Arc-continent Collision Research Articles

Composition of pre-Carboniferous siliciclastic rocks in Tasmania

Twelve hundred whole-rock compositions of the Proterozoic and Paleozoic rocks of Tasmania were compiled from a range of published and unpublished sources. We used these data to establish a chemostratigraphic evolution of the island and to resolve several problems in Tasmanian geology. Six chemostratigraphic mega-sequences were defined for Tasmania. The major events that separate these sequences are the onset of continental rifting (ca 700 Ma), arc–continent collision (ca 515 Ma), post-collisional volcanism (506 Ma) and then the return to continental conditions (500 Ma). Within this large-scale classification, we recognised smaller-scale changes in provenance. Within the Mesoproterozoic, there is a trend to more mafic rocks in the source region, which is interrupted by a short period where granites were prominent in the provenance. The Mesoproterozoic rocks of King Island have a subtly different provenance from the shallow water siliciclastic rocks of the Rocky Cape Group. The distribution of Cr across Tasmania can be attributed to two different events. First, the primitive basalts associated with Cryogenian continental rifting introduced a Cr signature associated with high TiO2. The ophiolite obduction event in the Cambrian produced a second Cr enrichment event dominated by chromite from supra-subduction-zone peridotite. These two events can be differentiated by the composition of the sedimentary rocks but are more clearly defined by the composition of detrital spinels. Within the East Tasmanian terrane, a trend to less weathered sources reflects the influx of young volcanic detritus at the end of the Silurian.

Neoproterozoic–early Paleozoic evolution of the southern Central Asian Orogenic Belt: Constraints from eclogites in the Beishan Orogenic Belt (NW China)

Eclogites provide important constraints on the processes of plate subduction, collision, and the overall tectonic evolution of orogens. The Gubaoquan eclogite is the only one identified in the Beishan Orogenic Belt, which constitutes the southernmost part of the Central Asian Orogenic Belt. U-Pb dating of the eclogite indicates a Neoproterozoic metamorphic age of 887 ± 7 Ma and an Ordovician age of 461 ± 15 Ma for the eclogite-facies metamorphism. Multi-proxy (zircon, monazite, rutile, and apatite) U/Th-Pb geochronology and trace element geochemistry reveal that they have experienced multiple tectonothermal events in the Neoproterozoic and Paleozoic. The protolith of the Gubaoquan eclogite is of continental origin, and along with the extensive distribution of the Neoproterozoic arc-related rocks probably formed near the periphery of Rodinia. Given the continental setting of the protolith of the Gubaoquan eclogite, we suggest that eclogite-facies metamorphism at ca. 461 Ma was due to subduction under the Shuangyingshan-Huaniushan arc, which is manifested as an arc-continental collision process.

Strain Accumulation Along the Eastern Java Back–Arc Thrust System Inferred from a Dense Global Navigation Satellite System Network

The back–arc thrust region in Eastern Java to Flores is significantly influenced by the arc–continent collision between the Australian Plate and the Eastern Sunda Arc, leading to a tectonic regime characterized by high seismic and volcanic hazards. This area has experienced several major earthquakes. However, back–arc thrust in Eastern Java remains absent from significant shallow earthquakes, which might indicate intense deformation. We conducted an analysis using recent and dense Global Navigation Satellite System (GNSS) observations from both continuous and campaign stations to develop a strain rate model and explore the detailed crustal behavior and strain accumulation within the Eastern Java back–arc thrust system. Our findings revealed varying values of compression and extension throughout the region, with compression values ranging from −2.24 to 0.086 μstrain/year. Additionally, we observed that the maximum shear strain rate and dilatation strain rate were within the ranges of 0.0013 to 1.12 μstrain/year and −2.24 to 0.698 μstrain/year, respectively. These findings could facilitate more informed strategies and improve preparedness for future seismic events.

A New Geological Map of the Marginal Basins of Eastern Papua New Guinea: Implications for Crustal Accretion and Mineral Endowment at Arc–Continent Collisions

Abstract Accretion of island arc terranes is a fundamental process of crustal growth and the formation of new continents. Convergent margin tectonics, both compressional and extensional, in accretionary orogens also control the origin and distribution of their contained mineral resources, including many of the world’s important Cu and Au deposits. However, the details of crustal growth and accretion are often lost because of deformation and selective preservation during subduction. The Melanesian Borderland, which includes the offshore regions of eastern Papua New Guinea and the Solomon Islands, contains several active and relict arc and backarc systems that have formed in response to more than 50 Ma of subduction and complex plate tectonic adjustments. The composite terrane is a region of some of the fastest growing crust on Earth and also spectacular mineral endowment, including three of the top ten porphyry Cu and epithermal Au deposits in the world. However, more than 80% of the belt is submerged, and so little is known about its geological evolution and makeup. Here, we present the first detailed geological map of the region in one map sheet, including the marginal deep ocean basins. The map identifies and groups the key lithostratigraphic formations and correlates associated tectonic events across the belt. The final compilation is presented at 1:1,000,000 scale, which is sufficient to allow quantitative analysis of crustal growth and accretion during ocean–continent collision throughout the region. The map shows the diversity of assemblages in accreting terranes that may eventually become part of a growing continent and highlights their complex formation and structural relationships. Because so much of that history has occurred offshore, the new map presents the first complete picture of the geology of the region in the critical period leading up to its eventual incorporation in the Australian continent.

First boron isotopes in the southern Jilin TTG series uncover a Neoarchean oceanic arc in the eastern North China Craton

The Neoarchean evolution of the eastern North China Craton (NCC) is still controversial. This study presents the first B isotopes, together with zircon U-Pb-Hf isotopes and whole-rock geochemical analyses, for the TTG and dioritic series in the Baishan area of the southern Jilin region. LA-ICP-MS zircon U-Pb results uncover the Neoarchean magmatic activities, including granodioritic gneisses (2648 ± 10 Ma and 2622 ± 8 Ma), and quartz dioritic gneiss (2539 ± 7 Ma). The 2.65–2.60 Ga TTG series exhibit intermediate calc-alkaline characteristics, with relatively lower Th/La ratios (0.11–0.41) and positive zircon εHf(t) values (+3.73-+7.93), suggesting that the TTG series were likely derived from partial melting of mafic lower crust. By contrast, the 2.54 Ga dioritic series show positive Zr, Hf and Eu anomalies, with relatively lower Nb/Zr ratios (0.013–0.028) and εHf(t) values (+2.00-+5.49), indicating that they were possibly produced by mixing of the mantle-derived magma and crustal melts. Importantly, the 2.65–2.60 Ga TTG series are characterized by positive whole-rock δ11B values of + 4.11-+15.08 ‰, resembling the Izu-Bonin-Mariana oceanic arc and South Sandwich Island arc volcanic rocks. The formation of these TTG rocks is attributed to 11B-rich fluids released by subducted oceanic slab and subsequent metasomatism of the subarc mantle wedge. Unlike the oceanic arc TTG series, the 2.54 Ga dioritic series exhibit lighter whole-rock δ11B values of − 4.23–−4.50 ‰, reflecting an arc-continental collision induced by slab breakoff and mantle-derived magma upwelling. Integrated with previous studies, it suggests that the subduction-collision process in the eastern NCC resulted from the co-evolution of oceanic arc and continental margin arc.

Metamorphism and Partial Melting at UHP Conditions Revealed by Microdiamonds and Melt Inclusions in Metapelitic Gneiss from Heia, Arctic Caledonides, Norway

Abstract Primary multiphase inclusions trapped in host minerals such as garnet may provide important information about the nature of fluids and melts and their crystallization products. The occurrence of melt and fluid inclusions in the same cluster suggests primary fluid-melt immiscibility during partial melting. Here we report the coexistence of diamond-bearing fluid inclusions with melt inclusions in metasedimentary UHP rocks of the Nordmannvik Nappe at Heia, in the Arctic Caledonides of Norway. Multiphase fluid inclusions (Type I) and primary melt inclusions (Type II) have been identified in garnet and studied in detail. Microscopic observations, Raman spectroscopy, FIB-SEM, and EDS analysis show that microdiamonds occur in situ, in multiphase fluid inclusions (Type I) distributed in clusters in the garnet mantle. The Raman spectra suggest partial transformation of diamond to disordered sp2-bonded carbon structure. Along with diamond, Type I inclusions contain (i) rutile and apatite as trapped solid phases, (ii) carbonates (magnesite-siderite) and Al-phyllosilicates (white mica, phlogopite, pyrophyllite) as daughter or step-daughter minerals, and (iii) CO2 as a residual fluid phase. Former melt inclusions (Type II) occur in the same microstructural position in the host garnet. They contain muscovite, paragonite, phlogopite, K-feldspar, plagioclase, albite and quartz as solid phases crystallized from a melt, and kyanite as accidentally trapped mineral. The occurrence of melt inclusions in the inner part of garnets thus suggests that garnet was growing in the presence of melt. Garnet is nearly homogeneous with respect to major elements Mg, Fe, Ca and Mn, expressed by pyrope (0.18–0.22 XPrp), grossular (0.09–0.12 XGrs), almandine (0.67–0.70 XAlm) and spessartine (0.01–0.03 XSps) except local Ca enrichment in the rim. Trace elements show decreasing HREE and Y patterns from the core to the mantle suggesting garnet growth according to the Rayleigh fractionation model. Phosphorus shows an elevated content in the core and mantle. A positive correlation between P and Na indicates a coupled NaPM2+−1Si−1 substitution in garnet. Minimum P–T conditions of 3.7 to 3.8 GPa and 840°C to 870°C for the peak metamorphic stage were estimated from garnet composition (XPrp = 0.22), zirconium-in rutile thermometry of rutile inclusions in garnet (747–977 ppm of Zr) and diamond/graphite stability boundary. Partial melting on a prograde P–T path was controlled by the decomposition of phengite in the presence of C–O–H fluid, producing peritectic garnet ± kyanite along with melt, in the diamond stability field. The coexistence of diamond-bearing multiphase fluid inclusions with melt inclusions suggests primary fluid-melt immiscibility at UHP conditions. During exhumation, the rock underwent decompression and second partial melting, leading to enrichment in Ca, Y, Cr and Sc of garnet rims. Microdiamonds found in metasedimentary crustal rocks at Heia provide new evidence of UHP metamorphism in the Nordmannvik Nappe of the Arctic Caledonides. The results favour a correlation with the pre-Scandian subduction and arc–continent collision events of the Caledonian Orogeny.

Characteristics of the seismogenic zone in an arc-continent collision belt: insights from seismic b values in Eastern Taiwan

Eastern Taiwan overlies a suture zone between the Eurasian Plate and the Philippine Sea Plate and is characterized by frequent earthquakes, often resulting in significant disasters. Notably, the region exhibits characteristics such as a high frequency of earthquakes and a short recurrence period for intense seismic events. While prior research has explored seismic b values across various periods in Taiwan, detailed investigations of the b value in the eastern region are lacking. This study employs the earthquake catalog compiled by the Taiwan Central Weather Administration to analyze spatial–temporal variations in b values in eastern Taiwan. The analysis encompasses seismic events occurring between January 1996 and June 2019. The seismic catalog is divided into three distinct time periods related to large seismic events: period I, 1996–2003 (the Chengkung earthquake); period II, 2003–2013 (the Ruisui earthquake); and period III, 2013–2019 (the Hualien earthquake). Our results indicate that most seismic events with a magnitude greater than 6 are associated with low b values. The overall b value increases during period II and then decreases substantially during period III. Although the estimated b values changed slightly, but the uncertainty in b values remained stable in this study. The epicenters of large earthquakes often overlap with areas with lower b values, especially in plate suture zones, which means that areas with lower b values usually have a higher probability of larger earthquakes. Given the extremely high potential for a catastrophic earthquake, mitigating measures should be adopted at all times.Graphical

Classification of volcanogenic massive sulfide deposits in North Qilian, China: Evidenced from lithostratigraphy and geodynamic setting

Volcanogenic massive sulfide (VMS) deposits are widely distributed both geographically and temporally, occurring from ancient Archean cratons to modern submarine volcanic environments, with a notable surge during the Paleozoic era. The North Qilian orogenic belt in China is a prominent Paleozoic VMS metallogenic province, shaped by complex geological processes such as the opening of the Qilian Ocean, oceanic subduction, and arc-continent collision. Previous research has constrained the timing of VMS mineralization in the North Qilian to between 440 and 470 Ma, identifying two primary deposit types: Kuroko-type and Cyprus-type. However, ongoing debates persist regarding the classification and geodynamic framework of these VMS deposits. The recent surge in international research on VMS deposit classification and tectonic settings has prompted a reassessment of VMS mineralization within the North Qilian belt. This study revisits the geological and geochemical characteristics of VMS deposits in the region, identifying two distinct types: Mafic VMS deposits and Bimodal-Felsic VMS deposits. Furthermore, the metallogenic dynamics of the Shijuli, Jiugequan, and Baiyinchang deposits have been re-evaluated in the context of the structural evolution and contemporary interpretations in this area.

Mountain building process of the Taiwan orogeny.

The Taiwan orogeny, an example of arc-continental collision, exhibits complex geological structures and rapid exhumation. Many models have tried and failed to fully capture the dynamics of these processes. We developed a comprehensive thermomechanical model that considers the transition from brittle to ductile behavior with depth, lithology-dependent erosion and observed decollement and backstop geometries. This model successfully reproduces the intricate structures observed within the Taiwan orogeny, aligns with structural complexities, metamorphic temperature profiles, thermochronological records, strain distributions, and the rates of exhumation and cooling and elucidates the roles of ductile deformation and ramp structures in forming the Hsuehshan Range and the Western fold and thrust belt. The insights from this model offer potential applicability to other orogenic wedges worldwide.

Opening and Closure of the Sulu Sea: Revealed by Its Peripheral Subduction and Collision Processes

The Sulu Sea is a small marginal sea in the western Pacific, but it is a very complex and tectonically active region, situated amidst the convergence of the Eurasian, Pacific, and India-Australian plates. Deciphering its geodynamic evolution is crucial, but our understanding of its opening, closure, and tectonic history remains inadequate. The main aim of this study was to systematically study the opening and subsequent closure of the Sulu Sea though discerning tectonic unconformities, structural features, and subduction-collision tectonic zones around margins of the sea. The interpreted sections and gravity anomaly data indicate that the NE Sulu Sea has undergone Neogene extension and contraction due to subduction and collision along the northern margins of the Sulu Sea, whereas the SE Sulu Sea gradually extended from northwest to southeast during the Middle Miocene and has subsequently subducted since the Middle Miocene along the southeastern margins of the Sulu Sea. Several subduction and collision boundaries with different characteristics were developed including continent-continent collision, arc-continent collision, and ocean-arc subduction. The different margins of the Sulu Sea showed distinct asynchronous subduction and collision processes. The northern margins of the Sulu Sea can be divided into three subduction-collision tectonic zones from west to east: the Sabah-Nansha block collision has occurred in NE Borneo since the Early Miocene, followed by the SW Palawan-Cagayan arc collision in SW Palawan Island since the Middle Miocene, and the NW Palawan-Mindoro arc collision since the Late Miocene with further oblique subduction of the Philippine Sea Plate. The southeastern margins can also be divided into two subduction tectonic zones from south to east: the SE Sulu Sea has subducted southward beneath the Celebes Sea since the Middle Miocene, followed by the southeastward subduction beneath the Philippine Sea Plate since the Pliocene. Since the Miocene, the interactions among the Australia-India, the Philippine Sea, and the Eurasian plates have formed the circum-Sulu Sea subduction-collisional margins characterized by microplate collisions, deep-sea trough development, and thick sediments filling in the orogenic foreland. This study is significant for gaining insights into the opening and closure of marginal seas and the dynamics of multiple microplates in Southeast Asia.

Applicability of Na/K geothermometer to the metapelitic non-volcanic geothermal fields in the Taiwan orogenic belt

Taiwan is situated at one of the world's most active orogenic belts with arc-continent collision. This event resulted in the burial and uplift of mudstones along the continental margin, transforming them into metapelitic mountains. These mountains intercept rainfall and serve as the driving force for deep water circulation, enabling meteoric fluids to carry residual heat to the surface, thus giving rise to hot springs. The Taiwan orogenic belt is home to over 100 hot springs, and some of the hot spring reservoir temperatures such as Chingshui, Tuchang-Jentse, Lushan, Chihpon, and Chinlun exceeds 160 °C. Geothermal development in Taiwan has been carried out in such hot spring areas without any volcanic activities.In order to assess reservoir temperatures and confirm the applicability of the Na/K geothermometer to such high temperature hot spring system, the concentrations of Na+, K+, and SiO2 were analyzed from geothermal wells. Considering the mineral composition of metapelitic host rock, a new Na/K geothermometer is proposed based on equilibrium between albite and illite:T>180∘C,T(∘C)=2474log(NaK)+3.73−273.15This formula is only applicable in a reducing fluid and does not involve the formation of clay minerals except illite. It also requires several years to reach equilibrium. When using this formula to estimate reservoir temperatures, careful consideration of various conditions is necessary. It is advisable to incorporate both quartz geothermometer and down-hole temperature measurements for a more accurate assessment. Combining the Na/K geothermometer with the quartz geothermometer, along with other geochemical data such as Cl−concentrations and δD and δ18O of fluid, helps to understand whether hydrothermal fluids have undergone evaporation, dilution, and/or mixing processes.

Damage asymmetry of the Chimei Fault, eastern Taiwan, and implications for deformation evolution

The mesoscale deformation structures in eastern Taiwan are considered to have recorded progressive deformation during rapid convergence and uplift in response to arc-continent collision. However, detailed deformation mechanisms and kinematic history of faulting remained poorly known. The Chimei Fault in eastern Taiwan thrusts the igneous forearc basement over the orogen-derived turbidites, and its outcrops provide opportunities to understand deformation mechanisms of the fault rocks across a bi-material fault during the arc-continent collision. To unravel the structural and mechanical architecture of the Chimei Fault, we performed field observations, paleostress analysis, and fold analysis. The Chimei Fault shows a fault core surrounded by damage zones. The width of the damage zones across the fault core is asymmetric, with the footwall turbidites exhibiting wider damage zone with higher fracture intensity than the hanging wall andesitic complex. Our paleostress analysis reveals that the mechanically stronger hanging wall can accommodate larger differential stress than the weaker footwall. Different deformation styles in the footwall damage zones, including pinch-and-swell structures, boudins, and postdating fractures, suggesting progressive deformation while sediment lithification in response to the activities of the Chimei Fault.

Middle Silurian–Middle Devonian Magmatic Rocks in the Eastern Segment of the Northern Margin of the North China Craton: Implications for Regional Tectonics

This paper presents a detailed study including LA-ICP-MS zircon U-Pb dating, geochemical, zircon Hf isotope, and whole rock Sr-Nd isotope analysis of magmatic rocks from the Yitong County, Jilin Province, NE China. These data are used to better constrain the Middle Silurian–Middle Devonian tectonic evolution in the eastern segment of the northern margin of the North China Craton (NCC). Zircon U-Pb dating results show that the Ximangzhang tonalite formed in the Late Silurian (425 ± 6 Ma); the basalt, andesite, and metamorphic olivine-bearing basalt in the Fangniugou volcanic rocks formed in the Middle Silurian (428 ± 6.6 Ma) and Middle Devonian (388.4 ± 3.9 Ma, and 384.1 ± 4.9 Ma). The Late Silurian tonalites are characterized by high SiO2 and Na2O and low K2O, MgO, FeOT, and TiO2, with an A/CNK ratio of 0.91–1.00, characteristic of calc-alkaline I-type granite. They are enriched in Rb, Ba, Th, U, and K, and depleted in Nb, Sr, P, and Ti, with positive εNd(t) (+0.35) and εHf(t) (+0.44 to +6.31) values, suggesting that they mainly originated from the partial melting of Meso–Neoproterozoic accretionary lower crustal material (basalt). The Middle Silurian basalts are characterized by low SiO2, P2O5, TiO2, and Na2O and high Al2O3, FeOT, and K2O, enriched in Rb, Ba, Th, U, and K and depleted in Nb, Ta, Sr, P, and Ti, indicative of shoshonitic basalt. The Late Silurian tonalites have positive εNd(t) (+4.91 to +6.18) values and primarily originated from depleted mantle magmas metasomatized by subduction fluids, supplemented by a small amount of subducted sediments and crustal materials. The Middle Devonian volcanic rocks exhibit low SiO2, TiO2, and Na2O and high K2O, and MgO, enriched in Rb, K, and LREEs and depleted in Nb, Ta, Sr, and HREEs, characteristic of shoshonitic volcanic rocks. Their εNd(t) (+2.11 to +3.77) and εHf(t) (+5.90 to +11.73) values are positive. These characteristics indicate that the Middle Devonian volcanic rocks primarily originated from depleted mantle magmas metasomatized by subduction fluids, with the addition of crustal materials or subducted sediments during their formation. Based on regional geological data, it is believed that the study area underwent the following evolutionary stages during the Silurian–Devonian period: (1) active continental margin stage of southward subduction of the Paleo–Asian Ocean (PAO) (443–419 Ma); (2) arc-continent collision stage (419–405 Ma); (3) post-collision extension stage (404–375 Ma); (4) active continental margin stage, with the PAO plate subducting southward once again (375–360 Ma).

The erosional and weathering response to arc–continent collision in New Guinea

Arc–continent collision is a fundamental stage in the plate-tectonic cycle that allows the continental crust to grow and can influence global climate through chemical weathering. Collision between Australia and the oceanic North Coast Range–New Britain Arc began in the Middle Miocene, resulting in uplift of the modern New Guinea Highlands. The temporal evolution of this collision and its erosional and weathering impacts is reconstructed here using sedimentary archives from the Gulf of Papua. Sr and Nd isotopes show dominant erosion from igneous arc-ophiolite crust, accounting for c . 40–70% of the total flux in the Early Miocene, and rising to c . 80–90% at 8 Ma, before falling again to 72–83% by the present day. Greater erosion from Australia-derived units accelerated in the Pliocene, like the classic Taiwan collision but with greater erosion from arc rather than continental units. Chemical alteration of the sediment increased through time, especially since c . 5 Ma, consistent with increasing kaolinite indicative of more tropical weathering. Erosion was focused in the high topography where mafic arc units are preferentially exposed. Comparison of sediment with bedrock compositions implies that the source terrains have been more efficient at removing CO 2 from the atmosphere compared with Himalayan drainages. Supplementary material : Details of analytical conditions, analytical results and compositions compiled from the GEOROC database are available at https://doi.org/10.6084/m9.figshare.c.7168147

Neoarchean granitoid magmatism and geodynamic process in the northeastern North China craton

Abstract The composition of Archean granitoid rocks changed from predominantly tonalite-trondhjemite-granodiorite (TTG) gneisses in the early Archean (4–3 Ga) to diversified granitoid rock assemblages in the late Archean (3.0–2.5 Ga), marking a crucial transformation in the geodynamic processes of early Earth. However, the reason for this major transition remains enigmatic because the petrogenetic features of different granitoid assemblages and their crust-mantle interactions during different periods are poorly understood. We use variations in the spatial-temporal distribution, lithological association, chemical composition, and petrogenesis of Neoarchean (2.7–2.5 Ga) granitoids and inferred correlative crust-mantle interactions in the Eastern Liaoning Range (ELR) of the northeastern North China craton to explore this geodynamic transition. The early Neoarchean (ca. 2.7 Ga) ELR granitoids were dominated by TTG gneisses, and the late Neoarchean (2.6–2.5 Ga) ELR granitoid typology and compositions became more complex, changing into TTGs and more K2O-rich granitoid rocks. The TTGs can be subdivided into a high-Ca group and a low-Ca group: The 2.71–2.68 Ga high-Ca group TTG magma originated from partial melting of subducted juvenile oceanic crust, and the low-Ca group TTG magma was derived from fractionation crystallization of the high-Ca group TTG magma. The chemical composition of the magmatic sources played a dominant role on the 2.60–2.50 Ga TTG magmatism: the high-Ca and low-Ca group TTG magmas came from low-K mafic rocks and tonalites, respectively. The 2.58–2.49 Ga K2O-rich granitoids can be divided into three petrogenetic series: (1) The high-Ca-Mg group K2O-rich granitoid magma originated from partial melting of high-K mafic rocks, (2) the low-Ca-Mg group K2O-rich granitoid magma was derived from partial melting of sedimentary rocks, and (3) the transition group K2O-rich granitoid magma was sourced from metagreywackes. The 2.71–2.68 Ga TTGs were generated in an island arc belt, and subducted slab melting and subsequent magmatic differentiation were the dominant mechanisms of the TTG magmatism. The 2.60–2.50 Ga diversified granitoids were formed in the oceanic-continental subduction process under the active continental margin; the complicated oceanic slab subduction and arc-arc and arc-continent collisions contributed to the diversity of late Neoarchean granitoid magmatism.

Genesis of the Devonian Habaqin ultramafic arc complex and associated low-grade Fe–Ti oxide mineralization in the northern North China Craton

In the northern North China Craton (NCC), abundant non-layered ultramafic complexes and associated low-grade Fe–Ti oxide ores (over 1000 million tons) were uncovered. However, their petrogenesis and metallogeny have remained unclear. The Habaqin complex is one of the larger intrusions of the region and hosts the largest low-grade magnetite occurrence. Here we present petrography, zircon U–Pb geochronology, mineral and whole-rock major and trace element compositions, and whole-rock Sr–Nd and zircon Lu–Hf isotopes of the complex to constrain its genesis. The complex includes early pyroxenite (∼75% clinopyroxene, ∼15% amphibole, ∼10% magnetite) and late hornblendite (∼80% amphibole, 15–20% magnetite, 0–5% apatite). Zircon grains from the hornblendite yielded a weighted mean 206Pb/238U age of 395 ± 2 Ma. The increasing whole-rock FeOtot and TiO2 contents from pyroxenite (FeOtot = 18.9 wt%, TiO2 = 1.31 wt%) to hornblendite (FeOtot = 19.1–30.4 wt%, TiO2 = 2.63–3.12 wt%) correlate with higher modal proportions of amphibole and magnetite. The pyroxenite and hornblendite display similar arc-like trace element characteristics of enrichment in LILEs and LREEs, and depletion in HFSEs. The complex formed by fractional crystallization of clinopyroxene, amphibole, magnetite, and apatite from a hydrous parent magma. Early removal of clinopyroxene caused H2O enrichment in evolved residual magmas and crystallization of magnetite and amphibole, forming low-grade mineralization with Ti-V-poor magnetite in hornblendite. The complex displays high initial 87Sr/86Sr ratios of 0.706413–0.707341, negative εNd(t) values of −16.0 to −14.2 and negative εHf(t) value of −30.6 to −12.0, suggesting a parent magma derived from an enriched lithospheric mantle, with possible existence of amphibole-bearing pyroxenite veins within the source. During the Early Devonian, the retreat of the subducted Paleo-Asian oceanic slab as well as arc-continental collision along the northern NCC induced partial melting of the veins and eventually formation of the complex.

Initial oceanic subduction triggered by arc–continent collision: An example from the convergence between the Paleo-Asian Ocean and the North China Craton

The driving mechanisms for initial oceanic subduction beneath a passive continental margin remain unclear. The Paleozoic convergence history between the North China Craton (NCC) and the Paleo-Asian Ocean provides an ideal opportunity to investigate the driving mechanisms of the onset of oceanic subduction. Our detrital zircon U–Pb dating results yield Middle Devonian to Permian ages (391–273 Ma) in Paleozoic strata within China's Aoji region, specifically in the Bainaimiao arc belt situated between the NCC and Central Asian Orogenic Belt (CAOB). Detrital zircon age spectra, εHf(t) values, and two-stage model ages of the Devonian to Permian sediments suggest zircon contributions from both the NCC and CAOB. Combined with data from various regions along the Bainaimiao arc belt, findings suggest that the Bainaimiao island arc was accreted to the northern margin of the NCC through arc–continent collision during the late Silurian, rendering the NCC margin passive until the end-Devonian. At this point, southward subduction in the Paleo-Asian Ocean beneath the NCC commenced and continued into the Permian, transforming the northern margin of the NCC from passive to active. This initial subduction (ca. 359 Ma) in the Paleo-Asian Ocean resulted from collision-induced magmatism and deformation due to the protracted convergence and also led to a reversal in subduction polarity. Subsequently, in response to Paleo-Asian Ocean subduction, the northern margin of the NCC underwent rapid uplift during the Carboniferous, which led to widespread exposure of the NCC basement rocks in the late Carboniferous.

The role of intra-oceanic arc in the growth of continental crust: Evidence from the Early Paleozoic Bainaimiao arc

The Early Palaeozoic arc-related formations in the northern margin of the North China Craton (NCC) belonging to the Bainaimiao arc belt is an important part of the eastern Central Asian Orogenic Belt (CAOB). The tectonic evolution of this belt remains controversial. Here we present detailed data on the geochronology and geochemistry on a newly identified Early Palaeozoic igneous suite from the Faku area in northern Liaoning. Zircon U–Pb dating of the Faku volcanic and intrusive rocks yielded weighted mean 206Pb/238U ages of ca. 458 Ma and 433–405 Ma, respectively, which represent their crystallization (eruption) times. Zircon Hf isotopic analyses show a low negative to positive εHf (t) values of − 0.33 to + 12.4, implying depleted characteristics of the source. The geochemical features of Laolingshan basaltic andesites display higher TiO2 and lower P2O5 contents, similar to that of mid-ocean ridge basalts, and relatively high Zr/Y and low Ta/Yb ratios, suggesting oceanic island arc basalt affinity. Therefore, we suggest that the Laolingshan basaltic andesites were formed in an intra-oceanic environment. The Bachagou granodiorites, with adakitic geochemical signatures, belong to the calc-alkaline and high-K calc-alkaline series, implying formation in an active continental margin tectonic setting. The Baerhushan granodiorites, which geochemically belong to S-type granites, were probably formed in a syn-collisional environment influenced by arc–continent collision. The Donggou granitoids, which have higher SiO2 and alkali and lower MgO and P2O5, show A-type granite features. Geochemical characteristics of the Donggou A-type granite suggest formation in an extensional setting caused by orogenic intermittent extension. The Baerhushan gabbro diorites, which display properties of both mid-ocean ridge and continental rift basalts, were produced under post-orogenic extensional tectonic setting after the arc–continent collision. Our study traces the Early Palaeozoic tectonic evolution of the south-eastern segment of the CAOB and the related accretionary tectonics.

Subduction polarity reversal facilitated by plate coupling during arc-continent collision: Evidence from the Western Kunlun orogenic belt, northwest Tibetan Plateau

Abstract Subduction polarity reversal usually involves the break off or tearing of the downgoing plate (DP) along the continent-ocean transition zone, in order to initiate subduction of the overriding plate (OP) with opposite polarity. We propose that subduction polarity reversal can also be caused by DP-OP coupling and can account for the early Paleozoic geological relationships in the Western Kunlun orogenic belt in the northwestern Tibetan Plateau. Our synthesis of elemental and isotopic data reveals transient (~2 m.y.) changes in the sources of early Paleozoic arc magmatism in the southern Kunlun terrane. The early-stage (ca. 530–487 Ma) magmatic rocks display relatively high εNd(t) (+0.3 to +8.7), εHf(t) (−3.6 to +16.0), and intra-oceanic arc-like features. In contrast, the late-stage (485–430 Ma) magmatic rocks have predominantly negative εNd(t) (−4.5 to +0.3), εHf(t) (−8.8 to +0.9), and higher incompatible trace elements (e.g., Th), similar to the sub-continental lithospheric mantle beneath the Tarim craton. This abrupt temporal-spatial variation of arc magmatism, together with the detrital zircon evidence, indicate that subduction polarity reversal of the Proto-Tethys Ocean occurred in a period of ~10 m.y., consistent with the time interval reflected by ophiolite age. This rapid polarity reversal corresponds with the absence of ultrahigh-pressure (UHP) metamorphic and post-collisional magmatic rocks, features normally characteristic of slab break-off or tearing. Numerical modeling shows that this polarity reversal was caused by plate coupling during arc-continent collision. This coupling modified the normal succession of arc-continent collision events, preventing slab break-off or tearing-induced buoyant rock rebound and asthenosphere upwelling. Our model successfully explains early Paleozoic orogenesis in the Western Kunlun orogenic belt and may be applied elsewhere where post-collisional magmatic and UHP rocks are absent.

Crustal thickness variation of the Dabie orogenic belt: Insights from detrital zircon evidence and geological significance

The Dabie orogenic belt is characterized by widely distributed Mesozoic ultrahigh-pressure metamorphic rocks. Together with the Qinling orogenic belt, it constitutes one of the most important collisional orogens in eastern Asia. Because of intense continental subduction and collision during the Mesozoic and subsequent denudation, it remains controversial whether pre-Mesozoic convergent events happened in the region of the Dabie orogenic belt. In this study, we reconstruct the crustal thickness variation of the Dabie orogenic belt based on detrital zircon data. Results reveal three stages of crustal thickening at ca. 900-800 Ma, ca. 530-400 Ma, and ca. 250-210 Ma that are likely associated with three major convergent events that happened between the North and South China Blocks since the Neoproterozoic. The first thickening stage is possibly related to long-term subduction-accretion-collision processes along the northern margin of the South China Block. The second one corresponds to early Paleozoic ocean closure and the arc-continent collision that happened between the North and South China Blocks. The third one is a most significant thickening that represents the final collision between the North and South China Blocks during the Mesozoic. The turning point (ca. 210 Ma) of the crustal thickness curve represents the cessation of ultradeep subduction and constrains the completion of Mesozoic continental collision. Late Archean crustal thinning may be related to the onset of plate tectonics. Overall, the fluctuations of crustal thickness and detrital zircon age populations from sediments of the Dabie orogenic belt suggest interaction among Chinese continental blocks is consistent with the evolution of global supercontinent cycles.