ANALOG MODELS OF TECTONIC RESURFACING AND IMPACT STRUCTURES ON GANYMEDE

Physical analog modeling was performed to test the interplay of tectonic groove formation and impact cratering on Ganymede. These models were performed to simulate formation of grooved terrain by normal faulting in response to distributed extension with pre-, syn-, and post-extension “impact crater structures” added during model development. The brittle lithosphere was represented by a 1 cm thick clay layer with extension distributed by a rubber sheet at its base. Impact crater structures were made by water droplets.

In models with pre-extension impact structures, faults began to form at ~5% extension and typically nucleated at impact crater rim edges with strikes parallel to the intermediate principal stress (extension-perpendicular) direction. These initial crater-rim faults eventually linked to other faults developed across the model at ~10% extension. This result suggests that faults initiate at the crater rims and link to regional trends, rather than regional fault systems reorienting toward pre-existing craters as has been suggested for Enceladus [1].

Syn-extension cratering models indicate that craters are quickly deformed (cut and offset) by reactivated pre-existing structures (normal fault scarps) and any additional strain (e.g., <1% extension) is quickly accommodated by splitting the impact craters along the pre-existing fault. This result is counterintuitive: one would interpret the impact crater as pre-dating the extension, rather than a relatively recent impact event. This suggests that interpretation of the relative timing of faulting versus impacts may be skewed by any additional extension and fault movement.

A blind test of crater retention was performed, where interpretation of a cratered, grooved terrain (33% extension) was mapped for all distinguishable craters. This result was then compared to the original cratered (pre-extension) model surface. Results indicate that >95% of craters were still recognizable after 33% extension. This suggests that tectonic resurfacing alone does not effectively erase crater rim structures and other processes such as image quality, erosion, impact gardening or cryovolcanism may have played a role.

[1] Martin and Kattenhorn, LPSC 2012, #2883.