NW-SE Shortening Research Articles

Structures and deformation phases affecting the Diagorou-Darbani greenstone belt south of Téra (Liptako, West Niger, and West African Craton)

The present study focuses on the geological formations of the Diagorou-Darbani greenstone belt of southern Téra in the Niger Liptako (NE portion of the Man Shield of the West African Craton). The main objective of this study is to characterize the deformation phases that affected the Diagorou-Darbani greenstone belt to the south of Téra. The methodology implemented is based on a structural analysis using field data. These formations are affected by two major deformation phases, D1 and D2. Phase D1 comprises three episodes: D1a, D1b and D1c. The first episode (D1a) developed the S1 cleavage (NE-SW). This episode is linked to a NW-SE shortening (N130°). The second episode (D1b) is marked by S2 crenulation cleavage, micro-folding and the dextral reactivation of N45° shear zones. This episode is linked to an E-W shortening. The third episode (D1c) is highlighted by the NW-SE S3 fracture cleavage and the sinistral reactivation of the N45° shear zones. A N-S to NNE-SSW shortening was obtained for episode D1c. Phase D2 is essentially brittle. It favoured the development of submeridian fractures and conjugate WNW-ESE (sinistral) and ENE-WSW (dextral) shear fractures. This deformation is compatible with a generally E-W direction of shortening.

Polyphase formation of a Neoarchean auriferous fault zone network in the Michipicoten greenstone belt, southern Superior craton

Correlating structurally distinctive fault zones for understanding an unknown deformation system at the regional scale remains a challenge for understanding orogenic evolution and gold endowment. The current study deals with this challenge in the southern Michipicoten greenstone belt (MGB) of the Superior craton focusing on a Neoarchean auriferous fault zone network. Three deformation events associated with episodic gold mineralization are revealed in the ca. 2745 Ma host granitoid: (1) NW‒SE shortening recorded by the subvertical Grace and Minto B fault zones and locally the inclined Jubilee and Hornblende fault zones; (2) top-to-NNE strike-slip to oblique faulting indicated primarily by the dominant structures of the Jubilee and Hornblende fault zones; and (3) top-to-NE extension demonstrated by the northeast-dipping Parkhill #4 and Cooper fault zones. Fault zone lithologies and mineral assemblages suggest that the localization of deformation for the formation of these fault zones was controlled by rheological heterogeneities and syn-deformation fluids. The first and second events are correlated with two shortening events in a gold-endowed, structurally and kinematically distinctive deformation zone of the northern MGB. This correlation based on deformation processes suggests a larger footprint of gold mineralization associated with a regional deformation in the MGB and has implications for investigating structural evolution of orogens and orogenic gold mineralization in general.

The Late Cenozoic crustal deformation in the northeastern periphery of the Qaidam Basin, northwest China

The northeastern periphery of the Qaidam Basin is a crucial region for comprehending the northeastward growth of the Tibetan Plateau, as it documents Late Cenozoic crustal deformation that elucidates the plateau's growth process. In this study, we reconstruct three stages of crustal deformation in the northeastern periphery of the Qaidam Basin during the Late Cenozoic based on interpretation of growth strata from five seismic profiles, structural mapping of the typical superimposed folds and detailed detrital zircon analysis within the study area. (1) During the Early Miocene to Late Miocene period (23–8.6 Ma), there was NW–SE extensional deformation in the northeast margin of the Qaidam Basin, which exerted control over the deposition of the Youshashan Formation. (2) The NW–SE shortening occurred during the Late Miocene period (8.6–8.1 Ma), subsequent to the deposition of the Youshashan Formation and preceding the deposition of the Shizigou Formation, resulting in a parallel unconformity between these two geological units. (3) The intense shortening of the NE–SW direction occurred during the Late Miocene and Pliocene epochs (8.1–2.5 Ma). The timing of this deformation aligns with the sedimentary age of the Shizigou Formation, suggesting that the initial deformation age may represent the onset of NE extrusion from the Tibetan Plateau towards the northeast margin of the Qaidam Basin. The present study not only delineates a Late Cenozoic structural dome resulting from two‐stage crustal shortening in the northeastern periphery of the Tibetan Plateau, but also provides a crucial evidence for reconstructing the Late Cenozoic intracontinental deformation process in this region.

Strain partitioning in the Patagonian Broken Foreland: influence of structural inheritance of early Andean deformation

In the context of Andean-type oblique convergence, strain partitioning between thrust and strike-slip tectonics is well documented in the arc region. However, the impact of this configuration in the retroarc remains poorly understood, especially in broken foreland systems where basement structures compartmentalize the retroarc into small intermontane sedimentary basins. The spatiotemporal analysis of tectonic evolution and the role of inherited weaknesses in this area are often debated. This study addresses these uncertainties by integrating geometric and kinematic analyses of tectonic structures within the Sañicó Massif in the North Patagonian foreland. Results reveal two deformational episodes. The initial Late Cretaceous to Paleocene episode represents a contractional deformation phase, with NW–SE shortening direction causing the tectonic inversion of pre-Andean rift depocentres. The second episode records a Neogene transpressional regime with both contractional and strike-slip deformation, with east–west to NE–SW shortening direction, which progressed under reactivation of pre-existing structures and generated new faults. This work demonstrates the Neogene propagation of the strike-slip regime towards the retroarc, defining strain partitioning at various scales and highlighting its interaction with pre-existing structures. These results enhance our understanding of the complex tectonic history in oblique subduction settings, providing significant evidence of the structural inheritance in retroarc systems.

Structural and geochronological constraints for the Mesozoic nappe structures of the Taqian–Fuchun thrust zone, eastern Jiangnan orogenic belt, South China

The NE‐trending Jiangnan orogenic belt has experienced multi‐tectonic episodes since the Mesozoic separates the Yangtze Block in the north‐west from the Cathaysia Block in the south‐east. The Taqian–Fuchun thrust zone in north‐east Jiangxi Province is located in the eastern Jiangnan orogenic belt. It is considered as an essential unit to understand the geometry, kinematics and dynamics of the Mesozoic nappe structures in the eastern Jiangnan orogenic belt and an ideal region to reveal the Mesozoic tectonic evolution in South China. Here, we present new detailed structural data coupled with zircon U–Pb and apatite fission‐track dating studies, establishing a four‐stage deformation history and describing the geometry, kinematics, ages and dynamic background. The Middle–Late Triassic NW–SE compression event (D1, 243–226 Ma) is mainly characterized by regional angular unconformity between the Lower and Upper Triassic and asymmetric folding of the underlying strata. The associated regional NW–SE shortening was related to the intercontinental collision. The Middle–Late Jurassic NW–SE compression event (D2, 175–160 Ma) is characterized by the angular unconformity between the Middle Jurassic and Cretaceous and the SE‐vergent imbricate nappe structures. The shortening has been associated with the NW‐ward subduction of the Paleo‐Pacific Plate. The Late Jurassic–Cretaceous NW–SE extension event (D3, 160–67 Ma) includes the transition stage from compression to extension (160–145 Ma) and the intensive extension stage (145–67 Ma). The former is characterized by the development of the extensional detachment structures and intermediate‐acid magmatism, while the latter is characterized by the development of Cretaceous extensional sedimentary basins and A‐type granites. This extension was correlated to the slab roll‐back of the Paleo‐Pacific Plate. The Paleocene–Eocene compression event (D4, 67–35 Ma) is manifested by the thrusting of metamorphic rocks in the Shuangqiaoshan Group to the Cretaceous red beds. This shortening possibly originated from the collision between the India and Eurasian Plates. This study provides new constraints on the Mesozoic structural style and establish a reliable geochronological framework of the Mesozoic tectonic evolutions of the eastern Jiangnan orogenic belt.

Lithostratigraphic analysis and characterization of the upper miocene deformation of the Beni Bou Ifroure massif (Jbel Harcha Unit) eastern Rif Morocco

In the eastern Rif the unit of Jbel Harcha which is part of Beni Bou Ifroure massif, the latter belongs to the Rif chain which was formed during the Alpine orogeny. Lithostratigraphic analysis of the geological map and field investigations shows that this unit is constituted by carbonate facies of limestone attributed to the lower and middle Jurassic. At the level of upper Jurassic and Cretaceous we observe metamorphic terms presented by schists. The structural examination allows to distinguish two types of deformation the first one is penetrative which is materialized by a metamorphism of the formations of upper Jurassic and Cretaceous whose direction of the planes of schistosity varies between N125 and N140. This type is linked to a NE-SW shortening, attributed to the Tortonian and materialized by a set of open and normal faults of direction N040 to N045. The second type is generally characterized by brittle structures presented by dextral strike-slip faults of direction N120 to N140 that intersect the ancient accidents. This episode linked to a N-S to NW-SE shortening is responsible for the N070 thrusting of the Jurassic rocks in the study area.

Mid‐Mesozoicto Cenozoic multiphase deformation in the Bayanwula Tectonic Belt, northern China

The Bayanwula Tectonic Belt (BTB) is located between the Alxa Massif and the Ordos Basin in the northwestern North China Craton (NCC). The Mid‐Mesozoic to Cenozoic deformation characteristics of the BTB is crucial for understanding the tectonic processes of eastern Asia during that time. Together with the regional geology, our field observation and structural analysis reveal that the BTB has undergone three phases of deformation since the Late Jurassic. The first phase of deformation (D1) is represented by NE–SW‐striking thrust faults involved in the Jurassic strata, indicating a phase of NW–SE shortening deformation. Based on the combination of angular unconformity between the Upper Jurassic and Lower Cretaceous strata, the timing of D1is constrained at the end of Jurassic and dynamically related to the westward subduction of the Palaeo‐Pacific Plate during the end of the Jurassic. The second one (D2) is characterized by the ~NE–SW‐striking normal faults and Lower Cretaceous syn‐sedimentary strata on both sides of the BTB, which show that a phase of ~NW–SE extension deformation occurred in the Early Cretaceous, dynamically related to the rollback of the Palaeo‐Pacific Plate in the Early Cretaceous. The third stage of deformation (D3) is represented by the NW–SE‐striking folds that involved the Pliocene strata, as well as dextral strike‐slipping of the East Bayanwula Fault and the West Helanshan Fault, indicating a phase of NE–SW shortening at the end of the Pliocene. Dynamically, the D3is related to the outward expansion of the Tibetan Plateau.

Jurassic contractional deformation in the central–western North China Craton in response to multi-plate convergence in the East Asia

The Jurassic multi-plate convergence in East Asia led to the intra-continental deformation in the North China Craton (NCC). However, much controversy is highlighted in the intra-continental deformation style and timing, and unanimous kinematics. The central-western North China Craton of the East Asia, typical of the Jurassic structural belts around the Ordos Block, is a key region to delineate the intra-continental deformation. Here, using new structural analysis, the definition of Jurassic growth strata, and paleo-stress inversion, grouping with our previous work on the NCC, we reconstructed a multi-directional shortening pattern in the central-western NCC during the Middle–Late Jurassic (170–160 Ma), which is characterized by N-S shortening along the northern margin of the NCC, by NW-SE shortening in the western margin and along the central zone of the NCC. In combination with regional structural analysis, we propose that the central-western North China Craton is roughly situated at the center of the multi-plate convergence during the Middle-Late Jurassic, and the southward compression was caused by the closing of the Mongolia-Okhotsk Ocean in the north, the northwestward compression by the subduction of paleo-Pacific plate beneath the East Asia continent in the east, and southeastward compression by the closure of the Meso-Tethys in the west.

Regional and local controls of hydrothermal fluid flow and gold mineralization in the Sheba and Fairview mines, Barberton Greenstone Belt, South Africa

High-grade gold-quartz-sulphide lodes of the Sheba-Fairview Complex (SFC) of gold mines in the Barberton Greenstone Belt of South Africa describe a wide range of geometries, orientations, controls, and a number of different and often contradicting models have been postulated to account for their formation. This paper aims to present a holistic model that describes the focussing of a regional-scale fluid flow into narrower, mineralized structures during the late-stage refolding and tightening of the first-order folds that host the mineralization.The auriferous reefs of the SFC are hosted by well-bedded, low-grade metamorphic, clastic sedimentary rocks of the Paleoarchaean Fig Tree and Moodies groups that are preserved in two regional-scale, strongly curved and refolded synclinal structures along the northern margin of the belt. The majority (85 %) of presently and historically mined orebodies occur in the broad hinge zone of the refolded synclines. This suggests the regional-scale fluid redistribution from fold limbs into the first-order fold hinge following regional hydraulic gradients during refolding. Ubiquitous bedding-parallel quartz (-carbonate-sulphide) veins and associated alteration underline the significance of bedding anisotropies and bedding-parallel flexural slip for regional-scale fluid flow during refolding. The focussing of these fluids and economic-grade gold mineralization occurs preferentially along contacts between lithologies with pronounced rheological contrasts. Lithological contacts combine the effects of strain localization in weaker units and the formation of fracture permeabilities in competent units across these contacts. Examples include kilometer-scale hinge-parallel ore shoots that are controlled by undulations (jogs) along low-displacement slip horizons between retrogressed ultramafic rocks and competent metasediments. In contrast, low-angle thrusts or steep reverse faults form accommodation structures related to the late-stage tightening of the first-order folds. These structures transect bedding at high angles and are, thus, ideally orientated to collect fluid from the regional system of bedding-parallel fluid flow.Mineralization in the SFC may be explained by the spatial and temporal coincidence of (1) late-stage NW-SE shortening and refolding, of (2) a well-bedded, anisotropic wall-rock sequence, associated with (3) regional-scale fluid redistribution along bedding planes during flexural slip, leading to (4) fluid focussing into either jog geometries or bedding discordant structures. The combination of these factors is unique to the SFC and accounts for the location of the main Barberton gold mines along the northwestern margin of the greenstone belt.

The effect of the Najd shear deformation on the Pan-African belt of the central Egyptian Nubian Shield: a synthesis for the post-collision tectonic events

This study concerns the structural setting of the central Egyptian-Nubian Shield (El Shalul area) utilizing field-structural, remote sensing, petrological and geochemical data. The exposed basement comprises ophiolitic-mélange, arc-related metavolcanics, metasediments, metagabbro-diorites and granitoids. The area experienced two stages of deformation, pre-Najd (∼850–630 Ma) and Najd-related (∼630–580 Ma). The pre-Najd stage is represented by the assembly of arc-terranes and their N-ward extrusion while the Najd-related stage encompasses three deformation phases. D1 is post-collision extensional event, depicting lateral spreading of tectonic terranes and NW-ejection of ophiolites. The emplacement of El Shalul granite (∼630 Ma) and deposition of molasse sediments in E-W and NW-SE extensional basins (Zeidun and Meesar) are D1- related. Following extension is a protracted phase of compression, shearing and transpression. It was commenced with NW-SE shortening (D2) and deformed the extensional basins by folding and thrusting with mild effect on the other basement units. Sinistral shearing (D3a) and transpression (D3b) along the NW-trending faults superseded the D2 compression, while dextral shearing (D3c) on the ENE-WSW and NE-SW faults overprinted the NW-SE penetrative structures and controlled the emplacement of post-granitic dykes. The significant conclusions of this study include (1) El Shalul granite complex is a large alkaline granitic sheet emplaced during a post-collision extensional regime and suffered the subsequent ∼630–580 Ma top-to-NW sinistral shearing and SW-directed thrusting (not a gneissic core complex) and (2) The NW-SE and NE-SW structural trends are not conjugated.

Carboniferous-Permian tectono-metamorphic evolution of the Pelvoux Massif (External Crystalline Massif, Western Alps), with discussion on flow kinematics of the Eastern-Variscan Shear Zone

Based on new structural, petrological and U-Th-Pb geochronological data, a reappraisal of the Variscan tectono-metamorphic history of the Pelvoux Massif (External Crystalline Massif, French Alps) is proposed with the aim to understand the flow pattern and kinematics of the Variscan partially molten crust and the Eastern Variscan Shear Zone. The Pelvoux Massif consists of high-grade metamorphic rocks of middle to lower crust, mostly migmatites, that record a prominent syn-metamorphic deformation event (D2) characterized by a pervasive NE-SW striking, steeply dipping, S2 foliation, and a network of anastomosed NS and NW-SE trending shear zones, the kinematics of which indicates a sinistral transpression. Relics of an early syn-metamorphic event (D1/M1) related to crustal thickening and top-to-the-east nappe stacking are also reported. Both the D1 and D2 features are interpreted as reflecting a NW-SE shortening event, firstly marked by dominant nappe stacking, and secondly overprinted by a sinistral transpression that started at peak metamorphism with the onset of crustal partial melting at ca. 650 °C during the late Visean (ca. 335–330 Ma). Ongoing sinistral D2 transpression in the partially molten middle-lower crust of the Pelvoux involved strain partitioning between C and C’ shear zones and horizontal longitudinal flow in the range 330–300 Ma. Along the anatectic front, vertical shortening and top-to-the-NW shearing (D3) is coeval with D2 and argue for southeastward motion of the partially molten crust. The contemporaneity between NW-SE directed transpressional flow and vertical shortening is supported by our radiometric data of D2 and D3 and attests for strain partitioning between the suprastructure and infrastructure during horizontal crustal flow under transpressive regime. The exhumation of deep-seated rocks during sinistral transpression followed a near isothermal (ca. 700 °C) evolution down to pressure of ca. 0.5 GPa in the period 325–306 Ma. The sinistral transpression recorded in the Pelvoux Massif might corresponds to an antithetic shear zone coeval with the dextral East-Variscan Shear Zone, proposed for this part of the Variscan orogen.

Geology, zircon U–Pb dating and εHf data for the Julie greenstone belt and associated rocks in NW Ghana: Implications for Birimian-to-Tarkwaian correlation and crustal evolution

The Julie greenstone belt of NW Ghana is characterized by a predominately volcanic succession of basalt with minor rhyolite and a mainly sedimentary succession of siltstone, shale and greywacke. The first unit is correlated with the Sefwi Group, and the second with the Kumasi Group of the Birimian Supergroup. The volcano-sedimentary succession is separated by a sheared unconformable contact from clastic sedimentary rocks, including sandstones and conglomerates, correlated with the Tarkwaian Group of Ghana. The supracrustal rocks are intruded by various granitoids. Two major deformational events have been identified. A regional N–S shortening event (D1) affected rocks of the Birimian Supergroup and associated granitoids. A later NW-SE shortening event (D2) affected both the Birimian and Tarkwaian units. Rocks have undergone regional greenschist to amphibolite facies metamorphism. Peak metamorphism took place during D2.Several samples of igneous and sedimentary rocks were subjected to U–Pb zircon dating and Lu–Hf isotope analyses. All zircons provided Paleoproterozoic ages in the range of 2112 ± 5 to 2337 ± 11 Ma, which is consistent with existing zircon ages from volcanic and plutonic rocks in various parts of Ghana, and other Birimian and Tarkwaian terrains within the West African Craton. Rhyolite of the Sefwi Group has an age of 2182 ± 3 Ma and marks a period of explosive felsic volcanism. Detrital zircon ages from greywacke of the Kumasi Group yield a maximum depositional age of 2158 ± 4 Ma. This age compares well to a maximum depositional age of 2154 ± 2 Ma defined in southern Ghana. Zircon ages from Tarkwaian sandstones indicate a maximum depositional age of 2135 ± 5 Ma, which is in accord with similar depositional ages for the Tarkwaian in SW Ghana and Houndé in Burkina-Faso. Thus the Tarkwaian rocks from the Julie greenstone belt area are correlative to those in SW Ghana and elsewhere. Detrital zircon ages point to a derivation from erosion of felsic volcanic and plutonic rocks within the Paleoproterozoic terrain. Detrital zircon ages of Birimian and Tarkwaian rocks show a ∼70% overlap. This suggest that the Tarkwaian detritus may have been derived from reworking of older Birimian rocks. Alternatively, both groups sampled a similar source but were deposited at different periods. Dated granitoids include a 2209 ± 5 Ma phase and a post-Tarkwaian intrusion of 2112 ± 5 Ma in age. The older granitoid is in sheared contact with basalt, and both share similar D1 structures.The ϵHf values for zircon grains from analyzed rocks are in the range of −1.78 to +6.37, in agreement with most Hf isotopic signatures currently available from the Paleoproterozoic Baoulé-Mossi Domain, and indicate crust components with apparent mantle derivation ages averaging c. 2300 Ma and ranging from c. 2100 to c. 2500 Ma.

Paleogeographic reconstruction of Mississippian to Middle Pennsylvanian basins in Nevada, southwestern Laurentia

Compilation of stratigraphic, sedimentological, and structural data on palinspastically restored maps reveals the Mississippian-Pennsylvanian paleogeography of Nevada in unprecedented detail, and has important implications for the development of the southwestern Laurentian margin. In contrast to previous interpretations of latest Devonian-earliest Mississippian tectonism, the maps show the major tectonic events to have been in late Middle Mississippian and Middle Pennsylvanian time. Regionally extensive unconformities mark both, with the deepest erosion in the northwest. Sub-unconformity structures record primarily NW-SE shortening, and synorogenic sediments were shed toward the east, southeast and south. These observations are consistent with protracted sinistral-oblique convergence in Nevada along the southwest Laurentian margin, rather than the W-E convergence invoked in previous interpretations. Terminology for late Paleozoic orogenies in Nevada must be revised accordingly. • Southwestern Laurentia experienced NW-SE shortening in the late Paleozoic. • Major tectonic evens in late Middle Mississippian and Middle Pennsylvanian. • Data consistent with sinistral-oblique margin throughout the late Paleozoic. • Data presented here are not consistent with E -W convergence in late Paleozoic.

A new insight into the structural evolution of Rosetta Fault, eastern margin of Herodotus Basin, East Mediterranean

While exploration activities are flourishing in both the offshore Nile Delta Basin and the Levant Basin, Herodotus Basin remains unexplored. The study of the complex tectonic evolution of this basin is mainly hindered by large water depths, insufficient and poor seismic imaging, as well as the scarcity of well penetrations. The present study offers a new insight into the tectonic history of the eastern margin of Herodotus Basin through detailed structural study of the Rosetta Fault. Detailed structural mapping of Rosetta Fault using 3D seismic and borehole data reveals its complicated deformation history. Together with other NE-SW oriented faults in the Levant Basin and the northern Egypt onshore area, Rosetta Fault experienced different phases of slip at different times including normal slip due to extensional deformation at Triassic to early Cretaceous times and reverse slip at Late Cretaceous to Tortonian times due to the convergence of Eurasia and Afro-Arabia. Contrary to the findings of some plate tectonic models, which consider NE-SW drift of Afro-Arabia and Eurasia, the present study suggests that the direction of Mesozoic extension in Herodotus Basin (as well as the Levant Basin and the northern onshore areas of Egypt) was NW-SE based on the orientations of Mesozoic active faults. Rosetta Fault also shows deformation by sinistral transtension at Messinian and Holocene times intervened by Plio-Pleistocene normal slip. When the Rosetta Fault was affected by normal slip and transtensional deformation at Messinian to Holocene times, the Herodotus Basin lying to the NW of it was affected by NW-SE shortening associated with the Hellenic subduction. The obvious contrast in the deformation style of Rosetta Fault and the Herodotus Basin is attributed to the irregular shape of the convergent plate boundary extending from south Cyprus to SE Crete.

The Cu–Pb–Zn-bearing veins of the Bou Skour deposit (Eastern Anti-Atlas, Morocco): structural control and tectonic evolution

In the central Saghro massif of the Moroccan Anti-Atlas belt, the Bou Skour polymetallic deposit is hosted within mafic to felsic rocks of the Ediacaran Saghro Group and the lower Ouarzazate Group together with Pan-African plutons and dykes. The mineralizations occur in a brittle-ductile shear zone as a vein-type system recently dated at 574.9±2.4Ma. In this contribution, a new multi-scale structural mapping and vein system analysis have been integrated to understand structural control and tectonic evolution of the Bou Skour deposit. The most important mineralized structures are known as “Filon Principal”, “Filon 1”, and “Filon 2” and are mainly hosted within NNW to NW transcrustal faults. They are represented as en-echelon tension gashes occasionally associated with horsetail satellite structures pointing to left-lateral strike-slip movement. The age and tectonic patterns are coherent with the NW–SE shortening of the last stage of the Pan-African orogeny rather than with post Pan-African events. Subsequent collapses and tilted blocks were accommodated by NE- to ENE normal and strike-slip faults in response to the Late Ediacaran–Cambrian extension events. Much later, probably during the Variscan or even Atlasic shortening, conjugated strike-slip reverse faults and related folds occurred, disrupting most of the rhyolitic dykes as well as the major mineralized structures.

New insights into active tectonics and seismogenic potential of the Italian Southern Alps from vertical geodetic velocities

Abstract. This study presents and discusses horizontal and vertical geodetic velocities for a low strain rate region of the south Alpine thrust front in northeastern Italy obtained by integrating GPS, interferometric synthetic aperture radar (InSAR) and leveling data. The area is characterized by the presence of subparallel, south-verging thrusts whose seismogenic potential is still poorly known. Horizontal GPS velocities show that this sector of the eastern Southern Alps is undergoing ∼1 mm a−1 of NW–SE shortening associated with the Adria–Eurasia plate convergence, but the horizontal GPS velocity gradient across the mountain front provides limited constraints on the geometry and slip rate of the several subparallel thrusts. In terms of vertical velocities, the three geodetic methods provide consistent results showing a positive velocity gradient, of ∼ 1.5 mm a−1, across the mountain front, which can hardly be explained solely by isostatic processes. We developed an interseismic dislocation model whose geometry is constrained by available subsurface geological reconstructions and instrumental seismicity. While a fraction of the measured uplift can be attributed to glacial and erosional isostatic processes, our results suggest that interseismic strain accumulation at the Montello and the Bassano–Valdobbiadene thrusts it significantly contributing to the measured uplift. The seismogenic potential of the Montello thrust turns out to be smaller than that of the Bassano–Valdobbiadene fault, whose estimated parameters (locking depth equals 9.1 km and slip rate equals 2.1 mm a−1) indicate a structure capable of potentially generating a Mw>6.5 earthquake. These results demonstrate the importance of precise vertical ground velocity data for modeling interseismic strain accumulation in slowly deforming regions where seismological and geomorphological evidence of active tectonics is often scarce or not conclusive.

The Late Cenozoic crustal shortening in the north‐east margin of the Qilian Shan: Evidence from the Fengle Basin, Gansu Province

The north‐east margin of the Qilian Shan forms the front of the northeastward expansion of the Tibetan Plateau. Its Cenozoic crustal shortening is significant for understanding the uplift and growth of the Tibetan Plateau. The Fengle Basin, in the north‐east margin of the Qilian Shan, is characteristic of the typical regional superimposed deformation in Cenozoic strata, documenting the Cenozoic tectonic evolution process in the north‐east margin of the Tibetan Plateau. In this study, we conducted large‐scale geological mapping and regional structural analysis in the Fengle Basin, and rebuilt the two phases of Late Cenozoic crustal shortening deformation in this area: (a) The NW–SE shortening deformation in the Middle–Late Miocene led to the formation of NE‐striking folds in the Fengle Basin, and a hiatus between the Lower and Upper formations of the Gansu Group, probably linked with the far‐field effect of the northwestward subduction of the Pacific Plate. (b) The NE–SW shortening in the Late Miocene–Early Pleistocene overprinted the early NE‐striking folds, resulting in the development of a large‐scale dome structure in this area. The NE–SW shortening is associated mainly with the northeastward growth of the Tibetan Plateau. This study provides crucial evidence for the reconstruction of the intracontinental deformation process in the northeastern periphery of the Tibetan Plateau.

A case study of superposed structures in the tectonic interference zone between the Southern Brasília and Ribeira orogens, southeastern Brazil

The superposition of the Ribeira Orogen (590-560 Ma) on the southern segment of the Southern Brasília Orogen (630-605 Ma) generated a region known as the tectono-metamorphic interference zone. This zone is characterized by the almost orthogonal superposition of structures and metamorphic isograds attributed to the Ribeira Orogen on older structures and metamorphism belonging to the Southern Brasília Orogen.A flat-lying nappe stack characterizes the Southern Brasília Orogen, and it presents top to the east tectonic transport with intense ductile deformation inside the nappes, visible by the development of a strong E-W stretching lineation and related sheath folds. In the Ribeira Orogen more open upright folds, with axial planes dipping steeply to SE predominate, often with a down dip stretching lineation.In the study area, located in this interference zone, descriptive criteria permit grouping of three sets of structures, attributed to three deformation phases, Dn, Dn+1 and Dn+2, here understood as either separated in time or parts of a progressive deformation. Dn produced the main schistosity, Sn, dipping steeply to the south/southeast; associated tight folds and a strong stretching lineation (Ln), plunging shallowly to E/NE, are also ascribed to this phase. Dn+1 generated open to tight regional folds with NE-SW axes and axial planes dipping moderate to steeply to SE. Gentle to open Dn+2 folds with subvertical ENE-WSW trending axial planes refolded older structures locally. Superposed structures between these phases, of type I (Dome and Basin), type II (Mushroom) and type III (Walking Stick) were recognized. The attitude of the structures of these three phases and the type of interference patterns allow to interpret Dn as related to the northeastward tectonic transport in the southern part of the Southern Brasília Orogen and Dn+1 and Dn+2 as reflecting the NW-SE shortening typical for the Ribeira Orogen deformation. The folds and the interference pattern between Dn and Dn+1 are predominantly coaxial. Our understanding of this coaxiallity is that the strong NE-SW linear anisotropy related to thrusting to NE during the Southern Brasília Orogen (Dn) was used as fold axes by the NW-SE shortening related to the Ribeira Orogen.

Seismic Imaging of Collapsed-Anticline Diapirs in Central Tunisia

Central Tunisia is characterized by major fault systems, being ornamented by salt diapirs of the Late Triassic evaporite-rich interval. Salt movement began in the Late Triassic and continues to the present-day. Lasting halokinesis create pillows, diapirs, salt wall and salt-cored folds, sometimes, with collapse graben above. Salt diapir structures have been mapped and many regions collapsed diapirs are, perhaps, associated to salt removal. These structures were eroded resulting exposure and sub-aerial erosion by the Late Cretaceous to Paleogene uplift and post-Middle Miocene. The initial studies and findings related to salt structures in Tunisia suggesting a clear correlation between diapiric uplift and local tectonic structures. In particular, the N‒S and NW‒SE shortening trends during the Neogene and Quaternary folding strongly controlled the development of rows of diapirs and salt walls. The salt activities are controlled by tectonics as well as differential loading in the Triassic sediments over long distances, displaying that the mobilization of Triassic sediments covered the whole region and not just the zones near the single diapiric structures. Here we will focus also in the salt related plays and the associated petroleum systems with particular emphasis on trap types, reservoir and hydrocarbon migration pathways. Obviously, all these elements are linked together to certain degree and controlled by the salt tectonics.

Temporal variations in the dynamic evolution of an overriding plate: Evidence from the Wulong area in the eastern North China Craton, China

Abstract The evolution of overriding-plate deformation, and the mechanisms responsible for this deformation, are debated. One area where these processes can be investigated is the eastern North China Craton (NCC) in China, which was situated in an overriding-plate position relative to the subducting Paleo-Pacific Plate during the Jurassic and Cretaceous. Here we constrain the structural evolution of the Jurassic and Cretaceous using new structural, stress field, and geochronological data from the Wulong area. The results show that the first phase of deformation (D1) produced a series of SE-dipping reverse shear zones and parallel folds in response to NW-SE shortening at 157–146 Ma (Late Jurassic). Based on microscopic observations and quartz c-axis analysis, it is suggested that the temperature during D1 deformation was 500 ± 50 °C. A second phase of contractional deformation (D2) at 146–132 Ma (earliest Early Cretaceous) gave rise to numerous NE-SW–striking sinistral faults and shear zones. The majority of D2 structures display ductile fabrics in the southwest of the Wulong area and brittle deformational features in the northeast, thus indicating enhanced exhumation in the former area. Microstructures of D2 sinistral shear zones indicate deformation temperatures of 300–400 °C. Inversion of fault slip data from the sinistral faults demonstrate that N-S compression was responsible for the D2 structures. The third phase of deformation (D3) was related to WNW-ESE extension during the middle to late Early Cretaceous (132–100 Ma). This extensional phase produced a series of NE-SW–striking normal faults and reactivated pre-existing structures. Dikes and plutons were emplaced during the D3 deformation, synchronous with the peak destruction of the NCC. Our results indicate that the eastern NCC showed temporal variations in stress and strain during the Jurassic and Cretaceous. Consistent with the slab-driven model, we suggest that this behavior represents the response of the overriding-plate to changes in subduction kinematics.