Retroarc Foreland Research Articles

New constraints on the tectonic history of the basement of the Western Cordillera and coastal forearc of Ecuador

The Western Cordillera and forearc of the Northern Andes (north of 5° S) are constructed from allochthonous terranes floored by oceanic crust. A paucity of accurate geochronological data from the ultramafic and mafic basement sequences of the Western Cordillera and Coastal region of Ecuador has lead to distinct differences in published tectonic models, with different allochthonous units and contrasting timelines of accretion and collision. We present new zircon UPb and groundmass 40Ar/39Ar dates of the basement units, which have been combined with new whole rock geochemical and isotopic data to constrain their tectonic histories prior to and during their accretion to South America. Ultramafic and mafic rocks with oceanic plateau affinities can be divided into two plateau sequences, where an inboard, younger plateau (85–92 Ma; Pallatanga Block) is sutured against South America, and was modified by a pre-accretionary intra-oceanic arc (Pilatón-Pujilí arc) that was terminated by the accretionary process. An older, outboard oceanic plateau sequence (∼120 Ma) forms the basement to a series of coastal blocks within the present forearc (Piñon, San Lorenzo, Pedernales and probably the Esmeraldas blocks). The outer plateau also hosts a pre-accretionary intra-oceanic arc (Pascuales – San Lorenzo arc), which remained active during and post-accretion (San Lorenzo – Rio Cala arc). Coeval changes in palaeomagnetic declination, the onset of rapid exhumation (>1 km/My) of the Early Cretaecous continental margin and sedimentation within the newly formed retro-arc foreland basin and foreland region supports a model where both oceanic plateau sequences accreted to South America in a single accretion event at 75–70 Ma. Thus, it is likely that the accreted oceanic plateau was composite, and included both the younger and older plateau sequences prior to accretion. We test an alternative model where the inner (younger) and outer (older) oceanic plateaus accrete in sequence, although this fails to account for the timing of block rotations in the forearc.

Maastrichtian-Cenozoic erosional history of the northern Peruvian Amazonian Andes implications for the Eastern Cordillera evolution (Huallaga Basin, northern Peru)

Late Cretaceous-Cenozoic Andean mountain building may have experienced various phases of orogenesis in response to variations the dip angle of the subducting slab, distinct magmatic pulses, and shortening rates of the orogen. The timing of the Eastern Cordillera (EC) erosion and the relationship between the Andean orogenesis and the establishing of the transcontinental Amazon River remains unclarified. The erosional history of the Amazon Andes and the timing of these orogenic events may be revealed by the late Cretaceous-Cenozoic sedimentary record of the Amazonian retroarc foreland basin. We investigate the provenance of the Maastrichtian-Cenozoic deposits of the Huallaga Basin based on major and trace elements concentrations, SmNd isotopic composition, and UPb zircon dating. We also refined the Oligocene paleoenvironment and calculated Paleogene sedimentation rates. Our results show that despite the 25 Myr-long sedimentary hiatus, both the Maastrichtian and Eocene units show dominant sourcing from the magmatic arc of the Western Cordillera (WC). Increases in Paleozoic and Famatinian zircon grains and a shift toward more negative ƐNd(0) values, indicate dominant EC sources during the Oligocene to middle Miocene. This change in provenance area is Rupelian in age based on the Maximum Likelihood Age (MLA) of JUA22 (29.70 ± 0.62 Ma), suggesting that the onset of Peruvian EC erosion started at ∼30 Ma. The erosion of the EC was accompanied by an increase in sedimentation rates and the development of a meandering fluvial system. Finally, a substantial decrease in zircon grains derived from the Cretaceous and Cenozoic Andean arcs from late Miocene to Recent sediments suggests no contribution of the WC. In contrast, an increase in Paleozoic magmatic arc zircon grains indicates sources in the EC. We compare our findings to constrain the erosional history of the Amazonian Andes and investigate the relationship between the timing of EC uplift and the onset of the transcontinental Amazon drainage system during the Cenozoic.

The Paleoproterozoic Trans-Australian Orogen: Its magmatic and tectonothermal record, links to northern Laurentia, and implications for supercontinent assembly

The 2.1−1.79 Ga Trans-Australian and Canadian Trans-Hudson orogens preserve a common record of Himalayan-scale orogenesis and voluminous Cordilleran-style magmatism behind which turbidite-dominated sedimentary sequences evolved in a backarc or retroarc foreland setting. Successive cycles of subduction retreat and advance drove the orogenic process, culminating in continent-continent collision and closure of a shared and formerly contiguous ocean basin—the Paleoproterozoic Diamantina and Manikewan oceans. Cordilleran-style arc magmatism in proto-Australia commenced along the southern reaches of the Diamantina Ocean with emplacement of the 2005−1975 Ma Dalgaringa Batholith along the leading edge of the Pilbara Craton (Gascoyne Province) before both it and its host craton docked against the Yilgarn Craton, resulting in the Glenburgh Orogeny. After a brief episode of post-kinematic granitic magmatism from 1965 Ma to 1945 Ma, tectonic activity switched to the opposing margin of the Diamantina Ocean in what is now northern Australia, where three more cycles of upper plate orogenesis and Cordilleran-style magmatism occurred from 1890 Ma to 1850 Ma, 1840 Ma to 1810 Ma, and 1810 Ma to 1760 Ma along a convergent continental margin extending from the Kimberley and Pine Creek regions southward through the Mount Isa domain into the eastern Gawler Craton. Batholiths developed along this margin include granites of both low- and high-Sr/Y composition, with the more adakitic varieties interpreted to have been intruded during periods of enhanced asthenospheric upwelling accompanying the opening of one or more slab windows following slab breakoff, tearing, and/or subduction of an actively spreading oceanic ridge. Terminal collision between the North and South Australian (Mawson) cratons at ca. 1790 Ma brought this succession of subduction-related events to a close, although neither this event nor the corresponding Trans-Hudson Orogen need equate to final assembly of the Nuna supercontinent. Instead, the 1870 Ma peak in global compilations of magmatic and detrital zircon ages may be interpreted more simply as the result of elevated tectonism and magmatism along a Paleoproterozoic Cordilleran-style continental plate margin that was transcontinental in scale and continued uninterrupted from proto-Australia into northern Canada and beyond.

Kinematic evolution of the Huincul High, Neuquén basin (Argentina) - Sequential restoration and analysis of inversion structures

This research integrated sequential section restoration, detailed seismic attribute analysis, and quantitative fault analysis for key inversion structures along the western Huincul High, a prominent E-W basement discontinuity in the Mesozoic Neuquén Basin. Section restoration of this retroarc foreland basin, indicated that the area inherited a non-uniform basement with a c.a. 30 km wide trough likely related to the Palaeozoic Gondwanan orogeny. This, combined with important Early – Middle Jurassic subsidence (rates of 40mmy−1), provided accommodation for the deposition of the thick Lower – Middle Jurassic Los Molles formation. Restoration also showed the occurrence of two main phases of inversion characterised by distinct styles of accommodation of shortening. Middle to Late Jurassic inversion had a higher degree of horizontal shortening of around 1.18mmy−1, which was accommodated predominantly by newly created shallow thrust faults exhibiting limited vertical displacement. Meanwhile, Early Cretaceous inversion promoted folding and reactivation of normal faults with large, inverted structures attesting up to c.a.1500m of vertical displacement and non-uniform lateral propagation. Seismic attribute analysis highlighted that inversion promoted internal deformation in the hangingwall of the main inverted structures, in the form of a dense network of secondary fractures up to 1 km in length, perpendicular to the strike of the reactivated structures.

Sedimentary Record of the middle Cretaceous uplift across the Gangdese magmatic arc system in Southern Tibet

AbstractSedimentary basins adjacent to subduction‐related continental arcs provide important archives for deciphering the intricate history of convergent plate margins. The east‐west trending Gangdese magmatic arc was one of the most predominant topographic features located at the southern margin of Tibet before the arrival of the Indian plate. However, the detailed Cretaceous growth and evolution across the arc system remains ambiguous. Stratigraphy of the adjacent Xigaze forearc basin provides a well‐preserved and well‐exposed record of the tectonic and magmatic evolution of the arc throughout the Cretaceous period. We report new stratigraphic, sedimentological, geochronological, and provenance analyses of the Quarry Ridge sandstone in the Xigaze forearc basin along with compiled zircon U‐Pb ages (n = 9674) and Lu‐Hf isotopic signatures (n = 3389) from the Gangdese arc, the Xigaze forearc basin, and the Linzhou retroarc foreland basin to reconstruct the Early to middle Cretaceous magmatism and uplift of the Gangdese arc and concurrent sedimentary responses within both basins. Exhumation of the arc initiates at around 113 Ma suggested by arc detritus first arriving in both basins. Another episode of inferred uplift occurs at around 108 Ma, which resulted in coarse‐grained sedimentation in adjacent basins, preventing Central Lhasa detritus from reaching the Xigaze forearc basin further south and a facies and provenance change within the Linzhou basin. Finally, a third episode at around 101 Ma is reflected by deposition of the progradational Quarry Ridge clastic succession and marks the initiation of a substantial coarse‐grained depositional stage in the Xigaze forearc basin. Our study emphasizes the connection between coarse‐grained deposition in the forearc basin and arc magmatism and uplift. This study also provides an orogen‐scale assessment of the history of arc magmatism, uplift, and sedimentation across the Gangdese magmatic arc system, which supports interpretations that Tibet was already characterized by complex and substantial topographic relief during the Cretaceous before the collision between the Indian and Eurasian plates.

Facies analysis for the Neoarchean Itchen and Sherpa formations of the Winter Lake greenstone belt, Slave craton, Northwest Territories, Canada

Facies analysis for the Neoarchean Itchen and Sherpa formations of the Winter Lake greenstone belt, Slave craton, Northwest Territories, Canada

Neogene to modern foreland basin development in the Sub-Andean zone of southern Bolivia and northern Argentina, 21−23°S

The Sub-Andean retroarc region is a unique example of an active continental-scale retroarc foreland basin system. Heavily targeted for hydrocarbon exploration, the region hosts a large volume of subsurface data coupled to surface studies dedicated to refining its evolution in time and space. This paper presents a regional correlation of stratigraphic markers from seismic reflection and well logs across the Sub-Andean foothills at 23−21°S in southern Bolivia and northern Argentina, which reveals the contrasting along-strike history of Mesozoic to Cenozoic tectonics that preceded the foreland basin setting. Supported by published geochronological data and new zircon U-Pb maximum depositional ages, we describe the depositional transition from pre-Andean to Andean stratigraphy and discrete episodes of foreland basin subsidence and shortening. Based on interpreted stratigraphic breaks, we define the extent and stepwise evolution of this foreland basin, which was characterized by the progressive eastward migration of foreland basin depozones. Based on restored thickness profiles, we present flexural models of basin subsidence for the Sub-Andean foothills region. The modeling of discrete episodes of foreland basin subsidence refines the widely accepted bimodal elastic strength in the foreland basin at 21−23°S, which is weaker in the western ranges (∼20 km effective elastic thickness) and stronger eastward (>40 km). Modeling results also reveal minimum values of subsidence rates (up to 1.2 mm/yr) in the sequential foredeep depozones and suggest that the modeled tectonic load migration—as constrained by the record of syntectonic strata—probably increased over time through the incorporation of Sub-Andean rocks into the orogenic wedge.

Carboniferous to Triassic polyphase tectonic transition in the western North China craton: A retroarc basin response to termination of the middle segment of the Paleo-Asian Ocean

Knowledge of the closure of the archipelago-type southern Paleo-Asian Ocean has been limited by uncertainty regarding whether the Alxa tectonic belt was isolated from the North China craton by an ocean around the Helanshan tectonic belt. Newly released seismic reflection profiles across the Alxa-Ordos border showed that the Alxa tectonic belt and Ordos Basin were located in a paleogeographically linked basin throughout the Paleozoic, indicating that the Tianshan and Solonker sutures were contiguous. The ca. 320−285 Ma successions in the Helanshan tectonic belt and surroundings, fed by a northeasterly Inner Mongolia continental arc source, display a retrogradational stacking pattern along with diabase sill emplacement. This inferred retroarc extensional setting was coeval with asthenospheric upwelling and thinning of the continental arc driven by retreating subduction of the Paleo-Asian Ocean. The subsequent ca. 280−260 Ma sedimentary hiatus coincided with magmatic flare-up, crustal thickening, and retroarc foreland formation in the Inner Mongolia continental arc, indicating a geodynamic transition from retroarc extension to compression in the mid-Permian. Then craton-scale drainage reorganization occurred during the Early Triassic (ca. 250−230 Ma), manifested by the discharge of the Middle Triassic fluvial system southeastward to the central Ordos Basin; this was steered by southeastward expansion of the Alxa tectonic belt during the final termination of the Paleo-Asian Ocean. Postcollision lithospheric adjustment since ca. 230 Ma resulted in vigorous alkaline magmatism and supracrustal stretching in the Inner Mongolia continental arc as well as mafic magmatism and rifting in the study area. Hence, Carboniferous to Triassic polyphase tectonic transitions in the western North China craton were retroarc basin expressions related to complicated subduction-closure processes in the southern Paleo-Asian Ocean.

Wrapping a Craton: A Review of Neoproterozoic Fold Belts Surrounding the São Francisco Craton, Eastern Brazil

A synthesis of the evolution of the Neoproterozoic belts or orogens surrounding the São Francisco craton (SFC) in northeastern and southeastern Brazil is presented. Emphasis is placed on recognizing the superposition of sedimentary basins, from rift to passive margin to retroarc and foreland, as well as identifying three diachronic continental collisions in the formation of the SFC. The Tonian passive margin occurs in the southern Brasília Belt with the Vazante, Canastra, and Araxá Groups. During the Tonian, island magmatic arcs and basins developed in front and behind these arcs (fore- and back-arcs). Subsequently, in the Cryogenian–Ediacaran, a retroarc foreland basin developed with part of the Araxá Group and the Ibiá Group, and finally, a foreland basin developed, which was filled by the Bambuí Group. A tectonic structure of superimposed nappes, with subhorizontal S1–2 foliation, formed between 650 and 610 Ma, is striking. In the northern Brasília Belt, there is the Stenian passive margin of the Paranoá Group, the Tonian intrusion of the Mafic–Ultramafic Complexes, and the Mara Rosa Island magmatic arc, active since the Tonian, with limited volcanic–sedimentary basins associated with the arc. A thrust–fold belt structure is prominent, with S1 foliation and late transcurrent, transpressive tectonics characterized by the Transbrasiliano (TB) lineament. The Cryogenian–Ediacaran collision between the Paranapanema and São Francisco cratons is the first collisional orogenic event to the west. In the Rio Preto belt, on the northwestern margin of the São Francisco craton, the Cryogenian–Ediacaran Canabravinha rift basin is prominent, with gravitational sediments that represent the intracontinental termination of the passive margin that occurs further northeast. The rift basin was intensely deformed at the Ediacaran–Cambrian boundary, as was the Bambuí Group. On the northern and northeastern margins of the São Francisco craton, the Riacho do Pontal and Sergipano orogens stand out, showing a comparable evolution with Tonian and Cryogenian rifts (Brejo Seco, Miaba, and Canindé); Cryogenian–Ediacaran passive margin, where the Monte Orebe ophiolite is located; and Cordilleran magmatic arcs, which developed between 620 and 610 Ma. In the Sergipano fold belt, with a better-preserved outer domain, gravitational sedimentation occurs with glacial influence. A continental collision between the SFC and the PEAL (Pernambuco-Alagoas Massif) occurred between 610 and 540 Ma, with intense deformation of nappes and thrusts, with vergence to the south and accommodation by dextral transcurrent shear zones, such as the Pernambuco Lineament (PE). The Araçuaí belt or orogen was formed at the southeastern limit of the SFC by a Tonian intracontinental rift, later superimposed by a Cryogenian–Ediacaran rift–passive margin of the Macaúbas Group, with gravitational sedimentation and glacial influence, and distally by oceanic crust. It is overlain by a retroarc basin with syn-orogenic sedimentation of the Salinas Formation, partly derived from the Rio Doce cordilleran magmatic arc and associated basins, such as the Rio Doce and Nova Venécia Groups. A third continental collision event (SF and Congo cratons), at the end of the Ediacaran (580–530 Ma), developed a thrust–fold belt that deforms the sediments of the Araçuaí Belt and penetrates the Paramirim Corridor, transitioning to the south to a dextral strike-slip shear zone that characterizes the Ribeira Belt.

Tectonic and climatic significance of Oligocene-Miocene eolian sandstones in the Andean foreland basin of Argentina

Late Oligocene-early Miocene aridification in the retroarc foreland basin adjacent to the southern central Andes was recorded by widespread eolian conditions that coincided with accelerated subsidence driven by the main phase of Andean tectonic loading. An extensive eolian dune system, which is rare in most foreland basins, indicates specific conditions in terms of climate (aridity), atmospheric circulation, orography, sediment sources, dispersal patterns, and accommodation space. Detrital zircon U-Pb geochronological results for eolian sandstones spanning 20 foreland localities in northwestern to west-central Argentina, from 22°S to 36°S, reveal relatively localized Andean sources rather than regional cratonic provenance. Clastic detritus was largely derived from Phanerozoic igneous and sedimentary rocks of the Andean magmatic arc and retroarc fold-thrust belt during initial shortening-induced uplift of hinterland regions such as the Western Cordillera, Principal Cordillera, and Frontal Cordillera. This provenance record provides the earliest evidence for major westerly winds, transporting Andean detritus broadly eastward to the foreland basin (with common axial northward deflections) during a climate shift marked by the latest Oligocene-earliest Miocene inception of arid conditions. In addition to the climatic implications, independent stratigraphic data provide the basis for a compilation of sediment accumulation histories showing that eolian deposition was synchronous with accelerated subsidence attributable to enhanced Andean shortening. We propose that accelerated Andean uplift in the latest Oligocene-early Miocene generated rain-shadow conditions contemporaneous with increased sediment accommodation in the foreland basin, underscoring the important influence of tectonic processes on regional climate.

The role of tectonic inheritance in the development of an Andean retroarc foreland basin system: The Acre Basin (NW Brazil)

The Andes, located on the western edge of the South American platform, corresponds to a classic example of subduction, which results in one of the most extensive mountain ranges on Earth. However, little is still understood about the area of influence of the fold-thrust belt in the deformation of the distal retroarc region to the east, close to the craton. In this context, Acre Basin is one of the least understood provinces, located in the Peruvian flat slab, a region that involves one of the greatest deformations in the Andes. Therefore, this research aims to understand the tectono-stratigraphic evolution of the Acre Basin and its relationships with the sub-Andean basins through 2D seismic lines and exploration wells. The definition and mapping of six seismic units aged between the Devonian and the Neogene, confirmed by restoration, indicated a tectonic history compatible with the main events recorded in the sub-Andean basins, marked by an intercalation between extensional rift and compressional regimes, with an important role of basement and structural inheritance in deposition and in the structural style of deformation. Seismic units representative of the Famatinian, Gondwanide, Juruá and Andean orogenies, and the Pangea breakup were identified. The current positioning of the forebulge was conditioned by a locally non-elastic mechanism of forebulge uplift related to the upper Jurassic basement high (Envira High Arch), Cenozoic reactivation of Triassic rift faults and by the uplift of intraforeland basement blocks in thick-skinned tectonics during the Miocene. Thus, in addition to placing the Acre Basin in the context of sub-Andean basins, these deposits help to understand the geodynamic mechanisms and the complexity of Andean deformation even in regions distal to the fold-thrust belt.

Provenance of a Late Permian retroarc foreland basin along the eastern Gondwanan margin: northern Sydney Basin, eastern Australia

Abstract The Upper Permian sedimentary successions in the northern Sydney Basin have been the subject of several stratigraphic, sedimentological and coal petrographic studies, and recently, extensive U-Pb zircon dating has been carried out on tuffs in the Newcastle Coal Measures. However, detailed petrographic and geochemical studies of these successions are lacking. These are important because a major change in tectonic setting occurred prior to the Late Permian because of the Hunter-Bowen Orogeny that caused the uplift of the Carboniferous and Devonian successions in the Tamworth Group and Tablelands Complex adjacent to the Sydney Basin. This should be reflected in the detrital makeup of the Upper Permian rocks. This study provides data that confirms major changes did take place at this time. Petrographic analysis indicates that the source area is composed of sedimentary, felsic volcanic and plutonic and low-grade metamorphic rocks. Conglomerate clast composition analysis confirms these results, revealing a source region that is composed of felsic volcanics, cherts, mudstones and sandstones. Geochemical analysis suggests that the sediments are geochemically mature and have undergone a moderate degree of weathering. The provenance data presented in this paper indicate that the southern New England Orogen is the principal source of detritus in the basin. Discrimination diagrams confirm that the source rocks derive from an arc-related, contractional setting and agree with the provenance analyses that indicate sediment deposition in a retroarc foreland basin. This study offers new insights on the provenance and tectonic setting of the Northern Sydney Basin, eastern Australia.

Andean-type orogenic plateau as a trigger for aridification in the arcs of northeast Pangaea

The interplay between continental motions during the assembly of Pangaea and late Palaeozoic climate change, including severe glaciation and global aridification, remains enigmatic. Here we identify the provenance of Permian–Early Triassic sediments that recorded climate change of North China and estimate palaeoelevation to constrain tectonic-climate interaction during the assembly of northeast Pangaea. Detrital zircon U-Pb-Hf analysis indicates the sediments were locally sourced from the ancient basement and associated with a late Palaeozoic (410–260 million years ago) continental arc, devoid of input from juvenile arcs of the Altaids. These sediments were interpreted as deposited in a retroarc foreland basin ascribed to subduction of the Palaeo-Asian Ocean. Crustal thickness estimated from whole-rock La/Yb yields an average value of 58 ± 11 km, which corresponds to a palaeoelevation of 3.8 ± 0.7 km. The results reveal the existence in North China of an orogenic plateau comparable to the Altiplano of the Andes that blocked moisture transport from the ocean and served as an important orographic barrier to trigger Permian aridification.

Ordovician chitinozoans and review on basin stratigraphy, biostratigraphy and paleobiogeography of northern Argentina along the Proto-Andean margin

Ordovician strata exposed across the Cordillera Oriental and the Sierras Subandinas in northwestern Argentina were part of a large retroarc foreland basin developed along the Proto-Andean margin within the Central Andes in South America. A revised chitinozoan biostratigraphy along and across-strike for the Tremadocian, Floian, Dapingian, Katian and Hirnantian stages, calibrated with other fossil groups in the basin, allow pinpointing the most characteristic events that affected the basin fill testing global versus local controls in accommodation, and suggesting comparisons with other peri-Gondwanan records. According to the chitinozoan data, the glacially-related Ordovician deposits in northwestern Argentina are restricted to the Hirnantian, and unconformably overlie late Katian deposits. In the Caspalá area (Cordillera Oriental), an interval with synsedimentary deformation and reworked chitinozoans correlate with glacially-related deposits in other sites of the eastern part of the basin (Río Capillas and Mecoyita areas). A glacial waning stage is determined by a thin interval of organic‐rich black shales with sparse dropstones at the top of the Zapla Formation, containing Spinachitina oulebsiri associated with Desmochitina gr. minor, which together are typical latest Hirnantian components in other regions of Gondwana. Our study strengthens the foreland systems tract for the Ordovician Central Andean Basin with a volcanically fed interarc and foredeep depozone to the west (Puna region); a lower-accommodation forebulge depozone in the central area (mostly the Cordillera Oriental region); and a backbulge depozone (Sierras Subandinas and Sierras de Santa Bárbara) extending as far as the eastern Paraná Basin (reaching Paraguay and Brazil). Contemporaneous unconformities driven by global sea-level fluctuations were amplified or reduced due to deepening-narrowing or widening-shallowing, allowing contrasted accommodation, respectively associated to loading and relaxation. Ordovician chitinozoans from the Central Andean Basin indicate Northern, Western and peri-Gondwanan affinities, although locally some more cosmopolitan species described in Baltica, Avalonia and South China, are also recorded.

Provenance and geotectonic setting of the Paleoproterozoic Cerro Figurita formation (Río de la Plata Craton, Uruguay)

The Cerro Figurita Formation (CFFm) represents a clastic sedimentation approximately 3000 m thick which underwent low greenschist metamorphic conditions. The sedimentary sequence is dominated by polymictic conglomerates and sandstones deposited in an environment of alluvial fans that evolve to marine turbidites. The geochemistry of the CFFm reveals derivation from sources with a mix composition similar to unrecycled Upper Continental Crust; alteration increases towards the top of the sequence (CIA 45–92). The contribution of mafic (probably ophiolitic) source rocks is revealed by petrography and low values of Th/Sc (0.3–1.5), Zr/Sc (6–20), Th/U (3–6) and high values of Cr/V (1.1–12.2); slightly negative Eu/Eu* anomalies (0.7–0.9) would indicate the presence of plagioclase in the source rocks. TDM ages are between 2001 and 2269 Ma, and the ƒSm/Nd values along with the relationship between εNd(t) andTh/Sc ratio indicate a provenance from an andesitic arc component. Detrital zircon age patterns are dominated by 2160, 2163 and 2177 Ma peaks, with the youngest zircon showing an age of 2112 ± 21 Ma, confirming a provenance from the Florida central granitic gneiss belt (FB). It is noteworthy the presence of subordinate populations of detrital zircon grains with ages of 2772, 2935 and 3222 Ma, indicating the presence of an inherited felsic source of Archean age, not yet detected in the Piedra Alta Terrane (PAT), and probably located within the Nico Pérez Terrane. A multi-approach to provenance analyses integrating geochemistry, petrography, U–Pb zircon ages, and Nd isotopes indicate ongoing active tectonism during the Orosirian in the PAT, whereas a retroarc foreland basin geotectonic setting is suggested for the CFFm deposition.

Along-strike tectonic evolution of the Neogene Bermejo foreland basin and Eastern Precordillera thrust front, Argentina (30-32°S)

The Bermejo retroarc foreland basin system formed in flexural response to Cenozoic crustal thickening in the Andean orogenic system, specifically, the eastward propagation of the Precordillera fold-thrust belt and the basement-involved uplift of the Sierras Pampeanas. Previous work in the region has mainly focused on the mechanisms and expression of flat slab subduction and the structural geometry of the basement-involved Sierras Pampeanas and east-directed Precordillera fold-thrust belt at depth, advancing our understanding of the Bermejo basin history north of 31°S. However, the along strike evolution of the basin system to the south remains unresolved and contrasting tectonic models have proposed the Bermejo basin evolved synchronously versus asynchronously through time. Our study seeks to constrain the along-strike Neogene tectonics of the Bermejo basin via well-exposed Miocene fluvial stratigraphic intervals along the Eastern Precordillera, integrated with detrital zircon U–Pb geochronology provenance and detrital apatite (U–Th)/He thermochronology datasets. New data from two Neogene stratigraphic sections in the southern Bermejo basin constrain deposition between 13 and 6 Ma. Dominant fluvial-lacustrine mudstones, siltstones, and sandstones transition into fluvial-megafan deposits capped by alluvial fan conglomerate facies, tracking the eastward migration of Precordillera deformation. The cessation of sedimentation, and thermal history models of apatite (U–Th-Sm)/He thermochronology ages, indicates basin incorporation into the orogenic wedge by 6 Ma. When we compare our southern datasets with previous constraints from the northern Bermejo basin, we observe, from north to south: (1) a time-transgressive trend in basin initiation, (2) a ∼3 km decrease in stratigraphic thicknesses, and (3) older exhumation along the thrust front. These trends highlight the asynchronous nature of the Bermejo foreland basin system and along-strike variability of Precordillera thrust-front evolution.

Structural and tectonic assessment of the western Huincul High, Neuquén Basin (Argentina)—The role of structural inheritance and mechanical stratigraphy in inversion systems

AbstractThe Neuquén Basin is a major Mesozoic sedimentary depocentre located in the retroarc foreland of the Argentinian Andes. The basin hosts world renowned inversion systems that have been the target of georesource exploration for the last three decades. The Huincul High is a structurally and economically prominent ca. 270 km long, E–W trending feature that formed by the accretion of exotic Palaeozoic terranes, influencing subsequent Mesozoic deformation in the basin. Exploration in the Huincul High has been mainly focused on the shallow part of the inversion structures leaving a limited understanding of the deep structural architecture and early tectonic evolution, particularly in the western reaches of the high. This research reveals that Late Triassic extensional faulting was followed by widespread thermal subsidence in the Early Jurassic, as shown by the occurrence of an extensive ca. 60 km long, ca. 20 km wide, NE–SW‐trending, central depocentre. In the Early Jurassic, as contraction ensued across this regional sag basin, atypical inversion geometries were developed. These exhibited prominent thickening in the hanging‐wall and, strikingly, in the footwall of reactivated faults. The style of inversion was also markedly influenced by the mechanically weak stratigraphy of the thick, Lower Jurassic, Los Molles formation that promoted broad inversion folding, inhibited shortcut fault creation, and decoupled post inversion deformation from earlier faulting. Quantitative fault analysis suggests that the reactivated faults originated during the Late Triassic extensional phase as separate ca. 10 km long fault segments. The analysis also indicates that segmentation of extensional faults, as well as their orientation to the later contractional vector (SH), spatially dictated style and magnitude of inversion. This research highlights the critical role played by structural inheritance and mechanical stratigraphy in the development of inversion in the Neuquén Basin, which might be of relevance for characterising inversion systems elsewhere. This research also proposes an evolutionary model for the western reaches of the Huincul High that suggests crustal weakening and thermal sag in the Early Jurassic. Moreover, the model highlights a previously unknown late Early Cretaceous transtensional phase that overprints the main Early Jurassic–Early Cretaceous inversion.

An Unusually Warm Upper‐Crust in the Late Paleozoic North China Continental Arc: Implications for the Thermal Modification of the Giant Bayan Obo REE Deposit

AbstractThe genesis and timing of formation of the giant Bayan Obo deposit, the world's largest rare earth element (REE) deposit in the western part of the late Paleozoic northern North China continental arc (NCA), are highly controversial due to complex mineral assemblages and reported ages of mineralization. We conducted new zircon U‐Pb and40Ar/39Ar dating of metamorphic and igneous Neoarchean to Permian mid‐to upper‐crustal rocks exhumed along a north−south corridor across the western NCA and its retroarc foreland. The results show that the mid‐ to upper‐crust of the western part of the NCA has been strongly affected by thermal modifications during arc construction in the late Paleozoic, while the retroarc foreland remained thermally stable. Our results first reveal an unusually warm upper‐crust around Bayan Obo during the late Paleozoic with high geothermal gradients of 50.0 ± 8.3 to 88.3 ± 8.3°C/km and strong thermal modification of the upper‐crust during arc construction. This unusually warm upper‐crust and high geothermal gradients resulted in intensive thermal perturbations and recrystallization of REE‐bearing minerals in the Bayan Obo deposit, as well as formation of high‐grade REE ores and complete or partial resetting (U‐)Th‐Pb isotopic systems of REE minerals. Our identification of the unusually warm upper‐crust and high geothermal gradients in the western part of the NCA provides important constraints on genesis, timing and thermal modification of the giant Bayan Obo deposit, as well as other REE deposits with complex isotopic ages.

Provenance analysis of Paleozoic strata in the Falkland/Malvinas Islands: Implications for paleogeography and Gondwanan reconstructions

New U-Pb geochronological, Hf isotopic, heavy mineral, and sandstone petrographic results for Paleozoic clastic deposits of the Falkland/Malvinas Islands help address renewed debates on the plate tectonic history, regional paleogeography, and basin evolution of this geologic enigma prior to Mesozoic breakup of Gondwana. The Falkland/Malvinas Islands have been considered either an autochthonous part of the South American continent or part of an independent microplate displaced from the southeastern corner of Africa. We report detrital zircon U-Pb results (n = 1306 LA-ICPMS ages) for 11 sandstone samples from the Silurian-Devonian West Falkland Group (N = 7 samples, n = 837 grains) and Carboniferous-Permian Lafonia Group (N = 4 samples, n = 469 grains). Detrital zircon age distributions for the West Falkland Group point to consistent contributions from Neoproterozoic-Cambrian (650–520 Ma) and Mesoproterozoic (1100–1000 Ma) sources. Heavy mineral assemblages and sandstone petrographic data from these samples indicate significant input from recycled sediments. A potential shift in sediment sources during deposition of the Lafonia Group is indicated by the appearance of late Paleozoic (350–250 Ma) and Proterozoic (2000–1200 Ma) age populations, decreased proportions of stable heavy minerals, and a shift to juvenile Hf values for < 300 Ma zircons. The provenance change can be attributed to the onset of subduction-related arc magmatism and potential regional shortening and crustal thickening in southwestern Gondwana during the Permian transition of a passive margin into an active, retro-arc foreland basin. The detrital zircon age distributions identified here reflect potential source regions in southern Africa and/or the Transantarctic Mountains in Antarctica. These results are most readily accommodated within a Gondwana reconstruction that includes the Falkland/Malvinas Islands as a rotated microplate originating on the eastern side of southern Africa as part of the Gondwanide fold-thrust belt spanning from the Ventania region of Argentina through the Cape region of South Africa and into the Ellsworth and Pensacola mountains of Antarctica.

New stratigraphic and paleoenvironmental constraints on the Paleogene paleogeography of Western Amazonia

The rise of the Andes and the associated propagation of the retroarc foreland basin during the Mesozoic Cenozoic in western South America shaped the paleogeography and paleoenvironmental settings of Western Amazonia. Much attention has been paid to the Neogene evolution of the Amazonian Basin, but few studies have investigated in detail the paleoenvironments of Western Amazonia during the Paleogene. We present a multi-proxy study that includes new biostratigraphic and paleontologic data, the interpretation of depositional environments and zircon U–Pb data from the Upper Cretaceous-Paleogene sedimentary sequence exposed in the Huallaga Basin (northern Peru). The biostratigraphic dating suggests that the lower part of the sequence is Maastrichtian in age. The maximum depositional age and maximum likelihood age according to the U–Pb zircon dating of Paleogene sedimentary rocks indicate Lutetian to Bartonian ages (from 43.5 ± 0.64 Ma to 37.6 ± 0.85 Ma). These results reveal a hiatus in the depositional record during Paleocene time. Two depositional systems can be distinguished: a lacustrine system composed of red mudrocks interbedded with thick sandstone layers and carbonate beds, and a siliciclastic tide-dominated system composed of fine-to medium-grained sandstones associated with tidal bundles, reactivation surfaces and heterolithic stratifications. However, the carbon and oxygen stable isotope values in carbonates tend to characterize a freshwater system, with a transition to brackish conditions toward the upper part of the section (Bartonian), thereby suggesting the presence of an estuary system. Finally, we suggest that the Bartonian shallow marine incursion recorded in the Huallaga Basin occurred from the north through the Caribbean Sea, and that it might have played a role in regional biodiversity patterns in the Paleogene.