Raman Spectra of Shocked Minerals 1: Olivine

Abstract

Abstract— The Raman spectrum of olivine contained in a chip of the Twin Sisters Peak dunite shocked to 22.2 GPa is essentially identical to the spectrum of unshocked olivine in this rock. The Raman spectra of a powder of the rock shocked to 20.1 GPa and of chips shocked to 59.5 GPa and 60.7 GPa show strong and broad low‐frequency features with crests at 475 cm−1, 556 cm−1, and 572 cm−1, and strong as well as broad high‐frequency features near 1100 cm−1. We conclude that these features are most likely due to the formation of “olivine glass” with a considerable degree of three‐dimensional Si‐O‐Si linkage, having scattered domains of greatly variable grain size, internal structure, and, possibly, chemical composition. We cannot conclude with our results at hand whether olivine shocked to the highest pressures has not decomposed to very fine‐grained MgO plus an SiO2‐rich glass. We also conclude from our results that the structural changes are not likely to have formed in the laser beam of the measurement.

Raman spectroscopy of olivine in dunite experimentally shocked to pressures between 5 and 59 GPa

“…In both studies, olivine was used as the shock indicator. The broad feature at 1100 cm −1 , initially thought to be due to the formation of "olivine glass" (Heymann and Cellucci 1988), was absent in the olivine spectra of all chondrites. The shocked meteoritic olivine spectra were almost identical to the spectra of the unshocked olivine, and it was concluded that the absence of the 1100 cm −1 Raman band and the strong luminescence in the heavily shocked chondrite samples were a result of thermal annealing due to fairly slow cooling from the initial shock temperatures.…”

“…Many petrographic studies on naturally and experimentally shock-metamorphosed minerals have been conducted (e.g., with regard to olivine, Stˆffler 1972;Reimold and Stˆffler 1978;Bauer 1979;Stˆffler et al 1991;Bischoff and Stˆffler 1992). In contrast, Raman and infrared spectroscopic studies of shocked olivine (Besson et al 1982;Heymann and Cellucci 1988;Durben et al 1993;Miyamato and Ohsumi 1995) are still limited, and they do not yet provide conclusive information on the exact shift in wave number or broadening of full width at half maximum (FWHM) values that can be expected for a specific olivine composition at a given shock pressure. Although the published experimental work covers a large pressure range (0-133 GPa), individual studies often did not report the actual wave number shifts in the Raman lines for shocked olivine.…”

“…These experiments produced no evidence of high-pressure phases of olivine or pyroxene in the pressure range of 12-133 GPa. Heymann (1990) performed a study of 37 shocked ordinary chondrites using Raman spectroscopy to determine if a broad feature that had been apparent in a previous study (Heymann and Cellucci 1988) of experimentally shocked Twin Sisters Peak dunite was also present in heavily shocked chondrites. In both studies, olivine was used as the shock indicator.…”

Raman spectroscopic study of four Spanish shocked ordinary chondrites: Cañellas, Olmedilla de Alarcón, Reliegos and Olivenza

“…Englert et al (1980) detected a shift to higher wavelength in the position of the Raman line under compressive forces. Heymann & Cellucci (1988) specifically compared the Raman spectra of chondritic laboratory-impacted olivines and non-impacted olivines. For a pressure of 22.2 GPa, the two were identical.…”

“…Such deformations can be studied with Raman spectroscopy. Several authors have used this technique to evaluate crystal deformation in highly shocked meteorites (Englert et al 1980;Heymann & Cellucci 1988;Heymann 1990;Chen & Xie 1992;Miyamoto & Ohsumi 1995;Hezel et al 2008;Weselucha-Birczynska & Zmudzka 2008; among others), but no specific Raman studies have been performed on minerals from weak-to-moderately shocked chondrites to our knowledge.…”