HR: 1340h
AN: DI33A-1124    [Abstracts]
TI: Ordering kinetics in double carbonates and implications for processes at subduction zones
AU: * Hammouda, T
EM: t.hammouda@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans, 5 rue Kessler, Clermont-Ferrand, 63000, France
AU: Koga, K T
EM: k.koga@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans, 5 rue Kessler, Clermont-Ferrand, 63000, France
AU: Katsura, T
EM: tkatsura@misasa.okayama-u.ac.jp
AF: ISEI, Okayama University, Misasa, Tottori-ken, 682-0193, Japan
AU: Andrault, D
EM: D.Andrault@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans, 5 rue Kessler, Clermont-Ferrand, 63000, France
AU: Martin, A
EM: A.Martin@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans, 5 rue Kessler, Clermont-Ferrand, 63000, France
AB: The identity of carbonate mineral species that are present on the solidus of carbonate bearing lithologies is the critical information that determines the solidus phase relations and element partitioning. Experimental determinations of pressure and temperature conditions of dolomite breakdown reaction, dolomite = magnesite + aragonite (or calcite), carried out over the last five years show disparities that have been attributed to the disorder state in dolomite starting materials and subsequent equilibration during the experiments. We have conducted high-pressure, in-situ synchrotron experiments at SPring8 (BL04B1) using multi-anvil apparatus to determine ordering state of dolomite during this reaction. Four dolomite breakdown experiments were conducted at pressures, from 3 to 7 GPa and temperatures, from 600 to 1200°C. We have crossed the dolomite breakdown reaction at three points between 4 and 5.5 GPa and have determined that dolomite is stable at 7.4 GPa and 1090°C. Our results agree with quench studies of Luth (2001 CMP141:222) and Buob et al. (2006 AmMim91:435) at 5 GPa and above. We disagree with those of Sato and Katsura (2001 EPSL184:529) and Morlidge et al. (2006 CMP152:365). Our data point at 4 GPa does not fall on any extrapolated curve of any previous investigation. Ordering state of dolomite in our experiments are consistent with those of Luth (2001) and results presented by Antao et al. (2004 AmMin89:1142) show a systematic offset, suggesting disagreement on pressure and temperature calibration. We have also observed that kinetics of disordering is relatively rapid in the order of tens of minutes. On the contrary reversal kinetics (i.e. to create ordered state) is sluggish. Only small fraction of reversal ordering has occurred within 2 hours of heating. We consider that this asymmetric kinetics of the order- disorder reaction is a cause of disparity of the previous quench experiments
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 3630 Experimental mineralogy and petrology
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting