Delimitation of volcanic conduits in intraplate settings in Northeastern Mexico: coupling geophysics, structural geology and geochemistry

Intraplate volcanism occurs within tectonic plates and is associated either with hotspots or with the development and propagation of fractures induced by intraplate stresses, and thinning of the crust. In northeastern Mexico, specifically in San Luis Potosí (SLP), Plio-Quaternary intraplate volcanic activity has been documented, linked to normal faulting. Notable examples include the Los Encinos and Santo Domingo volcanic fields, which host intraplate lava cones of trachybasaltic and basanitic composition, dated at 10.6–13.6 Ma and ~0.35 Ma, respectively. This activity, occurring along the boundaries of geotectonic provinces, forms the primary focus of this study.

Monogenetic volcanic complexes are aligned in a NW-SE direction across SLP, together with regional fault systems associated with the western margin of the Sierra Madre Oriental fold and thrust province. The peculiar occurrence of this volcanism motivated this research, with the aim to determine the geometry and extent of volcanic conduits through potential field methods, morpho-structural analysis and geochemistry.

For this study, a regional geophysical analysis was conducted using magnetometry and gravimetry. Eleven volcanic structures located along the NW-SE alignment were sampled. Petrographic analyses revealed that nine cones exhibit trachybasaltic compositions, characterized by high concentrations of olivine, clinopyroxene, alkali feldspar, and calcic plagioclase phenocrysts. One cone displays a trachyandesitic composition with amphibole, pyroxene, and sodic plagioclase crystals, while another is dacitic, containing pyroxene, amphibole, and biotite crystals. Gravimetric data indicate high anomalies over the trachybasaltic monogenetic complexes, underscoring density contrasts with the dacitic cone and emphasizing structural alignments of N–S faults in the NW region of the studied area and NW–SE faults in the SE region. Additionally, magnetometric data further revealed three primary anomalies, potentially corresponding to remnants of conduits that facilitated magma ascent, with the central region displaying the highest structural complexity.