HR: 0800h
AN: V41C-1414    [Abstracts]
TI: HP and HT Polymorphism of AlPO$_{4}$ and its Solubility in SiO$_{2}$ -Stishovite : Implication for Phosphorus Geochemistry
AU: * Brunet, F
EM: brunet@geologie.ens.fr
AF: ENS-Geologie, LAboratoire de Geologie 24 rue Lhomond, Paris, 75005 France, Metropolitan
AU: Tetsuo, I
EM: irifune@dpc.ehime-u.ac.jp
AF: GRC-Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577 Japan
AU: Takeshi, S
EM: sanehira@sci.ehime-u.ac.jp
AF: GRC-Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577 Japan
AU: Daisuke, Y
EM: yamazaki@sci.ehime-u.ac.jp
AF: GRC-Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577 Japan
AU: Toru, S
EM: shinmei@sci.ehime-u.ac.jp
AF: GRC-Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577 Japan
AB: The understanding of phosphorus behavior in the deep Earth requires to evaluate the ability of minor phosphorus to be incorporated in the octahedral site of high-pressure mineral structures. For that purpose, we studied the solubility of AlPO$_{4}$ in SiO$_{2}$-stishovite, the extend of which will indicate the phosphorus affinity for octahedral oxygen coordination. The choice of those compounds was also motivated by their importance in material sciences (e.g. pressure induced amorphization properties). Synthetic AlPO$_{4}$ (berlinite) as well as a 1 to 2 molar mixture of AlPO$_{4}$ (berlinite) : SiO$_{4}$ (quartz) where encapsulated separately in a Pt container and held together at $1600\deg$C, 18 GPa (4.5 h) in the 2000-ton split-sphere apparatus at GRC (Matsuyama, Japan). In the second capsule, micrometer-size stishovite crystals could be analyzed using the electron microprobe and revealed around 0.5 wt.% P$_{2}$O$_{5}$ (balanced by Al$_{2}$O$_{3}$). Berlinite, in the first capsule, totally reacted at HP and HT into a form which could not be quenched. This result was the incentive for a characterization of AlPO$_{4}$ polymorphism using in-situ HP-HT x-ray diffraction (Spring 8, BL04B1). Upon compression in the MgO-based assembly, the diffraction pattern of AlPO$_{4}$ berlinite showed indication of partial amorphization in keeping with the non-hydrostatic nature of the pressure cell at room temperature. Upon the first heating stage, crystallization of another AlPO$_{4}$ polymorph had occurred at $600\deg$C, 6.9 GPa (gold scale) in a first experiment and $900\deg$C, 17.3 GPa in a second one. The corresponding diffraction pattern could be indexed in the InPO$_{4}$ -structure (Cmcm) where Al is octahedrally coordinated whereas P is fourfold. No other transformation was identified up to 21 GPa, $1600\deg$C. Although, no rutile-type structure was observed for AlPO$_{4}$ up to 21 GPa, phosphorus, which is likely to be stored in garnet down to the transition zone, is expected to be further incorporated into silicate structures to greater depths.
DE: 3919 Equations of state
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
DE: 1025 Composition of the mantle
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting