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Long-lived subduction and accretion of the Paleo-Asian Ocean (PAO) led to the formation of the Central Asian Orogenic Belt (CAOB). The central part of the southern CAOB is crucial to understand the tectonic evolution of the entire CAOB. However, the Paleozoic evolution and the final closure of the central PAO are controversial, and the nature of the Early Paleozoic basins is confusing. The relatively complete Paleozoic strata are well-preserved in Zhusileng area in the central part of the southern CAOB and provide an ideal object to constrain the Paleozoic tectonic setting of the PAO. In this study, detrital zircon U-Pb dating and sedimentological and paleocurrents analyses are conducted on the Cambrian-Devonian strata and Lower Permian strata. Most detrital zircons from the Cambrian-Devonian strata have Precambrian ages, while the detrital zircons from the Lower Permian strata are mainly of Paleozoic age. The North China Craton, Alxa Block and Tarim Craton are not the provenances of the Cambrian-Devonian strata. The central part of the southern CAOB was located in a passive continental margin setting during the Cambrian to Ordovician and received the detritus from the Beishan Orogenic Belt. During the Silurian to Middle Devonian, a nearly east-west-trending foreland basin that resulted from the collision between the Zhusileng-Hangwula terrane and southern Mongolian microcontinent developed. From the Late Devonian to Early Permian, bidirectional subduction of the PAO occurred between the Alxa Block and Zhusileng-Hangwula terrane, resulting in numerous arc-related magmatic rocks. Detritus in the Lower Permian strata was mainly from the Paleozoic magmatic rocks and Cambrian-Devonian strata in Zhusileng and surrounding areas. The Late Paleozoic shortening deformation and the switch of the tectonic setting from subduction/collision to post-collision occurred in the central part of the southern CAOB imply that the central PAO closed between the Early and Late Permian.

The Alxa Block is an important component of the North China Craton, but its metamorphic basement has been poorly studied, which hampers the understanding of the Alxa Block and the North China Craton. In this study, we conducted geochronological and geochemical studies on three TTG (tonalite–trondhjemite–granodiorite) gneisses and one granitic gneiss exposed in the Langshan area of the eastern Alxa Block to investigate their crustal evolution. The zircon U-Pb dating results revealed that the protoliths of the TTG and granitic gneisses were formed at 2836 ± 20 Ma, 2491 ± 18 Ma, 2540 ± 38 Ma, and 2763 ± 42 Ma, respectively, and were overprinted by middle–late Paleoproterozoic metamorphism (1962–1721 Ma). All gneiss samples had high Sr/Y ratios (41–274) and intermediate Mg# values (44.97–55.78), with negative Nb, Ta, and Ti anomalies and moderately to strongly fractionated REE patterns ((La/Yb)N = 10.6–107.1), slight Sr enrichment, and positive Eu anomalies, displaying features of typical high-SiO2 adakites and Archean TTGs. The magmatic zircons from the 2.84 Ga and 2.49 Ga TTG rocks had low εHf(t) values of −1.9–1.7, and −3.83–2.12 with two-stage model ages (TDMC) of 3.24–3.11 Ga and 3.10–3.01 Ga, respectively, whereas those from the 2.54 Ga TTG rock exhibited εHf(t) values ranging from −1.1 to 3.46 and TDMC from 3.0 Ga to 2.83 Ga, suggesting that the crustal materials of the basement rocks in the eastern Alxa Block were initially extracted from the depleted mantle during the late Paleoarchean to Mesoarchean era and were reworked in the late Mesoarchean and late Neoarchean era. By contrast, the Alxa Block probably had a relative younger crustal evolutionary history (

Intracontinental deformation is an inseparable element of the evolutionary history of orogenic belts. It can reactivate and intensely modify the structures of previous orogenic belts due to remote ...

NE Asia has experienced Significant extensional events in the Early Cretaceous, including related volcanic rocks, extensional basins, metamorphic core complexes (MCCs), and low-angle detachment fau...

The Mesozoic to Cenozoic intraplate deformation of the North China Craton (NCC) is an intriguing phenomenon that led to different evolutions of the Ordos Basin and the eastern part of the N...

The northern Alxa Block occupies a key position in the southern margin of Central Asian Orogenic Belt (CAOB) and records late Paleozoic subduction and closure processes of the Paleo–Asian Oce...

The Ordos Basin has experienced a complicated tectonic evolution since the Palaeozoic. Its multi-stage evolution was closely related to the tectonic events that occurred along plate boundaries. The...

New apatite fission track (AFT) dating was applied to the Xuefeng Mt. Range and Yuanma Basin to constrain the Cenozoic exhumation process of the southeastern Yangtze Block, South China. The analyzed samples in this study have AFT ages ranging from 27.9 ± 2.5 to 61.5 ± 5.9 Ma, which are younger than the deposition or crystallization ages of the host rocks. The AFT analysis and thermal history modeling indicate that both the Xuefeng Mt. Range and the Yuanma Basin underwent significant exhumation during the early Cenozoic (ca. 60–40 Ma). These samples were rapidly exhumed to near the surface during this period. Our results suggest that an important tectonic event occurred along or near regional fault zones (e.g., the Qinhang Fault) in South China during the early Cenozoic (ca. 60–40 Ma). However, it is difficult to relate this event to the Eastern Sichuan fold belt, which is much older and is characterized by large-scale folding and thrusting. Combined with fieldwork in the Yuanma, Xupu, and Xinning basins, we refute the Cretaceous “Pan-Yangtze Basin” that was proposed to have been separated by the uplifted Xuefeng Mt. Range after the Late Cretaceous. The exhumation stage from ca. 60 Ma to 40 Ma was an important period during which plate movements across the eastern Asian and Pacific regions were reorganized. The early Cenozoic tectonothermal event in South China can be attributed to a change in the direction and speed of the subduction of the Pacific Plate beneath the Eurasian Plate. An Oligocene-Miocene cooling event was also recorded in the eastern Xuefeng Mt. Range, which we tentatively attribute to the activity of dextral faults in this area as a far-field effect of the collision between the Indian and Eurasian plates.

How and when the Paleo-Asian Ocean was finally closed still is a hot topic open to debate. Here we presented geochronological (laser ablation inductively coupled plasma mass spectrometry, LA–ICP–MS, and 40Ar/39Ar), geochemical, and Sr–Nd–Hf isotopic data for the granitoids from the NE Alxa block in the southern margin of the Central Asian Orogen Belt, northern China, in an attempt to constrain the closure of the Paleo-Asian oceanic branch in this region. These granitoids were dated at 268–255 Ma. They show distinct adakitic signatures of high Sr/Y (19–100) and (La/Yb)N (13–50) ratios, and low Y (3.98–16.50 ppm) and Yb (0.24–1.46 ppm) concentrations. They are also characterized by relatively high K2O/Na2O ratios (0.7–1.37), and low MgO (0.22–0.75 wt%), Cr (1.41–9.96 ppm), and Ni (0.36–6.31 ppm) contents and variable Mg# values (26–50). In addition, they display negative eHf(t) (−16.46 to −7.48) and eNd(t) (−14.2 to −9.83) and high (87Sr/86Sr)i (0.7072–0.7196) and Th (7.33–14.10 ppm), indicating that they were most likely generated by partial melting of thickened continental lower crust up to ~59 km thick. This thickened crust was built on the early Permian transitional Alxa crust (~32 km thick), likely caused by the rifting related to the upwelling of mantle plume. Consequently, the NE Alxa block could have witnessed a tectonic transition during the mid-Permian from rifting to arc–continent collision and resultant crustal thickening following the closure of the Paleo-Asian oceanic branch. The subsequent upwelling of asthenosphere in response to the delamination of the orogen during the middle–late Permian provided thermal source for the adakitic magmatism.

The apatite fission track (AFT) ages and thermal modeling of the Longshoushan and deformation along the northern Hexi Corridor on the northern side of the Qinghai-Tibetan Plateau show that the Longshoushan along the northern corridor had experienced important multi-stage exhumations during the Late Mesozoic and Cenozoic. The AFT ages of 7 samples range from 31.9 Ma to 111.8 Ma. Thermal modeling of the AFT ages of the samples shows that the Longshoushan experienced significant exhumation during the Late Cretaceous to the Early Cenozoic (∼130–25 Ma). The Late Cretaceous exhumation of the Longshoushan may have resulted from the continuous compression between the Lhasa and Qiangtang blocks and the flat slab subduction of the Neo-Tethys oceanic plate, which affected wide regions across the Qinghai-Tibetan Plateau. During the Early Cenozoic, the Longshoushan still experienced exhumation, but this process was caused by the Indian-Eurasian collision. Since this time, the Longshoushan was in a stable stage for approximately 20 Ma and experienced erosion. Since ∼5 Ma, obvious tectonic deformation occurred along the entire northern Hexi Corridor, which has also been reported from the peripheral regions of the Qinghai-Tibetan Plateau, especially in the Qilianshan and northeastern margin of the plateau. The AFT ages and the Late Cenozoic deformation of the northern Hexi Corridor all indicate that the present northern boundary of the Qinghai-Tibetan Plateau is situated along the northern Hexi Corridor.

The North China Craton (NCC) experienced important tectonic events during the Meso-Cenozoic as implied by many geological studies. Combined with existing low-temperature thermochronological data, new apatite fission track (AFT) and zircon (U Th)/He data from the Luliangshan and Taihangshan mountains in this study reveal that the central NCC experienced tectonothermal events during the Meso-Cenozoic, i.e., ca. 150 Ma, 110–80 Ma, 50–40 Ma and 30–20 Ma. The Late Jurassic event caused the formation of the Luliangshan basement-involved anticline. The main folding and thrusting in the central NCC developed in the Mesozoic instead of the Cenozoic and resulted from the low-angle subduction of the Paleo-Pacific ocean plate beneath the Eurasian Plate during the Late Jurassic; and the Late Cretaceous tectonic event stopped the Early Cretaceous extension across the eastern Asia, thrusting and sinistral strike-slip faulting occurred across the central NCC, which was possibly caused by a collision along the southeastern boundary of eastern Asia. The early Cenozoic event in central NCC was coeval with an event occurring throughout eastern Asia and may have been a regional response to changes in the movement direction and velocity of the Pacific Plate, and this event may have resulted in the formation of rift basins in the eastern NCC. The whole central NCC experienced uplift during this period in isostatic readjustment to this extension.

In this study, new structural field data and geological observations are coupled with remote sensing analysis and compilation of previous published work to establish a new kinematic framework for the neotectonic reactivation of the Alxa block, China. The Alxa block occupies a key position in Central Asia north and east of the contractional and sinistrally transpressive deforming zones of the Qilianshan-Hexi Corridor-easternmost Altyn Tagh Fault and Beishan deforming belts, south of the sinistrally transpressive southernmost Gobi Altai, and west of – or overlapping with - Ordos block extensional and transtensional graben systems. In addition, the Alxa block is internally transected by important fault systems (Bayan Nuru, Bayanwula, Chahanbulage) that record previously unrecognized Late Cenozoic activity. Active mountain building processes in the Alxa block show remarkable variation from large extensional horst blocks (Helanshan, SW Langshan, SW Yabrai) to localized uplifts along sinistral wrench-belts (Bigesitai) to dominantly contractional (Longshoushan) and sinistral transpressional ranges (Helishan). The triangular wedge-shape of the Alxa block likely pre-disposed it to eastward extrusion in response to NE-directed India-Eurasia collision-derived compressional stresses from the south, and E-W tensional forces driven by Pacific margin rollback to the east. A combination of inherited regional lithospheric structure and the modern east-directed geodetically derived crustal velocity field led to: 1) crustal thinning and subsidence of the Ejina basin to the west in the wake of the eastward extruding Alxa block, and 2) distributed sinistral transtension and crustal extension within the Alxa block interior, and in the Hetao and Yinchuan grabens to the east.

The ages of diabase outcropping on the southern Alxa Block and in related tectonic setting are not well constrained, but are important for exploring the tectonic evolution of the southern Alxa Block. The ages of the zircons from the diabase intruding the Middle–Late Cambrian Xiangshan Group were measured using sensitive high-resolution ion microprobe II (SHRIMPII) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and the weighted mean ages of 276.8 ± 7.9 Ma and 276.2 ± 9.7 Ma were obtained, respectively. The major elements in the diabase indicate that it may belong to the tholeiitic series. With specific features of the rare earth elements (REEs) and trace elements, potentially affected by the continental crust based on the observed strong positive Pb anomaly, the diabase was produced in an intra-plate extension environment. Similar diabase/basalts were also found along the southern margin of the Alxa Block. Combined with sedimentary, palaeo-current, mafic, and felsic ro...

The tectonic affinity of the Alxa Block is important in the reconstruction of the paleogeographical evolution of China. The early Paleozoic strata (the Dahuangshan Formation and Xiangshan Group) of the southern and eastern Alxa Block have consistent rock compositions, similar depositional ages, paleocurrents, detrital zircon age distributions, and cumulative probability curves of crystallization ages for detrital zircon grains relative to the depositional ages, and were deposited in similar slope basins. All these data indicate that the early Paleozoic strata of the Alxa Block were sourced predominantly from Neoproterozoic orogenic belts in the eastern Gondwana continent, instead of the Alxa Block to the north, the North China Block to the east and the North Qilian Orogenic Belt to the south. During the early Paleozoic, the Alxa Block was an independent block with the South China Block (SCB) to the west and the North China Block (NCB) to the east and situated to the northwest of the eastern Gondwana with its long axis trending north northwest–south southeast, and it belonged to a passive continental margin dipping to the north northwest, with the eastern part of the margin located closer to the eastern Gondwana. The Hexi Corridor is part of the Alxa Block and a part of the same slope basin during the early Paleozoic. The southern boundary of the Alxa Block is now the front thrust of the North Qilian Shan.

Detrital zircon LA-ICP-MS U–Pb ages of the Paleozoic strata in the southeastern Alxa Block indicate that the primary provenance did not change between the Devonian and the Early Carboniferous. Except for a sample from the Cambrian strata, the Early Paleozoic North Qilian Orogenic Belt may have been a major source of Paleozoic sediments in the study area. The main source of Lower–Middle Devonian sediments was the Early Paleozoic North Qilian Orogenic Belt. The source of the Upper Devonian sediments was the Alxa Block, while the North China Block was a minor contributor. The deformation of the Cambrian and Devonian Systems in the southeastern Alxa Block indicates that a strong east–west compression event occurred in the study area before the Early Carboniferous. The paleocurrents of the Upper Devonian in the southeastern Alxa Block indicate that the source was located to the north and was not the North Qilian Orogenic Belt to the south. Moreover, the deposition of the Upper Devonian in the southeastern Alxa Block was a response to a strong deformation event that occurred along the eastern boundary of the Alxa Block during the Late Devonian and Early Carboniferous. The North China Block became the primary source during the Early Carboniferous, and the Alxa Block was a minor source. A regional stratigraphic comparison also indicates that similar depositional environments were present until the Carboniferous and Permian on the Alxa Block and North China Block. All of these data indicate that amalgamation of the Alxa Block and the North China Block occurred between the Late Devonian and the Early Carboniferous.

The development of normal faults is controlled by many factors, among which mechanical layers or pre-existing fabrics play an important role in the growth of normal faults. It is widely accepted that normal faults are rarely continuous surfaces but are zones composed of fault segments, heterogeneously distributed fault rocks of various compositions, slip bands, blocks and other deformation elements. Listric normal faults, particularly those developed in metamorphic crystalline rocks or preexisting fabric-developed basements, may be composed of subparallel faults in cross-sections, linked by extensional duplex structures. Here, we choose a listric rift-bounding fault rooted in foliation developed basements, the Langshan normal fault in the northwest corner of the Ordos Block, to conduct an outcrop analysis of fault geometry and linkage behavior from cross-sectional views. The Langshan normal fault zone is composed of mixed regions of high- and low-angle segments linked by duplex structures at various scales. Mylonitic foliations play a significant role in the formation of fault segments and the evolution of the listric fault zones. Lines of evidence show that small en echelon faults initiated from preexisting foliations. Local stress perturbation between overstepping faults results in the formation of duplex structures and displays a high fracture density, which serve to the coalesce of fault segments. Consequently, the progressive localization of strain onto a large listric fault is achieved by progressive development of extensional duplexing among fault segments in cross-sections. These extensional duplexes imply a scale-invariant property, based on which we can extrapolate this pattern occurs on larger scales and is verified by seismic data. The case of Langshan piedmont fault demonstrates the possibility of a listric fault being formed by subparallel planner faults and highlights the effects of preexisting fabrics on the evolution of listric faults, especially in basement fabrics developed regions along the fault.

Sinistral transpressive deformation occurs in the region north of the Altyn Tagh fault due to the Indo-Eurasian collision. In this region, several late Cenozoic faults have developed, and the Sanweishan fault is the key feature with clear landforms. In this study, slip rate measurements combined with several dating methods imply that the Sanweishan fault has been active with sinistral strike-slip rates of 0.33 ± 0.04 mm/a since 14 ka BP and 0.28 ± 0.03 mm/a since 20 ka BP, which are more than an order of magnitude smaller than that of the ATF to the south. The horizontal displacements are 1.7–5.5 m in the eastern segment and 25.0–76.0 m in the middle and western segments of the Sanweishan fault. The increment of horizontal displacement along the main Sanweishan fault is 3.0–4.0 m between paleoearthquakes, and the magnitude of the latest paleoearthquake on the middle and eastern segments of the fault is up to M = 7.2–7.5. The whole length of the Sanweishan fault is ~360 km or longer, which include active faults in the Yangguan and Danghe Reservoirs in the west. More components of thrusting occur on the western and eastern segments of the Sanweishan fault. The growth of the Sanweishan fault is similar to that of the ATF, but the former fault is younger, and its slip rate is much smaller. The differential slip rates on the Sanweishan fault and ATF may result in the clockwise rotation and eastward movement of the intervening block, which compresses regions to the northeast.

The North China Craton (NCC) is fundamentally characterized by Mesozoic intraplate deformation controlled by preexisting basement fabrics and far-field stress fields. In this study, a structural analysis of typical outcrops and representative sections was conducted to investigate the Mesozoic deformation in the central NCC. Our analysis indicates that this Mesozoic deformation is a typical example of thick-skinned tectonics and that the central NCC experienced two stages of deformation during this period. The first stage was driven by nearly east-west maximum compressional stress during the Late Jurassic, which led to the development of north-south-trending structures in the central NCC, such as the Luliangshan range and Qinshui Basin. The second stage involved NNW-SSE maximum compressional stress during the Late Cretaceous, which resulted in the development of east-west-trending structures and the activation of large sinistral strike-slip faults, such as the Huoshan-Fushan fault. The key mechanism for the deformation during the Late Jurassic was the low-angle subduction of the Paleo-Pacific Plate beneath the NCC, which also laid the foundation for the later destruction of the craton during the Cretaceous. Moreover, a Late Cretaceous collision between the southeastern Eurasian continent and an unknown block or oceanic plateau may have resulted in the subsequent deformation of the NCC.

The detrital zircon ages of the Early Paleozoic Xiangshan Group in the southeastern Alxa Terrane show that the lower age limit for the Xiangshan group is 512 Ma. The Xiangshan Group is older than the Middle Ordovician strata in the study region and is the Middle–Late Cambrian in age, which is the same age as the fossils found in it. The detrital zircon ages record the Grenville and Pan-African Orogenic Events, and the major age peaks are 963 Ma, 1179 Ma, 551 Ma and 2517 Ma. The North China Terrane, the Alxa Terrane and the Qilian Orogenic Belt were not the provenances of the Xiangshan Group. The age spectrum of the Xiangshan Group is similar to terranes associated with eastern Gondwana. The sandstone composition modes of the Xiangshan Group indicate that the source areas were the recycled orogenic belts. The zircons in the Xiangshan Group with an age peak at ca. 963 Ma may come from the Eastern Ghats–Rayner orogenic belt or other terranes located to the north of eastern Gondwana. The zircons with a peak at ca. 1179 Ma may come from the Wilkes–Albany–Fraser orogenic belt. Those with a peak at ca. 551 Ma may come from the Prydz–Darling orogenic belt, and the zircons with a peak at ca. 2517 Ma may be from northern India and the Yilgarn Craton in Western Australia. Similar paleontology, paleomagnetic data and detrital zircon age spectra indicate that the Alxa Terrane was located to the east of the South China Terrane and to the north of the eastern Gondwanan continent (present coordinates).

The continuous Cenozoic strata in the Xining Basin record the growth and evolution of the northeastern Qinghai–Tibetan Plateau. Here, the mechanisms and evolution of the Xining Basin during the Cenozoic were investigated by studying the sedimentary facies of 22 Cenozoic sections across the basin and detrital zircon U-Pb ages of three Cenozoic sections located in the eastern, central and western basin, respectively. In the Eocene (ca. 50–44 Ma), the India-Eurasia Collision affected the northeastern Qinghai–Tibetan Plateau. The Central Qilian Block rotated clockwise by ca. 24° to form the Xining Basin. The Triassic flysch sediments surrounding the basin were the primary sources of sediment. Between ca. 44–40 Ma, the basin enlarged and deepened, and sedimentation was dominated by saline lake sediments. Between ca. 40–25.5 Ma, the Xining Basin began to shrink and dry, resulting in the deposition of saline pan and saline mudflat sediments in the basin. After ca. 20 Ma, the Laji Shan to the south of the Xining Basin was uplifted due to the northward compression of the Guide Basin to the south. Clasts that eroded from this range dominated the sediments as the basin evolved from a lacustrine environment into a fluvial system. The Xining Basin was an extensional basin in the Early Cenozoic, but changed into a compressive one during the Late Cenozoic, it was not a foreland basin either to the Kunlun Shan or to the western Qinling Shan in the whole Cenozoic. The formation and deformation of the Xining Basin are the direct responses of the India-Eurasia Collision and the growth of the Qinghai-Tibetan Plateau.

The Laji Shan and Daban Shan which are located along the southern and northern margins of the Xining Basin in the northeastern Qinghai–Tibetan Plateau, experienced important multi-stage exhumations during the Cenozoic. The apatite fission track (AFT) dating of 19 samples along four north–south sections in the Laji Shan and Daban Shan showed that the AFT ages of the Laji Shan from 88 Ma to 12 Ma and the ages of the Daban Shan are between 60 and 32 Ma. All these AFT ages are significantly younger than their host rock formation or sediment deposition ages. Thermal modeling of the AFT data indicated that the Laji Shan had undergone important exhumation events in the Late Cretaceous, ca. 50–30 Ma, and 17–8 Ma, whereas the only significant thermal event in the Daban Shan occurred at ca. 50–30 Ma. The exhumation of the Laji Shan during the Late Cretaceous may result from the Lhasa–Qiangtang collision. During 50–30 Ma, the Central Qilian Block rotated clockwise relative to the South Qilian Block, which led to the formation of the Xining Basin. The slow uplift of the Laji Shan and Daban Shan in this period was the isostatic adjustment of the footwalls of normal faults along the two margins of the Xining Basin. The exhumation of the Laji Shan during 17–8 Ma resulted from compression due to the clockwise rotation of the South Qilian Block relative to the Central Qilian Block, causing the inversion of the Xining Basin, a marked change in the sedimentary environments and a rapid increase in sedimentation rates.