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The Antarctic plate occupies a unique geodynamic setting being mostly surrounded by divergent or transform margins. Major intracontinental basins and highlands characterize its bedrock, buried under the 34 Ma East Antarctic Ice Sheet (EAIS). Their formation atop of the cratonic lithosphere in the interior of East Antarctica remains a major open question. Post-Mesozoic intraplate extensional tectonic activity has been proposed for their development and is supported by this work. Here we focus on the Adventure Subglacial Trench (AST) whose origin is poorly constrained and controversial, as currently available geophysical models suggest either extensional or compressional tectonic origin. The AST is an over 250-km-long, 60-km-wide subglacial trough, elongated in the NNW–SSE direction adjacent to the westernmost flank of the Wilkes Subglacial Basin, and is parallel to regional scale alignments of magnetic and gravimetric anomalies. Geophysical campaigns allowed better definition of the AST physiography showing its typical half-graben geometry. The rounded morphology of the western flank of the AST was simulated through tectonic numerical modelling. We consider the subglacial landscape to primarily reflect a preserved relict of the tectonic processes affecting the interior of East Antarctica in the Cenozoic, due to the negligible erosion/deposition capability of the EAIS. The bedrock morphology was replicated through the activity of the listric Adventure Fault, characterized by a basal detachment at the base of the crust (34 km) and a vertical displacement of 2.5 km. This length suggests its regional/crustal importance. The predicted displacement is interpreted either as a newly formed fault or as the partial reactivation of a weaker zone along a major Precambrian crustal-scale tectonic boundary. The extensional regime in the AST is part of a more extensive 800-km long intraplate corridor characterized by nearly along-strike extension in Cenozoic times with a left-lateral transpressional component. This corridor may represent the effect of far-field stresses induced by plate motions. [ABSTRACT FROM AUTHOR]

Major discrepancies are observed between experimental trials of PRRS-virus (PRRSV) infection in isolation facilities and observations made in the field on farm. Owing to the above, a cohort study was carried out in a farrow-to-finish, PRRSV-infected pig farm to characterize the time-course of the virus-specific immune response in two groups of replacement gilts. Despite the occurrence of three and two distinct waves of infection in groups 1 and 2, respectively, the large majority of animals showed little if any PRRSV-specific response in an interferon-gamma release assay on whole blood, whereas non-specific responses were consistently observed. To rule out any possible bias of our test procedure, this was used along with an ELISPOT assay for interferon-gamma-secreting cells with the same reagents on a group of PRRS-virus infected pigs in isolation facilities. A very good agreement was shown between the two sets of results. Also, as opposed to the PRRS model, plenty of Pseudorabies virus-vaccinated pigs under field conditions scored positive in another experiment in the interferon-gamma release assay, ad hoc modified for the Pseudorabies virus. Our results indicate that under field conditions poor or no development rather than delayed development of the PRRS virus-specific interferon-gamma response could be the rule for a long time in non-adult pigs after PRRS virus infection. Housing and hygiene conditions, as well as heavy exposure to environmental microbial payloads in intensive pig farms could adversely affect the host's immune response to PRRS virus and partly account for the discrepancies between experimental and field studies. [ABSTRACT FROM AUTHOR]

Abstract: We describe the structural and petrophysical evolution of extensional fault zones developed in low porosity, poorly lithified, quartz-dominated sandstones from the Mio-Pliocene continental Barreiras Formation, NE Brazil. We studied eight fault zones developed as sands were lithified. Fault displacement ranges from a few centimetres to ∼50 m. A diagnostic feature of the studied fault zones is the lack of deformation bands, which typically develop in high porosity sand(stone)s. Structural and microstructural analyses, grain size and shape analyses, porosity and pore size analyses, and laboratory and in situ permeability measurements show relationships between deformation processes and hydrologic properties. Undeformed rocks are very poorly sorted, medium- to fine-grained, clay-rich sandstones with an average intergranular porosity of about 3%. Sandstones in damage zones record non-destructive dilatant granular flow and formation of opening-mode intergranular extensional fractures, which increase porosity, pore connectivity and permeability. Deformation in fault cores evolved from particulate flow to compactional cataclastic flow, with progressive grain size reduction increasing the amount of silt- and clay-size fractions. Porosity was dramatically reduced to an average value of 0.2% and permeability is generally lower than the related protoliths. All this evidence highlights a conduit/barrier behaviour of the studied fault zones, which significantly differs from the sealing behaviour of deformation band fault zones commonly observed in high-porosity sandstones. [ABSTRACT FROM AUTHOR]

Abstract: The evolution of deformation patterns during thrust-related folding is of importance for both industrial and academic purposes because of the control that it exerts on the migration and accumulation of fluids in reservoirs. The link between structural position and deformation pattern has been described in both theoretical and field works. On the other hand, the well-documented dependence of deformation structures on the mechanical rock properties and on the environmental conditions indicates that, during folding, structural, stratigraphic, and environmental variables interact to control the deformation pattern within folds. In this work we describe the deformation pattern of the Mt. Catria anticline (Northern Apennines, Italy) and we investigate its variability with (1) the across-strike structural position, and (2) the rock type in the same structural position. Point (1) allowed us to identify and use the syn-folding deformation structures to constrain the fold kinematics. The result of point (2) analyses allowed us to divide the exposed Umbro-Marchean multilayer into three major mechanical units characterised by specific deformation mechanisms and patterns. [Copyright &y& Elsevier]

Abstract: Fault-propagation folding is a common folding mechanism in thrust-and-fold belts and accretionary prisms. Several geometrical models relating the fold shape to the ramp shape have been proposed. In all these models, ramps always emanate from a basal fault and propagate upwards. We have developed a new kinematic and geometric model of fault-propagation folding, named double-edge fault-propagation folding. The model simulates folding at thrust ramps as a function of their nucleation site and propagation history within the folded multilayer. The fold shape depends on the initial length and location of the ramp, its dip, and the S/P ratio (i.e. incremental ramp slip versus propagation) of both the upper and lower ramp tips. This solution increases the geometrical flexibility of fault-propagation folding reducing, for example, the direct dependence between the backlimb dip and the ramp dip, as double-edge fault-propagation folding is characterised by a backlimb panel not necessary parallel to the ramp. Non-parallelism between the ramp and the backlimb is commonly observed in thrust-related anticlines, within fold-and-thrust belts and accretionary prisms. The excess layer-parallel shear imposed by the development of double-edge fault-propagation folding can be easily accommodated by discrete faulting and/or penetrative deformation. The dependence of the fold shape on the fault behaviour provides a tool for including the role of mechanical stratigraphy and environmental conditions of deformation into kinematic models. Natural examples of anticlines that could be modelled by double-edge fault-propagation are presented. [Copyright &y& Elsevier]

The axial zone of the Ethiopian Rift is made up of Quaternary extensional fractures and normal faults. Field analysis was performed to study the mechanism of development of the normal faults. The collected data show that the normal faults (1) are subvertical at surface, (2) have dilation proportional to the throw, and (3) end laterally as extension fractures, that is, tension fractures which gradually decrease in dilation. The minimum measured opening of normal faults is 2 m and the maximum measured dilation of the extension fractures is 4 m. The minimum measured length of normal faults is 800 m and the maximum measured length of the extension fractures is 400 m. The collected data suggest that the normal faults nucleate from wider extension fractures in the axial zone. When the extension fractures reach critical dimensions (length=∼800 m and dilation=2–4 m, corresponding to a predicted depth of ∼700 m), the shear rupture behavior controls the further propagation of the fractures at depth. This mechanism has close similarities with models previously proposed for fault formation along the oceanic ridge of Iceland. This suggests common rifting processes along diverging plates, independently from the oceanic or continental nature of the lithosphere. [Copyright &y& Elsevier]

GNSS networks in Antarctica are a fundamental tool to define actual crustal displacements due to geological and geophysical processes and to constrain the glacial isostatic models (GIA). A large network devoted to the detection and monitoring of crustal deformations in the Northern Victoria Land (Victoria Land Network for DEFormation control – VLNDEF), was monumented during the 1999–2000 and 2000–2001 field campaigns, as part of Italian National Program for Antarctic Research and surveyed periodically during the Southern summer seasons. In this paper, GPS observations of VLNDEF collected over a more than 15-year span, together with various selected POLENET sites and more than 70 IGS stations, were processed with Bernese Software, using a classical double difference approach. A solution was obtained combining NEQs by means of ADDNEQ2/FODITS tools embedded in Bernese Software. All the Antarctic sites were kept free and a subset of 50 IGS stations were used to frame VLNDEF into ITRF2008. New evidence provided by analysis of GPS time series for the VLNDEF network is presented; also displacements along the vertical component are compared with the recently published GIA models. The absolute velocities indicate an overall displacement of the northern Victoria Land region along the south-east direction (Ve = 10.6 mm/yr, Vn = −11.5 mm/yr) and an average uplift rate of Vu = 0.5 mm/yr. Two GIA models have been analyzed: ICE-6G_C-VM5a proposed by Argus et al. (2014), Peltier et al. (2015) and W12A_v1 by Whitehouse et al. (2012a,b). Up rates, predicted over the VLNDEF sites by the mentioned GIA models, have been extracted and compared with those observed. A preliminary comparison with GPS-derived vertical rates shows that the Victoria Land ICE-6G_C-VM5 and W12A_v1 GIA models predict overestimated uplift rates of 0.7 and 0.9 mm/yr weighted mean residuals respectively. The mean horizontal relative motions within the Victoria Land (VL) area are in most cases negligible, while only a few points exhibit horizontal velocities greater than the confidence level. Such a residual horizontal velocity field could represent some of the tectonic characteristics affecting VL, characterized by block faulting, tilting along NE striking and SE dipping extensional faults. Uplift rates, highlighted in the present paper depict a well defined spatial pattern in the investigated areas. Northward, all sites show a general positive trend up to 2.3 mm/yr. In the central and southern areas small negative trends (up to −1.3 mm/yr) were detected in the vertical displacements. Only the site VL06, located atop the Mt. Melbourne volcano, does not concord with such a general reading, as it is representative of the volcanic complex’s evolution. Observed and predicted uplift rates increase westward (inland) where the ice-load increases. The same behavior is predicted southward by the GIA models; whereas GPS values decrease toward the south pole, due to the movements of a few sites reflecting the neotectonic phenomena acting in the Victoria Land region. [ABSTRACT FROM AUTHOR]

Abstract: Fault tip regions, relay ramps and accommodation zones in between major segments of extensional fault systems provide zones of additional structural and stratigraphic complexities and also significantly affect their hydraulic behaviour. The great interest for both academic and industrial purposes encouraged specific studies of fault tip regions that, in some cases, produced controversial results. We approached the study of fault tip regions by integrating structural, AMS and stratigraphic analyses of the tip of an extensional growth fault system in the Tarquinia basin, on the Tyrrhenian side of the Northern Apennines. Detailed structural mapping indicates the occurrence of systematic relationships between the orientation of the main subsidiary fault zones, the orientation and position of the two main joint sets developed in the fault damage zones, and the overprinting relationships between the two main joint sets themselves. Microstructural analysis of fault core rocks indicates a progression of deformation from soft-sediment to brittle conditions. The AMS study supports the evolution of deformation under a constantly oriented stress field. By combining this multidisciplinary information we propose an evolutionary model for the tip of the extensional growth fault system that accounts for the progressively changing sediment rheological properties, and for the time dependent subsidiary deformation pattern by invoking the interplay between the regional stress field and the local, kinematically-derived one by fault activity. We also speculate on the overall implications for fluid flow of the proposed evolutionary model. [Copyright &y& Elsevier]

Abstract: Understanding the genetic relationships of folding-related deformation structures is of importance for both academic and industrial purposes. We analysed the three-dimensional deformation pattern of the Añisclo anticline, in the southern Pyrenees. The specifically designed statistical method includes sequential steps of statistical and spatial data analysis and classification. Our results indicate that pressure solution cleavage frequency exhibits a spatial distribution that depends on the position within the fold. Conversely, such a dependence does not occur in joints and veins. Consequently, our data suggest that pressure-solution cleavage is the most appropriate deformation structure for unravelling fault-fold kinematics in carbonate multilayer. In particular, we found that the spacing of solution cleavages (S) is related to the corresponding bed thickness (H). This supports the use of H/S value for deformation intensity quantification instead of spacing. In the Añisclo anticline, analysis of H/S indicates the occurrence of three main deformation panels whose restoration suggests that fold evolution progressed from layer-parallel shortening, to décollement folding, up to thrust breakthrough, and fault-propagation folding. Comparison of H/S values with finite strain data indicates that line-length was not preserved during fold evolution. This evidence has important implications for the kinematic interpretation of layer-parallel shortening and cross-section balancing. [Copyright &y& Elsevier]