HR: 0800h
AN: P11B-0108    [Abstracts]
TI: Tectonic Resurfacing of Icy Planets via Extensional Necking Instabilities: Modeling the Formation of Ganymede's Grooved Terrain
AU: * Bland, M T
EM: mbland@lpl.arizona.edu
AF: University of Arizona, Kuiper Space Science Bldg #92 1629 E. University, Tucson, AZ 85721 United States
AU: Showman, A P
EM: showman@lpl.arizona.edu
AF: University of Arizona, Kuiper Space Science Bldg #92 1629 E. University, Tucson, AZ 85721 United States
AB: Evidence of tectonic resurfacing of icy satellites has been observed througout the solar system. The classic example of such resurfacing is Ganymede's grooved terrain, which has been suggested to result from a necking instability during an epoch of lithospheric extension. Using a linearized analytical model, Dombard and McKinnon (2001) calculated growth rates of a necking instability as a function of wavelength and demonstrated that, under conditions of high heat flow, the fastest-growing modes have wavelengths and growth rates consistent with Ganymede's grooves. However, questions remain as to whether nonlinear, finite strain effects influence groove formation. Furthermore, it is important to elucidate whether such processes are capable of completely disrupting older, preexisting terrains. We present two-dimensional, finite-element models of extensional necking instabilities in an icy lithosphere under conditions that are appropriate to Ganymede at the time of groove formation. The model employs recent rheological laboratory data including both dislocation creep and grain-boundary-sliding flow mechanisms. Plastic flow is included in the form of a Drucker-Prager plastic yield criterion appropriate for rock-like material. Free parameters in the model include the strain rate, vertical temperature gradient, rheology, and initial topographic perturbation. Our simulations show that quasi-periodic structures are produced under a range of conditions that are relevant to Ganymede. At small strains, the growth of these instabilities occurs in agreement with analytical models: growth is greatest for high temperature gradients (30 K/km or greater). However, at finite strains instability growth departs from the predictions of analytical models. The inclusion of finite strain is therefore essential to a complete understanding of tectonic resurfacing processes in regions of significant extension. The discrepancies between analytical and numerical models at finite strains, and their causes, will be discussed in detail.
DE: 5475 Tectonics (8149)
DE: 6222 Ganymede
SC: Planetary Sciences [P]
MN: Fall Meeting 2005