Abstract The mechanisms by which new subduction zones form remain highly debated. Here we use Permo‐Triassic strata to evaluate potential mechanisms for initiation of the Talkeetna‐Bonanza Arc of the northern North American Cordillera. New mapping and analysis of Permian and Upper Triassic strata on the Alaska Peninsula suggest a period of uplift followed by extension and rapid subsidence. Extension and subsidence beginning in the late Carnian‐early Norian coincided with syn‐initiation slab rollback and the formation of supra‐subduction zone crust 50 km trenchward of our study area. We then integrate our findings with a synthesis of Permo‐Triassic stratigraphic relationships across the Insular terrane. We find that unconformity development occurred at the plate scale, where deformation and erosion was concentrated inboard of a Paleozoic arc sequence that is unconformably overlain by Upper Triassic volcanic and sedimentary strata. As subduction initiated in the Late Triassic (ca. 235 Ma), the upper plate experienced rifting, bimodal volcanism, and the eruption of flood basalts interpreted by some workers as plume‐derived. Two subduction initiation mechanisms may be consistent with this geologic record: (a) forced initiation involving a subduction polarity reversal linked to convergence between fringing arc terranes and western Laurentia during the greater Sonoma Orogeny; or (b) plume‐induced subduction initiation which invokes no specific paleogeographic configuration. Forced initiation is consistent with pre‐initiation unconformity development but does not account for the eruption of plume‐derived flood basalts. Plume‐induced subduction initiation explains the petrogenesis of the flood basalts but does not account for regional Permo‐Triassic unconformity development and Late Triassic rifting.
Abstract The Chhattisgarh Basin of central India is one of the largest Meso‐Neoproterozoic intra‐cratonic “ Purana ” basins and its origin and tectonic evolution have long been debated. While its surface geology and depositional framework are well constrained, the deep crustal architecture remains poorly understood. To investigate the crustal structure, we analyze broadband seismic data from 30 stations deployed across the Chhattisgarh Basin, adjoining Tirodi Gneiss and Gondwana sediments, the Bastar Craton, and the Eastern Ghats Mobile Belt (EGMB) using receiver functions. Our results reveal a sharp, and nearly flat Moho beneath the Chhattisgarh Basin and Bastar Craton, with an average depth of ∼38 km. The presence of clear crustal multiples beneath the Chhattisgarh Basin and Bastar Craton indicates a relatively undisturbed crustal fabric. No seismic evidence is found for either intra‐cratonic rifting or foreland basin development beneath the Chhattisgarh Basin. Instead, the observed crustal architecture supports a model where sedimentation was controlled by sea‐level fluctuations and infilling of localized topographic depressions within the Bastar Craton. Across the Central Indian Shear, the Moho gently deepens northward toward the Tirodi Gneiss. The Gondwana sediments along the basin's northeastern fringe exhibit a comparatively gradational Moho. In contrast, the EGMB is characterized by an average crustal thickness of ∼48 km, an eastward‐dipping Moho, and pronounced Moho offsets, reflecting significant crustal heterogeneity and preserving deep‐crustal signatures of tectonic processes associated with the assembly of Rodinia and Gondwana. These results provide new constraints on the crustal architecture and tectonic evolution of the Chhattisgarh Basin and adjoining domains.
Abstract Siluro–Devonian continental collision in the Scandinavian Caledonides is documented by meso‐ and microstructures in eclogite and split‐stream U–Pb petrochronology of zircon from the Western Gneiss Region (WGR) of Norway. A 3–5 km‐wide shear zone (Sandane Shear Zone) spanning the central WGR separates the Baltica autochthon from overlying >5 km thick gneiss sheets that include much of the WGR domain. Eclogite within the shear zone is deformed while eclogite outside it is mostly undeformed. High‐pressure rocks in the hanging wall and footwall record the same peak metamorphism between 420 and 400 Ma. Prograde U–Pb dates in the footwall begin between 460 and 450 Ma, consistent with long‐term underthrusting at dips between 20° and 40° and average vertical rates of ∼1.8 mm yr −1 . Zircon growth in the hanging wall universally began after c. 435 Ma, implying distinctly later and faster burial (∼2.6 mm yr −1 ). These different metamorphic paths question the long‐held view that the central WGR is part of the Baltica lower plate. The two structural levels enjoyed the same eclogite‐facies metamorphism, but their journeys leading to this concluding episode of the collision were separate.
Abstract Large‐scale intracontinental deformation within the framework of plate tectonics is common, yet difficult to explain reasonably. The Central Asian Orogenic Belt (CAOB) not only experienced large‐scale shortening deformation during the closure of Paleo‐Asian Ocean, but also underwent polyphasic, intense intracontinental deformation. There currently exist many debates regarding the scale, timing, extent of these deformations, and their tectonic backgrounds. Through structural mapping in the Zhusileng area of the central southern CAOB and regional analysis, our study shows that the previously identified large‐scale thrust structure along the Sino‐Mongolian border is the result of the superposition of three thrusting events that had different vergence directions. The main deformation period ranges from Late Permian to Early Triassic (280–255 Ma), rather than the previously well‐known Middle to Late Jurassic or Late Triassic. The main structures in the mapping area consist of a nearly east–west striking and top‐to‐the‐south thrust belt, a north–south striking and top‐to‐the‐east thrust belt, a large ring‐shaped ductile shear zone, and scattered north‐ or south‐trending thrust faults that cut through the above‐mentioned structures. The early nearly east–west trending thrust belt is consistent in orientation and timing with deformations in other regions of the CAOB, resulting from the final closure of the Paleo‐Asian Ocean during the Late Permian. The later eastward‐directed thrusting is related to the clockwise rotation of a large composite batholith caused by widespread ductile shearing along the entire CAOB dated after ca 255 Ma. During the middle to late Mesozoic, the CAOB was affected by the Mongol‐Okhotsk orogeny to the north, but the resulting thrust displacement was limited.
Abstract The assembly of Gondwana involved several Pan‐African orogens, although their extension into ice‐covered Antarctica remains contentious. Particularly problematic is our understanding of the Kuunga orogenic system in East Antarctica, including its eroded architecture and temporal evolution. The remote Charcot Province, at the easternmost extent of the Antarctic Kuunga Orogen, presents a key opportunity to test recent tectonic models. Here we investigate the geological history of Alligator Island, a rarely visited exposure of the Charcot Province. Field relationships, petrography and zircon U–Pb–Hf geochronology indicate that the Alligator Island migmatitic gneisses originated from a Mesoarchean (c. 2.97–2.95 Ga) volcano‐sedimentary package. Metamorphism during the Neoarchean (c. 2.76 Ga) was characterized by channeled melt migration. An apparent tectonic quiescence followed until the Ediacaran–Cambrian (580–540 Ma) when high‐strain melt‐present deformation led to pervasive migmatitic textures and tight folding. Zircon Hf isotopic signatures from anatectic 580–540 Ma grains indicate that melt was sourced from crust older than 3.0 Ga. Melt metasomatism affected whole rock chemistry and feldspar Pb–Pb compositions highlighting complex interactions within the crust. Correlations within the Charcot Province suggest that Alligator Island's Mesoarchean volcano‐sedimentary package was deposited on a basement complex possibly represented by Paleo‐Mesoarchean gneisses exposed 40–60 km to the east at Cape Charcot and Davis Peninsula. Overall our findings are consistent with a recent model in which Charcot Province rocks formed through gravitational spreading within the Kuunga orogenic system during Gondwana assembly, and enhance our understanding of the tectonic processes shaping East Antarctica.
Abstract Porphyry Cu systems are most commonly preserved in Cenozoic magmatic arcs of the Circum‐Pacific belt. However, Paleozoic magmatic arcs in the Tien Shan of western Central Asia host some of the world's largest porphyry Cu–Au accumulations. The limited abundance of Paleozoic porphyry Cu–Au systems is suggested to be controlled by post‐mineralization exhumation and erosion. As a result, quantifying the magnitude of exhumation remains critical in the development and exploration of Paleozoic porphyry Cu–Au systems. Hereinto addressing the role of exhumation of porphyry preservation, we report 19 new zircon and apatite fission track (∼213–154 and 177–133 Ma) and apatite (U–Th)/He (∼124–90 Ma) ages from the worldclass late Paleozoic Almalyk porphyry Cu–Au district (46 Mt Cu and 5,700 t Au) in the western Tien Shan, Uzbekistan. Integrated with published geo‐ and thermochronological data sets, we quantify the cooling and exhumation of the Almalyk district. We identify three phases of cooling, including Late Triassic–Early Jurassic (∼1.9°C/Ma), Late Jurassic–Early Cretaceous (∼4.1–17.8°C/Ma), and Late Cretaceous to the present day (∼0.6–0.8°C/Ma). The first two phases of cooling events are associated with accelerated exhumation (from ∼0.08 mm/yr to 0.16–0.71 mm/yr), due to accretion and associated shortening of the Qiangtang and Lhasa blocks onto the southern Eurasian margin, respectively. From the late Cretaceous until present day erosion rates have remained relatively low (∼0.02–0.05 mm/yr). Together, these data suggest that burial by the Upper Carboniferous–Lower Permian volcano‐sedimentary rocks and slow exhumation from the Late Cretaceous until present are critical factors in the preservation of the Almalyk district. The exhumation history was correlated with crustal shortening and associated strain accommodated by strike‐slip reactivation of the Talas–Fergana Fault and folding and thrusting in the Northern Pamir–Southern Tien Shan contact during the Mesozoic–Cenozoic. We suggest that strain partitioning by major fault zones during the Cenozoic has been key in the preservation of the Almalyk district.
Abstract Owing to the low N‐S convergence rates between Adria and Europe, crustal deformation rates in the Alps and its forelands are low. Active tectonics are, therefore, difficult to study, especially as non‐tectonic landscape forming processes can erase or modify the tectonic surface imprint. Large‐scale and dense seismological data recently offered insights into earthquakes and into the lithospheric structure beneath the Alps. Recent field studies added data on geological archives of active tectonics. In this review, we summarize the results from studies of seismic tomography, geodesy, seismology, historical seismology, archeoseismology, on‐fault and off‐fault paleoseismology, and fault gouge dating, focusing on the eastern part of the Alps during the last c. 1 Ma. We discuss the influence of the lithosphere on the localization of deformation, and we draw a generalized picture of active deformation. We show that deformation is primarily accommodated across the South Alpine Front (∼2 mm/yr out of max 3 mm/yr total shortening) and NW‐SE striking strike‐slip faults in western Slovenia (∼1.5 mm/yr shear). Large fault systems in the interior of the Eastern Alps are still actively accommodating extrusion of crustal material toward the east at very low rates (0.5–1.0 mm/yr). Diffuse deformation and clusters of seismicity are observed in the interior of the Alps. Minor shortening occurs at the North Alpine Front. Crustal strength controls the localization of deformation resulting in non‐deforming blocks. Neogene slab break‐off events do not control the present‐day deformation. Instead, present‐day uplift of 1.5–2 mm/yr correlates to areas glaciated during the Last Glacial Maximum.
Abstract The Tibetan Plateau records active deformation during the ongoing India‐Asia collision, yet the mechanisms for its crustal thickening and surface uplift remain debated. In eastern Tibet, uplift of the Min Shan is attributed to either mid‐crustal channel flow or localized slip along thrust faults, but neither model adequately explains the combination of high topography, eastward‐decreasing slip rates along major strike‐slip faults, and uplift of the Min Shan in the footwall of the Minjiang thrust fault. We integrate new geologic mapping, structural data, and reinterpretation of a 55‐km‐long seismic reflection profile across the western Min Shan to investigate the mechanism of its uplift. Our mapping and seismic reflection interpretations reveal a west‐vergent tectonic wedge bounded by an east‐dipping thrust ramp beneath the Min Shan and west‐dipping roof thrusts of the Minjiang fault to the west. Tectonic wedging explains uplift of the Min Shan, development of the wedge‐top Roergai Basin, and deflection of the Yellow River within the basin. Furthermore, we newly document distributed conjugate strike‐slip faults across the eastern plateau interior that accommodate east‐west shortening and explain the eastward decrease in slip rates along major strike‐slip faults. Our tectonic wedge interpretation for the uplift of the Min Shan challenges models of channel flow in this region while the documentation of regionally distributed conjugate strike‐slip faults suggests that rigid block models of eastward extrusion are oversimplified.
Abstract Rayleigh‐Taylor instabilities within the upper mantle are investigated as a mechanism for the uplift of rift‐margin mountain ranges within the continents. Our focus is on the Transantarctic Mountains (TAM). These mountains form at the margin between East and West Antarctica and have been free from the effects of subduction for about 500 million years. Lying behind and subparallel to the TAM is the Wilkes Subglacial Basin. The TAM–Wilkes Subglacial Basin pairing, with a characteristic wavelength of ∼500 km over a strike length of about 3000 km, is identified as one of the key physiographic signatures predicted by a migrating Rayleigh‐Taylor instability in the mantle. Such a persistent wavelength ( λ ) can be attributed to a maximum, and therefore dominant, growth rate for a Rayleigh‐Taylor instability given by λ ≈ πh, where h is the thickness of the layer that participates in the instability. 2D finite‐element analysis shows such an instability is plausible as it evolves from a step‐like displacement, initiated by extension or strike‐slip motion in the mantle lithosphere, and migrating laterally with time. Data from both Antarctica and New Zealand are synthesized to propose a rift and transform (sinistral strike‐slip) plate boundary within the Ross Embayment, which would have initiated the instability. A key finding of this study is that a 50 my gap between two dominant exhumation episodes in the TAM is common to other passive margins and is a natural outcome of the viscous, non‐linear, growth rate for a Rayleigh Taylor instability.
Abstract Late Pliocene to Pleistocene inversion in the Turkana Rift, observed on seismic reflection data and in outcrop, presents a tectonic paradox by indicating local shortening in an overall extensional setting. Previous studies attributed this inversion either to the reactivation of obliquely oriented structural weaknesses or to reorientation of the far‐field stress field. While both of these mechanisms would operate in a broad region, inversion in Turkana is confined to a narrow ∼50 km zone. Strikingly this zone appears to be bordered by two N‐S oriented zones of voluminous dike intrusion within the Northern and Southern segments of Lake Turkana. Here, we propose a causal relationship between inversion and localized dike intrusion. We first revisit the timing of inversion structures and magmatism in Turkana and second conduct geodynamic forward modeling that explicitly accounts for dike injection. The results demonstrate that dike emplacement at two parallel locations can generate sufficient shortening to trigger tectonic inversion in the intervening region, offering a mechanistic explanation for this enigmatic phase of deformation. Furthermore, the models suggest that faults actively respond to magmatic forcing, providing new insights into the interplay between magmatism and structural evolution in rift settings.
Paleomagnetic data from 269 Pliocene basalt flow sites and 10 sites in the Candelaria Junction Tuff constrain Pliocene vertical-axis rotation from Mono Lake, California to the Marietta Salt Marsh, Nevada. Our data refine efforts to track strain transfer from the Garlock Fault northward through Owens Valley, the Mina Deflection, and into the Walker Lane Belt (WLB). Rotation estimates from basalts and the Candelaria Junction Tuff reveal spatially variable vertical-axis rotations consistent with patterns observed west, east, and north of the study area. The new data record both clockwise and counterclockwise rotations among individual structural crustal blocks, supporting a modified simple-shear model in which sinistral-normal slip and block rotation operate within a distributed shear couple between the Eastern California Shear Zone and the WLB. Newly identified rotations in the Adobe Hills and southern Huntoon Valley area extend the known footprint of Pliocene deformation to the eastern shore of Mono Lake. As the Sierra Nevada block translates northwestward, the Mina Deflection accommodates strain through block rotation, fault interaction, and localized extensional basin formation. The paleomagnetic constraints presented here add key temporal and kinematic insight into this evolving plate-boundary hinge and provide foundational data for future efforts to better constrain and refine aspects of displacement transfer models for the region.
The tectonic evolution of the Tibetan Plateau, including the timing and magnitude of crustal thickening and surface uplift, is debated during the transition from oceanic subduction to India-Asia collision. Previous studies of the Gangdese magmatic orogen show a similar to 3-3.5 km apparent discrepancy between the elevations obtained from stable-isotope-based paleoaltimetry and those inferred from paleo-crustal thickness estimates during the subduction-collision transition. Here, we use thermo-mechanical numerical modeling to investigate how subduction of the leading Indian continental margin influences Gangdese topography. We impose slab breakoff at prescribed depths using a viscosity-reduction "control box" to assess its topographic effects. Our results show that a similar to 25 km-thick subducted Indian continental crust can provide sufficient buoyancy to rapidly uplift the elevation of southern Tibet to similar to 4 km after initial India-Asia contact. In the imposed shallow-breakoff scenarios (80-120 km depth), slab breakoff has only transient effects on surface elevation. This study highlights how discordant results from geochemical Mohometry and paleoaltimetry proxies may be reconciled. Mohometry-derived elevations capture only the buoyancy of the upper-plate crust, whereas paleoaltimetry proxies reflects the total elevation supported by deeper buoyancy, including the subducted Indian crust. Our results are consistent with a synchronous India-Asia collision, the continental nature of Greater India, and a stepwise increase in Gangdese elevation during the early Paleogene.
Abstract Members of the editorial board of Tectonics express their appreciation to those who served as peer reviewers for the journal in 2025.
Abstract Serpentinite plays a major role in the geodynamics of subduction zones. However, the processes by which serpentinite is incorporated into accretionary complexes, and the extent to which it interacts chemically and physically with accretionary lithologies, remain unclear. To address these issues, we conducted geological, geochemical, and Raman spectroscopic analyses of the Nakaguro Serpentinite in SW Japan. This serpentinite was incorporated into the Cretaceous Shimanto Accretionary Complex (AC) that subducted to depths corresponding to the pumpellyite–actinolite metamorphic facies. The Nakaguro Serpentinite crosscuts and penetrates the block‐in‐matrix structures typical of the Shimanto AC. The serpentinite consists of lizardite and Cr‐spinel with Cr/(Cr + Al) <0.57, suggesting an oceanic lithosphere origin. Significant SiO 2 ‐ and CO 2 ‐dominated metasomatism occurred along the contact between the serpentinite and the lithologies of the Shimanto AC. However, mass balance calculations indicate that the degree of metasomatism cannot be explained by simple mass transfer. Instead, metasomatism involved the influx of silica‐ and carbon‐bearing external fluids, resulting in mass and volume gains. Structural analysis of the vein network indicates that metasomatism occurred in a reverse‐faulting stress state that was regulated by steady‐state stress along the plate boundary. We hypothesize that the Nakaguro Serpentinite derived from serpentinized oceanic lithosphere ascended diapirically into the overlying accretionary complex. One possible pathway for this ascent was along outer‐rise faults developed in the subducting oceanic plate. Our working model provides new insights into the fluid‐mediated metasomatism and the transfer of serpentinites across the plate boundary at depths shallower than the forearc mantle wedge.
Syros island preserves pristine high-pressure metamorphic rocks and provides invaluable insight into subduction zone processes. Contrasting views on the structural history impede placing the island in a clear tectonic framework, limiting the broader impact of preserved information. We present a new geological map of Syros, based on field mapping and recent petrochronological evidence for sequential peak subduction metamorphism from 52 to 43 Ma for the Kampos, Chroussa and Posidonia subunits. Compiled P-T-t constraints show that retrograde metamorphism varies: cooling during decompression (Kampos subunit), isothermal decompression (Chroussa subunit) and warmer greenschist overprinting at lower pressures (Posidonia subunit). Phengite Rb/Sr and 40Ar/39Ar ages show a further downward trend of younger ages and wider age ranges. We present a tectonic model for exhumation that explains the contrasting kinematics recorded on the Kastri and Kini shear zones that separate these subunits. The brittle Kastri fault juxtaposed top-to-SW mylonites of the Kampos subunit against top-to-NE mylonites of the Chroussa subunit, which we interpret to reflect sequentially active extrusion wedges. The Kini shear zone records top-to-E deformation from eclogite to greenschist facies, reflecting wedge extrusion of the Posidonia subunit and Miocene reactivation as a detachment unroofing a core complex in South Syros. Low-angle brittle extension is also recorded on the Vari and Kastri shear zones, by reactivation of former subduction contacts. Based on similarities with Naxos and Sifnos, we call this the Central Cycladic Detachment system, which showcases a style of extension along parallel detachments causing thinning of the CBU, which may explain downward-increasing conditions of metamorphic overprinting.
Abstract The post‐collisional evolution of orogenic belts is commonly marked by high‐temperature metamorphism and widespread magmatism, yet the processes linking collision to post‐collisional dynamics remain difficult to reconstruct due to limited exposure of deep‐crustal levels and uncertainties in the determination of pressure‐temperature conditions and geochronology. The southern Variscan belt provides a rare opportunity to investigate these processes through the exposure of deep‐crustal sections, as shown in the Alps, where early Devonian‐Carboniferous Variscan subduction and collision were followed by a Permian post‐collisional exhumation. In the Valpelline Series (western Alps), Permian deep‐crustal exhumation has been constrained by integrating U‐Pb zircon geochronology with pressure‐temperature estimates. Building on these constraints, we explore the post‐collisional evolution using 2D numerical modeling of a convergent‐divergent tectonic system and compare predicted pressure‐temperature‐time paths with those inferred from the Valpelline Series. The results show a strong agreement between the metamorphic evolution recorded in the rocks and the trajectories predicted by the models during post‐collisional stages. The transition from convergence to extension involved the reactivation of the inherited structures, their progressive migration from the lower to the upper plate, and the development of shallow sedimentary basins, consistent with regional Alpine observations. The best fit is obtained in models that invoke a rapid shift from convergence to forced extension at plate margins near the Permo‐Carboniferous boundary, rather than a prolonged gravitational collapse of the southern Variscan belt. These findings indicate that early Permian basin formation and deep‐crustal exhumation were primarily controlled by plate‐boundary forces rather than long‐lasting gravitational processes.
Long‐term rates of crustal uplift in southern Calabria and NE Sicily are incompletely understood due to limited information about the age of marine terraces at 1.0–1.3 km above sea level (asl). This study provides a new constraint on high‐elevation terrace ages through integrated analysis of geochronology, stratigraphy, shoreline modeling, and fault‐zone morphology. 40 Ar/ 39 Ar step‐heating experiments on glass from a tuff in marine claystone of the Argille di Spadafora, NE Sicily, yield reproducible age spectra with a mean age of 0.481 ± 0.019 Ma (±2σ). The Argille di Spadafora and equivalent marl in southern Calabria are overlain by Pleistocene marine terrace deposits, indicating the terraces are younger than 0.50 Ma. Paleoshoreline modeling at Campo Piale, southern Calabria, suggests an age of 525–590 ka for a terrace at 600–630 m asl: this is an overestimate because it assumes no fault offsets, tilting or structural warping despite geomorphic evidence for these processes. We correlate the 630‐m terrace to the marine terrace at 1.0–1.3 km asl by mapping it up a gently inclined relay ramp between the Cittanova and Sant’Eufemia faults, and geomorphic evidence for fault offset of the terrace. We conclude that marine terraces up to 1.0–1.3 km asl are all <0.50 Ma, roughly half the widely cited estimate of 1.0 ± 0.2 Ma. The revised age suggests an average uplift rate >2.5 mm/y for the highest terrace, and variable throw rates up to 1.0 mm/y on normal faults that cut the terraces.
In many areas of active faulting, the continuity of normal faults with short or incomplete historical earthquake records and more subdued topographic expressions is not fully understood and consequently the seismic potential of these faults is often underestimated. One example of a poorly understood normal‐fault bounded system is the South Gulf of Evia rift, Greece, where the location and evolution of the major basin bounding normal faults is not well constrained. We integrate geomorphic and structural field data, including the documentation of uplifted marine terraces, wavecut notches and beachrock, with topographic analyses, geodetic data and analysis of river long profiles to constrain the locations, footwall geometries and structural evolution of 8 active normal faults bounding the Southern margin of the South Gulf of Evia. By combining these data sets we resolve vertical ground motion and fault growth over a range of timescales from 10 5 –10 6 yrs to the past 12 kyrs. We propose that this fault system is formed of two fault groups comprised of both partially and fully linked segments. By comparing reconstructions of footwall relief with previously interpreted sparker seismic reflection and OBS data in the eastern offshore region of the Gulf, we suggest total slip rates in the order of 2–3 mm/yr for the eastern faults. These fault linkage scenarios suggest that the western faults may have a total linked length of ca. 20 km, whilst the eastern faults may have a total linked length of ca. 43 km with a maximum credible earthquake size of Mw 7.0.
Southern Italy and eastern Sicily have been the site of several destructive historical earthquakes. Here at the junction between the western edge of the Calabrian subduction zone and the Malta Escarpment several strike-slip faults have been mapped, which may be the surface expression of the lateral slab tear fault and are candidate sources for some of these earthquakes. The North Alfeo Fault is the northern portion of a 140-km-long fault system extending from the southeastern flank of Mount Etna and cutting the western edge of the Calabrian accretionary prism. High resolution bathymetric mapping (1 m grid spacing) conducted by unmanned submersibles along a 15-km-long segment of the North Alfeo Fault reveals alternating transpressive pop-ups and lozenge shaped transtensional basins. A pronounced triangular plateau occurs where the fault-trace bends by 15 degrees and is cross-cut by N-S-trending domino fault blocks. Analog modeling performed using granular materials above a dextral strike-slip boundary reproduces the large-scale features of the North Alfeo Fault, including imbricated transpressive pop-ups, lozenge shaped basins, and secondary splays oriented 20-25 degrees (clockwise rotation) from the primary fault trace. The clockwise splay rotation implies dextral kinematics and is consistent with known earthquake focal mechanisms showing dextral strike-slip for fault planes oriented generally NW-SE. The fresh surface morphology, the length of the North Alfeo Fault segment, and sedimentary stratigraphy and chronology indicate 3-6 m of fault offset has occurred in the past similar to 16,000 years, consistent with the generation of magnitude six earthquakes.
The evolution of the Alpine-Provence foreland is characterized by multiple deformation phases since the Mesozoic, representing successive compressional and extensional episodes. The precise timing and spatial evolution of these deformation phases remain poorly constrained due to the lack of absolute geochronological data. Here, we present U-Pb dating and stable isotope analysis (delta 18O and delta 13C) of calcite associated with brittle deformation in the sedimentary cover between the Vercors and Vaucluse massifs in south-eastern France. Combined with paleostress reconstructions, the results allow to refine the dynamics of deformation across the Alpine-Provence foreland. Our results indicate that North-South compression, related to the Pyrenean orogeny, is recorded since ca. 92 Ma. Combined with previously published U-Pb data from SE France, these results support the existence of a regional-scale compressive phase affecting the sedimentary cover during the Upper Cretaceous, and predating the commonly accepted onset of Pyrenean shortening based on global-scale reconstruction (similar to 84 Ma). A second, Paleogene, deformation pulse is also related to the Pyrenean orogeny. During the Oligocene, E-W extension is associated with the development of the West-European Rift System, highlighted by ages of ca. 33 Ma in the Vocontian basin and ca. 25 Ma in the Vaucluse. Finally, Alpine E-W compression reactivated pre-existing faults ca. 22 Ma onward. This age is structurally linked to the formation of the foreland fold-and-thrust belt in response to the exhumation of the external crystalline massifs related to a thick-skinned deformation mode. The stable isotope data indicate the preservation of a primary isotopic signature in the dated calcites.
