HR: 0800h
AN: MR31A-0143    [Abstracts]
TI: Mineral physics of the perovskite to post-perovskite transition in CaIrO3 - seismological implications for the lower mantle
AU: * Tronnes, R G
EM: r.g.tronnes@nhm.uio.no
AF: Natural History Museum, Geology, Univ. of Oslo Box 1172, Oslo, N-0318, Norway
AU: Stolen, S
EM: svein.stolen@kjemi.uio.no
AF: Dept. of Chemistry, Univ. of Oslo, Oslo, N-0315, Norway
AU: Boffa-Ballaran, T
EM: Tiziana.Boffa-Ballaran@Uni-Bayreuth.DE
AF: Bayerisches Geoinstitut, Univ. of Bayreuth, Bayreuth, D-95440, Germany
AU: Frost, D J
EM: Dan.Frost@uni-bayreuth.de
AF: Bayerisches Geoinstitut, Univ. of Bayreuth, Bayreuth, D-95440, Germany
AU: Balic-Zunic, T
EM: TONCI@geol.ku.dk
AF: Dept. of Geography and Geology, Univ. of Copenhagen, Copenhagen, DK-1210, Denmark
AU: Olsen, L A
EM: lao@geol.ku.dk
AF: Dept. of Geography and Geology, Univ. of Copenhagen, Copenhagen, DK-1210, Denmark
AB: In the system CaIrO3 the perovskite (pv, Pbnm) to post-perovskite (ppv, Cmcm) phase transition is accessible at 1-5 GPa and 1450-1610 C. Both of the CaIrO3-phases are quenchable to ambient conditions, making the system suitable for studies of crystallographic, crystal chemical and mineral physical properties that may provide important guidelines to the behaviour of MgSiO3-based compositions of the lower mantle. Combined results from experimental phase relations, experimental pV-EoS [1], thermal expansivity and density functional theory (DFT) modeling [2] provide insights into the seismologic and geodynamic features of the pv-ppv-transition in the lowermost mantle. Experimental phase relations in the 1-5 GPa range and DFT modeling give Clapeyron slopes for the pv-ppv-transition of 24.5 and 19 MPa/K, respectively, which is about twice the published dp/dT-slopes of the MgSiO3-system. The compressibility of the CaIrO3-crystal structures derived from pv-EoS experiments and DFT-modelling are very similar. In ppv the b-axis compressibility is about twice that of the other two axes. In pv the a- and c-axis compressibilities exceed that of the b-axis by factors of 3 and 2, respectively. The bulk modulus change of the pv to ppv transition is negative, whereas the DFT-derived shear moduli of the two phases give a positive delta-G of the same transition. These results are consistent with DFT-modelling of the MgSiO3-system and with seismological data [3,4]. The apparent suitability of the CaIrO3-component as a low-pressure analogue for the lower mantle MgSiO3-component in terms of crystallographic and mineral physics properties has encouraged an investigation of the incorporation of trivalent cations. By studying the incorporation of a small selection of ions with variable radii in CaIrO3-based pv and ppv, we are searching for systematic relations between various trivalent cation proportions, substitution mechanisms and elasticity parameters. [1] T Boffa-Ballaran, RG Tronnes, D Frost, Equations of state of CaIrO3 perovskite and post-perovskite phases. Am Mineral 92, Oct. 2007. [2] S Stolen, RG Tronnes, The perovskite to post-perovskite transition in CaIrO3: Clapeyron slope and changes in bulk and shear moduli by density functional theory. Phys Earth Planet Int 164, 50-62, 2007. [3] J Wookey, S Stackhouse, J-M Kendall, J Brodholt, GD Price, Efficacy of the post-perovskite phase as an explanation for the lowermost-mantle seismic properties. Nature 438, 1004-1007, 2005. [4] T Lay, J Hernlund, EJ Garnero, MS Thorne, A post-perovskite lens and D" heat flux beneath the central Pacific. Science 314, 1272-1276, 2006.
DE: 3621 Mantle processes (1038)
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting