We invite contributions that integrate geology, geophysics, geochemistry, and numerical modeling to decode how continents act as planetary-scale regulators, driving the development of habitability through various tectonic processes, from pre-plate tectonics to plate tectonics, including plate subduction, collision, accretion, and coupled tectonics-topography-climate processes.
Eclogite formation from lower crustal rocks requires high pressure at relatively low temperature in the presence of water. Due to the high temperature regime in the early Earth and the sparse observations of eclogitic rocks at the surface, it is generally expected that such rocks are rare in cratons. Our recent results show that large amounts of eclogitic lower crustal rocks are present below the seismic Moho in the Baltic Shield1. Such eclogites in various metamorphic grades may explain the high topography of the Scandes mountain range in northern Fennoscandia2. Our findings suggests that the amount of sub-Moho eclogite can be generally underestimated globally!
Eclogitization may also play a major role in plateau formation in Tibet, where new addition of mafic underplate to the overthickened crust may immediately transform into eclogite, which founder each time the eclogite layer exceeds a critical thickness3. The whole continental crust in the central Lhasa Block has low seismic velocity (<6.7 km/s), which indicates that this thickest crust on Earth is felsic down to the Moho at 80 km depth, explaining half the present topography by isostasy. However, underplating and partial melt in the crust are also required to explain the high elevation of the Tibetan Plateau and other major plateaux worldwide4.
By interpretation of >18,000 km of seismic profiles, we document that a mafic crustal layer is generally preserved in Proterozoic orogens but absent in Phanerozoic orogens5. This indicates a change in the global subduction style at the onset of the Phanerozoic, which caused massive eclogitization of lower crust in orogens and recycling of the eclogitic rocks into the mantle. The resulting buoyant felsic crust lifted continents above sea level, which enabled onshore life to develop, thus explaining the Neoproterozoic oxidation event and the explosion of life in the Phanerozoic.
1. Buntin, S. et al. Long-lived Paleoproterozoic eclogitic lower crust. Nature Communications 12 (2021). https://doi.org/10.1038/s41467-021-26878-5
2. Kahraman, M. et al. Northern Scandinavian mountains supported by a low-grade eclogitic crustal keel. Nat Commun 16, 606 (2025). https://doi.org/10.1038/s41467-025-55865-3
3. Wang, G., Thybo, H. & Artemieva, I. M. No mafic layer in 80 km thick Tibetan crust. Nature Communications 12, 1069 (2021). https://doi.org/10.1038/s41467-021-21420-z
4. Zhou, Z., Thybo, H., Artemieva, I. M., Kusky, T. & Tang, C. C. Crustal melting and continent uplift by mafic underplating at convergent boundaries. Nat Commun 15, 9039 (2024). https://doi.org/10.1038/s41467-024-53435-7
5. Xia, B., Artemieva, I. M. & Thybo, H. Phanerozoic emergence of global continental collision and onset of massive crustal eclogitization. Geology 53 (2025). https://doi.org/10.1130/g52647.1
How to cite: Thybo, H., Xia, B., Wang, G., Zhou, Z., and Artemieva, I.: Importance of Eclogites from Cratonisation to the Phanerozoic Explosion of Onshore Life, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11399, https://doi.org/10.5194/egusphere-egu26-11399, 2026.
After subduction of the oceanic plate and continental collision, ancient orogenic belts could be reactivated as intracontinental orogens or rift zones. These intracontinental weak zones often experienced multiphase deformation, magmatism, erosion and sedimentation, which raise ambiguity in interpretation of geological records. The Xuefengshan belt in central South China is generally regarded as the Early Neoproterozoic collision zone between the Yangtze and Cathaysia blocks, and behaved as the western boundary of the widespread Mesozoic deformation and magmatism in South China. However, recent study found SE-dipping mantle reflections beneath the eastern Yangtze Craton, suggesting a fossil subduction zone during the assembly of the Yangtze Craton. Here we combined a 2400-m-deep borehole in the Xuefengshan belt, high-resolution deep seismic and electrical structures, rock physics, and geological data to investigate the crustal structure of the eastern Yangtze Craton. Our results confirm the buried Paleoproterozoic orogen beneath Neoproterozoic strata of the eastern Yangtze Craton. The variations of the Moho depth and the lithospheric thickness, distribution of seismic reflections, low velocity anomalies and high conductivity anomalies in the Xuefengshan belt reveal multiple reworking events, including the Neoproterozoic intracontinental rifting and crustal thinning, the Triassic thrusting, magma underplating and granite intrusion, the basement-involved fold-and-thrust belt in the Mid-Late Jurassic, as well as crustal extension and graben development in the Cretaceous. Therefore, the Xuefengshan belt provides a unique example how tectonic inheritance controlled crustal reworking of an intracontinental orogenic belt.
How to cite: Wang, Q., Jiang, W., Deng, X., Ye, G., Zhang, Y., Dong, S., and Gao, R.: Crustal structure and tectonic inheritance in the eastern Yangtze Craton: Reworking history of a buried Paleoproterozoic orogenic belt, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21728, https://doi.org/10.5194/egusphere-egu26-21728, 2026.
Mantle plumes are commonly believed to generate uplift of their overlying lithosphere, while also impacting climate and life. However, sedimentary deposits show a component of subsidence during plume-lithosphere interaction, challenging traditional uplift-only models of plume-lithosphere interaction. We investigate whether plume-induced delamination can induce subsidence as well as uplift through computations of plume-lithosphere interaction. When a denser lithospheric keel delaminates, initial plume ascent will induce ~2 km of uplift, followed by a more rapid ~2 km of subsidence over a few millions of years as the dense lithospheric keel delaminates. Delamination, distinct from back-arc extension and slab-induced flow, may explain observed subsidence patterns during continental flood basalt activity, such as those seen in the Paraná Flood Basalt, Columbia River Flood Basalt, Deccan Traps and Congo Basin regions.
How to cite: Shi, Y.-N., Morgan, J., Chen, L., Hou, Z., Zhao, L., Li, Z.-H., Araujo, M., and Gurnis, M.: Subsidence Amidst Uplift: Lithosphere Delamination During Plume-Lithosphere Interaction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3735, https://doi.org/10.5194/egusphere-egu26-3735, 2026.
The Paleoproterozoic Trans-North China Orogen (TNCO) is central to understanding the assembly of the North China Craton and the Columbia supercontinent. However, whether the metamorphic variations across the TNCO reflect diachronous tectonic events or differential exhumation processes remains a subject of ongoing debate. This study investigates the Daqian garnet-bearing amphibolites from the Zanhuang Complex to constrain the P–T–t evolution of the central TNCO.
Phase equilibria modeling reveals a well-preserved clockwise P–T trajectory characterized by peak high-pressure (HP) amphibolite-facies metamorphism (M2: 1.32–1.63 GPa, 715–750 °C), followed by near-isothermal decompression (M3: 0.61–0.88 GPa, 680–718 °C). Multi-mineral LA-ICP-MS U–Pb geochronology uncovers a significant temporal decoupling between peak and cooling stages: metamorphic zircons record the peak collision at ~1.87 Ga, whereas titanite, rutile, and apatite yield convergent cooling ages at ~1.81 Ga.
Our data indicate that the terrane experienced a prolonged deep-crustal stagnation (~60 Myr) with negligible cooling (<1 °C/Myr), followed by a pulse of extremely rapid exhumation (~22.5 °C/Myr) at ~1.81 Ga. We argue that the Zanhuang Complex underwent synchronous collision at ~1.87 Ga with the rest of the TNCO. Consequently, the observed regional metamorphic variations are not a result of diachronous tectonic arrival but rather reflect differential exhumation and isostatic rebound following lithospheric delamination. This rapid ~1.81 Ga event marks the definitive gravitational collapse of the orogen, providing new insights into the terminal stages of Paleoproterozoic orogenesis.
How to cite: Zhang, W., Liu, P., Zou, L., Du, L., Yang, C., and Zhao, G.: From Deep Residence to Rapid Exhumation: Constraints on the ~1.81 Ga Collapse of the Trans-North China Orogen from the Zanhuang Complex, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19275, https://doi.org/10.5194/egusphere-egu26-19275, 2026.
As the dominant component of Earth's early continental crust, tonalite-trondhjemite-granodiorite (TTG) suites offer critical insights into the crust-mantle dynamic systems and geodynamic regime for the early Earth (>2.5 Ga). Although TTGs are generally accepted to have originated from partial melting of hydrated metabasalt, specific conditions and mechanisms remain enigmatic, which has sparked intense debate over the geodynamic settings of the early Earth. Here, we conduct thermodynamic-geochemical modellings to systematically compare the roles that pressure, bulk H2O content, and source rock composition play in shaping TTG magmas. We find that pressure is the first-order factor controlling the formation and compositional diversity of TTG. Our modellings also predict the optimal melting conditions for different types of TTGs, which are further validated by the ranges of magmatic H2O contents recorded by apatite and zircon from global TTG samples. We propose an apatite-based melt hygrometer and apply it to Archean TTGs for the first time. Combined with the results from the zircon hygrometer, our data show that high-pressure TTGs have the highest H2O contents (7 – 12 wt.%), whereas the low-pressure TTGs have the lowest (4 – 7 wt.%), matching our prediction of the optimal H2O contents for TTG melts. We show that high-pressure TTG is likely derived from fluid-fluxed melting at subcrustal depths (14 – 16 kbar), a process readily explained by subduction rather than intraplate crustal formation models. Furthermore, the temporal and spatial distribution of both high-pressure TTGs and arc-like basalts points to subduction that likely started as a localized phenomenon and transitioned to a global-scale process at about 3.0 Ga.
How to cite: Wang, H., Cai, K., Sun, M., Li, W., Chen, M., and Xia, X.: Diverse genesis of early Earth’s continental crust hints the geodynamic transition at about 3.0 Gyrs ago, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2041, https://doi.org/10.5194/egusphere-egu26-2041, 2026.
Earth’s Middle Age (1.8-0.8 Ga) witnessed prolonged stability of the Nuna supercontinent, yet its breakup history remains enigmatic. We analyse the spatiotemporal evolution of arc and anorogenic magmatism, sedimentary deposition, and large igneous provinces (LIPs) emplacement during this period. Our results reveal that retreating accretionary orogens and back-arc extension occurred along the Laurentia-Baltic margins of Nuna from around 1.8 Ga to 1.5 Ga. The retreating mode was likely linked to elevated mantle temperatures, which, as supported by numerical models, enhanced rapid slab rollback and formation of wide back-arc basins. Importantly, LIPs during this interval were predominantly confined to Nuna’s margins, while widespread intracontinental plumes only emerged at 1.4-1.3 Ga. We propose that Nuna’s breakup was delayed until this time because earlier subduction delivered cold, dense oceanic lithosphere to the core-mantle boundary, inhibiting the rise of hot mantle plumes beneath the supercontinent. Only after this material was sufficiently heated could buoyant, hot mantle plumes rise beneath the continental blocks and drive fragmentation. This protracted stability maintained a warm upper mantle status, which weakened the continental lithosphere and reduced surface erosion, linking deep geodynamic processes to the environmental stasis of the ‘Boring Billion’.
How to cite: Zhu, Z., Cawood, P., Campbell, I., and McKenzie, R.: What drove the delayed breakup of Nuna during Earth’s Middle Age? , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16299, https://doi.org/10.5194/egusphere-egu26-16299, 2026.
The Archean continental crust, dominated by tonalite–trondhjemite–granodiorite (TTG) suites, is widely interpreted to have formed through partial melting of a hydrous mafic protolith. However, the nature of this protolith remains highly debated. Proposed sources include hydrothermally altered supracrustal basalts recycled to melting depths, as well as unaltered, mantle-derived gabbros emplaced into the lower crust by mantle plumes. Silicon and quadruple sulfur isotopes are powerful discriminants between these scenarios because they directly trace the relative supracrustal contributions to felsic continental crust. Here, we integrate whole-rock silicon and quadruple sulfur isotopes data from Neoarchean granitoids in the North China Craton to constrain the origin and evolution of their mafic protoliths. These granitoids display non-chondritic Δ³³S (to ~−0.06‰) and elevated δ³⁰Si (−0.09‰ to −0.05‰), which indicate supracrustal origin and contrast with previously reported mantle-like zircon δ¹⁸O values. A global compilation of Δ³³S and δ³⁰Si data shows that granitoids formed after 3.8 Ga consistently exhibit enriched δ³⁰Si and non-zero Δ³³S. Together, these observations indicate that Archean continental crust was generated by partial melting of supracrustal basalt rather than unmodified mafic cumulates.
How to cite: shang, K., Zhang, J., Wang, Z., Cawood, I., Cui, Y., Li, M., Chang, R., Shen, Y., and Zhao, G.: Coupled S-Si isotopes reveal supracrustal origin of Archean continental crusts, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18167, https://doi.org/10.5194/egusphere-egu26-18167, 2026.
The North China Craton (NCC) preserves geological records from the Eoarchean to the Neoarchean, providing a window into the secular evolution of Earth's early continental crust. By integrating zircon U-Pb-Hf-O isotopes, whole-rock geochemistry, and calculated magmatic physicochemical parameters (oxygen fugacity, fO2; water content, H2O) for felsic rocks from the NCC, we identify three distinct evolutionary stages marked by fundamental shifts in magmatic characteristics. The Paleo–Mesoarchean (~3.8–3.2 Ga) felsic rocks are dominated by sodic tonalite-trondhjemite-granodiorite (TTG) suite characterized by low K2O/Na2O ratios and high positive εHf(t) values. Their low magmatic fO2 (ΔFMQ –3 to 0) and H2O content (4–8 wt%) reflect partial melting of low-K juvenile sources under reduced and relatively dry conditions. A pivotal transition occurred during the mid-Mesoarchean (~3.0 Ga), with high K2O/Na2O ratios, elevated zircon εHf(t), increased whole-rock Nb/Ta ratios and a subtle rise in both magmatic fO2 and H2O. We attribute these signatures to an early pulse of crustal growth and recycling of subduction-related fluids. By the Neoarchean, the zircon εHf(t) values dropped significantly, indicating extensive crustal reworking, while zircon δ18O, magmatic fO2 and H2O rose dramatically (fO2:ΔFMQ -1.5 to +3; H2O: 6–16 wt%), comparable to modern arc magmas. These Neoarchean oxidized and hydrous felsic magmas were likely generated through effective water-fluxed melting of early-formed, underplated crust derived from the metasomatized mantle wedge. Notably, the redox and hydration evolution of the Archean crust in the NCC deviates from that of the global detrital zircon or TTGs records, suggesting that the onset of plate subduction could be diachronous across different cratons. Meanwhile, the convergence of these magmatic parameters at ~2.5 Ga marks a globally synchronous tectonic transition. Our findings also demonstrate that magmatic oxidation and hydration evolution could provide critical constraints on crust-mantle interactions.
How to cite: Liu, Y., Wang, C., and Song, S.: Redox and hydration evolution of Archean felsic magmatism in the North China Craton, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9435, https://doi.org/10.5194/egusphere-egu26-9435, 2026.
The late Neoarchean to early Paleoproterozoic era represents a key period for the formation and evolution of the Earth’s early continental crust. It is characterized by a transition from intense global magmatism and significant crustal growth to dramatically reduced magmatism with increasing crustal reworking. The tonalite-trondhjemite-granodiorite (TTG) and dioritic rocks constitute the dominant component of the early continental crust, and their petrogenesis and tectonic setting provide critical insights into the formation mechanism of the continental crust. In this contribution, we present a systematic geochronological, geochemical, and zircon Hf-O isotopic study for the late Neoarchean and early Paleoproterozoic TTG and dioritic gneiss in Eastern Hebei, North China Craton.
Zircon U-Pb dating shows that the late Neoarchean TTG and dioritic gneiss rocks have protolith crystallization ages of 2.55–2.52 Ga and metamorphic ages of 2.51–2.47 Ga and ~2.45 Ga. The early Paleoproterozoic trondhjemitic gneiss yields protolith crystallization ages of 2.45 Ga and inherited zircon ages of 2.55 Ga. Accordingly, a prolonged tectonothermal events (2.55–2.45 Ga) occurred in Eastern Hebei.
The late Neoarchean TTG gneiss samples shows geochemical affinities akin to adakitic rocks, characterized by high concentrations of SiO2, Al2O3, and Sr, low concentrations of MgO, Y and Yb, as well as high Sr/Y and (La/Yb)N ratios. They can be divided into two groups. The first group has low MgO, Cr, and Ni contents, coupled with the positive zircon εHf(t) (3.0 to 7.3) and δ18O values of 5.36–6.59 ‰, indicating that it was derived from partial melting of juvenile thickened lower crust. The second group contains high MgO, Cr, and Ni contents, which are more consistent with the TTG rocks derived from partial melting of subducted oceanic crust. A majority of positive zircon εHf(t) values (0.2–5.2) and lower δ18O values (5.58–6.54 ‰) suggest its magmatic source of juvenile crust. Notably, some zircons display negative εHf(t) values (-2.6 to -0.2) and higher δ18O values (7.19–7.47 ‰), indicating the involvement of ancient crust materials. The dioritic gneiss has moderate SiO2 content, high CaO, MgO, Cr, Ni, Sr, and Ba contents, as well as high K2O/Na2O and (La/Yb)N ratios, akin to the Archean sanukitoids. They are enriched in large-ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs), combined with their positive zircon ɛHf(t) values (4.0–6.4) and slightly higher δ18O values (5.99–6.42 ‰), suggesting a metasomatized mantle source. In addition, they show large variations in (Hf/Sm)N, high Nb/Ta and Zr/Hf ratios, and low Nb/Zr ratios, implying that both subducted fluids and slab-derived melts are metasomatic agents. The 2.45 Ga trondjemitic gneiss shows similar geochemical and zircon Hf-O isotopic characteristics to the above mentioned first group TTG gneiss, further supporting that it was a continuation of the late Neoarchean magmatism.
Based on the diverse sources of the studied 2.55–2.45 Ga granitoid gneisses and regional geological data, we propose that the vertical mantle plume coexisted with the horizontal slab subduction in Eastern Hebei in the late Neoarchean to early Paleoproterozoic.
The research was funded by the National Key Research and Development Program of China (2024YFF0808000).
How to cite: Jing, J., Liu, Q., Han, Y., Yao, J., Zhang, D., Sun, C., Zheng, J., and Zhao, G.: Late Neoarchean to early Paleoproterozoic magmatism and its tectonic setting in Eastern Hebei, North China Craton, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4248, https://doi.org/10.5194/egusphere-egu26-4248, 2026.
A mechanically weak mid-to-lower crust is widely invoked to explain plateau uplift, lateral lower-crustal flow, and lithospheric removal beneath southern Tibet, yet the processes responsible for such long-term weakening remain debated. Classical models relying on thermal softening of plagioclase or widespread partial melting are challenged by the low water solubility of plagioclase and by geotherms that are too cool to sustain pervasive melting. Here, we propose that arc-magmatic amphibole enrichment is primary control on deep-crustal rheology, seismic anisotropy, and tectonic evolution in southern Tibet. Here we show that modest hydration (1.0-1.5 wt.% H2O) stabilizes amphibole as a major phase (50-65 vol.%) at 30-55 km depths, transforming initially strong plagioclase-pyroxene-dominated lithologies into weak, anisotropic amphibolite. Phase‑equilibrium modeling combined with experimentally calibrated mineral rheology demonstrates that such amphibole‑rich assemblages are significantly less dense and up to two orders of magnitude weaker than their anhydrous equivalents. The resulting viscosity structure and seismic anisotropy align with geodetic constraints on ductile crustal flow and with the observed distribution of lower‑crustal earthquakes. At pressures greater than ~1.6–1.8 GPa (~55–60 km depth), amphibole breaks down to garnet + clinopyroxene, increasing density and promoting eclogitization that facilitates lithospheric delamination. Fluids released during amphibole breakdown may transiently weaken the lowermost crust and contribute to lower-crustal seismicity, but do not account for the long-lived regional weakness. Our results provide a unified, process-based frame work linking pre‑collisional arc magmatism to present‑day rheology, seismic structure, and the tectonic evolution of southern Tibet.
How to cite: Zhang, J. and Wang, X.: Amphibole enrichment weakens the mid-to-lower crust of southern Tibet, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22730, https://doi.org/10.5194/egusphere-egu26-22730, 2026.
Recent observations have challenged the traditional view that most continental lithosphere remains largely stable and maintains its primary structure following formation. It is now evident that in both convergent systems and mantle plume settings, continental lithosphere can be extensively destructed. This occurs through mechanical deformation or melt-rock interaction, leading to processes such as delamination or dripping of the lower lithospheric mantle. In this work, we focus on the convergent systems along the Tethyan Belt to examine the specific modes of continental lithosphere destruction and the factors or settings that govern the evolution of continental deformation.
As a weak overriding continent, the Central Iran Block has been greatly reworked by the collision between the Arabia and Eurasia, resulting in a nascent orogenic plateau. Through this process, continental deformation is initially localized within weak zones-the Alborz and Zagros belts-before gradually becoming more homogeneous to form a small, low-altitude plateau.
Acting as a rigid overriding continent, the South China Block underwent a protracted subduction of the Paleo-Pacific Plate, which triggered cyclical contraction and extension events in the Mesozoic. Within a single cycle, compression weakens the east margin of the thick continental lithosphere beneath the western South China Block; subsequent extension then destructs this part, leaving a thinned lithosphere. This progressive destruction model illustrates how a rigid continent responds to a continuous subduction setting.
Another example of a rigid overriding continent is the east North China Craton. Unlike South China, this region was modified during the Triassic continent collision. During this event, continent subduction bulldozed the lithosphere mantle and low crust of North China and then rebuilt it with materials of the subducting plate.
In summary, the process of continent destruction depends on the structure of the overriding plate and the stage of convergence (subduction vs. collision).
(1) Intensity of destruction: Continental destruction is generally more intense during collision than during subduction.
(2) Stress distribution: Stress tends to be localized during the early stages of continental destruction but gradually becomes more homogenized as collision progresses.
(3) Rigid continent dynamics: In rigid continents, destruction typically initiates at the border of the lithospheric root via delamination or dripping. Within episodic subduction/collision systems, this destruction can become cyclical, significantly reducing the overall size of the rigid continental lithosphere.
How to cite: Chu, Y., Lin, W., Chen, L., Wan, B., Faure, M., and Allen, M. B.: Modes of continental lithosphere destruction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16032, https://doi.org/10.5194/egusphere-egu26-16032, 2026.
Mountain-building processes typically involve complex tectonic evolution marked by multiple episodes of metamorphism and deformation. Accurately constraining the timing of individual deformation events is essential for reconstructing tectonic history and deciphering geodynamic processes. However, structural overprinting, polymetamorphism, and the scarcity of datable minerals often hinder conventional geochronological methods from isolating and dating discrete deformation phases. In this study, we employ 40Ar/39Ar stepwise crushing geochronology on fluid inclusions within syn‑kinematic tourmaline from leucogranite dykes and quartz veins in the Chinese Altai orogen. As a key tectonic unit in central Asia, this orogen has a well‑established deformation, magmatic, and metamorphic geochronological framework, including Devonian and Permian reworking events, making it an ideal natural laboratory for validating dating results. Tourmaline, a chemically robust borosilicate with low potassium content and abundant fluid inclusions, is widely distributed in deformed terranes. Owing to its higher K/Ar isotopic closure temperature compared to micas and K‑feldspars, tourmaline represents an ideal mineral for 40Ar/39Ar geochronology targeting fluid inclusions.
Based on detailed structural and petrological constraints, three sets of syn‑kinematic tourmaline samples were analyzed via 40Ar/39Ar stepwise crushing:
Tur I: Oriented tourmaline crystals within Devonian rigid leucogranitic dykes, aligned parallel to the Permian (D3) fold axial plane. These tourmalines formed from high-temperature boron‑rich fluids derived from dehydration of surrounding metasedimentary rocks, which infiltrated tensile gaps generated during shortening of the earlier rigid dyke, and are interpreted as syn‑D3 axial‑planar tourmaline.
Tur II: Disordered tourmaline from a syn‑D3 axial‑planar leucogranitic dyke, formed by melt injection into tensional gaps during compression of the rigid metasedimentary country rocks. The tourmalines represent a syn‑magmatic crystallization product from boron‑rich melts.
Tur III: Undeformed tourmaline occurring near the contact between a syn‑D3 axial‑planar quartz vein and its host Devonian leucogranitic dyke. The quartz veins formed by fluid injection into tensile gaps during the D3 event, and the tourmaline likely crystallized during fluid-rock interaction.
The three tourmaline sets yielded well‑defined 40Ar/39Ar plateau ages from primary fluid inclusions (PFIs) of approximately 320 Ma, 275 Ma, and 260 Ma. The PFI ages are consistent with 40Ar/39Ar step‑heating ages obtained from the crushed tourmaline powder, which primarily record argon released from the mineral lattice and thus correspond to the crystallization age of tourmaline. These results indicate that the Permian deformation initiated around ~320 Ma and continued until ~260 Ma, which aligns well with the established geochronological framework for Permian reworking in the Chinese Altai. Our study demonstrates that 40Ar/39Ar dating of fluid inclusions directly constrains the timing of tourmaline crystallization and the associated deformation. This approach overcomes limitations of traditional geochronometers by targeting deformation‑related fluids rather than recording cooling ages. The findings highlight tourmaline fluid inclusion geochronology as a powerful tool for directly dating tectonic events, particularly in reworked terranes where conventional methods face challenges. This technique offers a novel approach to reconstructing orogenic histories within complex metamorphic belts.
How to cite: Xiao, M. and Zhao, G.: Constraining deformation timing in orogenic systems with fluid inclusion 40Ar/39Ar geochronology of syn-tectonic tourmaline, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19622, https://doi.org/10.5194/egusphere-egu26-19622, 2026.
The deep lithosphere influences mineral resource distribution and the planet’s habitability, yet probing its architecture remains challenging. The present-day lithospheric architecture is a terminal, time-integrated image shaped by long-term geological processes, among which magmatism plays a pivotal role. However, the exact relationship between ancient magmatic events and present-day lithospheric architecture has not been fully explored. In this study, we investigate Late Carboniferous to Middle Permian magmatic rocks in West Tianshan, SW Central Asian Orogenic Belt, using multi-proxy isotopic and elemental mapping and thermodynamic phase equilibrium modeling. Using radiogenic (Hf-Nd) isotope spatial imaging, we here show that felsic rocks constitute two distinct domains: an isotopically depleted domain (IDD) to the north and an isotopically enriched domain (IED) to the south. The two domains correspond well to differences in geophysical properties revealed by seismic and gravity data. The lower crust of IDD was built by magmatic differentiation of intermediate magmas sourced from an oceanic subduction-modified mantle. In contrast, the lower crust of IED was constructed through the differentiation of sanukitoid magmas derived from an ancient crust-metasomatized mantle, with variable-degree involvement of Tarim supracrustal relaminant. These findings directly link geophysical contrasts in the lithosphere to variations in deep-time magmatism, including mantle source heterogeneity and lower crustal differentiation. The study suggests that ancient magmatic rocks cannot only provide fresh insights into the dynamic processes that have shaped the lithosphere over geological time scales, but also be powerful proxies to understand present-day lithospheric architecture.
How to cite: Huang, H., Wang, T., Gómez-Frutos, D., and Castro, A.: Late Paleozoic magmatism set the stage for the present-day lower crust of West Tianshan, SW CAOB, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18244, https://doi.org/10.5194/egusphere-egu26-18244, 2026.
The compressional collision between the Indian and Eurasian plates has formed an extensive continental deformation zone and the Himalayan orogen belt, generating several east-west trending giant fault zones. Among these predominantly thrust fault zones, the South Tibetan Detachment System (STDS) is the only normal fault, extending over 2000 kilometers, and thus has become the largest single existing detachment fault system in the world . The STDS sharply separates the shallow un-metamorphosed or weakly metamorphosed Tethyan Himalayan Sequence (THS) from the deep high-grade metamorphosed, partially melted Greater Himalayan Crystalline Complex (GHC). The emergence of the STDS has revised the traditional view that compression and extension cannot coexist. During the entire Himalayan orogenic process, it has played a crucial controlling role in mountain uplift, the exhumation of high-grade metamorphic rocks at the root of the orogen, and the formation and migration of leucogranites. With the advancement and widespread application of high-pressure experiments, phase equilibrium simulation calculations, EBSD fabric analysis, and in-situ trace element-isotope dating techniques, significant progress has been achieved in STDS research, while new questions have also been raised. This study systematically reviews the new progress and existing controversies regarding the STDS and the Himalayan orogenic process, covering key aspects such as the active period of the STDS, genetic mechanisms, its relationship with leucogranites, and the geometry and kinematics of the Tethyan Himalayan D′ecollement (THD). By using multi-isotopic geochronology, the activity period of THD is determined, which further restricts the transition time from the southward movement of THD to the northward movement of STDS.
Acknowledge
This work was supported by the Deep Earth Probe and Mineral Resources Exploration - National Science and Technology Major Project (Grant No. 2024ZD1001006) and the National Natural Science Foundation of China (Grant No. 42472285, U2444202) and the Basic Research Fund of the State Key Laboratory of Deep Earth and Mineral Exploration (JKYDM2025203).
How to cite: Dong, H., Tang, Z., Fei, R., Song, Y., and Zeng, L.: The Miocene tectonic transform of the South Tibetan Detachment System (STDS), eastern Himalayan, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15297, https://doi.org/10.5194/egusphere-egu26-15297, 2026.
Foreland fold–thrust belts act as key engines of continental growth and reworking by accommodating crustal shortening and internal deformation during long-term continental evolution. Within these systems, the formation and propagation of thrust wedges represent the primary mechanisms by which shortening is accommodated and translated into the horizontal growth of orogenic belts. However, current understanding of thrust wedge evolution in foreland systems remains largely based on static structural interpretations, providing limited quantitative and time-resolved constraints on kinematics, strain partitioning, and wedge propagation mechanisms.
Here we investigate thrust wedge formation and propagation in a multilayered continental crust using analogue sandbox experiments inspired by the Western Xuefeng fold–thrust belt of South China, a representative intracontinental orogenic system. Two sets of experiments were designed to simulate different detachment configurations and lateral variations in rheology. Anisotropy of magnetic susceptibility (AMS) and particle image velocimetry were integrated to quantitatively constrain strain distribution, kinematic evolution, as well as velocity and vorticity fields within thrust wedges.
By reproducing multilayered deformation in foreland fold–thrust belts, the sandbox experiments provide a quantitative framework to link thrust wedge propagation with the redistribution of strain and the horizontal growth of orogenic belts. The experiments reveal that the cover sequence deforms as three distinct tectonic levels, each characterized by specific thrust wedge geometries: stacked thrusts forming an active roof duplex at the bottom level, box-shaped anticlines at the middle level, and imbricate systems with chevron-shaped folds at the upper level. In Model 2, a lithological transition from shale to siltstone across the Lower Cambrian Qiyueshan Fault led to mechanical coupling between the middle and bottom levels in the west, producing thrust wedges with chevron anticlines above a single shallow detachment. In contrast, the southeast region, controlled by three detachments and surface erosion, developed box-shaped anticlines. These observations indicate that abrupt lateral changes in lithology strongly influence thrust wedge styles and transitions. Furthermore, AMS measurements capture the magnitude and orientation of strain within the wedges, highlighting how lithofacies variations modulate deformation mechanisms and strain partitioning.
Based on quantitative analyses of wedge kinematics and strain, we propose a new thrust wedge dominated multilayered propagation model in the Western Xuefeng fold–thrust belt. This framework connects local wedge dynamics to continental-scale crustal evolution, providing a basis for understanding fold–thrust dynamics in intracontinental orogens worldwide.
How to cite: Kong, F., Yan, D., Qiu, L., Zhou, Z., Hao, Z., and Lin, X.: Thrust Wedge Dominated Multilayered Propagation Using Finite Strain Sandbox Modeling: Growth of the Western Xuefeng Fold-Thrust Belt, South China Block, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5756, https://doi.org/10.5194/egusphere-egu26-5756, 2026.
Fold-and-thrust belts commonly exhibit along-strike variability in shortening, rock uplift, and exhumation. It often remains unclear how strongly these reflect lower lithospheric processes. The South Tianshan is an active intracontinental orogen and characterised by southward propagation of deformation into the northern Tarim foreland. Along the South Tianshan–Tarim Basin interface, foreland deformation, cooling histories, and drainage (re-)organization vary strongly along-strike and geophysical constraints indicate the underthrusting of Tarim block northward beneath the Tianshan. This suggests weak lithospheric coupling. To validate this prediction, we examine four transects along the northern margin of the Tarim Basin, by using forward thermo-kinematic modelling of sequentially restored and balanced cross-sections.
Our models quantify the timing, geometry, and magnitude of fault-driven rock uplift across the four transects and we use this to evaluate the role of crustal deformation in driving foreland exhumation, surface uplift and subsequent drainage organization. Existing low-temperature thermochronological datasets, including apatite fission-track (AFT) and apatite (U–Th)/He (AHe) ages, are used to validate model predictions of regional cooling histories.
Best-fit models reproduce the thermochronological data across four transects, demonstrating that fault-driven deformation exerts first-order control on exhumation. At Kuqa, young, reset AHe cooling ages (~25–5 Ma) in the foreland are linked to rock uplift along structural ramps at ~10 km depth as part of subsurface blind duplex formation. The delayed activation (~5–0 Ma) of shallower ramps at 3–7 km depth generated the rock uplift required for the formation of frontal anticlines (Qiulitage at Kuqa and Atushi–Kashi at Kashi) that partially reset the AFT system. Such foreland deformation is largely accommodated above décollements at multiple depths, and the slip is partitioned along thick (~2–4 km) Paleogene (Kuqa) and Miocene (Kashi) evaporites at a minimum of 8–10 km depth. At Keping, motion along a shallower décollement at ~5 km depth, and an additional ~12 km of out-of-sequence thrusting on the Kekebukesansha Fault at ~10 Ma is required to fit observed ages (~11.5 Ma). Replicating older cooling ages preserved in the hinterland (~30 Ma Kashi and ~40 Ma Kuqa) is achieved by ~7–10 km of displacement along the South Tianshan Thrust System (STS) at shortening rates of ~0.5–1.2 mm/yr. This reflects a diachronous initiation of the STS at ~25 Ma and ~36 Ma. The shortening rate at Keping is consistently higher (~4 mm/yr), Kuqa and Kashi exhibit ~0.5mm/yr that increases to ~1.5–2.5 mm/yr. This acceleration is associated with growth of the foreland anticlines at Kuqa and thrusting of the Keketamu structure at Kashi during ~15–10 Ma.
Our results suggest that the along-strike variability in thermochronological signals along the South Tianshan is primarily linked to crustal deformation, without invoking lower lithospheric involvement. Our modelled surface uplift scenarios, furthermore, provide a tectonic framework to explain the transition from transverse to longitudinal drainage patterns, highlighting how fold–and–thrust belt evolution drives drainage reorganization. These findings are consistent with a flat-lying Moho beneath the Tarim, seismicity largely within ~30 km depth, and a stiff lithosphere rheology. Together, these observations support a largely decoupled upper and lower lithosphere along the South Tianshan-Tarim Basin interface.
How to cite: Zhong, C., Eizenhöfer, P., Persano, C., Gilgannon, J., and He, Z.: Decoupled Upper-Crustal Deformation and Foreland Growth in Intracontinental Orogens: A Thermo-Kinematic Perspective from the South Tianshan, Central Asia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6687, https://doi.org/10.5194/egusphere-egu26-6687, 2026.
The South Tibetan Detachment System (STDS) represents a major extensional shear zone separating the Greater Himalayan Sequence (GHS) from the Tethyan Himalayan Sequence (THS), yet its long-term tectonomagmatic evolution remains poorly understood. The Dhauliganga Valley (Uttarakhand, NW Himalaya) is one of the few transects where the STDS is excellently exposed from Malari to Goting for ~10 km along its strike, remarkably showing cross-cutting relationship of the Paleozoic orthogneisses and Neoproterozoic mylonites and migmatite, which are further intruded by at least two generations of Mio–Oligocene leucogranites. Zircon U–Pb geochronology integrated with major, trace and rare-earth element geochemistry of representative granites and leucogranites constrain the timing and source characteristics of the magmatic events associated with the STDS and are crucial to develop a tectonic model that explains the role of the STDS as a fundamental Cambro–Ordovician terrane boundary that was subsequently reactivated during Cenozoic orogeny.
Field observations and microstructural analyses in the STDS zone document a polyphase deformational history characterized by multi-phase shearing, syn-tectonic melt emplacement and overprinting brittle deformation. Structural and microstructural fabrics capture an evolution from D2 top-to-SW thrusting to D3 top-to-NE brittle–ductile extension with oblique-slip and transtensional components, producing a high-angle shear geometry unique to this transect.
Detrital zircon populations from folded psammitic gneiss in the footwall preserve Neoproterozoic inheritance (~1075–860 Ma), overprinted by the Cambro–Ordovician granitoids with crystallization ages of 498.92 ± 5.5 Ma and 486.54 ± 2.3 Ma. It is hypothesized that STDS facilitated the emplacement of an extensive ~200km Cambro–Ordovician granite belt from Sutlej to Dhauliganga Valleys in NW Himalaya during the Kurgiakh/Bhimphedian Orogeny. In the post-orogenic phase, the STDS acted as a proto-tectonic marginal extensional boundary that facilitated the denudation of these granites and gneisses into the Tethyan basin resulting in a >10 km-thick THS.
Leucogranites within the uppermost GHS yield ages from Late Eocene to Early Oligocene (35–23 Ma) indicating magmatism associated with SW-directed contraction and crustal thickening (35.3 ± 1.8 Ma, 33.99 ± 1.07 Ma). These leucogranites exhibit tight isoclinal folds with NE-dipping axial surfaces. Syn-tectonic emplacement occurred in the Late Oligocene–Early Miocene (25.03 ± 0.54 Ma 23.68 ± 0.94 Ma), followed by extension-induced exhumation. Magmatic activity abruptly ceased along the STDS in this transect by 13.30 ± 0.30 Ma, after a protracted melt generation and emplacement for nearly 10.0 Ma.
Whole-rock geochemistry indicates that both Paleozoic granitoids and Miocene leucogranites represent syn-collisional, peraluminous crustal melts generated via fluid-absent muscovite-dehydration melting under high-pressure conditions.
This study proposes a tectonomagmatic evolutionary framework for the STDS in the Dhauliganga Valley, a Paleozoic terrane boundary and a reactivated Cenozoic extensional structure mediating melt emplacement, strain localization and exhumation. The persistence of a complex thermal history suggests a foundation for future isotopic and thermochronological investigations into the architecture and rheology of the Himalayan orogen.
How to cite: Deshmukh, G., Jain, A. K., Mukherjee, P. K., and Dixit, R.: The South Tibetan Detachment System: A Cambro–Ordovician terrane boundary reactivated during Cenozoic Himalayan collision in the NW Himalaya, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-803, https://doi.org/10.5194/egusphere-egu26-803, 2026.
Precambrian rocks preserved within the orogenic belt are interpreted as the Precambrian basement of their respective tectonic units. Their rock assemblages, formation ages, detrital zircon age spectra, and zircon Lu-Hf isotopic composition are commonly used to explore tectonic affinities with potential provenances. This issue is critically important, as it is integral to understanding the architecture and evolution of orogenic belt, as well as the amalgamation and fragmentation of supercontinents.
The tectonic affinities of ancient blocks and microcontinents within the Central Asian Orogenic Belt (CAOB) have aroused many controversies in recent years, hindering a comprehensive understanding of the tectonics of the CAOB. The South Gobi microcontinent (SGM), a significant component of the middle segment of the southern CAOB, has long been controversial because many questions remain regarding its existence and nature. This study focuses on the Chinese part of the SGM—the Zhusileng-Hangwula tectonic zone (ZHTZ) in northwestern China—to investigate the nature of its Precambrian basement. Systematic field-based zircon U-Pb-Hf isotopic and whole-rock elemental analyses were conducted on plutonic and metasedimentary rocks.
The intrusions previously thought to be from Paleozoic time are now known to contain crystallization ages of 1462 Ma, 1365 Ma, and 884 Ma; a large number of ca. 1.4 Ga xenocrystal zircons; and numerous metamorphic zircons with ages of 939 Ma. Additionally, a two-mica quartz schist from the Beishan Group constrains the maximum depositional age to 1130 Ma. When integrated with previous studies, these data indicate that the Precambrian basement of the SGM, represented by the basement of the ZHTZ, underwent tectonothermal events at ca. 1.4 Ga and ca. 0.9 Ga, and deposited extensive late Mesoproterozoic–early Neoproterozoic siliciclastic-rich successions.
Based on these features, the SGM basement likely originated from northeastern Laurentia, possibly as a part of the Valhalla orogen. Furthermore, the weak tectonic affinity between the southern CAOB and adjacent ancient blocks or cratons suggests that some parts of the southern CAOB might not have been derived from the accretionary evolution of the flanking cratons, but rather from the accretion of microcontinents that originated from Laurentia.
How to cite: Wang, Z., Zhang, J., Qu, J., Zhang, B., Zhao, H., Liu, J., Wu, C., Chen, Y., Zhang, Y., Qiao, M., Yang, Y., and Tian, Y.: The Nature of Precambrian Basement of South Gobi Microcontinent in Central Asian Orogenic Belt, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-715, https://doi.org/10.5194/egusphere-egu26-715, 2026.
Chemical mohometry refers to the use of the geochemistry of arc magmas and/or magmatic minerals to infer depth to the Moho. This increasingly popular method in tectonics research relies on correlations between Moho depth and either trace element concentrations or their ratios, e.g., Hf, Ba, Sr/Y, La/Yb, Th/Yb, europium anomaly (Eu/Eu*), etc. These correlations are widely viewed to reflect depth-dependent changes to mineral stabilities, especially for feldspar and garnet. Here, we revisit the foundational whole-rock datasets to assess the influence of data scatter on calibrations. We also assess the effects of the following factors that influence mineral stabilities and melt geochemistry: oxygen fugacity (fO2), water fugacity (fH2O), temperature, and fractional crystallization of major and accessory minerals.
The following, depth-independent behaviors are evident:
- Data scatter is large – a single Moho depth is typically represented by 50-75% of the global range in a single trace element concentration or ratio. Calibrations are statistically robust only after averaging hundreds of data points.
- Different arcs have systematically different compositions, even at the same Moho depth, leading to systematic errors of ~10 km for some systems.
- Increasing fH2O can depress plagioclase stability by 200 °C and increase garnet stability by hundreds of MPa. These changes to mineral stabilities strongly influence alkaline earth and rare-earth element concentrations and ratios (e.g., Sr/Y, La/Yb, etc.).
- Increasing fO2 changes mineral assemblages and modes, and generally increases Eu/Eu* and apparent Moho depth.
- Increasing temperature changes melt fraction and mineralogy, and can strongly influence Sr/Y, La/Yb, Th/Yb, and (at low pressure) Eu/Eu*.
- Crystallization of accessory minerals, especially titanite, can strongly increase La/Yb. Sr/Y, and Eu/Eu* in separated liquids, leading to spuriously increasing calculated Moho depth.
- Realistic variations in fO2, fH2O, temperature, and fractionation can each shift calculated Moho depth by 10-20 km.
These behaviors lead to the following conclusions:
- Application of mohometry to the rock record should average hundreds of measurements per time slice. Such large datasets are rarely available, and may not be feasible to collect.
- Concurrent changes to temperature, fO2, and fH2O should be quantified, otherwise uncertainties in either calculated Moho depth or changes to Moho depth through time are tens of km.
- Crystallization sequences in genetically related magmas should be assessed to determine whether crystallization of trace phases affects trace-element concentrations and ratios used for mohometry.
- Systematic sampling errors are difficult to avoid and lead to systematic but unknown errors in estimated Moho depth.
- Extremely large datasets (hundreds of measurements per time slice) are rare, and simultaneous changes to fO2, fH2O, temperature, and melt fractionation are difficult to estimate. Consequently, future success in mohometry will require major streamlining of data collection and development of routine geochemical proxies for intensive parameters.
- Calculations to date of Moho depth using geochemical mohometry do not consider covariation in intensive parameters, melt fractionation, and/or sampling errors, so should be viewed as unreliable.
How to cite: Kohn, M., Roman, G., Lopez, A., Yakymchuk, C., and Glazner, A.: Critical evaluation of chemical mohometry 1: Calibration datasets and influences of intensive parameters on arc magma geochemistry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14780, https://doi.org/10.5194/egusphere-egu26-14780, 2026.
Retreating accretionary orogens exhibit a paradoxical capacity to sustain crustal shortening and growth contemporaneous with dominant upper plate extension. Deciphering the dynamic coupling between mantle flow and crustal evolution is critical in understanding orogenic mechanisms within such retreating systems, with profound implications for subduction zone dynamics and continental growth processes. Here we integrate high-resolution 2D numerical simulations, with quantitative geological boundary conditions from the Paleozoic Altaides archetype, to establish an endogenic orogenic mechanism driven by slab rollback-induced mantle circulation during retreating subduction. Our models demonstrate that spontaneous mantle upwelling and convections could systematically govern (1) progressive trench-directed arc migration, (2) self-organized forearc-arc-backarc-intraplate tectonic zoning, (3) crustal thickening-extension cycles and diachronous coexistence, (4) crustal growth and stabilization through intense bimodal magmatism with juvenile isotopic signatures, all of which characterize the Altaides and other archetypal retreating accretionary orogens. This intrinsic interplay between slab rollback, mantle upwelling, and upper plate response offers a unified framework to interpret accretionary orogens via deep Earth-surface interactions. This work was financially supported by Project (JLFS/P-702/24) of Hong Kong RGC Co-funding Mechanism on Joint Laboratories with the Chinese Academy of Science, National Science Foundation of China (Grants 424B2048, 42176064), and Australian Research Council (FL160100168).
How to cite: Cui, X., Wang, L., Cawood, I., Cawood, P., Dai, L., Yao, J., Wang, D., Sun, M., and Zhao, G.: Endogenic mantle-driven orogenesis of retreating accretionary orogens: implications for the continental growth and stabilization, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4483, https://doi.org/10.5194/egusphere-egu26-4483, 2026.
Unraveling the tectono-thermal history of medium- to low-grade belts will place important constraints on the regional tectonic evolution. There exists a Barrovian metamorphic belt in the Lüliang Group, Trans-North China Orogen (TNCO) of the North China Craton (NCC). Representative rock samples from chlorite zone, biotite zone, garnet zone and staurolite–kyanite zone have been collected to delineate the P–T–t evolution. A two-stage prograde P–T path characterized by heating first and then pressurizing is recovered from the garnet zone by phase equilibria modeling. The peak P–T conditions are constrained to be ~7.0 kbar/560 ℃. Decompression-dominated P–T paths involving Pmax (6.8–9.2 kbar/515–565 ℃) and Tmax (4.6–6.5 kbar/560–615 ℃) stages are obtained from the staurolite–kyanite zone. Metamorphic zircon from the staurolite–kyanite zone and garnet from the garnet zone yield U-Pb ages of 1850 ± 31 Ma and 1882 ± 67 Ma, respectively. Biotite from the biotite zone gives an 40Ar/39Ar age of 1762 ± 3 Ma. The geochronological results indicate that metamorphism of the Lüliang Group is younger than the formation age of the TNCO (~1.95 Ga), but is coeval to the subduction–collision orogeny (1.90–1.82 Ga) along the northern margin of the NCC. The distribution of the Barrovian metamorphic belt is also parallel to the latter orogen (E–W-trending). Consequently, combining with field observations and regional geological evolution, it is inferred that the genesis of Barrovian metamorphism accompanying with crustal thickening in the Lüliang Group may be related to the stress propagated from the 1.90–1.82 Ga orogeny along the craton’s northern margin.
How to cite: Qian, J., Yin, C., Zhang, J., Gao, P., Lu, C., and Wu, S.: Metamorphic P–T–t evolution of the Lüliang Group, North China Craton: Insights from phase equilibria modeling and geochronology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7129, https://doi.org/10.5194/egusphere-egu26-7129, 2026.
Orogenic high-strain zones are fundamental features of the continental lithosphere. These structures accommodate plate convergence and influence the distribution of crustal deformation. However, the specific rheological processes that govern these zones across different tectonic settings remain a subject of investigation. Here, we integrate quantitative data from three distinct systems in China: the Hulin Complex (subduction), the Shangdan Shear Zone (collision), and the Diancang Shan (lateral extrusion). Our goal is to establish a grounded framework for how high-strain zones evolve. Our analysis shows that deformation follows a predictable path influenced by temperature, fluid activity, and strain partitioning.
We identify a consistent relationship between deformation style and kinematic vorticity (Wk). In the deep crust where temperatures exceed 650°C, deformation is characteristically diffuse. Data from the early Shangdan and Diancang Shan complexes indicate that this phase is dominated by pure shear (Wk =0.24–0.41). In these high-temperature regimes, pure shear contributes approximately 65% of the total strain. This mechanism facilitates vertical crustal thickening during the initial stages of plate interaction. As the crust cools to mid-crustal conditions between 300°C and 550°C, a mechanical transition occurs. Strain concentrates into narrow, high-strain paths. This localization coincides with a sharp increase in Wk to 0.53–0.74. This shift demonstrates that simple shear becomes the dominant mode for accommodating plate movement as the orogen matures.
Our integrated dataset suggests that these high-strain zones operate within a “stress window” of 10–50 MPa. Within this range, the crust adjusts its internal fabric to match tectonic driving forces. In subduction systems like the Hulin Complex, rapid slab rollback triggers thermal softening. This process drops differential stress to a minimum of 13–14 MPa and promotes regional extension. In contrast, collisional systems like the Shangdan Shear Zone support higher stresses between 33 and 45 MPa to drive mylonitization. We find that the transition from slow, diffuse flow to rapid, localized shear is non-linear. External factors often trigger this change. In the Shangdan Shear Zone, fluid influx acts as a catalyst. It increases strain rates by two orders of magnitude, from 10−15 to 10−13 s−1. Similarly, in the Diancang Shan, partial melting helps maintain high strain rates of 10−12 s−1 despite decreasing temperatures.
We conclude that high-strain zones function as dynamic features of the continental crust. They manage deformation by adjusting the ratio of pure shear to simple shear in response to the local thermal and fluid environment. Early-stage diffuse flow accommodates initial convergence through thickening. Later, localized simple shear facilitates lateral extrusion or exhumation. This mechanical flexibility allows the continental lithosphere to endure complex plate cycles. Our findings provide a quantitative framework for predicting how shear zones behave in active orogenic belts. These data bridge the gap between mineral-scale observations and large-scale tectonic processes.
How to cite: Zheng, H.: Rheological Evolution and Strain Partitioning in Orogenic High-Strain Zones: Constraints from Subduction to Collision, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8705, https://doi.org/10.5194/egusphere-egu26-8705, 2026.
Peraluminous granites are widely regarded as products of crustal reworking in continental interiors and are genetically linked to Sn–W–rare metal mineralization (e.g., Li, Be, Nb, Ta, Cs, Rb). However, the mechanisms of heat transfer responsible for generating peraluminous magmas, as well as the role of the mantle in these processes, remain debated. To address these questions, we investigated the origin of the Xingluokeng granite—a peraluminous granite in the Wuyi terrain of the Cathaysia Block that hosts large-scale tungsten mineralization—through zircon U–Pb and Hf isotopic analysis and numerical modeling of heat transfer. The modeling incorporates geologically plausible ranges of ancient crustal thickness and crustal heat production.
Autocrystic zircons from the granite (~150 Ma) exhibit strongly negative εHf(t) values (–25.72 to –7.01), which fall within the range of inherited zircons (600–1000 Ma) and the highest-density values of Neoproterozoic detrital zircons in the Cathaysia Block. This suggests no detectable mantle-derived mass contribution. The Mesozoic upper crust in the Wuyi terrain and other regions in the Block, represented by fine-grained clastic sediments, has an average heat production of ~2.9 μW m⁻³, while amphibolite- to granulite-facies rocks, representing the middle–lower crust, range from ~0.6 to 4 μW m⁻³. These values exceed present-day global averages for continental crust (upper crust: ~1.68 μW m⁻³; middle–lower crust: ~0.19–1 μW m⁻³). When combined with moderate crustal thickening (~50 km) and a normal mantle heat flux, such elevated crustal heat production can drive partial melting of metasedimentary rocks in the middle–lower crust over a thermal relaxation period of ~30–50 Ma.
Crustal radiogenic heating also warms the upper mantle, facilitating partial melting of mafic rocks and giving rise to volumetrically minor mafic dykes coeval with peraluminous granites in the same region. Consequently, the presence of such dykes does not necessarily imply that the mantle supplied significant heat or material for the associated peraluminous magmas. High crustal heat production coupled with crustal thickening appears to be a common feature in other parts of the Cathaysia Block, suggesting that the above conclusions may also apply to other Mesozoic peraluminous granites in South China.
How to cite: Liu, X.-C.: Thermal links between crustal radiogenic heating and peraluminous granites: a case study in Wuyi terrain, southeastern China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4641, https://doi.org/10.5194/egusphere-egu26-4641, 2026.
Continental lithospheric thinning can accelerate upper-crustal exhumation by reducing lithospheric strength and reorganizing topography, yet the magnitude, spatial attenuation, and time lag of this coupling are rarely quantified in a way that is directly comparable between regions. We integrate new apatite fission-track (AFT) and zircon (U–Th)/He (ZHe) data with regional thermochronology compilations and time-dependent crustal-thickness reconstructions for the eastern North China Craton, and apply the same standardized workflow to the Lhasa terrane (southern Tibet) and the western North American Cordillera—three regions that record rollback-related thinning by extension and/or gravitational removal of dense lower lithosphere (delamination or foundering). Using a multi-thermochronometer age-pair method, we calculate exhumation-rate time series and spatially resolved exhumation-rate maps, and we evaluate their correspondence to coeval crustal thickness variations through time. In North China, exhumation rates during the main thinning episode are highest near thinning centers and decrease toward the continental interior, defining a proximal-to-distal attenuation pattern. Across all studied regions, thinner crust systematically corresponds to higher mean exhumation rates, indicating a robust, negative association between crustal thickness and exhumation intensity during thinning. Cross-correlation between crustal thickness T(t) and exhumation rate E(t) is most negative (Pearson R = −0.8 to −0.9) when exhumation lags thinning by ~5–10 Myr, implying a multi-million-year delay between crustal thinning and the regional exhumation response. Together, these results provide quantitative constraints on the timescales and spatial footprint of deep–surface coupling during continental lithospheric thinning.
How to cite: Liang, Y., He, Z., and De Grave, J.: Lagged and spatially attenuated negative coupling between crustal thickness and exhumation during lithospheric thinning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3970, https://doi.org/10.5194/egusphere-egu26-3970, 2026.
Deciphering the extensive magmatic records of the Rodinia supercontinent preserved within the Tarim Craton provides valuable insights into the geodynamics of supercontinent evolution. Here, we report ~790 Ma OIB-type mafic dykes from the North Altyn Tagh belt in the southeastern margin of the Tarim Craton. Zircon U-Pb dating and geochemical analyses reveal that these dykes are typical continental flood basalts, which display light rare earth elements (LREE) enriched patterns with Eu depletion, along with slight enrichment of Nb and Ta and depletion of Sr. Chemical and thermodynamic modelling suggest that these mafic dykes were originated from a garnet-spinel mantle source modified by subduction-related fluids, with an estimated partial melting degree of ~10%. This was followed by fractional crystallization of Ol-Cpx-Pl during subsequent magma evolution process. Therefore, the OIB dykes identified here indicate that the Tarim Craton had already rifted from Rodinia, likely around ~790 Ma. This, together with review of overall Neoproterozoic magmatic records across the Tarim Craton, along with detrital zircon ages and Hf isotopic data, demonstrates that the craton preserves complete record of the transition from Rodinia convergence to rifting. Moreover, the Tarim Craton, Central Altyn, Qilian-Qaidam-East Kunlun, Yangtze Block and Cathaysia Block were located along the periphery of Rodinia and all recorded the super-mantle plume that broke the Rodinia supercontinent at 850–740 Ma. The plume activity partially overlapped with circum-Rodinia subduction. Overall, the contribution of subduction fluid to Rodinia OIB type plume magmatism and the spatial-temporal correlation of super mantle plume and circum-Rodinia subduction suggest that the Rodinia breakup mantle plume was likely induced by circum-Rodinia subduction. These findings therefore argue for the "top-down" model for supercontinent breakup dynamics, emphasizing the critical role of subduction-induced mantle plume that broke up the Rodinia supercontinent. This study demonstrates that subduction drives supercontinent fragmentation, clarifying how subduction zones and mantle plumes interact within Earth's supercontinent cycles.This research is funded by the NSFC Grants (42322208), National Key R&D Program of China (2023YFF0803604), the Natural Science Foundation of Shaanxi Province (2023JCXJ‐20 and 2021JCW‐18), the Project (JLFS/P-702/24) of Hong Kong RGC Co-funding Mechanism on Joint Laboratories with the Chinese Academy of Science, and the State Key Laboratory of Continental Dynamics (201212000174).
How to cite: Zhao, X., Yao, J., Zhao, G., Han, Y., Liu, Q., Zhang, D., and Chen, L.: ~790 Ma OIB-type mafic dykes in the North Altyn Block, southeastern Tarim: insights into the reconstruction and geodynamics of Rodinia breakup , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2736, https://doi.org/10.5194/egusphere-egu26-2736, 2026.
Knowing the size of Greater India is essential to constrain the geodynamic processes of India-Asia collision and Tibetan Plateau uplift, which, however, remains highly controversial, with existing estimates ranging from several hundreds (~400-950) to thousands (~1800-3000) of kilometers. Here, we report new paleocurrent measurements of the Upper Triassic turbidites (Langjiexue Group) from northern Tethyan Himalaya, supplemented with compiled provenance analyses, to help decipher the extent of Greater India. Well-preserved flute casts indicate mostly westward paleocurrents, suggesting a primary source located to the east (present coordinates) of the depositional area. In addition, compiled detrital zircon data reveal a similar east-west distribution, with samples exhibiting Australian-affinities (i.e., dominated by ~1170-1075 and ~575-530 Ma age populations) mostly found to the east of 91E°, whereas samples showing Indian-affinities (i.e., dominated by ~980-860 and ~565-505 Ma age populations) are generally limited to the west of 92E°. Importantly, the Langjiexue Group is characterized by a dominant age population of ~280-220 Ma (peak at ~238 Ma) with bimodal zircon εHf(t) values (peaks at ~–1.2 and +6.8), matching well with those of coeval magmatic/sedimentary records in West Antarctica, but differing from those in eastern Australia, the Bird’s Head region, and the Lhasa terrane. Considering similar age patterns found in the Exmouth Plateau (NW Australia), we infer a large-scale transcontinental sediment transport pathway for the Langjiexue Group, which originated from West Antarctica, passed through West and NW Australia, and ultimately deposited offshore along northern (Greater) India in the Late Triassic. Therefore, the eastern margin of Greater India most probably reached to the Exmouth Plateau, implying an extent of ~1950 ± 260 km in the Late Triassic. This consideration is consistent with the recent estimate of ~1950 ± 970 km based on Early Cretaceous paleomagnetic data from eastern Tethyan Himalaya.
How to cite: Xue, S. and Zhang, X.: Defining the expanse of Greater India: Insights from the Upper Triassic Langjiexue Group of northern Tethyan Himalaya, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5036, https://doi.org/10.5194/egusphere-egu26-5036, 2026.
The subduction and closure of the Proto-Tethys Ocean dominated a significant global tectonic event in the Phanerozoic, which established the foundational tectonic framework for East Asia. Particularly, the North Altyn ophiolitic mélange belt recorded the subduction-collision history of the North Altyn segment of the Proto-Tethys Ocean, but the spatial-temporal distribution of related convergent margin successions is poorly constrained. The late Cambrian to late Ordovician Elantage Formation and Lapeiquan Group in the northern Altyn belt are coeval with the North Altyn ophiolite and therefore preserve key records of the evolution of the North Altyn Ocean. Detailed petrography, detrital zircon age patterns, isotopes, and geochemical characteristics indicate that these stratigraphic sequences were deposited in retro-arc and fore-arc basins at ca. 520-440 Ma, respectively. εHf(t) values suggest that arc magmatic rocks from the northern margin of the Central Altyn Block are the main provenances for the Elantage Formation, whereas the provenance of Lapeiquan Group is dominated by arc magmatic rocks within the North Altyn ophiolitic mélange belt. A ca. 520-440 Ma trench-continental arc and retro-arc basin system in the northern Altyn further suggest a Silurian closure time for the North Altyn segment of the Proto-Tethys Ocean. In addition, together with a review of age and spatial patterns of the ophiolites, trench-arc systems, metamorphism, and magmatic rocks across the other East Asian continental blocks, we argue for a diachronous closure of the Proto-Tethys Ocean from the Ordovician to the Late Silurian. This research was funded by the National Key R&D Program of China (grant 2023YFF0803604), National Natural Science Foundation of China (grants 42322208).
How to cite: Chen, L. and Yao, J.: Delineating convergent continental margin basin systems in the North Altyn belt: implications for diachronous closure of the Proto-Tethys Ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5413, https://doi.org/10.5194/egusphere-egu26-5413, 2026.
Earth’s deep water cycle plays a fundamental role in plate tectonics, magmatism, and crustal differentiation. This study investigates the pathways and mechanisms of water transport from Earth’s interior to the continental crust by analyzing zircon water contents, U-Pb-Hf-O isotopes, and whole-rock geochemistry from granulite xenoliths in the Tuoyun Basin, Western Tianshan. We identified three distinct zircon generations: Neoproterozoic protolith zircons (~800-600 Ma) with high water contents (median: ~404 ppm), Paleozoic-Mesozoic metamorphic zircons (~600-100 Ma) showing pronounced water depletion (median: ~55 ppm), and Cretaceous-Paleogene host-basalt zircons (median: ~166 ppm). The elevated water contents and mantle-like δ18O values in the protolith and host-basalt zircons, combined with positive Nb-Ta anomalies and enriched Hf isotopes, indicate that the parental magmas were likely derived from a hydrous mantle transition zone rather than supracrustal sources. We propose a novel two-stage transport model where hydrous mantle-derived magmas first underplated the lower crust to form the protolith; subsequent granulite-facies metamorphism then dehydrated these rocks with a calculated efficiency of ~86%, releasing fluids that ascended to trigger mid-crustal water-fluxed melting and granitic magmatism. These findings provide direct geochemical evidence that granulite dehydration in the lower crust is a critical link in the deep-water cycle, facilitating the transport of mantle-derived water to the surface and driving the progressive maturation of the continental crust.
Acknowledgement: This study was financially supported by funding from the National Natural Science Foundation of China Major Project (41890831), the University of Hong Kong (HKU) Internal Grants for Member of Chinese Academy of Sciences (102009906) and for Distinguished Research Achievement Award (102010100), the Hong Kong RGC grants (JLFS/P-702/24 and 17308023), and the National Key Research and Development Program of China (2023YFF0803804).
How to cite: Zhao, D., Zhao, G., and Wang, X.: Deep-Mantle Water Transport into the Continental Crust: Insights from Zircon Water and Hf-O Isotopes in Granulite Xenoliths, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21933, https://doi.org/10.5194/egusphere-egu26-21933, 2026.
The redox state of magmas serves as a key indicator of Earth's evolutionary processes, recording pivotal events such as changes in atmospheric composition, the emergence of life, and major tectonic shifts. This study utilizes zircon oxygen fugacity (ΔFMQ), an igneous oxybarometer, to explore the temporal variations in magma redox states across Earth's history. We find that the zircon ΔFMQ declines from 4.2–3.8 Ga, likely reflecting the Late Heavy Bombardment. A subsequent increase in ΔFMQ from 3.8–3.0 Ga is linked to processes such as water recycling in supracrustal materials and the thickening of continental crust. After 2.5 Ga, fluctuating ΔFMQ trends mirror the cycles of supercontinent formation, where introversion involves the subduction of reduced sediments from interior oceans, and extraversion involves oxidized sediments from exterior oceans. Our findings demonstrate the power of zircon ΔFMQ as a tool for tracing magma redox evolution, shedding light on significant geological processes and their timing in Earth's history.
How to cite: Wang, X., Zhao, G., and Zhao, D.: Tracing Magmatic Redox Evolution Through Earth's History Using Zircon Geochemistry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21874, https://doi.org/10.5194/egusphere-egu26-21874, 2026.
Oceanic arcs are crucial sites for producing new continental crust. However, how the continental crust has acquired its bulk “andesitic to dacitic” compositions is not well understood. To address this issue, we carry out an integrated study for granitoids from the East Junggar oceanic arc, Central Asian Orogenic Belt. All the granitoid samples with ages of 332–280 Ma have high SiO2 but low MgO contents, indicating a dominant crustal source. Based on zircon O isotopes, these granitoids can be divided into three groups: Group I (5.0 ± 0.46‰, 2SD), Group II (8.6 ± 0.47‰ to 9.4 ± 0.52‰, 2SD) and Group III (6.8 ± 0.36‰ to 7.4 ± 0.48‰, 2SD) with mantle-like, elevated and intermediate zircon δ18O ratios, respectively. The formation of Group I granitoids can be ascribed to partial melting of juvenile mafic crust, while Group II and III granitoids were likely derived from a mixed source of juvenile mafic crust and supracrustal rocks in variable proportions. Combined with their depleted mantle-like zircon εHf(t) values (+11.6 to +13.5), it is inferred that these supracrustal rocks were mainly isotopically unevolved, immature volcanogenic sediments. The zircon Hf–O isotope array is compatible with mixing between juvenile mafic crust and supracrustal volcanics (40–70% for Group II and 20–40% for Group III) in their magma sources. The incorporation of supracrustal rocks into such high-δ18O granitoids was likely associated with fore-/intra-arc basin closure triggered by arc–arc collision. Our results thus highlight the role of supracrustal recycling induced by collisional events in driving the compositional differentiation of oceanic arc crust from basaltic to felsic.
How to cite: Zhang, Y. and Huang, R.: Maturation of East Junggar oceanic arc related to supracrustal recycling driven by arc-arc collision, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20976, https://doi.org/10.5194/egusphere-egu26-20976, 2026.
The North China Craton, as one of the oldest cratons globally, preserves a complete record of Neoarchean (2.7–2.5 Ga) crustal evolution in its western Yinshan Block. However, there remains controversy regarding the late Neoarchean crustal evolution process and geodynamic setting of the Yinshan Block. Therefore, this study focuses on the rock assemblages in the Wuchuan Xiwulanbulang, Zhulagou, Hongshanzi, and Guyang areas of the Yinshan Block, including TTG gneisses, dioritic gneisses, and monzogranitic gneisses, as well as metamorphic mafic rocks (komatiites, komatiitic basalts, and tholeiites) in the Hongshanzi area. Systematic petrological, geochronological, whole-rock geochemical, and Sr-Nd-Pb-Hf isotopic studies were conducted on these rocks. Combined with previous research findings, we propose that the Neoarchean crustal evolution of the Yinshan Block can be divided into three stages: (1) (~2.7 Ga) dominated by mantle-derived magma underplating and initial continental crust formation, resulting in thickened mafic lower crust and minor TTG rocks; (2) (~2.7–2.53 Ga) characterized by the large-scale formation of TTG rocks and dioritic rock assemblages. The TTG rocks exhibit high (La/Yb)N and Sr/Y ratios, low MgO, Ni, Cr, and Mg# contents, and positive zircon εHf(t) and εNd(t) values. Their geochemical and isotopic features indicate derivation from partial melting of thickened mafic lower crust. The dioritic rocks display geochemical characteristics similar to Archean sanukitoids, likely originating from partial melting of thickened mafic lower crust with minor mantle input. (3) (~2.53–2.50 Ga) marked by the mixing and partial melting of earlier-formed TTG rocks and ancient crust, leading to the formation of potassium-rich granites, signifying the completion of cratonization.
Current understanding of the Neoarchean geodynamic regime in the Yinshan Block remains debated: (1) Some scholars have discovered Neoarchean high-Mg andesites (Archean sanukitoids) and high-Mg basalt-rhyolite bimodal suites in the region, suggesting that Neoarchean crustal growth in the Yinshan Block was primarily driven by plate subduction; (2) Other researchers argue that Neoarchean crustal growth in the Yinshan Block occurred mainly under a mantle plume regime. This study first reports a suite of late Neoarchean (~2.53 Ga) metamorphic mafic rocks in the Hongshanzi area. Through comprehensive petrological analysis, whole-rock geochemistry, and Nd-Hf isotopic analysis, these metamorphic mafic rocks are likely to have formed in a tectonic environment involving mantle plume-ridge interaction. Therefore, integrating the geochemical characteristics of coeval TTG gneisses, dioritic gneisses, and potassium-rich granitic gneisses, we propose that Neoarchean crustal growth in the Yinshan Block was primarily driven by mantle plume activity.
How to cite: Wang, X.: Late Neoarchean magmatic evolution and tectonic significance in the southern margin of the Yinshan Block, North China Craton, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17556, https://doi.org/10.5194/egusphere-egu26-17556, 2026.
The Gaozhou region is situated in the southwestern Cathaysia Block of South China and represents the core of the Yunkai Terrane. Field geological mapping at a scale of 1:50,000 was undertaken for this study, coupled with geochemical analysis of both garnet-bearing and garnet-free biotite-plagioclase gneisses. Detailed petrography, mineral chemistry, and phase equilibrium modeling were further performed on garnet-biotite-plagioclase gneisses. Analytical results reveal that both garnet-bearing and garnet-free biotite-plagioclase gneisses share common geochemical features: high SiO₂ and Al₂O₃ contents, low TiO₂ content, low Na₂O/K₂O and Fe₂O₃T/K₂O ratios, high (La/Yb)N ratios, and negative Eu anomalies. These rocks are also depleted in Nb, Ta, Zr, and Hf, while showing enrichment in large-ion lithophile elements (LILEs) such as Rb, Th, and U. The inferred protolith is a sequence of clay-bearing greywacke with minor intercalated arkose, classifying it as a paragneiss. Based on petrological observations, two stages of metamorphic assemblage development in the garnet-biotite-plagioclase gneiss are identified: the peak assemblage of Grt+Pl+Bt+Kfs+Ms+L+Qz and the retrograde assemblage of Pl+Bt+Kfs+Ms+Qz. Constraints from mineral composition and phase equilibrium modeling yielded peak P-T conditions of 740-750 °C and 1.15-1.2 GPa, and the rocks subsequently experienced retrograde conditions below 650 °C. These findings define a clockwise P-T path involving cooling and decompression after the peak stage, indicative of an early crustal thickening event followed by rapid exhumation or uplift. Existing geochronological data place the timing of metamorphism in the Cathaysia Block during 460-400 Ma. Consequently, the metamorphic basement in the Gaozhou region recorded Early Paleozoic high-pressure amphibolite-facies metamorphism, revealing that the Yunkai Terrane was involved in the Caledonian crustal thickening event.
How to cite: Chen, D., Yin, C., Qian, J., and Wang, X.: Protolith attributes, metamorphic P-T evolution of the metamorphic basement in the Gaozhou region, western Guangdong: Implications for Early Paleozoic tectonic dynamics of South China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17371, https://doi.org/10.5194/egusphere-egu26-17371, 2026.
The geodynamic mechanism that shaped the growth and evolution of Neoarchean continental crust has always been controversial. Here, we employ mercury (Hg) isotopes to investigate the petrogenesis of 3.1–2.5 Ga granitoids from the North China Craton (NCC). Samples older than 2.6 Ga exhibit near-zero ∆199Hg values (−0.1 to 0.1‰), consistent with derivation from primitive mantle or reworked Eo–Paleoarchean crust. In contrast, those emplaced at 2.6–2.5 Ga display bimodal Δ199Hg signatures, reflecting dual mercury sources: primitive mantle (near-zero Δ199Hg) and recycled marine Hg (positive Δ199Hg). The ∆199Hg turnover around 2.6–2.5 Ga reject meteorite-impact, heat-pipe, and sagduction models for late Neoarchean NCC evolution and instead support subduction-driven tectonics as the dominant mechanism for surface-material recycling and crustal growth.
How to cite: Chang, R.: Mercury isotopic turnover in 2.6–2.5 Ga granitoids: Evidence of oceanic subduction on late Neoarchean Earth, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17017, https://doi.org/10.5194/egusphere-egu26-17017, 2026.
The origin and tectonic regime of Jurassic granites in Southeast (SE) China have remained controversial for decades. This study focuses on the granites exposed in Fogang and Xinxing Batholiths in central Guangdong and conducts geochemical and geochronological analyses of whole-rock and zircon. Mineralogical and geochemical data show that these granites are high-K calc-alkaline I-type granites. SIMS U-Pb dating on magmatic zircons yields consistent 206Pb/238U ages ranging from 158 Ma to 163 Ma, suggesting that these granites were emplaced during this period. Whole-rock Sr-Nd isotopic analysis reveal that these granites are characterized by initial Sr87/Sr86 ratios of 0.6802 to 0.7072 and negative εNd(t) values of -9.5 to -8.2. In addition, in-situ zircon Hf-O isotopic analysis shows negative εHf(t) values of -12.34 to -0.56 and high δ18O values of 7.64 ‰ to 10.08 ‰. Above characteristics suggest that these granites were probably formed by mixing supracrustal sedimentary components with minor mantle-derived magma. Thus, the granites from the Fogang and Xinxing Batholiths in SE China are interpreted to have been generated by the reworking of Proterozoic crust triggered by asthenosphere upwelling or mafic magma underplating. These Jurassic granites represent anorogenic magmatism, probably generated in an intraplate extensional setting due to the flat slab foundering beneath SE China.
How to cite: Lai, Z., Yin, C., and Qian, J.: Geochemical and Sr–Nd–Pb–Hf–O isotopic compositions of Jurassic granites in central Guangdong, SE China: Constraints on petrogenesis and tectonic setting, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16523, https://doi.org/10.5194/egusphere-egu26-16523, 2026.
A pattern of asynchronous uplift influenced drainage reorganization in the North Ordos Basin (NOB) of central China in Triassic times. In this study, the source-sink system of the NOB was reconstructed, and the source area was identified, based on an analysis of petrology, geochronology, and palaeocurrent direction analysis, offering a new perspective on the interaction between deep tectonic processes and surface responses in the northern part of the North China Block (N-NCB). Our zircon age data reveal three prominent peaks for the Palaeoproterozoic, Mesoproterozoic, and Upper Palaeozoic, suggesting that the N-NCB may have acted as the source area for the NOB. During the Late Triassic interval, increased zircon ages (1500–1800 Ma) indicate an enhanced influx of detrital material from the central N-NCB. Furthermore, analysis of thin sections and petrographic modal com[1]positions indicates a change in source areas from solely recycled orogenic sources to a combination of recycled orogenic and magmatic arc sources. The youngest zircon ages (~233.6 Ma) from the tuffaceous siltstone mark this transition, with palaeocurrent data supporting a change in the source area from the western to the central N[1]NCB after this time. This transition underscores the impact of the asynchronous uplift of the N-NCB on the source-to-sink system of the NOB, providing an innovative perspective for reconstructing the southward sub[1]duction process of the Okhotsk Plate and associated back-arc extension along the N-NCB.
How to cite: Xu, Y., He, D., Li, D., and Huang, H.: Triassic evolution of source-to-sink drainage systems in the North Ordos Basin of central China: Impact of asynchronous uplift history, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16316, https://doi.org/10.5194/egusphere-egu26-16316, 2026.
Crustal thickness represents a key parameter for understanding the geodynamic behavior and tectonic evolution of the continental crust, but its estimation remains challenging. Several trace element geochemical proxies in arc rocks have been proposed to infer crustal thickness, yet they do not account for other factors that also influence the chemistry of magmas, including oxygen fugacity (fO2), water fugacity, temperature and accessory mineral fractionation. Proxy calibrations also require significant averaging of data before robust correlations appear, leading to some preference for detrital zircon as a geochemical proxy because many data can be collected quickly.
The geochemistry and geochronology of the Gangdese arc in southern Tibet has been extensively studied, and several mohometry proxies have been tested using analyses in this region. In this study, we tested correlations among trace elements, temperature, and fO2 through analysis of detrital zircon in modern sands from the central region of the Gangdese arc. The geochemistry of detrital zircon has been shown previously to parallel whole-rock changes, so its geochemistry should serve as a mohometry proxy. LA-ICP-MS spot analyses simultaneously resolved U-Pb ages and trace element concentrations. Temporal changes in europium anomaly, Th/Yb, and Sm/Yb – all proposed as mohometers – were compared with previous zircon and whole-rock data, as well as with geochemical proxies for temperature (Ti proxy) and fO2 (Ce proxy).
With decreasing age from ~90 to ~15 Ma, zircon data show correlated changes with decreasing temperature and increasing Th/Yb, Eu anomaly, and fO2. Sm/Yb shows no clear trend through time, although all measurements correlate positively with temperature. Previously published whole-rock La/Yb shows large scatter in ~90 Ma samples, and a significant increase between ~55 and ~15 Ma, in parallel with Th/Yb, Eu anomaly, and fO2, and opposite temperature.
Although increases in La/Yb and Eu anomaly have previously been interpreted to indicate an increase in crustal thickness between at least ~60 Ma and ~15 Ma, our new data show these trends cannot be decoupled from correlated trends in fO2 and temperature. Thus, as yet, a trend in crustal thickness through time is not resolvable for the Gangdese arc and likely not for other locations, too. These observations highlight the need for methodological and theoretical improvements that correct for effects of other parameters that influence magma chemistry besides crustal thickness.
How to cite: Roman, G., Kohn, M. J., Lopez, A., Yakymchuk, C., and Glazner, A. F.: Critical evaluation of chemical mohometry 2: Correlated changes in geochemistry, fO2, and temperature in the Gangdese Arc, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14629, https://doi.org/10.5194/egusphere-egu26-14629, 2026.
The North China Block (NCB), sandwitched between the Paleotethys and Paleo-Asian Ocean realms, played a pivotal role in the assembly and breakup of the Pangea supercontinent during the Paleozoic to Mesozoic. Yet the kinematic evolution of the NCB across the Pangea cycle—particularly its latitudinal drift, rotational behavior, and potential response to global-scale true polar wander (TPW)—remains debated due to data gaps in key intervals. We integrate new and published high-quality paleomagnetic data from the NCB spanning the Carboniferous to Jurassic to reconstruct its motion and assess TPW contributions. Our results show that the NCB resided at low paleolatitudes (～5–10°N) during the Late Carboniferous to the earliest Permian (～300 Ma), consistent with coeval equatorial faunal assemblages. Throughout the Permian, the NCB underwent persistent northward drift and clockwise rotation, culminating in the final closure of the Paleo-Asian Ocean by the Late Permian to Early Triassic. This trajectory aligns with the motion of Laurussia, indicating that the NCB had become an integral part of Pangea by the end of the Permian. In contrast, Early Jurassic volcanic rocks yield complex magnetization patterns with three distinct directional groups (shallow NW, moderate NE, and steep inclinations), suggesting either complicated response to the Jurassic Monstershift TPW event or multi-phase overprinting by regional tectonics. Critically, when compared with the apparent standstill of the adjacent Mongolia Block—which remained near ～30°N throughout the Carboniferous due to the counteraction between northward plate motion and southward TPW—the NCB’s steady northward migration provides a robust reference frame for isolating TPW signals in East Asia. We propose that the decoupled kinematics between the NCB and Mongolia during the Permo-Carboniferous reflects differential responses to the same TPW event, highlighting the necessity of multi-block analyses to disentangle plate tectonic motion from true polar wander in supercontinent cycles.
Keywords: North China Block; Pangea; Paleo-Asian Ocean; Paleomagnetism; True Polar Wander; Supercontinent cycle
Acknowledgments
This research is funded by the Natural Science Foundation of China (NSFC) (42372254), National Key R&D Program of China (2023YFF0803604, 2024YFF0808000)
How to cite: Zhang, D., Huang, B., Liu, W., Zhao, Q., Han, Y., Yao, J., Liu, Q., and Zhao, G.: Kinematics of the North China Block during Pangea Assembly and breakup in the Mantle Reference Frame and Their Implications for True Polar Wander, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12935, https://doi.org/10.5194/egusphere-egu26-12935, 2026.
The Neoproterozoic mafic-ultramafic rocks exposed along the northern margin of the Tarim craton record the evolution of the Rodinia supercontinent and have been extensively studied. However, there has been long-lasting debates regarding the geodynamic processes responsible for these rocks. Some researchers suggested that the Neoproterozoic mafic-ultramafic intrusive rocks in northern Tarim may be the product of an independent mantle plume, whereas recent studies proposed that subduction process also contributed to the formation of these rocks. Different models have varying implications for the reconstruction of the Rodinia supercontinent, which further leads to the ambiguous paleogeographic position of the Tarim craton within the Rodinia supercontinent. Therefore, investigating the petrogenesis and tectonic setting of the Neoproterozoic intrusive rocks in the northern Tarim craton is crucial for constraining the paleogeographic location of the Tarim craton.
In this paper, we report whole-rock geochemical data of the ~810 Ma Quruqtagh mafic rocks and 660-600 Ma Aksu mafic rocks at the northeastern and northwestern margins of the Tarim craton, respectively, to evaluate their petrogenesis and tectonic setting. New findings provide constraints on the role and paleogeographic position of the Tarim craton during the Neoproterozoic evolution of the Rodinia supercontinent. The Quruqtagh Group I mafic rocks have OIB (oceanic island basalt) characteristics, including enrichments in light rare earth elements (LREEs; [La/Yb]N=11.6-12.2), no obvious Eu anomalies (Eu*=0.96-1.10), and relative enrichments in large ion lithophile elements (LILEs, e.g., Ba, Rb, Sr) and high field strength elements (HFSEs, e.g., Nb, Ta, Ti). Meanwhile, they show the relatively high Th/Yb (1.22-1.61), Nb/Yb (11.5-21.1), and low TiO2/Yb (0.51-0.66) ratios of the samples, within the OIB fields on the relevant discrimination diagrams. Accordingly, the Group I mafic rocks might have formed in an intracontinental extensional environment. In contrast, the Quruqtagh Group II mafic rocks have the characteristics of CAB (continental arc basalt). They are characterized by slight LREEs enrichments ([La/Yb]N = 1.25-2.49), relative enrichments of LILEs (e.g., Rb, Ba, Sr), and significant depletions in the HFSEs (e.g., Nb), suggesting that a continental arc setting.
Similar to the Quruqtagh Group I mafic rocks, the ~660-600 Ma Aksu mafic rocks exhibit OIB-like geochemical characteristics. They show significant LREEs enrichments ([La/Yb]N = 7.56-8.84) and slightly positive Eu anomalies (Eu* = 1.02-1.12). Their high Th/Yb (0.88-1.15) and TiO2/Yb (1.15-1.75) ratios and low Th/Nb (~0.1) ratios are akin to the OIB affinities. The Aksu mafic rocks display elevated Zr/Y ratios (6.58-8.89) and plot within the within-plate basalt fields on Ti-Zr-Y and Nb-Zr-Y discrimination diagrams, suggesting derivation from magmas generated in an intracontinental extensional setting.
The ~810 Ma Quruqtagh mafic rocks with both OIB and CAB characteristics, were probably subjected to subduction processes, and the 660-600 Ma Aksu OIB-like mafic rocks originated in an intracontinental extensional setting. Therefore, the northern margin of the Tarim craton likely experienced multiple episodes of subduction in the Neoproterozoic in response to the peripheral evolution of the Rodinia supercontinent.
This study was financially supported by the National Key Research and Development Program of China project (grant 2024YFF0808000).
How to cite: Zheng, J., Liu, Q., Zhang, D., Jing, J., Cao, M., Sun, C., and Zhao, G.: Geochemistry and tectonic setting of Neoproterozoic mafic rocks from the northern Tarim craton, NW China: Constraints for the evolution of the Rodinia supercontinent, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9557, https://doi.org/10.5194/egusphere-egu26-9557, 2026.
Ultrahigh-temperature metamorphism represents the most thermally extreme crustal metamorphism, defined by peak conditions of >900 °C and 0.7-1.3 GPa, and is typically preserved in rare Mg-Al-rich rocks. In this contribution, we report the identification of UHT mafic granulites from the Pikwitonei Granulite Domain, located in the Northwestern Superior Province. Based on petrographic observations and mineral chemical analyses, these mafic granulites can be subdivided into two types according to whether the rock includes garnets or not. Both two types of mafic granulites record three distinct metamorphic stage: (1) The pre-Tmax stage is marked by clinopyroxene-plagioclase-biotite inclusions in garnet core, and amphibole-plagioclase-magnetite-ilmenite inclusions in clinopyroxene core. (2) The Tmax stage is defined by a coarse-grained matrix assemblage of garnet/amphibole, clinopyroxene, orthopyroxene and magnetite. (3) Late development of garnet-quartz symplectite and amphibole along pyroxene rim represents the post-Tmax assemblage of garnet-bearing and garnet-free mafic granulites, respectively. Phase equilibrium modelling of these mafic granulites, carried out in the NCKFMASHTO system using the GeoPS software package, yields anticlockwise P-T paths, with peak P-T conditions of 940-1030 °C / 0.82-0.88 GPa (garnet-bearing type) and 1020-1040 ℃ / 0.68-0.85 GPa (garnet-free type). Metamorphic zircon U-Pb dating gives a mean 207Pb/206Pb age of 2680±11 Ma for garnet-bearing granulites and a continuum of ages from 2673±32 to 2543±21 Ma for garnet-free granulites. These results, combined with previous studies, suggest that this UHT event occurred prior to 2.68 Ga and underwent a prolonged cooling period during 2.67 to 2.54 Ga. One-dimensional thermal modelling results indicate that radiogenic heat production merely heated the rock to 640 °C at a depth of 35 km. Integrating metamorphic P-T-t paths with thermal calculation in the Pikwitonei Granulite Domain, we propose that this UHT event was probably triggered by extra mantle heat input from asthenospheric upwelling.
How to cite: Wang, X., Yin, C., Lin, S., Couëslan, C. G., and Qian, J.: Metamorphic evolution and tectonic significance of Archean ultrahigh-temperature mafic granulites from the Northwestern Superior Province, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7443, https://doi.org/10.5194/egusphere-egu26-7443, 2026.
Plate tectonics and supercontinent cycles are the first-order drivers of Earth’s environmental evolution, helping to establish and maintain a habitable surface. The middle Neoproterozoic to Cambrian period recorded dramatic transitions towards Earth’s present-day environment, including the Neoproterozoic Oxidation Event (NOE) and the Cambrian explosion. Key tectonic factors that contributed to changes in Earth’s surface systems during this period, however, are largely confined to conceptual models. We provide deep time quantitative constraints on these changes through documenting the scale of global orogens and modeling continental freeboard conditions using whole-rock geochemical data. The results indicate that the Gondwana assembly formed a 9000 km long orogenic system with a global mean crustal thickness of over 55 km, comparable to a mean elevation of approximately 3 km above sea-level, comparable to that of the modern Alpine-Himalayan system. This resulted from establishment of the Earth’s contemporary plate tectonic regime and associated thermal state that allowed whole plate continental deep-subduction. Modeled continental exposure peaked during Gondwana assembly at 31 % of Earth’s surface area, exceeding that for both preceding and subsequent time frames. This indicates maximum continental freeboard and resultant subaerial exposure. The combination of significant lateral extent, high topographic relief and extensive low-latitude distribution of the Gondwana’s collisional orogenic belts resulted in maximum weathering and erosion intensity, supplying an exceptionally high-level sediment flux to the ocean and corresponding with high seawater Sr isotope and phosphorous (P) input. This profoundly changed seawater compositions and enhanced marine productivity, likely triggering NOE and providing environmental conditions conducive for the Cambrian explosion. This research is funded by the NSFC grants (42322208), the National Key R&D Program of China (grants 2022YFF0802700 and 2023YFF0803604).
Keywords: topography, crustal thickness, mountain elevation, subaerial continental crust, Gondwana assembly, the Cambrian explosion
References:
Cawood, P. A., Chowdhury, P., Mulder, J. A., et al., 2022. Secular Evolution of Continents and the Earth System. Reviews of Geophysics, 60: e2022RG000789.
Chowdhury, P., Cawood, P.A., Mulder, J. A., 2025. Subaerial Emergence of Continents on Archean Earth. Annu Rev Earth Planet Sci. 53: 443–478.
Yao, J. L., Cawood, P. A., Zhao, G. C., et al., 2021. Mariana type ophiolites constrain establishment of modern plate tectonic regime during Gondwana assembly. Nature Communications, 12: 1489.
Zhao, G.C., Han, YG., LI, J.H., Yao, J.L., Liu, Q., Zhang, D.H., Wang, C., Tang, Q., Zhang, J., Yin, C.Q., Zhang, G.W., 2022. Environmental effects of assembly and breakup of supercontinents. Acta Geologica Sinica, 96(9): 3120-3127.
How to cite: Yao, J., Cawood, P., Cui, X., Zhao, G., Han, Y., Liu, Q., Zhang, D., Cui, P., Yang, H., and Zhao, X.: Maximum continental freeboard and topographic relief during Gondwana assembly likely triggered the Cambrian explosion, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2135, https://doi.org/10.5194/egusphere-egu26-2135, 2026.
Emergent continental crust with subaerial exposure is important for the evolution of Earth’s surface system and the development of habitability, and it is evident that early Archean local emergence of continental crust occurred in several Archean cratons. However, it remains unresolved if the North China Craton, which preserves ancient (4.1–4.0 Ga) crustal remnants, had emergent continental crust during the early Archean. Here we report geochronological and geochemical data on Paleo–Mesoarchean potassic granites in Eastern Hebei, within the North China Craton, to trace whether or not there was any early Archean exposed landmass in this craton. We constrain that the studied potassic granites formed at ca. 3.2 Ga, and their bulk-rock and zircon Hf isotopic geochemistry reveals that they were produced by anatexis of Paleoarchean tonalite-trondhjemite-granodiorite (TTG) crust. Their low zircon δ18O values should have been inherited from their Paleoarchean TTG source, and 18O-depletion of this Paleoarchean TTG source was achieved through high-temperature hydrothermal alteration with and the infiltration of isotopically-light meteoric water into the shallow crust, prior to the ca. 3.2 Ga anatexis. The identification of Paleoarchean TTG crust altered by meteoric water in Eastern Hebei indicates the emergence of continental crust in the North China Craton during the early Archean, and this Paleoarchean continental emergence could have been associated with magmatic underplating during mantle plume activities, which is also evidenced by the Paleoarchean enriched plume remnants in Eastern Hebei.
How to cite: Wang, C., Chu, H., Song, S., Zhao, G., Allen, M. B., and Fu, B.: Paleoarchean continental emergence in the North China Craton indicated by low δ18O granites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7082, https://doi.org/10.5194/egusphere-egu26-7082, 2026.
The assembly and breakup of the Rodinia supercontinent and the subsequent formation of the Gondwana megacontinent represent a pivotal stage in Earth’s history, involving the transition of plate tectonic regime and the evolution of Earth’s habitability. Located to the southeast of the Tarim Craton, the South Altyn Tagh hosts extensive Neoproterozoic granitic gneiss. Previous studies on these rocks proposed multiple interpretations regarding their petrogenesis and tectonic setting, leading to a significant debate about the paleogeographic position of the South Altyn Tagh within the Rodinia supercontinent. In addition, the correlation between the early Paleozoic metamorphic ages recorded in the Neoproterozoic granitic gneiss and the amalgamation of the Gondwana remains underexplored.
This study focuses on the Xiaoluke (Xgn), Yuemaqige (Ygn), and Wengulu (Wgn) Neoproterozoic granitic gneiss in the Bashiwake area of the South Altyn Tagh. To constrain the crystallization and metamorphic ages, petrogenesis, and tectonic setting of these rocks, a petrological, geochronological, and geochemical data is presented. Zircon U-Pb dating yields the protolith crystallization ages of 924±8 Ma and 924±9 Ma for the Wgn and Ygn granitic gneiss, respectively, and 902±6 Ma for the Xgn samples. Combined zircon and titanite U-Pb dating constrained the metamorphic ages of the Xgn granitic gneiss to 554-459 Ma. The granitic gneiss rocks in this study are composed primarily of granodioritic and monzogranitic gneiss. They are characterized by high SiO₂ contents (68.2-76.1 wt.%), FeOT/MgO ratios (1.5-6.2), and K₂O/Na₂O ratios (0.98-3.4), classified as ferroan and high-K calc-alkaline to shoshonitic granitoids. Furthermore, they mostly display enrichments in light rare earth elements (LREEs) relative to heavy rare earth elements (HREEs), accompanied by distinctly negative Eu anomalies (Eu/Eu*=0.3-0.7). Specifically, the ca. 924 Ma granitic gneiss exhibits Al2O3/(CaO+Na2O+K2O) (A/CNK) ratios of 1.01-1.22, relatively low Zr + Nb + Ce + Y values (181-341 ppm), and negative zircon εHf(t) values (-13.4 to 0.2), akin to peraluminous S-type granites derived from ancient crust related to collision. Comparatively, the ca. 902-895 Ma samples display variable A/CNK ratios (0.91-1.07), higher Zr + Nb + Ce + Y values (377-1083 ppm), and positive zircon εHf(t) values (3.3 to 6.7), similar to A-type granites originating from juvenile materials in a post-collisional setting.
Therefore, we propose that the South Altyn Tagh experienced a transition from a syn-collisional setting at ca. 924 Ma to a post-collisional setting at ca. 902-895 Ma, in response to the final amalgamation of the Rodinia supercontinent. The subsequent metamorphic events occurring between 554 Ma and 460 Ma were probably related to the formation of the Gondwana megacontinent.
This study was financially supported by the National Natural Science Foundation of China (grant 42272249).
How to cite: Yang, M., Liu, Q., Han, Y., Yao, J., Zhang, D., and Zhao, G.: Neoproterozoic Granitic Gneiss from the South Altyn Tagh, NW China: Constraints on Rodinia Assembly and Gondwana Formation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4752, https://doi.org/10.5194/egusphere-egu26-4752, 2026.
Long-lived subduction and variable plate geometry of the Paleo-Pacific plate resulted in multiple episodes of both extensional and contractional deformation. While tectono-magmatic evidence provides critical insights into the tectonic evolution of the South China Block (SCB), the timing and dynamic mechanisms governing the transition from late Early Cretaceous contraction to large-scale intraplate extension remain contentious. Here, we present zircon U-Pb ages, geochemical data, and Hf isotopic data for 5 samples from the NNE-trending dioritic dikes and granodiorites in the Changle-Nan’ao Fault Zone, Southeast China, as well as crustal thickness reconstructions based on Sr/Y and (La/Yb)N geochemical proxies to constrain the crucial tectonic transition in the late Early Cretaceous. Our samples exhibit comparable zircon U-Pb ages (105–103 Ma) and are characterized by enrichment in LILEs, pronounced depletion in HFSEs, and variable εHf(t) values. These features suggest that they derived from the mixing of felsic and mantle-derived mafic melts, differentiated at successive stages through fractional crystallization. Notably, the intrusion of the dioritic dikes along the fault zone highlights a phase of extensional activity. Integrated magmatic geochemistry and sedimentary stratigraphic records, coupled with crustal thickness data indicating a reduction to ~40 km before ~120 Ma followed by significant thickening to a peak of ~60–70 km at ~105 Ma, suggest two tectonic transitions at ~120 Ma and ~105 Ma, respectively. It is noteworthy that the extension observed in the coastal region due to slab break-off was manifested as coeval contraction in the inland region at ~105 Ma, which was subsequently followed by widespread extension across SE China. We propose that the tectonic transitions between the compression and extension were driven by changes in subduction angle of Paleo-Pacific slab, specifically the evolution from flat-slab subduction to slab roll-back and steepening.
How to cite: Zheng, H., Gong, J., Wu, H., Deng, H., Hao, Y., Zhu, K., Yu, Z., Huang, J., Chen, H., and Yang, S.: Latest Early Cretaceous tectonic transition from contraction to large-scale extension in Southeast China: Insights from the magmatism along the Changle-Nan’ao Fault Zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7412, https://doi.org/10.5194/egusphere-egu26-7412, 2026.
Metamorphic pressure-temperature-time (P-T-t) paths are critical records of crustal thermomechanical evolution, yet the growing documentation of both clockwise (CW) and counterclockwise (CCW) paths within single high-grade terranes complicates straightforward correlations with specific tectonic settings. The Eastern Hebei Complex in the eastern North China Craton, which preserves coexisting Neoarchean CW and CCW P–T paths, offers an ideal natural laboratory to investigate such seemingly contradictory metamorphic features and to reconcile the ongoing debate over its tectonic setting.
In the eastern part of the complex (Eastern Tectonic Domain, ETD), Neoarchean mafic and felsic granulites from the Taipingzhai, Qianan, and Caozhuang areas record 2.52–2.48 Ga CCW P–T paths with peak ultra-high temperature (UHT) conditions (>900°C), interpreted as evidence for a sagduction setting. In contrast, the western part (Western Tectonic Domain, WTD) contains identified Neoarchean ophiolitic mélanges. Geochemical data from ultramafic-mafic blocks in the Zunhua and Shangying areas indicate that these mélanges incorporate both Neoarchean forearc oceanic lithosphere fragments and exhumed subducted slab materials. Metamorphic blocks within the mélange (mafic granulite, garnet amphibolite) and the surrounding pelitic granulite matrix record different peak P–T conditions, defining CW P–T paths ranging from 715–850°C and 9.4–13.6 kbar at 2.48–2.46 Ga. Furthermore, Neoarchean UHP peridotite and eclogite-facies garnet clinopyroxenite have been documented in this belt. These metamorphic features are analogous to those recorded in tectonic mélanges of well-established Phanerozoic orogens. The coexistence of petrogenetically diverse blocks, derived from varying depths, indicates their entrainment, mixing, and exhumation within a subduction channel during plate convergence, followed by tectonic juxtaposition with the gneissic matrix.
Thermodynamic modeling indicates that these blocks experienced near-isothermal decompression, interpreted as rapid exhumation from varying depths within a subduction channel. The coeval CCW paths documented elsewhere in the complex are interpreted to result from the downward advection of isotherms during incipient subduction. The full spectrum of metamorphic P–T conditions and paths (CW and CCW) documented in the complex closely resembles patterns in post-Archean orogens, revealing the spatiotemporal evolution of thermal structure and perturbations during subduction-accretion. Our findings demonstrate that the lithological assemblages and diverse metamorphic records can be reconciled within a unified plate tectonic model, without invoking sagduction. The study emphasizes the necessity of integrating litho-tectonic unit classification and regional structural-metamorphic analyses over reliance on isolated P–T path before making tectonic interpretations.
How to cite: Ning, W., Wang, L., and Kusky, T.: Caution in linking localized metamorphic P–T paths to tectonic settings, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6093, https://doi.org/10.5194/egusphere-egu26-6093, 2026.
The South China Block (SCB) experienced multi-stage tectono-magmatic events during the Mesozoic, forming a broad and episodic intracontinental orogenic belt. It is controversial whether the driving force of the Mesozoic intracontinental orogeny in the SCB is related to the far-field effects of plate convergence. To better understand the driving mechanism of intracontinental orogeny, we conducted a detailed structural investigation of the Xingguo area in southern Jiangxi Province, located in the central part of the SCB. Two regional-scale buckling superposed folds were identified as the Chayuan arcuate syncline of the fold axis protruding to the north (Type 2a interference pattern) and the Xiefang syncline of the fold axis extending NW–SE (Type 1d interference pattern). Although there are differences in fold interference patterns, the Chayuan arcuate syncline and Xiefang syncline were formed by the superimposition of the Middle–Late Triassic NE–SW shortening and the Middle–Late Jurassic nearly E–W shortening. This phenomenon of the differential fold interference patterns in the same tectonic setting is determined by the difference in geometric characteristics of their initial folds. Combined with the variation of the Mesozoic paleostress field, it is considered that the Mesozoic intracontinental orogeny in the SCB is mainly controlled by the far-field stress propagation generated by plate interactions. Based on the analysis of tectonic architecture, we propose that the Mesozoic tectonic evolution of the SCB experienced a transformation from multi-plate convergence in the Triassic to Andean-type subduction in the Jurassic. This tectonic transformation finally resulted in the reactivation of the Precambrian multi-terrane collage of the SCB.
How to cite: Li, C. and Wang, Z.: Differential fold interference patterns in an intracontinental orogen: Insights from superposed buckle folding in southern Jiangxi Province,South China Block, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4628, https://doi.org/10.5194/egusphere-egu26-4628, 2026.
Detrital low-temperature thermochronology has become a widely used tool to infer source-area exhumation histories and catchment-averaged erosion rates. However, a fundamental question remains insufficiently explored: to what extent do detrital thermochronological age distributions faithfully record the full spectrum of bedrock exhumation events within a drainage basin? In particular, it is unclear which exhumation phases are robustly captured, which are selectively amplified, and which may be systematically filtered by geomorphic and fluvial processes. Here we address this problem using the Lhasa river catchment in southern Tibet as a natural laboratory, where abundant bedrock low-temperature thermochronological data coexist with multiple detrital samples from tributaries and the trunk stream. Our approach treats detrital signals as the outcome of a transfer process from bedrock exhumation to river sediments, rather than as a direct proxy. We first compile and statistically characterize bedrock-derived exhumation phases using age-elevation relationships and cooling-path constraints, which serve as physically grounded prior information. Detrital age distributions are then binned consistently with these bedrock exhumation phases, allowing a direct comparison of their relative importance. To quantify potential biases, we develop a bedrock-detrital transfer framework that compares the expected contribution of each exhumation phase, parameterized by its spatial extent and inferred exhumation rate, with its observed detrital fraction. This enables us to identify amplified versus suppressed exhumation signals. We further evaluate the role of geomorphic filtering by integrating catchment-scale metrics, including channel steepness index, hypsometric integrals, and relief, as proxies for erosion and sediment transport efficiency. Finally, we apply a Bayesian forward-inverse framework to estimate catchment-averaged exhumation rates from detrital thermochronological data, partially calibrated by bedrock constraints, and assess under which geomorphic conditions these estimates converge with bedrock-derived exhumation rates. Our results aim to provide a quantitative framework for interpreting detrital thermochronology and for assessing when, and why, detrital records succeed, or fail to capture source-area exhumation histories.
How to cite: Song, S. and He, Z.: Evaluating the fidelity of detrital thermochronology as a recorder of catchment-scale exhumation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3146, https://doi.org/10.5194/egusphere-egu26-3146, 2026.
Posters virtual: Wed, 6 May, 14:00–18:00 | vPoster spot 1a
EGU26-8520 | ECS | Posters virtual | VPS30
Formation of A-type charnockite and constraints on deep crustal anatexis in early Paleozoic orogen, South ChinaWed, 06 May, 14:18–14:21 (CEST) vPoster spot 1a
Charnockite is generally regarded as a product of high-temperature melting; however, its specific origin, generation, and preservation mechanisms, as well as its relationship to high-grade metamorphism or deep crustal reworking, remain poorly constrained. During the early Paleozoic, the South China Block underwent intense orogeny that resulted in significant crustal shortening and thickening, subsequently inducing widespread anatexis and extensive S-type granites. This study identifies ~431 Ma charnockites containing granulitic enclaves that were exposed in the Yunkai massif, providing key insights into the early Paleozoic crustal reworking and deep crustal melting behaviors in South China. The body displays A-type characteristics with crustal reworking zircon isotopic features (δ18O = 8.0–9.8 ‰; εHf(t) = - 11.5 to - 3.4). The charnockite and its enclaves show identical mineral assemblages and comparable orthopyroxene chemical compositions. The two anhydrous minerals of orthopyroxene and garnet are identified as of peritectic and magmatic origins given their textural features and geochemical compositions. Moreover, petrographic observations and bulk geochemical data argue that the peritectic minerals were derived from the entrainment of their granulitic sources. Crystallization phase modeling indicates orthopyroxene would have been completely hydrated and formed biotite when water contents exceed ∼0.3 wt.% near the solidus. Water-in-zircon analysis and thermodynamic modeling indicate low magma water contents (∼0.15 wt.%; 135 ppm, zircon water medians) for the Gaozhou charnockite from early crystallization to final solidification. CO2‐rich fluids flushed the charnockite reservoir further contributing to the stabilization of the orthopyroxene. Accordingly, the Yunkai charnockite reveals deep crustal melting processes involving anhydrous minerals entrained in a low-water environment. This low-water environment correlates with high-temperature melting of granulite-facies rocks in the lower crust and the presence of CO₂-rich fluids within the system. Regional magmatic-metamorphic-tectonic data indicate that the formation of the Yunkai A-type charnockite occurred within a post-orogenic extension regime, representing the peak of intracrustal reworking in South China.
How to cite: yang, H. and Yao, J.: Formation of A-type charnockite and constraints on deep crustal anatexis in early Paleozoic orogen, South China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8520, https://doi.org/10.5194/egusphere-egu26-8520, 2026.
