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The sources of shallow slow earthquakes at subduction zone fronts remain unclear, but are commonly attributed to faults and shear zones. Structural studies of modern and ancient shallow accretionary prisms — wedge-shaped stacks of sediments and volcanic deposits scraped from subducting slabs and accreted onto the overriding plates at convergent plate boundaries — document a plethora of brittle structures associated with metres to plurikilometre-scale overturned and recumbent folds. These folds are the product of rock buckling and shearing at the front of subduction zones. At present, such structures are not commonly considered in models of the dynamics of accretionary wedges at the timescale of the seismic cycle, instead focusing on the role played by slip on major faults. Here we argue that fold-related brittle structures might also be associated with transient deformation events at elevated strain rates and in the presence of high fluid pressure. They have the potential to cause distributed microearthquake swarms occurring under low effective normal stress in accretionary prisms, and to affect the distribution of surficial displacement. Folding-related brittle deformation structures in accretionary wedges may contribute to shallow seismicity in subduction zones, according to a compilation of structural evidence.

Petrographical and geochemical data from the Togo structural unit (TSU), also referred to as the Atacora structural unit, are presented together with the existing dataset; geochemical and age data from the sedimentary and metasedimentary rocks from the passive margin sequences of the Dahomeyide belt in Ghana to infer their provenance and depositional setting and expand the discussion on the Rodina–Gondwana supercontinent assembly during the Pan-African orogeny. The metasedimentary rocks of the TSU are quartzites and phyllites. The framework grains of the quartzites consisting dominantly of quartz and small amounts of feldspar grains and relict lithic fragments classify them as quartz arenite, subarkose and sublitharenite. Generally, the studied rocks show similar rare-earth element and multi-element patterns, which imply derivation from similar sources. Elemental ratios, including (La/Lu)N, Th/Sc and La/Sc, suggest sediments sourced from intermediate to felsic rocks. Provenance and depositional setting indicators of the TSU suggest deposition in a passive margin setting, with the West African and Amazonian cratons’ granitoids and granitic gneisses as possible provenance, akin to siliciclastic rocks of the Buem structural unit and the Voltaian Supergroup of the Volta Basin. The deformational history of the TSU is similar to those of the Buem structural unit and the eastern margin of the Voltaian Supergroup, indicating the effect of the Pan-African orogeny on the passive margin of the Dahomeyide belt. We, therefore, propose the formation and evolution of a Neoproterozoic passive margin unit, which was tectonically deformed during the Rodinia–Gondwana supercontinent cycle.

Fotouni-Kékem shear zone (FKSZ) and the Nyakong-Manyi shear zone (NMSZ) are respectively located to southwest and northwest of the N50E branch of the central Cameroon shear zone (CCSZ). Three deformation phases are recorded in these shear zones including, D 1 , D 2 and D 3 . The D 1 phase, with σ 1 applied in the NE-SW direction, is remnant and poorly represented, whose structures (NW–SE S 1 foliation) were transposed by the late D 2 and D 3 phases related structures. The D 2 phase is an early sinistral shear phase, with σ 1 applied in the WNW-ESE direction, which developed NNW-SSE to NNE-SSW S 2 foliation, B 2 shear band boudins, F 2 knee-like folds and asymmetric fish-like structures. The D 3 phase is a NE-SW dextral mylonitic shear phase, with σ 1 applied in the NW–SE direction, responsible the development of S 3 foliation, P 3 recumbent and overturn folds, B 3 shear band boudins, σ-type sigmoids and asymmetric amphibole fishes. Pyroxene amphibolite (PA) occurs as slab stones, banded to lens-like, egg-like enclaves, folded bands, sheared and/or boudinaged green to dark green rocks displaying NE-SW preferred orientation. It displays heterogranular nematoblastic texture marked by amphibole (60%, hornblende), plagioclase (≈20%) and clinopyroxene (15 à 20%) porphyroblasts dispersed in between medium-grained mineral showing preferred orientation. Under microscope, PA evidenced a polyphasic prograde-peak-retrograde high-grade regional metamorphism. Prograde-peak phase is evidenced by primary mineral paragenesis (stable amphibole + pyroxene + plagioclase + K-feldspar) and microstructures, which indicate granulite facies. This occurs during the D 1 deformation phase. retromorphic relic-like pyroxene crystals displaying amphibole-plagioclase-quartz-opaque minerals assemblage, which follows the peak metamorphism, related to relaxation during D 2 - D 3 , evidence retrograde phase. Early sinistral syn- D 2 and late dextral syn- D 3 mylonitic events, whose microstructures evidence high-grade deformation setting, overprinted this regional metamorphism. This polyphasic activation of the CCSZ during these mylonitic events ( D 2 - D 3 ) stretched, sheared, folded dismembered and scattered amphibolites along the Pan-African mobile zone during late phases of the Pan-African orogeny. Geochemical data indicate that PA derives from mafic protoliths originating from a garnet lherzolite reservoir melting that was contaminated by both subducted sediment and slab-derived fluids as evidenced by the slightly positive ƐNd 600Ma (+ 1.27). The model age (T DM  = 1.25 Ga) with initial 87 Sr/ 86 Sr ratios of 0.70488 suggest an ancient Mesoproterozoic crust that underwent metamorphic transformation during the collisional (burial) and post collisional (exhumation) stapes of the Pan-African orogeny.

The South Indian Granulite Terrane is traversed by several crustal scale shear zones, however the tectonic significance of the shear zones are poorly understood. The tectonic relevance of the Bavali Shear Zone (BSZ) ‒ in the WNW extremity of the Moyar Shear Zone ‒ at the interface between the Paleoarchean to Neoarchean Western Dharwar Craton (WDC) in the north and the late Neoarchean Nilgiri block in the south is poorly constrained. The most conspicuous feature in the WDC is a set of N-striking gently-plunging upright folds and N-striking dextral shear zones (deformation D 4 ). These D 4 structures are superposed on a shallowly-dipping D 3 recumbent folds and gently-dipping mylonite fabrics in a suite of anatectic gneisses, lower-grade supracrustal rocks and foliated granitoids. In regional scale, the D 3 fold axes curve into the WNW-striking BSZ (D 5 deformation), a steep-dipping transpressional shear zone with dextral kinematics. The BSZ is characterized by steeply-plunging stretching lineations sub-parallel to the hinges of reclined folds on the pre-shearing fabrics in the lithologies of the adjacent cratons. Syn-D 5 charnockite veins suggest the BSZ formed at T > 850 °C. Existing U–Pb (zircon) dates and monazite chemical dates (this study), indicate that the deformation-metamorphism-magmatism in the WDC and the Nilgiri block occurred between 3400 and 2500 Ma; by contrast the high-T D 5 oblique crustal shortening in the BSZ contemporaneous with multiple felsic emplacements was active between 830 and 720 Ma. The BSZ collision orogeny possibly preceded the eventual integration of the Greater India landmass with the Gondwanaland during the early-Palaeozoic. Graphical abstract

In the North China block, the south Liaodong Peninsula massif is an elliptical metamorphic core complex (MCC) with a long axis trending NE-SW. In cross-section view, it is asymmetric, with a steeply dipping northwestern flank and a gently dipping southeastern flank. It consists of three lithotectonic units: a gneissic migmatite unit, a Paleo- to Meso-Proterozoic micaschist-slate unit, and a Neoproterozoic to Mesozoic sedimentary cover. Three deformation events related to extensional tectonics are distinguished in the study area: D1 is a ductile deformation related to the exhumation of the MCC; the following event, D2, corresponds to the development of recumbent folds formed during the early exhumation of the MCC; and the youngest event, D3, corresponds to brittle normal faulting that controlled the opening of a Cretaceous continental half-graben basin. A pre-D1 event characterized as northward verging is interpreted as the result of N-S shortening that occurred in the Late Triassic during the final stages of the collision between the North and South China blocks. The ductile and brittle structures were developed coevally, with synkinematic plutonism and formation of half-grabens. New 40Ar/39Ar and U/Pb Cretaceous ages obtained from the mylonitic granodiorite, gneissic migmatite, orthogneiss, and granite indicate that the south Liaodong Peninsula MCC is contemporaneous with other Cretaceous extensional structures, such as numerous syntectonic plutons bounded by ductile normal faults, MCC, and half-graben basins, described in eastern China. Among the several hypotheses proposed to account for the Mesozoic extension along the eastern margin of Eurasia, lithosphere convective removal appears to be the most likely.

Amphibolite facies supracrustal rocks interleaved with granite mylonites constitute a shallowly dipping carapace overlying granulite facies anatectic basement gneisses in the Giridih-Dumka-Deoghar-Chakai area that spans ~11,000 km2 in the Chottanagpur Gneiss Complex (CGC). Steep N-trending tectonic fabrics in the gneisses include recumbent folds adjacent to the overlying carapace. The basement and carapace are dissected by steep-dipping sinistral shear zones with shallow/moderately plunging stretching lineations. The shear zones trend NNE in the north (north-down kinematics) and ESE in the south (south-down kinematics). Chemical ages in metamorphic monazites in the lithodemic units are overwhelmingly Grenvillian in age (1.0–0.9 Ga), with rafts of older domains in the basement gneisses (1.7–1.45 Ga), granitoids (1.4–1.3 Ga), and the supracrustal rock (1.2–1.1 Ga). P-T pseudosection analysis indicates the supracrustal rocks within the carapace experienced postthrusting midcrustal heating (640–690°C); the Grenvillian-age P-T path is distinct from the existing Early Mesoproterozoic P-T path reconstructed for the basement gneisses. Quartz opening angle thermometry indicates that high temperature (~600°C) persisted during deformation in the southern shear zone. Kinematic vorticity values in carapace-hosted granitoid mylonites and in steep-dipping shear zones suggest transpressional deformation involved a considerable pure shear component. Crystallographic vorticity axis analysis also indicates heterogeneous deformation, with some samples recording a triclinic strain. The basement-carapace composite was extruded along an inclined channel bound by the steep left-lateral transpressional shear zones. Differential viscous extrusion during crustal shortening coupled with the collapse of the thickened crust caused midcrustal flow along flat-lying detachments in the carapace.

A regional study starting from detailed geological mapping has been carried out in the Malpica‐Tui Complex of Galicia in NW Spain. The complex is formed by two units representing pieces of the external edge of Gondwana, subducted and exhumed during the Variscan collision. The study shows that synsubduction and early synexhumation structures in continental subduction channels tends to be obscured and even erased once exhumation is complete. Detailed structural analysis, matched with the knowledge of the history, and available data for other Galician basal units have elucidated the major structures developed during the subduction‐exhumation process. The results include evidence of the plate convergence causing early Variscan continental subduction of the Gondwana margin. Subduction was followed by exhumation driven by ductile thrusting within the subduction channel, which, in turn, provoked crustal duplication in the subducted slab and modified the initial tectonometamorphic architecture of the subduction wedge. The next step was accretion to the adjacent continental domains, placing the subduction wedge on top of unsubducted parts of the Gondwana margin via ductile thrusting. Thrusting was preceded by progressive propagation of a train of recumbent folds toward the foreland that affected the previous structural stack. Subsequent transference of oceanic (Rheic) and peri‐Gondwanan terranes to the Gondwana margin took place by out‐of‐sequence thrusting followed by crustal extensional collapse and strike‐slip tectonics. Key Points Structural patterns of exhumation of high‐pressure rocks based on field data Linkage between structural and metamorphic evolution in subduction channels Megastructures developed within a continental subduction‐exhumation channel

The Montagne Noire located in the southern part of the French Massif Central represents the northern part of the South-Variscan Foreland. It is subdivided into three parts. The granite-migmatite Axial Zone dome is surrounded by non- or weakly metamorphosed Paleozoic sedimentary series. Both northern and southern flanks of the Montagne Noire dome are deformed by km-scale, south to southeast facing recumbent folds and thrusts sheets. The Raman Spectroscopy of Carbonaceous Material (RSCM) method, carried out in the low-grade metamorphic rocks of the southern flank of the Montagne Noire, yielded temperatures comprised between 400 °C near the dome, and 230 °C in the southern domain. Three Raman geothermometers were used to cover this temperature range. RSCM temperatures comply qualitatively with previous estimates based on illite crystallinity, conodont color alteration, and fluid inclusions carried out in the same area, which document a metamorphic temperature increase towards the dome. The isotherms cut across the different nappe contacts and are oriented parallel to the southern margin of the Axial Zone. This temperature distribution supports the idea that the thermal structure was acquired during the Axial Zone dome emplacement. The thermal structure acquired during the recumbent folds emplacement and burial of the sedimentary series is totally overprinted by the doming event. In addition, in a domain relatively remote from the Axial Zone dome, the RSCM measurements yielded significantly higher temperatures than illite crystallinity. This discrepancy points to a higher sensitivity of RSCM to short-lived thermal events than illite crystallinity, possibly because of more efficient kinetics of the carbonization reaction. On the other hand, high RSCM temperatures analysed far from the Axial Zone, between 300 °C and 360 °C could be explained by the presence of granitic plutons under the foreland basin. La Montagne Noire, située dans la partie sud du Massif Central français, représente la partie nord de l’avant-pays varisque. La zone est divisée en trois parties. Le dôme granite-migmatite de la zone axiale est entouré de séries sédimentaires paléozoïques pas ou faiblement métamorphisées. Les flancs nord et sud du dôme de la Montagne Noire sont déformés par des plis d’échelle kilométrique, déversés vers le sud sud-est. La méthode de spectrométrie Raman de la matière carbonée (RSCM), réalisée dans les roches de bas grade métamorphique du flanc sud de la Montagne Noire, a donné des températures comprises entre 400 °C près du dôme et 230 °C dans le domaine sud. Trois géothermomètres Raman ont été utilisés pour couvrir cette gamme de température. Ces températures RSCM sont qualitativement conformes aux estimations précédentes basées sur la cristallinité de l’illite, la couleur d’altération des conodontes et les inclusions fluides effectuées dans la même zone, qui démontrent une augmentation de la température vers le dôme. Les isothermes traversent les différents contacts de nappe et sont orientées parallèlement à la marge sud de la zone axiale. Cette distribution de température suggère que la structure thermique a été acquise lors de la mise en place du dôme de la zone axiale. La structure thermique acquise lors de la mise en place des plis couchés et de l’enfouissement des séries sédimentaires est ainsi totalement effacé par le dôme. De plus, dans un domaine relativement éloigné du dôme de la zone axiale, les mesures RSCM ont donné des températures significativement plus élevées que la cristallinité de l’illite. Cette divergence indique une sensibilité plus élevée du RSCM face à la cristallinité de l’illite aux événements thermiques de courte durée, probablement en raison d’une cinétique plus efficace de la réaction de carbonisation/graphitisation. D’autre part, de fortes températures RSCM analysées loin de la Zone Axiale, entre 300 °C et 360 °C, pourraient être expliquées par la présence de plutons granitiques sous le bassin d’avant-pays.

The southwestern flank of the Hellenic fold and thrust belt, situated along the southern edge of the Dinarides–Albanides–Hellenides continental convergent zone, was examined for reconstructing the tectonic deformation. This investigation presents an integrated study of onshore sedimentological and structural analyses, as well as offshore seismic lines, across the Pliocene–Pleistocene sedimentary succession in Zakynthos Island. Back-thrust faults, using the Triassic evaporites as decollement surface, during the Pliocene, and coeval diapiric intrusions formed three sub-basins on the hangingwall of the Kalamaki back-thrust fault. This interaction is responsible for the growth of the Skopos Mountain and the soft sediment deformation that formed synclines and slumps, respectively. Back-thrust and strike-slip faults were active during the early Pleistocene, and diapiric intrusions modified the bathymetry on the sea floor, giving rise to slumps and recumbent folds. At least five events of synsedimentary diapiric intrusions have been recognized and are marked by five slump horizons. During the Holocene, the diapiric intrusions between the Kalamaki back-thrust and the Vrachionas anticline could be either related to normal faults or gravitationally driven.