Raman–Mo¨ssbauer–XRD studies of selected samples from ‘‘Los Azulejos” outcrop: A possible analogue for assessing the alteration processes on Mars

摘要

The outcrop of ‘‘Los Azulejos” is visible at the interior of the Can˜adas Caldera in Tenerife Island (Spain). It exhibits a great variety ofalteration processes that could be considered as terrestrial analogue for several geological processes on Mars. This outcrop is particularlyinteresting due to the content of clays, zeolite, iron oxides, and sulfates corresponding to a hydrothermal alteration catalogued as ‘‘Azulejos”type alteration. A detailed analysis by portable and laboratory Raman systems as well as other different techniques such as X-raydiffraction (XRD) and Mo¨ssbauer spectroscopy has been carried out (using twin-instruments from Martian lander missions: Mo¨ssbauerspectrometer MIMOS-II from the NASA-MER mission of 2001 and the XRD diffractometer from the NASA-MSL Curiosity mission of2012). The mineral identification presents the following mineral species: magnetite, goethite, hematite, anatase, rutile, quartz, gregoryite,sulfate (thenardite and hexahydrite), diopside, feldspar, analcime, kaolinite and muscovite. Moreover, the in-situ Raman and Micro-Raman measurements have been performed in order to compare the capabilities of the portable system specially focused for the nextESA Exo-Mars mission. The mineral detection confirms the sub-aerial alteration on the surface and the hydrothermal processes bythe volcanic fluid circulations in the fresh part. Therefore, the secondary more abundant mineralization acts as the color agent of therocks. Thus, the zeolite–illite group is the responsible for the bluish coloration, as well as the feldspars and carbonates for the whitishand the iron oxide for the redish parts. The XRD system was capable to detect a minor proportion of pyroxene, which is not visible byRaman and Mo¨ssbauer spectroscopy due to the ‘‘Azulejos” alteration of the parent material on the outcrop. On the other hand, Mo¨ ssbauerspectroscopy was capable of detecting different types of iron-oxides (Fe3+/2+-oxide phases). These analyses emphasize the strengthof the different techniques and the working synergy of the three different techniques together for planetary space missions.