High Pressure and High Temperature Study of Magnesiochromite and Its Geophysical Implications

Author

N M Tauhid Belal Khan, The University of Western OntarioFollow

Degree

Master of Science

Program

Geophysics

Supervisor

Dr. Sean Shieh

Abstract

Magnesiochromite (MgCr₂O₄) is commonly found in the Earth’s crust, upper mantle, meteorites, and possibly in lunar crust. Synchrotron X-ray diffraction measurements of MgCr₂O₄ using double-sided laser heating diamond anvil cell showed the dissociation of MgCr₂O₄ to Cr₂O₃+MgO at ~15 GPa and to Mg₂Cr₂O₅+Cr₂O₃ below and above ~1500 K, respectively. At above 20 GPa, only a single phase CaTi₂O₄-type structure of MgCr₂O₄ was observed at 1400-2000 K. Fitting the pressure-volume data of CaTi₂O₄ type structure of MgCr₂O₄ with Birch-Murnaghan equation of state yields volume at ambient condition (V₀) = 264.4(8) ų, bulk modulus (K₀) = 185.4(4) GPa, and pressure derivative of the bulk modulus (K₀’) = 4; and for CaTi₂O₄ type structure of natural chromite: V₀ = 261(1) ų, K₀ = 175.4(2) GPa, K₀’ = 4, and mLd-type Mg₂Cr₂O₅ yields: V₀ = 338.9(8) ų, K₀ = 186.5(6) GPa, K₀’ = 4. Obtained phase diagram and bulk modulus data provide important information to better understand the structure and dynamics of the deep earth.

Recommended Citation

Khan, N M Tauhid Belal, "High Pressure and High Temperature Study of Magnesiochromite and Its Geophysical Implications" (2015). Electronic Thesis and Dissertation Repository. 2902.
https://ir.lib.uwo.ca/etd/2902