The episodic stick-slip behavior of megathrust faults in subduction zones can lead to severe earthquakes and tsunamis that pose a catastrophic threat to coastal populations. It is therefore of great importance to study their seismogenic conditions and earthquake activity. The subduction zones of Sumatra and Java, located seaward of the Sunda Arc, are geographically neighboring, but their earthquake phenomena differ significantly. The Sumatra subduction zone has been the scene of numerous very strong earthquakes (Mw > 8), including the 2004 Sumatra earthquake of magnitude Mw 9.1, while the Java subduction zone has experienced only a limited number of large earthquakes, with a maximum magnitude of less than Mw 8. So far, the underlying mechanism explaining this seismological mismatch between these two margins remains enigmatic. To determine the possible cause, we first calculated the 2D steady-state subduction zone thermal model using the finite element method off the coast of Sumatra and Java based on regional tectonic settings. We then extracted the pressure-temperature (P-T) conditions of the megathrusts and analyzed their relationship to the mineral composition of the megathrust shear zone, the serpentine metamorphic reaction, the frictional behavior, and the characteristics of historical earthquakes. Based on the modeling results, we found that the Sumatra megathrust can trigger large earthquakes in both the crustal and mantle regions from the seafloor to a depth of 60 km, covering a seismogenic zone of about 200 km in width. In contrast, the predicted seismogenic zone off the coast of Java is mainly restricted to the crustal region (< 20 km depth), with a width of less than 50 km. The main reason for this discrepancy is primarily related to the age of the subducted oceanic crust and the depth of the arc crustal Moho. The very hot oceanic crust off the coast of Sumatra enhances the metamorphic reaction of the serpentine minerals below the shallow part of the mantle wedge from the velocity-strengthening minerals lizardite/chrysotile to the velocity-weakening mineral antigorite, which facilitates the generation and rupture of earthquakes. In contrast, the P-T condition of the Java subduction is too cold to promote such a metamorphic reaction and thus facilitate earthquake rupture below the mantle wedge.
How to cite: Xia, Y., Kopp, H., Ye, L., Ma, B., Luo, H., Klaeschen, D., and Lange, D.: Why does the Sumatra subduction zone host more giant earthquakes than Java? Thermal structure and mineralogical insights, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12342, https://doi.org/10.5194/egusphere-egu25-12342, 2025.
An advanced analysis was conducted on the triggered 'non-volcanic' tremors (NVT) around Tambora volcano in West Nusa Tenggara, Indonesia by 35 teleseismic earthquakes with a magnitude of at least seven and epicentral distance of over 1,000 km between 2020 and 2022. The waveform data were taken from the Indonesian Agency for Meteorology, Climatology and Geophysics (BMKG). The identification of triggered tremors was based on the visual detection of high-frequency bursts (1-10 Hz and 2–8 Hz) of non-impulsive and prolonged seismic energy, exhibiting coherence across multiple seismic stations and modulation by teleseismic surface waves. Among the 35 earthquakes studied, we identified four teleseismic events that triggered NVT in West Nusa Tenggara. The 2021 Mw 7.4 and Mw 8.1 Kermadec, 2021 Mw 7.3 Vanuatu and 2022 Mw 7.7 Papua New Guinea earthquakes have triggered NVT in this region. We use envelope waveform cross-correlation to locate tremors. The study revealed that amplitudes of surface waves play a crucial role in determining the triggering potential, with an observed triggering threshold of approximately 0.1 cm/s, or dynamic stress 7–8K Pa. The triggered tremors were initiated by Rayleigh surface waves. It has been observed that triggering potential is controlled by the peak ground velocity (PGV), frequency, and dynamic stress.
Keywords: Non volcanic tremor; triggering threshold; PGV; frequency; dynamic stress; envelope waveform. cross correlation
How to cite: Simamora, M.Si, B. M. M., Supendi, P., Nugraha, A. D., Zulfakriza, Z., Daryono, D., and Riama, N. F.: Non-Volcanic Tremors Along West Nusa Tenggara, Indonesia Triggered by Large Teleseismic Earthquakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-502, https://doi.org/10.5194/egusphere-egu25-502, 2025.
Myanmar, located at the southern edge of the Eastern Himalayan Syntaxis, plays a crucial geological role in understanding the interaction between the Indian and Eurasian plates. While previous studies have employed various methods to investigate the subducting slab beneath Myanmar, the fine-scale structure of the slab, particularly beneath the Indo-Burma Ranges, remains unresolved. In this study, we utilize seismic data from a dense seismic array across the Indo-Burma Ranges in central Myanmar to investigate the structural characteristics of the subducting slab. Using receiver function analysis, we identify a series of seismic discontinuities associated with the subducting Indian slab. By integrating geodetic and seismicity data, our imaging reveals that the Indian slab beneath central Myanmar is a continental slab and highlights the presence of a shear zone or detachment layer above it. These findings provide new insights into the subduction process and contribute to a deeper understanding of the tectonic evolution of the Indo-Burma region.
How to cite: Li, B. and Wang, X.: Seismic evidence for a detachment layer above the subducted continental Indian slab beneath the Indo-Burma Ranges , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14259, https://doi.org/10.5194/egusphere-egu25-14259, 2025.
The initiation of subduction zones has remained a contentious and unresolved issue due to the extraordinary forces required and the scarcity of realistic examples. Taiwan, a prominent arc-continent collision zone characterized by dual-slab subduction systems, offers a unique opportunity to investigate subduction polarity reversal (SPR) between the Eurasian and Philippine Sea plates, i.e., a process considered a key mechanism for forming new subduction channels. In this study, we utilize high-resolution 3-D seismic tomography to delineate the detailed morphology of the Eurasian plate and assess the potential for new subduction zone initiation driven by SPR. Our findings reveal significant deformation of the Eurasian plate influenced by the buoyant and rigid Kuanying and Peikang Highs, including slab break-off beneath northern Taiwan and lateral rupture beneath central Taiwan. We propose that the presence of a rigid and buoyant block within a pre-existing subduction zone facilitates SPR, ultimately triggering the formation of a new subduction system during an arc-continent collision.
How to cite: Wang, T., Hu, H., Zhao, D., Niu, X., and Ruan, A.: New subduction channel triggered by buoyant blocks during the arc-continent collision beneath Taiwan: Seismic evidence from P-wave tomography, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2658, https://doi.org/10.5194/egusphere-egu25-2658, 2025.
The Molucca Sea subduction zone, located between the southern Philippines and northeastern Indonesia, forms a U-shaped divergent double subduction (DDS). Based on previous research, the subduction was initiated in the Sangihe region at 20 Ma, followed by the second subduction in the Halmahera region at 10 Ma. However, the mechanism of initiating the second subduction resulting in DDS remains unknown. In this study, we simulated a series of models by presetting a single subduction zone with the convergence of continents to examine the conditions for the initiation of the second subduction of DDS. By modifying parameters of plate age, subduction angle, and convergence rate. Our preliminary results indicate that plate age has little influence on the formation of DDS. A lower preset angle of the first subduction slab (< 30°) tends to favor the second subduction initiation, while a higher preset angle results in single subduction only. Furthermore, we found that the convergence rate of two continental plates is a critical factor controlling DDS formation. The second subduction will initiate with a higher total convergence rate (> 7 cm/yr), particularly when the rate of the subducted plate exceeds 6 cm/yr. Our results are comparable to the existing asymmetric DDS under the Molucca Sea.
How to cite: Cheng, Z., Liang, D., Ding, W., and Zhang, F.: Double subduction initiation in Molucca Sea: Insights of numerical modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17142, https://doi.org/10.5194/egusphere-egu25-17142, 2025.
The Molucca Sea area, situated on the southwestern side of the Philippine Sea in eastern Indonesia, is critical research area for the study of the ocean-continent coupling effect and subduction dynamic system of the western Pacific. Despite its significance as a research hotspot, several research gaps exist in this region. We aim to address two outstanding scientific issues: the cause of the Sangihe forearc thrust (SFT) in Molucca Sea, and the mechanism of volcanic discontinuity and migration of Halmahera arc. Numerical simulation is utilized to analyze these issues.
For the SFT in Molucca Sea, our results show that plate boundary stress and volcanic loading are two critical factors affecting forearc thrusting during asymmetric divergent double subduction (DDS). In the northern part of the DDS in Molucca Sea, the SFT is primarily caused by plate boundary stress. This stress is mainly generated by the southwestward subduction of the Philippine Sea Plate. In contrast, the SFT in the southern part of the DDS is mainly caused by the effects of differential volcanic loading. The effect of volcanic loading on the Halmahera forearc is considerably stronger than that on the Sangihe forearc, resulting in more severe vertical deformation and subsidence of the former. Consequently, the Sangihe forearc, which exhibits less vertical deformation, is thrust over the Halmahera forearc.
For the mechanism of volcanic arc migration in Halmahera, our results show that the dehydration depth of subduction slab and the temperature structure of mantle wedge are closely linked to the rates of subducting or overriding plates. A lower rate of subducting plate or a higher rate of overriding plate is favorable for arc magmatism. Changes in the rates of subducting and overriding plates are identified as the cause of the magmatic activity interruption and volcanic migration of Halmahera arc after the Middle Miocene. During the Miocene-Pliocene period, the rate of subducting plate was lower than the westward convergence rate of the eastern microplate, which created a high-temperature zone favorable for arc magmatism. However, starting in the Middle Pliocene, the rate of subducting plate became close to the westward convergence rate of the eastern microplate fragments due to the tilted subduction of the Philippine Plate, which was unfavorable for arc magmatism. This led to the interruption of volcanic activity and the westward migration of the volcanic arc. In the Holocene, the westward migration of Halmahera arc was blocked, leading to an accelerated convergence of the eastern microplate. As a result, the volcanic activity of Halmahera arc resumed in a new location with a high-temperature zone favorable for arc magmatism.
How to cite: Fang, G.: Numerical simulation and dynamic analysis of ocean-continent coupling effects in Molucca Sea area, Indonesia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1974, https://doi.org/10.5194/egusphere-egu25-1974, 2025.
The Rakhine Basin is a Tertiary foredeep basin along the eastern fringe of the Bay of Bengal covers an area of 165,000km2, with Tertiary foredeep sediments up to 20km . Consecutive discoveries of biogas fields (Shwe, Thalin, Pyi Thit and Aung Siddhi) suggest the Rakhine Basin has great exploration potential for biogas. However, the accumulation of biogas fields are complex and the main controlling factors of accumulation are still uncertain, also led to many exploratory wells failure.
In paper, the anatomical and statistical analysis of the 36 major biogas fields in the world suggests that the biogas fields generally have eight mail geological conditions, including young sediments, shallow burial depth, high sedimentation rate, rich content of organic matter, tectonic setting or structural traps, cap rocks, in-situ generation & charge and low temperature gradient. The Rakhine Basin also has the 8 geological conditions, but the biogas reservoir is controlled by three key factors, according to research.
First, the relatively good source rocks (TOC ≥0.5%), . The lower limit of TOC of biogas source rock is 0.46% by the chemical analysis and theoretical calculation of modern sediment samples. TOC = 0.46% is a critical value, when TOC＞0.46%, the biogas generated can be greater than biogas adsorbed in the formation and dissolved in the formation water, and extra biogas can be accumulation. At last, the TOC is identified minimum of 0.5%.
Second, the large-scale inter-bedded sandstones. Thin inter-bedded sandstones provide plenty of biochemical reaction interfaces, favoring methanogens to thrive and produce large amounts of biogas. The large-scale inter-bedded sandstones of the Shwe biogas field in the Rakhine Basin is 1500-2000 km2, and the gas reservoir is 40-60 km2. Preliminary established the scale of sandstone at least is more than 1000 km2. At the same time, the large scale sandstone is also conducive to the capture of biogas in a large area.
Third, the structural traps. The large biogas fields in Rakhine basin and in other basins are always on the 4-way-dip anticlines. Biogas fields discovered in lithologic traps are always small and not commercial. Therefore, the positive structure controls the enrichment and accumulation of biogas in the Rakhine Basin.
Based on the research of the three key control factors, the risks of biogas exploration in the Rakhine Basin is reduced, and this understanding can be applied to the biogas exploration in deep-water sedimentary basins of continental margin in the world.
How to cite: Wang, X.: Key controlling factors of biogas accumulation in foredeep basin of subduction zone: A case study of the Rakhine Basin in Myanmar, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1976, https://doi.org/10.5194/egusphere-egu25-1976, 2025.
Xisha Area is located in the northern part of the South China Sea. The water depth is about 1000m to 3000m. Since Cenozoic , the Xisha area has experienced dual effects of extension and strike slip on the western margin, forming a special tectonic background of continental slope uplift. Overall, the Xisha area belongs to the continental slope system of the northern South China Sea. It is separated by the Qiongdongnan Basin to the north, on the west connected to the Yuedong Shelf , and on the south and east ,adjacent to the deep-sea basin. It has developed three stages of sedimentation: fault depression, fault depression transformation, and depression. During the transition and depression periods, carbonate platform sediments developed due to rising sea levels and lacking of injection of terrestrial debris. After the Middle Miocene, the Xisha area was deep-water sedimentary environment on the continental slope, dominated by deep-sea to semi deep-sea sediments, with carbonate platform sediments developed on local uplifts. Under the special tectonic background, two types of deep-water sedimentary systems developed in the Xisha Sea during the Miocene period.
During Miocene ,the Xisha Sea area was marine sedimentary environment, with developping two different types of deep-water sedimentary bodies. One type is a deep-water channel supplied by terrestrial debris from the Yuedong River system, and the other is a deep-water channel supplied by carbonate debris from the Xisha Platform. Deep water channels supplied by terrestrial debris are mainly influenced by ancient topography and sea level rise and fall, with strong mobility and mutual cutting characteristics between channels; Deep water channels supplied by carbonate rock debris are mainly influenced by ancient topography, with vertical accretion as the main source and weak mobility of the channels.
The deep water channels filled with terrestrial debris developed in the research area are a process of low sea level and early marine invasion from the early to late stages of channel development. From the early stage to the late stage ,the limitation of deep water channels gradually becoming weaker, and the channels developping from a single channel with strong restriction in the early stage to a composite channel with multiple single channels cutting and overlapping each other in the middle stage, and then to late stage channel complexes and channelized lobes.
In the Late Miocene, deep-water channels filled with carbonate rock debris developed in the Xisha Sea area, mainly in the depressions between the Guangle Platform and the Xisha Platform and on the east side of the Huaguang sag. This type of deep-water channel developed in the early Late Miocene, and on seismic profiles, the reflection characteristics in the upstream and downstream are relatively similar, mainly consisting of a single channel vertically stacked. However, the location of the channel is different, and the characteristics of the channel also changed. The filling material of this type of channel is carbonate rock debris from the Xisha Platform, which has strong paleotopographic limitations and is mainly vertically accreted.
How to cite: Yang, Z.: Deep water sedimentary characteristics of expansion transformation margin in the Xisha area of the South China Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2028, https://doi.org/10.5194/egusphere-egu25-2028, 2025.
During the final stages of seafloor spreading in the East Sub-basin (ESB) of the South China Sea (SCS), the spreading ridge transitioned from slow to ultraslow before the complete cessation. Post-spreading volcanic activity has obscured the original structures along the extinct spreading ridge (ESR), complicating interpretations of spreading-related tectonics. Using independent tomographic inversion of P- and S-wave data, we constructed a detailed VP/VS model along a profile perpendicular to the ESR, offering critical insights into crustal lithology and tectonic processes of the ESR.
A total of 1749 PSP’ arrivals were obtained, with uncertainties of 0.08 to 0.18 s due to picking error and traveltime correction. To reveal S-wave velocities beneath the sedimentary basement, P-wave velocities were fixed by overdamping the sedimentary layer during Tomo2d modeling, achieving an RMS misfit of 0.148 s and a normalized χ² of 1.37. Vp/Vs ratios were calculated based on the P- and S-wave tomography models, which reveals no distinct layering, predominantly ranging between 1.70 and 1.90. A low VP/VS ratio anomaly (<1.70, LRA) is identified in the model distance ~38-82 km, extending to ~1.0 km depth and coinciding with the low-velocity zone at the top of Layer 2. Additional low VP/VS anomalies are observed at both ends of the profile, but limited ray coverage and large uncertainties (>0.05) render these poorly resolved structures and excluded from further discussion.
The most striking feature in the VP/VS model are high-ratio anomalies (HRA) in the central portion of the model. One of these HRAs (~1.9-1.99) extends from ~6.0 to ~11 km at depth in the thin oceanic crustal domain, spanning Layer 2 and Layer 3. In the mantle beneath this HRA, a high VP/VS zone (>1.8) coincides with the low S-wave velocity anomaly. Within these significantly thinned crustal regions, the abnormally high VP/VS ratios suggest the intrusion of serpentinites into the oceanic crust. These observations indicate a substantial reduction in magma supply during the terminal phases of spreading, resulting in rugged basement morphology, an unusually thin crust, and the near absence of lower crust. During this period, tectonic extension dominated seafloor spreading and the crustal fracturing facilitated seawater infiltration into the upper mantle, promoting serpentinite formation and intrusion.
How to cite: Jiang, H., Huang, H., He, E., and Qiu, X.: Hydration Processes in the Crust and Upper Mantle of an Extinct Spreading Ridge in the Eastern Sub-Basin, South China Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6370, https://doi.org/10.5194/egusphere-egu25-6370, 2025.
Over 60% of the global oceanic crust forms at intermediate to fast spreading mid-ocean ridges, making the study of the lower ocean crust crucial for understanding magma processes, and the interactions between hydrothermal circulation and serpentinization during seafloor spreading. However, direct observations of gabbroic cumulates in the lower crust remain scarce. Previous studies have identified lower crustal reflections (LCRs) beneath mature oceanic crust in the big oceans, with these reflections formed due to faulting, lithological layering, or ductile shear zones. Here, we employed extensive multi-channel seismic data to investigate the crustal structure in the East Sub-basin of the South China Sea. Our analysis revealed a network of LCRs located between the COT and the early-formed oceanic crust (before the ridge jump) on both sides of the basin, where the basement exhibits a relatively smooth with minor faults, and the Moho layer is distinctly identifiable. These LCRs are concentrated in the central segment of the basin, particularly in the right side of the Zhongnan Fault Zone, while they become sparse or completely absent in other regions. Additionally, our examination of LCR length and dip angles along ridge-normal and ridge-parallel profiles revealed remarkable uniformity, challenging the shear zone model that anticipated only ridge-ward LCRs in the southern part of the basin. We propose that the observed LCRs are magma intrusions, potentially formed during periods of unstable seafloor spreading following continental breakup or subsequent magma intrusions occurred nearby off-axis ridges. This study enhances our understanding of the magma processes during crustal accretion in the marginal basin.
How to cite: Wang, L., Sun, Z., Zhang, B., Liu, Y., and Xu, Z.: Seismic Structure of the Lower Ocean Crust in the South China Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14362, https://doi.org/10.5194/egusphere-egu25-14362, 2025.
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 εNd(t) values ranging from -6.24 to -5.09 and predominantly negative εHf(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 εNd(t) values (-5.68 to -5.50) and positive εHf(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.
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.
The South China Sea (SCS), lying at the junction of the Philippine Sea Plate, Eurasian Plate, and Indo-Australian Plate, has a complex tectonic history, featuring numerous extension and magmatism events. One crucial aspect in the evolution is the formation of the high-velocity lower crust (HVLC, ~7.0–7.5 km/s) through deep magma intrusion or underplating. The presence or absence of the HVLC and its formation time hold crucial importance for understanding its evolution. However, there has long been a persistent and unresolved ambiguity regarding the origin and formation time of the HVLC in the SCS, especially within the Chaoshan Depression. The Chaoshan Depression, located in the northeastern SCS margin, has been identified as a Mesozoic forearc basin associated with the Dongsha Rise's magmatic arc. OBS profiles across the Chaoshan Depression consistently indicate a 2-12 km thick continuous HVLC. The HVLC might have formed from Mesozoic magmatic underplating. Also, it could be the result of Cenozoic magmatic activities related to the Hainan plume.
The foundation for discussing the origin and formation of the HVLC in the Chaoshan Depression lies in its structure and actual presence. The newly acquired OBS data in 2021 in the Chaoshan Depression, with the station spacing reduced from 20 - 80 km to 5 km, significantly enhances the lateral resolution. The results show that the crust of the Chaoshan Depression is thinner than previously reported and the previously identified HVLC in the northern Chaoshan Depression is actually absent, suggesting a potential overestimation of the HVLC in the northern continental margin of the SCS. Based on a more feature - based analysis (the Tc - Th diagram, a scatter plot of crustal thickness vs. HVLC thickness), we tentatively suggest that the HVLC in the northern Chaoshan Depression shows a positive Tc - Th correlation. This indicates a process that can be reconstructed by post - formation tectonic events like extension. Also, the thin HVLC aligns with thinner crust areas and pre-Cenozoic faults. All above suggest that the HVLC in the northern Chaoshan Depression might have formed before continental rifting and was thinned during the continental rifting. In contrast, the HVLC in the southern Chaoshan Depression shows a negative correlation, indicating no post - formation tectonic modification. Therefore, the southern area might be a product of Cenozoic magmatism, and our survey line might represent the northernmost boundary of Cenozoic magmatic activities.
How to cite: Zhang, J. and Wei, X.: Discontinuous Distribution and Tectonic Thinning Characteristics of the High-Velocity Lower Crust in the Northern Chaoshan Depression, South China Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7660, https://doi.org/10.5194/egusphere-egu25-7660, 2025.
Posters virtual: Tue, 29 Apr, 14:00–15:45 | vPoster spot 2
EGU25-3894 | ECS | Posters virtual | VPS28
Formation and inversion of a short-lived continental back-arc basin in Southeastern TibetTue, 29 Apr, 14:00–15:45 (CEST) | vP2.11
The differences in the tectonic interpretation of ophiolite suites have become a major issue of the debate in the tectonic reconstruction of an ancient orogenic belt, especially when it comes to subduction polarity. In this regard, the Sanjiang Paleo-Tethyan Orogenic Belt in the southeastern Tibetan Plateau provides an excellent case study. The Sanjiang Paleo-Tethyan Orogenic Belt in the northern, eastern, and southeastern Tibet is bounded by the western Jinshajiang‒Garzê‒Litang suture to the north and the Shuanghu‒Changning‒Menglian suture to the south and west. The southern Jinshajiang Suture separates the Zhongzha Block to the east and the eastern Qiangtang Block to the west. The tectonic nature of the NNW-trending southern Jinshajiang ophiolitic mélange remaining controversial. A detailed linear traverse mapping was c across the southern Jinshajiang ophiolitic mélange, with a focus on pillow lavas and the structural relationship between the lavas and their country rock (Paleozoic sedimentary rocks). The results of a field study, in conjunction with new geochronological data and geochemical data, have enabled the identification of the Zhongdian continental back-arc basin. This basin was filled with a flysch succession and at least two horizons of pillow basalt from 267 to 254 Ma. The fining- and thinning-upward nature of the sedimentary succession, widespread syndepositional folds and syndepositional breccias, and submarine channel sediments, as well as intensive basaltic volcanism suggest that this back-arc basin generated in a typical extensional environment. The inversion of the back-arc basin was completed within a relatively short period of one million years (254~253 Ma), resulting in the development of overturned folds of the flysch succession and a latest Permian to Early Triassic back-arc foreland basin in front of the folded belt. Whole-rock geochemical data for the basalts and coeval gabbros suggest that the petrogenetic process of the basalts in the back-arc basin is likely comparable to that of basalt in a rift system as well, which is a lithospheric extension induced uplift of lithospheric mantle and asthenosphere and allowing decompression partial melting of the mantle peridotite. The late stage pillow basalts exhibit a stronger arc signature than the earlier massive basalt and diabase. The Zhongdian back-arc basin is considered to be an extinct continental and arc-type back-arc basins, which are characterized by thick crust, shallow bathymetry, and may not evolve into “normal” oceans. The formation and inversion of the Zhongdian back-arc basin are believed to have been caused by rollback and subsequent break-off of the subducted oceanic slab. During the inversion, the crust shortening occurred predominantly in the back-arc basin, while the southwestern shoulder of the back-arc basin, which was weakly deformed, was shifted north-eastward for ~30 km. The formation process of the Zhongdian back-arc basin is comparable to that of a typical continental rift system, the asymmetric architecture of which has mostly been inherited by the structures formed during the basin inversion. The southern Jinshajiang ophiolitic mélange is representative of the inverted Zhongdian back-arc basin, which is a short-lived, partially mature oceanic basin.
How to cite: Xin, D., Yang, T., Xue, C., Jiang, L., and Xiang, K.: Formation and inversion of a short-lived continental back-arc basin in Southeastern Tibet, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3894, https://doi.org/10.5194/egusphere-egu25-3894, 2025.
EGU25-2072 | ECS | Posters virtual | VPS28
Reconciling bathymetric anomalies of marginal sea basins through magmatic and cooling processesTue, 29 Apr, 14:00–15:45 (CEST) | vP2.12
Bathymetry of marginal sea basins is commonly deeper than the half-space cooling prediction for large oceans, but what controls this pattern is poorly understood. Here, based on abundant seismic sections with increasingly available databases, we perform an enhanced approach that specifically corrects for post-spreading cooling to reassess thermal subsidence across the Southwest Subbasin (SWSB) and the broader South China Sea (SCS) basin. We attribute the current excessive subsidence of the SCS basin primarily as a response to the post-spreading cooling process, which has global applicability to other marginal sea basins and accounts for at least 86% of the observed depth anomaly. Additionally, the mode of magma supply during seafloor spreading plays a crucial role in shaping reconstructed shallower bathymetry of the SCS basin relative to predictions from the half-space cooling model. A stronger magma supply deriving from the regional subduction system can explain the relatively shallow depth developed during the opening of the SCS compared to large oceans. In contrast, a westward decayed magma supply, driven by localized rift propagation induced by the inherited pre-Cenozoic heterogeneous lithospheric structure of South China, attributes to subsidence discrepancies among sub-basins and within the SWSB.
The sediment-corrected depth of most marginal seas is, on average, more than 500 m deeper than that of large oceans, with maximum anomalies ranging from -0.95 to -2.70 km (in 0.5° bins). The sediment-corrected depths exhibit statistically poor correlations with the spreading rate, indicating that the thermal evolution of marginal seas is not primarily controlled by the spreading rate, unlike large oceans. Neither can this anomaly be fully explained by dynamic topography driven by large-scale mantle convection or by localized variations in the degrees and patterns of subduction systems, although the latter may be an important factor influencing the bathymetry of still-active marginal seas. We interpret at least 44.5% of these anomalies as a result of long-term post-spreading thermal subsidence in inactive marginal seas, with magmatic processes influencing bathymetry during oceanic plate formation. We propose that the post-spreading secular cooling, together with the variable mode of magma supply and potential dynamic subsidence processes driven by subducting slabs, play pivotal roles in the formation of the topographic anomalies within the oceanic basins of marginal seas.
How to cite: Fang, P. and Ding, W.: Reconciling bathymetric anomalies of marginal sea basins through magmatic and cooling processes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2072, https://doi.org/10.5194/egusphere-egu25-2072, 2025.
EGU25-10226 | ECS | Posters virtual | VPS28
Pattern Analysis of The Magnetic Field Anomalies Associated with Earthquake Precursor in Molucca Sea Region for the 2020-2021 Period Using Multistation of Magnetic Precursor NetworksTue, 29 Apr, 14:00–15:45 (CEST) | vP2.22