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Microstructural characterization of metamorphic magnetite crystals with implications for oxygen isotope distribution

  • Scott D. Sitzman , Jillian F. Banfield EMAIL logo and John W. Valley
Published/Copyright: March 25, 2015
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American Mineralogist
From the journal American Mineralogist Volume 85 Issue 1

Abstract

The microstructures of magnetite crystals in three samples from a single outcrop of granulitefacies marble were characterized by transmission electron microscopy (TEM) to determine how exsolution history can affect physical properties and mineral reactivity during retrograde metamorphism. The microstructure of sample 90LP9 consists of dislocations, dislocation arrays (with dislocation spacings of 100 to 500 nm), and linear channels filled with layer silicates. Acid etching and ion milling of polished 90LP9 magnetite grains show dislocation arrays clustered near grain boundaries with rheologically hard magnetite, diopside, and monticellite, but rarely near grain boundaries with softer calcite. Sample LP204-1 magnetite grains contain coherent {100} Al-Mn-Fe-spinel precipitates (~40 nm diameter, ~1-3 nm thick, ~104 platelets/μm3) and very few dislocations. Larger, more widely spaced spinel precipitates are present in a third sample, 94AK3. Extremely low dislocation densities in powders of LP204-1 and intermediate dislocation densities in powders of 94AK3, compared with extremely high dislocation densities in powders of 90LP9, are related to strong dislocation pinning effects by precipitates. The different exsolution behavior of the three magnetite samples is attributed to small, but important, differences in Al content. Because dislocations can provide fast pathways for exchange that enhance diffusion, especially in very slowly cooled rocks, these microstructural results may explain previously reported subgrain-scale oxygen isotopic heterogeneity in 90LP9 magnetite compared with relative isotopic homogeneity in LP204-1 magnetite

Received: 1998-5-27
Accepted: 1999-9-4
Published Online: 2015-3-25
Published in Print: 2000-1-1

© 2015 by Walter de Gruyter Berlin/Boston

Articles in the same Issue

  1. Eclogite-facies relics and inferred ultrahigh-pressure metamorphism in the North Dabie Complex, central-eastern China
  2. Application of INVEQ to the geothermobarometry of metamorphic rocks near a kyanite-sillimanite isograd, Mica Creek, British Columbia
  3. Microstructural characterization of metamorphic magnetite crystals with implications for oxygen isotope distribution
  4. Coexisting monazite and allanite in peraluminous granitoids of the TribečMountains, Western Carpathians
  5. Effect of alkalis, phosphorus, and water on the surface tension of haplogranite melt
  6. Direct observation of immiscibility in pyrope-almandine-grossular garnet
  7. On the cluster analysis of grains and crystals in rocks
  8. Experimental approach to constrain second critical end points in fluid/silicate systems: Near-solidus fluids and melts in the system albite-H2O
  9. Estimation and testing of standard molar thermodynamic properties of tourmaline end-members using data of natural samples
  10. An investigation of matrix effects in the analysis of fluorine in humite-group minerals by EMPA, SIMS, and SREF
  11. New data on the crystal-chemistry of fluoborite by means of SREF, SIMS, and EMP analysis
  12. Effect of aluminum on Ti-coordination in silicate glasses: A XANES study
  13. XAFS study of Cu model compounds and Cu2+ sorption products on amorphous SiO2, γ-Al2O3, and anatase
  14. Oxidation-reduction mechanism of iron in dioctahedral smectites: I. Crystal chemistry of oxidized reference nontronites
  15. Oxidation-reduction mechanism of iron in dioctahedral smectites: II. Crystal chemistry of reduced Garfield nontronite
  16. 15N NMR study of nitrate ion structure and dynamics in hydrotalcite-like compounds
  17. 29Si and 27Al MAS-NMR spectroscopy of b-eucryptite (LiAlSiO4): The enthalpy of Si,Al ordering
  18. The nuclear and magnetic structure of “white rust”—Fe(OH0.86D0.14)2
  19. In-situ study of the R3̅ to R3̅c phase transition in the ilmenite-hematite solid solution using time-of-flight neutron powder diffraction
  20. In situ X-ray diffraction investigation of lawsonite and zoisite at high pressures and temperatures
  21. A shell model for the simulation of rhombohedral carbonate minerals and their point defects
  22. Optical properties of natural and cation-exchanged heulandite group zeolites
  23. The crystal structure of gearksutite, CaAlF4(OH)· H2O
  24. A new anhydrous amphibole from the Eifel region, Germany: Description and crystal structure of obertiite, NaNa2(Mg3Fe3+Ti4+)Si8O22O2
  25. Kinoshitalite, Ba(Mg)3(Al2Si2)O10(OH,F)2, a brittle mica from a manganese deposit in Oman: Paragenesis and crystal chemistry
  26. The crystal structure of parisite-(Ce), Ce2CaF2(CO3)3
  27. High-pressure synthesis of Na2Mg6Si6O18(OH)2—a new hydrous silicate phase isostructural with aenigmatite
https://doi.org/10.2138/am-2000-0103

Articles in the same Issue

  1. Eclogite-facies relics and inferred ultrahigh-pressure metamorphism in the North Dabie Complex, central-eastern China
  2. Application of INVEQ to the geothermobarometry of metamorphic rocks near a kyanite-sillimanite isograd, Mica Creek, British Columbia
  3. Microstructural characterization of metamorphic magnetite crystals with implications for oxygen isotope distribution
  4. Coexisting monazite and allanite in peraluminous granitoids of the TribečMountains, Western Carpathians
  5. Effect of alkalis, phosphorus, and water on the surface tension of haplogranite melt
  6. Direct observation of immiscibility in pyrope-almandine-grossular garnet
  7. On the cluster analysis of grains and crystals in rocks
  8. Experimental approach to constrain second critical end points in fluid/silicate systems: Near-solidus fluids and melts in the system albite-H2O
  9. Estimation and testing of standard molar thermodynamic properties of tourmaline end-members using data of natural samples
  10. An investigation of matrix effects in the analysis of fluorine in humite-group minerals by EMPA, SIMS, and SREF
  11. New data on the crystal-chemistry of fluoborite by means of SREF, SIMS, and EMP analysis
  12. Effect of aluminum on Ti-coordination in silicate glasses: A XANES study
  13. XAFS study of Cu model compounds and Cu2+ sorption products on amorphous SiO2, γ-Al2O3, and anatase
  14. Oxidation-reduction mechanism of iron in dioctahedral smectites: I. Crystal chemistry of oxidized reference nontronites
  15. Oxidation-reduction mechanism of iron in dioctahedral smectites: II. Crystal chemistry of reduced Garfield nontronite
  16. 15N NMR study of nitrate ion structure and dynamics in hydrotalcite-like compounds
  17. 29Si and 27Al MAS-NMR spectroscopy of b-eucryptite (LiAlSiO4): The enthalpy of Si,Al ordering
  18. The nuclear and magnetic structure of “white rust”—Fe(OH0.86D0.14)2
  19. In-situ study of the R3̅ to R3̅c phase transition in the ilmenite-hematite solid solution using time-of-flight neutron powder diffraction
  20. In situ X-ray diffraction investigation of lawsonite and zoisite at high pressures and temperatures
  21. A shell model for the simulation of rhombohedral carbonate minerals and their point defects
  22. Optical properties of natural and cation-exchanged heulandite group zeolites
  23. The crystal structure of gearksutite, CaAlF4(OH)· H2O
  24. A new anhydrous amphibole from the Eifel region, Germany: Description and crystal structure of obertiite, NaNa2(Mg3Fe3+Ti4+)Si8O22O2
  25. Kinoshitalite, Ba(Mg)3(Al2Si2)O10(OH,F)2, a brittle mica from a manganese deposit in Oman: Paragenesis and crystal chemistry
  26. The crystal structure of parisite-(Ce), Ce2CaF2(CO3)3
  27. High-pressure synthesis of Na2Mg6Si6O18(OH)2—a new hydrous silicate phase isostructural with aenigmatite
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