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The Ti-saturation surface for low-to-medium pressure metapelitic biotites: Implications for geothermometry and Ti-substitution mechanisms

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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

The Ti content of biotite can serve as a geothermometer for graphitic, peraluminous metapelites that contain ilmenite or rutile and have equilibrated at roughly 4-6 kbar. The relationship between Ti- coutent, temperature, and Mg/(Mg + Fe) value was calibrated empirically using an extensive natural biotite data set (529 samples) from western Maine and south-central Massachusetts in combination with the petrogenetic grid of Spear et al. (1999). The calculated Ti-saturation surface is curved such that for a given Mg/(Mg + Fe) value, Ti concentration increases as a function of temperature in a nonlinear' fashion, and for a given temperature Ti concentrations decrease with an increase in Mg/(Mg + Fe). The fit to the Ti-saturation surface can be reformulated as the geothermometric expression: T = {[In(Ti) - a - c(XMg)3]/b}0.333, in which T is temperature in degrees Celsius, Ti is the number of atoms per formula unit (apfu) normalized on the basis of 22 O atoms, XMg is Mg/(Mg + Fe), a = -2.3594, b = 4.6482 x 1O-9 and c = -1.7283. The calibration range for this expression is XMg = 0.275-1.000, Ti = 0.04-0.60 apfu, and T = 480-800 0C. Precision of the Ti-in-biotite geothermometer is estimated to be ±24 0C at the lower temperature range and improves to ±12 °C at higher temperatures. Application of the Ti-in-biotite geothermometer to ilmenite- or rutile-bearing, graphitic, peraluminous metapelites equilibrated at 3-6 kbar is generally consistent with independent temperature determinations, but with some deviations that represent local reequilibration. Consequently, the Ti systematics in biotite can also serve as the basis of a very sensitive indicator of chemical equilibrium, or lack thereof. Applica­tion of the geothermometer to metapelites not containing the requisite mineral assemblages can lead to minor-to-significant errors in estimated temperatures.

Biotite Ti-substitution mechanisms are controlled by several factors. Based on the biotite calibra­tion data set, magnesian biotites (XMg> 0.65) incorporate Ti in accordance with the exchange vector TiAl2R-1Si-2, where R is the sum of the divalent cations Mg + Fe + Mn. This substitution mechanism is primarily a response to misfit of the octahedral and tetrahedral layers in magnesian biotites. Inter­mediate biotites (XMg <0.65), particularly at higher temperatures, exhibit enhanced Ti concentrations, most consistent with the Ti-deprotonation TiO2R-1(OH)-2, exchange vector. Dominance of Ti-deprotonation substitution is largely a function of reduction of H2O activity at higher metamorphic grades. Supplementary biotite data from metaluminous amphibolites and mafic granulites, metamorphosed isothermally with variable H2O activities, reveal that Iow-Al biotite incorporates significantly higher concentrations of Ti relative to peraluminous biotite as a result of a combination of the exchange vec­tors Ti02R-1(0H)-2 and RSiAl-2, substituting in roughly an 8:1 ratio.

Received: 2004-9-30
Accepted: 2004-10-11
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.2005.1498

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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