Raman spectroscopy of natural silica in Chicxulub impactite, Mexico

Abstract

A series of natural silica impactite samples from Chicxulub (Mexico) was investigated by Raman microprobe (RMP) analysis. The data yield evidence for high-pressure shock metamorphism in the rock. The impactite contains three polymorphs of silica: the original α-quartz, and two high-pressure varieties -coesite and disordered quartz representing various degrees of crystallinity. We found systematic changes in frequencies and half-widths of the Raman bands, caused by increasing irregularities of bond-lengths and bond-angles and a general breaking-up of the structure as a result of impact events. Therefore, RMP is an adequate tool for measuring the crystallinity of disordered quartz. The half-width Γ and the frequency ω of the symmetric Si-O-Si stretching vibrational band (A 1 mode) of the SiO 4 tetrahedra are the most amenable parameters for estimating the degree of crystallinity. In well-crystallized quartz, Γ = 5 cm −1 and ω = 464 cm −1 , while in highly disordered quartz this line shifts up to ω = 455 cm −1 and broadens up to Γ = 30 cm −1 . The Raman lineshapes appear to depend strongly on the degree of lattice disorder subsequent to impact events. To cite this article: M. Ostroumov et al., C. R. Geoscience 334 (2002) 21-26.  2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS Raman spectroscopy / impactite Chicxulub / disordered quartz / MexicoRésumé -Spectroscopie Raman de silices naturelles dans l'impactite de Chicxulub, Mexique. Une série d'échantillons naturels dans une impactite de silice provenant du cratère de Chicxulub (Mexique) a été étudiée par microspectroscopie Raman. Cette technique nous montre que la roche a subi un métamorphisme de choc de haute pression. L'impactite contient trois polymorphes de silice: le quartz α et deux variétés à haute pression -coésite et quartz désordonné -, représentant divers degrés de cristallinité. On observe des changements systématiques dans les fréquences et les demi-largeurs des bandes Raman, provoqués par une augmentation des irrégularités dans les longueurs et les angles des liaisons Si-O-Si sous l'effet de l'impact. Par conséquent, la spectroscopie Raman peut être employée pour mesurer la cristallinité du quartz désordonné. La demi-largeur et la fréquence de la bande caractéristique des liaisons Si-O-Si (mode A 1 ) sont les paramètres les plus appropriés pour estimer ce degré de cristallinité. Cette bande a une fréquence de 464 cm −1 (demi-largeur 5 cm −1 ) pour le quartz cristallin et 455 cm −1 (demi-largeur 30 cm −1 ) pour le quartz hautement désordonné. Son profil spectral dépend fortement du degré de désordre engendré dans le réseau par les événements d'impact. Pour citer cet article : M. Ostroumov et al., C. R. Geoscience 334 (2002) 21-26.  2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS spectroscopie Raman / impactite de Chicxulub / quartz désordonné / Mexique * Correspondence and reprints.

Shock‐metamorphic petrography and microRaman spectroscopy of quartz in upper impactite interval, ICDP drill core LB‐07A, Bosumtwi impact crater, Ghana

“…MicroRaman analysis of the coesite yielded diagnostic spectral peaks matching those reported previously from other examples of synthetic and natural coesite ( Fig. 11b; Table 4) (Boyer et al 1985;Ostroumov et al 2002).…”

“…Raman peak frequencies (in cm −1 ) between 75 and 1200 cm −1 for coesite (Cs) in quartz (Qtz) from suevite sample BOS-8, upper impactite unit, drill core LB-07A, Bosumtwi crater, compared with other selected spectra. Ostroumov et al (2002). e Unshocked quartz, sample BOS-8, this study; analytical methods described herein.…”

Scanning electron microscopy, cathodoluminescence, and Raman spectroscopy of experimentally shock‐metamorphosed quartzite

“…The positions and widths of peaks in the Raman spectra of our unshocked and 12 GPa samples are in good agreement with these previous studies. Raman spectra and characteristic bands of coesite and stishovite have been reported by Boyer et al (1985), Serghiou et al (1995), Lounejeva et al (2002), andOstroumov et al (2002). Boyer et al (1985) found that the strongest coesite line is at 521 cm −1 , with other characteristic lines at 117, 177, and 271 cm −1 , while Serghiou et al (1995), in laser-heated diamond cell experiments, found that coesite exhibits 3 relatively strong Raman bands at 489, 552, and 790 cm −1 , and stishovite shows a strong peak at 790 cm −1 .…”

“…However, some studies of glasses and of high-pressure polymorphs of quartz exist (cf., Boyer et al 1985) that are relevant to impact studies. These include the investigation of the Raman properties of coesite from the Vredefort dome, South Africa (Halvorson and McHone 1992), coesite in suevite from the Chicxulub impact structure, Mexico Ostroumov et al 2002), natural and synthetic coesite (Boyer et al 1985), the coesite-stishovite transition (e.g., Serghiou et al 1995), the densification behavior of silica glasses in shock experiments (Okuno et al 1999), and tektites and impact glasses (Faulques et al 2001) The pre-shock temperature of the target rock also influences the formation and crystallographic orientation of PDFs. Reimold (1988), Huffman et al (1993), and Huffman and Reimold (1996) presented the results of shock experiments with quartzite and granite at room temperature (25°C) and preheated to 450°C and 750°C.…”

Mineralogical and geochemical studies of hardened subsurface layers in soils of the Azufres and Atecuaro volcanic calderas, southwestern Mexico

“…An advantage of both Raman and IR techniques is that vibrational spectroscopy gives information on the short-range ordering and, therefore, clearly has a higher sensitivity than XRD techniques to samples with strong structural disorders. Raman scattering is well adapted for the study of disordered soil minerals, particularly in the case of silica, natural and synthetic glasses (Ostrooumov et al 2002). The Raman spectra obtained from selected areas of the thin sections are shown in Fig.…”