HR: 14:25h
AN: P33C-04    [Abstracts]
TI: Evidence for Material Removal and/or Subsidence of the Martian Lithosphere from a Global Dataset of Surface Faults.
AU: * Dimitrova, L L
EM: Lada.Dimitrova@stonybrook.edu
AF: Stony Brook University, Department of Geosciences, Stony Brook University, Stony Brook, NY 11794, United States
AU: Holt, W E
EM: William.Holt@stonybrook.edu
AF: Stony Brook University, Department of Geosciences, Stony Brook University, Stony Brook, NY 11794, United States
AU: Haines, A J
EM: ajh50@cam.ac.uk
AF: Cambridge University, Department of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ, United Kingdom
AU: Schultz, R A
EM: schultz@mines.unr.edu
AF: University of Nevada, Department of Geological Sciences and Engineering, University of Nevada, Reno, NV 89557, United States
AB: The normal faults associated with the formation of Tharsis extend over almost half of Mars, and hence have been the major focus for studies of lithospheric deformation, e.g., the membrane and flexure model of Banerdt and Golombek [2000] and the gravitational potential model (GPE) of Dimitrova et al [2006]. Recent orbital exploration has led to the creation of expanded fault data sets and we extend these studies to use the global fault data from Knapmeyer et al [2006] to evaluate the suitability of the data for lithospheric stress models and constraints on the crustal evolution on Mars. We perform a Kostrov moment tensor summation to estimate the total strain tensor associated with the fault segments, where we assume a uniform amount of slip for each fault as a first approximation. We use an objective inner product measure to estimate the misfit of the GPE associated model of stress to the calculated strain. We perform inversions minimizing the surface integral of the misfit for additional stresses due to GPE variations or membrane displacements. The normal faults mapped to-date are clustered in the western hemisphere around Tharsis, and hence, are (1) well fitted by the GPE model and (2) provide little to no constraint on processes elsewhere. On the other hand, the reverse faults are much more uniformly distributed and provide better constraints; in particular, reverse faults in high topography areas are ill fitted by the GPE model. Inversions for minimized misfit to the reverse faults show that a GPE model with additional variations in crustal density alone of ± 57 kg.m^-3, mantle density alone of ± 207 kg.m^-3, or both crustal and mantle density of ± 34 kg.m^-3, can fit the majority of the reverse and normal faults. A GPE model with additional membrane displacement model fails to improve significantly the fit to the reverse faults even for spherical degree and order 18 cut-off. A GPE model with additional variation in densities (± 69 kg.m^-3 for the crust, ± 212 kg.m^-3 for the mantle, ± 185 kg.m^-3 for both the crust and the mantle) and membrane displacement of ± 185 m provides the best fit. Inversion results for both normal and reverse faults show correlated changes in GPE and membrane displacements, requiring additional GPE and/or upward vertical displacement under Tharsis and Margaritifer Terra and Meridiani Planum, and Argyre Planitia in the western hemisphere and Hellas and Utopia Planitia in the eastern hemisphere. While the results for Tharsis may reflect deviations from the average crustal density as proposed by Neumann et al [2004], which will significantly affect the base GPE model, the remaining areas can be explained by a combination of removal of material and subsidence after the fault formation. This interpretation is also consistent with these areas associated with very large craters and/or networks of outflow channels.
DE: 5475 Tectonics (8149)
DE: 6225 Mars
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8164 Stresses: crust and lithosphere
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting