Igneous mineralogy at Bradbury Rise: The first ChemCam campaign at Gale crater

International audienceTextural and compositional analyses using Chemistry Camera (ChemCam) remotemicroimager and laser-induced breakdown spectroscopy (LIBS) have been performed on fivefloat rocks and coarse gravels along the first 100 m of the Curiosity traverse at Bradbury Rise.ChemCam, the first LIBS instrument sent to another planet, offers the opportunity to assessmineralogic diversity at grain-size scales (~ 100 μm) and, from this, lithologic diversity. Depthprofiling indicates that targets are relatively free of surface coatings. One type of igneous rock isvolcanic and includes both aphanitic (Coronation) and porphyritic (Mara) samples. Theporphyritic sample shows dark grains that are likely pyroxene megacrysts in a fine-grainedmesostasis containing andesine needles. Both types have magnesium-poor basalticcompositions and in this respect are similar to the evolved JakeMatijevic rock analyzed furtheralong the Curiosity traverse both with Alpha-Particle X-ray Spectrometer and ChemCaminstruments. The second rock type encountered is a coarse-grained intrusive rock (Thor Lake)showing equigranular texture with millimeter size crystals of feldspars and Fe-Ti oxides. Such arock is not unique at Gale as the surrounding coarse gravels (such as Beaulieu) and theconglomerate Link are dominated by feldspathic (andesine-bytownite) clasts. Finally, alkalifeldspar compositions associated with a silica polymorph have been analyzed in fractured fillingmaterial of Preble rock and in Stark, a putative pumice or an impact melt. These observationsdocument magmatic diversity at Gale and describe the first fragments of feldspar-richlithologies (possibly an anorthosite) that may be ancient crust transported from the crater rimand now forming float rocks, coarse gravel, or conglomerate clasts