Magnetic Structure of the Ischia volcanic island, Southern Italy

Valeria Paoletti,Giovanni Florio,Maurizio Fedi

doi:10.4401/ag-7550

Abstract

We carried out a study of the structures of the volcanic island of Ischia by the analysis and interpretation of high-resolution aeromagnetic data and by a newly compiled in-land gravity data set. The comparison between the vertical gradient of gravity data and pole-reduced magnetic data was performed through semblance analysis and highlighted a correspondence between the main magnetic and gravity highs over the lava and green tuff deposits (e.g., Punta Imperatore, Mt. Trippodi, Zaro, Mt. Rotaro, Mt. Epomeo). Our analysis also highlighted the simultaneous presence of a magnetic minimum and a gravimetric maximum in the central part of the island, mainly visible in the long-period components of the two data sets. This may be due to the existence of a partially demagnetized structure with positive density contrast, representing the island's igneous basement. The boundaries of the lava and tuffs deposits of the island were clearly pointed out by the maxima of the total horizontal gradient maps of magnetic and gravity data. Those maxima also show the position of several lineaments, in good agreement with the mapped faults of the island.

Highlights

The island of Ischia (Figure 1a) is the westernmost volcanic field of Phlegrean Fields, a volcanic area of Southern Italy that includes Campi Flegrei and the island of Procida [Orsi et al 1996]
We carried out a study of the structures of the Island of Ischia by the coupled analysis of high-resolution aeromagnetic data and a recently compiled in-land gravity data set
A semblance analysis of magnetic and gravity data along four profiles crossing the most prominent anomalies of the island pointed out a correspondence between magnetic and gravity highs over the lava and green tuff deposits

Summary

Introduction

The island of Ischia (Figure 1a) is the westernmost volcanic field of Phlegrean Fields, a volcanic area of Southern Italy that includes Campi Flegrei and the island of Procida [Orsi et al 1996]. Several other faulty systems cut the deposits in the other sectors of the island [de Vita et al 2006, Nappi et al 2010] (Figure 1b) This structural setting seems to result from the interplay between regional and local tectonics [Orsi et al 1991 and Acocella and Funiciello 1999]. The island is composed of volcanic rocks (mostly trachytes and phonolites, and minor shoshonites and latites; Figure 2a), marine sediments and landslide deposits [e.g., Vezzoli 1988, Orsi et al 1992, D’Antonio et al 2012] The presence of these deposits is related to the interplay of tectonism, volcanism, erosion, sedimentation and slope instability throughout the island history [de Vita et al 2006]. We support our interpretation by a previous modeling of potential field data and by the temperature data measured in deep thermal wells of the island [Paoletti et al 2015]

The Magnetic Field of the Ischia Island

Conclusions