GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 3.2 173 High-resolution magnetic and gamma-ray airborne survey at Socorro Island, Mexico V. Paoletti 1 ,M. D’Antonio 1 , R. Supper 2 , S. Gruber 2 , K. Motschka 2 1 Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse, University Federico II, Naples, Italy 2 Geological Survey of Austria, Vienna, Austria Introduction. The Island of Socorro (Fig. 1) is located 700 km off the western coastline of Mexico at the northern Mathematicians Ridge, an abandoned mid-ocean ridge spreading centre. Together with several other islands (e.g., San Benedicto and Clarion) and numerous seamounts, the so called Revillagigedo archipelago represents post-abandonment alkaline magmatism [e.g., Taran et al. (2002) and references therein]. The last volcanic event in the area of Socorro took place in 1993 (e.g., Siebe et al. , 1995), when a submarine basaltic eruption threatened the small settlement on the island. Until today, due to the remote location of the island, little knowledge is available concerning the subsurface structure of the volcanic edifice. In support of plans of the Mexican government to enlarge the settlement on the island, a combined geophysical survey was conducted in February 2009 to open up new resources for local groundwater supply. Investigations were focused on determining the resistivity structure of the shallow subsurface of the volcanic edifice, as this parameter is directly related to the water content of subsurface structures. However other parameters such as clay content, fluid conductivity and temperature control the subsurface resistivity and these parameters normally show significant variations in volcanic areas. Thus, we conducted other investigations/analyses over the island, such as airborne magnetic, electromagnetic and gamma-ray measurements in order to have an overall view of the main structural/lithological features of the island. The aim of this work is to retrieve information about the surface and subsurface geology of the island based on the analysis and interpretation of magnetic and gamma-ray airborne data, integrated with available geo-volcanological information. Fig. 1 – Geologic sketch-map of Socorro Island (Carballido-Sanchez, 1994).