HR: 0800h
AN: P41A-0216    [Abstracts]
TI: Petrography and Mineralogy of a Unique Spherical CAI in the Murchison (CM2) meteorite
AU: * Kudo, K
EM: kudokntr@ganko.tohoku.ac.jp
AF: Department of Earth and Planetary material sciences, Graduate School of Science, Tohoku University, 6-3 Aoba Aramaki Asa Aoba-ku, Sendai, 980-8578, Japan
AU: Fujimaki, H
EM: h-fujimaki@mail.tains.tohoku.ac.jp
AF: Department of Earth and Planetary material sciences, Graduate School of Science, Tohoku University, 6-3 Aoba Aramaki Asa Aoba-ku, Sendai, 980-8578, Japan
AB: Chondritic meteorite consist of three major components: refractory CAIs, less refractory ferromagnesian silicate spherules called chondrules, and a fine-grained matrix. It is generally believed that CAIs and chondrules formed in the solar nebula (a disk of dust and gas surrounding the proto-Sun) by high-temperature processes that included condensation, evaporation, and for all chondrules and many CAIs, subsequent melting during multiple brief heating episodes (1). Calcium-aluminum-rich inclusions (CAIs) from chondritic meteorites are widely considered to represent the first materials that formed in the solar nebula (2). I discovered for the first time a unique spherical CAI, which consist of spinel, diopside, calcite, and PCP in the Murchison (CM2) meteorite. The unique spherical CAI seems to be surrounded amoeboidal materials. Its size is approximately 1.5mm and this is large when comparing with the average size of chondrules in the all chondrites. Its shape is like chondrules, but fusion organization which is characteristic of chondrules is denied by absence of the glass and mesostasis. The whole area of the unique spherical CAI , it can see abundant void spaces. The unique spherical CAI never melts after the formation. Also, bulk composition is similar to Ca-Al-rich chondrules discovered in ordinary chondrites, or CAI of CV carbonaceous chondrite. Comparison with normal CAI, its may be generated from different formation processes. The inside of the unique spherical CAI, spinel, diopside, calcite and PCP coexist each other. Replacement is not seen. Therefore, the unique CAI is thought to be mixture of high temperature condensation minerals and low temperature materials as well as PCP in the early solar nebula. A recent study suggests that carbonate may form as a result of non-equilibrium condensation in the presence of water vapor in circumstellar environments (3). The textual occurrences of calcite in the unique spherical CAI are clearly compatible with such a scenario. References 1. MacPherson G. J. et al., Meteorites and the Early Solar System, 746-808 (1988) 2. Allegre C. J. et al., Geochim. et Cosmochim. Acta 59, 1445-1456 (1995) 3. Toppani A. et al., Nature 437, 1121-1124 (2005)
DE: 1028 Composition of meteorites (3662, 6240)
DE: 3662 Meteorite mineralogy and petrology (1028, 6240)
DE: 6240 Meteorites and tektites (1028, 3662)
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting