Laser Raman microspectrometry of metamorphic quartz: A simple method for comparison of metamorphic pressures

Abstract

A Laser Raman microspectrometry method was applied to metamorphic quartz in quartz-eclogite-, epidote-amphibolite-, and amphibolite-facies rocks to assess the quantitative correlation between the Raman frequency shift and metamorphic pressure. Quartz crystals sealed in garnet and other phases have a higher frequency shift than those in the matrix. Furthermore, the quartz inclusions show a frequency shift specifi c to the individual host crystals in eclogites (garnet ≈ kyanite > omphacite ≈ epidote). These observations imply that the residual pressures retained by quartz inclusions depend on elastic parameters of the host crystals, as discussed by previous researchers. The Raman frequency shift of quartz inclusions in garnet systematically increases with increasing peak metamorphic pressures from the amphibolite facies (0.30-0.55 GPa/470-570 °C), through the epidote-amphibolite facies (0.8-1.1 GPa/470-635 °C) to the quartz-eclogite facies (2.1-2.5 GPa/660-710 °C). Calibrations based on experimental work suggest that the measured Raman frequency shifts signify residual pressures of 0.1-0.2, 0.4-0.6, and 0.8-1.0 GPa for these three groups of metamorphic rocks, respectively. Normal stresses (internal pressures) of quartz inclusions in garnet, numerically simulated with an elastic model, and inferred pressure-temperature conditions at peak metamorphic stage are compatible with the residual pressures estimated from the frequency shifts. Laser Raman microspectroscopic analysis of quartz is a simple and effective method for (1) comparison of pressure conditions in metamorphic rocks formed under various pressure-temperature conditions, and (2) detection of a higher-pressure signature in metamorphic rocks extensively recrystallized during the subsequent exhumation and hydration stage.

Is quartz a potential indicator of ultrahigh-pressure metamorphism? Laser Raman spectroscopy of quartz inclusions in ultrahigh-pressure garnets

“…For different UHPM complexes the maximum upshift of the main Raman quartz bands (up to 477 cm À1 ) was documented for partly transformed coesite inclusions , corresponding to residual pressures of up to 1.6 GPa, (using the calibration of Hemley, 1987). Unlike Enami et al (2007), we found no correlation between the residual pressure and the size of the inclusions. Table 4.…”

“…The Raman shift of quartz was recently tested on natural samples in order to estimate the effect of peak metamorphic pressure on residual pressure within the quartz inclusions (Enami et al, 2007). For different UHPM complexes the maximum upshift of the main Raman quartz bands (up to 477 cm À1 ) was documented for partly transformed coesite inclusions , corresponding to residual pressures of up to 1.6 GPa, (using the calibration of Hemley, 1987).…”

“…The effect of pressure and temperature on quartz Raman bands positions is experimentally well known (Hemley, 1987;Schmidt & Ziemann, 2000). A quartz geobarometer has been calibrated recently on metamorphic quartz from quartz-eclogite, epidote-amphibolite, and amphibolitefacies rocks (Enami et al, 2007). In this paper, we study the application of the quartz geobarometer to coesite-and diamond-grade metapelites from the Kokchetav complex, Northern Kazakhstan and diamond-grade eclogite xenoliths from the Mir kimberlite pipe, Yakutiya, Russia.…”

Compositional zoning and inclusions of garnet in Sanbagawa metapelites from the Asemi-gawa route, central Shikoku, Japan

“…Residual pressure retained by quartz completely sealed in garnet was measured using Raman spectra with a parameter of ∆ω 1 = ω 1 standard − ω 1 sample (Enami et al, 2007). The ∆ω 1 values are 5.5 -7.0 cm −1 in the garnet zone samples, and most values in the oligoclase -biotite zone samples are less than 8.5 cm −1 (Fig.…”

A Raman spectroscopic study of a fulgurite

“…Colomban (2000Colomban ( , 2001 has described this complex picture in an elegant way, invoking several types of chain, sheet and three-dimensional structures labelled Q 0 -Q 4 , which can be assigned as follows: Q 0 , representing monomer SiO 4 units, with bands in the region 850-800 cm −1 ; Q 1 , representing Si 2 O 7 groups, with a band near 950 cm −1 ; Q 2 , silicate chains with bands in the region of 1100-1050 cm −1 ; Q 3 , silicate sheets with a band near 1100 cm −1 ; and Q 4 , representing SiO 2 and tectosilicates with a band in the range of 1250-1150 cm −1 . Additionally, spectral features may arise from crystalline quartz and its modifications caused by pressure or temperature extremes, for which the parent Si=O band occurs at 465 cm −1 (Jayaraman et al 1987;McMillan et al 1992;Schmidt & Ziemann 2000;Enami et al 2007). Figure 2 presents a typical spectrum collected from a glass bubble within a fulgurite specimen.…”