Post-collisional magmatism contains important clues for understanding the reworking and growth of continental crust,as well as lithospheric delamination and orogenic collapse.Early Devonian magmatism has been identifi...Post-collisional magmatism contains important clues for understanding the reworking and growth of continental crust,as well as lithospheric delamination and orogenic collapse.Early Devonian magmatism has been identified in the North Qilian Orogenic Belt(NQOB).This paper reports an integrated study of petrology,whole-rock geochemistry,Sm-Nd isotope and zircon U-Pb dating,as well as Lu-Hf isotopic data,for two Early Devonian intrusive plutons.The Yongchang and Chijin granites yield zircon U-Pb ages of 394-407 Ma and 414 Ma,respectively.Both of them are characterized by weakly peraluminous to metaluminous without typical aluminium-rich minerals,LREE-enriched patterns with negative Eu anomalies and a negative correlation between P_(2)O_(5) and SiO_(2) contents,consistent with geochemical features of I-type granitoids.Zircons from the studied granites display negative to weak positive ε_(Hf)(t)values(−5.7 to 2.1),which agree well with those of negative ε_(Nd)(t)values(−6.4 to−2.9)for the whole-rock samples,indicating that they were derived from the partial melting of Mesoproterozoic crust.Furthermore,low Sr/Y ratios(1.13-21.28)and high zircon saturation temperatures(745℃ to 839℃,with the majority being>800℃)demonstrated a relatively shallow depth level below the garnet stability field and an additional heat source.Taken together,the Early Devonian granitic magmatism could have been produced by the partial melting of ancient crustal materials heated by mantle-derived magmas at high-temperature and low-pressure conditions during postcollisional extensional collapse.The data obtained in this study,when viewed in conjunction with previous studies,provides more information about the tectonic processes that followed the closure of the North Qilian Ocean.The tectonic transition from continental collision to post-collisional delamination could be constrained to~430 Ma,which is provided by the sudden decrease of Sr/Y and La/Yb ratios and an increase in zircon ε_(Hf)(t)values for granitoids.A two-stage tectonic evolution model from continental collision to post-collisional extensional collapse for the NQOB includes(a)continental collision and crustal thickening during ca.455-430 Ma,characterized by granulite-facies metamorphism and widespread low-Mg adakitic magmatism;(b)post-collisional delamination of thickened continental crust and extensional collapse of orogen during ca.430-390 Ma,provided by coeval high-Mg adakitic magmatism,A-type granites and I-type granitoids with low Sr-Y ratios.展开更多
Geodynamic mechanism responsible for the generation of Silurian granitoids and the tectonic evolution of the Qilian orogenic belt remains controversial. In this study, we report the results of zircon U–Pb age, and sy...Geodynamic mechanism responsible for the generation of Silurian granitoids and the tectonic evolution of the Qilian orogenic belt remains controversial. In this study, we report the results of zircon U–Pb age, and systematic whole-rock geochemical data for the Haoquangou and Liujiaxia granitoids within the North Qilian orogenic belt and the Qilian Block, respectively, to constrain their petrogenesis, and the Silurian tectonic evolution of the Qilian orogenic belt. Zircon U–Pb ages indicate that the Haoquangou and Liujiaxia intrusions were emplaced at423 ± 3 Ma and 432 ± 4 Ma, respectively. The Haoquangou granodiorites are calc-alkaline, while the Liujiaxia granites belong to the high-K calc-alkaline series.Both are peraluminous in composition and have relatively depleted Nd isotopic [ε_(Nd)(t) =(-3.9 – + 0.6)] characteristics compared with regional basement rocks, implying their derivation from a juvenile lower crust. They show adakitic geochemical characteristics and were generated by partial melting of thickened lower continental crust. Postcollisional extensional regime related to lithospheric delamination was the most likely geodynamic mechanism for the generation of the Haoquangou granodiorite, while the Liujiaxia granites were generated in a compressive setting during continental collision between the Qaidam and Qilian blocks.展开更多
The Qilian Orogen Zone(QOZ), located in the north margin of the Tibetan Plateau, is the key area for understanding the deformation and dynamics process of Tibet. Numerous geological and geophysical studies have been c...The Qilian Orogen Zone(QOZ), located in the north margin of the Tibetan Plateau, is the key area for understanding the deformation and dynamics process of Tibet. Numerous geological and geophysical studies have been carried out on the mechanics of the Tibetan Plateau deformation and uplift; however, the detailed structure and deformation style of the Qilian Orogen Zone have remained uncertain due to poor geophysical data coverage and limited resolution power of inversion algorithms. In this study, we analyze the P-wave velocity structure beneath the Qilian Orogen Zone, obtained by applying multi-scale seismic tomography technique to P-wave arrival time data recorded by regional seismic networks. The seismic tomography algorithm used in this study employs sparsity constraints on the wavelet representation of the velocity model via L1-norm regularization. This algorithm can deal efficiently with uneven-sampled volumes, and can obtain multi-scale images of the velocity model. Our results can be summarized as follows:(1) The crustal velocity structure is strongly inhomogeneous and consistent with the surface geological setting. Significant low-velocity anomalies exist in the crust of northeastern Tibet, and slight high-velocity anomalies exist beneath the Qaidam Basin and Alxa terrane.(2)The Qilian Orogen Zone can be divided into two main parts by the Laji Shan Faults: the northwestern part with a low-velocity feature, and the southeastern part with a high-velocity feature at the upper and middle crust.(3) Our tomographic images suggest that northwestern and southeastern Qilian Orogen Zones have undergone different tectonic processes. In the northwest Qilian Orogen Zone, the deformation and growth of the Northern Tibetan Plateau has extended to the Heli Shan and Beida Shan region by northward overthrusting at the upper crust and thickening in the lower crust. We speculate that in the southeast Qilian Orogen Zone the deformation and growth of the Northern Tibet Plateau were of strike-slip style at the upper crust; in the lower crust, the evidence suggests ductile shear extrusion style and active frontage extension to the Alxa terrane.(4) The multi-scale seismic tomography technique provides multiscale analysis and sparse constraints, which has allowed to us obtain stable, high-resolution results.展开更多
The Qilian Orogenic belt is one of the typical orogenic belts globally and a natural laboratory for studying plate tectonics.Many researchers have studied the ophiolite and high pressure and ultra-high pressure metamo...The Qilian Orogenic belt is one of the typical orogenic belts globally and a natural laboratory for studying plate tectonics.Many researchers have studied the ophiolite and high pressure and ultra-high pressure metamorphic rocks in the Qilian orogen and obtained valuable achievements.However,a hot debate exists on the basement property,the distribution of ophiolite,and the boundaries of tectonic units.Large-scale high-precision aeromagnetic surveys have recently been conducted in the Qilian Orogenic belt and adjacent areas.In this study,we are trying to analysis the tectonic framework of the Qilian Orogen using 1:500,000 aeromagnetic data.The results provide geophysical perspectives for studying the structural framework and deformation of this area.According to the aeromagnetic∆T anomaly map,the central and Southern Qilian have the same magnetic anomaly feature that noticeably differs from the North Qilian Orogenic belt and the Qaidam Block.This result indicates that the central and Southern Qilian have a unified magnetic basement and differ from the North Qilian orogenic belt and Qaidam Block.The map shows the distribution of ophiolite in the North Qilian orogenic belt.Linear magnetic anomalies represent the ophiolites because the mafic–ultramafic rocks usually have high magnetic susceptibility.The ophiolite belts are continuously distributed in the western part of North Qilian orogenic belt and have a large scale.However,the scale of the ophiolite belt and the outcropping of mafic–ultramafic rocks reduces when they pass through Qilian County to the east.The results indicate differences in the evolution process between the eastern and western parts of North Qilian,with Qilian County as the transition zone.This study also systematically defines the geophysical boundaries of the Qaidam Block,Qilian Block,North Qilian Orogenic belt,and Alxa block.It is proposed that the sinistral displacement of the Altun Fault is adjusted and absorbed by the series of NE-trending faults in the Qilian orogen and merge into the Longshoushan–Gushi Fault.The extension of the North Qilian Orogenic belt is strengthened by the neotectonics movement along the shearing direction,which separated the North Qilian Orogenic belt into several segments and formed a series of northeast-trending faults.展开更多
The Qilian Orogen marks the junction of the North China, South China and Tarim cratons. The mechanism of continental growth during the formation of the orogen remains unclear. Based on detailed fieldwork, we present a...The Qilian Orogen marks the junction of the North China, South China and Tarim cratons. The mechanism of continental growth during the formation of the orogen remains unclear. Based on detailed fieldwork, we present a systematic study of petrography, mineral chemistry and phase equilibria of garnet amphibolites from the Hualong Group, which represents the Precambrian basement in the southern accretionary belt of the Qilian Orogen. The garnet amphibolites mainly consist of amphibole, plagioclase, garnet and quartz, with minor pyroxene, biotite and ilmenite. A peak stage of upper amphibolite facies to low-temperature granulite facies metamorphism and retrograde metamorphism in the amphibolite facies affected the samples. Garnet has a homogeneous composition of Alm66-71Grs14-17Prp9_12Sps3-s, amphibole is ferro-hornblende, biotite belongs to the ferro-biotite species and pyroxene is dominated by orthopyroxene with few clinopyroxene. Pseudosection modeling of the garnet amphibolite samples indicates clockwise P-T paths. The samples witness peak metamorphism at conditions of -4.9-6.3 kbar and -755-820 ℃ in the upper amphibolite facies to low- temperature granulite facies, and retrograde cooling and decompression at conditions of-2.5-3.1 kbar and -325-545 ℃. It is inferred that peak metamorphism with high temperature and low pressure occurred at ca. 450 Ma during northward subduction of the South Qilian oceanic crust beneath the central Qilian Block. When continental collision occurred between the central Qilian and the Qaidam blocks, the Hualong Block was aecreted onto the South Qilian accretionary complex and experienced amphibolite facies retrograde metamorphism at ca. 440 Ma.展开更多
The Caledonian North Qilian orogenic belt lies between the North China plate and the Qaidam mi-croplates, and resulted from the collision among the Qaidam microplate, mid-Qilian block and the North China plate. The or...The Caledonian North Qilian orogenic belt lies between the North China plate and the Qaidam mi-croplates, and resulted from the collision among the Qaidam microplate, mid-Qilian block and the North China plate. The orogen initiated from the rifting of the Late Proterozoic Rodinia, and then it experi-enced stages of Cambrian rift basin and Ordovician archipelagic oceanic basin, and foreland basin during Silurian to Early-Middle Devonian. The average ratios of Al/(Al+Fe+Mn), Al/(Al+Fe), δ Ce, Lan/Ybn and Lan/Cen from cherts of Cambrian Heicigou Formation are 0.797, 0.627, 1.114, 0.994 and 1.034 re-spectively. In the NAS standardized REE distribution pattern, the cherts from Xiangqianshan is slightly HREE enriched, and the cherts from Ganluci and Shiqingdong are plane. All of these features indicated that Cambrian cherts of the Heicigou Formation originated from a continental margin rift background. On the contrary, the average ratios of Al/(Al+Fe+Mn), Al/(Al+Fe), δ Ce, Lan/Ybn, Lan/Cen of the Ordovician chert from Dakecha, Cuijiadun, Shihuigou, Laohushan, Heicigou, Maomaoshan, Bianmagou, Da-chadaban, Baiquanmen, Jiugequan and Angzanggou, are respectively 0.72, 0.58, 0.99, 1.09 and 0.96 respectively. Their NAS standardized REE distribution patterns of most Ordovician cherts are plane mode or slightly HREE enriched. The REE distribution pattern of few samples of cherts are slightly LREE enriched. Characteristics of sedimentary geochemistry and tectonic evolution demonstrated that the Cambrian-Ordovician cherts, associated with rift, oceanic, island arc and back-arc volcanic rocks, was not formed in a typical abyssal oceanic basin or mid-oceanic ridge. On the contrary, they formed in a deepwater basin of continental margin or a archipelagic ocean tectonic setting. Several Early Paleo-zoic ophiolite belts in North Qilian and adjacent periphery Qaidam microplate imply that an archipelagic ocean during Ordovician existed in the east of Pro-Tethys.展开更多
The Laojunshan Formation is a suite of molasse formed during the rapid uplift of the North Qilian Orogenic Belt (NQOB). Forty-one samples of sandstone have been collected from the Sunan and Minle sections in the weste...The Laojunshan Formation is a suite of molasse formed during the rapid uplift of the North Qilian Orogenic Belt (NQOB). Forty-one samples of sandstone have been collected from the Sunan and Minle sections in the western sector and the Gulang and Jingyuan sections in the eastern sector of the NQOB belt. Geochemical analyses of those samples indicated: 1) The MgO+Fe2O3T and Al2O3/SiO2 values are higher, and K2O/Na2O ratios are lower in the western sector than those in the eastern sector. 2) All of them are depleted in Nb and Ta elements. The samples from the western sector are depleted in Rb element and enriched with Sc, Co, Ni, V, and Cr elements in the Upper Crust-normalized patterns. However, those from the eastern sector are depleted in Sr without enrichments of Sc, Co, Ni, V, and Cr. 3) All of the samples display a right-inclined REE pattern af- ter Chondrite-normalized REE pattern. But LaN/YbN and Eu/Eu* ratios of the samples from the western sector are lower than those of the samples from the eastern sector. These geochemical characteristics suggest the prominent input of mafic clast with minor granitic rocks into the Sunan area, felsic clast into the Gulang and Jingyuan area, and both mafic and felsic clast into the Minle area. The angular shapes of gravels imply that these ill-sorted sediments were deposited near their sources without recy- cling. Geochemical features above also demonstrated that no major chemical weathering occurred for the western provenance, but deposits in the eastern sector resulted from low or middle degree chemical weathering. Evidences combining tectonic discriminations and comparisons with potential provenances revealed that sediments in the Sunan area were derived mainly from the North Qilian Continental arc, whereas sediments in the Minle, Gulang, and Jingyuan areas were derived not only from the North Qilian Continental arc but also from the basement of the Middle Qilian block. Integrated with the characteristics of development of Silurian and Devonian, these imply that the orogeny of NQOB is diachronous in the trending direction due to the oblique collision.展开更多
The crustal S-velocity structure and radial anisotropy along a dense linear portable seismic array with 64 broadband seismic stations were investigated from ambient noise tomography with about one-year-long ambient no...The crustal S-velocity structure and radial anisotropy along a dense linear portable seismic array with 64 broadband seismic stations were investigated from ambient noise tomography with about one-year-long ambient noise recordings. The array transverses the southern part of the central North China Craton(CNCC) and western NCC(WNCC) from east to west and reaches the adjacent Qilian Orogenic Belt(QOB). The phase velocity structures of Rayleigh waves at 5–35 s and Love waves at 5–30 s were measured. The crustal S-velocity structures(Vsv and Vsh) were constructed from the dispersion data(Rayleigh and Love waves,respectively) from point-wise linear inversion with prior information of the Moho depth and average crustal Vp/Vs ratio. The radial anisotropy along the profile was calculated based on the discrepancies between Vsv and Vsh as 2×(Vsh.Vsv)/(Vsh+Vsv). The results show distinct structural variations in the three major tectonic units. The crustal architecture in the southern CNCC is complicated and featured with wide-distributed low-velocity zones(LVZs), which may be a reflection of crustal modification resulting from Mesozoic-Cenozoic tectonics and magmatic activities. The pronounced positive radial anisotropy in the lower-lowermost crust beneath the Shanxi-Shaanxi Rift and the neighboring areas could be attributed to the underplating of mantle mafic-ultramafic materials during the Mesozoic-Cenozoic tectonic activation. In southern Ordos, the overall weak lateral velocity variations, relative high velocity and large-scale positive radial anisotropy in mid-lower crust probably suggest that the current crustal structure has preserved its Precambrian tectonic characteristics. The low-velocity westward-dipping sedimentary strata in the Ordos Block could be attributed to the Phanerozoic whole-basin tilting and the uneven erosion since late Cretaceous. Integrated with previous studies, the systematic comparison of crustal architecture was made between the southern and northern part of CNCC-WNCC. The similarities and differences may have a relation with the tectonic events and deformation histories experienced before and after the Paleoproterozoic amalgamation of the NCC. The nearly flat mid-crustal LVZ beneath the southern QOB weakens gradually as it extends to the east, which is a feature probably associated with crustal vertical superpositionand ductile shear deformation under the intensive compressional regime due to the northeastward growth and expansion of the Tibetan Plateau.展开更多
As the main part of the “central mountain system” in the continent of China, the Qinling, Qilian and Kunlun orogenic belts have been comprehensively and deeply studied since the 1970s and rich fruits have been reape...As the main part of the “central mountain system” in the continent of China, the Qinling, Qilian and Kunlun orogenic belts have been comprehensively and deeply studied since the 1970s and rich fruits have been reaped. However, these achievements were mostly confined to an individual orogenic belt and the study of the mutual relationship among the three orogenic belts was obliged to depend on comparative studies. Different views were produced therefrom. The material composition and structural features of the junction region show that there are several epicontinental and intracontinental transform faults developed in different periods. Restricted by these transform faults, the large-scale lateral movements and, as a consequence, complicated magmatism and tectonic deformation took place in the orogenic belts. According to these features, the authors put forward a three-stage junction and evolution model and point out that there is not a single junction zone traversing from west to east but that the three orogenic belts have been joined progressively by the epicontinental and intracontinental transform faults.展开更多
The Lajishan orogenic belt is one of the E-W-trending Caledonian orogenicbelts within the Qinling-Qilian orogenic system. It was formed upon the Jiningian basement byintensive taphrogenesis. Its major characteristics ...The Lajishan orogenic belt is one of the E-W-trending Caledonian orogenicbelts within the Qinling-Qilian orogenic system. It was formed upon the Jiningian basement byintensive taphrogenesis. Its major characteristics comprise the prominent faulting along the northand south boundaries, the highly complicated petrological and petro-geochemical features of thevolcanic rock series, and the development of a new type of ophiolite suite. In terms of tectonicanalysis and the sequential analysis of tectonic settings of magmatic rocks, it is suggested thatthe Lajishan orogenic belt has undergone a complete 'opening-closing' cycle, which can be furtherdivided into 3 second-order 'opening-closing' cycles. The composite characteristics of the'opening-closing' movement show that Laji Mountain is a typical fault orogenic belt. The faultorogenic belt is one of the most important types of intracontinental orogens. It is of criticaltheoretical and practical significance to summarize the characteristics and the diagnostic criteriaof this kind of orogenic belts, and study the mechanism of their formation and build models of theirevolution.展开更多
The Caledonian orogenic belt of the North Qilian Mountains is an intensely active structure belt. In the process of the Late Caledonian syn-orogeny, the North Qilian-Hexi Corridor area was situated on the tectonic bac...The Caledonian orogenic belt of the North Qilian Mountains is an intensely active structure belt. In the process of the Late Caledonian syn-orogeny, the North Qilian-Hexi Corridor area was situated on the tectonic background of a syn-orogenic basin. In response to the orogenic process of the North Qilian Mountains, typical earthquake event deposits—seismites of the Silurian were widely distributed around Hanxia of Yumen City, the Liyuan River of Sunan County and Biandukou of Minle County. In the Hanxia area, where seismites are typically developed, clastic deposits of tidal-flat facies are the background deposits of the Hanxia Formation. The earthquake event deposits are characterized by sandy mudstone veins, synsedimentary microfractures, micro-corrugated laminations and earthquake breccias, which in turn constitute complex seismites, featuring seismic corrugation, shattering and liquefied sandy mudstone veins, auto-clastic breccias and intraclastic parabreccias. The seismites and tidal flat deposits formed typical sequences of earthquake event deposits.展开更多
The South Qilian belt mainly comprises an early Paleozoic arc-ophiolite complex, accretionary prism, microcontinental block, and foreland basin. These elements represent accretion-collision during Cambrian to Silurian...The South Qilian belt mainly comprises an early Paleozoic arc-ophiolite complex, accretionary prism, microcontinental block, and foreland basin. These elements represent accretion-collision during Cambrian to Silurian time in response to closure of the Proto-Tethyan Ocean in the NE of the present-day Tibet Plateau. Closure of the Proto-Tethyan Ocean between the Central Qilian block and the Oulongbuluke block and the associated collision took place from NE to SW in a zipper-like style. Sediment would have been dispersed longitudinally SW-ward with a progressive facies migration from marginal alluvial sediments toward slope deep-water and deep-sea turbidites. This migration path indicates an ocean basin that shrank toward the SW. The Balonggongga'er Formation in the western South Qilian belt represents the fill of a latest Ordovician-Silurian remnant ocean basin that separated the Oulongbuluke block from the Central Qilian block, and records Silurian closure of the Proto-Tethyan Ocean and subduction beneath the Central Qilian block. However, alluvial deposits in the Lajishan area were accumulated in a retro-foreland basin, indicating that continent-continent collision in the eastern South Qilian belt occurred at c. 450–440 Ma. These results demonstrate that the Proto-Tethyan Ocean closed diachronously during early Paleozoic time.展开更多
The Qilian orogenic belt is the northernmost orogen of the Tethyan domain and connects the Altaids to the north. It contains an assembly of Precambrian micro-continental fragments, early Paleozoic island arcs, accreti...The Qilian orogenic belt is the northernmost orogen of the Tethyan domain and connects the Altaids to the north. It contains an assembly of Precambrian micro-continental fragments, early Paleozoic island arcs, accretionary complexes, ophiolites, forearc and backarc basins, and high-pressure(HP) metamorphic rocks, indicating a long history of accretionary processes. Spatially, this orogen is adjacent to the Tarim, Qaidam, and North China blocks, which also extends into accretionary orogenic belts to the east and SW such as the Qinling and Kunlun belts. Abundant ophiolites in this orogen record the closure of an early Tethyan Ocean and amalgamations between micro-continents of North China, Qaidam, and Tarim. Thus, the ages and tectonic settings of these ophiolites within this belt provide important information regarding evolution of the Proto-Tethys Ocean and assembly of micro-continental blocks, which aids understanding of the spatial and temporal relationship of this orogen within the Tethyan realm. Dismembered ophiolites sporadically crop out along the northern margin of the South Qilian belt, and, from east to west, are locally referred to as the Lajishan, Gangcha, Muli, and Dadaoerji ophiolites. Much attention had been paid to these ophiolites, and several competing models for the tectonic evolution of this belt have been suggested. Considerable disagreement remains in respect of the temporal and spatial framework of the Qilian Orogen and details such as timing of subduction(s) and associated polarities, early collision events, and final closure of oceanic basins. In particular, the formation age and tectonic setting of Muli arc-ophiolite complex remains unknown, which limits understanding of the tectonics of the South Qilian belt and the history of the Proto-Tethys Ocean. The Muli arc-ophiolite complex is distributed over 20 km^2 west of the township of Muli in the western segment of the South Qilian Belt and consists of serpentinite, dunite, cumulate gabbro, basalt, plagiogranite, and chert. Field mapping results demonstrate that these units have been largely destroyed by faulting and generally occur as blocks/slices. They are tectonically interlayered with Upper Ordovician – Lower Silurian siliciclastic turbidite. Arc-ophiolite rocks are intruded by 470–450 Ma subduction-related granitoid plutons and are unconformably overlain by shallow marine to non-marine sediments of Permian-Jurassic age. Basalts show typical subduction-related calc-alkaline geochemical affinity, representing portions of an island arc. Geochemical results for plagiogranites and spinels from serpentinite demonstrate that the Muli arc-ophiolite complex represents a super-subduction zone(SSZ)-type ophiolite. U-Pb zircon data indicate formation associated with southward subduction of the Proto-Tethyan Ocean during a short interval between 539–522 Ma. Voluminous Late Ordovician-Early Silurian deep-water marine siliciclastic and volcaniclastic turbidites and volcanic arc rocks are exposed to the south of the Muli arc-ophiolite complex, whereas fluvial coarse-grained sandstones and conglomerates unconformably overlie the Cambrian-Middle Ordovician ophiolite-arc systems in the eastern South Qilian Belt. These indicate that closure of the Proto-Tethys Ocean was diachronous during the early Paleozoic.展开更多
The middle Qilian orogenic belt and Lajishan orogenic belt, both of which were formed in the Caledonian, strike NW-SE direction across southeast Qilian Mountains and their basement consists of pre-Caledonian metamorph...The middle Qilian orogenic belt and Lajishan orogenic belt, both of which were formed in the Caledonian, strike NW-SE direction across southeast Qilian Mountains and their basement consists of pre-Caledonian metamorphic rocks with lozenge-shaped ductile shear zones in the crystalline basement. The blunt angle between the conjugated ductile shear zones ranges from 104° to 114°, indicating approximate 210° of the maximum principal stress. The plateau ages of muscovite ^40Ar/^39Ar obtained from the mylonitized rocks in the ductile shear zones of Jinshaxia-Hualong-Keque massif within the middle Qilian massif are (405.1±2.4) Ma and (418.3±2.8) Ma, respectively. The chronology data confirm the formation of ductile shear zones in the Caledonian basement metamorphic rocks during the Caledonian orogeny. Furthermore, on the basis of basement rock study, precise timing for the closing of the Late Paleozoic volcanic basin (or island-arc basin) and Lajishan ocean basin is determined. This provides us a new insight into the closing of ocean basin in the structural evolution of orogenic belt.展开更多
基金supported by the Natural Science Foundation of Shandong Province(Grant No.ZR2022QD055)the Taishan Scholars(Grant No.tstp 20231214)the National Natural Science Foundation of China(Grant No.42372247).
文摘Post-collisional magmatism contains important clues for understanding the reworking and growth of continental crust,as well as lithospheric delamination and orogenic collapse.Early Devonian magmatism has been identified in the North Qilian Orogenic Belt(NQOB).This paper reports an integrated study of petrology,whole-rock geochemistry,Sm-Nd isotope and zircon U-Pb dating,as well as Lu-Hf isotopic data,for two Early Devonian intrusive plutons.The Yongchang and Chijin granites yield zircon U-Pb ages of 394-407 Ma and 414 Ma,respectively.Both of them are characterized by weakly peraluminous to metaluminous without typical aluminium-rich minerals,LREE-enriched patterns with negative Eu anomalies and a negative correlation between P_(2)O_(5) and SiO_(2) contents,consistent with geochemical features of I-type granitoids.Zircons from the studied granites display negative to weak positive ε_(Hf)(t)values(−5.7 to 2.1),which agree well with those of negative ε_(Nd)(t)values(−6.4 to−2.9)for the whole-rock samples,indicating that they were derived from the partial melting of Mesoproterozoic crust.Furthermore,low Sr/Y ratios(1.13-21.28)and high zircon saturation temperatures(745℃ to 839℃,with the majority being>800℃)demonstrated a relatively shallow depth level below the garnet stability field and an additional heat source.Taken together,the Early Devonian granitic magmatism could have been produced by the partial melting of ancient crustal materials heated by mantle-derived magmas at high-temperature and low-pressure conditions during postcollisional extensional collapse.The data obtained in this study,when viewed in conjunction with previous studies,provides more information about the tectonic processes that followed the closure of the North Qilian Ocean.The tectonic transition from continental collision to post-collisional delamination could be constrained to~430 Ma,which is provided by the sudden decrease of Sr/Y and La/Yb ratios and an increase in zircon ε_(Hf)(t)values for granitoids.A two-stage tectonic evolution model from continental collision to post-collisional extensional collapse for the NQOB includes(a)continental collision and crustal thickening during ca.455-430 Ma,characterized by granulite-facies metamorphism and widespread low-Mg adakitic magmatism;(b)post-collisional delamination of thickened continental crust and extensional collapse of orogen during ca.430-390 Ma,provided by coeval high-Mg adakitic magmatism,A-type granites and I-type granitoids with low Sr-Y ratios.
基金funded by Gansu Provincial Natural Science Foundation (Grant Numbers 21JR7RA503 and22JR5RA819)the Fundamental Research Funds for the Central Universities (Grant lzujbky-2021-ct07)+1 种基金the Key Talent Project of Gansu Province (2022-Yangzhenxi)the National Second Expedition to the Tibetan Plateau (2019QZKK0704)。
文摘Geodynamic mechanism responsible for the generation of Silurian granitoids and the tectonic evolution of the Qilian orogenic belt remains controversial. In this study, we report the results of zircon U–Pb age, and systematic whole-rock geochemical data for the Haoquangou and Liujiaxia granitoids within the North Qilian orogenic belt and the Qilian Block, respectively, to constrain their petrogenesis, and the Silurian tectonic evolution of the Qilian orogenic belt. Zircon U–Pb ages indicate that the Haoquangou and Liujiaxia intrusions were emplaced at423 ± 3 Ma and 432 ± 4 Ma, respectively. The Haoquangou granodiorites are calc-alkaline, while the Liujiaxia granites belong to the high-K calc-alkaline series.Both are peraluminous in composition and have relatively depleted Nd isotopic [ε_(Nd)(t) =(-3.9 – + 0.6)] characteristics compared with regional basement rocks, implying their derivation from a juvenile lower crust. They show adakitic geochemical characteristics and were generated by partial melting of thickened lower continental crust. Postcollisional extensional regime related to lithospheric delamination was the most likely geodynamic mechanism for the generation of the Haoquangou granodiorite, while the Liujiaxia granites were generated in a compressive setting during continental collision between the Qaidam and Qilian blocks.
基金supported by the National Natural Science Foundation of China(41574045,41590862)State Key Laboratory of Earthquake Dynamics(LED2013A06)
文摘The Qilian Orogen Zone(QOZ), located in the north margin of the Tibetan Plateau, is the key area for understanding the deformation and dynamics process of Tibet. Numerous geological and geophysical studies have been carried out on the mechanics of the Tibetan Plateau deformation and uplift; however, the detailed structure and deformation style of the Qilian Orogen Zone have remained uncertain due to poor geophysical data coverage and limited resolution power of inversion algorithms. In this study, we analyze the P-wave velocity structure beneath the Qilian Orogen Zone, obtained by applying multi-scale seismic tomography technique to P-wave arrival time data recorded by regional seismic networks. The seismic tomography algorithm used in this study employs sparsity constraints on the wavelet representation of the velocity model via L1-norm regularization. This algorithm can deal efficiently with uneven-sampled volumes, and can obtain multi-scale images of the velocity model. Our results can be summarized as follows:(1) The crustal velocity structure is strongly inhomogeneous and consistent with the surface geological setting. Significant low-velocity anomalies exist in the crust of northeastern Tibet, and slight high-velocity anomalies exist beneath the Qaidam Basin and Alxa terrane.(2)The Qilian Orogen Zone can be divided into two main parts by the Laji Shan Faults: the northwestern part with a low-velocity feature, and the southeastern part with a high-velocity feature at the upper and middle crust.(3) Our tomographic images suggest that northwestern and southeastern Qilian Orogen Zones have undergone different tectonic processes. In the northwest Qilian Orogen Zone, the deformation and growth of the Northern Tibetan Plateau has extended to the Heli Shan and Beida Shan region by northward overthrusting at the upper crust and thickening in the lower crust. We speculate that in the southeast Qilian Orogen Zone the deformation and growth of the Northern Tibet Plateau were of strike-slip style at the upper crust; in the lower crust, the evidence suggests ductile shear extrusion style and active frontage extension to the Alxa terrane.(4) The multi-scale seismic tomography technique provides multiscale analysis and sparse constraints, which has allowed to us obtain stable, high-resolution results.
基金supported by the National Natural Science Foundation of China grant(U2244220)China Geological Survey Project grant(DD20190551,DD20230351)。
文摘The Qilian Orogenic belt is one of the typical orogenic belts globally and a natural laboratory for studying plate tectonics.Many researchers have studied the ophiolite and high pressure and ultra-high pressure metamorphic rocks in the Qilian orogen and obtained valuable achievements.However,a hot debate exists on the basement property,the distribution of ophiolite,and the boundaries of tectonic units.Large-scale high-precision aeromagnetic surveys have recently been conducted in the Qilian Orogenic belt and adjacent areas.In this study,we are trying to analysis the tectonic framework of the Qilian Orogen using 1:500,000 aeromagnetic data.The results provide geophysical perspectives for studying the structural framework and deformation of this area.According to the aeromagnetic∆T anomaly map,the central and Southern Qilian have the same magnetic anomaly feature that noticeably differs from the North Qilian Orogenic belt and the Qaidam Block.This result indicates that the central and Southern Qilian have a unified magnetic basement and differ from the North Qilian orogenic belt and Qaidam Block.The map shows the distribution of ophiolite in the North Qilian orogenic belt.Linear magnetic anomalies represent the ophiolites because the mafic–ultramafic rocks usually have high magnetic susceptibility.The ophiolite belts are continuously distributed in the western part of North Qilian orogenic belt and have a large scale.However,the scale of the ophiolite belt and the outcropping of mafic–ultramafic rocks reduces when they pass through Qilian County to the east.The results indicate differences in the evolution process between the eastern and western parts of North Qilian,with Qilian County as the transition zone.This study also systematically defines the geophysical boundaries of the Qaidam Block,Qilian Block,North Qilian Orogenic belt,and Alxa block.It is proposed that the sinistral displacement of the Altun Fault is adjusted and absorbed by the series of NE-trending faults in the Qilian orogen and merge into the Longshoushan–Gushi Fault.The extension of the North Qilian Orogenic belt is strengthened by the neotectonics movement along the shearing direction,which separated the North Qilian Orogenic belt into several segments and formed a series of northeast-trending faults.
基金funded by the National Natural Science Foundation of China (No. 41520104003)the National Key R & D Program of China (No. 2016YFC0600403)+1 种基金the China Geological Survey (No. DD20160201)the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) (Nos. CUGL170404, CUG160232)
文摘The Qilian Orogen marks the junction of the North China, South China and Tarim cratons. The mechanism of continental growth during the formation of the orogen remains unclear. Based on detailed fieldwork, we present a systematic study of petrography, mineral chemistry and phase equilibria of garnet amphibolites from the Hualong Group, which represents the Precambrian basement in the southern accretionary belt of the Qilian Orogen. The garnet amphibolites mainly consist of amphibole, plagioclase, garnet and quartz, with minor pyroxene, biotite and ilmenite. A peak stage of upper amphibolite facies to low-temperature granulite facies metamorphism and retrograde metamorphism in the amphibolite facies affected the samples. Garnet has a homogeneous composition of Alm66-71Grs14-17Prp9_12Sps3-s, amphibole is ferro-hornblende, biotite belongs to the ferro-biotite species and pyroxene is dominated by orthopyroxene with few clinopyroxene. Pseudosection modeling of the garnet amphibolite samples indicates clockwise P-T paths. The samples witness peak metamorphism at conditions of -4.9-6.3 kbar and -755-820 ℃ in the upper amphibolite facies to low- temperature granulite facies, and retrograde cooling and decompression at conditions of-2.5-3.1 kbar and -325-545 ℃. It is inferred that peak metamorphism with high temperature and low pressure occurred at ca. 450 Ma during northward subduction of the South Qilian oceanic crust beneath the central Qilian Block. When continental collision occurred between the central Qilian and the Qaidam blocks, the Hualong Block was aecreted onto the South Qilian accretionary complex and experienced amphibolite facies retrograde metamorphism at ca. 440 Ma.
基金Sponsored by the National Natural Science Foundation of China (Grant Nos. 40672080 and 40621002)the Developing Plan of Innovation Group of Ministry of Education of China (Grant No. IRT0546)
文摘The Caledonian North Qilian orogenic belt lies between the North China plate and the Qaidam mi-croplates, and resulted from the collision among the Qaidam microplate, mid-Qilian block and the North China plate. The orogen initiated from the rifting of the Late Proterozoic Rodinia, and then it experi-enced stages of Cambrian rift basin and Ordovician archipelagic oceanic basin, and foreland basin during Silurian to Early-Middle Devonian. The average ratios of Al/(Al+Fe+Mn), Al/(Al+Fe), δ Ce, Lan/Ybn and Lan/Cen from cherts of Cambrian Heicigou Formation are 0.797, 0.627, 1.114, 0.994 and 1.034 re-spectively. In the NAS standardized REE distribution pattern, the cherts from Xiangqianshan is slightly HREE enriched, and the cherts from Ganluci and Shiqingdong are plane. All of these features indicated that Cambrian cherts of the Heicigou Formation originated from a continental margin rift background. On the contrary, the average ratios of Al/(Al+Fe+Mn), Al/(Al+Fe), δ Ce, Lan/Ybn, Lan/Cen of the Ordovician chert from Dakecha, Cuijiadun, Shihuigou, Laohushan, Heicigou, Maomaoshan, Bianmagou, Da-chadaban, Baiquanmen, Jiugequan and Angzanggou, are respectively 0.72, 0.58, 0.99, 1.09 and 0.96 respectively. Their NAS standardized REE distribution patterns of most Ordovician cherts are plane mode or slightly HREE enriched. The REE distribution pattern of few samples of cherts are slightly LREE enriched. Characteristics of sedimentary geochemistry and tectonic evolution demonstrated that the Cambrian-Ordovician cherts, associated with rift, oceanic, island arc and back-arc volcanic rocks, was not formed in a typical abyssal oceanic basin or mid-oceanic ridge. On the contrary, they formed in a deepwater basin of continental margin or a archipelagic ocean tectonic setting. Several Early Paleo-zoic ophiolite belts in North Qilian and adjacent periphery Qaidam microplate imply that an archipelagic ocean during Ordovician existed in the east of Pro-Tethys.
基金supported by National Natural Science Foundation of China (Grant Nos. 40672080 and 40921062)"111" Project (Grant No. B08030)Excellent Youth Teacher Fund of China University of Geosciences (Wuhan)
文摘The Laojunshan Formation is a suite of molasse formed during the rapid uplift of the North Qilian Orogenic Belt (NQOB). Forty-one samples of sandstone have been collected from the Sunan and Minle sections in the western sector and the Gulang and Jingyuan sections in the eastern sector of the NQOB belt. Geochemical analyses of those samples indicated: 1) The MgO+Fe2O3T and Al2O3/SiO2 values are higher, and K2O/Na2O ratios are lower in the western sector than those in the eastern sector. 2) All of them are depleted in Nb and Ta elements. The samples from the western sector are depleted in Rb element and enriched with Sc, Co, Ni, V, and Cr elements in the Upper Crust-normalized patterns. However, those from the eastern sector are depleted in Sr without enrichments of Sc, Co, Ni, V, and Cr. 3) All of the samples display a right-inclined REE pattern af- ter Chondrite-normalized REE pattern. But LaN/YbN and Eu/Eu* ratios of the samples from the western sector are lower than those of the samples from the eastern sector. These geochemical characteristics suggest the prominent input of mafic clast with minor granitic rocks into the Sunan area, felsic clast into the Gulang and Jingyuan area, and both mafic and felsic clast into the Minle area. The angular shapes of gravels imply that these ill-sorted sediments were deposited near their sources without recy- cling. Geochemical features above also demonstrated that no major chemical weathering occurred for the western provenance, but deposits in the eastern sector resulted from low or middle degree chemical weathering. Evidences combining tectonic discriminations and comparisons with potential provenances revealed that sediments in the Sunan area were derived mainly from the North Qilian Continental arc, whereas sediments in the Minle, Gulang, and Jingyuan areas were derived not only from the North Qilian Continental arc but also from the basement of the Middle Qilian block. Integrated with the characteristics of development of Silurian and Devonian, these imply that the orogeny of NQOB is diachronous in the trending direction due to the oblique collision.
基金supported by the National Natural Science Foundation of China(Grant Nos.41225016,91414301&41688103)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB03010802)
文摘The crustal S-velocity structure and radial anisotropy along a dense linear portable seismic array with 64 broadband seismic stations were investigated from ambient noise tomography with about one-year-long ambient noise recordings. The array transverses the southern part of the central North China Craton(CNCC) and western NCC(WNCC) from east to west and reaches the adjacent Qilian Orogenic Belt(QOB). The phase velocity structures of Rayleigh waves at 5–35 s and Love waves at 5–30 s were measured. The crustal S-velocity structures(Vsv and Vsh) were constructed from the dispersion data(Rayleigh and Love waves,respectively) from point-wise linear inversion with prior information of the Moho depth and average crustal Vp/Vs ratio. The radial anisotropy along the profile was calculated based on the discrepancies between Vsv and Vsh as 2×(Vsh.Vsv)/(Vsh+Vsv). The results show distinct structural variations in the three major tectonic units. The crustal architecture in the southern CNCC is complicated and featured with wide-distributed low-velocity zones(LVZs), which may be a reflection of crustal modification resulting from Mesozoic-Cenozoic tectonics and magmatic activities. The pronounced positive radial anisotropy in the lower-lowermost crust beneath the Shanxi-Shaanxi Rift and the neighboring areas could be attributed to the underplating of mantle mafic-ultramafic materials during the Mesozoic-Cenozoic tectonic activation. In southern Ordos, the overall weak lateral velocity variations, relative high velocity and large-scale positive radial anisotropy in mid-lower crust probably suggest that the current crustal structure has preserved its Precambrian tectonic characteristics. The low-velocity westward-dipping sedimentary strata in the Ordos Block could be attributed to the Phanerozoic whole-basin tilting and the uneven erosion since late Cretaceous. Integrated with previous studies, the systematic comparison of crustal architecture was made between the southern and northern part of CNCC-WNCC. The similarities and differences may have a relation with the tectonic events and deformation histories experienced before and after the Paleoproterozoic amalgamation of the NCC. The nearly flat mid-crustal LVZ beneath the southern QOB weakens gradually as it extends to the east, which is a feature probably associated with crustal vertical superpositionand ductile shear deformation under the intensive compressional regime due to the northeastward growth and expansion of the Tibetan Plateau.
文摘As the main part of the “central mountain system” in the continent of China, the Qinling, Qilian and Kunlun orogenic belts have been comprehensively and deeply studied since the 1970s and rich fruits have been reaped. However, these achievements were mostly confined to an individual orogenic belt and the study of the mutual relationship among the three orogenic belts was obliged to depend on comparative studies. Different views were produced therefrom. The material composition and structural features of the junction region show that there are several epicontinental and intracontinental transform faults developed in different periods. Restricted by these transform faults, the large-scale lateral movements and, as a consequence, complicated magmatism and tectonic deformation took place in the orogenic belts. According to these features, the authors put forward a three-stage junction and evolution model and point out that there is not a single junction zone traversing from west to east but that the three orogenic belts have been joined progressively by the epicontinental and intracontinental transform faults.
基金the Doctoral Programme of Higher Education 97049119 the National Natural Science Foundation of China grant 40072062.
文摘The Lajishan orogenic belt is one of the E-W-trending Caledonian orogenicbelts within the Qinling-Qilian orogenic system. It was formed upon the Jiningian basement byintensive taphrogenesis. Its major characteristics comprise the prominent faulting along the northand south boundaries, the highly complicated petrological and petro-geochemical features of thevolcanic rock series, and the development of a new type of ophiolite suite. In terms of tectonicanalysis and the sequential analysis of tectonic settings of magmatic rocks, it is suggested thatthe Lajishan orogenic belt has undergone a complete 'opening-closing' cycle, which can be furtherdivided into 3 second-order 'opening-closing' cycles. The composite characteristics of the'opening-closing' movement show that Laji Mountain is a typical fault orogenic belt. The faultorogenic belt is one of the most important types of intracontinental orogens. It is of criticaltheoretical and practical significance to summarize the characteristics and the diagnostic criteriaof this kind of orogenic belts, and study the mechanism of their formation and build models of theirevolution.
基金supported by the National Natural Science Foundation of China(No.49972078).
文摘The Caledonian orogenic belt of the North Qilian Mountains is an intensely active structure belt. In the process of the Late Caledonian syn-orogeny, the North Qilian-Hexi Corridor area was situated on the tectonic background of a syn-orogenic basin. In response to the orogenic process of the North Qilian Mountains, typical earthquake event deposits—seismites of the Silurian were widely distributed around Hanxia of Yumen City, the Liyuan River of Sunan County and Biandukou of Minle County. In the Hanxia area, where seismites are typically developed, clastic deposits of tidal-flat facies are the background deposits of the Hanxia Formation. The earthquake event deposits are characterized by sandy mudstone veins, synsedimentary microfractures, micro-corrugated laminations and earthquake breccias, which in turn constitute complex seismites, featuring seismic corrugation, shattering and liquefied sandy mudstone veins, auto-clastic breccias and intraclastic parabreccias. The seismites and tidal flat deposits formed typical sequences of earthquake event deposits.
基金the National Natural Science Foundation of China(Grants 41672221,41872241)China Geological Survey(Grants DD20190006,DD2016020104)IGGCAS Open Research Foundation(SKLK201702)。
文摘The South Qilian belt mainly comprises an early Paleozoic arc-ophiolite complex, accretionary prism, microcontinental block, and foreland basin. These elements represent accretion-collision during Cambrian to Silurian time in response to closure of the Proto-Tethyan Ocean in the NE of the present-day Tibet Plateau. Closure of the Proto-Tethyan Ocean between the Central Qilian block and the Oulongbuluke block and the associated collision took place from NE to SW in a zipper-like style. Sediment would have been dispersed longitudinally SW-ward with a progressive facies migration from marginal alluvial sediments toward slope deep-water and deep-sea turbidites. This migration path indicates an ocean basin that shrank toward the SW. The Balonggongga'er Formation in the western South Qilian belt represents the fill of a latest Ordovician-Silurian remnant ocean basin that separated the Oulongbuluke block from the Central Qilian block, and records Silurian closure of the Proto-Tethyan Ocean and subduction beneath the Central Qilian block. However, alluvial deposits in the Lajishan area were accumulated in a retro-foreland basin, indicating that continent-continent collision in the eastern South Qilian belt occurred at c. 450–440 Ma. These results demonstrate that the Proto-Tethyan Ocean closed diachronously during early Paleozoic time.
基金granted by the National Natural Science Foundation of China(Grant No.41872241 and 41672221)
文摘The Qilian orogenic belt is the northernmost orogen of the Tethyan domain and connects the Altaids to the north. It contains an assembly of Precambrian micro-continental fragments, early Paleozoic island arcs, accretionary complexes, ophiolites, forearc and backarc basins, and high-pressure(HP) metamorphic rocks, indicating a long history of accretionary processes. Spatially, this orogen is adjacent to the Tarim, Qaidam, and North China blocks, which also extends into accretionary orogenic belts to the east and SW such as the Qinling and Kunlun belts. Abundant ophiolites in this orogen record the closure of an early Tethyan Ocean and amalgamations between micro-continents of North China, Qaidam, and Tarim. Thus, the ages and tectonic settings of these ophiolites within this belt provide important information regarding evolution of the Proto-Tethys Ocean and assembly of micro-continental blocks, which aids understanding of the spatial and temporal relationship of this orogen within the Tethyan realm. Dismembered ophiolites sporadically crop out along the northern margin of the South Qilian belt, and, from east to west, are locally referred to as the Lajishan, Gangcha, Muli, and Dadaoerji ophiolites. Much attention had been paid to these ophiolites, and several competing models for the tectonic evolution of this belt have been suggested. Considerable disagreement remains in respect of the temporal and spatial framework of the Qilian Orogen and details such as timing of subduction(s) and associated polarities, early collision events, and final closure of oceanic basins. In particular, the formation age and tectonic setting of Muli arc-ophiolite complex remains unknown, which limits understanding of the tectonics of the South Qilian belt and the history of the Proto-Tethys Ocean. The Muli arc-ophiolite complex is distributed over 20 km^2 west of the township of Muli in the western segment of the South Qilian Belt and consists of serpentinite, dunite, cumulate gabbro, basalt, plagiogranite, and chert. Field mapping results demonstrate that these units have been largely destroyed by faulting and generally occur as blocks/slices. They are tectonically interlayered with Upper Ordovician – Lower Silurian siliciclastic turbidite. Arc-ophiolite rocks are intruded by 470–450 Ma subduction-related granitoid plutons and are unconformably overlain by shallow marine to non-marine sediments of Permian-Jurassic age. Basalts show typical subduction-related calc-alkaline geochemical affinity, representing portions of an island arc. Geochemical results for plagiogranites and spinels from serpentinite demonstrate that the Muli arc-ophiolite complex represents a super-subduction zone(SSZ)-type ophiolite. U-Pb zircon data indicate formation associated with southward subduction of the Proto-Tethyan Ocean during a short interval between 539–522 Ma. Voluminous Late Ordovician-Early Silurian deep-water marine siliciclastic and volcaniclastic turbidites and volcanic arc rocks are exposed to the south of the Muli arc-ophiolite complex, whereas fluvial coarse-grained sandstones and conglomerates unconformably overlie the Cambrian-Middle Ordovician ophiolite-arc systems in the eastern South Qilian Belt. These indicate that closure of the Proto-Tethys Ocean was diachronous during the early Paleozoic.
基金This paper is financially supported by the projects of 1:250 000 Scale Regional Geological Survey of Linxia, and Dingxi (No. 200413000007) from Ministry of Land and Resources of China.
文摘The middle Qilian orogenic belt and Lajishan orogenic belt, both of which were formed in the Caledonian, strike NW-SE direction across southeast Qilian Mountains and their basement consists of pre-Caledonian metamorphic rocks with lozenge-shaped ductile shear zones in the crystalline basement. The blunt angle between the conjugated ductile shear zones ranges from 104° to 114°, indicating approximate 210° of the maximum principal stress. The plateau ages of muscovite ^40Ar/^39Ar obtained from the mylonitized rocks in the ductile shear zones of Jinshaxia-Hualong-Keque massif within the middle Qilian massif are (405.1±2.4) Ma and (418.3±2.8) Ma, respectively. The chronology data confirm the formation of ductile shear zones in the Caledonian basement metamorphic rocks during the Caledonian orogeny. Furthermore, on the basis of basement rock study, precise timing for the closing of the Late Paleozoic volcanic basin (or island-arc basin) and Lajishan ocean basin is determined. This provides us a new insight into the closing of ocean basin in the structural evolution of orogenic belt.