Ni in chrome pyrope garnets: a new geothermometer

Proton microprobe analyses of the minerals in garnet-peridotite xenoliths from kimberlites show that the partitioning of Ni between chrome pyrope garnet and olivine is strongly temperature(T)-dependent. The range of Ni contents in olivines is small relative to that in the analyzed garnets; a geothermometer therefore can be derived, based only on the Ni content of garnet. This allows estimation of T for single Cr-pyrope grains, such as the inclusions in diamonds, if these can be assumed to have equilibrated with olivine.