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Dissolution-reprecipitation of zircon at low-temperature, high-pressure conditions (Lanzo Massif, Italy)

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Published/Copyright: April 1, 2015
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American Mineralogist
From the journal American Mineralogist Volume 93 Issue 10

Abstract

An eclogite facies meta-plagiogranite from the Lanzo massif (western Alps, Italy) contains crystals of zircon intimately associated with allanite. Zircon displays different microtextures ranging from pristine, euhedral, and magmatic to fractured, porous varieties with mosaic zoning, and pervasive recrystallization into euhedral microcrystals. Fractures and voids in the recrystallized zircon microcrystals are mainly filled by high-pressure Na-rich pyroxene. Electron backscattered diffraction analysis revealed a similar crystallographic orientation for primary magmatic zircon crystals and microcrystals, with less than 2° misorientation among neighboring microdomains. The textural change is coupled with chemical and isotopic modifications: recrystallized zircon domains contain significantly less Th and light- to mid-REE, but are richer in Sr than magmatic zircon crystals. Magmatic zircon preserves the protolith U-Pb age of 163.5 ± 1.7 Ma, whereas zircon microcrystals have a mean age of 55 ± 1 Ma. The coexisting allanite also contains inclusions of Na-rich pyroxene and has chemical features (elevated Sr and Ni contents and lack of Eu anomaly) indicating formation at high pressure. Despite being associated texturally with zircon, allanite yields a younger Th-Pb age of 46.5 ± 3.0 Ma, suggesting that the Lanzo unit remained at relatively high pressure conditions for ~8 m.y.

Zircon recrystallization proceeded with volume reduction and loss of material to an alkaline metamorphic fluid that acted as the agent for a coupled dissolution-reprecipitation process. Recrystallization occurred with minimum transport, in a low-strain environment, and was not significantly enhanced by metamictization. The source of the fluid for zircon recrystallization is most probably related to prograde devolatilization reactions in the surrounding serpentinite.

Keywords: U-Th-Pb geochronology; allanite; EBSD; plagiogranite; Lanzo peridotite
Received: 2007-11-28
Accepted: 2008-4-4
Published Online: 2015-4-1
Published in Print: 2008-10-1

© 2015 by Walter de Gruyter Berlin/Boston

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  1. Amorphous materials: Properties, structure, and durability: Atomic structure and transport properties of MgO-Al2O3 melts: A molecular dynamics simulation study
  2. Amorphous Materials: Properties, structure, and durability: Oxidation state of iron in hydrous phono-tephritic melts
  3. Amorphous materials: Properties, structure, and durability: Quantitative Raman spectroscopy: Speciation of Na-silicate glasses and melts
  4. Dissolution-reprecipitation of zircon at low-temperature, high-pressure conditions (Lanzo Massif, Italy)
  5. High-pressure behavior of gypsum: A single-crystal X-ray study
  6. Presence and zoning of hydrous components in leucite from the Alban Hills volcano, Rome, Italy
  7. Herderite from Mogok, Myanmar, and comparison with hydroxyl-herderite from Ehrenfriedersdorf, Germany
  8. Application of Raman spectroscopy to quantify trace water concentrations in glasses and garnets
  9. Neutron diffraction study of δ-AlOOD at high pressure and its implication for symmetrization of the hydrogen bond
  10. A simple predictive model for the thermal expansion of AlSi3 feldspars
  11. New data on PGE alloy minerals from a very old collection (probably 1890s), California
  12. High-pressure study on lead fluorapatite
  13. High-pressure Al-rich hexagonal phases—What are their kin?
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  15. Thermodynamic mixing properties of Rb-K feldspars
  16. Demicheleite, BiSBr, a new mineral from La Fossa crater, Vulcano, Aeolian Islands, Italy
  17. A lattice dynamical study of the aragonite and post-aragonite phases of calcium carbonate rock
  18. Water in natural olivine—determined by proton-proton scattering analysis
  19. Factors affecting heat transfer in natural SiO2 solids
  20. A solution model for high-temperature PbS-AgSbS2-AgBiS2 galena
  21. Incorporation of molybdate anion into β-FeOOH
  22. Disordering of Fe2+ over octahedrally coordinated sites of tourmaline
  23. Raman spectroscopy of CaIrO3 postperovskite up to 30 GPa
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  25. The crystal structure of kelyanite, (Hg2)6(SbO6)BrCl2
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https://doi.org/10.2138/am.2008.2874
Keywords for this article
U-Th-Pb geochronology; allanite; EBSD; plagiogranite; Lanzo peridotite

Articles in the same Issue

  1. Amorphous materials: Properties, structure, and durability: Atomic structure and transport properties of MgO-Al2O3 melts: A molecular dynamics simulation study
  2. Amorphous Materials: Properties, structure, and durability: Oxidation state of iron in hydrous phono-tephritic melts
  3. Amorphous materials: Properties, structure, and durability: Quantitative Raman spectroscopy: Speciation of Na-silicate glasses and melts
  4. Dissolution-reprecipitation of zircon at low-temperature, high-pressure conditions (Lanzo Massif, Italy)
  5. High-pressure behavior of gypsum: A single-crystal X-ray study
  6. Presence and zoning of hydrous components in leucite from the Alban Hills volcano, Rome, Italy
  7. Herderite from Mogok, Myanmar, and comparison with hydroxyl-herderite from Ehrenfriedersdorf, Germany
  8. Application of Raman spectroscopy to quantify trace water concentrations in glasses and garnets
  9. Neutron diffraction study of δ-AlOOD at high pressure and its implication for symmetrization of the hydrogen bond
  10. A simple predictive model for the thermal expansion of AlSi3 feldspars
  11. New data on PGE alloy minerals from a very old collection (probably 1890s), California
  12. High-pressure study on lead fluorapatite
  13. High-pressure Al-rich hexagonal phases—What are their kin?
  14. Leucite at high pressure: Elastic behavior, phase stability, and petrological implications
  15. Thermodynamic mixing properties of Rb-K feldspars
  16. Demicheleite, BiSBr, a new mineral from La Fossa crater, Vulcano, Aeolian Islands, Italy
  17. A lattice dynamical study of the aragonite and post-aragonite phases of calcium carbonate rock
  18. Water in natural olivine—determined by proton-proton scattering analysis
  19. Factors affecting heat transfer in natural SiO2 solids
  20. A solution model for high-temperature PbS-AgSbS2-AgBiS2 galena
  21. Incorporation of molybdate anion into β-FeOOH
  22. Disordering of Fe2+ over octahedrally coordinated sites of tourmaline
  23. Raman spectroscopy of CaIrO3 postperovskite up to 30 GPa
  24. The thermal behavior of richterite
  25. The crystal structure of kelyanite, (Hg2)6(SbO6)BrCl2
  26. Comparison of crystallographic orientations between living (Emiliania huxleyi and Gephyrocapsa oceanica) and fossil (Watznaueria barnesiae) coccoliths using electron microscopes
  27. Letter. Iron partitioning between perovskite and post-perovskite: A transmission electron microscope study
  28. Letter. An isosymmetric phase transition of orthopyroxene found by high-temperature X-ray diffraction
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