Lateral shearing and its relevance to the deformation histories of icy satellites

Proceedings of the NASA-Idaho Space Grant Consortium Research Symposium 2: 22-23.

Icy shells of outer solar system satellites are often pervasively fractured, including moons of Jupiter (Europa; Ganymede), Saturn (Enceladus; Dione), Uranus (Ariel; Miranda; Titania), and Neptune (Triton). Brittle deformation may be driven by tidal forcing, meteorite impacts, endogenic processes (e.g., thermal diapirism; cryomagmatic intrusion; tectonic displacements), and topographic loading. Most of these are primary processes with straightforward cause and effect relationships with fracturing; however, some ice shell deformation is secondary. For example, tectonic displacements (movement along faults) are a primary response to differential forcing, such as tidal effects induced by the nearby planetary body. This tectonic activity is prevalent where tidal bulges oscillate (e.g., above a liquid layer) in response to an orbital eccentricity. A secondary effect of these tectonic motions is that the ice shell is locally or regionally stressed by compression or extension adjacent to a fault, which may itself induce fracturing or faulting. In addition, shear heating due to frictional sliding may cause ice to melt or remobilize, resulting in localized deformation along a fault zone. The theoretical mechanics of secondary tectonic deformation due to shearing is used to demonstrate its relevance to the deformation of Europa's ice shell. Lateral shearing effects are manifested by localized fracturing in the form of tailcracks and anti-cracks, cusp development along curved cracks called cycloids, and crustal contraction along fault zones in response to shear heating, constructing edifices called ridges. Similar deformation may exist on other icy satellites where there is a significant source of stress to drive lateral shearing.

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