The mafic-ultramafic complex near Finero (Ivrea-Verbano Zone), I. Chemistry of MORB-like magmas

Geochemical data are presented for the meta-igneous, mafic-ultramafic complex near Finero. This complex is in contact with a phlogopite-bearing mantle peridotite and is subdivided into the Internal Gabbro unit, the Amphibole Peridotite unit, and the External Gabbro unit. The Internal Gabbro and the Amphibole Peridotite units consist of coarse-grained, chemically heterogeneous cumulates, whereas the External Gabbro unit is generally massive, chemically more uniform and approximately representative of the residual melt with MgO contents between 6.6 and 9.1% and Mg numbers between 38 and 58. Both whole-rock and mineral contents of Ni and Cr are significantly higher (at similar Mg numbers) in the Amphibole Peridotite unit than in the Internal Gabbro unit. The most straightforward interpretation of this is that the Amphibole Peridotite unit accumulated after the influx of fresh mafic (or ultramafic) magma into the magma chamber. Major-element chemical trends are continuous from the Amphibole Peridotite unit to the External Gabbro unit and are consistent with closed-system fractionation with no further addition of magma or contamination by wall or roof rock assimilation. In the External Gabbro unit, total FeO and TiO₂ contents are strongly correlated with each other (and with P₂O₅ and Zr) and reach values as high as 19 and 4%, respectively, indicating an advanced degree of crystal fractionation along a tholeftic trend. The External Gabbro samples have generally smooth normalized trace element patterns, which are consistent with being representative of a liquid composition. The residual nature of the External Gabbro magma is also indicated by negative Eu and Sr anomalies, clear evidence for prior feldspar fractionation. REE patterns are otherwise indistinguishable from N-type MORB, but Th and U are significantly more depleted than in MORB. This Th and U depletion is similar to that found in olivine basalts and picrites on Iceland and Hawaii; its origin is not well understood. No evidence is seen for any assimilation of crystal material, in sharp contrast with the situation of the igneous complex in Val Sesia near Balmuccia, where the magma composition is dominated by assimilation of crust. We suggest that the heat provided by at most two injections of magma near Finero was insufficient to induce crystal anatexis, in contrast with the excess heat supplied by multiple magma injections at Balmuccia.     

Coastal processes and environmental hazards: the Buenos Aires (Argentina) and Venetian (Italy) littorals

The Buenos Aires (Argentina) and Venice (Italy) coastlands have experienced significant saltwater contamination of the phreatic aquifer, coastal erosion, hydrodynamic changes and relative sea level rise processes due to natural and man-induced factors. These factors expose coastal areas to morpho-hydro-geological hazards, such as soil desertification, frequency and degree of flooding, littoral erosion, and the silting of river mouths and channels. Man-made interventions and actions, such as beach mining, construction of coastal structures and exploitation of aquifers without an adequate knowledge of the hydrology setting and an adequate management program, worsen these natural hazards. Uncontrolled human activity induces environmental damage to the overall coastal plains. The coastal plains play an important role in the social/economic development of the two regions based on land use, such as agriculture, horticulture, breeding, and tourism, as well as industry. Results of investigations on saltwater contamination, sea level rise and morphological changes recently performed in these two coastal areas are presented here.     

Shallow earthquakes in a viscoelastic shear zone with depth-dependent friction and rheology

Summary. Most crustal earthquakes of the world are observed to occur within a seismogenic layer which extends from the Earth's surface to a depth of a few tens of kilometres at most. A model is proposed in which the shear zone along a transcurrent plate margin is represented as a viscoelastic medium with depth-dependent power-law rheology. A frictional resistance linearly increasing with depth is assumed on a vertical transcurrent fault within the shear zone. Such a model is able to reproduce a continuous transition from the brittle behaviour of the upper crust to the ductile behaviour at depth. Assuming that the shear zone is subjected to a constant strain rate from the opposite motions of the two adjacent plates, it is found that there exists a maximum depth H below which tectonic stress can never reach the frictional threshold: this may be identified as the maximum depth of earthquake nucleation. The value of H is consistent with observations for plausible values of the model parameters. The stress evolution in the shear zone is calculated in the linear approximation of the constitutive equation. A change in rigidity with depth, which is also introduced in the model, may reproduce the high vertical gradient of shear stress, which has been measured across the San Andreas fault, and the fact that most earthquakes are nucleated at some depth in the seismogenic layer. A crack which drops the ambient stress to the dynamic frictional level is then introduced in the model. To this aim, a crack solution is employed without a stress singularity at its edges, which is compatible with a frictional stress threshold criterion for fracture. A constraint on the vertical friction gradient is obtained if such cracks are assumed to be entirely confined within the seismogenic layer.     

Stability of the sponge assemblage of Mediterranean coralligenous concretions along a millennial time span

The Mediterranean coralligenous substratum is a hard bottom of biogenic origin, mainly composed of calcareous algae, growing in dim light conditions. Sponges are among of the most representative taxa of the coralligenous assemblages, with more than 300 recorded species of different habits: massive, erect, boring and insinuating. When sponges die, their siliceous spicules remain trapped in the biogenic concretion, offering the opportunity to describe the coralligenous spongofauna over a very long span of time, virtually dating back to a large part of the Holocene period. The data reported here were obtained from core samples collected from four coralligenous concretions. Each block was collected in a different locality of the Ligurian Sea: Santo Stefano Shoals, Bogliasco, Punta del Faro (Portofino Promontory) and Punta Manara. Radiocarbon age determinations indicate for these conglomerates a maximal age between 1600 and 3100 years. The spicules trapped in the cores show deep dissolution marks in the form of circular holes on their surface or present an enlargement of the axial canal. However, their original shape, generally intact, suggests the absence of mechanical injuries and allows a tentative identification at the species level. The analysis of these old spicules reveals an ancient sponge assemblage composed of 30 recognisable species. This indicates that almost one half of the sponge community today settled on coralligenous substrata has been present in the conglomerates for their entire existence.     

Characterization of particulate matter in the Apulia Region (South of Italy): features and critical episodes

The chemical composition of PM₁₀ and PM_2.5 samples collected during two seasonal monitoring campaigns at residential, urban and industrial Apulia Region- sites was investigated. Ionic fraction, carbonaceous compounds and Polycyclic Aromatic Hydrocarbons were determined for all samples. High correlations among PM data collected in the investigated sites suggested the regional character of particulate matter. It was also confirmed by five days back trajectories analysis. Moreover, no significant seasonal trend in PM mass concentration was observed in the investigated sites. These results, relevant for the area under investigations, were not observed in the North of Italy and Europe and allow to conclude that PM₁₀ and PM_2.5 cannot be considered ‘good’ indicators for the evaluation of local anthropic contributions to air quality. On the contrary, the high levels of Polycyclic Aromatic Hydrocarbons found in Taranto sampling sites suggested that PAHs can be a better indicator for this purpose. This result is also relevant in order to weigh the importance of industrial area and to suggest right policy control to decision makers.     

Pressure-induced phase transition in Mg0.8Fe0.2O ferropericlase

Combined X-ray powder diffraction, Mössbauer, and XANES spectroscopy in situ experiments revealed the transformation of cubic (Mg_0.8Fe_0.2)O ferropericlase to a rhombohedrally distorted phase at 35(1) GPa and room temperature. The Mössbauer spectroscopy results show that the rhombohedral distortion does not involve magnetic ordering. Combined with data from the literature, our results imply that the cubic to rhombodedral transition occurs in (Mg,Fe)O under conditions of non-hydrostatic stress over a wide range of composition (0.2≤x _Fe≤1).     

The use of the slope–area function to analyse process domains in complex badland landscapes

This paper explores the effectiveness of the widely-used functional relationship between drainage area (A in m²) and slope (S in m/m) to identify local process domains and aid interpretation of process interactions in a complex badland landscape. In order to perform this investigation, a series of sub-basins tributary to the Formone River in the Orcia catchment (central Italy) were selected as a suitable study area within which to explore our questions, given these basins' general representativeness of local terrain, the availability of a high resolution digital terrain model and previous extensive geomorphological research. Eroding basins containing both calanchi and landslides are common in the sub-humid badland landscape of central Italy, where field observation identifies a complex pattern of erosive processes associated with a history of uplift, despite which parts of the local landscape appear disconnected. Results reveal that the shape of all S–A curves (plotted using S data binned on log A) is comparable with that described in the literature, although sub-basins containing calanchi generally plot with higher S values than non-calanchi ones, except in the ‘fluvial’ section of the plots. Second, when viewed on total data (non-binned) S–A plots, landslide source area domains and calanchi domains are entirely coincident in all basins, supporting a cause–effect relationship. Additional plotting of the frequency characteristics of the raw data in a new way supports the interpretation that calanchi frequently initiate in landslide scars. In general though, although the S–A plots can contribute to the disentanglement of geomorphological behaviour in some complex erosional landscapes, it became apparent that in this landscape, process domains do not separate out with clarity along the A axis as suggested by theory. Despite this, an alternative, broader-scale morphoevolutive model can be proposed for the development of within-landslide calanchi, driven by changes to basin connectivity to the base channel. © 2018 John Wiley & Sons, Ltd.     

The relationship between websterite and peridotite in the Balmuccia peridotite massif (NW Italy) as revealed by trace element variations in clinopyroxene

 Field, mineralogical and petrological data are presented on a newly found carbonatite occurrence associated with “kamafugite” lava at Cupaello, central Italy. This carbonatite occurrence is part of the Late Pleistocene Umbria-Latium ultra-alkaline district (ULUD) which extends southwards within the Apennines to Mount Vulture, delineating an important magmatic province along the most peripheral belt of the Tyrrhenian extensional tectonic system. This province is distinct, but probably related genetically with the more abundant and common leucite-bearing assemblages of the Roman Comagmatic Region and represents the first reported occurrence of carbonatite assemblages in the Mediterranean Basin. The Cupaello suite indicates that primary or near-primary mantle silicate melts of “kamafugitic” composition are transitional with Ca-carbonatite liquid and provides direct evidence of immiscibility of carbonatite from “kamafugite” magma. It is inferred that a primary mantle origin of Ca-carbonatites is conditional upon a potential silicate magma that may be coupled with the carbonatite, but may not have reached the surface. The data indicate a strong genetic link between ULUD Ca-carbonatites and some African analogues, supporting the view that their genesis depends on similar source and associated tectonic conditions. Received: 17 January 1995 / Accepted: 14 June 1995