Abstract
Recrystallization rims are a common feature of zircon crystals that underwent metamorphism. We present a microstructural and microchemical study of partially recrystallized zircon grains collected in polymetamorphic migmatites (Valle d’Arbedo, Ticino, Switzerland). The rims are bright in cathodoluminescence (CL), with sharp and convex contacts characterized by inward-penetrating embayments transgressing igneous zircon cores. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data and transmission electron microscopy (TEM) imaging indicate that the rims are chemically and microstructurally different from the cores. The rims are strongly depleted in REE, with concentrations up to two orders of magnitude lower than in the cores, indicating a significant loss of REE during zircon recrystallization. Enrichment in non-formula elements, such as Ca, has not been observed in the rims. The microstructure of zircon cores shows a dappled intensity at and below the 100 nm scale, possibly due to radiation damage. Other defects such as pores and dislocations are absent in the core except at healed cracks. Zircon rims are mostly dapple-free, but contain nanoscale pores and strain centers, interpreted as fluid inclusions and chemical residues, respectively. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages show that the recrystallization of the rims took place >200 Ma ago when the parent igneous zircon was not metamict. The chemical composition and the low-Ti content of the rims indicate that they form at sub-solidus temperatures (550-650 °C). Recrystallization rims in Valle d’Arbedo zircon are interpreted as the result of the migration of chemical reaction fronts in which fluid triggered in situ and contemporaneous interface-coupled dissolution-reprecipitation mechanisms. This study indicates that strong lattice strain resulting from the incorporation of a large amount of impurities and structural defects is not a necessary condition for zircon to recrystallize. Our observations suggest that the early formation of recrystallization rims played a major role in preserving zircon from the more recent Alpine metamorphic overprint.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Redetermination of the structure of 5C pyrrhotite at low temperature and at room temperature
- Thermal elastic behavior of CaSiO3-walstromite: A powder X-ray diffraction study up to 900 °C
- Magnesiohögbomite-2N4S: A new polysome from the central Sør Rondane Mountains, East Antarctica
- Hanjiangite, a new barium-vanadium phyllosilicate carbonate mineral from the Shiti barium deposit in the Dabashan region, China
- Combined neutron and X-ray diffraction determination of disorder in doped zirconolite-2M
- Focused ion beam preparation and characterization of single-crystal samples for high-pressure experiments in the diamond-anvil cell
- Phase stability and elastic properties of the NAL and CF phases in the NaMg2Al5SiO12 system from first principles
- Redistribution of REE, Y, Th, and U at high pressure: Allanite-forming reactions in impure meta-quartzites (Sesia Zone, Western Italian Alps)
- MAS NMR measurements and ab initio calculations of the 29Si chemical shifts in dumortierite and holtite
- Aluminum ordering and clustering in Al-rich synthetic phlogopite: {1H} → 29Si CPMAS HETCOR spectroscopy and atomistic calculations
- Cell assemblies for reproducible multi-anvil experiments (the COMPRES assemblies)
- Recrystallization rims in zircon (Valle d’Arbedo, Switzerland): An integrated cathodoluminescence, LA-ICP-MS, SHRIMP, and TEM study
- Temperature and humidity effects on ferric sulfate stability and phase transformation
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- Variations in elastic and anelastic properties of Co3O4 due to magnetic and spin-state transitions
- High-pressure behavior of space group P2/n omphacite
- Twinning in pyromorphite: The first documented occurrence of twinning by merohedry in the apatite supergroup
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- Coupled (Li+, Al3+) substitutions in hydrous forsterite
- Crystal chemistry of trioctahedral micas-2M1 from Bunyaruguru kamafugite (southwest Uganda)
- Menchettiite, AgPb2.40Mn1.60Sb3As2S12, a new sulfosalt belonging to the lillianite series from the Uchucchacua polymetallic deposit, Lima Department, Peru
- Adolfpateraite, K(UO2)(SO4)(OH)(H2O), a new uranyl sulphate mineral from Jáchymov, Czech Republic
- Amorphous materials: Properties, structure, and durability
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- Letter. Determination of the oxidation state of Cu in substituted Cu-In-Fe-bearing sphalerite via μ-XANES spectroscopy
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