Detecting the Pressure and Bulk Composition Effect on the Al-OH Absorption Band of White Micas: Case Studies in Northwest Turkey and the Franciscan Complex of California
Abstract
Dioctahedral white micas are common constituents of many metamorphic rocks from low to ultrahigh pressure conditions. Experimental studies, along with phase equilibrium modeling, have established a solid framework for interpreting compositional variation in sodic and potassic white micas by constraining the pressure and temperature (P-T) conditions of metamorphism and have shown that the celadonite content of white mica is strongly dependent upon pressure.
Visible and near-infrared (Vis/NIR, 350-2500 nm) spectra of metapelites have documented that variation in the wavelength position of the Al-OH absorption band ( 2200 nm) of white micas is a direct function of octahedral cation substitutions, primarily the aluminoceladonite exchange. Therefore, variations in Vis/NIR spectra of metamorphic rocks with white micas provide first-order quantitative data regarding P-T conditions accompanying metamorphism. The results of this study will answer the following questions: 1) Do changes in P at a given T in a metamorphic terrane affect the spectroscopic and compositional variations in white micas? and 2) If there is a P control, at constant T, then what would be the effect of the phase assemblage of bulk rocks on white mica spectra and crystal chemistry with respect to the interpretation of metamorphic conditions? Preliminary results have shown direct evidence for the correlation between Al-OH absorption band and white mica composition over different metamorphic terranes. To verify these results and further document the bulk composition and P control on Al-OH absorption band, field and spectroscopic work will be conducted in Franciscan Complex of California and Camlica metamorphics of NW Turkey. We will report on micro-infrared spectroscopy, FTIR, and EMPA on selected samples to assess the reliability of field-based Vis/NIR measurements in providing first-order quantitative information regarding the P-T conditions in collisional tectonic settings.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMMR21B0058B
- Keywords:
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- 3919 Equations of state;
- MINERAL PHYSICSDE: 3924 High-pressure behavior;
- MINERAL PHYSICSDE: 3954 X-ray;
- neutron;
- and electron spectroscopy and diffraction;
- MINERAL PHYSICSDE: 3994 Instruments and techniques;
- MINERAL PHYSICS