Garnet‐perovskite transformation in CaGeO<sub>3</sub>: In‐situ X‐ray measurements using synchrotron radiation

Susaki, Junichi; Akaogi, Masaki; Akimoto, Syun‐iti; Shimomura, Osamu

doi:10.1029/gl012i010p00729

Cited by 116 publications

(34 citation statements)

References 8 publications

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“…The furnace assemblies consist of a ZrO 2 sleeve, a stepped LaCrO 3 heater with inner MgO pieces, and a molybdenum disc or ring between the furnace and the WC cubes. Pressure was calibrated based on the coesite/stishovite (Yagi and Akimoto 1976;Zhang et al 1996) and forsterite/wadsleyite (Morishima et al 1994) transitions for the 14/8 assembly, and on the coesite/stishovite and CaGeO 3 -garnet-perovskite (Susaki et al 1985) transitions for the 18/11 assembly. Temperature was controlled by a B-type (Pt 94 Rh 6 /Pt 70 Rh 30 ) thermocouple, and no correction for the effect of pressure on the emf was applied.…”

Section: Experimental Apparatus and Sample Preparationmentioning

confidence: 99%

Melting of carbonated pelites at 8–13 GPa: generating K-rich carbonatites for mantle metasomatism

Grassi

Schmidt

2010

Contrib Mineral Petrol

100

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The melting behaviour of three carbonated pelites containing 0-1 wt% water was studied at 8 and 13 GPa, 900-1,850°C to define conditions of melting, melt compositions and melting reactions. At 8 GPa, the fluidabsent and dry carbonated pelite solidi locate at 950 and 1,075°C, respectively; [100°C lower than in carbonated basalts and 150-300°C lower than the mantle adiabat. From 8 to 13 GPa, the fluid-present and dry solidi temperatures then increase to 1,150 and 1,325°C for the 1.1 wt% H 2 O and the dry composition, respectively. The melting behaviour in the 1.1 wt% H 2 O composition changes from fluid-absent at 8 GPa to fluid-present at 13 GPa with the pressure breakdown of phengite and the absence of other hydrous minerals. Melting reactions are controlled by carbonates, and the potassium and hydrous phases present in the subsolidus. The first melts, which composition has been determined by reverse sandwich experiments, are potassium-rich Ca-FeMg-carbonatites, with extreme K 2 O/Na 2 O wt ratios of up to 42 at 8 GPa. Na is compatible in clinopyroxene with D cpx=carbonatite Na ¼ 10À18 at the solidus at 8 GPa. The melt K 2 O/Na 2 O slightly decreases with increasing temperature and degree of melting but strongly decreases from 8 to 13 GPa when K-hollandite extends its stability field to 200°C above the solidus. The compositional array of the sediment-derived carbonatites is congruent with alkali-and CO 2 -rich melt or fluid inclusions found in diamonds. The fluid-absent melting of carbonated pelites at 8 GPa contrasts that at B5 GPa where silicate melts form at lower temperatures than carbonatites. Comparison of our melting temperatures with typical subduction and mantle geotherms shows that melting of carbonated pelites to 400-km depth is only feasible for extremely hot subduction. Nevertheless, melting may occur when subduction slows down or stops and thermal relaxation sets in. Our experiments show that CO 2 -metasomatism originating from subducted crust is intimately linked with K-metasomatism at depth of [200 km. As long as the mantle remains adiabatic, lowviscosity carbonatites will rise into the mantle and percolate upwards. In cold subcontinental lithospheric mantle keels, the potassic Ca-Fe-Mg-carbonatites may freeze when reacting with the surrounding mantle leading to potassium-, carbonate/diamond-and incompatible element enriched metasomatized zones, which are most likely at the origin of ultrapotassic magmas such as group II kimberlites.

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Section: Experimental Apparatus and Sample Preparationmentioning

confidence: 99%

Melting of carbonated pelites at 8–13 GPa: generating K-rich carbonatites for mantle metasomatism

Grassi

Schmidt

2010

Contrib Mineral Petrol

100

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“…The multianvil experiment was performed at GFZ Potsdam with a 18/11 assembly, which was calibrated at room temperature against the phase transitions in Bi metal [4,5]. Calibrations at high temperature are based on the following phase transitions: , garnet-perovskite for CaGeO 3 [6] and coesite-stishovite for SiO 2 [7]. Stepped graphite heaters were employed, and temperatures were measured with type-C thermocouples.…”

Section: Methodsmentioning

confidence: 99%

Ambient-temperature high-pressure-induced ferroelectric phase transition in CaMnTi2O6

et al. 2017

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The ferroelectric to paraelectric phase transition of multiferroic CaMnTi 2 O 6 has been investigated at high pressures and ambient temperature by second-harmonic generation (SHG), Raman spectroscopy, and powder and single-crystal x-ray diffraction. We have found that CaMnTi 2 O 6 undergoes a pressure-induced structural phase transition (P 4 2 mc → P 4 2 /nmc) at ∼7 GPa to the same paraelectric structure found at ambient pressure and T c = 630 K. The continuous linear decrease of the SHG intensity that disappears at 7 GPa and the existence of a Raman active mode at 244 cm −1 that first softens up to 7 GPa and then hardens with pressure are used to discuss the nature of the phase transition of CaMnTi 2 O 6 , for which a dT c /dP = −48 K/GPa has been found. Neither a volume contraction nor a change in the normalized pressure on the Eulerian strain is observed across the phase transition with all the unit-cell volume data following a second-order Birch-Murnaghan equation of state with a bulk modulus of B 0 = 182.95(2) GPa.

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“…Pressure assemblies were calibrated at room temperature against the phase transitions in Bi metal (Lloyd 1971;Piermarini and Block 1975). Calibrations at higher temperature are based on the following phase transitions CaGeO 3 garnet-perovskite (Susaki et al 1985); SiO 2 coesite-stishovite (Akaogi et al 1995); Mg 2 SiO 4 α−β transition (Morishima et al 1994). The temperature was measured using a W5%Re-W26%Re thermocouple.…”

Section: Methodsmentioning

confidence: 99%

Breakdown of hydrous ringwoodite to pyroxene and spinelloid at high P and T and oxidizing conditions

et al. 2008

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From the Rietveld refinement we identified spl as spinelloid III (isostructural with wadsleyite) and/or spinelloid V. As we used water in excess in the experiments the run products were also analyzed for structural water incorporation. Adding Mg to the system increases the stability field of ringwoodite to higher oxygen fugacity and the spinel structure seems to accept higher Fe 3+ but also water concentrations that may be linked. At oxygen fugacity corresponding to MtW conditions similar phase relations in respect to the breakdown reaction in the Fe-end-member system were observed but with a strong fractionation of Fe into spl and Mg into coexisting cpx. Thus, through this strong fractionation it is possible to stabilize very Fe-rich wadsleyite with phase at P-T conditions of the transition zone but because of the oxidizing conditions and the Fe-rich bulk composition needed one would expect it more in subduction zone environments than in the transition zone in senso stricto.

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Garnet‐perovskite transformation in CaGeO₃: In‐situ X‐ray measurements using synchrotron radiation

Cited by 116 publications

References 8 publications

Melting of carbonated pelites at 8–13 GPa: generating K-rich carbonatites for mantle metasomatism

Melting of carbonated pelites at 8–13 GPa: generating K-rich carbonatites for mantle metasomatism

Ambient-temperature high-pressure-induced ferroelectric phase transition in CaMnTi2O6

Breakdown of hydrous ringwoodite to pyroxene and spinelloid at high P and T and oxidizing conditions

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Garnet‐perovskite transformation in CaGeO3: In‐situ X‐ray measurements using synchrotron radiation

Cited by 116 publications

References 8 publications

Melting of carbonated pelites at 8–13 GPa: generating K-rich carbonatites for mantle metasomatism

Melting of carbonated pelites at 8–13 GPa: generating K-rich carbonatites for mantle metasomatism

Ambient-temperature high-pressure-induced ferroelectric phase transition in CaMnTi2O6

Breakdown of hydrous ringwoodite to pyroxene and spinelloid at high P and T and oxidizing conditions

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Garnet‐perovskite transformation in CaGeO₃: In‐situ X‐ray measurements using synchrotron radiation