Accumulating multidisciplinary evidence reveals that plate tectonic processes have played a pivotal role in Cenozoic paleoclimate changes, with Neo-Tethyan magmatic spurts matching well with the Early Eocene Climatic Optimum (EECO; ca. 53-50 Ma). However, the tectonic driving mechanism of the subsequent (ca. 49-34 Ma) global long-term cooling after the EECO still remains contentious. Here, we compile available magmatic records from southern Eurasia, together with a global dataset of magmatic rocks/zircons and a recent well-constrained uplift history of the Tibetan Plateau, to uncover the tectonic processes regulating Eocene paleoclimate changes. The combined data, along with geologic observations, highlight a widespread reduction in magmatic activities and volcanic/metamorphic CO₂ outgassing throughout southern Eurasia in the middle to late Eocene, which probably resulted from the termination of Neo-Tethyan subduction and consequent coupling and flat subduction of the Indo-Australian plate after Neo-Tethyan slab break-off. Particularly, we find that the gradual decrease in atmospheric CO₂ concentration and temperature dropping after EECO was synchronous with southern Eurasian magmatic wanning, but was inconsistent with the uplift history of the Tibetan Plateau. Such a strong synchronicity led us to propose southern Eurasian magmatic shutdown as the main tectonic driver of Eocene global cooling.

How to cite: Zhang, X., Xue, S., and Xi, J.: Southern Eurasian magmatic shutdown triggered Eocene global cooling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3405, https://doi.org/10.5194/egusphere-egu25-3405, 2025.

The Jiangnan Orogen (JO) is widely recognized as the collisional suture between the Yangtze and Cathaysia Blocks in South China, marked by intense Neoproterozoic magmatism, however, the precise geochronological constraint of the collision event remains controversial. This study focuses on geochronological and geochemical analyses of granitic rocks from the Guibei region of the western JO. The Sanfang, Yuanbaoshan, and Pingying plutons, composed of granites, exhibit zircon U-Pb ages ranging from 825 to 833 Ma. Granodiorites of the Caigun pluton and gabbro intrusion near the Sanfang pluton yield zircon U-Pb ages of approximately 833 Ma and 856 ± 8.0 Ma, respectively. These ages collectively indicate that these rocks represent products of the Neoproterozoic magmatic event. Neoproterozoic granites are characterized by high A/CNK ratios, low Ga/Al ratios, and Zr + Nb + Ce + Y contents, which are consistent with the classification of S-type granites. The Neoproterozoic granites display similar ε_Nd(t) values ranging from -6.24 to -5.09 and predominantly negative ε_Hf(t) values (< 0). Their linear geochemical variations suggest an origin from partial melting of crustal basement rocks followed by extensive fractional crystallization. The Neoproterozoic granodiorites exhibit high SiO₂ and Al₂O₃ contents, elevated K₂O/Na₂O ratios, low Mg# values, enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depletion in high field strength elements (HFSEs) and heavy rare earth elements (HREEs), suggesting an arc-related origin for these granodiorites. They are also characterized by decoupled Nd and Hf isotopes, with negative ε_Nd(t) values (-5.68 to -5.50) and positive ε_Hf(t) values (> 0), suggesting a likely origin from the partial melting of a fluid-modified lithospheric mantle, with the assimilation of crustal components. The geochemical variations observed in these Neoproterozoic granites and granodiorites indicate their formation within collision- and arc-related settings, respectively, suggesting that the transition from a subduction-dominated regime to a collisional setting within the JO likely occurred around 830 Ma.

How to cite: Cao, J.: Formation of the Jiangnan Orogen: Constraints from the geochronological and geochemical compositions of the Neoproterozoic granitoids, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2644, https://doi.org/10.5194/egusphere-egu25-2644, 2025.

As a crucial geological, climatic, and ecological boundary in the southeastern margin of the Tibetan Plateau (SEMTP), the topographic evolution of Diancang Shan (DCS) remains unclear due to the lack of direct constraints on its paleoelevation. Here, we quantitatively reconstructed changes in annual mean temperature (ANNT) based on palynological data from the terrestrial Dasongping section (∼ 7.6–1.8 Ma) in the Dali Basin, located at the northeastern margin of DCS in Yunnan, China. Integrating the thermochronological data from the eastern and southern margins of DCS, we have clarified the paleotopographic evolution of DCS during this period: the paleoelevation of DCS likely exceeded 2000 m a.s.l. (above sea level) due to initial normal faulting at ∼ 7.6 Ma, possibly comparable to the current average elevation (∼ 2200 m a.s.l.) of the surrounding Dali Basin region. Significant growth occurred between ∼ 5.0 and ∼ 3.5 Ma, with at least ∼ 1000 m uplift gain in the northern segment and up to ∼ 2000 m in the southern segment of DCS, caused by the intensification of normal faulting activities. Finally, the northern segment of DCS reached the elevation of ∼ 3500 m a.s.l. after ∼ 1.8 Ma. Our findings suggest that the quantitative ANNT reconstruction, combined with thermochronological and sedimentary data, can significantly improve constraint on the paleotopographic evolution of DCS.

How to cite: Zhang, C., Wu, H., Zhao, X., Deng, Y., Jia, Y., Zhang, W., Li, S., and Deng, C.: Rapid topographic growth of Diancang Shan, southeastern margin of the Tibetan Plateau, since 5.0–3.5 Ma , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8322, https://doi.org/10.5194/egusphere-egu25-8322, 2025.

The Vigan High is located off west Luzon Island and is in the forearc basin of the Manila Trench, where the Eurasian Plate subducts eastward beneath the Philippine mobile belt. The Manila forearc basin exhibits complex structures involved in onshore faulting, seamount subduction, and slab tearing. To investigate the forearc basin of the Manila subduction system between ~16°N and 18°N, we utilized multi-channel seismic reflection data, Sparker seismic reflection data, and bathymetric data collected onboard R/V Legend in 2022 and 2023. Multi-channel seismic reflection data was also acquired on board R/V Ocean Researcher 5 in 2014. The study area can be divided into a northern region dominated by convergent environments and a southern region characterized by extensional environments. In the north region, the Vigan High consists in thrust and strike-slip faults. These faults are distributed along the central part of the Vigan High, with fault planes dipping towards the center. It indicates that the Vigan High is associated with a positive flower structure due to transpression. The strike-slip component of the structure is likely an offshore extension of the onshore Philippine Fault Zone. South of 17°N, seismic data reveal predominantly normal faults. Multi-channel seismic reflection data reveal an unconformity. Folded structures exist beneath the unconformity, and normal faults exist above it. This phenomenon suggests that the region changed from a convergent to an extensional regime. This transition may be related to a slab tearing of the subducted South China Sea slab. The structural difference between the northern and southern regions highlights the significant stress variation in the forearc basin of the Manila subduction system.

How to cite: Tsai, Y.-J., Hsu, S.-K., Tsai, C.-H., Lin, L.-K., Wang, S.-Y., Yeh, Y.-C., and Armada, L.: The structure and origin of the Vigan High off West Luzon Island, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3944, https://doi.org/10.5194/egusphere-egu25-3944, 2025.

Seamount subduction plays a pivotal role in shaping subduction zone dynamics, significantly influencing deformation processes and seismicity. This study examines the crustal and upper mantle deformation associated with seamount subduction beneath northern Luzon, where the South China Sea Plate underthrusts the region. We employed local S-wave splitting techniques to characterize the deformation and present seismological evidence of seamount subduction’s role in modulating subduction dynamics.

Our findings reveal a dominant trench-normal fast-axis orientation, aligned with the P-axis from crustal earthquake focal mechanisms, across most forearc stations. This pattern differs from the trench-parallel fast-axis commonly observed in other forearc settings such as northeastern Japan, Cascadia, and Sumatra. The frequency-dependent delay times and trench-normal fast-axis orientation suggest seismic anisotropy associated with fluid-filled cracks aligned with the prevailing stress field, influenced by the seamount subduction.

Notably, delay times increase with focal depth, highlighting that the effects of seamount subduction extend from the overriding crust into the subducting slab. These results offer direct seismological evidence of seamount subduction shaping subduction zone dynamics, promoting aseismic creep and small earthquakes through fracture network formation. This study enhances to the understanding of the complex interactions within subduction zones and underscores the importance of seamount subduction in these processes. 

How to cite: Cao, L., He, X., Zhao, L., Huang, B.-S., Hao, T., Zhao, M., Qiu, X., He, E., Wan, K., and Yuan, H.: Seamount Subduction's Influence on Subduction Zone Dynamics: Seismological Insights from Northern Luzon, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2105, https://doi.org/10.5194/egusphere-egu25-2105, 2025.

The Bohai Sea, one of China’s four marginal seas, is also the country’s most resource-rich area in terms of offshore oil and gas reserves. The central Bohai Bay Depression (Bohai Central Depression) has a maximum sedimentary thickness of up to 7-8 km, and a distinct geothermal anomaly is observed at the depression’s center. During the formation of the Bohai Central Depression, the compression of sediments induces a series of physical changes and thermal effects. These effects not only influence the tectonic thermal evolution during sedimentation but also affect the oil and gas reservoir formation in the sedimentary strata. In this study, a theoretical model considering sediment compression effects was developed using COMSOL, to simulate the sediment compression process and the geothermal structure and thermal evolution history in the central depression of the Bohai Sea. The results indicate a strong correlation between the sediment compression effect in the Bohai Central Depression and the underlying geothermal anomalies. Sediment compression alters the porosity of the reservoir, leading to changes in the geothermal structure and thermal evolution characteristics of the reservoir. The compression of sediments impedes heat transfer within the reservoir, increasing the basal temperature and reducing the overall geothermal gradient. Our thermal modeling results provide significant scientific insights into understanding the thermal effects of sediment compression in the Bohai Central Depression and its implications for oil and gas accumulation.

How to cite: He, Y.: Numerical simulation on tectonic thermal evolution at 8km in the Bozhong Depression considering sediment compression effects, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1315, https://doi.org/10.5194/egusphere-egu25-1315, 2025.

Geological observations have revealed a rapid evolution and obvious east–west difference in the North Sulawesi subduction zone. The Celebes Sea plate has inserted itself under the north arm of the Sulawesi Islands and the north arm of the Sulawesi Islands has rotated clockwise at the same time. The rotation of the north arm of the Sulawesi Islands may play an important role in facilitating tectonic processes like the slab rollback of the Celebes Sea plate. In view of the east–west differences along the north Sulawesi subduction zone, a numerical model with the convergence rate of the plates as the basic variable is established to quantitatively describe the evolution process of the north Sulawesi subduction zone. Our results reproduce the east–west differences of the subducting Celebes Sea plate, showing a shallow–deep–shallow subduction style. We suggest that the variable velocity ratio of the overriding plate to the subducting slab may be the main reason for the differential subduction along the strike of the North Sulawesi subduction zone. We therefore conclude that the residual slab and the rate of the eastern continental plate limit the downward movement of the subducted slabs of the eastern Sulawesi, and the tectonic location beyond the rotation radius influences the subduction morphology of the extreme western Sulawesi. Moreover, the widespread extension since Pliocene at the western Sulawesi is not affected by the rotating overriding plate.

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How to cite: Song, T. and Chen, X.: Numerical modeling of North Sulawesi subduction zone: Implications for the East-West differential evolution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8069, https://doi.org/10.5194/egusphere-egu25-8069, 2025.

                           The Origin of High-Curvature Banda Subduction Zone: Insights from Lithosphere-Scale Analog Modeling

                                                         Yuwei Liu, Weiwei Ding, Chunyang Wang, Zhengyi Tong, Xiangtian Wen

                              Key Laboratory of Submarine Geosciences & Second Institute of Oceanography, MNR, Hangzhou 31002, China

Abstract:

The Banda Arc is located at the easternmost end of the Southeast Asian circum-subduction system. It is known for its prominent 180° curvature and complex kinematic pattern. The origin of the arc involves various dynamic processes, such as oceanic-continental subduction and arc-continent collision. Previous studies have analyzed and characterized the slab morphology, stagnation depth, deep interactions, and mantle flow of the Banda arc-shaped subducting zone, using a variety of seismological methods, such as seismic tomography, receiver functions and anisotropy analysis. However, there is still a lack of consensus on the formation mechanism and dynamic model of the highly curved subduction zone, i.e., one slab model vs two slab model. Three-dimensional lithosphere-scaled analog modeling is an effective method for studying the deformation mechanisms of subduction zones. In this study, 3-D lithosphere-scaled analog modeling is used to investigate the formation mechanism of the highly curved Banda subduction zone. The experimental process incorporates the morphological, structural, and deformation characteristics of the study area, establishing corresponding models involved continental and oceanic lithosphere, upper mantle. Our preliminary simulation results suggest that the formation of the highly curved Banda subduction zone may be closely related to the arcuate concave morphology of the continental margin on the northern edge of Australia (paleo-Banda embayment). During the rollback of the oceanic slab, the irregular edges of the continental lithosphere significantly influences the geometric evolution of the trench, resulting in the final trench shape similar to the edge morphology of the continental block. The incorporation of continental crust into the subduction processes results in a progressive reduction in the subduction rate, which may ultimately lead to the cessation of subduction. Consequently, the subducted slab retains a relatively steep angle within the mantle. The primary factor contributing to the decreased trench retreat rate and subduction rate is the substantial positive buoyancy of the continental lithosphere. Our models suggest that the Banda subduction zone, characterized by its high curvature, may be formed in the “one slab model”.

How to cite: Liu, Y.: The Origin of High-Curvature Banda Subduction Zone: Insights from Lithosphere-Scale Analog Modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1880, https://doi.org/10.5194/egusphere-egu25-1880, 2025.

The subduction of oceanic plateaus is a global phenomenon that reshapes the tectonic configuration of subduction systems and plays a crucial role in water cycling and volatile fluxes. While previous studies have primarily focused on the processes occurring after plateaus into subduction zones, but the effects of subducting oceanic plateaus on bending and hydration before subduction remain unclear. Using wide-angle seismic data perpendicular to the trench, we investigated these processes as the Caroline Plateau approaches the trench. The P-wave velocity structure shows a gradual increase in crustal thickness from ~7.5 km beneath the trench and outer trench slope, 9.0–12.0 km in the outer rise region, to 16.0–17.0 km beneath the plateau, indicating that the Caroline oceanic plateau is approaching the trench. Seismic velocities near trench axis are lower than those in other subduction zones and at Challenger Deep to the east, where the trench is far from the oceanic plateau. These low seismic velocities, combined with a narrower array of normal faults, suggest that the participation of the oceanic plateau in the subduction process reduces the width of bending fault zone parallel to the trench, while increasing fracturing, serpentinization in the lithosphere ahead of the plateau. Along the trench, the juxtaposed subduction of the oceanic plateau and oceanic crust influences the tectonic configuration of the overriding plate, highlighting the impact of incoming oceanic plateau on subduction dynamics.

How to cite: He, E., Qiu, X., Li, Y., Grevemeyer, I., Zhao, M., Wang, Y., and Chen, C.: The effect of subducting oceanic plateau on the bending and hydration processes in the southern Mariana trench, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3730, https://doi.org/10.5194/egusphere-egu25-3730, 2025.

We have deployed 21 of our developed broad-band Ocean‐bottom seismometers (OBSs) along Mussau Trench in September 2024 with 100% recovery, and 19 OBSs recorded completed seismic data. A total of ~830 short‐duration events (SDEs) were picked manually after data preprocessing using the STA/LTA results. Commonly, the SDE seismic signal often described by all of these characteristics: (i) one single‐wave train with no identified P nor S wave arrivals, (ii) duration <1 s, and (iii) a dominant frequency usually between 4 and 30 Hz. In many areas, SDEs have been associated with gas‐ or fluid‐related processes near cold seeps or hydrothermal vents, although fish bumps, instrumental, or current‐generated noise have been proposed as possible sources. Our results show that the bending plate area has the largest number of SDE, which indicates strong hydrogen hydrothermal activities in this area. 

How to cite: Wang, Y., Ren, A., Hao, T., Wei, S., and Sun, W.: The fluid-related short-duration events recorded by the OBS in the Mussau Trench, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21158, https://doi.org/10.5194/egusphere-egu25-21158, 2025.

Located on the subduction boundary between Indo-Australia and Eurasia plates, the Sumatra region is considered as one of the most active tectonic regions in the world. The existence of the Sumatran trench, abundant arc volcanism, as well as multiple fault segments on the mainland make this region a suitable place to study crustal and upper mantle structures. Furthermore, studying the structures of the arc and the overriding lithosphere is crucial for understanding the tectonic evolution and geohazard potential in Sumatra, particularly in relation to megathrust earthquakes and arc volcanism. The goal of this study is to image the shear wave structure of the crust and upper mantle beneath Sumatra based on ambient noise tomography. We incorporate three seismic networks in this region for the continuous data from January 2022 to December 2023 from 140 broadband stations. We construct Rayleigh wave group and phase velocity maps for 10-60 s using Fast Marching Surface Tomography and then invert these for the shear wave structure with applying transdimensional Bayesian inversion method. The obtained model in the shallower depth shows prominent low velocity near the Sumatra trench probably associated with the mantle wedge. On the other hand, high velocities primarily detect the geometry of the lithosphere beneath Sumatra. In the deeper part, high velocity delineates the subduction slab beneath this region and low velocity may define magma structure beneath major volcanoes, such as the Toba caldera. With further interpretation, the result can contribute to better understanding of the development of the major arc volcanoes in a relationship with the slab subduction and associated modification of the overriding lithosphere.

How to cite: Ariwibowo, S., Kim, J., and Kim, S.: Crustal and Upper Mantle Structure Beneath Sumatra Based on Seismic Ambient Noise Tomography, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14550, https://doi.org/10.5194/egusphere-egu25-14550, 2025.

Along-strike heterogeneity of pre-existing Mesozoic structures have caused different rift-to-drift features from east to west of the South China Sea (SCS). The southwestern margins have undergone prolonged extension and propagating seafloor spreading, leading to crustal structures significantly different from the northeastern SCS margin. The geodynamic mechanism of the termination of seafloor spreading in the SCS is still enigmatic.

In this study, we present a ~780 km long P-wave velocity model across the two conjugate continental margins and the oceanic basin at the southwestern propagating tip in the SCS from a wide-angle seismic refraction profiling. We use joint refraction and reflection seismic tomographic inversion and a layer-stripping approach to obtain the velocity structure. We show that the crustal thickness varies from ~6–23 km in the extended continental domain to <5 km in the oceanic basin. Significant asymmetry in velocity structures is observed in both the continental and oceanic domains, across the mid-ocean ridge. The continental crust of the Nansha Block in the southwestern SCS margin has a velocity structure and a mid-crustal layer (Vp=6.0-6.5 km/s) comparable to those of the Xisha Block. In contrast, the conjugate continental crust in the northern margin features a thinner upper crust with a high velocity gradient and lacks a mid-crustal layer. Stretching factors show that the upper and lower crusts of the southern continental margin are uniformly extended. However, the upper crust of the northern continental margin is much more stretched than its lower crust. The fault-driven stretching factor calculated on the coincident multi-channel seismic profile is much smaller than the stretching factors of the upper crust calculated from crustal thinning, suggesting that the initial crustal thickness may be much less than 32 km. In the ocean basin, we observe high P-wave velocities with high gradient at 2-3 km below the top of the sedimentary basement, and they increase to 7.5 km/s at a depth of 6 km below the basement. Our results suggest that a highly serpentinized mantle underlies a thin oceanic crust at the southwestern tip of the SCS basin, and the magmatic budget was inadequate near the end of the southwestward spreading propagation of the SCS. 

How to cite: Zhang, J., Wu, Z., Li, Y., Grevemeyer, I., and Li, C.-F.: Asymmetric continental crust stretching and seafloor spreading of the southwestern South China Sea: New insights from wide-angle seismic data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9118, https://doi.org/10.5194/egusphere-egu25-9118, 2025.