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

Abstract

Shock metamorphism in chondritic parent bodies produces typical textures, visible under the microscope, which are a consequence of structural deformation of the crystals. Such deformations can be studied with Raman spectroscopy. The vibrational characteristics of olivines and pyroxenes, structurally deformed by weak-to-moderate shock metamorphism, have been determined on four Spanish ordinary chondrites (Cañellas, Olmedilla de Alarcón, Reliegos and Olivenza). Such deformations would affect, in principle, the band positions and widths of the Raman spectra peaks. The measured band positions and relative intensities are consistent with chemical composition for olivines and pyroxenes, but show little influence on the degree of shock. However, the full spectral band width of the silicate internal modes shows some dependence on the impact grade, which could be attributed to inhomogeneous effects produced by the impacts.

Shock heterogeneity and shock history of the recently found ordinary Csátalja chondrite in Hungary

“…Sim i larly to olivines, the FWHM of the ma jor band at 1004 cm -1 of unshocked py rox enes are char ac ter ized by FWHM val ues of 10 cm -1 . Ac cord ing to Rull et al (2010), shocked py rox enes in the S3-S4 chondrites show 16-21 cm -1 FWHM at the ma jor band of 1009 cm -1 near to unshocked pyrox enes with FWHM near to 10 cm -1 . The FWHM val ues of pyrox enes in the Csátalja sam ples vary be tween 12 and 30 cm -1 (Csátalja-1: 12-30 cm -1 , Csátalja-2: 15-30 cm -1 ), which exceed the S3 shock level.…”

“…Pub li ca tions based ref er ences of FWHM val ues were compared to the Raman spec tro scopic and FTIR mea sure ments of olivines and py rox enes in this work. The unshocked olivines are char ac ter ized by main dou blet peak po si tions of 820 and 850 cm -1 (Rull et al, 2010), with FWHM 10 cm -1 (Miyamoto and Ohsumi, 1995). Ac cord ing to Miyamoto and Ohsumi (1995), the shocked ol iv ine with 21 cm -1 FWHM (char ac ter ized also by the cor re spond ing peak shift) pro posed shock stage is 15 GPa, 900°C.…”

“…The shock-pro duced change in peak po si tions and FWHM val ues were com pared to min eral ref er ence data from unshocked sam ples of Earth-based ma te ri als, where the compositional rea sons (mea sured by EMPA for the sam ples ana lysed in this work) for changes were ex cluded by us ing the same com po si tion ref er ence min er als (dis played in Ap pen dices 1 and 2, col umns 1 and 2). In gen eral, the peak po si tions shifted to higher wavenumbers in in fra-red and Raman spectros copy (Ap pen di ces 1 and 2 col umn 2, col umn 6) with increas ing shock stages (es ti mated ini tially by op ti cal ob ser vation, then com pared to Raman FWHM val ues of shocked mineral ref er ence ma te rial, Rull et al, 2010), and show shift and broad en ing of peaks (Ap pen di ces 1 and 2 col umns 4 and 8) Shock heterogeneity and shock history of the recently found ordinary Csátalja chondrite in Hungary 437…”

“…The ref er ences used are from ar ti ficially pro duced pres sure-driven lab o ra tory-based de for ma tion tests, so the FWHM val ues are def i nitely from pres sure-driven crys tal line lat tice de for ma tion. The unshocked olivines are char ac ter ized by main dou blet peak po si tions of 820 and 850 cm -1 (Rull et al, 2010), with FWHM of 10 cm -1 (Miyamoto and Ohsumi, 1995). Ac cord ing to Miyamoto and Ohsumi (1995), the shocked ol iv ine with 21 cm -1 FWHM points to a shock stage of 15 GPa, 900°C.…”

“…The feldspar spec tra (oligoclase-lab ra dor ite) were com pared to those of Free man et al (2008), the py rox enes to Huang et al (2000), and the olivines to Kuebler et al (2006). The FWHM val ues (mea sured man u ally in Crys tal Sleuth as the width at the half of the max i mum peak in ten sity) were used to im prove shock stage iden ti fi ca tion; us ing the crys tal line lat tice dis or der ing they produce what could be iden ti fied in peak changes, and the val ues were com pared to Rull et al (2010) for py rox enes and olivines, and to Fritz et al (2005) in the case of feld spars.…”