Paleo-Asian Ocean Research Articles

Final subduction-closure process of the Paleo-Asian Ocean in the middle segments of the southern Central Asian Orogenic Belt: Constraints from Permian volcanic rocks and late Triassic mafic dike swarms

The final subduction-closure process of the Paleo-Asian Ocean (PAO) in the middle segments of the southern Central Asian Orogenic Belt (CAOB) is widely debated. Linear arc-related pyroclastic sedimentary rocks and subsequent mafic-alkaline intrusive rocks parallel to the orogenic belt provide valuable constraints on ocean closure. Linearly distributed volcanic samples from the northern margin of the Alxa Block have zircon UPb ages ranging from 272 to 271 Ma, displaying arc geochemical signatures and large ranges of variation (−14.4 to +6.4) of zircon Hf isotopic composition. The Honggueryulin mafic dikes in the Nuoergong–Langshan Belt (NLB) with zircon and apatite UPb dating of 232–231 Ma show a clear geochemical imprint of subduction components with enrichment of light rare earth elements and large-ion lithophile elements (e.g., K, Rb, and Ba) and depletion of high-field-strength elements (e.g., Nb, Ta). The whole-rock major and trace elements and Sr–Nd–Hf isotopic compositions suggest that the Late Triassic mafic dikes mainly originated from a lithospheric mantle that had been metasomatized by subduction-related fluids. Coupled with published data, our geochronological and geochemical data support an east–west-trending Late Triassic alkaline–mafic intrusive rock belt distributed along the northern margin of the Alxa Block–North China Craton, which was formed in a post-orogenic intraplate extensional setting. These pyroclastic sediments and mafic dikes in the NLB document the tectonic transition from the Permian subduction to the Late Triassic post-orogenic extension. Therefore, the final closure of the PAO in the middle segments of the southern CAOB is constrained to between the Early and Middle Triassic.

Neoproterozoic basin evolution of the northern Tarim craton from back-arc rift to passive continental margin: Implications for the opening of the South Tianshan Ocean

The Neoproterozoic strata in the northern Tarim craton holds valuable tectono-sedimentary insights regarding the opening time and mechanisms of the South Tianshan Ocean, as well as the tectonic reconstruction of the Tarim craton during the breakup of Rodinia. However, debates remain around the Cryogenian–Ediacaran proto-basin type and evolution, as well as the lack of regional geological correlation at a basin scale. In this study, we employed seismic, drilling and outcrop data to conduct a combined tectono-stratigraphic and sedimentary filling analysis of the Cryogenian–Ediacaran strata in the northern Tarim craton, aiming to decipher the Neoproterozoic basin evolution. Our findings show that the deposition of the Cryogenian strata was controlled by normal faults, representing a rift basin receiving sedimentary materials from both the northern Tarim craton and the Central Tianshan block. In contrast, the Ediacaran developed as a depression basin featured by a wedge-shaped deposition with frequent sea-level fluctuations and simple detrital input from the northern Tarim craton, indicative of a passive margin basin. Such a Neoproterozoic basin evolution of the northern Tarim craton, from the Cryogenian rift to the Ediacaran passive margin, likely resulted from a back-arc extension due to the separation of the Central Tianshan arc from the Tarim craton. These results provide new constraints on the initial opening time of the South Tianshan Ocean at ca. 633 Ma and reveal the Neoproterozoic tectonic affinity of the Central Tianshan block and the northern Tarim craton. Our work also implies that the Tarim craton was located on the periphery of Rodinia, and the South Tianshan Ocean may not be a primary ocean basin of the Paleo-Asian Ocean.

Geochemical evidence for terrigenous sediment recycling in the Late Permian subcontinental lithospheric mantle of the northern North China Craton

Understanding the recycling process of subducted slab in subduction zones is vital to deciphering the heterogeneity of cratonic mantle and the variable compositions of continental arc igneous rocks. This study presents a comprehensive analysis of zircon U-Pb ages, Hf-O isotopes, hornblende major elements, whole-rock major and trace elements, as well as Sr-Nd-Hf isotopes of mafic igneous rocks from the northern North China Craton. These data constrain metasomatic processes in the cratonic mantle. The Late Permian mafic igneous rocks (ca. 254−252 Ma) studied are characterized by arc-like trace element signatures and enriched whole-rock Sr-Nd-Hf isotopes, with (87Sr/86Sr)i ratios of 0.7063−0.7076, εNd(t) values of −18.0 to −9.3, and εHf(t) values of −29.7 to +0.5. In addition, they also have elevated zircon δ18O values of 5.9‰−7.0‰, and variable zircon εHf(t) values of −19.4 to +6.0. These features suggest the rocks were derived from an enriched mantle with the involvement of terrigenous sediments. We propose that the subcontinental lithospheric mantle of the northern North China Craton was mainly metasomatized by terrigenous sediment-derived hydrous melt during the southward subduction of the Paleo-Asian Ocean. Moreover, partial melting of the metasomatic mantle may be triggered by the slab rollback related to the closure of the Paleo-Asian Ocean in the Late Permian, which resulted in the formation of the mafic igneous rocks studied. Thus, the Late Permian igneous rocks studied provide petrological and geochemical evidence of the crust-mantle interaction during the subduction of the Paleo-Asian Ocean.

How does a soft collision orogen uplift and collapse? Insight from the eastern Central Asian Orogenic Belt

The mechanism of uplift and collapse is critical for understanding orogenic evolution within the Wilson cycle. The Central Asian Orogenic Belt (CAOB) represents one of the largest Phanerozoic accretionary orogens on Earth, experiencing terminal soft collision following the closure of the Paleo-Asian Ocean. However, the timing and mechanism of crustal thickening and thinning in the eastern CAOB remain unclear. Here, we present geochronological, mineralogical, geochemical, and Sr-Nd-Hf isotopic data of the newly identified Late Triassic bimodal dike associations in the easternmost CAOB. The ca. 236−230 Ma mafic dikes can be divided into two groups based on petrographic and geochemical characteristics. Major element modeling using the MELTS software indicates that they evolved via independent differentiation paths. Trace element and isotope simulations reveal that the ca. 236−230 Ma mafic dikes originated from the 4%−10% partial melting of spinel- to garnet-lherzolite lithospheric mantle sources over a range of depths, with varying inputs of asthenospheric mantle materials. Coeval ca. 233 Ma felsic dikes exhibit adakitic geochemical characteristics and strong imprints of crust-mantle interaction, suggesting derivation from melting of a heated juvenile mafic lower crust as a result of the upwelling of asthenospheric mantle. The formation of bimodal dike associations records the transition from lithospheric mantle thinning to delamination. Integrating a large dataset and employing multiple geochemical proxies, our results reveal that the crust of the easternmost CAOB reached a thickness of 54 ± 3 km at ca. 280−255 Ma, likely resulting from magmatic underplating due to rollback of the subducting Paleo-Asian Oceanic slab. This region underwent a further slight increase in crustal thickness to 61 ± 2 km at ca. 254−237 Ma in response to limited tectonic shortening associated with soft collision orogeny before it thinned to 45 ± 13 km at ca. 236−210 Ma due to lithospheric delamination during post-collisional extension. Our findings reveal that the uplift of the eastern CAOB was primarily driven by magmatic underplating, with minimal contribution from tectonic shortening. Lithospheric delamination emerged as an important factor leading to the eventual collapse of the eastern CAOB. Compared to typical hard collisional orogens (e.g., the Himalaya-Tibet orogen), the CAOB experienced significantly weaker tectonic shortening followed by similar lithospheric delamination during post-collisional extension. This study highlights the importance of integrating geochemical and isotopic data in quantifying the complex evolutionary histories of ancient collisional orogenic belts.

Where and when the Paleo-Asian Ocean was closed: new evidence from the Tuquan ophiolite

The Solonker suture marks the location of the final collision in southeastern Central Asian Orogenic Belt (CAOB). However, it is observed that the suture is obscured at the western margin of the Songliao Basin. Fortunately, the recently discovered Tuquan ophiolite is one of the important fragments within the Solonker suture. Testings of samples from the Tuquan ophiolite yielded LA-ICP-MS zircon U–Pb chronological data with weighted mean of 206 Pb/ 238 U ages from 265 ± 5 Ma to 279 ± 6 Ma which were interpreted to represent the formation age of the Tuquan ophiolite from the late Cisuralian to Guadalupian. The geochemical characteristics of the Tuquan ophiolite is related to supra-subduction zone features. We suggest that it represents an important bidirectional subduction event involving the oceanic crust of the Paleo-Asian Ocean beneath the Mongolia Block and the North China Craton during the early to late Permian. Integrating these findings with previous research indicates that the final subduction of the Paleo-Asian Ocean persisted until at least the late Permian. Our study provides further insights, indicating that the discovery of the Tuquan ophiolite could be regarded as the eastern extension of the Solonker suture. This finding will provide new constraints on the evolution of the southeastern CAOB.

Continental crustal growth in the post-collisional setting: Insights from the Late Triassic high-Mg andesites in the eastern Central Asian Orogenic Belt

The Central Asian Orogenic Belt represents the most important site of crustal growth in the Phanerozoic. However, the intricate evolution of multi-ocean regimes has given rise to uncertainties surrounding the processes of Mesozoic tectonic evolution and the dynamics of crustal growth. In this study, we conducted detailed geochronological and geochemical analyses of andesites collected from the eastern Central Asian Orogenic Belt. Zircon U-Pb dating results show that these andesites formed during the Late Triassic (ca. 235 Ma), and the Ti-in-zircon thermometer reveals high magma temperatures (>1100 °C) during their genesis. The elevated Mg# values at moderate SiO2 content of these Late Triassic andesites indicate an affinity with high-Mg andesites (HMAs). Notably, the andesites exhibit relatively low K2O/Na2O ratios, high Sr/Y ratios, significant depletion of Nb and Ta, and trace element patterns resembling typical HMAs from the western Aleutian Islands. These characteristics suggest that they likely originated from the partial melting of subducted eclogite. Furthermore, the HMAs display relatively high zircon εHf(t) values and depleted whole-rock Sr-Nd isotopic compositions, which is indicative of a depleted mantle source. Therefore, we propose that these andesites were generated through the interaction of the subducting slab−derived melts and overlying mantle wedge. Considering that the final closure of the Paleo-Asian Ocean took place before the Late Triassic, these andesites probably erupted in a post-collisional setting. The formation of these HMAs could be best explained by the upwelling asthenosphere triggered by the break-off of the oceanic slab, which also contributed to continental crustal growth in Northeast China.

Tectonic evolution of the early permian Junggar basin: Insights into a foreland basin shaped by lithospheric folding

Foreland basins are shaped by the sedimentary architecture and lithospheric flexure due to the sediment load, slab pull, orogenic growth, and asthenospheric mantle flow. However, it is challenging to differentiate foreland basins from rift basins due to the destructive effects of multiphase orogenesis. Situated at the core of the western Central Asian Orogen Belt, the Junggar Basin holds vital clues regarding the closure of the Paleo-Asian Ocean. There is debate regarding whether it was a compressional foreland basin or an extended rift after the closure of the surrounding oceans. Furthermore, uncertainties persist regarding the fate of the residual oceanic crust and the precise tectonic processes during the collision of the ocean-arc-continent system. Understanding the basin's style during the early Permian period is crucial for deciphering its dynamic tectonic history. This study leverages regional seismic data to reevaluate the overall structure of the Junggar Basin, providing insights into its tectonic context and the mechanisms of intraplate deformation during the early Permian period. The findings reveal significant early Permian deformation features characterized by varying strata thicknesses and unconformities, signifying continuous tectonic activity during deposition. The western and southern depressions that developed from the late Carboniferous to early Permian are in keeping with compressional dynamics and reflect a foredeep basin, while the central uplift corresponds to a forebulge. This study posits that the observed foreland basin system was shaped by lithospheric flexure at the end of the late Carboniferous and lithospheric buckling in the early Permian, which contributed to the creation of uplifted Mosuowan-Baijiahai forebulge in the interior. The Junggar Basin featured a convergent dynamic environment, although the surrounding orogen transitioned into a postcollisional orogen in the Central Asian Orogenic Belt during the early Permian.

An Early Permian transpressional continental arc and arc-arc collision recorded in the Baidunzi Complex, southern Central Asian orogenic belt, NW China

Our multidisciplinary study of the southern Beishan orogen in NW China, situated between the Tienshan and Solonker suture zones, sheds light on the closure of the Paleo-Asian Ocean and termination of orogeneses in the Central Asian Orogenic Belt. We identify the Baidunzi Complex, an exotic Permian transpressional continental arc terrane, characterized by sheared and isoclinally folded metasedimentary and syn-kinematic plutonic rocks transformed into upper greenschist to amphibolite tectonites. The complex comprises basement rocks of thick-bedded orthoquartzite and orthogneiss, the Carboniferous to Permian meta-sedimentary strata including volcaniclastic sedimentary rocks, marble, and marl interlayered psammite, and the Baidunzi Intrusive Suite featuring 294–289 Ma hornblende diorite, tonalite, granodiorite, and granite. The Late intrusive rocks, including leuco-granite to trondhjemite sills and a stitching gabbro unit, suggest an amalgamation age of 281–280 Ma between the Baidunzi and Ganquan arcs. The spatial and temporal linkage between the Baidunzi continental arc and the Liuyuan backarc-Ganquan arc suggests they were either built on a coeval doubly vergent subduction system or from the same north-vergent subduction system and structurally juxtaposed by sinistral convergence. Geochronological and Hf isotope evidence, along with continental rock affinity, indicates a close association between the Baidunzi Complex and the northern margin of the Tarim Craton during the Gondwana breakup and Pangea assembly.

Late Paleozoic slab rollback events in the southeastern part of the Central Asian orogenic belt: Implications for Paleo-Asian Ocean subduction and continental crust growth

The Central Asian orogenic belt is considered to be the largest Phanerozoic accretive orogenic belt on Earth. The late Paleozoic magmatic rocks in central Inner Mongolia are crucial for understanding continental crust growth and the tectonic evolution of the southeastern part of the Central Asian orogenic belt. We present comprehensive geochemical, isotopic, and geochronological data from three late Paleozoic magmatic units in the Mandula area, west of the Solonker suture zone. Zircon U-Pb dating indicates that these rocks formed during the late Carboniferous (316−304 Ma). The Mandula high-Mg diorites exhibit high MgO (3.9−6.5 wt%), high Mg# (61−69), and depleted Nd-Hf isotopic compositions, generated through interaction between a metasomatized mantle and slab melts with the overlying sediments. The Mandula granodiorites display adakite geochemical characteristics with high Sr/Y mass ratios (29−52), high MgO (1.7−2.2 wt%), and high Mg# (52−54), formed by partial melting of the oceanic slab with the addition of overlying sediment. Mafic microgranular enclaves have consistent ages, Sr-Nd-Hf isotope compositions, and hornblende crystallization temperature-pressure conditions with their host granodiorite, formed from a cognate magma associated with the host granodiorites through cumulate. We propose that two phases of slab rollback took place during the late Paleozoic southward subduction-accretion of the Paleo-Asian Ocean. The first phase corresponded to the transformation of low- to medium-angle slab subduction, while the second phase led to subduction-related extension. Considering the tectonic-magmatic evolution, crustal maturity, and thickness variations in the late Paleozoic southeastern part of the Central Asian orogenic belt, we propose that prolonged subduction and slab rollback promoted continental crust growth. The Central Asian orogenic belt coincides temporally and spatially with the Phanerozoic Pangea cycle, suggesting that continuous subduction and supercontinent amalgamation significantly contributed to continental crust growth.

Formation of the Lianhuashan Cu deposit in the southern Great Xing’an Range, NE China: Constraints from fluid inclusions, whole-rock geochemistry, zircon U–Pb geochronology, and H–O–S–Pb isotopes

The medium-sized Lianhuashan Cu sulfide deposit is located in the southern Xing’an Range of Inner Mongolia, NE China. The zoned massive sulfide vein ores are hosted mainly in the Permian Dashizhai Formation, and the ore veins are controlled by NW–NNW-trending structures. The ore-forming process comprises four stages: arsenopyrite–quartz (I); chalcopyrite–pyrite–quartz (II); pyrite–chalcopyrite–sphalerite–galena–quartz (III); and ore-barren sulfide–quartz–carbonate (IV). Three types of fluid inclusions (FIs), namely vapor-rich two-phase (LV-type), liquid-rich two-phase (VL-type), and daughter mineral-bearing three-phase (SL-type), are distinguished. Stage I, II and III contain all types of FIs (LV-, VL-, and SL-type), with homogenization temperatures (Th) of 268–462°C, 230–382°C and 180–340°C and salinities of 3.4–52.3, 3.4–44.5 and 3.7–39.9 wt% NaCl eqv., respectively, whereas stage IV has only VL-type FIs, with Th = 152–232°C and salinity = 3.4–7.9 wt%. Fluid geochemical data show that the Lianhuashan ore fluids were of medium–high temperature (236–382 °C), high-salinity (31.5–44.5 wt%), and relatively oxidizing conditions, typical of a NaCl-H2O system. The microthermometric and H–O isotope data (δ18OH2O = − 9.0 to 6.1 ‰; δD = − 149.0 to − 99.0 ‰) indicate that the ore fluids were initially magmatic with later meteoric water incursion. The sulfide S (δ34S = − 2.9–3.8 ‰) and Pb (206Pb/204Pb = 17.954 − 18.492, 207Pb/204Pb = 15.427 − 15.739, 208Pb/ 204Pb = 37.815 − 38.357) isotopes support that the metals were magmatic-derived. Fluid boiling, cooling, and meteoric water mixing were likely the main ore precipitation mechanism at Lianhuashan.We suggest that Cu minerals at Lianhuashan were precipitated with boiling at ∼ 1km depth. For the ore-forming granodiorite porphyry (zircon U-Pb age: 252.8 ± 1.8 Ma), geochemical data indicate that the primary magma was formed by partial melting of the thickened or delaminated lower crust. Integrating the available age, geological, and geochemical evidence, we suggest that mineralization at Lianhuashan is spatial–temporal and genetically associated with the granodiorite porphyry, and was formed in a volcanic arc setting after the Paleo-Asian Ocean closure.

Subduction retreat recorded in the southern Beishan orogenic collage of the Central Asian Orogenic Belt: New evidence from deep seismic reflection profiling

The crustal and upper mantle structure of the Beishan orogenic collage, which serves as the southern part of the middle Central Asian Orogenic Belt, provides crucial insights into the history of the multiple openings and closings of the Paleo-Asian Ocean during the Paleozoic. There is considerable dispute over the eventual closure position, timing, and subduction polarity of the Paleo-Asian Ocean, particularly in the southern Beishan orogenic collage. The main cause of these controversies is the lack of a high-resolution lithospheric structure in this area. In this study, we first present a 140-km-long, high-resolution seismic reflection profile taken across the northern Dunhuang Block and the southern Beishan orogenic collage. The seismic imaging provides new constraints on the structure of the lower crust, the Moho, and the upper mantle beneath the southernmost Central Asian Orogenic Belt. A subhorizontal reflector in the middle crust, two sets of north-dipping reflectors from the lower crust to the upper mantle, and several south-dipping reflectors in the upper crust in the northern part of the profile were imaged. Based on our study and other geological, chronological, and geophysical data, we propose that the two sequences of north-dipping reflectors from the lower crust to the upper mantle represent two stages of north-dipping subduction of the southern branch of the Paleo-Asian Ocean. The first stage in the southern Beishan orogenic collage is Late Silurian−Early Devonian, and the second stage is late Carboniferous−Early Permian. The two-stage subduction process gave rise to the Huaniushan arc and the subsequent Shibanshan arc, respectively. These findings provide new constraints on the controversial subduction polarity and the multistage amalgamation of the microcontinental blocks and arcs in the southern Central Asian Orogenic Belt.

Late Paleozoic tectonic switching and metallogenic evolution of the southern Yili arc terrane, NW China

Recognition of tectonic switching is of great significance for understanding the formation and evolution of ancient accretionary orogenic belts and can provide insights into metallogenic evolution. The western Tianshan orogenic belt, which lies within the southern Central Asian Orogenic Belt (CAOB), experienced a prolonged tectono-magmatic evolution during the late Paleozoic in response to evolution of the Paleo-Asian Ocean. The aim of this contribution is to constrain the subduction process and timing of tectonic switching from subduction to collision in southern parts of the western Tianshan. To address this, we present the results of an integrated investigation of whole-rock major and trace element and Sr-Nd-Hf isotope data, together with zircon U-Pb ages for late Paleozoic volcanic rocks from the southern Yili arc terrane of the southern western Tianshan. Based on the temporal-spatial distribution of different compositions of volcanic rocks, three distinct episodes of magmatism have been recognized, including: 1) ∼ 380 – ∼340 Ma, this episode of magmatism has high Ce/Y ratios of basalts and Ho/Yb ratios of felsic rocks, and show large variations in εHf(t) (−9.6 to + 15.6) and εNd(t) (−5.2 to + 5.4) values, which is interpreted to be originated from a mantle source with variable input of slab-derived components incorporated in a trench advance setting; 2) ∼ 340 – ∼320 Ma, this episode of magmatism shows low Ce/Y ratios of basalts and Ho/Yb ratios of felsic rocks, and relatively higher εHf(t) (−3.8 to + 14.6) and εNd(t) (−1.5 to + 5) values, reflecting crust-mantle interactions and likely formation in a back-arc basin environment; 3) ∼ 320 – ∼300 Ma, this episode of magmatism has Ce/Y ratios of basalts and Ho/Yb ratios of felsic rocks, and mostly positive εHf(t) (−1.1 to + 14.5) and εNd(t) (+1.6 to + 8.4) values, suggesting continent–continent collision between the northern Tarim Craton and the southern limb of the Kazakhstan composite continent (i.e., Yili and Chinese Central Tianshan Block). Consistently, the two tectonic switching events (ca. 340 Ma and ca. 320 Ma) were temporally associated with skarn Zn-Pb and orogenic Au mineralization in southern Yili arc terrane, respectively. This study presents an example of multiple tectonic switching and metallogenic evolution in hot accretionary orogens.

Paleozoic-Mesozoic multistage tectonic evolution of the North Qilian Shan revealed by detrital zircon U-Pb and fission-track double dating

Knowledge of the tectonic history of the North Qilian Shan contributes to our understanding of the formation of the Tibetan Plateau. However, when the North Qilian Shan were formed has been controversial. We report new detrital zircon U-Pb (n = 899) and double dating fission track and U-Pb (n = 450) results from nine samples of Lower Cretaceous and Oligocene sandstone units, integrating with published geochronology and thermochronology data in order to reconstruct the evolution history of the North Qilian Shan. Nine samples from this unit show detrital zircon fission track age populations that center at: 636–603, 495, 406–331, 290–266, 247–224, 193–151, and 144–102 Ma. These fission track data are older than their corresponding depositional ages, suggesting that the fission track ages are unreset and record magmatic-related cooling or exhumation stages of the North Qilian Shan since the Late Neoproterozoic. Deconvolved fission track peak ages document major cooling events associated with the opening of the North Qilian Ocean at 636–603 Ma. Late Cambrian peak age (495 Ma) is attributed to the early phase of the subduction of the North Qilian Ocean. The Devonian period exhibited a cooling phase between 406 and 381 Ma, corresponding to the collision event between the Qaidam terrane, Central Qilian Shan, and Alxa Block. The peak age of 331 Ma signifies the cooling event associated with the subduction of the Paleo-Asian Ocean. The peak ages during the Early-Middle Permian period (290–266 Ma) provide evidence of significant exhumation events that occurred during the Late Paleozoic era. These events were linked to the subduction of the Paleo-Tethys Ocean to the south and the Paleo-Asian Ocean to the north. The Triassic peak ages (247–224 Ma) unveil exhumation signals in the North Qilian Shan region that were generated by the far-field effect of the collision between the Qiangtang and Kunlun terranes. During the Jurassic (193–151 Ma) and the Early Cretaceous periods (144–102 Ma), the exhumation of the North Qilian Shan region was a consequence of the subduction of the Neo-Tethys Ocean and the collision between the Lhasa and Qiangtang blocks, respectively. The peak ages of the Xinminpu Formation in the Early Cretaceous (123–121 Ma) are in close proximity to their depositional age (125–105 Ma), indicating that the North Qilian Shan underwent rapid exhumation during this period. The peak ages observed in the Oligocene Baiyanghe Formation (31–24 Ma) from 144 to 102 Ma, indicate that it has been influenced by the recycled sediments originating from the Cretaceous Xinminpu Formation. The North Qilian Shan gradually emerged during the late Paleozoic and Mesozoic eras, providing the foundation for its subsequent reactivation in the Cenozoic era. The multi-stage cooling or exhumation events of North Qilian Shan since Late Neoproterozoic reflect the complex formation process of the northeastern margin of Tibetan Plateau.

Collisional orogeny between the Siberian and Sino-Korean paleoplates: Evidence from geochronology and metamorphism of the metamorphic ophiolite mélange in the Banlashan area near the Xar Moron River in the southeastern Central Asian orogenic belt

As the largest Phanerozoic accretionary orogenic belt, whether the Central Asian Orogenic Belt (CAOB) experienced a strong collisional orogenic process after Paleo-Asian Ocean (PAO) closure remains controversial. The age and P-T conditions recorded by metamorphic rocks could be used to study the thermal and tectonic regimes during orogenic processes, providing constraints for orogenic evolution. In this paper, the geochronology and metamorphism of a newly discovered metamorphic ophiolite mélange in the Banlashan area near the Xar Moron River in the southeastern CAOB were studied. The association and age of the metamorphic ophiolite mélange protoliths are similar to those of the Xar Moron River ophiolite belt to the north. The metamorphic ages of different ophiolite mélange lithologies are all late Permian (250.2–256.5 Ma), indicating that the Siberian and Sino-Korean paleoplates collided during the late Permian. The metamorphic pressure and temperature recorded by the garnet amphibolite block in the ophiolite mélange could reach 8.5–8.8 kbar and 700–725 ℃. The core-to-rim zoning of garnet indicates that the garnet amphibolite underwent a clockwise P–T path, which is the typical metamorphic feature of collisional orogens. The ophiolite mélange metamorphic features, combined with regional magmatic, metamorphic, sedimentary and tectonic deformation data, indicate that a strong collisional orogeny occurred rather than a soft orogeny between the Siberian and Sino-Korean paleoplates after the PAO closure.

Tectonic evolution and source rocks development of the super oil-rich Bohai Bay Basin, East China

The Bohai Bay Basin, as a super oil-rich basin in the world, is characterized by cyclic evolution and complex regional tectonic stress field, and its lifecycle tectonic evolution controls the formation of regional source rocks. The main pre-Cenozoic stratigraphic system and lithological distribution are determined through geological mapping, and the dynamics of the pre-Cenozoic geotectonic evolution of the Bohai Bay Basin are investigated systematically using the newly acquired high-quality seismic data and the latest exploration results in the study area. The North China Craton where the Bohai Bay Basin is located in rests at the intersection of three tectonic domains: the Paleo-Asian Ocean, the Tethys Ocean, and the Pacific Ocean. It has experienced the alternation and superposition of tectonic cycles of different periods, directions and natures, and experienced five stages of the tectonic evolution and sedimentary building, i.e. Middle–Late Proterozoic continental rift trough, Early Paleozoic marginal-craton depression carbonate building, Late Paleozoic marine–continental transitional intracraton depression, Mesozoic intracontinental strike-slip–extensional tectonics, and Cenozoic intracontinental rifting. The cyclic evolution of the basin, especially the multi-stage compression, strike-slip and extensional tectonics processes in the Hercynian, Indosinian, Yanshan and Himalayan since the Late Paleozoic, controlled the development, reconstruction and preservation of several sets of high-quality source rocks, represented by the Late Paleozoic Carboniferous–Permian coal-measure source rocks and the Paleogene world-class extra-high-quality lacustrine source rocks, which provided an important guarantee for the hydrocarbon accumulation in the super oil-rich basin.

Sedimentary provenance supports a mid-paleozoic tectonic connection between the Junggar and Altai terranes in central Asia

The provenance of Precambrian detritus in the Junggar and Altai terranes provides crucial constraints on the peri-Siberian accretionary tectonic evolution in the middle Paleozoic. The Precambrian detrital zircons have no coeval magmatic equivalents in the Junggar terrane but show U–Pb age spectra and εHf(t) values comparable to those in the Altai terrane. The correlations suggest that the old detrital materials in the Junggar and Altai terranes were most likely derived from the Siberia craton and adjacent Tuva-Mongolian microcontinent. Paleozoic zircons in the Junggar terrane display a εHf(t) pattern from large spread to dominantly positive values at ca. 420–410 Ma. Such an abrupt change points to an accretionary tectonic transition from an advancing to retreating mode during mid-Paleozoic time, synchronous with similar tectonic switch occurring in the Altai terrane. Taking into account the temporal and spatial relations in sedimentation, tectonism and arc magmatism, we propose that the Junggar terrane had once collided onto the peri-Siberian Altai terrane to receive abundant old detritus from the Siberian continent in the Silurian–early Devonian. They were subsequently separated at ca. 420–410 Ma, possibly due to the slab rollback of the subducting Paleo-Asian Ocean (PAO) plate. These results constrain an Early Paleozoic tectono-paleogeographic boundary of the CAOB along the North Tianshan–Solonker suture zone, and also imply a long-lived PAO subduction was responsible for the Neoproterozoic to Paleozoic accretionary orogenesis at the margins of southern Siberia, eastern Kazakhstan, and northern Gondwana.

How long did the Paleo-Asian Ocean take from initial subduction to slab rollback?: Revelation of early Paleozoic magmatism in the eastern Boshchekul-Chingiz arc

How long did the Paleo-Asian Ocean take from initial subduction to slab rollback?: Revelation of early Paleozoic magmatism in the eastern Boshchekul-Chingiz arc

Spatiotemporal evolution of the early Permian multi-source-to-sink system in the northwestern margin of the North China Block: Implications for the paleogeographic reconstruction along the southern margin of the Paleo-Asian Ocean

The northwestern margin of the North China Block, situated at the intersection of multiple tectonic units, presents a complex geological setting that challenges paleogeographic reconstructions. The subduction and closure of the Paleo-Asian Ocean have further complicated the understanding of sediment provenance during the Early Permian. In this study, we integrated sedimentological, geochemical, and UPb dating methods to delineate the Early Permian source-to-sink systems along the northwestern margin of the North China Block. The identification of four key source-to-sink systems—the Alxa, Langshan, Serteng–Wula, and Jining–Daqing—reveals a pronounced east–west provenance differentiation, indicative of the regional tectonic and sedimentary responses to subduction of the Paleo-Asian Ocean.During the Shanxi Formation deposition, the western regions were dominated by the Inner Mongolian continental island arc as a principal sediment source, fostering distal meandering river deltas. Conversely, the eastern regions were predominantly influenced by the North China Block basement, leading to the deposition of proximal, shallow meandering river deltas. As the Shihezi Formation deposition ensued, the western source-to-sink systems continued to receive sediments from the uplifted Inner Mongolian Arc, transitioning to distal braided river deltas amidst an orogenic setting. Meanwhile, the eastern systems, particularly Jining–Daqing, showed increased contributions from the North China Block basement, forming mixed-source, shallow braided river deltas.This research provides a refined understanding of the spatiotemporal evolution of source-to-sink systems and their responses to the tectonic setting, offering valuable insights into the paleogeographic evolution along the southern margin of the Paleo-Asian Ocean.

A Carboniferous to Permian tectono-paleogeographic reconstruction for the southernmost Central Asian Orogenic Belt

The Central Asian Orogenic Belt was formed by the subduction to closure of the Paleo-Asian Ocean (PAO). However, it is highly controversial about the closing time of the PAO, especially its middle segment in the northern Alxa orogenic belt (NAOB). In this study, the new and published zircon U–Pb and Hf data for the Carboniferous to Permian sediments across the NAOB have been integrated to reply the above problem. The depositional ages have been constrained as the Carboniferous to Permian by the detrital zircon ages, fossil assemblages and stratigraphic correlation. The Carboniferous sandstones are dominated by the Paleozoic zircons (mainly around 380–510 Ma) with a few Precambrian zircons. The late Cambrian to early Carboniferous zircons with positive to slightly negative εHf(t) values were probably sourced from the orogen itself. The early Paleozoic zircons with slightly to extremely negative εHf(t) values and the late Archean to Paleoproterozoic zircons were likely derived from the surrounding cratonic blocks in the south. For the Permian samples, the Carboniferous to Permian age signal is enhanced. The Permian zircons yield similar age peaks around 278–279 Ma and similar εHf(t) values, and thus shared a similar source. Thus, the Carboniferous to Permian sediments received detritus across the PAO, indicating the closure of the PAO. Subsequently, the NAOB entered into an extensional setting based on the detrital zircon age patterns, rift-related volcanic rocks and basin analysis. Finally, a tectono-paleogeographic reconstruction from the Carboniferous relic sea and marine transgression to Permian marine regression-transgression-regression with crustal extension was proposed.

When the Jilin-Heilongjiang Ocean was closed: constraints from zircon U-Pb and Ar-Ar dating of the Heilongjiang Complex in NE China

There has been an academic discussion and debate over the timing of the overlap and transition between the closure of the Paleo-Asian Ocean and the subduction initiation of the Paleo-Pacific Ocean. This geological process is recorded by the Jilin-Heilongjiang high-pressure metamorphic belt located at the easternmost end of Central Asia Orogenic Belt (CAOB). To address this issue, we investigated the Heilongjiang Complex exposed in Yilan and Huanan regions using geological, geochemical, LA-ICP-MS zircon U-Pb and Ar-Ar isotopic dating techniques. Geochemical studies indicate that the protoliths of the Yilan blueschist consist of subalkaline basalt formed in an oceanic island environment. The LA-ICP-MS zircon U-Pb analyses yielded zircon crystallization ages of 247±4 Ma, 259±3 Ma, 252±5 Ma and 266±3 Ma. Ar-Ar analyses yielded phengite ages of 185±2 Ma and 177± 2Ma for a micaschist and a muscovite-albite schist in Huanan area, respectively. Our findings indicate that the opening of the Jilin-Heilongjiang Ocean occurred during the late Permian to early Triassic (266-247 Ma), and its subduction occurred during the early Triassic to early Jurassic epochs (247-185 Ma). This result provides new constraints on the timing of the overlap and transition between the closure of the Paleo-Asian Ocean and the subduction initiation of the Paleo-Pacific Ocean.