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Due to the scarcity of rock samples, the Hadean Era predating 4 billion years ago (Ga) poses challenges in understanding geological processes like subaerial weathering and plate tectonics that are critical for the evolution of life. The Jack Hills zircon from Western Australia, the primary Hadean samples available, offer valuable insights into magma sources and tectonic genesis through trace element signatures. However, a consensus on these signatures has not been reached. To address this, we developed a machine learning classifier capable of deciphering the geochemical fingerprints of zircon. This allowed us to identify the oldest detrital zircon originating from sedimentary-derived S-type granites. Our results indicate the presence of S-type granites as early as 4.24 Ga, persisting throughout the Hadean into the Archean. Examining global detrital zircon across Earths history reveals consistent supercontinent-like cycles from the present back to the Hadean. These findings suggest that a significant amount of Hadean continental crust was exposed, weathered into sediments, and incorporated into the magma sources of Jack Hills zircon. Only the early operation of both subaerial weathering and plate subduction can account for the prevalence of S-type granites we observe. Additionally, the periodic evolution of S-type granite proportions implies that subduction-driven tectonic cycles were active during the Hadean, at least around 4.2 Ga. The evidence thus points toward an early Earth resembling the modern Earth in terms of active tectonics and habitable surface conditions. This suggests the potential for life to originate in environments like warm ponds rather than extreme hydrothermal settings.

An outstanding question in the geological evolution of the Chilean Andes is the cause of the westward shift and relocation of magmatism from the High Andes (HA) to the Coastal Cordillera (CC) during the Late Triassic, Pre–Andean stage. The spatiotemporal distribution of Permian–Triassic–Jurassic igneous rocks in northern‐central Chile (20°S–32°S) reveals a significant westward magmatic shift of ∼120 km during the Norian time. Despite diverse proposed models, the precise geodynamic mechanism behind this shift remains unclear. To address this, we used 2D numerical modeling to investigate two contrasting scenarios: (a) subduction rollback and (b) subduction transference/jump and reinitiation by terrane accretion. Our modeling results strongly support Scenario B, where mantle density and the size of the oceanic plateau are crucial for triggering subduction jump and reinitiation. This model aligns with geological and geophysical evidence and offers new insights into unraveling the Pre– and Early–Andean evolution. Plain Language Summary: After decades of research, the geodynamic mechanism behind the Late Triassic westward relocation of magmatism from HA to CC in northern‐central Chile remains unresolved. This study employs 2D numerical experiments to investigate two competing scenarios: subduction rollback and subduction transference/jump and reinitiation by terrane accretion. Subduction models are tailored to the Andean margin, evaluating slab geometry and magmatic arc position to best fit geological observations. Key subduction parameters such as subducting plate velocity and slab age are constrained by paleoreconstructions for the study region and period. Factors like mantle density and the size of the oceanic plateau are critical triggers for subduction jump and reinitiation. Modeling results favor the terrane accretion scenario, revealing a ∼120 km westward magmatic shift for a 300 km‐wide oceanic plateau with a depleted mantle. This aligns with geological and geophysical observations, including Late Triassic subduction initiation with a new magmatic arc in CC and a lower mantle slab gap beneath the southwestern Pangea margin due to possibly catastrophic slab loss in the Middle–Late Permian. This study shed light on previously overlooked processes like oceanic plateau accretion/obstruction, slab detachment and eduction, and subduction jump and reinitiation, advancing our understanding of Triassic Pre–Andean evolution. Key Points: 2D numerical models investigate the evolution of the Pre− and Early−Andean margin through two contrasting geodynamic scenariosModeling supports subduction transference/jump and reinitiation over subduction rollback, unraveling the Pre– and Early–Andean evolutionTerrane accretion model supports a Late Triassic westward shift of the Andean magmatism, aligning with geological and geophysical evidence [ABSTRACT FROM AUTHOR]

Subduction of water masses serves as a critical linkage between the surface and subsurface ocean, playing a crucial role in redistributing heat, carbon, and nutrients in the ocean. This process significantly influences global climate and marine ecosystem dynamics. Analyzing five ocean reanalysis data sets, we reveal a distinctive see‐saw pattern in anomalous subduction rates between western and eastern Subtropical Mode Water (STMW) formation areas. This pattern is predominantly driven by variations in latent heat flux, which modulates the late‐winter mixed layer depth. We demonstrate that late‐winter Aleutian Low (AL) activity induces these anti‐phase variations through its impact on latent heat flux. Notably, the Pacific Decadal Oscillation (PDO) significantly influences this subduction see‐saw pattern. During PDO warm phases, AL southward shift intensifies the anti‐correlated variations. Conversely, during cold phases, AL northward shift weakens its influence on ESTMW area, resulting in a less stable anti‐phase relationship. Plain Language Summary: Subduction is the process where water from the surface sinks into deeper layers of the ocean. This process is crucial because it moves important elements like heat, carbon, and nutrients from the surface to the depths below. Understanding how subduction changes is essential for elucidating climate change and biogeochemical cycles. Subduction rates in the North Pacific reveal a pattern like see‐saw: when the subduction rate increases in western Subtropical Mode Water (STMW) formation area, it often decreases in eastern STMW formation area. This see‐saw pattern is mainly caused by latent heat flux, through modulation of the late‐winter mixed layer depth. The late‐winter Aleutian Low plays an important role in this process. When it shifts in position or changes intensity, it affects latent heat flux, creating this west–east see‐saw pattern in subduction. Furthermore, this subduction see‐saw pattern is stronger during the warm phase of the Pacific Decadal Oscillation compared to the cold phase. Key Points: North Pacific shows a subduction see‐saw pattern between western and eastern STMW areas, driven by mixed layer depth variationsLate‐winter Aleutian Low activity induces anti‐phase subduction variations through its impact on latent heat fluxPacific Decadal Oscillation modulates the strength of the subduction see‐saw pattern, stronger in warm phases, weaker in cold phases [ABSTRACT FROM AUTHOR]

The paper presents new geological, geochronological, geochemical and Nd-Sr isotopic data on the Meso- Neoproterozoic dolerites of the Siberian Craton. New U-Pb baddeleyite and apatite ages of a E-W-trending dyke and two sills from southeastern Siberia are 982 ± 11, 977 ± 7, 970 ± 31 and 972 ± 60 Ma, respectively, extending the area of distribution of the event by more than 100 km to the north. The Sette-Daban intrusions are subalkalic mostly low-Ti dolerites, although high-Ti dolerites have been locally documented as well. Trace element abundances in dolerites vary from typical to E-MORB to OIB with arc-like signatures represented by high Th/Yb and low TiO2/Yb ratios. All dolerite samples display moderately positive εNd(t) values varying from +3.3 to +7.7 and indicating the magmas were derived from a depleted mantle source. E-MORB and OIB intrusions are attributed to the different degree of interaction of magma between the depleted asthenospheric mantle and regions within the sub-continental lithospheric mantle (SCLM) that were metasomatically enriched during earlier subduction events. Available data on Sette-Daban event distribution, composition and duration satisfy the characteristics of a typical Large Igneous Province (LIP). Similar age 1000–950 Ma mafic magmatism is also recognized in the Baltic and Amazonian cratons and can be potentially correlated with the Sette-Daban event. [ABSTRACT FROM AUTHOR]

Subduction of the Cocos and Nazca oceanic plates beneath the Caribbean plate drives the upward movement of deep fluids enriched in carbon, nitrogen, sulfur, and iron along the Central American Volcanic Arc (CAVA). These compounds fuel diverse subsurface microbial communities that in turn alter the distribution, redox state, and isotopic composition of these compounds. Microbial community structure and functions vary according to deep fluid delivery across the arc, but less is known about how microbial communities differ along the axis of a convergent margin as geological features (e.g., extent of volcanism and subduction geometry) shift. Here, we investigate changes in bacterial 16S rRNA gene amplicons and geochemical analysis of deeply-sourced seeps along the southern CAVA, where subduction of the Cocos Ridge alters the geological setting. We find shifts in community composition along the convergent margin, with communities in similar geological settings clustering together independently of the proximity of sample sites. Microbial community composition correlates with geological variables such as host rock type, maturity of hydrothermal fluid and slab depth along different segments of the CAVA. This reveals tight coupling between deep Earth processes and subsurface microbial activity, controlling community distribution, structure and composition along a convergent margin. [ABSTRACT FROM AUTHOR]

Largescale volcanic eruptions and earthquakes are occurring frequently in the Philippines, and research has shown that slab metamorphism and diversity alter the impacts of subducted oceanic plates by changing water‒carbon productivity and interplate stability. Within the framework of the thermal evolution history of subducting slabs, the relationships between subduction zone seismicity characterized by both regular megathrust earthquakes and slow slip events of various magnitudes and long-term slab dehydration–decarbonation evolution in the Philippines remain poorly understood. Here, we constructed a comprehensive thermal model incorporating 3-D slab geometric data for the incoming plate and a 3-D subduction velocity field based on the MORVEL plate motion dataset for the Philippine subduction zone with high spatial and temporal resolutions. Our findings reveal that subduction seismicity and arc volcanism are prominent in belt-shaped regions with high thermal gradients (> 5 °C/km) and large-scale slab dehydration (> 0.05 wt%/km). Dehydration of serpentinite in ultramafic rocks in the subducting slab and decarbonation of carbonate minerals preferentially contribute to the generation and transport of fluids and carbonate melts, thus facilitating seismicity and carbon-rich magmatism. Our results suggest that slab geometry diversity-induced juxtaposed slab dehydration-decarbonation processes play a vital role in the generation of megathrust earthquakes below the forearc. [ABSTRACT FROM AUTHOR]

ABSTRACT Comprehending pre‐suture geological setting and post‐suture intricate tectono‐thermal chronicle in a crustal‐scale orogeny and discerning the temporal connections among different tectonic domains within an orogen yields valuable insights into worldwide tectonic phenomena leading to the reconstruction of paleogeographic configurations of fragmented crustal components within erstwhile supercontinents. Since the tectonic evolution of the Indian subcontinent during the Proterozoic remains a topic of discussion due to multiple controversial views, the Central Indian Tectonic Zone (CITZ) offers a great archive for the protracted geological history of subduction, collision, and suturing of northern Indian cratonic blocks (NIC; composed of Bundelkhand and Aravalli cratons) and southern Indian cratonic blocks (SIC; composed of Bastar, Singhbhum, and Dharwar cratons). Events belonging to two Supercontinents namely, Columbia (ca. 2100 to 1800 Ma) and Rodinia (ca. 1200 to 900 Ma) are embedded within the geological history of CITZ, as it records multiple events that occurred between the Paleoproterozoic and Neoproterozoic. In this backdrop, the present contribution attempts (i) the deconvolution of pre‐suture (pre‐CITZ formation) plate margin basin depositional history including tracking of detrital provenance, and (ii) a review of different stages of collision and suturing as the plate margin evolved in the form of an orogen subsequent to the closure of the basin. A back‐arc basin setup in a subduction margin is recommended for the Mahakoshal Basin which witnessed several tectonic pulses resulting in the formation of alluvial fans/fan deltas along the basin shoreline. It is suggested that the basin was open, at places, even after ca. 1700 Ma, and received sediments. [ABSTRACT FROM AUTHOR]

This study uses a 2D high-resolution thermo-mechanical coupled model to investigate the dynamic processes of deep plate hydration, dehydration, and subsequent magmatic activity in ocean-continent subduction zones. We reveal the pathways and temporal evolution of water transport to the deep mantle during the subduction process. Plate dehydration plays a critical role in triggering partial melting of the deep mantle and related magmatic activity. Our study shows significant differences in the volumes of melt produced at different depths, with dehydration reactions in deeper regions being weaker compared to shallower ones. It takes a longer time to reach the suitable P-T conditions for hydrous melting in the deep mantle. The results highlight the geophysical significance of water transport in deep subduction zones and its role in magmatic processes, particularly in the formation of magma chambers beneath continental plates. [ABSTRACT FROM AUTHOR]

The Qinling Orogenic Belt (QOB) is a multi‐stage orogenic belt recording subduction and collision processes. The ductile shearing deformation with different properties and ages is developed on the boundary of the different litho‐tectonic units, which can be used to decipher the tectonic evolution of the QOB. Previous studies mainly concentrated on the pre‐Late Mesozoic shearing deformation, while the Late Mesozoic shearing deformation received less attention. It restricts the understanding of the Late Mesozoic tectonic evolution of the QOB. Hence, we conducted detailed field structural analysis and laboratory analysis of the Shagou shear zone (SGSZ) in the middle part of the Shangdan suture zone (SDSZ). The SGSZ, developed in the southern margin of the Baliping pluton, is an S–SSW‐dipping sinistral strike‐slip ductile shear zone with a top‐to‐the‐ESE shear sense. The mylonite protoliths are voluminous Late Triassic granites (200–215 Ma) and a small amount of Neoproterozoic granites (759 Ma) and Early Cretaceous granites (145 Ma). Microstructures and geothermobarometer results suggest that the ductile shearing deformation occurred under high greenschist–low amphibolite‐facies conditions (400–650°C) at middle crustal depths (13–21 km). Zircon U–Pb and amphibole‐biotite 40Ar/39Ar dating results constrain the timing of shearing deformation to 135–145 Ma and the rapid exhumation of the SGSZ to 115–135 Ma. Combining with the regional data, we consider that the sinistral strike‐slip shearing deformation in the SGSZ controls and accommodates the south‐eastward extrusion of the East SQB under the intracontinental compression. Subsequently, the intracontinental extension led to the rapid exhumation of the SGSZ. [ABSTRACT FROM AUTHOR]

The study presents analysis of 1 year 15 min cycle radon data using artificial neural network (ANN) in an attempt to estimate earthquake prediction time near Indo-Burman subduction line. The region was found to be seismically active and radon anomalies respond well to it, when majority of the radon anomalies peaks and selected earthquakes correlated. The observation also shows that application of non-linear technique ANN to a non-linear data like radon seems a promising approach in predicting geophysical phenomena at one of the most seismically active region of the world. [ABSTRACT FROM AUTHOR]

Crustal growth is closely associated with the oceanic subduction process, although the precise mechanism involved remains poorly constrained. Northeast (NE) China is an important component of the largest accretive orogenic belt worldwide – Central Asian orogenic belt. Its accretionary process was dominated by the Paleo-Asian and Paleo-Pacific Oceans; thus, NE China can provide a promising insight to explore this complex mechanism. We report new geochronological, geochemical and Hf isotopic compositions of the igneous rocks found in the Central Jilin Province, NE China. The geochronological results reveal that these igneous rocks were formed during 174.7 − 167.7 Ma (i.e. Early−Middle Jurassic). The quartz diorite and monzogranites from the northeastern margin of the North China Craton have high Sr (314 − 757 ppm) content, (La/Yb)N (7.11 − 29.9) and Sr/Y (41.50 − 157) ratios, low Y (2.03 − 12.97 ppm) and Yb (0.30 − 1.34 ppm) contents, exhibiting adakitic features. Coupling with their significant negative εHf(t) values (−32.51 to − 5.45), we propose that these igneous rocks were originated from the partial melting of an ancient thickened lower crust. In contrary, the syenogranite, granite porphyry, and porphyritic monzogranite from the Zhangguangcai and Jiamusi blocks are characterized by high K calc-alkaline, low MgO (0.03 − 0.88 wt.%), Zr + Nb + Ce + Y (141 − 462 ppm) contents and Sr/Y (0.93 − 17.40) ratios, indicating an affinity of I−type granite. In view of their positive εHf(t) values (5.41 to 9.47), we suggest that they were originated from the partial melting of a juvenile lower mafic crust. Despite they have different magma sources, all the Jurassic igneous rocks exhibit typical geochemical signatures associated with subduction, such as enriched in large ion lithophile elements and depleted in high field strength elements. Considering the spatial-temporal distribution of coeval igneous rocks within the region, we propose that the Early Jurassic is the early subduction of the Paleo-Pacific Ocean. The Jurassic igneous rocks can be divided into two categories, one with high Sr/Y ratios and negative Hf isotope, and the others with low Sr/Y ratios and positive Hf isotope, which may indicate that crustal architecture in subduction zone has a significant effect on continental crustal growth and reworking in NE China. [ABSTRACT FROM AUTHOR]

The Pannonian Basin, situated in Central Europe, is surrounded by the Alpine, Carpathian and Dinaric orogens. To understand its tectonic characteristics and evolution, we determine a shear wave velocity model of its crust, mantle lithosphere and asthenosphere consistently by jointly inverting Rayleigh wave phase velocities measured consistently from earthquake (EQ) and ambient noise (AN) data. For the AN data, continuous waveform data were collected from 1254 stations, covering an area within 9° from the centre of the Pannonian Basin during the time period from 2006 to 2018. This data set enabled the extraction of over 164 464 interstation Rayleigh phase-velocity curves, after applying a strict quality control workflow. For the EQ data set more than 2000 seismic events and about 1350 seismic stations were used in the broader Central and Eastern European region between the time-span of 1990 to 2015, allowing us to extract 139 987 quality controlled Rayleigh wave phase-velocity curve. Using the combined data set, a small period- and distance-dependent bias between ambient noise and earthquake measurements, mostly below 1 per cent but becoming larger towards longer periods has been found. After applying a period and distance dependent correction, we generated phase-velocity maps, spanning periods from 5 to 250 s. 33 981 local dispersion curves were extracted and a new approach is introduced to link their period-dependent roughness to the standard deviation. Using a non-linear stochastic particle swarm optimization, a consistent 3-D shear wave velocity model (PanREA2023) encompassing the crust and upper mantle down to 300 km depth was obtained with a lateral resolution reaching about 50 km at the centre of the study area for shorter periods. The crust beneath the Carpathian orogen exhibits a distinct low-velocity anomaly extending down to the Moho. It is referred to as Peri-Carpathian anomaly. Similar anomalies were observed in the Northern Apennines, while the Eastern Alps and Dinarides, as collisional orogens, generally demonstrate higher velocities in the upper crust. High crustal shear wave velocities are also evident in the Bohemian Massif and the East European Craton. The brittle upper crust of the Pannonian Basin is characterized by alternating NE–SW trending high- and low-velocity anomalies: the western and central Pannonian low-velocity anomalies and the Transdanubian and Apuseni high-velocity anomalies related to Miocene sedimentary basins and intervening intervening interbasinal highs exposing Pre-Cenozoic rocks including crystalline basement rocks. Beneath the Southeastern Carpathians, a NE-dipping slab was identified, extending to depths of at least 200 km, while a slab gap is evident beneath the Western Carpathians. A short south-dipping Eurasian slab was imaged beneath the Eastern Alps down to only 150–200 km depth. The Adriatic lithosphere is subducting near-vertically dipping beneath the Northern Apennines, and a slab gap was observed beneath the Central Apennines. In the Northern Dinarides, a short slab was evident, reaching depths of around 150 km. The Southern Dinarides featured a thinned but possibly incompletely detached slab. [ABSTRACT FROM AUTHOR]

We present a new 3-D radially anisotropic seismic velocity model EARA2024 of the crust and mantle beneath East Asia and the northwestern Pacific using adjoint full-waveform inversion tomography. We construct the EARA2024 model by iteratively minimizing the waveform similarity misfit between the synthetic and observed waveforms from 142 earthquakes recorded by about 2000 broad-band stations in East Asia. Compared to previous studies, this new model renders significantly improved images of the subducted oceanic plate in the upper mantle, mantle transition zone, and uppermost lower mantle along the Kuril, Japan, Izu-Bonin and Ryukyu Trenches. Complex slab deformation and break-offs are observed at different depths. Moreover, our model provides new insights into the origins of intraplate volcanoes in East Asia, including the Changbaishan, Datong-Fengzhen, Tengchong and Hainan volcanic fields. [ABSTRACT FROM AUTHOR]

Subduction-zone fluid–rock interactions have a direct impact onto elemental and isotopic homogeneity of progressively buried and exhumed crustal lithologies by providing an interface for local mass-transfer and enhancing metamorphic reactions. In order to assess the scales of fluid mobility, chemical and isotopic inheritance, as well as resulting degrees of isotopic heterogeneity in the exhumed high-pressure lithologies, we performed the detailed mineralogical, in-situ trace-element and Rb–Sr isotope studies, combined with P–T–X thermodynamic modelling of representative eclogites from the Alag Khadny accretionary complex (SW Mongolia). The eclogites (garnet + omphacite + phengite + rutile + quartz + retrograde amphibole and clinozoisite) display records of subduction-related burial to 540–625 °C and 1.7–2.1 GPa, with the enclosed phengite supposed to be in equilibrium at prograde-to-peak conditions. Trace-element signatures, including Cs/Rb (0.03–0.08) and Ba/Rb (7.1–13.8) ratios of phengite, are consistent with moderately to strongly altered protoliths of eclogites, which is supported by elevated δ18O values and in-situ Rb–Sr constraints on the initial (87Sr/86Sr)I ratios of phengite within 0.70549–0.70957. Partial backward rehydration (~ 0.5–1.0 wt% of H2O added) during decompression from 1.6 to 1.2 GPa produced amphibole- and clinozoisite-bearing assemblages, did not significantly affect LILE systematics and variable 87Rb/86Sr ratios of phengite. Limited Rb and Ba loss from phengite during recrystallization is suspected in the evidently deformed eclogites based on the LILE mineral–fluid and phengite–amphibole partitioning data. No exclusive evidence is found in amphibole for LILE-rich metasedimentary fluid with high (87Sr/86Sr)I released into eclogites. Instead, unradiogenic 87Sr/86Sr (0.70279–0.70301) of clinozoisite highlights metasomatic addition from the underlying mafic crust or dehydrated peridotitic mantle. Variable deformation-enhanced fluid-rock interaction during early exhumation was recorded by in-situ phengite Rb-Sr geochronology at 568 ± 9 Ma, which is considered a direct fluid flow snapshot and place a new minimum age constraint for the peak subduction burial. We argue that, except cases of apparent metasomatic origin of phengite, its (87Sr/86Sr)I ratios may be a sensitive tracer for the eclogite precursor alteration due to limited Sr mobility. Sample-scale Rb-Sr isotopic heterogeneities may be preserved in the orogenic eclogites due to multi-stage retrograde hydration and should be taken into account while interpreting the bulk-rock Sr isotope data. [ABSTRACT FROM AUTHOR]

US Geological Survey (USGS) National Seismic Hazard Models (NSHMs) are used extensively for seismic design regulations in the United States and earthquake scenario development, as well as risk assessment and mitigation for both buildings and infrastructure. This 2023 update of the long-term, time-independent Alaska NSHM includes substantial changes to both the earthquake rupture forecast (ERF) and ground motion models (GMMs). The ERF includes numerous additions to the finite-fault model, considers two deformation models, and introduces updated declustering and smoothing algorithms in the gridded background seismicity model. For the Alaska–Aleutian subduction zone, megathrust earthquakes occur on an updated structural and segmentation model, and the moment magnitude (M) 8+ rupture and rate model include a logic tree branch that considers slip rates derived from geodetic models of interface coupling. The megathrust model considers multiple models of down-dip width, and magnitudes are computed using newly developed scaling relations. For subduction intraslab events and subduction interface events with M < 7, the 2023 update uses a smoothed seismicity model with rupture depths derived from Slab2. The 2023 model updates GMMs in all tectonic settings using the recently published Next Generation Attenuation Subduction (NGA-Sub) GMMs for subduction interface and intraslab events, and the NGA-West2 GMMs for active crustal settings. Collectively, additions and updates to the Alaska NSHM result in hazard increases across most of south-central Alaska relative to the previous model, published in 2007. These changes are primarily due to the adoption of updated rate models for the large-magnitude interface events and the NGA-Sub GMMs that have much higher aleatory variability (sigma), consistent with global observations, and that include models of epistemic uncertainty. [ABSTRACT FROM AUTHOR]

The magmatic complex along the Marsa Alam-Idfu transect, Central-Eastern Desert of Egypt, represents the northern segment of the Arabian–Nubian Shield (ANS), which developed within the framework of the East African Orogen. The basement rocks of the Arabian-Nubian Shield have been developed through three distinct phases of magmatic activity: the island-arc, the syn-orogenic, and the post-orogenic phases. Transitioning of the magmatic phases from the syn-orogenic to the post-orogenic, identifies changing the tectonic regime from a compressional to an extensional setting. The scarcity of comprehensive regional geochronological data that rely on precise isochron methods, such as the zircon U-Pb technique, could limit the comprehensive understanding of this region's geological and tectonic history. That would raise a number of uncertainties ranging from the timing of the different magmatic activities and timing of changes in the tectonic regime to the existence of the pre-Pan-African crust in the CED. Our study provides new insights into the aforementioned uncertainties through zircon U-Pb dating of different rock units along the Marsa Alam-Idfu transect, CED, Egypt. The resulting ages ranged from 729 ± 3 Ma to 570 ± 2 Ma, constraining the temporal evolution of the ANS in the studied region into (1) the island-arc phase, represented by a metamorphic sample with an age of 729 ± 3 Ma. (2) the syn-orogenic phase, represented by calc-alkaline and alkaline granitic samples with ages ranging from 699 ± 4 Ma to 646 ± 2 Ma. These two phases indicate initiation of the compressional subduction regime in the CED since 729 ± 3 Ma and being dominated till 646 ± 2 Ma. (3) the post-orogenic phase, represented by metavolcanics, volcanic rocks, and alkaline plutonic samples with ages ranging from 623 ± 3 Ma to 570 ± 2 Ma. This phase suggests dominance of the compressional-to-extensional tectonic transition setting from 623 ± 3 Ma to 600 ± 1 Ma along with the Dokhan volcanism and activation of post-collision tensional regime activated at 582 ± 3 Ma. Our findings discourage the proposed dominance of the island-arc and syn-orogenic phases in the CED and the classical restriction of older magmatic activity to calc-alkaline granitic rocks and younger magmatic activity to alkaline granitic rocks. Additionally, we identified evidence of local magmatic sources by dating five grains with Mesoproterozoic (pre-Arabian–Nubian Shield) xenocrysts with ages ranging from 1549 ± 4 to 1095 ± 25 Ma. [ABSTRACT FROM AUTHOR]

We report a new model of radially anisotropic crustal and upper mantle structure of the western United States (WUS324) obtained from full waveform inversion of earthquake data. We ran three multiscale inversion stages beyond model WUS256 (Rodgers et al., 2022, https://doi.org/10.1029/2022jb024549) allowing them to approach convergence to fit a larger data set to a shorter minimum period of 16 s. WUS324 is based on 324 total iterations from its starting model, significantly more (16 times) than previous studies. Waveform misfit reductions are 66%–70% for both the inversion data and an independent validation data set providing confidence in the predictive power of the model. WUS324 provides much better fits and reveals shear wavespeed, vS, structure of this large region with more detail than previous waveform tomography models. We show representative images demonstrating the resolution of diverse seismic structure across this highly heterogeneous region including oceanic lithosphere, subducting slabs and continental magmatism. Plain Language Summary: Seismic tomography allows seismologists to infer properties of the inaccessible solid Earth through interpretations of seismic waves measured at the surface. Full waveform inversion tomography uses three‐dimensional (3D) wave propagation simulations to image subsurface structure as well as improve physical models for numerical modeling of seismograms. This study used powerful high‐performance computers to run many simulations of a large set of earthquake waveforms sampling the western United States to create a new model of seismic wavespeeds. The model spans the volume from the surface through the crust to the upper mantle from the Pacific Ocean to the Great Plains and from Mexico to Canada. By running many more inversion iterations and fitting shorter periods and wavelengths this study resulted in better waveform fits and imaged more detail compared to previous waveform tomography studies. The new model can be used for better understanding of the thermal and compositional state of the region or to improve simulations of new events, say to characterize ground motions or sources. Key Points: A new seismic model of the western US (WUS324) is obtained from full waveform inversion where stages are iterated to approach convergenceThe model is based on significantly more multiscaleiterations and fits waveforms with periods 16–100 s much better than previous modelsWUS324 images diverse seismic heterogeneity across a large region including subducting slabs and continental magmatism [ABSTRACT FROM AUTHOR]

We investigate the relationship between the seismogenic behavior of global megathrusts and various subduction parameters. We performed a parametric approach by implementing three decision tree‐based Machine Learning (ML) algorithms to predict the b‐value of the frequency‐magnitude relationship of seismicity as a non‐linear combination of subduction variables (subducting plate age and roughness, slab dip, convergence speed and azimuth, distance to closest ridge and plate boundary). Using the Shapley Additive exPlanations (SHAP) to interpret the ML results, we observe that plate age and subduction dip are the most influential variables. The results suggest that older, shallow‐dipping plates contribute to low b‐values, indicating higher megathrust stress. This pattern is attributed to the higher rigidity of older plates, increasing flexural strength, and generating a shallow penetration angle, increasing the frictional interplate area and intensifying the megathrust stress. These findings offer new insights into the non‐linear complexity of seismic behavior at global scale. Plain Language Summary: We carried out a study to investigate how certain characteristics of subduction zones, where one tectonic plate slides under another, influence the earthquakes behavior. Using different machine learning algorithms we examined how different variables in these zones affect the relative amount of small versus large earthquakes, parameterized by the slope of a log‐normal relationship between frequency and magnitude of events, known as the b–value. Our analysis showed that the age of the subducting plate and the angle at which it dips under another plate are the most influential factors in earthquake behavior. In particular, we found that older plates with shallow subduction angles are associated with higher stress at the subduction interface, which in turn, increases the probability of large earthquakes, decreasing the b‐value. This is because older, colder plates are more rigid than young and hot plates, which increases their resistance to bending, augmenting the contact area between the plates and the friction between them. These findings shed light on the complex dynamics of seismic activity on a global scale and provide valuable information for understanding the earthquake behavior worldwide. Key Points: The non‐linear relationship between subduction parameters and seismogenic behavior, as represented by the b‐value, is exhibitedPlate age and subduction angle are shown as the most impactful parameters in megathrust stress worldwideOlder subducting plates with lower subduction angles are associated with lower b‐values, implying higher megathrust stress, and viceversa [ABSTRACT FROM AUTHOR]

Multistage plate subduction plays a crucial role in magmatism; however, the mechanisms by which deep geodynamic processes govern volcanism in the Alaska subduction zone remain controversial. Using numerous travel-time data from several seismic arrays, we constructed high-resolution tomographic models to investigate the velocity structure of the Pacific Plate and Yakutat slab. Our tomographic results revealed high-velocity anomalies in the Pacific Plate and Yakutat slab, while the low-velocity areas within the Pacific Plate were identified as slab tears. We suggest that the Pacific Plate transitioned from oblique subduction along the Aleutian volcano chain to lower-angle subduction beneath the Pacific-Yakutat Plate interaction zone, forming two slab tears that enhance hot asthenosphere materials upwelling. The partial melting of the mantle wedge induced by Pacific slab dehydration and the concurrent upwelling of mantle materials jointly drove volcanism in the transition zone. Conversely, the flat subduction of the Yakutat slab into the mantle wedge overlying the Pacific slab effectively hindered the upwelling of hot hybrid materials, cooling the Pacific mantle wedge. These results offer a new perspective on the influence of slab dynamics on volcanic and magmatic processes in the region and represent an advancement in our understanding compared to previous studies, which did not resolve the tears within the slab or their geodynamic implications at this level of detail. [ABSTRACT FROM AUTHOR]

Ophiolites, mostly formed via subduction initiation at proto-forearcs, exhibit a unique variation of mantle-derived magmatism from MORB-like to low-Ti tholeiitic and bainitic-like affinities. Such variation was suggested to form chromite deposits spanning high-Al to high-Cr types. Nevertheless, the origin of diverse magmatism during subduction initiation and their linkages to different chromite deposits has long been enigmatic. Here we show elemental and Os isotopic compositions of different chromitites from the Zambales ophiolite, Philippines. Combined with data from ophiolites worldwide, high-Al and high-Cr chromitites are revealed to result from low-Ti tholeiitic and boninitic-like magmatism, respectively. Proto-forearc mantle had few chromitites generated during MORB-like magmatism, but afterwards, it was modified first by slab fluids and later by continuous asthenospheric upwelling in the context of slab densification and rollback. The latter modification elevated the geothermal gradient and replenished fertile components in the proto-forearc mantle progressively, inducing increasingly higher degrees of mantle melting and Cr-richer magmatism and chromitites. Varied rates of slab rollback are the fundamental driving force for the evolution of infant subduction zones. Relevant non-uniform motion induces thermo-chemical variations in the underlying mantle, generating diverse magmatism and chromite ores. [ABSTRACT FROM AUTHOR]

The magmatic and metamorphic evolutions of the Muslim Bagh Ophiolite (MBO) can help understand the relationship among supra-subduction ophiolite, subduction initiation, and the spreading centre in the forearc. Here, we investigated the whole-rock chemistry, mineral composition, P–T conditions, and K–Ar ages of the MBO and its associated units. The whole-rock and magmatic clinopyroxene compositions indicate that the MBO amphibolites and tholeiitic basalts of the underlying Bagh Complex originated in a supra-subduction setting and mid-ocean ridges, respectively. Late Cretaceous oceanic island basalts found in the Bagh Complex and the Bibai Formation occurred in oceans and near the passive continental margin of western India, respectively. Metamorphic Mg-hornblendes in the MBO amphibolites record low-P/T type upper amphibolite-facies metamorphism (2.4–2.9 kbar, 612–690 °C), indicating a > 50 ºC/km geothermal gradient. The K–Ar hornblende and plagioclase ages suggest contemporaneous low-P/T type metamorphism at ca. 78–71 Ma in the MBO formed in a forearc and tholeiitic ridge-related magmatism of ca. 78–77 Ma in the Bagh Complex, indicating a spreading ridge was active during the subduction. Our results, combined with plate kinematic reconstructions of the Neotethys Ocean in the previous studies, suggest that the abnormally high geothermal gradient in the MBO could be due to orthogonal ridge subduction near the triple junction after the ca. 80 Ma subduction initiation in the forearc. It is also likely that the geothermal gradient in the MBO dropped from >50 °C/km at 78–71 Ma, through 35–45 °C/km, to <25 °C/km at approximately 65 Ma due to gradual steepening of the subducting slab, followed by the obduction of the MBO during the Paleocene to Eocene period. [ABSTRACT FROM AUTHOR]

Serpentinites associated with metamafic and metaplagiogranitic rocks occur sporadically within metasedimentary schists in the Yuli belt. Such metaigneous rocks are considered to represent ophiolitic protoliths and some contain high-pressure (HP) metamorphic minerals or assemblages. However, the origin and metamorphism of these serpentinites have long been a mystery. This study systematically investigates the four major serpentinite-bearing exposures at the Fengtien, Wanjung, Tsunkuanshan, and Chinshuichi. The results reveal that the serpentinites are of two different protoliths on the basis of relict chromian spinel composition. Cr-spinel compositions of the Fengtien and Tsunkuanshan samples are characterised by moderate Cr# [Cr/(Cr + Al)] (0.45–0.57), relatively high Mg# [Mg/(Mg+Fe2+)] (0.59–0.79), but low Fe3+# [Fe3+/(Fe3++Cr+Al)] (0.02–0.06), reflecting an abyssal peridotite type protolith. By contrast, Cr-spinel compositions of the Wanjung and Chinshuichi samples show high Cr# (up to 0.74) and Fe3+# (0.03–0.08), but low Mg# (<0.6), indicating a forearc mantle peridotite origin. Peak metamorphic conditions of the serpentinites are represented by the assemblage of antigorite + magnetite + chlorite + olivine + diopside, which is estimated as up to 550°C but the pressure cannot be constrained quantitatively. Based on field relations, it is inferred that the serpentinites, associated HP metaigneous rocks, and garnet-bearing metasedimentary schists were metamorphosed isofacially. Despite two origins, the peridotitic protoliths were all subjected to hydration and subduction processes. We suggest that precursors of the serpentinites, metaigneous rocks, and metasedimentary schists were juxtaposed and metamorphosed at intermediate to great depths (~35–55 km) of a subduction zone. Therefore, the Yuli belt serpentinites and associated rocks likely represent exhumed materials from a palaeo-subduction interface. [ABSTRACT FROM AUTHOR]

We apply the stable potassium isotope system (41K/39K) to well-studied Mariana arc lavas, in which inter-island geochemical variability has been interpreted to reflect near constant addition of an aqueous fluid flux, that dominantly samples the subducting mafic oceanic crust and variable amounts of sediment melt addition to the sub-arc mantle wedge. The nature of the sediment component in the Mariana arc lavas remains enigmatic, with a mixture of melts from all subducted sediment lithologies and the altered-mafic oceanic crust seeming likely, but some interpretations point towards a component from melting of the volcaniclastic sediment alone. We present K isotopic data on a set of well-characterised Mariana arc lavas and sediment samples (from Ocean Drilling Program site 801). Our data show that the majority of Mariana arc lavas are isotopically heavy (ẟ 41K), by up to ∼0.2 ‰, relative to mid-ocean ridge basalt (MORB), but most of the subducting sediment samples are slightly isotopically lighter than, or indistinguishable from MORB. The volumetrically important volcaniclastic sedimentary unit however is significantly isotopically lighter than MORB, by ∼0.8 ‰, which reflects marine diagenetic processes. Thus, volcaniclastic material significantly influences the bulk sediment K isotope composition. We show that ẟ 41K compositions of the Mariana arc lavas can be reproduced by the addition of an aqueous fluid with isotopically heavy K (relative to MORB) and an additional fraction of an incompatible-element-enriched isotopically light melt component. Modelling of K isotopes together with K/La and radiogenic Nd indicate that the melt component is best explained by a mix of melts from bulk sediment and altered-mafic oceanic crust. Our results show that distinctive K isotopic variations in subduction zone inputs and K isotopic fractionation during dehydration reactions makes K a useful tracer of subduction zone processes. [ABSTRACT FROM AUTHOR]

In the Alpine Corsica, the Schistes Lustrés Complex consists of a stack of high-pressure metamorphic oceanic and continental units originated during the Late Cretaceous-Middle Eocene closure of the Western Tethys oceanic basin. This complex also includes the Bagliacone-Riventosa Fm. i.e. a thick succession of metaturbidites, whose interpretation is still matter of debate. In this paper, we provide the stratigraphic, metamorphic, and structural evidence that the Bagliacone-Riventosa Fm. belongs to the sedimentary cover of the Middle to Late Jurassic metaophiolites of the Inzecca Unit. The reconstructed succession of the Inzecca Unit thus comprises metaophiolites topped by metacherts and by the Erbajolo, Pietraggiolo and Bagliacone-Riventosa Fms. The former two formations derived from hemipelagic deposits whereas the latter two include both siliciclastic and carbonate turbidites. This succession is affected by a polyphase deformation history that is recognized as the same in all the metasedimentary formations, as testified by their structural field relationships. In addition, these formations experienced the same pressure-temperature metamorphic path, indicating their involvement in a subduction zone. This picture provides new evidence for the mechanism of underplating and exhumation of the oceanic slices within the frame of the subduction zone that developed since Late Cretaceous in the Western Tethys oceanic basin. [ABSTRACT FROM AUTHOR]

The presence of an Eocene subduction event, in addition to Jurassic and Cretaceous ones, in the Rhodopes of Greece and Bulgaria is controversial. We report the first dating of an eclogite from the Lower Allochthon of the Rhodopes. The eclogite is a mafic lens enclosed in orthogneiss of the Arda‐2 Unit at Chepelare, Central Rhodopes. It was metamorphosed under conditions of ca. 25 kbar, 700–750°C. Garnet grains have outward‐increasing Mg contents and omphacite inclusions with the highest jadeite contents in their rims, indicating garnet growth under increasing pressure. Lu–Hf geochronology yielded an age of 48.7 ± 1.5 Ma. The age is linked to a late stage of garnet growth close to peak pressure, i.e. to subduction. [ABSTRACT FROM AUTHOR]

The origin of alkali basalts with distinctive time-integrated low U/Pb (low μ , LOMU) from East Asia is controversial due to the complex geochemical and tectonic signatures reported from this region. We report new data on the petrology and geochemistry of the Higashi-Matsuura and Kita-Matsuura alkali basalts from Southwest Japan, which confirm the presence of a LOMU-type mantle component below the Japanese Islands, similar to East Asian intraplate volcanoes. We use whole rock geochemistry and mineral chemistry to determine mantle melting, magma evolution conditions and isotopic evolution of the LOMU mantle source. Petrological studies show that the Higashi-Matsuura alkali basalts (~3 Ma) were derived from a hydrous mantle source with ~880 μg/g H2O, at a pressure of 1.8 to 2.3 GPa at a mantle potential temperature of ~1300°C. Trace element modelling concludes that these basalts may have been generated through the hydrous upwelling and partial melting of the asthenospheric mantle containing ~15% dehydrated eclogitic component. Higashi-Matsuura alkali basalts show 206Pb/204Pb values of 17.72 to 18.04 which are among the lowest values from Southwest Japan. Relatively older (6–8 Ma) alkali basalts from the Kita-Matsuura area showing similar physicochemical characteristics, do not show LOMU-type isotopic trends. Trace element and Pb–Sr–Nd isotopic data indicate that the Higashi-Matsuura mantle component is similar to the extreme LOMU components reported from the Northeast China alkali basalts, as well as the recently discovered Petit Spot volcanoes on the Pacific Plate. We model the origin of the LOMU signature from the lowest reported Pb isotope ratios in East Asia, from intraplate alkali basalts in Northeast China. Our model suggests that at least two separate subduction events of marine sediments, at 1.8 and 2.2 Ga, are required to explain the observed Pb isotopic variation in the East Asian region. Other LOMU type basalts from East Asia, including Southwest Japan and Petit Spot, define a linear trend between the Xiaogulihe basalts and lithospheric mantle xenoliths, with 40% to 60% Pb in Higashi-Matsuura basalts being derived from the lithospheric mantle during upwelling. This suggests that the LOMU array in East Asia may have been formed by mixing between multiple ancient, subducted sediment components accumulated at the mantle transition zone for about 2 billion years, and its recent upwelling due to dehydration of the stagnant Pacific slab and related melting of the metasomatised asthenospheric mantle. [ABSTRACT FROM AUTHOR]

The horizontal propagation of slab detachment (slab tearing) is known to control lateral migration of the mountain uplift along the collisional belt. However, along‐strike differential collision due to an oblique passive margin geometry can make the topography response more complex. In this study, we employ 3D thermomechanical modeling to distinguish between the lateral migration of the mountain topography driven by slab tearing and oblique continental collision itself. In our models, slab breakoff is triggered by the transition from oceanic to continental subduction, occurring earlier on one side of the passive margin than on the other due to the initial oblique configuration. However, once slab breakoff has begun, it spreads horizontally in the form of tearing at high velocity (∼38–118 cm yr−1), and associated topographic uplift also propagates with the same velocity. In contrast, the along‐strike migration of subsequent continental collision and related topographic uplift propagation is typically much slower (∼2–34 cm yr−1). Similarly, the vertical magnitude of surface uplift caused by slab tearing is higher (up to 10 mm yr−1) than the following collision phase (<4 mm yr−1). The parametric analysis reveals that slab tearing velocity and the associated horizontal propagation of mountain uplift depends on obliquity angle and slab age, whereas the migration of collision‐induced topographic growth is controlled by the convergence velocity and obliquity angle. Finally, we show that presence of microcontinental block detached from the passive margin leads to spatial and temporal transition from horizontal to vertical slab tearing and more intense syn‐collisional mountain building. Plain Language Summary: Continental collision begins after the complete subduction of the oceanic domain, initially located between the colliding continents. As the oceanic slab has negative buoyancy, it detaches from the positively buoyant continental plate shortly after the start of continental collision. Slab detachment leads to a rapid uplift of the surface topography and usually moves sideways, a process known as slab tearing. Slab tearing in turn results in a lateral propagation of the topographic uplift along the continental margin. However, if the colliding plate margins are initially at an angle to each other, an oblique continental collision occurs, which can also lead to along‐strike migration of the mountain uplift. To differentiate between the topography response to slab tearing and oblique continental collision, we have carried out 3D numerical modeling. Our parametric analysis reveals that the rate of slab tearing and the associated horizontal propagation of mountain uplift primarily depend on the angle of collisional obliquity and the age of the subducting oceanic slab, whereas the velocity of plate convergence controls the migration of collision‐induced topographic growth. Our findings also indicate that the surface uplift associated with slab tearing is more pronounced and spreads laterally much faster than during following oblique continental collision. Key Points: We explored numerically in 3D the topography response to horizontal slab tearing during retreating oblique continental collisionHorizontal slab tearing can initiate before collision due to the transition from oceanic to continental subduction below fore‐ and back‐arc domainSurface uplift associated with slab tearing is more pronounced and spreads laterally much faster than in the subsequent collision phase [ABSTRACT FROM AUTHOR]

Fluid overpressure from the water released by subducted sediments and oceanic crust is an important mechanism for generating earthquakes via brittle failure and frictional instability. If unstable, such fault materials may also host diverse fault reactivation mechanisms from slow slip events to moderate‐sized earthquakes in cold subduction zones. We examine this hypothesis for glaucophane gouge ‐ a key index minerals for blueschist facies ‐ at lower confining stresses where behavior is poorly understood. We measure friction and stability at temperatures of 100°C–500°C and effective normal stresses of 50–200 MPa, to explore the controls of temperature, stresses and excess pore fluid pressures on fault friction. The frictional coefficient of glaucophane at representative temperatures and stresses is ∼0.70, insensitive to temperature but with a slight increase at lower effective stresses. Elevating temperature promotes a transition from velocity‐strengthening to weak velocity‐weakening behavior, indicating the destabilizing effect of high temperature downdip in subduction zones. Reducing effective normal stress or concomitantly elevating pore fluid pressure further strengthens the velocity‐weakening response and would be manifest as moderate‐sized earthquakes. Our results support the potential for enhanced unstable sliding of glaucophane gouges at lower effective stresses and blueschist facies temperatures ‐ with weak to moderate velocity‐weakening responses upon fluid pressurization vital for understanding the abundance of slow slip to moderate‐sized earthquakes apparent in cold subduction zones. Plain Language Summary: Blueschist facies present in subduction zones with lower thermal gradient host abundant slow‐slip and dynamic earthquakes—such events requiring critical stress conditions. Such blueschist layers are characterized by abundant fluids that are released as the slab descends and heats—resulting in large excess fluid pressures that may trigger slip on faults at depth. We measure the frictional properties of simulated faults containing glaucophane powders representative of these blueschist products at temperatures, stresses and especially fluid overpressures representative of the descending slab at the plate boundary. Results indicate a temperature‐independent high frictional strength but a transition to unstable slip at both higher temperatures and increased fluid pressures. In the intermediate‐depth subduction zone, depending on the fluid pressure, it is possible to generate earthquakes in a diverse range of modes such as slow‐slip events through moderate‐sized earthquakes. This can explain documented observations in this region. Our results highlight the importance of fluid pressurization and effective stress reduction in controlling such slow‐slip and moderate‐sized events at higher temperatures and for understanding earthquakes in subduction zones. Key Points: Frictional stability of glaucophane gouge is P‐T dependent, with a change from v‐s to v‐w at ∼300°C with enhanced v‐w at lower stressesMinor v‐w of glaucophane gouge at critical stress conditions is favorable for slow slip events in subduction zonesFrictional stability of glaucophane gouge upon fluid overpressures supports the observation of abundant intermediate‐depth earthquakes [ABSTRACT FROM AUTHOR]

Thermal runaway is a ductile localization mechanism that has been linked to deep‐focus earthquakes and pseudotachylyte formation. In this study, we investigate the dynamics of this process using one‐dimensional, numerical models of simple shear deformation. The models employ a visco‐elastic rheology where viscous creep is accommodated with a composite rheology encompassing diffusion and dislocation creep as well as low‐temperature plasticity. To solve the nonlinear system of differential equations governing this rheology, we utilize the pseudo‐transient iterative method in combination with a viscosity regularization to avoid resolution dependencies. To determine the impact of different model parameters on the occurrence of thermal runaway, we perform a parameter sensitivity study consisting of 6,000 numerical experiments. We observe two distinct behaviors, namely a stable regime, characterized by transient shear zone formation accompanied by a moderate (100–300 K) temperature increase, and a thermal runaway regime, characterized by strong localization, rapid slip and a temperature surge of thousands of Kelvin. Nondimensional scaling analysis allows us to determine two dimensionless groups that predict the model behavior. The ratio tr/td ${t}_{\mathrm{r}}/{t}_{\mathrm{d}}$ represents the competition between heat generation from stress relaxation and heat loss due to thermal diffusion while the ratio Uel/Uth ${U}_{\text{el}}/{U}_{\text{th}}$ compares the stored elastic energy to thermal energy in the system. Thermal runaway occurs if tr/td ${t}_{\mathrm{r}}/{t}_{\mathrm{d}}$ is small and Uel/Uth ${U}_{\text{el}}/{U}_{\text{th}}$ is large. Our results demonstrate that thermal runaway is a viable mechanism driving fast slip events that are in line with deep‐focus earthquakes and pseudotachylyte formation at conditions resembling cores of subducting slabs. Plain Language Summary: Thermal runaway is a mechanism that concentrates material deformation into thin layers without breaking the material and has been linked to earthquakes more than 70 km below the surface. This study uses one‐dimensional computer models with a complex material behavior and conducts 6,000 numerical experiments to investigate the influence of different parameters like temperature, deformation rate and material properties. Results show two distinct behaviors, namely a stable regime with slow sliding and a temperature rise of 100–300 K or thermal runaway with fast movement and a temperature increase of a few thousand Kelvin. We find two dimensionless ratios that are combinations of the input parameters and can predict the behavior. The ratio tr/td ${t}_{\mathrm{r}}/{t}_{\mathrm{d}}$ compares heat production to heat loss, and the ratio Uel/Uth ${U}_{\text{el}}/{U}_{\text{th}}$ compares stored elastic energy to thermal energy. If the first ratio is small and the second ratio is large, thermal runaway occurs. Our results show that thermal runaway could cause fast deformation events like earthquakes and produce thin layers of molten rock in conditions that are typical for subducting plates. Key Points: Numerical investigation of thermal runaway in visco‐elastic material with diffusion creep, dislocation creep and low‐temperature plasticityNondimensional scaling analysis reveals two dimensionless groups governing the occurrence of thermal runawayDuctile localization can cause slip events in line with deep earthquakes and pseudotachylyte formation at subducting slab core conditions [ABSTRACT FROM AUTHOR]

The extremely oblique Indo‐Burma subduction zone exhibits dextral strike‐slip faulting along the Sagaing, Kabaw, and Churachandpur‐Mao Faults as well as east‐west shortening between the Sagaing Fault and Bengal Basin. Through regional stress analysis, considering areas from central Tibet, around the eastern Himalaya Syntaxis, to Burma, it has been determined that the principal compressive stress directions align with the principal strain rates. The northeast‐southwest oriented compressive stress direction from the western Shan Plateau continues into Burma. Notably, P axes align with the topographic gradients, and T axes are sub‐parallel to the topographic contours in the Shan Plateau region south of 27°N. These stress patterns are consistent with a gravitational potential energy induced crustal and mantle flow. The alignment of the fast shear wave with the maximum strain rate and the colinear NW‐SE to E‐W fast direction of the SKS wave and T axis determined from focal mechanisms in the Shan Plateau suggest that the mantle lithosphere deforms in concert with the crust. We suggest crust and mantle flow south of the Red River Fault has resulted in widening of the lithosphere in the Shan Plateau in an east‐west direction. Therefore, the Sagaing Fault has bowed approximately 50–100 km westward if we assume that the Sagaing Fault was originally straight. Our results of regional stress inversion are consistent with late Miocene to present E‐W shortening in the Indo‐Burma subduction zone resulting from the release of gravitational potential energy from the central Tibetan Plateau. Plain Language Summary: The movements of the Earth's crust in the Indo‐Burma region are partially caused by India sliding underneath southeast Asia at an angle. The Sagaing Fault, along with other strike‐slip faults in the Indo‐Burma area, accommodates the motion of India and Asia. Even though India and Asia pushing together mostly causes east‐west compression in Burma and the far east of Bangladesh, only about half of the displacement comes from their collision. It's unclear what causes the remaining east‐west displacement. We suggest that the additional compression in Bangladesh and Burma happens because of the collapse of the Tibet Plateau and the flow of the Earth's lithosphere out of central Tibet. Key Points: The E‐W shortening of the Burma Plate is an effect of the release of gravitational potential energy from the central Tibetan PlateauGeometry and kinematics of the sinistral faulting in the Shan Plateau are consequences of radially directed compression from fan‐shaped lithospheric flowLithospheric flow around the southeast margin of the Tibetan Plateau has affected stress in northern southeast Asia and Burma [ABSTRACT FROM AUTHOR]

Despite significant study, when and how plate tectonics initiated on Earth remains contentious. Geologic evidence from some of Earth's earliest cratons has been interpreted as reflecting the formation of initial continental blocks by non‐subduction processes, which then trigger subduction initiation at their margins. Numerical models of mantle convection with a plastic yield stress rheology have shown this scenario is plausible. However, whether continents can trigger subduction initiation has not been tested with other rheologies. We, therefore, use numerical models of mantle convection with an imposed continental block to test whether continents facilitate subduction initiation with a grain‐damage mechanism, where weak shear zones form by grain size reduction. Our results show that continents modestly enhance stresses in the lithosphere, but not enough to significantly impact lithospheric damage or subduction initiation: continents have minimal influence on lithospheric damage or plate speed, nor does subduction preferentially initiate at the continental margin. A new regime diagram that includes continental blocks shows only a small shift in the boundary between the mobile‐lid and stagnant‐lid regimes when continents are added. However, as we do find that stresses are modestly enhanced at the continental margin in our models, we develop a scaling law for this stress enhancement to more fully test whether continents could trigger subduction initiation on early Earth. We find that lithospheric stresses supplied by continents are not sufficient to initiate subduction on the early Earth on their own with grain‐damage rheology; instead, additional factors would be required. Plain Language Summary: How plate tectonics initiates on Earth is controversial. One possibility is that primitive continents trigger subduction initiation at their margins; an idea our study tests with computer models. We specifically use a mechanism called grain‐damage in our model, where weak zones that allow for subduction develop due to grain size reduction. The results showed only modest effects on lithospheric damage from the addition of continents. Continents do not appear to dictate the subduction initiation location, as subduction initiates readily both at continent margins and far from margins. In addition, plate boundaries do not get weaker nor do plates move faster with continents included. We observe slightly higher stress at continental margins, which leads to plate tectonics developing for a few models where it otherwise would not have. However, scaling our results to early Earth conditions, we find continents do not impart enough stress in the lithosphere on their own for subduction to initiate by grain size reduction. Other factors may have been important during this critical phase in our planet's history. Key Points: We test whether continents can trigger subduction initiation on the early Earth using convection models with grain‐damageModel results show continents do not necessarily lead to subduction initiation, imparting only a minor increase in lithospheric stressScaling analysis shows that continents are not capable of triggering subduction on the early Earth [ABSTRACT FROM AUTHOR]

Studying the basement characteristics and tectonic evolution of the proto-Yap Izu–Bonin–Mariana arc system can provide essential clues for understanding the subduction process in the Western Pacific Ocean. The Yap arc is a part of the Izu–Bonin–Mariana (IBM) arc, but the origin and formation time of the metamorphic basement rocks of the Yap arc still need to be determined. In this paper, we present the first systematic and detailed chronological, mineralogical, whole-rock major element and trace element research on metamorphic basement rocks from four stations in the Southern Yap arc and discuss the origin of the metamorphic basement rocks in the Southern Yap arc. The results show that the single mineral U-Pb ages of titanites and 40Ar/39Ar ages of amphiboles in the Southern Yap arc are 19.3 and 19.4 Ma, respectively, which are consistent within the error ranges, and these ages represent the metamorphic age of the basement rocks. The amphibolite is mainly produced via the metamorphism of back-arc basin basalt (BABB) and forearc basalt (FAB). The temperature and pressure conditions of this metamorphism are 446.5–641.6 °C and 0.24–0.73 GPa, the facies series of which is the medium P/T series. This study provides important data for understanding the Yap subduction system and the early evolution of the proto-IBM Arc. [ABSTRACT FROM AUTHOR]

During the Late Paleozoic–Early Mesozoic Era, the sediment transport system and tectonic regime in the southeastern margin of the South China Block (SESCB) all changed, significantly affected by the Paleo-Pacific subduction. However, controversy exists about the Paleo-Pacific subduction's initiation time. This study uses detrital zircon U-Pb ages to discuss the Late Triassic source-to-sink system in the SESCB. It provides some references for the Paleo-Pacific subduction process based on crucial age information and zircons' trace elements. The paleogeography and similarity of detrital zircon age distribution indicate that three sinks were found in the SESCB during the Late Triassic: 1. the Yangchun-Kaiping-Gaoming area, comprising major age ranges of 260–220, 460–400, and 1 200–800 Ma, which might be sourced from the Yunkai terrane; 2. the Jiexi-Kanshi-Nanjing area, characterized by the significant age component of 2 000–1 800 Ma, which corresponded to the Wuyi terrane; 3. the Xinan area, consisting of significant age groups of 290–250 and 380–320 Ma, which might be sourced from the magmatic rocks formed by the Huinan Movement and Paleo-Pacific subduction. Note that 290–250 Ma zircons were widely distributed in the Upper Triassic strata, and their trace elements suggested the existence of a magmatic arc near the SESCB during the 290–250 Ma. Thus, we propose that the Paleo-Pacific subduction might have begun in the Early Permian. [ABSTRACT FROM AUTHOR]

The paper presents first data on isotopic U–Pb study (LA-ICP-MS method) of zircon from intrusive rocks of the Kensu pluton situated in the eastern part of the deep-seated fault system of the "Nikolaev Line." This pluton of high-potassic (shoshonitic series) rocks is accompanied by the Kensu deposit and other occurrences of skarn and porphyry W–Mo–Cu–Au mineralization. Together with the other Au, W, and Cu deposits and occurrences, they are parts of the extended metallogenic belt of Tien Shan. The concordant isotopic U–Pb age data for zircon autocrysts from the rocks of the consecutive intrusive phases span over the interval of approximately 325 to 302 Ma. This interval comprised the crystallization of monzogabbro (321 ± 4 Ma), monzonite (319 ± 4 Ma), camptonite (306 ± 4 Ma), syenite (307 ± 6 Ma), quartz syenite (305.5 ± 2 Ma), and quartz monzonite (305 ± 3 Ma). Zircon antecrysts dated at 316–325 Ma to 335–345 Ma have also been identified. The age data obtained are consistent with the age of subduction processes defined for the western part of the Middle Tien Shan. However, both geochemical characteristics of the rocks from the Kensu pluton and a distinct W–Mo mineralization related to this pluton contradict the subduction-related setting of the pluton emplacement but, instead, point out the post-collisional setting of the intrusion emplacement. This discrepancy can be explained by a "scissor-like" (from east to west) closure of the Turkestan paleoocean that has resulted in the post-collisional regime in the eastern part of the "Nikolaev Line," whereas subduction continued in its western part. The rocks also contain zircon xenocrysts with a much older age (in to order of 1.9 Gb) that probably represents the age of the Tarim craton basement rocks; this indicates an involvement of the ancient material in the magma generation. [ABSTRACT FROM AUTHOR]

A unique feature of the Kamchatka Peninsula is an extensional structure running for more than 400 km along the peninsula—the Central Kamchatka Depression (CKD). Some geodynamic models associate the formation of the CKD with the movements of East Kamchatka toward the Pacific Ocean due to retreat of the northern edge of the subduction zone. However, isotope–geochronological data on the time of the CKD formation have been lacking up to the present time. Therefore, we could not directly associate the CKD emergence with the stages of the Kamchatka tectonic evolution and the intensity of its recent deformations. This work presents the chemical compositions and K–Ar ages of effusive rocks from the KL-1 borehole drilled in the northern part of the CKD. Samples from the depth interval of 50–475 m, represented by medium-K basalts and high-K basaltic trachyandesites date back to 0.7 to 1.5 Ma. By their composition, these rocks are close to effusive rocks forming the base of the Klyuchevskaya group of volcanoes. Before this study, the age of the effusives had been estimated as much younger, up to 0.3 Ma. Below, in the interval of 475–505 m, a pack of sands and boulder conglomerates was described. They unconformably overlap the aphyric and olivine–pyroxene porphyritic andesibasalts with interlayers of volcanic ash and volcanic sands of the same composition. At the depth of 905–1513 m, the borehole recovers highly altered tuffs, mafic and intermediate in composition, interbedded with andesites and andesibasalts. The K–Ar estimation of 3.5 ± 0.4 Ma was obtained for the least altered sample of medium-K andesibasalt from the depth of 1255 m. We suggest that the altered effusives at 905 m and below are associated with the completion of accretion of the Kronotskii Island Arc and with the formation of the modern structure of the Kamchatka Peninsula. The CKD setting occurred after this event in the interval of 1.5–3.5 Ma. [ABSTRACT FROM AUTHOR]

The Qinling‐Dabie‐Sulu orogen is the eastern part of the Central China Orogenic Belt. Looking back on previous studies of the sedimentary record we systematically compiled the dataset of detrital zircon U–Pb ages and Hf isotopes for this orogenic belt. The dataset incorporates a comprehensive compilation of 32,449 detrital zircon U–Pb ages and 979 Hf isotopes. The findings demonstrate that distinct tectonic units within the orogenic belt exhibit unique tectonic evolution histories during various geological epochs. This dataset can be used to constrain the tectonic framework and orogenic evolution including ocean subduction, continental collision and orogen exhumation. It can be integrated with other geological datasets to improve our understanding of the Central Orogenic Belt in China, and possibly plate tectonics globally. [ABSTRACT FROM AUTHOR]

Seismic and tsunami hazard modelling and preparedness are challenged by uncertainties in the earthquake source process. Important parameters such as the recurrence interval of earthquakes of a given magnitude at a particular location, the probability of multifault rupture, earthquake clustering, rupture directivity and slip distribution are often poorly constrained. Physics-based earthquake simulators, such as RSQSim, offer a means of probing uncertainties in these parameters by generating long-term catalogues of earthquake ruptures on a system of known faults. The fault initial stress state in these simulations is typically prescribed as a single uniform value, which can promote characteristic earthquake behaviours and reduce variability in modelled events. Here, we test the role of spatial heterogeneity in the distribution of the initial stresses and frictional properties on earthquake cycle simulations. We focus on the Hikurangi–Kermadec subduction zone, which may produce M w > 9.0 earthquakes and likely poses a major hazard and risk to Aotearoa New Zealand. We explore RSQSim simulations of Hikurangi-Kermadec subduction earthquake cycles in which we vary the rate and state coefficients (a and b). The results are compared with the magnitude-frequency distribution (MFD) of the instrumental earthquake catalogue and with empirical slip scaling laws from global earthquakes. Our results suggest stress heterogeneity produces more realistic and less characteristic synthetic catalogues, making them particularly well suited for hazard and risk assessment. We further find that the initial stress effects are dominated by the initial effective normal stresses, since the normal stresses evolve more slowly than the shear stresses. A heterogeneous stress model with a constant pore-fluid pressure ratio and a constant state coefficient (b) of 0.003 produces the best fit to MFDs and empirical scaling laws, while the model with variable frictional properties produces the best fit to earthquake depth distribution and empirical scaling laws. This model is our preferred initial stress state and frictional property settings for earthquake modelling of the Hikurangi–Kermadec subduction interface. Introducing heterogeneity of other parameters within RSQSim (e.g. friction coefficient, reference slip rate, characteristic distance, initial state variable, etc.) could further improve the applicability of the synthetic earthquake catalogues to seismic hazard problems and form the focus of future research. [ABSTRACT FROM AUTHOR]

On 16 April 2013, an M w = 7.7 earthquake struck the border of Iran and Pakistan in the central part of the Makran subduction zone with a reported depth of 80 km by USGS. This rare event in this poorly instrumented region helps to shed light on the kinematics of the subducting slab. We investigate source parameters of the Saravan intraslab normal earthquake using RADARSAT-2 SAR images in three ascending tracks, nine permanent GNSS sites and teleseismic data. The maximum coseismic displacement occurred at the SRVN GNSS station with 54.1 mm southeast horizontal and 42.7 mm upward vertical displacements. The coseismic ascending InSAR displacement maps illustrate a continuous and smooth NE-trending elliptical shape deformation pattern with a maximum of ∼29 cm of displacement away from the satellite. We use 25 broad-band teleseismic P-waveforms to estimate the focal mechanism of the main shock. A joint uniform inversion of InSAR, GNSS and teleseismic data reveals a NW-dipping SW-striking fault and a primarily normal-faulting earthquake with a minor right-lateral strike-slip component. The static slip distribution of the InSAR coseismic maps localizes variable slip at depths between 50 and 81 km with a maximum amplitude >3 m at 60–75.5 km depth, rupturing the oceanic crust of the subducted slab. The kinematic slip distribution exhibits a well-constrained slip pattern with a nucleation depth of 65 km. The source time function indicates that the earthquake reaches its maximum moment tensor release at ∼8 and ∼16 s. The NE-trend of the Saravan earthquake slip pattern, the orientation of the volcanic arc, and the distribution of the intraslab intermediate-depth normal earthquakes provide new insights into slab geometry in the central Makran subduction zone. We suggest that the slab bending at the hinge of subducting Arabian Plate is oblique along a NE–SW direction parallel to the volcanic arc rather than the shoreline or deformation front, and it is likely to be the reason for an oblique volcanic arc in the Makran subduction zone. These new constraints on the Makran slab geometry will help further studies in establishing realistic coupling maps for seismic hazard assessment. [ABSTRACT FROM AUTHOR]

Concrete-filled coupled composite plate shear walls (also known as as SpeedCore walls) are gaining acceptance for construction in seismic region throughout North America. Design provisions for this lateral load-resisting system have already been added to ASCE 7-22 and to the American Institute of Steel Construction Seismic Design Provisions. Adequacy of the seismic design parameters used for this structural purpose has been validated in the USA using the FEMA P695 methodology. An interest was expressed by the practicing engineering community to use these walls in Canada, which requires demonstration of satisfactory seismic performance within the Canadian context. As such, new analyses are needed using Canadian-specific sets of ground motions to confirm the adequacy of the seismic design parameters proposed for implementation of these composite walls in the National Building Code of Canada. This paper presents the results of these analyses, showing that the proposed seismic performance factors are appropriate for this structural system in Canada. [ABSTRACT FROM AUTHOR]

The Jijal Complex is considered one of the largest Neo-Tethyan remnants in the intra-oceanic Cretaceous–Palaeogene Kohistan Arc of Pakistan. This complex largely consists of gabbros, peridotites, and chromitites. Previous studies documented the genesis of gabbros and chromitites in detail; however, detailed geochemistry and magma genesis were lacking. In this investigation, we present whole-rock geochemical and platinum group elements (PGEs) data of Jijal peridotites (dunites and harzburgites). The objectives of this study are to elucidate magmatic processes and tectonic regimes involved in the formation of peridotites, factors influencing the concentration and dispersion of PGEs in them, and their tectonic evolution. The investigated peridotite samples are depleted in magmaphile major elements (Al2O3: 0.23–0.57, TiO2: 0.01–0.04, and CaO: 0.08–0.69 wt%), relative to the primitive mantle values, reflecting melt-rock interaction during their magmatic evolution. In addition, rare-earth element (REE) contents in harzburgites are relatively higher compared to the dunites; however, both rock types exhibit depletion with respect to the chondrite-normalized values. The obvious negative anomalies of Nb, Zr, and enriched LREE and large ion lithophiles collectively substantiate their association with depleted arc-type mantle components, metasomatism, and melt/fluid-rock reactions after partial melting episodes. Bulk-rock and geochemical modelling of PGEs data of the peridotites suggest their shallow depth spinel-bearing depleted heterogeneous mantle source and generation from refractory mantle residuum along with boninitic signatures in a supra-subduction zone (SSZ). The PGE's geochemistry additionally reveals that partial melting, fractionation, metasomatism, and sulphur under-saturation were the key factors that controlled the concentration and distribution of PGEs in the studied rocks. The boninitic features of the Jijal peridotites are equated with intraoceanic fore-arc followed by subduction initiation, and melt-rock reactions in a hydrated forearc mantle, indicating robust evidence of mantle depletion and pervasive refertilisation in an embryonic Neo-Tethyan arc system. Tectonically, the investigated rocks encapsulate vestiges of the Cretaceous Tethyan Ocean and record multifaceted history from boninitic to slab-proximal island arc affinity in compliance with an intraoceanic SSZ fore-arc regime coherent with the subduction inception. [ABSTRACT FROM AUTHOR]

The tectonic regime is an important factor controlling the formation of ore deposits, and magmatic rocks generated in different tectonic regimes are characterized by contrasting ore affinities and mineralization styles. A series of early Carboniferous volcanogenic massive sulphide (VMS) deposits occur in the western segment of the Dananhu Arc in the Central Asian Orogenic Belt. In contrast, coeval magmatic rocks in the middle segment are devoid of VMS copper mineralization but host porphyry copper deposits. However, the relationship between tectonic setting and mineralization still needs to be clarified. Herein, we synthesize the new and existing geochemical data of the Carboniferous arc rocks of the Dananhu Arc, showing diverse arc magmatism and contrasting Cu mineralization styles in the western and middle segments. Magmatic rocks in the western segment are consistent with normal island arc origin. In contrast, magmatic rocks in the middle segment of the Dananhu Arc have adakite-like affinities. The magmatic rocks in the western segment were derived from the partial melting of the juvenile lower crust triggered by slab rollback in an extension setting. In contrast, the rocks in the middle segment originated from partial melting of the subducted slab that was triggered by flat subduction. The extension setting coupled with high temperature magmatic activity induced the circulation of the hydrothermal fluids, which were critical to the development of the Xiaorequanzi VMS deposit. Copper would become progressively enriched in the fractionating melt under the high–fO2 condition, and the compressional regime caused by flat subduction reduces the 'leakage' of hydrothermal fluids, which are favourable for the formation of the porphyry mineralization in the middle segment. It is, therefore, evident that variations in the tectono-magmatic setting across the Dananhu Arc played an important role in generating the diversity of Cu deposit types and variable ore affinities throughout the Eastern Tianshan. [ABSTRACT FROM AUTHOR]

This study focuses on the post-Miocene neotectonic evolution of the slope-perched sedimentary basins around the Eastern Korean Continental Margin and which category these basins could be classified into. The Hupo Basin, the largest neotectonic sedimentary basin on the Eastern Korean Continental Margin, comprises three key geological components: 1) Neotectonic Sequence, which has divergently filled the Hupo Basin since the Early Pliocene, 2) Hupo Fault, a N-S striking, high-angle thrust (or reverse) fault that bounds the Hupo Basin to the east, and 3) Hupo Bank, a N-S elongated submarine wave-cut platform that sits on top of the uplifted eastern Hupo Fault block. On the basis of stratigraphic and structural restoration, we conclude that the Hupo Basin was formed by the compressional uplift of the Hupo Bank during the incipient subduction of the Ulleung Basin crust after the Miocene. Given the morphostructural features of the Hupo Basin and its host incipient subduction system, we categorize it as a sort of piggyback basins. The basin-forming process shown in this study is commonly found in numerical models that simulate modern cases of subduction initiation around the world. [ABSTRACT FROM AUTHOR]

Serpentinite dehydration in subduction zones plays a pivotal role in geochemical cycling on Earth. A number of geochemical studies on arc magmas have elucidated the contributions of serpentinite-derived fluids to mantle sources. However, due to complex geological overprints during subduction zone processes, discerning serpentinite signatures in exposed metamorphic rocks within fossil subduction zones remains challenging. In this study we address these difficulties through in-situ investigations of tourmaline, the geochemistry of which reflects the host environment as well as potential fluid-induced processes. The presence of zonations in tourmaline makes it an excellent recorder of consecutive geological events. Integrated major and trace elements along with in-situ boron isotopes of tourmaline from the high-pressure Sopron area (Hungary) in the Eastern Alps were used to unravel fluid action sourced from serpentinite. Despite the presence of color zoning, tourmaline in the orthogneiss (Tur-G) has low X Mg [Mg/(Mg + Fe)] of ca. 0.3–0.6 and δ11B values of around −11 ‰, along with variable trace element compositions. Petrological observations and geochemical analyses suggest that the inner domains of Tur-G are of igneous origin, while the outer rims are likely affected by subsequent metamorphic events. Tourmaline in metasomatized kyanite-quartzite (Tur-K) veins exhibits distinct geochemical zoning, and preserves metamorphic cores and fluid-induced rims. The inner domains of Tur-K display low X Mg (<0.6), relatively high trace element concentrations and δ11B values of less than −10 ‰, whereas the overgrowths exhibit extremely high X Mg values (>0.99), low trace element concentrations and high δ11B values reaching up to +21 ‰, clearly indicating the incorporation of serpentinite-derived Mg-11B-rich fluids. Through comparison with other metamorphic and metasomatic tourmalines in (ultra)high-pressure rocks globally, we establish that tourmaline with high X Mg > 0.85 and δ11B values >0 ‰ may serve as an effective proxy for detecting serpentinite-derived fluids in subduction zones. [ABSTRACT FROM AUTHOR]

We present the latest magnetotelluric models on profiles in the northeastern part of Slovakia and the southeastern part of Poland. These models are focused on deciphering the tectonic structures at the contact of the Inner Carpathians with the European Platform in this area. For the Inner Carpathian block, we propose the term Carpathia. Profile SA-01 shows shallower structures and the parallel MT-05 profile shows deeper structures. These models are also correlated with the seismic profile CEL-05. All results are compatible and show an original subduction-collisional structure, which was later replaced by a transpressive-transtensional one. The most striking structures are thick highly conductive subhorizontal zones in the middle crust and a tectonically controlled deep vertical conductive structure—the Carpathian conductive zone. Other significant structures, which also appear in the seismic section, are back thrusting of Flysch Belt and the Klippen Belt basement (Penninic crust) uplift. [ABSTRACT FROM AUTHOR]

[Display omitted] • Igneous geochemistry used to map paleoelevations of South America. • Maps for Cenozoic-present broadly agree with independent constraints. • Results identify areas for improvement in global paleoelevation models. Mountains and mountain ranges, often situated at convergent plate margins, play a pivotal role in many fields of the Earth, climate, and biological sciences. Reconstructing past episodes of mountain building from the geological rock record is one of the main challenges for unravelling the ancient physical geography of Earth's surface. Established methods for quantifying past elevations traditionally relied on sedimentary rocks, but in recent years, alternative approaches have emerged on the basis that geochemical signatures of magmatic rocks formed in convergent settings correlate with crustal thickness or elevation. Consequently, methods based on igneous samples have the potential to allow quantitative mapping of past topographic change for large spans of space and time where existing maps are largely based on a qualitative approach. Here, we investigate the application of paleoelevation estimates derived from geochemistry using the western margin of South America as a case study. We investigate their consistency with independent indicators of past elevations such as stratigraphy, stable isotopes, fossils etc. for Cenozoic samples along the Andean margin. For older times, we compare the estimated paleoelevations with more general aspects of the geological record, as well as paleoelevations from global paleogeography models widely used in climate modelling studies, to evaluate the extent to which these models are consistent with the igneous geochemical proxies. We find that estimates based on multiple geochemical proxies, and which account for variations in elevation as a function of MgO, are preferable to those based on individual proxies. The multi-mohometer estimates yield estimates of elevation that better match both present-day topography and Cenozoic paleoelevations, and retain more samples during the data filtering stage. In deeper time, we show that igneous geochemistry quantifies changes in elevation related to documented phases of crustal thickening and thinning, and is thus likely to allow improvements to existing maps of paleotopography. [ABSTRACT FROM AUTHOR]

Thermodynamic, experimental and field studies have suggested that organic compounds could be stable, and in some cases predominate over inorganic carbon species, within subduction zones under high pressure and high temperature (HP-HT) conditions. Beyond sedimentary organic matter of biological origin, solid organics can be inherited from hydrothermal circulation at mid-ocean ridges or abiotically formed by carbonate destabilization in the slab. To assess the fate of solid organic compounds during subduction, HP-HT experiments using piston-cylinder and multi-anvil presses have been performed at 700–1000 °C and 3–7 GPa. Different starting solids were tested, including either synthetic polycyclic aromatic hydrocarbons (PAHs) alone, with (i.e., 1-hydroxypyrene, 1-pyrenebutyric acid) or without (pyrene) oxygen-bearing functional groups, or a mixing of pyrene and antigorite. Our results show that increasing P–T conditions lead to the formation of hydrogenated (±oxygenated) graphitic carbon preserving a high level of structural disorder, far from graphite structure. We also observe the formation of aqueous fluids during experiments at 700 °C and 3 GPa with oxygen-functionalized PAHs, suggesting quick water release from solid organic compounds at HP-HT in subduction zones. Pyrene-antigorite experiments reveal various mineral assemblages depending on redox conditions. Oxidizing conditions favor the formation of magnesite-enstatite-coesite while reducing conditions promote forsterite-enstatite-graphitic carbon assemblages. Our results finally highlight the limited reactivity of solid organic compounds when exposed to aqueous fluids derived from serpentinite under reducing conditions which could facilitate the recycling of organic carbon into the deep mantle. [ABSTRACT FROM AUTHOR]

The Pacific large low-shear-velocity province (LLSVP), as revealed by cluster analysis of global tomographic models, hosts multiple internal anomalies, including a notable gap (~20° wide) between the central and eastern Pacific. The cause of the structural gap remains unconstrained. Directly above this structural gap, we identify an anomalously thick mantle transition zone east of the East Pacific Rise, the fastest-spreading ocean ridge in the world, using a dense set of SS precursors. The area of the thickened transition zone exhibits faster-than-average velocities according to recent tomographic images, suggesting perturbed postolivine phase boundaries shifting in response to lowered temperatures. We attribute this observation to episodes of Mesozoic-aged (250 to 120 million years ago) intraoceanic subduction beneath the present-day Nazca Plate. The eastern portion of the Pacific LLSVP was separated by downwelling because of this ancient oceanic slab. Our discovery provides a unique perspective on linking deep Earth structures with surface subduction. [ABSTRACT FROM AUTHOR]

We observe high‐frequency scatterers consistent with the interpretation of a tabular high‐velocity structure under the Indian Ocean as an ancient subducted slab. We use a previously rarely used raypath, P waves scattered in the slab into PKP waves (P∗ ${\mathrm{P}}^{\ast }$PKP), from 12 earthquakes and explosions in five locations recorded on the antique LASA (Large Aperture Seismic Array) located in Montana, United States. The scatterers concentrate in the mantle transition zone and ∼ ${\sim} $1,500 km depths, in the locations where the fast anomalies in the tomography broaden and strengthen. Our inference that the slab lingers in the upper‐ and mid‐mantle despite subducting and detaching more than 130 million years ago suggests that models of slabs sinking into the mantle may have to accommodate such long‐term stagnation. Plain Language Summary: Through study of a novel raypath of seismic waves identified on a large, high‐quality seismographic array, we find evidence of an ancient subducted slab residing beneath the Indian Ocean. Our investigation reveals the presence of high‐frequency scatterers nestled approximately 500 and 1,500 km deep. Notably, these scatterers locate within fast anomalies observed in tomographic imaging. Despite having undergone subduction and detachment over 130 million years ago, this slab remains suspended mid‐mantle. Such longevity challenges prevailing models of subduction dynamics by indicating protracted stagnation of subducted lithospheric material within the Earth's mantle. Key Points: A unique raypath P*PKP is utilized to detect heterogeneities in the mantleStrong scattering coincides with a hypothesized ancient subducted slab beneath the Indian OceanThis Southeast Indian Slab may have stagnated more than 100 Ma, which is unusually long [ABSTRACT FROM AUTHOR]

The extensively distributed Early Permian mafic rocks in the Qiangtang Terrane of the central Tibetan Plateau are the magmatic records of separation of this terrane from the Gondwana. Nevertheless, the origins and mantle source characteristics of these rocks continue to be subjects of debate. This study reports zircon U-Pb and Lu-Hf isotopic and whole-rock geochemical and Sr-Nd-Hf isotopic data on gabbros exposed in the Zougou Region, western Qiangtang Terrane. Our zircon U-Pb isotope age suggests that the Zougou gabbros (ZGs) were formed at ca. 290 Ma, representing newly discovered Early Permian mafic rocks within the Qiangtang Terrane. The ZGs display geochemical affinities with within-plate-basalts given that they are tholeiitic and have high Zr/Y and Ti/V ratios. Compared to previously examined Early Permian mafic rocks in the western Qiangtang Terrane, the ZGs are characterized by their distinct, nonradiogenic Nd (εNd(t) = -0.54 to −2.18) isotopic signatures, which cannot be attributed to crustal contamination or assimilation. This assertion is supported by their uniform whole-rock εNd(t), εHf(t), and zircon εHf(t) values, as well as by magma mixing modelling. In conjunction with regional geology, we propose that the ZGs were derived from an isotopically enriched lithospheric mantle metasomatized by previous subduction events. Furthermore, the positive decoupling of Hf-Nd isotopes (ΔεHf(t) =  +2.21 to + 2.72), negative Nb-Ta anomalies, and variable Ba/Th ratios within the ZGs indicate that the metasomatic agents were fluids released from oceanic sediments. Our study provides insights into the compositions of the lithospheric mantle beneath the Qiangtang Terrane during the Permian, which is pivotal to discriminating the role of asthenospheric and lithospheric components in the formation of the contemporaneous mafic rocks in response to Gondwana break-up. [ABSTRACT FROM AUTHOR]

ABSTRACT Subduction zones are the primary locations of material exchange between the crust and mantle, and thus, arc igneous rocks are extensively examined to explore crust–mantle interactions during oceanic subduction. In this study, the Sr‐Nd‐Hf isotopic compositions and elemental characteristics of the Yinwaxia mafic dykes from the Shibanshan–Huaniushan arc in the southern Beishan Orogen were investigated to determine their petrogenesis and explore crust–mantle interactions during the subduction of the Liuyuan Ocean. The dykes were subdivided into two groups based on their geochemical composition and spatial distribution. Group I dykes in the northern Yinwaxia area possess depleted light rare earth elements and slightly enriched large‐ion lithophile elements, indicated by relatively high ratios of Rb/Nb (1.4–82), Ba/Nb (6–408), and Cs/Nb (0.13–2.74), and low ratios of Th/Yb (0.03–0.39), Th/Nb (0.10–0.83), and (La/Yb)N (0.33–1.36). Further isotopic composition study revealed that low values of (87Sr/86Sr)i (0.7028–0.7052), and high values of εNd(t) (4.9–9.1) and εHf(t) (13.2–24.0), which suggests that the mantle source of Group I dykes was metasomatized by aqueous fluids. In Group II dykes located in the southern Yinwaxia area, enrichment of light rare‐earth elements and large‐ion lithophile elements was observed, featuring lower ratios of Rb/Nb (0.5–16.7), Ba/Nb (13–51), and Cs/Nb (0.15–1.56), but higher ratios of Th/Yb (0.25–2.64), Th/Nb (0.19–1.49), and (La/Yb)N (1.09–2.98) compared to Group I. Furthermore, Group II dykes exhibited higher values of (87Sr/86Sr)i (0.7051–0.7077) and lower εNd(t) (−1.7 to +3.8) and εHf(t) (3.7–9.4) isotopic compositions, which suggests that the slab fluids involved in their mantle source were dominated by sediment‐derived melts. The difference between the mafic dykes from Groups I and II suggests the addition of steadily increasing amounts of sediment‐derived melt in their mantle source; moreover, the increased (La/Yb)N ratio and decreased εNd(t) with increasing distance from the Liuyuan mélange are records of the spatial evolution of the composition of the slab fluids during the oceanic subduction of Liuyuan Ocean in the early Permian. [ABSTRACT FROM AUTHOR]