The Integration of Magnetic Data in the Neapolitan Volcanic District
Total Page：16
File Type：pdf, Size：1020Kb
The integration of magnetic data in the Neapolitan volcanic district V. Paoletti M. Secomandi M. Fedi G. Florio A. Rapolla Dipartimento di Scienze della Terra, UniversitaÁ di Napoli Federico II, Largo S. Marcellino 10, 80138 Naples, Italy ABSTRACT volcanic structures. In those cases magnetic data set should enable the characterization of data can locate buried structures such as line- the main buried volcanic structures such as In this paper we present an example of aments, faults, and volcanic and intrusive vents and calderas, providing a better under- the integration of airborne and marine structures. As noted by Finn (1999), compos- standing of the connection between tectonics magnetic data sets measured in the Nea- ite data sets allow a more complete view of and volcanism in the Neapolitan volcanic politan area, southern Italy. The integra- patterns and trends that individual data sets district. tion involved detailed data measured re- may not provide. The author gives an over- cently in the Phlegrean Fields, in the view of the procedures for merging magnetic THE NEAPOLITAN VOLCANIC Somma-Vesuvis area and in the Bay of Na- surveys into a regional digital compilation and DISTRICT: GEOLOGICAL ples, that produced a high-resolution mag- shows, through the illustration of the case of FRAMEWORK AND GEOPHYSICAL netic map of the whole active volcanic dis- Washington State, the usefulness of these pro- STUDIES trict. The data sets partially overlapped cedures for providing synoptic views of re- and characterized varying ¯ight height and gional features. Chiappini et al. (1999, 2002) The Neapolitan volcanic district is located line spacing. Integration was therefore per- merged magnetic data acquired in the Antarc- on the Tyrrhenian margin of the Campanian formed through several procedures includ- tic region over the areas of the Ross Sea and Plain (Fig. 1A). This plain was formed during ing continuation between general surfaces. the Transantarctic Mountains in the frame- the Plio-Pleistocene as the result of the com- The integration produced a new, detailed, work of the Antarctic Digital Magnetic Anom- plex geodynamic events connected with the draped magnetic data set of the Neapolitan aly Project. They produced an integrated grid opening of the Tyrrhenian Sea and the anti- region characterized by a terrain clearance that resulted in a fundamental tool for regional clockwise rotation of the Italian Peninsula of 200 m, giving a meaningful overall view interpretation of the tectonic and geologic (Scandone et al., 1991). A tensile stress re- of the volcanic area. The study of the main characteristics of this area of Antarctica. Da- magnetic features of the area was carried gime thus affected the Tyrrhenian margin, maske (1999) gives another example of the out by computing the horizontal gradient of causing N-S and NNW-SSE normal faults, and compilation of an integrated aeromagnetic the pole-reduced draped data. The analysis then NW-SE and NE-SW normal faults and map from data sets ¯own over areas with very of the obtained map showed the presence of W-E strike-slip faults (e.g., Doglioni, 1991). different topographies in the Antarctic region lineaments of preferential magma upwell- Along the Campanian border, the Quaternary (Central Queen Maud Land). Golynsky et al. ing and buried volcanic structures and al- basin of the Bay of Naples was produced by (2002) merged airborne and marine magnetic lowed the delineation of a geovolcanological NE-SW±trending normal faults. Intense vol- observations in East Antarctica and adjacent and structural framework of the whole Ne- canism has characterized this area since the seas of the Indian Ocean and compiled an in- apolitan volcanic district. late Miocene. This volcanic activity seems to tegrated magnetic anomaly map that provided be in close spatial relation with the NE-SW Keywords: aeromagnetic survey, marine new insight on the tectonic features of the East faults (e.g., Bruno et al., 2003). The present magnetic survey, data sets integration, Antarctic. Campanian volcanism started 1±2 Ma (Capal- magnetic data analysis. In this paper we present and analyze a new, di et al., 1985). Currently the active areas are detailed magnetic map of the whole Neapoli- the island of Ischia (last eruption in 1302), the INTRODUCTION tan active volcanic district, southern Italy (Fig. Phlegrean Fields (last eruption in 1538), and 1). This was obtained by merging recently ac- the Somma-Vesuvius (last eruption in 1944). Magnetic anomaly maps provide insights quired airborne, land, and marine magnetic The products of the Campanian volcanism be- for a better understanding of the geologic, tec- measurements. long to two cycles: an older cycle (Miocene- tonic, and geothermal characteristics of an In this study we aim to gain insights into Pleistocene), evidences of which were only area. This is particularly true for volcanic the characteristics of the Neapolitan volcanic found in the Parete 2 Well (see Fig. 2), and a zones, where recent volcanic activity and vol- area from an overall view of its magnetic ®eld. second cycle related to the previously men- canoclastic deposits often cover important The analysis of the newly merged magnetic tioned Plio-Pleistocene extensional tectonics. Geosphere; October 2005; v. 1; no. 2; p. 85±96; doi: 10.1130/GES00003.1; 7 ®gures. For permission to copy, contact [email protected] q 2005 Geological Society of America 85 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/1/2/85/3332344/i1553-040X-1-2-85.pdf by guest on 30 September 2021 PAOLETTI et al. Figure 1. A: Location of study area. B: Neapolitan volcanic district, southern Italy. The so-called Roman Comagmatic Province, to depths of a few thousand meters below sea A study of the distribution of the magneti- which includes the Vesuvian and the Phle- level (mbsl) (Carrara et al., 1973; Bruno et al., zations in the Vesuvian area by detailed air- grean volcanic districts, belongs to this second 1998). The Trecase 1 well, drilled inside the borne data is described in Paoletti et al. cycle (Fig. 1B). Vesuvius volcanic area, detected the sedimen- (2004). A boundary analysis of the data clear- The main characteristics of the Bouguer tary basement at ;1700 mbsl (Bernasconi et ly showed the southern rim of the caldera of anomaly map of the Campanian Plain (Florio al., 1981). Rock magnetism measurements Mount Somma. In the area surrounding the et al., 1999) are intense maxima correspond- from Somma-Vesuvius and the Trecase 1 well Somma-Vesuvius edi®ce, the authors detected ing to carbonatic reliefs bordering the plain (Cassano and La Torre, 1987) showed mag- the magnetic anomaly pattern of the lateral and a wide minimum area broken up by Ve- netization values ranging from 6.8 A/m (lavas boundaries of some buried small volcanic suvius and Parete highs. The horizontal gra- from Vesuvius) to 0.5 A/m (tuffs), and an in- structures and showed some magnetic trends dient of these data shows some maxima tense remanent magnetization, with a Koe- possibly consistent with trends detected by aligned in three E-W lineaments, two of which nigsberger ratio of ;8.6. other geophysical studies (Fedi et al., 2005b; border the Acerra depression to the north and The presence of a shallow magma chamber Bruno et al., 1998). the south, and the third is South of Vesuvius. (between 4 and 10 km bsl) was assumed from The Acerra depression is closed by two other a study of ¯uid inclusions of ejected nodules The Bay of Naples NE-SW alignments of maxima that seem to (Belkin and De Vivo, 1993). However, seis- cut the Vesuvius and Phlegrean Fields volca- mic studies (Zollo et al., 1996; De Natale et In the Bay of Naples, a morphologic struc- nic area (Fig. 2). al., 1998) seem to exclude the presence of a ture formed by a continental shelf, a continen- magmatic melt above 4±5 km bsl in the Ve- tal slope, and a basin can be identi®ed (Milia, The Vesuvian Area suvian area. Gravity studies (Cella et al., 1999; Aiello et al., 2001). In the northern area 2003) detected a deeper intracrustal low den- of the bay, the Phlegrean Fields offshore, the Somma-Vesuvius is a stratovolcano char- sity source that was interpreted as being the shelf is irregular and characterized by the acterized by products of both explosive and main magmatic reservoir of the volcanic ac- presence of monogenic volcanoes, small cal- effusive eruptions. The complex is formed by tivity of the whole Neapolitan region. The deras, tuff cones, and lava extrusion (Milia, an older volcanic center (Mount Somma), presence of such a deep magmatic source was 1999). The bay is dominated by two subma- which underwent a calderic collapse, and a also proposed by Rolandi et al. (2003) on the rine canyons: the Magnaghi and the Dohrn more recent one, Mount Vesuvius. It is located basis of geochemical, stratigraphic, and struc- Canyons (Fig. 1B). The Magnaghi Canyon is in an area where a carbonate basement extends tural studies. ;15 km long, has a trilobate head, and has 86 Geosphere, October 2005 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/1/2/85/3332344/i1553-040X-1-2-85.pdf by guest on 30 September 2021 INTEGRATION OF MAGNETIC DATA Figure 2. Geological sketch map of the Campanian Plain (Bonardi et al., 1988). Solid black lines indicate the main faults singled out by seismic studies (Bruno et al., 1998, 2003; Milia and Torrente, 1999), barbs are on the downthrown side. Dashed lines show fault location extrapolated from seismic data. Blue lines show the main gravimetric and magnetic lineaments identi®ed by Florio et al., 1999. Yellow lines indicate the faults in Ischia Island (quoted in Nunziata and Rapolla, 1987).