +e +e
Kapoeta +C
Krahenberg -a +a -a
Leighton + O/Ob 0 + +/+C + + + + +/+b
Pan t a r Of +f
St. Mesmin 0 0 0 + 0 0 + - - -
Tyanes Island 0 +/+b + + + + 0 + + -/+b
Weston + 0/Ob 0 + + 0 0 + + +/+b
Note to Table T.
All entries oetrimined from dark/light ratios: i, rat 
	
'1.1; 0, ratio
>0.90 but <1.1; -, ratio <0.90. All entries ha y ed upon rewults of this
study and/or by others where noted: n-Kemhe and Miiller (1969); h-Rieder
and Uanke (1969); c-Clark et al. (1967); d-Laul et al. (1470 a,b), ease
et al. (1973); e-Hertrgen et al. (1978);f-Keed (1963).
15
I
I
Figure Captions
Fig. 1. Volatile element enrichment/uniformity/depletion of dark, gas-containin';
portions relative to co-existing light parts of Vas--rich chondrites. All atomic
abundances are expressed ss proportions of cosmic (i.e. Cl) abundances. Numbers
indicate da.k/light ratios for each element. Cesium is uniquely enriched (i.e.
ratio ='1.1) in all chondrites. Tysnes Island and Leighton exhibit the largest
amount and number of enriched elements but In is significantly depleted (i.e.
ratio <0.90) in the dark part of Tysnes Island while other elements are uniformly
concentrated (0.90 < ratio <1.1) in both parts of a given chondrite. In no case
does the enrichment pattern seem to reflect addition of a primitive component
of any known chondritec type (see text).
Fig. 2. Correlation of Bi and T1 excess in the dark portions of four gas-rich
chondrites. These data correlate at >99% confidence level and suggest that the
covariance of these elements is a characteristic of DA,M in chondrites.
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On volatile element trends in gas-rich meteorites

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