A Fault Surface Exposed on Mercury

Abstract Mercury's tectonic history has been dominated by global contraction as the planet shrinks and cools. Previously, fault dips have been indirectly estimated by measuring offsets to the rims of craters displaced by fault movement. Here we present the first observations of a fault surface exposed in three dimensions, in this case within a volcanic vent. We use shadow measurements to determine the depth of the vent and have measured the dip of the fault as 28o ±5. This is towards the shallower end of previous dip estimates used to estimate global contraction. If it is representative, it suggests global contraction at the higher end (5.7 – 7.1 km) of previously published estimates.