Evaluation of LIBS-based imaging for the detection of minor and trace elements in minerals with microscopic-scale resolution.

We present a breadboard prototype to perform in situ dating applicable to planetary exploration. Based on the K-Ar dating method and using instruments inspired by flight-proven analytical components, 'KArMars' ablated a geological sample under high vacuum with a quadrupled ultraviolet (UV at 266 nm) Nd:YAG laser. During ablation, the K content of the target material was given by laserinduced breakdown spectroscopy and the released 40 Ar was measured with a quadrupole mass spectrometer. Because K was measured as a concentration and 40 Ar as a count of atoms, these values were converted using the ablated mass given by the product of the density and the ablated volume. The uncertainties of the age measurement were < 15%. The quality of the K-Ar measurements was enhanced by the advantages of UV laser ablation such as the minimisation of thermal effects on argon diffusion. This work demonstrates that a specialised instrument inspired by this set-up could provide in situ absolute geochronology with sufficient precision for scientific investigations, particularly where the crater density counting provides higher uncertainties on Mars.Keywords: geochronology, K-Ar, laser ablation, laser-induced breakdown spectroscopy, mass spectrometry, in situ analysis.Nous pr esentons un prototype d edi e a la datation in situ pour l'exploration plan etaire. Bas e sur la m ethode de datation K-Ar et inspir e par instruments d ej a spatialis es, « KArMars » ablate un echantillon de basalte plac e sous ultravide avec un laser Nd:YAG puls e quadrupl e a 266 nm. Lors de l'ablation, le plasma emet un spectre qui une fois analys e, fournit la concentration en K par la technique LIBS et l'ablation lib ere l' 40 Ar qui est quantifi e par un spectrom etre de masse quadrupolaire. Comme nous mesurons la concentration de K et le nombre d'atomes d' 40 Ar, ces valeurs doiventêtre converties par la masse ablat ee qui est le produit du volume ablat e par la densit e. Les principaux int erêts d'utiliser un laser UV concernent l'efficacit e d'ablation et la minimalisation des effets thermiques, ce qui limite la diffusion d'Argon. Les incertitudes sur la mesure de l'âge peuventêtre de 15%. Ce travail d emontre qu'un instrument spatial bas e sur ce principe pourrait fournir des datations absolues in situ et ce avec une pr ecision suffisante pour ajuster les courbes de densit e de crat eres qui, sur Mars, peuvent avoir des fortes incertitudes.Mots-clés : g eochronologie, K-Ar, ablation laser, LIBS, spectrom etrie de masse, analyse in situ.