Active Margin Research Articles

Tectono‐climatic and depositional environmental controls on the Neolithic habitation sites, Vaigai River Basin, Southern India

The establishment, development and abandonment and/or destruction of ancient civilizations were catalytically controlled by geomorphic features such as lakes and rivers and the climate. This paper examined the possible influence of tectonism and climate on six habitations of the ancient Vaigai River Basin civilization in South India, using multiple proxies such as grain size, geochronology and geochemistry of the sedimentary archives. The tectonic setting of the basin changed between the active margin and passive margin; the discriminant diagrams suggested varying provenance and changing climatic conditions over the mid‐ and‐late Holocene. Tectonic activism and quiescence, base‐level change in the channel morphology led to the burial/marooning of the first habitation surface. Overall, arid conditions were punctuated with catastrophic flooding and peak discharge (flood) destroyed the second, third and fourth habitation sites. These flooding events were characterized by moderate weathering (CIA) and high values of Al, Fe and Rb/Sr and low Ca/Mg in the sediment records. The abandonment/destruction of the fifth habitation also occurred during an arid interval (droughts), possibly caused by weak monsoon. Along with the interactions between tectono‐climatic and fluvial geomorphic factors, the new results provided avenues to (a) check and recognize the archives for 8.2 and 4.2 ka‐like events in this part of the world, and (b) the utility of integrated analyses to constrain on the civilizational histories of the mankind.

First record of Reticulinella? kaeveri in the Laffan and Ilam formations (Zagros fold and thrust belt, SW Iran): new constraints on the chronostratigraphic calibration of the Arabian Plate sequence stratigraphy

Over the past two decades, sequence stratigraphy has proven to be a valuable tool in addressing challenges arising from the inconsistent application of lithostratigraphic nomenclature across diverse geological provinces. It has been particularly successful in achieving regional correlations within the Cretaceous deposits of the Arabian Plate. The key sequence stratigraphic surface in the currently adopted standard sequence stratigraphic scheme is the K150 SB, marking the transition from a passive to an active margin along the eastern edge of the Arabian plate. Despite its importance, the chronostratigraphic age of this surface is poorly constrained. In the Zagros FTB, the uppermost part of the Sarvak Formation, just below the K150 SB, was recently assigned to the upper part of middle Turonian to upper Turonian, based on the presence of Reticulinella? kaeveri. Our research reveals that the range of R.? kaeveri extends above the K150 SB as this species is also present in the Laffan and base of Ilam formations. The Last Occurrence of this taxon provides a new chronostratigraphic marker of the upper Turonian within the Ilam Formation. This finding proves that more Turonian deposit are present in the study area than was previously recognized. We have studied the deposits enclosing the K150 SB in outcrop sections and wells along a transect from basin to platform margin to inner platform setting. Based on planktonic foraminifera and calcareous nannofossils biostratigraphy of basinal sections and sequence stratigraphic correlation to carbonate platform sections, the age of the uppermost part of the Sarvak Formation, immediately below the K150 SB, is firmly constrained within the interval lower Turonian–lower part of middle Turonian. Sequence stratigraphic correlation from basin to platform interior reveals also that the oldest deposits above the K150 SB are not younger than late Turonian. Our new data represents a significant improvement in the chronostratigraphic calibration of sequence stratigraphy in the Cretaceous of the Zagros fold-and-thrust belt.

Slab Subduction and Pull Link Magmatism at Active and Passive Continental Margins

AbstractSubduction leads to voluminous arc magmatism at active continental margins; however, the potential far‐field geodynamic connections with coeval magmatism along opposing passive margins, are rarely investigated. Here we report large‐scale and parallel mafic dike swarms on the South Qinling passive margin, whose geochemical features record the thick and cold subcontinental lithospheric mantle beneath passive margin was gradually replaced by thin and hot one during the early Paleozoic. The subduction of the Proto‐Tethys oceanic lithosphere led to arc magmatism along the active margin, shortly after the rift‐related mafic dike swarms occurred along the passive margin. Subsequent to the continuous oceanic subduction including the ridge‐margin collision, mantle upwelling and slab rollback eventually triggered large‐scale rift‐related magmatism and the opening of new ocean basin at passive margin, and also back‐arc magmatism on the active margin. We highlight slab subduction and pull link the geodynamic processes at active and passive continental margins, which improves our understanding of plate tectonics.

Toroidal flow around the Tonga slab moved the Samoan plume during the Pliocene

Abstract Age-progressive seamount tracks generated by lithospheric motion over a stationary mantle plume have long been used to reconstruct absolute plate motion (APM) models. However, the basis of these models requires the plumes to move significantly slower than the overriding lithosphere. When a plume interacts with a convergent or divergent plate boundary, it is often deflected within the strong local mantle flow fields associated with such regimes. Here, we examined the age progression and geometry of the Samoa hotspot track, focusing on lava flow samples dredged from the deep flanks of seamounts in order to best reconstruct when a given seamount was overlying the mantle plume (i.e., during the shield-building stage). The Samoan seamounts display an apparent local plate velocity of 7.8 cm/yr from 0 to 9 Ma, 11.1 cm/yr from 9 to 14 Ma, and 5.6 cm/yr from 14 to 24 Ma. Current fixed and mobile hotspot Pacific APM models cannot reproduce the geometry of the Samoa seamount track if a long-term fixed hotspot location, currently beneath the active Vailulu’u Seamount, is assumed. Rather, reconstruction of the eruptive locations of the Samoan seamounts using APM models indicates that the surface expression of the plume migrated ~2° northward in the Pliocene. Large-scale mantle flow beneath the Pacific Ocean Basin cannot explain this plume migration. Instead, the best explanation is that toroidal flow fields—generated by westward migration of the Tonga Trench and associated slab rollback—have deflected the conduit northward over the past 2–3 m.y. These observations provide novel constraints on the ways in which plume-trench interactions can alter hotspot track geometries.

Kinematics of the Kahramanmaraş triple junction and of Cyprus: evidence of shear partitioning

Triple junctions involving convergent plate boundaries extend beyond local implications, which is crucial for studying the geology of convergent plate boundary zones. However, kinematic models overlook Cyprus-Anatolia motion due to limited geodetic constraints. Our study area comprises Cyprus, southern Turkey, and the Levant coast, focusing on the Kahramanmaraş triple junction, where a destructive earthquake sequence occurred on February 6, 2023. We present precise positioning data merged with published velocities, constructing an up-to-date velocity field for the interseismic period. Employing two kinematic approaches, we analyze its tectonic implications. In Cyprus, we find the relative motion of Africa (Sinai Plate) and Anatolia is partitioned between convergence in the Cyprus subduction, with a rate of 3.5–6.2 mm/yr, progressively decreasing from west to east and left-lateral transpressive Kyrenia fault, situated along the northern coast of Cyprus, with rate 3.3–4.2 mm/yr. The relative strike-slip motion between Arabia and Anatolia is partitioned between the East Anatolian Fault (slip rates 5.2–6.2 mm/yr) and some secondary faults such as Çardak and Malatya faults (slip rates 2.0–1.7 mm/yr respectively) and causes distributed deformation for a 50–60 km wide region. The largest second invariant strain rate tensors from the continuum kinematic model also coincide with the same region, the East Anatolian shear zone. A shear partitioning system exists around the Kahramanmaraş triple junction, from Cyprus to southeast Turkey. The Levant Fault has a 3.5–4.7 mm/yr left-lateral slip rate, decreasing northward as part of it is transferred to offshore faults. Strain rates appear relatively small in the Taurus range and Adana/Cilicia basin, transitioning from extensional/transtensional to compressional from east to west.

Oceanic Plateau and Spreading Ridge Subduction Accompanying Arc Reversal in the Solomon Islands

AbstractWe study the collision of the Ontong Java Plateau, reversal of the Solomon Islands arc, and subduction of the Woodlark Basin spreading ridge in the southwest Pacific. Double‐sided subduction and intra‐arc deformation, not just polarity reversal, characterize the rapid Australia‐Pacific plate convergence. The rifted margins of the 0–6.2‐Ma Woodlark Basin separate its unflexed young lithosphere without a trench from the older flexed lithosphere with >8‐km‐deep trenches subducting to either side. A gap evident in the seismicity and tomography between the NE‐subducted slabs of the Solomon Sea and Australia plates indicates that the Woodlark lithosphere likely melts and/or is quickly (<1 m.y.) resorbed into the mantle. A section of the Pacific Plate remains attached within the gap and provides the slab pull to form the Malaita accretionary prism. Quaternary arc‐composition volcanoes that occur on both sides of the Woodlark Basin subduction front are not sourced from a mantle wedge overlying a Wadati‐Benioff zone, but come from and through breaks in the young incoming and subducting lithosphere and the overturning mantle beneath. Though the basin is too weak to sustain plate flexure, arc volcanoes on the subducting crust result in locally strong coupling to the forearc, manifest by tsunamigenic earthquakes. At 150–400‐km depth, the subducted slabs under the Solomon Islands are near vertical. They are near‐horizontal between the 410 and 660‐km mantle discontinuities beneath the Woodlark Basin and further south, whereas beneath the Solomon Sea Basin they dip southwest and penetrate the 660‐km discontinuity, having been detached by the north‐dipping Solomon Sea slab.

Primena vremenski promenljivih graničnih uslova za brzinu konvergencije ploča pri numeričkom modelovanju obdukcije ofiolita

2D numerical geodynamic modelling applied in this paper gives a better insight into the process of obduction of two distinct ophiolite belts during the closure of a single ocean. Closure of the ocean is achieved by imposed convergence of the tectonic plates. In the created numerical themomechanical models, the influence of the variable velocity of the tectonic plate motions is analyzed. Convergence rate variation is modelled with the goal of achieving obduction and the permanent emplacement of ophiolites via complex evolution of the plate velocities. The basis of the model is the closure of an ocean through a flat intra-oceanic subduction, during which the plates change intensity and direction of their motion. Divergent phase of the evolution leads to the short-lived spreading of the new oceanic domain in from which, after the final closure, one of the two ophiolite belts originates.

Tectonic control on the palaeogeographic evolution of thrust‐top basins at the active margin of the Guadalquivir Basin (central Betic Cordillera, S Spain)

AbstractThe Guadalquivir Basin is the foreland basin of the Betic Cordillera (S Spain). Closest to the orogen, several thrust‐top basins evolved during the Late Miocene in the central part of the cordillera. Here, we study the Upper Miocene deposits in five of these satellite basins: Montefrío, Iznájar‐Cuevas de San Marcos, Antequera, Bobadilla Estación and Teba, in order to (1) update the stratigraphic framework, (2) infer a depositional model, (3) establish the relationship between sedimentary record and tectonic context and (4) reconstruct the palaeogeography of the area during the Late Miocene. Upper Miocene sediments mostly consist of mixed carbonate‐terrigenous deposits. Facies characterization allows inferring a sedimentary model corresponding to a ramp with foreshore deposits changing to a shoal belt offshore in the inner ramp. Swaley and hummocky cross‐stratified deposits formed in the transition to the middle ramp, and plane parallel carbonate beds in the distal middle‐outer ramp. Factory facies, dominated by rhodoliths and bryozoans, also occur in the middle‐outer ramp environments. Silts and marls formed in the deepest outer ramp and basin settings respectively. Breccias accumulated at the toe of palaeocliffs and conglomerates and massive coarse sands were deposited in fluvio‐deltaic systems. Conglomerates and sands were also reworked as gravity flows and redeposited offshore. Local facies include rudstones‐grainstones displaying large‐scale trough‐cross bedding formed in a strait in Montefrío, and marls with chalky carbonates deposited in a shallow marine, sheltered lagoon with hydromorphic soils in Bobadilla Estación. The study basins evolved in an N‐S compressive tectonic context responsible of the emersion of the main Betic reliefs. Concomitantly, E‐W and ESE‐WNW extension originated the main depocentres. The influence of the tectonic activity on the sedimentary infills is indicated by the presence of synsedimentary deformations and several diachronic unconformities, which are younger westward. Tectonism, in turn, also controlled the palaeogeographic evolution during the late Tortonian‐early Messinian interval.

Short-lived active margin magmatism preceding Variscan collision in the Western French Massif Central

This paper presents and discusses new geochronological and petrological data on a suite of calc-alkaline plutons composed predominantly of diorites and tonalites from the West Massif Central. Their petrochemical fingerprints are compatible with partial melting of a hydrous mantle wedge followed by fractional crystallization of amphibole and plagioclase before final emplacement between 5 and 8 kbar within the continental upper plate of a subduction system. In situ U-Pb zircon dating on tonalites yields a fairly narrow age range of 365−354 Ma (including uncertainties) for igneous crystallization. These calc-alkaline plutons imply active margin magmatism near the Devonian-Carboniferous boundary and are contemporaneous with the back-arc magmatism and HP metamorphism as dated by recent studies. However, such isolated igneous bodies do not form a transcrustal magmatic arc but rather represent dispersed plutons emplaced within less than 30 Myr when all data from the Variscan belt of France are considered. In Limousin, they intrude migmatitic paragneisses and retrogressed eclogites from the Upper Gneiss Unit (UGU), suggesting that the high pressure rocks were already exhumed at 19−30 km depth before 365 Ma. Moreover, the diorites and tonalites are never found within units below the UGU. It therefore suggests that these tectono-metamorphic units of the Western French Massif Central were piled up after 354 Ma. Altogether these results support the monocyclic model for Variscan geodynamics in the French Massif Central, with the transition between oceanic subduction and continental collision taking place between Upper Devonian and Lower Carboniferous.

Geochemistry of Miocene sediments of the Middle and South Caspian basins (within Azerbaijan): climate, chemical maturity and provenance

Geochemical and petrographic characteristics of the Miocene rocks of the Shamakhi-Gobustan trough (South Caspian basin) and the North Absheron uplift zone (Middle Caspian basin) indicate that these sediments contain products of erosion of the magmatic rocks of the Eurasian continent’s active margin - the volcanic arc of the Lesser Caucasus, as well as granitic basement of the Garabogaz High and Mesozoic-Eocene sedimentary strata of the Middle Caspian basin and the Greater Caucasus. The uplift of the Greater Caucasus, which began in the Middle Eocene as a result of the collision of the Afro-Arabian and Eurasian plates, brought to the exposure of the Mesozoic-Eocene sedimentary rocks of the Tethys Ocean that were deposited from the detrital material of the disintegrated igneous rocks of the Lesser Caucasus and the granitic basement of the Russian platform. The clastic material of these eroded Cretaceous-Eocene sedimentary rocks was accumulated in the Miocene basin that caused the geochemical characteristics of the Miocene sediments demonstrating the occurrence of igneous rocks of active margins or products of their erosion in the sources area. The accumulation of thick quartz-containing sand beds in the Chokrakian time (analogous to the Langhian stage) in a number of fields of the Shamakhi-Gobustan trough was the result of the exposure removal to the surface of quartz-rich Cretaceous rocks of the Greater Caucasus because of collisional processes, and their intensive erosion due to humidization of the climate during the Middle Miocene climatic optimum. Judging by the geochemical characteristics, during deposition of shale mudrocks the arid conditions prevailed. Keywords: Miocene; South Caspian and Middle Caspian basins; geochemistry; provenance; climate; geodynamic setting.

Tectono‐Stratigraphic Insights on the Dynamics of a Complex Subduction Zone, Northern Peruvian Forearc

AbstractTwo main types of subduction are recognized around the world: accretionary and erosive. The northern Peruvian margin is a well‐known example of a margin subjected to subduction erosion, but to date the along‐margin variability and temporal changes in subduction process and forearc basin evolution have not been characterized in detail. Interpretation of regional seismic lines and integration of oil‐industry wells and seafloor data captures the erosive nature of subduction underneath the forearc with only a minor accretionary component to the north. Episodes of uplift driven by plate coupling were followed by normal faulting/extensional collapse due to plate decoupling. This mechanism explains the dominance of normal faulting across the forearc until the Oligocene with a slight reactivation within the Miocene. The subduction history is complex and includes a reduction in plate convergence rate related to forearc crustal shortening, represented by large‐scale structures including the Peru fault (reactivated) and the Illescas fault‐propagation anticlines of the Northwest Peru transpressional system. This crustal deformation started in the Miocene. Integration with magnetic anomaly data indicates that activity of the present‐day transpressional system driven by tectonic escape of the Nazca Sliver toward the northeast, may explain the seismicity gap in southern Ecuador and northern Peru. An evolutionary model of the northern Peruvian margin shows how subduction zone geodynamics left its erosive fingerprint in the forearc basin configuration.

Transient response feedback control for horizontal vibration of high-speed elevator car with prescribed performance

The high-speed elevator car is subject to violent horizontal vibration due to the wind pressure generated by the ventilation hole of the elevator rapid operation, improper adjustment of the gap and steps at the joint of the elevator car guide rail, pitting corrosion or wear on the guide surface of the guide shoe, inadequate installation and adjustment of the guide shoe or guide rail and so on. Aiming at the problems of poor transient convergence and real-time performance, low control accuracy and stability of the existing active control algorithm for the horizontal vibration control variables of the elevator car system, a transient response feedback control strategy with specified performance is proposed in this paper. Firstly, a six degree of freedom elevator car system model is established, and the state space equation is constructed based on the linear fractional transformation algorithm; Secondly, a class of preset transient performance function is introduced to construct the convergence boundary in advance to ensure that the system control variables are strictly constrained within this boundary, and the stability of the transformed variables is ensured by equivalent transformation; Finally, four different control methods including passive control, H2/H∞ control, PID control and transient response feedback control proposed in this paper are compared and analyzed by using MATLAB under two typical guideway excitation. The simulation results show that the proposed transient response feedback control strategy reduces the root mean square value and maximum value of the horizontal displacement acceleration of the elevator car system by more than 81%, effectively suppresses the horizontal vibration of the elevator car, and ensures the transient and steady-state performance of the elevator car system.

Compositional changes with incremental growth of the Quxu granite batholith, southern Tibet: Evidence from geochronology and geochemistry

How to reconstruct the detailed processes and identify the key factors of incremental growth to form a large granite batholith is controversial. Such in-depth investigations along convergent plate boundaries are of great importance for better understanding the growth and reworking of continental crust. This work presents an integrated study of SIMS (secondary ion microscope) U-Pb geochronology, trace elements and oxygen isotopes of zircon, microstructure and chemistry of plagioclase, and whole-rock elemental geochemistry and Sr-Nd isotopes to decipher the temporal compositional change and incremental growth of the Quxu granitoid batholith in the Gangdese magmatic belt, southern Tibet. The Quxu host granitoids are mainly metaluminous and calc-alkaline to high-K calc-alkaline in geochemistry, whilst the melanocratic microgranular enclaves (MMEs) and mafic dykes vary from calc-alkaline to shoshonitic series. New SIMS zircon U-Pb data suggest a prolonged history (ca. 16.6 Myr) for the Quxu batholith accompanied by several episodes of intermediate–mafic magma replenishments. Zircon δ18O and whole-rock (87Sr/86Sr)i values fluctuate from ∼5.6‰ to ∼6.8‰ and from 0.7038 to 0.7085, respectively, while the whole-rock εNd(t) values show a fluctuated decrease from +5.2 to −4.5 with time. The calculated Ti-in-zircon temperature (574–903 °C) and oxygen fugacity (ΔFMQ –0.9 to ΔFMQ +3.2) of the granitoid magmas fluctuated as well. The youngest group of the host granitoids is distinguished by the most elevated Th/La (>1.5) and Th/Ce (>1.0) ratios and K2O contents (>3.0 wt%) with evolved isotopic compositions, implying pronounced incorporation of supracrustal materials into the source region. Microstructural and compositional features of zircon and plagioclase from the host granitoids indicate that the incremental assembly of Quxu batholith was foremost facilitated by multiple episodes of magma recharge with distinct compositions and sources. The temporal variations of magma condition and composition throughout the lifetime of the magma reservoir highlight the importance of determining the longevity of batholiths and clarifying the discrepancy of individual magma pulses before deciphering the genesis of composite batholith. The aforementioned Sr–Nd–O isotopes show good correlations with the fluctuating whole-rock (La/Yb)N (2.7–68.5) and zircon Eu/Eu* (0.02–1.26) ratios, which further affirms episodic syn-collisional crustal thickening and episodic input of supracrustal material in magma sources. Based on the spatiotemporal variations of geochemistry, we propose a zoned incremental growth model to better illuminate the detailed processes of the incremental amalgamation of the Quxu batholith.

Achieving a Comprehensive Microseismicity Catalog through a Deep-Learning-Based Workflow: Applications in the Central Ecuadorian Subduction Zone

ABSTRACT Although seismological networks have densified along the Ecuadorian active margin since 2010, visual phase reading, ensuring high arrival times quality, is more and more time-consuming and becomes impossible to handle for the very large amount of recorded seismic traces, even when preprocessed with a detector. In this article, we calibrate a deep-learning-based automatized workflow to acquire accurate phase arrival times and build a reliable microseismicity catalog in the central Ecuadorian forearc. We reprocessed the dataset acquired through the OSISEC local onshore–offshore seismic network that was already used by Segovia et al. (2018) to produce a reference seismic database. We assess the precision of phase pickers EQTransformer and PhaseNet with respect to manual arrivals and evaluate the accuracy of hypocentral solutions located with NonLinLoc. Both the phase pickers read arrival times with a mean error for P waves lower than 0.05 s. They produce 2.7 additional S-labeled picks per event compared to the bulletins of references. Both detect a significant number of waves not related to seismicity. We select the PhaseNet workflow because of its ability to retrieve a higher number of reference picks with greater accuracy. The derived hypocentral solutions are also closer to the manual locations. We develop a procedure to automatically determine thresholds for location attributes to cull a reliable microseismicity catalog. We show that poorly controlled detection combined with effective cleaning of the catalog is a better strategy than highly controlled detection to produce comprehensive microseismicity catalogs. Application of this technique to two seismic networks in Ecuador produces a noise-free image of seismicity and retrieves up to twice as many microearthquakes than reference studies.

Tarim rotation mechanism and the differential deformation responses along the Tian Shan

SUMMARY Rotation of rigid blocks within continental interiors far from the plate convergence boundary is an unusual process, the dynamics of which is not clear. The Tarim block, as a rigid Precambrian block in central Asia, is surrounded by the Tibetan–Pamir plateau to the south and Tian Shan mountains to the north. Numerous geophysical data suggested that the Tarim block experienced significant clockwise rotation in the Cenozoic. Meanwhile, contrasting deformation patterns and associated topographic responses were observed between the western–central and eastern Tian Shan. The relationship among the India–Asia collision, Tarim rotation, and Tian Shan responses are poorly constrained. Here, a series of large-scale, high-resolution 3-D numerical models were constructed. The model results reveal that the collision of the indenting Indian lithosphere with the southwestern rim of the Tarim block triggers clockwise rotation of the Tarim block. Further on, the Tarim rotation produces differential deformation responses along the strike of Tian Shan, that is convergence-induced higher compression and strong uplifting in central Tian Shan but divergence-induced less compression and moderate uplifting in eastern Tian Shan. Thus, the Tarim rotation serves as an indispensable linkage between the Tibetan plateau evolution and the far-field Tian Shan activation.

Impact of hydrological changes and vertical motions on Pleistocene marine environments of the eastern coast of the island of Rhodes (Greece)

The island of Rhodes in the eastern Mediterranean Sea is situated in an area affected by an ongoing plate convergence, and its Pleistocene marine environments were influenced by recurring hypoxia and changes in organic matter fluxes. This makes the island an important site to study the influence of orbital-driven climate changes and tectonic-induced vertical motions on the marine benthic ecosystems in near-coastal areas at local and regional scales. We investigated the Early and Late Pleistocene sediment sections at Agathi Beach and Lardos, located on the middle-eastern coast of the island. Our results show variations in oxygen and food levels at the sea floor, including transient phases of enhanced fresh-water and nutrient input to near-coastal environments. These phases occurred at times of Northern Hemisphere summer insolation maxima, simultaneously to the formation of sapropels in the deep-sea basins of the eastern Mediterranean Sea. The application of a benthic foraminiferal transfer function revealed that both sections were influenced by tectonic-driven long-term and short-term vertical motions with higher rates than expected on the island of Rhodes. While Agathi Beach underwent two short-term cycles of uplift and subsidence, Lardos indicates at least three cycles with average rates of vertical motion as high as 8.6 mm/a.

Article Review/ The Tectonic Evolution of Erbil Area (Ne Iraq) as a Part of the Northeastern Margin of the Arabian-Nubian Plate Throughout Albian-Early Eocene

The Albian-Early Eocene tectonic evolution of the Zagros Foreland Basin of the High Folded Zone in the Iraqi Kurdistan region has been studied based on the recent foreland basin system concept. This study showed that during the cretaceous (Albian – Cenomanian) there was a geodynamic shift from a passive margin to a foreland basin system phase, not to an active margin phase as mentioned in the previous studies. The advance of the continental margin of the Arabian-Nubian Plate (ANP) toward the subduction zone imposed a tectonic load leading to the form of a flexural wave. The consequences of the last tectonic event were reflected by the continuous deposition of the Balambo Formation. in a foredeep depozone. This happened concomitantly with a flexural emergence of the continental shelf further to the west forming a forebulge depozone represented by the deposition of reefal facies of the Qamchuqa Formation. These geodynamic changes are considered here to represent the Megasequence boundary between the Tectonic Megasequence (TMS) of AP8 and AP9. The last sequence of the passive margin was the Qamchuqa Formation Which is called the Pre-Orogenic Carbonate Platform and was separated from the Bekhme Formation by regional unconformity (Megasequence boundary). The latter is represented by the Lower Sequence of the foreland basin system, which is called the Syn-Orogenic Carbonate Platform (SCP). During the Middle Campanian, the Zagros foreland basin started with the underfilled stage, and it was entirely clear by the end of the Cretaceous comprising a broad threefold subdivision of depositional realms that translated into three stratigraphic units known as trinity underfilled units of foreland basin system. The lower carbonate unit, the pelagic and hemipelagic unit, and the upper flysch clastic unit are represented by Bekhme, Shiranish, and Tanjero Formations respectively. All of these units were superimposed during basin depocenter migration and became younger toward the southwest in front of progressing the orogenic wedge toward the Arabian Craton. During the late Maastrichtian to Paleocene – Early Eocene, the Zagros foreland basin underwent a transition from underfill to fill the stage. Deep exhumation of the orogenic wedge and ophiolite assemblage had supplied the clastic sediment of the Kolosh Formation into the basin covering the foredeep and most of the forebulge and backbulge depozones.

Tectonic significance of the late-Ediacaran syn-orogenic basin in the easternmost portion of the Paraguay Belt, Tocantins Province, central Brazil

Sedimentary provenance studies using detrital zircon U–Pb ages represent an important tool to investigate the evolution of orogenic basins and to suggest tectonic settings and paleogeography reconstructions when it comes to supercontinent modeling. Syn-orogenic basins worldwide are characterized by a large proportion of zircons with ages close to the maximum depositional period, reflecting the proximity of recently formed magmatic rocks. In this work, we combine field observations, detrital zircon U–Pb ages, whole-rock Sm–Nd and mica Ar–Ar isotopic analyses to constrain the final tectonic evolution of a restricted basin located in a poorly studied region at the easternmost limit of the Paraguay Belt in the Tocantins Province, central Brazil. The investigated area corresponds to the boundary sector of the Paraguay Belt and the Brasília Belt and is also transected by the strike-slip fault system associated with the Transbrasiliano Lineament. This sector was previously mapped as part of the Cuiaba Group, internal zone of the Paraguay Belt. We provide 465 new detrital zircon U–Pb data with ages distributed from the early Cambrian to the Archean, with approximately 60% of the analyzed grains derived from Ediacaran-Cryogenian sources. The maximum depositional age of the basin is defined at ca. 590 Ma, constrained by the youngest age peak and an evident provenance shift in detrital input in the Paraguay Belt was demonstrated. The syn-orogenic character of the basin is inferred based on the main peak of the detrital zircon population age distribution around 600 Ma, which is very close to the maximum depositional period and points to a short time between erosion, deposition, and burial processes. The muscovite 40Ar/39Ar age of ca. 536–546 Ma obtained for muscovite schist metamorphosed under greenschist facies conditions indicates that the regional thermal regime was maintained up to the early-Cambrian in the area. The minimum fast cooling rate of 25 °C/Myr defined in the investigated area is constrained by the 40Ar/39Ar analysis of biotite (549.16 ± 1.30 Ma) from a syn-to late-kinematic granodiorite intrusion. The very rapid magma emplacement occurred into relatively shallow crustal levels through the associated strike-slip faults. The Transbrasiliano Lineament would have facilitated the rapid unroofing of the study area and therefore the syn-orogenic deposition in a foreland domain at the final phase of West Gondwana amalgamation. The studied metasedimentary rocks represent a transition phase from the passive margin sedimentation (Cuiabá Group) to an orogenic phase, constraining an inversion event in the West Gondwana around ca. 590 Ma. The data provide evidence of a late orogenic basin that was formed contemporaneously with the evolution of an active margin between the Amazonian Craton and the eastern blocks/cratons (São Francisco-Congo and Rio de la Plata cratons and Paranapanema Block) close to Cambrian times. Our results support the existence of the younger Clymene Ocean and the subsequent final assembly of West Gondwana in the Cambrian.

New insight on the structural architecture of northern Tunisia with a multidisciplinary approach: Association of Miocene piggy-back basin and active Plio-quaternary out-of-sequence thrusts

In order to better understand the intricate structural architecture of northern Tunisia, we use a multidisciplinary approach that includes field observations, geomorphic, sedimentological, and gravity data across this area. We offer a model of progressive thrusting in which four deformation phases occurred in the context of plate convergence (i) Uplift of the Jebel Ichkeul Triassic succession via a NE-trending thrust fault during the Eocene; (ii) Advance of Numidian thrust sheets during the late Oligocene-Middle Miocene, causing the formation of the Lake Ichkeul/Jalta as being piggy-back basin; (iii) Initial out-of-sequence thrusting during the Late Miocene, resulting in the formation of the Sejnane and El Mejel basins with syntectonic Pliocene infill; and (iv) Subsequent out-of-sequence thrusting during the Early Pleistocene, leading to the formation of the Oued (River) Zyatine basin with a syntectonic Quaternary deposits. We used the gravity data analysis to mark the thicknesses of syntectonic deposits and their bounding thrust faults. The kinematic analysis indicates the occurrence of progressive multiphase out-of-sequence thrusting events with thrusts verging to the southeast. The combination of climate and mechanical fractures induced gradually long-term damage and changed the original landscape of the evidenced out-of-sequence thrusts. Furthermore, the existence of local normal faults in the backlimbs and reverse faults in the forelimbs, together with the drainage network type, earthquakes, the slope erosion, and the aggraditional terrace system, implies a gradual landscape evolution of thrust topography. This physical evolution occurred following an active tectonics across the exhibited out-of-sequence thrusting since the Pliocene.

Два эпизода надсубдукционного интрузивного магматизма в пределах Печорской зоны фундамента Печорской синеклизы

The Pechora Basin is the largest tectonic structure of the Pechora Plate. It is located between the Timan and the Cis-Ural Foredeep. The Upper Precambrian sedimentary-metamorphic and igneous rocks of the basement are completely overlain by a sedimentary cover, therefore, the geological structure of the basement is known only on the basis of geophysical data and core samples from boreholes up to 5 km deep. The basement has a heterogeneous structure. It includes complexes of the Late Precambrian passive margin of the East European continent, which compose the Timan megablock (Izhma zone with Timan adjoining from the southwest) and formations formed in an active margin geodynamic setting combined into the Bolshezemel megablock (Pechora and Bolshezemel zones). The boundary between megablocks is the Pripechora fault (suture) zone. The age of igneous rocks of the basement is debatable; therefore, U-Pb (SIMS) studies of single zircon grains are undertaken to specify it. The article presents petrogeochemical data and U-Pb (SIMS, SHRIMP-RG) ages of zircon grains from plutonic rocks of the Pechora zone belonging to the Bolshezemel megablock drilled by two boreholes at depths of ~ 4.5 km. The obtained results indicated two episodes of island-arc magmatism. The first took place at the end of the Riphean, and the second was confined to the Early–Late Vendian boundary. The age of gabbrodiorites from the 1-Severny Savinobor borehole, interpreted as early island-arc rocks, is 673 ± 7 Ma. Late island-arc plagiogranites from the 1-Novaya borehole yield the age of 564 ± 5 Ma and precede the orogenic granitoids of the Pripechora fault zone which are dated (U-Pb) to 555—544 Ma.