Most Mars minerals in a nutshell: Various alteration phases formed in a single environment in Noctis Labyrinthus

Patrick Thollot (1) , Nicolas Mangold (1) , V. Ansan (1) , Stéphane Le Mouélic (1) , Ralph Milliken (2) , Janice Bishop , Catherine Weitz , Leah Roach , John Mustard , Scott Murchie (3)

1 LPG - Laboratoire de Planétologie et Géodynamique [UMR 6112]
2 CEEES - Department of Civil and Environmental Engineering and Earth Science [Notre Dame]
3 APL - Johns Hopkins University Applied Physics Laboratory [Laurel, MD]

A closed depression in the Noctis Labyrinthus region of Mars (at 10.4S, 98.6W),believed to have formed in the Late Hesperian, holds an inner pit partially filled withseveral hundred meters of stratified material. Compact Reconnaissance ImagingSpectrometer for Mars (CRISM) visible-near infrared reflectance data reveal signaturesof numerous hydrated minerals including halloysite/kaolinite, Fe-smectite, Si-OH bearingphases and Fe-sulfates (polyhydrated, monohydrated, and hydroxylated types, includingjarosite). We use CRISM data, high resolution imagery (HiRISE) and HRSC (HighResolution Stereo Camera) derived elevation to analyze the morphology, composition andstratigraphy of these materials. We propose an alteration sequence including formationof acid sulfate solutions from groundwater and magmatic sulfur, which then locally alteredthe basaltic bedrock and layered sediments mainly deposited from volcanic tephra, formingFe-smectite and Fe-sulfates. The mineral variability can mostly be explained by localvariations in the pH of the altering fluids, with original acidity being buffered bydissolution of primary minerals; and by variable fluid input and evaporation and/orfreezing rates (resulting in various water/rock ratios). This site shows local formation ofalmost all classes of minerals identified thus far on Mars without invoking globalconditions. Processes related to local volcanic activity and associated hydrothermalismwere able to produce, during an era in which the climate is believed to have been cold,a large variety of hydrated minerals. This study highlights the importance of the geologicalsetting of hydrated minerals in the understanding of Mars geologic and climatic evolution.

Domaines: Planète et Univers [physics]; Planétologie; Minéralogie

Patrick Thollot, Nicolas Mangold, V. Ansan, Stéphane Le Mouélic, Ralph Milliken, et al.. Most Mars minerals in a nutshell: Various alteration phases formed in a single environment in Noctis Labyrinthus. Journal of Geophysical Research. Planets, 2012, 117 (E11), pp.n/a-n/a. ⟨10.1029/2011JE004028⟩. ⟨hal-02305919⟩