Formation of Grooved Terrain on Ganymede: Extensional Instability Mediated by Cold, Diffusional Creep

Details Formation of Grooved Terrain on Ganymede: Extensional Instability Mediated by Cold, Diffusional Creep Formation of Grooved Terrain on Ganymede: Extensional Instability Mediated by Cold, Diffusional Creep

Mar 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996lpi....27..317d&link_type=abstract

Lunar and Planetary Science, volume 27, page 317

Mathematics

Logic

3

Extensional Instability, Ganymede, Grooved Terrain, Ice Rheology, Lithosphere

Scientific paper

The formation of grooved terrain is an outstanding problem in planetary geology, as it is intimately related to the major event in Ganymede's geological history: the replacement of more than half of the satellite's ancient, dark terrain by bright terrain. The morphology of the bright terrain is dominated by sets of subparallel, linear-to-sinuous ridges and troughs -- the grooves. The predominant model for groove formation is a necking-type extensional instability. The most complete analysis to date is due to Herrick and Stevenson, who applied the Basin-and-Range formation model of Fletcher and Hallet (as first proposed by Fink and Fletcher). In this model the instability arises when a strong plastic or brittle layer and underlying viscous substrate undergo extension. Herrick and Stevenson found that on Ganymede it is very difficult to generate a sufficiently strong instability to account for the spacing of the grooves. They modeled the ductile lower layer as dominated by dislocation-mediated creep with power-law stress exponents of ~= 4-5, consistent with available experimental measurements. Recent experiments by Goldsby and Kohlstedt and Durham et al. indicate that in some geological situations the creep of ice can be dominated by grain-size sensitive, diffusional mechanisms with power-law exponents of ~= 1-2. In addition, Herrick and Stevenson used present-day surface temperatures. Here, we argue that because of the dimmer younger Sun and the relatively high albedo of bright terrain at the time of groove formation, the relevant surface temperatures were significantly lower. Both incorporation of a more Newtonian ductile region and lower temperatures serve to better decouple the brittle surface layer from the substrate, leading to stronger instabilities. As a consequence, we find that it is possible to generate sufficiently strong instabilities at the proper topographic wavelengths to form the grooved terrain on Ganymede.

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