Internal Structure and Early Thermal Evolution of Mars from Mars Global Surveyor Topography and Gravity

Abstract

Topography and gravity measured by the Mars Global Surveyor have enabled determination of the global crust and upper mantle structure of Mars. The planet displays two distinct crustal zones that do not correlate globally with the geologic dichotomy: a region of crust that thins progressively from south to north and encompasses much of the southern highlands and Tharsis province and a region of approximately uniform crustal thickness that includes the northern lowlands and Arabia Terra. The strength of the lithosphere beneath the ancient southern highlands suggests that the northern hemisphere was a locus of high heat flow early in martian history. The thickness of the elastic lithosphere increases with time of loading in the northern plains and Tharsis. The northern lowlands contain structures interpreted as large buried channels that are consistent with northward transport of water and sediment to the lowlands before the end of northern hemisphere resurfacing.

Geological Processes and Evolution

“…Any theory for formation of the northern plains must reconcile the major geological differences between the northern lowlands and the southern uplands as well as distinctive differences in average crustal thickness (e.g., Zuber et al, 2000). One possibility is that the lowlands result from thinning associated with magma ocean cumulate overturn (Hess and Parmentier, 2001).…”

Regional drainage of meltwater beneath a Hesperian‐aged south circumpolar ice sheet on Mars

“…In places the ridges on the basin floors extend up local topographic gradients. As discussed by Zuber et al [2000], the regional topographic gradient of the Martian crust, and in particular the southern uplands, is likely to have been stable for much of Martian geologic history. Thus, assuming the general regional topography of the south polar region was the same as it is today during the Hesperian, the observation that the Sisyphi ridges extend up local topographic gradients is consistent with an esker scenario [Shreve, 1972[Shreve, , 1985Hallet, 2001a, 2001b].…”

Anomalous tilt of Isidis Planitia, Mars

“…Utopia basin adjacent to Isidis basin has a substantial positive gravity anomaly [Sjogren, 1979;Zuber et al, 2000]. Searls and Phillips [2004] and Banerdt [2004] argue that this anomaly could be due to as much as 20 km of fill located in Utopia basin.…”

“…By changing the lithospheric thickness, load thickness, load density and lithospheric density it was possible to change the magnitude and position of the bulge. Two curves were eventually constructed, one using a 120 km [Searls and Phillips, 2004] elastic thickness and one using 100 km [Zuber et al, 2000] elastic thickness for comparison. The curves were then compared to the current topography.…”