A RECALIBRATION OF THE GARNET-OLIVINE GEOTHERMOMETER AND A NEW GEOBAROMETER FOR GARNET PERIDOTITES AND GARNET-OLIVINE-PLAGIOCLASE-BEARING GRANULITES

Abstract

The garnet‐olivine Fe‐Mg exchange geothermometer and the garnet‐olivine‐plagioclase geobarometer have been simultaneously calibrated using reversed experimental data based on the model reactions image and image between 900 and 1500 °C at 9.1–95.0 kbar and between 4.7 and 7.0 kbar at 750–1050 °C, respectively. The resulting garnet‐olivine thermometer reproduces experimental temperatures mostly within ±75 °C and the garnet‐olivine‐plagioclase barometer reproduces experimental pressures well within ±0.19 kbar. These new thermobarometers use the same garnet and olivine activity models and are thermodynamically consistent. Application of these thermobarometers to garnet peridotites from mantle xenoliths, orogenic garnet peridotites over the world and the Adirondack olivine‐bearing metagabbros yielded reasonable P–T results. The present garnet‐olivine thermometer can be used to measure medium‐high‐grade to ultrahigh‐grade, low‐pressure to ultrahigh–high‐pressure garnet peridotites and metagabbros, whereas the garnet‐olivine‐plagioclase barometer has limited application to garnet‐olivine‐plagioclase‐bearing granulites.