Orogenic Architecture Research Articles

A Reappraisal of Nappe Structures and Strain Patterns in the Core of the Variscan Orogen (French Massif Central)

AbstractMajor influences on the architecture of orogens include the overall thermal conditions of orogeny (hot vs. cold) and the angle of collision (orthogonal vs. oblique). In the French Massif Central of the Variscan orogen, a cold‐orogen style crustal nappe architecture was interpreted in the Haut‐Allier, located in the core of the orogen. Based on this model, the Variscan orogenic crust is described as the superposition of three main allochthonous tectonic units juxtaposed along major thrust faults. However, based on a detailed structural analysis, we have found instead that the region is dominated by a network of anastomosing conjugate and coeval dextral and sinistral shear zones striking WNW‐ESE and ENE‐WSW, respectively. The dextral WNW‐trending shear zones are predominant, whereas the sinistral NE shear zones are mainly located in the eastern part of the massif. Between these sub‐vertical shear zones, a sub‐horizontal foliation is observed. Our results indicate that all planar fabrics were partially synchronous during suprasolidus low‐pressure‐high‐temperature conditions. Strain partitioning occurred from high‐temperature suprasolidus conditions to subsolidus retrogression and may represent orogen‐parallel flow, suggesting hot‐orogen style. These results call into question the validity of the crustal nappe model in the Haut‐Allier. Based on new structural data and related observations, we propose a new model in which metamorphic gaps between tectonic units are explained by the juxtaposition of different structural domains by displacement along strike‐slip shear zones.

Shortening and extrusion in the East Anatolian Plateau: How was Neogene Arabia-Eurasia convergence tectonically accommodated?

Deformation in orogenic belts is typically widely distributed but may be localized to form discrete, fast-moving fault zones enclosing semi-rigid microplates. An example is the Anatolian microplate, which is extruding westwards from the East Anatolian Plateau in the Arabia-Eurasia collision zone along the North and East Anatolian Faults that cause devastating earthquakes, including those of February 6, 2023 in Southeast Anatolia. Here, we summarize the orogenic architecture of the East Anatolian Plateau and its underlying kinematic history since the Cretaceous, and use this to reconstruct the tectonic situation that existed at the onset of and during the development of the Neogene East Anatolian Plateau and the Anatolian microplate. The orogen first formed in the late Cretaceous by subduction-accretion of microcontinental lithosphere below Neotethys oceanic lithosphere. Then, in Paleogene time, the accretionary orogen underwent regional upper plate extension, causing crystalline crust exhumation and deep-marine basin formation. From early Miocene time onwards, the extended orogen shortened again and must have accommodated ∼350 km of convergence, making crust up to 45 km thick, and causing >2 km of uplift. Since the ∼13 Ma onset of North Anatolian Fault formation, microplate extrusion absorbed no more than 25 % (∼65 km) of Arabia-Eurasia convergence and even during this time alone, >200 km of convergence must have been accommodated by continued ∼N-S shortening. We highlight the need for field studies of the East Anatolian Plateau to identify where and how this major shortening was accommodated, what role it played in plateau rise and the onset and dynamics of microplate extrusion, and to better assess seismic hazards.

First identification of late Mesozoic intraplate magmatism in the Chinese north Tianshan: implications for the orogenic architecture and crustal evolution

The formation and dynamics of granitoids in an intra-continental setting are crucial for understanding the architecture and evolution of continental crust. Here, we report geochronological, geochemical and Sr–Nd–Hf isotopic data for newly discovered late Mesozoic granitic intrusions in the Tianshan belt, northwestern China. These granitoids are I-type granites derived from an igneous precursor and were emplaced at c . 145–132 Ma. They have positive ε Nd ( t ) values and young Nd model ages, together with relatively low Sr/Y ratios, indicating that they might have originated from partial melting of the juvenile lower crust. There is a prominent decoupling between zircon Hf and bulk-rock Nd isotopes, which may have resulted from the early crystallization of Ti-rich minerals. These granitic intrusions also display subduction-related geochemical characteristics, which are probably inherited from Paleozoic crustal sources that were metasomatized by subduction-related fluids. We conclude that these late Mesozoic granitoids were emplaced in an intra-continental setting, and were probably triggered by thermal relaxation owing to crustal shortening and thickening. These data further imply that the Tianshan changed into crustal reworking during the Mesozoic from its prominent crustal growth in the Paleozoic. Supplementary material: LA-ICP-MS zircon U–Pb dating results, whole-rock major and trace element compositions, whole-rock Sr–Nd isotopic data and zircon Lu–Hf isotopic data are available at https://doi.org/10.6084/m9.figshare.c.7167890 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Thrust-related metamorphism in Carboniferous slates of southern Patagonia (South America): the fate of forearc successions

The Devonian to early Carboniferous western margin of Patagonia (South America) includes a NW–SE-trending magmatic arc associated with a NE-dipping palaeo-subduction zone. Along the Andean region of southern Patagonia, the Eastern Andean Metamorphic Complex developed in a forearc position and consists of a succession of very low- to low-grade metaturbidite–metabasic rocks emplaced from the Devonian to Carboniferous. There are significant uncertainties surrounding this metamorphic complex, mainly related to the tectonosedimentary setting of the basin and the subsequent conditions of deformation and metamorphism, which hinder our understanding of the orogenic architecture. To reveal the links between tectonics and metamorphism, we conducted a structural analysis and sampled metapelites to measure the illite crystallinity along a regional structural cross-section in the Eastern Andean Metamorphic Complex. Our analysis reveals broadly lower to upper anchizonal metamorphism roughly synchronous with deformation along northwards-verging thrusts. These findings support the development of a forearc hyperextended basin that was subsequently closed during the Gondwanide Orogeny (late Paleozoic), a model that reconciles previous proposals suggesting passive margin v. back-arc basin models. This closure led to the emplacement of supra-subduction zone ophiolites and turbidites over the continent through the landwards migration of brittle–ductile reverse shear zones. Supplementary material: Measurements of the Kübler index are available at https://doi.org/10.6084/m9.figshare.c.7160849 Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

Complementarity of Hf isotopes from detrital and igneous zircon: an example from the Central Gneiss Belt, Grenville Province, Ontario

Combined U–Pb and Hf isotopic analysis of detrital and igneous zircon provides information about variations in crustal addition versus reworking through time. However, whereas detrital zircon data from only a few samples can provide information about extended periods of orogenic activity, this approach lacks the geological context that comes with studying igneous zircon and may not record mid- and deep-crustal sources or sources isolated from sites of deposition. Conversely, igneous zircon is likely to miss sources that were removed by later tectonic activity, but which may be preserved in the detrital record. The Central Gneiss Belt of the southwest Grenville Province in Ontario has a relatively well-understood orogenic architecture and records active-margin growth and reworking between ca. 1900 and 1200 Ma. We present U–Pb and Hf isotope data of zircon from 30 orthogneiss samples ranging in age from ca. 1750 to 1250 Ma, covering all tectonostratigraphic levels of the Central Gneiss Belt. As expected, the detrital and igneous datasets display many of the same overall features, such as crustal growth along the southwest Laurentian active margin; however, there are also some distinct differences. In particular, sedimentation appears to have taken place near the active margin, with little or no input from distal inboard sources, thus missing this significant component of reworked crust. This study highlights the need for a combination of detrital and igneous samples to provide the most complete picture of long-lived accretionary orogenic systems.

IESDB – the Iberian Evaporite Structure Database

Abstract. Evaporites flow in the solid state under relatively low differential stress and have unique mechanical properties compared to other sedimentary rocks. Worldwide, they control the structural and stratigraphical architecture of many basins and orogens in ancient and active tectonic settings. Moreover, they host mineral deposits and play a key role in petroleum systems because they typically act as seals due to their low permeability, and their ability to flow results in the formation of structural hydrocarbon traps such as folds and faults in their encasing rocks. Additionally, evaporite structures can be used as subsurface storage sites for geo-energy applications and nuclear waste. The systematic characterisation of subsurface evaporite structures is thus key for the development of geoscience-based technologies to address societal challenges. Owing to their value, massive amounts of surface and subsurface information about (among others) the stratigraphy, structure, geochemistry, and petrophysical properties of evaporite structures and their surrounding rocks have been acquired by Earth scientists, petroleum and mining exploration companies, and geological surveys. However, the data often appear segregated (i.e. in the form of database fragments, scientific articles, and unpublished reports), are not systematically organised, and are sometimes not fully accessible. This contribution presents the Iberian Evaporite Structure Database (IESDB), the first comprehensive assessment that focuses on evaporite structures carried out in any region of the world. The IESDB includes information and figures for 150 evaporite structures and their surrounding rocks inventoried in Spain and Portugal and is sourced from other six thematic databases and more than 1500 published and unpublished scientific documents. The database targets undeformed to slightly deformed evaporite successions, outcropping and buried diapirs, evaporite-cored anticlines, evaporite-detached thrusts, and allochthonous evaporite bodies. Collated data include information about the structure, stratigraphy, event chronology, surface and subsurface data availability, mining activity, and key bibliographic references. The IESDB follows the FAIR principles of database management (Findable, Accessible, Interoperable, and Reusable) and is presented as an interactive web page and an open-access database, where indexed structures can easily be selected from a map or browser and filtered by a search engine. The IESDB intends to be a useful resource for teaching (i.e. pointing out examples of exceptional evaporite outcrops), academic and industry research (i.e. identifying knowledge deficits on specific structures or tectonic settings), and for the sustainable exploration and appraisal of mineral resources and geo-energy applications (i.e. representing a terminus a quo for site selection and suitability assessment). The framework provided by the IESDB is an opportunity to enhance the scientific research on Iberian evaporite structures in Spain and Portugal and to take advantage of their scientific and economic potential to tackle important societal challenges faced by these countries. The IESDB is freely available at https://iesdb.eu (last access: 15 June 2023) and the datasets can be downloaded from https://doi.org/10.20350/digitalCSIC/14586 (González-Esvertit et al., 2022).

THE VOLGA-DON COLLISIONAL OROGEN IN THE EAST EUROPEAN CRATON AS THE PALEOPROTEROZOIC ANALOGUE OF THE HIMALAYAN-TIBETAN OROGEN

The ca 2.0 Ga Volgo-Don fold-and-thrust belt, about 500 km in width and at least 600 km in length, covering an area of about 300000 square kilometers intervenes between the Archean Sarmatian and Volgo-Uralian proto-cratonic blocks of the East European Craton, both of which are coupled with 200–300 km thick sub-continental lithospheric mantle keels. The focus of this paper is the elucidation of its nature in order to answer the basic question how this and other thrust-and-fold belts could be formed in the Paleoproterozoic, and whether they are the same as or different from modern collision orogens. The active Himalayan-Tibet orogen is commonly thought of as the most extensively studied large, bi-verging fold-and thrust belt continental collision zone which may provide insight into key tectonic mechanisms for an understanding of orogenic processes in the Earth’s geological past. Precambrian orogens are tentatively perceived yet as something that was distinct from recent orogenic styles and was due to the initial elevated geotherm and higher radio-genic heat production in the early Earth.In this paper we report for the first time the revealation of the large, slightly eroded divergent Paleoproterozoic Volgo-Don orogen which is mostly composed of juvenile metasediments and comprises well-preserved patterns of the crustal orogenic architecture which are characteristic of the archetypal Himalayan-Tibet collisional orogen rather than of hot/ultra-hot Precambrian orogens based on numerical modeling.

Large-scale Permo-Triassic back-arc extensions of the Mongol- Okhotsk Ocean

The Late Paleozoic−Mesozoic Mongol-Okhotsk orogenic belt marks the final aggregation of East Asia. The geodynamics of the Mongol-Okhotsk oceanic plate subduction are still poorly understood due to its curved orogenic architecture, complex kinematics, and the protracted active continent margin that developed during oceanic subduction. Here, we report the discovery of an ophiolite within the southern paleo-active margin of the Mongol-Okhotsk orogenic belt. The ophiolitic slices are composed of serpentinites, metagabbros, and metabasalts, and interleaved with deformed volcaniclastic rocks. Using zircon U-Pb dating, we determined an age of 253 ± 2 Ma for the metagabbro, which suggests that the ophiolite formed during the Late Permian. Geochemical data and geologic relationships indicate that this ophiolite formed in a back-arc setting. The contemporaneous granitic dikes (ca. 255 Ma) intruding the basalts of the ophiolite were likely formed by crustal anatexis during the back-arc extension. Detrital zircon in sandstone associated with the ophiolite shows a prominent peak age of ca. 273 Ma that probably represents the sediments of the back-arc basin. Combining our discovery with the available data from the literature, we suggest that a >5000-km-long back-arc extension belt existed in the southwestern segment of the Mongol-Okhotsk belt, which indicates a probable Western Pacific-type active margin rather than the previously proposed Andean-type margin that formed during the Permo-Triassic period.

Climatic control on the location of continental volcanic arcs

Orogens and volcanic arcs at continental plate margins are primary surface expressions of convergent plate tectonics. Although it is established that climate affects the shape, size, and architecture of orogens via orographic erosion gradients, the ascent of magma through the crust and location of volcanoes along magmatic arcs have been considered insensitive to erosion. However, available data reveal westward migration of late-Cenozoic volcanic activity in the Southern Andes and Cascade Range where orography drives an eastward migration of the topographic water divide by increased precipitation and erosion along west-facing slopes. Thermomechanical numerical modeling shows that orographic erosion and the associated leeward topographic migration may entail asymmetric crustal structures that drive the magma ascent toward the region of enhanced erosion. Despite the different tectonic histories of the Southern Andes and the Cascade Range, orographic erosion is a shared causal mechanism that can explain the late-Cenozoic westward migration of the volcanic front along both magmatic arcs.

ARCHAEAN AND PALEOPROTEROZOIC OROGENS OF THE FENNOSCANDIAN SHIELD: COMPARATIVE ANALYSIS OF ARCHITECTURE AND CRUSTAL EVOLUTION

Comparative analysis of the structure and mineralogical composition of major structural-mineralogical complexes and the evolution of the Meso-Neoarchean Karelian-Belomorian-Kola and the Paleoproterozoic Lapland-Kola and Svecofennian orogen of the Fennoscandian Shield was performed. It is noted that the lithosphere of the former (Archean) is 200-250 km thick, while the latter is 150- 200 km thick. Overlapping-overthrust structures contribute mostly to the earth’s crust architecture of both orogens. 3.0-2.6 and 2.0-1.65 Ga ago, each of them displayed spreading, subduction, collision and mantle plumes, and the general sequence of these events is comparable to Phanerozoic. The formation of both the Archean and Paleoproterozoic orogens took about 350 Ma. This shows that the Archean and Paleoproterozoic orogens do not differ in geodynamic nature from each other and from modern structures of this type.

COLLISIONAL OROGENESIS AT PALEOPROTEROZOIC: TECTONICS OF NATURAL OROGENS VS. NUMERICAL MODELS A.A. SHCHIPANSKY

We consider in detail the deep tectonics of the Paleoproterozoic Volgo-Don collisional orogen in the East-European Craton. Its reconstruction suggests that this fold-and thrust belt represents a slightly eroded divergent orogenic building filled mostly with juvenal metasediments and comprises well-preserved patterns of the crustal orogenic architecture which are characteristic of the archetypal Himalayan-Tibet collisional orogen which are characteristic of the archetypal Himalayan-Tibet collisional orogen rather than being explored through a number of numerical modeling on hot/ultra-hot Precambrian orogens.

The role of flat slab subduction, ridge subduction, and tectonic inheritance in Andean deformation

AbstractConvergent plate boundaries show sharp variations in orogenic width and extent of intraplate deformation. Analysis of late Cenozoic contractile deformation along the Andean mountain front and adjacent foreland highlights the contrasting degrees of deformation advance toward the plate interior. The retroarc positions of the Andean topographic front (marked by frontal thrust-belt structures) and foreland deformation front (defined by isolated basement block uplifts) range from 300 to 900 km inboard of the trench axis. Over the ~8000 km arcuate length of the Andes (10°N to 55°S), four discrete maxima of inboard deformation advance are spatially co-located with the Peruvian (5°S–14°S) and Pampean (27°S–33°S) zones of flat slab subduction, the subducted Chile Ridge (45°S–48°S), and the anomalously thick Paleozoic stratigraphic wedge of Bolivia (17°S –23°S). The spatial correspondence of retroarc shortening with specific geodynamic configurations demonstrates the mechanical role of flat slab subduction, slab window development, and combined structural and stratigraphic geometries in shaping the orogenic architecture of Cordilleran margins, largely through lithospheric strengthening, weakening, and/or tectonic inheritance.

Reply to comment on “Preparing the ground for plateau growth: Late Neogene Central Anatolian uplift in the context of orogenic and geodynamic evolution since the Cretaceous”

• Our discussion of plateau margin uplift is unaffected by proposed Paleogene uplift. • Earlier plateau interior uplift supports a conclusion of multiple drivers of uplift. • Earlier lithospheric dripping possible if Miocene volcanism has another cause. • Mechanisms for plateau rise may be evaluated against the orogenic architecture.

Wedge tectonics in South China: constraints from new seismic data

Collisional orogens form when tectonic forces amalgamte fragments of Earth’s continental lithosphere. The sutures between individual fragments, or terranes, are potential sites of weakness that facilitate subsequent continental breakup. Therefore, the lithospheric architecture of collisional orogens provides key information for evaluating the long-term evolution of the continental interior: for example, the South China Block (SCB), where the tectonic history is severely obscured by extensive surface deformation, magmatism, and metamorphism. Using new passive-source seismic models, we show a contrasting seismic architecture across the SCB, with three prominent crustal dipping structures across the Jiangnan Orogen. Combined with constraints from multi-disciplinary regional geophysical datasets, these pronounced dipping patterns are interpreted as relict wedge-like lithospheric deformation zones initiated in the fossil collisions that assembled the Yangtze Block and the SCB. The overall trend of these tectonic wedges implies successive crustal growth along paleo-continental margins and is indicative of northward subduction and docking of accretional terranes. In contrast, no such dipping structures are preserved in the Cathaysia Block, indicating a weak and reorganized lithosphere. The variations in the deformation responses across the SCB reflect the long-term modifications of the lithosphere caused by prolonged collision and extension events throughout the tectonic history of the SCB. Our results demonstrate the critical roles that suture zones played in the successive growth and evolution of the continental lithosphere.

Controls of mantle subduction on crustal-level architecture of intraplate orogens, insights from sandbox modeling

Subduction of mantle lithosphere can initiate in the continental interior and acts as an important mechanism for intraplate orogeny. However, the associated kinematic response in the upper crust is still poorly resolved, hindering identification and investigation of mantle subduction during intraplate orogeny. Here we conducted sandbox experiments incorporating mantle-subduction-type and traditional indentation-type convergence to explore their difference in crustal-level orogenic architecture and deformation kinematics. We demonstrate that mantle-subduction-type convergence enhances orogen expansion above the subducting plate, whereas indentation-type convergence promotes deformation propagation toward the overriding plate. Such contrast leads to systematic variations in deformation sequence, structural style, and the first-order orogen geometry. We also show that changes of convergence mode leave distinct structural relics. Out-of-sequence faulting occurs when indentation-type convergence replaces the mantle-subduction-type mode. Conversely, the overprinting of mantle subduction on an earlier indentation mode triggers immediate in-sequence, foreland-propagating thrusting. Additionally, the influence of mantle-subduction-type convergence concentrates within the subducting plate when under a combined convergence involving opposite-direction indentation and mantle-subduction. This creates a special pattern of deformation localization comparable to the distribution of present-day seismicity and topography observed in the active Qilian Shan fold-thrust (northern Tibetan Plateau), confirming a bi-directional compression state during its recent evolution. Our modeling results can provide insights into the geodynamics of other intraplate orogens.

Terminal tectono-magmatic phase of the New England Orogen driven by lithospheric delamination

The recognition of lithospheric delamination as a mechanism for magmatism and uplift is under-recognized in the geological record. A pertinent example is the terminal phase of the New England Orogen in eastern Australia, where current explanations of slab roll-back-driven extension are incompatible with plate motions in the Late Triassic. Although abundant mafic rocks are present, almost all Late Triassic temporal information is from felsic rocks. To investigate potential Late Triassic mafic magmatism in the New England Orogen, we date a series of tholeiitic and alkaline mafic products in its back-arc (Sydney Basin) using plagioclase 40Ar/39Ar and apatite U-Pb geochronology. We obtained a plagioclase 40Ar/39Ar plateau age of 202.77 ± 0.68 Ma (2σ) from tholeiitic magmatic products and an apatite U-Pb age of 202 ± 7 Ma (2σ) from a proximal alkaline sill some 70 m deeper, both of which overlap within uncertainty. Complementary trace element geochemistry shows that the tholeiitic and alkaline magmatic products were derived from a similar deep, garnet-bearing source, which we attribute to upwelling asthenosphere underneath a thickened lithosphere. Our data suggest that extension occurred ∼10 m.y. later in the back-arc basin than along its arc, further supporting the notion that slab roll-back could not have caused this terminal phase of Late Triassic extension in the New England Orogen. The Late Triassic magmatism in the New England Orogen is best explained by lithospheric delamination as it accounts for the orogenic architecture, chemical signature of the ca. 200 Ma products and spatio-temporal distribution of Late Triassic magmatic products.

Tectonostratigraphy and major structures of the Georgian Greater Caucasus: Implications for structural architecture, along-strike continuity, and orogen evolution

AbstractAlthough the Greater Caucasus Mountains have played a central role in absorbing late Cenozoic convergence between the Arabian and Eurasian plates, the orogenic architecture and the ways in which it accommodates modern shortening remain debated. Here, we addressed this problem using geologic mapping along two transects across the southern half of the western Greater Caucasus to reveal a suite of regionally coherent stratigraphic packages that are juxtaposed across a series of thrust faults, which we call the North Georgia fault system. From south to north within this system, stratigraphically repeated ~5–10-km-thick thrust sheets show systematically increasing bedding dip angles (<30° in the south to subvertical in the core of the range). Likewise, exhumation depth increases toward the core of the range, based on low-temperature thermochronologic data and metamorphic grade of exposed rocks. In contrast, active shortening in the modern system is accommodated, at least in part, by thrust faults along the southern margin of the orogen. Facilitated by the North Georgia fault system, the western Greater Caucasus Mountains broadly behave as an in-sequence, southward-propagating imbricate thrust fan, with older faults within the range progressively abandoned and new structures forming to accommodate shortening as the thrust propagates southward. We suggest that the single-fault-centric “Main Caucasus thrust” paradigm is no longer appropriate, as it is a system of faults, the North Georgia fault system, that dominates the architecture of the western Greater Caucasus Mountains.

Crustal architecture and tectonic evolution of the southernmost Río de la Plata Craton and its Neoproterozoic–Paleozoic sedimentary cover: Insights from 3D litho-constrained stochastic inversion models

In the last decade, several models have been proposed to explain the location and geometry of the southern margin of the Archean–Paleoproterozoic Río de la Plata Craton. However, these topics and the regional distribution of the Neoproterozoic–Paleozoic sedimentary cover of the craton are still widely debated. This contribution presents a 3D litho-constrained gravity inversion model of the southern sector of the Río de la Plata Craton, based on the integration of geological, geophysical, and petrophysical data. The distribution of the Neoproterozoic–Paleozoic sedimentary cover of the region is reassessed considering a common and protracted geological history of the three morphotectonic units involved in the study area: the Tandilia System, the Claromecó Basin, and the Ventania System. Our results provide key information on the location and geometry of the southern margin of the Río de la Plata Craton that supports its relationship with the Neoproterozoic Brasiliano/Pan-African Orogeny and, subsequently, with the Paleozoic Terra Australis and Gondwanide orogenies. In this context, the Neoproterozoic basement of the Ventania System was dextrally transported from the Brasiliano/Pan-African Orogen during the late Ediacaran–early Cambrian and thrusted over the Río de la Plata Craton and its Neoproterozoic–early Paleozoic sedimentary cover during the Permian. Likewise, our 3D model also shed new insights into the orogenic mechanisms of deformation transfer from the North Patagonian Massif to the Ventania System. The deep crustal geometry determined for the latter suggests intraplate deformation, mainly due to the Permian reactivation of the boundary between the Río de la Plata Craton and the Brasiliano/Pan-African basement. This implies that the Ventania System was mechanically disconnected from the Permian orogenic front located further southwest in the North Patagonian Massif, thus challenging previous models of orogenic architecture for the region.

Deciphering paleogeography from orogenic architecture: Constructing orogens in a future supercontinent as thought experiment

Orogens that form at convergent plate boundaries typically consist of accreted rock units that form an incomplete archive of subducted oceanic and continental lithosphere, as well as of deformed lithosphere of the former upper plate. Reading the construction of orogenic architecture forms the key to decipher the pre-orogenic paleogeographic distribution of oceans and continents, as well as bathymetric and topographic features that existed thereon such as igneous plateaus, seamounts, microcontinents, or magmatic arcs. Current classification schemes of orogens divide between settings associated with termination of subduction [continent-continent collision, continent-ocean collision (obduction)] and with ongoing subduction (accretionary orogenesis), alongside intraplate orogens. Perceived diagnostic features for such classifications, particularly of collisional orogenesis, hinge on dynamic interpretations linking downgoing plate paleogeography to upper plate deformation, plate motion changes, or magmatism. Here, we show, however, that Mesozoic-Cenozoic orogens that undergo collision almost all defy these proposed diagnostic features and behave as accretionary orogens instead. To reconstruct paleogeography of subducted and upper plates, we therefore propose an alternative approach to navigating through orogenic architecture: subducted plate units comprise nappes (or mélanges) with Ocean Plate Stratigraphy (OPS) and Continental Plate Stratigraphy (CPS) stripped from their now-subducted or otherwise underthrust lower crustal and mantle lithospheric underpinnings. Upper plate deformation and paleogeography respond to the competition between absolute motions of the upper plate and the subducting slab. Our navigation approach through orogenic architecture aims to avoid <i>a priori</i> dynamic interpretations that link downgoing plate paleogeography to deformation or magmatic responses in the upper plate, to provide an independent basis for geodynamic analysis. From our analysis we identify ‘rules of orogenesis9 that link the rules of rigid plate tectonics with the reality of plate deformation. We use these rules for a thought experiment, in which we predict orogenic architecture that will result from subducting the present-day Indian Ocean and colliding the Somali, Madagascar, and Indian margins using a published continental drift scenario for a future supercontinent as basis. We illustrate that our inferred rules (of thumb) generate orogenic architecture that is analogous to elements of modern orogens, unlocking the well-known modern geography as inspiration for developing testable hypotheses that aid interpreting paleogeography from orogens that formed since the birth of plate tectonics.

Nature, Origin, and Evolution of the Pyrenean‐Cantabrian Junction

AbstractWe investigate the present‐day orogenic architecture of the Pyrenean‐Cantabrian junction corresponding to a boundary between inverted rift segments using seismic interpretation, field data, and borehole information. This junction was formerly attributed to a major NNE‐SSW striking Pamplona transfer fault segmenting the Basque‐Cantabrian and Mauléon basins during both rifting and convergence. Our study shows that the orogenic architecture results from a strong decoupling between the thick‐skinned (basement‐involved) and the thin‐skinned (detached in the Upper Triassic evaporites) modes of deformation. The evaporites decoupling horizon was responsible for the transport and allochthony of the former rift basins over large distances on top of the Basque massifs and the Ebro and Aquitaine foreland basins. A crustal‐scale cross‐section depicts the allochthony of the Basque massifs forming a crustal wedge over the crusts of Iberian, Ebro, and Eurasian affinity. Three‐dimensional analysis of the present‐day architecture suggests that two phases of rifting and related basins can be recognized: the Late Jurassic‐Barremian and the Aptian‐Cenomanian basins. Furthermore, we show that during the Aptian‐Cenomanian, the Mauléon and Basque‐Cantabrian rift segments spatially overlapped north and south of the Basque massifs and were controlled by WNW‐ESE striking extensional faults. These results discard the existence of a major Pamplona transfer fault and argue for NNE‐SSW direction of extension during the mid‐Cretaceous. This study emphasizes the role of inheritance during rifting and reactivation and provides a new syn‐rift template, which controlled the Alpine reactivation. Finally, these results have major implications for the Iberia‐Eurasia plate boundary and the kinematics of the North Pyrenean basins.