Phyllosilicate Diversity and Past Aqueous Activity Revealed at Mawrth Vallis, Mars

Abstract

Observations by the Mars Reconnaissance Orbiter/Compact Reconnaissance Imaging Spectrometer for Mars in the Mawrth Vallis region show several phyllosilicate species, indicating a wide range of past aqueous activity. Iron/magnesium (Fe/Mg)–smectite is observed in light-toned outcrops that probably formed via aqueous alteration of basalt of the ancient cratered terrain. This unit is overlain by rocks rich in hydrated silica, montmorillonite, and kaolinite that may have formed via subsequent leaching of Fe and Mg through extended aqueous events or a change in aqueous chemistry. A spectral feature attributed to an Fe 2+ phase is present in many locations in the Mawrth Vallis region at the transition from Fe/Mg-smectite to aluminum/silicon (Al/Si)–rich units. Fe 2+ -bearing materials in terrestrial sediments are typically associated with microorganisms or changes in pH or cations and could be explained here by hydrothermal activity. The stratigraphy of Fe/Mg-smectite overlain by a ferrous phase, hydrated silica, and then Al-phyllosilicates implies a complex aqueous history.

Characterization and Calibration of the CheMin Mineralogical Instrument on Mars Science Laboratory

“…Recent observations of hydrated silicate minerals by the CRISM instrument on Mars Reconnaissance Orbiter have validated these observations and provided an even more detailed picture of the distribution of hydrous phyllosilicates on the Martian surface Bishop et al 2008). OMEGA and CRISM data also suggest the presence of diverse clay minerals, including Fe,Mg,Al-phyllosilicates, kaolin group minerals, chlorites, and serpentine minerals, along with a variety of hydrous sulfate minerals.…”

Mineral paragenesis on Mars: The roles of reactive surface area and diffusion

“…Provided the existence of an alternative source of anions, mainly derived from volcanic volatiles [ Halevy and Head , 2014], it is expected that these ions would have bonded in evaporites (i.e., sulfates). However, in most localities on Mars, evaporites are commonly absent in clay‐dominated sediments [ Bandfield et al ., 2003; Bishop et al ., 2008; Ehlmann et al ., 2008; Osterloo et al ., 2008]. As a particular example, evaporites in Gale crater are the result of postdepositional fluid migration, in different late‐stage episodes of fluid flow; therefore, clays and evaporites at Gale have very different depositional histories, occurring spatially closely but with deposition times separated by hundreds of millions of years [ Nachon et al ., 2014; Rapin et al ., 2016].…”

The science process for selecting the landing site for the 2011 Mars Science Laboratory

“…3) marks a candidate landing site that is characterized by a thick, widespread, and layered sequence. Exposed rocks incorporate phyllosilicates and likely reflect a complex aqueous history and alteration of basalt Bishop et al, 2008;Loizeau et al, 2007;Michalski and Noe Dobrea, 2007;Poulet et al, 2005;Wray et al, 2008). Within the Mawrth sequence, Al-phyllosilicates overlie Fe/Mg phyllosilicates without any observable inter-bedding.…”

“…The phyllosilicates also outcrop well to the south of Mawrth Vallis (Noe Dobrea et al, 2010) and such a broad extent could imply they formed in situ. Although the Mawrth layered materials may reflect pedogenic alteration (Loizeau et al, 2010) or aqueous alteration of volcanic ash deposits , the depositional setting remains uncertain Bishop et al, 2008;Michalski and Noe Dobrea, 2007;Noe Dobrea et al, 2010;Wray et al, 2008).…”