High P-T Single-Crystal Elasticity of Zircon by Brillouin Spectroscopy

Understanding the natural petrologic and tectonic processes, such as slab subduction, requires accurate determination of the metamorphic pressure (P) and temperature (T) conditions of the exhumed rocks. Recent development of elastic thermobarometry based on the difference between the thermo-elastic properties of mineral inclusions and their hosts allows constraining the formation P-T conditions of the inclusion/host system without assuming thermodynamic equilibrium. However, the reliability of elastic thermobarometry heavily depends on the accurate determination of the high P-T single-crystal elastic properties of relevant minerals. In this study, we performed the first high P-T single-crystal elasticity measurements of zircon, which is one of the most common inclusion/host minerals in metamorphic rocks, using Brillouin spectroscopy at high Ps up to 7 GPa and high Ts up to 700 K. The single-crystal elastic properties of zircon at ambient conditions were determined as: ρ₀ = 4.6674(4) g/cm³, Ks = 231(3) GPa, G = 108(11) GPa, C₁₁ = 428(2) GPa, C₃₃ = 484(3) GPa, C₄₄ = 113.5(8) GPa, C₆₆ = 46.9(8) GPa, C₁₂ = 75(2) GPa, and C₁₃ = 151(1) GPa. We also obtained the P and T derivatives of the elastic moduli as ∂Ks₀/∂P = 5.0(2), ∂Ks₀/∂T = −0.019(2) GPa/K, ∂G₀/∂P = 0.73(6), ∂G₀/∂T = −0.011(1) GPa/K. Compared with other common rock forming minerals (e.g., quartz, pyroxene, olivine), zircon is extremely incompressible (high Ks) and its stiffness (Ks) has relatively small T dependence, making it an ideal mineral for the application of elastic thermobarometry. Finally, we utilized the high P-T single-crystal elasticity data of zircon and garnet to evaluate the potential applications of zircon-garnet in elastic thermobarometry via elastic modelling.