We have determined the equation of state of a hexagonal Al-rich type NAL phase Σ2.00[Al4.98Fe0.10Ti0.05 Si0.88]Σ6.01O12, an aluminum host mineral that is likely to occur in subducted oceanic crusts (mid-oceanic ridge basaltic (MORB)) in the Earth's lower mantle. Angle-dispersive X-ray powder diffraction experiments were conducted up to 36 GPa at room temperature at the BL04-B2 at Spring-8. Fitting a third-order Birch-Murnaghan equation of state to the data gives a bulk modulus of K0 = 214 (±2) GPa with K′0 = 3 (±0.1), a volume V0 = 184.55(6) Å3 and a zero-pressure density of ρ0 = 4 g/cm3. When K′0 is fixed at 4, the value of K0 = 202.3 (±0.9) GPa. These values are comparable to those for similar anhydrous hexagonal aluminous phases reported previously by Ono et al. [Phys. Chem. Minerals 29 (2002a) 527]. The density of NAL phase is lower than that of other minerals (excluding the CF phase) co-existing in the subducted oceanic crust, such as Mg-perovskite, Ca-perovskite and stishovite. We find that the elastic properties of the hexagonal Al-rich phase do not change despite substantial variations in Si, Al, Fe, Mg, Na and K content in the NAL chemical composition.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Physics and Astronomy (miscellaneous)
- Space and Planetary Science