Timing of explosive volcanism on Mercury: A morphological and spectral analysis

Abstract

Explosive volcanic activity on Mercury extended after the end of the widespread effusive volcanism era. While prior research has recognized a prolonged period of explosive volcanic activity, the specific eruption timing for individual pyroclastic deposits remains unknown. In this study, we explore the evolution of explosive volcanism by examining the relationship between the morphological degradation of the vents and spectral changes in the associated deposits. We find a diverse range of spectral properties in pyroclastic deposits, which are typically characterized by increased brightness, a red spectral slope, and a higher curvature compared to the average surface. Rather than presenting a unique spectral signature, these deposits exhibit spectral parameters that span the range of most units on Mercury. We observe a trend between the deposit spectra and the vent degradation characterized by a rapid initial darkening and flattening over time followed by stabilization. The oldest deposits reach a steady state with no further spectral changes. To explain these temporal variations in spectral properties, we propose three potential processes: space weathering, mixing with the background and changes in pyroclast size over time. We examine the implications of space weathering on spectral properties and discuss the eruption timeline for each scenario. The saturation of spectral changes induced by space weathering acts over a period of 1 Gyr. We suggest that a large portion of the pyroclastic deposits identified to date, which have a marked spectral contrast with the surrounding terrain, have been emplaced by recent explosive volcanic eruptions.