Oxygen isotope partitioning among the minerals in igneous and metamorphic rocks

Abstract

Using data on naturally occurring oxygen isotope fractionation among coexisting minerals in igneous and metamorphic rocks and previously derived relations, the authors deduce expressions for the temperature dependence of the isotopic disproportionation among the minerals quartz, feldspar, pyroxene, olivine, garnet, muscovite, biotite, amphibole, ilmenite, and magnetite. The expressions are only valid at temperatures greater than about 500°C. Oxygen isotope analyses on separated minerals (quartz, feldspar, pyroxene, olivine, garnet, muscovite, biotite, amphibole, ilmenite, magnetite) published prior to 1974 are reviewed and listed. The great majority of igneous and metamorphic rock samples for which three or more coexisting minerals have been analyzed separately has conserved a state of oxygen isotopic exchange equilibrium. Retrograde effects are common in plutonic and acidic volcanic rocks.