Kattenhorn, S.A., Hurford, T.A. (2009)
Tectonics of Europa.
In: Europa, Pappalardo, R.T., McKinnon, W.B., Khurana, K., eds, University of Arizona Press, 199-236.
Europa has experienced significant tectonic disruption over its visible history. The description, interpretation, and modeling of tectonic features imaged by the Voyager and Galileo missions has resulted in significant developments in four key areas addressed in this chapter: (1) The characteristics and formation mechanisms of the various types of tectonic features; (2) The driving force behind the tectonics; (3) The geological evolution of its surface; and (4) The question of ongoing tectonics. We elaborate upon these themes, focusing on the following elements: (1) The prevalence of global tension, combined with the inherent weakness of ice, has resulted in a wealth of extensional tectonic features. Crustal convergence features are less obvious but are seemingly necessary for a balanced surface area budget in light of the large amount of extension. Strike-slip faults are relatively common but may not imply primary compressive shear failure, as the constantly changing nature of the tidal stress field likely promotes shearing reactivation of preexisting cracks. Frictional shearing and heating thus contributed to the morphologic and mechanical evolution of tectonic features. (2) Many fracture patterns can be correlated with theoretical stress fields induced by diurnal tidal forcing and long-term effects of nonsynchronous rotation of the icy shell; however, these driving mechanisms alone probably cannot explain all fracturing. Additional sources of stress may have been associated with orbital evolution, polar wander, finite obliquity, ice shell thickening, endogenic forcing by convection and diapirism, and secondary effects driven by strike-slip faulting and plate flexure. (3) Tectonic resurfacing has dominated the ~40-90 Myr of visible geological history. A gradual decrease in tectonic activity through time coincided with an increase in cryomagmatism and thermal convection in the icy shell, implying shell thickening. Hence, tectonic resurfacing gave way to cryomagmatic resurfacing through the development of broad areas of crustal disruption called chaos. (4) There is no definitive evidence for active tectonics; however, some tectonic features have been noted to postdate chaos. A thickening icy shell equates to a decreased tidal response in the underlying ocean, but stresses associated with icy shell expansion may still sufficiently augment the contemporary tidal stress state to allow active tectonics.