Tectonic Transport Research Articles

Paipote fold-and-thrust belt, a key element in understanding the upper crustal shortening mechanisms of the Central Andean forearc

The crustal shortening of the Andean forearc in northern Chile was accommodated by a combination of both thin- and thick-sinned structural styles. However, fold-related inversion of normal faults appears to be the most important structures in the area. To understand the upper crustal shortening mechanisms that acted during the tectonic uplift of this region, an original structural investigation was carried out, integrated with outcrop and regional-scale observations, balanced cross-sections, and pre-shortening restorations of structures exposed along the Paipote fold-and-thrust belt. On this basis, we presented the first balanced cross-section of this region extending for nearly 27 km is presented. The structural styles consisted of east-directed asymmetrical folds involving Paleozoic to Cenozoic strata. The folds were kinematically related to inverted normal faults and thrust ramps that penetrated downward into the basement. The inverted structures resulted from the reverse reactivation of preexisting Upper Paleozoic to Jurassic west-dipping, basement-rooted normal faults that accommodated the tectonic extension that preceeding the Andean orogenesis. The reverse-reactivation of these extensional structures controlled the development of east-verging anticlines, along which the Mesozoic syn-rift strata were elevated above their regional elevation. Other folds exhibit the typical geometry of fold-related thrust ramps (fault–bend folds and fault–propagation folds). These are proposed to result from the development of low-angle thrusts propagating across precursor normal faults with shortcut trajectories, that detach along Jurassic shales, thus forming complex thin-skinned structures in shallow structural levels. The latter is responsible for accommodating a major crustal shortening (nearly 5 km). The east-directed tectonic transport direction was influenced by the original attitude of precursor extensional faults.

Morpho‐Tectonic Evolution of the Southern Apennines and Calabrian Arc: Insights From Pollino Range and Surrounding Extensional Intermontane Basins

AbstractThe evolution of topography in forearc regions results from the complex interplay of crustal and mantle processes. The Southern Apennines represent a well‐studied forearc region that experienced several tectonic phases, initially marked by compressional deformation followed by extension and large‐scale uplift. We present a new structural, geomorphic and fluvial analysis of the Pollino Massif and surrounding intermontane basins (Mercure, Campotenese and Castrovillari) to unravel their evolution since the Pliocene. We constrain multiple tectonic transport directions, evolution of the drainage, and magnitude and timing of long‐term incision following base level falls. Two sets of knickpoints suggest two phases of base level lowering and allow to estimate ∼500 m of long‐term uplift (late Pleistocene), as observed in the Sila Massif. On a smaller spatial scale, the evolution and formation of topographic relief, sedimentation, and opening of intermontane basins is strongly controlled by the recent increase in rock uplift rate and fault activity. At the regional scale, an along‐strike, long‐wavelength uplift pattern from north to south can be explained by progressive lateral slab tearing and inflow of asthenospheric mantle beneath Pollino and Sila, which in turn may have promoted extensional tectonics. The lower uplift of Le Serre Massif may be explained as result of weak plate coupling due to narrowing of the Calabrian slab. The onset of uplift in the Pollino Massif, ranging from 400 to 800 ka, is consistent with that one proposed in the southern Calabrian forearc, suggesting a possible synchronism of uplift, and lateral tearing of the Calabrian slab.

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.

Thermochronology of the Laojunshan–Song Chai Granite Gneiss Massif (North Vietnam, South China)

A reconstruction of the tectonothermal evolution of the Laojunshan–Song Chai granite gneiss massif (North Vietnam, South China) was carried out, based on summaries of the latest isotopic and fission-track dating results. The recorded wide range (420–465 Ma) of the age of granite gneiss rocks testifies to the long-term existence of a partially molten layer at a depth of 20–30 km for several tens of Ma. By the Devonian–early Carboniferous, a section of the excessively thickened crust was denudated, the massif was exhumated to the level of the upper crust, and isotope systems were “frozen”. The rate of uplift of the rocks of the massif is estimated to be about 0.2–0.5 mm/year. In the further history of the granite gneiss massif, episodes of repeated burial to a depth of about 13 km are recorded, associated with the Indosinian collision. The rocks have experienced metamorphism of the amphibolite-green schist facies, accompanied by tectonic transport in the form of a thrust sheet. Over the next 200 Ma, the uplift of the massif and the erosion of the overlying strata occurred in discrete pulses, during a sequence of active tectonic events. Thus, the thermochronological and P-T history of the Laojunshan–Song Chai massif is a kind of chronicle of regional tectonic–thermal events. In the history of the massif, traces of two orogenic cycles associated with the collision of the Cathaysia and Yangtze blocks in the Lower Paleozoic and the Indosinian collision in the Triassic are recorded.

Mississippian olistostromes of Iberia revisited: tectonic drivers of synorogenic carbonate platform/reef destruction

This paper reviews the synorogenic basins formed on the Gondwana side of the Variscan Orogen of Iberia, highlighting the widespread occurrence of calciturbiditic formations and olistostromes containing reef limestone olistoliths in Iberia's Variscan basins. Using key examples from the Variscan Orogen for comparison (the Azrou–Khenifra and Rhenohercynian basins), the significance of these olistostromes and flyschoid deposits is discussed. Our tectonic models of the Variscan belt in Iberia propose possible drivers of synorogenic carbonate platform/reef destruction responsible for the origin of calciturbidites and olistostromes. One model proposes the formation of an orogenic plateau via the lateral flow of partially molten orogenic roots in the context of Laurussia–Gondwana convergence following the destruction of the Rheic Ocean and slab retreat of the Gondwana (lower) plate. An alternative model invokes subduction of Palaeotethys oceanic lithosphere beneath the Gondwana (upper) plate. Both emphasize the Mississippian occurrence of a significant thermal anomaly beneath Gondwana that favoured strong lithosphere thinning, creating ideal conditions for synorogenic carbonate platform/reef destruction and the formation of calciturbidite deposits and olistostromes in Iberia. The Variscan palaeotopography would look similar in both situations. Distinguishing between these models is therefore not straightforward, with differences in the kinematics of regional tectonic transport in the superstructure of Mississippian gneiss domes. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

Morpho-structural signatures of neotectonic activity along the HFT bound Himalayan mountain front in Kathgodam-Chorgallia sector of NW Himalaya, India

Thrusting supports the development of diverse landforms and deformational structures in the Himalayan Frontal Thrust (HFT) region between Kathgodam and the Chorgallia sector, according to this study. The influence of the active tectonic condition in the area was analyzed using seven geomorphic indices, which also underlined the importance of morpho-structural study utilizing remote sensing, geomorphic indices, tectono-geomorphic landforms, field evidence, and luminescence dating. The investigation of sub-basins surrounding the HFT reveals moderate to high tectonic activity, with tectonic activity concentrating in the eastern half and decreasing toward the west. A topographic discontinuity was also observed in the region as indirect active tectonic evidence. Hanging wall rocks have well-preserved features that govern tectonic transport direction, and the HFT in this region is emergent. Shear sense indications point to southerly tectonic migration, with a few modest northward shear senses indicating northward movement, which might be attributable to reverse thrusting along the HFT at some time during the Outer Himalaya's tectonic history. Petrographic investigations reveal sustained frontal deformation at various intervals, with well-preserved thrust-induced deformation fingerprints in deformed rocks throughout the Jam Raula and Sukhi nadi sections. Micro thrust duplexes, or micro-scale asymmetrical drag folds, are shown in thin section investigations as a result of HFT-related brittle-ductile deformation at moderate temperature and pressure. The sandy unit from the Quaternary sediments yields 10 ± 0.8 ka, 11.8 ± 0.7 ka, 17 ± 1 ka, and 56 ± 3 ka quartz OSL dates, demonstrating the migration of hanging wall rocks on footwall post-Siwalik fluvial deposits along the HFT plane and reactivation of the HFT in the study area.

In-sequence tectonic evolution of Ediacaran nappes in the southeastern branch of the Brasília Orogen (SE Brazil): Constraints from metamorphic iterative thermodynamic modeling and monazite petrochronology

The metamorphic and kinematic evolution of medium-high grade rocks of the Andrelândia Nappe System (ANS), the orogenic wedge of the Southern Brasilia Orogen (SBO), was investigated in this work. Field and microstructural observations were combined with metamorphic petrology (i.e., iterative thermodynamic modeling) and monazite petrochronology to reconstruct the tectono-metamorphic history of the ANS rocks. The Liberdade Nappe experienced prograde metamorphism at ca. 610 Ma, achieving peak metamorphic conditions of ca. 650 °C and 9.5–10 kbar. This stage was followed by isothermal decompression linked to tectonic transport toward SE, at ca. 570 Ma. On the contrary, the Andrelândia Nappe experienced prograde metamorphism later, at ca. 580 Ma, reaching peak metamorphic conditions of ca. 680 °C and 11–12 kbar. The obtained results indicate that each nappe of the Andrelândia System records a single metamorphic cycle of burial and decompression, although it took place at different ages over a period of ca. 60 myr, from 630 to 570 Ma. The nappes experienced prograde and retrograde metamorphism whose ages progressively decreased toward the bottom of the nappe stack. We attribute this pattern to propagation of older buried material from the orogenic wedge (i.e., Liberdade Nappe), via thrust-and-fold, upon recently accreted rocks (i.e., Andrelândia Nappe), conducting a younger metamorphism event on the footwall of the ductile thrusted nappes. This mechanism is consistent with the ANS in-sequence fold-and-thrust architecture.

Reply to comment on Díaz-Bravo et al. (2022)

The space-time analysis of the evolution of Cretaceous-Paleogene magmatism by Díaz-Bravo et al. (2022), identifies the development of a continuous magmatic arc along the continental margin, contradicting the migration of the arc towards the continent as a consequence of flattening of the Farallon plate (Damon et al., 1981). This magmatism was developed simultaneously in the interior of the continent and interrupted during the Paleocene. Consequently, our conclusions are not an adaptation of magmatic ages in the context of planar subduction as suggested by Chávez-Cabello and Ramírez-Peña (2023). Including U–Pb ages from a few missing Cretaceous plutons in our analysis do not change our model at all but enrich it.The study of regional deformation was not part of the objectives of our work, but we pointed out some issues about the temporality of magmatism and deformation previously documented, trying to prevent future misinterpretations. We show here that magmatism was emplaced at the beginning and end of the Late Cretaceous deformation phase of the Mexican Fold and Thrust Belt, and it was absent during the Paleocene-Eocene deformation stage. We ruled out tectonic transport of the Cretaceous plutons, or we think that it should be negligible considering how far (hundreds of kilometers) are these and other plutons from the paleo-trench. Furthermore, plutons such as Pico de Teyra were not located in the thin-skinned cover and others such as El Milagro and La Pólvora do not present deformation features. A large syn-tectonic displacement scenario should be changed dramatically the texture of these rocks, but large parts of these plutons preserve magmatic textures and some of them do not show evidence of deformation. Also, is very likely that the P-T conditions in such large transportation, would induce recrystallization and resetting of some isotopic systems (i. e., K–Ar) but it is not observed or has not been documented. We highlight the contributions we have made to the knowledge of the intracontinental plutons studied and the adequate documentation of our work. Finally, we insist that pre-Mesozoic basement is little known in the study area, despite the documented geophysical data.

Proterozoic basins of the Bundelkhand Craton, India: Correlations and significance in understanding the tectonic evolution

The Bundelkhand Craton and associated basins of Peninsular India have received interest for debates related to research on their records of biological evolution, particularly reported occurrences of materials akin to triploblastic animals. Data related to geochronology and key tectono-stratigraphic markers of the block have been critically analysed and a model of evolution during the Proterozoic Eon is presented. The basement block, the Bundelkhand Granite Complex, evolved in three phases: Phase I (3551-3190 Ma), Phase II (2780-2550 Ma) and Phase III (2450-2250 Ma), followed by tectono-thermal events between the phases, representing temporal unconformities of ∼400 Ma and ∼100 Ma. The last phase of evolution was terminated with the amalgamation of the North Indian Block with the South Indian Block, forming the Satpura Orogen (phase IA) at ∼2250 Ma, which included the Singhbhum Orogenic belt. Orogenic collapse/extension at ∼2150 Ma developed a series of sedimentary basins running parallel to the orogenic belt. These Paleoproterozoic basins include the Mahakoshal, Bijawar, Sonrai and Gwalior basins around the Bundelkhand Granite Complex. The adjacent cratons also developed contemporaneous basins for the deposition of the Aravalli Supergroup (in the Western Indian Block), Cuddapah Supergroup (in the South Indian Block) and a proto-ocean at the site of the Eastern Ghats, extending towards the northern margin of the Singhbhum Block. All these basins had an inversion phase of 1950-1800 Ma, ending with the development of the Aravalli Orogen as well as Satpura Orogen (phase IB) and closing of sedimentation in the Paleoproterozoic basins. A new phase of extension at ∼1750 Ma initiated deposition of the Semri Group and Delhi Supergroup in the Northern and Western Indian blocks. The event was associated with the amalgamation of East Antarctic Block with the South Indian Block forming the Eastern Ghats (phase I)-Dalma Orogen. The later stage of Eastern Ghats (phase I)-Dalma Orogeny ∼1500 Ma was contemporaneous with the Delhi Orogeny (North Delhi Orogeny). The principal compressions acting opposite to each other during the Delhi Orogeny (with southeastward tectonic transport) and Eastern Ghats (phase I)-Dalma Orogeny (with northwestward tectonic transport) caused the second uplift of the Satpura Orogen (Satpura Orogeny II), as well as the uplift of the North Indian Block, developing a first-order spatio-temporal unconformity of ∼300 Ma gap above the Semri Group, till the extensional stress regime of ∼1200 Ma initiated deposition of the Kaimur Group. The closing of the Kaimur Basin took place during the Grenvillian Orogeny of ∼1100 Ma, which developed the Eastern Ghats (phase II) – Rayner Orogen on the eastern margin of Peninsular India. The far-field stress of the Eastern Ghats Orogeny (phase II) developed inversion/uplift in the Satpura Orogen and deposition of the Rewa Group in the North Indian Block. A second uplift of the Eastern Ghats (Eastern Ghats Orogeny phase II) and the Delhi Orogen (South Delhi Orogeny) at ∼1000-950 Ma closed the deposition of the Rewa Group and initiated deposition of the Bhander Group in the North Indian Block and the Sirohi Group in the Western Indian Block. The Pindwara Orogeny of ∼850 Ma in the Western Indian Block caused uplift of the North Indian Block and closed the deposition of the Bhander Group. The orogenic movements at ∼1500 Ma and ∼1100-950 Ma were associated with continental amalgamations along the western and southeastern margin of India, but did not involve any amalgamation in the central part of India, which was affected by reactivation/uplift of an older structural fabric.

The poly-orogenic Paleozoic rocks of Cuesta del Rahue area (Precordillera Neuquina, Argentina) and their significance in marking the southern end of the Chanic orogenic belt

In the Cuesta del Rahue area, located in the Precordillera Neuquina (northern Argentine Patagonia), late Paleozoic turbiditic rocks with maximum depositional age of ca. 389 Ma were affected by three orogenic events. The oldest orogenic event is the Chanic orogeny (Late Devonian–early Carboniferous) that is characterized by folds with NNE vergence. This deformation is developed in low-grade to very low-grade metamorphic conditions, which allowed the development of a slaty/rough cleavage. The main Chanic structure is an asymmetric fold with a large normal limb tilted by the more recent orogenic events. The characteristics of the deformation and metamorphism allows us to assign the Cuesta del Rahue outcrop to the external hinterland of the western wedge of the Chanic orogen. Early to late Carboniferous igneous rocks intruded the Paleozoic rocks of the Cuesta del Rahue area and crosscut the Chanic structures. After the Chanic orogeny, the Gondwanan orogeny (late Carboniferous–early Permian) took place. The main structures of the Gondwanan orogen are thrust and related folds with SSW vergence that fold the large Chanic normal limb and also affect Carboniferous igneous rocks. The Gondwanan deformation was developed under non-metamorphic conditions, and Permian igneous rocks crosscut the Gondwanan structures. Mesozoic regional extension related to the beginning of the Andean cycle and the formation of the Neuquén Basin gave rise to normal faults and small-scale extensional folds. Finally, the Andean orogeny, developed during the Cenozoic in the study area, also affected the Cuesta del Rahue Paleozoic rocks, with the development of compressional structures related to the Aluminé thrust and fold belt. The main Andean structure in the study area is the NW–SE Rahue fault, which links the E–W Piedra Santa tear fault with the NNE–SSW Catán Lil reverse fault. The Rahue fault has a SW tectonic transport direction. It uplifted the Cuesta del Rahue area and placed Paleozoic rocks on top of Mesozoic and Cenozoic rocks. The Piedra Santa fault partially reactivated the Huincul right-lateral and left-lateral Chanic transverse faults that define the southern end of the doubly vergent Chanic orogen, giving rise to the current Huincul lineament.

Multiple fabrics in the Tavares pluton (NE Brazil): Insights on the interplay between emplacement mechanism, internal magmatic processes, and tectonic deformation

Internal dynamic processes and contemporaneous deformation may produce multiple magmatic fabrics and structures during the crystallization of granitic plutons. Here we report the case of the Tavares pluton (Borborema Province, northeastern Brazil), a ∼160 km2 NE-SW elongate pluton bounded in the north and southeast by dextral and sinistral shear zones, respectively. A remarkable feature of this pluton is the occurrence of numerous elliptical flow-related structures delineated by mafic schlieren resulting from the interaction of dioritic and granitic melts. We analyzed airborne geophysical data, conducted a field and anisotropy of magnetic susceptibility (AMS) study at the pluton scale, and detailed the magnetic fabric of two elliptical structures. The pluton has a well-developed magmatic foliation defined by the shape preferred orientation of K-feldspar megacrysts and planar concentrations of mafic minerals. The foliation trajectories are concentric and inwardly dipping, indicating a lopolith shape for the pluton. NE-trending magmatic shear zones and faults attest to sinistral shearing before complete crystallization. The dominant AMS fabric at pluton scale, represented by NE-to NNE-trending magnetic foliations with steep dips associated with lineations of moderate to shallow plunges, is consistent with the sinistral strain regime. In contrast, the magnetic foliation and lineation in the two elliptical structures dip moderately to the east, with the magnetic foliation commonly transecting the orientation of the mafic schlieren. We relate this latter fabric to regional contraction, characterized by top-to-the-west tectonic transport in the country rocks, during pluton construction. We propose that (i) tectonic overpressure due to regional compression assisted progressive pluton inflation by floor subsidence, generating the concentric magmatic fabric, and (ii) a small component of noncoaxial shear during bulk contraction led to sinistral shearing in the late stages of crystallization. We found no evidence for shear zone-controlled pluton emplacement. Instead, (i) the SE-bounding sinistral shear zone is restricted to the pluton vicinity, suggesting nucleation due to thermal softening of country rocks by the pluton, and (ii) magmatic foliations and lineations that could be related to the N-bounding dextral shear zone are absent. Also, the available geochronological data suggest that emplacement of the Tavares pluton predated by several tens of millions of years the intrusion of well-documented syn-transcurrence plutons in the Borborema Province. Therefore, the spatial association of the Tavares pluton with strike-slip shear zones is not strong enough evidence to assume a shear zone control on pluton emplacement.

Multiscale structural analysis of an Epiligurian wedge-top basin: insights into the syn- to post-orogenic evolution of the Northern Apennines accretionary wedge (Italy)

Wedge-top basins represent useful tectonic elements for the characterisation of the evolution of their underlying accretionary wedge in space and time, as their final state of deformation sums up the bulk shortening and structural instability conditions of the wedge. Here, we present the geometric and kinematic patterns of deformation structures deforming the wedge-top Epiligurian basins of the Northern Apennines (Italy). Our main goals are to generate an evolutionary model to account for the syn- to post-orogenic evolution of the Epiligurian basins and to infer the building style of the Northern Apennines wedge during continental collision. Mesoscale structural analysis shows that common and widely distributed thrust and normal fault arrays deform the entire Epiligurian stratigraphic succession infilling the broadly E-vergent wedge-top basins. Thrusts are invariably cut by later NW–SE and NE-SW-striking normal and oblique fault systems characterised by fault planes that mutually intersect at all scales to form polygonal patterns. Remote sensing analysis of the tectonic structures affecting the Epiligurian formations confirms the variable orientation of both thrusts and normal faults within the different studied stratigraphic successions. As a whole, results suggest a polyphase tectonic evolution of the Epiligurian wedge-top basins during the widening of the Northern Apennines accretionary wedge towards the foreland by frontal accretion. The recognised main phases are: (i) syn-orogenic compression accommodating overall tectonic transport towards the eastern quadrants; (ii) post-orogenic extension genetically related to the extension of the inner zone of the Northern Apennines; (iii) more recent extension forming collapse-induced normal faults spatially arranged in polygonal patterns.

Structural inheritance and style within the Getic Depression, South Carpathians, Romania

The Carpathians are part of the Alpine orogen, and the Getic Depression (or Getic fold belt) is located to the south of the South Carpathian. Underthrust beneath the fold belt is the Moesian Platform lower plate. This foreland depocenter can reach a depth of up to 10 km and evolved in an oblique convergent setting from latest Cretaceous-Paleogene and was shortened during the Badenian-middle Sarmatian (middle to late Miocene, 16–8 Ma) and Pliocene to recent. Thus far, in previous publications, the role of the structural grain of the lower plate was poorly constrained. For the fold belt, contrasting interpretations implied a range of shortening magnitudes and contrasting fault pattern. This contribution shows seven balanced cross sections that rely on seismic reflection and well data. One section, just outside and to the south of the fold belt, gives insights into the fault network of the Moesian Platform. In that section we see 35 km of north westward directed normal sense extension that creates a set of rotated fault blocks. Growth strata within the half grabens attest to Permo-Lower Triassic extension age. The individual normal faults merge at depth into a common detachment that rises monotonously towards the east and forms a domal-shaped, arched detachment. This is the structural grain that we project down plunge towards the north beneath the fold belt. The interpreted six sections that lie in the tectonic transport direction show that structures in the western part of the Getic fold belt are compatible with the inversion on the underlying Permo-Lower Triassic extensional fault. Ubiquitous truncation of Oligocene strata by overlying units suggest inversion started during late Oligocene (intra-Burdigalian). The Badenian-Sarmatian shortening further deforms the pre-existing contractional features and the shortening increases from 5 km on the west to at least 17 km on the east. NW-SE oriented transfer zones with normal faults separate the fold belt domains with diverging displacement vectors and eastward increasing shortening. Two main salt levels within the fold belts’ sediment pile are laterally discontinuous hence they only have local significance in the deformation. The frontal part of the fold belt consists predominantly of Badenian-Sarmatian synkinematic units as the fold belt propagated into the foredeep units, this interpretation requires less shortening in the frontal structures compared to earlier solutions. Due to the lack of characteristic features on the studied sections, we infer that the Getic fold belt did not evolve as a transtensional depocenter during the lower Miocene as suggested by earlier publications.

Exhumation timing of the Cordón del Portillo, Frontal Cordillera, supports the east-vergent model for the growth of the southern central Andes

The timing of contraction, uplift and exhumation of the Cordón del Portillo (33.5–34°S), Frontal Cordillera, southern Central Andes, remains unresolved. This fact has led previous studies to postulate opposite west- and east-growing orogen models. Here, we present the first apatite fission-track (AFT) ages from samples at the Cordón del Portillo, and apatite (U–Th)/He dates (AHe), which allow us to clearly recognize a ca. 15 to 5 Ma period of rapid cooling, interpreted as the record of exhumation of the Frontal Cordillera basement. We present a kinematic evolution of the area that supports these timing of exhumation and a tectonic transport towards the east. Our results agree with previous AHe dating and detrital AFT, which suggest ongoing exhumation pre-14 Ma and peak of exhumation at ca.15 Ma, respectively. It is also in concordance with regional geology and thermochronology pointing to a similar onset of exhumation of the Cordón del Plata, Frontal Cordillera, further north. Moreover, a rising Cordón del Portillo during the early to middle Miocene, contemporaneous with the beginning of sedimentation in the intermontane Alto Tunuyán Basin, implies that Miocene sedimentary rocks were not deposited in a contiguous foreland basin but in an isolated basin separated by topographic highs in the Frontal Cordillera. Finally, our data indicate an eastward shift in the focus of Andean deformation during the Miocene, jumping into the Frontal Cordillera after contraction started in the fold-and-thrust belt of the Principal Cordillera (west of the Cordón del Portillo) at ca.18 Ma, standing for the east-vergent model of tectonic evolution proposed for the Andes.

Crystalline basement from Laguna Amarga metamorphic complex in the high Andes of western Catamarca, Argentina (27° 15’ - 27° 40’ south): Petrology, structure and geodynamic implications

The Laguna Amarga Metamorphic Complex is a major stratigraphic component of the southern Central Andes. The occurrence of crystalline basement pieces extensively exposed in the western Andes of Catamarca (Argentina), has been known for decades, nevertheless, a lack of detailed field-based and geochronological survey has precluded an accurate correlation of the Laguna Amarga Complex with other basement exposures in the Central Andes. The Laguna Amarga Metamorphic Complex outcrops in several fault-bounded blocks spread over about 360 km2, always underlying Neopaleozoic strata and Neogene volcanic strata from the Central Volcanic Zone. The northern part of the complex consists of amphibolite-facies metamorphic rocks derived from sedimentary and igneous precursors grouped in an association named Cazadero Grande. The original stratigraphic succession was interbedded siliciclastic sediments, carbonaceous, and mafic rocks. The southern segment of the complex is dominated by granulite-facies migmatites and ortho-amphibolites grouped in an association called Los Aparejos. In the Cazadero Grande Association, four deformational events are recognized. The first three phases gave rise to an imbricate S-verging over-thrusting system and prevailing tectonic transport to the south in response to progressive non-coaxial strains. The mineral assemblages linked to the metamorphic climax equilibrated coeval with the early stages of fabric-forming deformation. The posthumous fourth phase of deformation produces gentle folds with kilometer-scale wavelengths whose axial planes (non-penetrative) have an NNE strike, and are as related to Andean deformation. Three incremental deformation events coeval with the metamorphic climax are registered in the Los Aparejos Association that indicate a kinematics transport to the east. First U–Pb zircon ages are reported for the Laguna Amarga Metamorphic Complex. Age distributions are polymodal, but the dominant populations make well-defined clusters. The most prominent concord age peak is at 389 Ma, revealing the age of the metamorphic climax. Another noteworthy aspect is the presence of dominant Mesoproterozoic concord age peaks (1119-1082 Ma), interpreted as inheritance ages of their protolith. A point to highlight is the absence of ages reflecting the source with Brasiliano-Pan-African orogenic ages that dominates detrital provenance from the West Gondwana. The Mesoproterozoic protolith ages allow the correlation of this metamorphic complex with nearby basement detached from Laurentian realms. The analysis of the ages shows that the metamorphic peak and the generalized deformation that affected the entire basement of the complex developed in the Middle Devonian (Eifelian), this being a very little known event for the Paleozoic evolution of western Gondwana. The work discusses how a better understanding of the crystalline basement of the high Andes impacts the geodynamic history of the proto-Andean Gondwana margin. It also provides new information on the geodynamic configuration of the Lower to Middle Paleozoic and its link with the processes of accretion-collision of terranes.

Tectono-stratigraphic evolution, regional structure and fracture patterns of the Zagros fold-thrust belt in the Duhok region, Kurdistan, northern Iraq

This study is the first detailed investigation of the tectono-stratigraphy, regional structure and mesoscopic fractures of the Zagros fold-thrust belt in the Duhok region, Kurdistan, Northern Iraq, and is based on field studies, remote sensing-GIS analyses, cross-section restorations, and tectonic analysis of key structures. The Duhok fold belt is a frontal zone of the north-western part of the Zagros fold and thrust belt in the Kurdistan region near the north-eastern margin of the Arabian Plate. It is characterized by WNW-ESE striking, doubly-plunging, upright symmetric to asymmetric detachment folds that involve ~8.2–10.9 km of Paleozoic to Quaternary strata. These folds vary from 5 to 75 km long, 4–20 km wide and have a surface relief (caused by basement uplift) up to 3.2 km. Five regional and twelve local structural cross-sections were constructed parallel to the regional SSW tectonic transport and perpendicular to the fold axial trends. Section lengths vary between 4.94 km and 101.55 km. Two main detachment levels have been inferred for the Duhok fold belt. A deep basal detachment was placed at the base of the Paleozoic successions within the Ordovician shales of the Khabour Formation at depths from 8 km to 10 km. Shallower, intermediate detachment levels occur within the shales and evaporites of the Mid-Upper Permian and Upper Jurassic strata at depths 1.7 km in the frontal sectors to around 5.5 km in the hinterland. The thickness of the Paleozoic succession in the Duhok fold belt is ~2 km. Deformation by thin-skinned detachment folding together with thick-skinned thrusting is inferred to have occurred in the Duhok region from the Mid Miocene through to the Present-Day. The maximum NNE-SSW-directed shortening produced by detachment folding was about 18.62 km (19.71%) over a section length of 94.45 km. The maximum shortening along thrust faults was around 1.98 km (1.95%) over a section length of 101.55 km. The mesoscopic fracture patterns in the study area were grouped into two major extension sets, four major shear-hybrid sets and eight minor shear-hybrid sets. Field characteristics and relative chronology indicate that most of the fractures are tectonic in origin, and they developed before (i.e., pre-folding fractures) and during (i.e., early- and late-folding fractures) the Mid Miocene folding in the Duhok fold belt.

Spatio-temporal variation of fluid flow behavior along a fold: The Bóixols-Sant Corneli anticline (Southern Pyrenees) from U–Pb dating and structural, petrographic and geochemical constraints

This study integrates field structural data, petrographic and geochemical (δ18O, δ13C, Δ47, 87Sr/86Sr, and elemental composition) analyses and U–Pb dating of calcite veins cutting the Bóixols-Sant Corneli anticline (Southern Pyrenees) in order to date and to investigate the spatio-temporal relationships between fluid flow and fold evolution. This E-W trending anticline grew from Late Cretaceous to Paleocene at the front of the Bóixols thrust sheet deforming pre-growth and growth sedimentary sequences. U–Pb dating reveals Late Cretaceous to late Miocene deformation ages, which agree with the age of growth strata deposition and the sequence of deformation interpreted from field and microstructural data. Dates coeval (71.2 ± 6.4 to 56.9 ± 1.4 Ma) and postdating (55.5 ± 1.2 to 27.4 ± 0.9 Ma) Upper Cretaceous to Paleocene growth strata are interpreted to record: (i) the growth of the Bóixols-Sant Corneli anticline during the Bóixols thrust emplacement, and (ii) the tightening of the anticline during the southern tectonic transport of the South-Central Pyrenean Unit. Other ages (20.8 ± 1.2 to 9.0 ± 4.6 Ma) postdate the folding event and have been associated with the collapse of the Bóixols-Sant Corneli anticline. The geochemistry of calcite veins indicates that the fluid flow behavior varied across the Bóixols-Sant Corneli anticline through its growth, showing a compartmentalized fluid system. In the hinge of the anticline and in the upper Santonian to middle Campanian syn-orogenic sequence along the footwall of the Bóixols thrust, the similar petrographic and geochemical features between all calcite cements and host rocks point towards a locally-derived or well-equilibrated fluid system. Contrarily, along large faults such as the Bóixols thrust, and in the anticline limbs, the geochemistry of vein cements indicates a different scenario. Cements in large faults yielded the lightest δ18O values, from −8 to −14 ‰VPDB, and variable enrichment in δ13C, 87Sr/86Sr, elemental composition and δ18Ofluid. This is interpreted as the migration of fluids, through fault zones, that evolved from distinct fluid origins. Cements in the fold limbs exhibit δ18O and δ13C between −8 and −6 ‰VPDB and between −10 and + 2 ‰VPDB, respectively, the lowest Sr contents and the lowest precipitation temperatures, suggesting that the anticline limbs recorded the infiltration and evolution of meteoric waters. The paleohydrological system in the Bóixols-Sant Corneli anticline was restricted to the Bóixols thrust sheet. The Upper Triassic evaporitic basal detachment likely acted as a lower fluid barrier, preventing the input of fluids from deeper parts of the Pyrenean crustal thrust system. This study provides a well-constrained absolute timing of fracturing and fluid flow during basin inversion and folding evolution and highlights the suitability of U–Pb geochronology to refine the age of fractures and veins and their sequential evolution in orogenic belts.

Tectonic inversion of listric normal faults in the foreland of the Rinkian Orogen (Maarmorilik, central West Greenland)

Integration of field structural data and 3D-photogeology from the southern part of the Rinkian Orogen, in central West Greenland, indicates that Paleoproterozoic marbles of the Mârmorilik Formation were deformed by two compressional events in the foreland of the orogen, associated with tectonic inversion of normal faults. Tectonic transport and folding post-date the Rinkian metamorphism (c. 1830–1800 Ma) with the first event characterized by NNE-SSW oriented compression and tectonic stacking of folded calcitic marbles (Black Angel Tectonic Unit), above slightly deformed dolomitic marbles (South Lakes Tectonic Unit). The second event caused the inversion of NE-SW trending normal faults during NW-SE oriented compression. Field observations reveal that the normal faults have a listric geometry and were inverted after c. 20° tilting to the NE of the Maarmorilik carbonate platform. The style of tectonic inversion reflects the amount of extension accommodated along the listric faults showing rollover anticlines and extensional fault-bend-folds in the hanging wall, then inverted as thrust anticlines, back-thrusts antithetic to the normal fault or normal faults passively truncated by younger thrusts. This paper shows the power of 3D-photogeology that can provide observations of lithostratigraphic units and structural data to allow investigation of remote areas from otherwise inaccessible outcrops.

The rise and demise of deep accretionary wedges: A long-term field and numerical modeling perspective

Abstract Several decades of field, geophysical, analogue, and numerical modeling investigations have enabled documentation of the wide range of tectonic transport processes in accretionary wedges, which constitute some of the most dynamic plate boundary environments on Earth. Active convergent margins can exhibit basal accretion (via underplating) leading to the formation of variably thick duplex structures or tectonic erosion, the latter known to lead to the consumption of the previously accreted material and eventually the forearc continental crust. We herein review natural examples of actively underplating systems (with a focus on circum-Pacific settings) as well as field examples highlighting internal wedge dynamics recorded by fossil accretionary systems. Duplex formation in deep paleo–accretionary systems is known to leave in the rock record (1) diagnostic macro- and microscopic deformation patterns as well as (2) large-scale geochronological characteristics such as the downstepping of deformation and metamorphic ages. Zircon detrital ages have also proved to be a powerful approach to deciphering tectonic transport in ancient active margins. Yet, fundamental questions remain in order to understand the interplay of forces at the origin of mass transfer and crustal recycling in deep accretionary systems. We address these questions by presenting a suite of two-dimensional thermo-mechanical experiments that enable unravelling the mass-flow pathways and the long-term distribution of stresses along and above the subduction interface as well as investigating the importance of parameters such as fluids and slab roughness. These results suggest the dynamical instability of fluid-bearing accretionary systems causes either an episodic or a periodic character of subduction erosion and accretion processes as well as their topographic expression. The instability can be partly deciphered through metamorphic and strain records, thus explaining the relative scarcity of paleo–accretionary systems worldwide despite the tremendous amounts of material buried by the subduction process over time scales of tens or hundreds of millions of years. We finally stress that the understanding of the physical processes at the origin of underplating processes as well as the forearc topographic response paves the way for refining our vision of long-term plate-interface coupling as well as the rheological behavior of the seismogenic zone in active subduction settings.

Tectonic Transport Directions, Shear Senses and Deformation Temperatures Indicated by Quartz c-Axis Fabrics and Microstructures in a NW-SE Transect across the Moine and Sgurr Beag Thrust Sheets, Caledonian Orogen of Northern Scotland

Moine metasedimentary rocks of northern Scotland are characterized by arcuate map patterns of mineral lineations that swing progressively clockwise from orogen-perpendicular E-trending lineations in greenschist facies mylonites above the Moine thrust on the foreland edge of the Caledonian Orogen, to S-trending lineations at higher structural levels and metamorphic grades in the hinterland. Quartz c-axis fabrics measured on a west to east coast transect demonstrate that the lineations developed parallel to the maximum principal extension direction and therefore track the local tectonic transport direction. Microstructures and c-axis fabrics document a progressive change from top to the N shearing in the hinterland to top to the W shearing on the foreland edge. Field relationships indicate that the domain of top to the N shearing was at least 55 km wide before later horizontal shortening on km-scale W-vergent folds that detach on the underlying Moine thrust. Previously published data from the Moine thrust mylonites demonstrate that top to the W shearing had largely ceased by 430 Ma, while preliminary isotopic age data suggest top to the N shearing occurred at ~470–450 Ma. In addition, data from the east coast end of our transect indicate normal-sense top down-SE shearing at close to peak temperatures at ~420 Ma that may be related to the closing stages of Scandian deformation, metamorphism and cooling/exhumation.