ICE SHELL FRAGMENTATION AND CATACLASTIC FEATURES SUGGEST REGIONAL DISTRIBUTED SHEARING ON EUROPA

Europa, an icy moon of Jupiter, has a uniquely young surface age (~40–90 Myr) that implies ongoing resurfacing of its ice shell. However, current modeling of global stresses created by tidal deformation of a floating ice shell cannot account for the surface geometry of specific locations displaying regional deformation, such as Argadnel Regio. Although evidence is mounting in support of a plate tectonic paradigm to explain some of the regional deformation on Europa, past studies have been restricted to a few, isolated areas making it impossible to infer if Europan plate tectonics is: global or localized, continuous or intermittent, current or ancient. In this work, diagnostic deformation features are identified and described which lend further support for lateral migration of icy plates but which have not been previously investigated in that context, specifically en echelon sigmoidal bands and cataclastic disaggregation of icy plates in Argadnel Regio. Broad-scale mapping of these features in ArcGIS at 1:1,000,000 scale is supplemented by higher-resolution (1:200,000) mapping of a 180 km x 180 km area that encompasses a portion of a sigmoidal feature, allowing for analysis of its structure and deformation history. The geometry and NE-SW orientation of the mapped sigmoidal features is consistent with distributed left-lateral shearing across the region and may represent multiple stages of motion during progressive propagation of the sigmoidal bands. Counterclockwise rotation of icy micro-plates in the regions between adjacent sigmoidal bands is reminiscent of deformation in terrestrial left-lateral fault zones, and may imply a large-scale cataclastic process is at work. Cataclasis on Earth is a brittle process that involves shearing in granular rocks, leading to the fracturing, rolling, and mechanical breakdown of granular fragments. Similar observations in Argadnel Regio suggest a process of fragmentation, rotation, and reduction of microplate size into progressively smaller rotating blocks. The geometry and orientation of these features suggests a substantial portion of the ice shell experienced distributed left-lateral shearing, intensely deforming the surface of this broad, yet localized region, and ostensibly is related to plate-tectonic-like, differential lateral motions in the ice shell.