Large-scale doming on Europa: A model of formation of Thera Macula

Abstract

To cite this version:Loïc Mével, Eric Mercier. Large-scale doming on Europa: A model of formation of Thera Macula.. Planetary and Space Science, Elsevier, 2007, pp.915-927 AbstractSince Galileo spacecraft reveals Europa's surface at high and medium resolution, deformation and processes affecting the relatively young surface have been more accurately defined. This work reports the observations carried out on a large-scale feature of the south hemisphere, Thera Macula. It is shown that Thera presents common points with many other features including small-scale domes, lenticulae and large-scale chaotic area (disrupted ancient surfaces lying on a dark matrix), but remains singular through its asymmetric morphology. On the basis of observations, we propose a scenario for the setting of Thera Macula. It involves a large-scale doming (40-70 km in radius) of the pre-existing surface associated to ductile deformations, and the consecutive collapse of the created megadome associated to brittle disruption of blocks and flow of low viscosity material over the surrounding ridged plains. The processes responsible for each stage of the proposed scenario have been investigated. Both cryomagmatic and diapiric origins are discussed and confronted to observations. Finally, comparison of similar features at various scales suggests that Thera Macula by its originalities (asymmetry, rounding bulge) may have preserved the intermediate stages of the formation of subcircular chaos at least up to about 50 km in radius. A common evolution and endogenic origin for multi-scale hot spot features is proposed: 1) the doming stage, 2) the collapse and extrusion stage, and 3) the relaxation stage.

Chaotic Terrain on Europa

“…16b) (Pappalardo et al, 1998a), analogous to salt diapirs on Earth. Diapirs have been used to explain collections of similar-sized small domes (Rathbun et al, 1998) as well as large dome features such as Murias Chaos (Figueredo et al, 2002) and Thera Macula (Mével and Mercier, 2007). As discussed below, such diapirs typically arise due to either thermal or compositional buoyancy.…”

“…This behavior is clearly different from the observed wide size-spectrum of chaos regions. While it is possible that some large chaos regions are generated by merging diapirs (Spaun et al, 1999;Figueredo and Greeley, 2004;Schenk and Pappa-lardo, 2004;Mével and Mercier, 2007), the wide size range of individual, roughly axisymmetric features is difficult to explain by such merging.…”

Downward Oxidant Transport Through Europa's Ice Shell by Density‐Driven Brine Percolation

“…A large thermal perturbation, indicated in Figure 1a, that thins the conductive lid is clearly necessary to induce significant near‐surface partial melting (Sotin et al., 2002). What happens close to the surface is not clear but likely involves the collapse of the brittle surface ice on top of the partially molten region (Mével & Mercier, 2007; Schmidt et al., 2011; Walker & Schmidt, 2015) and the extrusion of this mush along fractures. Here we assume that this process leads to exchange between the oxidized layer and the partial melt and that the oxidants are mixed throughout the near‐surface brine by porous media convection within the mush (Liang et al., 2018; Neufeld et al., 2010).…”

“…A large thermal perturbation, indicated in Figure 1a, that thins the conductive lid is clearly necessary to induce significant near-surface partial melting (Sotin et al, 2002). What happens close to the surface is not clear but likely involves the collapse of the brittle surface ice on top of the partially molten region (Mével & Mercier, 2007;Schmidt et al, 2011;Walker & Schmidt, 2015) and the extrusion of this mush along fractures.…”

Ice-Ocean Exchange Processes in the Jovian and Saturnian Satellites

“…In this model, a heat source at the base of the icy shell facilitates melting of the overlying ice, exposing the ocean below and leading to the formation of plates equivalent to icebergs that float in a matrix of refrozen ocean material (Greenberg et al 1999;Thomson and Delaney 2001). The diapirism model for chaos formation proposes that the morphology of chaotic terrain and pits, spots, and domes (collectively termed lenticulae) represents the surface expression of rising diapirs Rathbun et al 1998;Figueredo et al 2002;Mével and Mercier 2007). Such diapirs would develop due to either thermal or compositional buoyancy within the ice shell (Barr and Showman 2009).…”