Poster session
For this reason, constraints on brittle and ductile strain localisation and on their precise age of activation are increasingly relevant. This acquires a higher importance by looking at the architecture and mechanics of extensional detachments, where through-time superposed domains with different mineralogy and, thus, petrophysical properties, dramatically change the mechanical response of shear- and fault zones during progressive deformation. Coexisting or partitioned seismic vs. aseismic deformation, as well as repeated cycles of shear zone weakening/hardening and syn-tectonic fluid flow and fluid-rock interactions, might be governed by this through-time (and still partially underinvestigated) structural complexities.
- What guides this different deformation response of shear and fault zones?
- What allows the initiation and evolution of detachment zones, should they be continental or oceanic, and which processes act coevally or diachronously?
- What is the link between detachment formation and hydrothermal activity?
- What is the role of tectonic or thermal inheritance in the formation of LANFs and detachments?
All contributions fostering discussions on these points are welcome in this session, including comparisons between continental and oceanic systems. We encourage the submission of research based on a multidisciplinary and multiscale approach, encompassing, among others, field analysis, seismic and other geophysical investigations, numerical and laboratory modelling and absolute dating and petrological constraints of syn-kinematic fabrics and mineralisation.
The thermal, physical, and chemical processes of detachment faults profoundly influence the dynamics of continental lithosphere far beyond the fault zones. The conditions and timing of deformation in detachment fault zones are therefore important to investigate in order to evaluate how these faults are dynamically linked to tectonic processes over a wide range of spatial scales, laterally and vertically.
Detachments are exhuming structures in which the amount of exhumation accommodated by a particular fault ranges from a few to tens of kilometers. This magnitude depends primarily on the total extension, its spatial distribution/localization, and the buoyancy of the exhumed crust. Exhumation-related deformation is accompanied by (hydro)thermal processes that may be recorded in the composition and zoning of minerals such as quartz and micas, particularly in lithologies such as quartzites that may preserve a diachronous record of deformation in incompletely-overprinted domains. These minerals provide pressure-temperature-time-deformation information, as well as serving as geochemical tracers of syn-tectonic fluid-rock interaction. Excellent examples are the detachment-footwall quartzites of metamorphic core complexes (mcc) in the North American Cordillera. Results of integrated microstructure, thermobarometry, geochemistry, and thermochronology studies track the conditions and timing of deformation during exhumation and cooling. In cases of detachment faults bounding exhumed deep crust, footwall rocks display a sharp metamorphic gradient caused by a combination of thinning and shearing. Metamorphic conditions and paths may reflect exhumation trajectories rather than maximum temperature/depth; this is supported by numerical models that predict that rocks from similar pre-extension depths can be exhumed during extension to create an apparent progressive metamorphic sequence from detachment faults into mcc footwalls.
Integrated studies from nature and numerical experiments also give insights at a larger scale, indicating that regions of thickened continental crust flow towards regions of thinner crust, driving contraction in the latter. Formation of detachment faults may be driven actively by extension of the lithosphere and/or by gravitational crustal flow away from the orogenic core and towards the foreland, where coeval thrusting may occur. In this case also, pressure-temperature-time-deformation studies coupled with geochemistry provide insights into the mechanisms, conditions, and timing/rates of mass redistribution in orogens. The significance of this phenomenon is indicated by the prevalence in orogens of coeval domains of extension (detachment faulting / metamorphic core complexes) and contraction (fold-and-thrust belts).
How to cite: Whitney, D., Teyssier, C., and Rey, P.: How detachments connect shallow and deep crust during mass redistribution in orogens, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10064, https://doi.org/10.5194/egusphere-egu26-10064, 2026.
Understanding how continental rifts propagate requires resolving the interactions between tectonic and geodynamic processes operating over different timescales. The Corinth Rift in southern Greece provides a natural laboratory in which active subduction, back-arc extension, and inherited crustal structures interact within a rapidly evolving continental rift system. The rift architecture is characterized by shallow-dipping low-angle normal faults (LANFs), such as the Chelmos Fault, in the south, and a series of high-angle normal faults (HANFs) that developed in the hanging walls of the LANFs toward the north. Stratigraphic and volcanic records suggest two main rifting phases: an early phase between ~5.0 and ~2.0 Ma and a younger phase from ~2.0 Ma to the present. However, the timing and propagation of fault development remain poorly constrained due to the lack of direct tectonic and exhumation data from carbonate rocks. Here, we apply low-temperature carbonate thermochronology to footwall samples from major faults to quantitatively constrain tectonic exhumation across the Corinth Rift. Our preliminary results suggest that rifting initiated during the Early Pliocene with activity along low-angle detachments and subsequently migrated northward to distributed high-angle normal faulting since the Early Pleistocene. Consistent with stratigraphic and volcanic constraints, our data support a two-stage rift evolution and provide independent constraints on the timing and spatial propagation of faulting. More broadly, this study demonstrates the potential of carbonate thermochronology as a quantitative tool for constraining tectonic exhumation in carbonate-dominated rift systems worldwide.
How to cite: Arriga, G., Rossetti, F., Fellin, M. G., Crosetto, S., Ballato, P., Zhang, J., Tsukamoto, S., and Faccenna, C.: Tectonic exhumation of the Corinth Rift (Greece): preliminary results from low-temperature carbonate luminescence thermochronology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7952, https://doi.org/10.5194/egusphere-egu26-7952, 2026.
Oceanic core complexes (OCCs) are key features of the oceanic crust, yet their geometry and formation remain poorly constrained as the oceanic crust is largely submerged. While the Troodos Ophiolite is one of the most well-preserved ophiolites in the world, the tectonic origin of the Southern Troodos Fault Zone (STFZ) remains contested, with interpretations suggesting either a leaky transform fault zone or an OCC setting. This study investigates the kinematics and structure of the tectonic contacts surrounding the Akapnou Forest Complex (AFC) in the STFZ by field mapping and drone photogrammetric models. Fieldwork reveals that domed mantle material, interpreted as an OCC, is bounded by a high-angle serpentinite shear zone (HASSZ), interpreted as the segment end of a mid-oceanic ridge, and multiple low-angle serpentinite shear zones (LASSZs), interpreted as detachment faults. The LASSZs have a consistent top-to-WNW movement. Three distinct LASSZs were identified, suggesting the detachment system evolved through multiple stages. Initial detachment localized along the ultramafic cumulates that subsequently isostatically folded, causing the detachment to step up to a shallower rheological horizon through the sheeted dike-gabbro transition. This younger detachment underwent multiple locking events, creating rafted blocks of the hanging wall. Laterally, fault locking may have varied. Lower friction closer to the segment end allowed for continuous slip, facilitating mantle exhumation to the surface. We conclude that the AFC represents a fossil OCC, and the derived conceptual model provides key insights into the multi-stage dynamics of mantle exhumation along sequentially localized detachment zones.
How to cite: Jeijsman, M., Hegeman, P., Wessels, R., Symeou, V., and Beniest, A.: Multi-stage detachment localization and evolution of the Akapnou Forest Oceanic Core Complex, Troodos Ophiolite, Cyprus, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-596, https://doi.org/10.5194/egusphere-egu26-596, 2026.
The Western Anatolia–Aegean region is characterized by active extension and well-documented seismicity. Yet the relationships among fault geometries, the depth distribution of earthquakes, and crustal strain patterns remain poorly understood. In particular, the existence of two outward-dipping low-angle normal faults in the central Menderes Massif poses a challenge to current geodynamic and seismological interpretations. In this study, we investigate the evolution of low-angle ductile–brittle shear zones using high-resolution viscoplastic thermo-mechanical forward models. Employing the finite-element code ASPECT, we simulate the initiation and development of shear zones in extensional settings, explicitly coupling surface processes and syn-extensional sedimentation to assess how progressive sediment loading may influence fault evolution. The model domain spans 500 km in width and 150 km in depth, and we explore two sets of models that vary in extension velocity and crustal layering. Our results show that shear zones initiate as high-angle (50°–55°) structures and progressively rotate to lower angles (30°–35°) as deformation localizes, suggesting that low-angle fault geometries may arise through time-dependent processes rather than pre-existing configurations. The models further indicate that the brittle–ductile transition extends into the upper portions of the lower crust, consistent with observed seismicity depths of 20–25 km beneath the Gediz Graben. By integrating model predictions with regional seismicity patterns, this work provides new constraints on the mechanical stratification and fault-system evolution of extended terranes, offering improved insight into active faulting and the characterization of seismogenic zones.
How to cite: Çavdar, E. N., Göğüş, O. H., Brune, S., and Bodur, Ö.: Understanding crustal strain and seismicity in normal faults and shear zones, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-986, https://doi.org/10.5194/egusphere-egu26-986, 2026.
Large-magnitude earthquakes capable of rupturing to the surface have rarely occurred along detachment faults or low-angle normal faults (LANFs), leaving their seismic potential and related co-seismic damage poorly constrained. Here we document the presence of pulverized rocks formed during final slip stages of the Miocene Waterman Hills detachment (Mojave extensional belt, California).
The Waterman Hills detachment accommodated ~40-50 km of top-to-NE extension and juxtaposes syn-extensional Miocene volcanic and sedimentary sequences onto syn-extensional granodiorites intruded into amphibolite-facies meta-sedimentary and meta-igneous rocks. Early bivergent doming of the metamorphic core complex initiated at amphibolite-facies conditions and localized into NE-dipping mylonites in the greenschist facies, coevally with intrusion and stretching of the granodioritic pluton at ~7-10 km depths. Progressive strain localization led to greenschist-facies mylonitic and ultramylonitic horizons that were overprinted by brittle faulting. The latter includes: (i) gently-dipping (≤30°) anastomosing foliated cataclasites and breccias cemented by chlorite + quartz + epidote ± calcite ± albite, crosscut by (ii) pseudotachylytes and tourmaline-cemented ultracataclasites and fault surfaces, crosscut by (iii) steeply-dipping (>60°) calcite-hematite-cemented faults and veins. The tourmaline- and calcite-cemented faults crosscut both the footwall and hanging wall rocks, pinning the current juxtaposition during final stages of the detachment slip.
Patchy meter-thick lenses of pulverized siliceous rocks are found in the uppermost ~11 m of the footwall damage zone and show very little evidence of post-pulverization displacement. Pulverization occurred at the latest, shallowest stage of detachment faulting, only in the stiffest, fine-grained siliceous footwall lithologies, consistent with the inference that co-seismic tensile stress perturbation due to propagating seismic ruptures caused rock pulverization. The pulverized rocks recorded repeated events of extensional fracturing and healing.
We interpret these pulverized rocks to have recorded the cumulative effects of multiple MW 5-6 earthquakes propagating to depths ≤ 2 km, in agreement with experimental constraints on dynamic rock pulverization. Our discovery represents the first documentation of dynamic off-fault damage in the footwall of a LANF and demonstrates that shallow portions of LANFs can locally experience co-seismic stress conditions sufficient to induce pulverization, despite their unfavorable orientation for slip.
How to cite: Masoch, S. and Rowe, C.: Co-seismic selective rock pulverization in the footwall of a Miocene low-angle normal fault, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8084, https://doi.org/10.5194/egusphere-egu26-8084, 2026.
Paleo-seismic indicators, such as pseudotachylytes and ultracataclasites, provide direct insight into the weakening mechanisms that promote deformation along shear zones during the co- and interseismic cycles. These structures are particularly relevant along low-angle normal faults, where the fault geometry necessitates efficient weakening mechanisms to enable seismic slip. The Okanagan Valley Shear Zone (OVSZ) is a crustal-scale low-angle normal fault that facilitated Eocene exhumation of the Shuswap metamorphic core complex, the largest core complex in North America. Although previous work has reported the presence of pseudotachylyte veins along the detachment, their origin and significance have yet to be investigated. We conducted fieldwork at a central exposure of the OVSZ footwall in the southern Okanagan Valley (British Columbia, Canada), where amphibolite and quartzofeldspathic gneisses display a strong WNW-trending stretching lineation and S-C and S-C-C' fabrics indicating top-to-W kinematics. Apparent pseudotachylyte veins hosted within the gneiss were identified and sampled for 2D microstructural and geochemical characterization. These analyses provide the foundation for evaluating the deformation mechanisms governing strain localization along the OVSZ. In outcrop, the "pseudotachylytes" occur as thick (5 mm–16 cm), laterally continuous layers of black, glassy material that are sub-parallel to the host-rock foliation (~069/14) and lack offshoot injection veins or vein networks typical of pseudotachylytes. Preliminary scanning electron microscopy (SEM) imaging and energy-dispersive spectroscopy (EDS) of the veins reveal an ultra-fine-grained matrix (<0.5µm–5µm) primarily composed of anhedral biotite (~65%), quartz (~22%), and plagioclase (~13%) grains, with curved to irregular grain boundaries. The vein matrix exhibits a strong foliation defined by aligned biotite grains. This foliation wraps around heavily rounded, equant to elongated host-rock porphyroclasts (30 µm–2.2 mm) of plagioclase and quartz, with minor apatite and monazite. Many plagioclase porphyroclasts display δ- and σ-type mantles that record a top-to-the-west sense of shear. Bands of dynamically recrystallized quartz (grain diameters of <10–120 µm; band widths of 45–220 µm) commonly form quarter fold structures around feldspar porphyroclasts. Contacts between the veins and host rock range from sharp boundaries, locally marked by recrystallized quartz bands (up to 0.74 mm), to transitional zones characterized by progressive grain-size reduction from ~1.8 mm to ~2 µm toward the vein boundary. Collectively, these preliminary microstructural observations are more consistent with ultramylonitic layers produced by intense localized ductile deformation than with frictional melts. These results suggest that slip along low-angle normal faults may involve limited frictional heating and instead be accommodated predominantly by solid-state processes, producing seismic indicators that differ from classical pseudotachylyte structures associated with steeper faults.
How to cite: Rolfe, O. and Dubosq, R.: Friction or fiction: seismic indicators along the Okanagan Valley Shear Zone (Western Canada), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8477, https://doi.org/10.5194/egusphere-egu26-8477, 2026.
Over the past decade, high-quality industrial 3D seismic surveys acquired along both the northern (Lei et al., 2018; Zhang et al., 2020) and southern (Legeay et al., 2024) rifted margins of the South China Sea (SCS) have imaged and documented the development of low-angle normal faults (<30°) locally accommodating the formation of metamorphic core complexes. Such structures had previously been recognized only in field analogues, such as the Aegean region or the Basin and Range Province. In this contribution, we present new high-resolution 3D seismic data that enable us to map, observe, and characterize the tectono-sedimentary evolution of hyper-extended rift basins associated with crustal thinning and deformation.
The SCS exhibits a wide rift domain characterized by large-scale crustal boudinage, expressed as a series of hyper-extended basins separated by basement highs. Rifting in the SCS initiated during the early Cenozoic and evolved with a NE–SW-oriented oceanic propagation between 32 and 16 Ma. This extensional event overprinted a pre-existing Andean-type orogenic system, defined by a Mesozoic magmatic arc extending from Borneo to Korea above the west-dipping Pacific subduction zone. A major tectonic reorganization occurred during the Late Cretaceous following the collision of the Luconia block with the active Eurasian margin. This pre-rift configuration resulted in a highly heterogeneous basement composition, including remnants of the magmatic arc, the Luconia block, and intervening thrust wedges.
Our observations across several hyper-extended rift basins from both the northern and southern SCS margins highlight the three-dimensional geometry of low-angle fault systems characterized by corrugated and domal morphologies. The hanging walls are composed of extensional allochthonous blocks consisting of pre-rift sediments and basement rocks, while the syn-rift infill is organized into alternating wedges bounded by antithetic faults relative to the main low-angle detachment systems.
At depth, the footwalls display shallow-dipping seismic reflections interpreted as reactivated thrust wedges that likely facilitated the development of low-angle extensional structures.
The exhumation of deeper crustal levels is spatially correlated with zones of maximum displacement along the normal faults, which locally exhibit domal geometries and evidence for sheath folding.
How to cite: Ringenbach, J.-C. R. and Mohn, G.: 3D Seismic observations into the Development of Extensional Low-Angle Normal Faults and Metamorphic Core Complexes: South China Sea, Malaysia , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3541, https://doi.org/10.5194/egusphere-egu26-3541, 2026.
The classical two end-member classification of continental rifting (magma-rich vs. magma-poor) fails to explain the atypical thermo-mechanical conditions of the Qiongdongnan Basin (QDNB), located southeast of Hainan Island along the northern margin of the South China Sea. The basin is surrounded by Late Cenozoic magmatism commonly linked to deep-seated mantle upwelling associated with the putative Hainan mantle plume. The QDNB exhibits pronounced west–east variations in deformation style, reflecting strong spatial heterogeneity in lithospheric strength. These characteristics suggest that time-dependent mantle-lithosphere interactions played a critical role in controlling rift evolution.
Integrated analyses of multiple seismic profiles reveal strong along-strike contrasts in structural style and subsidence history within the QDNB. Following the onset of South China Sea break-up in the early Oligocene (~32-30 Ma), the QDNB rifted diachronously from east to west and subsequently transitioned into the post-rift stage in the same direction, culminating at ~23 Ma. The western QDNB displays a strongly asymmetric architecture with a mid-crustal detachment system and records a relatively late onset of rapid subsidence at ~5.5 Ma. In contrast, the eastern QDNB is characterized by a more symmetric structure approaching complete continental rupture, accompanied by an earlier phase of rapid subsidence at ~10.5 Ma. These contrasting detachment styles and subsidence histories indicate distinct thermo-mechanical regimes, with rapid extension and cooling promoting lower-crustal embrittlement in the east, whereas more prolonged extension under longer-lived thermal weakening conditions maintained ductile lower-crustal behavior in the west.
To test these interpretations quantitatively, we perform a series of two-dimensional thermo-mechanical numerical models that explicitly incorporate westward migration of a secondary mantle plume associated with the Hainan mantle plume together with slab-pull forces from subduction of the Proto-South China Sea. By systematically varying plume migration contributions, the models evaluate its relative role in generating along-strike heterogeneity in extension style, subsidence history, and lower-crustal rheology within the QDNB. The modelling results highlight that plume migration exerts a first-order control on the thermal field of the QDNB, providing a key mechanism for the observed non-uniform lithospheric extension.
How to cite: Li, C., Koptev, A., Pons, M., and Brune, S.: Non-uniform lithospheric extension of the Qiongdongnan Basin driven by Hainan mantle plume migration: Insights from thermo-mechanical 2D modelling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15610, https://doi.org/10.5194/egusphere-egu26-15610, 2026.
This study investigates the fault zones of a low-angle extensional structure along the southern South China Sea (SCS) rifted margin. The SCS in Southeast Asia is the best-known marginal basin. It is characterized by a V-shaped oceanic domain formed by seafloor spreading propagating from northwest to southeast between the earliest Oligocene and middle Miocene. Rifting produced broad margins (>600 km) with hyper-extended basins exhibiting varying degrees of crustal thinning. Our study focuses on the southern edge of Dangerous Grounds, in the proximal domain of the southern SCS margin, at its transition to the Sabah Trough.
High-resolution 3D seismic data reveal a well-defined top-basement low-angle normal fault zone. The continental basement preserves evidence of a former orogenic wedge characterized by succession of shallow dipping reflectors similar to thrust sheets. Although not drilled, this geometrical relationship is consistent with imbricated thrust sheets of metasediments likely associated with the Yanshan orogen.
The fault surface exhibits pronounced corrugations with wavelengths of 500m-1 km and a fault zone thickness of up to several 500-700m meters based on seismic resolution. Seismic reflections immediately beneath the fault surface show shear zones of variable thickness with phacoidal blocks, analogous to structures observed in oceanic core complexes.
Overlying the fault surface, we identify dismembered blocks ranging from tens of meters to kilometers in size. They are interpreted as basement material scrapped from the underlying basement made of imbricated thrust sheets. These “rider blocks” are associated with seismic facies consistent with breccias, forming a discontinuous cover over the fault plane. Breccias are interpreted in two categories: mechanical breccias dragged as a tail downdip of the allochthons and classical sedimentary breccias associated with the fault scarps.
These observations provide new insights into the geometry, kinematics, and lateral variability of low-angle normal fault systems, with implications for the evolution of hyper-extended rifted margins.
How to cite: Mohn, G. and Ringenbach, J.-C.: 3D seismic anatomy of a low angle normal fault in the southern South China Sea rifted margin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19229, https://doi.org/10.5194/egusphere-egu26-19229, 2026.
Rider blocks (or extensional allochthonous blocks) represent small blocks of pre-rift sediments and/or basement rocks transported over long-offset extensional fault zones. They are often related to low-angle normal faults (LANFs), with dips of less than 30°, and are commonly observed in post orogenic context and in rifted margins. However, the mechanisms controlling the formation, transport, and dismantling of rider blocks along LANFs remain poorly constrained. This raises critical questions regarding the origin of the blocks (hanging wall versus footwall), the influence of rheology, their three-dimensional geometry, and their evolution during extension. Addressing these issues is essential for improving our understanding of extensional processes, including continental crust thinning and the overall architecture, tectonic and sedimentary evolution of sedimentary basins.
Here, we present new observations from both active and fossil extensional systems: southern South China Sea rifted margin offshore Malaysia, and a fossil analogue preserved in Err and Bernina LANF systems within the lower Austroalpine nappes of the Central Alps, investigated through new fieldwork approaches.
To bridge the scale gap between seismic and field observations, we created Digital Outcrop Models (DOMs) in the Err and Bernina units, covering an area of 42.925 km². These DOMs are based on Structure-from-Motion photogrammetry and constitute the FATDOM database, which is openly available under FAIR (Findable, Accessible, Interoperable, and Reusable) conditions. The high resolution of the 12 DOMs enables centimetre- to decimetre-scale analysis, allowing detailed mapping of the spatial evolution of LANFs and the tectono-sedimentary architecture of the overlying rider blocks.
Based on these new observations, we present a new classification of rider blocks and identify three different types defined by their size, geometry, and mode of formation. The first type consists of blocks composed of pre-rift sediments that are passively transported along the LANFs and locally dismembered. The second type, either hanging-wall or footwall derived, preserves both basement and pre-rift sediments. Finally, the third type corresponds to break-away blocks in-between two LANF systems. For each type, we provide a detailed interpretation of their internal structure, including lithological variations, deformation patterns, and fault architecture across multiple scales. These field-based observations are further illustrated by examples from 3D reflection seismic data from the southern South China Sea rifted margin.
Our iterative comparison between present-day rifted margins and fossil analogues enables us to propose a conceptual model for the formation of rider blocks related to LANFs, applicable to extensional systems worldwide (e.g., Basin and range, Papua New Guinea…), and providing new insights into the dynamics of LANFs.
How to cite: Morzelle, L., Mohn, G., Tugend, J., Betlem, P., and Ringenbach, J.-C.: Formation and dismantling of rider blocks related to low-angle normal faults in rifted margins, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10273, https://doi.org/10.5194/egusphere-egu26-10273, 2026.
Low-angle normal faults (LANFs) and extensional detachments commonly nucleate and evolve within complex three-dimensional strain fields, especially where strike-slip motion interacts with extension in post-orogenic settings. In many orogens (Norway, the Aegean, Turkey, Variscan Europe), field evidence shows that transtensional transfer zones exert a first-order control on the geometry of metamorphic core complexes and on the activation of low-angle shear zones. Despite this, the mechanics allowing LANFs to initiate, rotate, and exhume deep crustal rocks in oblique strike-slip systems remain poorly constrained, and existing numerical studies rarely allow detachment localisation to emerge without kinematic prescription.
We present new three-dimensional thermo-mechanical models that track the spontaneous development of LANFs and metamorphic core complexes in transtensional right-lateral systems. Boundary conditions impose only far-field oblique motion; the location and orientation of strike-slip faults and low-angle detachments are not prescribed but arise from crustal rheology and stress evolution. We test three end-member crustal architectures capturing different forms of tectonic inheritance: a homogeneous reference column (REF), a vertically heterogeneous but continuous Buckling column, and a Nappe Stack column containing a weak décollement inherited from crustal-scale nappe stacking.
The models reveal that tectonic inheritance exerts the primary control on LANF initiation and MCC geometry in 3D transtension. Nappe Stack configurations produce large low-angle detachments and a-type metamorphic domes with significant exhumation, whereas Buckling configurations generate oblique wide rifts with incomplete exhumation, and REF architectures form non-detached spreading domes. These results show that the evolution of LANFs and detachment systems in transtensional environments strongly depends on inherited crustal layering, the 3D strain field, and the degree of strike-slip partitioning.
How to cite: Le Pourhiet, L., Jourdon, A., Plunder, A., and Bergogne, M.: Emergent Low-Angle Detachments in 3D Transtension: Influence of Crustal Inheritance and Strike-Slip Partitioning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17121, https://doi.org/10.5194/egusphere-egu26-17121, 2026.
Large-offset oceanic detachment faults play a key role in accommodating asymmetric plate spreading at slow and ultraslow mid-ocean ridges. IODP Expedition 399 drilled a 1268-m-deep borehole (Hole U1601C; 30°N, Mid-Atlantic Ridge) into the footwall of an oceanic detachment near the southern wall of Atlantis Massif, recovering variably serpentinized peridotites (~70%) with lesser gabbro (~30%). In contrast, Hole U1309D (IODP Expeditions 304/305), drilled ~5 km to the north toward the segment center, predominantly recovering gabbros (99%).
Previous paleomagnetic analyses of reoriented, declination-constrained samples from Hole U1309D (Morris et al., 2009) document ≥46±6° of anticlockwise footwall rotation around a horizontal, ridge–parallel axis; the majority of this rotation occurred after the C1r.1r chron (i.e. within the past 781k years). The magnitude of this rotation is consistent with predictions from conventional single-axis flexural rotation models that use the average site inclination (–38° for U1309D) as input. In contrast, our new paleomagnetic analyses of Hole U1601C show characteristic remanent magnetizations with inclinations that match the site-specific expected geomagnetic field at the time of magnetization acquisition (~ –49°, independent of rock type). Applying single-axis rotation models to these U1601C inclinations implies minimal horizontal-axis rotation (~<20°), despite the site lying in the same footwall beneath the same detachment surface, some 5 km from U1309D. The consistent inclinations recorded by serpentinized peridotites and gabbros at U1601C constrain the timing of deformation, indicating that <20° rotation occurred below ~350 °C, after formation of magnetite during serpentinization, and little to no rotation between gabbroic remanence acquisition (~580°C), and later magnetite-forming serpentinization.
These contrasting inclination results (U1309D vs U1601C) indicate that both sites are not easily explained by a simple, single rotation axis, and instead imply that vertical transport dominated footwall exhumation at U1601C. A vertically dominated component may reflect the mechanical influence of the adjacent transform fault, which could act to shallow rotation axes. Together, these paleomagnetic findings point to spatially heterogeneous structural evolution within a single oceanic core complex. Possible structural frameworks and evolutionary pathways for the Atlantis Massif will be discussed.
How to cite: Lopes, E., Tikoo, S., Parsons, A., Kuehn, R., John, B., and Deans, J.: Complex Kinematics During Exhumation of the Atlantis Massif: New Paleomagnetic Evidence from Hole U1601C, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14895, https://doi.org/10.5194/egusphere-egu26-14895, 2026.
