Caloris Basin, Mercury: An Analysis of Cross-Cutting Tectonic Structures

Abstract:

The Caloris basin on Mercury, measuring approximately 1,550km in diameter, is the largest recognized impact basin on Mercury and among the largest in our solar system. It is host to the Caloris Planitia, the interior smooth plains of the basin, which feature several distinct types of tectonic structures. Contractional wrinkle ridges are generally present throughout the basin, while two distinct sets of extensionally produced graben are found mainly in separate regions; the complex of radial linear graben known as Pantheon Fossae is located in the central region of the basin, while a set of more randomly oriented and concentric graben are found approximately midway between the basin’s centre and its circumference. Although the zones where these two extensional sets occur are mainly distinct, there are some instances of spatial overlap. This work focuses on constraining the relative timing of these diverse structural features, thus helping to unravel the deformational history of the basin by analyzing the geometries and kinematics of the graben and ridges in areas where the structures cross-cut each other. We also seek to quantify and constrain the local strains and stresses associated with these structures. This analysis will further guide future kinematic and mechanical models of Caloris, with end member descriptions ranging from a single mechanism to account for the simultaneous deformation of structures, for interactions which show no consistent order of deformation throughout the basin, to one or more deformational mechanisms driving a multi-stage or sequential deformation, for interactions that demonstrate a clear order of cross-cutting relations.