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The origin of orthopyroxene/biotite + plagioclase coronas from the Bolangir anorthosite complex (India), and implications for reconstructing P-T paths

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Published/Copyright: March 28, 2015
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American Mineralogist
From the journal American Mineralogist Volume 90 Issue 2-3

Abstract

Mineralogical-textural analysis of a multi-layered plagioclase (Pl) + orthopyroxene/biotite (Opx/Bt) vermicular microstructure around garnet from the Bolangir anorthosite massif is presented. X-ray images demonstrate the garnet was zoned prior to decomposition, with Mg decreasing toward its rim, and Mn, Ca, and XFe [= Fe/(Fe + Mg)] increasing. On decomposition, the Ca zonations in garnet were truncated by the consuming garnet margin. By implication, the retreat velocity of the garnet margin was faster than the diffusive velocity for Ca within the garnet. By contrast, the pre-decomposition Fe, Mn, and Mg variations in garnet were considerably modified adjacent to Opx + Pl, but were unaffected adjacent to Bt + Pl intergrowths. In the corona, XFeOpx and XFeBt decrease toward garnet, whereas the An content in associated Pl increases from An50 to An80-83. Thermo-barometry involving nearest neighbor Opx, Grt, Pl, and Qtz indicate that the corona formed at 6.0 ± 1.0 kbar, 750 ± 50 °C. At the isothermal-isobaric condition of decomposition, the compositional variation across the Bt + Pl corona is explained best by the inward retreat of the garnet margin at a velocity faster than the fastest diffusing element (Fe, Mn). In zones where garnet decomposed to Opx + Pl, the velocity of the consuming garnet margin was such that the intra-garnet Fe, Mn redistribution was aborted in transit.

The compositions and volume proportions of vermicular orthopyroxene and plagioclase in the multi-layered corona are best approximated by the NCFMAS reaction Grtss + Pl1 (± Qtz) → Opx + Pl2. The early formed/matrix plagioclase (Pl1) and inward-retreating garnet (Grtss) margin provided the necessary components for successive Opx + Pl2 layers to grow at Grt-Pl1 interfaces. Tie-line topology in ACFN space indicates Pl2 to be An-rich relative to Pl1. The mineralogical relations indicate the CFMAS reaction, Grtss + Qtz → Opx + An, to be an inadequate analogue of the actual decomposition. Consequently, to assume that the texture indicates near-isothermal decompression across the low-dP/dT CFMAS reaction is possibly an oversimplification.

Received: 2003-9-25
Accepted: 2004-10-25
Published Online: 2015-3-28
Published in Print: 2005-2-1

© 2015 by Walter de Gruyter Berlin/Boston

Articles in the same Issue

  1. Comparative planetary mineralogy: Valence state partitioning of Cr, Fe, Ti, and V among crystallographic sites in olivine, pyroxene, and spinel from planetary basalts
  2. The origin of orthopyroxene/biotite + plagioclase coronas from the Bolangir anorthosite complex (India), and implications for reconstructing P-T paths
  3. Dellaventuraite, NaNa2(MgMn23+Ti4+Li)Si8O22O2, a new anhydrous amphibole from the Kajlidongri Manganese Mine, Jhabua District, Madhya Pradesh, India
  4. Successive zoning of Al and H in hydrothermal vein quartz
  5. The Ti-saturation surface for low-to-medium pressure metapelitic biotites: Implications for geothermometry and Ti-substitution mechanisms
  6. Thermochemistry of hydrotalcite-like phases in the MgO-Al2O3-CO2-H2O system: A determination of enthalpy, entropy, and free energy
  7. Igneous thermometers and barometers based on plagioclase + liquid equilibria: Tests of some existing models and new calibrations
  8. Thermodynamic properties of the Tschermak solid solution in Fe-chlorite: Application to natural examples and possible role of oxidation
  9. Experimental data on the Tschermak substitution in Fe-chlorite
  10. Nanometer-sized, divalent-Mn, hydrous silicate domains in geothermal brine precipitates
  11. Geometric crystal chemical models for structural analysis of micas and their stacking polytypes
  12. Fundamental difference between synthetic powder and natural or synthetic single-crystal 1M micas: Geometric homo-octahedral vs. geometric meso-octahedral sheets
  13. The crystal structures of synthetic Fe2(SO4)3(H2O)5 and the type specimen of lausenite
  14. Experimental study of plagioclase rim growth around anorthite seed crystals in rhyodacitic melt
  15. Luminescence study of defects in synthetic as-grown and HPHT diamonds compared to natural diamonds
  16. Molar absorptivities of OH and H2O in rhyolitic glass at room temperature and at 400–600 °C
  17. Ordering and elasticity associated with low-temperature phase transitions in lawsonite
  18. Formation of metastable cubic-perovskite in high-pressure phase transformation of Ca(Mg, Fe, Al)Si2O6
  19. Oxygen isotope heterogeneities and diffusion profile in composite metamorphic-magmatic garnets from the Pyrenees
  20. Unmixed spinel in chromitite from the Iwanai-dake peridotite complex, Hokkaido, Japan: A reaction between peridotite and highly oxidized magma in the mantle wedge
  21. Mn-bearing “oxy-rossmanite” with tetrahedrally coordinated Al and B from Austria: Structure, chemistry, and infrared and optical spectroscopic study
  22. Geochemical applications of the simple salt approximation to the lattice energies of complex materials
  23. Letter: A method for controlling alkali-metal oxide activities in one-atmosphere experiments and its application to measuring the relative activity coeficients of NaO0.5 in silicate melts
  24. Letter: Very low solubility of rutile in H2O at high pressure and temperature, and its implications for Ti mobility in subduction zones
  25. Letter: Microscopic strain in synthetic pyrope-grossular solid solutions determined by synchrotron X-ray powder diffraction at 5 K: The relationship to enthalpy of mixing behavior
  26. Letter: Ferrous hydroxy carbonate is a stable transformation product of biogenic magnetite
https://doi.org/10.2138/am.2005.1487

Articles in the same Issue

  1. Comparative planetary mineralogy: Valence state partitioning of Cr, Fe, Ti, and V among crystallographic sites in olivine, pyroxene, and spinel from planetary basalts
  2. The origin of orthopyroxene/biotite + plagioclase coronas from the Bolangir anorthosite complex (India), and implications for reconstructing P-T paths
  3. Dellaventuraite, NaNa2(MgMn23+Ti4+Li)Si8O22O2, a new anhydrous amphibole from the Kajlidongri Manganese Mine, Jhabua District, Madhya Pradesh, India
  4. Successive zoning of Al and H in hydrothermal vein quartz
  5. The Ti-saturation surface for low-to-medium pressure metapelitic biotites: Implications for geothermometry and Ti-substitution mechanisms
  6. Thermochemistry of hydrotalcite-like phases in the MgO-Al2O3-CO2-H2O system: A determination of enthalpy, entropy, and free energy
  7. Igneous thermometers and barometers based on plagioclase + liquid equilibria: Tests of some existing models and new calibrations
  8. Thermodynamic properties of the Tschermak solid solution in Fe-chlorite: Application to natural examples and possible role of oxidation
  9. Experimental data on the Tschermak substitution in Fe-chlorite
  10. Nanometer-sized, divalent-Mn, hydrous silicate domains in geothermal brine precipitates
  11. Geometric crystal chemical models for structural analysis of micas and their stacking polytypes
  12. Fundamental difference between synthetic powder and natural or synthetic single-crystal 1M micas: Geometric homo-octahedral vs. geometric meso-octahedral sheets
  13. The crystal structures of synthetic Fe2(SO4)3(H2O)5 and the type specimen of lausenite
  14. Experimental study of plagioclase rim growth around anorthite seed crystals in rhyodacitic melt
  15. Luminescence study of defects in synthetic as-grown and HPHT diamonds compared to natural diamonds
  16. Molar absorptivities of OH and H2O in rhyolitic glass at room temperature and at 400–600 °C
  17. Ordering and elasticity associated with low-temperature phase transitions in lawsonite
  18. Formation of metastable cubic-perovskite in high-pressure phase transformation of Ca(Mg, Fe, Al)Si2O6
  19. Oxygen isotope heterogeneities and diffusion profile in composite metamorphic-magmatic garnets from the Pyrenees
  20. Unmixed spinel in chromitite from the Iwanai-dake peridotite complex, Hokkaido, Japan: A reaction between peridotite and highly oxidized magma in the mantle wedge
  21. Mn-bearing “oxy-rossmanite” with tetrahedrally coordinated Al and B from Austria: Structure, chemistry, and infrared and optical spectroscopic study
  22. Geochemical applications of the simple salt approximation to the lattice energies of complex materials
  23. Letter: A method for controlling alkali-metal oxide activities in one-atmosphere experiments and its application to measuring the relative activity coeficients of NaO0.5 in silicate melts
  24. Letter: Very low solubility of rutile in H2O at high pressure and temperature, and its implications for Ti mobility in subduction zones
  25. Letter: Microscopic strain in synthetic pyrope-grossular solid solutions determined by synchrotron X-ray powder diffraction at 5 K: The relationship to enthalpy of mixing behavior
  26. Letter: Ferrous hydroxy carbonate is a stable transformation product of biogenic magnetite
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