Orals: Wed, 6 May, 08:30–10:10 | Room -2.31
The tectonic history of Southeast Asia has been largely shaped by extensive subduction, with thousands of kilometers of lithosphere subducted since the Mesozoic. The tectonics of the Indonesia-Philippines region are particularly complex, with the convergence of the Australian plate from the south, the Indian plate from the west, and the Philippine Sea plate from the east. This region also features several deformation zones involving several microplates, whose kinematic reconstructions remain poorly understood. In this study, we use full-waveform adjoint tomography to elucidate the seismic absolute P- and S-wave velocity structure in the crust and mantle beneath Southeast Asia. We have collected a large waveform dataset from all available broadband seismic stations within and surrounding Southeast Asia, including a dense array in the Philippines. The inversion optimizes the normalized correlation coefficient between observed and synthetic seismograms within individual time windows. This approach allows us to fit regional multipathed waveforms and provides high-resolution seismic velocity images from the crust to depths of about 1000 km. Our model clearly reveals subducting slabs in the upper mantle beneath the Indonesia-Philippines region, including the Sumatra and Java slabs, the opposingly dipping Manila and Philippine Sea slabs, the Sangihe and Halmahera slabs beneath the Molucca Sea, and the Celebes Sea slab. These slabs correlate well with seismicity and show varying depth extents and dip angles. They behave differently when interacting with the mantle transition zone, with the southern Sumatra, Java, and Sangihe slabs clearly penetrating through the 660-km discontinuity. In addition, we identify several detached slab fragments in the upper mantle, including one beneath the Sulu Sea, likely associated with subduction at the Negros trench, and another northwest-dipping structure east of Sulawesi. In the mantle transition zone and lower mantle, we observe several broad fast anomalies beneath the South China Sea and the Philippine Sea plate that are disconnected from shallower slabs. These anomalies may correspond to the subducted Proto-South China Sea slab and the East Asian Sea slab, respectively, as proposed by recent tectonic reconstructions. Furthermore, our model shows a slab-like fast structure in the transition zone and lower mantle beneath northern Borneo, potentially representing a subducted and detached slab from the northwest Borneo Trough. Our high-resolution tomographic images provide new insights on how these slabs interact with the 660 km discontinuity as they have descended into the lower mantle.
How to cite: Liu, C., Sandvol, E., Grand, S., and Sevilla, W.: Imaging Subducting and Detached Slabs Beneath Southeast Asia Using Full-Waveform Tomography, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19549, https://doi.org/10.5194/egusphere-egu26-19549, 2026.
The island of New Guinea occupies the northern margin of the Australian Plate and has experienced rapid northward motion over the past ~30 million years. This movement led to collisions with volcanic island arcs on the Pacific Plate, producing some of Earth’s youngest mountain belts. These tectonic interactions not only reshaped the landscape but also created conditions for species diversification by fragmenting habitats, isolating ecosystems, and expanding land area. As volcanic islands accreted and were progressively uplifted, montane environments became separated from surrounding lowlands, promoting endemism across individual mountain ranges, exemplified by taxa such as Birds of Paradise. Understanding when and how these volcanic islands formed and collided with the Australian margin is therefore critical for linking tectonic processes with palaeo-landscape evolution and the development of megadiverse regions such as New Guinea.
The Cyclops Mountains provide a key example of this process. They represent a remnant volcanic island arc and ophiolite complex that was obducted onto the northern Australian margin in the early Miocene. Along with other accreted island fragments across northern New Guinea, the Cyclops Mountains were further uplifted and became increasingly isolated from lowland environments during final arc–continent collision in the Pliocene. This tectonic isolation fostered the development of distinct montane ecosystems that today host highly localised species, including Attenborough’s long-beaked echidna (Zaglossus attenboroughi), highlighting the dominant influence that collisional tectonic processes have had on New Guinea’s biogeographic evolution.
Here we present a new workflow for resolving the links between tectonic processes and palaeo-ecosystem change in active collision zones. By integrating geological fieldwork, palaeogeographic reconstructions, geochronology, biostratigraphy, and organic biomarker analyses, we reconstruct the emergence, submergence, and uplift of volcanic islands in the Cyclops Mountains from the Eocene through the Plio-Pleistocene, providing new insight into how tectonics shape long-term environmental and biological change.
How to cite: Webb, M., Hikmy, I. G., Gold, D., Morib, G., Magill, C., Kempton, J., and Gough, A.: Tectonic–ecosystem interactions in collision zones: a case study from the Cyclops Mountains of Indonesian New Guinea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6730, https://doi.org/10.5194/egusphere-egu26-6730, 2026.
Plate tectonics describes Earth’s lithosphere as a mosaic of rigid plates whose interactions drive volcanism, seismicity, mountain building, and crustal recycling. While oceanic crust is continuously created and destroyed as a conveyor belt, continental crust is commonly viewed as buoyant and long-lived. However, global geochemical estimates reveal a major imbalance between continental crust production and preservation, implying that large volumes of continental material have been recycled into the mantle throughout Earth’s history. The lack of direct geological evidence for this loss represents a key gap in our understanding of long-term Earth’s tectonic evolution.
Here, we address this problem using the record of NE Japan, a long-lived subduction system that preserves sedimentary and magmatic archives linked to arc processes. We analyze magmatic and detrital zircon U–Pb ages, Hf isotopes, and trace element (TE) geochemistry from forearc (sedimentary) and arc (igneous) units. Detrital zircon populations define age peaks at ~430, 360, 270, 184, 112, and 7 Ma, accompanied by a progressive loss of older zircon components through time. Hf isotopic data show three major shifts in crustal contribution that coincide with changes in the dominant age populations. In addition, REE systematics in igneous zircons indicate significant changes in magmatic redox conditions. Igneous zircon U/Yb ratios shift from enriched mantle/crustal values in 450–430 Ma samples to mantle values in ~270 Ma samples, documenting replacement of continental lithosphere with juvenile material. Ti-in-zircon temperatures show thermal pulses at ~430 Ma and ~270 Ma, supporting episodic magmatic flare-ups.
The sedimentary record reveals episodic magmatic flare-ups combined with sustained tectonic erosion, leading to the progressive removal of older crustal sources. A major Late Carboniferous event marks the complete loss of Precambrian crust beneath the arc, while we interpret that Cretaceous melting of the Permian arc crust might be linked to mid-ocean ridge subduction. These observations indicate cryptic continental loss beneath the NE Japan forearc. The igneous record corroborates the forearc sedimentary signal and provides additional constraints on the origin and evolution of individual crustal blocks. Together, the results are consistent with a Late Cambrian–Ordovician arc collision and help constrain the mechanisms responsible for large-scale continental loss beneath the NE Japan forearc during the Carboniferous, which should be accounted for in tectonic and paleogeographic reconstructions.
How to cite: Pastor Galán, D., Ganbat, A., Miyashita, A., and Tsujimori, T.: Recovering Missing Continental Crust to Understand Paleozoic Tectonic Evolution in East Asia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6861, https://doi.org/10.5194/egusphere-egu26-6861, 2026.
It is known that the current lithosphere of the South China Block is as thin as 60-70 km, yet what mechanisms modified the lithospheric structure remain highly controversial. Here we apply a new joint seismic inversion algorithm of body wave arrival times, surface wave dispersion data and teleseismic receiver functions to image lithosphere velocity structure of South China. Tabular high-velocity anomalies are imaged at depths of ~90–150 km in the asthenosphere beneath the convergent belt between the Yangtze and Cathaysia blocks that remain weakly connected with the stable Yangtze lithosphere. Based on obtained seismic images and available geochemical data, we interpret these detached fast wavespeed anomalies as partially destabilized lower lithosphere that initially delaminated at 180–170 Ma and has relaminated to their original position after warming up in the mantle by now. We conclude that delamination is the most plausible mechanism for the lithospheric modification and the formation of a Mesozoic Basin and Range-style magmatic province in South China by triggering adiabatic upwelling of the asthenosphere and consequent lithospheric extension and extensive melting of the overlying crust. Moreover, it also has a major control on the rich deposits of various metals in South China.
How to cite: Zhang, H. and Hou, Z.: Lithospheric delamination controls the Mesozoic Magmatic Province in South China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21953, https://doi.org/10.5194/egusphere-egu26-21953, 2026.
The Tethyan tectonic domain ranks among the world's most prolific hydrocarbon provinces. However, its eastern segment exhibits comparatively lower petroleum potential, significantly contrasting with the Middle East, with substantial variations in petroleum geological conditions across different basins. However, the fundamental geodynamic controls underlying this disparity remain poorly constrained. Through systematic analysis of the tectonic evolution of the eastern Tethys (including collision, rifting, drift, and accretion of major Gondwana-derived blocks) alongside the developmental characteristics and petroleum geology of associated basins, this study reveals that the nature, morphology, and scale of the underlying continental blocks exert fundamental controls on the formation and preservation of hydrocarbon-rich basins. These blocks are categorized into three types: large cratons, ribbon terranes, and microcontinental blocks. Large cratonic blocks (e.g., India, South China, North China, Tarim) possess high deformation resistance, with major tectonic deformation predominantly confined to their margins. Consequently, they typically preserve multiphase superimposed basins even related to pre-Gondwana rifting, developing multiple petroleum systems with substantial resource potential. In contrast, ribbon terranes (e.g., Lhasa, Qiangtang, Sibumasu) exhibit weak basements and commonly undergo pervasive modification by subsequent collisional and subduction-related tectonism. Only basins formed during the latest tectonic stage are effectively preserved, with locally favorable petroleum geological conditions. Similarly, microcontinental blocks in eastern Indonesia primarily preserve hydrocarbon-rich basins from the latest tectonic phase. However, Australian-affiliated blocks within this group, remaining in the relatively early stages of collision, can additionally retain continental margin deposits from the northern Australian block. The nature of the basement fundamentally dictates the development and modification of overlying petroliferous basins. This study provides a novel perspective for understanding differential hydrocarbon enrichment patterns across macroscopic regions.
How to cite: Zhu, W., Fu, X., Shijie, Z., Zengyuan, Z., and Zhiwei, Z.: Differential Hydrocarbon Enrichment Patterns in the Eastern Tethys: Insights from Supercontinent Breakup and Assembly, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22862, https://doi.org/10.5194/egusphere-egu26-22862, 2026.
The Sumatra subduction zone, characterized by oblique subduction, ranks among the most tectonically and magmatically active regions on Earth. This unique dynamic regime has forged a suite of prominent geological features, including the large-scale strike-slip Great Sumatran Fault, recurrent and often devastating mega-earthquakes, and vigorous arc volcanism crowned by the Toba supervolcano. The collection of these phenomena establishes the region as an unparalleled natural laboratory for probing the fundamental couplings between plate tectonic dynamics, crustal deformation, and magmatic processes in an oblique convergence setting. Our recent integrated seismological studies provide new, multi-scale constraints on this system. Specifically, high-resolution seismic imaging reveals along-strike bending and morphologic complexity of the subducting slab, which directly modulates plate coupling and influences the nucleation segments of megathrust ruptures. Precise relocation of medium-sized earthquakes further refines the megathrust geometry and defines trench-parallel seismicity belts bracketing the seismogenic zone. The along-strike variations of these belts and the steeper dip angles of the down-dip belt are well correlated with strong gradients in slab geometry, controlling rupture distribution. Beneath the Toba volcanic area, our joint shear-wave velocity and attenuation model resolves a multi-level magma plumbing system with a distinct column–corridor–reservoir architecture. This system is co-located with fluid-rich fault zones, pointing to a tectonically mediated pathway for melt migration from the mantle wedge to shallow storage. These findings provide mechanistic links between regional geodynamics and localized hazard expression. Building on this foundation, our ongoing research integrates multidisciplinary observations towards a comprehensively investigation of the Sumatran subduction system and its surroundings. Through systematic global comparison, we aim to elucidate the dynamics of oblique subduction and its fundamental controls on continental deformation, volcanic evolution and the spatiotemporal patterns of major geological hazards.
How to cite: Chen, L., Wei, J., Feng, M., Wang, X., Liu, Q., Wang, X., Wei, S., Zhao, L., Triyono, R., and Rohadi, S.: Seismological Research Progress on Tectonic Deformation and Magmatisc System in the Sumatran Oblique Subduction Zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15779, https://doi.org/10.5194/egusphere-egu26-15779, 2026.
Faults are lithospheric fracture zones that undergo substantial displacement driven by tectonic stress, serving as direct indicators of crustal kinematics. Compared to other fault varieties, normal faults are typically less influenced by multi-stage tectonic superposition. Their relatively straightforward structural styles make them ideal candidates for modeling fault evolution. Modes of fault evolution have long been disputed between the constant-length and tip-propagation models, but questions remain: are traditional frameworks overly reductive, or does the hybrid model offer a more accurate representation of geological reality?
South China underwent two distinct extensional episodes during the Late Mesozoic, resulting in extensional structures and detachment faults. The Yuechengling area preserves a comprehensive record of these events; specifically, the Tianhu Fault and the Ziyuan Detachment Fault correlate closely with these episodes, providing an ideal laboratory for studying detachment fault evolution. Low-temperature geochronology and thermal history inversions reveal that the Tianhu Fault initiated southward propagation at 140 Ma, accompanied by rapid cooling. While the fault's tips transitioned to a slow-cooling phase at 40 Ma, the central segment reached this stage as early as 70 Ma. Conversely, the Ziyuan Detachment Fault initiated at approximately 100 Ma and did not enter a slow-cooling regime until 40 Ma. The evolution of the Tianhu Fault concurs with the hybrid model, whereas the Ziyuan Detachment Fault initiated synchronously across its strike at 100 Ma, arguing for the constant-length model. We attribute this differential evolution to variations in rock mechanical properties, extension rates, and fluid activity.
Although Cenozoic extensional structures in South China are primarily concentrated in southeastern offshore regions—leaving few visible deformation markers—our data suggest that Cenozoic extension was superimposed onto Late Mesozoic faults, driving the continuous uplift and cooling of their hanging walls. This process is consistent with the Late Mesozoic–Cenozoic tectonic migration from the northwest of the South China Block toward the South China Sea. The transition to slow cooling at 40 Ma likely reflects a regional stress field shift: the opening of the South China Sea absorbed major extensional stress, effectively terminating far-field effects within the continental interior.
How to cite: Liu, T. and Chu, Y.: Structural evolution of the Ziyuan detachment of the Yuechengling dome and its tectonic implications to the Late Mesozoic-Cenozoic extension in South China , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22619, https://doi.org/10.5194/egusphere-egu26-22619, 2026.
This study investigates the tectonic connection between the southern East China Sea Basin (ECSB) and the opening of the South China Sea (SCS). By integrating sedimentary records, seismic stratigraphy, and detrital zircon geochronological evidence, we propose that the tectono‑sedimentary evolution of the southern ECSB is closely linked to the opening and subsequent contraction of the SCS.
During the Paleocene‒Eocene, the southern ECSB (represented by the Lishui‒Jiaojiang Sag) and the basins around Taiwan exhibited highly similar evolutionary features: synchronous marine transgression, extensive paralic to shallow‑marine deposition, and diffuse extension lacking distinct boundary faults. This pattern contrasts sharply with the narrow, fault‑controlled half‑grabens in the northern ECSB. A key piece of evidence is the development of a major breakup unconformity in both regions during the late Eocene‒early Oligocene. This unconformity is characterized by truncation and tilting without compressional structures and corresponds in time to the initial opening of the SCS.
Detrital zircon U‒Pb dating provides independent support for the tectonic correlation between the two regions. Late Eocene sediments in the southern ECSB display a distinct provenance signature, with age spectra highly consistent with those of the northeast Mindoro block on the southern SCS margin, indicating that both belonged to the same continental block prior to breakup. Furthermore, the subsequent subduction and contraction of the SCS oceanic crust beneath the Philippine Sea Plate has brought the present‑day southern East China Sea into a subduction‑related tectonic setting.
Based on the synchronicity of sedimentary‑tectonic evolution and provenance links, combined with previous reconstructions of subducted slabs, we propose that before the opening of the SCS, its northern passive margin extended eastward, encompassing the southern ECSB. The Paleogene extension, sedimentary infill, development of the breakup unconformity, and subsequent tectonic processes in the southern ECSB were thus predominantly controlled by the rifting/spreading and eventual consumption of the eastern SCS. This understanding provides a new perspective for deciphering the tectonic connectivity of the East Asian continental margin.
How to cite: Fu, X. and Zhu, W.: Tectonic affinity between the southern East China Sea Basin and the northern South China Sea margin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22651, https://doi.org/10.5194/egusphere-egu26-22651, 2026.
Based on multi-channel seismic profiles, we have found that northern end of the Philippine Fault Zone (PFZ) is extended to the offshore area of Luzon Island. The northern terminus of the PFZ is terminated at the Manila Trench near ~119°E and ~17.5°N. As a result, the Manila Trench is segmented into two segments off the west Philippine. In fact, we can recognize four roughly NW-SE trending fault zones off west Luzon; the southernmost branch could be the offshore extension of the principal NW-SE trending PFZ in central Luzon. A new transform fault of ~40 km long has been formed to connect the northern and the southern Manila Trench segments. Because the slip along the PFZ was estemated to be 2 to 2.5 cm/yr, it implies that the age of occurrence of the PFZ is 1.5 to 2 Ma. Our age estimation of the PFZ is more or less coherent with geologic observation inland. However, the trend of the Manila Trench has changed ~35° counterclockwise from north to south. Coinciding with the NW-SE trending PFZ in central Luzon, the Manila subducting slab beneath central Luzon has been segmented as revealed by seismic tomography and seismicity. The northern subducted slab dips 40° eastward, while the southern slab dips 80° eastward. The segmentation of the Manila subduction zone along the NW-SE trending principal PFZ could predominate earthquakes, regional kinematics and crustal deformation.
How to cite: Hsu, S.-K., Wu, W.-N., Lin, L.-K., Wang, S.-Y., Yeh, Y.-C., Armada, L. T., and Dimalanta, C. B.: Tectonic segmentation of the Manila subduction zone and its implication, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7570, https://doi.org/10.5194/egusphere-egu26-7570, 2026.
How to cite: Tan, E., Lee, Y.-H., Chen, C.-H., and Hung, S.-H.: Thermomechanical models of the arc-continent collision in Taiwan, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22352, https://doi.org/10.5194/egusphere-egu26-22352, 2026.
Posters on site: Wed, 6 May, 16:15–18:00 | Hall X2
Following cessation of rifting, the continental margin basins of the East and South China sea entered a post-rift stage, during which basement subsidence has traditionally been attributed to lithospheric cooling and thermal contraction. However, quantitative analyses from multiple sub-basins indicate that rapid or accelerated subsidence persisted into the post-rift period and locally exceeds predictions of classical thermal subsidence models. This is anomalous subsidence compared to simple rift models. In this study, we conduct a comparative analysis of post-rift subsidence histories in several representative basins in the East and South China seas. Regional porosity-depth relationships were established based on drilling data or generic models, and backstripping analyses were performed to reconstruct tectonic subsidence histories after accounting for sediment loading. Thermal subsidence and stretching factors were further calculated and compared with theoretical extensional subsidence models. Our results show that pronounced anomalous subsidence has developed since ~5.3 Ma in the Xihu Sag of the East China Sea, since ~5 Ma in the Yinggehai-Song Hong Basin, since ~2–5.3 Ma in the Qiongdongnan Basin, and since ~18 Ma in the Zhu III Depression and Baiyun Sag of the Pearl River Mouth Basin. Although these accelerated subsidence events all occurred during the post-rift stage, they exhibit marked differences in timing and persistence between basins. The mismatch between observed subsidence and model-predictions suggests that post-rift subsidence cannot be explained solely by lithospheric cooling, but is likely influenced by additional processes such as deep-seated mantle up or downwelling, tectonic reactivation, or mid and lower crustal flow driven by sedimentary loading. These findings highlight the stage-dependent and diachronous nature of post-rift anomalous subsidence in the East and South China sea marginal basins and provide new quantitative constraints on post-rift basin dynamics and sedimentary responses.
How to cite: Zhao, X., Li, C.-F., and Clift, P.: A Comparative Study of Anomalous Post-rift Subsidence in the East and South China seas, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13723, https://doi.org/10.5194/egusphere-egu26-13723, 2026.
Tectonic structures associated with continental rifting depend on numerous factors: the nature and mechanical behaviour of the stretched lithosphere, geological inheritance, thermal conditions, and geodynamic forces. The South China Sea exhibits a complex geodynamic history, marked by pre-existing structures (granitoids, etc.). Oceanic accretion in the South China Sea began in the east around 32 Ma and propagated southwestward around 22 Ma, accompanied by a change in the extension direction. Spreading stopped around 16 Ma. The rifting phase lasted longer in the west, leading to the development of a wide rift, accompanied by core complexes and exhumed mantle.
Previous numerical modelling studies show that the formation of a wide rift requires a ductile lower crust and high temperatures at the base of the crust. Structural and thermal inheritance promotes distributed deformation. However, in 3D, an additional mechanism is required to slow down oceanic propagation in order to allow the formation of a wide rift. One possibility is the action of compressive stresses, which, in the case of the South China Sea, may be linked to the topography of the Indochinese block resisting rift propagation.
Here we explore another hypothesis for slowing an oceanic propagator: the transition from N–S extension to an N–S strike-slip system. The opening kinematics of the South China Sea remains debated, between (1) a pull-apart model linked to left-lateral motion along the Red River Fault associated with extrusion of the Indochinese block, and (2) a continental-rifting model induced by subduction of the proto–South China Sea. Modelling rift propagation toward a major transform fault allows us to assess how different kinematic scenarios influence the opening of the South China Sea, the formation of crustal structures, and topography. End-member models fail to reproduce a wide rift, whereas intermediate conditions better account for the slowing of rift propagation, the width of the rift, and the oblique localization of deformation in the southwest basin.
How to cite: Watremez, L., Le Pourhiet, L., Pubellier, M., Delescluse, M., Chamot-Rooke, N., Jourdon, A., and Zhou, F.: Testing the Pull-Apart vs. Subduction-Driven Rifting Debate with 3D Geodynamic Models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21741, https://doi.org/10.5194/egusphere-egu26-21741, 2026.
The South China Sea (SCS) formed in a forearc and post-orogenic environment related to the Mesozoic subduction of the Paleo-Pacific plate. It started rifting at >65 Ma and ended at 32 Ma in the eastern part and 23–19 Ma in the southwestern part, respectively. The driving mechanisms for the rifting of the SCS mainly include two models. One is the pull-apart basin model, which attributes the driving force to the collision between the Indian and Eurasian plates, inducing block extrusion along the Red River Fault System (RRFS) with sinistral strike-slip motion, while the other is the rifted basin model, which emphasizes the pull from the southward subduction of the Proto South China Sea (PSCS) plate, leading to dextral motion of the RRFS. In this study, we interpret a ~300 km-long seismic line with velocity structure by combining multi-channel seismic (MCS) and wide-angle seismic (WAS) data in the Qiongdongnan Basin (QDNB), which is located in the northwestern SCS and close to the RRFS. We identify a hyper-thinned continental crust with southward (oceanward)-dipping detachments cutting through the crust and sometimes offsetting the Moho vertically up to 8 km. This contrasts with most observations in the SCS that indicate northward (continent-ward) vergence of extensional crustal structures. Based on the thermo-mechanical model of Zhou et al. (2025), we interpret these structures as the products of reactivated orogenic inherited crustal structures. Combining other seismic observations in the northwestern SCS, there is an east to west transition in crustal vergence from northward to symmetric and then to southward. Furthermore, considering the location of our seismic line between the RRFS and the QDNB, we also propose that this reflects the influence of strike-slip motion along the RRFS, leading to preferential activity of southward-dipping crustal structures under the effect of a horsetail structure. This indicates a dextral activity of the southern RRFS during the SCS rifting, in agreement with the PSCS hypothesis.
How to cite: Zhou, F., Delescluse, M., Pubellier, M., Le Pourhiet, L., and Watremez, L.: Transition from continental- to ocean-verging crustal-scale normal faults in the northwestern South China Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9922, https://doi.org/10.5194/egusphere-egu26-9922, 2026.
The Manila–Taiwan–Ryukyu subduction system provides a natural laboratory for investigating the transition from active oceanic subduction to mature arc–continent collision at a complex plate junction. While dense geophysical observations across Taiwan are commonly interpreted in terms of arc–continent collision and crustal-scale orogenic processes, the contributions of underlying mantle circulation and interacting slabs remains poorly quantified. This deficiency is critical because subduction-driven mantle flow can influence regional stress and deformation over distances of up to ~600 km, the ~500-km-long Taiwan orogen—particularly where neighboring slabs interact through slab edges, slab gaps, and potential tearing or detachment. Here, we investigate these processes using three-dimensional finite-element geodynamic models ASPECT. Starting from an simplified double-subduction configuration, we isolate the first-order signatures of slab–slab interactions from the complexity of regional tectonics. Systematic sensitivity tests varying inter-trench distance and convergence geometry are conducted to quantify their effects on mantle flow and regional stress–strain patterns. To connect model dynamics to seismological observables, we further predict seismic anisotropy by tracking the development of crystal preferred orientation within the modeled mantle flow. Model prediction of stress, strain, and seismic anisotropy are compared with earthquake focal mechanisms, island-wide GNSS-derived strain rates and SKS splitting observations. These comparisons constrain the extent to which double-subduction–driven mantle flow contributes to geophysical observables, and they identify which observables are most sensitive to specific subduction parameters and slab–slab interaction geometries.
How to cite: Hu, W.-L. and Tan, E.: Geodynamic Modeling of Slab–Slab Interactions in the Manila–Taiwan–Ryukyu Subduction System , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2911, https://doi.org/10.5194/egusphere-egu26-2911, 2026.
Southeast Asia records a prolonged and complex tectonic history from the Permian to the Cenozoic, marked by the accretion of continental fragments, subduction-related magmatism, and repeated reorganization of plate boundaries. Within this framework, the Palawan Continental Block (PCB) contains one of the most complete records of Mesozoic–Cenozoic continental margin evolution in the western Philippines and records key evidence of pre-Cenozoic tectonic events. However, the genetic relationships among its internal tectonic blocks remain unresolved. This study utilizes zircon U–Pb geochronology and Hf isotopic data from Paleozoic to Cenozoic strata extending from northern Palawan to Mindoro Island to constrain the timing, provenance, and tectonic affinity of rocks forming the PCB.
Igneous and detrital zircons from the Mindoro Metamorphics define a coherent Middle to Late Permian age population (270–254 Ma) with uniformly low Th/U ratios (<0.1), indicating a major Permian tectonothermal event related to the Indosinian orogeny. Jurassic strata from northwest Panay yield distinct unimodal age peaks at ~252 Ma (Early Triassic) and ~174 Ma (Middle Jurassic). The Middle Jurassic population overlaps with unimodal Early to Middle Jurassic age peaks (189–182 Ma) from strata on Busuanga Island, recording the development of Yanshanian arc magmatism along the South China continental margin. The recognition of both Permian-Triassic Indosinian (ca. 255-202 Ma) and Jurassic-Cretaceous Yanshanian (ca. 200-100 Ma) tectono-magmatic signatures, characteristic of the South China margin, establishes a direct temporal and genetic link between the tectonic evolution of the PCB and that of southern China. Moreover, the comparable detrital zircon age spectra and Hf isotopic signatures of the Permian-Eocene strata from Palawan and Mindoro indicate derivation from a common continental source, supporting the interpretation of the PCB as a single continental fragment rather than a collage of discrete accreted terranes.
How to cite: Labis, F. A., Mouthereau, F., Pubellier, M., Le Pourhiet, L., Bulois, C., Larvet, T., Tabilog, A. E., Balanial, N., Valera, G. T., and Payot, B.: From Indosinian to Yanshanian tectonic events recorded in the Palawan Continental Block, Philippines: New constraints from zircon U-Pb-Hf isotopes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19323, https://doi.org/10.5194/egusphere-egu26-19323, 2026.
Formation of mantle plumes is often linked to the large low-shear-velocity provinces (LLSVPs) along the core-mantle boundary (CMB) evidenced by their strong spatial associations. However, a small portion of mantle plumes lie far from the major Pacific and African LLSVPs, and their formation cannot be explained by the classical models. Geophysical observations reveal that a few mantle plumes locate nearby the high seismic velocity anamolies (e.g., slab graveyard) along the CMB, indicating the influence of the subduction slabs on plume generation. In this study, we propose that the heterogenous accumulation of subduction slabs along the CMB may facilitate plume generation.
To test this hypothesis, we established a thermo-mechanically coupled numerical model. The model incorporated variations in slab distribution along the CMB to simulate slab graveyard heterogeneity and tracked the distribution of chemical components. The key results are: (1) In the models with heterogenous distribution of subduction slabs along the CMB, mantle plumes are formed induced by the lateral sliding of the heavy subduction slabs. This process is driven by gravity-induced migration and convergence of low-viscosity, high-buoyancy thermo-chemical material in the thermal boundary layer, which generates local thermal-buoyancy anomalies. (2) In the models with homogeneous distribution of subduction slabs or no subduction slabs, mantle plumes failed to form. (3) The initiation rate of mantle plumes correlates positively with slab accumulation height variations and thermal boundary layer thickness; conversely, a higher proportion of dense chemical components in the slab graveyard suppresses plume initiation.
Our modeling results may provide new insights on mantle plume formation away from the LLSVPs along the CMB, which could explain the observed mantle plumes that locate far from the LLSVPs in the present day.
How to cite: Liao, J., Xu, H., Li, Y., and Fan, Z.: Mantle plume formation away from the LLSVPs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10677, https://doi.org/10.5194/egusphere-egu26-10677, 2026.
The role of magmatism in modulating continental breakup remains a topic of debate1. We present new, high-resolution 3D seismic reflection data from the South China Sea that reveals voluminous lower crustal magmatism occurred ~7–10 Myr before breakup along a >1,000 km long, NE–SW trending belt offset 100 km landwards of the eventual continental rupture. Through integration with numerical geodynamic models of continental extension, we show that a thermal anomaly associated with such lower crustal magmatic intrusion facilitate continental breakup. Specifically, our models show focused magma intrusion weakens the crust, promoting strain localization and migration that can lead to continental rupture 10’s–100’s km away from the site of initial magmatism.
How to cite: Deng, H., Chen, H., Bodur, Ö., Thybo, H., Magee, C., Bai, Z., Rey, P., and Keir, D.: Continental breakup facilitated by lower crustal magmatism, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3631, https://doi.org/10.5194/egusphere-egu26-3631, 2026.
Most magmatism on Earth is linked to passive mantle upwelling at mid-ocean ridges, dehydration of subducting plates, or mantle plume, additionally, subduction zones are proposed to induce melting of hydrated mantle, thereby driving magmatism (Yang & Faccenda, 2020). Geophysical observations show that some global hotspot associated mantle plumes do not directly penetrate the mantle transition zone (MTZ) but stall beneath it, nevertheless, significant low velocity anomalies and volcanism persist in the upper mantle and lithosphere (Hua et al., 2022; Tang et al., 2014). This phenomenon indicates that deep stalled mantle plumes can trigger shallow magmatism, yet the underlying dynamic processes and mechanisms remain unclear.
To clarify the nature of such spatially discontinuous plume-related magmatism, we developed a thermodynamic-geodynamic coupled model to systematically explore its core dynamic processes and mechanisms (Gerya & Yuen, 2003). Results demonstrate that after ascending to the region beneath the MTZ, the mantle plume is trapped by the phase transition barrier at the 660 km depth boundary. Its sustained heating preferentially melts the hydrated mantle within the MTZ, weakening rock strength and forming a melt-enriched layer. Subsequent disturbances from the subducting plate ultimately drive the melt to breach the boundary barrier and ascend to the base of the lithosphere. The model confirms that hydrated mantle in the MTZ is the direct source of shallow ascending melt, which remains uncontaminated or only minimally contaminated by mantle plume material. This study further quantifies the regulatory effects of mantle plume temperature, water content of the MTZ hydrated mantle, and phase transition parameters at the 660 km boundary on melt generation, enrichment, and ascent.
Our model results are highly consistent with observed shallow low-velocity anomalies associated with global stagnant mantle plumes, providing a plausible explanation for magmatism in these regions. This research deepens our understanding of shallow volcanism, and provides a new dynamic perspective for interpreting the discontinuous distribution of upper mantle low-velocity anomalies and inferring the spatiotemporal characteristics of intraplate volcanism.
Reference
Gerya, T. V., & Yuen, D. A. (2003). Rayleigh–Taylor instabilities from hydration and melting propel “cold plumes” at subduction zones. Earth and Planetary Science Letters, 212(1-2), 47-62.
Hua, Y., Zhao, D., & Xu, Y.-G. (2022). Azimuthal anisotropy tomography of the Southeast Asia subduction system.Journal of Geophysical Research: Solid Earth, 127, e2021JB022854.
Tang, Y., Obayashi, M., Niu, F. et al.(2014). Changbaishan volcanism in northeast China linked to subduction-induced mantle upwelling. Nature Geoscience, 7, 470-475.
Yang, J., & Faccenda, M. (2020). Intraplate volcanism originating from upwelling hydrous mantle transition zone. Nature, 579, 88-91.
How to cite: Kou, J. and Liao, J.: Intraplate magmatism driven by secondary plumes in the upper mantle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22538, https://doi.org/10.5194/egusphere-egu26-22538, 2026.
Mud diapirs are widely observed offshore southwestern Taiwan and are generally interpreted to originate from the overpressured Gutingkeng Formation, which experienced rapid sedimentation. Fluid enrichment within this formation reduces its bulk density relative to the surrounding strata, allowing buoyancy forces to drive upward migration and diapir formation. However, recent gravity analyses challenge this classical diapirism model by indicating a positive density contrast associated with the observed diapirs. This apparent contradiction raises the question of whether buoyant diapirism can coexist with a positive density anomaly.
In this study, we use numerical simulations incorporating visco–elasto–plastic rheology to investigate the formation mechanisms of mud diapirs under varying physical conditions. The models explore the effects of viscosity, elastic moduli, and density contrasts between diapiric material and the overlying sedimentary layers. Our results demonstrate that diapiric structures with a positive density contrast can be successfully reproduced. We further show that diapirism is systematically accompanied by the development of sedimentary basins filled with unconsolidated sediments, which introduce a strong negative density contrast relative to surrounding rocks. Gravity forward modeling indicates that a sedimentary basin with a thickness of approximately 500 m is sufficient to generate a gravity anomaly of ~5 mGal, consistent with observed data. These results suggest that the presence of positive-density diapirs does not preclude buoyancy-driven ascent and can be reconciled through the combined effects of diapirism and syn-deformational sedimentation.
How to cite: Lee, F.-Y., Tan, E., and Le Pourhiet, L.: Probing into the Diapirism in Southwest Taiwan by Numerical Simulation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21221, https://doi.org/10.5194/egusphere-egu26-21221, 2026.
In Southeast Asia, the contact between oceanic plates of Pacific affinity (Caroline and West Philippine seas) and the Eurasia and Australia plates of continental nature is rarely marked by high mountain ranges. Instead, it is characterised by fold-and-thrust belts involving volcanic arcs and slices made of continent-derived sediments. At every location, the tectonic style results from the oblique docking of the oceanic plates against the continental margins.
In this compressional setting, we identify two discrete systems developing the one after the other. The first system is marked by arcuate frontal thrusts bounded by oblique strike-slip lateral ramps, that are ubiquitous and vary in size from a few tens of meters to a few tens of kilometers. The regional convergence obliquity leads to a migration of the plates contact with consecutive tectonic periods of 1 to 2 Myrs, controlling the rapid triggering of subduction jumps that progressively change the location of the plates boundary over time. The second system corresponds to the onset of shear partitioning marked by the formation of a new subduction zone along which long, subparallel strike-slip faults form. Therefore, these new structures intersect previous ones, and the resulting sliver plate is affected by a margin-parallel stretching regime accommodating the progression of the docking and velocity variations during the convergence.
Thus, our study describes the evolution from one system to the other in Taiwan, Northern Philippines, Southern Philippines, Eastern Indonesia and Papua New Guinea. It also highlights important shifts that are necessary to discriminate small, Recent-to-Actual displacements imposed by GPS data (from 0Ma to 2Ma) from those deduced from longer-term motions documented along the main faults. In the frontal units of the Taiwan foothills or in the Luzon sedimentary wedge, recent tectonic slices typically disappear as we go backward in time by just a few Ma. In Southern Philippines, compression began in the latest Miocene–earliest Pliocene times with flat-and-ramp system, before being progressively replaced by the N–S Philippine Fault throughout the entire archipelago. In Eastern Indonesia and Papua New Guinea, the Sorong Fault also crosscuts Mid-Miocene docking structures marked by the flat-and-ramps features. Any regional reconstruction requires to unravel the two systems and date them carefully.
How to cite: Bulois, C., Pubellier, M., Chamot-Rooke, N., Mouthereau, F., Delescluse, M., Labis, F.-A., Bufféral, S., and Le Pourhiet, L.: Tracking the subduction-collision transition in the Taiwan-Philippine-New Guinea regions: a simple structural scheme to assist kinematic reconstructions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14104, https://doi.org/10.5194/egusphere-egu26-14104, 2026.
The Tanintharyi Shelf in the Andaman Sea, a key yet understudied segment of the Indo-Eurasian plate collision-related back-arc basin, hosts a Cenozoic carbonate platform with substantial hydrocarbon potential. This study integrates high-resolution 2D/3D seismic reflection data, well logs, regional stratigraphy, and global tectono-climatic records to systematically decipher the origin, morphological evolution of this platform, with a focus on tectono-climatic coupling mechanisms. Our findings reveal that the platform did not develop as a typical continental shelf-marginal rimmed system but on a fault-bounded restricted basement high as isolated patch reef. The evolution of the platform was governed by a trinity of coupled factors: (1) the rift tectonics provide basement highs as substrate; (2) the eustatic sea-level fluctuations drove aggradation-backstepping cycles and subaerial exposure; (3) and the Neogene Tibetan plateau uplift intensified Asian monsoons, increasing siliciclastic input through the Irrawaddy-Salween river systems, ultimately drowning the platform. This study establishes a predictive tectonostratigraphic framework for fault-bounded carbonate platforms in back-arc rift settings, linking far-field tectonics (Tibetan uplift), regional structural dynamics, and local sedimentary processes.
How to cite: Luan, X.: Tectonic–climatic controls on the growth and drowning of carbonate platforms: evidence from the Tanintharyi Shelf, Andaman Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22558, https://doi.org/10.5194/egusphere-egu26-22558, 2026.
Izu-Bonin-Mariana (IBM) subduction zone, which situated in the western Pacific and eastern Japan, is a major segment of the Pacific subduction system. Based on the geochemical investigations of ophiolites (Ishizuka et al., 2011), IBM is generally considered initiated approximately 52–51 Ma through a gravitational collapse across the transform fault. And then the subsequential spontaneous subduction of IBM began, which corroborated by numerical simulations (Maunder et al., 2020; Ritter et al., 2024). However, recent studies indicate that the IBM has involved horizontal convergence in its subduction initiation (Li et al., 2022). Two-dimensional geodynamic models have verified that the early-stage IBM subduction pattern dominated by horizontal compression is consistent with geochemical observation (Liu et al., 2024), whereas the source of such horizontal forces remains unclear.
Geological reconstructions reveal that the initiation of IBM was synchronous with the subduction of Izanagi-Pacific Ridge. Based on that, we hypothesize that the subduction of the mid-ocean ridge played a important role in the initiation of this new subduction. To verify this idea, we use the 3D thermomechanical coupled numerical code I3VIS to construct a subduction model incorporating both the Izanagi-Pacific Ridge and the transform fault where IBM subduction initiated. Model results demonstrate that when the Izanagi-Pacific Ridge caused subduction obstruction, stress redistributed laterally, thereby inducing horizontal compression along the transform fault. The new subduction was first triggered locally, and then gradually expanded across the entire transform fault, ultimately forming the full-scale initiation of the new subduction zone.
This model confirms that the subduction obstruction of the mid-ocean ridge can redistribute local stress to lateral weak structures, thereby triggering the transition or expansion of the new subduction zone, which as a potential process for the initiation of the IBM subduction. This proposed model validates a new mechanics of subduction initiation driven by indirect factors, and provides novel insights into subduction dynamics.
Ishizuka, O., Tani, K., Reagan, M.K., Kanayama, K., Umino, S., Harigane, Y., Sakamoto, I., Miyajima, Y., Yuasa, M., Dunkley, D.J., 2011. The timescales of subduction initiation and subsequent evolution of an oceanic island arc. Earth Planet. Sci. Lett. 306, 229–240.
Maunder, B., Prytulak, J., Goes, S., Reagan, M., 2020. Rapid subduction initiation and magmatism in the western pacific driven by internal vertical forces. Nat. Commun. 11, 1874.
Ritter, S., Balázs, A., Ribeiro, J., Gerya, T., 2024. Magmatic fingerprints of subduction initiation and mature subduction: numerical modelling and observations from the izu-bonin-mariana system. Front. Earth Sci. 12, 1286468.
Li, H.-Y., Li, X., Ryan, J.G., Zhang, C., Xu, Y.-G., 2022. Boron isotopes in boninites document rapid changes in slab inputs during subduction initiation. Nat. Commun. 13, 993.
Liu, Liang, Li, H.-Y., Liu, Lijun, Ryan, J.G., Morgan, J.P., Ren, K.-X., Xu, Y.-G., 2024. Horizontally forced initiation of the izu-bonin-mariana subduction zone. Commun. Earth Environ. 5, 91.
How to cite: Wang, G. and Liao, J.: Mid-Ocean Ridge obstruction Cause A New Subduction zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10965, https://doi.org/10.5194/egusphere-egu26-10965, 2026.
