To address the lack of high-resolution gravity constraints on the deep structure of the northern Antarctic Peninsula trench-arc-basin system, this study integrates shipborne gravity data from Chinese Antarctic Research Expeditions (CHINARE) and publicly available cruises, and multi-source satellite gravity models (DTU21, SIO V32.1, EGM2008) to construct a fused gravity field. A 7-level discrete wavelet transform was applied, using a Low-Ship strategy (weighted low-frequency fusion, shipborne high frequencies). Results indicate that the V32.1 scheme achieves optimal accuracy with shipborne and satellite RMSE of 0.77 and 2.35 mGal, respectively; the DTU21 scheme performs comparably. Power spectral density analysis confirms incorporation of shipborne short-wavelength details while preserving satellite background field. Constrained by Moho depth fitting and isostatic residual gravity minimization with CRUST1.0 as reference, flexural isostatic inversion yields an effective elastic thickness of 5 km and average compensation depth of 25.0 km, with anomalies ranging from −70 to 130 mGal. Compared with Airy isostasy, the flexural model suppresses shallow topographic disturbances through mechanical filtering, characterizing the deep isostatic state. The anomaly pattern is controlled by the Hero Fracture Zone–trench–island arc–back-arc basin framework. Along the Hero Fracture Zone, a positive anomaly belt indicates lithospheric flexural upwarping and Moho uplift driven by left-lateral strike-slip and extension. The strong negative anomaly at the South Shetland Trench (~ − 60 mGal) reflects residual subduction drag following subduction cessation. The positive anomaly at the South Shetland Islands (~120 mGal) corresponds to magmatic intrusions within the arc crust. The NE–SW-oriented anomaly gradient in the Bransfield Basin indicates along-strike segmentation of back-arc extension. These features are corroborated by the SL2013sv shear-wave velocity model, in which a mantle velocity reversal beneath the Former Phoenix Plate provides evidence for thermal anomalies. This study elucidates the isostatic response mechanism of the trench-arc-basin system, providing high-precision gravity constraints for Antarctic plate margin evolution and deep geodynamics.
When aseismic ridges carried by the subducting oceanic plate enter a subduction zone, they reduce the trench depth and hence the relief of the convergent margin. The trench shallowing increases the deviatoric compression of the upper plate. While the increase in compression can be expected to promote mountain building and surface uplift, these effects have never been quantified. Here we use analytical and two-dimensional finite-element force-balance models to investigate the effects of trench shallowing and evaluate the influence of the initial trench depth, the megathrust dip angle, the slab curvature, the submarine surface slope angle, the density structure of the upper plate, the initial mountain height and the surface topography of the upper plate. Our modelling results indicate that the increase in deviatoric compression mainly depends on the total relief change, the trench depth prior to ridge subduction and the submarine surface slope angle during ridge subduction, with secondary influences from the mountain height and curvature of the plate interface, as well as the average dip angle and the density structure of the upper plate prior to subduction. Additional finite-element models with setups adjusted to the Kamchatka and Central American margins indicate that the surface uplift induced by trench shallowing accounts for nearly all of the maximum uplift in Kamchatka and approximately one-third in Central America. The remaining elevation increase in Central America may indicate passive uplift above the subducting ridge and an increase in shear stress along the plate interface.
The shallow megathrust (<15 km) at the northern Hikurangi margin hosts tsunami earthquakes and slow slip events (SSEs), which are proposed to be influenced by pelagic carbonates, high fluid pressure, and stress perturbations associated with seamount subduction. To constrain the rheologic and hydrologic structure of the plate boundary, we measured the strength, healing, and permeability of carbonates from IODP Expedition 375 Site U1520C. Experiments were performed on marl (34% clay) and chalk (2% clay) at effective pressures of 21 and 70 MPa and temperatures of 25 and 75 °C, representing in-situ conditions around the subducting Pāpaku Seamount. We conducted constant displacement rate and long-duration (102−106 s) slide-hold-slide experiments, along with flow-through permeability tests before and after a subset of these at 8 and 70 MPa effective pressure. Results show that marl permeability is 1–2 orders of magnitude lower (∼10−19−10−21 m2) than chalk (∼10−16−10−20 m2). In contrast to chalk, the permeability of marl is more sensitive to changes in effective pressure but less sensitive to shear strain. Because marl overlies chalk, its low permeability may maintain high fluid pressures thought to correlate with SSEs. Higher clay content also corresponds to higher strength under lower effective pressure and elevated temperature conditions, suggesting strain localization into chalk. We attribute this to the inhibition of both mechanical compaction and chemical weakening with increasing clay content. We found a lack of Dieterich-type healing in both lithologies, consistent with the low stress-drops of SSEs.
Here, we present new measurements of uppermost mantle Pn velocities across the Mendocino Fracture Zone (MFZ), eastern Pacific Ocean, derived from travel times of 19 regional earthquakes of magnitude from 2.4 to 5.4 recorded by hydroacoustic channels of 13 ocean-bottom electromagnetic instruments deployed in 2017. The MFZ offsets oceanic lithosphere of contrasting ages (8–33 Ma), providing a good setting to examine how lithospheric age, thermal structure, and seismic anisotropy influence Pn velocities. A total of 217 Pn arrivals were analyzed and corrected for the effect of azimuthal anisotropy using the empirical Pn velocity variation previously reported. The corrected Pn velocities range from 7.6 to 8.15 km/s and increase systematically with lithospheric age and decreasing path-averaged Moho temperature. Thermal modeling based on half-space cooling predicts an apparent velocity-temperature sensitivity of ~0.45 km/s per 100 °C, very similar to earlier estimations obtained from continental uppermost mantle peridotites, indicates that lithospheric cooling exerts a dominant control on uppermost mantle Pn velocities. Although directional variations in Pn velocities suggest a secondary contribution from seismic anisotropy associated with transform-parallel shear, limited azimuthal coverage restrain an independent anisotropic inversion. To our knowledge, this study provides the most extensive compilation to date of Pn velocity measurements and lithospheric age exclusively across oceanic transform faults (OTFs) and fracture zones (FZs). Comparisons of the MFZ results with previous Pn velocity measurements from other 12 OTFs or FZs in the Pacific (Blanco, Gofar, Quebrada, and Clipperton) and Atlantic (Chain, St. Paul, Romanche, Vema, Kane, Oceanographer, Charlie-Gibbs, and Black Spur) reveals a coherent increase in Pn velocity with lithospheric age across different slipping rates. Together, these results demonstrate that lithospheric cooling is the first-order control on uppermost mantle Pn velocities beneath OTFs and FZs, while anisotropy and local tectonic processes contribute to secondary effects.
The tectono-sedimentary evolution of the French of the Upper Rhine Graben (URG) has been investigated through a detailed basin analysis including a revision of the stratigraphy, sedimentology, subsidence distribution and structural network during rifting. The relationship with its western margin (Vosges) is examined through the history of its uplift, as defined by low temperature thermochronology. Five time thickness, structural and Source to Sink (S2S) maps detail the tectono-sedimentary evolution during rifting, including 1) the generation of isolated subsiding basins during the Lutetian to Bartonian and 2) the widening of the rift from the Bartonian to Rupelian to reach its present-day spatial extension. During rift growth, the fault pattern (N010-N020, and N040 to N070) and the thickness distribution highlighted limited change, indicating the development of an oblique rift under a broadly continuous stress regime. A new thermal history of the Vosges Massif is proposed, comprised of 1) a complex pre-rift history with two periods of cooling, (150 to 110 Ma) and (100 to 70 Ma), and 2) a syn-rift local uplift of rift shoulders around 40 Ma, followed by northward tilting associated with the Alpine collision (20 Ma). We tentatively relate the Late Cretaceous thermal event in the URG to the development of a large volcanic province, and possibly to a finger of NNE-ward flowing hot asthenospheric mantle. This episode might have influenced the rift location. We propose that the onset of rifting (around 40 Ma) was also related to the transmission of far-field stresses, particularly during the initiation of the European Continental Rift System, and that rifting developed over crustal anomalies related to mantle flow before rifting.
Stress is a key parameter in metamorphic reactions that is difficult to quantify and therefore its role remains a topic of intense debate. To determine the distribution of residual stress during plagioclase breakdown at high-pressure, fluid-present conditions we performed high-angular resolution electron backscatter diffraction (HR-EBSD). These analyses targeted plagioclase adjacent to grain boundaries that contain the initial reaction products of eclogitization. The samples are partially eclogitized granulites from the lower-crustal section exposed on Holsnøy, western Norway. Measurements of residual stress are supplemented by imaging of dislocations by (scanning) transmission electron microscopy and determining compositional variations by scanning electron microscope and electron probe micro analyzer. The results reveal intragrain residual stress heterogeneities in plagioclase on the order of hundreds of megapascals, dominantly caused by the elastic interaction between dislocations with a significant contribution of the developing chemical zonation during the reaction. In the example with less reaction progress, dislocations are scattered, whereas they are parallel to one another and more frequent in Ca-poorer section of the plagioclase. These observations are interpreted to indicate reorganization of dislocations with reaction progress. Dislocation configurations are modified during CaAl-NaSi interdiffusion in plagioclase, which occurs in response to the replacement reaction that forms clinozoisite. This demonstrates that compositional variations in plagioclase during ongoing reactions directly impact the residual stress distribution. Our results suggest that metamorphic reactions may cause significant grain-scale stress heterogeneity which is transient during ongoing reactions.
The Val d'Agri region (Southern Italy) hosts high-rate, diffuse seismicity, that has been attributed to the complex interplay of tectonic and anthropogenic processes. In this work we apply waveform similarity-based clustering, earthquake relocation, and moment tensor inversion to a newly developed high-resolution microseismic catalog. This combined approach allows us to image the geometry of active seismogenic structures and characterize their faulting style. Waveform similarity-based clustering identifies groups of earthquakes having highly similar waveforms, interpreted as likely associated with the same seismogenic structures. High-quality relocation of these events allows the delineation of planar features, suggestive of fault segments.The analysis of the largest events (M > 2) by moment tensor inversion provides constraints on the prevailing faulting style. Our results indicate that the seismicity in the analyzed time period predominantly occurs along steeply southwest-dipping seismogenic structures, with moment tensor solutions consistent with the regional extensional stress regime. We further analyze a seismic sequence occurred during the study timespan to investigate its spatio-temporal evolution and possible controlling processes. We explore scenario-based rupture models for the largest imaged structure using finite-fault ground-motion simulations, providing first-order physics-based constraints on potential ground-motion variability.
The volcano-tectonic history of the Danakil Depression represents the complete succession of rifting processes, spanning from incipient crustal rupture to the onset of sea-floor spreading. The Erta'Ale Volcanic Range (EVR), located in the central part of the Danakil Depression, is a subaerial segment of nascent oceanic crust and hosts well-exposed magmatic and tectonic features. In this study, we investigate the tectonic processes shaping rift-floor structures and the development of magmatic sill-induced domes within the volcanic range, using field observations, satellite image interpretations, digital elevation model (DEM) analysis, structural analysis, geophysical (seismic profile) interpretation, and borehole data analyses. The integrated results indicate that a variety of surface and sub-surface volcano-tectonic processes are very active within the thin crust of the Danakil Depression. Magmatic intrusions and/or sills are emplaced at the interface between thick evaporite deposits, specifically at the boundary between upper and lower rock salt units. These intrusions uplift the upper halite layers by ∼130 m, forming well-defined domes. Further analysis of the western sector of the volcanic range shows that large off-axis volcano-tectonic structures, including sill-induced domes, collapse calderas, and shield volcanoes, are linearly distributed exclusively along the western side of the rift floor, coincident with inherited structural weaknesses, and interpreted here as paleo-rift axes. Thus, our results demonstrate that the western side of the rift floor is more intensely faulted and intruded by magmatic bodies, resulting in a more fractured and more porous crust compared to its eastern counterpart.
Drainage captures have been studied to reconstruct former landscape conditions and subsequent modifications. Many study cases focus on drainage captures that produce evident or significant landscape changes. However, drainage captures may also occur as a series of small–scale or localized events with subtle expression and limited effects on the landscape. This latter scenario suggests that river network connectivity records one or multiple episodes of uplift and rainfall regime variations interacting with lithological arrangements. Here, we examined the Main Gulf Escarpment (MGE) on the Baja California Peninsula (Mexico) where the most recent phase of uplift enhancement has generated landscape avulsion, which influenced the deviation and reconnection of river networks by local drainage captures. We identified river junctions that may correspond to local drainage captures, which were used to divide fluvial networks into downstream and upstream segments. These subsets were compared and showed contrasting channel morphometries, supporting distinct landscape evolution histories from previous fluvial separation. Thus, the results obtained from the MGE demonstrate that a punctual uplift enhancement promoted a series of local drainage captures that changed river network connectivity.
The Timok Magmatic Complex (TMC), part of the Late Cretaceous Apuseni–Banat–Timok–Srednogorie (ABTS) volcano-sedimentary belt in the Carpatho-Balkanides, represents a case study of a basin developed within the overriding plate above two adjacent subduction systems of opposite polarity, the NE-dipping Neotethys and the W-dipping Ceahlău–Severin. This study reconstructs the tectonic evolution of the TMC basin through field-based structural and kinematic analyses to constrain the mechanisms controlling deformation in a multi-slab setting. The results define three successive deformation phases. The oldest phase records Late Cretaceous extension and asymmetric basin formation, characterized by strong strain localization along upper-crustal normal faults. This phase was controlled by rollback of the Neotethyan slab, enabling efficient transfer of deformation into the upper crust and direct coupling between active faulting and calc-alkaline magmatism. The subsequent phase corresponds to the latest Cretaceous–earliest Paleogene basin inversion, expressed by a progressive transition from contractional to transpressional deformation. This stage was controlled by the closure of the Ceahlău–Severin Ocean and the onset of Carpathian collision, with shortening localized along inherited extensional basin structures. The youngest phase reflects Oligocene–Middle Miocene post-orogenic deformation. It is characterized by strain partitioning and strike-slip faulting related to oroclinal bending of the Carpatho-Balkanides, which controlled segmentation and sedimentary reorganization of the TMC basin and the broader ABTS belt.
