Prolonged cooling and degassing of Apollo 17 volcanic glasses on the lunar surface

TL;DR

The study shows that Apollo 17 volcanic samples reveal prolonged cooling and degassing on the Moon's surface, suggesting pyroclastic deposits could sustain a temporary lunar atmosphere.

Contribution

The paper introduces extended thermal histories for lunar pyroclastic deposits, challenging previous degassing models.

Findings

Volatile depletion in Apollo 17 samples cannot be explained by free-flight degassing alone.

Prolonged cooling and degassing on the lunar surface lasted for years.

Pyroclastic deposits may have sustained a local transient lunar atmosphere.

Abstract

Studying lunar pyroclastic volcanism provides key insights into the thermo-chemical evolution of the lunar mantle and the Moon’s volatile budget. Pyroclastic deposits, although volumetrically minor compared to mare basalts, are derived from deeper, more primitive, and volatile-rich mantle sources. Here we synthesize volatile degassing recorded by Apollo 17 sample 74220, one of most studied pyroclastic deposits. By modeling the volatile degassing of olivine-hosted melt inclusions, melt embayments, and glass beads, we show that volatile depletion of these samples cannot be explained solely by degassing during free-flight, as previously proposed. Instead, the data require extended thermal histories, with beads undergoing slow cooling and prolonged degassing on the lunar surface for years, a scenario further supported by thermal modeling. Our findings suggest that pyroclastic deposits remained active volatile sources well beyond eruption, which is potentially important for sustaining a local transient lunar atmosphere and the long-term volatile cycle of the Moon.

The authors study volatile degassing recorded by Apollo 17 samples. They suggest that pyroclastic deposits remained active volatile sources well beyond eruption, helping to potentially sustain a local transient lunar atmosphere and the long-term volatile cycle of the Moon.

Figures