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

Abstract

[1] 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 Jake Matijevic 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.

Melting of the primitive martian mantle at 0.5–2.2 GPa and the origin of basalts and alkaline rocks on Mars

“…These samples were only analyzed with the ChemCam instrument (laser-induced breakdown spectroscopy), and precise bulk rock compositions are not available. However, chemical analyses highlighted an important compositional diversity ranging from basaltic to evolved and alkali-rich compositions similar to Jake_M (Sautter et al, 2014;Schmidt et al, 2014). Alkalibasalts and tholeiitic basalts might coexist in the same locality, as also observed in Gusev Crater.…”

“…Further studies of the infrared spectral data (Carter and Poulet, 2013;Christensen et al, 2005;Wray et al, 2013), new meteorite discoveries (Agee et al, 2013;Humayun et al, 2013), recent analyses by the Mars Science Laboratory mission (Stolper et al, 2013;Sautter et al, 2014), and re-interpretation of Pathfinder analyses (Foley et al, 2003) have also highlighted the presence of alkaline rocks, silicic rocks, and anorthosites. These occurrences indicate that the martian crust exhibits a larger compositional vari-ability than initially thought.…”

Gale crater and impact processes – Curiosity’s first 364 Sols on Mars

“…13H (to the right), named Stark, shows surprisingly high silicon content indicating a felsic composition. ChemCam analyses of igneous materials on the Hummocky Plains seem to generally reflect a felsic composition (Williams et al, 2013;Meslin et al, 2013;Sautter et al, 2014).…”

“…The rock Mara (Fig. 13B) exhibits a coarse-grained texture typical of slowly-cooled magmatic rocks, including dark millimeter-wide phenocrysts typical of mafic phases (i.e., pyroxene or olivine), separated by light-toned matrix likely dominated by feldspars (Sautter et al, 2014). Coronation and La Reine (Fig.…”

Volcanism and tectonism across the inner solar system: an overview

“…Rock compositional analyses at the Mars Exploration Rover 'Spirit' and Mars Science Laboratory 'Curiosity' landing sites provided evidence for a bulk-chemical, mineralogical and textural diversity of igneous samples (e.g. Squyres et al 2006;Sautter et al 2014). …”