Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.v23e2171h&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #V23E-2171
Other
[5480] Planetary Sciences: Solid Surface Planets / Volcanism, [8424] Volcanology / Hydrothermal Systems, [8425] Volcanology / Effusive Volcanism, [8450] Volcanology / Planetary Volcanism
Scientific paper
Volcanic rootless cones (VRCs) are typically generated by explosive molten fuel-coolant interactions (MFCIs) involving lava and groundwater. VRCs are significant in planetary environments because they imply the presence of active lava flows and an underlying volatile phase (e.g., groundwater or ice) at the time of cone formation. Rootless MFCIs require volatilization of groundwater before the core lava temperature descends below its solidus. Therefore, integrated geological mapping of VRC groups, age-dating of their host lava flow surfaces, and thermodynamic modeling of lava-permafrost interactions can provide constraints on where and when near-surface ground ice has been present in volcanic regions. This information is valuable for developing models of global climate change on Mars and for determining the relationships between climate and planetary volatile accretion, outgassing history, distribution of water and evolution of the hydrological cycle, abundance and stability of liquid water, surface weathering environments, and the development of environments that could support life. Photogeological mapping reveals that the Tartarus Colles Region, located in eastern Elysium Planitia (25-27°N, 170-171°E), Mars, includes >167 VRC groups ranging in area from <1 to 1258 km2 with a total area of 2014 km2. Crater size-frequency relationships suggest that the Tartarus Colles lava flow formed ~75-250 Ma ago. Within the Tartarus Colles Region, VRCs preferentially form where lava is >30 m thick. Based on the results of our thermodynamic modeling, we infer that VRCs did not form where the lava was <30 m thick because the upper 16-21 m of the substrate was partially desiccated. The common occurrence of VRCs in association with 30-60 m thick lava suggests that at the time of the cone-forming eruptions there was an ice table at <37 m depth. We therefore conclude that during the Late to Middle Amazonian a global cryosphere was present at mid-latitudes at a depth <37 m, but that it existed beneath a desiccated zone that was <16-21 m thick. These results are consistent with models that predict extended periods of intermediate obliquity during the past 250 Ma with obliquity excursions descending to below 32°, but above 25°. For measured lava flow thicknesses, cone group areas, and ground ice fractions ranging from 0.1 to 0.3, we estimate that ~3.7-22.5 km3 of ground ice could have been volatilized (i.e., melted or vaporized) by the time the lava flow solidified and that the temperature of the resulting hydrothermal system could have remained >273 K for a maximum of 1.3 × 103 years. The Tartarus Colles lava flow post-dates the Elysium rise unit and pre-dates the most recent activity associated with northern Cerberus Fossae. Consequently, this volcanic event may have been associated with changes in the regional state of stress that led to the formation of the fossae.
Fagents Sarah A.
Hamilton Christopher W.
Wilson Leslie
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