To Hydrthermal Activity

Hydrothermal activity has been present on Mars since early Noachian to recent times. Such a process has been recognized through the volcanism (Fig. 3A) that affected the crust water mobilization in the form of lacustrine and fluvial systems (Cabrol and Grin, 2001; Varnes et al., 2003; Schulze-Makuch et al., 2007), as well

Figure 2. Noachian deltaic deposits (Grant et al., 2007) infilling the Holden Crater in Mars (A-C) and preserved microbial mat structures in Archean deltaic materials (D-E) at Barberton Greenstone Belt, South Africa. (A) Mars Orbiter Camara (MOC) wide angle image of the Holden Crater area where a deltaic structure occurs (white rectangle). (B) THEMIS Visible Image V17376003 (Themis Public Data Releases, Planetary Data System node, Arizona State University at http://themis-data. asu.edu) showing the deltaic structure filling the crater. (C) High Resolution Imaging Science Experiment (HiRISE) image PSP_001468_1535 (supported by the NASA/JPL/University of Arizona at http://hirise.lpl.arizona.edu), onboard the Mars Reconaissance Orbiter (MRO) unlocking the deltaic-like sequence that were sedimented inside the crater. (D) detail and (E) outcrop images of preserved microbial mats occurring in deltaic siliciclastic materials of the 3.2 Ga Archean Moodies Group of South Africa.

Figure 2. Noachian deltaic deposits (Grant et al., 2007) infilling the Holden Crater in Mars (A-C) and preserved microbial mat structures in Archean deltaic materials (D-E) at Barberton Greenstone Belt, South Africa. (A) Mars Orbiter Camara (MOC) wide angle image of the Holden Crater area where a deltaic structure occurs (white rectangle). (B) THEMIS Visible Image V17376003 (Themis Public Data Releases, Planetary Data System node, Arizona State University at http://themis-data. asu.edu) showing the deltaic structure filling the crater. (C) High Resolution Imaging Science Experiment (HiRISE) image PSP_001468_1535 (supported by the NASA/JPL/University of Arizona at http://hirise.lpl.arizona.edu), onboard the Mars Reconaissance Orbiter (MRO) unlocking the deltaic-like sequence that were sedimented inside the crater. (D) detail and (E) outcrop images of preserved microbial mats occurring in deltaic siliciclastic materials of the 3.2 Ga Archean Moodies Group of South Africa.

Figure 3. Context image of the Apollinaris Patera shield volcano (A) showing geomorphic structures related to caldera collapse, sediment infilling and water activity as fan-channeled pattern emerging southwards out from the crater, as well as a strong volcano erosion operated by gullies. Such a volcanic building was likely the scenario of hot fluid production displayed as geysers, volcanic chimneys or any other geothermal phenomenon (image was composed using the PIGWAD GIS Mapping system, courtesy USGS Astrogeological Research Program at http://astrogeology.usgs.gov). (B) Image PIA09491 silica-rich soil uncovered by Spirit at Gusev Crater that might be interpreted as a consequence of geothermal mineralization of silica-enriched fluids or a strong leaching on basaltic precursors inducing a secondary silica enrichment (courtesy of NASA/JPL-Caltech). (C) Crater caldera of the Kilauea volcano (Island of Hawaii) showing geothermal activity that produce sulfur and silica rich deposits around (withe arrows) (credited by Professor Raymond Arvidson and Thomas Stein). (D) Silicified bacili-like microbial structures in sinter deposits of the Rotokawa Geothermal Field in New Zealand. (Credit: Dr. Richard Schinteie.)

Figure 3. Context image of the Apollinaris Patera shield volcano (A) showing geomorphic structures related to caldera collapse, sediment infilling and water activity as fan-channeled pattern emerging southwards out from the crater, as well as a strong volcano erosion operated by gullies. Such a volcanic building was likely the scenario of hot fluid production displayed as geysers, volcanic chimneys or any other geothermal phenomenon (image was composed using the PIGWAD GIS Mapping system, courtesy USGS Astrogeological Research Program at http://astrogeology.usgs.gov). (B) Image PIA09491 silica-rich soil uncovered by Spirit at Gusev Crater that might be interpreted as a consequence of geothermal mineralization of silica-enriched fluids or a strong leaching on basaltic precursors inducing a secondary silica enrichment (courtesy of NASA/JPL-Caltech). (C) Crater caldera of the Kilauea volcano (Island of Hawaii) showing geothermal activity that produce sulfur and silica rich deposits around (withe arrows) (credited by Professor Raymond Arvidson and Thomas Stein). (D) Silicified bacili-like microbial structures in sinter deposits of the Rotokawa Geothermal Field in New Zealand. (Credit: Dr. Richard Schinteie.)

as silica-rich deposits discovered recently in the Gusev Crater (Professor Raymond Arvidson personal communication shown in Fig. 3B), which likely originated under acidic hot fluids.

On Earth, geothermal systems are often associated with volcanic centers (Fig. 3C), but also with hot springs that form minor structures which detection depends on the resolution of remote sensing instruments boarded in the orbiters. These geological systems introduce high silica and sulfur fluxes that induce high mineralization rates of a very resistant mineral-complexes as opaline silica currently forming sinters (Schinteie et al., 2007). Such a fast mineralization induces instantaneous silicification of living microbes (Jones et al., 2001; Walker et al., 2005) that facilitates preservation of organics over time. In some cases, silicification in geothermal systems produces exceptional replica of the microbial components (Fig. 3D) taking part in the community. Interestingly, silica preservation in some geothermal systems as the Parakiri Stream sourced in the Rotokawa Geothermal of New Zealand (Schinteie et al., 2007) occurs under acidic condition, as will be described in the following section. On the other hand, hot spring carbonate deposits have been also described to preserve biological information (Kazue, 1999). Although carbonates are pervasive on the surface regions of Mars, geothermal systems driven by CO2-rich solutions could be present in some areas of the planet. This is monsistent with the TES identification of very low concentrations of carbonate in the Martian dust (Bandfield et al., 2003). Moreover, some Mars meteorites have provided carbonates as a part of the rock forming mineral assemblages (Bridges et al., 2001), which suggest that these mineralogies were formed in some Mars environments.

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