Lunar Basaltic Sequential Eruption Phases: Gas Release Pattern Control on Lateral Variation and Vertical Structure of Eruption Products

Assessment of mare basalt gas release patterns during individual eruptions provides the basis for predicting the effect of vesiculation processes on the structure and morphology of associated features. We used basic principles of magma generation, ascent and eruption to examine the range of dike volumes, effusion rates, volatile species and release patterns as a function of time and eruption duration, subdividing eruptions into four sequential phases: Phase 1, dike penetrates surface, transient gas release phase; Phase 2, dike base still rising, high flux hawaiian eruptive phase; Phase 3, dike equilibration, lower flux hawaiian to strombolian transition phase; Phase 4, dike closing, strombolian vesicular flow phase. These phases result in a unifying quantitative conceptual model for the relationships among a wide and diverse range of observed volcanic landforms and structures. These four volatile release phases, together with total dike volumes, initial magma volatile content, vent configuration and magma discharge rate, can help relate the wide range of apparently disparate lunar volcanic features (e.g., pyroclastic mantles, small shield volcanoes, compound flow fields, sinuous rilles and their source depressions, long lava flows, pyroclastic cones, summit pit craters, irregular mare patches (IMPs), and ring moat dome structures (RMDSs)). In contrast to viewing the array of volcanic landforms each in isolation, these theoretical predictions provide the basis for placing lunar volcanic landforms into eruptive sequences from individual eruptive events, and linking them to potential variations in dike characteristics and evolution, effusion rates, and volatile contents, that can provide clues to the nature of magma source regions. We outline a series of predictions on lateral variation from the vents, and vertical variation in flow/deposit stratigraphy and show how these can be further tested by future human and robotic missions to specific lunar destinations.