Tectonic Resurfacing of Icy Satellites by Periodic Necking Instabilities: Application to Ganymede and Enceladus

Overview: Many of the icy satellites in our solar system include young, highly tectonized terrains. Two of the most prominent examples of such surfaces are Ganymede's grooved terrain and Enceladus' south polar tiger stripes, both of which appear to have ages of less than 1 Ga [1, 2]. While cryovolcanism likely has occurred and is occurring on these bodies, the lack of obvious cryovolcanic structures within the disrupted terrains themselves has lead many authors to suggest that tectonic processes alone were sufficient to completely disrupt the preexisting surface. Despite this, no quantitative investigations of tectonic resurfacing processes have been performed to date. We present two-dimensional numerical models of extensional necking instabilities under conditions relevant to Ganymede at the time of the proposed tectonic resurfacing. These models help constrain the conditions necessary for the formation of the grooved terrain. Furthermore, If we assume that tectonic disruption via a necking instability is not unique to Gany-mede, the models provide important insight into tec-tonic resurfacing on icy satellites such as Enceladus. Background: Ganymede's grooved terrain is composed of sets of roughly parallel, evenly spaced, gently undulating grooves with amplitudes of several hundred meters [3]. Groove sets are typically hundreds to 1000s of km long and ten to one hundred km wide [4]. Grooves visible in regional scale voyager and Galileo images have wavelengths of 4 km to 17 km with an average of 8 km [5, 6]. While groove morphology varies from one set to another, there does not appear to be any global pattern of groove wavelength or orientation. Necking instabilities are the most likely formation mechanism for Ganymede's grooved terrain [7]. The necking instability mechanism assumes that the litho-sphere is composed of a stiff, highly viscous surface layer underlain by a ductile substrate. As extension of such a domain occurs, any thickness perturbation in the layers will grow at a rate determined by the horizontal length scale of the perturbation and the details of the rheology assumed [8]. This results in a surface layer that is deformed into a series of periodic, undulating pinches and swells. Using a linearized analytical model, Dombard and McKinnon [9] applied the extensional necking instability model to the formation of Ganymede's grooved terrain. They 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 …