Late-stage effusive volcanism on Mercury: Evidence from Mansurian impact basins

Wright, J.; Rothery, D. A.; Balme, M. R. and Conway, S. J. (2017). Late-stage effusive volcanism on Mercury: Evidence from Mansurian impact basins. In: 48th Lunar and Planetary Science Conference, 20-24 Mar 2017, The Woodlands, Houston, Texas.



The globally extensive smooth plains of Mercury are believed to be mostly volcanic in origin. Wide-spread effusive volcanism on Mercury is thought to have ended by ~3.5 Ga due to secular cooling of the planet’s interior, and contraction of its lithosphere. As the planet cools and contracts, melt should be produced at a slower rate and in smaller volumes, so it will stall deeper and its escape routes will close. 3.5 Ga corresponds roughly with the end of Mercury’s Calorian system. Smooth plains younger than this have been reported, but are restricted to the interiors of impact basins, such as Rachmaninoff. If widespread effusive volcanism on Mercury ceased in response to cooling and contraction during the Calorian, then Mansurian impact basins are good places to search for late-stage effusive volcanism. Effusive volcanism should be favoured in impact basins, because they remove overburden, promote uplift, temporarily reset the preexisting stress regime, propagate fractures and deposit heat. If cooling and contraction were the main factors that controlled the decline of widespread volcanism on Mercury, then post-impact volcanism should similarly become less voluminous throughout the Mansurian. Smaller basins should have less post-impact volcanism because they produce shallower pathways for melt. Post-impact volcanism should also become less common throughout the Mansurian as Mercury continues to cool. Considering these expectations, we are conducting a global survey of Mansurian impact basins to study how effusive volcanism on Mercury waned as a con-sequence of global cooling and contraction.

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