GEOCHEMICAL AND PETROGRAPHIC STUDIES OF OLDHAMITE, DIOPSIDE, AND ROEDDERITE IN ENSTATITE METEORITES

In Qingzhen (EH3), oldhamite contains numerous types of inclusions and intergrows with other phases; but in equilibrated enstatite chondrite s and aubrites, it usually occurs as individual grains. I suggest that oldhamite in unequilibrated enstatite chondrites (UECs) crystallized from a melt, probably during chondrule formation. Subsequent thermal m etamorphism on the parent bodies further modified the oldhamite occurr ences in enstatite chondrites. This suggestion is consistent with the results of melting experiments on UECs and aubrites and with the volat ile element enrichments in this mineral. I analyzed minor and trace el ement abundances in diopside from two aubrites. These data and petrogr aphic observations suggest that diopside formed by igneous crystalliza tion. I report the first known occurrence of roedderite in an aubrite and its major, minor, and trace element concentrations. This mineral i s rich in alkalis but is depleted in siderophile and refractory lithop hile elements. A negative Sm anomaly was noted in albite from equilibr ated enstatite chondrites and aubrites.