Hydrothermal systems on Mars: an assessment of present evidence
Jack D. Farmer
NASAAmesResearch Center, MS 2 3 9 4
Moffett Field, CA94035-1000, USA
http://geology.asu.edu/jfarmer/pubs/...drothermal.pdf


Excerpts


The goals of this paper are to review evidence consistent with past hydrothermal
activity on Mars, and to discuss the broad range of geological features that may have
been formed by such processes.
page 2



Thermodynamic models indicate that hydrothermal mineralization could have been
a means for sequestering atmospheric gasses in the early Martian crust. Thus,
hydrothermal systems may have played a prominent role in loss of the early atmosphere
(Griffith Shock 1995). This is consistent with isotopic data from the Mars-derived
SNCmeteorites which indicate there has been an active and ongoing process of crus-tal-
atmosphere exchange throughout Martian history (see 1994). Hydro-thermal
convection provides the most compelling mechanism for such exchanges
(Jakosky Jones 1994). The young age of the suggests that hydrothermal sys-tems
could still be active on Mars, but given the instability of liquid water at the
surface, their expression is likely to be limited to localized anomalies in surface
tem-perature or atmospheric composition.
page 20



The great length of many Martian channels (hundreds of kilometres) requires
sustained periods of erosion and a long-term hydrological cycle. But to sustain the
erosion of valleys there must have been an effective mechanism for recharging local
aquifers. Recent climate models for early Mars suggest surface temperatures (-10 to
-20c) and an extensive subsurface cryosphere. This appears to be inconsistent with
extensive recharge through atmospheric precipitation. Alternatively, it has been
suggested that recharge of Martian aquifers was maintained by hydrothermal
convec-tion (Squyres Kasting 1994).
page 4


Geological evidence suggests that early outgassing of water on Mars was equivalent
to several hundred metres depth over the surface (Carr this volume). Much of
this water may yet remain in the crust as ground ice and permafrost.
page 5



Perhaps the most convincing geomorphic evidence for hydrothermal activity on
Mars is the observation of simple channel systems along the margins of impact craters
in ancient highland on Mars (Brakenridge et 1980).
In addition, the presence of iron-rich deposits of possible hydrothermal origin
observed on the floors of some chasmata (Geissler et al 1993) suggests intriguing
similarities to the stratiform ore deposits of many rifted basin settings on Earth.
More controversial are numerous examples of small channel systems on the slopes
of Martian stratovolcanoes And the presence of anomalous, high albedo
features near the crater rims Apollinaris Robinson Smith 1995) com-pares
favorably to fumarolic deposits found in similar locations on terrestrial vol-canoes.