Garnet sector and oscillatory zoning linked with changes in crystal morphology during rapid growth, North Cascades, Washington
-
Harold Stowell
,
Carlos Zuluaga
Abstract
Metamorphic garnet with sector zoning in the cores and oscillatory zoning in the rims grew during rapid heating of pelitic rocks in the Chiwaukum Schist. These types of compositional zoning are exemplified by sharp, but low amplitude, boundaries between broad petal-shaped sectors and between narrow concentric zones, respectively. Zoning is most obvious in calcium, which is inversely correlated with iron and magnesium content. Garnet habit inferred from the oscillatory calcium zoning and external morphology indicates a growth transition from early crystal forms with both trapezohedral and dodecahedral forms to later crystal forms dominated by trapezohedral faces. This transition is accompanied by changes in compositional sector zoning and may reflect the roles of local growth dynamics and external forcing mechanisms affecting growth of garnet. Subsequent modification of these textures produced patchy zoning in calcium. Electron backscatter diffraction confirms the inferred crystal growth habits and that compositional zoning occurs within single garnet crystals. Exchange thermobarometry and the peak mineral assemblages indicate that metamorphic conditions reached 640-670 °C at 6.9 kbar. These temperatures are sufficient to allow significant volume diffusion; therefore, preservation of the finely banded compositional zoning in garnet requires rapid heating and cooling. Garnet Sm-Nd ages and indistinguishable zircon U-Pb ages from adjacent orthogneiss bodies confirm that garnet grew rapidly during localized and short-lived heating adjacent to sill-like intrusions of tonalite.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- High-pressure Raman spectroscopic studies of ulvöspinel Fe2TiO4
- Brearleyite, Ca12Al14O32Cl2, a new alteration mineral from the NWA 1934 meteorite
- The 3.65 Å phase in the system MgO-SiO2-H2O: Synthesis, composition, and structure
- Water in upper mantle pyroxene megacrysts and xenocrysts: A survey study
- Mesoscale twinning and crystallographic registers in biominerals
- Radiation effects on cathodoluminescence of albite
- Structure refinement of high-pressure hexagonal aluminous phases K1.00Mg2.00Al4.80Si1.15O12 and Na1.04Mg1.88Al4.64Si1.32O12
- Elastic softening of metamict titanite CaTiSiO5: Radiation damage and annealing
- An experimental study of the diffusion of C and O in calcite in mixed CO2-H2O fluid
- Hydrochemical performance and mineralogical evolution of a dispersed alkaline substrate (DAS) remediating the highly polluted acid mine drainage in the full-scale passive treatment of Mina Esperanza (SW Spain)
- The effect of fO₂ on the partitioning and valence of V and Cr in garnet/melt pairs and the relation to terrestrial mantle V and Cr content
- An experimental study of OH solubility in rutile at 500–900 °C, 0.5–2 GPa, and a range of oxygen fugacities
- The growth interval of garnet in the UHP eclogites from the Dabie orogen, China
- Structural studies of NH4-exchanged natrolites at ambient conditions and high temperature
- Morphology and microstructure of magnetite and ilmenite inclusions in plagioclase from Adirondack anorthositic gneiss
- Thermodynamic properties of stishovite by low-temperature heat capacity measurements and the coesite-stishovite transition boundary
- Mechanisms of Cr and H incorporation in stishovite determined by single-crystal EPR spectroscopy and DFT calculations
- Paramagnetic interactions in the 31P NMR spectroscopy of rare earth element orthophosphate (REPO4, monazite/xenotime) solid solutions
- Garnet sector and oscillatory zoning linked with changes in crystal morphology during rapid growth, North Cascades, Washington
- Phase stability, elastic behavior, and pressure-induced structural evolution of kalsilite: A ceramic material and high-T/high-P mineral
- A new type of high-pressure low-flow metering valve for continuous decompression: First experimental results on degassing of rhyodacitic melts
- Substitution mechanisms and implications for the estimate of water fugacity for Ti-rich phlogopite from Mt. Vulture, Potenza, Italy
- Calibration for IR measurements of OH in apatite
- Electrolytic coloration and spectral properties of natural calcite crystals
- Compositional dependent compressibility of dissolved water in silicate glasses
- In situ monitoring of lepidocrocite bioreduction and magnetite formation by reflection Mössbauer spectroscopy
- Direct determination of europium valence state by XANES in extraterrestrial merrillite: Implications for REE crystal chemistry and martian magmatism
