The study of meteorites has produced a wealth of information about

these objects. Petrologic and chemical observations of meteorites have

shown the presence of planetary differentiates and of undifferentiated

aggregates resulting from nebular condensation and the interaction of

these aggregates due to metamorphism. Equilibrium chemistry in a solar

gas and in planetary environments has been an excellent guide to our

studies. Studies by several groups have yielded remarkable discoveries

about the early stages of planetary evolution and of precursor components

from the solar nebula and from the interstellar medium (ISM)

Wasserburg, G. J.

Caltech Authors - Main

308 Abstracts 
indicate an extraordinary bulk composition. A comparable composition 
had been reported previously for a portion of eucrite ALHA 78158 [2], 
but since ALHA 78158 is polymict, its composition is petrogenetically 
ambiguous. Compared to noncumulate eucrites, RKPA80224 has sig-
nificantly lower contents of REE (e.g., Sm = 0.87 !Lglg) and other in-
compatible elements (e.g., Ti = 3 mglg); and much lower Sm/Eu (1.19, 
vs. -2.63 for typical low-Sm noncumulate eucrites such as Juvinas). 
On the other land, RKPA80224 differs from recognized cumulate eu-
crites in many respects, including lower Mgi(Mg + Fe) (0.398, vs. 0.49-
0.64 for cumulate eucrites) and higher Eu/ AI (1.02 x IQ->, vs. 2-8 x 
I o-•). Conceivably RKP A80224 represents an extension of the Stann ern 
Trend, characterized by sharply increasing Sm with constant or mod-
erately decreasing Mgi(Mg + Fe), and putatively formed as primary 
partial melts. However, the low overall REE, Ti, etc., and especially the 
low Sm/Eu (positive Eu anomaly) strongly suggest that RKPA80224 
formed as a partial cumulate. Its relatively coarse, largely ophitic texture 
is comparable to the textures of unbrecciated portions of Pomozdino, 
a eucrite completely unlike RKPA80224 in composition but also in-
terpreted as a partial cumulate [3, 4]. The pyroxenes are thoroughly 
exsolved (exolution lamellae up to 12 !Lm across), indicating a prolonged 
history of slow cooling comparable to those for recognized cumulate 
eucrites [5]. Mass balance calculations, assuming that the K0 (Fe/Mg) 
for pigeonite = 0.30 [6], indicate that the parent melt of RKPA80224 
may have been along an extension of the Nuevo Laredo Trend, char-
acterized by moderately increasing Sm with sharply decreasing Mgi(Mg 
+Fe), and putatively formed by fractional crystallization of a melt (or 
melts) similar to relatively magnesian members of the Main Group 
eucrites [e.g., 2, 3, 6]. This model requires that the "trapped liquid" 
content of RKPA80224 be no more than -40 wt.%, because a TL 
content »40 wt.% would imply a Sm content for the parent melt far 
lower than any plausible extension of the Nuevo Laredo Trend. The 
Mgi(Mg + Fe) implied for the parent melt is only about 0.20. Stolper 
[6] noted that surprisingly ferroan melts, more ferroan than any known 
eucrite, are required to account for most cumulate eucrites. Meteorites 
such as RKPA80224 and Pomozdino tend to blur the distinction be-
tween cumulate and noncumulate eucrites. However, the putative ge-
netic distinction between Nuevo Laredo (Main-Group-linked fractional 
crystallization residue) and Stannern (primary partial melt) types of 
noncumulate eucrites still appears valid, and RKPA80224 appears to 
stengthen the case for most cumulate eucrites being linked to the Nuevo 
Laredo Trend. References: [I] ScoreR. and Mason B. (1982) Ant. Met. 
News!. 5, 31. [2] Smith M. R. and Schmitt R. A. (1981) LPS 12, 1014-
1015. [3] Warren P. H. and Jerde E. A. (1988) LPS 19, 1234-1235. [4] 
Yaroshevsky A. A. eta!. (1988) LPS 19, 1311-1312. [5] Takeda H. et 
a!. (1988) Abs. Sym. Ant. Met. 13th, 142-144. [6] Stolper E. (1977) 
GCA 41, 587-611. 
Ice Patterns and Surface Wind in the Setting of Antarctic Meteorites. 
Peter J. Wasilewski, 1 Gary R. Huss, 2 Jerry Wagstaff' and Carl Thomp-
son. 4 1NASA/Goddard Space Flight Center, Code 691, Greenbelt, MD 
20771 USA. 'Enrico Fermi Institute, U. of Chicago, Chicago, IL 
60637 USA. 'Lockheed EMSCO, 2400 NASA Rd. 1, Houston, TX 
77058 USA. 49 Exmouth Rd., Northcote, Auckland, New Zealand. 
During the 1987-88 Antarctic field season, about 3 70 meteorite pieces 
were picked up by the reconnaissance team on exposed blue ice patches 
west and northwest of Elephant Moraine. The ice patches exhibited 
distinctive surface texture and other features, such as topography, which 
suggest differences in horizontal and vertical velocities and consequently 
different ablation rates. In some cases, different velocity vectors and 
evidence of submergent and emergent patches could be implied by 
noting the appearance and orientation of the surface texture of the ice 
and the presence of shear bands and other structural characteristics. It 
is clear that a considerable differential movement within and between 
ice patches is characteristic and these dynamics must figure in the ap-
pearance of meteorites at the surface. 
In one location (Texas Bowl), surface winds appear to locally con-
centrate meteorites. The size distribution is narrow and the meteorite 
materials appear localized in an oriented, superimposed texture pro-
duced by shear which is subparallel to the prevailing wind direction on 
a steep slope. At the western end of Meteorite City near a discontinuity 
marked by pinnacles, a few heavily weathered meteorites were found, 
indicating long surface residence times for this site. On the farthest ice 
fields we visited, no meteorites were found. The surface of these fields 
was dominated by a regular and continuous oriented ripple pattern 
suggesting little or no significant ablation. 
From the field evidence, meteorites appear in greatest concentration 
on blue ice patches that have specific surface textures and related larger 
scale structural patterns. It is also clear that surface winds may be 
important locally in concentrating meteorites. 
Identification of Shock Induced Changes in Fe Spheres Using Magnetic 
Techniques. Peter Wasilewski. NASA/Goddard Space Flight Center, 
Code 691, Greenbelt MD 20771 USA. 
Solution annealed Cu ( 1.4 wt.% Fe) alloys were precipitation annealed 
at 650 oc and 750 oc to produce size controlled dispersions of non-
magnetic fccFe spherical precipitates. Discs of these alloys were then 
impacted at levels up to 5 GPa and then magnetically characterized 
after recovery. The impact transforms the fccFe to magnetic bccFe. 
Substructure in the precipitates before and after shock was characterized. 
Specimens studied had particle size distributions of 20-35 nm, 40-60 
nm, and 80-110 nm. The shock direction was located in the disc by 
measurement of angular variation of magnetic-coercivity. Magnetiza-
tion reversal is unique because of the near ideal magnetic properties of 
fine Fe particles having a narrow size distribution, a mean interparticle 
spacing dependent on size distribution, no clusters or agglomerates of 
any kind, the same substructure in all Fe particles, and no significant 
variation in particle shape. 
Magnetic hysteresis analysis is used to follow the magnitude of the 
shock induced magnetic anisotropy which is impact level dependent. 
The magnetic anisotropy can be eliminated by thermal anneal, sug-
gesting that not only shape change but the transformation microstructure 
is dependent on the structure of the shock wave. Alternating field 
demagnetization before and after anneal and thermal demagnetization 
of saturation remanence illustrate the influence of shock impact on the 
magnetic stability of the spheres. These effects are superimposed on the 
size dependent properties of the spheres. 
These results demonstrate that shock effects can be identified by mag-
netic techniques, and with calibration, the level of shock can be ascer-
tained. Information about the structure of the shock in the material is 
also attainable. These results apply directly to lunar samples and are 
the basis for analysis of the meteorites. 
Somewhere Over the Rainbow. G. J. Wasserburg. Division of Geological 
and Planetary Sciences, California Institute of Technology, Pasadena, 
CA 91125 USA. 
The study of meteorites has produced a wealth of information about 
these objects. Petrologic and chemical observations of meteorites have 
shown the presence of planetary differentiates and of undifferentiated 
aggregates resulting from nebular condensation and the interaction of 
these aggregates due to metamorphism. Equilibrium chemistry in a solar 
gas and in planetary environments has been an excellent guide to our 
studies. Studies by several groups have yielded remarkable discoveries 
about the early stages of planetary evolution and of precursor compo-
nents from the solar nebula and from the interstellar medium (ISM). 
The isotopic studies have established a rather well defined and short 
time scale ( -106 y) between some types of nucleosynthesis and the 
formation ofprotoplanetary materials and planets. The diverse isotopic 
anomalies which are unconnected to radioactive parents appear to result 
from incomplete mixing of debris from different stellar sources before 
formation of the solar system; some anomalies may come from processes 
in the early solar system itself. The magnitude of the isotopic effects 
which have been discovered has grown enormously, and the geometric 
scales at which they are found have correspondingly decreased to far 
below optical microscopic dimensions. The number of distinct isotopic 
effects has increased to populate a zoo of anomalies. We have now found 
the rainbow of interstellar dust and debris in meteorites. The "earliest" 
material has been the object of search for over three decades. 
The remarkable success of this venture is a testimony to the belief 
that meteorites are the key to our most ancient past. However, the 
astronomical sites where the components were produced is quite unclear, 
the nuclear astrophysical mechanisms are only generally defined (SPQR), 
and the fundamental processes in meteorites which governed their ag-
gregation and formation are obscure. We have many strong hints of the 
Abstracts 309 
precursor mechanisms; however, the chemical and physical processses 
which control the chemistry of the ISM and the collapsing gas and dust 
mixture and produced chondrules is at best poorly understood. We are 
in a stage where both meteoritical and astronomical studies are yielding 
marvelous discoveries and providing a general morphologic guide to 
the making of solar systems. What we now require is an understanding 
ofthe physical and chemical processes and reaction mechanisms which 
actually control the state of matter that went to make up the early solar 
nebula. Over the past two decades numerous astronomical observations 
have been made of dense molecular clouds- the placental medium from 
which the solar system formed. These clouds contain a rich range of 
compounds and diverse isotopic compositions. Recently a newly formed 
solar system has been found. We are rapidly discovering the morphology 
(fossils) of the phenomena leading to solar system formation and the 
relics which are our focus of attention. 
Having found the rainbow, we must now seek beyond it, both in 
theory and experiment, to understand what actually took place. Estab-
lishing the relationships of our observations to the basic cosmochemical 
processes will lead us to real understanding. 
Group and Type Compositions of Ordinary Chondrites: Excepting Vol-
atiles, No Relationship Between Type and Composition. John T. Was-
son, Gregory W. Kallemeyn and Alan E. Rubin. Institute of Geo-
physics, University of California, Los Angeles, CA 90024 USA. 
We have determined 25 elements in replicate samples of66 ordinary 
chondrites. Group compositions are in good general agreement with 
those determined in earlier studies. We observed some Mg-normalized 
abundance trends not previously defined: Na abundances are about 7% 
lower in H chondrites than in L and LL; LL Ga abundances are about 
12% lower than in Hand L; the Co/Ni ratio decreases by about 10% 
through H ~ L ~ LL. We cannot confirm earlier reports that refractory-
lithophile/Mg ratios are higher in H than in L or LL. 
Considerable interest attaches to the question of compositional dif-
ferences among petrographic types, since the common interpretation 
that types 4-6 reflect different degrees of metamorphic alteration of 
type-3 starting materials implies that, within each group, the different 
types should be isochemical except for highly volatile elements out-
gassed during metamorphism. With the exception of highly volatile Br, 
our data show no significant differences among petrographic types of L 
and LL chondrites. There is also no significant difference among H -group 
types 4-6. Our set ofH-related type-3 chondrites includes Dhajala and 
Sharps which show no significant compositional differences from H4-
6 chondrites, and Bremervorde and Tieschitz, which have siderophile 
abundances intermediate between H and L levels. The kamacite Co 
content and 0-isotope composition of Tieschitz show it to be more 
closely related to L than H, and the 0-isotope composition ofBremer-
vorde is also L-like. It seems probable that these latter meteorites are 
rare representatives of nebular materials intermediate in properties be-
tween H and L, and did not originate on either of these parent bodies. 
Our data also show that Albareto, Bjurbole, Cynthiana and Qidong 
have olivine and kamacite compositions and siderophile abundances 
between the upper L and lower LL limits. 
Siderophile abundances in the L3 falls Hedjaz and Khohar and LL3 
falls Bishunpur, Manych, Ngawi and Semarkona fall within the ranges 
defined by the type 4-6 members of the respective groups. We conclude 
that nebular accretion processes were the same for all types of each 
ordinary chondrite group. This is comforting, since even if mechanical 
processes late in nebular history led to a gradual fractionation in pla-
netesimal compositions, asteroids appear to have accreted somewhat 
later by the accumulation of planetesimals and smaller asteroids. This 
process would have led to the incorporation of such fractionated bodies 
at all levels in asteroid-size parent bodies. If degree of metamorphism 
was directly related to the radial depth within the asteroidal parent body, 
the early- and late-formed planetesimals should occur at all depths and 
show all degrees of metamorphism. 
Different Interplanetary Source Regions of Antarctic and Non-Antarctic 
H-Chondrites? The Noble Gas Record. H. W. Weber, L. Schultz and 
F. Begemann. Max-Blanck-Institut ftir Chemie, D-6500 Mainz, FRG. 
On the basis of differences in the concentrations of some trace ele-
ments it has been suggested that Antarctic and non-Antarctic chondrites 
have different parent populations (1, 2, 3), a proposition which is being 
debated, however (4, 5). 
Non-Antarctic H-group chondrites have a cosmic-ray exposure age 
distribution which is characterized by a peak at about 8 Ma. This peak, 
between nominal ages of 6 Ma and I 0 Ma, contains about 45% of all 
H-~hondrites and is interpreted as caused by a major collisional event, 
whtch spalled these meteorites off their parent body 8 Ma ago. If Ant-
arctic H-chondrites came from a different source population they might 
have a different exposure age distribution as well which, in particular, 
might not show the pronounced 8 Ma peak. 
60 
50 
til 
~ 40 
ro 
0 
..... 
0 
OJ 30 
z 
20 
1 
H-Chondrites 
D Non-Antarctic 
m Antarctic 
<Allan Hills) 
1 o 3·o s·o io 
Exposure Age [Ma] 
We have measured the concentration and isotopic composition of 
He, Ne, and Ar in 31 H-chondrites found on the Allan Hills ice fields. 
Exposure ages were calculated from cosmogenic 21 Ne, using the pro-
cedures given in (6). The results are shown in the figure together with 
the exposure age distribution of non-Antarctic meteorites as calculated 
by the same procedure from literature data. Note, that for such a com-
parison, possible uncertainties in the absolute values of the production 
rates are irrelevant. 
There is no obvious difference between the two distributions. The 8 
± 2 Ma peak contains 14 out of 31 cases (=45%), which is in perfect 
agreement with the result for the non-Antarctic suite of samples. Ac-
cording to mineralogical evidence (metamorphic grade classification) as 
well as radiogenic and solar wind noble gas data, at least 9 out of the 
14 samples in the 8 Ma peak are independent falls, which gives a min-
imum percentage of 35% (9 out of 26) belonging to this exposure age 
peak. We conclude that the exposure age distribution does not corrob-
orate the contention of an origin from different parent bodies of Ant-
arctic and non-Antarctic H-chondrites. A similar conclusion, based on 
9 Yamato H-chondrites, has been arrived at by Takaoka eta!. (7). Of 
course, the possibility cannot be excluded that the 8 Ma event was not 
restricted to a single parent body. In this case one would have to explain, 
however, why only H-chondrite parent bodies should have been affected 
and why it does not show up for L-chondrites. References: (I) Dennison 
J. E. eta!. (1986) Nature 319, 390. (2) Ligner D. W. eta!. (1987) 
Geochim. Cosmochim. Acta 51, 727. (3) Dennison J. E. et a!. (1987) 
Geochim. Cosmochim. Acta 51, 741. (4) Wetherill G. W. (1986) Nature 
319, 357. (5) Cashore J. eta!. (1988) Lunar Planet. Sci. 19, 168. (6) K. 
Nishiizumi eta!. (1980) Earth Planet. Sci. Lett. SO. 156. (7) N. Takaoka 
eta!. (1981) Mem. Nat!. Inst. Polar Res. (Tokyo) 20, 264. 
Macrochondrules in Ordinary Chondrites: Constraints on Chondrule 
Forming Processes. M. K. Weisberg, 1•2 M. Prinz' and C. E. Nehru. 1·' 
1Brooklyn College (CUNY), Brooklyn, NY 11201. 2Amer. Museum 
Nat. Hist., NY, NY 10024 USA. 


Somewhere Over the Rainbow

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