Track and thermoluminescence parameters in chondrules from the Kainsaz CO 3.2 chondrite have been studied. Obtained results elucidate their individual shock-thermal history and the early pre-accretion stage of the meteorite parent body formation

Kalinina, G. V.

Kashkarov, L. L.

English

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"''9N 4-1" 296
DIFFERENT RADIATION AND METAMORPHIC HISTORY
OF THE KAINSAZ CO 3.2 CHONDRULES
Kashkarov L.L., Kalinina G.V.V.I.Vernadsky Institute of
Geochem. and Analyt. Chem., Russian Acad. Science, Moscow, Russia
Track and thermoluminescence parameters in chondrules from
the Kainsaz CO 3.2 chondrite have been studied. Obtained results
indicate on their individual shock-thermal history on the early
pre-accretion stage of the meteorite parent body formation.
The pro-accretion stage of the chondrite formation is ane of
the mostly important in the history of these meteorites. A wide
variaty of the last years investigations (for example [1-3])
indicate that in this early stage not only the chondrules and
the mineral grain aglomeration processes ocoured, but the
principal metamorphic processes are related to this period. It
is possible that the last processes can be due to the local
cases of the shock-thermal reworking of the initial chondrite
matter. Mostly significant in so doing is proved that during the
whole subsequent history of the chondrite existence the thermal
conditions were not so critical that can to result in the total
flattening of the quite of a number of parameters which indicate
the heterogeneous character of the chondrite matter. To these
parameters in particular track and thermoluminescence (TL)
characteristics are related. The investigations of the identity
and difference of these parameters for the ordinary and the
carbonaceous chondrites acquire a great importance at present [4].
The aim of this work is the study of the radiation-thermal
history of the carbonaceous chondrite matter with help of the
complex measuring of the nuclear track and TL-parameters in the
chondrules of the low-metamorphic chondrite Kainsaz CO 3.2. The
chief objective in this case was the elucidation of the
essential siqns which give possibility to consider the radiation
and thermal conditions existed at the pro-accretion stage of
these meteorite parent body formation.
The track results obtained for the about 500 olivine
grains (higher than 30 _m in size) which were separated from 98
chondrules of the microgranular and porphiritic types are the
following: l)The total spread of the track density values ( _ )
is in the interval of three orders of magnitude (O.O03-2)lOacm -2
2)The track density due to the fission fragments of the uranium
nuclei, concentration of which for the searched olivine
crystals is in the interval (0.2-2.3) I0 -s g/g, is not higher
than 5.10acm -2 . 3)The part of the crystals with p _ 105cm -2
amounts to smaller than i0_. 4)Only in two crystals _ _ lOScm -2
was obsered. 5)The gradient 0 from the surface to inslde of the
individual grairls was detected in l_ine cases. These track
results indicate, that in the part of the carbonaceous chondrite
Kainsaz matter the traces of the early pre-accretion irradiation
were storaged. The fraction of this matter as compared to the
total crystal number under investigation is equal to a few
percentages and the integral irradiation dose is smaller by 2-3
orders of magnitude than for brecciated ordinary chondrites
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DIFFERENT RADIATION... Kashkarov L.L. et al.
matter, which was influenced by the intensive irradiation during
the regolith stage of their parent bodies formation.
The results of TL-investigations for the 50 individual
chondrules of the Kainsaz CO 3.2 in relation with the same
TL-parameters for chondrules of the Dhajala H 3.8 chondrite are
presented in Figure la,b. The character of the relationship
between TL-parameters - FWHM and the temperature peak maximum
T_eak - indicate that the chondrules under investigation
represent at least two different groups: for the first group the
both TL-parameters are in the very narrow interval (FWHM about
(27+7)oc and Tpeak (150+12)°C); however the second ehondrule
group is characterised by the directly proportional relationship
of these TL-parameters. In this ease FWHM values are increased
by more then two-fold that can be due to different dislocations
and electron trap level concentrations depending on the
different shock-thermal local events.
A correlation between track and TL-parameters for the
investigated chondrules was not observed that is in accordance
with a concept of local character of the relatively weak
thermal processes,presented in the pre-accretion solar
conditions.
References. l.Fredriksson K. (1983) - Chondrules and
origins ed. by E.A.King, Houston,44. 2.Kurat G. (1988)
Trans. R. Soc.Lond., A325, 459-482. 3.Ninagawa K. et al.
- Proc. NIPR Symp. Antarct. Meteorites, 4, 344-351. 4.
D.W.G. et al. (1991) - Ibid, 319-343.
shock-
nebula
their
-Phil.
(1991)
Sears
0 (D
0
I
Fig.l. TL-parameters FWHM and Tpeak relations in the individual
chondrules for the Kainsaz CO 3.2 (a) and Dhajala H 3.8
(b) chondrites.


Different radiation and metamorphic history of the Kainsaz CO 3.2 chondrules

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