Other
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p31g..03s&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P31G-03
Other
[5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [5480] Planetary Sciences: Solid Surface Planets / Volcanism, [8424] Volcanology / Hydrothermal Systems
Scientific paper
The caldera of the Syrtis Major volcanic complex shows evidence of a late-stage, chemically evolved eruption that emplaced a volcanic cone and an evolved dacitic lava flow. This cone and flow contain several light-toned deposits, spectrally defined, with the CRISM instrument, by a broad asymmetrical absorption centered at 2.21 μm that is characteristic of a Si-OH bond. Additional weak 1.4 and 1.9 μm OH- and H2O related absorption features were detected that combined with the 2.21 μm feature confirms the detection of hydrated silica (SiO2 nH2O). The deposits are expressed morphologically as low mounds in stereo HiRISE data that superpose and post-date the volcanic flows. This mineral detection and volcanic context is consistent with several formation mechanisms, notably volcanic outgassing leading to fumarole surface alteration or silica deposition in volcanically driven hot springs. Since current orbital observations do not allow conclusive determination of precise mechanism, we here focus on the hot spring silica depositional hypothesis and investigate what the current observations tell us about such a system. These deposits would occur as post-eruption volcanic heat-driven hydrothermal convection of ground and possibly magmatic waters. Convecting, heated water would dissolve the igneous minerals in the basalt that forms the majority of the caldera mobilizing significant silica. Silica saturated fluids that reach the surface cool and deposit amorphous silica as the silica solubility in the fluids decreases. The large size and mound building nature of individual deposits require a significant and sustained fluid source for deposition. That amorphous silica deposits were detected in several distinct regions illustrates the prevalence of this process in this volcanic complex. The largest deposit is located on the southern flank of the cone and forms a fan-shaped morphology as the material is sourced from a vent and flows downslope. Another small deposit was detected just west of the cone center near it's apex and appears to be exposed outcrop. The remaining detections are quasi-circular mounds on the caldera floor. One isolated large deposit is at the southern edge of the cone while the majority of deposits are in an 8,000 km2 field directly southwest of the cone that contains dozens of deposits of varying sizes. Recently confirmed deposits are also located in the far field, 10 km to the southwest of the cone but still confined to the dacite lava flow. These show that the deposits are more widespread than the immediate vicinity of the volcanic cone. This volcanically driven hydrothermal system and the resulting hot spring environments on Mars has significance for our understanding of Martian volcanic systems and for the search for habitability. Terrestrial hot springs are known to be ideal locations for microbial activity and for the sequestration and long-term preservation of biosignatures . Hot spring silica sinter deposits are among the best materials for preserving signs of habitability making the Nili Patera deposits an ideal location for future focused study.
Ehlmann Bethany L.
Murchie Scott L.
Mustard John F.
Skok John R.
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