DPS 2001 meeting, November 2001
Session 35. Icy Galilean Satellites I: Geology and Geophysics
Oral, Chairs: W. Moore, J. Moore, Thursday, November 29, 2001, 4:40-6:10pm, Regency GH

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[35.04] Polar Wander and Surface Convergence on Europa

A.R. Sarid, R. Greenberg, G.V. Hoppa, B.R. Tufts, P. Geissler (U. Arizona, LPL)

Two global issues are addressed by a survey of strike-slip faults on Europa, which (a) provides evidence for polar wander and (b) identifies sites of surface convergence. The survey covers the two broad surface swaths that run from the far north to far south in the leading and trailing hemispheres respectively, where Galileo images at 200m/pixel resolution were obtained for regional mapping purposes.

The evidence for polar wander may provide the first confirmation of that theoretically predicted phenomenon (Ojakangas and Stevenson, Icarus 81, 242, 1989). It follows from comparison of the distribution of strike-slip with predictions of the sense of shear from the theory of tidal walking (Hoppa et al., Icarus 141, 287,1999). The terrain in the leading and trailing hemispheres appears to have moved southward and northward, respectively, since strike-slip displacement occurred (i.e. very recently even relative to the short age of the surface). Thus the north pole of Europa has wandered, probably during the last few million years, from a location that is currently about 30o away in the leading hemisphere. Such polar wander probably also explains the inclined axes of symmetry that we have observed in the distribution of chaotic terrain, pits, and uplift features.

The identification of sites of surface convergence helps address the problem of balancing the global surface budget, given the substantial dilation along widely distributed tectonic bands. These results are obtained by reconstruction of two specific examples of strike-slip, which reveals displacement also associated with lateral convergence. In both locations, a similar type of "convergence band" is found. These features are not similar to compression features on other bodies, which may explain why they had previously been difficult to identify. They are similar in some respects to Agenor Linea, identified earlier as a candidate convergence site (Schenk and McKinnon, Icarus 79, 75, 1989).

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