Constraints on the expansion of Ganymede and the thickness of the lithosphere

Since grooved terrain has formed from extensional faulting of at least one half of the surface of Ganymede, grooves may be due to planetary expansion which can be constrained by determining the extension associated with groove formation. The geometry and kinematics of a fault or group of faults must be known in order to determine the extension. Although neither of these is known for grooves on Ganymede, geologically reasonable end members of the dip, displacement and extension of faults which bound the graben can be estimated in order to place valuable constraints on possible surface area and radius increases as well as on the thickness of the Ganymede lithosphere. Minimum lithosphere thickness is estimated to be 5 km in the Marius and 9 km in the Galileo regions, at the time of furrow formation, and 4 km at the time of groove formation.