Formation of Caloris Basin's Positive Mass Anomaly by Thermal Contraction During Its Postimpact Evolution

Abstract Caloris basin preserves a record of Mercury's volcanic and tectonic activity, including the long‐wavelength warping of its surface in the north‐south direction. As Mercury's largest mascon basin, identifying Caloris' configuration prior to volcanic infilling is a key step in determining the series of events that led to its current state. Here, we simulate the postimpact evolution of Caloris basin to explore the influence of cooling and isostatic adjustment on its configuration before volcanic plains emplacement. We find that the large volume of buoyant impact‐heated material uplifts the basin floor before cooling, explaining some of Caloris' long‐wavelength topographic variations. Subsequent thermal contraction and lithospheric thickening create a positive mass anomaly at Caloris' center before its volcanic infilling. This evolution shows a new mode of mascon formation—perhaps unique to Mercury where high impact velocities generate large volumes of impacted‐heated material—and provides a new interpretation of Caloris' geologic history.