Mathematics – Logic
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p31c..02g&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #P31C-02
Mathematics
Logic
3210 Modeling, 5475 Tectonics (8149), 5480 Volcanism (8450), 8010 Fractures And Faults, 8020 Mechanics
Scientific paper
Graben on Mars have often been interpreted to result from dike intrusion. On Earth field observations, geodetic data, and numerical models show that dike intrusion and normal faulting typically result in graben subsidence. Topography across the Krafla rift zone in Iceland has been successfully fit to the combined effects of subsurface dike inflation plus slip along two inward-dipping, dike-induced normal faults. Topographic profiles of graben in the Tharsis and Elysium regions on Mars show similar morphometric features. This morphologic similarity suggests a similar process at depth. Quantitative mechanical models of dike-induced graben topography on Mars have been elusive. We have now developed a boundary element model capable of predicting the topography of graben that have evolved through the combined processes of dike intrusion and related normal faulting. By analogy with the Krafla rift zone example and the previous model results, we calculate the amount of surface displacement expected on Earth for a vertical dike with a height of 4.5 km (dike top depth = 1.5 km, and dike bottom depth = 6.0 km), accompanied by two faults 6.0 km apart dipping toward the graben center at 55 degrees with a down-dip length of 6.0 km. The horizontal stress gradient is equal to the vertical lithostatic gradient (principal stress ratio = 1.0) for Earth assuming magmatic density of 2200 kg/m3 and crustal density of 2600 kg/m3, and the shear modulus is 24 GPa. We find that if gravity is the main factor affecting graben-related topography, Martian graben would produce topographic displacements that are 25% less than that of a terrestrial counterpart. Our models predict approximately 4 m and 3 m of maximum vertical displacement on Earth and Mars, respectively. Larger dikes suggested for Mars could produce uplifts of 10's of m. This relief is within the vertical precision of the MOLA data and will provide a direct test of the volcanic hypothesis of Martian graben.
Goudy Cheryl L.
Schultz Richard A.
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