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					       Pressure-Temperature Stability Studies of Talc and 10-Å phase using x-ray
                                 Arianna E.                  Gleason 1,                Martin             Kunz 1,        Stephen   Parry 2,   Alison   Pawley 2,                      and Simon M.                                            Clark 1,2.

                                 1Advanced           Light Source, Lawrence-Berkeley National Laboratory, MS 4R 0230, 1 Cyclotron Rd, Berkeley CA 94720
                                 2School        of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK.

                                                                                                                                                                                                Experimental Setup
                                                                                                                                                  -ALS Beamlines 12.2.2 and 11.3.1;
     The pressure-temperature phase boundary for talc plus water to 10-Å
                                                                                                                                                  probed with energies 20 to 30 keV
   phase conversion has been determined. Our data suggest that 10-Å phase
        may form at room temperature while at elevated pressures. X-ray                                                                           -Diffraction patterns acquired using
                                                                                                                                                  MAR345 image plate and Bruker CCD
         diffraction measurements of natural talc plus water at combined
    temperatures of 27oC – 450oC and pressures of 0-15 GPa were made at                                                                           -Resistively heated, membrane driven
       the Advanced Light Source beamlines 12.2.2 and 11.3.1. Elevated                                                                            DAC was used to reach P and T
      temperatures and pressures were achieved with a resistively heated,                                                                         -contained in gasket: natural talc +
     membrane driven diamond-anvil cell. The data were modeled using a                                                                            water + gold (pressure calibrant)                                                                                         Diamond-anvil cell [DAC] cylinder with heater and gasket
   monoclinic unit cell. Our data and proposed phase diagram are presented.
                                                                                                                                                                                                                        Data Analysis
                                                                                                                                                                                                                                                   Isotherms: we note the pressure range where the 002 peak discontinuity occurs.
                                                                                                                                       Lattice parameters for each phase (talc and gold)                                                          „Up‟ is compression of the DAC and „down‟ is decompression. The „down‟ points
                                                                                                                                        were determined using Le Bail whole pattern                                                                are not necessarily considered due to hysteresis. Straight lines drawn are only a
                                                           Introduction                                                                      refinement with the GSAS program.                                                                        o
                                                                                                                                                                                                                                                                                  guide for the eye.
                                                                                                                                                                                                                                                                                                                                                                            200 C: talc 002 vs. pressure
                                                                                                                                                                                                                                                  100 C: talc 002 vs. pressure

    Talc, Mg3Si4O10(OH)2, is a sheet silicate commonly                                                                                                   Basal spacing talc                                           9.3
                                                                                                                                                        peaks: 002 and 006                                            9.2

                                                                                                                                                                                                  002 positions (Å)
   formed as an alteration product from ultramafic rock.

                                                                                                                                                                                                                                                                                                                       talc 002 (Å)
                                                                                                                                                                                                                       9                                                                                                                                                                                            200deg up

    At elevated pressures and temperatures, H2O can fit                                                                                                  Diffraction pattern                                          8.9
                                                                                                                                                                                                                                                                                           100deg down

                                                                                                                                                                                                                                                                                           100deg up                                     8.8                                                                        200deg down
                                                                                                                                                       taken at ALS BL12.2.2                                          8.8

    between the TOT (tetrahedra-octaheadra-tetrahedra)                                                                                                 with Bruker CCD at 30



   layers of talc to form 10-Å phase. Volatile recycling,                                                                                                        keV                                                  8.5
                                                                                                                                                                                                                            0        2        4       6         8          10        12          14         16
                                                                                                                                                                                                                                                                                                                                                0   2           4       6             8    10
                                                                                                                                                                                                                                                                                                                                                                                      pressure (GPa)
                                                                                                                                                                                                                                                                                                                                                                                                    12        14        16       18        20

                                                                                                                                                                                                                                                          pressure (GPa)

  via oceanic slab subduction, plays a major geodynamic                                                                                                                                                                                               o
                                                                                                                                                                                                                                                  300 C: talc002 vs. pressure
                                                                                                                                                                                                                                                                                                                                                                        400 C: talc 002 vs pressure

   role triggering mass transfer, melting and volcanism. Unit Cell of Talc.                                                                                                                                           9.5

                                                                                                                                                                                                                      9.3                                                                                                                 9.3

                                                                                                                                                                                                                      9.2                                                                                                                 9.2

                                                                                                                                                                                                                                                                                                                      talc 002 (Å)
                                                                                                                                                                                                  talc 002 (Å)
                                                                                                                                                                                                                      9.1                                                                                                                 9.1

        The pressure-temperture [P-T]                                                                                                                                                                                  9
                                                                                                                                                                                                                                                                                               300 deg up
                                                                                                                                                                                                                                                                                                                                                                                                                             400deg up

      stability field for 10-Å phase, as a                                                                                                                                                                            8.8

       potential water carrier within the                                                                                                                                                                             8.6
                                                                                                                                                                                                                            0    2        4       6       8     10    12        14        16       18       20                                  0       2           4            6          8          10          12          14          16
      slab, is important to shed light on                                                                                                                                                                                                                 pressure (GPa)                                                                                                             pressure (GPa)

           the Earth‟s water budget.                                                                                                                When comparing our room temperature isotherm                                                                                                                                         9.8
                                                                                                                                                                                                                                                                                                                                                                        27 C: talc 002 vs. pressure

                                                                                                                                                                                                                                                                                                                                                                                                            27 deg upstroke

                                                                                                                                                 (27oC) data to compression data collected by S. Parry                                                                                                                                   9.6
                                                                                                                                                                                                                                                                                                                                                                                                            Parry 2004 Talc

                                                                                                                                                                                                                                                                                                                 talc 002 position (Å)

                                                                                                                                                 for both 10-Å phase and talc, we note a conversion of                                                                                                                                   9.2
                                                                                                                                                                                                                                                                                                                                                                                                            Parry 2004 10-A

                                                                                                                                                                                                                                                                                                                                                                                                            Talc Compression; Parry

                                                                                                                                                 talc to 10-Å phase with only the increase of pressure.                                                                                                                                   9                                                                 Poly. (Parry 2004 10-A)

                                                                                Schematic Diagram extracted from Gill 1981
                                                                                                                                                   Based on the transition pressures seen in the above                                                                                                                                   8.8


                                                                                                                                                    isotherm data, we can plot a more accurate phase                                                                                                                                            0           2                    4
                                                                                                                                                                                                                                                                                                                                                                                 pressure (GPa)
                                                                                                                                                                                                                                                                                                                                                                                                6                  8                  10

                                                                      Method                                                                      boundary between talc and 10-Å phase and generate
                                                                                                                                                                      P-T diagram.
                                                                                To determine the phase boundary between                                                                                                              P-T Plot for Talc and 10Å
                                                                                                                                                                                                                                                                                                                                          Talc; Gleason
                                                                                    talc and 10-Å phase we can collect                                                           14                                                                                                                                                       10-A; Gleason
                                                                                isothermal data across the zone where we                                                                                              10-Å                                     Enstatite + Stishovite +V                                                  Talc; Pawley
                                                                                 expect a “change”. This change is noted                                                                                                                                                                                                                  En+Stish;Pawley
                                                                                  by monitoring the basal spacing of talc                                                        10
                                                                                                                                                                                                                                                                                                                                          En+Cs; Pawley
                                                                                                                                                                Pressure (GPa)

                                                                                 during x-ray diffraction. We should be                                                           8                                                                                                              coesite

                                                                                   able to see a discontinuity in the 002                                                         6
                                                                                                                                                                                                                                                                                                   Enstatite +
                                                                                                                                                                                                                                                                                                   Coesite + V
                                                                                 spacing with pressure when water starts                                                          4
                                                                                   fitting into the talc structure for each                                                                Talc
    Plot extracted from: Parry S, Pawley A, Clark S, Jones R. 2004. In-situ high
  pressure synchrotron and X-ray diffraction study of talc and 10-Angstrom phase.                                                                                                 0
                                                                                                                                                                                      0   100     200                           300        400    500     600                         700               800                               900
                                                                                                                                                                                                                                         Temperature (oC)

                          References                                                                                                                      Discussion and Conclusions
- Parry S, Pawley A, Clark S, Jones R. 2004. In-situ high                                          9.35
pressure synchrotron and X-ray diffraction study of talc and
10-Angstrom phase. COMPRES Annual Meeting 2004.
                                                                                                                                         Prior to this study, the stability region of 10-Å phase within a                                                                                                                                                                   Extracted from Poli and Schmidt 2002

- Pawley, 2004 unpublished personal communication; pdf                                                                                     subducting slab was thought to be here. However, this new
received Dec.3, 2004.
- Pawley A, Redfern S, Wood B. 1995. Thermal                              In Talc stability
                                                                                                                                         version of the phase boundary would indicate that 10-Å phase
expansivities and compressibilities of hydrous phases in the                                                                              is also stable at lower pressures. The boundary‟s decrease in
system MgO-SiO2-H2O: talc, phase A and 10-Å phase.                        In 10-Å phase
Contributions to Mineral Petrology: Vol 122: 301- 307.                    stability                                                        slope from 150 – 500oC could mean that 10-Å phase is less
- Shim S, Duffy T, Kenichi T. 2002. Equation of state of
gold and its application to the phase boundaries near 660                 We need to see                                                  sensitive to temperature increases. 10-Å phase would reside
km depth in Earth‟s mantle. Earth and Planetary Science                   this jump.                                                       longer inside the slab‟s center (where it is cooler) and could
Letters: Vol. 203: 729-739.
                                                                                                                                                    carry more water in the slab as it subducts.

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