First experimental evaluation of zircon-in-garnet elastic thermobarometry at high pressures

Zircon inclusions in garnet (ZiG) can be used as an elastic thermobarometer to estimate the pressure-temperature (P-T) conditions of geologic processes. Although this method is being increasingly applied as a thermometer to natural samples, experimental evaluation of ZiG is limited and has not been investigated at geologically relevant pressures. We present the first high-pressure assessment of the reliability of ZiG thermobarometry by crystallizing almandine with zircon inclusions in piston-cylinder experiments between 700−900 °C and 2.0−3.0 GPa. Zircons entrapped in experiments at >2.0 GPa yield residual inclusion pressures within 1σ of predicted values and yield entrapment temperatures within 17−30 °C of experimental T. Zircon inclusions in experiments performed at 2.0 GPa yield average inclusion pressures that are ∼0.09 GPa higher than predicted values and therefore yield entrapment temperatures 65−73 °C higher than the experimental T. Evaluation of inclusion pressure trends shows that ZiG host-inclusion systems did not undergo non-elastic deformation during experimental exhumation, confirming that ZiG elastic thermobarometry can accurately record P-T conditions of garnet crystallization so long as zircon inclusions do not go into tension post-entrapment. Our high-pressure experiments suggest that the ZiG host-inclusion system may be applicable to a variety of geologic settings and processes, such as subduction zone metamorphism, partial melting, and contact metamorphism.