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An overgrowth model to explain multiple, dispersed high-Mn regions in the cores of garnet porphyroblasts

  • David M. Hirsch EMAIL logo , David J. Prior and William D. Carlson
Published/Copyright: March 31, 2015
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American Mineralogist
From the journal American Mineralogist Volume 88 Issue 1

Abstract

The central portions of garnet porphyroblasts from Harpswell Neck, Maine, exhibit small discrete regions of high Mn content, dispersed in three dimensions. Orientation contrast imaging (OCI) and quantitative crystallographic orientation measurements from electron backscatter diffraction (EBSD) patterns show that most garnet porphyroblasts contain no variations in crystallographic orientation. It is difficult to reconcile these data with a model in which each high-Mn region represents a discrete garnet nucleus.

An alternative hypothesis invokes a model of garnet growth in which precursor phases rich in Mn are overgrown, and their Mn is incorporated locally into the garnet structure. Although this model requires length scales for equilibration of Mn during the early stages of garnet growth that are shorter than any previously documented, that inference is consistent with the very low temperatures of garnet nucleation in these rocks, and with compositional evidence for progressively larger scales of equilibrium as reaction progressed.

Very short length scales for equilibration of Mn, identified in this study for the lowest-grade portion of the history of the rocks, call into question the common assumption of rock-wide equilibrium for Mn during garnet growth at low temperature. The absence of rock-wide equilibrium for Mn at low grade has potential negative implications for all common interpretive methods based in phase equilibria, including thermobarometric studies and thermodynamic analysis of the origin and meaning of zoning in low-grade garnet.

Received: 2002-2-12
Accepted: 2002-9-23
Published Online: 2015-3-31
Published in Print: 2003-1-1

© 2015 by Walter de Gruyter Berlin/Boston

Articles in the same Issue

  1. A molecular dynamics study of the behavior of sodium in low albite
  2. Observation and interpretation of paramagnetic defects in Brazilian and Central African carbonados
  3. Dissolution of gibbsite: Direct observations using fluid cell atomic force microscopy
  4. Polytypes and higher-order structures of antigorite: A TEM study
  5. An infrared spectroscopic study of the basic copper phosphate minerals: Cornetite, libethenite, and pseudomalachite
  6. Influence of F content on the composition of Al-rich synthetic phlogopite: Part I. New information on structure and phase-formation from 29Si, 1H, and 19F MAS NMR spectroscopies
  7. NMR evidence for formation of octahedral and tetrahedral Al and repolymerization of the Si network during dissolution of aluminosilicate glass and crystal
  8. Thermodynamic properties of hercynite (FeAl2O4) based on adiabatic calorimetry at low temperatures
  9. The formation of Sr silicates at low temperature and the solubility product of tobermorite-like Sr5Si6O16(OH)2 .5H2O
  10. Thermal equation of state of omphacite
  11. The effect of thermal decarbonation on stable isotope compositions of carbonates
  12. Synthetic MgAl2O4 (spinel) at high-pressure conditions (0.0001–30 GPa): A synchrotron X-ray powder diffraction study
  13. The stability of antigorite in the systems MgO-SiO2-H2O (MSH) and MgO-Al2O3-SiO2-H2O (MASH): The effects of Al3+ substitution on high-pressure stability
  14. The fusion curve of albite revisited and the compressibility of NaAlSi3O8 liquid with pressure
  15. Correction of secondary X-ray fluorescence near grain boundaries in electron microprobe analysis: Application to thermobarometry of spinel lherzolites
  16. An overgrowth model to explain multiple, dispersed high-Mn regions in the cores of garnet porphyroblasts
  17. Synchrotron X-ray diffraction study of the structure and dehydration behavior of todorokite
  18. Retrograde mineral reactions in saline fluid inclusions: The transformation ferropyrosmalite ↔ clinopyroxene
  19. The effect of ionizing radiation on uranophane
  20. Hydration, expansion, structure, and dynamics of layered double hydroxides
  21. Relict edenite in a garnet lherzolite from the Chinese Su-Lu UHP metamorphic terrane: Implications for metamorphic history
  22. Norrishite, K(Mn23+Li)Si4O10(O)2, an oxymica associated with sugilite from the Wessels Mine, South Africa: Crystal chemistry and 40Ar-39Ar dating
  23. The amblygonite (LiAlPO4F)-montebrasite (LiAlPO4OH) solid solution: A combined powder and single-crystal neutron diffraction and solid-state 6Li MAS, CP MAS, and REDOR NMR study
  24. An X-ray Rietveld, infrared, and Mössbauer spectral study of the NaMn(Fe1–xInx)2(PO4)3 alluaudite-type solid solution
  25. Gatelite-(Ce), a new REE-bearing mineral from Trimouns, French Pyrenees: Crystal structure and polysomatic relationships with epidote and törnebohmite-(Ce)
  26. Hydroxyl in clinopyroxene from the deep subducted crust: Evidence for H2O transport into the mantle
  27. A model for the structure of the hydrated aluminum phosphate, kingite determined by ab initio powder diffraction methods
  28. The crystal structure of synthetic autunite, Ca[(UO2)(PO4)]2(H2O)11
https://doi.org/10.2138/am-2003-0116

Articles in the same Issue

  1. A molecular dynamics study of the behavior of sodium in low albite
  2. Observation and interpretation of paramagnetic defects in Brazilian and Central African carbonados
  3. Dissolution of gibbsite: Direct observations using fluid cell atomic force microscopy
  4. Polytypes and higher-order structures of antigorite: A TEM study
  5. An infrared spectroscopic study of the basic copper phosphate minerals: Cornetite, libethenite, and pseudomalachite
  6. Influence of F content on the composition of Al-rich synthetic phlogopite: Part I. New information on structure and phase-formation from 29Si, 1H, and 19F MAS NMR spectroscopies
  7. NMR evidence for formation of octahedral and tetrahedral Al and repolymerization of the Si network during dissolution of aluminosilicate glass and crystal
  8. Thermodynamic properties of hercynite (FeAl2O4) based on adiabatic calorimetry at low temperatures
  9. The formation of Sr silicates at low temperature and the solubility product of tobermorite-like Sr5Si6O16(OH)2 .5H2O
  10. Thermal equation of state of omphacite
  11. The effect of thermal decarbonation on stable isotope compositions of carbonates
  12. Synthetic MgAl2O4 (spinel) at high-pressure conditions (0.0001–30 GPa): A synchrotron X-ray powder diffraction study
  13. The stability of antigorite in the systems MgO-SiO2-H2O (MSH) and MgO-Al2O3-SiO2-H2O (MASH): The effects of Al3+ substitution on high-pressure stability
  14. The fusion curve of albite revisited and the compressibility of NaAlSi3O8 liquid with pressure
  15. Correction of secondary X-ray fluorescence near grain boundaries in electron microprobe analysis: Application to thermobarometry of spinel lherzolites
  16. An overgrowth model to explain multiple, dispersed high-Mn regions in the cores of garnet porphyroblasts
  17. Synchrotron X-ray diffraction study of the structure and dehydration behavior of todorokite
  18. Retrograde mineral reactions in saline fluid inclusions: The transformation ferropyrosmalite ↔ clinopyroxene
  19. The effect of ionizing radiation on uranophane
  20. Hydration, expansion, structure, and dynamics of layered double hydroxides
  21. Relict edenite in a garnet lherzolite from the Chinese Su-Lu UHP metamorphic terrane: Implications for metamorphic history
  22. Norrishite, K(Mn23+Li)Si4O10(O)2, an oxymica associated with sugilite from the Wessels Mine, South Africa: Crystal chemistry and 40Ar-39Ar dating
  23. The amblygonite (LiAlPO4F)-montebrasite (LiAlPO4OH) solid solution: A combined powder and single-crystal neutron diffraction and solid-state 6Li MAS, CP MAS, and REDOR NMR study
  24. An X-ray Rietveld, infrared, and Mössbauer spectral study of the NaMn(Fe1–xInx)2(PO4)3 alluaudite-type solid solution
  25. Gatelite-(Ce), a new REE-bearing mineral from Trimouns, French Pyrenees: Crystal structure and polysomatic relationships with epidote and törnebohmite-(Ce)
  26. Hydroxyl in clinopyroxene from the deep subducted crust: Evidence for H2O transport into the mantle
  27. A model for the structure of the hydrated aluminum phosphate, kingite determined by ab initio powder diffraction methods
  28. The crystal structure of synthetic autunite, Ca[(UO2)(PO4)]2(H2O)11
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