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Outflow channel sources, reactivation, and chaos formation, Xanthe Terra, Mars |
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| Authors: | Jose AP Rodriguez Sho Sasaki James M Dohm Hideaki Miyamoto Goro Komatsu Justin C Ferris |
| Institution: | a Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan b 29-1-202 Tajiri-cho, Nakaharaku, Kawasaki 211-0014, Japan c Vernadsky Institute, Russian Academy of Sciences, Kosygin St. 19, Moscow 119991, Russia d Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721, USA e US Geological Survey, Denver, CO 80225, USA f Astrogeology Team, US Geological Survey, Flagstaff, AZ 86001, USA g Earthquake Research Institute, University of Tokyo, Tokyo 113-0032, Japan h International Research School of Planetary Sciences, Dipartimento di Scienze, Universita' d'Annunzio, Viale Pindaro 42, 65127 Pescara, Italy i Centro de Biología Molecular, Universidad Autónoma de Madrid, 28049 Cantoblanco, Madrid, Spain |
| Abstract: | The undulating, warped, and densely fractured surfaces of highland regions east of Valles Marineris (located north of the eastern Aureum Chaos, east of the Hydraotes Chaos, and south of the Hydaspis Chaos) resulted from extensional surface warping related to ground subsidence, caused when pressurized water confined in subterranean caverns was released to the surface. Water emanations formed crater lakes and resulted in channeling episodes involved in the excavation of Ares, Tiu, and Simud Valles of the eastern part of the circum-Chryse outflow channel system. Progressive surface subsidence and associated reduction of the subsurface cavernous volume, and/or episodes of magmatic-driven activity, led to increases of the hydrostatic pressure, resulting in reactivation of both catastrophic and non-catastrophic outflow activity. Ancient cratered highland and basin materials that underwent large-scale subsidence grade into densely fractured terrains. Collapse of rock materials in these regions resulted in the formation of chaotic terrains, which occur in and near the headwaters of the eastern circum-Chryse outflow channels. The deepest chaotic terrain in the Hydaspis Chaos region resulted from the collapse of pre-existing outflow channel floors. The release of volatiles and related collapse may have included water emanations not necessarily linked to catastrophic outflow. Basal warming related to dike intrusions, thermokarst activity involving wet sediments and/or dissected ice-enriched country rock, permafrost exposed to the atmosphere by extensional tectonism and channel incision, and/or the injection of water into porous floor material, may have enhanced outflow channel floor instability and subsequent collapse. In addition to the possible genetic linkage to outflow channel development dating back to at least the Late Noachian, clear disruption of impact craters with pristine ejecta blankets and rims, as well as preservation of fine tectonic fabrics, suggest that plateau subsidence and chaos formation may have continued well into the Amazonian Period. The geologic and paleohydrologic histories presented here have important implications, as new mechanisms for outflow channel formation and other fluvial activity are described, and new reactivation mechanisms are proposed for the origin of chaotic terrain as contributors to flooding. Detailed geomorphic analysis indicates that subterranean caverns may have been exposed during chaos formation, and thus chaotic terrains mark prime locations for future geologic, hydrologic, and possible astrobiologic exploration. |
| Keywords: | Mars Surface Geological processes |
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