A Study Of the Petrography, phase Chemistry, Volatile Inclusions And Intrinsic Oxygen Fugacity Of Composite Group II Ultramafic Xenoliths From San Carlos Arizona

Abstract

Composite ultramafic xenoliths were collected at Peridot Mesa, San Carlos, Arizona. These nodules were analyzed petrographically, by electron microprobe, and for intrinsic oxygen fugacity (IOF). Textures proved to be transitional between those of igneous and those of metamorphic petrogenetic environments. Phase chemistry interpretations were not totally consistent with either igneous or metamorphic models of formation. IOF data could not be used to unravel equilibrium relationships between solid phases, but were overprinted by reactions with volatiles contained in the minerals, chiefly CO2. These results indicate that the nodules were derived from a complex upper-mantle source region characterized by multi-phase igneous events with important intervening, probably sub-solidus, i.e. metamorphic, reactions between phases.