Tectonic Processes Research Articles

Insights on the structural framework of the Egyptian Eastern Desert derived from edge detectors of gravity data

Advanced geophysical techniques are used on Bouguer gravity data to unravel the structural complexity of the Eastern Desert. Using methods such as tilt angle (TA), enhanced horizontal gradient amplitude (EHGA), lineament analysis, and 2Dcrustal modeling, we are able to differentiate between deep and shallow gravity sources and delineate the area’s geologic features. Using fast Fourier transform, positive and negative anomalies are identified. The positive anomalies are interpreted as uplifted block, anticline features, or intrusive occurrences of denser rocks, whereas the negative anomalies are interpreted as downfaulted blocks, providing crucial insights. Lineament analysis suggests that the predominant tectonic force that shaped the area is in the northwest direction. Integration of TA and EHGA reveals nuanced structural patterns. The constructed structural map indicates a network of uplifted and downfaulted blocks intersected by strike-slip faults with a northeast trend. The 2D crustal modeling illustrates the diverse composition of granitic and basaltic rocks, with a discernible thinning of the continental crust toward the Red Sea offshore area. This significantly advances the understanding of the Eastern Desert’s geologic evolution, offering valuable insights into the tectonic processes and crustal dynamics.

Tectonic and climatic controls on plant biodiversity in the Hengduan Mountains, China

Mountainous regions contain some of the most dynamic landscapes in the world and host a majority of the global biodiversity hotspots. The Hengduan Mountains, located at the syntax of Eurasia and India, have a complex geological history associated with the hyperdiverse assemblage of species. Tectonics and geomorphic and climate processes in the Hengduan Mountains may have jointly caused the emergence of high biodiversity. We propose three mechanisms that may promote high-level montane biodiversity: habitat creation, habitat disruption, and habitat oscillations. We mapped species richness patterns for seed plants and computed phylogenetic endemism across the entire Hengduan region. We developed a set of geomorphic metrics regarding these mechanisms to link plant richness and phylogenetic endemism patterns. By estimating the component of species richness due to habitat heterogeneity, we isolate the component due to tectono-geomorphic processes. We found that regions of exceptionally high species richness are explained by a combination of habitat heterogeneity and tectono-geomorphic processes, while glaciation and high climate change velocity are associated with low richness, thus contributing to recent extinction. We interpret the richness of biodiversity hotspots in the Hengduan Mountains in terms of climatic and tectonic processes.

The Effective Elastic Thickness of the Lithosphere Reveals Tectonic Process and Lithospheric Rheology of the Eurasian Basin

ABSTRACTWe obtained the effective elastic thickness of the lithosphere (Te) in the Eurasian Basin using the fan‐shaped wavelet method. For ultraslow spreading ridges, the magmatic heat input is insufficient to form continuous quasisteady‐state magma lenses along the axis, resulting in significant variability in the rheological strength of the lithosphere. We suggested that the tectonic inheritance resulted in the different lithospheric rheology of WVZ and SMZ, consequently leading to distinct tectonic‐magmatic activities. The SMZ with less magmatic activity has a weaker lithosphere than that of the EVZ with extensive magmatism. We propose that the lithospheric rheology and thermal structure of ultraslow spreading ridge may be influenced not by the amount of magma supply but by the mode of magma emplacement.

Tufas record significant imprints of climate and tectonic activity over the past 600 ka: Evidence from a multi-story wedge in Northwest Africa

The Quaternary Period climatic oscillations, typically those driven by Milankovitch cycles, have significantly left profound imprints in the geological records. However, the potential of terrestrial archives, particularly tufa deposits, as archives for Quaternary climate remain relatively underexplored. This study aims to contribute to filling the gap in a data-scarce region (Northwest Africa) through investigating Middle Pleistocene to Holocene groundwater-fed tufa deposits, using fieldwork-based, process-oriented facies analysis and advanced 230Th technique. Eight stratigraphic sections were measured, identifying thirteen sedimentary facies grouped into four facies associations representing specific depositional settings: (i) fluvio-lacustrine and palustrine tufa, (ii) barrage cascade tufa with buttresses, (iii) tufa in channels with pools, and (iv) tufa in shallow braided channels with free-flowing water. The depositional system comprises a single multi-story wedge of vertically and laterally stacked barrage-cascade dammed-area systems.Our Integrated analysis revealed significant tufa growth during MIS 14, with implications for a warm and humid MISs 15–13 ‘extra-long interglacial’, consistent with multiple paleoclimate records. Such conditions would have supported late Acheulean hominin occupation and the emergence of Early Modern Humans in the region around 300 ka. The findings also highlight the possible impact of the Mid-Brunhes Event (MBE) on tufa deposition patterns, likely through CO2-climate feedbacks, underscoring the sensitivity of tufa records to global climatic changes. Moreover, the study outcomes suggest significant regional tectonic activity during the late Middle Pleistocene, causing counter-clockwise rotation and northward tilting of MIS 14 deposits. The associated seismic events may have modified the hydrogeological budget and, by extension, altered the balance between tufa aggradation and degradation. The rotation about the vertical axis suggests a bookshelf faulting mechanism driven by regional left-lateral strike-slip tectonics. Differential karstic dissolution and tectonic forces would have further contributed to deposit tilting. The study highlights the potential of tufa as a valuable terrestrial archive for understanding Quaternary climate dynamics and tectonic processes. Future research should aim to expand the chronological framework and further investigate the climatic and tectonic influences on tufa deposition in this data-scarce region. This can be achieved through additional 230Th dating, high-resolution stable isotope measurements on microbialites, particularly focusing on the significance of the Mid-Brunhes Event (MBE) in Northwest Africa.

Influence of tectonic evolution processes on burial, thermal maturation and gas generation histories of the Wufeng-Longmaxi shale in the Sichuan Basin and adjacent areas

The Wufeng-Longmaxi (WL) shale is widely distributed in the Sichuan Basin and adjacent areas in southwest China. The basin experienced multiple-stage complex tectonic movements, whose influences on burial, thermal maturation and gas generation histories in different areas are poorly understood. Based on a detailed study of the denudation stages, strata thickness, and thermal history of the basin, burial and thermal maturation histories of seven wells in different areas were modelled using PetroMod software. Due to the high maturity of the WL shale, a low-maturity Silurian Polish Llandovery shale was used for gold tube closed-system pyrolysis experiments to obtain kinetic parameters for evaluating methane generation history. The Polish shale was selected due to its depositional age, sedimentary environment and organic type, which are similar to the WL shale. The burial history of the WL shale can be divided into five stages: I. Early to Middle Silurian rapid burial; II. Caledonian uplift and denudation; III. Permian to Triassic sustained burial and denudation; IV. sustained burial since the Late Triassic; and V. Late Cretaceous to present sustained uplift and denudation. The thermal maturity of the WL shale in all wells increased with burial depth during stage IV. In addition, high calculated reflectance increments in wells JY1 and N201 during stage III occurred due to the relatively high basal heat flow and deep burial depth, resulting in higher current thermal maturities than in the other wells. The late Permian–Early Triassic and the Middle Jurassic–Early (or Late) Cretaceous were the key methane generation periods for wells JY1 and N201. In contrast, the other five wells had a single methane generation stage, mainly determined by burial and thermal maturation processes. The time of uplift and the amount of denudation during stage V, the current burial depth, the development of faults and fractures, high proportion of retention and the seal capacity of the overlying caprock are key factors for shale gas preservation. Hence, this study will help guide future shale gas development in the Sichuan Basin.

Eastward drainage-divide migrations driven by the spatial variations in precipitation and tectonic uplift contribute to the formation of the Parallel Rivers in the Hengduan Mountains, Southeastern Tibet

In the Hengduan Mountains (Southeastern Tibet), the south-draining Nmai Hka (Upper Irrawaddy), Nu (Upper Salween), Lancang (Upper Mekong), and Jinsha (Upper Yangtze) Rivers flow parallel and in proximity to each other, thus forming rather a unique geomorphic configuration (i.e., the Parallel Rivers). It has been suggested that this configuration is an outcome of tectonic shortening that “squeezed” the rivers together. Although the tectonic and surface processes in this region have been extensively studied, the processes that led to this configuration remain controversial. Here, we investigate the potential role of drainage-divide migration in forming the Parallel Rivers. We demonstrate, based on geomorphologic analysis of divide stability between the parallel rivers, that while the two western divides (Nmai-Nu, Nu-Lancang) are likely migrating eastward, the eastern divide (Lancang-Jinsha) is roughly stable. This pattern suggests that the formation of the Parallel Rivers is associated with an abutment of the migrating divides against the fixed one. GPS and precipitation data combined with prior research suggest that the migrations of the two western divides are driven by the spatial variations in precipitation and rock uplift. Concurrently the stability of the eastern divide is influenced by a combination of climatic and tectonic factors, as well as a historical river capture event. This implies that the formation of the Parallel Rivers has not necessarily been an outcome of east-west tectonic shortening but has been influenced by the spatial variations in precipitation and tectonic uplift.

Crustal silica content of East China: A seismological perspective and its significance

East China has experienced multiple periods of tectonic movements, which have contributed to the composition and rheological properties of its present crust. Estimating the composition of the crust is crucial for understanding the tectonic processes. Based on the teleseismic receiver functions with data from the National Seismic Network of China, we applied the H-κ-c method to obtain the crustal bulk VP/VS ratio and to constrain the SiO2 content in the crust. We estimated the SiO2 content to range from 50.89 wt% to 73.51 wt%, with an average value of 65.87 wt%, indicating a predominant felsic composition of the East China's crust. Our study suggests that the North-South Gravity Lineament (NSGL) is an approximate delimitator of the felsic and mafic crust in East China, hinting at a widespread deficiency of mafic lower crust in the east of the NSGL. The mafic crust is extensively distributed in the Taihang orogenic region (TSR) and WuLingshan gravity gradient belts (WLG), particularly in the Datong volcanic area, which manifests the mantle materials intraplating. The scatteredly distributed mafic crust at the east of the NSGL is mainly concentrated in the southeast coast of China and in the intersection region of the Tanlu Fault (TLF) and Sulu region. In Sulu region, the TLF may primarily provide a channel for the thermal intrusion from the underlying mantle lithosphere, which has increased the mafic content. The Pacific/Philippine Sea plate subduction has triggered a significant amount of crust-mantle material exchange below southeast China that resulted in a high degree of mafic crustal composition.

Paleomagnetic Data Bearing on the Origin of the Supra‐ Subduction Zone Ophiolites in Southeast Anatolia and the Progressive Closure of the Neotethys Ocean in the Eastern Mediterranean

AbstractThe Late Cretaceous supra‐subduction zone (SSZ) ophiolites in SE Anatolia form two parallel belts: the northern ophiolitic belt, which was emplaced onto the Tauride platform and a second southern belt emplaced on the Arabian platform. There are controversial hypotheses about the geometry and tectonic process of these ophiolites, which are still not well understood. Here, we test three alternative tectonic models for; (a) One single ocean which is defined by the İzmir‐Ankara‐Erzincan Ocean; (b) A southern branch of the Neotethys Ocean; (c) Two separate oceanic basins, which are the Berit Ocean and the South Neotethys Ocean. We present paleomagnetic results from 161 sites focusing on the sheeted dyke complex, cumulate gabbros, extrusive and sedimentary sequences of the Upper Cretaceous ophiolites in the SE Anatolian region. We also sampled the unconformable cover units from Middle Eocene and Miocene sedimentary rocks to distinguish emplacement related tectonic rotations from post‐emplacement tectonic rotations. Our data indicate that the southern ophiolites (Hatay ophiolite, cumulate gabbro + lava) were formed at a paleolatitude of and those of the northern ophiolites (Göksun, İspendere, Guleman ophiolite, cumulate gabbro + lava) were formed at a paleolatitude of . We hypothesize that the northern ophiolites were derived from the Ocean in a NW‐SE directed subduction zone between the Taurides and the Bitlis Pütürge massif, while the southern ophiolites, in contrast, were formed in the South Neotethys Ocean in a NNW‐SSE directed subduction zone farther northeast of the Taurides. Both the ophiolites reached their present position during Late Cretaceous to Middle Miocene, affected by rigid‐block rotations almost in counterclockwise sense.

Rapid shear zone weakening during subduction initiation

Subduction zones play a pivotal role in the mechanics of plate tectonics by providing the driving force through slab pull and weak megathrusts that facilitate the relative motion between tectonic plates. The initiation of subduction zones is intricately linked to the accumulation of slab pull and development of weakness at plate boundaries and, by consequence, the largest changes in the energetics of mantle convection. However, the transient nature of subduction initiation accompanied by intense subsequent tectonic activity, leaves critical evidence poorly preserved and making subduction initiation difficult to constrain. We overcome these limitations through a comprehensive analysis focused on Puysegur, a well-constrained extant example of subduction initiation offshore South Island, New Zealand. Through time-dependent, three-dimensional thermo-mechanical computations and quantitative comparison to new geophysical and geological observations, including topography, stratigraphy, and seismicity, we demonstrate that subduction initiation develops with a fast strain weakening described with a small characteristic displacement ([Formula: see text] 4 to 8 km). Potential physical mechanisms contributing to the strain weakening are explored and we find that the observed fast weakening may arise through a combination of grain-size reduction within the lower lithosphere and fluid pressurization at shallower depths. With the shared commonality in the underlying physics of tectonic processes, the rapid strain weakening constrained at Puysegur offers insights into the formation of the first subduction during early Earth and the onset of plate tectonics.

A new technique mapping submerged beachrocks using low-altitude UAV photogrammetry, the Altınova region, northern coast of the Sea of Marmara (NW Türkiye)

High-resolution aerial imagery captured from low altitudes enables the detailed reconstruction of the geomorphological features of submerged beachrocks and the quantification of their topographic complexity. These coastal deposits serve as vital indicators for estimating past sea-level positions and deformation, contributing to our understanding of climate and tectonic processes across various temporal and spatial scales. This study focuses on submerged beachrocks identified in the nearshore coastal area of Tekirdağ city (Altınova), and the existing knowledge regarding such geological formations is limited.Situated in the tectonically active western Marmara region, the coastal zone of The Tekirdağ-Altınova is influenced by the North Anatolian Fault Zone (NAFZ), which has significantly shaped the coastline over time. Utilizing unmanned aerial vehicle (UAV) data, we successfully isolated submerged beachrocks from other coastal deposits, identifying them at depths of 2 m below current sea level and extending approximately 5 km along the coast. This identification was facilitated by integrating high-resolution aerial imagery with morphological analysis techniques, specifically employing structure-from-motion photogrammetry to generate a dense point cloud for bathymetric mapping.The utilization of cost-effective UAV imagery facilitated the efficient monitoring of beachrocks. Geographic information systems (GIS) and the TerraceM application were employed to analyze the high-resolution bathymetry data (with a 5 cm resolution), enabling the precise estimation of shoreline angles and associated errors. These shoreline angles, which correspond to the past sea levels high stand, were mapped using swath profiles oriented perpendicular to the isobaths. Our findings reveal that the majority of submerged beachrocks exhibit shoreline angles between ∼ −0.7 m and −1.1 m. This study presents innovative methodologies for mapping the height and spatial distribution of beachrocks, as well as for reliably estimating reliable uplift rates in the nearshore area of Tekirdağ-Altınova.

Detrital zircon and apatite reveal Paleoproterozoic rifting along the eastern margin of the Yilgarn Craton

Detrital minerals within Proterozoic basins are commonly an extant record of now-destroyed crust and provide valuable constraints on ancient paleogeography and tectonic processes. However, reconstructing basin histories depends on discriminating potentially exotic, far-travelled (allochthonous) versus locally sourced (autochthonous) detritus. Detrital zircon from the Woodline Formation, a component of the Proterozoic Barren Basin at the margin of the Yilgarn Craton, Western Australia, closely matches the age and Hf isotopic signatures of magmatic units in the Paleo- to Mesoproterozoic Albany–Fraser Orogen (AFO). However, the provenance of some 2300–2000 Ma zircon detritus is not readily accounted for by known magmatism in the AFO nor the wider Western Australian Craton. To help resolve this enigmatic source, we present isotopic data (U–Pb, Lu–Hf) and trace element geochemistry for zircon and limited U–Pb data for scarce apatite collected from sand and rocks of the Woodline Formation. Based on Hf isotopic signatures, some of the detritus appears to be derived from the recently identified 2030–2010 Ma felsic-igneous Moonyoora Suite, representing the oldest known magmatic components of the AFO. Moreover, the isotopic data imply an earlier ca. 2250 Ma episode of mafic rift-related magmatism, potentially offering a glimpse into the earliest rifting stages along the Yilgarn Craton’s eastern margin. While Paleoproterozoic detritus is omnipresent in Woodline rocks, it is conspicuously absent from overlaying regolith, demonstrating that cover atop the Woodline Formation is imported and not locally derived. This disparity is important as it highlights that ongoing exploration efforts analysing unconsolidated regolith may not fully capture basement signatures.

Tectonic Inversion in Sediment-Hosted Copper Deposits: The Luangu Area, West Congo Basin, Republic of the Congo

Complex Neoproterozoic tectonic processes greatly affected the West Congo Basin, resulting in a series of dispersed copper deposits in the Niari Sub-basin, Republic of the Congo. Structural observation and analysis can help in understanding both the transportation pathways for copper accumulation and the detailed tectonic evolution processes. This study examines cases from four copper mine sites in the Luangu region of the Niari Basin, using a set of codes that consider the three regional tectonic regimes (extension, extrusion, and contraction) and three deformation criteria (maximum effective moment criterion, tensile fracture criterion, and the Coulomb criterion). By combining these two aspects, nine new codes are introduced: the extension maximum effective moment criterion (EM), extension tensile fracture criterion (ET), extension Coulomb criterion (EC), strike-slip maximum effective moment criterion (SM), strike-slip tensile fracture criterion (ST), strike-slip Coulomb criterion (SC), compression maximum effective moment criterion (CM), compression tensile fracture criterion (CT), and compression Coulomb criterion (CC). By analyzing and applying these codes to the selected sites, we show that the new codes can present a geometric coordination catering to an exhumation-related inversion process from extension, strike-slipping, to contraction. The existence of SM- and CM-related structures that occurred during regional extrusional and contractional events may indicate a deeper level of exhumation for layers related to copper deposits in the field sites. A new tectonic evolution model is presented, considering the hypothesis of vertical principal stress changes while the two horizontal principal stresses remain relatively constant during copper mineralization affected by the Western Congo Orogen. The application of the nine codes facilitates the determination of interrelations between different tectonic regimes.

Geotechnical Justification for Designing Landslide Prevention Measures

Abstract When designing anti-landslide measures, slope stability assessment is an important factor and is determined by conducting comprehensive engineering and geological studies on a slope with potential landslide risks. The results of correct engineering and geological justification for the design of anti-landslide measures lead to the preservation of the structure and safe operation of infrastructure facilities. Our experience shows that to eliminate the negative effects of landslide processes, it is necessary to accurately determine the engineering and geological conditions of the slope, including the stability of the slope, taking into account natural dynamic phenomena (seismicity of the territory and tectonic processes) and, if possible, to see the complete elimination of the causes that lead to landslide processes when developing anti-landslide measures. To achieve these goals, the geotechnical justification of the design is the only correct solution. Geotechnical justification of protective measures intended to protect the structural elements of the Baku-Russian Federation State Border highway, which is part of the north-south transport corridor and passes through the foot of a potentially landslide-hazardous slope west of the city of Shabran, is one of the most important conditions that increase the effectiveness of these measures. On a slope located 1500 meters southwest of the current research area, the results of our scientific research were not properly utilized and many of our warnings were not heeded, resulting in a landslide during construction, leading to serious damage to the road's structural elements (Fig. 1) and additional costs. This event once again confirms that landslides are the most common natural and man-made processes that pose a threat to the safe operation of infrastructure facilities, civil and industrial construction in mountainous and foothill areas (Shiraliyev et al., 2024)

Ductile Versus Brittle Tectonics in the Anatolian–Aegean–Balkan System

It is hypothesized that the present tectonic setting of the Anatolian, Aegean and Balkan regions has been deeply influenced by the different deformation styles of the inner and outer belts which constituted the Oligocene Tethyan system. Stressed by the Arabian indenter, this buoyant structure has undergone a westward escape and strong bending. The available evidence suggests that in the Plio–Pleistocene time frame, the inner metamorphic core mainly deformed without undergoing major fragmentations, whereas the orogenic belts which flanked that core (Pontides, Balkanides, Dinarides and Hellenides) behaved as mainly brittle structures, undergoing marked fractures and fragmentations. This view can plausibly explain the formation of the Eastern (Crete–Rhodes) and Western (Peloponnesus) Hellenic Arcs, the peculiar time-space features of the Cretan basins, the development of the Cyprus Arc, the North Aegean strike-slip fault system, the southward escapes of the Antalya and Peloponnesus wedges and the complex tectonic setting in the Balkan zone. These tectonic processes have mostly developed since the late Late Miocene, in response to the collision of the Tethyan belt with the Adriatic continental domain, which accelerated the southward bending of the Anatolian and Aegean sectors, at the expense of the Levantine and Ionian oceanic domains. The proposed interpretation may help us to understand the connection between the ongoing tectonic processes and the spatio-temporal distribution of major earthquakes, increasing the chances of estimating the long-term seismic hazard in the study area. In particular, it is suggested that seismic activity in the Serbo–Macedonian zone may be favored by the post-seismic relaxation that develops after seismic crises in the Epirus thrust front and inhibited/delayed by the activations of the North Anatolian fault system.

Палеотектонический анализ отложений нижнеапшеронской литофациальной пачки Астраханского Прикаспия

The paleotectonic analysis of the Apsheron deposits of the Astrakhan Caspian Sia is considered. The main at-tention is paid to the analysis of the deposits of the lower Apsheron lithofacies unit, which includes the study of the thickness of the deposits, the construction of maps of thicknesses and trend values, as well as the analysis of the wave pattern of seismic works carried out in the territory of the Astrakhan Caspian Sia. The results of the study showed that during the Lower Apsheron time, significant tectonic processes took place in the region, including the growth of salt domes and the formation of alluvial fans. These processes had a significant impact on sedimentation and the distribution of sediment thicknesses. The conclusions about the influence of salt dome tectonics on sedimentation, as well as the role of paleorelief in the formation of local thickness anomalies are presented as well. The results obtained are important for understanding the geological history of the region and assessing its oil and gas potential. The data presented in the article are based on the analysis of geological data, including seismic data, and the use of paleotectonic analysis methods. The article describes in detail the research methods and provides examples of specific results obtained during the work.

3D Surface Velocity Field Inferred from SAR Interferometry: Cerro Prieto Step-Over, Mexico, Case Study

The Cerro Prieto basin, a tectonically active pull-apart basin, hosts significant geothermal resources currently being exploited in the Cerro Prieto Geothermal Field (CPGF). Consequently, natural tectonic processes and anthropogenic activities contribute to three-dimensional surface displacements in this pull-apart basin. Here, we obtained the Cerro Prieto Step-Over 3D surface velocity field (3DSVF) by accomplishing a weighted least square algorithm inversion from geometrically quasi-orthogonal airborne UAVSAR and RADARSAT-2, Sentinel 1A satellite Synthetic Aperture-Radar (SAR) imagery collected from 2012 to 2016. The 3DSVF results show a vertical rate of 150 mm/yr and 40 mm/yr for the horizontal rate, where for the first time, the north component displacement is achieved by using only the Interferometric SAR time series in the CPGF. Data integration and validation between the 3DSVF and ground-based measurements such as continuous GPS time series and precise leveling data were achieved. Correlating the findings with recent geothermal energy production revealed a subsidence rate slowdown that aligns with the CPGF’s annual vapor production.

Mineralization processes in the Bainaimiao Cu-Au deposit in Inner Mongolia, China: Constraints from geology, geochronology, and mineralogy

The Central Asian Orogenic Belt underwent complex tectonic processes and is one of the most intensely accretionary areas globally. Porphyry copper deposits within the belt were likely subjected to deformation during tectonic processes. The Bainaimiao Cu-Au deposit is a typical example of a deformed porphyry deposit whose formation processes include a porphyry emplacement (Event I), a greenschist facies metamorphism (Event II), and a brittle deformation (Event III). Geochronology and trace element geochemistry of zircon, volatiles of magmatic apatite, along with the assemblages, textures, abundances, and compositions of phyllosilicates from these three events were investigated to unveil the physicochemical conditions under which the key geological events relevant to the deposit formation took place. LA-ICP-MS zircon U-Pb dating shows that the granodiorite porphyry in the northern and southern zones formed at 447.4 ± 1.6 to 445.8 ± 3.6 Ma and 436.1 ± 3.8 to 434.1 ± 3.3 Ma, respectively. The granodiorite porphyry in the northern zone has higher oxygen fugacity and Clmelt content but similar Smelt and Fmelt contents compared to the granodiorite porphyry in the southern zone. Microscopic and mineralogic observations point to Event I to be of high plagioclase (22–67 vol%) and quartz (6–40 vol%) content with a range of hydrothermal minerals related to potassic, phyllic, and propylitic alterations. Event II features high amphibole (38–83 vol%) or epidote-chlorite (up to 77 vol%) content with minerals precipitating along the schistosity planes. Event III is characterized by wide veins (3–80 cm) and the highest quartz (61–65 vol%) and calcite (12–19 vol%) content. Geothermometry results show the temperature of potassic and phyllic alterations of Event I to be ∼622 °C and ∼288 °C, respectively. Based on geothermometry and P-T pseudosections, the temperatures of metamorphism and metallic precipitation of Event II were ∼271–634 °C and 297–328 °C, respectively. Both mechanical and chemical mobilization of metallic elements results in Cu mineralization during Event II. The metallic precipitation temperatures of Event III spanned from 297 to 328 °C according to chlorite geothermometry. The ratios of Fe3+/Fetotal and Mg/(Mg + Fetotal) of biotite, chlorite Fe/(Fe + Mg), and white K-mica composition show the mineralizing fluid of Event III to be the most oxidized while that of Event II is the most reduced, F-rich and features the lowest water/rock ratio. This study suggests that deformation processes can increase the Cu mineralization grade of the deformed porphyry deposits through mobilization and re-precipitation of metallic elements.

Seismic evidence of an extremely thin crust along a 70 Ma slow-spreading crustal segment in the equatorial Atlantic Ocean

The oceanic crust at slow-spreading ridges is formed by a combination of magmatic and tectonic processes. Seismic tomographic studies, commonly used to determine crustal structures, indicate that mature slow-spreading crust has an average thickness of 6.1 ± 0.9 km, with a lower to upper crustal thickness ratio of 2.3. However, tomographic methods are based on high-frequency approximations and can only provide information about large-scale crustal structures. Using seismic full-waveform inversion applied to ocean bottom seismometer data, we report the presence of nearly uniform and extremely thin crust (4 ± 0.2 km) with a lower to upper crustal thickness ratio of 0.74 along an ∼100 km, 70 Ma crustal segment formed at the slow-spreading Mid-Atlantic Ridge in the equatorial Atlantic Ocean. This thin crust is underlain by a Moho transition zone that is 1 ± 0.5 km thick, resulting in a combined crustal and Moho transition zone thickness of 5 ± 0.6 km. The crustal thinning is primarily due to the thinning of the lower crust, suggesting that a significant part of the crust is formed by lava flows and dike intrusions. The presence of an extremely thin crust indicates a decrease in mantle temperature by at least 50 °C, suggesting a vast extent of the upper mantle thermal minimum in the equatorial Atlantic Ocean, and the absence of influence of the mantle from the Siera Leone mantle plume 70 m.y. ago.

Magnetotelluric evidence for the formation of the layered Sask Craton by flat slab subduction

Long-period magnetotelluric (MT) data were collected at 56 locations over the Sask Craton in 2021 and 2022. The data were combined with existing broadband data and inverted to produce a 3-D resistivity model of the Sask Craton and Trans-Hudson Orogen (THO). The model reveals a number of northeast striking electrically conductive crustal structures that extend into the mantle lithosphere. In the mantle lithosphere, these conductors coalesce into a single large low resistivity anomaly in the depth range 70–85 km termed the Northern Sask Craton (NSC) conductor. The resistivity of the NSC conductor is attributed to sulfides deposited along an interface between a flat slab that was accreted to the base of the pre-THO Sask Craton lithosphere during closure of the Manikewan Ocean. Kimberlites have erupted along the margin of the NSC conductor. The boundary of the conductor likely represents deep-seated faults and mantle terrane boundaries formed during flat slab subduction that allowed the ascent of kimberlite melts. The resistivity of the northeast-trending conductors can be interpreted as due to graphite and sulfides precipitated by past fluid or melt flow during ocean closure and orogensis. A number of these conductors are located beneath known mineral districts and trends and may represent source pathways for regional base and precious metal deposits. Other conductors may represent possible, previously unknown, regions hosting mineralization. Many of these conductors are associated with major regional faults and shear zones, which may be deep-seated features that helped to guide both kimberlites and mineralizing fluids. Of the prominent northeast-trending conductors west of the Sask Craton, one corresponds to the previously reported North American Central Plains (NACP) conductor. The new model shows that this conductor abruptly terminates at 54 °N and is not observed farther south in the model. This shows that the NACP is not as spatially continuous as previously suggested, suggesting that the tectonic processes that formed the THO were not as uniform along-strike as shown in existing tectonic models. The connection of one of the northeast-trending anomalies to the NSC conductor suggests that a previously unrecognized phase of east-dipping subduction may have occurred beneath the Sask Craton as the THO was formed.

Pulsed uplift of the South Tianshan since the Late Miocene indicated by the linear inversion on river longitudinal profiles

The early Cenozoic collision and subsequent continuous convergence between the Indian and Eurasian plates reactivated the Tianshan orogen in the Central Asia and caused multistage uplift of the mountain range. The modern Tianshan, with high mountain peaks of >7000 m, forms very prominent topography that profoundly affects the regional tectonics and climate. However, the late Cenozoic uplift process and topography growth of the South Tianshan remain controversial. River longitudinal profile inversion provides a distinctive way to reveal rock uplift history since the late Cenozoic. In this study, we presented linear inversion on river longitudinal profiles of four drainage basins originating from high mountains in the South Tianshan. The inversion results from two basins in the northern flank show fast and continuous increases in the uplift rates from about 0.1–0.2 mm/a to 0.6–1.0 mm/a since 4 Ma. While in the southern flank, the uplift rates of the two basins increased gradually from about 0.1 mm/a to 0.2 mm/a before 10 Ma and from 0.2 mm/a to 0.4 mm/a around 10 Ma and 6 Ma, respectively. Our results combined with recently published chronological data in this region indicate that the South Tianshan experienced a pulsed tectonic uplift process since the Late Miocene. Moreover, the pulsed tectonic uplift should lead to an elevated South Tianshan during 6–4 Ma, coinciding well with the ∼5.3 Ma extreme aridification in the Tarim Basin, thus supporting that the rain shadow effect caused by high topography of South Tianshan is a critical reason for aridification.