Innovative micro-Laser Induced Breakdown Spectroscopy of Enstatite Chondrites: preliminary data of Sahara 97072 EH3

The study of enstatite chondrites (ECs) may play an important role in understanding the evolution of Earth, inner Solar System and asteroid belt. ECs are very scarce among chondritic meteorites. The chemical composition of their silicates, sulphides and metals reflect their formation under highly reducing conditions. Most ECs are completely dry and lack any evidence of hydrous alteration, thus ECs were formed likely within the snow line and are good candidates to be considered the building blocks of inner planets, like Mercury. ECs represent the most reduced group among chondrites, featuring enstatite chondrules (FeO < 1 wt%), low olivine content, Fe-Ni alloy, and oxygen isotopic ratios that match the terrestrial fractionation line (TFL) and are subdivided in two groups: EH and EL, i.e. high and low Fe-metal content, respectively (Keil, 1968). In this work a thin section of the EC labelled Sahara 97072 EH3 previously investigated by multi-analytical approach (Manzari, 2010), was studied by means of Laser Induced Breakdown Spectroscopy (LIBS). LIBS advantages with respect to conventional analytical techniques are: simultaneous multi-element qualitative and quantitative analysis in real time, high sensitivity, stratigraphic analysis of a sample by profiling, especially sensitive to light elements such as C, B, Be, H and Li, no need of an analytical chamber, sampling and surface treatment (Senesi, 2014). Recently, the potentiality of LIBS was exploited even in remote elemental analysis of extraterrestrial rocks. LIBS technique was installed onboard of NASA Mars Science Laboratory rover named Curiosity, as part of ChemCam to provide chemical analyses on Martian rocks (Wiens et al., 2013; Gordon et al., 2014). In this study, an innovative LIBS prototype (Fig. 1a), operating with a Nd:YAG laser in double pulse configuration, was used coupled with a petrographic microscope (micro-LIBS) that allows chemical investigations directly on the thin section (Fig. 1b). This innovative approach enables to perform chemical analyses preserving a qualitative knowledge of the phases in a thin section taking into account the distribution of the grains, the texture and any preferred orientations at the microscale. In particular, qualitative micro-LIBS data (Fig. 1c) of metal-sulfide-nodules consisting of kamacite Fe, Ni, Cr-troilite, and oldhamite CaS resulted in good agreement with data previously obtained by SEM-EDS. Future investigations on martian meteorites using micro-LIBS will be carried out to validate the data obtained in remote mode by ChemCam.