Alba P. Santo

Volcanological and geochemical evolution of Filicudi (Aeolian Islands, south Tyrrhenian Sea, Italy)

This paper reports on field, petrological, geochemical and isotopic characteristics of volcanic rocks from Filicudi island (Aeolian Arc, southern Tyrrhenian Sea) with particular attention to the recognition of temporal and geochemical variations of magma activity. The Filicudi volcano consists of basaltic, basaltic andesitic, and high-K andesitic lavas, and pyroclastic deposits. It represents the emergent part of a complex structure, parallel to the main regional structural lineaments. Stratigraphic investigations and dating have defined four main cycles of activity interrupted by periods of quiescence. The main stratigraphic sequences reconstructed on Filicudi display irregular variations of rock evolution over time, with recurrent reversals to more basic compositions. Magmas erupted from different vents during the first three cycles of activity display overall similar petrological and geochemical characteristics. Some major and trace elements define slightly scattered correlations with silica. Sr abundances are particularly scattered with a large range of values in basic rocks. Sr isotope ratios range between 0.704270 and 0.704740 and do not exhibit good correlations with geochemical parameters. Fractional crystallization associated with several episodes of mixing processes and crust assimilation are considered to be responsible for the complex evolution of the Filicudi magma. Mafic magmas erupted during the last cycle of activity at La Canna centre show increasing K/Na, Mg/Al, Rb/Sr and decreasing Ba/Nb, Ba/Rb ratios in respect to the older basalts. These characteristics are considered to reflect a derivation from a different mantle source.

External PIXE and mu-PIXE measurements of elemental concentrations in volcanic rocks

Abstract PIXE measurements have been performed on volcanic rocks, using external 3 MeV proton beams of 50 to 200 μm diameter, at the KN3000 Van de Graaff accelerator of the Physics Department of the Florence University. Two or more Si(Li) detectors are used during each run and the elemental composition is computed from the peak areas obtained in the different detectors with an absolute procedure whose reliability has been checked by analyzing several geological standards. In order to obtain solid-liquid partition coefficients of trace elements, the groundmass composition has been determined by directly bombarding standard polished rock sections mounted on a glass support.

Oxygen Isotopic Variations in the Clinopyroxene from the Filicudi Volcanic Rocks (Aeolian Islands, Italy): Implications for Open-System Magma Evolution

Oxygen isotope data are reported for clinopyroxene phenocrysts from volcanic rock samples from Filicudi is- land, Italy, with the aim of investigating mechanisms of magma evolution and mantle source characteristics in a continen- tal arc volcano. Filicudi rocks range from calc-alkaline basalt to high-K andesite and dacite. Mafic rocks have MgO � 6-7 wt%, Mg# � 60, Ni < 50 ppm and Cr < 200 ppm, suggesting they represent evolved melts from more primitive man- tle-derived parents. Variations of Sr-Nd isotope ratios against silica and MgO suggest magma evolution under open- system. Oxygen isotope ratios on clinopyroxene phenocrysts from representative rocks are in the range  18 Ocpx = + 5.37 to + 6.20 ‰ SMOW, corresponding to  18 Omelt = + 5.6 to + 6.4 ‰ and display an overall, but poorly defined, positive corre- lation with 87 Sr/ 86 Sr and MgO and a rough negative correlation with SiO2. Basalts exhibit the highest  18 Ocpx values for the volcanic series studied. Together, major, trace element and isotopic data indicate complex, multistage polybaric evolu- tionary processes for the Filicudi magmas. A process of fractional crystallisation, accompanied by variable degrees of crustal assimilation, best explains the isotopic and petrological data of the Filicudi volcanics. Evolution processes are in- ferred to have occurred in distinct magma reservoirs sited at different depths. Magma contamination affected basalts more extensively than andesitic and dacitic magmas. This was a consequence of the higher temperature and lower viscosity of mafic melts that were able to assimilate higher amounts of crustal wall rocks. Therefore, andesites and dacites preserved stable and radiogenic isotopic compositions more closely than basalts. Combined trace element and isotopic data suggest that primitive magmas at Filicudi were generated in a heterogeneous and metasomatised mantle source, which underwent contamination by slab-derived fluids. When compared with the nearby islands, isotopic variations of Filicudi rocks re- semble more closely those found at Alicudi than at Salina and Vulcano. This suggests that the same kind of evolutionary processes occurred in the western island of Filicudi and Alicudi, whereas at Salina and Vulcano, in the central arc, mag- mas typically evolved by AFC processes, generating derivative melts that display higher Sr-O isotope compositions com- pared to parent basalts. These contrasting styles of magma evolution may be related to different structures of the plumbing systems of volcanic islands that were constructed in different sectors of the arc.

Magmatic evolution processes as recorded in plagioclase phenocrysts of Nea Kameni rocks (Santorini Volcano, Greece)

Abstract Compositional zoning in plagioclase (plg) mineral phase plays a relevant role in petrogenetic studies due to the wide possible compositional variation and high sensitivity to changes of chemical and physical conditions. In this work, major and some trace element abundances by electron microprobe (EMP) and secondary ion mass spectrometry (SIMS) analyses together with textural features by Nomarski differential interference contrast (NDIC) microscopy were obtained from plagioclase crystals of Nea Kameni dacitic rocks (Santorini Volcano, Greece). In the studied rocks, plagioclase crystals display a variety of textures such as fine-scale oscillatory zoning, resorption surfaces, sieved and patchy zones, and a wide variability of Anorthite (An) and trace element (TE) content. Based on some textural and compositional characteristics, an overall subdivision of plagioclase phenocrysts into two main groups was done: (1) clear crystals displaying a core composition in the range An 40-65%, high Sr, Ba, and LREE abundance; (2) crystals, generally sieved-core, showing a very Ca-rich core (An >75%) and low Sr, Ba and LREE content. The trace element composition of the melt that precipitated plagioclase was calculated; changes in melt composition generally correspond to changes in TE abundance in plagioclase. However, some high Ba melt or Sr melt values are not correspondingly present in the crystals or vice versa. The obtained data indicate a complex growth history of the studied plagioclase crystals. The broad range of An and TE abundance suggests that the pig under investigation experienced a broad spectrum of melt composition and/or chemical-physical condition of crystallisation. Group-2 pig cores are too anorthitic, Sr-rich and Ba-poor to have crystallised from an evolved melt, thus indicating disequilibrium with the host rocks; therefore, they were considered of xenocrystic origin. Evolutionary processes such as mixing and crystal-liquid mixing were proposed to have played an important role in determining many of the Nea Kameni plagioclase characteristics.

Proton non-Rutherford backscattering study of oxidation kinetics in Cu and Fe sulphides.

Abstract Non-Rutherford backscattering spectrometry (NBS) with 2.4 MeV protons was performed for depth profiling of oxygen in three species of copper and iron sulphides – pyrite, chalcopyrite and bornite – on both altered and fresh surfaces. The tarnished surfaces were obtained by bathing samples in H2O2 (35% vol.) for 100 and 1000 s. The spectra collected were compared to simulations to extract quantitative data on oxygen depth distributions for the different bathing times. The measurements have shown that the kinetics of oxidation has completely different patterns in the three investigated minerals.

The island of Elba (Tuscany, Italy) at the crossroads of ancient trade routes: an archaeometric investigation of dolia defossa from the archaeological site of San Giovanni

Dolia are large pottery containers used in Roman times for the storage and fermentation of wine. They were produced in specialized pottery workshops (figlinae) and were typically marked with specific epigraphical stamps, which represent a major tool to unravel their provenance and trade. In this work we present the preliminary results of a study of two dolia defossa, recently found at San Giovanni (Portoferraio, island of Elba, Italy) during 2012–2014 archaeological excavations in a Roman farm (late 2nd cent. BC-1st cent. AD), devoted to wine production and probably constituting the antecedent archaeological phase of the adjacent “Villa delle Grotte”. Based on archaeological (epigraphic) evidence, five different production areas have been hypothesized: 1) Elba island, where the dolia have been found; 2) the municipal figlinae in the Pisa territory; 3) the middle catchment of the Tiber river (central Latium) where “urban” figlinae occurred; 4) the figlinae of Minturno (southern Latium), a locality known both for wine production and exportation and for the presence of ancient figlinae; 5) the municipal figlinae in the Volterra territory. Archaeometric analysis of tempering agents intentionally added to the clay for the manufacturing of the dolia, particularly magmatic lithic fragments and clinopyroxene crystals, allowed us to suggest that the watershed of the central Tiber Valley - including different volcanic centres belonging to both Tuscany Magmatic Province (Monti Cimini) and Roman Magmatic Province (Monti Vulsini and Vico volcano) - could have been the most likely sites of production of the dolia found at San Giovanni. Alternatively, the site of Minturno (southern Latium) could be proposed.

Geochemical data on the 2005 lava flow of Barren Island volcano,Andaman Sea

The Barren Island volcano, belonging to the Andaman and Nicobar chain (Andaman Sea, Indian Ocean), is related to the subduction of the Indian Plate beneath the Burmese Plate. Its importance is relevant as the island represents the only active subaerial volcano in the Indian sub-continent and the northernmost active volcano of the Indonesian Volcanic Arc, one of the most tectonically active regions on Earth.

Approaching the study of rock “monuments”. The archaeological site of Pietralba (Upper Tiber Valley, Arezzo, Italy)

A multidisciplinary investigation of some open-air manufactured rocky blocks (both of Proto-historic and Medieval Age) found in the archaeological site of Pietralba (Arezzo, Italy) was performed. The Pietralba blocks display different typologies: a rectangular tub, an L-shaped tub, a throne, and a pyramid. Their study has been approached from the geo-morphologic, mineralogical and chemical standpoint with the threefold purpose of selecting how to better preserve the exposed surfaces from the atmospheric agents, of shedding light on their enigmatic use and, as a consequence, of developing a study-method never applied so far in this field. Even though rock “monuments” are largely widespread and constitute a very intriguing issue, just few studies have been carried out on such artefacts and they have never produced univocal and definitive outcomes regarding their use and age. Samples collected from the tubs were analysed in order to identify the mineralogical and chemical inorganic composition, as well as the possible presence of organic components.

NDIC and EMP Study of Plagioclase Mineral Zoning: An Example from Nea Kameni Lavas

Compositional zoning of plagioclase in magmatic rocks provides an insight into the crystal-lisation history, as this mineral is capable of recording even subtle physical and chemical changes in magmatic liquids. In this paper plagioclase phenocrysts in lavas from the island Nea Kameni of the Santorini volcanic complex (Aegean Sea, Greece) have been studied using Nomarski imaging and detailed electron microprobe scans. The combined use of these techniques permitted the reconstruction of accurate compositional zoning profiles. On the basis of textural and chemical characteristics plagioclase phenocrysts can be divided into two main groups: 1) crystals displaying a core composition in the range Anorthite 40–65%, generally characterised by an unzoned or poorly zoned clear core and by variously zoned mantle and rim; 2) crystals showing a very Ca-rich core (Anorthite >75%), often displaying a fine sieve-textured core and an oscillatory-zoned region mantling the core. These latter plagioclase crystals have been interpreted as xenocrysts. Their textural characteristics confirm this hypothesis and represent additional evidence that, in addition to fractional crystallisation, mixing processes played a role in the evolution of the Nea Kameni magmas.