Aeromagnetic anomalies and magnetic domains of the Jalisco Block, western Mexico

Abstract

The Jalisco Block (JB) in western Mexico has been considered as a margin terrane being detached from the North American plate along the Tepic-Zacoalco rift and Colima graben. In this study, an aeromagnetic analysis of the JB and surrounding areas is performed applying a series of geophysical filters and VOXI inverse model. The JB is characterized by two aeromagnetic domains (AMD). AMD-Ia located throughout the south-central section that borders the continental margin is characterized by positive magnetic anomalies extending from the Armería river to Banderas Bay. The AMD-Ia corresponds to the Puerto Vallarta batholith emplaced in the late Cretaceous. The AMD-IIa in the northern section is marked by negative magnetic anomalies over volcanic and volcano-sedimentary rocks, extending to the southern Sierra Madre Occidental. We propose that JB tectonic boundaries correspond to the aeromagnetic AMD-Ia eastern limit and AMD-IIa northern limit. Estimated depths from the radially average power spectrum for deep magnetic sources in the AMD-Ia are in the range of 5.4 km, and for shallow sources from 0.8 to 1.2 km. For AMD-IIa depths are 10.45 km for deep sources and 0.13 km for shallow sources. Depths for deep sources from the Euler deconvolution for the AMD-Ia range from 3.3 to 4.5 km and from 3.5 to 4.9 km for the AMD-IIa. Shallow source depths in the AMD-Ia are 0.2–0.3 km and near surface for the AMD-IIa. The integrated analysis shows five aeromagnetic domains, two associated with the JB and three with the surrounding areas. The VOXI inverse model allows to estimate the dimensions and location of magnetic sources in the reduced to the pole and upward continuations.