Samples of all available ureilites have been analyzed thermomagnetically. For three of the six (Dyalpur, Goalpara and Havero) evidence was found for only low-nickel metallic-iron as the magnetic component and the (saturation magnetization vs, temperature) curves were reversible. In the Novo Urei ureilite, magnetite in addition to low-nickel metallic-iron was indicated and again the Js-T curve was reversible. For the two badly weathered ureilites, Dingo Pup Donga and North Haig, indication was also found that both initial magnetite and low-nickel metallic-iron were present. However, the Js-T curves were somewhat irreversible and the final saturation magnetization was 20% and 50% greater than initially for North Haig and Dingo Pup Donga, respectively. This behavior is interpreted to be the result of magnetite production from a secondary iron oxide during the experiment

Herndon, J. M.

Larson, E. E.

Rowe, M. W.

Watson, D. E.

English

NASA Technical Reports Server

THERMOMAGNETIC ANALYSIS OF METEORITES, 4. UREILITES
M. W. Rowe and J. M. Herndon
Department of Chemistry
Texas A&M University
College Station, Texas (USA)
and
E. E. Larson
Cooperative Institute for Research in Environmental Sciences
University of Colorado/NOAA
Boulder, Colorado (USA)
and
D. E. Watson
U. S. Geological Survey
Boulder, Colorado (USA)
(N ASA -CR-1411-43) THEROMAAGNETIC ANALYSIS N75-146
OF. HETEORITES. ,4: .UREILITES (Texas A&M
Univ.) 13 p HC $3.25 CSCL 03B
3/ 050Unclas
G3/91.. 05059
https://ntrs.nasa.gov/search.jsp?R=19750006594 2020-03-23T00:27:58+00:00Z
Abstract - Samples of all available ureilites have been analyzed thermo-
magnetically. For three of the six (Dyalpur, Goalpara and Havero) we find
evidence for only low-nickel (. 2%) metallic-iron as the magnetic component
and the Js-T curves were reversible. In the Novo Urei ureilite, magnetite
in addition to low-nickel metallic-iron was indicated and again the Js-T
curve was reversible. For the two badly weathered ureilites, Dingo Pup
Donga and North Haig, indication was also found that both initial magnetite
and low-nickel metallic-iron were present. However, the Js-T curves were
somewhat irreversible and the final saturation magnetization was 20% and 50%
greater than initially for North Haig and Dingo Pup Donga, respectively.
This behavior is interpreted to be the result of magnetite production from
a secondary iron oxide during the experiment.
I. INTRODUCTION
In the first three papers of this series [1,2,3] we reported the
saturation magnetization vs. temperature (Js-T) analyses of all 38 of
the carbonaceous chondrites. This paper presents the results of similar
analyses of all six of the carbonaceous achondrites, the ureilites.
Although seven ureilites are known, one has been lost and is therefore not
available for study [4].
The achondrites in general are a chemically heterogeneous group of
meteorites classed together on the basis of their lack of chondrules, the
distinguishing feature of the chondrites. They are commonly more coarsely
crystallized than are the chondrites and appear more similar to terrestrial
rocks than do chondrites. In general achondrites are almost entirely lacking
in nickel-iron, the ureilites representing an exception to the rule. Thus
the ureilites form a unique group within the achondrites, being noteworthy
by the presence of carbon, of diamonds and appreciable nickel-iron.
The ureilites resemble both the olivine-hyperthene chondrites (on the
basis of their major elements) and the carbonaceous chondrites (on the basis
of chemistry especially with regard to carbon as well as petrologically).
Both Mueller [5] and Vdovykin [6] conclude that ureilites arise as the
product of shock recrystallization of carbonaceous chondrite material.
Wiik [7] argued that the ureilites were almost certainly not derived from any
other meteorite classes by the classic mechanism of differentiation; and
suggested that an alternative is that ureilites represent equilibrium conden-
sation products from the original cosmic nuclide mix of elements.
At one time the presence of diamonds in the ureilites was taken to
suggest that they must have originated deep within a parent body of lunar
size or greater [8,9]. However, there appears to be little doubt that the
ureilites have been heavily shocked [5,6,10,11] and the diamonds are now
2generally regarded to be of shock origin [10]. According to Anders [12]
and Wlotzka [13] there is little doubt that the carbonaceous material and
probably also the metal found within the veins of ureilites represents
foreign material introduced late in the history of the meteorite.
Whatever the detailed origin and history of the ureilites may be,
the presence of several weight per cent of carbon suggests some relation-
ship with the carbonaceous chondrites and so we now present thermo-
magnetic analyses of the ureilites following our similar analyses on the
carbonaceous chondrites [1-3].
The experimental technique utilized in this study was described earlier
[1,14] and will not be repeated here.
2. RESULTS AND DISCUSSION
In our studies of the thermomagnetic properties of the carbonaceous
chondrites we found that the Cl chondrites were characterized by containing
magnetite as the principal magnetic phase. Five of the 18 C2 and four of
the 13 C3 chondrites were similarly characterized. A second major grouping
with regard to magnetic characteristics of carbonaceous chondrites was occupied
by over half of the C2 and C3 chondrites. These were characterized most
prominently by the presence of a weakly magnetic substance (we think troilite)
which altered during the course of the experiment into magnetite. It was
found that the saturation magnetization was considerably larger at the end
of the experiment than observed initially, due to magnetite production.
Relatively few samples of the carbonaceous chondrites were found to contain
metallic nickel-iron, e.g., none of the Cl chondrites, five of the C2 chondrites,
five of the C3 chondrites and one of the two C4 chondrites.
3However the most persistent feature of the Js-T curve for the six
ureilites is the presence of low-nickel (< 2%) metallic-iron. Fig. la-c
sets forth the Js-T curves for the Dyalpur, Goalpara and Havero ureilites.
There is little evidence for any magnetic species other than the low-nickel
metallic-iron in these meteorites. There is a suggestion during the heating
portion of the Goalpara sample for a minor magnetite component (the inflection
point around 500-600*C), but it is absent during cooling. Basically, how-
ever, only low-nickel metallic-iron is indicated as a magnetic mineral.
The situation with respect to the thermomagnetic analysis of Novo Urei
(Fig. 2) is only slightly more complicated. There we see indication of a
substantial magnetite component accompanying the ever-present (in ureilites)
low-nickel metallic-iron. There is no evidence in either Fig. 1 or Fig. 2
for magnetite production during the course of the experiment.
The remaining two ureilites, Dingo Pup Donga and North Haig, are both
badly weathered samples as opposed to the other four which appear quite fresh
and unweathered. The Js-T curves of these two samples show indication of
initial magnetite, low-nickel metallic-iron and additional production of
magnetite during the course of the experiment. In our earlier work on the
carbonaceous chondrites, we attributed similar behavior to oxidation of triolite
to magnetite. However, Vdovykin [6] noted that both Dingo Pup Donga and
North Haig contain secondary oxides of iron, e.g. goethite (aFeOOH) and
limonite (FeOOH.n H20 Since the saturation magnetization of these oxides is
considerably lower than that of magnetite, we would expect a rise in satur-
ation magnetization if these secondary oxides are reduced to magnetite during
the course of the experiment. Since we maintain the oxygen fugacity in the
magnetite stability field, we would expect magnetite production from these
other iron oxides. At any rate the magnetite production raises the saturation
magnetization by only about 20% and 50% in the North Haig and Dingo Pup
Donga samples, respectively. This can be compared with the production
in the C2 and C3 chondrites in which magnetite production raised the satur-
ation magnetization by factors ranging from ~20% up to a factor of about 10,
commonly being a factor of 2-4. For comparison, Fig. 4a and b shows the
Js-T curves for iron powder run first under vacuum (-10 -5 torr) then under
stability conditions in our controlled atmosphere (in this case using only
8-1/2% H2 in N2). The behavior observed under vacuum conditions is obviously
unsatisfactory if one is dealing with a sample containing iron, especially
of small grain size such as found in ureilites and some C2 and C3 chondrites.
However, it is seen in Fig. 4b that the behavior under the controlled gas
system is much better. The slight decrease in the saturation moment on the
heating cycle between 400* and 7500C is probably due to a minor amount of
oxidation occurring even in this atmosphere. A stronger reducing atmosphere
(21% H2 in N2) has now been utilized and virtually coincident heating and
cooling paths were observed. The small amount of magnetite formed in Fig. 4b
during heating appears to have been reduced back to iron upon cooling. The
behavior in our atmosphere (especially with 21% H2 in N2) is far superior to
vacuum conditions and is certainly adequate for most purposes. Furthermore;
we have presented an extreme case, the finely divided powder presenting a very
large surface for possible oxidation. Better behavior might be expected
for meteorite materials run as whole pieces as is demonstrated by the data
shown in Fig. la-c, where the only magnetic component indicated was metallic-
iron of low nickel content and the curves are virtually coincident even when
the 8-1/2% H2 in N2 atmosphere was used.
A major advantage of our controlled atmosphere, i.e., maintaining stability
for samples containing both magnetite and iron, is demonstrated by the data
depicted in Fig. 2, the J -T curve for the Novo Urei ureilite. It can be
seen from this figure that two magnetic components are present. Upon heating
the saturation magnetization decreases rather abruptly at about 5800C as
the temperature rises above the Curie point of magnetite. Above that temp-
erature we observe a second component, metallic iron, which is indicated by
the Curie temperature of 770 0 C. This component is almost pure iron (s 2% Ni)
as indicated by the Curie temperature and lack of y c transition. (See
Fig. 5a in ref. [2] for an example of the y - a transition which occurred
in the Al Rais C2 chondrite). The most significant aspect of the Js-T curve
in Fig. 2 is demonstrated by the near coincidence of the heating and cooling
curves. This near coincidence attests to our ability to heat meteorite
samples (typically < 1 mg) to temperatures of -800°C without significantly
changing the oxidation state of the magnetite and metallic iron present. As
noted previously, the saturation magnetization of iron is greater than that
of magnetite. Thus, any change in the relative amount of iron and magnetite
present in the Novo Urei sample (due to oxidation or reduction) would have
caused the cooling curve to deviate significantly from the heating curve.
We have demonstrated here that, by maintaining the proper oxygen fugacity,
it is possible to heat carbonaceous meteorites containing magnetite, metallic
iron, or a combination of the two to temperatures as high as ~8000C without
significantly changing the oxidation state of those magnetic components.
From our samples of Dyalpur, Goalpara, HaverU or Novo Urei, we expect that
the Thellier technique could be readily applied for paleointensity estimates,
providing that the proper oxygen fugacity was maintained during heating.
ACKNOWLEDGEMENTS
This research was supported in part by the National Science Foundation
Grant GP-18716 and by the National Aeronautics and Space Administration
Grants Nos. NGR-06-003-181 and NGR-44-001-152. For supplying samples we
6are grateful to the following: Dr. R. Hutchison, British Museum of
Natural History, London; Dr. S. V. P. Iyengar, Geological Survey of India,
Calcutta; Dr. E. Olsen, Chicago Museum of Natural History; Dr. C. Pearson,
Western Australia Museum, Perth; and Dr. H. Papunen, University of Turku,
Finland.
REFERENCES
[1] E. E. Larson, D. E. Watson, J. M. Herndon and M. W. Rowe, Earth Planet.
Sci. Letters 21 (1974) 345.
[2] D. E. Watson, E. E. Larson, J. M. Herndon and M. W. Rowe, Earth Planet.
Sci. Letters, submitted (1974).
[3] J. M. Herndon, M. W. Rowe, E. E. Larson and D. E. Watson, Earth Planet.
Sci. Letters, submitted (1975).
[4] U. Marvin and J. Wood, Meteoritics 7 (1972) 601.
[5] G. Mueller, Meteorite Research, (editor P. Millman), D. Reidel, Holland
(1969).
[6] G. P. Vdovykin, Space Sci. Rev. 10 (1970) 483.
[7] H. B. Wiik, Meteoritics 7 (1972) 553.
[8] H. C. Urey, Astrophys. J. 124 (1956) 623.
[9] A. E. Ringwood, Geochim. Cosmochim. Acta 24 (1961) 83.
[10] M. E. Lipschutz and E. Anders, Geochim. Cosmochim. Acta 24 (1961) 83.
[Ill B. Mason, Meteorites, J. Wiley and Sons, New York (1962).
[12] E. Anders, Space Sci. Rev. 3 (1964) 583.
[13] F. Wltozka, Meteoritics 7 (1972) 591.
[14] E. E. Larson, R. P. Hoblitt and D. E. Watson, Geophys. J., in press (1974).
1 DYALPUR GOALPARA
Js(T)
JO
0 00 200 400 600 800 0 200 400 600 800
HAVERO
Js(T)
Jo
0 200 400 600 800
TEMPERATURE, 0C
Fig. I. Saturation magnetization vs. temperature (Js-T) curves for the
Dyalpur, Goalpara, and Haver6 ureilites. These curves are indicative
of the presence of low-nickel (< 2%) metallic-iron and no other
magnetic component.
NOVO UREI
Js(T)
Jo
0 200 400 600 800
TEMPERATURE, 0C
Fig. 2. Saturation magnetization vs. temperature (Js-T) curve for the Novo-
Urei ureilite. This curve indicates substantial contribution
from both magnetite and low-nickel (< 2%) metallic-iron as the
only magnetic minerals of any consequence in Novo-Urei.
DINGO NORTH HAIG
DINGO PUP
DONGA
Js(T) '
Jo
0 200 400 600 800 0 200 400 600 800
TEMPERATURE, OC TEMPERATURE, OC
Fig. 3. Saturation magnetization vs. temperature (Js-T) curves for the
two badly weathered ureilites, Dingo Pup Donga and North Haig.
These curves indicate a substantial contribution from both
initial magnetite and low-nickel (. 2%) metallic-iron. In addition
the presence of some substance, probably troilite, which alters
into magnetite during the course of the experiment is indicated
as evidenced by the increased saturation magnetization observed
upon cooling. This is similar to behavior noted in many C2 and
C3 chondrites [2,3].
IRON POWDER
(vacuum)
Js(T)
J, , , , L " "" 80
0 200 400 600 800
TEMPERATURE, OC
IRON POWDER
1-
Js(T)
Jo
0 200 400 600 800
TEMPERATURE, OC
Fig. 4. Saturation magnetization vs. temperature (Js-T) curves for iron
powder run under vacuum condition compared to that run under
controlled oxygen fugacity.. It is obvious that superior behavior
is found when the oxygen fugacity is controlled.


Thermomagnetic analysis of meterorites. 4: Ureilites

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