Remote laser-induced breakdown spectroscopy analysis of East African Rift sedimentary samples under Mars conditions

Laser-induced breakdown spectroscopy will be used by the ChemCam instrument on the Curiosity rover to obtain chemical analyses of the martian surface. Surficial and deeper hydrothermal processes on Mars have produced a diverse family of chemical and clastic sedimentary lithologies from primary igneous rocks through physical and chemical transport, deposition, and diagenesis. This study uses 16 samples from the East African Rift (EAR) as martian analogues to assess use of LIBS to evaluate weathering reactions in sedimentary rocks. Data were acquired at 9 m distance with samples under conditions designed to simulate Mars. Use of external validation, in which a few sedimentary samples are added to the validation set, coupled with choice of the first local minimum in the root mean square value in all the components of the validation model, provides optimal results in this data set. Accuracy is measured using root mean square error predictions for major elements in the sedimentary rocks, as expressed in wt.% oxides. Even lower errors can be obtained by using a more focused training set. These results are sufficiently accurate to usefully characterize the four competing kinds of chemical weathering reactions in paleosols (hydrolysis, oxidation, hydration, and salinization).