HR: 0800h
AN: V41A-1417    [Abstracts]
TI: Carbonate Stability and Melt Composition in Peridotite-CO₂ System to 20 GPa
AU: * Ghosh, S
EM: sujoy@ganko.tohoku.ac.jp
AF: Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AU: Ohtani, E
EM: ohtani@mail.tains.tohoku.ac.jp
AF: Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AU: Litasov, K D
EM: klitasov@ganko.tohoku.ac.jp
AF: Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AU: Suzuki, A
EM: a-suzuki@mail.tains.tohoku.ac.jp
AF: Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AU: Terasaki, H
EM: terasaki@mail.tains.tohoku.ac.jp
AF: Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AB: Carbon dioxide and water are the most important volatile constituents in the Earth and they produce drastic changes in the melting phase relations and partial melt compositions of the mantle peridotite. Study of the peridotite-CO₂ system is closely related to petrogenesis of kimberlite and diamond. There are a few high pressure mineral inclusions (i.e. majorite garnet and Ca and Mg perovskite) in diamond which suggest that kimberlites may be originated from the transition zone and lower mantle. The phase relations and melt compositions in the CO₂-bearing peridotite at high pressures are poorly constrained, however the kimberlite and basalt-CO₂ systems have been studied intensively. Simplified peridotite-CO₂ system (like CMS or CMAS) has been studied at pressures up to 12 GPa (Canil and Scarfe, 1990), whereas complex peridotite-CO₂ systems have been investigated only at lower pressures (up to 4 GPa, e.g. Wendlandt and Mysen, 1980). In this work we report the preliminary results on the phase relations and melt compositions of a model peridotite-CO₂ system determined at 10-20 GPa and temperature range from 1200 to 2100^oC. Our results show that solidus of carbonated peridotite is consistent with low-pressure data for CMAS-CO₂ system. Liquidus phase at 10-20 GPa is majorite garnet. At 10-15 GPa, crystallization sequence with decreasing temperature is garnet, olivine and clinoenstatite. Magnesite is the most important CO₂-rich phase stable in peridotite up to 1600^oC at 20 GPa. The partial melt formed by 10-25% melting at 10-20 GPa has high MgO (26-34 wt.%) and FeO (7.0-10.4 wt.%) and low SiO₂ (18-36 wt.%) and Al₂O₃ (0.5-1.3 wt.%) contents. It also contains 6-12 wt.% CaO, 0.6-2.0 wt.% Na₂O and 0.1-0.3 wt.% K₂O. The CO₂ contents in the melts are 14-32 wt.%. The SiO₂-poor nature of the partial melts is different from the results for melting of anhydrous or water-bearing peridotite. Partial melting of hydrous peridotite produces the melts enriched in SiO₂, which can be related to komatiite magmas. The composition of low degree partial melts (10%) in present experiments is close to magnesiocarbonatites, whereas higher degree melting (20-25%) produce melts, which is close to kimberlite magmas.
DE: 1012 Reactions and phase equilibria (3612, 8412)
DE: 1037 Magma genesis and partial melting (3619)
DE: 3621 Mantle processes (1038)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005