Geophysical investigation of Pleistocene volcanism and tectonics

Abstract

Magma upwelling forming volcanic plumbing systems in back arc settings is typically controlled by extensional tectonic structures of the upper crust. Here we investigate this process in the area between the volcanic arc of the Aeolian Islands and the Calabrian arc (SE Tyrrhenian Sea) by integrating morpho-bathymetry and reflection seismic data with the outcomes of "Inverse 3D magnetic modeling" of previously gathered aeromagnetic data. Morpho-bathymetric data highlight the presence of a seamount similar to 10 km offshore Capo Vaticano Promontory (eastern Calabria). This feature, named Capo Vaticano seamount is composed of a series of NE-trending ridges, the greatest of which (R1) is similar to 12 km long, and 2.4 km wide, displays asymmetric flanks with a landward steep slope, oblique morphological steps and elongated NE-trending rims. The position of the R1 ridge summit fits the Reduced-to-the-Pole peak of a high-intensity magnetic anomaly straddling Capo Vaticano Promontory and its offshore prolongation. Seismic and bathymetric data highlight two extensional fault systems affecting the offshore of Capo Vaticano Promontory during the Plio-Pleistocene: (a) a Pliocene NW-trending, SW-dipping normal fault system, and (b) a Pleistocene NE-trending, SE-dipping normal fault system. The younger system is composed of a series of en-echelon branching normal faults bounding the eastern side of the R1 ridge. Aeromagnetic data modeling imaged a complex 3 D-magnetized body below the R1 ridge exhibiting a sub-vertical conduit-like structure in the shallow part, and a NE-striking, sheet-like shape inclined by 45 degrees in depth. The location of the sub-vertical conduit coincides with the summit of the R1 ridge. The magma uprising at the root of the volcano was controlled by the Pliocene NW-trending faults whereas its further upwards migration was ostensibly controlled by the Pleistocene NE-trending faults. Both fault systems are responsible for the high level of fracturing that likely favored the upward migration of magma. The younger extensional systems also controls the present-day, mantle derived, fluid escapes observed at the summit of the R1 ridge. Relying on seismic stratigraphic evidence as well as the normal polarity of the magnetic anomaly, the R1 ridge probably started to form during the Olduvai chron (early Pleistocene, 1.81-1.96 Ma). Accordingly, the Capo Vaticano volcano may represent the result of magmatic activity that predates the Aeolian volcanic arc. (C) 2015 Elsevier Ltd. All rights reserved.