ZIRCON UNDER PRESSURE: STRENGTH, TEXTURE AND MICROSTRUCTURE

Zircon, ZrSiO₄, is a well-known accessory mineral on the Earth, Mars and Moon that preserves information for geochronology study and age determination for terrestrial planets in the solar system. The deformation of zircon is not uncommon and it can be attributed to short-term shockwave event such as the impact of meteorite or to long term stress-strain effect such as tectonism. In addition, deformation and strength of zircon is strongly correlated to its crystal structure and existing environments such as pressure and temperature. In this study, strength and deformation microstructure of zircon were investigated up to 32 GPa at room temperature using a diamond anvil cell and in situ powder radial X-ray diffraction using a synchrotron source. The data were processed using the lattice strain theory and the run product was analyzed by EBSD method. X-ray diffraction results show a bulk modulus of K_oT = 203±13 at pressure below 11 GPa, close to previous estimates but greater than that of olivine. Zircon, though strong under hydrostatic pressure, is surprisingly sensitive to differential stress. The differential stress supported by zircon gently increases from 0.4 to 5.0 GPa at pressure to 32 GPa. Zir(200) is the weakest plane and [001] texture develops in the population at pressures as low as 1 GPa. The {112} plane is the strongest under compression and microtwins in {112} orientation were observed in run products, suggesting formed within the zircon stability field. Zircon above 18 GPa partially transformed to reidite (20% of grains) and both phases show pervasive crystal-plastic deformation but lack microtwins. The experimental data demonstrate the susceptibility of zircon to deformation at crustal and upper mantle pressures, a susceptibility expected to increase at natural temperatures in the lithosphere.