Shock and thermal annealing history of the ALH 77005 Martian meteorite: a micro-Raman spectroscopical investigation

Abstract

We studied optical microscopic and micro-Raman spectroscopic signatures of shocked olivine from the ALH 77005 Martian meteorite sample. The purpose of this study is to document pressure and temperature-related effects in olivine over the entire sample, which can aid in understanding structural changes due to shock metamorphism and the post-shock thermal annealing processes of lherzolitic Martian meteorites. According to the optical microscope observations, three areas may be discernible in olivine of the ALH 77005 in the vicinity of the melt pocket. The first area is the thermally undisturbed part of a grain, which contains a high density of shock-induced planar microdeformations such as Planar Deformation Features (PDFs) and Planar Fractures (PFs). Compared to the first area, the second area shows less shock-induced microstructures, while the third area is a strongly recrystallized region, but not formed from a melt.A common Raman spectral feature of these olivines is a regular doublet peak centered at 823 and 852 cm -1 ; additionally, two new peaks at 535 and 755 cm -1 appear in the weakly annealed transition zones.

Chemical and mineralogical characterization of the Mineo (Sicily, Italy) pallasite: A unique sample

“…The altered relative intensity of the olivine Raman signals also suggests the possible occurrence of microstructures and crystallographic disorder, likely due to late shock processes ( Van de Moort ele et al 2007;Nagy et al 2008).…”

Detailed mineralogy and petrology of highly shocked poikilitic shergottite Northwest Africa 6342

“…This shift may be due to compositional differences, or the presence of multi-oriented small crystal domains in these grains (Farrell-Turner et al 2005). Previous Raman spectroscopy studies of shocked olivine in other poikilitic shergottites have observed an additional Raman peak at 750 cm À1 , indicating the presence of the high-pressure polymorph of olivine, wadsleyite (Gillet et al 2005;Nagy et al 2012). However, no high-pressure polymorphs are identified in NWA 6342.…”