A new thermodynamic analysis of the intergrowth of hedenbergite and magnetite with Ca-Fe-rich olivine
-
Jiawen Hu
,
Shide Mao
Abstract
Some errors and metastable phase relations are found in a recently reported oxygen fugacity-silica activity [logfO₂-loga(SiO2)] diagram of the fayalite-kirschsteinite-hedenbergite-magnetite-wollastonite (Fa-Kst-Hd-Mt-Wo) system at 400 °C and 1 kbar (Markl et al. 2001). Systematic thermodynamic analysis reveals that the composite exsolution lamellae of Mt and Hd in the olivine from the Ilimaussaq Intrusion, Greenland, should form when the reaction 3Fa+3Kst+O2 = 3Hd+2Mt is overstepped on rapid cooling. This process is also accompanied by favorable fO₂ and a(SiO2) conditions. It is also found that the reaction mechanisms from Ca-Fe-rich olivine (Fa+Kst) to Mt+Hd are very different above and below the equilibrium temperature of the Mt-absent reaction Hd+Kst = Fa+2Wo. The mechanisms above the equilibrium temperature are obviously simpler than those below the equilibrium temperature. Despite this difference, the two types of mechanisms have many features in common: (1) Mt and Hd can form in Ca-Fe-rich olivine on continuous cooling; (2) If a(SiO2) is not buffered, an increase in fO₂ alone is enough to transform Ca-Fe-rich olivine into Mt and Hd; (3) At a fixed fO₂ or a(SiO2), the formation of Mt and/or Hd on cooling requires appropriate a(SiO2) or fO₂; and (4) The increase in a(SiO2) is favorable to the formation of Hd, but it is not essential for the intergrown exsolution of Mt and Hd. These common features are closely related to the fact that the process from Fa+Kst to Mt+Hd is an entropy decreasing oxidation reaction.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Roebling Medal Lecture. The three partners of metamorphic petrology
- Relationship between structure, morphology, and carbon isotopic composition of graphite in marbles: Implications for calcite-graphite carbon isotope thermometry
- Crystal structure, mosaicity, and strain analysis of Hawaiian olivines using in situ X-ray diffraction
- Characterization of deep weathering and nanoporosity development in shale—A neutron study
- Structural water in ferrihydrite and constraints this provides on possible structure models
- Critical evaluation of the revised akdalaite model for ferrihydrite
- Neutron diffraction study of hydrogen in birnessite structures
- Pressless split-sphere apparatus equipped with scaled-up Kawai-cell for mineralogical studies at 10–20 GPa
- Dislocation microstructures in majorite garnet experimentally deformed in the multi-anvil apparatus
- Density of carbonated peridotite magma at high pressure using an X-ray absorption method
- Stability and bulk modulus of Ni3S, a new nickel sulfur compound, and the melting relations of the system Ni-NiS up to 10 GPa
- Far-infrared spectra of synthetic [4][(Al2-xGax)(Si2–yGey)](OH,OD,F)2-kinoshitalite: Characterization and assignment of interlayer Ba-Oinner and Ba-Oouter stretching bands
- High-temperature elasticity of polycrystalline orthoenstatite (MgSiO3)
- Anatomy of a metabentonite: Nucleation and growth of illite crystals and their coalescence into mixed-layer illite/smectite
- Zn-O tetrahedral bond length variations in normal spinel oxides
- A new thermodynamic analysis of the intergrowth of hedenbergite and magnetite with Ca-Fe-rich olivine
- Raman spectroscopic investigations of some Tl-sulfosalt minerals containing pyramidal (As,Sb)S3 groups
- A first record of strong structural relaxation of TO4 tetrahedra in a spinel solid solution
- The high-pressure behavior of orthorhombic amphiboles
- XAS determination of the Fe local environment and oxidation state in phonolite glasses
- Chemical variation and significance of micas from the Fregeneda-Almendra pegmatitic field (Central-Iberian Zone, Spain and Portugal)
- Light-induced molecular change in HgI2·As4S4: Evidence by single-crystal X-ray diffraction and Raman spectroscopy
- Low-temperature electron paramagnetic resonance studies on natural calumetite from Khetri copper mine, Rajasthan, India
- Chromatite and its Cr3+- and Cr6+-bearing precursor minerals from the Nabi Musa Mottled Zone complex, Judean Desert
- Hazenite, KNaMg2(PO4)2⋅14H2O, a new biologically related phosphate mineral, from Mono Lake, California, U.S.A.
- The fractional latent heat of crystallizing magmas
