Igneous mineralogy at Bradbury Rise: The first ChemCam campaign at Gale crater
Résumé
Textural and compositional analyses using Chemistry Camera (ChemCam) remote
microimager and laser-induced breakdown spectroscopy (LIBS) have been performed on five
float 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 assess
mineralogic diversity at grain-size scales (~ 100 μm) and, from this, lithologic diversity. Depth
profiling indicates that targets are relatively free of surface coatings. One type of igneous rock is
volcanic and includes both aphanitic (Coronation) and porphyritic (Mara) samples. The
porphyritic sample shows dark grains that are likely pyroxene megacrysts in a fine-grained
mesostasis containing andesine needles. Both types have magnesium-poor basaltic
compositions and in this respect are similar to the evolved JakeMatijevic rock analyzed further
along the Curiosity traverse both with Alpha-Particle X-ray Spectrometer and ChemCam
instruments. 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 a
rock is not unique at Gale as the surrounding coarse gravels (such as Beaulieu) and the
conglomerate Link are dominated by feldspathic (andesine-bytownite) clasts. Finally, alkali
feldspar compositions associated with a silica polymorph have been analyzed in fractured filling
material of Preble rock and in Stark, a putative pumice or an impact melt. These observations
document magmatic diversity at Gale and describe the first fragments of feldspar-rich
lithologies (possibly an anorthosite) that may be ancient crust transported from the crater rim
and now forming float rocks, coarse gravel, or conglomerate clasts.
Domaines
Sciences de la Terre
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JGR Planets - 2013 - Sautter - Igneous mineralogy at Bradbury Rise The first ChemCam campaign at Gale crater.pdf (2.42 Mo)
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