New Insights into Feeder Dike Swarms in Scoria Cones and Their Structural Control: A Case Study in the Michoacán-Guanajuato Volcanic Field

Abstract

Understanding the feeder systems in scoria cones is essential because they serve as the conduits that feed the most common eruptions worldwide. Feeder dikes and their emplacement are presumably controlled by the tectonic stress field. However, the mechanism of dike propagation and structural control in monogenetic scoria cones remains poorly understood, as well as the conditions that allow dike swarms in scoria cones and in low magma-flux monogenetic volcanic fields. This is the first direct study of a magma feeder system in the Michoacán-Guanajuato Volcanic Field in central México. Quarrying in the Cerrito Colorado scoria cone displays six orthogonal feeder dikes four of them are N-S oriented, parallel to the least compressive stress, intruding preexisting faults, and two are E-W oriented, perpendicular to the least compressive stress, forming their own fracture at the time of the eruption. Single feeder dikes are common in monogenetic volcanoes, but dike networks (swarms) can develop locally in the vicinity of scoria cones and other vent structures. We suggest that bifurcation of feeder dikes can result from temporary blockages of the conduit and during changes in the magma ascent rate and magma pressure. Feeder dikes at the surface can appear as tabular dikes, cylindrical conduits, or as a combination of both geometries. We suggest that tabular dikes splay-off tangentially, and cylindrical conduits bifurcate radially and axially to the main vent. Our study attests to the complexity and structural control that even small scoria cones can present.