Formation of chondrules in a thick dynamic regolith

Details Formation of chondrules in a thick dynamic regolith Formation of chondrules in a thick dynamic regolith

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.531s&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 531

Computer Science

Chondrites, Chondrule, Gas-Solid Interactions, Meteoritic Microstructures, Regolith, Asteroids, Charged Particles, Meteoritic Composition, Particle Tracks, Volatility

Scientific paper

Chondrule formulation resulted in the formation of four more-or-less discrete chondrule groups: the A1 chondrules that suffered considerable volatile loss and reduction during their formation and subsequently cooled slowly enough that the phenocrysts and melt remained at equilibrium; group A2, which are closely related to group A1 but for which volatilization caused Fe loss (but not Si loss) so that pyroxene became the dominant silicate; group B1, in which volatile loss and reduction were minimal but supercooling occurred during subsequent crystallization; and group A5, in which volatile loss and reduction did not occur and equilibrium was maintained between phenocrysts and melt during cooling. We suggest that a scenario for the formation of chondrules that is consistent with this variety of properties is that they are the product of impact on a thick dusty regolith of an accreting asteroid on which evaporated volatiles caused fluidization. This scenario explains why chondrules have some properties consistent with a nebula origin but avoids the difficulties associated with assuming nebula pressures and cosmic compositions for the gas. In such an environment, reduction and volatile loss would occur as a result of the most intense impacts, while a greater number of less-intense events would produce an environment with a high dust to gas ratio and with the properties of the group B chondrules. Such an environment would also permit size sorting displayed by the chondrite groups and explain prompt assembly and complementary compositions of components, high frequency of compound chondrules, lack of charged-particle tracks in chondrules, and the high frequency of occurrence of fine-grained rims on group A chondrules relative to group B chondrules.

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