The role of structural inheritance in continental break-up and exhumation of Alpine Tethyan mantle(Canavese Zone,Western Alps)

The Canavese Zone(CZ)in the Western Alps represents the remnant of the distal passive margin of the Adria microplate,which was stretched and thinned during the Jurassic opening of the Alpine Tethys.Through detailed geological mapping,stratigraphic and structural analyses,we document that the continental break-up of Pangea and tectonic dismemberment of the Adria distal margin,up to mantle rocks exhumation and oceanization,did not simply result from the syn-rift Jurassic extension but was strongly favored by older structu ral inheritances(the Proto-Canavese Shear Zone),which controlled earlier lithospheric weakness.Our findings allowed to redefine in detail(i)the tectono-stratigraphic setting of the Variscan metamorphic basement and the Late Carbonife rous to Early Cretaceous CZ succession,(ii)the role played by inherited Late Carboniferous to Early Triassic structures and(iii)the significance of the CZ in the geodynamic evolution of the Alpine Tethys.The large amount of extensional displacement and crustal thinning occurred during different pulses of Late Carbonife rous-Early Triassic strike-slip tectonics is wellconsistent with the role played by long-lived regional-scale wrench faults(e.g.,the East-Variscan Shear Zone),suggesting a re-discussion of models of mantle exhumation driven by low-angle detachment faults as unique efficient mechanism in stretching and thinning continental crust.     

Perspectives of a visible instrument on the VLTI

In this paper we present the most promising science cases for a new generation visible instrument on the VLTI and the conceptual idea for the instrumental configuration. We also present a statistical study of the potential targets that may be accessible for the different classes of objects and for the required spectral resolutions.     

Distribution and functional response of sublittoral soft bottom assemblages to sedimentary constraints

Mollusc and annelid polychaete macrofaunal assemblages were studied in a sublittoral sandy bottom of 1.8 km² extension, along the western Calabrian coast (low Tyrrhenian Sea). The strict coupling of the local sedimentary dynamics with the benthic assemblages was investigated on a small spatial scale (patchiness), at the mesoscale depth-related gradients and at the level of functional/trophic habits. Non-metrical correlations (ρ), index of dispersion (Di) and dispersion weighted abundances, averaged per depth level highlighted the response of some characteristic species to the patchiness of sediments as well as to the predominant environmental gradients. Species habits and trophic guilds, that were assessed in terms of biomass (wet weight) and secondary “pseudo-production” (abundance × biomass), clarified the differential functional response of the assemblages at different depth levels. Polychaetes reached 84.86% abundance and showed a highly clumped distribution of sessile species (Ditrupa arietina, Aponuphis brementi, Chone acustica, Spiophanes kroyeri); to a lower extent the motile species (Hyalinoecia tubicola, Marphisa bellii, Phylo foetida) were present. Molluscs reached 15.14% abundance and only some bivalve taxa showed significant aggregated distributions (Corbula gibba, Tellina donacina, Tellina distorta), whereas gastropod species were more evenly distributed. Total biomasses were almost equal between the two taxonomic groups (46.41 g WW on average). Biotic–environmental rank matching highlighted depth, very fine sands (60–200 μm), sorting grade, skewness index and pH as being the most influential factors in the distributions of some species, followed secondarily by coarse silts (40–60 μm) and coarser sands (200–2000 μm). Within the local context of water/sediment oligotrophy, the adaptive strategies of macrofauna to a highly seasonal supply of autochthonous phytoplanktonic seston associated with imported macro debris and terrigenous components were emphasized. Evidence of such a differential nutrient supply was the clear functional differentiation of the shallower levels from the deeper ones, and the presence of an intermediate zone which was selectively dominated, in terms of abundance and biomass, by microphagous filter/suspension feeders. Moreover, the shortage of burrowing deposit feeders as well as the prevalence of motile macrophagous omnivores beyond 20 m depth may be considered as ecologically correlated aspects.     

Revised seismotectonic model of NE Italy and W Slovenia based on focal mechanism inversion

The study is focusing on the stress and strain inversions from focal mechanisms in a revised seismotectonic zonation of northeastern Italy and western Slovenia. The recent increase of monitoring capability of the local seismic network, the updated geological-structural model of the area, and the novelties emerged from studies on the spatial organization of the seismicity allowed a redefinition of the seismotectonic zones. The stress and strain tensors inversion is inferred from 203 focal mechanisms, corresponding to earthquakes occurred between 1984 and 2016 with coda-duration magnitude range from 2.0 to 5.6. The inverted stress domains reveal an articulated picture of the interaction of the Adria microplate with the Eurasian plate. A dominant strike-slip stress field characterizes the eastern part of the area, while the seismotectonic zones of the central part are undergoing to thrusting regime. The stress pattern inferred in the western part of the study area outlines a complex picture with prevailing strike-slip regime and dominant compression only in a seismotectonic zone. The comparison of stress and strain tensor orientations evidences a relative uniformity of the crustal strength in the eastern and northwestern zones of the study area. The central and western zones appear to be characterized by planes of mechanical weakness not favorably oriented for failure with respect to the stress tensor.     

Numerical insights on the seismic behavior of a non-isolated historical masonry tower

In this paper, numerical insights on the seismic behavior of a non-isolated historical masonry tower are presented and discussed. The tower under study is the main tower of the fortress of San Felice sul Panaro, a town located near the city of Modena (Italy). Such a tower is surrounded by adjacent structural elements and, therefore, is not isolated. This historical monument has been hit by the devastating seismic sequence occurred in May 2012 in the Northern part of the Emilia region (the so-called “Emilia earthquake”), showing a huge and widespread damage. Here, in order to understand the behavior of the structure, its interaction with the adjacent buildings and the reasons of the occurred damage, advanced numerical analyses (both nonlinear static and dynamic) are performed on a 3D finite element model with different levels of constraint supplied by the adjacent structural elements and a detailed comparison between the simulated damage and the actual one is carried out. The results of the conducted numerical campaign show a good agreement with the actual crack pattern, particularly for the model of the tower that considers the adjacent structural elements.     

Rock slope failure in a recently deglaciated permafrost rock wall at Piz Kesch (Eastern Swiss Alps), February 2014

In February 2014, a rock pillar with a volume of around 150 000  m³ collapsed at Piz Kesch in the Eastern Swiss Alps. A reconstruction of the conditions prior to the event and of the event itself is presented on the basis of different sources of data. The methods applied include photogrammetry, terrestrial laser scanning, structural geological analysis, examination of meteorological data, carbon‐14 (¹⁴C) dating of organic material in permafrost ice from a tension crack and numerical modelling of likely modes of failure. Despite a complete lack of in situ measurements in the rock wall prior to the event and of direct observations during the event, the available data allow the determination of the approximate timing of the event as well as the structural predisposition, the probable mode of failure and the timescale of several millennia involved in the triggering of the failure of the rock pillar. The interdisciplinary analysis of this event contributes towards understanding the complex interaction of processes involved in large rock slope failures currently occurring in warming mountain permafrost regions. Copyright © 2016 John Wiley & Sons, Ltd.     

Late quaternary speleogenesis and landscape evolution in the northern Apennine evaporite areas

Gypsum beds host the majority of the caves in the north‐eastern flank of the Apennines, in the Emilia Romagna region (Italy). More than six hundred of these caves have been surveyed, including the longest known epigenic gypsum cave systems in the world (Spipola‐Acquafredda, ~11 km). Although this area has been intensively studied from a geological point of view, the age of the caves has never been investigated in detail. The rapid dissolution of gypsum and uplift history of the area have led to the long‐held view that speleogenesis commenced only during the last 130 000 years. Epigenic caves only form when the surface drainage system efficiently conveys water into the underground. In the study area, this was achieved after the dismantling of most of the impervious sediments covering the gypsum and the development of protovalleys and sinkholes. The time necessary for these processes can by constrained by understanding when caves were first formed. The minimum age of karst voids can be indirectly estimated by dating the infilling sediments. U–Th dating of carbonate speleothems growing in gypsum caves has been applied to 20 samples from 14 different caves from the Spipola‐Acquafredda, Monte Tondo‐Re Tiberio, Stella‐Rio Basino, Monte Mauro, and Castelnuovo systems. The results show that: (i) caves have been forming since at least ~600 kyr ago; (ii) the peak of speleogenesis was reached during relatively cold climate stages, when rivers formed terraces at the surface and aggradation caused paragenesis in the stable cave levels; (iii) ~200 000 years were necessary for the dismantling of most of the sediments covering the karstifiable gypsum and the development of a surface mature drainage network. Besides providing a significant contribution to the understanding of evaporite karst evolution in the Apennines, this study refines our knowledge on the timescale of geomorphological processes in a region affected by rapid uplifting. Copyright © 2016 John Wiley & Sons, Ltd.     

A 1D P-wave velocity model of the Gargano promontory (south-eastern Italy)

We investigate the elastic properties of the crust in the Gargano promontory, located in the northern part of the Apulia region (Southeastern Italy). Starting on April, 2013, a local-scale seismic network, composed of 12 short-period (1 Hz) seismic stations, was deployed on the Gargano promontory. Starting on October, 2013, the network was integrated with the recordings of nine seismic stations managed by the Italian Institute of Geophysics and Volcanology (INGV). The network recorded more than 1200 seismic events in about 15 months of data acquisition, with more than 700 small magnitude events localized in the Gargano promontory and surrounding areas. A Wadati-modified method allowed us to infer V_P/V_S = 1.73 for the area. A subset of about 400 events having a relatively smaller azimuthal gap (<200°) was selected to calibrate a 1D P-wave velocity model of the area, using the VELEST inversion code. The preferred model was obtained from the average of ten velocity models, each of them representing the inversion result from given initial velocity models, calibrated on previous geological and geophysical studies in the area. The results obtained under the assumption that V_P could decrease with depth are unstable, with very different depths of the top of low-velocity layers. Therefore, the velocity model was obtained from the average of the results obtained under the assumption that V_P cannot decrease with depth. A strong reduction of both RMS (about 58%) and errors on the location of the events was obtained with respect to the starting model. The final velocity model shows a strong velocity gradient in the upper 5 km of the crust and a small increase (from 6.7 to 7 km) at 30 km of depth. The epicenters of relocated events do not show clear correlations with the surface projection of known seismic faults. A cluster of the epicenters of the relocated events intersects almost perpendicularly the Candelaro fault trace at the surface.     

Palaeo- and rock-magnetic investigations across Jurassic-Cretaceous boundary at St Bertrand’s Spring,Drôme,France: applications to magnetostratigraphy

Palaeo- and rock-magnetic investigations of the St Bertrand’s Spring (Le Ravin de Font de St Bertrand) locality in France were carried out in order to contribute to, and improve, the stratigraphy of the Jurassic-Cretaceous boundary interval. Magnetic susceptibility shows slightly diamagnetic behaviour in the lowermost part of the profile and an increase (paramagnetic) towards its middle and upper parts. Rock-magnetic measurements throughout the section show magnetite as the main magnetic fraction, together with traces of hematite. Additionally, thermal demagnetization indicates the presence of goethite. Our magnetostratigraphy indicates three normal/reversed polarity sequences; possibly encompassing the magnetozones M19r to the M17n. This suggests that the St Bertrand section straddles the Tithonian/Berriasian boundary and reaches the middle Berriasian sensu lato.