Imaging the Two Magma Chambers of Tequila Volcano, Mexico, by Gravity Analysis

Abstract

The Tequila volcano is located on the northeastern margin of the Jalisco Block, along the Tepic-Zacoalco rift in western Mexico, and its latest activity has been dated at approximately 90 ka. In this study, we use the GGMplus gravity data set to perform 3D gravity inversions to depths of up to 8 km from the surface to explore the possible location of the two magma storage regions previously proposed for Tequila volcano. During the inversion process, models with 1000 and 250 m resolution were evaluated to image the magmatic plumbing system beneath the main volcanic edifice and the adjacent lava flows. The 1000 m resolution model reveals a shallow low-density region at about +500 masl beneath Tequila volcano, as well as a deeper anomaly located about 8 km southeast of the summit, at approximately −6000 mbsl; the locations of these anomalies match the location of previously positioned magma chambers proposed for this volcanic system. The inversion results also suggest a structurally controlled zone that may have facilitated magma ascent, including a narrow connection near −3300 mbsl between both low-density regions. The 250 m resolution model further resolves a bifurcation of the shallow low-density region beneath the summit depression, a geometry that may help explain the origin of the summit’s caldera-like morphology and its relation to the central spine. One possible interpretation is that the spine partially obstructed an earlier ascent pathway, promoting a change in the position of eruptive discharge and the development of a lateral conduit; the inferred traces of these possible pathways are illustrated here. The study area also includes the segment of the Santiago River closest to Tequila volcano, which trends NW; in this sector, the inversion identifies shallow low-density materials that may be related to sediment accumulation, as well as a narrow vertical feature extending to ~4100 mbsl, tentatively interpreted as a fault zone.