Opaline silica in young deposits on Mars

Abstract

High spatial and spectral resolution refl ectance data acquired by the Mars Reconnaissance Orbiter Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument reveal the presence of H 2 O-and SiOH-bearing phases on the Martian surface. The spectra are most consistent with opaline silica and glass altered to various degrees, confi rming predictions based on geochemical experiments and models that amorphous silica should be a common weathering product of the basaltic Martian crust. These materials are associated with hydrated Fe sulfates, including H 3 O-bearing jarosite, and are found in fi nely stratifi ed deposits exposed on the fl oor of and on the plains surrounding the Valles Marineris canyon system. Stratigraphic relationships place the formation age of these deposits in the late Hesperian or possibly the Amazonian, implying that aqueous alteration continued to be an important and regionally extensive process on Mars during that time.

Juvenile chemical sediments and the long term persistence of water at the surface of Mars

“…Recent data from the TES and THEMIS instruments further indicate large deposits of amorphous silica in western Hellas Basin (Bandfield, 2008). And more recently, a form of "hydrated silica" has been identified in Noachian terrains associated with detections of phyllosilicate minerals (Mustard et al, 2008); these detections are, however, spectrally distinct from the opaline silica deposits analyzed by Milliken et al (2008). We refer to these phases as amorphous and opaline/hydrated silica; as treated here, these include siliceous deposits in the form of coatings, residual leachates, or phases precipitated from solution (which can contain a number of compositional impurities).…”

“…Many of the same strata that contain opaline silica are thought to contain ferricopiapite, an Fesulfate mineral which forms at pH on the order of 1 or less (Milliken et al, 2008 (Morris et al, 2006). Schwertmannite, an iron oxyhydroxysulfate, rapidly decomposes to either jarosite or goethite over a range of pH and so its preservation on the martian surface could also indicate a water-limited history.…”

“…At Gusev Crater, opaline silica was identified in the Columbia Hills and interpreted as the product of intense aqueous activity, possibly related to hydrothermal processes (Squyres et al, 2008). Using orbital data, Milliken et al (2008) identified opaline silica in the visible/near infrared (vis/NIR) using data from the MRO CRISM instrument. These latter deposits, many of which are associated with Fe-sulfates, are of Hesperian age and effectively expand the spatial and potentially temporal occurrence of opaline silica on ancient Mars.…”

“…Hydrated silicates (including clays), sulfates and (hydr)oxides occur in exposures of Noachian and Hesperian age (~4.2-2.0 Ga; Ga: billion years), reflecting both spatial and temporal variation in acidity, volatile content and redox state (Ehlmann et al, 2008a;Milliken et al, 2008;Mustard et al, 2008;Squyres et al, 2008). Questions of habitability, however, require that we go beyond simple presence/absence to investigate the chemistry and persistence of that water.…”

New evidence for a magmatic influence on the origin of Valles Marineris, Mars

“…OMEGA and CRISM have both identified a significant number of locations of hydrated sulfates Gendrin et al, 2005;Murchie et al, in press) and hydrated phyllosilicates Poulet et al, 2005;Milliken et al, 2008b;Bishop et al, 2007;Mustard et al, 2007;Bishop et al, 2008a,b;McKeown et al, 2008;Mustard et al, 2008) on the Martian surface, as well as other hydrated minerals, such as hydrated silica (Milliken et al, 2008a,b;Bishop et al, 2008a). One such locality is the Claritas rise.…”