LAUSR

Abstract Detailed processing and analyses of aeromagnetic data supported by geological constraints shed new light on the structural framework and plumbing system of Huichapan Caldera and Nopala volcano in the northern sector of the Mexican Volcanic Belt. The interpretation of magnetic anomalies is complex due to the bipolar nature of the magnetic field so we applied reduction to the pole using a double fast Fourier transform to convert the magnetic anomalies into simplified patterns. Short optimal continuous analytical field filters enhanced subsurface and surface structures. The reduction to pole analysis filtered for the upward/downward continuation of potential field data improved both regional and detailed imaging since it was applied to different depths. Shallow subsurface structures as well as at depths of 1.25 km and 0.65 km, were correlated with the surface and regional features. The Huichapan Caldera has at least two contrasting ignimbrites. Results show that there are two large magnetic anomalies associated with different volcanic structures. The first one, a circular positive anomaly corresponds to the caldera rim and the other to the structure of the younger Nopala volcano to the west. Strong magnetic sources indicate the feeder dikes. This study provides geophysical evidence for the location of the head wall of the Huichapan caldera as well as a second rim on the south but E-W and NE-SW regional faulting has destroyed this older caldera on the north. Results show that the structures are tectonically controlled and that the caldera is open on the east and southwest. The trap door structure was associated with this regional fault.