METAL-SILICATE FRACTIONATION IN CHONDRITIC METEORITES: EXPERIMENTS UNDER

Unequilibrated chondrites consist of three major components, matrix, chondrules, and metal/sulfide grains. Chondrules and metal/sulfide grains exhibit re-stricted size distributions within major chondrite groups, a phenomenon referred to as fisize sortingfl [1], with average sizes ranging enough to serve as a guide to meteorite classification in some cases [2]. The process responsible for the fisortingfl of chondrules and metal grains is largely unknown. The only major con-straints are the average sizes, and the difference in average sizes of chondrules and grains and the composition of the materials. Possible processes can be divided into two major classes: Processes occurring in space (or the early solar neb-ula), and processes occurring on asteroidal bodies after ac-cretion. Within finebularfl processes, some attribute re-stricted size distributions to restrictions in the chondrule and metal formation process, and others attribute them to mag-netic separation or velocity-based separation [3]. Post-accretionary processes have attributed sorting to passage through an early fiatmospherefl, or to fluidization on de-gassing asteroidal bodies [4, 5]. The minimum gas velocity to fluidize a bed of particles of given grain diameter (