Short‐Term and Global‐Wide Effusive Volcanism on Mercury Around 3.7 Ga

Patches of small smooth plains cover a substantial portion of the Mercurian surface, but their origin and relation to the global evolution are not completely understood. Here, we update the global inventory of small smooth plains on Mercury, classifying their spatial distribution, absolute model ages, and possible origins. We reveal that both large and small smooth plains on Mercury were dominantly emplaced within ∼200 million years around 3.7 Ga, and at least ∼24.9% of the global surface was resurfaced during this period. Small smooth plains formed by effusive volcanism are preferentially located around the contemporaneous Caloris, Rembrandt, and Beethoven basins and at thin crust areas. We also report small smooth plains that were likely emplaced by basin ejecta. Together with the distribution of similarly aged large smooth plains, our results reveal that peaked formation of large impact basins may be a major trigger for this short‐term and global‐wide volcanism. Plain Language Summary The history of volcanism is a pulse curve of geodynamics of planetary bodies. Large smooth plains on Mercury were formed by effusive volcanism before 3.5 Ga. Small smooth plains occupy a substantial portion of this planet and they have a wider geographic distribution than larger ones, but their possible origins have not been systematically studied. The patchy occurrence of small smooth plains indicates that they may better represent the global thermal evolution. Here, we update the global distribution of small smooth plains and investigate the absolute model age and possible origin for each case. At least 123 of the 315 cataloged small smooth plains were likely emplaced by effusive volcanism that preferentially occurred at thin crust areas. Smooth plains, regardless of origins and sizes, were mainly formed in ∼200 million years around 3.7 Ga, revealing that >24.9% of Mercury surface was emplaced by short‐term effusive volcanism. The preferential occurrence of volcanic smooth plains around the Caloris, Rembrandt, and Beethoven basins suggests a possible trigger by these impact events. We report evidence showing that coeval and collocated small smooth plains can have different origins, as some smooth plains may be ponded ejecta deposits that were emplaced by contemporaneous impact basins. Key Points Global inventory of small smooth plains on Mercury is created, with an emphasis on their origins and absolute model ages Formation of smooth volcanic plains peaked at ∼3.7 Ga, wi