Giordano, Francesco

We highlight the fractal behaviour of marine measurement networks when determining the Earth's total magnetic field and the spatial trend of the field itself. This approach is a convenient alternative method of assessing the coverage of an area by a set of measurements whenever the environmental situations do not permit a regular distribution of the measurement points. The Earth's magnetic field is sampled in marine areas when the measuring apparatus is moving, even at low speeds, whilst attempts are made to respect the spatial planning which has been pre-determined on the basis of the resolution sought after. However, the real distribution of the measurements presents numerous disturbances which are mainly due to environmental factors. In the case of distributions containing vast areas with no measurement points it is no longer possible to apply Shannon's theorem in 1-D and 2-D. In our paper we apply the fractal theory to certain 1-D and 2-D measurement distributions order to obtain a coverage estimate of the area and the capacity of reconstructing the field. We also examine the trend of the power spectra S of numerous magnetic profiles noting that almost all of them illustrate the dependency with the frequency f in the form S » f-b which is characteristic (necessary condition) of self-similar or self affine fractals.

The aim of this work was to test several geophysical methods for the identification and study of submerged prehistorical coastlines and archaeological sites. This research program was carried out in collaboration with the <> in the Gulf of Pozzuoli and dealt in particular with the bathymetric strips extending from - 5 m to - 50 m Within these strips we identified the coastline dating from the Rornan period. former beach boundaries associated with the vertical movements of the earth's surface caused by seismic-volcanic activity, and the variations in sea level following the climactic changes throughout the last 15000 years. The UNIBOOM system was used for this part of the programme, perinittiilg the identification of several coastlines and submerged beaches lying at different levels. The use of a modern Side Scan Sonar - for the morphological invesdgation of the sea bed - in a zone which had been the object of numerous archaeological surveys in the past, permitted previously unknown structures near the Lacuus Baianus to be identified. Other features worth pointing out include the operating speed of the system (15000 m'lfirst minute approx) and its observation capacity in cloudy waters compared to visible radiation, as well as its ability to penetrate thin layers of mud which generally impede direct underwater observation.

On the Timpa delle Murge hill, located in the Lucania region close to Mt. Pollino (southern Apennines, Italy), Upper Jurassic – Lower Cretaceous metaigneous and metasedimentary rocks crop out, which are believed to represent fragments of Tethys oceanic crust obducted on continental crust during the Apennine orogenic phases. This ophiolitic sequenceincludes, from base upward: gabbros, pillow lavas, pillow breccias, and a pelagic sedimentary pile made up of radiolarian cherts, red and green shales, quartz-arenites and black shales. A few kilometers apart, the Episcopia - S. Severino Mélange includes serpentinized peridotites, likely representing fragments of an upper mantle portion. The radiolarian cherts were dated at 161 Ma based on their microfossil content, and this age is believed to be the end of oceanic crust generation in that area. Both serpentinites and the whole oceanic crust sequence were affected by subduction-related HP/LT metamorphism, marking a burying and exhumation episode occurred during the Late Oligocene-Early Miocene Apennine orogenesis. Only few literature data are available on the petrology of these rocks, thus a modern petrologic investigation is needed in order to better characterize this ophiolitic sequence, and shed light on the nature and history of this part of the Tethyan oceanic crust. In this contribution, major oxide and trace element geochemistry data will be illustrated forrepresentative shales and wackes from the Timpa delle Murge and Crete Nere formations. Geochemical modeling using compositional data of these metasedimentary rocks will be presented in order to find a possible link between the oceanic crust which was subducted during the Tethys closure, and subduction-related Tertiary-Quaternary volcanism of southern Italy.

This paper presents the results of an investigation carried out on young volcanic rocks from the Gedemsa and Fanta 'Ale complexes, located in the Main Ethiopian Rift, the site of an intense magmatism since Eocene–Oligocene. The earlier NW–SE direction of extension of the Rift, which generated NE–SW trending faults, rotated around E–W in Quaternary times, and produced the still active N to N–NE Wonji Fault System. The Gedemsa volcano is located in the central part of the Ethiopian Rift, about 100 km SE of Addis Ababa. It is characterized by a wide central caldera, about 8 km in diameter. The general stratigraphic sequence in the area includes, from base upwards, rift-floor ignimbrites, pantelleritic and subordinate trachytic pyroclastic deposits and lava flows and domes, and widespread basaltic deposits. The Fanta 'Ale volcanic complex is located in the northern part of the Main Ethiopian Rift, where the Afar depression begins. It is characterized by a summit caldera of which the diameter is about 4 km. This volcano erupted trachytic and rhyolitic lavas, whereas the most diffuse unit is an ignimbrite related to the caldera collapse. Explosive activity has occurred inside and outside the caldera, forming tuff cones and thick pumice-fallout deposits. The onlymafic unit is represented by a basaltic eruption that occurred in 1870 AD. Historical eruptions and intense fumarolic activity are evidence for the persistence activity of the Fanta 'Ale in this part of the Main Ethiopian Rift. New geochemical and Sr–Nd–Pb isotope data on representative samples from Gedemsa and Fanta 'Ale volcanoes are presented and discussed in order to shed light on the genesis of mafic and felsic magmas, the genetic link between them, and their possible interaction with the local crust. Volcanic rocks showa typicalmafic–felsic bi-modal distribution with fewintermediate terms (Daly Gap), as observed at regional scale along theMain Ethiopian Rift as well as on the plateau. Geochemical data and modeling suggest that magmas evolved mainly through fractional crystallization processes, accounting for the entire mafic–felsic compositional variation. However, Sr–Nd–Pb isotope data reveal also open-system evolution processes. The most differentiated, Sr-poor rhyolites suffered important low temperature contamination by shallow fluids of hydrothermal and/or meteoric origin. This affected mostly the Sr isotopic composition of whole-rocks, and much less that of separated feldspars that provide more reliable 87Sr/86Sr values.Mafic rocks, as well as the least contaminated felsic rocks, provide evidence for two components involved in the genesis and evolution of mafic magmas: a mantle component, carrying the isotopic composition of the Afar plume, and a crustal component, likely Pan-African sialic lower crust, that might have been added in smallamounts, about 2%, tomaficmagmas. The origin of the primarymagmas is inferred to have occurred by 7% partial melting of a mixed source region including both depleted and enriched mantle components

A continuous-coring borehole recently drilled at Camaldoli dellaTorre on the southern slopes of Somma^Vesuvius provides constraints on the volcanic and magmatic history of the Vesuvian volcanic area since c. 126 ka BP. The cored sequence includes volcanic units, defined on stratigraphical, sedimentological, petrological and geochemical grounds, emitted from both local and distal vents. Some of these units are of known age, such as one Phlegraean pre-Campanian Ignimbrite, Campanian Ignimbrite (39 ka), Neapolitan Yellow Tuff (14 9ka) and Vesuvian Plinian deposits, which helps to constrain the relative age of the other units.The main rock types encountered are shoshonite, phonotephrite, latite, trachyte and phonolite. The sequence includes, from the base upwards: a thick succession of pyroclastic units emplaced between 126 and 39 ka, most of them attributed to eruptions that occurred in the Phlegraean area; the Campanian Ignimbrite; the products of a local tuff cone formed between 39 ka and the deposition of the products of the earliest activity of the Mt. Somma volcano; the products of the Somma^Vesuvius volcano, which include from the base upwards a thick sequence of lavas, pyroclastic rocks and the products of a local spattercone dated between 3 7ka and AD 79.The data obtained from the study of the borehole show that, before the Campanian Ignimbrite eruption, low-energy explosive volcanism took place in the Vesuvian area, whereas mostly high-energy explosive eruptions characterized the Campi Flegrei activity. In the Vesuvian area, Campanian Ignimbrite deposition was followed by the eruption of a local tuff cone and a long repose time, which predated the formation of the Mt. Somma edifice. Since 18 3 ka (Pomici di Base eruption) the activity of Somma^Vesuvius became mostly explosive with rare lava effusions.The shallowest cored deposits belong to the Camaldoli dellaTorre cone, formed between the Pomici di Avellino and Pomici di Pompei eruptions (3 7 ka^AD 79). Newgeochemical and Sr^Nd^Pb^ B-isotopic data on samples from the drilled core, together with those available from the literature, allow us to further distinguish the volcanic rocks as a function of both their provenance (i.e. Phlegraean or Vesuvian areas) and age, and to identify different magmatic processes acting through time in the Vesuvian mantle source(s) and during magma ascent towards the surface. Isotopically distinct magmas, rising from a mantle source variably contaminated by slab- derived components, stagnated at mid-crustal depths (8^10 km below sea level) where magmas differentiated and were probably contaminated. Contamination occurred either with Hercynian continental crust, mostly during the oldest stages of Vesuvian activity (from 39 to 16 ka), or with Mesozoic limestone, mostly during recent Vesuvian activity. Energy constrained assimilation and fractional crystallization (EC-AFC) modelling results show that contamina- tion with Hercynian crust probably occurred during differentiation from shoshonite to latite. Contamination with limestone, which is not well constrained with the available data, might have occurred only during the transition from shoshonite to tephrite. From the ‘deep’ reservoir, magmas rose towards a series of shallow reservoirs, in which they differentiated further, mixed, and fed volcanic activity.