PHYSICAL ANALOG MODELS OF TECTONIC RESURFACING ON GANYMEDE

Grooved terrain on Ganymede has been interpreted as extensional ridge and trough formations. The effects of highly tectonized regions such as grooved terrain on pre-existing populations of craters are not entirely understood. It is possible that tectonic resurfacing may completely obliterate some craters, or make the craters difficult to recognize in images such as those produced by the Voyager and Galileo missions. However, whether this process is dominated by large scale block faulting or smaller scale intrablock faulting is unknown. Also, it is not clear that all syn-kinematically formed craters can be differentiated from pre-kinematic or post-kinematic craters. Physical analog modeling was performed to test the interplay of tectonic groove formation and impact cratering on Ganymede. These models 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.

Effects on the simulated "crater" populations were examined as a function of total extensional strain by performing size-frequency counts on images obtained at different stages of deformation. In order to test tectonic resurfacing, we examined the effects on pre-kinematic "crater" populations, in order to infer the first-order effects of distributed extension related to grooved terrain on pre-, syn-, and post-kinematic impact crater populations. Fault density and growth was analyzed in relation to the pre-kinematic impact crater structures, as these typically become nucleation sites for faults. 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. The results suggest 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.