Claudio Mazzoli

Phosphorus in cold-water corals as a proxy for seawater nutrient chemistry

Phosphorus is a key macronutrient being strongly enriched in the deep ocean as a result of continuous export and remineralization of biomass from primary production. We show that phosphorus incorporated within the skeletons of the cosmopolitan cold-water coral Desmophyllum dianthus is directly proportional to the ambient seawater phosphorus concentration and thus may serve as a paleo-oceanographic proxy for variations in ocean productivity as well as changes in the residence times and sources of deep-water masses. The application of this tool to fossil specimens from the Mediterranean reveals phosphorus-enriched bottom waters at the end of the Younger Dryas period.

Multiple titanium substitutions in biotites from high-grade metapelitic xenoliths (Euganean Hills, Italy): Complete crystal chemistry and appraisal of petrologic control

Abstract Biotites from metapelitic xenoliths included within trachytes from the Euganean Hills (Italy) were analyzed by single-crystal X-ray diffraction (XRD), electron microprobe (EMP), scanning electron microscope (SEM), secondary ion mass spectrometry (SIMS), and Mössbauer spectroscopy. These biotites are Ti-rich and occur in gneissic xenoliths that underwent regional high-T/low-P metamorphism, at about 750 °C, followed by pyrometamorphism during incorporation in the melt at temperatures close to 950 °C. Biotites are zoned, with TiO2 content ranging from 6.79 (cores) to 8.14 wt% (rims). SIMS measurements show that the H2O content is in the range 2.88-4.08 wt%. The simultaneous occurrence of high-Ti and high-H2O contents, and the main cation substitutions based on EMP analyses suggest that the role of Ti-oxy in these biotites is less important than Ti-vacancy and Ti-Tschermak substitutions. Single-crystal XRD confirms that the Ti-oxy exchange was indeed effective but not the dominant substitution mechanism. Based on our data and those taken from literature on petrologically well-constrained systems, we propose that there is a petrologic control on the type of Ti-substitution mechanisms. We consider two types of petrologic groupings for biotites: (1) group A consisting of biotites from H2O-free or H2O-poor petrologic environments (e.g., volcanic rocks, ultrabasic xenoliths, and crustal xenoliths in which biotite underwent incongruent melting): Ti substitution in these biotites occurs via Ti-oxy predominantly, or more specifically Fe3+-Ti-oxy; and (2) group B consisting of biotites from H2O-rich petrologic environments (e.g., metamorphic rocks and crustal granitoids): Ti-vacancy, or more specifically Fe3+-Ti-vacancy, is the dominant mechanism in them. It is concluded that during high-grade metamorphism the dominating type of Ti substitution in biotite is controlled by H2O activity.

μ-PIXE analysis of monazite for total U–Th–Pb age determination

Abstract U–Th–Pb chemical age determinations of monazite have been successfully determined using μ-PIXE at the Legnaro scanning proton microprobe facility, as well as the concentration of rare earth and other trace elements. Experimental details and the analytical procedure are described, and the results obtained are compared with data obtained using EMPA and SHRIMP II on the same analysed monazite grains, indicating that the μ-PIXE technique is an extremely powerful tool for monazite geochronology, both for the small error in the age determination, and in terms of detection limit, giving the possibility to date much younger monazite crystals than with EMPA. In addition, the high spatial resolution and the non-destructive character of this technique, potentially allows for the analysis of small monazite crystals along inclusion trails within porphyroblasts and/or present in the surrounding matrix, and to relate their age to that of the deformation in metamorphic rocks.

X-ray powder diffraction clustering and quantitative phase analysis on historic mortars

This paper describes the application of cluster analysis to X-ray powder diffraction patterns (XRPD) to define homogeneous groups of mortar-based materials according to their mineralogical composition. For this purpose, the diffraction patterns of 110 samples of mortars from the Temple of Venus (Pompeii, southern Italy) were used to test the method. Rietveld refinement, for quantitative mineralogical phase analysis, was performed on the most representative sample of each cluster. The mineralogical grouping yielded by cluster analysis of XRPD data turned out to be consistent with the petrographic groups.

Trachyte from the Roman aqueducts of Padua and Este (north-east Italy): a provenance study based on petrography, chemistry and magnetic susceptibility

This study presents the results of archaeometric analysis of the stones used to build the Roman aqueduct in Padua (northeast Italy), in order to identify the petrography and the quarry/ies of provenance from which the stones were exploited. The combined approach, involving petrographic, geochemical and magnetic susceptibility data, shows that the stones used for building the Roman aqueduct were of volcanic origin, with a trachyte composition, were quarried from two different localities in the Euganean Hills (Mt. Merlo and Mt. Oliveto) and that construction of the aqueducts, particularly of its various segments, both in the present-day city centre of Padua and in the Euganean Hills area, was centralised and managed by a single authority.

Experimental study of the seismic properties of the Eastern Alps (Italy) along the Aurina–Tures–Badia Valleys transect

Abstract In order to better constrain the interpretation and the nature of the seismic reflectors, experimental measurements at high confining pressure (up to 300 MPa) and room temperature of the compressional wave velocity (Vp) on 10 samples representative of the most common lithologies along the Aurina (Ahrntal), Tures (Tauferer Tal), and Badia (Abtei Tal) Valleys profile (Eastern Alps, Italy) have been performed. For each sample, the speed of ultrasonic waves was measured in three mutually perpendicular directions, parallel and normal to the rock foliation and lineation. The main results are: (a) Good agreement between the calculated vs. measured modal compositions of the considered rocks, indicating that they were presumably equilibrated at the estimated P – T conditions; therefore, the seismic properties are representative of the crustal level indicated by the thermobarometry. (b) Measured and calculated average Vp are in good agreement, and are typical of mid-crustal level (6.0–6.5 km/s). Only the amphibolites show Vp typical of the lower crust (7.2 km/s). (c) The seismic anisotropy of metapelites is very high (12–27%), both with orthorhombic and transverse isotropy symmetry; amphibolites are transversely isotropic with an anisotropy of 8%; orthogneisses and granitoids are isotropic or weakly anisotropic. (d) The contacts between amphibolites and all other rock types may generate good reflections, provided they are not steeply inclined. Although the metamorphic foliation remains steeply inclined, discordant buried sub-horizontal igneous contacts may be detected.

Comparison between major and trace element concentrations in garnet performed by EPMA and micro-PIXE techniques

Abstract This paper deals with the application of the electron and proton microprobe (EPMA and micro-PIXE) in order to determine major and trace elements in metamorphic garnet samples. The selected garnet samples come from a metapelitic rock belonging to the tectonic unit of Monte Rosa Nappe (Italy). Quantitative spot analysis profiles and compositional X-ray maps of both major and trace (yttrium) elements are reported. Major elements show a smoothed and continuous compositional zoning characterized by concentric variations from core to rim. Yttrium displays a strong enrichment in the core and a flat pattern at the rim. No correlation is shown between major and yttrium distribution. Only a rough correlation may be supposed with manganese. A good agreement was found between EPMA and micro-PIXE yttrium data, for values higher than 80–100 ppm. For lower values micro-PIXE technique is strongly recommended. The combination of X-ray two-dimensional maps and quantitative microanalyses allowed to evaluate the distribution of major and trace elements in a petrologically significative rock-forming mineral, to define the type of the chemical zoning and finally to attest difference in diffusivity between major and trace elements. Because of the slow diffusivity of yttrium, its quantitative determination in garnets is fundamental to reconstruct the temperature path suffered by polymetamorphic garnet-bearing rocks.

Paleochannel and beach-bar palimpsest topography as initial substrate for coralligenous buildups offshore Venice, Italy

We provide a model for the genesis of Holocene coralligenous buildups occurring in the northwestern Adriatic Sea offshore Venice at 17–24 m depth. High-resolution geophysical surveys and underwater SCUBA diving reconnaissance revealed meandering shaped morphologies underneath bio-concretionned rocky buildups. These morphologies are inferred to have been inherited from Pleistocene fluvial systems reactivated as tidal channels during the post- Last Glacial Maximum transgression, when the study area was a lagoon protected by a sandy barrier. The lithification of the sandy fossil channel-levee systems is estimated to have occurred at ca. 7 cal. ka BP, likely due to the interaction between marine and less saline fluids related to onshore freshwater discharge at sea through a sealed water-table. The carbonate-cemented sandy layers served as nucleus for subsequent coralligenous buildups growth.

Trachyte weathering in the urban built environment related to air quality

Decay of trachyte used as building stone in urban environment was investigated through the analysis of crusts and patinas found on trachyte of the Euganean Hills in the Renaissance city walls of Padua, northeastern Italy. Mineralogical and microstructural characteristics of the alteration products, as well as major- and trace-element chemical composition, were determined by optical microscopy, SEM–EDS and X-ray mapping, XRPD, and LA-ICPMS. The results are discussed referring to environmental parameters, in particular concerning air quality and anthropic pollution sources. The influence of composition of the stone and other neighboring materials on specific weathering processes is also debated. The formation of crusts and patinas turns out to be mainly due to exogenous processes. Enrichment in heavy metals and carbonaceous matter derives from the deposition of particulate emitted during fuel combustion by road vehicles, domestic heating and, secondarily, industrial activities. The particulate is typically cemented by calcite, mainly mobilized after dissolution from nearby mortar joints, or iron, released by leaching from iron-bearing minerals, reprecipitated according to pH fluctuations. Gypsum layers were rarely observed. Generally, composition of the weathering crusts and patinas of Euganean trachyte proves to be an informative marker for the relevant environmental conditions and their evolution.

Textural and Mineralogical Analysis of Volcanic Rocks by µ -XRF Mapping

In this study, µ-XRF was applied as a novel surface technique for quick acquisition of elemental X-ray maps of rocks, image analysis of which provides quantitative information on texture and rock-forming minerals. Bench-top µ-XRF is cost-effective, fast, and non-destructive, can be applied to both large (up to a few tens of cm) and fragile samples, and yields major and trace element analysis with good sensitivity. Here, X-ray mapping was performed with a resolution of 103.5 µm and spot size of 30 µm over sample areas of about 5×4 cm of Euganean trachyte, a volcanic porphyritic rock from the Euganean Hills (NE Italy) traditionally used in cultural heritage. The relative abundance of phenocrysts and groundmass, as well as the size and shape of the various mineral phases, were obtained from image analysis of the elemental maps. The quantified petrographic features allowed identification of various extraction sites, revealing an objective method for archaeometric provenance studies exploiting µ-XRF imaging.