Compositional and Morphological Variations of Effusive Lava Flows and Explosive Pyroclastic Deposits at the Caldera-Forming Gardner Shield Volcano on the Moon

Abstract

We identified a ∼31 km diameter caldera with a well-developed ring fault and ring dike structure at the Gardner shield volcano. Using Chandrayaan-1 Moon Mineralogy Mapper (M³) and Lunar Reconnaissance Orbiter (LRO) Diviner data, we investigated 15 effusive flow units and an explosive unit. Spectral analysis revealed compositional similarities between effusive and explosive eruptions, indicating a single sourced magmatic eruption. Detailed hyperspectral and multispectral analyses (visible, near-infrared, thermal infrared, and radar) indicate the presence of explosive pyroclastic material in the central part of the shield. We identified key morphological structures at the Gardner shield, including three major faults, the caldera's ring fault and ring dike structure, subsidence and resurgence crustal blocks, a graben, a parasitic cone, and extended lineaments beyond the previous work. Our analysis indicates that the well-developed Gardner caldera exhibits lower subsidence compared to Earth's calderas, likely due to the Moon's lower gravity and lower crustal density. These surficial structures preserve the evidence of subsurface magmatic chamber dynamics, making the Gardner shield a unique location for understanding the thermophysical evolution of a central vent shield regime on the Moon. We describe six evolutionary stages, evidenced by multiple volcano-tectonic structures, two distinct eruption styles, and the shield's relationship with the subsurface magmatic chamber, revealing a thermophysical evolution of a central-vent polygenetic shield volcano on the Moon, following a formation mechanism similar to those observed in the shield volcanoes on Earth and Mars.