Origin of the Bulge Topography Within Caloris Basin, Mercury

Caloris basin on Mercury has a massive circular bulge topography imprinted with unique fault sets. A variety of deformational processes have been proposed to have influenced their formation, including both global contraction and basin evolution, as well as the deposition and weight of the volcanic infill. However, the relationship between these processes and the amount of influence that each has had on the present-day morphology is not yet constrained. Through a combination of elevation and gravity data, we analyzed faults and subsurface structures of the basin and its surroundings. Analyses revealed spatial relationships between interior grabens and the basin's topography, putative buried rings, and evidence that areas of the basin rim are controlled by faults of the surrounding external plains. The flexure surface to the circular bulge was computed, providing the maximum weight load (4.48 × 1018 N) required to produce the topography. In this scenario, late doming during deposition at the basin center formed radial grabens, followed by degassing and compaction. This led to increased density at the basin center, which altered the isostatic equilibrium and encouraged a flexural response, in turn producing a circular bulge and concentric grabens around a central depression. Regional warping from global contraction remains a possible influence; however, deformation of the basin's perimeter shows inconsistencies with the locations of long-wavelength folds from previous studies. Contemporaneously with the flexural response, southeasterly striking faults from west of Caloris and reactivated basin bounding faults from a relic basin at the northern border have altered the rim elevation and geometry.