Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p44c..01g&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P44C-01
Physics
5455 Origin And Evolution, 5475 Tectonics (8149), 6255 Neptune
Scientific paper
Mars tectonics centers on Tharsis, an enormous elevated volcanic and tectonic bulge that is surrounded by radial extensional grabens and rifts and concentric compressional wrinkle ridges that together deform the entire western hemisphere and northern plains. Deformation in the eastern hemisphere is more localized in and around large impact basins and volcanic provinces. Extensional structures are dominantly narrow grabens (several km wide), although larger (100 km wide), deeper rifts are also present. Compressional structures are dominated by wrinkle ridges, interpreted to be folds overlying blind thrust faults, although larger compressional ridges and lobate (thrust fault) scarps have also been identified. Mapping of extensional structures in deformed regions that have rich stratigraphies shows that structures on Mars formed during 5 main stages, with about half forming during the Noachian >3.8 Ga, indicating that tectonic activity peaked early and generally decreased with time. Wrinkle ridge formation peaked in the Hesperian (both around Tharsis and in the eastern hemisphere), suggesting an overprint and modulation by global compressional cooling stresses. Lithospheric deformation models resulting from elastic-shell loading show that loading over the scale of Tharsis (large relative to the radius of the planet) is dominated by membrane stresses and produces the concentric extensional stresses around the periphery and the radial compressional stresses closer in that are needed to explain the radial grabens and rifts and concentric wrinkle ridges. Because elastic-shell models based on present-day gravity and topography can explain the observed distribution and strain of radial and concentric tectonic features, the basic lithospheric structure of the province has probably changed little since the Noachian and elastic support of the Tharsis load by a thickening lithosphere has been the dominant geodynamical mechanism. The origin of Tharsis required a positively buoyant mantle region accompanied by voluminous partial melting, of which a core-mantle plume is one possibility. This enormous volcanic load produced a moat around it, which shows up most dramatically as a negative gravity ring, and an antipodal bulge that contributes to the first-order shape and gravity field of the planet. If the load is composed of basaltic magmatic products, water released with the magma would be equivalent to a global layer up to 100 m thick, which might have enabled an early warm and wet martian climate.
Golombek Matt
Phillips Raquel
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