Kattenhorn, S.A., Prockter, L.M. (2013)

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Evidence for subduction and plate tectonics on Europa: relevance to surface age and astrobiology


GSA Abstracts with Programs, 45 (7), p.706, Paper #305-12.

Past studies of Europa's surface have been unable to explain an abundance of extensional features (e.g., dilational bands) yet a seeming lack of contraction. We present evidence for subduction, and hence plate tectonics, on Europa. We reconstruct geologic features in a 106,000 km2 candidate region to show that the current surface configuration required numerous translations and rotations of rigid plates. The reconstruction reveals ~100 km of missing surface that seemingly vanished along a 20-km-wide, band-like zone with unusual color characteristics. Mismatching geological features across this zone suggest an ~80-km-wide region may have subducted along a >300-km-long plate boundary. The candidate subduction zone is arcuate, has no topographic expression at image resolutions, and is partially bounded by transform faults. The overriding plate contains strike-slip faults consistent with strain partitioning related to oblique convergence. The surface of the overriding plate is pervasively dotted with patches of disrupted terrain, which we interpret as erupted cryolava, implying a significant subsurface thermal perturbation related to the potential subduction. Buoyancy constraints and a lack of contractional topography imply that the subducting slab does not enter the ocean directly. We thus interpret a thin (~several km), brittle lid overlying a thicker, convecting ice layer, with plate motions and subduction restricted to the brittle lid. The subducting plate is presumably consumed at a rate conducive to complete subsumption into the convecting layer. Our work potentially provides a new paradigm for interpreting Europa's young surface age (40-90 Myr). Subduction provides a mechanism to deliver nutrients from Europa's radiolytically processed surface to the ocean: crucial for astrobiology and habitability, reinforcing Europa as the primary target in future outer solar system exploration. If subduction exists, Europa would become the only other solar system body beyond Earth to exhibit plate tectonics, involving subduction (surface area removal), mid-ocean-ridge-like spreading (surface area creation at dilational bands), and transform motions. Such motions are presumably driven by convection in the deeper, warmer ice, evidenced by thermal upwellings at sites of chaos and lenticulae.

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