Analyzing Raman - Infrared spectral correlation in the recently found meteorite Csátalja.

ABSTRACT

Correlating the Raman and infrared spectra of shocked minerals in Csátalja ordinary chondrite (H4, S2, W2) with controlling the composition by EPMA measurements, we identified and improved various shock indicators, as infrared spectro-microscopic analysis has been poorly used for shock impact alteration studies of meteorites to date. We also provide reference spectra as SOM for the community with local mineralogical and shock alteration related context to support further standardization of the IR ATR based measurements. Raman band positions shifted in conjunction with the increase in full width half maximum (FWHM) with shock stage in olivine minerals while in the infrared spectra when comparing the IR band positions and IR maximal absorbance, increasing correlation was found as a function of increasing shock effects. This is the first observational confirmation with the ATR method of the already expected shock related disordering. In the case of shocked pyroxenes the well-known peak broadening and peak shift was confirmed by Raman method, beyond the level that could have been produced by only chemical changes. With increasing shock level the 852-864cm-1 and 1055-1071cm-1 FTIR bands finally disappeared. From the shock effect occasionally mixed mineral structures formed, especially feldspars together with pyroxene. Feldspars were only present in the shock melted volumes, thus produced by the shock effect itself. Based on the above mentioned observations in Csátalja meteorite the less shocked (only fractured) part witnessed 2-6GPa shock pressure with temperature below 100°C. The moderately shocked parts (minerals with mosaicism and mechanical twins) witnessed 5-10GPa pressure and 900°C temperature. The strongly shocked area (many olivine and pyroxene grains) was subject to 10-15GPa and 1000°C. The existence of broad peak near 510cm-1 and disappearance of other peaks of feldspar at 480 and 570cm-1 indicate the presence of maskelynite, which proposes that the peak shock pressure could reach 20GPa at certain locations. We identified higher shock levels than earlier works in this meteorite and provided examples how heterogeneous the shock effect and level could be at small spatial scale. The provided reference spectra support the future improvement for the standardization of infrared ATR based methods and the understanding of shock-related mineral alterations beyond the optical appearance.