Examining Infrared Reflectance Spectra of Shocked and Unshocked Granites from Lake St. Martin Impact Structure: Implications for Detection on Mars.

English Abstract:

Evidence for granitoid rocks on Mars has been obtained through remotely sensed imagery and spectroscopic data from the central uplifts of two craters near Syrtis Major. By investigating how to identify such materials with remote sensing techniques we can enhance the ability to detect exposed granitic and granitoid outcrops on the Martian surface. In order to do so, a spectroscopic-structural-compositional study of unshocked, shocked, and melted granites has been conducted. Samples were retrieved from various locations and depths at the Lake St. Martin (LSM) impact structure in central Manitoba. The goal of this study is to relate the spectral data to shock levels in order to better understand the possible effects of shock on the detectability of granitic rocks on Mars. The LSM samples have been analyzed using Fourier transform infrared reflectance spectroscopy, X-ray diffractometry (XRD) and X-ray fluorescence (XRF) spectroscopy.

Infrared spectra of the unshocked granitic country rock have a region of enhanced reflectance between ~1250 and 900 cm^-1 which show a number of superimposed and unresolved peaks that are consistent with the unshocked nature of these materials. The granitic melt samples have a less strongly-featured interval of higher reflectance between ~1250 and 900 cm^-1 which can be explained by the amorphization of silicates through shock. The shocked but unmelted samples have spectral features that are intermediate between the unshocked and melted granites, as can be expected, with more resolvable features on the reflectance hump than the melted spectra. By relating the spectral-structural-compositional data in terms of shock and melt we can gain a better understanding of how granitic rocks respond to impact shock and the effects of impact on their detectability by various remote sensing instruments.