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

Research areas:
Year:
2012
Authors:
Journal:
JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS
Volume:
117
Month:
APR 21
ISSN:
2169-9097
Abstract:
A closed depression in the Noctis Labyrinthus region of Mars (at 10.4
degrees S, 98.6 degrees W), believed to have formed in the Late
Hesperian, holds an inner pit partially filled with several hundred
meters of stratified material. Compact Reconnaissance Imaging
Spectrometer for Mars (CRISM) visible-near infrared reflectance data
reveal signatures of numerous hydrated minerals including
halloysite/kaolinite, Fe-smectite, Si-OH bearing phases and Fe-sulfates
(polyhydrated, monohydrated, and hydroxylated types, including
jarosite). We use CRISM data, high resolution imagery (HiRISE) and HRSC
(High Resolution Stereo Camera) derived elevation to analyze the
morphology, composition and stratigraphy of these materials. We propose
an alteration sequence including formation of acid sulfate solutions
from groundwater and magmatic sulfur, which then locally altered the
basaltic bedrock and layered sediments mainly deposited from volcanic
tephra, forming Fe-smectite and Fe-sulfates. The mineral variability can
mostly be explained by local variations in the pH of the altering
fluids, with original acidity being buffered by dissolution of primary
minerals; and by variable fluid input and evaporation and/or freezing
rates (resulting in various water/rock ratios). This site shows local
formation of almost all classes of minerals identified thus far on Mars
without invoking global conditions. Processes related to local volcanic
activity and associated hydrothermalism were 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
geological setting of hydrated minerals in the understanding of Mars
geologic and climatic evolution.