Lead in zircon at the atomic scale
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Masashi Kogawa
Abstract
Lead-doped zircon crystals, which were synthesized under three different conditions (Watson et al. 1997): dry at 1430 °C at atmospheric pressure without P2O5; wet at 900 °C at 1.5 GPa in the presence of P2O5; and wet at 800 °C at 1.0 GPa without P2O5, have been investigated to understand the mechanisms of Pb incorporation into zircon at the sub-micrometer scale, using various electron microscopy techniques including high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Four different mechanisms in which Pb may be incorporated into zircon have been identified. In the P-free synthesis, Pb-oxide hydrate particles, 50-200 nm in size, are embedded in zircon. Each Pb-particle is associated with a single vesicle, ~50 nm. Lead in the zircon structure is possibly incorporated under the detection limit value of energy-dispersive X-ray analysis (EDX) by means of: (1) Zr4+ = Pb2+ + 2H+ at less than ~0.1 wt%. In the system with P, Pb-phases occur in three different forms: Pb-rich domains concentrated along cleavage planes or grain boundaries without any evident crystal form; numerous Pb-phosphate particles, as large as 100 nm, embedded heterogeneously in the zircon crystal; and homogeneous distribution of Pb in the zircon structure at less than ~1 wt% as determined by EDX. These results suggest that charge balance is maintained by the xenotime-type coupled substitution: (2) Zr4+ + 2Si4+ = Pb2+ + 2P5+ with a possible minor contribution from mechanism 1. The apparent solubility limit of Pb, <1 wt%, is constrained mainly by the xenotime-type coupled substitution mechanism, which is probably due to increasing strain at higher Pb-concentrations. The presence of Pb2+ in natural zircon is consistent with the low-level Pb allowed by substitution mechanism 2, with only a minor contribution from substitution mechanism 1, the latter of which causes distortion in the local structure.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Mercury (Hg) mineral evolution: A mineralogical record of supercontinent assembly, changing ocean geochemistry, and the emerging terrestrial biosphere
- The 3.65 Å phase, MgSi(OH)6: Structural insights from DFT-calculations and T-dependent IR spectroscopy
- Vertical zonation of the Barcroft granodiorite, White Mountains, California: Implications for magmatic processes
- Minerals in cement chemistry: A single-crystal neutron diffraction and Raman spectroscopic study of thaumasite, Ca3Si(OH)6(CO3)(SO4)·12H2O
- A new high-pressure phase transition in natural Fe-bearing orthoenstatite
- Aluminum solubility in TiO2 rutile at high pressure and experimental evidence for a CaCl2-structured polymorph
- First record and timing of UHP metamorphism from zircon in the Xitieshan terrane: Implications for the evolution of the entire North Qaidam metamorphic belt
- Lead in zircon at the atomic scale
- Characterization of fluor-chlorapatites by electron probe microanalysis with a focus on time-dependent intensity variation of halogens
- An inversion-based self-calibration for SIMS measurements: Application to H, F, and Cl in apatite
- Second boiling effects on the Al-content of hornblende rims from an exhumed Cretaceous arc pluton, Stewart Island, New Zealand
- Heat transfer in plagioclase feldspars
- Transport properties and equation of state of 1-bar eutectic melt in the system CaAl2Si2O8-CaMgSi2O6 by molecular dynamics simulation
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- A first-principle investigation of antigorite up to 30 GPa: Structural behavior under compression
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- Leucostaurite, Pb2[B5O9]Cl·0.5H2O, from the Atacama Desert: The first Pb-dominant member of the hilgardite group, and micro-determination of boron in minerals by PIGE
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- Panguite, (Ti4+,Sc,Al,Mg,Zr,Ca)1.8O3, a new ultra-refractory titania mineral from the Allende meteorite: Synchrotron micro-diffraction and EBSD
- Buseckite, (Fe,Zn,Mn)S, a new mineral from the Zakłodzie meteorite
- Experimental calibration of the effect of H2O on plagioclase crystallization in basaltic melt at 200 MPa
- High-pressure and high-temperature titanium solution mechanisms in silicate-saturated aqueous fluids and hydrous silicate melts
- Thermodynamic behavior and properties of katoite (hydrogrossular): A calorimetric study
- Graphite in the martian meteorite Allan Hills 84001
