Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p52b..04w&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P52B-04
Physics
5400 Planetary Sciences: Solid Surface Planets, 5475 Tectonics (8149), 5480 Volcanism (6063, 8148, 8450)
Scientific paper
The Tharsis region of Mars is characterized by large volcanic and tectonic centers with distinct sets of graben systems. These Tharsis-radial graben systems have a simple graben morphology with long narrow grabens bounded by normal faults and a down-dropped flat floor unbroken by antithetic faults. Many of the radially oriented grabens have been inferred to form in response to intrusion of magmatic dikes. This interpretation is based primarily upon early physical and numerical (boundary element) models that were originally developed to understand surface deformation associated with dike emplacement on Earth. In this study, we constructed and analyzed two-dimensional discrete element models to test the hypothesis of shallow dike emplacement and widening as a primary mechanism for the production of grabens on Mars. In particular, our models are designed to explore the extent to which a widening subsurface dike, in the absence of regional extension or pre-existing faults, will induce near-surface graben formation. The use of discrete element models allows for the permanent deformation and material heterogeneity to be captured as opposed to boundary element models that are limited by an assumption of homogeneous elastic behavior. Our analyses consider both homogeneous materials as well as mechanical stratification. The results indicate that forcible widening of a dike alone is unlikely to produce grabens at the surface. In our models, surface deformation took the form of a synclinal trough between two anticlines rather than a graben. Formation of the trough was accomplished primarily through compression adjacent to the dike, causing contractional fold development up to the surface. The model evolution indicates that the primary deformation style of dike widening is via trough margin uplift rather than trough center subsidence and that the most distinctive topographic signature of an underlying dike would be parallel ridges formed by contractional folding on either side of a trough. In addition, this shouldering aside of a large volume of subsurface material would require high internal dike pressures to attain significant surface deformation. The presence of a mechanically strong layer in the models produced an overall increase in trough width and a decrease in the amplitude of surface uplift. This effect of material heterogeneity would likely impact any estimates of dike dimensions based solely on measurements of surface graben widths.
Smart Kevin J.
Wyrick Danielle
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