Short-wavelength contractional structures in crustal plateau fold belts on Venus: constraints on early thermal state

Details Short-wavelength contractional structures in crustal plateau fold belts on Venus: constraints on early thermal state Short-wavelength contractional structures in crustal plateau fold belts on Venus: constraints on early thermal state

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusm.p21a..05g&link_type=abstract

American Geophysical Union, Spring Meeting 2002, abstract #P21A-05

Mathematics

Logic

3210 Modeling, 5104 Fracture And Flow, 5475 Tectonics (8149), 8020 Mechanics, 8159 Rheology: Crust And Lithosphere

Scientific paper

Marginal fold belts within Venusian crustal plateaus are characterized by contractional tectonic features showing a range of spatial wavelengths from <100 m to >30 km. Previous studies have proposed that these features are folds formed by layer-normal compression during crustal plateau formation [e.g., 1] and that the characteristic deformation wavelength(s) expressed by these features reflect the thickness of a competent surface layer during deformation [1, 2]. We investigate the conditions under which the shortest wavelength features represented in these fold belts may have formed. Specifically, we report on finite element simulations of concurrent shortening and cooling in models with uniform composition and elasto-visco-plastic (EVP) rheology. The models are constrained by observations of crustal plateau marginal fold belts using Magellan SAR imagery and are motivated by the current plume tectonic hypothesis for crustal plateau formation [2, 3]. The models are unique because a) the EVP rheology more accurately represents the actual crust than viscous or viscoelastic models; and b) our models incorporate spatially uniform material properties but temperature-dependent rheology [4], so that the strength profile through the crust evolves with cooling. This allows local thermal and stress conditions to determine the instantaneous effective surface layer thickness and strength, which in turn determines surface topographic wavelengths. We find that short-wavelength contractional features can form under hot conditions consistent with the plume scenario but do not form under cooler conditions. The final model topography results from simultaneous brittle faulting and viscous folding. We conclude that the shortest-wavelength features preserved in marginal fold belts record an early stage of crustal plateau evolution and require an elevated thermal gradient and surface temperature. [1] Ghent, R.R., and V.L. Hansen 1999. Structural and kinematic analysis of eastern Ovda Regio,Venus: Implications for crustal plateau formation, Icarus, 139, 116-136. [2] Hansen, V.L. and J.J. Willis 1998. Ribbon terrain formation, southwestern Fortuna Tessera, Venus: implications for lithosphere evolution. Icarus, 321-343. [3] Phillips, R.J. and V.L. Hansen 1998. Geological evolution of Venus: A geodynamical and magmatic framework. Science, 279,1492-1497. [4] Mackwell, S.J., M.E. Zimmerman and D.L. Kohlstedt 1998. High-temperature deformation of dry diabase with application to tectonics on Venus. JGR 103, 975-984.

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