Petrology and Geochemistry of Carbonaceous Chondrites
Chondrites, a type of meteorite, are the most primitive samples
available with which to study the earliest history of the solar system.
Since the Earth evolved from similar materials, we are really studying
the earliest history of the Earth. There are three major chondritic
(chondrule-bearing) groups - the carbonaceous, the ordinary and the
enstatite chondrites. The carbonaceous or C chondrites are broken up
into six subgroups, the CI (Ivuna-type), CM (Murchison-type), CV
(Vigarano type), CO (Ornans-type), CR (Renazzo-type)
and CK (Karroonda-type). For each group, we characterize the
chondrules, the fine-grained matrix, the metal and sulfides, the
carbonates, the dark inclusions, and the aqueous alteration minerals.
We also collaborate with other research groups to get transmission
electron microscopy (TEM) data and geochemical data such as oxygen,
nitrogen and carbon isotopes. All of these data allow us to attempt to
determine the history recorded in these rocks: for example, we
distinguish those features which formed in the solar nebula from those
which formed on the parent body to which these materials accreted. We
interpret the history recorded in the dark inclusions, and compare them
with the matrix and chondrule rims. We try to determine the conditions
and the location of the aqueous alteration, and whether there has been
dehydration after aqueous alteration in those subgroups which are
anyhydrous. The history that we uncover is used in building models of
the processes and conditions in the solar nebula.
References
- Johnson, C.A. and Prinz, M. (1993) Carbonate compositions in CM and
CI chondrites and implications for aqueous alteration. Geochim.
Cosmochim. Acta 57, 2843-2852.
- Shaoxing, H., Jie, L., Prinz, M., Weisberg, M.K., Benoit,
P.H. and Sears, D.W.G. (1996) Chondrules: Their diversity and the role
of open-system processes during their formation. Icarus 122, 316-346.
- Weisberg, M.K., Prinz, M., Clayton, R.N. and Mayeda, T.K.
(1993) The CR2 (Renazzo-type) carbonaceous chondrites group and its
implications. Geochim. Cosmochim. Acta 57, 1567-1586.
- Weisberg, M.K., Prinz, M., Clayton, R.N., Mayeda, T.K.,
Grady, M.M. and Pillinger, C.T. (1995) The CR chondrite clan. Proc.
NIPR Symp. Antarct. Meteorites 8, 11-32.
- Weisberg, M.K. and Prinz, M. (1996) Agglomeratic
chondrules: Implications for the nature of chondrule precursors and
chondrule formation by incomplete melting, p. 119-127. Proc. Conf.,
Chondrules and the Protoplanetary Disk, Cambrige Univ. Press, 346 p.
Museum staff working on this project -
M. Prinz,
M.K. Weisberg.
