[en] Long classified as coral hydrozoans, Chaetetids are now considered as a group of very shallow marine hyper calcified sponges. As corals do, they grow by adding calcium carbonate under their pellicular living body in such a rhythmic and regular way that we suspect that sclerochronology is possible, based on the hypothetical annual growth bands of their skeleton. Regarding to its accurate lateral resolution of 5 μm by laser shot, micro-LIBS study was chosen to check its potential for such application. The LIBS apparatus is composed of a microscope coupled with a 266 nm Nd-YAG laser, delivering a 4 mJ-power per shot, and an ICCD camera. The acquisition of the spectra is made via the SE 200 spectrograph, on the large 190 nm to 1100 nm wavelength range. The entire longitudinal thin section of the specimen was analysed from the bottom to the top of the Ptychochaetetes section in a multi-elementary cartography for Ca-Mg-Sr elements. Sodium and Barium were also detected but trace amounts. The Mg/Ca concentrations are mainly between 400 and 600 mmol/mol considering an average value for each profile. This study shows that during the Ptychochaetetes growth, an obvious time-dependent heterogeneity in the chemical Mg/Ca and Sr/Ca composition can be observed. These variations demonstrate the possible use of this method for sclerochronological studies

[en] As a result of continuing instrumental development (Echelle spectrometer and ICCD detectors), micro-Laser Induced Breakdown Spectroscopy analysis may become an increasingly recognized analytical technique for determining elemental compositions of geologic materials. Best conditions of time resolution conditions (delay and time acquisition window) are estimated with respect to the collection geometry of optical plasma emission of our system. It turns out that the level of the Bremsstrahlung continuum emission is weak in the first tens of nanoseconds after the laser excitation pulse. The enlargement of the emission lines is identified in the first 100 ns but remains comparable to the spectral resolution of our system. Thus, results show that time-resolved conditions are not necessarily required to perform elemental analysis at the micrometric scale using LIBS, contrary to macro-LIBS. This suggests potential improvements of micro-LIBS analysis (sensitivity and spectral resolution) using non-intensified CCD connected with the laser pulse. However, in order to improve the detection of weak signals obtained with an ICCD detector, working at high gain, a new method of signal processing on two-dimensional Echelle images has been developed. This method, based on the comparison of two 2D images, allows the identification of group of pixels (particles) that can be considered as representative of actual signals. This methodology applied to LIBS spectra eliminates the majority of noise peaks, allows the identification of weak signals which were almost impossible to extract from the noise, and does not alter the intensity ratio between emission lines. This method overcomes the poor dynamics of ICCD used at maximum gains and opens new possibilities in micro-LIBS analysis

[en] The Chemistry Camera (ChemCam) instrument onboard Curiosity can detect minor and trace elements such as lithium, strontium, rubidium, and barium. Their abundances can provide some insights about Mars' magmatic history and sedimentary processes. We focus on developing new quantitative models for these elements by using a new laboratory database (more than 400 samples) that displays diverse compositions that are more relevant for Gale crater than the previous ChemCam database. These models are based on univariate calibration curves. For each element, the best model is selected depending on the results obtained by using the ChemCam calibration targets onboard Curiosity. New quantifications of Li, Sr, Rb, and Ba in Gale samples have been obtained for the first 1000 Martian days. Comparing these data in alkaline and magnesian rocks with the felsic and mafic clasts from the Martian meteorite NWA7533—from approximately the same geologic period—we observe a similar behavior: Sr, Rb, and Ba are more concentrated in soluble- and incompatible-element-rich mineral phases (Si, Al, and alkali-rich). Correlations between these trace elements and potassium in materials analyzed by ChemCam reveal a strong affinity with K-bearing phases such as feldspars, K-phyllosilicates, and potentially micas in igneous and sedimentary rocks. However, lithium is found in comparable abundances in alkali-rich and magnesium-rich Gale rocks. This very soluble element can be associated with both alkali and Mg-Fe phases such as pyroxene and feldspar. Here, these observations of Li, Sr, Rb, and Ba mineralogical associations highlight their substitution with potassium and their incompatibility in magmatic melts.

[en] The ChemCam instrument suite on the Mars Science Laboratory (MSL) rover Curiosity provides remote compositional information using the first laser-induced breakdown spectrometer (LIBS) on a planetary mission, and provides sample texture and morphology data using a remote micro-imager (RMI). Overall, ChemCam supports MSL with five capabilities: remote classification of rock and soil characteristics; quantitative elemental compositions including light elements like hydrogen and some elements to which LIBS is uniquely sensitive (e.g., Li, Be, Rb, Sr, Ba); remote removal of surface dust and depth profiling through surface coatings; context imaging; and passive spectroscopy over the 240-905 nm range. ChemCam is built in two sections: The mast unit, consisting of a laser, telescope, RMI, and associated electronics, resides on the rover's mast, and is described in a companion paper. ChemCam's body unit, which is mounted in the body of the rover, comprises an optical de-multiplexer, three spectrometers, detectors, their coolers, and associated electronics and data handling logic. Additional instrument components include a 6 m optical fiber which transfers the LIBS light from the telescope to the body unit, and a set of onboard calibration targets. ChemCam was integrated and tested at Los Alamos National Laboratory where it also underwent LIBS calibration with 69 geological standards prior to integration with the rover. Post-integration testing used coordinated mast and instrument commands, including LIBS line scans on rock targets during system-level thermal-vacuum tests. In this paper we describe the body unit, optical fiber, and calibration targets, and the assembly, testing, and verification of the instrument prior to launch. (authors)