Fold Axes Research Articles

Deciphering the complex history of the cabo frio high – SE brazilian continental margin

Extensive seismic reflection interpretation of the Cabo Frio High allowed better understanding of its proximal and distal structure. Seismic lines helped map the salt base and recognize the primary geological interfaces, unconformities, faults, and volcanic intrusions. The proximal Cabo Frio High is a continental basement uplift extending mainly into the Campos Basin. The Cabo Frio Outer High, which is of volcanic origin, lies between Santos and Campos Basins. This volcanism is concentrated at the crossing of two significant structures: Cruzeiro do Sul Lineament and Rio de Janeiro Fracture Zone. The Cabo Frio High fits an NW-SE fold axis, which is well correlated with distension along NW-SE direction generating a regional E-W sinistral plate movement, mainly related to the ENE-WNW sinistral Rio de Janeiro transfer zones. The accumulated uplift is approximately 4 km, achieved by at least four uplifting pulses. The uplifting starts in the Albian-Santonian, characterized by the elevation of the northeast portion of Cabo Frio High, followed by erosion. The sill and dikes intruded in the Upper Cretaceous, and the uplift of the southwest portion of the Cabo Frio High characterizes the second uplift pulse. Subaerial Eocene volcanos characterize the third uplifting pulse. The uplifting of the Blue Marker horizon (Oligocene) characterizes the last pulse.

Compressibility and shear compliance of a pore possessing an (n + 1)-fold axis of symmetry via the use of a conformal mapping function containing an arbitrary number of terms

We propose a simple yet effective method to determine the compressibility and the shear compliance of a pore possessing an (n + 1)-fold axis of symmetry with n ≥ 2 embedded in an infinite isotropic elastic body. The conformal mapping function which maps the exterior of the pore onto the exterior of the unit circle in the image plane contains an arbitrary number of terms. When the mapping function has N+1 terms, the compressibility and shear compliance are found by solving, respectively, sets of N and 2N coupled linear algebraic equations. Detailed numerical results for the compressibility and shear compliance of equilateral polygonal holes and a five-pointed star shaped hole are presented to demonstrate the proposed solution method.

Geological modeling of a tectonically controlled hydrothermal system in the southwestern part of the Pannonian basin (Croatia)

Geothermal energy is an important resource in the green economy transition. For the preservation of a geothermal resource it is crucial to assess its renewability and the sustainability of the exploitation. These aspects are influenced by the interaction among the physical, chemical, geological, and hydrogeological processes. The reconstruction of the geological assemblage allows the detailing of the geometries of the reservoir and fracture systems that influence the fluid flow and the water/rock interaction. The control of regional/local scale fault and fold systems on the development of the Daruvar hydrothermal system (DHS), located in Croatian part of the Pannonian basin, is detailed in this work. Field investigations were conducted to collect structural data on strata orientation and fault/fracture systems. The dataset was integrated with geological and geophysical data to develop composite geological profiles and a 3D geological model. Results display a pattern of generally N-S and E-W striking folds and cogenetic fracture systems with orientations parallel to the fold axes. The geological reconstruction was integrated with geophysical, hydrogeological, and geochemical data to propose a conceptual model of the DHS. The DHS is a topographically driven system hosted in a Mesozoic carbonate reservoir where E-W striking fracture systems are regional flow paths that enable infiltration of meteoric water to 1 km depth and its reheating in its reservoir area. In Daruvar, an anticline and fault/fracture systems accommodate the uplift of reservoir to shallow depths, promoting the bedrock fracturing and increase of the permeability field. These conditions favor the localized upwelling of thermal water resulting in four thermal springs (38°C and 50°C) in Daruvar city area. This work highlights the importance of employing a multidisciplinary approach to detail the complex interaction among the processes driving the geothermal resource.

Formation mechanism and structural evolution of recumbent fold nappes: New insights from the bizerte area, northern Tunisia

The structural analysis of the Bizerte area in northern Tunisia, utilizing well data and field observations, reveals a complex arrangement of fold structures characterized by recumbent fold nappes to local sheath-like fold structures, indicative of a deep detachment phenomenon. The genesis and present geometry of these fold structures unravel a multifaceted structural history: (i) In the Tortonian folding phase, a detachment mechanism may have initiated the formation of a horizontal shearing plane at the base of the Paleocene marls. The gradual evolution of syn-shear recumbent fold nappes into sheath folds within sedimentary to pseudo-metamorphic rocks is attributed to a flow perturbation process analogue to “layer-parallel shearing,” dictating the geometric configuration of folds subsequent to a simple shear inducing perturbations in pre-existing layer disturbances. (ii) During the Late Quaternary shortening phase, a NW-trending right lateral shear zone emerged, delineated by the reactivation of pre-existing faults under compression. The reorientation of the anterior fold axes is attributed to the counterclockwise rotation of rigid blocks within the framework of P-type conjugate fractures. (iii) The transition to thin-skinned tectonics, characterized by the uplift of previously buried material, was characterized by a significant increase in shortening during Neogene events, encompassed in the broader regional geodynamic context of continental collision. From the Lower Quaternary onward, the structural model exhibits a combination of layer-parallel and layer-normal shear processes.

Digital elevation model‐based lineament analysis of the Zindapir anticline, Sulaiman fold‐and‐thrust belt, Pakistan

The N‐S oriented Zindapir anticline is an eastward verging mega‐structure (~130 km along and ~40 km across the strike) in the eastern Sulaiman fold‐and‐thrust belt on the western margin of the Indian Plate in Pakistan. In this study, we carried out a lineament analysis of the anticline based on shuttle radar topographic mission (SRTM) images and digital elevation model (DEM) data to demonstrate the application of this technique for modelling of the fractured reservoirs. We used shaded relief images, variations in the vertical exaggeration, sun and azimuth angles to enhance the DEM data and structures in the area. Stereographic projections indicated that the anticline is an upright, asymmetrical, gentle, doubly plunging and east‐vergent fold. The synthesized lineament map of the fractures indicates a total of 402 fractures across the Zindapir anticline. A total of 204 and 198 fractures were observed in the eastern and western limbs, respectively. Statistical analysis portrayed that the lineaments of the majority of fractures followed northwest‐southeast (NW‐SE) and west‐northwest—east‐southeast (WNW‐ESE) trends. These are oblique or transverse to the fold axis and could be interpreted as shear and tensional fractures related to drag and compression along the western boundary of the Indian Plate. Our study provides an example of lineament analysis for structural characterization and modelling of fractured reservoirs in a collision‐mountain setting.

Structural architecture of the Mapimí Biosphere Reserve and its surroundings, north-central Mexico: New insights from U–Pb geochronology and interpreted structural data

The Mapimí Biosphere Reserve is in northeastern México, near the boundary between the Mesozoic Coahuila platform and the Mexican central basin. A large portion of the Reserve is a broad bolson where isolated mountains are surrounded by flat terrain. Two slightly elevated areas (benches) are subtle topographic features in the Reserve. There, in rolling hills occur folded, Upper Cretaceous – Paleogene, poorly-lithified and -exposed transitional and continental sediments and tilted Paleogene volcanic and subvolcanic rocks. Each bench occupies a band that is ∼75 × 20 km. A land strip where playa lakes and salt-flats occur separates the benches. Deformation style within the benches differ from those in regions where platform carbonates or Mexican central basin rocks dominate. Structures within the benches are gentle, open folds and medium sized (15 - 3 km in diameter) structural domes and basins. Furthermore, orientation of the fold axes shows a wide scatter. There is at least one folded structure in the Reserve that displays an interference pattern that indicates refolding. Post-Oligocene normal faults bound the benches and overprinted on the folded structures. However, the most important normal fault, which cuts in half two domes and one structural basin, lacks a clear topographic scarp. The occurrence of broad exposures of the Upper Cretaceous Indidura Formation in flat areas, interpreted as the footwall block of a major normal fault, is consistent with the interpretation that the benches are rocky pediments partially covered by alluvium and/or eolian sediments. Thus, it appears that Cenozoic extension has been inactive for a long period of time in this portion of the Mexican Basin and Range province. The best evidence of NNW, down to the SW normal faults within the Reserve is in the Sierra de Mohóvano. There, an array of domino-style normal faults cut Oligocene volcanic rocks and gravel deposits. The master fault of the domino array is adjacent and parallel to a fold in Mesozoic marine rocks.We attribute the unusual characteristic of the folds in the Reserve to 1) the region is near the boundary among the large calcareous platform and the basin, and the boundary had a significant curvature, concave toward the W. This geometry caused complex deformation during crustal shortening, as tectonic transport associated with the Mexican orogen is toward the NE, 2) a significant difference in competence between the poorly consolidated transitional and continental deposits and the more competent rocks in the carbonate platform also played a role in the formation of the structures, as folds in the benches formed during the waning stage of the Mexican orogen, as suggested by the detrital zircon U–Pb ages, which are as young as ∼30 Ma, 3) Oligocene magmatic activity caused the emplacement of laccoliths, which locally modified older folds forming domes, 4) finally, Basin and Range extension (<27 Ma) cut across the folded sediments and overlying volcanic rocks. Evidence of extension in the Reserve is subtle as normal faults have remained inactive for a long time, while isostatic uplift and erosion developed the pediment, effectively masked most fault scarps.

Paleostress Analysis Using Fracture Data, a Case Study of Kewa Charmula Anticline, Kurdistan Region, Northeastern Iraq

Fracture analysis was carried out through three adjacent traverses. The study area is considered a part of the Arabian Plate and geologically falls within the boundary between the Low Folded Zone and the High Folded Zone of the Western Zagros Fold-Thrust Belt in the Iraqi Kurdistan Region. Five formations are cropped out in this anticline, extending from the Late Oligocene up to the Late Miocene – Pliocene. Those formations are (Anah, Jeribe, Fatha, Injana, and Mukdadiya). In addition, identify an Oligocene unit the Kirkuk Group, represented by the (Anah Fn.) that no other studies have previously referred to, in addition, to observing the Jeribe Formation along Tilyan Gorge. About 350 fracture planes were measured for the study and classified into sets and systems concerning their relations to the three mutually perpendicular geometrical axes (tectonic axes). Tension sets are (ac), which are formed by extension along the fold axis accompanying direct compression perpendicular to the fold trend, whereas the (bc) set is supposed to be the product of relaxation that motivated the primary compressional stress. The shear systems are each of hk0, h0l, and 0kl developed successively during direct compression and subsequent relaxation episodes of each tectonic stress. The results of the paleostress analyses showed that there is a general coincidence in the direction of the major stress axis (σ1) and the minor stress axis (σ3), which were derived from the joints (fracture planes). Joints are presented as sets and systems. The analysis of joint attitudes revealed that the joints might be due to the influence of the main horizontal compression paleostress in the direction NE – SW that is responsible for folding, or they might be caused by the stretching of the outer arc for the folded layers. According to field observations and paleostress studies, the region experienced four stress stages. The first is a main compressive tectonic phase in the NE – SW direction. The second phase is the second compressive tectonic stress in the direction NW – SE. The third was a NE – SW extension tectonic phase that originated during the final uplift stage of folding and it is representative of the major fold trend. The fourth is the NW – SE extension face considered as the extension stress connected to the principal NE – SW compressive stress.

The role of long-term preparatory factors in mass rock creep deforming slopes: insights from the Zagros Mts. belt (Iran)

The long-term evolution of slopes affected by Mass Rock Creep deformations is controlled by both time-invariant predisposing factors, such as the geo-structural inheritance, and time-dependent preparatory conditions, including regional uplift and landscape evolution rates. However, the relationship among Deep-seated Gravitational Slope Deformations, drainage network evolution, and tectonics remains poorly defined. Here, we focused on an undocumented Deep-seated Gravitational Slope Deformation affecting an area of about 8 km2 in the SE tip termination of the Siah Kuh anticline in the Lorestan arc (Zagros Mts., Iran), upstream to the Mountain Front Fault. To assess the evolution processes which involved the slope up to the present, we integrated quantitative geomorphic analysis, optically stimulated luminescence dating of geomorphic markers, and SAR interferometry techniques. In detail, we semi-automatically extracted the river terrace treads to which we associated an elevation above the thalweg based on the Relative Elevation Model allowing the order definition. The plano-altimetric distribution of the treads and the OSL ages of two levels of strath terraces sampled in the field have been correlated along the river longitudinal profile, allowing the estimation of an uplift rate of 2.8 ± 0.2 mm year−1 and 0.42 ± 0.03 mm year−1, respectively upstream and downstream of the Mountain Front Fault. SAR interferometry was used to spot present-day shallow ground displacements associated with the ongoing slope deformation, by processing 279 satellite Sentinel-1 (A and B) radar images of the ascending and descending orbit spanning from 06 October 2014 to 31 March 2019. Different landslide mechanisms were distinguished across the fold axis, rototranslative to lateral spreading interpreted as two different evolutionary stages of the same process transposed spatially through the fold axis. Indeed, the rototranslative mechanism represents an advanced stage of the strain evolution while the lateral spreading is an earlier one. Finally, we infer that the variability in the spatial distribution of the slope deformation styles and patterns in the Lorestan arc is strictly related to the coupled evolution of the drainage system and tectonics. Involved volumes (from 0.6 up to 44 km3), local relief (from 400 up to 2000 m), incision rates (from 0.8 to 2.8 ± 0.2 mm year−1), and persistence time (from 104 to 105 years) represent the most important preparatory conditions and are predisposed by a moderately dipping downslope (from 8 to 25°) sedimentary sequence characterised by units with significantly different rheological behaviour.

Tectonic transport direction of allochthonous units in the northwest of the Central Taurides (Türkiye)

This study aimed to determine the tectonic transport direction in the southeastern Sultandağları Massif based on tectonic structures observed in deformed rocks. The study area, which contains many allochthonous units, is located in the eastern parts of the Isparta Angle and includes part of the Central Taurides. The basement rocks in the study area consist of Permo-Carboniferous metacarbonate and metaclastic alternations. These Paleozoic units are overlain by Mesozoic phyllites, metaconglomerates and metacarbonates above an angular unconformity. These units are tectonically overlain by Late Cretaceous sedimentary and ophiolitic complexes, while these are unconformably overlain by Miocene-Quaternary sedimentary and volcanic rocks. The study area, which presents a giant anticlinorium geometry with NW- SE trend and inverted to the SW on map scale between the settlements of Çay (Afyon) - Yenidoğan (Konya), was deformed at least three times by orogenic movements before the Miocene and gained fold, cleavage, and nappe-thrust structures. With the Alpine orogenic events, the region acquired Type-2 and Type-3 refolded interference patterns and outcrop-scale sheath folds, which are unique to shear zones. The fold axes in the region present a wide range of orientations but dominantly plunge NW and SE. Structural analyses using the Hansen slip method revealed that the allochthonous units were transported from NE to SW along a plane oriented N 10°–40° W and dipping 20°–40° NE in its current location. Other structures also confirm this top to SW tectonic transport direction.

Investigating subduction orogeny dynamics of Manabhum high in the Upper Assam foreland basin, NE India by geophysical data-based modelling

The Manabhum structural high, situated on the southern bank of the Brahmaputra River in the foreland part of the Upper Assam basin, is characterised by an elongated NNW-SSE direction of the fold axis. This study utilises seismic and satellite gravity data to model subsurface geological cross-sections across the Manabhum structure, providing insights into the presence of high-density material at the basement level, supported by the distribution of ophiolites at varying depths. The Manabhum, a compressional structure controlled by the complex folding involved in the Mishmi Hills and Naga Schuppen belt, subjected to compression at different stages, presents an excellent opportunity to understand subduction orogeny involving the collision between the Indian plate and the Tethys oceanic lithosphere subducting beneath the Myanmar continental lithosphere.

Transpression or polyphase deformation along craton margins: Insights from the Archean–Proterozoic boundary near Sudbury, Canada

Continental margins vary in composition and configuration, resulting in complex structural geometries during deformation. One example is the Archean–Proterozoic boundary near Sudbury, Canada, where the Creighton-Victoria Deformation Zone (CVDZ) contains both reverse dip-slip and dextral strike-slip kinematic indicators. To resolve if these structures formed during a single transpression event or multiple overprinting events, the orientation, relative timing and style of the CVDZ are compared to those of adjacent regional structures. Regional fold axes and their axial planar foliation are subparallel to the steeply-plunging stretching lineation and steeply-dipping foliation, respectively, along the CVDZ. Phase equilibria modelling of syn-tectonic staurolite-chloritoid assemblages indicates that the regional folds and foliation formed at 480–565 °C, similar to temperatures estimated for the formation of dip-slip quartz crystallographic preferred orientations (CPO) along the CVDZ. This suggests that the CVDZ, regional folds and foliation formed during the same regional folding and reverse shearing event. Major lateral lithological changes and inflections in the orientation of the craton margin controlled the formation of structures, and evidence for regional transpression, such as strike-slip kinematic indicators, steeply-plunging stretching lineation, and obliquity of regional folds with respect to major shear zones, resulted from polyphase deformation and transcurrent reactivation of the Superior craton margin.

Anisotropic Reversible‐Jump McMC Shear‐Velocity Tomography of the Eastern Alpine Crust

AbstractThe eastern Alpine crust has been shaped by the continental collision of the European and Adriatic plates beginning at 35 Ma and was affected by a major reorganization after 20 Ma. To better understand how the eastern Alpine surface structures link with deep seated processes, we analyze the depth‐dependent seismic anisotropy based on Rayleigh wave propagation. Ambient noise recordings are evaluated to extract Rayleigh wave phase dispersion measurements. These are inverted in a two step approach for the azimuthally anisotropic shear velocity structure. Both steps are performed with a reversible jump Markov chain Monte Carlo (rj‐McMC) approach that estimates data errors and propagates the modeled uncertainties from the phase velocity maps into the depth inversion. A two layer structure of azimuthal anisotropy is imaged in the Alpine crust, with an orogen‐parallel upper crust and approximately orogen‐perpendicular layer in the lower crust and the uppermost mantle. In the upper layer, the anisotropy tends to follow major fault lines and may thus be an apparent, structurally driven anisotropy. The main foliation and fold axis orientations might contribute to the anisotropy. In the lower crust, the N‐S orientation of the fast axis is mostly confined to regions north of the Periadriatic Fault and may be related to European subduction. Outside the orogen, no clearly layered structure is identified. The anisotropy pattern in the northern Alpine foreland is found to be similar compared to SKS studies which is an indication of very homogeneous fast axis directions throughout the crust and the upper mantle.

Regional-scale 3D modelling in metamorphic belts: An implicit model-driven workflow applied in the Pennine Alps

Leveraging a high resolution geological and structural dataset acquired over decades of fieldwork, we build the 3D structural model of a portion of the highly deformed core of the Alpine orogen, in the Northern Aosta Valley. The model represents tectonic contacts separating the tectono-metamorphic units outcropping along the section between Mont Blanc and Monte Rosa, and it covers an area of ca. 1500 km2. The input source data include original 1:10,000 geological surveys synthetised in a 1:75,000 tectonic map, and a dense database of structural stations. After a first orientation statistics study of the structural field database, our workflow develops through structural interpretation in vertical cross-sections that allow including in the modelling process structural drivers such as crosscutting relationships, interference patterns, kinematic constraints and fold morphology from detailed field studies. Three-dimensional interpolation on a tetrahedral mesh using the implicit Discrete Smooth Interpolator method follows, using also foliation and fold axes data as interpolation constraints. After describing the workflow and the model, we discuss the difficulties of modelling in polydeformed metamorphic complexes. In particular, we address the issue of modelling shear zones, refolded, isoclinal and/or recumbent folds and dense networks of faults, that characterise the geology of the Northern Aosta Valley.

Joint Studies In The Western Part Of Ikom-Mamfe Basin, Lower Benue Trough, Nigeria

The Ikom-Mamfe basin, also called the Mamfe embayment, is a bifurcation of the Benue trough in southeastern Nigeria and southwestern Cameroun. The basin is about 130km long, 60km wide basin and is filled with about 4km thick sedimentary rocks. Deformational events led to gentle folding of rocks in the basin and emplacement of magmatic rocks. Systematic and detailed field studies were carried out in eight (8) locations within the study area, in which the orientations of 1437 joints and 102 veins were acquired. Two sets of orthogonal joints observed in the study exhibited symmetry with respect to the directions of the fold axes and were dominated by high-angle dips averaging about 80o. This implies a syntectonic origin of these structures also during their propagation, the maximum principal stress directions (σ1) were orientated in two different directions NW- SE and NNE-SSW for DI and D2 respectively. The relative strength of deformation during DI was greater than D2 and it was also unfolded that the ‘ac’ extension joints trending NW- SE and NNE-SSW hosted relatively thicker veins in both DI and D2. These joints served as better conduits for mineralizing fluids and also most suitable directions for future prospecting.&#x0D;

Reconstructing the stratigraphy and structure of the Alaşehir Graben (Western Anatolia): Evidence for a high-angle origin of the Alaşehir detachment fault and layer-parallel shortening during the Miocene time

Western Anatolia is a well-known continental extension province in the world. The most distinctive structural elements of the region are E-W trending grabens. The Alaşehir Graben forms the boundary between the northern and central parts of the Menderes Massif. It trends E-W from Ahmetli to Turgutlu and NW-SE from Salihli to Alaşehir. This paper documents the outcomes of fieldwork along the southern margin of the Alaşehir Graben between the Salihli and Alaşehir areas.&#x0D; &#x0D; The tectonostratigraphy of the southern margin of the Alaşehir Graben is divided into the footwall and hanging wall of the Alaşehir detachment fault. The footwall comprises the Bayındır and Bozdağ Nappes and the syn-extensional Salihli granitoid intruding the Bayındır Nappe. The hanging wall consists of the Çine Nappe and Neogene-Quaternary sedimentary rocks, and Miocene fills tectonically overlying the Çine Nappe, which is above the Alaşehir detachment fault in the Alaşehir area.&#x0D; &#x0D; Structural data show three types of master fault sets, including (i) the low-angle Alaşehir detachment fault, which is composed of cataclastic rocks; (ii) low-angle normal faults, which are devoid of any cataclastic rocks; and (iii) Plio-Quaternary high-angle normal faults cutting them. Two different low-angle normal faults were coeval and active during the Miocene, and low-angle normal faults were synthetic and antithetic faults of the Alaşehir detachment fault. Their initial position was high-angle and the original position had 55°-75° dip during the Miocene. In the Salihli and Alaşehir segments, several major fold geometries are defined in the footwall and hanging wall of the Alaşehir detachment fault. The fold axis is NE-trending and plunges mainly northeast in the Salihli segment in the footwall of the Alaşehir detachment fault. The other is ~ E–W-trending and plunges mainly west in the Alaşehir segment in the footwall and hanging wall of the Alaşehir detachment fault. They are associated with extensional structures formed by layer-parallel shortening during the Miocene. The Alaşehir detachment fault, as indicated by the difference in fold axes between the Salihli and Alaşehir segments, was cut and back-rotated by Plio-Quaternary high-angle normal faults and tilted to the south.

Structural Architecture and Mineralogical Relationship in Chitradurga Schist Belt, Dharwar Cration, South India

Abstract: The succession in the late Archaean supracrustal belts in the Chitradurga region begins with basal quartz-pebble conglomerates and quartzites which were deposited on a basement of tonalitic--granitic gneisses, ca. 3000 Ma, containing tracts and enclaves of older supracrustal rocks. Thebasal beds are overlain by basic metalavas and amphibolites interbeddedwith crossbedded quartzites and siliceous phyllites. This series passes up into siliceous phyllites, locally containing a large lenticular mass of polymict conglomerate (Talya Conglomerate), overlain by banded iron formations and siliceous phyllites including sporadic chert pebble conglomerates. Greater subsidence in part of the basin accommodated greater thicknesses of basic volcanic and acid pyroclastic rocks, the latter being more abundant at higher levels. With progressive deepening of the whole basin, finegrained, graded greywackes and local polymict conglomerates (Aimangala Conglomerate) were deposited ; the turbidite sequence forms the youngest sedimentary rocks exposed.Estimated total stratigraphic thickness is at least 10 km indeeper parts of the basin. Deformation led to a series of upright anticlines and synclines and relatedLS fabrics with extreme variations in plunge of the coaxial fold axes and Lfabrics within axial surfaces which maintain a steep orientation. Low-grademetamorphism outlasted the deformation. Sedimentation and volcanism in the Chitradurga supracrustal belt is linkedto variable subsidence of the basement foundation, probably as a result of rifting. The structural evolution of the belt followed as a direct continuation of events that controlled the depositional and volcanic history. Variable displacement of the basement during theselate Archaean events in the Karnataka craton took place on shear zones and related fractures that acted as channels for water and CO: asindicated by vein minerals and alteration products. Uplift of basement segments and their distension by granitic diapirs led to deformation of thesupracrustal cover made ductile by its high water content

Deformation Sequence and Paleofluids in Carbonate Buckle Folds Under Transpression (Pag Anticline, External Dinarides, Croatia)

AbstractContractional deformation structures at the front of transpressional orogens display complex three‐dimensional geometries deviating from the interpretative templates commonly applied in thrust belts. Accordingly, detailed constraints on deformation patterns and associated paleofluid circulation are desirable, especially for fracture geometry and permeability predictive purposes. The Pag anticline, which is located in the Dinaric fold and thrust belt, provides an appropriate field site for studying fold‐ and fault‐related deformation structures in a transpressive setting. We performed a multiscale structural analysis together with petrographic and stable isotope characterization of the deformation‐related calcite cements. Structural mapping suggests that the Pag anticline is a detachment fold developed mainly by buckling, since large‐scale thrust faults are absent. Fold tightening in a transpressive setting produced a complex deformational structure including two sets of N‐S right‐lateral and E‐W left‐lateral late‐stage strike‐slip fault sets trending oblique to the NW‐SE fold axis. The pre‐folding deformation pattern includes incipient normal faults likely related to the forebulge stage, veins and stylolites coherent with NE‐SW layer parallel shortening contraction in a strike‐slip regime, and metric to decametric scale conjugate thrusts coherent with layer parallel shortening in a compressive regime. Buckle folding preceded propagation of a series of accommodation structures during fold tightening. Petrographic and isotopic data indicate meteoric alteration of the Cretaceous platform carbonates in the prefolding stage, likely due to forebulge subaerial exposure. Layer parallel shortening and early syn‐folding veins involved formational fluids resulting from mixed marine and meteoric fluids during folding at shallow burial conditions. Eventually, meteoric fluid infiltrated again along strike‐slip faults, acting as cross‐formational conduits in the postfolding stage.

Analogue experiments on releasing and restraining bends and their application to the study of the Barents Shear Margin

Abstract. The Barents Shear Margin separates the Svalbard and Barents Sea from the North Atlantic. During the break-up of the North Atlantic the plate tectonic configuration was characterized by sequential dextral shear, extension, and eventually contraction and inversion. This generated a complex zone of deformation that contains several structural families of overlapping and reactivated structures. A series of crustal-scale analogue experiments, utilizing a scaled and stratified sand–silicon polymer sequence, was used in the study of the structural evolution of the shear margin. The most significant observations for interpreting the structural configuration of the Barents Shear Margin are the following. Prominent early-stage positive structural elements (e.g. folds, push-ups) interacted with younger (e.g. inversion) structures and contributed to a hybrid final structural pattern. Several structural features that were initiated during the early (dextral shear) stage became overprinted and obliterated in the subsequent stages. All master faults, pull-apart basins, and extensional shear duplexes initiated during the shear stage quickly became linked in the extension stage, generating a connected basin system along the entire shear margin at the stage of maximum extension. The fold pattern was generated during the terminal stage (contraction–inversion became dominant in the basin areas) and was characterized by fold axes striking parallel to the basin margins. These folds, however, strongly affected the shallow intra-basin layers. The experiments reproduced the geometry and positions of the major basins and relations between structural elements (fault-and-fold systems) as observed along and adjacent to the Barents Shear Margin. This supports the present structural model for the shear margin.

The design of a double-fold blade wind turbine with flat-plate blade sections

This study presents a double-fold blade wind turbine design with flat plate blade sections that enables the usage of sheet-like materials and a cheaper fabrication method. The purpose of the current study is to analyze the performance of the blades, which are mainly controlled by four factors, namely the root fold-axis, tip fold-axis, root fold, and tip fold angles. The computational fluid dynamics results show that double-fold design configurations outperform single-fold configurations. For example, the highest peak power coefficient for the single-fold case (root fold-axis, root fold, and tip fold angles of 30°, 15°, and 0° respectively) is 0.2018, while it is 0.2565 for the double-fold case (root fold-axis, tip fold-axis, root fold, and tip fold angles of 30°, 30°, 37.5° and 30° respectively). These findings gave new insights into the relationships between the fold axes and fold angles and the power coefficients of the proposed double-fold blade design.

Analysis of Joints Patterns in Albian to Santonian Strata on the Eastern Flank of the Abakaliki Anticlinorium: Implications on Paleostress Conditions and Fluid Flow Properties in an Unconventional Petroleum System

An analysis of joint patterns were carried out on multiple exposures in Albian to Turonian strata belonging to the Abakaliki Formation (Asu River Group) and the Eze-Aku Formation (Eze-Aku Group) on the eastern flank of the Abakaliki Anticlinorium of the Southern Benue Trough. The analysis was carried out using FracPaQ a MATLAB based toolbox for quantification of fracture patterns. The tool was used to calculate fracture density, and intensity of the traces; to quantify scaling distributions, and to determine dilation tendencies, slip tendencies, and to quantify connectivity, and fluid flow directions. Analysis show the presence of two major joint systems: A Major Cross-Fold Joint (CF-J) system -orthogonal to the regional fold axes- consisting of the CF-J1 set trending NW/SE (315&amp;plusmn;5&amp;deg;), and a subordinate Longitudinal Joint System (L-J) -subparallel to the fold axes- consisting of a NE-SW L-j1 set, an ENE-WSW (60&amp;deg;&amp;plusmn;5&amp;deg;) L-j2 set, and an E-W trending L-j3 set. Fracture patterns show intensity and density ranging from 11.2395- 53.3443 m-1 and 85.2747- 629.5928 m-2 respectively. Joints in the NE-SW show high dilation and low slip tendencies given a NW-SE directed maximum principal horizontal stress &amp;sigma;H stress field. The units of the Abakaliki Formation show better connectivity and lower permeability anisotropy as both fracture systems are well developed in those units. These joints, having formed in the period leading up to the Santonian inversion would have been ideal conduits for migration and flow of hydrocarbon and mineral fluids. The Cross-Fold System precedes the folding episode in the Santonian period and is likely a result of overpressure conditions due to disequilibrium compaction in the Albian- Turonian strata in an initial compressive regional tectonic stress field. The Longitudinal System formed later and is related to the outer-arc flexure of the folded units taking advantage of the nascent cleavage structures in the folded shale units.