Fold Interference Research Articles

Gold concentration during polyphase deformation: Insights from Boulanger Project, French Guiana

The Boulanger gold deposit is hosted within the Rhyacian greenstone belts from the Guiana shield located within the North Guiana Through, French Guiana. The Boulanger deposit is characterized by a complex polyphase deformation and mineralization history involving a coaxial shortening phase, D1, followed by a transcurrent deformation event, D2. The main ore bodies consist of a series of quartz-tourmaline-pyrite-carbonate extension and shear veins in response to NNE-SSW shortening event (D1), and adjacent altered host-rocks. The proximal alteration bordering the vein system is characterized by pyrite-tourmaline (main ore assemblage). This shortening event is followed by transcurrent deformation, D2. Locally, D2 is expressed by the formation of N020-030 narrow zones (F2 axial trace) along which D1 structures are reoriented. The structural analysis performed on both S1/0 foliation and on geophysical data interpretation highlights the presence of Type-1 interference patterns. These zones are associated with significant gold enrichment and the presence of a new ore assemblage dominated by pyrrhotite-pyrite. Quantitative structural analysis approach, based on measured foliations (S1/0) and gold grade demonstrates that D2-related folding is associated with important gold endowment. These findings suggest that the characterization of the exact fold interference pattern is fundamental for the targeting of favorable enriched zones at the deposit scale.

Enhanced structural analysis through a hybrid analogue-digital mapping approach: Integrating field and UAV survey with microtomography to characterize metamorphic rocks

This study focused on collecting structural data orientations of a crustal-scale shear zone (Palmi Shear Zone, PSZ, southern Calabria, Italy) by integrating various analytical and field-based techniques. The PSZ consists of deformed metamorphic rocks (migmatitic biotitic paragneiss, marbles, and skarns) showing multiple folding phases, and Hercynian tonalites and pegmatites (306-290 Ma), crosscut by Late Hercynian leucocratic dykes (ca. 290 Ma). Multi-sized clasts composed of different lithologies are preserved on clean outcrop surfaces, and are sheared into both σ - and δ -type objects that collectively suggest opposing senses of shear. The study incorporates structural analysis of folds, field and aerial surveys (UAV), digital mapping, and microcomputed tomography. Various kinematic indicators were observed in the PSZ, indicating a mix of factors influencing the shear strain patterns (e.g. fold interference patterns, different rock types with high viscosity contrast). The findings suggest a clear consistency between structural data inferred from 3D VOM (Virtual Outcrop Model) and those collected directly in the field, confirming the occurrence of both sinistral and dextral shear in the PSZ, providing important insights into the tectonic evolution of the Calabrian-Peloritani Terrane.

Formation of a dome-and-basin fold interference pattern by granite intrusions

Folding of layered sequences is influenced by the presence of igneous intrusions, which form competent bodies that control fold distribution. Here, we show an example from the Broken River Province (northeastern Australia), where macroscopic folding affected sedimentary rocks and felsic intrusions, forming a dome-and-basin pattern. Field relations indicate synkinematic emplacement of the granitic intrusions, which occur as folded sill-like microgranitic bodies, mildly deformed stocks at structural domes, and undeformed granite that cuts across the folded sedimentary sequence. U-Pb zircon ages from the various intrusions yielded an age range of 335−320 Ma, thus constraining the timing of folding. The deformed zone is restricted to an ∼30-km-wide corridor bounded by two crustal-scale shear zones. Kinematic indicators show that folding was generated by dextral transpression, giving rise to the dominant orientation of folds. Domes and basins are generally concentrated in the proximity of the granitic intrusions, indicating that their development was likely controlled by the synkinematic emplacement of these plutons. The volume of granite added to the exposed section could have altered the local strain regime, switching the horizontal stretching direction during transpression to a shortening direction. We therefore suggest that forced intrusion of synkinematic plutons into a confined transpressional zone (dominated by flattening strain) can create local constrictional strain where shortening occurs in two broadly orthogonal horizontal directions. The results demonstrate a link between Carboniferous granitic dome-and-basin patterns and syn-transpressional magmatism. It is plausible that similar processes were responsible for the development of granitic dome-and-basin patterns in Archean terranes.

Functional small peptides for enhanced protein delivery, solubility, and secretion in microbial biotechnology.

In microbial biotechnology, there is a constant demand for functional peptides to give new functionality to engineered proteins to address problems such as direct delivery of functional proteins into bacterial cells, enhanced protein solubility during the expression of recombinant proteins, and efficient protein secretion from bacteria. To tackle these critical issues, we selected three types of functional small peptides: cell-penetrating peptides (CPPs) enable the delivery of diverse cargoes into bacterial cytoplasm for a variety of purposes, protein-solubilizing peptide tags demonstrate remarkable efficiency in solubilizing recombinant proteins without folding interference, and signal peptides play a key role in enabling the secretion of recombinant proteins from bacterial cells. In this review, we introduced these three functional small peptides that offer effective solutions to address emerging problems in microbial biotechnology. Additionally, we summarized various engineering efforts aimed at enhancing the activity and performance of these peptides, thereby providing valuable insights into their potential for further applications.

Petrochronologic constraints on inverted metamorphism, terrane accretion, thrust stacking, and ductile flow in the Gneiss Dome belt, northern Appalachian orogen

AbstractGneiss domes are an integral element of many orogenic belts and commonly provide tectonic windows into deep crustal levels. Gneiss domes in the New England segment of the Appalachian orogen have been classically associated with diapirism and fold interference, but alternative models involving ductile flow have been proposed. We evaluate these models in the Gneiss Dome belt of western New England with U‐Th‐Pb monazite, xenotime, zircon, and titanite petrochronology and major and trace element thermobarometry. These data constrain distinct pressure–temperature–time (P‐T‐t) paths for each unit in the gneiss dome belt tectono‐stratigraphy. The structurally lowest units, Laurentia‐derived migmatitic gneisses of the Waterbury dome, document two stages of metamorphism (455–435 and 400–370 Ma) with peak Acadian metamorphic conditions of ~1.0–1.2 GPa at 750–780°C at 391 ± 7 to 386 ± 4 Ma. The next structurally higher unit, the Gondwana‐derived Taine Mountain Formation, records Taconic (peak conditions: 0.6 GPa, 600°C at 441 ± 4 Ma) and Acadian (peak: 0.8–1.0 GPa, 650°C at 377 ± 4 Ma) metamorphism. The overlying Collinsville Formation yielded a 473 ± 5 Ma crystallization age and evidence for metamorphic conditions of 650°C at 436 ± 4 Ma and 1.2–1.0 GPa, 750–775°C at 397 ± 4 to 385 ± 6 Ma. The structurally higher Sweetheart Mountain Member of the Collinsville Formation yielded only Acadian zircon, monazite, and xenotime dates and evidence for high‐pressure granulite facies metamorphism (1.8 GPa, 815°C) at circa 380–375 Ma. Cover rocks of the dome‐mantling The Straits Schist records peak conditions of ~1 GPa, 700°C at 386 ± 6 to 380 ± 4 Ma. Garnet breakdown to monazite and/or xenotime occurred in all units at circa 375–360 and 345–330 Ma. Peak Acadian metamorphic pressures increase systematically from the structurally lowest to highest units (from 1.0 to 1.8 GPa). This inverted metamorphic sequence is incompatible with the diapiric and fold interference models, which predict the highest pressures at the structurally lowest levels. Based upon P‐T‐t and structural data, we prefer a model involving, first, circa 380 Ma thrust stacking followed by syn‐collisional orogen parallel extension, ductile flow, and rise of the domes between 380 and 365 Ma. Garnet breakdown at circa 345–330 Ma is interpreted to reflect further exhumation during collapse of the Acadian orogenic plateau. These results highlight the power of integrating petrologic constraints with paired geochemical and geochronologic data from multiple chronometers to test structural and tectonic models and show that syn‐convergent orogen parallel ductile flow dramatically modified earlier accretion‐related structures in New England. Further, the Gneiss Dome belt documents gneiss dome development in a syn‐collisional, thick crust setting, providing an ancient example of middle to lower crustal processes that may be occurring today in the modern Himalaya and Pamir Range.

The Late Mesozoic Intracontinental contraction–Extension Transition in the Beishan Fold‐Thrust Belt, Central Asia: Constraints From Structural Analysis and Apatite (U–Th)/He Thermochronology

AbstractThe late Mesozoic Beishan fold‐thrust belt occupies a key position in central Asia, figuring importantly in our understanding of intracontinental deformation in response to far‐field plate‐boundary forces. To determine when and how the Beishan fold‐thrust belt was developed, we conducted detailed field mapping, structural analysis, and apatite (U–Th)/He (AHe) thermochronology in the Hongliudaquan area, southeastern Beishan Range. The study area exposes the Hongliudaquan fold and thrust system, consisting of the southern Hongliudaquan thrust nappe and autochthonous fold sets. The nappe experienced >16 km northward thrust‐induced translation. The autochthonous fold sets strongly deformed Lower–Middle Jurassic strata showing diverse trends of kilometer‐scale basins and ranges. We interpret that this fold interference pattern was produced in a constrictional deformation field, which underwent synchronous shortening in two orthogonal directions. This stain history was related to synchronous imbricate thrusting, duplex formation, and strike‐slip faulting at different structural levels. Restoration of the Hongliudaquan fold and thrust system yields a minimum of ∼27% (∼10.1 km) north–south shortening strain. Thrusting and nappe emplacement within the Beishan fold‐thrust belt may have started in the late Middle Jurassic and persisted until the Early Cretaceous (∼140–133 Ma). Our AHe data also record ∼124–115 Ma cooling related to footwall exhumation during subsequent normal faulting, indicative of the late Mesozoic intracontinental contraction–extension transition. The Beishan fold‐thrust belt initiated in central Asia via the late Mesozoic reactivation of the Paleozoic–early Mesozoic Beishan orogen as a result of the far‐field responses to multi‐directional plate convergence around Asia.

Fold interference pattern and crustal decoupling in northern Tanzania

High-temperature granulite facies metamorphism and deformation evolved through Neoproterozoic tectonic processes in large parts of southeastern Africa. The Eastern Granulites of Tanzania, one example for these extreme conditions, show progressive decoupling between lower and middle crust together with progressive cooling and rheology stratification. Coupled deformation during earliest stages of deformation arises from extremely small viscosity contrast of all minerals and rocks at granulite facies metamorphic conditions around 850 °C. With cooling of the orogen rheology stratification increases and deformation decouples into horizontal stretching through gravity driven channel flow in the lower crust and thickening and horizontal west-east shortening in the middle/upper crust. As soon as a stiff and cold indenter, represented by external parts of the Archean Tanzania Craton (Western Granulites) enters the system, the indenter acts as lower crustal ramp along which deep crustal units are exhumed and displaced towards the foreland. During this orogenic period the crust was fully stratified and a second phase of decoupling, detachment over crustal scale ramp, occurs. Superposition with late orogenic north-south shortening structures resulted in type 1 fold interference pattern and formation a of dome-and-basin geometry in northeastern Tanzania. Structural modelling of fold superposition helps to explain the complex structural pattern and to predict sites of decollement horizons. By comparison with fold interference pattern exposed in southern Madagascar we define different types of dome-and-basin formation. Those with neglectable rheology contrast are viscosity determined where mixing of upper and lower crustal material is enabled by vertical flow folding. Those with strong viscosity contrast are mechanically determined where domes and basins are formed by changes in regional principal stress directions.

Differential fold interference patterns in an intracontinental orogen: Insights from superposed buckle folding in southern Jiangxi Province, South China Block

The South China Block (SCB) experienced multi-stage tectono-magmatic events during the Mesozoic, forming a broad and episodic intracontinental orogenic belt. It is controversial whether the driving force of the Mesozoic intracontinental orogeny in the SCB is related to the far-field effects of plate convergence. To better understand the driving mechanism of intracontinental orogeny, we conducted a detailed structural investigation of the Xingguo area in southern Jiangxi Province, located in the central part of the SCB. Two regional-scale buckling superposed folds were identified as the Chayuan arcuate syncline of the fold axis protruding to the north (Type 2a interference pattern) and the Xiefang syncline of the fold axis extending NW–SE (Type 1d interference pattern). Although there are differences in fold interference patterns, the Chayuan arcuate syncline and Xiefang syncline were formed by the superimposition of the Middle–Late Triassic NE–SW shortening and the Middle–Late Jurassic nearly E–W shortening. This phenomenon of the differential fold interference patterns in the same tectonic setting is determined by the difference in geometric characteristics of their initial folds. Combined with the variation of the Mesozoic paleostress field, it is considered that the Mesozoic intracontinental orogeny in the SCB is mainly controlled by the far-field stress propagation generated by plate interactions. Based on the analysis of tectonic architecture, we propose that the Mesozoic tectonic evolution of the SCB experienced a transformation from multi-plate convergence in the Triassic to Andean-type subduction in the Jurassic. This tectonic transformation finally resulted in the reactivation of the Precambrian multi-terrane collage of the SCB.

Double-folding and thrust-front geometries associated with the Timanian and Caledonian orogenies in the Varanger Peninsula, Finnmark, North Norway

On Varanger Peninsula, the roughly NW–SE-trending Trollfjorden–Komagelva Fault Zone separates Neoproterozoic successions that accumulated in a shallow-marine platformal domain to the SW of the fault from deep-marine basinal to deltaic sediments to the NE. In Ediacaran time the fault scarp acted as a buttress in a period of basinal inversion during the top-to-the-SW, contractional Timanian orogeny. During the subsequent, top-to-the-SE to -ESE, polyphase Caledonian orogenesis the fault acted as a dextral strike-slip megafracture and lateral ramp. In the northeastern terrane, Timanian and Caledonian fold interference has produced several examples of double-folding and intersecting cleavages. In the southwestern terrane, the Lower Allochthon Gaissa Thrust Belt overlies the Parautochthon, below which a 45 km long deformation front has been mapped. Tectonic shortening within this frontal zone varies from top-to-the-SSE in the west to top-to-the-ESE in the east. Imbricate thrust sheets disrupt the succession in the northeastern terrane, below which a floor décollement is speculated to emerge as a frontal fault along a prominent footwall of the precursor fault that acted on the seabed in outermost Varangerfjorden. By use of potential field data, the Caledonian structures on Varanger can be followed to the north into the Barents Sea where the nappe pile in the pre-Carboniferous basement reaches a thickness of several kilometres. Thematic collection: This article is part of the Fold-and-thrust belts collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-belts

Structural analysis of layered evaporites using internal deformation patterns: Examples from Santos and Campos basins, Brazil

The Santos and Campos basins, offshore southeastern Brazil, contain layered evaporite sequences (LES) deposited during the Late Aptian, marking the end of lacustrine and beginning of restricted marine conditions. Density and velocity differences between evaporite minerals such as halite, anhydrite, carnalite, tachyhydrite and other bittern salts result in strong seismic impedance contrasts and therefore enable excellent stratal imaging of internal salt deformation. Different acoustic responses allow a detailed analysis of the internal deformation of evaporites, with the corresponding mechanical properties providing constraints on regional salt flow in the Santos and Campos basins. Detailed mapping and analysis of deformed LES support conclusions from cross-section restorations and provide insight on local salt flow and deformation mechanisms. This study utilizes kinematically restored regional sections to characterize overall basin-wide salt flow, while leveraging salt facies and their control on internal salt fold styles to demonstrate localized salt deformation. The important results from this study are the following. a) Santos and Campos basins are linked extension-contraction systems, however pre-existing basin-wide changes in paleo-topography represents a fundamental control in the overall salt flow, accounting for much of the downdip contraction in the middle of the basins rather than the toe of the system. b) Salt mobilization due to gravity initiated early and there is evidence that it was contemporaneous with evaporite deposition in many parts of the basins. Intrasalt unconformities and stratigraphic features are presented to support this conclusion. c) Mechanical stratigraphy within the LES play an important role in controlling intra-salt structural styles, and their fold interference patterns can be used to understand salt deformation in great detail. These results can be applied to better investigate a spectrum of salt tectonic problems in the basins and elsewhere, such as regional and localized salt flow, sub-regional prediction of weld kinematics and local prediction of weak salt units for drilling hazard analysis.

Along-strike variation of fault-related inversion folds within curved thrust systems: The case of the Central-Northern Apennines of Italy

The along-strike variation of fault-related inversion folds within curved thrust systems is documented by presenting cases from the Central-Northern Apennines of Italy. Fold structures are reconstructed by integrating geological field data and structural restoration of various key balanced cross-sections, which are also constrained by the detailed interpretation of panoramic views, geological field mapping, and structural analysis. The lateral variation from fault-bend to fault-propagation folding is promoted by selective reverse reactivation of precursor, mainly rift-related, normal faults preferentially located along the oblique and frontal ramps. Their space variability is identified within single curved thrust systems of three different size testifying a scale-invariant phenomenon. Fault-bend reactivation and fault-propagation shortcut folding produce a characteristic fold interference pattern at the salient apex of the curved thrust system. The transition style depends on the pattern of the inherited normal fault template and on the amount of shortening achieved in the salient zone. The modest amount of shortening resulting from fault-related inversion folding along regional curved thrust systems is consistent with a basement-involved thick-skinned thrusting style. Recognition of fault-related inversion fold styles and of their along-strike variations represents a useful predictive tool when unravelling the kinematic evolution of curved orogenic belts resulting from positive inversion. Inversion fold development modes and their diagnostic features are also important for investigations of subsurface Earth resources.

Post-Oligocene evolution of Indo-Burma wedge: Insights from deformation structures of Tripura Mizoram fold belt

The Tripura Mizoram fold belt (TMFB) belongs to the widest segment of the outer wedge of Indo-Burma Wedge (IBW). The structure of the outer wedge is characterized by a series of north-south trending anticlines-and-synclines of varying tightness, which progressively decreases towards the foreland direction. To explain their development, earlier workers proposed the model of fault-related folding, assuming that crustal shortening between India and Burma occurred dominantly by brittle deformation. However, our field investigations in TMFB reveal imprints of unequivocal ductile deformation, including interference of folds. Based on new structural map coupled with outcrop-scale structures, we recognize the existence of multi-ordered folds in the Neogene sequence of TMFB. However, the complexity of folding increases toward the hinterland part of wedge. We substantiate the spatial variations of penetrative ductile structures of TMFB with laboratory experiments under oblique convergence. Model results show consistency with the existence of along-strike variations of deformation intensity in the outer wedge of IBW, which gradually increases southward with narrowing the width of the wedge. Combining our field observations and laboratory experiments with earthquake focal depth distributions around TMFB, we propose that stratigraphic horizons of the entire outer wedge are mechanically weak to have deformed dominantly by brittle faulting.

Thermostability Engineering of a Class II Pyruvate Aldolase from Escherichia coli by in Vivo Folding Interference

The use of enzymes in industrial processes is often limited by the unavailability of biocatalysts with prolonged stability. Thermostable enzymes allow increased process temperature and thus higher substrate and product solubility, reuse of expensive biocatalysts, resistance against organic solvents, and better “evolvability” of enzymes. In this work, we have used an activity-independent method for the selection of thermostable variants of any protein in Thermus thermophilus through folding interference at high temperature of a thermostable antibiotic reporter protein at the C-terminus of a fusion protein. To generate a monomeric folding reporter, we have increased the thermostability of the moderately thermostable Hph5 variant of the hygromycin B phosphotransferase from Escherichia coli to meet the method requirements. The final Hph17 variant showed 1.5 °C higher melting temperature (Tm) and 3-fold longer half-life at 65 °C compared to parental Hph5, with no changes in the steady-state kinetic parameters. Additionally, we demonstrate the validity of the reporter by stabilizing the 2-keto-3-deoxy-l-rhamnonate aldolase from E. coli (YfaU). The most thermostable multiple-mutated variants thus obtained, YfaU99 and YfaU103, showed increases of 2 and 2.9 °C in Tm compared to the wild-type enzyme but severely lower retro-aldol activities (150- and 120-fold, respectively). After segregation of the mutations, the most thermostable single variant, Q107R, showed a Tm 8.9 °C higher, a 16-fold improvement in half-life at 60 °C and higher operational stability than the wild-type, without substantial modification of the kinetic parameters.

Disome-seq reveals widespread ribosome collisions that promote cotranslational protein folding

BackgroundThe folding of proteins is challenging in the highly crowded and sticky environment of a cell. Regulation of translation elongation may play a crucial role in ensuring the correct folding of proteins. Much of our knowledge regarding translation elongation comes from the sequencing of mRNA fragments protected by single ribosomes by ribo-seq. However, larger protected mRNA fragments have been observed, suggesting the existence of an alternative and previously hidden layer of regulation.ResultsIn this study, we performed disome-seq to sequence mRNA fragments protected by two stacked ribosomes, a product of translational pauses during which the 5′-elongating ribosome collides with the 3′-paused one. We detected widespread ribosome collisions that are related to slow ribosome release when stop codons are at the A-site, slow peptide bond formation from proline, glycine, asparagine, and cysteine when they are at the P-site, and slow leaving of polylysine from the exit tunnel of ribosomes. The structure of disomes obtained by cryo-electron microscopy suggests a different conformation from the substrate of the ribosome-associated protein quality control pathway. Collisions occurred more frequently in the gap regions between α-helices, where a translational pause can prevent the folding interference from the downstream peptides. Paused or collided ribosomes are associated with specific chaperones, which can aid in the cotranslational folding of the nascent peptides.ConclusionsTherefore, cells use regulated ribosome collisions to ensure protein homeostasis.

The enigmatic curvature of Central Iberia and its puzzling kinematics

Abstract. The collision between Gondwana and Laurussia that formed the latest supercontinent, Pangea, occurred during Devonian to early Permian times and resulted in a large-scale orogeny that today transects Europe, northwest Africa, and eastern North America. This orogen is characterized by an “S” shaped corrugated geometry in Iberia. The northern curve of the corrugation is the well-known and studied Cantabrian (or Ibero–Armorican) Orocline and is convex to the east and towards the hinterland. Largely ignored for decades, the geometry and kinematics of the southern curvature, known as the Central Iberian curve, are still ambiguous and hotly debated. Despite the paucity of data, the enigmatic Central Iberian curvature has inspired a variety of kinematic models that attempt to explain its formation but with little consensus. This paper presents the advances and milestones in our understanding of the geometry and kinematics of the Central Iberian curve from the last decade with particular attention to structural and paleomagnetic studies. When combined, the currently available datasets suggest that the Central Iberian curve did not undergo regional differential vertical-axis rotations during or after the latest stages of the Variscan orogeny and did not form as the consequence of a single process. Instead, its core is likely a primary curve (i.e., inherited from previous physiographic features of the Iberian crust), whereas the curvature in areas outside the core is dominated by folding interference from the Variscan orogeny or more recent Cenozoic (Alpine) tectonic events.

Thermostability enhancement of the Pseudomonas fluorescens esterase I by in vivo folding selection in Thermus thermophilus.

Prolonged stability is a desired property for the biotechnological application of enzymes since it allows its reutilization, contributing to making biocatalytic processes more economically competitive with respect to chemical synthesis. In this study, we have applied selection by folding interference at high temperature in Thermus thermophilus to obtain thermostable variants of the esterase I from Pseudomonas fluorescens (PFEI). The most thermostable variant (Q11L/A191S) showed a melting temperature (Tm ) of 77.3 ± 0.1°C (4.6°C higher than the wild-type) and a half-life of over 13 hr at 65°C (7.9-fold better than the wild-type), with unchanged kinetic parameters. Stabilizing mutations Q11L and A191S were incorporated into PFEI variant L30P, previously described to be enantioselective in the hydrolysis of the (-)-enantiomer of the Vince lactam. The final variant Q11L/L30P/A191S showed a significant improvement in thermal stability (Tm of 80.8 ± 0.1°C and a half-life of 65 min at 75°C), while retaining enantioselectivity (E > 100). Structural studies revealed that A191S establishes a hydrogen bond network between a V-shaped hairpin and the α/β hydrolase domain that leads to higher rigidity and thus would contribute to explaining the increase in stability.

Aerial interference of Hercynian folds and their morphological peculiarities in the Bani Geopark of southern Morocco

The Bani Geopark of southern Morocco belongs to the chain of Anti-Atlas; it is characterized by a very heterogeneous ductile deformation, materialized by the succession of two Hercynian folding phases. The latter were controlled by Precambrian basement fractures that played into normal faults that replayed in reverse faults at the end of the Hercynian orogeny. It will be shown that this adaptation of the base to the cover propagates and amortizes laterally and vertically, giving rise to a very heterogeneous deformation. In the Tata-Akka region, the interference of these two phases of folding is spectacular in aerial view. In several places, it has generated structural patterns, some of which are known as “egg tray,” which show a great diversity of relief shapes after erosion processes. Other interference patterns recall the shape of mushrooms belonging to the second type according to the Ramsay classification. Of these facts, it presents a scientific interest for the researchers, esthetic for the geotourism, and educational in the field of Earth sciences. In this work, we will first highlight the general characteristics of the two phases of folding in the Tata-Akka area; then, we will try, through a scientific mediation, in a tourist perspective, to understand the origin, singularity, and value of forms of relief involved in this type of deformation. It is also a question of showing the pedagogical integration concerning the close relations between the folded geological structure and the formation of relief in the potential tourist circuits of the Bani Geopark of southern Morocco.

Fold interference patterns in Meso-Proterozoic Champaner fold belt (CFB) Gujarat, western India

This paper documents three phases of folding within the Meso-Proterozoic Champaner Fold Belt (CFB) located at the eastern part of Gujarat, western India. The first phase ( $$\hbox {F}_{1})$$ displays WNW plunging $$\hbox {F}_{1}$$ fold of moderately inclined nature in the schists of the Khandia Formation. The second phase ( $$\hbox {F}_{2})$$ refolded $$\hbox {F}_{1}$$ along a similar trend to produce folds of tight isoclinal nature in the Khandia and Narukot quartzites. Additionally, these $$\hbox {F}_{1}$$ folds depict second-order tight, and $$\hbox {F}_{2}$$ folds as first-order open type in the younger sequences of the CFB with varying amplitude vs. wavelength ratio. The ratio for $$\hbox {F}_{1}$$ folds ranges from 2:1 to 3:1, obtained along 3–4 m length across 3–6 $$\hbox {m}^{2}$$ area, whereas for $$\hbox {F}_{2}$$ folds the ratio ranges from 1:4 to 1:5 and is obtained along 1–2.5 km length across 0.5–1.5 km $$^{2}$$ area. The fold interference pattern developed on account of $$\hbox {F}_{1}$$ and $$\hbox {F}_{2 }$$ folds has resulted into Type-III or hook-shaped geometry regionally. The last phase of folding is characterised by N–S trending $$\hbox {F}_{3}$$ folds of open type over kilometre long limbs of $$\hbox {F}_{1}$$ and $$\hbox {F}_{2}$$ folds. The superposition of $$\hbox {F}_{1-3 }$$ folds developed map scale Type-I or Dome and Basin geometry over Type-III superposed folds. The overall compressional direction for $$\hbox {F}_{1}$$ and $$\hbox {F}_{2}$$ folds ranges from N–S to NNE–SSW and for $$\hbox {F}_{3}$$ ranges from E–W to ESE–WNW.

Interference fold patterns in regional unidirectional stress fields: A result of local kinematic interactions

Folds are commonly found in association with ductile shear zones. However, superimposed folding contemporaneous with shearing is rarely reported. Here, we describe a macroscopic fold interference pattern with geometry intermediate between types 1 and 2 related to development of adjacent transcurrent shear zones. The interference fold pattern is located in a compartment bounded, on the eastern side, by an ENE-trending, dextral shear zone that connects with a NE-trending, sinistral shear zone, and, on the western side, by a NE-trending sinistral shear zone. A first folding episode produced NW-trending, SW-verging inclined folds and a later one NE-trending, upright folds. Folds of the first event are attributed to a local contractional strain field induced by the growth of the shear zones with opposed kinematics whereas the later folding episode and nucleation of the western shear zone reflects regional NW-SE contraction. Folding of a macro-scale NW-trending fold by NE-trending folds produced the fold interference structure. In contrast with most cases of types 1 and 2 fold interference patterns, in the present case no change on the orientation of regional stress axes is required.

Superimposed deformation of the Solonker Belt and nearby regions in western Inner Mongolia, China

AbstractThe deformation of the Solonker Belt and nearby regions is helpful for understanding the tectonic evolution of the Central Asian Orogenic Belt. This study carried out structural analysis in the Mandula and Ganqi areas of western Inner Mongolia, including the Solonker Belt, the Southern Orogenic Belt and the northern Yinshan Belt (Langshan range). Our results reveal that the Solonker Belt, the Southern Orogenic Belt and the northern Yinshan Belt underwent two stages (D1 and D2) of deformation during the Mesozoic period. The D1 stage produced the NNE-directed thrusts and asymmetric folds, indicating a NNE–SSW contraction. The northern Yinshan Belt, the Southern Orogenic Belt and the Solonker Belt formed as a series of NNE-verging tectonic nappes. The D2 stage developed the NE-trending folds and the SE- or NW-directed thrusts that cross-cut the D1 structures. The two events of nearly orthogonal or oblique shortening gave rise to the superimposed structures (e.g. fold interference patterns). The quartz veins that filled the fractures of the D1 deformation contain zircons of Middle Triassic U–Pb ages. The new dating data, along with the regional sedimentary hiatus, led us to infer that the D1 stage of deformation occurred in Middle Triassic time and the D2 stage occurred in Late Jurassic time. We consider that the D1 stage of deformation resulted from a convergent event, which might be related to the closure of the Palaeo-Asian Ocean or limited, narrow ocean basins; and the D2 stage of deformation was the far-field result of subduction of the Palaeo-Pacific Ocean and the closure of the Mongol-Okhotsk Ocean.