Abstract
Many populated areas in the world (e.g., Flagstaff, AZ; Auckland, NZ; Mexico City, MEX) lie within active monogenetic volcanic fields that typically contain small volcanic cones and explosive maar craters formed over the course of a single eruptive cycle. Although much work has focused on the eruptive behaviour of monogenetic volcanoes, little geological information exists about their subsurface development and how the movement of magma through Earth’s shallow crust modulates the location and style of hazardous volcanic eruptions. Determination of the dynamics of magma intrusion and the transition from a coherent magma's ascent to its explosive fragmentation is crucial to our understanding of the controls on explosive versus effusive eruptive behaviour, thus to better evaluation of risks in a certain area. This study aims to determine the processes and relative timing of activity that took place below the ground surface of the deeply-eroded but well-preserved Jagged Rocks Complex, a cluster of monogenetic volcanoes within the Miocene Hopi Buttes Volcanic Field in northeastern Arizona, by combining detailed structural mapping, volcanological observation, paleomagnetic and geochemical analysis. The Jagged Rocks Complex, exposed at ~ 350 m below the pre-eruptive surface, comprises a well-preserved intrusive network, including dikes, sills and inclined sheets, associated with different type of fragmental bodies including buds, pyroclastic massifs and a diatreme, that represent different extents of shallow-depth fragmentation. These exposures at the Jagged Rocks Complex provide an excellent natural laboratory for examining the subsurface record of volcano initiation, and for constraining interpretations of processes controlling upward migration of magma from intrusion to eruption. This multidisciplinary approach allows an investigation at different levels from the source region to the surface, and aims to shed the light on the processes that regulate eruptions not only within monogenetic volcanic fields but also within small basaltic volcanoes in general.