Tectonic Inversion Research Articles

Connecting the Iberian Range with the Basque-Cantabrian Basin: The structure of the Sierra de Atapuerca (Spain)

We present a structural model of the Sierra de Atapuerca which constitutes the transition zone between the Iberian Range and the southwestern Basque Cantabrian Basin, NW Spain, where the Sierra de Atapuerca is located. The interpretation integrates both subsurface well and seismic hydrocarbon exploration data with surface geology. According to our interpretation, the Sierra de Atapuerca consists of a pop-up basement involved structure and is part of a NW-SE transpressive strike-slip band formed by high-angle faults segmented by transfer faults with a NE-SW direction. All this strike-slip alignment is located in the northern area of the Duero Basin and forms the footwall of the Duero North Thrust, which has transported the Folded Band and the Burgalesa Platform over this area thanks to a Triassic detachment, in a thin-skinned tectonics context. The Rojas and NW Demanda tectonic arcs represent the structural terminations of the Basque-Cantabrian Basin and Iberian Range domains, respectively, with the Sierra de Atapuerca located between both. The current structure of this zone is the result of an Alpine tectonic inversion of a previous Mesozoic extensional configuration, inherited from late Hercynian faults.

Tectonic inversion of Late Miocene extensional deformations in northeastern Tunisia (Cap Bon Peninsula–Sahel area)

Tectonic inversion of Late Miocene extensional deformations in northeastern Tunisia (Cap Bon Peninsula–Sahel area)

Palaeostress state around a rising salt diapir inferred from seismic reflection data

A 3D seismic volume and borehole data from the Dutch North Sea are used to investigate the palaeostress state around a rising salt diapir. The results show radial, polygonal and keystone faults around the diapir of interest, which are separated into eight zones based on their geometry, strike and overall distribution. Principal fault families include: a) 400–3500 m long radial faults developed in flanking and corner areas of the salt diapir, and known to have accommodated the stretching resulting from its rise, b) 200–1500 m long polygonal faults providing a record of the stress conditions farther from radial faults, and c) 1000–1800 m long keystone faults controlled by the rise of a buried salt pillow during Paleogene tectonic inversion. Stress inversions for 10,401 interpreted faults reveal that the maximum principal palaeostress (σ1) is close to vertical, whereas intermediate and minimum principal palaeostresses (σ2 and σ3) are sub-horizontal, though variable in their magnitudes and orientations. Palaeostresses in flanking zones of the salt diapir show marked differences when compared with corner zones, but the combination of minimum principal palaeostresses from all flanking and corner zones formed a triangular stress ring around the salt diapir. Importantly, the width of this stress ring was not only associated with the rise of the salt diapir, but also largely influenced by adjacent salt structures. Additionally, minimum principal palaeostresses estimated from polygonal fault systems are nearly normal to the boundary between polygonal and radial faults, implying that the rise of the salt diapir influenced the stress field in the outer part of its flanks. Stress inversion is shown here as a key method to understand the palaeostress state around the salt diapirs with triangular geometry and multiple growth stages, providing insights into their evolving stress states. This work also has implications to the analysis of salt diapirs, and their adjacent strata, in areas posed for carbon sequestration, gas storage, and the production of oil and gas.

Andean evolution, orogenic deformation and uplift of the Western Cordillera and Altiplano of southern Peru, northern Bolivia and Chile: Eocene-Oligocene lithospheric delamination

Reappraisal of Andean evolution in southern Peru, northern Bolivia and northern Chile provides support for models of orogenic cyclicity in which Andean crustal shortening in the Western Cordillera led to Eocene-Oligocene lithospheric delamination which triggered a renewed pulse of Andean uplift. The sedimentary fill of the Arequipa "rift" back-arc basin (Rhaetian-Neocomian) was controlled by two major graben-bounding fault systems: the Condoroma-Caylloma and Cincha-Lluta-Incapuquio; as well as the Cusco-Lagunillas fault system separating the back-arc region from the Cusco-Puno high. These thinned cortical inherited structures, were the most favourable places to undergo a positive tectonic inversion at the beginning of Andean compression (Albian), and then during Late Cretaceous-Paleocene shortening, they continued to develop as east-vergent crustal decollements which allowed crustal doubling and Western Cordillera thickening. The crustal thickening of >45 km took place along the Condoroma-Caylloma inverted graben where the lower crust, which was probably enriched in basalts, was subjected to high-pressure metamorphism leading to eclogitization, and became denser than the underlying mantle lithosphere and therefore delamination occurred. The subsequent asthenospheric upwelling led to lithospheric thinning, asthenospheric mantle magmatism of the first stage of Andahuaylas-Yauri batholith emplacement (∼48-43 Ma), which crystallized under temperatures of 1200–700 °C and pressures of 1.0–0.5 GPa (>40-30 km deep). This process was followed by the rapid surface uplift of the Western Cordillera that reached 3.1 km and fed the Kayra and Lower Moquegua basins, located on the Altiplano and in the forearc respectively. The delamination process was still active during 43–30 Ma, with second-stage magmatism of the Andahuaylas-Yauri batholith, emplaced continuously from deep mafic intrusions (40-30 km) to superficial porphyries (3 km). This indicates an important uplift of the Western Cordillera to 3.3 km, supported by mantle upwelling and the continuous flat-slab compression that prevented normal faults from developing, and rather produced the shortening of the delaminated crust. The Anta-Soncco foreland basins (43-30 Ma) of the Altiplano and Moquegua basin of the forearc, received the products of Cordilleran denudation at a rate of up to 700 m/My. The alkaline potassic magmatism (29–27 Ma) could represent episodes of post-delamination magmatism and the late stage of flat subduction.

Tectonic inversion of the Dnipro-Donets basin. Part 3. Tectonic style of deformations

The purpose. The peculiarities of the spatial distribution and tectonic style of collisional deformations of the riftogenic structure of the Dnipro-Donets Basin were investigated. Method. Kinematic and paragenetic analyses were used, structural drawings were studied, kinematic models of alpine-type deformations in the folded floors of the southeastern segment of the Basin were compiled. The results. It was found that the riftogenic structure along the strike different style and intensity of inversion complications was been undergone. The structural border between the weakly and significantly located territory along the meridian of the city of Balaklia was determined. To the west of the border the rift downthrows acquired arc-shaped contours and a pendulum structure due to horizontal movements. Zones of Hercynian folding are divided into separate branches by echelon systems of landslides located diagonally to their axes. To the east of the border, at first the regional board faults bend to the west, and then to the east of the city of Donetsk, the northern ones bend to the east, and the southern ones - to the southeast. The zones of nearboard and axial regional faults are destroyed, and because of this, the lines of the Kochubiyivsko-Volvenkivskyi and Sosnivsko-Stepkivskyi axial salt dome shafts are interrupted. The relic is the Axial fault with the Druzhkiv-Komyshuva shaft adapted to it. Instead of a reset rift, a shear-thrust inversion frame of orocline form was formed. Alpinotype dislocations on most of the territory of the Basin are weakly pronounced (scattered, low-amplitude faults and uplifts), but the southeastern segment significant fault-folding and cover-thrust deformations has undergone. The analysis of the structure of the Oligocene-Miocene sediments shows that neotectonic structures in the sole of the Cenozoic cover and the daytime relief are reflected. On the northern board of the Basin, a number of arc-like elongated uplands that located in the hanging wings of the Hercynian thrusts were formed. A sign of uplands` formation in the geodynamic environment of transpression is oscillating articulation and diagonal placement relative to shear-thrust zones. Scientific novelty. By the analysis of structural pictures of Elements of tectonics characteristic of transpression zones was identified. For the first time the nature of alpine-type deformations on kinematic models was identified. The Cenozoic movements along the re-mobilized zones of the Hercynian thrusts formed dynamically coupled ensembles of neotectonic structures was established. The hinged-jointed structural parageneses were formed by the mechanism of longitudinal elongation of the geological space due to the horizontal movements of right kinematics over the zones of dynamic influence of shear-thrusts of the foundation. It was found the tectonic style of the latest deformation ensembles is inherent in the platform fold-thrust geostructures of the tectonic breakaway. For the first time the newest platform structure - the West-Donetsk tectonic orocline of cover-folding deformations was identified. Practical significance. Data on the distribution of alpine-type complications of the West-Donets Graben for paleogeodynamic reconstructions and improvement of the regional scheme of tectonic zoning of the Dnipro-Donetsk Basin can be used.

Tectonic inversion of the Abanico basin eastern border and the structuring of the Aconcagua thrust-fold belt, southern Central Andes at 32°-33°S

Previous geologic studies and structural interpretations of the Meso-Cenozoic units in the Andean Principal Cordillera, between 32°- 33°S, have faced many difficulties due to the strong variability in volcanic deposits' thickness, the structural complexity that affects the involved units, and the scarcity of geochronological data that prevents defining a clear boundary between them. Structural-lithologic work carried out between 32°45′-33°S allowed us to recognize and define 4 different lithologic units along the Aconcagua-Juncal river valleys: one marine sedimentary unit assigned to the Cretaceous Mendoza Group and Late Jurassic exposures from the Río Damas/Tordillo Formation, and 3 volcano-sedimentary units mainly associated with Cenozoic volcanism represented by the Farellones, Abanico, and Cristo Redentor formations. The stratigraphic-structural model proposed in this work also allows for defining 3 structural domains throughout the study area: a western domain close to the Pocuro Fault Zone, a central domain, and an eastern domain close to the Alto del Juncal Fault Zone, next to the Chile-Argentina international border. The western and central domains show folds with larger wavelengths than the eastern domain, while the eastern domain shows intense deformation related to the emplacement and evolution of the Aconcagua fold and thrust belt. This deformation results from tectonic events which mainly occurred between the Upper Oligocene and Miocene. In the study region, these events caused a minimum shortening of ∼30 km in the Principal Cordillera. Based on the collected information, the Alto del Juncal Fault is also interpreted as the eastern Abanico basin bounding fault in which the Aconcagua fold-thrust belt is rooted.

Evidence for structural control of mare volcanism in lunar compressional tectonic settings

One of the long-standing enigmas for lunar tectonic-thermal evolution is the spatiotemporal association of contractional wrinkle ridges and basaltic volcanism in a compressional regime. Here, we show that most of the 30 investigated volcanic (eruptive) centers are linked to contractional wrinkle ridges developed above preexisting basin basement-involved ring/rim normal faults. Based on the tectonic patterns associated with the basin formation and mass loading and considering that during the subsequent compression the stress was not purely isotropic, we hypothesize that tectonic inversion produced not only thrust faults but also reactivated structures with strike-slip and even extensional components, thus providing a valid mechanism for magma transport through fault planes during ridge faulting and folding of basaltic layers. Our findings suggest that lunar syn-tectonic mare emplacement along reactivated inherited faults provides important records of basin-scale structure-involved volcanism, which is more complex than previously considered.

Emplacement and accumulation of magmatic products in contractional structures: How does it occur? Insights from Central Andes of northern Chile

Structural and stratigraphic data demonstrate that the magmatism in northern Chile was accompanied by shortening related to the development of fold and thrust belts. However, how magmatic products were emplaced and accumulated in the contractional structures is an unresolved question. We, therefore, integrated field and seismic data from the regions of the Pampa del Tamarugal, Salar de Punta Negra Basin, and the Hornitos Fold and Thrust Belt to determine the main structures that facilitated the magma accumulation. The syn-kinematic granitic intrusions in the Hornitos Fold and Thrust Belt were preferably emplaced along fold-related thrusts. In this region, magma migrated along thrust ramps and finally accumulated into the core of the anticlines and broken synclines. Subsidiary and vertical tensional fractures controlled the magma accumulation in the hinge zone and at the axis of the folds. The seismic data from the Pampa del Tamarugal and Salar de Punta Negra Basin present evidence of buried volcanoes on inversion anticlines. During the tectonic inversion of the pre-existing Late Paleozoic to Mesozoic half-graben structures in the regions, magma migrated along the master faults and finally accumulated into the core of the inversion anticlines as sills or was expulsed to the surface as volcanoes, as evidenced by the Punta Negra Monogenetic Volcano.

The effects of positive tectonic inversion structures on the formation of thrust systems on the western Domeyko Cordillera, northern Chile: Implications for the orogenic development of the outer Andean forearc

This work aims to propose a novel structural setting for the outer Andean forearc. Specifically, we propose a new deformation mechanism related to thrusting belt systems induced by positive tectonic inversion processes in the western flank of the Domeyko Cordillera in northern Chile. Thrust belt systems have been rarely understood for the outer Andean forearc; in fact, the mention of thrusting is scarce and structural interpretations are restricted only to strike-slip faulting and positive tectonic inversion processes. In this study, we have constructed novel balanced cross-sections from new structural fieldwork and combined them with 2-D reflection seismic line re-interpretations, thus offering new ideas about the evolution and development of the forearc of the Central Andes. Based on this, we propose integrated kinematic models that describe the relationships between inherited extensional structures, positive tectonic inversion structures, and the formation of thrust systems. The proposed balanced cross-sections have been restored to a pre-shortening condition. In this way, two structural styles are proposed for the western flank of the Domeyko Cordillera. The first corresponds to west-directed positive tectonic inversion structures, which expose and extrude the Middle Jurassic syn-rift deposit of the ancient Mesozoic rift basin. The second consists of east-directed thin-skinned thrust systems, mainly affecting the Upper Cretaceous to Eocene volcano-sedimentary synorogenic sequences. The interaction between inversion structures and thrust system structural styles would generate a west-directed intracutaneous wedge. Finally, the minimum shortening obtained from our balanced cross-section restorations is ca. 11% for the Río Loa and the San Salvador Canyons segment and ca. 56% for the Quebrada Mala segment. The formation of thrusting structures is controlled by a major detachment fault activated from a regional-scale angular unconformity, which we have named the Quebrada Mala detachment fault. An important part of the shortening was taken up and accommodated by buttressing structures and their associated intraformational detachment-thrust levels.

Deciphering multi-phase inversion tectonics in the southern Dezful Embayment: insights from the Rag-e-Sefid Oilfield, SW Iran

ABSTRACT Identification of inversion tectonics and inverted structures is very important in petroleum exploration and production due to the positive or negative impacts they can exert on the hydrocarbon traps. In order to characterize the occurrence of multi-phase inversion tectonics and its effect in the Rag-e-Sefid Oilfield, located in the southern Dezful Embayment (SW Iran), this research describes the structural style and deformation history through structural and tectono-sedimentary analyses. The results obtained from the interpretation of seismic profiles and the investigation of the geometry of the sedimentary layers across the growth structures indicate that the Rag-e-Sefid anticline is created from multiple fault-propagation folds. The final shape and geometry of the Rag-e-Sefid anticline are affected by the Rag-e-Sefid and Nourooz-Hendijan-Izeh Faults activity. The deformation history in the north-western part of the Rag-e-Sefid anticline is older than the south-eastern part of it. The Rag-e-Sefid Fault set in the north-western and south-eastern parts of the Rag-e-Sefid Oilfield experienced activity at least during seven and four tectonic phases, respectively. Multiple fault-propagation folding and the fold axis rotation in the north-western part of the Rag-e-Sefid anticline controlled by the presence of several décollement surfaces and the occurrence of inversion tectonics along the pre-existing basement structures. Three-phase inversion tectonics along the Nourooz-Hendijan-Izeh Fault and the Rag-e-Sefid Fault set in the north-western part of the Rag-e-Sefid Oilfield occurred at the Late Devonian-Carboniferous (positive inversion), Permian-Early Triassic (negative inversion), and Late Cenomanian-Early Turonian (positive inversion) boundaries and modified the evolutionary history of the sedimentary basin. The inversion affected hydrocarbon trap development at the Late Cretaceous and controlled their current conditions in the southern Dezful Embayment. Based on the hydrocarbon migration in these regions from the Late Miocene to the present day, the N-S trending (Pan Africa trend) north-western part of the Rag-e-Sefid anticline has a larger share of oil and gas compared to the NW-SE trending (Zagros trend) south-eastern part. The results of this study could add data to worldwide examples of the positive impact of tectonic inversion on the hydrocarbon traps development in the foreland of a collisional orogen.

Structural geometry and tectonic evolution of an Early Cretaceous rift crossing the Nile Valley in Upper Egypt

Two-dimensional (2D) seismic reflection data tied to well logs are used to present new insights on the structural geometry and tectonic evolution of an Early Cretaceous rift crossing the Nile Valley in Upper Egypt. This rift extends to ∼260 km long in a NW-SE direction, and 80–100 km wide, and was previously unstudied due to a lack of subsurface data. It is named here as the Upper Egypt Rift. It is divided into three depocentres, or segments, from southeast to northwest: The Kharit, Nuqra, and Komombo basins, filled with thick (ca. 3700 m) continental to open marine Lower Cretaceous-Campanian/Maastrichtian strata. The Kharit and Komombo basins are NW-striking fault-bounded half-grabens associated with NE-dipping syn-rift rocks. They are linked by a major N–S oriented normal fault bounding the eastern side of the Nuqra basin and terminate in two overlapping synthetic transfer zones. This rift geometry is controlled by the reactivation of a Precambrian Najd-parallel (N125°E) shear zone during rift initiation. Seismic cross-section restoration indicates a multiphase extensional history for the Upper Egypt Rift. The first rift episode occurred during the Berriasian-Valanginian and the early Aptian as a result of the opening of the South Atlantic, and was influenced by the tectonic evolution of the Neotethys Ocean as well. The second rift locally developed in the area during the Cenomanian-Turonian and was characterized by extrusive alkaline volcanics and intrusive rocks. Rift-related Natash volcanics and trachyte plugs of Cenomanian/Turonian age are exposed at the eastern side of the Nuqra basin but not recorded in the Komombo and Kharit basins. Soon after that, the whole basin experienced mild tectonic inversion synchronously with the Syrian Arc compressional events. Rotated fault blocks and slightly inverted anticlines thus comprise the main hydrocarbon trapping structures in the Komombo basin. Further work is required to define the time-dependent relationship between oil migration and trap development in the Upper Egypt Rift.

Heterogeneity of the Ailaoshan–Song Ma ophiolitic mélange and its palaeogeographic implications for the evolution of Eastern Palaeo-Tethys

In comparison with ophiolite, ophiolitic mélange, especially its matrix, contains more information about the evolution of the relevant ocean. The evolution of the eastern Palaeo-Tethys recorded a whole Wilson cycle of numerous continental blocks such as the South China Block and Indochina Block, including rifting away from the Gondwana continent, subsequent northward migration and final collage with the Laurasia continent. Based on structural geology, detrital zircon, and related geochemical analyses, the Ailaoshan–Song Ma ophiolitic mélange can be divided into M1, M2, and M3 units with distinct detrital zircon age spectra and εHf(t) values suggesting for different provenances. These units are in faults-contact along the orogenic belt, indicating a strike–parallel heterogeneity of the ophiolitic mélange. To further understand the heterogeneity of these ophiolitic mélanges, five samples from the matrix of the Ailaoshan ophiolitic mélange were collected to be conducted detrital zircon UPb dating and LuHf isotope analyses. All samples share the same zircon age spectrum, with two obvious age peaks at 430 and 960 Ma, which is comparable with the M1 unit. These results imply that the northwestern Ailaoshan ophiolitic mélange segment can be subdivided into M1 in the interior and M2 in the exterior rather than the previous division, indicating a strike–perpendicular heterogeneity. Based on their geometries (NE-dipping) and depositional ages (M1, 310–270 Ma; M2, 260–240 Ma), the elder M1 unit was thrusted upon the younger M2 unit, indicating a tectonic inversion. This inversion, which is associated with the whole geometry of the Ailaoshan belt, is ascribed to the transpressive deformation of the Cenozoic Red River Fault. These spatial heterogeneities well match the different evolutionary stages of the eastern Palaeo-Tethys.

Role of inheritance during tectonic inversion of a rift system in basement-involved to salt-decoupled transition: analogue modelling and application to the Pyrenean–Biscay system

Abstract. The reactivation of former rift systems and passive margins during tectonic inversion and their incorporation into fold-and-thrust belts result in significant structural differences not only between internal and external domains, but also along-strike. The Basque–Cantabrian and Asturian systems are among the best examples to address the role of along-strike changes in rift inheritance since they show a transition from salt to basement-inherited structures divided by a transition zone separating thick- from thin-skinned structural domains. While both domains have been widely described in the literature, the transfer system separating the two has not been sufficiently investigated due to poor seismic imaging and the lack of large-scale outcrops. This contribution aims to address the linkage between basement-controlled (i.e. thick-skinned) and salt-decoupled (i.e. thin-skinned) domains and to describe how deformation is accommodated in the transitional zone between these domains. An experimental programme based on analogue models has been designed that was inspired by the transition from the thin-skinned Basque–Cantabrian Pyrenees to the east to the thick-skinned Asturian Massif to the west. As observed in nature, experimental results show that oblique structures (at low angle with the shortening direction) form in the transitional domain, and their location depends on the linkage of the active structures occurring in both surrounding thick- and thin-skinned domains at different positions. Nevertheless, their orientation and evolution are controlled by the underlying decoupling horizon (i.e. salt). The deformation in the thick-skinned domain produces significant topography over a narrow deformation area due to the lack of effective decoupling levels. On the contrary, deformation in the thin-skinned domain is more distributed due to decoupling, resulting in a wider deformation area of less topography. As a result, syn-contractional sedimentation occurs mainly in the foreland basin in front of the thick-skinned domain, whereas it is observed in the foreland but also in piggyback basins in the thin-skinned domain.

Review of tectonic inversion of sedimentary basins in NE and N Brazil: Analysis of mechanisms, timing and effects on structures and relief

Most intraplate areas worldwide are under compression characterized by thrust and strike-slip deformations. The sources of the stresses in these regions are a combination of far-field (regional) stresses (e.g., ridge push, slab pull, lithospheric drag) and near-field (local) stresses (e.g., topography, lateral and vertical anisotropy of strength or elastic properties, erosion, flexural bending, overloading, buoyancy of low-density regions). These intraplate regions are sites favorable for the tectonic inversion of sedimentary basins. Here, we review the tectonic inversions of the sedimentary basins in NE and N Brazil, which comprise a significant part of the South American intraplate (the South American Platform). These regions have been under compression since the Late Cretaceous. Reports of post-rift basin inversions derived from seismic profiles, fault-slip data, and topography have been described in the Sergipe-Alagoas, Paraíba, Potiguar, Ceará, Rio do Peixe, Araripe (NE Brazil), and Solimões (N Brazil) basins. Reports of inversions in the rift phase have also been described in the Araripe Basin. The present-day stress field indicates that inversions in NE Brazil can mainly be characterized as strike-slip and thrust fault regimes, whereas in N Brazil, inversions have occurred under reverse stress regimes. The most frequent inversion structures are reactivated faults, folds, and dome structures affecting the topography and the consequent uplift of rift and post-rift sedimentary units. Inversions have led to the reactivation of continental-scale structures, such as the strike-slip dextral shearing of the Transbrasiliano lineament, which affected rift and post-rift units in the Equatorial Margin of Brazil. The small crustal thickness of these areas favors inversion, as indicated by the most recent Moho depth map of South America. The interplay between far-field and near-field stresses explains the stress pattern in NE and N Brazil, where inversions have been observed.

MODELING OF HYDROCARBON GENERATION ZONES AND MIGRATION PATHWAYS OF AN OIL FIELD OF PRECASPIAN REGION, KAZAKHSTAN

This article highlights the features of geological (basin) modeling of various zones and migration routes and presents the assessment of resources of the oil field in the Precaspian region in western Kazakhstan. A brief overview of geochemical features of the basin is presented using modern assaying and visualization software packages. The preferred method of constructing 1D models is indicated, and the results of such 1D modeling derived from the results of basin modeling are presented. Additional data points (including paleowater depths, sediment-water interface temperatures and heat flows) as boundary conditions were collected and included in the modeling software for data calibration and cross-checking purposes. For all 1D models produced in this study, Jurassic source rocks were deemed to have entered the oil window in Cretaceous time with the critical moment occurring in Late Cretaceous and Early Paleogene. The implied tectonic history of the basin suggests two possible periods of trap formation: tectonic inversion in the Middle Jurassic and possible folding during late Alpine orogeny which began in Late Cretaceous or early Eocene. While the Middle Jurassic traps can undoubtedly be filled with hydrocarbons, there is no such high degree of certainty with regards to traps formed after Late Cretaceous, as those traps were formed after peak migration periods.

Formation and evolution of the strike-slip faults in the central Sichuan Basin, SW China

Based on 3D seismic and drilling data, the timing, evolution and genetic mechanism of deep strike-slip faults in the central Sichuan Basin are thoroughly examined by using the U-Pb dating of fault-filled carbonate cement and seismic-geological analysis. The strike-slip fault system was initially formed in the Late Sinian, basically finalized in the Early Cambrian with dextral transtensional structure, was overlaid with at least one stage of transpressional deformation before the Permian, then was reversed into a sinistral weak transtensional structure in the Late Permian. Only a few of these faults were selectively activated in the Indosinian and later periods. The strike-slip fault system was affected by the preexisting structures such as Nanhuanian rifting normal faults and NW-striking deep basement faults. It is an oblique accommodated intracratonic transfer fault system developed from the Late Sinian to Early Cambrian to adjust the uneven extension of the Anyue trough from north to south and matches the Anyue trough in evolution time and intensity. In the later stage, multiple inversion tectonics and selective activation occurred under different tectonic backgrounds.

The Late Cretaceous tectono-sedimentary evolution of northern Poland – A seismic perspective on the role of transverse and axial depositional systems during basin inversion

This paper describes a new tectono-sedimentary model of the Late Cretaceous evolution of the northern, peripheral part of the Polish Basin, strongly influenced by inversion tectonics and fed by transverse and parallel depositional systems. The study area is located in northern Poland, in the boundary zone between the southeastern marginal part of the East European Craton and the northeastern margin of the Mid-Polish Anticlinorium, a regional inversion structure that runs northwest-southeast across the entirety of Poland. Traditionally, a “layer-cake” geological model, mainly based on borehole data, has been employed to characterize the regional depositional architecture of the Upper Cretaceous succession. Our new interpretation is based on regional geo-seismic transects, including the unique, regional high-resolution PolandSPAN™ seismic survey, calibrated by deep wells. The upper Albian – Upper Cretaceous succession was subdivided into five regional seismic stratigraphic units. Within these units, seismic facies and corresponding lithofacies representing siliciclastic and carbonate-siliceous depositional systems are described. The relative role of transverse and parallel depositional systems, including bottom currents, was recognized. Bottom current activity was documented by numerous, previously unknown seismostratigraphic features such as changes in lateral thickness, unconformities, and incisions. Two recognized contour current systems (N–S and NW–SE) operated along the edges of inversion structures that were uplifted in the Late Cretaceous – Palaeogene. A very significant rearrangement of this part of the Polish Basin, highlighted by a regional unconformity mappable over the entire study area, took place in the Campanian – Maastrichtian.

Polyorogenic structure of the San Rafael Block, Mendoza, Argentina: New data for the interpretation of the Chanic Orogen

The Paleozoic pre-Carboniferous rocks of the San Rafael Block, located to the east of the Los Reyunos Gondwanan Thrust, show Chanic structures (Late Devonian–early Carboniferous) with east vergence, which were generated in the absence of metamorphism. This Paleozoic succession is unconformably located on the basement of Cuyania. The rocks, located to the west of the Los Reyunos Thrust, were deformed by two fold episodes, the first and main (D1) west verging, developed under low to very low-grade metamorphic conditions, and the second (D2) east verging and mainly developed near Los Reyunos Reservoir. Therefore, the Los Reyunos Thrust must be considered a reactivation of a Chanic structure during the Gondwanan Orogeny (late Carboniferous–early Permian). The ancient Chanic thrust could be responsible for the overlay of the hinterland of the western branch of the Chanic Orogen on the foreland of its eastern branch, at the end of the collision between the Cuyania and Chilenia subplates. The results of this work have been related to those of nearby areas located to the north and west, which has allowed the elaboration of a model that explains the characteristics of the Chanic Orogen in this area. During the Carboniferous, the Los Reyunos Thrust was reactivated as a normal fault, facilitating the sedimentation of carboniferous rocks thousands of meters thick in its hanging wall and later, during the Gondwanan deformation, it underwent a tectonic inversion. During the Andean cycle, the Permian–Triassic beds of the Choiyoi Group were deposited in relation to NW–SE trending normal faults, giving rise to rollover structures. Finally, during the Cenozoic, Andean compression gave rise to the formation of an open antiform, in whose core is the Mesoproterozoic–Paleozoic basement of the San Rafael Block.

Structural Analysis of Kirthar Fold Belt, Lower Indus Basin, Balochistan, Pakistan; Implications from Compression and Inversion Tectonics

The current research work mainly focuses on tectonic evolution of the Central Kirthar Fold Belt. It also deals with the structural impact of the Late Cretaceous/Paleocene, Indian-Eurasian collision on the Central Kirthar Fold Belt which is situated in the western shear zone of Indian Plate. The Kirthar Fold Belt is different from the rest of western shear zone because it is mainly deformed by compressional tectonics which has created wide anticlines, narrow synclines and overturned folds as shown by geological mapping. It has been observed that thin-skinned deformation has played a major role in structural disharmony which is mainly seen in the Early Eocene Ghazij and Oligocene Nari formations. Seismic data shows thick-skinned deformation because the faults seem to penetrate deeper stratigraphic levels. Involvement of the basal decollement and the penetration of the interpreted faults to the level of basement rocks is also evident from the exposure of Jurassic/Cretaceous rocks at surface on the western part of the mapped area. Cross sections data shows that Kirthar Thrust Fault has a structural throw around 3-4 km in the Kirthar Folded Zone featuring deformational front while the seismic data and well data shows that this intensity decreases in the Kirthar Foredeep Zone towards east where the structural throw is about 2-3 km. Restoration of cross sections show an overall 17.3% shortening which shows that the area is under influence of compressional stresses.

Genesis of the Yangjiakuang gold deposit, Jiaodong peninsula, China: Constraints from S-He-Ar-Pb isotopes, and Sm-Nd and U-Pb geochronology

Located in the Penglai-Qixia-Fushan Gold Belt, the Yangjiakuang gold deposit formed in the marble of the Paleoproterozoic Fenzishan Group is different from the previous altered rock-type gold deposits whose host gold-bearing rocks are Archean gneiss and Mesozoic granite. Two gold orebodies have been explored within the Yangjiakuang gold deposit, and both of them were controlled by the Yangjiakuang syncline. Three ore-forming stages have been recognized, including the pyrite-sericite stage (I), the gold, polymetallic sulfide, and quartz stage (II), and quartz-calcite stage (III). The calcites, which represent the main metallogenic stage (II) at Yangjiakuang gold deposit, yielded a Sm-Nd isochron age of 123.5 ± 8.1 Ma (MSWD = 0.042). Subsequent geologic events were recorded by quartz diorite porphyrite dyke which are dated at 122.75 ± 0.66 Ma (MSWD = 1.5) by zircon LA-ICP-MS U-Pb dating. It is suggested that the gold mineralization took place in the early period of Early Cretaceous. The in situ δ34S values of pyrites from two stages have a narrow range from + 5.65 to + 9.63‰ with an average value of 8.14‰, which indicate that the source of δ34S is related to the Guojialing granite and the Fenzishan Group. The lead isotopic compositions of pyrites (206Pb/204Pb = 16.615 to 16.832; 207Pb/204Pb = 15.275 to 15.403; 208Pb/204Pb = 36.829–37.470) show a consistent origin of the lower crust. The measured 3He/4He (40Ar/36Ar) of hydrothermal fluids in pyrites are 0.641–1.132 Ra (637.5–1162.7), indicating that the ore-forming fluid originating from a mixing of crustal and mantle components. It is suggested that the gold mineralization is associated with extensional tectonic inversion caused by the rollback of the subducting Izanagi Plate during the early Cretaceous, which triggered partial melting of mantle and lower crust, and subsequent magma mixing and exsolution of ore-bearing fluids. These fluids extracted ore-forming materials from the enclosing rocks of the Jiaodong Group, the Fenzishan Group, and the Guojialing granite to form the ore-forming fluids.