1,721,008 research outputs found
Evidences for Neogene-Quaternary tectonics in Svalbard
No full textSvalbard locates along the De Geer Transform Fault that separates the kinematics of North Atlantic and Arctic Ocean and are a continental rise along the North Atlantic portion of this transform. A fold and thrust belt of Paleogene age boards theWestern margin of the Spitsbergen with a NNW-SSE trend. In the ‘60s theWest – Spitsbergen fold and trust belt was related to the relative movements between Laurentia and Eurasia. Specifically, it was regarded to be a transpressive orogen developed at the intra-continental De Geer Transform margin between the Barents and the Greenland Shelves. This setting was suggested by the necessity of a continental transform off the western margin of Svalbard needed to restore the relative openings of the North Atlantic-Arctic Ocean basins, and the Paleogene age of the fold-belt. Later structural studies in other areas of Svalbard suggested that convergent tectonics have been prevailing during much of the fold and thrust development. However this belt can hardly be regarded as a classical orogen resulting from an active continental margin for the lack of evidence for subduction, synorogenic magmatism, metamorphism or a thickened crust. On the other hand, it would be difficult to merely relate this fold and thrust belt to the De Geer Transform Fault. According to Authors a transform fault should produce structures with vergence away from the fault on both sides, whereas the found direction of tectonic transport in North Greenland is the same as in Spitsbergen, i.e. to the E and NE. In this way the transform separation of North-Greenland and Spitsbergen should postdate the formation of the Tertiary North-Greenland and Spitsbergen fold and trust belt. This rises the question on possible Neogene-Quaternary tectonics in Spitsbergen. Evidence for this younger tectonics includes the occurrence of Quaternary volcanism and thermal springs in the northern part of Spitsbergen and the moderate seismicity in Nordaustlandet. Other clues supporting a recent tectonics derive from the analysis of satellite images and air photos, including the glacier and fluvial drainage suggesting a strong tectonic control. Moreover some authors have found in Ny Alesund an uplift rate from GPS measurements higher than those predicted by postglacial rebound models, again suggesting a tectonic contribution. Preliminary results from field work in the Brogger peninsula confirmed the presence of Neogene-Quaternary tectonics. Marine terraces and fluvio-glacial deposits show several N-S elongated steps along the northern projection of N-S trending faults cutting the Meso-Cenozoic rocks. N-S trending faults have been systematically found in Devonian to Tertiary rocks. These faults are characterised by right-lateral, strike-slip movements and the presence of near surface to sub aerial mineralizations on their surfaces, including kinematic indicators. N-S faults with the same kinematics show the presence of deformed Quaternary clastic, unconsolidated deposits within their shear zones. All the found brittle deformation evidence are compatible with the kinematics of the recent activity of the De Geer Transform Fault
Tectonic signature on the ice cap surface pattern in Dome C area, East Antarctica
No full textThe bedrock morphology in Dome C area in East Antarctica is characterised by the presence of a series of elongated depressions separating ridges, with the Aurora and Concordia trenches representing the major depressions with a length of over 100km. In this area the ice cap reaches a thickness of up to 4000 m, leaving the possibility to have water formation and accumulation at its bottom. Vostok Lake is the largest, most famous among these subglacial depression. The geodynamic scenario responsible for the tectonic origin of these structural depression is not still clear: some Authors hypothesise the existence of an Early Paleozoic regional rifting, others propose a Paleozoic compressional tectonic setting. TheAurora and Concordia trenches can be associated to the Vostok Lake to the West, and together form a set of elongated, roughly N-S to NNW-SSE structural depressions, not perfectly parallel. Therefore, it is reasonable to frame their evolution within a NE-SW trending trans-extensional corridor characterised by left lateral, strike-slip shear, with the depressions associated to faults in horse tail geometry (Cianfarra et al., 2003). The relative young age of the Antarctic Ice Cap, about 38 Ma, compared with the old, Mesozoic age of the former, peneplanised landscape constrains the age of these sharp and fresh structures in Late Cenozoic time. The majority of the observed lakes and depressions are situated in relatively close proximity to ice divides where both the surface slope and ice velocity is small. The presence of this morphology induces variations in the surface texture of the ice cap either due to the movements of the ice sheet on the roughness of the bedrock morphology, and/or to the interaction with active tectonic processes. A series of preferential orientations may relate also to exogenous processes as regional winds. The resulting textural anisotropy of the ice surface can be easily detected from regional scale remotely sensed images. Radarsat mosaic of Antarctica proved a useful tool to investigate the active tectonic processes of the bedrock. Automatic lineament domain analysis performed on a pre-processed subset of the radarsat mosaic allowed to identify the morphological alignment of the surface ice cap whose origin is connected with Cenozoic tectonic processes acting in the bedrock. Images were processed by a series of dedicated algorithms (among which threshold slicing and edge continuity enhancement) to enhance linear textural variations. An original algorithm developed in SID software allowed to detect the main lineament domains of the surface ice cap in the investigated area. The statistical (gaussian) analysis eventually made possible to understand the nature of the linear texture changes as observed in the regional scale images by discriminating features directly produced by wind activity and the tectonic induced linear features. SID analysis showed that the main lineament domain detected on the ice sheet surface is compatible with the principal N-S to NNW-SSE morpho-tectonic bedrock directions in Dome C area (Aurora, Concordia and Vostok structural depression) and that morpho-tectonic directions control the ice-sheet dynamics in the investigated area
Inferring bedrock Cenozoic tectonics from ice surface pattern in the Dome C area, East Antarctica
No full textEast Antarctica is a Precambrian craton where the thickness of the crust is about 35-40 km. The main geological structures are buried by the extensive continental ice sheet apart from sparse outcrops along the perimeter of the continent. Present understanding of the tectonic evolution of East Antarctica mainly derives from remotely sensed images and geophysical data. Bedrock physiography in Dome C-Vostok region is characterised by Vostok Lake, Aurora and Vincennes basins. A relief region includes the Vostok Subglacial Highlands, the Gamburtsev Subglacial Mountains and the Belgica Subglacial Highlands. Several model have been proposed to tectonically explain the presence of these depressions: the existence of an Early Paleozoic regional rifting, a Paleozoic compressional tectonic setting or else a glacial erosional origin. It is possible to frame the origin and evolution of Lake Vostok and Dome C structural depressions within a common geodynamic scenario: they form a set of elongated, roughly N-S to NNW-SSE structural depressions related to a NE-SW trending trans-extensional corridor. The relative young age of the Antarctic Ice Cap, about 38 Ma, compared to the old, Mesozoic age of the former, peneplanised landscape constrains the age of these structures in Late Cenozoic time. The presence of this subglacial morphology induces variations in the surface texture of the ice cap either due to the movements of the ice sheet on the roughness of the bedrock morphology, and/or to the interaction with active tectonic processes. A series of preferential orientations may relate also to exogenous processes. The analysis of the resulting textural anisotropy of the ice surface detected on the Radarsat mosaic of Antarctica proved a useful tool to investigate the active tectonic processes of the bedrock An original algorithm developed in SID software allowed to detect the main lineament domains of the surface ice cap in the investigated area. Gaussian analysis eventually made possible to understand the nature of the linear textural anisotropy by discriminating features produced by exogenous process and the tectonic induced linear features. SID analysis showed that the main lineament domains detected on the ice sheet surface are compatible with the principal N-S to NNW-SSE morpho-tectonic bedrock directions in Dome C-Vostok region (Aurora, Concordia and Vostok structural depression) and that morpho-tectonic directions control the ice-sheet dynamics in the investigated area
Extensional tectonics in the East Antarctica craton: The Aurora and Concordia Trenches, Dome C
No full textIce cap surface lineaments in the Vostok-Dome C area, East Antarctica. What are they telling us on the East Antarctica craton tectonics?
No full textSince the recent discovery of subglacial lakes beneath the East Antarctic ice cap, the international scientific community have performed extensive geophysical investigations in order to define the poorly known bedrock physiography of the East Antarctic craton. Increasingly available satellite images of remote regions of the globe have provided preliminary constraints for unravelling the tectonic evolution of the East Antarctic plate. Radio echo sounding (RES) data collected in the Vostok-Dome C region revealed the presence of regional, elongated subglacial valleys, namely the Aurora and Concordia trenches (Tabacco et al. 2003). Their marked asymmetric morphology is similar to that of the Vostok lake depression and relates to the activity of two crustal west-dipping listric normal faults of Cenozoic age with a length of over 100 km (Cianfarra et al., 2003). The Radarsat mosaic of Antarctica shows abrupt changes in tones that run across the mosaic and have a length of hundreds to thousands of kilometres. The mosaic therefore reveals for the first time the presence of regional-scale sub-parallel linear features on the ice cap surface expressed on the image mosaic as sharp tonal variations and marked textural anisotropies (see Fig. 1). These intriguing linear features, up to several hundreds of kilometres long and less than 4-5 kilometres wide, will be referred to as lineaments, following Wise (1969) and Wise et al. (1985). This work investigates how the lineament pattern detected on the ice surface relates to the morpho-tectonic setting of the bedrock in the Vostok-Dome C region. Lineaments detected on the Radarsat mosaic of Antarctica and on the ice surface and bedrock morphology DEMs cluster in domains (sensu Wise et al., 1985), similarly to lineaments in emerged regions. Short, well defined lineaments detected on the high-pass spatially filtered Radarsat image depend on the roughness of the bedrock, which is determined by the tectonic setting of the area. Longer lineaments detected on the high-pass spatially filtered Radarsat image relate to ice cap dynamics. These conclusions agree with the findings of Wise et al. (1985), who demonstrated that regional lineaments on the surface of our planet are the surface expression of recent or active tectonic stress fields in the brittle upper crust. The East Antarctic Ice Sheet represents a thin “film” when compared with the about 34 km-thick continental crust. This “film” records tectonic processes in the more brittle upper crust, despite differences in the velocity (up to 2 orders of magnitude) of ice dynamics and tectonics. Radarsat images of Antarctica proved to be an effective tool for investigating ice dynamics and bedrock tectonics in the Vostok-Dome C area
Geodynamic constraints of the peri-Tyrrhenian orogen (Tyrrhenian Sea-Apennines) from lineament swarm analysis
No full text""\\"Regional geodynamics is responsible of a series of effects. that notably include tectonics and seismicity. They in turn control. the morphology of the surface of the planet. The regional. dimension of the peri-Tyrrhenian orogen reveals that its. evolution is deeply involved in a lithospheric scale dynamics. As. a result, we expect different observable and\\\\\\\/or measurable effects. at the various scales from the outcrop evidences to the subcontinental. deformation corridors. Effects at the various scales. not necessarily are directly related, and their relations should be. carefully understood taking into account both their geometry and. spatial distribution. A classical example is represented by an en. echelon system. Each single fracture is the effect of a local. extension, yet their spatial distribution shows that these local. stresses are the effect of a larger scale shear zone with a different. orientation.. Remotely sensed images proved the existence on the Earth. surface of linear features with dimensions spanning over three. order of magnitude: from hundreds of meters to thousand of. kilometers. Such features are referred to image lineaments and. are generally related to alignment of morphological features in. continental environment such as onshore crests, ridges, valleys. and troughs. In the oceans lineaments relate to the scars. associated to the seafloor spreading and fracture zones. Synthetic. scale images of tectonically active regions revealed the existence. of groups of regional scale lineaments on the earth surface. appearing as image textural anisotropies. They clusters around. preferential orientations to form lineament domains. These. domains occupies well defined areas to form lineament swarms.. Lineament domain analysis on regional scale images of the. Earth surface proved a useful tool to investigate regions. characterized by active tectonics (Wise et al., 1985; Funiciello et. al., 1977; Cianfarra & Salvini, 2008).. Both the Tyrrhenian Sea and the Apennines are geodynamic. blocks within the collisional puzzle between Africa and Europe. in the Central Mediterranean area.. In this work we explore the possible relations between these. two blocks by lineaments analysis. The found lineament domains. were interpreted as reflecting the structural grain of these two. geodynamic regions. Lineament detection was done by using. original automatic methods. Domains were identified by. statistical analysis. This work analyses lineaments detectable by. simulating different directions of lighting condition on the. DEMs. This allowed to properly evaluate the influence of the. light condition changes in the lineaments produced by. morphological features. The comparison among the analyses. showed that the different lighting conditions induce rotations of. few degrees of the mean azimuth of each lineament domain. This. rotation relate to the result of two contrasting effects: tectonics,. that tends to enhance linear morphologies, and erosion that. progressively smoothes them. Lineament domains characterised. by small rotations relate to morphologies where the tectonic. processes prevail on the erosional ones. Lineament domains. therefore have rotations inversely proportional to their tectonic. activity.\\""
Recent snow cover variability in the Italian Alps
No full textThe historical record of snow duration (from 1950 to 2009) and of snowfall (from 1960 to 2009) collected in the Italian Alps are presented and analysed. A reduction of the snow cover duration and of the snowfall stronger in springtime was detected during the last 40 years with the greatest decreasing rate during the 1990s. The last decade is characterised by a recovery from the documented decreasing trend mainly evident between 800 m and 1500 m. Principal component trend analysis of the snow duration and of the snowfall showed a long term decreasing trend. The change point test showed the existence of breakpoints between 1984 and 1994 that characterise the snow duration and snowfall time series analysed by elevation range and by seasons. These breakpointsmark a drastic trend variability in the time series: a positive trend characterises the time series before the breakpoint and a decreasing trend characterises the historical record after the breakpoint. The described negative trends result from the documented decrease in winter and spring precipitation. This in turn may either relate to a change in fraction of liquid to solid precipitation, and/or be associated to an increase of the temperatures. Northern Hemisphere and Italian Alps snow cover trends strongly correlate in the frequency domain. Among the dominant frequencies the 11.2 period was detected that may relate to the 11-year solar activity cycl
The role of fault surface geometry in the evolution of the fault deformation zone: comparing modeling with field example from the Vignanotica normal fault (Gargano, Southern Italy)
No full textFaults have a (brittle) deformation zone that can be described as the presence of two distintive zones: an internal Fault core (FC) and an external Fault Damage Zone (FDZ). The FC is characterized by grinding processes that comminute the rock grains to a final grain-size distribution characterized by the prevalence of smaller grains over larger, represented by high fractal dimensions (up to 3.4). On the other hand, the FDZ is characterized by a network of fracture sets with characteristic attitudes (i.e. Riedel cleavages). This deformation pattern has important consequences on rock permeability. FC often represents hydraulic barriers, while FDZ, with its fracture connection, represents zones of higher permability. The observation of faults revealed that dimension and characteristics of FC and FDZ varies both in intensity and dimensions along them. One of the controlling factor in FC and FDZ development is the fault plane geometry. By changing its attitude, fault plane geometry locally alter the stress component produced by the fault kinematics and its combination with the bulk boundary conditions (regional stress field, fluid pressure, rocks rheology) is responsible for the development of zones of higher and lower fracture intensity with variable extension along the fault planes. Furthermore, the displacement along faults provides a cumulative deformation pattern that varies through time. The modeling of the fault evolution through time (4D modeling) is therefore required to fully describe the fracturing and therefore permeability. In this presentation we show a methodology developed to predict distribution of fracture intensity integrating seismic data and numerical modeling. Fault geometry is carefully reconstructed by interpolating stick lines from interpreted seismic sections converted to depth. The modeling is based on a mixed numerical/analytical method. Fault surface is discretized into cells with their geometric and rheological characteristics. For each cell, the acting stress and strength are computed by analytical laws (Coulomb failure). Total brittle deformation for each cell is then computed by cumulating the brittle failure values along the path of each cell belonging to one side onto the facing one. The brittle failure value is provided by the DF function, that is the difference between the computed shear and the strength of the cell at each step along its path by using the Frap in-house developed software. The width of the FC and the FDZ are computed as a function of the DF distribution and displacement around the fault. This methodology has been successfully applied to model the brittle deformation pattern of the Vignanotica normal fault (Gargano, Southern Italy) where fracture intensity is expressed by the dimensionless H/S ratio representing the ratio between the dimension and the spacing of homologous fracture sets (i.e. group of parallel fractures that can be ascribed to the same event/stage/stress field)
Inferring sealing properties of faults in carbonates by comparing field examples with stress evolutionary models
No full textPermeability in carbonates is strongly influenced by the presence of fracture patterns. Carbonate rocks achieve fracturing both during diagenesis and tectonic processes. Spatial distribution of brittle deformation rules the secondary permeability of carbonatic rocks and therefore the accumulation and the pathway of deep fluids (ground-water, hydrocarbon). This is particularly true in the development of faults where damage zone and fault core show different hydraulic properties. In this work we studied the brittle deformation in carbonates related to fault kinematics to better understand the hydraulic properties of fault rocks. Quantitative analyses of brittle deformation from field measurements were compared to numerical models performed by FRAPtre software. This numerical tool allows to study the 4D evolution of stress/ brittle deformation in fault related rocks
Preliminary Geodynamic Section of Central Italy between 41° and 42° N parallels
No full text""The Central Mediterranean region represents the zone where. the evolution of the Thetian collisional chain appears the most. complex (Bigi et al., 1991; Cavinato et al., 1994; Parotto et al.. 1996; Amato et al. 1997; Cassano et al., 2001; Cassinis at al,. 2003; Billi & Salvini, 2003). In the Central Italian peninsula the. chain is elongated roughly NW-SE and results from the Thetian. suture by the collision between a European and an African. microplate. The sector between the N 41° and N 42° parallels is. one of the most complicate tiles of this puzzle (Salvini, 1993).. Important geodynamic differentiations are present along both. sides (Favali et al, 1993; De Alteriis, 1995).. An ideal E-W transect, from W, locates four main. geodynamic blocks (Fig. 1). To the W is the Sardinia-Corsica. Block of European origin with relics of the sedimentary wedge of. his Thetian margin to the E (Bigi et al, 1991). It follows the. Tyrrhenian Sea, a basin characterized by thinned continental. crust topped with Miocene-Quaternary marine sediments directly. lying on Paleozoic basement (Patacca et al., 1990; Serri et al.,. 2001).. The third block corresponds to the Italian Peninsula with its. Apenninic structures that constitutes the orogen of the chain. (Accordi & Carbone, 1988; Parotto & Praturlon, 2004). The. accretionary prism continues to the E offshore, and it is still. active, in the Adriatic Sea (Patacca & Scandone, 2004). This is. the last block and represents the African margin underthrust to. the chain and it is characterized by a meso-cenozoic carbonate. succession deposited in shallow to open seawaters.. The main accepted geodynamic interpretation states that the. Sardinia block represents a European microplates separated in. Oligocene times (about 38 Ma, Patacca et al., 2008 and ref.. therein). The Apennines is the accretionary prism formed from. the collision in Mio-Pliocene times of the collision between this. microplate and the sedimentary wedge of the Adriatic plate of the. African domain (Adriatic Sea). Many geological evidences still. wait to be properly framed:. i) the substantial lack of the European sedimentary wedge in. the reconstruction of the collision zone;. ii) slices of deep water sedimentary successions associated. with ophiolites, related to the suture zone, outcrop both to the N. and to the S (Southern Apennines);. iii) along the proposed section slices of deep water sediments. has been identified in front of both the westernmost and the. easternmost sides of the chain;. iv) carbonate facies in the Apennines shows in Mesozoic. times deeper waters conditions in the most eastern successions. that is towards the African microplate (Accordi & Carbone,. 1988);. v) in eastern Sardinia a Mesozoic succession of shallow water. limestone outcrop (Tacchi), belongs to the European sedimentary. wedge (Bigi et al., 1991), and shows strong analogies with the. westernmost portions of the Apennine carbonate platforms. (comp. Accordi & Carbone, 1988).. A preliminary, admissible balanced cross sections between. the 41°N and the 42° N parallel has been prepared at the regional. scale by using the layered-HCA method as implemented in the. numerical FORC software (Salvini et al, 2001; Salvini F. &. Storti F., 2004). This section has been compared to the computed. lithosphere flexure of the region as derived from the present. topographic profile.. Results provide the possible framing of the Apennine block. within the African vs European domains, and the location of their. suture zone. Found geometry may represent the basis for a. complete geodynamic study of this complex region."
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