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Mineralogical effects on the detectability of the postperovskite boundary

  1. Vitali Prakapenkab
  1. aDepartment of Earth, Atmospheric, and Planetary Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139; and
  2. bCenter for Advanced Radiation Sources, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637
  1. Edited by Russell J. Hemley, Carnegie Institution of Washington, Washington, DC, and approved December 23, 2011 (received for review June 14, 2011)

  1. Fig. 1.

    X-ray diffraction patterns of (AC) Ca-free pyrolitic, (DF) San Carlos olivine, and (GI) MORB compositions measured at high pressure and temperature. The major peaks are indicated for Pv (blue circles), pPv (red circles), Fp (open circles), CaCl2-type silica (open square), α-PbO2-type silica (square with cross), CF phase (open up triangle), Ca-Pv (open down triangle), the gold internal pressure calibrant (Au), rhenium gasket (Re), argon or neon pressure medium (Ar or Ne), and nitrogen (N). A few unidentified lines are noted by “?” (Supporting Information). Backgrounds were subtracted. The diffraction intensities are plotted as a function of inverse interplanar distance.

  2. Fig. 2.

    The pressure-temperature conditions for the stability of Pv, Pv?+?pPv, and pPv in (A) calcium-free pyrolitic, (B) San Carlos olivine, and (C) MORB compositions. The right- and left-pointing triangles represent data points measured along the forward and reverse paths, respectively, and the large circles represent the data points obtained directly from heating of amorphous starting materials. Blue, green, and red triangles represent observations of Pv, Pv?+?pPv, and pPv, respectively. The solid black lines are the phase boundaries determined from our data. The Clapeyron slope of the boundary was obtained from Catalli et al. (4) (Supporting Information). The black symbols are the data points from previous studies in related compositions (6, 18, 23). Error bars are 1σ uncertainties.

  3. Fig. 3.

    Depth and thickness of the Pv?-?pPv boundary in binary and ternary systems reported in (A) experimental [C09 (4), M04 (6), A10 (5), T05 (7), N07 (8)] (Supporting Information) and (B) computational [A05 (9), O05 (10), M05 (11), C05 (12), Z06 (13), T08 (22), C08 (14)] studies, and in (C) multiphase, multicomponent systems reported in this study (SCO: San Carlos olivine). The locations of the bars indicate the depth range of mixed phase regions. The experimental results are plotted for a temperature of 2,500?K. The computational results are plotted with respect to their estimates on the transition pressure for MgSiO3. In (C), the dark colored regions show the lower bound for the thickness whereas the dark and light regions together represent an upper bound obtained from Fig.?2. The error bar in (C) represents the uncertainty in transition depth from the pressure scale (1σ?=??±?5?GPa). The uncertainty in the thickness should be smaller, because it relies on difference in pressure within the same scale.

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