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

Research areas:
Year:
2014
Authors:
  • V. Sautter
  • C. Fabre
  • O. Forni
  • M. J. Toplis
  • A. Cousin
  • A. M. Ollila
  • P. Y. Meslin
  • S. Maurice
  • R. C. Wiens
  • D. Baratoux
  • Nicolas Mangold
  • Stéphane Le Mouélic
  • O. Gasnault
  • G. Berger
  • J. Lasue
  • R. A. Anderson
  • E. Lewin
  • M. Schmidt
  • D. Dyar
  • B. L. Ehlmann
  • J. Bridges
  • B. Clark
  • P. Pinet
Journal:
JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS
Volume:
119
Number:
1
Pages:
30-46
Month:
January
ISSN:
2169-9097
Abstract:
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 (similar to 100 mu m) 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.