Fe2+ -Mg partitioning between garnet, magnesiowüstite, and (Mg,Fe)2SiO4 phases of the transition zone
-
Daniel J. Frost
Abstract
The partitioning of Fe and Mg between garnet coexisting with olivine, wadsleyite, ringwoodite and magnesiowüstite solid solutions has been measured between 9 and 19 GPa and 1400-1700 ℃. In addition to studying exchange reactions involving the pyrope-almandine garnet solid solution, majoritic garnets forming in a natural peridotite bulk composition have been also examined. Metallic Fe was added to all bulk compositions to buffer the Fe3+ concentration at its lowest possible level. Partitioning data between pyrope-almandine garnet and ringwoodite were combined with data for garnet-magnesiowüstite and ringwoodite-magnesiowüstite partitioning to refine thermodynamic mixing properties for these solid solutions at 18 GPa and 1400 ℃. A multiple non-linear regression employing cation exchange data between these 3 solid solutions yielded the following well-constrained values for the differences in symmetric solid-solution interaction parameters: WmwFeMg - WringFeMg = 8.8(2) kJ/mol, WmwFeMg - WgtFeMg = 12.8(5) kJ/mol,WringFeMg - WgtFeMg = 4.0(4) kJ/mol.
These differences were then solved simultaneously to give, on a single site basis: WmwFeMg = 13.2(3) kJ/mol, WringFeMg= 4.4(2) kJ/mol, WgtFeMg = 0.3(3) kJ/mol.
In a peridotite composition, the occurrence of majorite and grossular garnet components produced a measurable influence on the Fe-Mg partitioning, however, the combined effect was relatively small because each individual component affected the partitioning in an opposite direction. These data, combined with previously determined phase relations in the Mg2SiO4-Fe2SiO4 system, were used to calculate the influence of garnet Fe-Mg partitioning on the pressure intervals of divariant (Mg,Fe)2SiO4 phase transformations in the transition zone. Results show that the presence of garnet reduces the pressure interval over which the (Mg0.9,Fe0.1)2SiO4 olivine to wadsleyite transformation occurs in a peridotite composition to 0.35 GPa (10 km) in comparison to 0.5 GPa in a garnet-free system. This width, however, is still greater than the estimated width of 4 km for the 410 km discontinuity observed in some regions of the Earth as inferred from high frequency reflected and converted seismic waves. The existence of garnet in a peridotite composition in the mantle cannot, therefore, be the only explanation as to why the 410 km discontinuity is, in some regions of the Earth, apparently sharper than experimental estimates for the (Mg0.9,Fe0.1)2SiO4 olivine to wadsleyite transformation. The wadsleyite to ringwoodite transformation is reduced to 0.8 GPa (25 km) compared to 1 GPa in the garnet-free system.
© 2015 by Walter de Gruyter Berlin/Boston
Artikel in diesem Heft
- Structure, metal-insulator transitions, and magnetic properties of FeO at high pressures
- The high-temperature behavior of defect hydrogen species in quartz: Implications for hydrogen isotope studies
- Thermal stability and vibrational spectra of the sheet borate tuzlaite, NaCa[B5O8(OH)2]·3H2O
- Hydrogen-bonded water in laumontite I: X-ray powder diffraction study of water site occupancy and structural changes in laumontite during room-temperature isothermal hydration/dehydration
- In-situ determination of mineral solubilities in fluids using a hydrothermal diamond-anvil cell and SR-XRF: Solubility of AgCl in water
- Pressure-induced phase transition in malayaite, CaSnOSiO4
- Equation of state of stishovite to lower mantle pressures
- Chemical transfer during redox exchanges between H2 and Fe-bearing silicate melts
- Trace-element partitioning between alkali feldspar and peralkalic quartz trachyte to rhyolite magma. Part I: Systematics of trace-element partitioning
- Trace-element partitioning between alkali feldspar and peralkalic quartz trachyte to rhyolite magma. Part II: Empirical equations for calculating trace-element partition coefficients of large-ion lithophile, high field-strength, and rare-earth elements
- Four generations of accessory-phase growth in low-pressure migmatites from SW New Hampshire
- Mineralogy, chemistry, and formation of oxidized biotite in the weathering profile of granitic rocks
- Experimental study of zircon coarsening in quartzite ±H2O at 1.0 GPa and 1000 ℃, with implications for geochronological studies of high-grade metamorphism
- Biotite dissolution processes and mechanisms in the laboratory and in nature: Early stage weathering environment and vermiculitization
- Fe2+ -Mg partitioning between garnet, magnesiowüstite, and (Mg,Fe)2SiO4 phases of the transition zone
- Interlayer structure and dynamics of Cl-bearing hydrotalcite: far infrared spectroscopy and molecular dynamics modeling
- Si-Al disorder and solid solutions in analcime, chabazite, and wairakite
- Cafetite, Ca[Ti2O5](H2O): Crystal structure and revision of chemical formula
- Order-disorder approach to calcioaravaipaite, [PbCa2Al(F,OH)9]: The crystal structure of the triclinic MDO polytype
- Ab initio investigation of the structures of NaOH hydrates and their Na+ and OH– coordination polyhedra
- Another step toward understanding the true nature of sartorite: Determination and refinement of a ninefold superstructure
- Letter. Ultrapotassic clinopyroxene from the Kumdy-Kol microdiamond mine, Kokchetav Complex, Kazakhstan: Occurrence, composition and crystal-chemical characterization
- Letter. Determination of planetary basalt parentage: A simple technique using the electron microprobe
Artikel in diesem Heft
- Structure, metal-insulator transitions, and magnetic properties of FeO at high pressures
- The high-temperature behavior of defect hydrogen species in quartz: Implications for hydrogen isotope studies
- Thermal stability and vibrational spectra of the sheet borate tuzlaite, NaCa[B5O8(OH)2]·3H2O
- Hydrogen-bonded water in laumontite I: X-ray powder diffraction study of water site occupancy and structural changes in laumontite during room-temperature isothermal hydration/dehydration
- In-situ determination of mineral solubilities in fluids using a hydrothermal diamond-anvil cell and SR-XRF: Solubility of AgCl in water
- Pressure-induced phase transition in malayaite, CaSnOSiO4
- Equation of state of stishovite to lower mantle pressures
- Chemical transfer during redox exchanges between H2 and Fe-bearing silicate melts
- Trace-element partitioning between alkali feldspar and peralkalic quartz trachyte to rhyolite magma. Part I: Systematics of trace-element partitioning
- Trace-element partitioning between alkali feldspar and peralkalic quartz trachyte to rhyolite magma. Part II: Empirical equations for calculating trace-element partition coefficients of large-ion lithophile, high field-strength, and rare-earth elements
- Four generations of accessory-phase growth in low-pressure migmatites from SW New Hampshire
- Mineralogy, chemistry, and formation of oxidized biotite in the weathering profile of granitic rocks
- Experimental study of zircon coarsening in quartzite ±H2O at 1.0 GPa and 1000 ℃, with implications for geochronological studies of high-grade metamorphism
- Biotite dissolution processes and mechanisms in the laboratory and in nature: Early stage weathering environment and vermiculitization
- Fe2+ -Mg partitioning between garnet, magnesiowüstite, and (Mg,Fe)2SiO4 phases of the transition zone
- Interlayer structure and dynamics of Cl-bearing hydrotalcite: far infrared spectroscopy and molecular dynamics modeling
- Si-Al disorder and solid solutions in analcime, chabazite, and wairakite
- Cafetite, Ca[Ti2O5](H2O): Crystal structure and revision of chemical formula
- Order-disorder approach to calcioaravaipaite, [PbCa2Al(F,OH)9]: The crystal structure of the triclinic MDO polytype
- Ab initio investigation of the structures of NaOH hydrates and their Na+ and OH– coordination polyhedra
- Another step toward understanding the true nature of sartorite: Determination and refinement of a ninefold superstructure
- Letter. Ultrapotassic clinopyroxene from the Kumdy-Kol microdiamond mine, Kokchetav Complex, Kazakhstan: Occurrence, composition and crystal-chemical characterization
- Letter. Determination of planetary basalt parentage: A simple technique using the electron microprobe
