ORIGIN AND METAMORPHIC REDISTRIBUTION OF SILICON, CHROMIUM, AND PHOSPHORUS IN THE METAL OF CHONDRITES

Chromium, silicon, and phosphorus concentrations of 0.1 to 1 percent b y weight are common in metal grains in the least metamorphosed ordinar y and carbonaceous chondrites. These concentrations are fairly uniform within single chondrules (but different from chondrule to chondrule) and are inversely correlated with the fayalite concentrations of the c hondrule olivines. This relation shows that these chromium, silicon, a nd phosphorus concentrations could not have been established by conden sation or equilibration in the solar nebula but are the result of meta l-silicate equilibration within chondrules. Two generations of inclusi ons made by the exsolution of those elements have been identified: One formed during chondrule cooling and the other formed during metamorph ism. The distribution and composition of the latter in type 3 to type 5 chondrites are consistent with increasing metamorphism relative to t ype 2 and type 3.0 material.