Discerning Subvolcanic Deformation and Magma Emplacement Geometries: The utility of Combined Paleomagnetic and Anisotropy of Magnetic Susceptibility Studies

Here we report paleomagnetic and anisotropy of magnetic susceptibility (AMS) data from three monogenic volcanic centers. Our data reveal that monogenic magma feeder systems are far more complex in terms of the evolution of the magma plumbing system, subvolcanic deformation, and the intrinsic and extrinsic controls on the final magma source geometry, outer cinder cone morphology, and eruptive dynamics. We hypothesize that these various factors collectively orchestrate the development of monogenic volcanic constructs and their associated subvolcanic magma feeder systems. Paleomagnetic and AMS data from the 1) Lemptégy Volcano, France, 2) Trosky Volcano, Czech Republic, and 3) Cienega Volcano, USA indicate that monogenic volcanoes, although commonly perceived as simple evolve in a complex manner. The question we pose here is what governs the evolution of the volcanic construct and the magma feeder system? As we show, the regional tectonics, and hence the regional stress/strain field, do not have a strong control on the upper emplacement geometries and magma flow path even if feeder dykes do follow the trend. We argue that the dynamics of the magma flow once it nears the eruptive edifice remains poorly understood, thus producing a large gap in our current knowledge on active volcanic evolution. Combining detailed paleomagnetic, AMS, and structural studies as well as basic field mapping provide the needed data to constrain the evolution of these systems. We suggest that shallow magmatic systems beneath monogenetic volcanoes, and likely other shallow magma systems (e.g., laccoliths), and even large edifices, are not strongly controlled by the local and regional stress fields and bear little on the growth of the shallow magma feeder systems (<1km). The simple external structure of monogenetic volcanoes hides a rather complex magmatic plumbing system that dynamically evolves during the life of the volcano. As we show, the well-exposed roots of these volcanoes reveal that the growth of a volcano occurs not due to simple central axis feeder systems but rather through interplay of local structures (including basement lithology), magmatic effects, and construct evolution throughout the lifetime of the volcano. We pose that no two systems evolve in an absolutly predictable manor. We further hypothesize that this is likely the case in larger volcanic systems as well as in deep-seated igneous intrusions.