Mechanisms of faulting in and around Caloris basin, Mercury

The distribution of faulting in and around the Caloris basin on Mercury provides constraints on the planet's early lithosphere and tectonic history. By means of a series of finite element models we test a range of ideas regarding lithospheric structure, surface loading, and shallow flow proposed to account for early contractional features and younger extensional features on the basin floor as well as contractional tectonic features exterior to the basin. Early‐stage thrust faults within the basin are well matched by the stress field accompanying flexural subsidence in response to partial infilling of a broad basin floor, while younger normal faulting can be the result of flexural uplift in response to later‐stage emplacement of an exterior annulus of smooth plains deposits. A proposed scenario in which later‐stage inward flow of the lower crust induces uplift of the basin floor can, under some conditions, yield extension in the basin, but not in a manner consistent with the observed distribution of normal faults. Thrust faulting on the exterior smooth plains can be the result of local subsidence accompanying the emplacement of these units but may also have been influenced by global contraction. Our results lead to the prediction that the gravity anomaly associated with the Caloris basin and surroundings should consist of a central positive anomaly (mascon) and an annular gravity high separated by a ring of lower gravity. Gravity and topography measurements to be made by the MESSENGER mission will provide a test of this prediction and more generally of the models developed here.