Geophysical modeling of La Primavera caldera and its relation to volcanology activity based on 3D susceptibility inversion and potential data analysis

Abstract

La Primavera (LP) is a rhyolitic caldera located in the western sector of the Trans-Mexican Volcanic Belt (TMVB). LP is located close to the triple point junction of the Chapala, Colima and Tepic-Zacoalco rifts. To understand the internal structure of the LP and its relationship with the Tepic-Zacoalco rift we carried out a geophysical study with different techniques. Satellite gravity, airborne data followed by ground-based gravity and magnetic surveys were used to performed semi-quantitative analysis to understand the structure of the LP. Residual gravity anomalies (22–15 mGal) occuring on the entire volcanic structure are attributed to its rhyolitic nature. Aeromagnetic anomalies ~125 nT occur on the south and western portions of LP. Analyzed lineaments in the area (Tilt Derivative Algorithm) follow predominantly regional NW-SE and W-E trends. Modeled Werner anomalies, identify the presence of numerous contacts and dikes, especially along main faults, such as Rio Caliente, La Gotera, Mesa Nejahuete, and the caldera ring fracture. Strikinlgy, the higher parts of intrusive bodies and dikes appear at variable depths ≤7.3 km beneath San Miguel and Las Planillas domes. These results were replicated by using an Euler's solution map. The deepest parts of these bodies occur at around 7.8 km south of Las Planillas and El Tajo domes. We developed a 3D smooth model of the magnetic susceptibility isosurfaces with five magnetized bodies beneath the LP structure. Depth and geometry of surface volcanic structures were determinate, thus providing a preliminary visualization of the main isosurface of 0.0343 SI located in the southern area of the caldera. Additionally, the upper part of the magnetic source is 5.5 km in depth. The present study, therefore, reveals the presence of various intrusive bodies existing at different depths inside the caldera. Further, structures and lineaments within the caldera provide evidence for understanding the presence of intrusive bodies, geological structures associated with the caldera structure and geothermal activity.