Continents with cratonic cores can resist deformation, and thus survive billions of years in the geological record. Tectono-thermal reworking is a key process in continental evolution because it alters composition and structure of some continents, weakens, and finally destructs or even dismembers them. Typical examples of reworked continents develop in subduction or collision settings, mostly situating in East Asia, Western North America, or the Tethyan collisional zones. 

In western Pacific, East Asian continental margins suffered extensive continental reworking and lost part of their continental lithosphere and developed a wide (>1000 km) extensional province. Across the South China Block, Mesozoic cyclical tectonics destructed a large portion of its cratonic lithosphere. Such strongly modified continent represents an ideal target to reveal the process and mechanism of continental reworking.

We analyzed and synthesized the structural evolution of extensional domes and illustrated the process of lithospheric thinning of Mesozoic South China before Cenozoic rifting of the large marginal seas. Structural and geochronology data of the extensional domes in the SCB indicate Cretaceous two-stage extension, a weaker extension during the early extension, and a faster and stronger extension in the later extension. Unlike the previous rapid, one-cycle delamination model occurred in the North China Craton, the destruction process of South China operates in a cyclical, progressive manner in which compression destabilized the edge of the cratonic lithosphere and the following extension destructs the unstable part to thin the lithosphere. This process, as an endmember of lithospheric destruction mechanisms, requires cyclical tectonics of the subduction zone and the overriding plate, which has been widely reported in the Cordilleras of the eastern Pacific margin. The progressive lithosphere destruction model may also explain how ancient cratons shrink by subduction-related tectonics.

How to cite: Chu, Y., Liu, T., Lin, W., Michel, F., Meng, L., Wei, W., Ji, W., and Xue, Z.: Cyclical continental extension reworks and destructs the cratonic lithosphere of South China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13639, https://doi.org/10.5194/egusphere-egu24-13639, 2024.

The geodynamics and plate tectonics of the South China Sea (SCS)-Taiwan region since Miocene times are uncertain because the former extent and tectonic configuration of the subducted easternmost SCS along the Manila trench is uncertain. Here we unravel the regional kinematic context from main offshore constraints including published unfolding of the Manila slab from seismic tomography, which provides insight on restoring the subducted part of the SCS. We reconstruct a whole northern SCS continent-ocean boundary (COB) that consists of a northeastern SCS COB segment (called ‘S3’), trending N070° that roughly parallels the present SCS shelf; a 350-km long ~N-S trending segment S2 that steps north to Hualien; and, a third segment S1 that extends from east of Hualien beneath the Ryukyu subduction zone trending N085° that ends near Miyako Island in the Ryukyus.

We demonstrated that the two-plate kinematic model is the best framework to explain the existing data. The boundary between Eurasia and Philippine Sea plate is a ~NS oriented left-lateral lithospheric shear fault called the Manila transcurrent fault (MTF). The MTF initiated ~18 Ma at the onset of the tear and progressively moved eastward, creating the intra-oceanic Luzon arc. The MTF ancestor was a N337° oriented left-lateral shear fault, while the HB-PSP/EU motion was changing to N307°, allowing the HB-PSP plate to subduct between the two lips of a westward propagating tear fault until ~7 Ma. Since ~7 Ma, the MTF-PFZ constantly moved westward and 23° clockwise rotated from N337° to ~NS, which began collision ~7 Ma ago along the EU margin. Plate kinematic reconstructions from ~18 Ma to Present are synthesized in terms of continental or oceanic nature of the main PSP-HB and EU entities before their subduction that provide new understanding on Taiwan, PSP-SCS kinematics, and regional histories. This work is supported by Key projects of the Chinese National Natural Science Foundation (contracts 91958212, 42106078).

How to cite: Zhao, M., Sibuet, J.-C., Wu, J., Liu, S., and Cheng, J.: Geodynamic and kinematic model of the South China Sea and regional plates since the end of seafloor spreading, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3290, https://doi.org/10.5194/egusphere-egu24-3290, 2024.

The South China Sea (SCS) located at the intersection of the three intercontinental plates of Eurasia, IndiaAustralia, and the Pacific Oceanis, is a typical marginal sea basin formed by the seafloor spreading under the tectonic background of plate convergence. Many crustal-scale studies indicate that the SCS basin has undergone asymmetric spreading, multi-phase ridge jumps, and intense post-spreading volcanic activity. Due to the lack of seismic data in the oceanic basin of the SCS, it remainsunclear about the scale and basin control of the Zhongnan fault, the magma source depth of the SCS basin, and the transport channel after the cessation of seafloor spreading. Phase velocity derived from ambient noise surface wave tomography may provide useful information to shed light on the mechanisms of the aforementioned problems. From October 2019 to July 2020, a 3D Ocean Bottom Seismometers (OBS) passive seismic observation experiment was carried out by the Second Institute of Oceanography, Ministry of Natural Resources (SIOMNR) in a broad area of the SCS. Based on the seismic ambient noise data recorded by 16 OBSs in the SCS basin, we inverted the phase velocity images over a period range of 10–20 s using ambient noise surface wave tomography. Our results indicate that the Zhongnan fault zone is a lithospheric-scalefault, which played a regulating role in the last oceanic ridge transition of the SCS basin from the East Subbasin to the Southwest Subbasin. In addition, the low-velocity body in the north flank of the Southwest Subbasin extends from the post-spreading seamounts on the ocean crust to the uppermost mantle (i.e., about 10–30 km), which indicates an oblique magma migration during the postspreading volcanism.

How to cite: Cheng, L., Fang, Y., Niu, X., Li, T., Dong, C., Zhao, Y., Hu, H., Kong, F., Tan, P., Ruan, A., Lu, S., Fan, J., Muhammad, H. J., Ding, W., Li, J., and Du, X.: Lithospheric velocity structure of South China Sea basin from ocean bottom seismometer ambient noise tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3360, https://doi.org/10.5194/egusphere-egu24-3360, 2024.

The 2018 Lombok earthquake demonstrated the hazard that the Flores Thrust possesses and highlighted our lack of knowledge on this crustal scale backarc thrust. The Flores Thrust extends from west to east, located at the backarc of the Lesser Sunda Islands, Indonesia. Here we construct the geometry model of the Flores Thrust by fitting the best surface on the relocated and filtered intraplate seismicity using simulated annealing and interpolating using the FastRBF^TM algorithm. The thrust has a flat and a ramp component where the flat is generally constant, inclined ~5° southward, but limited between eastern Bali and western Sumbawa due to the sediment-filled North Bali-Lombok Basin. The ramp of the thrust is dipping southward with a 38° average dip, where the dip increases eastward from Bali (27°-37°) to Lombok (28°-38°), Sumbawa (30°-50°), and western Flores (40°-58°), but then shallower in central Flores (29°-39°). The segmented geometry of the Flores Thrust with varying dips from west to east might be related to the complex geological history and the heterogeneity of both the upper and lower plates in the Lesser Sunda region. Based on our analysis of the volcano distribution, the seismogenic zone of Flores Thrust is constrained by arc volcano distribution; bounded by volcanoes at the western tip (Raung, Ijen, and Baluran in Java) and the eastern tip (Lereboleng and Lewotobi in Flores) while the deeper part is terminated by the along-arc distribution of volcanoes or where the temperature exceeds the brittle-ductile transition zone (>450°C). The proximity between the Flores Thrust and the volcanism might also suggest its interplay during the thrust development. The presence of high-K backarc volcanoes, Tambora and Sangeang Api, to the north of the low-K basaltic-andesitic dominated volcanoes in Sumbawa (e.g., Sangenges and Sorumundi) suggest a possible northward arc migration, closer to the thrust, and a complex interaction between arc volcanism and thrust development. Therefore, the complexity of the Flores Thrust geometry and its interplay with the volcanism should be investigated further, to mitigate the greater effects of any geological hazards in the region.

How to cite: Andikagumi, H. and Bradley, K.: The Geometry and Thermal Fault Models of Flores Thrust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13946, https://doi.org/10.5194/egusphere-egu24-13946, 2024.

This study explores the formation of Oceanic Core Complexes (OCCs), hypothesized to arise from long offset, active normal faults that exhume the lower crust and upper mantle to the ocean floor. OCCs are predominantly observed in asymmetric crustal accretion zones, especially where magma supply is limited, such as in slow-spreading mid-ocean ridges. Traditional observational approaches, mostly perpendicular to these ridges, have suggested that spreading rates are a critical factor in OCC genesis. However, a lack of comprehensive data along the strike of mid-ocean ridges has limited our understanding of the interaction between tectonic and magmatic processes in OCC formation.

Our investigation commenced with the utilization of recently acquired seismic data from the spreading center of the West Philippine Basin. This exceptional dataset has allowed us to chronologically trace the development of multiple distinct OCC structures along the mid-ocean ridge. Complemented by satellite gravity data, we further verified the interpretation of the OCC. The results indicate significant density variability within OCCs, ranging from 2.55 to 3.3 g/cm^3, in contrast to the narrower range of 2.74 to 3.1 g/cm^3 observed in normal oceanic crust. The integration of seismic interpretation and gravity data inversion exposes an alternating sequence of magma-poor and magma-rich segments along the ridge axis. This sequence demonstrates a shift in magmatic activity, transitioning from Penrose-type to Chapman-type crust, characterized by the sequential development of detachment faults and OCCs, ultimately reverting to Penrose-type in the eastern segment. Consequently, our findings propose that, in addition to spreading rates, the localization and delocalization of strain along structural strikes play a pivotal role in OCC evolution. This perspective provides a nuanced understanding of the dynamic interactions between tectonic and magmatic processes that shape the oceanic crust.

How to cite: Zhao, J., Zhao, Y., Ding, W., and Manatschal, G.: Seismic and Gravity Data Analysis of Oceanic Core Complexes in the West Philippine Basin: Insights into Along-Strike Variations and Formation Processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3335, https://doi.org/10.5194/egusphere-egu24-3335, 2024.

The Sunda arc convergent plate subduction tectonic system in Southeast Asia is one of the most active convergent plate boundary zones in the world. Early studies suggest that the Sunda arc subduction system is mainly characterized by subducted accretionary plate margin and typical accretionary prism forearc uplift landform. The latest research found that the Roo Rise, the most eastern section of the Christmas Island Seamount Province in the Wharton Basin of the eastern Indian Ocean, has reached the Java Trench region with plate movement. Compared with the “normal” oceanic crust subduction process in other regions of the Sunda arc, the Roo Rise “Uplift” structure triggered different subduction geological processes in the Sunda arc system. Combined with previous research results, the nature of Roo Rise are comprehensively summarized and understood, including the lithology and chronological origin, and the deep subduction structure characteristics of the “Rise-Trench” area. To further enhance the understanding of the early forearc subduction erosion process, including local accretionary prism front edge collision “concave”, differential uplift of forearc uplift, the compression and narrowing of the forearc basin. We discuss the response characteristics of the backarc basin to the new subduction tectonic framework of “Rise-Trench-Arc-Basin” by using two-dimensional multichannel seismic data interpretation for the first time. At present, a new stage of compressional tectonic movement is taking place in the backarc Kendeng-Madura strait basin. We believe that the characteristics of the shallow compressional anticline are the direct tectonic deformation response in the backarc basin under the new “vertical orthogonal fast and high angle” subduction structure framework formed by the Roo Rise.

How to cite: Ran, W., Lu, Y., Jiang, T., Liu, H., and Shang, L.: The Nature and the response characteristics of the Roo Rise to subduction zone in the eastern Indian Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6931, https://doi.org/10.5194/egusphere-egu24-6931, 2024.

The tearing of the subducting plate, which also named slab window, is prominent in the Java subduction zone. Mantle tomography data indicate plate tearing, supported by short-lived activity of K-rich volcanoes. Despite the acknowledged tearing phenomenon, the formation mechanism is less understood. Along the trench (95°E-120°E), we conducted 1707 profiles at 10 km intervals perpendicular to the subduction zone. Using five key parameters (1. Depth of the input oceanic plate; 2. Oceanic age of the input plate; 3. Trench depth; 4. Accretionary prism crest; 5. Accretionary prism slope), we illustrated bathymetric changes along each profile. Furthermore, utilizing data from over 40,000 earthquake depths, we imaged the subduction plate's configuration. Our study reveals distinct characteristics in the Java subduction system (110°-115°E). The input plate is 2500-3000 m shallower, the trench depth is 800-1200 m shallower, the accretionary prism crest is 1500-2000 m shallower, and the subduction angle is approximately 15° lower than surrounding subducting zones. A correlation between slab dip angles and the depth of the trench and prism crest indicates that the anomalous shallower bathymetry in the 110-115°E region is likely due to the decreased slab dip angles. This suggests that, at present, there is less likely thick buoyant oceanic crust is subducted beneath the Java trench, blocking its subduction and forming a slab window evident in tomography data.

How to cite: Tan, P. and Kong, F.: The mechanism of the tearing of the Java subducting plate comes from the constraints by surface bathymetry data and earthquake depth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3041, https://doi.org/10.5194/egusphere-egu24-3041, 2024.

This study investigates the crustal structure and Cenozoic magmatism in the northwestern South China Sea (SCS), based on the long-cable multi-channel seismic reflection profiles, together with gravity and magnetic data, and adjacent wide-angle refraction profiles. Basins/sags are bounded by large listricnormal faults (fault throws ≥ 0.5 km) and massifs are cut off by normal faults with small offsets (fault throws < 0.5 km) in the northwestern SCS. These structures are penetrated by magmatic edifices showing positive gravity and magnetic anomalies. Syn-rift magmatic intrusions/extrusions were intense in the basins/sags and continent-ocean transition zone while post-rift magmatism was widespread from basins/sags to massifs with the most intense stage occurring from 5.5 to 2.6 Ma. Based on previous geophysical and geochemical results, we suggest that syn-rift mantle upwelling from partial melting initiated seafloor spreading magmatic activities, whereas plume-related mantle upwelling contributed to the magmatism during and after seafloor spreading in the northwestern SCS. Stretching factors show that the upper and lower crusts have experienced differential extension from basins/sags to massifs. The nonuniform crustal extension resulted from upper crustal faulting and lower crustal flow. Particularly, the lower crustal flow was probably linked with the combined action of magmatic heating, mantle flow shearing stresses, and sediment loading, resulting in crustal boudinage and reestablishment of an equilibrium state over long distances.

How to cite: Gao, J., Lüdmann, T., Li, C.-F., Li, L., Tian, L., Qin, Y., and Song, T.: Crustal structures and Cenozoic magmatism in the northwestern South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3791, https://doi.org/10.5194/egusphere-egu24-3791, 2024.

International Ocean Discovery Program (IODP) Expeditions on the northern continental margin of the South China Sea (SCS) have nullified the early notion that the SCS is a magma-poor margin. However, there are continuing debates on how the rapid transition from continent to ocean is supported by geochemical and petrologic data, and whether such a process was related to plate subduction or mantle plume activities. Here we present the bulk-rock and plagioclase phenocryst geochemistry of basalts generated during the early spreading (initial and steady ocean) stage of SCS basin extension, which were drilled at IODP Sites U1500 and U1503, respectively. Combined with published data from the late spreading stage of the basin, the new measurements provide an excellent opportunity to examine the magmatic processes associated with the evolution of the SCS basin. Our results reveal that SCS basalts generally exhibit higher Al contents than global mid-ocean ridge basalts, particularly at lower MgO contents, similar to the characteristics of modern arc basalts. Nevertheless, their origins are site-specific and complex. Some U1503 basalts display strong subduction signals in terms of trace elements, and their correlations with Al₂O₃ content suggest that they are products of partial melting of the mantle wedge, closely related to the northward subduction of proto-SCS. This subduction had a significant effect on triggering the opening of the SCS, rather than by a mantle plume. Basalts from the other sites, including Site U1500, exhibit significant accumulation of plagioclase. Moreover, the An values of the plagioclase in Site U1500 basalts increase with the increase of host magma Al contents, indicating that the floatation mechanism cannot account for plagioclase accumulation. Therefore, we propose that the high abundance of plagioclase in Site U1500 basalts requires rapid ascent of magma, supporting a rapid rifting and strong magmatism during the initial opening of the SCS.

How to cite: Tian, L., Wang, W., Castillo, P. R., and Wu, T.: Petrogenesis of high-alumina basalts in South China Sea: Implications for magmatic processes associated with the opening of an oceanic basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6883, https://doi.org/10.5194/egusphere-egu24-6883, 2024.

In the regime of plate tectonics, subduction of an oceanic plate generally terminates with the collision and accretion of continental terranes. Then, a new subduction zone may form in the neighboring oceanic plates, which is defined as the terrane collision-induced subduction initiation (SI). Based on the analyses of western Pacific subduction system in the Cenozoic, three types of collision-induced SI have been observed: subduction polarity reversal, subduction transference and far-field subduction. However, the dynamics and controlling factors of SI mode selection after terrane collision are not clear. In this study, a multi-terrane collision model has been conducted with variable rheological strength of continental terranes and different convergence velocities. The model results indicate that the relative strength of the terranes controls the SI mode selection, with the new subduction zone tending to form beneath weaker terranes. In addition, the higher convergence velocity can facilitate the collision-induced SI. An analytical study of force balance has been further conducted, which provides the mechanical explanation for the numerical prediction of weak overriding terrane as a favorable SI site. The numerical models and force balance analyses are further compared with the natural cases in the western Pacific subduction system. It indicates that subduction polarity reversal is the most favorable mode after terrane collision in the western Pacific, possibly due to the weakness of overriding plate during the preceding subduction-induced fluid/melt activity. This comprehensive study provides systematic constraints for the dynamics of collision-induced subduction jump, especially for the western Pacific subduction zones in the Cenozoic.

How to cite: Cui, F. and Li, Z.-H.: Terrane collision-induced subduction initiation: Mode selection and implications for western Pacific subduction system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4872, https://doi.org/10.5194/egusphere-egu24-4872, 2024.

Tectonic tremors (TTs), composed of a swarm of low-frequency earthquakes (LFEs), constitute a type of slow earthquakes characterized by a lack of high-frequency energy. Previous studies have suggested that slow earthquakes, which usually occur near the megathrust earthquake rupture zones, are crucial for deepening our understanding of seismic activity. The Northern Sulawesi subduction zone (NSSZ) is situated at the convergence of the Eurasian, Australian, and Philippine Sea plates, experiencing frequent earthquakes that may trigger local tsunamis due to the complex tectonic setting. Until now, the lack of shallow observations has limited the understanding of the shallow tectonic structure beneath the NSSZ. We observe episodic shallow TTs using 8 Ocean Bottom Seismometers (OBS) deployed near the NSSZ, indicating the presence of stable sliding near the subduction boundary. Our research results reveal that the locations of shallow TTs align with the boundary of the weakly coupled plate interface where the relative Coulomb stress is weaker. Additionally, we discover that the sedimentary environment in the shallow subduction zone and the dehydration of serpentinite within the plates provide favorable conditions for high pore fluid pressure, thereby promoting the occurrence of shallow TTs. Furthermore, we try to establish a connection between deep earthquakes and shallow TTs, exploring the possibility of deep-seated stress propagating from the deep crust to the shallow seismic zone through faults or plate boundaries.

How to cite: Jiang, C., Zhang, J., and Hao, T.: Shallow tremors in the northern sulawesi subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7595, https://doi.org/10.5194/egusphere-egu24-7595, 2024.

Crustal thickness (H) and bulk V_p/V_s ratio (k) are widely used to understand crustal deformation and probe tectonic evolution of plates. In the study, 17 pairs of H and k are obtained based on the H-k stacking of receiver functions in the Java subduction zone, among which 14 pairs are corrected for sedimentary effect by applying a resonance removal procedure. The measured crustal thicknesses of Java Island range from 30.2 to 36.5 km, with an average of 32.5 km, and the crustal thicknesses of the Lesser Sunda Islands are strongly variable, ranging from 20.1 to 34.1 km. The crust thickness in the island arc is consistent with that of the extended crust, and the crust thickness of Java Island is on average thicker than that of the Lesser Sunda Islands. This characteristic is consistent with the current extension environment caused by trench retreat and crustal movement, and the stretching stress increases from west to east. The study area has extremely high V_p/V_s ratios, ranging from 1.80 in western Java, to an average of 2.0 in central and eastern Java, and up to 2.2 on average in the Lesser Sunda Islands. The V_p/V_s ratios increase from west to east, which we attribute to: (1) The history of block collision and volcanic activity of the Java subduction zone gradually decrease from west to east, resulting in relatively weak crustal magmatic activity in western Java; (2) The crust of the Lesser Sunda Islands is subjected to the stronger stretching stress, which makes it easier for the mantle material intrusion; (3) The significant variation of crustal thicknesses and widespread lateral crustal dips and faults of the Lesser Sunda Islands provide good vertical channels for the intrusion of basic mantle materials.

How to cite: Liu, Z., Kong, F., Yu, Y., and Li, J.: Crustal structure along the island arc of the Java subduction zone from receiver functions and its tectonic implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8227, https://doi.org/10.5194/egusphere-egu24-8227, 2024.

How to cite: Xia, Y., Kopp, H., Klaeschen, D., Geersen, J., Ma, B., and Schnabel, M.: Subduction of Seamounts and Ridges along the Java Margin, Indonesia: Impacts on Structural Geology and Seismic Activity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11171, https://doi.org/10.5194/egusphere-egu24-11171, 2024.

Nansha Trough, located in the southern part of Nansha Block, is an important boundary of the southern continental margin of the South China Sea, which has undergone complex tectonic superposition process, and is an important area for studying the subduction extinction of the Proto-South China Sea and the current expansion of the South China Sea. In this study, we make use of a new multi-channel seismic profile, which is almost parallel to the distribution of Nansha Trough, to systematically identify and analyze the magmatic activity in Nansha Trough for the first time, and combine the geophysical data such as gravity and magnetism to determine the attributes of seamounts in the trough. We found that all the seamounts in the trough were formed by magmatism, and underwent multiple episodes of magmatism, some of the seamounts were deposited with huge thick carbonate layers on the top. The magmatic rock mass in the trough shows different gravity and magnetic anomaly characteristics on the east and west sides, which may be related to magmatic stage, magmatic source and magmatic differentiation. Unlike the widely developed post-rift magmatism in the northern passive margin of the South China Sea, most magmatic activities in the Nansha Trough seem to ceased around 16Ma, which may be related to the dehydration and melting caused by the subduction plate rotation in the Proto-South China Sea.

How to cite: Guo, C. and Tang, Y.: Magmatism in the Nansha Trough on the southern continental margin of the South China Sea: Recent evidence from seismic profiles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7401, https://doi.org/10.5194/egusphere-egu24-7401, 2024.