Deformation of Zircon Under High Pressure

English Abstract:

Zircon (ZrSiO₄) is a strong and refractory mineral and can retain trace elements such as U, Th and Pb for age determination and evolution of early Earth. Isotopic data obtained from zircon can provide insightful information about evolution of crust and mantle differentiation. Moreover, zircon can be used as an indicator for impact deformations. It is believed that zircon age determination may correlate with its microstructures. Deformation of zircon can affect diffusion and thus result in uncertainties in age determination. Therefore, deformation study of zircon may have significant implications for the dynamics and evolution of planets. Study of zircon under high pressure can help us to understand mechanical and elastic properties of zircon and determine the nature of deformations at mantle conditions.

Angle-dispersive X-ray diffraction in a radial geometry using a diamond anvil cell was performed at beamline X17C, National Synchrotron Light Source, Brookhaven National Laboratory. Our results showed that zircon is sensitive to stress and weak deformation was observed even at 1 GPa. Ratios of differential stress to shear modulus (t/G) are in the range of 0.002- 0.008 at pressure to 30 GPa. Differential stress supported by zircon showed that (200) is the weakest plane and could be responsible for the onset of deformation. Zircon to reidite transformation was found at above 18 GPa, which is slightly lower than previous studies. Our results suggested shear strength may play a key role for the transition. Our volume data fitted to Birch-Murnaghan equation of state yielded a bulk modulus of 270.03±4.6 GPa (K₀=4), in broad agreement with previous reports. Weak texture in (100) was observed at low pressure and became more profound with pressure. At pressure above 11-13 GPa, (100) texture rotated towards to (111) due to the applied stress.