Geophysical modelling of Isla Isabel: a volcanic island on the Mexican continental margin

Abstract

AbstractIsla Isabel is a small island located on top of a 20 km-long bathymetric bulge, part of the continental shelf of Nayarit in the vicinity of the mouth of the Gulf of California; it is of volcanic origin with tuff cones, basaltic flows and Surtseyan-type explosion craters exposed. Geophysical surveys were carried out in order to model the geological bodies associated with the local gravity and magnetic fields. 2D and 3D models are presented, and a 1D inversion model is derived from magnetotelluric data. Analysis of the density models of the upper 1400 m suggests two growth stages for Isla Isabel in this depth range: the first one reaching 800 m in depth and the second one projecting from that depth to the surface. The corresponding magnetic susceptibility models concur with this observation. The bodies projected to the surface appear to correspond to diatremes. The 1D magnetotelluric inversion shows two conductive anomalies within the crust between 3–5 and 8–17 km, followed by a resistive substratum that coincides with the seismically derived limit of the Earth's crust at the island's position.