Double subduction zones manifest in three distinct configurations: divergent double subduction (e.g., the Molucca Sea and Mediterranean subduction zones); convergent double subduction, characterized by regions with subduction zones dipping in opposite directions (e.g., the Caribbean Plate and Southeast Asia); and same-dip double subduction (SDDS). The SDDS system includes both ancient and active examples, such as the Mesozoic Neothetyan arc system and the late Cenozoic Nankai-Ryukyu/Izu-Bonin-Marianas SDDS. Recent studies have underscored the significant geodynamic effects of SDDS initiation, particularly its role in accelerating major plate motions. Investigations of the Ryukyu/Izu-Bonin-Marianas SDDS, where the Pacific Plate subducts beneath the Philippine Sea Plate, which in turn subducts beneath the Eurasian Plate along the Ryukyu-Nankai Trench, suggest that this system triggers steepening of the Pacific slab and advances the trench. These findings open exciting new possibilities for understanding active margin dynamics and the scale at which double subduction influences tectonics. While most SDDS research has concentrated on the direct effects within the zone of double plate convergence, the broader implications of SDDS on adjacent plate margin tectonics remain largely unexplored. To address this, we examine the geological evolution of Northeast Japan in connection with the fusion of the Philippine Sea Plate and the initiation of the Ryukyu/Izu-Bonin-Marianas SDDS, comparing this reconstructed evolution with new 3-D geodynamic models. Our results indicate that this SDDS system, pulling the Pacific trench westward, drives northward trench propagation and plate margin compression that affect both the Northeastern Japan arc and backarc regions. Therefore, the initiation of the Ryukyu/Izu-Bonin-Marianas SDDS around 10-5 Ma accounts for the puzzling origin of plate kinematics that facilitated non-collisional orogeny and backarc subduction initiation in Northeast Japan from 6-3.5 Ma. The orogenic effects of SDDS initiation reveal a novel mechanism by which subduction zones achieve the critical plate kinematic conditions necessary for non-collisional mountain building. These results not only provide valuable insights into the seismotectonic dynamics of Northeast Japan, a region known for its catastrophic megathrust and intraplate earthquakes, but also enhance our understanding of plate margin tectonics in relation to many proposed ancient SDDS systems.
How to cite: Gianni, G., Guo, Z., Holt, A., and Faccenna, C.: Double subduction-induced orogeny in Northeast Japan and ancient margins, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18644, https://doi.org/10.5194/egusphere-egu25-18644, 2025.
The North China Craton is an important example of extensive craton thinning and partial destruction. While the significant thinning of the eastern part of the craton is well-documented, the underlying mechanism driving this process remains a subject of considerable debate. Proposed explanations include mantle perturbation and thinning linked to multiple subduction zones, eclogitization of the lower crust followed by lithospheric foundering, a weak mid-lithospheric discontinuity (MLD) induced delamination, and hydration weakening caused by slab dehydration or water transport from the mantle transition zone. A common limitation among these hypotheses is their inability to account for the partial nature of the craton's destruction, where the eastern half experienced extensive thinning and magmatic activity, while the western part remained largely stable.
To investigate the evolution and potential mechanisms of craton destruction, we developed two-dimensional Cartesian box models in a finite difference code LaMEM. These models explore the effects of hydration weakening via low-angle slab dehydration, the role of the MLD, and the influence of lower crustal eclogitization. Our findings indicate that the eastern half of the craton has to be significantly weakened and denser than the underlying mantle to undergo destruction. This partial weakening may result from hydration, facilitated by a low-angle or flat subducting slab which could act as a primary source of water. To align with the observed geological timescale of craton destruction (20–30 million years), the hydration process must outpace the diffusive timescale of water in the upper mantle. Accelerated hydration may have been driven by magmatic infiltration, particularly carbonatite volcanism, which could provide rapid pathways for water diffusion within the craton. Our models suggest that without sufficient weakening, neither the presence of an MLD nor a dense lower crust alone can lead to the craton's destruction.
How to cite: Piccolo, A., Paul, J., and Spang, A.: Destruction of the North China Craton due to hydration weakening, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8883, https://doi.org/10.5194/egusphere-egu25-8883, 2025.
Southeast Asia is surrounded by active subduction zones and has a complex tectonic history. It hosts the Indo China block in the west and the South China Sea in the east. Cenozoic intraplate volcanic activity widely spans the Indo China block and the South China sea. These volcanics are not related to any arc volcanism or the opening of the South China Sea during the Miocene. Here, we present an interpretation of a new high resolution seismic tomography model FWEA23, in southeast Asia. We observe extensive slow shear velocity (Vs) anomalies in FWEA23 across most of southeast Asia, extending from the surface down to ~660 km, resembling one or more plumes. We observe the evidence for a strong upwelling beneath Hainan island and the Leizhou peninsula and a weaker one beneath eastern Vietnam, Thailand and Laos. These upwellings spread laterally in all directions beneath southeast Asia at shallow depths (less than ~220 km). We address the tectonic implications of the plume head at shallow depths as well as the deeper origins of the Hainan plume. At depths < 220 km, the slow anomaly extends westward to the Sagaing fault, eastward to the active subduction zones, and northward to ~26°N latitude. We also observe that the asthenospheric mantle (100 - 220 km) beneath southeast Asia is slower than the global average shear velocity of oceanic asthenosphere, implying that the mantle beneath Southeast Asia is warmer than the global adiabat. Additionally, our model indicates a shallow Lithosphere-Asthenosphere boundary (LAB) in the region. We infer that the lateral spreading of the plume at shallow depths is thermally eroding the base of the lithospheric mantle. Also, this lateral spreading could explain the consistency in timing and geochemical features between the Cenozoic intraplate volcanism and the Hainan volcano. We also observe flat, isolated high Vs anomalies in the mantle transition zone, that we interpret as the remnants of subducted slabs. We observe low Vs anomalies in the gaps between the high Vs anomalies. We suggest that these stagnant slabs create a thermal boundary layer on top of the lower mantle by trapping the heat beneath. The built-up heat increases the temperature of the ambient mantle and triggers thermal upwellings that ascend through the slab-gaps.
How to cite: Banerjee, R., Liu, C., Grand, S. P., Sandvol, E., Mitra, S., Liang, X., and Wei, S.: Super-adiabatic asthenosphere in southeast Asia - its tectonic and magmatic implications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7565, https://doi.org/10.5194/egusphere-egu25-7565, 2025.
SE Asia exposes an intensely deformed, long-lived accretionary orogen that hosts accreted fragments of oceanic and continental crust, such as the Sula Spur and Argoland fragments that were derived from the Pangea-Tethys realm and the Proto-South China Sea that was derived from the Panthalassa realm. The geologic record in the SE Asia accretionary orogen provides the incomplete remains of subducted lithosphere and forms the basis for reconstructing lost tectonic plates and paleogeography. Reconstructing these plates and their paleogeography is challenging, and often leads to widely different reconstructions, due to the difficulty to integrate multidisciplinary data sources from e.g., stratigraphy and sedimentology, metamorphism and geochemistry, paleomagnetism, and paleontology. To overcome this challenge, we develop 'orogenic architecture diagrams' to systematically compile and interpret multidisciplinary information at the scale of nappes that form the building blocks of orogens and reconstruct paleogeography and plate tectonics based on the interpreted geological histories of those building blocks. We identify upper plate-derived ophiolites and magmatic units, and lower plate-derived Ocean Plate Stratigraphy (OPS) or Continental Plate Stratigraphy (CPS). Upper plate continents consist themselves of accretionary and magmatic units of earlier orogenic phases. We apply this concept to the SE Asia accretionary orogen, illustrate how this approach enables reconstructing the paleogeography of the Sula Spur, Argoland, and Proto-South China Sea, and integrate this into regional reconstructions.
How to cite: Advokaat, E., Maremmani, A., van de Lagemaat, S., and van Hinsbergen, D.: Using Orogenic Architecture Diagrams to reconstruct paleogeography: applications to the Sula Spur, Argoland and the Proto-South China Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7339, https://doi.org/10.5194/egusphere-egu25-7339, 2025.
The South China Marginal Sea (SCS) is a Marginal Sea Basin characterized by several failed continental rifts preceding continental break-up and subsequent seafloor spreading. The oldest phase of rift propagation is located in the northeast South China Sea (NE SCS). We present new work constraining the tectonostratigraphic evolution and crustal structure of this NE SCS margin, which we compare with that of the adjacent Pearl River Mouth Margin (PRMM). To achieve this, subsurface mapping from reflection seismic data was used together with crustal thickness determined from gravity inversion to identify multiple stages of deformation, crustal domains, and related depositional environments on the NE SCS rifted margin.
Within the NE SCS margin, from north to south, four crustal domains were interpreted: (i) the proximal (i.e., Northern Rift System and Penghu-Peikang High), (ii) narrow necking (i.e., Tainan Basin, Central High, and its southern vicinities), (iii) wide distal (i.e., Southern Rift System, Southern High, and narrow continent-ocean transition – COT), and (iv) oceanic. On the heterogeneous continental crust, three main Cenozoic tectonosedimentary stages took place: (1) rift (Late Paleocene to Early Oligocene); (2) post-rift (Early Oligocene to Late Miocene), and (3) foreland (Late Miocene to Early Oligocene).
Rifting was synchronous throughout the NE SCS, following an NE-SW structural trend. Syn-rift sedimentation patterns and seismic facies analysis suggest deltaic to marine environments in the proximal domain and a sediment-starved deep marine setting in the distal domain. During post-rift punctual structural reactivation occurred in the Penghu-Peikang and Central highs, controlling paleo-reliefs only flooded during maximum transgressive periods. Shelf-dominated deposition prevailed north of the Central High, while deep marine is observed to its south. This pattern persisted during the foreland stage.
The crustal structure of the NE SCS strikingly differs from that of the PRMM. Although PRMM crustal architecture results from widespread crustal boudinage, the narrow necking and sparseness of faulting in the Southern High of the adjacent NE SCS suggest that parts of its crust are showing different initial rheologies. This distinct crustal structure is related to the inherited Mesozoic history of the region: the PRMM Cenozoic history evolved on a magmatic arc, while the NE SCS records not only the remnants of this arc (proximal domain) but also an accretionary prism (Southern Rift System) resultant of the docking of an allochthonous tectonic block (the Southern High) to the south.
The Cenozoic sedimentary infilling of PRMM and NE SCS shows an interplay between paleogeography and eustatic variations. The syn-rift sedimentary thickness variations are directly related to the proximity of the sink area with emerged portions of the Eurasia continent, such as in Penghu, Baiyun, and Liwan Basins. Subordinately, the proximity and subaerial exposure of structural highs (e.g., Penghu, Central, and Yunli High) also affected syn-rift sedimentary thickness. During the syn-rift stage, PRMM sediments were predominantly deposited in lacustrine environments, while sedimentation in the NE SCS was fully marine. Post-rift sedimentation is similar in both margins.
How to cite: Rodrigues de Vargas, M., Mohn, G., Tugend, J., Kusznir, N., Lin, A., and Lin, L.-F.: Crustal structure, structural style, and tectonostratigraphy of the Northeast South China Sea rifted margin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17640, https://doi.org/10.5194/egusphere-egu25-17640, 2025.
The combination of zircon U-Pb geochronology, trace element geochemistry and Hf isotopes have become an extremely popular tool for provenance studies and paleogeographic reconstructions. Here, we present an integrated study of zircon U-Pb-Hf isotopic and geochemical constraints from two basement complexes in western Luzon, Philippines. Basement rocks from these areas offer insights into the geologic and tectonic development of northern Philippines and its correlation with adjacent areas in southeast Asia. We also include Mesozoic rocks from Taiwan for comparison. Exposed in western Luzon, the Zambales Ophiolite Complex (ZOC) preserves a complete ophiolite sequence that spans almost the entire Zambales range. Further north of the ZOC, the Dos Hermanos Mélange (DHM) is considered a tectonic mélange and forms the basement complex in NW Luzon. The presence of both magmatic and inherited zircons from this unit poses essential questions concerning their origin and provenance. Igneous zircons (n=34) from a gabbroic clast in this mélange gave a weighted mean 206Pb/238U age of 114.85 ± 0.85 Ma interpreted as the crystallization age of the gabbro. The εHf(t) values between -25.4 to -3.5 suggests a crustally contaminated mantle-derived magma formed in a continental setting. Older zircons from the same sample show inherited ages clustering at ca. 235 Ma (n=3), 760 Ma (n=2), 1860 Ma (n=8), and 2460 Ma (n=3). These older zircons have heterogenous εHf(t) values from -25.2 to +2.0 suggesting a strong crustal contribution. The results also suggest the involvement of ancient crustal material with Yanshanian (200-60 Ma), Indosinian (250-200 Ma), and Paleoproterozoic (2800-1600 Ma) age populations, consistent with a provenance comparable to the detrital zircons from the Cathaysian Block in southeast China. Conversely, detrital zircons from a mica schist (another clast in the mélange) yielded two prominent age groups peaking at 187 Ma (n=15) and 225 Ma (n=90). These zircons have εHf(t) values from +15.6 to +11.1 suggesting derivation from juvenile crust in the Late Triassic time. By contrast, detrital zircon grains from the sediments overlying the ZOC record two significant ages peaking at 43 Ma (n=21) and 107 Ma (n=3). The Eocene zircons are characterized by very high εHf(t) values (+11.8 to +15.9) indicative of primitive magmas that represent juvenile additions to the crust. The older Cretaceous zircons, on the other hand, have slightly lower εHf(t) values (+0.2 to +10.6) pointing to a less juvenile composition. Interestingly, these older zircons have similar geochemical and isotopic compositions as the zircons in the gabbro from the DHM. Our study provides further evidence for the presence of continental fragments beneath western Luzon. Combining these with literature data, we propose that the Mesozoic rocks from the DHM and ZOC were formed in the same tectonic setting which represents an old piece of continent that rifted off the South China continental margin during the opening of the South China Sea (SCS). This resulted in the subduction of the proto-SCS beneath the Philippine Sea Plate (PSP) and eventually collided with the rest of the western PSP in the Cenozoic.
How to cite: Labis, F. A., Mouthereau, F., Laurent, O., Brichau, S., Pasco, J., Valera, G. T., Payot, B., and Dimalanta, C.: Detrital zircon U-Pb-Hf and trace element analyses reveal basement of western Luzon, Philippines originates from Mesozoic proto-South China Sea (SCS) rifted continent , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4856, https://doi.org/10.5194/egusphere-egu25-4856, 2025.
The Taiwan Strait features rifted basins connected to the South China Sea rifted margin, followed by foreland basins that thicken toward the orogenic belt. Extensive Late Miocene basaltic rocks, dated between 16 and 8 million years ago using K-Ar methods, are widespread across the Taiwan Strait. Despite this, the offshore distribution of these basalts and the basin-scale magmatic plumbing system remain poorly understood. To comprehend offshore igneous formation in the Taiwan Strait, we conducted approximately 4,000 kilometers of multichannel seismic (MCS) profiles to identify strong-amplitude reflectors referring to basaltic layers. The geophysical characteristics of these reflectors, exceeding an order of magnitude in amplitude, were correlated with offshore drillings to confirm their lithology and age.
Our findings reveal that basalt distribution within the Taiwan Strait forms a northeast-southwest oriented zone, with basalts concentrated into northern and southern groups that align with the regional basement highs, specifically the Peikang and Kuanyin Basement Highs. The basaltic layers demonstrate tabular and continuous, with a single reflector suggesting a thickness of approximately a few meters to decimeters. These sequences are divided vertically into four to five distinct layers and erosional surfaces atop magmatic additions, suggesting episodic intrusion and extrusion events over time.
Additionally, we identified large-scale doming structures with diameters of approximately 70 kilometers in the south, and the estimated vertical uplift reaches 1 to 2 seconds of two-way travel time, corresponding to several hundred meters. The evolving plumbing system has influenced the deformation of preexisting sedimentary sequences and earlier igneous rocks in the vicinity of the Penghu Islands. Onshore drilling and outcrop data also indicate the coeval stratigraphic hiatus within the Late Miocene Nanchuang Formation in southwestern Taiwan. These extensive basaltic sequences provide feasible insights into magma-related crustal or mantle emplacement into the evolving magma pathways within the rifted basins.
The mapping delineates the spatial distribution of basalt in the Taiwan Strait, enhancing the understanding of its offshore plumbing system in shallow depth. Extensive magmatism in this region modified the sedimentary succession and probably crustal structure prior to orogeny, influencing the subsequent development of the fold-thrust belt and overall surface structural evolution.
How to cite: Chang, S.-P., Lin, P.-C., Hsu, H.-H., Mirza, A., Chen, Y.-P., Lin, Y.-X., Chen, S.-C., and Lin, Y.-J.: Basin-Scale Spatial Distribution and Plumbing Systems of Magmatism in the Taiwan Strait, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13065, https://doi.org/10.5194/egusphere-egu25-13065, 2025.
The Singapore Strait is located at the tectonic transition zone between the eastern Indochina-East Malaya Block and western Sibumasu block. Recent studies have examined the structural architecture and tectonic evolution of its bedrock, but there is uncertainty regarding the younger deformation. Moreover, limited fault exposures inland make it difficult to determine the full extent of structural geology. Mapping offshore faults and understanding their structural evolution are crucial for assessing marine geohazards, infrastructure development, coastal management, and fostering a comprehensive understanding of Southeast Asia’s complex geological framework.
To investigate the offshore faults distribution and their geometric features in the Singapore Strait, we acquired single-channel seismic reflection profiles and multibeam bathymetric data. The integration of seismic reflection, bathymetric, and gravity anomaly data elucidates the position, continuity, and configuration of the offshore faults in the Singapore Strait. Faults and folds orientated NW-SE are mostly located in western Singapore, whereas the eastern region is characterised by a network of buried channels. In the western area, predominant ENE-WSW, NW-SE, and N-S striking fault structures are in accord with a dextral shear that had developed in the Mesozoic. However, we observed some faults that contradict the dextral strike-slip PDZ (e.g., NW-SE strike-slip and (N)NE-(S)SW thrust). Moreover, a potential half graben boundary fault along the southwestern island delineates the western and eastern regions, where the isopach thickness map of the late Quaternary strata exhibits an increase in thickness towards this boundary fault. This evidence indicates a possible fault reactivation during the latest Cenozoic tectonic history.
How to cite: Nugraha, A., Chua, S., Green, A., Schattner, U., Yu Ting, Y., Zaky, D., Satiawan, S., Slogrove, D., Horton, B., and Switzer, A.: Seismic Reflection of Offshore Faults in the Singapore Strait: Implications for Fault Architecture and Basin Formation , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8277, https://doi.org/10.5194/egusphere-egu25-8277, 2025.
The Philippine Archipelago resulted from a series of subduction events, the most recent being still active, and arc-continent collision, forming today a series of active volcanic fields and ophiolites. As such the Philippine Mobile Belt constitutes a unique place where to study the spatial distribution and origin of mantle degassing fluxes during plate convergence.
We present the geochemical composition of 12 gas samples collected from various locations across the Philippine archipelago. These include samples from Luzon Island-specifically five wells from the MakBan volcanic geothermal field- three bubbling springs in the Laguna region (Silva, Hernandez, and Silva 2 springs), and a bubbling seep near a river at Poon Bato in Zambales. Additional samples were collected from three bubbling springs on Palawan Island (Bato Bato, Sta. Lourdes, and Sta. Lucia hot springs).
Preliminary results of major compound geochemistry reveal two main fluid families. Samples from the geothermal area are dominated by isotopically heavy CO₂ (-4 to -2‰ VPDB), with concentrations reaching 97%. These samples also contain H₂S (up to 2%) and H₂ (up to 0.6%) with δD_H₂ values ranging from -490 to -440‰ VSMOW. Their composition, coupled with measured ³He/⁴He ratios of up to 6.8 R/Ra, indicates a mantle origin influenced by volatiles from the subduction zone. In contrast, samples from the Laguna springs are characterized by high N₂ concentrations (up to 78%) and CO₂ (up to 15%) with δ¹³C_CO₂ values around -10‰ VPDB, suggesting significant interaction with shallow aquifers that may contain dissolved air (e.g., ASW-like N₂).
On Palawan Island, the gas compositions vary: CO₂ (60%) and N₂ (29%) dominate at Sta. Lourdes spring, while N₂ and CH₄ dominate at Bato Bato (N₂ = 68%; CH₄ = 20%) and Sta. Lucia springs (N₂ = 85%; CH₄ = 5%). The Poon Bato seep in Zambales consists mainly of N₂ (75%), H₂ (8%), and CH₄ (4%). The emissions from Bato Bato, Sta. Lucia, and Poon Bato are associated with ultramafic rocks of ophiolite complexes. Factors such as elevated pH values at Bato Bato and Sta. Lucia (pH = 9.5–10), high H₂ concentrations with δD_H₂ = -724‰ at Poon Bato, and the presence of potentially inorganic CH₄ (δ¹³C_CH₄ = -40 to -20‰ VPDB) suggest that serpentinization is a likely origin for these fluids.
Further interpretation of gas origins will benefit from ongoing analyses of noble gas data, which are currently in progress.
How to cite: Battani, A., de la Paix Izerumugaba, J., Gabo-Ratio, J. A., Payot, B., Niedermann, S., Mouthereau, F., and Ranchou-Peyruse, A.: Geochemical Study of Fluids Across the Philippine Archipelago and Their Link to the Underlying Mantle, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21066, https://doi.org/10.5194/egusphere-egu25-21066, 2025.
Petrological studies on the evolution of the nascent island arc and the slab-mantle wedge interface provides clues on process that occur during incipient stages of subduction. In this study, the layered mafic-ultramafic sequence of the Central Palawan Ophiolite (CPO) and radiometric dates for its metamorphic sole are presented. The CPO is a Late Eocene-Early Oligocene fossil oceanic lithosphere which experienced Tethyan-type subduction following a mid-ocean ridge inversion. Mafic-ultramafic sequences of the CPO are exposed in Simpocan (gabbronorites) and Bacungan (olivine websterites, clinopyroxenites, dunites and minor gabbronorites). These rocks represent the lower crust to upper mantle cumulate section of the CPO fossil island arc based on the low forsterite (Fo86-88) and NiO contents (= 0.10-0.27 wt. %) of their olivines, high spinel Cr# (= 0.55-0.65), and high anorthite contents (An89-94) of plagioclases comprising the sequence. This is further supported by P-T estimates for the equilibration of these cumulates at 880-940°C, 5-7 kbars. The conditions indicate that the mafic-ultramafic cumulates represent magmas which stagnate at or near the Moho Transition Zone of the CPO oceanic crust.
In order to constrain the timing of the subduction event, zircons were separated from the metamorphic sole of CPO referred to as the Dalrymple Amphibolite. Specifically, U-Pb ages (concordia intercept age = 35.20 ± 0.26 Ma) were obtained for the metamorphic overgrowth rims of the matrix sample B214-2G. These rims have lower Th/U ratios (= 0.04-0.34) than the inherited cores (0.25-3.35). Detailed investigation by previous works on the petrogenesis and P-T-D history of a kyanite-garnet-biotite-hornblende schist (sample B214-2G) preserved peak metamorphic conditions (~700 °C, 13kbars) and was not significantly affected by the later retrograde metamorphism of the mélange complex. Our results reveal the timing of prograde metamorphism of the subducting slab at moderately low P/T gradients (~16 °C/km) linked with incipient subduction. Together with compiled radiometric ages for the CPO by previous works (= ~35.2424 – 40.01 Ma), these results indicate that CPO-related rifting of the proto-South China Sea persisted even as subduction has begun at ~35 Ma. Furthermore, the similar age between the protolith of the Amphibolite (= 35.242 and 35.862 Ma) obtained in an earlier work with our weighted mean age of metamorphism (=35.46 ± 0.18 Ma) supports a rapid rate of reversal from spreading to subduction in induced subduction zones (~1 Ma). Similar observations on nascent arcs have thus far largely been limited to the Cretaceous Semail Ophiolite and its metamorphic sole. Since the paleogeothermal gradient preserved CPO mélange complex is significantly cooler than Semail and other ophiolites, our results may also indicate the short timeframe (~1-2 Ma) needed to cool the slab-mantle interface from the very low P/T gradients during very early stages of subduction initiation (>25°C / km), to geothermal gradients more comparable to hot subduction zones (~16 °C/km).
How to cite: Payot, B., Valera, G. T., Kawakami, T., Sakata, S., and Hirata, T.: Timelines of induced subduction zones in inverted spreading centers: Records in the Central Palawan Ophiolite, Philippines, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21406, https://doi.org/10.5194/egusphere-egu25-21406, 2025.
The Sibela Mountains of Bacan island in eastern Indonesia contain one of the Earth’s youngest metamorphic complexes, now exposed at elevations up to 2000 m. Exhumed basement consists of Permo-Triassic (c. 249-257 Ma) granitoids and metamorphic rocks. Mica 40Ar/39Ar and apatite (U-Th-Sm)/He data from these rocks indicate that they were rapidly exhumed in the Pleistocene (c. 0.7 Ma) accompanied by partial melting. The rapid exhumation observed on land was associated with significant subsidence in adjacent basins offshore that reach depths up to 2.4 km. Neogene metamorphic core complexes and other metamorphic complexes are well-known from eastern Indonesia, and they usually record much higher exhumation rates than those reported from older classic metamorphic core complexes found in other parts of the world and require a different formation mechanism. Unlike classic metamorphic core complexes that are characterized by low-angle detachment faults, the Bacan metamorphic rocks were exhumed on steep bounding normal faults forming a rectilinear block pattern. A similar exhumation mechanism can be observed on the island of Sulawesi. We suggest such complexes be termed metamorphic block complexes (MBC). The Bacan MBC is exceptionally young and like the other east Indonesian complexes was rapidly exhumed during subduction rollback.
How to cite: Breitfeld, T., Hennig-Breitfeld, J., Hall, R., White, L. T., Forster, M. A., Armstrong, R. A., and Kohn, B. P.: Age, origin and tectonic controls on rapid Pleistocene exhumation of the Sibela Mountains, Bacan, Indonesia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16533, https://doi.org/10.5194/egusphere-egu25-16533, 2025.
Only limited orogens show preserved markers of collision initiation, so that this specific stage is generally not integrated in plate tectonic models attempting to reconstruct their evolution. In SE Asia, this is the case of the Philippine Mobile Belt in the Philippines and Taiwan, but basement elements involved in the growth of the belt are generally not integrated to fully comprehend the construction of the region.
The geological evolution of the Philippine-Taiwan region includes extensional, compressional and transform settings overlapping in space and time since the Late Cretaceous. The resulting tectonic blocks move along major reactivated and newly-formed fault systems shaping the conjugate Eurasia/Australia margins of the South China Sea and accommodating the oblique subduction of the Philippine Sea Plate below Eurasia. Large-scale kinematic models generally describe well the clockwise rotation of the Philippine Sea Plate that drives the regional compression obliquely to the plate boundary since the Eocene. However, the detailed origin, geometry and motion of internal tectonic blocks of the Philippine Mobile Belt are often hypothetical due to the lack of onshore and offshore geological correlations.
In the frame of the research project COLLISEA (ANR-22-CE49-0015), we have collected a comprehensive geological and geophysical dataset to map accurately pre-accretionary structures and to decipher how these elements were involved during the subduction-collision transition. Until 2 Myrs (Pleistocene), the tectonic motion is reconstructed using GPS data. Then, detailed geological mapping enables us to model further motions until at least 15-20 Myrs (Early Miocene). Doing so, we progressively unfold the Philippine Mobile Belt and propose palaeogeographic reconstructions of the various tectonic blocks through the last 20 Myrs. This enables to discuss the variations of velocity and deformation styles along the plate boundary and to give new insights on geological parameters involved in the collision initiation.
How to cite: Bulois, C., Pubellier, M., Mouthereau, F., Chamot-Rooke, N., Larvet, T., Labis, F. A., and Delescluse, M.: Temptative assessment of tectonic blocks affinities to reconstruct the Philippine-Taiwan region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17173, https://doi.org/10.5194/egusphere-egu25-17173, 2025.
The Taiwan orogeny is well-regarded as a key location for studying the initial stages of collision and the interactions between tectonics and surface processes. Another significant yet relatively less explored aspect of this orogeny is its obliquity. In this region, two distinct types of obliquity can be identified: (1) the oblique convergence between the Eurasian plate and the Philippine Sea plate, which creates a transpressional regime leading to strain partitioning, and (2) the orientation of the inherited margin structure from the South China Sea relative to the direction of convergence.
How do the obliquity of inherited structures and convergence affect the thermal structure and strain localization within the orogen?
To address this question, we develop a 3D thermo-mechanical model of oblique subduction-collision using pTatin3D. This model accounts for erosion-sedimentation processes using diffusion, thermo-dynamically consistent densities, and new Navier-slip type boundary conditions specifically designed for oblique setting. We aim to conduct two parametric studies: one focusing on the obliquity of the convergence, while the other focuses on the obliquity imposed by the structural inheritance. By comparing simulations results with thermo-chronological models and structural observations, we target the development of a framework to help interpreting geological observations and records in the highly 3D Taiwann region.
How to cite: Larvet, T., Jourdon, A., Le Pourhiet, L., Mouthereau, F., and Bulois, C.: 3D numerical modeling of the collision at Taiwan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21083, https://doi.org/10.5194/egusphere-egu25-21083, 2025.
Sedimentary geochemistry, particularly whole-rock, trace element, and rare earth element analyses, has proven to be an effective tool for provenance studies, especially in geologically complex regions such as the Philippines. These techniques enhance the delineation of tectonic boundaries and provide critical insights into a region's petrogenesis and tectonic evolution.
In Northern Luzon, Philippines, much of the geological framework of the Central Cordillera Range has been established through field investigations and mineral exploration. While geochemical research has largely concentrated on igneous lithologies, recent studies on sedimentary sequences within the Baguio Mineral District – specifically the Late Oligocene to Early Miocene Zigzag Formation and the Middle to Late Miocene Klondyke Formation – have helped constrain the source rock composition and tectonic setting of these units. This study employs sedimentary geochemical techniques to investigate analogous Oligocene-Miocene clastic successions exposed in southwestern Mountain Province, northwest of the Baguio Mineral District.Geochemical signatures from these clastic units indicate derivation from igneous source rocks and deposition within a sedimentary basin associated with an oceanic island arc system. Paleontological and geochronological data suggests a Middle Miocene unconformity. This event is likely associated with the transition from a west-verging to an east-verging subduction in Luzon, as suggested by previous studies in the region. These results offer additional constraints into the geodynamic evolution of northern Luzon throughout the Oligocene-Miocene, contributing to a more refined understanding of the region’s tectonic history and its broader implications for the evolution of the Philippine Mobile Belt.
How to cite: Sangalang, K. J., Novero, M. J., Gabo-Ratio, J. A., Dimalanta, C., Payot, B., Garcia, Ma. Y. R., Amoroso, J. A. V., Manalo, P., Takahashi, R., Jabagat, K., and Lee, Y.-H.: Provenance and tectonic evolution of Oligocene-Miocene clastic sequences in the Mountain Province, north Luzon, Philippines , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21181, https://doi.org/10.5194/egusphere-egu25-21181, 2025.
The South China Sea margins have been studied in depth due to the considerable amount of available seismic lines, and displays evidence of variable composition such as granitoids, as well as a clear structure of crustal boudinage. The continental margin has been stretched over a large distance (1000Km), in a wide rift style. The stretching took place within the subducting plate, thus implying a weak hot lithosphere . As the crust is injected by plutons since the Triassic that migrated toward the SE until the late Early Cretaceous and those plutons are mostly located on the NW margin of the SCS . To the west of the Cretaceous volcanic arc, the crust is devoid of plutons except for isolated Miocene ones, and is inferred to be the former crust of a continental block (Luconia Block) docked against the margin in the Early Cretaceous. The orogen formed by this time correlates with the Yenshanian Orogen which extends from Vietnam to NE China.
Here we concentrate the modelling effort on the effect of heterogeneous heat production distribution on continental rifting by focusing on the SCS a wide rift that succeed to continental break up across a post-orogenic crust that display lateral variation in lithologies and heat production. All simulations are solved with pTatin a method that solves for conservation of energy and momentum in a nonlinear incompressible viscous fluid which viscosity depends on strain rate, temperature, pressure and stress.
The model geometry is simple. It consists of a 1000 km wide by 250 km deep domain constituted of a 40 km mechanically homogeneous crust that might be coupled (modelled with Diorite flow law) or decoupled (modelled with Quartz flow law) from the lithospheric mantle. The mantle rocks (Dry Olivine) extend down to 250km depth. In order to mimic the presence of plutons, we use a gaussian distribution of radiogenic heat production in map view and affect its value to the whole column of upper crust. The Gaussian characteristic half-width (sigma) is set to 6 km. The position in x-z of the gaussian/pluton is random but the number of plutons is chosen to ensure an average spacing of 50 km.
We find that the presence of the pluton belt influence significantly the strain rate distribution in the early stage of rifting both at lithospheric scale, by defining zone of distributed vs localized deformation, and at crustal scale by influencing the location of faults and basins. In the later stage of rifting the imprint of plutons belt become less important and the mechanical layering of the lithosphere rules which basins are abandoned and which basins continue their activity. None the less the initial presence of the plutonic belt oblique to the direction of extension induces a typical en-echelon pattern that we obtain compares well with the data in the continental rifting stage of the SCS. We find that, given the configuration of the simulation, a change in kinematics is necessary to explain the orientation of the magnetic anomaly in the west subbasin.
How to cite: Le Pourhiet, L., Pubellier, M., Jourdon, A., and Zhou, F.: Impact of thermal inheritance on South China Sea rifting : insight from 3D thermo-mechanical simulations , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17235, https://doi.org/10.5194/egusphere-egu25-17235, 2025.
The South China Sea Margin is a good natural laboratory featuring polyphase rifting processes that began in the late Eocene and ended late Miocene. The breakup first occurred in the East Sub-basin, and the expansion direction shifted from a north-south orientation to a northwest-southeast orientation around 23 Ma, with the propagation of new oceanic crust forming the Southwest Sub-basin. Most previous studies have suggested that the heterogeneity of the continental crust, such as the thickness of the lithosphere, primarily controlled the location and direction of ridge propagation. However, the involvement of magmatic activity is still not fully understood, nor is its influence during the breakup process of the Southwest Sub-basin.
This study investigates the crustal structure and the magmatic activity by integrating multichannel seismic (MCS) profiles and shipborne gravity around Taiping Island (Spratly Islands). Five pre-stack time migration profiles further enhanced imaging of lateral stratigraphic variations, providing spatial distribution. The Moho surface in the South China Sea was derived by inverting global Bouguer anomaly data with constraints from Moho depths obtained through OBS and seismic survey data and integrating other stratigraphic interfaces from seismic profiles; these boundaries construct a 2D gravity model.
Gravity simulation results reveal the presence of a high-density igneous body in the continent-ocean transition (COT) east of Taiping Island (Spratly Islands) by comparing seismic interpretations with different densities. The tentative magmatic body corresponds to the area of high-amplitude, high-angle reflectors in seismic profiles overlain by post-rift sediments. Among the five seismic profiles analyzed in this study, high-density bodies were identified in the easternmost profile, absent in profiles located approximately 40 km westward, suggesting a limited western extent. The seismic observation inferred that the magmatic formation occurred during the latest rifting phase in the southwest sub-basin of the South China Sea.
Therefore, this study suggests distinct magmatic intrusions within the South China Sea crust during the spreading of the southwest sub-basin. The location of these high-density bodies is near the boundary between the East Sub-basin and the Southwest Sub-basin and close to the southern segment of the Zhongnan Fault. The formation of these high-density bodies may provide more insights to discover magmatism involving the ridge propagation process.
How to cite: Chen, K.-H., Chang, S.-P., Hsieh, H.-H., Mirza, A., Chang, J.-H., Hsu, H.-H., Pubellier, M., and Delescluse, M.: Geophysical Characteristics of Breakup Magmatism in the Southern South China Sea Margin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16669, https://doi.org/10.5194/egusphere-egu25-16669, 2025.
The Andaman and Sumatra subduction zone exhibits unique tectonic behavior, notably characterized by the overturning nature of the subducting slab, setting it apart from other subduction zones. This study investigates the complexities of this phenomenon using high-resolution numerical simulations conducted with the Advanced Solver for Problems in Earth's ConvecTion (ASPECT) software. The simulations, spanning a geological timescale of 15 million years, reveal intricate details about the dynamics of the subducting Indo-Australian plate. The relatively dense subducting slab, with a density of 3300 kg/m³, interacts with the curved and segmented geometry of the subduction zone, leading to distinct stress distributions and unique slab dynamics. The thermal structure, influenced by a serpentinized mantle wedge in the overriding plate with a lower density of 2950 kg/m³ and thermal conductivity of 1 W/m·K, further modifies the subduction process by altering the thermal gradient and buoyancy forces. The trench rollback rate of 5 cm/year, coupled with hydration, serpentinization, and viscosity variations (ranging from 1e20 to 1e22 Pa·s), plays a significant role in driving slab deformation and overturning. Ambient mantle flow, modeled with a gravitational force of 9.81 m/s², interacts with the subducting slab, generating torques and forces that contribute to its overturning behavior. The high-resolution capabilities of ASPECT enabled the capture of fine-scale features and long-term dynamics, offering valuable insights into the region's tectonic mechanisms. This study not only advances our understanding of the Andaman and Sumatra subduction zone but also holds significant implications for seismic hazard assessment and geodynamic research. Future work will incorporate three-dimensional models and explore additional factors such as fluid migration and mantle flow heterogeneities to further elucidate subduction dynamics.
How to cite: Saini, S. and Roy, P. N. S.: Overturning Nature of the Subducting Slab in the Andaman and Sumatra Subduction Zone: A Numerical Study using ASPECT, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5473, https://doi.org/10.5194/egusphere-egu25-5473, 2025.
High-resolution bathymetry and sub-bottom profiler data from the northern Manila Trench forearc region reveal two distinct morphotectonic features. The first set of features consists primarily of NW-SE trending faults, interpreted as offshore splays of the Philippine Fault Zone (PFZ). These faults are evidenced by offset submarine canyons, linear valleys, and fault scarps, indicating a dip-slip component likely resulting from complex deformation at the termination of the PFZ. The second set mainly comprises N-S trending normal faults, which are inferred to have been formed by forearc flexure caused by the partial subduction of the Scarborough Seamount Chain.
The NW-SE trending faults reflect tectonic deformation associated with the strike-slip activity of the PFZ, while the N-S trending normal faults highlight the impact of the varying seafloor topography of the subducting slab on the forearc region. However, the relationship between the forearc normal faults and the PFZ splays remains unclear due to observational limitations. Further investigation is needed to explore potential links between the normal faults and other nearby fault systems, including the Lingayen Gulf Fault System and the East Zambales Fault. This study provides new insights into the tectonic complexity of the northern Manila Trench forearc region, with implications for understanding the region’s broader tectonic setting.
How to cite: Maglalang, E. J. M., Sayen, K. M. F., Armada, L. T., Dimalanta, C. B., Hsu, S.-K., and Yumul, G. P.: Analysis of shallow structures and seafloor morphology in offshore western Luzon, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21011, https://doi.org/10.5194/egusphere-egu25-21011, 2025.
Upper mantle heterogeneity is the consequence of mantle differentiation throughout the Earth’s history, driven by material transportation within the upper mantle and across the planet’s surface to the lower mantle. The resulting heterogenic domains likely evolved through time, reflecting the dynamic mantle evolution in deep time. Previous studies mainly relied on present-day basalts (e.g., MORB and OIB) to understand the upper mantle heterogeneity (e.g., O’Nions et al., 1980; Stracke et al., 2005, 2022; Yang et al., 2021). However, the spatiotemporal evolution of ancient mantle heterogeneity remains poorly constrained.
In this study, we developed a technique to reconstruct upper-mantle domains back in time by restoring the basalts and published Pb isotopic ratios to their eruption locations using multiple plate reconstruction models including Müller et al. (2019). We test the new technique in the Southwest Pacific region, reconstructing the Zealandia-Antarctic geochemical domain and its boundary with the adjacent Pacific and Indian domains in the past ~60 Ma.
How to cite: Wu, J. T.-J., Qian, S., and Wu, J.: Reconstructed Upper-mantle Heterogeneity Domains in the Southwest Pacific since the Cenozoic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16703, https://doi.org/10.5194/egusphere-egu25-16703, 2025.
Posters virtual: Tue, 29 Apr, 14:00–15:45 | vPoster spot 1
EGU25-21462 | Posters virtual | VPS22
Understanding the arc-continent collision zones in western Philippines: Novel insights from the Romblon Island Group and the Central Zamboanga PeninsulaTue, 29 Apr, 14:00–15:45 (CEST) | vP1.22
The continent-derived nature of the western Philippines (Palawan-Mindoro Microcontinental Block; PCB) contrasts with the island arc-dominated eastern Philippines (Philippine Mobile Belt; PMB). Petrological investigation on the P-T-D history of the metamorphosed rocks in between these two terranes and how they relate to the broader tectonic events are however lacking. In this study, we examined rock units related to the arc-continent collision events in two areas: the Romblon Island Group and the central Zamboanga Peninsula.
In central Philippines, the Romblon Metamorphic Complex (RMC) represents the PCB-derived materials. The RMC consists of metapelitic and metapsammitic paraschists in Tablas, Romblon, and Sibuyan with minor orthoschists and marbles. Using two-feldspar geothermometery, and Raman Spectrometry of Carbonaceous Material, the temperature variations revealed a low P/TStage 1 metamorphism of all RMC units with peak T and P values of about 450-540°C at <5 kbars. Based on tensional structures (e.g. boudins) and preserved metapelitic-metapsammitic interlayering, we attribute this Stage 1 to the PMB continental rifting and subsequent shallowing of the paleogeothermal gradient. The RMC paraschists which are adjacent to the Sibuyan Ophiolite Complex (SOC) meanwhile register significantly higher T at the same low P conditions (= 570-630 °C). This suggests a second stage of higher T deformation and metamorphism directly linked with the juxtaposition of the continental RMC and the island arc SOC. This is consistent with the subsolidus shearing and metamorphism of the isotropic gabbro units of the SOC with preserved P-T conditions of about 500-800°C.
The southern extension of the PCB-PMB collision is even less understood although earlier works extend the arc-continent suture zone in Mindanao Island, southern Philippines. The purported boundary of the continent-derived Zamboanga Peninsula and the island arc Eastern Mindanao is the northwest-southeast trending Siayan-Sindangan Suture Zone. Our field mapping in central Zamboanga Peninsula however revealed a distinct northeast-southwest trending suture zone of an apparent arc-continent collision zone. Across this NE-SW suture zone, the lithologies progress from the paraschists of the Gutalac Metamorphic Complex (GMC) in the northeast to the amphibolites of the Dansalan Metamorphic Complex (DMC). Further southeast, the residual peridotites and pillow lavas with intercalated chert, deep marine turbidites and limestones of the Polanco Ophiolite Complex (POC) are exposed. Such progression hints at a NE-SW convergence of an ancient arc (POC) with its metamorphic sole (DMC) against the continent-derived GMC following the consumption of an ancient oceanic basin.
How to cite: Valera, G. T., Badillo, J. K., Tabilog, A. E. S., Balanial, N. M., Alcancia, M. L., and Payot, B. D.: Understanding the arc-continent collision zones in western Philippines: Novel insights from the Romblon Island Group and the Central Zamboanga Peninsula, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21462, https://doi.org/10.5194/egusphere-egu25-21462, 2025.
