Ancient Geodynamics and Global-Scale Hydrology on Mars

Abstract

Loading of the lithosphere of Mars by the Tharsis rise explains much of the global shape and long-wavelength gravity field of the planet, including a ring of negative gravity anomalies and a topographic trough around Tharsis, as well as gravity anomaly and topographic highs centered in Arabia Terra and extending northward toward Utopia. The Tharsis-induced trough and antipodal high were largely in place by the end of the Noachian Epoch and exerted control on the location and orientation of valley networks. The release of carbon dioxide and water accompanying the emplacement of approximately 3 x 10(8) cubic kilometers of Tharsis magmas may have sustained a warmer climate than at present, enabling the formation of ancient valley networks and fluvial landscape denudation in and adjacent to the large-scale trough.

Geological Processes and Evolution

“…These volcanics are therefore likely the load that caused the flexure around Tharsis. This enormous load appears to have produced a flexural moat, which shows up most dramatically as a negative gravity ring, and an antipodal dome that explains the first order topography and gravity of the planet (Phillips et al, 2001). New altimetric data provide evidence that the circum-Tharsis mid-Hesperian wrinkle-ridge system extends into the northern lowlands, a radius of 7000 km from the center of Tharsis .…”

“…New altimetric data provide evidence that the circum-Tharsis mid-Hesperian wrinkle-ridge system extends into the northern lowlands, a radius of 7000 km from the center of Tharsis . Many ancient fluvial valley networks, which may have formed during an early warmer and wetter period on Mars, flowed down the present large-scale topographic gradient, further arguing that Tharsis loading was very early (Phillips et al, 2001). It is in fact possible that the formation of Tharsis actually produced this early warmer and wetter environment.…”

“…It is in fact possible that the formation of Tharsis actually produced this early warmer and wetter environment. If the load is composed of volcanics as suggested by fine layers within Valles Marineris (McEwen et al, 1999), water released with the magma would be equivalent to a global layer up to 100 m thick, which could have had a significant impact on the martian climate (Phillips et al, 2001). …”

A lake in Uzboi Vallis and implications for Late Noachian–Early Hesperian climate on Mars

“…1 and 2) and emerges from Argyre basin before traversing northward along the southwestern flank of the ''Chryse trough'' (Baker, 1982;Parker, 1985;Phillips et al, 2001;Saunders, 1979). Hale (125 Â 150 km in diameter) and Bond (111 km in diameter) craters on the northern margin of Argyre largely buried the basin outlet, but Uzboi originates at nearly full width and has only a few, much smaller tributaries, supporting the contention that it was fed by overflow from Argyre basin (Grant and Parker, 2002;Parker, 1985).…”

Forward mechanical modeling of the Amenthes Rupes Thrust Fault on Mars

“…The population of lobate scarps that includes Amenthes Rupes formed during the Late Noachian to Early Hesperian [Watters and Robinson, 1999] (or-3.8 Ga in age [Zuber, 2001]), deforming ancient highland rocks in an early episode of crustal deformation following the period of heavy bombardment. Because the global-scale effect of Tharsis as recently proposed [Phillips et al, 2001] predicts broad uplift in this region, with slope gradient more nearly parallel to the trends of lobate scarps instead of normal to them, Amenthes and associated lobate scarps may relate more directly instead to the early development of the crustal dichotomy [Watters, 1993, The magnitude, distribution, and sense of offset are first specified along the fault, then the stresses and material displacements in the vicinity of the fault are completely determined by using the stress functions for an elastic halfspace [Okada, 1992]. The halfspace solution increases the near-surface displacements above a thrust fault relative to their values in an infinite faulted medium.…”