Mathematics – Logic
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p41a..07p&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P41A-07
Mathematics
Logic
5415 Erosion And Weathering, 5455 Origin And Evolution, 5475 Tectonics (8149), 5480 Volcanism (8450), 6225 Mars
Scientific paper
Scientific results from the Mars Global Surveyor (MGS) mission have profoundly changed our views of the global geological history of Mars. We now know that the crustal dichotomy between the northern lowlands and southern highlands is a very early feature in martian history (earliest Noachian or pre-Noachian) and the global pole-to-pole slope must have been in place since earliest times. We also understand that after the development of the dichotomy, the Tharsis rise began to form in the early Noachian and its mass was largely in place by the end of this epoch. Tharsis loaded the lithosphere of the entire planet and, along with the pole to pole slope, continues to control the long-wavelength shape of the planet. Valley network orientations are largely controlled by this long-wavelength shape, so much of the observed population must have postdated a good deal of the formation of Tharsis. Above the Noachian basement the northern lowlands are filled with only a few kilometers of early Hesperian volcanic plains units upon which are superimposed only hundreds of meters of material dominantly sedimentary in origin. Hesperian volcanic plains are pervasively distributed around the planet and are characterized by wrinkle ridges --- possibly an indication of a period of global contraction. Images (MOC) and altimetry data (MOLA) from MGS show that depositional and erosional processes were vigorous in early martian history. Sedimentary layers up to several kilometers thick are observed by MOC in a number of regions, though their depositional origins --- subaqueous, volcanic, and/or aeolian --- remain unclear. Intense erosional episodes are less ambiguous: MOLA data show, for example, that in the vicinity of the prime meridian several million cubic kilometers of material were removed from the martian highlands and presumably transported to the northern lowlands. The Noachian climate on Mars may have approached clement conditions, allowing liquid water at the surface, or at least in the shallow subsurface, to facilitate widespread erosion. However, the martian highlands are characterized by a plethora of closed basins, indicating a lack of integration, and hence maturity, of drainage systems. Favorable surface temperatures may have been enabled through volatile release to the atmosphere by Tharsis volcanism. The waning of volcanic activity may have set the stage for a growing cryosphere and for the creation of later outflow channels by ice-driven pressure buildup and water release in deep aquifers.
Hanna Jeffrey C.
Hynek Brian Michael
Jakosky Bruce M.
Phillips James R.
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