Abstract
Zircon crystals from lateritic soils at Nsimi, Cameroon, were investigated using electron microprobe analysis (EMPA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Raman spectroscopy to determine the extent of radiation damage from alpha-decay events. The soils belong to a small watershed developed on granitic rocks of the Congo craton (2.9 Ga). Interactions with fluids are evidenced by significant CaO (up to 1.5 wt%), Al2O3 (up to 2.9 wt%), and Fe2O3 (up to 2.9 wt%) concentrations in UO2 rich regions (0.05 to 1 wt%) of the zircon. Regional heating up to 500 °C, related to the Pan-African orogeny about 0.6 Ga ago, has lead to the recrystallization of the radiation-damaged grains and the formation of a nanoporous microstructure. The correlation observed between the presence of dissolution features and the actual damage state of zircon shows that zircon dissolution occurs under tropical weathering conditions and with preferential dissolution of the highly radiation-damaged regions. Congruent dissolution of zircon and the limited mobility of Zr are supported by the absence of zirconium oxide precipitates in the fractures of weathered grains of zircon.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Evaluation of image classification routines for determining modal mineralogy of rocks from X-ray maps
- Atomic structure and formation mechanism of (301) rutile twins from Diamantina (Brazil)
- Significance of the depth-related transition montmorillonite-beidellite in the Bouillante geothermal field (Guadeloupe, Lesser Antilles)
- High-pressure infrared spectra of talc and lawsonite
- Proton dynamics in letovicite: Part I. Static 1H and 15N NMR MAS experiments and lineshape simulations
- Proton dynamics in letovicite: Part II. Static 2H NMR experiments and lineshape simulations
- Chemical and structural variations at augite (100) deformation twin boundaries
- Comparative compressibility and structural behavior of spinel MgAl2O4 at high pressures: The independency on the degree of cation order
- Multiple breakdown and chemical equilibrium of silicic clinopyroxene under extreme metamorphic conditions in the Kontum Massif, central Vietnam
- Direct EXAFS evidence for incorporation of As5+ in the tetrahedral site of natural andraditic garnet
- Deformation-controlled cation diffusion in tourmaline: A microanalytical study on trace elements and boron isotopes
- Scandium-45 NMR of pyrope-grossular garnets: Resolution of multiple scandium sites and comparison with X-ray diffraction and X-ray absorption spectroscopy
- Partitioning of trace elements among coexisting crystals, melt, and supercritical fluid during isobaric crystallization and melting
- Thermal diffusivity of aluminous spinels and magnetite at elevated temperature with implications for heat transport in Earth’s transition zone
- High-pressure structure and bonding in CaIrO3: The structure model of MgSiO3 post-perovskite investigated with time-of-flight neutron powder diffraction
- Application of major- and trace-element geochemistry to refine U-Pb zircon, and Sm/Nd or Lu/Hf sampling targets for geochronology of HP and UHP eclogites, Western Gneiss Region, Norway
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- Coexistence of twisted and untwisted crystals: An impurity/structural order model with implications for agate patterns
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- Hydrogen analysis in minerals by continuous-flow mass spectrometry
- Re-examination of berlinite (AlPO4) from the Cioclovina Cave, Romania
- Letter. Valence state partitioning of Cr between pyroxene-melt: Effects of pyroxene and melt composition and direct determination of Cr valence states by XANES. Application to Martian basalt QUE 94201 composition