We present a new integrated tectonostratigraphic framework for the proximal-to-distal rifted margin of the Northeast South China Sea, based on a review of seismic and borehole observations, as well as crustal thickness variations determined from a gravity inversion scheme. The structural domains of the NE SCS shaped by Cenozoic rifting include the proximal (Northern Rift System and Penghu-Peikang High), necking (Tainan Basin, Central High, and its southern vicinities), and distal domains (Southern Rift System and Southern High). Rifting (Late Paleocene to Early Oligocene) occurred synchronously throughout the margin and was accommodated by large-offset and low-angle normal faults. This resulted in localized rift basins filled by marine/deltaic sedimentary rocks in the proximal domain and a sediment-starved, likely deep-marine setting in the distal domain. During the post-rift period (Early Oligocene to latest Miocene), shelf-dominated deposition prevailed north of the Central High, whereas a deep-marine environment is interpreted to its south. This overall trend persisted during the foreland basin sedimentation linked to the Taiwan orogen (latest Miocene to recent). The comparison of the NE SCS rifted margin with the adjacent Pearl River Mouth rifted margin shows differences in both their crustal structure and sediment infilling history. Their contrasting crustal structures are interpreted as a response to rifting processes that differ due to initially contrasting crustal rheology and the proximity/magnitude of sediment source areas. More generally, this study highlights how the dynamic evolution of marginal sea basins drives rapid changes in rifting styles and sedimentary infill during and after rifting.

Abstract. Structure-from-motion (SfM) photogrammetry provides new possibilities for the interpretation of complex geological objects and settings through the digitalization of outcrops in the form of Digital Outcrop Models (DOMs). This study focuses on the acquisition, processing, and georeferencing of 12 DOMs targeting the Err and Bernina low-angle normal faults (LANFs) in the Central Alps. This area exceptionally preserves remnants of Jurassic rifting. Extensive Unmanned Aerial Vehicle (UAV) -based field campaigns (2022–2025) over 43 km², covering 1710 m elevation difference, combined with differential GNSS and regionally-available surface data, produced 12 high-resolution DOMs and associated products (point clouds, textured meshes (DOMs), tiled models, orthomosaics, and DEMs) with centimeter to decimeter resolution. A total of 15 control points per DOM were used to georeference and quality assure the digital data assets, 5 of which function as reference check points (CPs). Within the twelve DOMs, the total ground control points (GCPs) root mean square error (RMSE) ranges from 0.02 to 1.47 m and the RMSE of the CPs ranges from 0.49 to 3.11 m. Individual DOMs within the Fossil Alpine Tethys rifted margin DOM (FATDOM) Dataset reveal detailed internal fault structures, lithological variations, fracture networks, and tectono-sedimentary relationships, offering new insights into the architecture and kinematic evolution of LANFs that also extend to the seismic scale. Comparison of our DOMs with seismic data in present-day systems can be used to bridge the scale gap between local structural observations and regional interpretations. Beyond tectonic implications, the high resolution of our resulting DOMs enables a wide range of geoscientific applications including geomorphological studies focused on the monitoring of deglaciation. The data described in this paper are available on Zenodo under https://doi.org/10.5281/zenodo.18940068 (Morzelle et al., 2026).

The South China Marginal Sea (SCS) is a Marginal Sea Basin characterized by several failed continental rifts preceding continental break-up and subsequent seafloor spreading. The oldest phase of rift propagation is located in the northeast South China Sea (NE SCS). We present new work constraining the tectonostratigraphic evolution and crustal structure of this NE SCS margin, which we compare with that of the adjacent Pearl River Mouth Margin (PRMM). To achieve this, subsurface mapping from reflection seismic data was used together with crustal thickness determined from gravity inversion to identify multiple stages of deformation, crustal domains, and related depositional environments on the NE SCS rifted margin.Within the NE SCS margin, from north to south, four crustal domains were interpreted: (i) the proximal (i.e., Northern Rift System and Penghu-Peikang High), (ii) narrow necking (i.e., Tainan Basin, Central High, and its southern vicinities), (iii) wide distal (i.e., Southern Rift System, Southern High, and narrow continent-ocean transition – COT), and (iv) oceanic. On the heterogeneous continental crust, three main Cenozoic tectonosedimentary stages took place: (1) rift (Late Paleocene to Early Oligocene); (2) post-rift (Early Oligocene to Late Miocene), and (3) foreland (Late Miocene to Early Oligocene).Rifting was synchronous throughout the NE SCS, following an NE-SW structural trend. Syn-rift sedimentation patterns and seismic facies analysis suggest deltaic to marine environments in the proximal domain and a sediment-starved deep marine setting in the distal domain. During post-rift punctual structural reactivation occurred in the Penghu-Peikang and Central highs, controlling paleo-reliefs only flooded during maximum transgressive periods. Shelf-dominated deposition prevailed north of the Central High, while deep marine is observed to its south. This pattern persisted during the foreland stage.The crustal structure of the NE SCS strikingly differs from that of the PRMM. Although PRMM crustal architecture results from widespread crustal boudinage, the narrow necking and sparseness of faulting in the Southern High of the adjacent NE SCS suggest that parts of its crust are showing different initial rheologies. This distinct crustal structure is related to the inherited Mesozoic history of the region: the PRMM Cenozoic history evolved on a magmatic arc, while the NE SCS records not only the remnants of this arc (proximal domain) but also an accretionary prism (Southern Rift System) resultant of the docking of an allochthonous tectonic block (the Southern High) to the south.The Cenozoic sedimentary infilling of PRMM and NE SCS shows an interplay between paleogeography and eustatic variations. The syn-rift sedimentary thickness variations are directly related to the proximity of the sink area with emerged portions of the Eurasia continent, such as in Penghu, Baiyun, and Liwan Basins. Subordinately, the proximity and subaerial exposure of structural highs (e.g., Penghu, Central, and Yunli High) also affected syn-rift sedimentary thickness. During the syn-rift stage, PRMM sediments were predominantly deposited in lacustrine environments, while sedimentation in the NE SCS was fully marine. Post-rift sedimentation is similar in both margins.

Low-angle normal faults (LANFs), characterized by dips of less than 30°, are frequently observed in rifted margins. Despite extensive research, the mechanical processes governing LANFs remain poorly constrained, raising critical questions about the angle at which they initiate, their evolution during extension, their three-dimensional geometry, and related deformation in the hanging-wall and footwall. Addressing these issues is essential for understanding extensional processes in such tectonic settings, including thinning of the continental crust and the exhumation of mantle material in rifted margins.The Err and Bernina extensional detachment systems, within the lower Austroalpine nappes of the Central Alps, offer a rare natural laboratory for studying LANFs. Formed during the Jurassic rifting in the distal Adriatic rifted margin preceding the formation of the Alpine Tethys, these LANFs are exceptionally well-preserved despite the subsequent deformations from the Alpine orogeny.This study presents results from extensive field campaigns conducted between 2022 and 2024, during which high-resolution data were collected over a ~100 km² area using Unmanned Aerial Vehicle (UAV) surveys supplemented by field mapping. Rigorous quality control and processing ensured the generation of 3D high-resolution digital outcrop models (DOMs) of the Err and Bernina extensional detachment systems, implementing differential positioning and SwissTopo terrain data for a resulting spatial error of less than 1 meter. The DOMs provide centimetre to decimetre-scale details that facilitate mapping of the spatial evolution of LANFs and the tectono-sedimentary architecture of the overlying allochthonous blocks. Detailed interpretations reveal their internal structure, including lithological changes, deformation patterns, and fault structures at various scales. Additionally, we characterized the sedimentary basins formed during the Jurassic extension, shedding light on their development and spatial relationships with the detachment systems. Comparison of our findings with seismic data across present-day low-angle normal fault systems bridges the scale-gap between detailed field-based analyses and large-scale seismic interpretations, providing crucial new insights to the evolution of LANFs.

Continental lithosphere extension leads to necking and breakup, forming conjugate rifted margins that vary from symmetric to asymmetric morphologies. Although such differences are commonly linked to variations in initial lithospheric rheology, along-strike transitions between symmetric and asymmetric margins within single rift systems point to additional controlling factors. Structural inheritance, causing mechanical anisotropy in the continental lithosphere, is commonly suggested to influence rift evolution. Here we present novel geodynamic models of lithospheric extension incorporating inherited mechanical anisotropy using a transversely isotropic visco-plastic rheology coupled to the director vector approach. By systematically varying anisotropy strength and initial fabric orientation, we demonstrate that mechanical anisotropy alone can explain the transition from symmetric to asymmetric rifting. In our models, isotropic materials favor symmetric rifting dominated by pure shear deformation, while anisotropic materials promote asymmetric rifting driven primarily by simple shear. This transition occurs at low initial fabric angles and moderate anisotropy strengths. Our results offer a novel and robust mechanism for the formation of both symmetric and asymmetric conjugate margins and suggest that along-strike variations in structural inheritance-and thus mechanical anisotropy-can produce contrasting deformation styles within a single rift system. These findings highlight the critical role of mechanical anisotropy in shaping rifted margins and influencing the tectonic evolution of continental lithosphere.

The Mid-Norwegian volcanic rifted margin and its NE-Greenland conjugate formed in relation to continental breakup in the latest Palaeocene to earliest Eocene during the emplacement of the North Atlantic Igneous Province (NAIP). The development of the NAIP and opening of the North Atlantic occurred contemporaneous to the Paleocene Eocene Thermal Maximum (PETM) which corresponded to a rapid 5-6 °C global warming episode.The cause of this rapid global warming, explored as part of IODP Expedition 396, is thought to relate to the thermogenic gases released to the atmosphere via thousands of hydrothermal vents. The thermogenic gases were produced by contact metamorphism of carbon-rich sediments during widespread sill emplacement from the NAIP. The potential of hydrothermally-released greenhouse gases to influence climate depends strongly on the water depth at which they get released. Unless it is released in a shallow marine environment most methane will be oxidized before it reaches the atmosphere.Early results from IODP Expedition 396 have documented that at least one of the Mid-Norwegian hydrothermal vents was emplaced in shallow marine to potentially sub-aerial conditions. The aim of this contribution is to constrain further the paleo-water depth at which hydrothermal vents formed along the other parts of the mid-Norwegian volcanic rifted margin. This study focuses on an integrated workflow of quantitative geophysical and geodynamic analyses calibrated by new IODP drilling results and structural and stratigraphic observations. We use a 3D flexural-backstripping, decompaction and reverse thermal subsidence modelling to predict the palaeobathymetry and palaeostructure at keys stages of the syn- to post-breakup evolution that can be compared with palaeo-water depths estimated from biostratigraphic data. Results provide new constraints on the paleobathymetry of hydrothermal vent complexes required to confirm whether the global warming recorded by the PETM was triggered by the magma-rich continental breakup leading to the opening of the northeast Atlantic Ocean.

Simulations of accretionary prisms are most of the time realized either using a simplified set up that cannot account for the evolution of temperature with the growth of the prism nor deformable basement or using a very large size simulation of the complete subduction zone using a larger resolution locally. The first method is over-simplified and discards the possibility to study crustal scale accretionary prism, the second method is very costly numerically. Here, we present simulations of accretionary prisms that use 1/ heatflux as boundary condition allowing the temperature at the base of the model to evolve as the accretionary prism grows and 2/ flexural deformation of the basement in response to the growth of the accretionary prism. This new boundary condition is very cheap to compute as we implemented it by solving analytically the flexure equation using sinus decomposition and image method. We then present a set of numerical simulations of crustal scale accretionary prism with particular focus on the geometry of the subducting basement in order to better understand how the alternation between period of subduction erosion and accretion affects the geometry of the accretionary prism and its thermal history as a function of the rigidity of the subducting plate. We compare our simulations with a set of east-west trending seismic profiles located southwest of Taiwan showing along strike structural variations of the accretionary prism.

Marginal Seas are extensional basins formed in a convergent setting near active subduction zones. They are characterized by a short life (

The wide rifting mode that preceded the opening of the South China Sea (SCS) in the Cenozoic generated a set of Paleogene rift basins presently buried under thick post-rift sedimentary infill. Much of the tectonostratigraphic evolution of the South China Sea is now relatively well-constrained (e.g., Pearl River Mouth Basin). However, the SCS's northeasternmost part (i.e., the Tainan margin sensu lato), which might represent the oldest passive margin segment, remains to be integrated into the framework of the rifting and opening of the SCS. This work aims to review and revisit the tectonostratigraphic evolution of the Tainan margin. To do so, an integrative approach has been used combining the analysis of seismic reflection and gravity data. We use 3D gravity inversion to determine the distribution of Moho depth and crustal thickness within this margin segment. The gravity inversion scheme incorporates a lithosphere thermal gravity anomaly correction, which is critically important because of the elevated geothermal gradient within the young oceanic lithosphere of the South China Sea and its continental margins. In the Tainan margin, results show contrasted crustal domains from the continental shelf, to the distal margin and oceanic domain. Only limited crustal thinning is observed over the continental shelf where a succession of rift basins is documented (i.e., Taihsi, Nanjihtao, and Penghu basins) that are part of the Northern Rift System. In contrast, the distal Tainan margin shows greater crustal thinning to less than 10 km thick under an aborted breakup basin, thereby forming the Southern Rift System. To the south, this basin is separated from the unambiguous oceanic domain (6 to 8 km thick) by a comparatively thicker crustal block (~ 10 to 15 km thick). This crustal block forms the Southern High where numerous volcanic edifices and magmatic intrusions are observed or inferred. Half-grabens of the Northern Rift System are controlled by counter-regional faults and filled by Paleocene to Eocene syn-rift sediments. For the distal domain, no well calibration is available. There, we identified several seismic units bounded by regional unconformities. Our results show relatively thin syn-rift sediments locally controlled by a low-angle normal fault system in the Southern Rift System. In contrast, thick post-rift sequences are observed except over the Southern High. Based on our results, we propose a review of structural style and age correlations from the continental shelf to the distal domains of the Tainan margin. To illustrate along-strike variations of the crustal structure and stratigraphic style, we build an array of regional geological cross-sections that are further compared with existing observations in the adjacent Pearl River Mouth Basin.

Rocks at various lithospheric depths commonly display a fabric, resulting in mechanical anisotropy. The mechanical response of such anisotropic rocks depends on both the intensity of the anisotropy and the orientation of the fabric relative to the applied stress. Despite its potential significance, the role of mechanical anisotropy in governing lithospheric strength and deformation style during extension remains poorly constrained. Here, we investigate how mechanical anisotropy influences the deformation of the lithosphere under tectonic extension. We use two-dimensional numerical models of lithospheric deformation that incorporate a non-linear, transversely isotropic model. Both viscous and plastic rheologies are direction-dependent, and fabric orientations evolve using the director-vector approach. We perform simulations of continental extension and show that mechanical anisotropy is a major factor in the development of continental rifts. It influences the architecture of rift basins and reduces the driving force required for rifting. We explore the role of extensional velocity and find that it has only a second-order influence on the evolution of rift systems. Furthermore, we investigate the relative contributions of crustal and mantle anisotropy, and highlight that mantle anisotropy plays a more significant role. The driving forces required for continental rifting are quantified and systematically analyzed. Compared to isotropic models, the required driving force is reduced by up to a factor of three when mechanical anisotropy is included. As a result, forces below 10 TN/m can be achieved, which is consistent with estimates from the geological record. Plain Language Summary Rocks deep in the Earth's outer shell, the lithosphere, often have internal structures (called "fabrics") that make them behave differently depending on the direction of the force applied. This directional behavior, known as mechanical anisotropy, can influence how the Earth's lithosphere stretches during tectonic processes like continental rifting. In this study, we used computer simulations to test how different strengths and directions of rock fabric affect how the lithosphere deforms when pulled apart. We found that these factors can strongly change the way the lithosphere stretches and deforms. Importantly, we discovered that when mechanical anisotropy is included in the models, the amount of force needed to start rifting is much lower, up to three times less, than in models that ignore it. These lower force levels match well with what is observed in nature, helping us better understand how continents break apart over time.

This contribution explores the formation and evolution of hyper-extended basins, associated with the early stage of core complex formation, controlled by low-angle normal faults active at <30 degrees. Based on a high-resolution industrial 3D seismic reflection survey along the southern margin of the South China Sea (SCS) (Dangerous Grounds), we mapped and analyzed the 3D geometry of low-angle normal fault systems and the related stratigraphy. Two main hyper-extended basins were documented, filled by up to 6 km of sediments including pre- to post-rift sequences. The observed normal faults on depth migrated seismic sections show an average dip angle of <30 degrees and appear planar, characterized by continuous reflections with no clear steepening at depth and sole-out on distinct decollement levels. Detailed fault surface mapping reveals the occurrence of km-scale corrugations together with large wavelength undulation. The formation of these hyper-extended basins is associated with polyphased syn-rift infill during the development of the low-angle normal faults. The first syn-rift sequence appears as chaotic and discontinuous packages that has been dismembered and fragmented during the activity of low-angle normal faults. The second syn-rift package shows unexpected sedimentary wedges developing successively toward the footwall and the hangingwall. This geometry results from the interplay between the main low-angle normal fault and antithetic faults defining a so-called extensional fishtail. The deep structure of these basins shows nascent domes with limited evidence of magmatism. Eventually, these basins likely capture the earliest stage of core complex development in the proximal margin of the southern SCS.

Crustal geometries imaged at rifted margins show contrasted first-order morphologies (wide and narrow, symmetric or asymmetric conjugates). This contribution aims to review the mechanisms of continental lithospheric thinning and types of extensional structures that control the formation of rifted margins. We illustrate, using a two-layer numerical model (one for the crust and one for the mantle), how different modes of lithospheric thinning shape the end-member crustal geometries of rifted margins depending on the initial thermal conditions and extension rates. As already known, the activation of narrow or wide modes of lithospheric thinning depends on the rheological behaviour of the lower crust and its efficiency as a decoupling layer. Morphologies generated by narrow lithospheric thinning modes compare well with Atlantic-type rifted margins (e.g., Iberia–Newfoundland) while wide lithospheric thinning modes better apply to marginal seas characterized by higher initial geothermal gradients (e.g., South China Sea). Finally, we also emphasize that continental lithosphere thinning is depth-dependent, part of which is transient and cannot easily be measured in natural systems.

We investigate the crustal structure of the Northeastern (NE) South China Sea (SCS) rifted margin to constrain its crustal thickness and basement nature with implications for the Mesozoic and Cenozoic evolution of the SCS. First-order interfaces interpreted from seismic reflection data were integrated into a 3D gravity inversion scheme to determine Moho depth and crustal thickness variations. A joint inversion of seismic and gravity data allowed us to determine crustal density variations along 2D profiles. The distal margin of the NE SCS is divided into two distinct crustal domains: the Southern Rift System (SRS), and the Southern High (SH). The SRS shows an extremely thinned crust on top of which thick Cenozoic sequences are observed. It is separated from the oceanic crust (similar to 6-8 km thick) by the SH, a comparatively thicker crustal domain (similar to 10-15 km thick) with significant magmatic additions. The distal NE SCS margin formed during the Cenozoic rifting of the SCS. The SH likely corresponds to a polygenic piece of crust, recording polyphase magmatic activity since the Mesozoic, with potentially significant activity during Cenozoic post-rift time. The NE SCS margin is conjugate to Palawan whose basement is considered to be part of the exotic Luconia microcontinent that collided with Eurasia during the Late Cretaceous. Basement similarities between Palawan and the SH are highlighted, suggesting that the latter might also be part of Luconia. Our results suggest that the docking/suture zone between Eurasia and Luconia might have acted as a preferred zone for the Cenozoic rift development.

Many of the world's rifts and rifted margins have developed within former orogens. The South China Sea (SCS) formed during Cenozoic rifting by utilizing pre-existing orogenic structures, like thrust faults, thickened crust, and corresponding thermal weaknesses. The mechanisms explaining how inherited structures influence the spatiotemporal evolution of a rift remain a topic of on-going research. Here, we explore the impact of orogenic inheritance on rift evolution through a numerical forward model that reproduces geodynamic and landscape evolution processes. By imposing time-dependent phases of shortening and extension, we model rifted margin formation that is consistent with the available geological and geophysical observations of the SCS. Our numerical models allow us to identify thrust faults that are reactivated as normal faults during extensional phases. Not all pre-existing thrust faults, however, undergo full reactivation, as their behavior is influenced by variations in lithospheric strength and the pre-existing structural discontinuities. We further show that inherited orogenic structures compete with each other during extensional reactivation and ultimately govern the location of continental breakup. Our results provide valuable insights into the broader implications of inherited orogenic structures and how they affect subsequent rift system evolution.

SUMMARY In this paper, we use a new workflow to substantiate the characterization of a prominent, deep sediment conductor in the hyperextended Bjørnøya Basin (SW Barents Sea) previously identified in smooth resistivity models from 3-D deterministic inversion of magnetotelluric data. In low-dimensionality environments like layered sedimentary basin, 1-D Bayesian inversion can be advantageous for a thorough exploration of the solution space, but the violation of the 1-D assumption has to be efficiently handled. The primary geological objectives of this work is therefore preceded by a secondary task: the application of a new machine learning approach for handling the 1-D violation assumption for 21 MT field stations in the Barents Sea. We find that a decision tree can adequately learn the relationship between MT dimensionality parameters and the 1-D–3-D residual response for a training set of synthetic models, mimicking typical resistivity structures of the SW Barents Sea. The machine learning model is then used to predict the dimensionality compensation error for MT signal periods ranging of 1–3000 s for 21 receivers located over the Bjørnøya Basin and Veslemøy High. After running 1-D Bayesian inversion, we generated a posterior resistivity distribution for an ensemble of 6000 1-D models fitting the compensated MT data for each 21 field stations. The proportion of 1-D models showing ρ < 1 Ω·m is consistently beyond 80 per cent and systemically reaches a maximum of 100 per cent in the Early Aptian–Albian interval in the Bjørnøya Basin. In hyperextended basins of the SW Barents Sea, the dimensionality compensation workflow has permitted to refine the characterization of the deep basin conductor by leveraging the increased vertical resolution and optimal used of MT data. In comparison, the smooth 3-D deterministic models only poorly constrained depth and lateral extent of the basin anomaly. The highest probability of finding ρ < 1 Ω·m is robustly assigned to the syn-tectonic Early Aptian–Albian marine shales, now buried at 6–8 km depth. Based on a theoretical two phase fluid-rock model, we show that the pore fluid of these marine shales must have a higher salinity than seawater to explain the anomaly ρ < 1 Ω·m. Therefore, the primary pore fluid underwent mixing with a secondary brine during rifting. Using analogue rift systems in palaeomargins, we argue that two possible secondary brine reservoir may contribute to deep saline fluid circulation in the hyperextended basin: (1) Permian salt-derived fluid and, (2) mantle-reacted fluid from serpentinization.

Three boreholes drilled during the International Ocean Discovery Program (IODP) Expedition 396 have yielded unexpected findings of altered granitic rocks covered by basalt flows, interbedded sediments and glacial mud near the continent-ocean transition of the mid-Norwegian margin. U-Pb and K-Ar geochronological analyses were conducted on both protolithic and authigenically formed K-bearing minerals to determine the age of granite crystallisation and subsequent alteration episodes. The granite's crystallisation age based on 104 zircons is 56.3 +/- 0.2 Ma, and subsequent exhumation along with alteration/weathering events took place between 54.7 +/- 1 and 37.1 +/- 1 Ma. This intrusion represents the youngest granite discovered in Norway and intruded at an extremely shallow crustal level before a rapid rift-to-drift transition. The shallow emplacement of granitic rock and its fast exhumation before and during the onset of volcanism holds significant implications for the syn- and post-breakup tectonic evolution of volcanic margins.

Microscopic images of discrete samples were acquired using a scanning electron microscope (SEM) and captured as image files. These files were uploaded along with a brief description and a record of the microscopic conditions when the image was taken.

Figure F1.Multichannel Seismic Profile HV-7-96