Evidence for weathering on early Mars from a comparison with terrestrial weathering profiles

Research areas:
Year:
2011
Authors:
Journal:
ICARUS
Volume:
216
Number:
1
Pages:
257-268
Month:
November
ISSN:
0019-1035
Abstract:
Phyllosilicates on Mars are widespread in the ancient crust suggesting
the presence of liquid water at the martian surface and therefore warmer
conditions during its early history. However, the role of the ancient
climate in the alteration process, which produced these phyllosilicates,
remains under debate, because similar mineral assemblages can be
produced by hydrothermal alteration at depth. This paper focuses on the
origin of coincident outcrops of Fe/Mg bearing phyllosilicates and
Al-bearing phyllosilicates, which are observed in several regions of
Mars. We performed a detailed mineralogical comparison between a section
in Nil Fossae, Mars, and a weathering profile located at Murrin Murrin,
Western Australia. The Murrin Murrin profile is developed in Archaean
serpentinized peridotite massifs over a similar to 40 m thick sequence.
It has three alteration zones: the serpentine mineral saprolite is found
at the bottom, immediately overlain by Fe/Mg-bearing smectites and then
Al-bearing phyllosilicates (kaolinite) mixed with iron hydroxides. This
example illustrates how Al-dominated minerals can derive from the
alteration of initially Al-poor ultramafic rocks by the intense leaching
of Mg2+. This mineralogical sequence is very similar to that detected
locally in Nil Fossae by orbital spectroscopy. By analogy, we propose
that the mineral assemblage detected on Mars is the result of long-term
weathering, and thus could be the best evidence of past weathering as a
direct result of a climate significantly warmer than at present. (C)
2011 Elsevier Inc. All rights reserved.