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Numerical modeling of subduction on Europa

Presentation #210.01D in the session Ocean Worlds: Tectonics, Surfaces, and Ionospheres (Oral Presentation)

Published onOct 23, 2023
Numerical modeling of subduction on Europa

The surface of Europa shows a variety of morphological features, often unique among the known icy bodies. Scarcity of impact craters indicates a very young surface (≤ 90 Myr), most likely a consequence of recent, or even active, tectonic processes driven by a combination of tidal deformation, internal dynamics and orbital interactions. Modeling work has found that an extension of the ice shell can trigger material transport from the subsurface ocean to the surface, in accordance with the morphology of numerous extensional bands [1]. While harder to identify, compressional features have also been detected. The reconstruction of geologic features revealed that almost a 100-km-wide region was missing, possibly sank by subduction [2,3,4]. If it occurred, subduction would have profound consequences for Europa’s habitability. It is, however, not clear what is the mechanism driving the compression. Processes such as global melting, polar wander, or nonsynchronous rotation could account for sufficient compressive stress, but in the absence of self-sustaining plate tectonics, the extent of the deformation is limited to only a few kilometers. Numerical models assuming a half-subducted salt-rich porous plate concluded that it is rather unlikely to maintain such a process in the long term [5,6]. Here we address this issue by modeling compression of initially undamaged shell composed of pure ice. Using a 2D finite element model with visco-elasto-plastic rheology, free surface, and phase transition at the ice-water interface, we show that convergence can result either in subduction or in building positive topography. The scenario depends mainly on the shell thickness and the heat transfer regime, suggesting that the convergent events on Europa might have occurred during the period of high orbital eccentricity, when the ice shell was thin and conductive [7].

References: [1] Howell and Pappalardo (GRL, 2018), [2] Kattenhorn and Prockter (Nat. Geosci., 2014), [3] Collins et al. (JGR: Planets, 2022), [4] Mével and Mercier (PSS, 2005), [5] Howell and Pappalardo (Icarus, 2019), [6] Johnson et al. (JGR: Planets, 2017), [7] Hussmann and Spohn (Icarus, 2004).

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