Abstract

The compression behavior of Al-bearing stishovite was investigated by powder X-ray diffraction up to 40 GPa with the BL13A beamline at the Photon Factory (KEK, Japan). A reliable equation of state for stishovite was obtained using a diamond anvil cell coupled with a yttrium-aluminum-garnet (YAG) laser-heating. A sample containing 2.1 wt% Al2O3 was heated using a YAG laser at each pressure increment to relax deviatoric stress. X-ray diffraction measurements were carried out at 300 K using the angle-dispersive technique. A least squares refinement of the data yielded equation of state parameters where the bulk modulus Ko = 282 (±2) GPa when the first pressure derivative of the bulk modulus Ko′ was fixed at 4. The effect of Al is to decrease slightly the bulk modulus of stishovite and increase the density of the subducted oceanic crust. The enhanced compressibility of Al-bearing stishovite certainly has geophysical and geochemical implications for the fate of the subducted slab, as this mineral is the main constituent of subducted mid-oceanic ridge basalt (MORB) in the Earth’s mantle.

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