Structural Geology and Numerical Rheological Modeling on Venus

My research interests focus on planetary crustal deformation in response to tectonic driving forces. My current work involves incorporating the results of structural analysis using remotely sensed data to constrain mathematical simulations of crustal deformation.

Current and past research : My Ph.D. research investigates the structural evolution of ancient crustal plateaus on Venus in order to help distinguish between two prominent models for crustal plateau formation: a) formation above large mantle upwellings, or plumes; and b) formation above cylindrical downwellings. These plateaus likely formed during a past thermal regime characterized by globally thin lithosphere, and the deformation preserved there provides an opportunity to study Venus’ former tectonic style. The first phase of my thesis work consisted of mapping tectonic structures preserved at the plateau Ovda Regio using high-resolution Magellan synthetic aperture radar (SAR) imagery. At Ovda Regio, extensional "ribbon" structures (long, narrow, shallow, periodically spaced graben) and contractional folds overlap spatially and are mutually cross-cutting. Because Venus lacks erosion and sedimentation, timing relations among suites of tectonic structures are generally unclear. At Ovda Regio, wavelengths and structural styles provide the only constraints on the sequence of deformation, and hence the plateau’s tectonic history. Analysis of ribbon and fold wavelengths suggests that ribbons most likely predate folds at Ovda Regio (Ghent and Hansen 1999), accompanied by a deepening brittle-ductile transition as would occur in a cooling crust. This scenario supports a mantle upwelling hypothesis for crustal plateau formation.

To further test the feasibility of this hypothesis, I am currently using two-dimensional finite element simulations of concurrent cooling and shortening of a crustal block to examine the impact of a mobile brittle-ductile transition on the wavelengths of surface structures. The finite element model uses a temperature dependent elasto-visco-plastic (EVP) rheology. This rheology allows the BDT and the surface structures to evolve naturally, controlled by temperature and strain rate, rather than requiring the modeler to specify their locations, depths, or geometries a priori . This model represents an advance relative to earlier models that approximated crustal rheology as viscous or elastic-plastic. It is also the first quantitative thermo-mechanical treatment of the evolution of crustal plateau structures. In addition to providing a test of the upwelling hypothesis, this work will result in a generally applicable approach for modeling crustal deformation that eliminates many common oversimplifications.

Future projects : I plan to extend my research to include work on Earth and other planets, as well as continuing work on Venusian tectonics. My immediate interests are as follows.

1) Plate boundary-related deformation on Earth . Finite element models using EVP rheology are uniquely suited for investigating the details of deformation in the upper crust in response to stresses imposed by plate boundaries. Models of these structures — for example, fault-fold complexes in accretionary prisms or spatially periodic faults in the oceans - constrained by observations from field or remote data, would help to constrain present and paleostresses, which in turn impact global mantle flow and plate motion models. In addition, understanding the details of plate boundary deformation has implications for questions relating to the nature and degree of mechanical coupling across plate boundaries.

2) Further application of crustal deformation modeling to planets . The techniques discussed above are applicable to all planets and satellites for which data are available. As data for Mercury, Mars and the icy satellites accumulate, coupled observational and modeling approaches will provide our best opportunity for interpreting the processes operating on those bodies. The type of model I am currently using for Venus can be adapted to reflect any type of rheology, including ice, and thus represents an excellent technique for modeling deformation processes throughout the solar system.

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