Abstract | The geologic history of Mercury has been interpreted to fall into two
distinct periods: an early history that was dominated by the successive emplacement of generations of effusive volcanic plains, followed by a protracted period of cooling and contraction dominated by the formation of lobate scarps and other compressional tectonic features. The MESSENGER mission also revealed previously unanticipated evidence for explosive volcanism on Mercury in the form of vents surrounded by pyroclastic deposits. The timing of this explosive volcanic activity, and the distribution of vent ages across the surface of the planet provides critical information on the thermal evolution of Mercury's interior.
Several lines of evidence have been used to suggest that the largest, and brightest vent and deposit, Nathair Facula, is less than 1Ga; while additional crater superposition evidence supports explosive volcanic activity during the Mansurian and Kuiperian periods. Here, we present new geomorphological evidence supporting the conclusion for young explosive volcanism on Mercury. Through use of a relative degradation classification system, we can investigate vent age independently of host crater age. All of our analyses continue to support the conclusion that not only was explosive volcanism occurring in Mercury's recent geologic past, but the majority of explosive volcanic vents on Mercury may have formed well after the cessation of effusive volcanism. This has significant implications for thermal models of Mercury's evolution, which must now provide mechanisms for melt production and magma ascent well past what was thought possible. These results pose the additional question of whether or not explosive volcanism occurred during the interval between the cessation of effusive plains emplacement and the formation of the recognized explosive vents. We discuss how Bepi-Colombo imaging strategies can be leveraged to understand this fascinating aspect of Mercury's geologic history. |
