The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Giacomo Corti - One of the best experts on this subject based on the ideXlab platform.
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Modelling the influence of pre-existing brittle fabrics on the development and architecture pull-apart basins
Journal of Structural Geology, 2020Co-Authors: Giacomo Corti, Rosa Nencini, Pietari SkyttäAbstract:Abstract We use new analogue modelling experiments to analyse the development of pull-apart basins in an upper crust characterised by the presence of pre-existing discrete fabrics. As in previous models, lateral movement of rigid basal plates induced strike-slip deformation of a sand-pack. Local Extension allowing the formation of a pull-apart basin was produced by the step-over geometry of the master faults; in this area, a basal silicone layer was introduced to distribute deformation and reproduced a weaker crust in the basin. Conditions of neutral, overlapping and underlapping interacting master faults were reproduced. The model upper crust, modelled by a sand mixture, was characterised by the presence of pre-existing structures; the orientation of these inherited heterogeneities was systematically varied in different experiments. Model results indicate that, depending on their orientation with respect to the strike-slip displacement, pre-existing structures can be reactivated both within and at the margins of the pull-apart basins. Inside the basin, reactivation occurs when the pre-existing structures are orthogonal or sub-orthogonal to the strike-slip displacement; in this case, the pre-existing fabrics delay the development and linkage of cross-basin faults and increase the complexity of the deformation pattern giving rise to a new set of faults characterised by an atypical trend. Pre-existing fabrics oblique to the local Extension Direction may be partly reactivated in the central part of the basin as segments of cross-basin faults. At the margins of the pull-apart, reactivation occurs if the fabrics spatially coincide with the lateral boundaries of the silicone layer. In these conditions, reactivation allows a faster development of the border faults, which are less segmented than in the homogenous models; this also results in a more regular final geometry of the pull-apart.
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spatial variability of volcanic features in early stage rift settings the case of the tanzania divergence east african rift system
Terra Nova, 2014Co-Authors: Ilaria Isola, Francesco Mazzarini, Marco Bonini, Giacomo CortiAbstract:Close relationships between deformation and volcanism are well documented in relatively late evolutionary stages of continental rifting, whereas these are poorly constrained in less mature rifting stages. To investigate the control of inherited structures on faulting and volcanism, we present a statistical analysis of volcanic features, faults and pre-rift fabric in the Tanzania Divergence, where volcanic features occur extensively in in-rift and off-rift areas. Our results show that in mature rift sectors (Natron), magma uprising is mostly controlled by fractures/faults responding to the far-field stress, whereas the distribution of volcanism during initial rifting (Eyasi) is controlled by inherited structures oblique to the regional Extension Direction. Off-rift sectors show a marked control of pre-rift structures on magma emplacement, which may not respond to the regional stress field. Thus, the use of off-rift magmatic features as stress indicators should take into account the role of pre-existing structures.
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re orientation of the Extension Direction and pure Extensional faulting at oblique rift margins comparison between the main ethiopian rift and laboratory experiments
Terra Nova, 2013Co-Authors: Giacomo Corti, Melody Philippon, Federico Sani, Derek Keir, Tesfaye KidaneAbstract:In this study, we draw on a unique combination of well-resolved fault-slip data and earthquake focal mechanisms to constrain spatial variations in style of faulting in the obliquely extending Main Ethiopian Rift, East Africa. These data show that both boundary and internal faults – oblique and orthogonal to the plate divergence (PD) respectively – exhibit almost pure dip-slip motion, and indicate significant local deflection in orientation of the Extension Direction at rift margins. Scaled analogue models closely replicate the multidisciplinary observations from the rift and suggest that the process is controlled by the presence of a deep-seated, pre-existing weakness – oblique to the Direction of PD – that is able to cause a local rotation in the orientation of the Extension Direction at rift margins. Minor counterclockwise block rotations are required to accommodate the difference in slip Direction along the different fault systems, as supported by existing and new palaeomagnetic data from the rift.
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evolution and characteristics of continental rifting analog modeling inspired view and comparison with examples from the east african rift system
Tectonophysics, 2012Co-Authors: Giacomo CortiAbstract:Abstract The evolution and characteristics of narrow continental rifting are illustrated in this paper through a review of recent lithospheric-scale analog models of continental Extension compared with selected examples from the East African Rift System. Rift location is controlled by reactivation of lithospheric-scale pre-existing weaknesses; in these areas, the initial phases of rifting correspond to the activation of few, large-offset boundary faults that accommodate basin subsidence, which can be at places strongly asymmetric. The plan-view geometry of rift faults is primarily related to the relative orientation of the lithospheric weakness with respect to the Extension Direction: orthogonal rifting gives rise to long, Extension-orthogonal boundary faults with associated pronounced subsidence, whereas oblique rifting results in a general en-echelon arrangement of faults and basins with less subsidence. Inherited fabrics having variable orientation with respect to the rift trend may control rift architecture at both regional and local scales. In these initial phases, widespread magmatism may encompass the rift, with volcanic activity localized along major boundary faults, transfer zones and limited portions of the rift shoulders (off-axis volcanism). Progressive Extension leads to a change in deformation style from the few, large-offset boundary faults at the rift margins to dense fault swarms – with limited vertical motions – affecting the rift floor where the magmatic activity is concentrated. In these areas of focused tectono-magmatic activity (the so-called magmatic segments) the thinned lithosphere is strongly modified and weakened by the extensive magma intrusion, and Extension is facilitated and accommodated by a combination of magmatic intrusion, dyking and faulting. The feedback between strain localization, magma injection and lithospheric weakening is self-reinforcing, facilitating the rupture of the continental lithosphere. At this stage, magmatic segments (as for instance in the Northern Main Ethiopian Rift) act as incipient slow-spreading mid-ocean ridges, developing within a lithosphere that is transitional between continental and oceanic.
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tectonic inheritance and continental rift architecture numerical and analogue models of the east african rift system
Tectonics, 2007Co-Authors: Giacomo Corti, Jolante Van Wijk, S A P L Cloetingh, C K MorleyAbstract:[1] The western branch of the East African Rift is composed of an arcuate succession of elongate asymmetric basins, which differ in terms of interaction geometry, fault architecture and kinematics, and patterns of uplift/subsidence and erosion/sedimentation. The basins are located within Proterozoic mobile belts at the edge of the strong Tanzanian craton; surface geology suggests that the geometry of these weak zones is an important parameter in controlling rift development and architecture, although other processes have been proposed. In this study, we use lithosphere-scale numerical models and crustal-scale analogue experiments to shed light on the relations between preexisting structures and rift architecture. Results illustrate that on a regional scale, rift localization within the mobile belts at the curved craton's western border results in an arcuate rift system, which implies that under a constant Extensional stress field, part of the western branch experienced orthogonal Extension and part oblique Extension. Largest depocenters are predicted to form mostly orthogonal to the Extension Direction, and smaller depocenters will form along the oblique parts of the rift. The varying Extension Direction along the rift zone furthermore results in lengthwise varying rift asymmetry, segmentation characteristics, and border fault architecture (trend, length, and kinematics). Analogue models predict that discrete upper crustal fabrics may influence the location of accommodation zones and control the architecture of Extension-related faults at a local scale. Models support that fabric reactivation is responsible for the oblique-slip kinematics on faults and for the development of Z-shaped or arcuate normal faults typically documented in nature.
Haakon Fossen - One of the best experts on this subject based on the ideXlab platform.
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Subseismic deformation in the Vaza-Barris Transfer Zone in the Cretaceous Recôncavo-Tucano-Jatobá rift system, NE Brazil
Journal of Structural Geology, 2018Co-Authors: Cleber Peralta Gomes, Renato Paes De Almeida, Haakon Fossen, Bruno SalmoniAbstract:Abstract We investigate the subseismic structural expression of the major Vaza-Barris Transfer Zone in the Early Cretaceous Tucano rift basin, NE Brazil based on field observations. Subseismic structures in the Tucano rift fill encompass cataclastic deformation bands, deformation band clusters and deformation band faults. In general, these subseismic structures indicate a ∼120° Extension Direction and document oblique Extension across the N-S Tucano Rift, consistent with the movement Direction inferred from plate-scale reconstructions. The transfer zone itself is dominated by a large population of NE-SW trending deformation band structures that developed into deformation band faults making a high angle to the transfer zone. The deformation band faults are quite evenly distributed along the transfer zone, which we attribute to Extension related to its arcuate cross-sectional shape with flanks dipping toward the rift margins. Additional subordinate structures, many of which are oriented parallel to the transfer zone, show strike-slip dominated motion, and indicate that the finite strain field in the transfer zone involves a component of NNW-SSE shortening in addition to the main Extension along the transfer zone. In terms of subseismic fault prediction, however, the evenly distributed zone-perpendicular structures dominate and could impose restrictions on fluid flow along the zone. This macro-permeability anisotropy should be considered in an injection/production scenario in a transfer zone of the type described here. Although other transfer zones may have different geometries and therefore different subseismic characters, an important observation made here is the close correspondence between first-order geometry (in our case an arch-shaped transfer zone) and subseismic deformation (arch Extension). In addition, the observation of deformation band faults in the Banzae Member of the Marizal Formation shows that rifting lasted through the Aptian and possibly into the Albian.
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basement structure and its influence on the structural configuration of the northern north sea rift
Tectonics, 2017Co-Authors: Hamed Fazlikhani, Jan Inge Faleide, Haakon Fossen, Robert L. Gawthorpe, Rebecca E BellAbstract:The northern North Sea rift basin developed on a heterogeneous crust comprising structures inherited from the Caledonian orogeny and Devonian post-orogenic Extension. Integrating two-dimensional regional seismic reflection data and information from basement wells we investigate the pre-rift structural configuration in the northern North Sea rift. Three seismic facies have been defined below the base rift surface: 1) relatively low-amplitude and low-frequency reflections, interpreted as pre-Caledonian metasediments, Caledonian nappes and/or Devonian clastic sediments; 2) packages of high-amplitude dipping reflections (>500 ms thick), interpreted as basement shear zones; and 3) medium-amplitude and high frequency reflections interpreted as less sheared crystalline basement of Proterozoic and Paleozoic (Caledonian) origin. Some zones of Seismic Facies 2 can be linked to onshore Devonian shear zones whereas others are restricted to the offshore rift area. Interpreted offshore shear zones dip S, ESE and WNW in contrast to W to NW dipping shear zones onshore W Norway. Our results indicate that Devonian strain and ductile deformation was distributed throughout the Caledonian orogenic belt from central South Norway to the Shetland Platform. Most of the Devonian basins related to this Extension are, however, removed by erosion during subsequent exhumation. Basement shear zones reactivated during the rifting and locally control the location and geometry of rift depocenters, e.g. in the Stord and East Shetland basins. Pre-rift structures with present-day dips >15° were reactivated, although some of the basement shear zones are displaced by rift faults regardless of their orientation relative to rift Extension Direction.
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structural geology of the huldra field northern north sea a major tilted fault block at the eastern edge of the horda platform
Marine and Petroleum Geology, 2003Co-Authors: Haakon Fossen, Jonny Hesthammer, Tord Erlend Skeie Johansen, Trond Olav SygnabereAbstract:Abstract The Huldra fault block is a rotated major fault block on the east margin of the Viking Graben in the northern North Sea. Unlike the rest of the Horda Platform area, the Jurassic section in the Huldra fault block was rotated more than 20° during slip on the listric Huldra fault, which forms a low-angle detachment beneath the Huldra fault block. The fault block is interpreted as resulting from marginal collapse of the Horda Platform after relief along the eastern margin of the Viking Graben built up in early parts of the middle to late Jurassic rifting history. The collapse resulted in NW directed transport of the Huldra fault block, consistent with a previously postulated change in Extension Direction from W–E to NW–SE toward the end of the Jurassic period. Minor faults within the Hulrda fault block are consistent with E–W Extension and thus may have formed early during the late Jurassic rifting phase. Nevertheless, the crest (Huldra Field) seems surprisingly intact, considering its proximity to a major fault zone. Deformation bands studied from core material are non-cataclastic and concentrated in zones. Evidence for smearing along a cored fault surface indicates that minor subseismic faults may be sealing. Production data from the field indicate good communication between most wells, suggesting that the subseismic faults and deformation band zones that are present in the reservoir have relatively small influence on the flow of gas in the reservoir.
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Extension displacement and block rotation in the larger gullfaks area northern north sea determined from map view restoration
AAPG Bulletin, 1996Co-Authors: Delphine Rouby, Haakon Fossen, P R CobboldAbstract:Numerical map view restoration of the larger Gullfaks area on the western side of the Viking Graben reveals a Late Jurassic apparent displacement field that is slightly divergent, with displacement vectors trending east-northeast-west-southwest to east-southeast-west-northwest. The predominant Extension Direction is east-west in the Gullfaks field, changing to east-southeast-west-southwest in the Gullfaks Sor area. We relate the divergent pattern to Extensional collapse over low-angle Extensional detachments in the eastern part of the area. The detachments also explain the anomalously high Extensions in this same area. Total Extension in the horizontal plane is estimated to be 19% on average in the larger Gullfaks area, whereas it is 42 and 33% in Gullfaks and Gullfaks So , respectively. Block rotations (about vertical axes) are minor (mostly <5°). Calculated fault-slip Directions indicate that major north-south-striking faults are mostly dip-slip, whereas accommodation faults or transfer faults, oriented at high angles to the major faults, tend to be oblique slip. In general, numerical or manual map view restoration is useful before choosing and balancing vertical sections. In most of the Gullfaks area, strain is close enough to plane strain and block rotations are small enough for section balancing to be reliable. East-west sections should be chosen across the main Gullfaks field, and east-southeast-west-northwest sections in the Gullfaks Sor area.
D M Gravley - One of the best experts on this subject based on the ideXlab platform.
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spatial and temporal variations in magma assisted rifting taupo volcanic zone new zealand
Journal of Volcanology and Geothermal Research, 2010Co-Authors: J V Rowland, C J N Wilson, D M GravleyAbstract:Abstract Taupo Volcanic Zone (TVZ), New Zealand, is a NNE-trending rifting arc, active for ~ 2 Myr, with a 125-km-long central segment characterized by exceptionally voluminous rhyolite volcanism. The volcanic segmentation reflects along-axis variations in magmatism with implications for the thermal state of the crust and consequent rifting dynamics. Along the zone to the north and south of Central TVZ, the limbs of broad monoclines, disrupted to various degrees by normal faults, dip SE against major NW-facing fault zones. In these northern and southern segments, the loci of magmatism (shown by the position of volcanoes) and rifting (manifested by the distribution of seismicity and modern ( 20 km and width > 1 m oriented perpendicular to the Extension Direction; 2) fault slips of
Guiting Hou - One of the best experts on this subject based on the ideXlab platform.
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Mechanism of the Mesozoic African rift system: Paleostress field modeling
Journal of Geodynamics, 2019Co-Authors: Ge Min, Guiting HouAbstract:Abstract The Mesozoic African rift system is an important continental rift system related to the Central African Shear Zone. While several geological models have been discussed, the mechanism of the Mesozoic African rift system is still unclear. One model proposed that the mechanism of the Mesozoic African rift system was inherited from the Benue Trough, which is a failed arm of the Guinea triple junction. Other models suggested that the mechanism of the Mesozoic African rift system could be clarified by the spreading of the Atlantic and weak lithospheric zones, such as the Pan-African suture zone. In this research paper, we create a shell model that considers spherical curvature, the heterogeneous structure of the African basement framework, and a combination of the upwelling St. Helena plume and seafloor spreading. The calculation of the model is solved through the finite element software ANSYS, and the modeling results match the actual geological evidence. In this study, nine other models are created with altered rock parameters or boundary constraints and compared to the original model to examine the influence of these factors. Compared to the nine comparative models, the original model best reflects the calculated results, which indicates that the coupling of the St. Helena mantle plume and ocean-ridge spreading caused the initial lithospheric rifting at ∼130 Ma and that the heterogeneities within Africa did not affect the Extension Direction of the rift basin but did influence the location of the rift basin.
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geodynamics of the east african rift system 30 ma ago a stress field model
Journal of Geodynamics, 2018Co-Authors: Ge Min, Guiting HouAbstract:Abstract The East African Rift System (EARS) is thought to be an intra-continental ridge that meets the Red Sea and the Gulf of Aden at the Ethiopian Afar as the failed arm of the Afar triple junction. The geodynamics of EARS is still unclear even though several models have been proposed. One model proposes that the EARS developed in a local tensile stress field derived from far-field loads because of the pushing of oceanic ridges. Alternatively, some scientists suggest that the formation of the EARS can be explained by upwelling mantle plumes beneath the lithospheric weak zone (e.g., the Pan-African suture zone). In our study, a shell model is established to consider the Earth’s spherical curvature, the lithospheric heterogeneity of the African continent, and the coupling between the mantle plumes and the mid-ocean ridge. The results are calculated via the finite element method using ANSYS software and fit the geological evidence well. To discuss the effects of the different rock mechanical parameters and the boundary conditions, four comparative models are established with different parameters or boundary conditions. Model I ignores the heterogeneity of the African continent, Model II ignores mid-ocean spreading, Model III ignores the upwelling mantle plumes, and Model IV ignores both the heterogeneity of the African continent and the upwelling mantle plumes. Compared to these models is the original model that shows the best-fit results; this model indicates that the coupling of the upwelling mantle plumes and the mid-ocean ridge spreading causes the initial lithospheric breakup in Afar and East Africa. The Extension Direction and the separation of the EARS around the Tanzanian craton are attributed to the heterogeneity of the East African basement.
Giuseppe Pezzotti - One of the best experts on this subject based on the ideXlab platform.
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evaluation of crack tip stress fields on microstructural scale fracture in al al2o3 interpenetrating network composites
Acta Materialia, 2009Co-Authors: Robert J Moon, Mark Hoffman, Jurgen Rodel, Shigemi Tochino, Giuseppe PezzottiAbstract:The influence of local microstructure on the fracture process at the crack tip in a ceramic–metal composite was assessed by comparing the measured stress at a microstructural level and analogous finite element modelling (FEM). Fluorescence microprobe spectroscopy was used to investigate the influence of near-crack-tip stress fields on the resulting crack propagation at the microstructural scale. The high spatial resolution was effective at mapping the localized crack-tip stress distributions within the complex Al–Al2O3 phase morphologies, where the localized stress distribution about the crack tip within the Al2O3 phase could be measured. Regions of high-localized tensile stress within the microstructure resulting from a combination of applied load and thermal residual stress were identified and could be used in predicting the subsequent crack Extension Direction. Stress distributions calculated from spectroscopy results were compared with microstructural level FEM of the same structure and general agreement between the two techniques was observed.
