Recent advances in numerical and laboratory modeling have enhanced our understanding of subduction zone processes. However, challenges remain in achieving a consistent picture of the controlling parameters of subduction dynamics. Variations in methodologies, model setups, and input assumptions often lead to contrasting conclusions across geochemical, geodetic, tectonic, and modelling studies.
This session focuses on the dynamics of subduction zones from processes occurring at the Earth’s surface to interactions deep within the mantle, and on the physical mechanisms that control deformation and magmatism in the overriding plate. Topics include, but are not limited to: subduction geometry, kinematics, and dynamics; mineralogical processes in subduction; dynamics, generation and migration of fluids and melts; controls on volcanic arcs; subduction-induced seismicity; role of sediments and volatiles; influence of subducting seamounts, LIPs and ridges; links between surface tectonics, slab dynamics and mantle flow; slab delamination and break-off; imaging subduction processes; and the role of subduction dynamics in the supercontinent cycle.
We invite contributions from across disciplines — including geodynamics, geophysics, geochemistry, petrology, volcanology and seismology — to discuss subduction dynamics at all scales from the surface to the lower mantle, in both present-day and ancient natural laboratories. We particularly encourage integrative studies that bridge observations, models and scales. While the session is Earth-focused, we also welcome contributions that place subduction in a broader planetary perspective.
Orals: Tue, 5 May, 08:30–15:40 | Room K2
Subduction initiation in Atlantic-type oceans is a fundamental process in the evolution of oceanic basins, described by the Wilson cycle. However, it is widely known that subduction zones are not easy to initiate and require a combination of factors, including forcing from nearby active subduction zones. There are currently three subduction systems in the Atlantic: the Lesser Antilles, Scotia and Gibraltar arcs. In recent years, these subduction systems have been studied using a combination of methods, including advanced numerical models that have yielded new insights into the dynamics of subduction initiation. Both the Scotia and Lesser Antilles arcs seem to be cases of subduction transfer from the Pacific into the Atlantic, while the Gibraltar Arc may constitute a case of a direct invasion of a Mediterranean slab. Here, we will briefly review the main characteristics of these arcs and present recent geodynamic models of their evolution. Models show that, while these arcs share some commonalities, they are also fundamentally different. These results suggest that despite subduction initiation being a non-trivial process, it is an unescapable outcome of the Earth’s oceans evolution.
This work is supported by FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020 - https://doi.org/10.54499/LA/P/0068/2020, UID/50019/2025, https://doi.org/10.54499/UID/PRR/50019/2025, UID/PRR2/50019/2025
How to cite: Duarte, J. C., Riel, N., Schellart, W. P., Rosas, F., and Almeida, J.: Subduction invasion of the Atlantic, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7953, https://doi.org/10.5194/egusphere-egu26-7953, 2026.
Plagiogranites are the felsic plutonic rocks occurring amidst a suite of predominantly mafic and ultramafic rocks. Their occurrence ranges from newly formed oceanic crust to Archean ophiolites, and they are usually associated with the crustal section, i.e., gabbros and sheeted dykes. Sometimes, they have been observed in the mantle sections as well. The Andaman ophiolite (AO) is a dismembered ophiolite suite located on the forearc of the Andaman subduction zone, where the Indian plate obliquely subducts beneath the Burma microplate. Plagiogranites of the AO are found to be intruding into gabbros and serpentinized mantle peridotites. They have been dated to 98-93Ma, and are contemporaneous with the other rocks of the ophiolite. Earlier studies propose that these have been generated by crystal fractionation or an immiscible separation from a parental basaltic magma. In this study, we utilize new whole-rock geochemical data and Sr-Nd isotopic ratios of these rocks to constrain their petrogenesis. Geochemically, these rocks are classified as diorites to tonalites-trondhjemites, characterized by plagioclase+amphibole+quartz assemblage. Petrographic observations reveal that euhedral plagioclase and amphiboles were the early crystallizing phases, while anhedral quartz crystallized later in the sequence. The plagiogranites exhibit LREE-enriched patterns on chondrite-normalized plots and negative Nb-Ta and Zr-Hf anomalies on primitive mantle-normalized plots, suggesting derivation from a metasomatized source. Sr-Nd isotopic compositions strongly overlap with other rocks of the ophiolite suite, pointing to a common mantle parentage. Low TiO2 contents, overlapping trace element patterns with the mafic rocks of the AO, and REE-SiO2 systematics negate the possibility of plagiogranite formation by fractional crystallization from a basaltic magma. The occurrence of amphiboles in the plagiogranites suggests that the parent magma was hydrous, implying that liquid immiscibility was not the genetic mechanism. Therefore, we explore the possibility that they are crystallized products of a high-magnesian andesitic magma (HMA) derived by the partial melting of a metasomatized mantle source at low pressure, followed by fractional crystallization of plagioclase±amphibole, to explain their genesis and the observed compositional variation. We demonstrate, using the results of alphaMELTS simulations, that compositional variation and the mineral assemblages observed in the plagiogranites of the AO can be explained by this model and suggest that derivation from HMAs is a viable mechanism for the genesis of plagiogranites in similar settings. We propose that the plagiogranites of AO have formed during the initiation of an intra-oceanic subduction, which can explain their geochemical features and geochronological results.
How to cite: Gandrapu, S. B., Ray, J. S., and Bhutani, R.: Plagiogranites derived from high-Mg Andesitic magmas: An example from the Andaman Ophiolite, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-684, https://doi.org/10.5194/egusphere-egu26-684, 2026.
Subduction initiation remains a key open problem in geodynamics. One hypothesis for the spontaneous initiation of subduction is passive margin collapse triggered by grain damage: a rapid plunge in grain size in the lower parts of the lithosphere leads to strong rheological weakening and the formation of a localised shear zone that facilitates subduction. This mechanism has been proposed and tested in 1D models (Mulyukova & Bercovici, 2018), but has not been incorporated into fully dynamic subduction models because grain-size-dependent rheologies have a high complexity and computational cost. As a result, its viability as a trigger for subduction initiation remains uncertain.
Here we present high-resolution 2-D thermo-mechanical models that test whether grain damage can enable passive margin collapse and subduction initiation. We model the life cycle of an entire oceanic plate from mid-ocean ridge formation to the potential collapse at the passive margin (or stable evolution if no collapse occurs). The lithosphere is represented as a two-phase assemblage of 60% olivine and 40% pyroxene, which are well-mixed at the grain scale. Because grains of each phase impede the growth of the other through Zener pinning, grain growth is suppressed relative to single-phase compositions. This promotes strain localisation due to grain size reduction. Simulating this process requires accurate tracking of the mineral grain size, which is both history-dependent and sensitive to stress changes. Recent advancements in the community code ASPECT, including a higher-order particle method and adaptive time stepping for the grain-size evolution equation via the ARKode solver, now make this feasible.
Our models demonstrate that subduction initiation by grain damage is possible, but only within a narrow range of grain size evolution parameters. Passive margin collapse requires that a large fraction of deformational work in cold lithospheric regions is partitioned into interface damage rather than dissipated as shear heating. Even under these favourable conditions, additional weakening is needed to break the upper ≥15 km of the plate. In our models, we impose a narrow, weak zone to represent this shallow weakening. Elevated stresses in and around the weak zone promote grain damage, producing a grain size plunge and associated viscosity drop at mid- to lower-lithosphere depths. The resulting zone of small grain size propagates downward through the lower lithosphere until a narrow, continuous shear zone forms that enables passive margin collapse. However, the same imposed weak zone does not lead to subduction initiation in otherwise identical models with a fixed grain size.
These results indicate that grain damage alone is unlikely to be the primary trigger for passive margin collapse, but that it can substantially enhance strain localisation and modulate the conditions for subduction initiation when combined with additional weakening mechanisms.
References: Mulyukova, E., & Bercovici, D. (2018). Collapse of passive margins by lithospheric damage and plunging grain size. Earth and Planetary Science Letters, 484, 341-352.
How to cite: Dannberg, J., Saxena, A., Gassmöller, R., Fraters, M., and Li, R.: Geodynamic Modelling of Passive Margin Stability with Grain Damage: Conditions for Subduction Initiation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14019, https://doi.org/10.5194/egusphere-egu26-14019, 2026.
Fluid production from dehydration reactions and fluid migration in the subducting slab impact various subduction processes, including intraslab and megathrust earthquakes, episodic tremor and slip, mantle wedge metasomatism, and arc-magma genesis. To better understand these processes, it is crucial to determine the migration and the resulting distribution of fluids within the slab and along the slab surface.
A variety of geophysical observations and field studies suggest that intraslab updip fluid migration is plausible, yet quantitative numerical investigations of this process remain limited. So far, only models that incorporate compaction pressure gradients generated by fluids released during dehydration reactions have offered a convincing mechanism [1]. These models, however, are still not widely explored, and the influence of pre-subduction hydration of the oceanic mantle is particularly poorly constrained. In our study [2], we use a 2-D two-phase flow model to investigate this effect under various initial slab-mantle hydration states and slab thermal conditions, both of which impact the depth extent of the stability of hydrous minerals. We focus on the lateral shift between the site of dehydration reactions and the location of fluid outflux at the top of the slab due to intraslab updip migration. Our simulations indicate that prominent updip pathways develop along the segments of antigorite and chlorite breakdown fronts that run sub-parallel to the slab interface. The resulting updip fluid migration to depths as shallow as 30–40 km increases the volume of fluids that flux out across the slab surface at relatively shallow depths. Such behavior is most pronounced in young (< ~30 Ma), warm slabs, where the stability zones of hydrous phases in the incoming oceanic mantle are relatively thin (< ~20-km thick), enabling the development of the slab-parallel dehydration fronts that enhance updip flow.
[1] Wison et al., 2014, https://doi.org/10.1016/j.epsl.2014.05.052
[2] Cerpa & Wada, 2025, https://doi.org/10.1029/2024JB030609
How to cite: Cerpa, N. and Wada, I.: Hydration state of the incoming plate and updip fluid migration in the slab mantle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5051, https://doi.org/10.5194/egusphere-egu26-5051, 2026.
The dehydration of altered oceanic lithosphere is a source of aqueous fluids in subduction zones. Serpentine minerals, hosting ~ 13 wt.% H2O, are one of the main water carriers of the hydrated oceanic mantle. Antigorite, the stable serpentine mineral in deep subduction conditions, breaks down at temperature above 600 °C (Atg-out reaction), releasing free aqueous fluid. Compilation of bulk compositions of oceanic and exhumed subduction-collision zones serpentinites from the literature indicates that brucite (Brc) should also be an important hydrous (30 wt.% H2O) component of the oceanic lithosphere. Thermodynamic modeling with an updated thermochemical database shows that the Brc + Atg = Ol + H2O reaction (Atg-Brc reaction) occurs at lower temperature and can even produce more fluid than the Atg-out reaction. Moreover, the Atg-Brc reaction occurs in a narrow temperature range (< 10 °C), implying relatively high dehydration rates in the slab. Furthermore, the released aqueous fluid is calculated to be highly magnesian (> 1 mol/kg) with MgOaq as the dominant aqueous species. We studied the products of the Atg-Brc reaction in Zermatt-Saas (Swiss Alps) and Mont Avic (Italian Alps) meta-ophiolites, involved in the Alpine subduction. The development of metamorphic olivine and Ti-clinohumite veins within metamorphic serpentinites crosscut by pure magnesian brucite (Mg# > 99) indicates strong magnesian segregation, in agreement with thermodynamic modeling. From the size of the segregation, it is estimated that a Mg-rich fluid interacted with the host rock for around a hundred years before being drained. Finally, based on the idea that dehydration reactions can trigger seismicity in subduction zones, we located in a PT diagram the Low-Frequency Earthquakes (LFE) recorded in present-day subduction zones (Mexican, Nankai and Cascadia). The conditions under which these LFE are generated coincide with the PT conditions of the Atg-Brc dehydration reaction, supporting its central role as a main source of aqueous fluid in subduction zones.
How to cite: Legros, E., Malvoisin, B., Brunet, F., El Yousfi, Z., Batanova, V., Sobolev, A., and Auzende, A.-L.: Massive Mg-rich fluid release across the brucite + serpentine reaction in subduction zones, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20466, https://doi.org/10.5194/egusphere-egu26-20466, 2026.
Increasing pressure and temperature causes progressive dehydration of subducted oceanic lithosphere. This process generates incompatible trace element and halogen-enriched fluids that migrate into the mantle wedge, thereby causing metasomatism across a large depth range. Apatite is a common constituent of metasomatic assemblages in mantle wedge peridotites and melange zones, indicating that phosphorus is a significant component of the trace element flux directed into the mantle wedge. During progressive subduction, tuite [γ-Ca3(PO4)2] forms from apatite at depths of ~220-230 km (7-7.5 GPa) and ~250-280 km (8-9 GPa) in basaltic and peridotitic lithologies, respectively, thereby replacing apatite as phosphorus-saturating phase and major carrier of Y+REE, LILE, U and Th. The significance of Ca-phosphates compared to silicates for phosphorus and incompatible trace element storage and transport is expected to evolve with increasing depth and temperature. Upon crossing the upper-to-lower mantle boundary, major phosphorus and/or LREE carriers such as majoritic garnet and ringwoodite disappear, while new competitors for LILE-LREE-HFSE storage, such as davemaoite, the CAS-phase, and K-hollandite emerge (e.g. Hirose et al., 2004; Suzuki et al., 2012). No experimental data are currently available on the distribution of incompatible trace elements in Ca-phosphate-bearing assemblages at P-T conditions covering this depth interval. This study aims to address the gap in our understanding of upper-to-lower mantle trace element fluxes (1) by determining incompatible trace element concentrations in tuite and its coexisting phases within a peridotite bulk composition at pressures straddling the upper-to-lower mantle transition, and (2) by assessing the role of tuite in trace element storage and transport across this boundary. For this purpose, multi anvil experiments were performed at 15 to 25 GPa and 1600 to 2000°C, using a moderately fertile peridotite doped with 3% synthetic β-Ca3(PO4)2, approximately 2200 µg/g Cl and Br, each, and 1% of a trace element mix containing Y+REE along with selected LILE, HFSE and light elements (Li, B, Be) with concentrations in the range 1-230 µg/g.
In metasomatized peridotites, Ca-phosphates are stable only if the bulk phosphorus concentration exceeds the saturation capacity of the coexisting silicate-(oxide) assemblage. In this case, apatite and tuite can be present throughout the upper and in the uppermost lower mantle and constitute principal hosts of REE, LILE, U, and Th in this depth range. Upon entry of peridotite into the lower mantle, the breakdown of Ca-P-bearing majorite leads to the formation of davemaoite and tuite, both phases becoming the dominant incompatible trace element carriers. In the absence of Ca-phosphates, clinopyroxene, majoritic garnet and davemaoite dominate incompatible trace element storage in the upper and uppermost lower mantle.
Hirose, K. et al., (2004) Phys. Earth Planet. Inter. 146, 249-260.
Suzuki, T. et al., (2012) Phys. Earth Planet. Inter. 208-209, 59-73.
How to cite: Pausch, T., Joachim-Mrosko, B., Ludwig, T., and Konzett, J.: Incompatible trace element transport in phosphorus enriched peridotitic mantle across the upper to lower mantle boundary, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16495, https://doi.org/10.5194/egusphere-egu26-16495, 2026.
The Hellenic–Aegean subduction zone is a key natural laboratory for studying convergent margin dynamics, with well-documented surface deformation, upper-crustal geology, and deep mantle processes such as slab rollback. The architecture of the subduction system at intermediate depths (∼50–150 km), however, still remains insufficiently resolved.
Using receiver-function analyses from a dense seismic network deployed across the Peloponnesus and central Greece within the EU-funded THALES WAS RIGHT project, we have resolved the three-dimensional geometry of the subducting slab Moho in unprecedented detail. These studies revealed a systematic segmentation of the Ionian oceanic lithosphere by nine trench-normal, subvertical fault zones that remain seismically active at intermediate depths beneath the entire Peloponnesus and the marine forearc domain. This fault-controlled architecture provided compelling evidence for slab tearing and highlights the role of internal slab deformation. Clustered seismicity in the mantle wedge above the tear faults suggests their potential role as pathways for fluid migration.
These slab faults appear to influence seismicity up to the forearc backstop. New results from ocean-bottom seismometer local tomography in the forearc domain further illuminate upper plate structural segmentation. We image a strongly imbricated upper-crustal wedge composed of blocks with contrasted P-wave velocities overlying the megathrust down to ~30 km depth. These blocks likely correspond to accreted terranes previously inferred from geological reconstructions but never imaged seismically. Beyond their geodynamic significance, this segmentation may modulate megathrust slip behaviour, as illustrated by our study of the Methoni earthquake. We propose that in the southwestern Hellenic subduction zone, megathrust rupture propagation is limited by the combined effects of small-scale upper-plate discontinuities and larger-scale lower-plate segmentation associated with slab tearing.
Complementary receiver-function results reveal a low-velocity layer -over 200km wide- located within the mantle wedge, below the shallow Aegean Moho and above the slab top at depths of ~50–70 km. Owing to the dense 2-D profile coverage, we resolve that this layer is segmented into distinct panels that closely mirror the along-strike segmentation of the retreating slab. This layer may represent inherited underplated material accreted during earlier subduction episodes, in a process analogous to the accretion of the Hellenic tectonostratigraphic terranes. Our observation of slab-parallel segmentation provides a key constraint on mantle wedge rheology, implying that slab faulting not only governs slab dynamics, associated upper plate deformation and fluid flow pathways but also structurally organizes the mantle wedge. Future finer scale imaging derived from multiscale analysis methods and synthetic modelling are planned to better constrain the nature of this layer and its role in fluid transfer and mantle wedge seismicity.
How to cite: Sachpazi, M., Laigle, M., Kapetanidis, V., Diaz, J., Gerset, A., Galve, A., Charalampakis, M., and Kissling, E.: Slab Tearing, Fluid Pathways, and Seismic Segmentation in the Hellenic–Aegean Subduction Zone Revealed by Receiver Functions and OBS Tomography, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21443, https://doi.org/10.5194/egusphere-egu26-21443, 2026.
Constraining the complex nonlinear feedbacks between patterns of fluid transport and solid deformation in subduction systems remains a key area of research towards understanding subduction zone seismicity, magmatism, and volatile cycling. In this study, we use 2D geodynamic simulations to constrain how distinct physical approximations for reactive volatile transport and fluid-solid coupling affect both long-term subduction dynamics and fluid transport pathways.
The simulations use the open-source geodynamic software package ASPECT, which provides a framework for modeling coupled nonlinear viscoplastic deformation and reactive fluid transport in combination with a free surface, adaptive mesh refinement, advanced nonlinear solvers, and massive parallel scaling. Fluid–rock interaction follows a previously published parameterization of volatile–rock interaction within subduction systems (Tian et al., 2019), which provides an analytical solution for water partitioning between bound and free water phases across pressure–temperature space for sediment, mid-ocean ridge basalt, gabbro, and peridotite lithologies. We simulate fluid transport as either partially coupled Darcy flow (ignoring compaction terms) or fully coupled two-phase flow following the McKenzie equations (including compaction terms) (McKenzie 1984). In both cases, fluid–solid coupling also occurs through exponential reduction of the solid viscosity as a function of the volume of free-water. Furthermore, we examine the additional fluid-solid coupling through a reduction in the brittle strength of the solid in the presence of free-water and of the solid viscosity as a function of the bound H2O content.
Consistent with previous work, our model results demonstrate that the choice of partially or fully coupled two-phase flow significantly impacts fluid pathways, and that increased fluid–solid coupling leads to increased convergence rates between the subducting and overriding plates. When ignoring compaction terms, the partially coupled Darcy models promote vertical fluid pathways as the slab dehydrates, while including compaction prevents immediate release of the fluid from the subducting plate, promoting updip fluid pathways within the slab before fluids are released into the mantle wedge. Significantly, fluid release into the mantle wedge in the deeper and mechanically strong portions of the slab does not occur until a sufficiently high porosity is reached to locally reduce the solid viscosity and thereby enable the compaction pressure to overcome compaction viscosities.
Extensive serpentinization of the subducting mantle lithosphere enables the transport of large fluid volumes to beyond the arc. When including the full degree of fluid–solid coupling (including additional brittle and ductile weakening), this large volume of fluid carried to the back-arc promotes sufficient weakening of the overriding plate to drive the dynamic initiation of back-arc spreading. In contrast, reduced degrees of serpentinization inhibit back-arc rifting. We propose that variations in mantle lithosphere hydration provide a fundamental control on the occurrence of back-arc spreading, with less hydrated subducting plates corresponding to subduction zones lacking back-arc extension.
How to cite: Douglas, D., LaCombe, F., Xue, L., Naliboff, J., Dannberg, J., and Myhill, R.: Investigating the Role of Fluid–Solid Coupling on Subduction Dynamics and Fluid Pathways, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12482, https://doi.org/10.5194/egusphere-egu26-12482, 2026.
Trench curvature, as the surface expression of the three-dimensional subduction system, has a close affinity with the subduction dynamics; however, the underlying mechanisms remain enigmatic. Back-arc basins, as natural products of subduction zone evolution, record the development of arcuate trenches. Most modern back-arc basins occur in the western Pacific, where subduction zone trenches commonly exhibit no-linear geometries. Among them, the Japan Sea represents a typical example, characterized by the trench convex toward the subducting plate.
Here, we present major and trace element together with Sr-Nd-Mg isotopic data of back-arc basalts (BABB) drilled along strike in the Japan Sea to explore the potential link between trench curvature and lateral variations in subducted materials. The Nb/Zr ratios of BABB in the central segment increase and subsequently decrease, whereas those in the north show a markedly delayed decrease, which indicates that the central back-arc basin had reached a mature spreading stage. In addition, Nd isotopic values of central BABB show higher than those in the south, indicating a negligible contribution from slab-derived components. This implies that the central back-arc basin is located far away from the trench and experienced nearly complete extension. These observations reveal pronounced along-strike variations in the extent of back-arc spreading, with the northern basin remaining nascent, whereas the central segment has evolved to a mature stage. This is consistent with the observation that the central segment of the trench develops a progressive curvature toward the subducting plate, suggesting that the evolution of back-arc spreading exerts a primary control on trench curvature. In particular, along-strike changes in Mg isotopes reveal the lateral variations in volatile cycling. BABB from the northern region with limited spreading exhibit extremely heavy δ26Mg values (−0.30‰ to +0.34‰), suggesting contributions of water-dominated fluids derived from serpentinite. In contrast, BABB from the central region with mature back-arc spreading show relatively light δ26Mg values (-0.57‰ to 0.06‰), primarily reflecting the involvement of deep subducted carbonates.
The spatial variations in volatile cycling correlate well with the extent of back-arc spreading. Volatiles reduce mantle viscosity and weaken the overlying mantle wedge, thereby regulating mantle rheology. It is noted that the magnitude of this effect varies substantially among different volatile species. Among them, carbon exerts a stronger influence on mantle rheology than water (Fei et al., 2013; Kono et al., 2014). This is consistent with the greater extent of back-arc spreading in the central segment, suggesting that along-strike variations in volatile cycling modulate the mantle rheology, thereby governing the evolution of trench curvature.
This work was financially supported by the National Key R&D Program of China (Grant 2022YFF0801002) and the National Natural Science Foundation of China (Grant 42372065).
References:
Fei et al., 2013, Nature, v. 498, p.213-215.
Kono et al., 2014, Nature Communications, v. 5, p.5091.
How to cite: Zhao, W.-Y. and Wang, F.: Along-strike variations in volatile cycling control trench curvature associated with back-arc spreading, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6329, https://doi.org/10.5194/egusphere-egu26-6329, 2026.
The mechanisms that have been proposed to control the position of volcanic arcs in subduction zones can be broadly divided into two categories. Geophysical and geodynamical studies emphasize a “deep-thermal control” related to the thermal state of the subducting plate and the mantle wedge, whereas field-based regional studies highlight a “tectonic control” driven by deformation and the tectonic configuration of the overriding plate. While the deep-thermal controls have been widely investigated statistically at the global scale, the influence of overriding-plate tectonics on arc position remains underexplored.
In this study, we investigate both perspectives for the majority of present-day subduction zones, with a particular focus on tectonic controls. We first build an accurate dataset of the position of the Holocene arc volcanoes, using the Smithsonian Institution Global Volcanism Program, with respect to the subducting plate as defined by the Slab2.0 model (Hayes et al., 2018). We then construct a dataset describing the mean tectonic regime of arc regions by inverting the stress state from focal mechanisms compiled from global and regional catalogs, complemented by information on major active geological structures near the arc. These two datasets, arc location relative to the subducting plate and tectonic regime in the arc vicinity, are combined to address the dominant control on the volcanic arc position.
In regions such as those spanning from the Mariana Islands to the southern Kuril Islands and the Tonga-Kermadec subduction zones, we find that slab-top depth beneath the volcanic front (i.e., the volcanoes closest to the trench, HVF) increases with slab age and decreases with increasing subduction velocity. These trends are consistent with the volcanic front position being primarily controlled by the thermal state near the slab top or within the proximal mantle wedge.
In contrast, in regions lacking trends indicative of deep-thermal controls (i.e., Indonesia), another control likely dominates. In particular, we show that in Mexico-Central America and the Ryukyu-Nankai subduction zones, HVF values vary with the tectonic regime: HVF tends to be slightly lower in extensional settings than in compressional ones. Our interpretation is that, in these regions, deep-thermal controls are overprinted by the tectonic regime of the overriding plate.
For a large subset of regions, including the Andes and the Alaska-Aleutian subduction zones, we do not identify any clear signal.
At the global scale, arcs governed by deep-thermal controls seem to occur mostly where the overriding plate is oceanic, whereas those whose position varies with the tectonic regime are mainly found in continental settings, suggesting the influence of the overriding-plate nature.
How to cite: Bonnamy, L., Cerpa, N., Lallemand, S., and Arcay, D.: Evaluating the role of the overriding-plate tectonics on the position of arc volcanism, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6502, https://doi.org/10.5194/egusphere-egu26-6502, 2026.
Subduction zones are inherently three-dimensional systems and exhibit pronounced trench-parallel variability in key observables, including the deformation style of the overriding plate, trench migration rates, slab geometry, and mantle flow patterns. Geodynamic models typically invoke external mantle flow and/or along-strike variations in the properties of the subducting slab to explain this variability, often neglecting the influence of the overriding plate, despite growing evidence of its strong control on subduction dynamics. In this study, we use self-consistent three-dimensional numerical models to explore how along-strike heterogeneities in the overriding plate structure can generate significant variations in subduction dynamics and mantle flow. Our results demonstrate that trench-parallel variations in overriding plate thickness produce large along-strike differences in trench retreat velocities, leading to strongly arcuate trench geometries.
We further conducted a suite of models incorporating a mechanically weak zone in the subducting plate, representing the subduction of a transform fault oriented perpendicular to the trench. These experiments show that along-strike variations in overriding plate thickness can promote vertical slab tearing and segmentation of the subduction system into distinct slab segments. Slab tearing facilitates focused mantle upwelling through the tear, potentially triggering tear-related magmatism during slab rollback. Natural examples of subduction zones characterized by vertical slab tears include the Melanesian subduction system, the South Shetland margin and the Tyrrhenian–Apennines collision system. We propose that the interplay between overriding plate heterogeneity and the subduction of transform faults has been a key factor controlling oroclinal bending and subduction segmentation in the Mediterranean region.
How to cite: Negredo, A. M., Gea, P. J., Mancilla, F. dL., Li, H., and Billen, M. I.: Subduction segmentation induced by along-strike variations in overriding plate structure, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19998, https://doi.org/10.5194/egusphere-egu26-19998, 2026.
Preserving vital insights into deep-crustal processes and the tectonic evolution of the Tonian northwestern Yangtze Block, the Liujiaping intrusive complex remains enigmatic regarding its precise petrogenesis and tectonic context. Herein, we present new data on petrography, zircon U–Pb geochronology, zircon Hf isotopes, whole-rock major and trace elements, whole-rock Sr–Nd isotopes and mineral chemistry of the Xiangfengkou granodiorite, the Maoping granite and the Chenjiagou granite from the Liujiaping batholith. LA–ICP–MS zircon U–Pb dating reveals their crystallization ages at ca. 802–796 Ma in the Tonian. The Xiangfengkou granodiorite is characterized by high A/CNK ratios of 1.00–1.10 and molar (Fe+Mg) values of 0.08–0.11. Zircons exhibit εHf(t) values of −0.39 to +6.79, while the whole rocks have initial 87Sr/86Sr ratios of 0.707189–0.708169 and εNd(t) values of −1.07 to +0.55. The Maoping and Chenjiagou granites show similar geochemical compositions (A/CNK=0.94–1.09, molar Fe+Mg=0.03–0.05), with zircon εHf(t) values ranging from +1.26 to +7.93, initial 87Sr/86Sr ratios of 0.706313–0.706315, and εNd(t) values of 0.00 to +0.32. All samples display a pronounced negative correlation between A/CNK and Fe + Mg, indicative of the typical high-mafic I-type granitoid characteristics. Combined mineralogical and geochemical data suggest that these granitoids were mainly generated by the partial melting of a newly formed mafic lower crust. The notably high Fe, Mg, Ti and Ca contents further imply the entrainment of Fe-Mg-Ti-Ca-rich minerals during melt segregation. Strong positive correlations between Ti and Ca contents with maficity, as well as a negative correlation between A/CNK and maficity, indicate that a peritectic assemblage entrainment process involving transitional minerals (e.g., clinopyroxene, plagioclase and ilmenite) occurred during biotite-hornblende coupled melting. The geochemical, isotopic and mineralogical evidence collectively support the view that the Liujiaping granitoids formed in a subduction-related active continental margin setting. Together with previous studies, these results further demonstrate that the northwestern to western margin of the Yangtze Block was part of a long-lived subduction-related active continental margin, consistent with its tectonic position along the periphery of the Rodinia supercontinent.
How to cite: Li, Y.: Tonian crustal melting triggered by subduction along the Rodinia periphery: Evidence from the Liujiaping batholith, NW Yangtze Block, South China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6351, https://doi.org/10.5194/egusphere-egu26-6351, 2026.
Arc magmatism plays a critical role in continental crustal growth and the formation of significant metal deposits, including granite-related tin (Sn) systems. However, the mechanisms governing Sn transport and isotopic fractionation at convergent margins remain poorly constrained due to a lack of systematic studies across spatial variations (arc-front to rear-arc) and magmatic-hydrothermal transitions. In this study, we present high-precision Sn isotopic data for lavas, pumices, and hydrothermal products from Whakaari (arc-front) and Taranaki (rear-arc) in the Kermadec system, alongside magmatic H2O concentrations estimated from clinopyroxene. Whakaari lavas exhibit significant variation (δ122/118Sn = –0.241‰ to 0.361‰). The heaviest values are attributed to extensive shallow degassing (>40%), with Rayleigh modeling indicating the preferential partitioning of light Sn isotopes into the vapor phase—a process corroborated by low magmatic water contents (avg. 0.83 wt.%). In contrast, Taranaki samples show limited variation (δ122/118Sn = 0.124 to 0.235‰). While amphibole and titanomagnetite fractionation may lower bulk-rock values, these processes cannot explain why both volcanoes are isotopically lighter than MORB (0.367 ± 0.087‰).
We propose that this light Sn signature originates from the subducted slab. Simulations suggest that the addition of 5–20% reduced, Cl-rich fluids derived from altered oceanic crust (AOC) can effectively lower arc magma δ122/118Sn. Regardless of the specific redox mechanism, slab-derived fluids dominate the Sn budget of the mantle wedge and the resulting arc magmas. Our results suggest that widespread light Sn isotope signatures serve as a diagnostic feature of fluid-mediated mass transfer in subduction zones. By combining spatial variations from arc-front to rear-arc, this study provides a robust geochemical framework to decipher slab-mantle interactions and the dynamic cycling of metals at convergent margins.
How to cite: Jiang, W., She, J., Davidson, A., Chen, C., Firth, C., Turner, S., Li, W., Ireland, T., Sossi, P., Wu, J., and Cronin, S.: Tin isotope fractionation in arc magmas controlled by degassing and slab input, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7076, https://doi.org/10.5194/egusphere-egu26-7076, 2026.
Whether and how subduction results in water enrichment at the base of the mantle transition zone (MTZ) remain elusive. The major orogenic belts of the Asian continent, including the Central Asian, Tethyan, and Alpine–Himalayan belts, which record extensive subduction processes, offer an ideal target to address the hydration of the MTZ and its relationship with subduction. Here, we map water content at the MTZ base by combing mineral physics constraints on hydrous pyrolite and global seismic observations of velocity structure and 660-km discontinuity topography. Our results indicate an average global water content of approximately 0.13 wt%, with pronounced hydration anomalies in parts of Asia. Linking these anomalies with reconstructions of past subduction events since 410 Ma reveals extensive water delivery to the MTZ, particularly beneath the Baikal region and across northwestern China, Kyrgyzstan, Uzbekistan, Kazakhstan, Afghanistan, Turkmenistan, Iran, and western Pakistan, where water content exceeds 0.5 wt%. These results connect ancient subduction history to present-day mantle hydration, offering new insights into Earth’s deep water cycle and highlighting the MTZ as a key reservoir for water.
How to cite: Liu, J., Wu, Z., Wang, W., Xiao, W., and Mao, Z.: Hydration at the Base of the Mantle Transition Zone by Ancient Subductions in Asia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3122, https://doi.org/10.5194/egusphere-egu26-3122, 2026.
The Mantle Transition Zone (MTZ) is a geophysically and geochemically significant yet incompletely constrained region of Earth’s interior. Among the high-pressure mineral phases stable under MTZ conditions, akimotoite is especially relevant in the context of cold subducting slabs. The phase transition between akimotoite and bridgmanite near the 660 km discontinuity is thought to influence slab behaviour and associated mantle features. Experimental and meteoritic studies have shown that akimotoite can incorporate a range of cations, such as Fe and Al, which may significantly affect its phase stability and the pressure–temperature conditions governing its transformation to bridgmanite. In this study, we employ first-principles calculations within the quasi-harmonic approximation to quantify the thermodynamic and thermoelastic effects of cationic substitution on the akimotoite-to-bridgmanite transition. To capture realistic mantle compositional variability, we construct a two-phase coexisting region for Fe- and Al-bearing systems to better constrain the solid solution effect in this regime. Our results demonstrate that increasing Fe2+ content significantly decreases the akimotoite–bridgmanite transition pressure and enhances the acoustic velocity contrast across the boundary. The associated modification of the Clapeyron slope implies possible changes in slab buoyancy and stagnation behaviour near the 660-km discontinuity (Pandit et al., 2025). These results underscore the importance of compositional effects in modulating phase stability and provide new constraints on the role of the akimotoite–bridgmanite transition in MTZ subduction dynamics.
Reference:
Pandit, P., Chandrashekhar, P., Sharma, S., & Shukla, G. (2025). Effect of Fe2+ on akimotoite to bridgmanite transition: Its implication on subduction dynamics. Geochemistry, Geophysics, Geosystems, 26(3), e2024GC012010.
How to cite: Pandit, P. and Shukla, G.: Compositional Effects on the Akimotoite–Bridgmanite Phase Transition and Their Significance for Subducting Slab Behavior, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-590, https://doi.org/10.5194/egusphere-egu26-590, 2026.
The seismic expression of Earth's 410 km discontinuity varies across tectonic settings, from sharp, high-amplitude interfaces to broad transitions—patterns that cannot be explained by equilibrium thermodynamics without invoking large-scale thermal or compositional heterogeneities. Laboratory experiments show the olivine ⇔ wadsleyite phase transition responsible for the 410 is rate-limited, yet previous numerical studies have not directly evaluated the sensitivity of 410 structure to kinetic and rheological factors. Here we investigate these relationships by coupling a grain-scale, interface-controlled olivine ⇔ wadsleyite growth model to compressible simulations of mantle plumes and subducting slabs. We vary kinetic parameters across seven orders of magnitude and quantify the resulting 410 displacements and widths. Our results reveal an asymmetry between hot and cold environments. In plumes, high temperatures produce sharp 410s (2–3 km wide) regardless of kinetics. In slabs, kinetics exert first-order control on 410 structure through three regimes: (1) quasi-equilibrium conditions producing narrow, uplifted 410s and continuous slab descent; (2) intermediate reaction rates generating broader, deeper 410s with metastable olivine wedges resisting downward slab motion; and (3) ultra-sluggish reaction rates causing slab stagnation with re-sharpened, deeply displaced 410s (< 100 km). Rheological contrasts modulate these kinetic effects by controlling slab geometry and residence time in the phase transition zone. These findings demonstrate that reaction rates strongly influence 410 structure in subduction zones, establishing the 410 as a potential seismological constraint on upper mantle kinetic processes, particularly in cold environments where disequilibrium effects are amplified.
How to cite: Kerswell, B., Wheeler, J., Gassmöller, R., Davies, J. H., Papanagnou, I., and Cottaar, S.: Beyond Equilibrium: Kinetic Thresholds and Rheological Feedbacks Create a Potentially Complex 410 in Slab Regions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6886, https://doi.org/10.5194/egusphere-egu26-6886, 2026.
Although based off the elegant theory of thermal boundary layer, the evolution of oceanic plate remains debated, especially regarding its fate after subduction. Traditional geodynamic exercises tend to approximate oceanic subduction using regional 2D or 3D models, but models that evaluate the full history of subduction are still rare, largely due to the challenge in reproducing realistic Earth subduction and unaffordable computational costs. In recent years, we devoted to the development of multi-scale subduction models with data assimilation that simultaneously simulate all relevant subduction processes through geological history while taking various observational constraints into account. Based on these models, we revisited several aspects of the evolving oceanic slabs within the convective mantle. For example, we examined the trajectory of subducted slabs over time, quantified the sinking rate of slabs, as well as reevaluated the driving forces of plate motion, the asthenosphere-lithosphere interaction, and associated plume dynamics. In this presentation, we will share our recent progress on these topics.
How to cite: Liu, L., Cao, Z., Li, Y., Li, X., Dong, H., and Peng, D.: Revisiting the temporal evolution of oceanic subduction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6193, https://doi.org/10.5194/egusphere-egu26-6193, 2026.
Slab breakoff is most commonly associated with continental collision. However, recent geodynamic studies have documented slab breakoff in non-collisional subduction settings, indicating that additional mechanisms may facilitate slab failure. The processes enabling breakoff in the absence of pronounced buoyancy contrasts remain poorly understood. Here, we use two-dimensional thermo-mechanical numerical models to investigate the role of weak crustal-scale heterogeneities embedded within a subducting oceanic plate on slab breakoff dynamics. The models are developed using the ASPECT code coupled with the Geodynamic World Builder for the setting of the initial geometry of the models. We systematically vary the viscosity, length, and distance to trench of weak crustal strips representing inherited compositional heterogeneities, such as sedimentary depocenters. Our results suggest that in models where the subducting slab is fixed or subjected to slow push from the lateral boundary, low-viscosity heterogeneities strongly localize deformation at the subduction interface. Meanwhile, the slab may stretch within the asthenosphere and accelerate as it sinks, ultimately leading to slab necking and breakoff. We identify a clear relationship between slab breakoff depth and the distance of the weak strip from the trench, with breakoff occurring at shallower depths for more trench-distal heterogeneities. This behaviour arises from the combined effects of enhanced slab pull and the presence of weak material farther from the trench, which localizes deformation at shallower depths and promotes shallow slab breakoff. Following slab breakoff, subduction commonly resumes when remnants of the weak strip remain at the plate interface, initiating a second phase of subduction. In addition, we find that the presence of a weak strip increases trench retreat velocities by up to a factor of two compared to a homogeneous reference model. These results demonstrate that relatively small-scale variations in oceanic crustal strength can precondition subducting slabs for breakoff without the need for continental collision, providing a viable explanation for episodic slab detachment observed in natural subduction zones.
How to cite: Sharma, M., Jiménez-Munt, I., María Negredo Moreno, A., María Gómez-García, Á., Pons, M., Faccenna, C., Vergés, J., Torne, M., Zhang, W., and García-Castellanos, D.: Slab Breakoff Induced by Weak Crustal-Scale Heterogeneities, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4702, https://doi.org/10.5194/egusphere-egu26-4702, 2026.
The Antarctic Peninsula preserves the life cycle of a subduction zone from initiation to demise. The Antarctic-Phoenix subduction zone was active from the Late Jurassic till the initiation of its demise, 53Ma1. This demise was triggered by the collision of the Antarctic-Phoenix spreading ridge with the subduction zone trench, leading to the development of a slab window. This ridge crest-trench interaction occurred segmentally from the southern end of the arc to the northern end. Today three segments of the mid-ocean ridge exist west of the South Shetland Islands, but there is no longer any subduction, leaving a paleo-subduction zone. The progressive shut down and subsequent lack of overprinting or tectonic events, allows an assessment of the stages of collision and slab-window formation, and the impact this has had on the magma generation and volcanism.
Limited work has been conducted on linking the evolution of the volcanism with the evolution of the subduction zone, however, recent efforts have worked to classify different geochemical groups within the subduction volcanism and to assess the spread of geochronological data2,3. From this, it has been possible to highlight some key questions which warrant further data collection and analysis.
This work focusses on the assessment of a potential migration of the volcanic axis trench-wards in response to the approaching mid-ocean ridge. It also works to marry the spatial and temporal assessment with a geochemical analysis. With the aim to observe changes in mantle conditions and magma generation through the evolving geochemistry of the volcanic activity and link it to the changing tectonic setting.
To achieve this, 64 additional major and trace element analysis, and 14 new U-Pb dates have been collected. Which have been applied to a spatial analysis and detailed tectonic/coastal reconstruction. From this a new look at the structure, evolution and impact of subduction demise and slab-window formation within the Antarctic Peninsula can be gleaned.
References:
[1] Smellie, et al. (2021), Geological Society of London, Memoirs, https://doi.org/10.1144/M55-2020-14
[2] Leat and Riley (2021a), Geological Society of London, Memoirs, https://doi.org/10.1144/m55-2018-68
[3] Leat and Riley (2021b), Geological Society of London, Memoirs, https://doi.org/10.1144/m55-2018-52
How to cite: Lucas, K., Barry, T., Greenfield, C., Riley, T., Leat, P., and Smellie, J.: Towards a Reconstruction of the Magmatic and Tectonic Evolution of the Demise of the Antarctic Peninsula Subduction Zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13587, https://doi.org/10.5194/egusphere-egu26-13587, 2026.
Olivine, as the first crystallization product from basaltic melt, provides important information about the magma origin. Here we provide a detailed textural, major and trace element, and noble gas isotope compositional data for a alkaline basalt suite from the Persani volcanic field (PVF) of the Carpathian-Pannonian Region. This is the youngest monogenetic volcanic field (1,3 Ma - 0,6 Ma) formed in a geodynamically still active zone. A descending, vertical lithospheric slab result in frequent earthquakes, whereas nearby, another young volcanic system is found (Ciomadul). The alkali basalt magmas were formed due to decompression melting in the asthenosphere, at 60–80 km depth.
Thus, olivine composition can be used to characterize the nature of asthenospheric mantle in a postcollisional area. Noble gas isotope ratios, especially the 3He/4He, are sensisitve indicators of the mantle composition. There are relatively comprehensive data on mantle xenoliths, however, only sporadic data are from olivine crystals of basalts. This is due the challenge of such studies, because of the need of clean olivine separates and detection of low amount of gases from the primary fluid inclusions.
In the Carpathian-Pannonian Region, we firstly detected noble gas isotopes from phenocrysts of basaltic rocks. We sampled different eruption products of the PVF from different eruption episodes. Following a multi-step sample preparation process, we analysed the olivine separates with noble gas mass spectrometer. Petrographic characteristics and major element composition of most olivine phenocrysts suggest crystallization from primary basaltic magma. Due to fast magma ascent, the olivine crystals preserved the original noble gas isotope ratios in their primary fluid inclusions in most samples.
We got relatively low, ~2-5 R/Ra values (3He/4He of the sample divided by 3He/4He of the atmosphere) which are lower than the R/Ra values obtained from the olivine and pyroxene crystals of lithospheric mantle xenoliths in the PVF alkaline basalts (~6 R/Ra), suggesting geochemical differences between the local asthenospheric and lithospheric mantle. Our results are also significantly lower than the usual R/Ra of the depleted mantle (~8 R/Ra). The low values can be explained by metasomatism of the asthenospheric magma source region with crustal fluids during former subduction and/or 4He addition to the asthenosphere from the radioactive decay of U and Th originated from the subducted lithospheric slab. Another possible explanation could be the lithologic heterogeneity of the magma source region. The Mn, Ca and Zn content of olivine autocrysts also indicate the presence of recycled crustal material in the mantle source, in agreement with the noble gas isotope compositional data. Our results suggest that in a postcollisional setting the asthenosphere is contaminated by recycled crustal material and subduction-related fluids.
How to cite: Pánczél, E., Harangi, S., Molnár, K., Czuppon, G., and Lukács, R.: Major, trace element and noble gas isotope composition of olivine from the alkaline basalts of the Persani Volcanic Field, Romania: constraints on the magma source region, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1256, https://doi.org/10.5194/egusphere-egu26-1256, 2026.
The pressure-temperature (P-T) evolution of subduction‐zone plate interfaces controls metamorphism, fluid flow, deformation, and seismicity. However, temperature estimates derived from exhumed rocks frequently exceed those predicted by subduction models, particularly at pressures below ~2.5 GPa. There are two main types of numerical subduction models: models that simulate subduction only without exhumation and models that simulate subduction and simultaneously ongoing exhumation. To investigate the discrepancy between modelled and rock-based temperature estimates, published numerical models that simulate both subduction and rock exhumation are re-examined. The analysis demonstrates that, at equivalent pressure, subduction plate interface temperatures are substantially lower during pure subduction (without exhumation) than during later stages when subduction and exhumation occur simultaneously. This increase in temperature results from advective heat transport, whereby exhuming rocks transfer heat from deeper, hotter regions to shallower levels of the subduction interface. Clockwise P-T paths recorded by exhumed rocks are consistent with this mechanism. Accounting for exhumation-related heat advection significantly improves agreement between modeled interface temperatures and rock-based P-T estimates. This heat advection effect is illustrated using as representative example the two-dimensional petrological-thermo-mechanical model of Vaughan-Hammon et al. (2022), which successfully reproduces P-T paths and metamorphic facies distributions in the Western Alps. Comparisons between interface P-T profiles during pure subduction and during combined subduction-exhumation stages show that interface temperatures at a given pressure can be elevated by more than 200 °C once exhumation initiates. A scaling analysis based on the Péclet number (Pe) combined with systematic two-dimensional numerical simulations of heat advection and diffusion along a channel generalize these results and provide a criterion for assessing the thermal impact of exhumation. Where exhumation occurs along the subduction interface and Pe > 1, advective heat transport can substantially raise interface temperatures. This framework applies to both oceanic and continental subduction zones and offers a potential explanation for the long-standing mismatch between subduction model temperature predictions and rock-based P-T data, particularly those associated with clockwise P-T paths.
Reference
Vaughan‐Hammon, J. D., Candioti, L. G., Duretz, T., & Schmalholz, S. M. (2022). Metamorphic facies distribution in the Western Alps predicted by petrological‐thermomechanical models of syn‐convergent exhumation. Geochemistry, Geophysics, Geosystems, 23(8), e2021GC009898, https://doi.org/10.1029/2021GC009898.
How to cite: Schmalholz, S. M.: Heat advection during exhumation can explain high temperatures along the subduction plate interface, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10328, https://doi.org/10.5194/egusphere-egu26-10328, 2026.
Fluids from subducted slabs are thought to play a major role in mass transfer between the solid Earth and the atmosphere, yet their properties are typically inferred rather than observed. Direct evidence is rare because of their transient properties and later melting and tectonism overwriting their signatures. The active Woodlark rift in southeastern Papua New Guinea exposes the youngest known (ca. 5 Ma) ultrahigh-pressure (UHP) terrane on Earth. Structural data indicates that the PNG UHP terrane was exhumed as a diapir that rose through the former mantle wedge within the active continental rift. Multiple eclogites within the UHP terrane preserve evidence for metasomatic interaction with a fluid that crystallized apatite+Fe-rich dolomite+zircon+rutile+multiple sulfur phases (pyrite, anhydrite, barite) in a vein-like network within the matrix. The zircon associated with the fluid also contain abundant multi-phase solid inclusions, including nanogranite and carbonate-bearing assemblages, plus omphacite and anhydrite+pyrite inclusions that suggest crystallization at high-pressures (>1.6 GPa). To investigate the source and composition of the fluid, we collected major- and trace-element data and Sr-Nd isotopes from apatite and dolomite and trace-element data from rutile in the vein network. Apatite is more enriched in F and OH, compared to Cl, and also is enriched in SO3 and Sr. Apatite yields uniform εNdi = ~+3 and initial 87Sr/86Sr = ~0.70427. Dolomite is enriched in Sr and LREE and yields 87Sr/86Sr = ~0.70424. Finally, rutile yields Nb/Ta of 15–26, falling mostly within chondritic- to superchondritic values. The mineral assemblage and their trace-element signatures indicate the phases crystallized out of a fluid at eclogite-facies conditions, likely during early exhumation, and that overall, the fluid was volatile-rich (C-O-H-S-F) and transported abundant incompatible (Zr, Hf, Ti, Nb, Ta) and heat-producing (K, U, Th) elements. The fluid is interpreted to be sourced from subducted, carbonate-rich sediments from earlier subducted oceanic crust. The fluid ascended from the downgoing plate to metasomatize sub-arc mantle. Subsequently, the UHP terrane was subducted and then interacted with fluids derived from this metasomatized mantle, as both the UHP terrane and former mantle wedge underwent near isothermal-decompression within the active rift. The results have multiple implications. Fluids with this composition can lead to the formation of exotic lava/magma compositions, such as ultrapotassic and alkaline lavas. In addition, the presence of sulfate phases and the elevated SO3 content in apatite indicates the fluid was oxidized, which enhances the potential to form porphyry copper-gold deposits commonly associated with arc systems. Finally, the superchrondritic Nb/Ta values observed in the rutile crystallized from the fluid indicate that some of the missing elements of the Nb-Ta paradox are likely stored within the metasomatized mantle. This study is the first to directly sample the composition of these fluids captured by subducted crustal rocks moving through a former mantle wedge, rather than relying on inferences from exhumed peridotites or volcanic rock compositions.
How to cite: Gordon, S. M., DesOrmeau, J. W., Weinberg, R. F., Fisher, C. M., Hammerli, J., Kemp, A. I. S., Shields, J., Little, T. A., and Tomkins, A.: Metasomatization of the mantle by slab-derived silicic- and carbonate-rich fluids: a record from the world’s youngest UHP terrane, Papua New Guinea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7936, https://doi.org/10.5194/egusphere-egu26-7936, 2026.
Numerical experiments have shown that the presence of fluid or melt during exhumation of deeply subducted ultrahigh-pressure (UHP) eclogite significantly reduces the bulk strength and density, promoting exhumation. However, quantitative studies of the leucosome volume in natural migmatitic eclogites as a proxy for the amount of melt present during exhumation are rare, hindering a deeper understanding of exhumation dynamics of mafic crust. Here, we report results of a systematic study from an extensive outcrop of migmatized eclogite within host gneisses at General's Hill in the Sulu belt, China. Two types of leucosome are distinguished at outcrop and thin-section scales: one type was derived exclusively from UHP eclogite and the other represents a blend of melts derived from both eclogite and host gneiss. We develop a comprehensive set of quantitative methods to estimate the total leucosome volume and the proportion derived from eclogite, and to evaluate the density change of mafic crust due to the presence of melt and effects of retrogression during exhumation. First, we identified leucosome types, subsequently verified by petrographic analysis, and estimated leucosome proportion along one-dimensional transects totaling ~239 meters in length. Second, we estimated the area of different leucosome types using two-dimensional drone-based orthophotos covering ~4000 m2 in area. Based on linear proportion or area as a proxy for volume, the total leucosome amount in the migmatized mafic crust varies from 20 to 30 vol.% with ~83% of the leucosome sourced from eclogite. Retrogression during exhumation leads to between 5 and 19% density reduction of the eclogites on a per sample basis compared to representative unmigmatized UHP eclogites from the adjacent Yangkou Bay outcrop, and overall, the presence of leucosome leads to between 18 and 20% density reduction of the local mafic crust investigated in this study. These results provide critical parameterized constraints for use in geodynamic models of exhumation of eclogite-dominated tectonic units in continental subduction zones.
How to cite: Yan, C., Wang, L., Chen, Z., Brown, M., Yang, X., and Zhang, M.: Quantitative Estimation of Leucosome Volume in Migmatized Eclogite and Implications for Exhumation Dynamics of Mafic Crust, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-268, https://doi.org/10.5194/egusphere-egu26-268, 2026.
Modern day crustal evolution is controlled by plate tectonics. I-type magmatism dominates Phanerozoic crustal growth and has been extensively used to study modern subduction systems and slab-mantle interactions. In contrast, Archean geodynamics remain poorly constrained, with no consensus on the existence of a primitive form of plate tectonics or subduction. This uncertainty largely results from a preservation bias: most Archean crust has been destroyed, and the surviving rock record shows an overprint of billions of years of overlapping, non-mutually exclusive processes such as metamorphism or hydrothermal alteration. As a result, identifying primary geochemical signatures indicative of specific Archean geodynamic mechanisms is not straightforward. In this work, we present a viable Phanerozoic proxy to Archean geodynamics using a global assessment of geochemical and experimental data. A comparison between Phanerozoic post-collisional magmatism and the Archean sanukitoid suite reveals a conspicuous geochemical resemblance based on major and trace element criteria. This common signature is coherent with derivation from a metasomatized-mantle source. The requirement for mantle metasomatism by felsic, upper-crustal material implies a mechanism capable of juxtaposing upper crust with the lithospheric mantle, potentially through continental subduction. Although this geochemical parallel does not necessarily imply a tectonic analogy, it demands active geodynamics during the Archean capable of generating hybrid lithospheric sources. Together, these observations support the use of Phanerozoic magmatic analogues as a framework for investigating Archean geodynamic processes.
How to cite: Gómez-Frutos, D. and Moreira, H.: Proxying Archean subduction using Phanerozoic I-type magmatism, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9603, https://doi.org/10.5194/egusphere-egu26-9603, 2026.
Subduction zone initiation (SZI) represents a critical step in the evolution of plate tectonics, yet its controlling mechanisms remain debated. While SZI is commonly classified as induced or spontaneous depending on the dominance of far-field convergence or local buoyancy forces (Stern, 2004; Stern and Gerya, 2018), geological and numerical studies suggest that purely spontaneous subduction at passive margins is unlikely under present-day conditions (Arcay et al., 2020; Lallemand and Arcay, 2021). Nevertheless, passive margins are characterised by strong lateral contrasts in density, rheology, thermal structure and sedimentary loading, which may generate gravitational instabilities capable of locally weakening the lithosphere.
In this study, we investigate whether gravitational instabilities at passive margins can act as a preconditioning mechanism for subduction, facilitating induced SZI and influencing the early evolution and geometry of the subduction zone once convergence is applied. We perform several hundred two-dimensional thermo-mechanical simulations using the finite-element code FALCON (Regorda et al., 2023), modelling a passive margin.
The models include an initial gravitational phase, followed by an induced convergence phase with velocities ranging from 0.01 to 1 cm/yr. To systematically explore lithospheric weakening, we vary viscous weakening intervals and plastic weakening laws, allowing us to quantify deformation localization through strain-rate analysis near the margin.
Our results show that, for sufficiently weak rheological configurations, gravitational instabilities lead to transient strain-rate localization within the passive margin, controlled by plastic weakening at shallow levels and viscous weakening at depth. The mechanically damaged zone may be efficiently reactivated when convergence starts. In these cases, subduction initiates and develops readily into a coherent subduction interface, particularly at moderate to high convergence rates.
References
Arcay, Diane, Serge Lallemand, Sarah Abecassis, and Fanny Garel (2020). “Can subduction initiation at a transform fault be spontaneous?” In: Solid Earth 11. DOI: 10.5194/se-11-37-2020.
Lallemand, Serge and Diane Arcay (2021). “Subduction initiation from the earliest stages to self-sustained subduction: Insights from the analysis of 70 Cenozoic sites”. In: Earth-Science Reviews 221. DOI: 10.1016/j.earscirev.2021.103779.
Regorda, Alessandro, Cedric Thieulot, Iris van Zelst, Zoltán Erdős, Julia Maia, and Susanne Buiter (2023). “Rifting Venus: Insights From Numerical Modeling”. In: Journal of Geophysical Research: Planets 128. DOI: 10.1029/2022JE007588.
Stern, Robert J. (2004). “Subduction initiation: Spontaneous and induced”. In: Earth and Planetary Science Letters 226. DOI: 10.1016/j.epsl.2004.08.007.
Stern, Robert J. and Taras Gerya (2018). “Subduction initiation in nature and models: A review”. In: Tectonophysics 746. DOI: 10.1016/j.tecto.2017.10.014.
How to cite: Fedeli, V., Regorda, A., and Marotta, A. M.: Preconditioning of subduction zone initiation at passive margins by gravitational instabilities, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4050, https://doi.org/10.5194/egusphere-egu26-4050, 2026.
Ophiolites, as fragments of ancient oceanic lithosphere emplaced onto continental margins, offer a valuable record of the magmatic, tectonic, and mantle processes that shaped former oceanic basins. This study investigates crust–mantle interactions within ophiolite complexes of the northeastern Himalaya using a multi-proxy geochemical approach that integrates whole-rock major and trace element chemistry, mineral chemistry, isotopic signatures, and Platinum Group Element (PGE) systematics. PGEs provide a robust means of tracing mantle processes due to their sensitivity to degrees of partial melting, sulphur saturation, and redox conditions. By examining PGEs in mantle-derived peridotites, chromitites, and associated crustal rocks, this research aims to delineate the roles of partial melting, fractional crystallization, and post-magmatic alteration in shaping the composition of ophiolitic sequences. The study further assesses how variations in PGE distribution reflect differences in tectonic setting, from mid-ocean ridge to supra-subduction zone environments. Through comparative analysis of ophiolites formed in diverse geodynamic contexts, this work addresses existing gaps in understanding the processes governing ophiolite genesis and emplacement during subduction, obduction, and continental collision. The results are expected to refine current models of oceanic lithosphere formation, improve constraints on mantle melting regimes, and enhance interpretations of crust–mantle evolution in convergent margin systems. Overall, this research contributes to a more comprehensive understanding of mantle geochemistry, magmatic differentiation, and tectonic reconstruction in the northeastern Himalayan region.
How to cite: Chaubey, M.: Exploring Crust–Mantle Relationships in Northeastern Himalayan Ophiolites Through Integrated Geochemical and PGE Systematics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-978, https://doi.org/10.5194/egusphere-egu26-978, 2026.
The tectonic history of the New Hebrides Island Arc (NHIA) is complex and characterized by collisions of oceanic plateaus, subduction interface rotation, as well as fragmentation and ultimately subduction polarity changes. Despite the intricate tecto-magmatic evolution of the NHIA, geochemical data are sparse and the geodynamic processes governing magmatism in the NHIA are poorly understood.
Between 14° and 17° South, along the New Hebrides Trench, collision and subsequent subduction of the d’Entrecasteaux Zone (DEZ) with the NHIA results in various erosional and accretionary processes. The DEZ encompasses the North d’Entrecasteaux Ridge (NDR) and Bougainville Guyot, which represent the immediate interface of the collision zone. In the vicinity of New Caledonia, the DEZ was previously interpreted as a horst-graben system, while the Bougainville Guyot is commonly referred to as part of a southern seamount chain.
Here, we present new geochemical and Sr-Nd-Hf-Pb isotopic data on volcanic rocks from drill sites 831 (Bougainville Guyot), 828 (NDR), 829 (NHIA fore-arc), as well as from the island of Espiritu Santo which formed in the Miocene Melanesian island arc. Drill site and volcanic arc samples differ distinctly in Nd-Hf isotopic records, indicating that fore-arc samples from drill site 829 comprise accreted material from the subducting plate, while the island arc samples exhibit a mantle source consistent with previous arc formation above Indian MORB-like mantle.
In addition, our new data suggest a strong slab-derived fluid influence on the chemical composition of samples from all locations. Relatively radiogenic Sr isotopic records together with negative Nb-Ta anomalies and positive Pb anomalies in samples originating the d’Entrecasteaux Zone, support the model that the DEZ represents a fossil island arc.
We refine the understanding of the tectonic evolution of the NHIA by providing further geochemical constraints on the mantle composition and magma genesis of arc, fore-arc as well as of the subducting DEZ. Isotope and trace element data of the NDR and Bougainville Guyot resemble island arc tholeiites from the Mariana and Kermadec island arcs. Thus, the DEZ probably represents an immature island arc, implying that such magmatically thickened and therefore buoyant structures can be subducted.
How to cite: Baumann, N. B., Haase, K. M., Schneider, K. P., Regelous, M., and Chivas, A. R.: Geochemical Evidence for Island Arc Subduction Beneath the New Hebrides Island Arc, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16907, https://doi.org/10.5194/egusphere-egu26-16907, 2026.
Active arc basalts have higher Sr/Nd ratios than the bulk continental crust. The significant delamination of low-density Sr-bearing plagioclase-rich lower arc crust cumulates is unlikely. Here, we compile geochemical data from 1875 – 0 Ma arc basalts (5.5-6.5 wt.% MgO) and demonstrate that Phanerozoic fossil (6.2 – 52.8; average: (26.5 ± 11.5 (1 σ)) and active (27.8 – 67.9; average: 42.1 ± 9.8 (1 σ)) arc basalts have higher average Sr6/Nd6 ratios than those of Proterozoic fossil arcs (6.6 – 45.4; average: 16.9 ± 9.8 (1 σ)). There were increases in the average Sr6/Nd6 ratios of arc basalts at 800 – 600 and 150 – 100 Ma. The average Sr/Nd ratios of global subducting sediment (12) and depleted mantle (14) are considerably lower than those of active arc basalts. The Sr6/Nd6 ratios of active arc basalts do not correlate with Th6/La6, 143Nd/144Nd and 87Sr/86Sr and crustal thickness. Active arc basalts have high Nd6/Sr6 and Sr6/Th6 and low 87Sr/86Sr ratios. This indicates the high Sr6/Nd6 ratios are not influenced by crustal thickness or siliciclastic sediment subduction but rather slab-derived fluids. Higher Sr contents in seawater due to increased continental weathering associated with the rise of the continents in the Neoproterozoic, and increases in the amount of abiogenic and biogenic carbonate being subducted at 800 and 150 Ma, respectively, led to the high Sr6/Nd6 ratios of basalts from Phanerozoic fossil and active arcs. The increase in the Sr contents of seawater led to the generation of more Sr-rich basaltic magmas following the dehydration and/or melting of altered oceanic crust. The subduction of pelagic carbonates after 150 Ma resulted in the generation of the high Sr6/Nd6 of basaltic lavas from active arcs. Therefore, the compositions of basaltic arc lavas track temporal changes in the global Sr and C cycles.
How to cite: Sotiriou, P., Regelous, M., and Haase, K.: Compositions of basaltic arc lavas track temporal changes in the global Sr cycle , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1461, https://doi.org/10.5194/egusphere-egu26-1461, 2026.
Granitoid magmas are abundant in subduction zones and form large portions of the upper continental crust. However, the formation of granitoid magmas remains debated, with models proposing (1) evolution from mantle-derived mafic melts by assimilation-fractional crystallization (AFC), (2) partial melting of lower to middle continental crust induced by mafic underplating, and (3) partial melting of metasomatized pyroxenite in the mantle. Since the Oligocene, slab rollback and trench retreat have caused the Aegean subduction zone to migrate approximately 350 km southwestward, resulting in extensive mafic to felsic magmatism with numerous granitoid intrusions in the region. We present new whole-rock major and trace element data together with Sr-Nd-Pb isotope compositions for the 15 to 8 Ma granitoids from Tinos, Mykonos, Naxos, Paros, Lavrion, and Serifos, as well as metasedimentary rocks of the Cycladic Blueschist Unit (CBU) from Tinos, Syros, Andros, and Sifnos. The CBU metamorphic rocks comprise low-grade metamorphic schists, marbles, and high-pressure mélanges and were subducted at the Aegean subduction zone. The metasediments received a high-pressure metamorphic imprint between 55 and 30 Ma. They exhibit element compositions similar to modern Eastern Mediterranean sediments, but many have higher initial 207Pb/204Pb and 208Pb/204Pb than the sediments from the Hellenic Trench. These differences indicate that the composition of subducted sediments changed over time at the Aegean subduction zone. Most granitoids display geochemical signatures characteristic of arc magmas and represent an isotopic end-member of Aegean magmatism in Sr-Nd-Pb isotope space. The isotopic compositions of many granitoids overlap with those of sediments and CBU metasediments, whereas others display distinctly more radiogenic (Pb) signatures. The Cyclades Continental Basement has much higher Sr isotope ratios than the granitoids. Consequently, the isotope composition of the granitoids does not support partial melting of lower continental crustal rocks. Partial melting of metasomatized pyroxenite is unlikely, as most granitoids lie on fractional crystallization trends. The high Th/Nd and low Ce/Pb of the granitoids indicate a fractionation of these elements by accessory minerals during partial melting of the upper crustal rocks. We propose that most granitoid magmas in the Aegean form by fractional crystallization of mafic magmas derived from mantle sources modified by subducted upper continental crustal components. The granitoids require a more radiogenic (Sr and Pb) subducted component than observed in the CBU metasediments or modern sediments, possibly related to the subduction of microcontinental fragments.
How to cite: Wolf, J., Haase, K. M., Regelous, M., Stouraiti, C., Bröcker, M., Hars, E. M., and Voudouris, P. C.: Geochemical and Isotopic Constraints on the Genesis of Granitoids in the Aegean Subduction Zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17281, https://doi.org/10.5194/egusphere-egu26-17281, 2026.
We present new zircon U–Pb–Hf and whole-rock geochemical data for Late Jurassic–Early Cretaceous volcanic rocks of the Great Xing’an Range, NE China, to constrain the influence of overprinting by the Mongol–Okhotsk and Paleo-Pacific tectonic regimes on NE Asia. The results of SIMS and LA–ICP–MS zircon U–Pb dating indicate that the late Mesozoic volcanism in the Great Xing’an Range occurred in three stages: Late Jurassic (158–153 Ma), early Early Cretaceous (ca. 141 Ma), and late Early Cretaceous (131–130 Ma). Based on our results and data from the literature, we revise the late Mesozoic stratigraphic framework of the Great Xing’an Range. The Middle Jurassic hiatus in the northern part of the range suggests crustal thickening related to the closure of the Mongol–Okhotsk Ocean. Late Jurassic andesites are geochemically similar to adakites generated by partial melting of delaminated lower crust. The early Early Cretaceous volcanic rocks are dominated by A-type rhyolites with zircon eHf(t) values of + 5.3 to + 10.1 and TDM2 ages of 857–498 Ma, which suggest that the primary magma was derived via partial melting of newly accreted crust. The Late Jurassic–early Early Cretaceous volcanic rocks were formed in an extensional environment related to the collapse of thickened lithosphere after the closure of the Mongol–Okhotsk Ocean. The late Early Cretaceous A-type rhyolites, bimodal volcanic rocks, and coeval rift basins were formed in an extensional setting related to westward subduction of the Paleo-Pacific Plate.
How to cite: Li, Y.: Late Mesozoic stratigraphic framework of the Great Xing’an Range, NEChina, and overprinting by the Mongol–Okhotsk and Paleo-Pacifictectonic regimes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7429, https://doi.org/10.5194/egusphere-egu26-7429, 2026.
The subduction zones are vital places for material cycling and energy exchange between the Earth's surface and interior. Previous researches mainly focuses on the effects of deep magma activities in controlling surface processes. However, the influence of surface processes on the nature of arc magmas in subduction zones remains poorly understood. Nevertheless, subducted sediments may preserve records of surface climatic fluctuations, leading to distinct chemical heterogeneities in Earth's interior. Northeast (NE) Asia, as a typical region of sequential tectonic regimes, provides potential in studying various influences of surface processes on the nature of arc magmas in subduction zones owing to occurrence of Permian and early Mesozoic mafic arc rocks with different geochemical features.
Previous studies suggest that the early Permian calc-alkaline volcanic rocks in the eastern margin of the Jiamusi Massif, together with the Yuejinshan accretionary complex, reveal that westward subduction of the Paleo-Asian oceanic plate occurred beneath the Jiamusi Massif, whereas the Late Triassic and Early Jurassic calc-alkaline igneous rocks, along with the coeval porphyry-type Cu-Mo deposits and Jurassic accretionary complexes in eastern Jilin and Heilongjiang provinces (NE China), indicate that the initial subduction of the Paleo-Pacific plate beneath Eurasia took place during the Late Triassic-Early Jurassic.
New whole-rock Mo-Zn-Sr-Nd-Pb isotopic data for these early Permian (293 Ma) and the Late Triassic (202–213 Ma)-Early Jurassic (183–185 Ma) mafic igneous rocks indicate: 1) that the synergistic changes in Sr-Nd-Pb isotope compositions have revealed the contribution of global subducting sediments (GLOSS); 2) that the consistent Zn isotopic compositions (δ66Zn = 0.20‰ to 0.30‰), similar to those of mid-ocean ridge basalts (MORB, δ66Zn = 0.28‰ ± 0.06‰; Wang et al., 2017), excluded the potential contribution of carbonates (generally low δ66Zn) and the mantle partial melting (no correlations with MgO); 3) that the early Permian basaltic rocks exhibit generally lighter Mo isotopic signatures (δ98Mo = -0.99‰ to -0.07‰) compared to the depleted MORB mantle (DMM, δ98Mo = -0.204‰ ± 0.008‰; McCoy-West et al., 2019), suggesting that the early Permian mafic arc magmas were sourced from a lithospheric mantle modified by oxidized sediment; and 4) that the Late Triassic-Early Jurassic gabbros display generally heavier Mo isotopic compositions (δ98Mo = -0.18‰ to 0.54‰) than DMM, suggesting the Late Triassic-Early Jurassic gabbros were sourced from a lithospheric mantle modified by reduced sediment. Taken together, we conclude that the lithospheric mantle in NE Asia experienced the transformation from oxidized to reduced sediment modifications during early Permian to early Mesozoic and that different surface processes control nature of arc magmas in subduction zones. These conclusions are also supported by the late Paleozoic-early Mesozoic stratigraphic records. In summary, our investigation demonstrates that arc magmas exhibit limited geochemical variability in non-redox-sensitive elemental signature despite extreme environmental perturbations, but redox-sensitive isotopes (such as Mo) could serve as sensitive tracers of recording climatic fluctuations, especially in paleo-surface redox events.
This work was financially supported by the National Natural Science Foundation of China (Grant: U2244201).
- Wang et al. (2017). Geochimica et Cosmochimica Acta, 198, 151–167.
- McCoy-West et al. (2019). Nature Geoscience, 12, 946–951.
How to cite: Zhang, W., Tang, J., Xu, W., Wang, F., and Hong, K.: Effects of surface processes on nature of arc magmas in subduction zones revealed by Mo-Zn isotopes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4812, https://doi.org/10.5194/egusphere-egu26-4812, 2026.
Subduction zones are the main sites of surficial material transfer from subducted slab into the mantle wedge. Increasing numbers of studies have proposed a material-transport models that subducted mélanges detach as solid-state diapirs from the slab-top and then partially melt at higher temperatures as they ascend through the mantle wedge (Nielsen and Marschall, 2017). While the ability to diapiric melting of subducted mélanges was previously constrained in experimental and numerical models, the conditions for its formation were poorly investigated in actual subduction zones.
Here, we report major- and trace-element, and Sr-Nd-Mg-Zn isotopic results for the Oligocene syenites in NE Asia, inferring their affinity with diapiric melting of subducted mélanges as well as mantle dynamics. Furthermore, we investigate the partial melting behaviors of natural mélanges at estimated P-T conditions at which mélange melting begins. These syenites exhibit Hf-Nd fractionation but little variation in Nd isotopes (Nielsen and Marschall, 2017). Moreover, these syenites have heavy Mg isotopic compositions (δ26Mg=−0.02‰~+0.57‰), consistent with the inferred residual components of mélange after dehydration, jointly supporting the mélange-diapir melting model. Our results and the tectonic setting indicate that melting of mélange diapirs occurred preferentially during tectonic transitions, such as the formation of a back-arc basin triggered by trench-perpendicular mantle flow. The low-viscosity mantle with an incompressible stress field triggered melting of the mélange diapirs. We roughly constrain the P-T conditions at which mélange melting begins. These syenites have higher LREEs and HFSEs contents than the experimental melts of subducted mélange, which is consistent with the addition of the carbonated silicate melts derived from the carbonated peridotites. The Zn-Sr-Nd isotopic compositions of syenites exhibit trends toward carbonated peridotites, jointly indicating the interaction between molten subducted mélange and carbonated peridotites. Generation of carbonated silicate melts occurs at ≤6 GPa. Moreover, magnesite was involved in the magmatic processes of carbonated peridotites, as recorded by relatively heavy Zn isotopic compositions with depleted Sr and Nd isotopic compositions. Magnesite is stable at pressures of ≥4.5 GPa. Therefore, the Oligocene mélange diapiric melting possibly occurred at the asthenospheric depths assumed by the seismic tomography (Tamura et al., 2002; Hong et al., 2024).
We further investigate the partial melting behaviors on natural sediment-dominated mélange materials from the NE Asian Margin. We performed a series of three melting experiments using large-volume press at estimated P-T conditions (4-6 GPa, 1300-1400 ℃). Partial melts produced in our experiments have trace-element abundance patterns that are typical of alkaline arc lavas, such as enrichment in LILEs and depletion in Nb and Ta. The major- and trace-element compositions of experimental melts are consistent with the Oligocene syenites in NE Asia. These findings confirmed that mélange diapiric melting more possibly occurred in asthenosphere, which is deeper than the depth inferred in previous studies.
This work was financially supported by the National Natural Science Foundation of China (Grant 42372065 and 424B2017).
References:
Hong, et al., 2024, Geology, v. 52, p. 539-544.
Nielsen, and Marschall, 2017, Science Advances, v. 3.
Tamura, et al., 2002, Earth and Planetary Science Letters, v. 197, p. 105-116.
How to cite: Hong, K., Wang, F., and Xu, W.: The conditions for Oligocene diapiric melting of the subducted mélange in the NE Asia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6402, https://doi.org/10.5194/egusphere-egu26-6402, 2026.
Subduction zones represent primary sites for material exchange between the mantle and crust. Over the long course of geological history, the mantle is frequently subjected to superimposed reworking by materials derived from distinct subduction zones. However, relatively few studies have focused on mantle multi-stage metasomatism driven by different tectonic systems. The Xing’an Massif, situated in the eastern segment of the Central Asian Orogenic Belt, was influenced by the Mongol-Okhotsk and Paleo-Pacific tectonic systems during the Mesozoic. Consequently, systematic analysis of spatiotemporal geochemical variations in Mesozoic igneous rocks across this region provides valuable constraints for deciphering mantle multi-stage metasomatism. Here, we report integrated elemental and Sr-Nd-Pb-Mo isotopic analyses of the Late Triassic and late Early Cretaceous basaltic andesites from the Xing’an Massif. The Late Triassic samples exhibit elevated δ98/95Mo values (+0.49‰ to +0.56‰), which are significantly higher than the normal mantle value of -0.20‰ ±0.01‰. They also show enrichment in fluid-mobile elements (e.g., Ba, Cs) and high Sr/Nd ratios (34 to 36). Combined with high Ce/Mo ratios (115 to 145) and moderately enriched Sr-Nd-Pb isotopic compositions, these features indicate the mantle source originated from the partial melting of a mantle wedge metasomatized by both serpentinite-derived fluids and sediment-derived melts during the southward subduction of the Mongol-Okhotsk oceanic plate. The late Early Cretaceous basaltic andesites exhibit high δ98/95Mo values (-0.13‰ to +0.70‰) and pronounced enrichment in fluid-mobile elements, demonstrating geochemical affinities to the Late Triassic rocks. This similarity implies that the late Early Cretaceous mantle source components were inherited from pre-existing Late Triassic metasomatized mantle domains. However, their more enriched Sr-Nd-Pb isotopic compositions than those of Late Triassic counterparts suggest the addition of subsequent sediment melts contributed to their mantle source. Magmatism, tectonism, and paleomagnetic evidence indicate that the eastern segment of the Mongol-Okhotsk Ocean closed during the Middle Jurassic to Early Cretaceous. Therefore, these additional sediment melts should have been derived from the Paleo-Pacific Plate. Collectively, this study identifies the multi-stage metasomatism of mantle by materials derived from different subduction zones, thereby providing new constraints for reconstructing the multi-stage tectonic transition processes and the spatiotemporal extent of their impacts in Northeast Asia.
This work was financially supported by the China National Science and Technology Major Project (No. 2024ZD1001104) and the National Natural Science Foundation of China (No. U2244201).
How to cite: Xue, Y., Tang, J., Xu, W., Wang, F., and Wang, Z.: Lithospheric mantle multi-stage metasomatism: Constraints from Sr-Nd-Pb-Mo isotopes of Mesozoic basaltic andesites in the Xing'an Massif, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6355, https://doi.org/10.5194/egusphere-egu26-6355, 2026.
Volatile cycling in subduction zones plays a pivotal role in regulating long-term carbon storage and the habitability of Earth's deep biosphere. In particular, serpentinization of the subducting lithospheric mantle at outer-rise regions plays a pivotal role in shallow volatile cycling, facilitating both carbonation and the production of reduced volatiles such as hydrogen and methane. These reactions not only contribute to deep carbon storage but also provide chemical energy for sustaining subsurface microbial ecosystems. However, volatile fluxes associated with this process remain poorly constrained, primarily due to the inaccessibility of the outer-rise mantle, the scarcity of direct samples, and the inherent limitations of geophysical resolution at depth. Consequently, the partitioning and fate of slab-derived volatiles prior to deep subduction remain critical unknowns. Here, we present high-resolution two-dimensional visco-elasto-plastic models that simulate coupled serpentinization and carbonation within the faulted oceanic mantle seaward of the trench. Our results show that carbonation efficiency is primarily governed by the degree of serpentinization and the partial pressure of CO₂ in infiltrating fluids. These findings provide quantitative constraints on volatile processing in the shallow slab mantle and underscore the role of tectonically focused hydration in shaping deep carbon fluxes. More broadly, they highlight how slab deformation influences the geochemical and energetic architecture of Earth's deep subsurface.
How to cite: Zhang, R., Yang, J., and Zhao, L.: Coupled Serpentinization and Carbonation in the Outer-Rise Mantle: Implications for Slab Volatile Budgets, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10383, https://doi.org/10.5194/egusphere-egu26-10383, 2026.
Subduction zones provide a structured pathway for the transfer of Earth-surface materials into the mantle, whereby slab dehydration and melting release water-rich components primarily into the mantle wedge, regulating their initial entry into the convecting upper mantle.
Recent studies (e.g., Yang et al., 2021) suggest that the upper mantle can be broadly divided into subduction-modified and subduction-unmodified domains at a global scale. The former is widely distributed in the Indian Ocean and in parts of the Atlantic, reflecting the asthenospheric metasomatism and recycling associated with subducted materials. In contrast, the subduction-unmodified domain is largely restricted to the Pacific basin and shows little evidence for the involvement of subducted components. This contrast highlights the critical role of circum-Pacific region, which has experienced nearly continuous subduction for at least the past 200 Myr, and may have acted as a long-existing “subduction shield”, limiting the dispersal of slab-derived materials into the Pacific mantle, and providing an ideal setting to examine how long-term subduction processes have contributed to upper mantle heterogeneity. However, whether such large-scale geometry patterns can be reproduced dynamically, and whether it is geodynamically reasonable to classify the upper mantle into subduction-modified and subduction-unmodified domains mantle, remain open questions.
In this study, we employ CitcomS, a finite-element geodynamic code that solves thermo-chemical convection in a spherical shell, to simulate mantle convection and examine the transport of subduction-modified material through the upper mantle, constrained by GPlates-derived plate velocities based on published plate tectonic reconstruction model. Passive tracers are introduced to track material transport over time. By identifying tracers that pass through the mantle wedge, we determine materials acquire subduction signals and evaluate how they are redistributed within the convective mantle.
This analysis provides a quantitative framework for accessing whether the modeled mantle can be conceptually classified into subduction-modified and subduction-unmodified regions, and for investigating how long-term subduction contributes to global upper-mantle heterogeneity. More broadly, our results offer a new perspective for investigating the long-term dynamic evolution of the circum-Pacific subduction system and its role in shaping mantle structure.
How to cite: Yeh, C. Y., Wu, J. T.-J., and Tan, E.: Testing the link between Panthalassa tectonic evolution and subduction-modified mantle heterogeneity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12622, https://doi.org/10.5194/egusphere-egu26-12622, 2026.
There are three main types of volcanism on Earth: rifting volcanism at diverging plate margins (e.g. mid-ocean ridges), arc volcanism at converging plate margins (e.g. Japan and the Andes), and intraplate volcanism occurring relatively far from plate boundaries. Identifying the source of intraplate volcanism, however, remains one of the most challenging problems in geoscience.
Intra-oceanic volcanoes (e.g. Hawaii) are generally attributed to the ascent of hot and buoyant mantle material (plumes) rising from the core–mantle boundary (CMB). These volcanoes are characterised by frequent eruptions (every few years), a clear age progression (volcanic landforms are older away from the active eruption centre), sub-alkaline tholeiitic magmas, and high 3He/4He ratios, indicating a deep mantle source.
In contrast, intraplate continental volcanoes are more enigmatic. They typically display sporadic eruptions (every few thousand years), no systematic age progression, alkaline and SiO2-undersaturated magmas, and low 3He/4He ratios, which exclude a deep mantle reservoir. Several volcanic provinces in the Mediterranean region exhibit these features.
Among them, a group of provinces located north of the Alps constitutes the European Cenozoic Rift System (ECRiS): (1) Massif Central (France), (2) Eifel (Germany), (3) Eger Rift (Czech Republic), and (4) Pannonian Basin (Hungary). Seismic tomography beneath these regions reveals slow seismic velocity anomalies in the upper mantle, interpreted as warm or partially molten material, overlying fast velocity anomalies in the mantle transition zone (MTZ). These fast anomalies are commonly interpreted as cold, stagnant slabs subducted during the closure of the Tethys Ocean.
Plumes rising from the MTZ differ fundamentally from those originating at the CMB. Their ascent is thought to be driven primarily by the chemical buoyancy of relatively light and possibly volatile-rich material, whereas CMB plumes (e.g. Hawaii and Iceland) are driven by the thermal buoyancy of very hot mantle material (>3000 K). A recent hypothesis proposes that intraplate volcanism within the ECRiS is caused by hydrous plumes generated by flux melting of the subducted Tethyan oceanic crust, now stagnating in the MTZ beneath Europe. This geodynamic setting is referred to as a Big Mantle Wedge (BMW).
How to cite: Marzotto, E.: Unravelling the Origin of European Cenozoic Rift System (ECRiS) Intra-Continental Volcanism, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12955, https://doi.org/10.5194/egusphere-egu26-12955, 2026.
The pull force exerted by the down-going subducting oceanic slabs is the primary force driving the motion of the tectonic plates. This force has been shown to generate tensional stresses within the trailing part of subducting plates, which can induce extensional reactivation of inherited discontinuities and weaknesses, such as passive margins. Surprisingly, compressive intraplate stress conditions have also developed during subduction at the trailing passive margins, such as in northern Africa, resulting in spectacular geological fold-and-thrust belts. Whether these compressional features were formed due to the processes acting at the subduction plate boundary (e.g., the arrival of continental fragments into the subduction zone) or, instead, are related to the dynamics of the leading oceanic slab (e.g., the arrival of the down-going slab to the 660-km-deep mantle discontinuity) is unclear.
Here we present a series of 2D numerical subduction models, utilizing the ASPECT geodynamic code. The models are kinematically driven, mimicking the far-field boundary forces acting on the subducting plate. We track the evolution of stresses and strains within the trailing passive margins, incorporated as a weak and thin crust between the oceanic and continental domains. Our preliminary results suggest that the stress field in the trailing passive margin responds to the behavior of the slab at depth. During the slab’s free sinking phase or during slab rollback, slab sinking rates across the upper mantle exceed the prescribed plate velocity, resulting in extensional stresses that are transmitted to, and concentrated at, the passive margin. In contrast, during the anchoring of the slab to the lower mantle (i.e., at 670 km depth) and during slab folding, the rates at which the leading slab is sinking in the upper mantle are lower than the prescribed plate velocity, inducing intraplate shortening at the trailing passive margin. The timescales and temporal behavior of passive margin deformation match those of slab dynamics, with fast slab buckling behavior leading to likewise fast oscillating stress changes in the margins. Our results may help explain the observed switches between tensional and compressional phases at the northern African passive margins and the overall heterogeneity of passive margin deformation styles within subducting plates, ranging from normal faulting and magmatism to shortening and folding.
How to cite: Fisch, G., Brune, S., Pons, M., and Granot, R.: Can subducting slab dynamics induce intraplate shortening at the trailing passive margins?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10032, https://doi.org/10.5194/egusphere-egu26-10032, 2026.
The dip angle of subducting slabs is one of the key factors controlling mantle flow and upper-plate tectonic evolution. In the extreme case, flat subduction forms when the dip angle of the slab is less than 15°. Although this scenario accounts for only about 10% of the present-day global subduction system, it has profound geological significance for continental tectonic evolution, magmatic activities, and mantle–crust interactions. Previous studies have proposed multiple mechanisms influencing the evolution of slab dip, with the proposed controlling factors including the properties of the overriding plate, the buoyancy of the subducting slab, and plate convergence rates; however, a unified dynamical understanding has not yet been established. Based on a global geodynamical model with data assimilation that systematically simulates subduction evolution over the past 200 Ma, we quantitatively investigate the relationship between slab dip and its dynamical origin. We select representative subduction systems in East Asia, South America, and North America to analyze the evolution of slab dip over time from subduction initiation to termination.
The results reveal a new mechanism controlling slab dip angle: dynamic pressure in the mantle wedge. As subduction proceeds, the dynamic pressure in the mantle wedge generally decreases, leading to an increasing pressure difference across the subducting slab; this directly reduces the slab dip angle over time, as confirmed from all subduction zones considered. More tests show that the lateral pressure difference also fluctuates with time, with the slab dip angle demonstrating the same variation, further confirming their causal relationship. We conclude that this lateral force represents an important new mechanism driving changes in slab dip.
How to cite: Li, X. and Liu, L.: Slab dip angle variation controlled by evolving lateral pressure gradients, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9783, https://doi.org/10.5194/egusphere-egu26-9783, 2026.
The interaction between subducting seamounts and overriding sediments perturbs the stress field and effective strength, affecting the conditions for megathrust earthquake generation and likely weakens interplate coupling. In the westernmost Nankai Trough around Hyuga-nada, M8-class earthquakes have not been reported yet. The Kyushu–Palau Ridge (KPR), marking the boundary between the Shikoku Basin and the West Philippine Basin (WPB), is subducting beneath Hyuga-nada. Slow earthquakes are frequently observed around the subducted KPR (sKPR). Key controlling factors for earthquake generation include seamount geometry, stress perturbations induced by subduction, and weakening plus permeability enhancement due to fracturing of the overriding strata.
In addition to estimating the BSR-derived heat flow, we conducted seafloor heat flow measurements, combined with interpretation of reflection seismic data, to delineate the morphology of the overriding plate and near-surface deformation structures. The sKPR lies beneath the Toi Seamount (Tsmt, exposed above the seafloor). Its eastern and western edges coincide with magnetic anomaly boundaries, while its northern edge corresponds to the northern slope of Tsmt. The coincidence between steep basement slopes and areas of frequent low-frequency tremors (LFTs) suggests that LFT activity is controlled by the “edges” of sKPR.
The influence of KPR subduction is evident in seafloor morphology and deformation structures. Numerous faults and lineaments are identified beneath the seafloor, with compressional structures dominant to the N–NW and extensional structures to SE. In the N–NW, multiple NE–SW trending ridges are present, and thrusts formed during accretionary prism development may have been exhumed by seamount collision. In contrast, the SE side is characterized by abundant collapse and landslide deposits.
Heat flow estimated from BSR depths around sKPR is ~40 mW/m² or lower, consistent with surface heat flow measurements, reflecting the cold (old) nature of the subducted sKPR and WPB. On the northern (leading) side, BSR-derived heat flow is lower (~25 mW/m²) above SW–NE trending thrust faults. This is likely due to seamount-driven compression and thickening of sediments, and reducing the thermal gradient. Blockage of sediment transport by Tsmt, also promotes thickening and cooling. Conversely, surface heat flows exceeding 300 mW/m² were observed near thrusts in front of Tsmt. While water temperature fluctuations, deep-sea turbidites, or slope erosion may contribute, the proximity to the base of a thrust-fault scarp, the identification of a low-velocity zone near the LFT cluster from OBS data, and chemical anomalies in pore waters suggest fluid expulsion along fault conduits under frontal compression. Poroealstic modeling supports this interpretation, showing pore fluid circulation induced by seamount loading if high permeability around the KPR is assumed. The fluid discharge is driven by the horizontal compression leading to overpressure and the fault pathway formation. However, the number of data points remains limited, alternative explanations cannot be excluded. Direct evidence of fluid discharge (e.g., biological communities) is lacking. Verification must therefore await future investigations.
How to cite: Kinoshita, M., Hashimoto, Y., Hamada, Y., Toki, T., and Nakata, R.: Morphological and geothermal features around subducted seamount in Hyuga-Nada, western Nankai Trough, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8436, https://doi.org/10.5194/egusphere-egu26-8436, 2026.
Deep earthquakes within subducting slab into the mantle transition zone (MTZ) often exhibit spatial variations along the strike of the slab. Existing mechanisms, including dehydration embrittlement, transformational faulting, and thermal shear instability, have been proposed to explain the cause of deep earthquakes; however, these hypotheses fail to account for the deep earthquake cluster within stagnant slab. Given that variable water input plays a crucial role in the distribution of seismicity within the arc system, spatial variations in the transport of subducted water could potentially control the clustering of deep-focus earthquakes in the MTZ. Northeast (NE) Asia is an ideal region to investigate this problem, where the Pacific slab stagnates continuously from north to south and extends westward for <1000 km in the MTZ, with deep seismicity occurring in clusters in the MTZ. Meanwhile, previous studies have shown that surficial water can be transported to the MTZ in this region (Xing et al., 2024), and the thermal state of subducting slab beneath NE Japan exhibits along-strike variability, with slab temperature decreasing gradually from north to south (Wada et al., 2015), implying the potential spatial variations in deep water cycling.
Here, we report major and trace element compositions, together with Sr-Nd-B isotopic data of basalts in NE Asia to trace deep water cycling and investigate the spatial co-variations between water carriers and deep earthquakes in Northeast Asia. Our results reveal prominent along-strike differences in B isotopic compositions. Northern arc basalts from Hokkaido show heavy and variable δ11B values (−14.55‰ to +6.47‰), whereas associated intraplate basalts have light δ11B values (−10.44‰ to −5.15‰). In contrast, southern arc basalts from Honshu display homogeneous and light δ11B values (−4.7‰ to −3.1‰; Moriguti et al., 2004), against variable intraplate region (−8.42‰ to +7.71‰). These contrasts reflect distinct carriers transporting water into the MTZ. In the north, dehydration of hydrous minerals leaves minimal water carried by nominally anhydrous minerals, which corresponds to the absence of deep-focus earthquakes in the MTZ. Conversely, dense hydrous magnesium silicates transport large amounts of water into the MTZ in the south, consistent with a notable cluster of deep-focus earthquakes. Therefore, we conclude that water carriers into the MTZ critically control along-strike earthquake clustering.
This work was financially supported by the National Key R&D Program of China (Grant 2022YFF0801002) and the National Natural Science Foundation of China (Grant 42372065).
References:
Wada et al., 2015, Earth and Planetary Science Letters, v. 426, p. 76-88.
Moriguti et al., 2004, Chemical Geology, v. 212, p. 81-100.
Xing et al., 2024, Nature Geoscience, v. 17, p. 579-585.
How to cite: Wang, F. and Zhao, W.-Y.: Spatial clustering of deep earthquakes controlled by water carriers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6115, https://doi.org/10.5194/egusphere-egu26-6115, 2026.
The nominally unhydrous wadsleyite and ringwoodite present in the mantle transition zone (MTZ), can contain up to 1–2 wt% of water, which creates large potential water storage capacity of this upper mantle zone. However, whether these water reservoirs in the MTZ can be eventually filled remains debatable. We developed new empirical model of deep hydrous mantle melting and performed systematic investigation of water dynamics in the MTZ by using new 2D thermo-hydro-mechanical-chemical (THMC) upper mantle models. Our results suggest that relatively cold solid-state mantle upwellings can start from thermally relaxed hydrated stagnant subducted slabs present at the bottom of the MTZ. These water-bearing plumes rise to and interact with the wadsleyite-olivine phase transition. Depending on the water content and temperature of these thermal-chemical plumes, they may trigger hydrous melting by water release from the wadsleyite upon its conversion to olivine. The hydrous melts are less dense than the solid matrix and rise upward in the form of either melt diapirs or porosity waives. Similar dehydration-induced melting process is also documented for subducting slabs crossing the lower MTZ boundary, where they can generate buoyant melt diapirs rising through the MTZ. Based on the investigated water dynamics, we propose that relatively small amounts of water (<0.1 wt%, <0.2 ocean masses) and a geologically moderate duration (<500 Myr) of the transient water residence should be characteristic for the MTZ. These findings also have implications for the long-term stability of the surface ocean mass on Earth and Earth-like rocky exoplanets due to rather small dynamic water storage in the MTZ.
How to cite: Gerya, T., Moccetti Bardi, N., Karato, S., and Murakami, M.: Transient water storage in the mantle transition zone governed by subduction and water-induced buoyancy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3055, https://doi.org/10.5194/egusphere-egu26-3055, 2026.
Diachronous slab break-off around the Adriatic microplate is inferred to occur with contrasting timing and kinematics on its western (Apennine) and eastern (Dinaride–Hellenide) margins. While the Apennines exhibit long-lived slab rollback followed by laterally migrating slab break-off, the eastern margin appears to have experienced earlier continental-collision-related shortening and slab break-off. To investigate the controlling factors on slab break-off and tearing in such a double-sided, oppositely dipping subduction system, we conduct 3D thermo-mechanical numerical experiments in which two subduction zones interact through a shared lower plate. We vary three key parameters: (1) the initial length of the oceanic lithosphere, (2) the initial subduction trench obliquities on each side (symmetric vs. asymmetric), and (3) oceanic plate ages, which collectively control the slab rollback velocity, trench rotation, interacting mantle flow, slab break-off, and tear propagation. In a symmetric reference experiment (with identical initial trench obliquity and oceanic plate length on both sides), closure of the short oceanic segment does not immediately trigger slab break-off. Instead, oceanic subduction evolves into intra-continental subduction, followed by a late-stage slab break-off. In contrast, on the longer oceanic segment, slab rollback drives trench retreat and rotation, causing progressive lateral plate decoupling that propagates along strike, and slab break-off initiates after the retreating trench meets the continent, long before continental collision. Asymmetric experiments (with different initial trench obliquity and oceanic plate length) demonstrate diachronous slab break-off on opposite sides. Here, on the shorter oceanic domain with lower trench obliquity, earlier continental collision and slab break-off occur, whereas on the longer oceanic domain with higher trench obliquity, slab rollback persists for a longer duration, accompanied by pronounced trench rotation, resulting in delayed slab break-off and tear propagation. Overall, our results indicate that (1) oceanic closure alone is not always sufficient to trigger slab break-off, (2) trench rotation linked to obliquity is a key factor controlling delayed slab break-off and tear propagation, and (3) a shorter oceanic domain with lower margin obliquity facilitates earlier continental collision and slab break-off. We propose that the tectonics around the Adriatic microplate can be interpreted as an interactive two-sided asymmetric subduction system in which the western margin evolves through obliquity-driven trench rotation and delayed slab break-off propagation, whereas the eastern margin experiences earlier slab break-off due to continental collision.
How to cite: Maiti, G., Andrić-Tomašević, N., Koptev, A., Faccenna, C., and Gerya, T.: Diachronous slab break-off in oppositely-dipping double subduction system: Insights from 3D numerical experiments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11741, https://doi.org/10.5194/egusphere-egu26-11741, 2026.
Speakers
- João Duarte, Lisbon, Portugal
- Sree Bhuvan Gandrapu, Pondicherry University, India
- Juliane Dannberg, GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany
- Nestor Cerpa, CNRS, France
- Emma Legros, Université Grenoble Alpes, France
- Tristan Pausch, University of Innsbruck, Austria
- Maria Sachpazi, NATIONAL OBSERVATORY OF ATHENS, Greece
- Daniel Douglas, Boston College, United States of America
- Wen-Yuan Zhao, Jilin University, China
- Lorine Bonnamy, University of Montpellier, France
- Ana Negredo
- Yongcheng Li, Northwest University, China
- Weicheng Jiang, China University of Geosciences, China
- Jiyu Liu, University of Science and Technology of China, China
- Priyanka Pandit, Indian Institute of Science Education and Research Kolkata, India
- Buchanan Kerswell, University of Liverpool, United Kingdom
- Lijun Liu, Institute of Geology and Geophysics, CAS, China
- Madhusudan Sharma, Geociencias Barcelona (GEO3BCN - CSIC), Spain
- Katie Lucas, University of Leicester, United Kingdom
- Emese Pánczél, HUN-REN CSFK, Hungary
- Stefan Markus Schmalholz, University of Lausanne, Switzerland
- Stacia Gordon, University of Nevada-Reno, United States of America
- Chao Yan, China University of Geosciences, Wuhan, China, China
- Daniel Gómez Frutos, Univeristy of Portsmouth, United Kingdom
- Valeria Fedeli, Università degli Studi di Milano, Italy
- Monika Chaubey, National Geophysical Research Institute, India
- Nils Björn Baumann, FAU Erlangen-Nürnberg, Germany
- Paul Sotiriou, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany
- Julian Wolf, Friedrich-Alexander-Universität, Germany
- Yu Li, Institute of Geology and Geophysics, Chinese Academy of Sciences, China
- Wushuang Zhang, Jilin University, China
- Kechun Hong, Jilin University, China
- Yiting Xue, Jilin University, China
- Rui Zhang, CAS, China
- Chia-Yu Yeh, National Taiwan University, Taiwan
- Enrico Marzotto, University of Potsdam, Germany
- Guy Fisch, Ben-Gurion university of the Negev, Israel
- Xiaoyi Li, Zhejiang Ocean University, China
- Masataka Kinoshita, The University of Tokyo, Japan
- Feng Wang, Jilin University, China
- Taras Gerya, ETH Zurich, Switzerland
- Giridas Maiti, Karlsruhe Institute of Technology (KIT), Germany