Unstable Extensional Tectonics on Enceladus: Forming Ridge-and-Trough Terrain

Details Unstable Extensional Tectonics on Enceladus: Forming Ridge-and-Trough Terrain Unstable Extensional Tectonics on Enceladus: Forming Ridge-and-Trough Terrain

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p13b0174b&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #P13B-0174

Mathematics

Logic

5422 Ices, 5475 Tectonics (8149), 8149 Planetary Tectonics (5475)

Scientific paper

Geologic mapping of Enceladus, both pre and post Cassini, suggests that the satellite has undergone numerous episodes of resurfacing throughout its history (e.g. Plescia J. B. and Boyce J. M. 1983 Nature 301, Schenk, P. and Seddio S. 2006 DPS 38 abstract). As has been proposed for Ganymede's grooved terrain, much of this resurfacing may have occurred via tectonic disruption of the surface (e.g. Head et al. 1997 Lunar Planet. Sci. 28 abstract) during periodic episodes of tidally driven heating (Wisdom 2004 AJ 128). Such heating can cause global expansion of the body, leading to unstable extension of the lithosphere and the formation of periodically spaced ridges and troughs via periodic necking instabilities. High resolution Cassini images reveal that ridge-and-trough terrain is, in fact, present on Enceladus, lending plausibility to this resurfacing scenario (Rathbun et al. 2005 AGU abstract). We numerically model the formation of necking instabilities under Enceladus-like conditions to quantitatively evaluate the feasibility of unstable extensional tectonics to both disrupt preexisting terrain and create large amplitude quasi-periodic ridges and troughs. We find that unstable extension in Enceladus' low-gravity environment produces relatively strong instability growth when compared to instability growth on larger, high-gravity bodies such as Ganymede. The ridges and troughs formed by such extension have amplitudes of up to 200 m and topographic wavelengths between 2 km and 28 km. Assuming large strains (~30%) are locally available, instability growth is most effective at low thermal gradients (~5-10 K km-1) and moderate strain rates (10-13 s-1. Further, we find that the formation of extensional instabilities is capable of partially resurfacing preexisting topography 10 m to 100 m in amplitude. Strain localization is an essential component of necking instability growth. While instabilities will naturally occur in an extending icy lithosphere (as described above), the growth rates of these instabilities are generally insufficient to produce deformation with amplitudes of ~500 m or more (as is seen on Enceladus) if local strains are less than ~30%. However, strain localization, either by faulting or by strain weakening, can increase growth rates of necking instabilities and thereby increase surface deformation. Using the numerical model described above we investigate how various types of strain localization affect instability growth in the context of forming Enceladus' ridge-and-trough terrain.

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