Abstract

ARZATE, Jorge A.; ROMO-LOZANO, Héctor M.; PLAEN, Raphael De  and  CORBO-CAMARGO, Fernando. The magmatic system of the Colima Volcano from magnetotelluric and ambient noise data. Rev. mex. cienc. geol [online]. 2023, vol.40, n.1, pp.71-84.  Epub Dec 02, 2025. ISSN 2007-2902.  https://doi.org/10.22201/cgeo.20072902e.2023.1.1707.

Here we present the results obtained from the 3D inversion of the full impedance of 21 magnetotelluric soundings in the frequency range of 1000-0.05 Hz. The results confirm the existence of a flat lying conductor at a depth of 2-4 km bmsl under the Colima Volcano (CV) acting as a natural cap seal of the Colima Volcanic Complex hydrothermal system. Model results along five EW vertical sections extracted from the 3D inverted impedance show that the upper crust (<15 km) in the northern sector of the CVC is far more resistive (>1000 ohm·m) and compact than in the southern zone, where it becomes more conductive and apparently more fragmented.

The combined results of horizontal and vertical resistivity slices and sections reveals a vertical conductor (10-20 ohm·m) of ellipsoidal shape under the Colima Volcano, which extend from about 5 km bmsl down to at least 15 km bmsl. The approximate dimensions of the major and minor axis of the elliptical conduit along the fault are about 20 km and 5 km respectively. The major axis of the ellipsoidal enhanced conducting pathway is parallel to a NS fault segment off the main NE-SW fault system, which suggests that this fault segment is currently controlling the magmatic fluids ascent.

Down to about 15-18 km bmsl the crust becomes widespread conductive, coinciding with a flat body of low shear-wave velocity (<3.2 km/s) under the Colima Volcano at similar depths. This low density and low resistivity flat lying mush reservoir contains H2O-rich melts prone to be polarized electrically and to polarize the surrounding medium. The supporting evidence suggest that the recent and near-future activity of the CV is closely related to a deep flat magmatic source rather than to a shallow magmatic chamber, and that the triggering mechanism of recurrent magmatic activity of the CV may have an electrical component.

Keywords : magnetotellurics; 3D inversion; vertical conductor; mush reservoir; Colima Volcano, Mexico.

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