Abstract Fifty per cent of orogens have a thick-skin character, and have evolved from passive margin and intra-cratonic rift systems. One group of thick-skin provinces can be found at both pro- and retro-wedges of orogens associated with advancing subduction zones, that is, orogenic wedges whose advance vectors oppose the mantle flow. A second group can be found at pro-wedges of orogens associated with retreating subduction zones, that is, orogens whose advance vectors have the same direction as mantle flow. A third group is formed in intra-plate settings where mechanical strengthening is produced by internal shortening. Thick-skin province development is controlled by driving factors such as individual plate movement rates, overall convergence rates, orogen movement sense with respect to mantle flow, and pro-wedge v. retro-wedge location. These driving factors are themselves constrained by numerous internal and external factors. This introductory chapter focusses primarily on least-deformed case areas in order to understand the role of different factors in controlling the evolution of thick-skin tectonic provinces from the initial inversion stage to full accretion stage.

Abstract The northern front of the Cenozoic Tien Shan mountains in Kazakhstan comprises east- to NE-trending thrust-related basement uplifts. Some of these are open, asymmetric anticlines, whereas others are fault-bounded blocks. Where emergent and exposed, the bounding faults dip steeply at 45–70°. Large-wavelength open folds in the Cenozoic cover also overlie basement structures. The Palaeozoic basement of volcanic, (meta-) sedimentary and granitic rocks contains older structures such as folds, slaty cleavage, faults and dykes. Some Cenozoic faults truncate all earlier structures, just as some Cenozoic folds are independent of the attitudes of underlying stratified basement rocks. The strongest control on the Cenozoic structure is exerted by steep, NW-striking basement faults that induce along-strike segmentation and lateral terminations of some basement ridges. A few of these basement faults had already been reactivated as normal faults during a Cenozoic phase of east–west extension that preceded folding and thrusting. Some normal faults show reactivation as dextral strike-slip faults during the contractional phase, which is still active today. Since the NE to east trend of the main basement ranges has no obvious precursor structures, we interpret the thick-skinned structures to essentially reflect the modern shortening direction, modulated but not dominated by pre-existing basement faults. Variations in local kinematics over time are probably due to strain partitioning in the anisotropic basement, not to changing far-field stresses. The occurrence of steep dip-slip reverse faults apparently unrelated to reactivation presents an unsolved mechanical paradox similar to some low-angle normal faults.

Abstract In many compressive zones, there is a risk of undercharged hydrocarbon prospects as a result of timing, that is, the growth of the structure is younger than the main fluid migration phase. The North Ucayali Basin represents a setting of this type, where locating the earliest structures is crucial for well placement. In the North Ucayali Basin, the variable amount of erosion at the top of the structures shows that they are not uniformly recent. Although the growth of early structures may be explained by the reactivation of inherited features during shortening, evaporitic pillows may represent an alternative factor controlling the localization of deformation in the studied area. Indeed, subsurface data reveal the presence of flat salt domes that have an influence on thrust localization. The existence and tips of such efficient gliding surfaces concentrate the strain and, as a result, localize the early zones of deformation. Analogue models designed to study these phenomena highlight the crucial role of salt pillows as potential weak zones localizing deformation ahead of the propagating wedge. These models also emphasize the need to constrain certain parameters that have been previously disregarded, including the thickness of the brittle layers between the main décollement level (if present) and the pillows, as well as their burial depth.

Abstract The Oriente Basin is part of the retro-arc foreland basin system that developed in the zone of transition between the Central Andes and the Northern Andes since Late Cretaceous times. It is deformed by thick-skinned tectonics related to the inversion of pre-Cretaceous extensional fault systems, which have broken the basin into three tectonic domains during three mean periods of inversion (Late Cretaceous–Palaeocene, Early Eocene and Miocene). The northern part of the present-day Sub-Andean wedge-top corresponded, during the Late Cretaceous, to the forebulge depozone. The NNE–SSW Sacha–Shushufindi Corridor (SSC) extends from the northern region of the Oriente foredeep to the Sub-Andean Cutucú Cordillera. It results from inversion of the Late Triassic–Early Jurassic rifting. The eastern Capiron–Tiputini Inverted System (CTIS) results from the inversion of the normal faults of the Late Jurassic back-arc basin. The Ishpingo–Tambococha–Tiputini (ITT) trend is located in the present-day forebulge depozone of the basin. This position presents favourable conditions for oil biodegradation. Source rocks throughout the Oriente Basin are immature or poorly mature. A large part of oil accumulations must be explained by long-distance migration from the west, before the Eocene uplift of the Cordillera Real, or from the south.

Abstract Structures mapped in the southern Cordillera Oriental of the Andes show an unexpected geometry in an east–west cross-sectional view, with a remarkable predominance of west-directed thrusts. Although some of the Andean structures trend north–south perpendicular to the main east–west direction of Andean shortening, many of them clearly differ from this expected orientation. This peculiar structural style has been largely related to the inversion of the Cretaceous Salta Rift Basin; however, some of these anomalously trending Andean folds and faults do not result from the inversion of Cretaceous faults. This lack of inversion of some Cretaceous structures becomes evident where west-dipping extensional faults rest in the footwall of west-directed thrusts instead of developing east-directed thrusts, as would be expected. Detailed study of several structures and examination of the geometry and facies distribution of several basins highlight not only the role played by the inversion of Cretaceous extensional faults on the geometry of the Andean structures, but also that played by basement anisotropies on the development of both the Cretaceous extensional faults and the Andean contractional structures.

Abstract The study area is located within the Central Andes, a complex region composed of different structural styles. The region is characterized by highly elevated basement cored ranges, which abruptly break the foreland plain. These ranges were uplifted mainly by deep detached high-angle faults or by the inversion of former extensional faults of the Cretaceous rift. Palaeozoic orogenies generated crustal scale discontinuities in the basement, some of them reactivated during the Andean orogeny. Sedimentary sequences and layers architecture in the basins bordering ranges recorded the tectonic evolution of the region. Basement, syn–rift, post-rift and three foreland stages were interpreted in the seismic sections according to the arrangement of the horizons and the main outcropping geological units in bordering ranges. Based on seismic data sets and field data, here we document a particular style of activation of basement faults. Thick-skinned structures that are not always related to the tectonic inversion but to the reactivation of older basement anisotropies represent a paradox since they were not active during the rifting stage. A flat slab subduction and a subsequent angle recovery conditioned the structural evolution of the area.

Abstract In the south-verging portion of the western Pyrenean Orogen, a Mesozoic basin and part of the adjacent continental margin were deformed during the Pyrenean collisional stage. The slight obliquity between extensional and compressional trends, and the presence of a Mesozoic Transfer Zone, implied that both extensional domains were exposed along-strike of the belt in the same structural position. These two areas are not only characterized by the widespread reactivation of inherited fault systems but also by different styles of deformation related to the presence or absence of an evaporitic detachment level. To the east, in the Mesozoic basin, a large-displacement south-directed low-dipping thrust detached above Triassic evaporites is present. To the west, in the Mesozoic continental margin, thick-skinned and deeply rooted right-lateral and reverse faults become first-order elements. The presence of a strike-slip component produced the eastwards extrusion of the eastern portion of the Mesozoic continental margin, which imposed an along-strike shortening at the edge of the extruded block. The transitional area from thin- to thick-skinned style of deformation, from a dip-slip to a transpressive framework, and the area accommodating the extrusion are located along a north–south-orientated band representing the southern extension of a Mesozoic Transfer Zone.

Abstract The Atlas, Eastern Cordillera and Pyrenees are thick-skinned thrust-fold belts formed by tectonic inversion of rift basins in continental settings. A comparison of shortening between them shows a gradation from 20–25% in the central High Atlas, to 25–30% in the Eastern Cordillera, and c. 40% in the Pyrenees. Accordingly, there is a structural variation from interior zones with low structural relief and isolated basement massifs in the first two cases, to an axial culmination of stacked basement thrust sheets in the Pyrenees. This results in marked topographic and drainage variation: the High Atlas and Eastern Cordillera contain axial plateaus dominated by structure-controlled longitudinal rivers and orogen flanks with slope-controlled transverse rivers, whereas the Pyrenees show a two-sided wedge profile dominated by transverse rivers. In spite of singularities exhibited by each orogen, we propose that this spatial variation can be understood as reflecting different degrees of evolution in mountain building. Rapidly incising, transverse rivers are capturing earlier longitudinal streams of the Atlas and Eastern Cordillera, thus reducing their axial plateaux, which will eventually disappear into a transverse-dominated drainage. This pattern of landscape evolution may be characteristic of inversion orogens as they develop from initial stages of inversion to full accretion.

Abstract Structural, sedimentological, well and seismic data from the Kura basin show that the geometry of deformation has been largely determined by thick-skin structures occurring along margins of depressions filled with upper Oligocene–lower Miocene Maykop formation, flanked by highs without Maykop record. Thin-skin structures are detached inside the shaly Maykop formation and inside shale horizons of the Sarmatian–Pontian section. The main shortening took part during Sarmatian–Pontian, followed by subordinate shortening during Akchagylian–present. The thick-skin architecture formed first, reactivating pre-existing rift grain on the foreland plate that refused to flex underneath the load of advancing orogens. The thin-skin architecture developed subsequently, deforming thick-skin structures. During the Oligocene–early Miocene, the foreland basin behaved as a flexural basin, reacting by prominent fill asymmetry to Oligocene loading by the advancing Lesser Caucasus and earliest Miocene–early Sarmatian loading by advancing Greater Caucasus. Subsequently, the basin recorded only vertical movements responding to new orogen loading events. Each loading event was recorded by a shift of marine depositional environments northwestwards, up the SE-plunging Kura Valley. Conversely each quiescence period was recorded by their retreat southeastwards, towards the Caspian Sea. Supplementary material: Discussion of the observations from geological and seismic cross sections, additional outcrop photos and data, lithostratigraphic charts of the Greater Caucasus, the Adjara–Trialet and the Eastern Pontides, heat flow map and of the Kura basin, depth distribution of earthquake hypocentres for the Kura basin region, and Apulia map and cross section are available at http://www.geolsoc.org.uk/SUP18626

Abstract The geometry, kinematics and evolution of thick- and thin-skinned fold and thrust-belts have been characterized for many tectonic provinces. However, the impact of prior extension in the structural evolution of fold and thrust-belts remains under-appreciated. We use a series of balanced cross sections across areas of thin- and thick-skinned tectonics superimposed over former extensional structures in order to characterize the style of deformation, segmentation and displacement magnitude. We detect the style of fault linkage in foothill settings adjacent to inversion belts. The most relevant aspect is the presence of inherited ‘soft linkages’ generating zones of displacement deficit, which in contraction interact laterally with en-echelon inverted segments via ‘detachment linkages’. We document the temporal development and interaction between inverted faults and fault splays branching from them where both are coeval but where the frontal fault tips propagate more slowly during Oligocene and Early Miocene times. Later, during the Neogene, the frontal fault splays slip faster than the main inversion fault. The structural style of thrust-belt development displays along-strike variations, which reflect the changes in sedimentation rates and mechanical conditions of deformation. However, the timing and magnitude of shortening remain uniform along-strike.

Abstract The Magdalena Valley fold-and-thrust belt is a tectonic province associated with inverted rift zones. This belt displays a narrow and discontinuous deformation front indicating association with inversion tectonics. We show the differences with an analogue belt on the eastern side of the Eastern Cordillera (Llanos foothills). To do that we use structural data (seismic, wells and geological maps) which characterize different structural geometries as well as palaeocurrents, provenance and thermochronology to analyse the timing of deformation. The new datasets allowed us to detect that inversion is limited whenever the stresses are more orthogonal to the rift structures, whereas the mountain front is more segmented in comparison to the Eastern Foothills because of the absence of a continuous low basal friction detachment horizon and a pronounced eastwards basement dip. These two factors favoured fault hard linkage. It is remarkable that, in spite of the distinct segmentation, all the different segments in the Magdalena belt are coeval. Supplementary material: U–Pb Zircon data are available at: http://www.geolsoc.org.uk/SUP18630 .

Abstract We use the Eastern Cordillera of Colombia as an example in early stages of inversion orogen showing still modest values of shortening. The style of deformation recorded in this orogenic chain seems to be strongly influenced by two main factors. The first is the pre-compression geometry of the rift basin, conditioning the strong heterogeneity imparted by a trough filled with Jurassic to Neocomian sediments limited by Precambrian and Palaeozoic high-angle walls. The second factor is the orientation of the stress regime with respect to the main normal faults during the inversion. If the stress field is of pure compression, the normal faults are not extensively inverted and the deformation is accommodated mainly in terms of footwall shortcuts. On the other hand, in transpressive regimes the inversion of the former normal faults is more common and the footwall shortcuts are not dominant structures. No significant lateral variations in tectonic shortening are found in the Eastern Cordillera. Finally we emphasize the role of buckle folds in the internal parts of the inversion orogens and give a cautionary note when interpreting these structures in terms of fault-related folding using the well-documented example of the Soapaga fault area.

Abstract The inversion of Mesozoic extensional structures in the Northern Andes has controlled the location of syn-orogenic successions and the dispersal of detritus since latest Maastrichtian time. Our results are supported by detailed geological mapping, integrated provenance (petrography, heavy minerals, geochronology) analysis and chronostratigraphical correlation (palynological and geochronology data) of 13 areas with Palaeogene strata across the central segment of the Eastern Cordillera. Spatial and temporal variation of sedimentation rates and provenance data indicate that mechanisms driving the location of marginal and intraplate uplifts and tectonic subsidence vary among syn-orogenic depocentres. In the late Maastrichtian–mid-Palaeocene time, crustal tilting of the Central Cordillera favoured reverse reactivation of the western border of the former extensional Cretaceous basin. The hanging wall of the reactivated fault separated two depocentres: a western depocentre (in the Magdalena Valley) and an eastern depocentre (presently along the axial zone of the Eastern Cordillera, Llanos foothills and Llanos Basin). In late Palaeocene–early Eocene time, as eastern subduction of the Caribbean Plate and intraplate magmatics advanced eastwards, reactivation of older structures migrated eastwards up to the Llanos Basin and disrupted the eastern depocentre. In early Eocene time, these three depocentres were separated by two low-amplitude uplifts that exposed dominantly Cretaceous sedimentary cover. Syn-orogenic detrital sediments supplied from the eastwards-tilted Central Cordillera reached areas of the axial domain of the Eastern Cordillera, whereas unstable metamorphic and sedimentary fragments recorded in the easternmost depocentre were supplied by basement-cored uplifts with Cretaceous and Palaeozoic sedimentary cover reported in the southern Llanos Basin. This tectonic configuration of low-amplitude uplifts separating intraplate syn-orogenic depocentres and intraplate magmatic activity in Palaeocene time was primary controlled by subduction of the Caribbean Plate. Supplementary material: Appendix 1 presents detailed descriptions of analytical methods used in this manuscript. Appendixes 2 to 4 include raw data of sandstone petrography, heavy minerals and U–Pb detrital zircon geochronology, respectively. All this material is available at http://www.geolsoc.org.uk/18597 .

Abstract A combination of new surface and subsurface structural data, new stratigraphic data on conventional provenance, facies and palaeocurrents, low-temperature thermochronology and detrital zircon U–Pb provenance data provides a comprehensive account of the timing of deformation in the intermountane Middle Magdalena basin of the Central Colombian Andes, and allows evaluation of the style of foreland basin deformation associated with tectonic inversion. This robust dataset enabled documentation of focused tectonic activity in two competing low-relief basement structures to the east and west of the present Middle Magdalena Valley during the Palaeogene, earlier than previously recognized. Cenozoic sediment accumulation of a sedimentary pile up to 7 km thick in the Middle Magdalena Basin created a large original taper angle in this part of the north Andes. At that time, when the detachment rocks were deeply buried, the original larger taper angle facilitated the forelandward advance of deformation instead of promoting its stagnation. Supplementary material: Raw data results from geochronometrial analyses are available at: http://www.geolsoc.org.uk/SUP18627

Abstract The initial stages of tectonic inversion and the mechanisms of selective reactivation and abandonment of pre-existing normal faults during contractional orogenesis are explored in a partially buried Cenozoic thrust belt in the Andes of Colombia. A multidisciplinary approach that includes subsurface structural mapping, multimethod thermochronometry and detrital zircon U–Pb geochronology reveals the extent of a Palaeogene thrust belt buried underneath the Cenozoic strata of the Middle Magdalena Valley Basin. A less oblique orientation with respect to compressive stress and shorter traces in faults of the Middle Magdalena Valley Basin with respect to faults in the western part of the Eastern Cordillera, apparently acted as deformation inhibitors of the Magdalena faults in advanced Neogene stages of inversion. Protracted Cenozoic eastwards tilting of the Central Cordillera and the tectonic load from the uplifting Eastern Cordillera favoured the accumulation of a thick Cenozoic sedimentary sequence in an, at least episodically, closed basin. All the above-mentioned conditions helped to block deformation in the Magdalena Basin, favouring deformation to be taken up by structures in the western Eastern Cordillera. These relationships underscore the importance of buried structural records in elevated hinterland basins, in which the low-relief stratigraphic cover overlies a complex subsurface record, potentially including large magnitudes of deformation during early orogenesis. Supplementary material: Tables and figures on the laboratory methods for the thermochronometrical and geochronometrical analyses are available at http://www.geolsoc.org.uk/SUP18601 .

Abstract The Cenozoic stratigraphic infill of hinterland and foreland basins in central Colombia holds the record of basin development during tectonic inversion of rift in the context of subduction orogenesis. A comprehensive review of detrital U–Pb geochronologic and thermochronologic data reveals that activation of interconnected fault systems in the hinterland Magdalena Valley and the Eastern Cordillera occurred coevally since Paleocene time. Longitudinal basins were fed by detritus shed from the Central Cordillera carried along axial drainage systems in open basins in times where slow deformation rates prevailed. Faster deformation since Oligocene resulted in the transient formation of internally drained basins. Differential along-strike exhumation and subsidence patterns in the Eastern Cordillera and the foredeep, respectively, document tectonic acceleration since late Miocene, which we attribute to superimposed collision of the Panama arc leading to oroclinal bending in the Cordillera. Our data documents that the inherited structural grain led to the formation of longitudinal drainage patterns, even in closed basins, which seem to be a general feature of early stages of inversion. We hypothesize that the presence of more humid climatic conditions and faster tectonic rates along the range’s eastern margin favoured the development of internally drained basins, as has also been shown in the Central Andes. Supplementary material: Methods details (zircon grains preparation, zircon U–Pb measurements, laboratory conditions and input constraints for AFT thermal modelling) and repository are available at http://www.geolsoc.org.uk/SUP18628