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Considerable controversy concerns the consumption and closure processes of the North and South Altyn Oceans resulting in the formation of the North Altyn Tagh subduction-accretion belt and the South Altyn Tagh subduction-collision belt in the Altyn Tagh orogen in southeastern Tarim. This study focused on U–Pb ages and Hf isotopes of detrital zircons from early Paleozoic sedimentary rocks in the Central Altyn Tagh terrane. Our dating results revealed that the studied sedimentary rocks were deposited at ca. 467–429 Ma. The predominant early Paleozoic detrital zircons demonstrate negative εHf(t) values, highlighting their derivation from the coeval intermediate-felsic magmatic rocks sourced from ancient supracrustal materials with enriched isotopes. These inferred, enriched intermediate-felsic magmatic rocks were probably generated in different consumption and closure processes of the North and South Altyn Oceans, based on geochronology and geochemistry of the early-middle Paleozoic intermediate-felsic magmatic rocks in the Altyn Tagh orogen. A number of ca. 520–490 Ma detrital zircons were primarily derived from the coeval, enriched intermediate-felsic magmatic rocks in the local Central Altyn Tagh terrane and the adjacent North Altyn Tagh subduction-accretion belt associated with the advancing subduction of the North Altyn Ocean. The ca. 490–470 Ma detrital zircons are most prominent and suggest a derivation from the coeval, enriched magmatic rocks subject to the rollback of the North Altyn Ocean. These inferred magmatic rocks might have once existed in the region but have been intensely exhumed to be source material for the studied sedimentary rocks. A few ca. 450 Ma detrital zircons indicate a provenance from the North Altyn Tagh subduction-accretion belt during collision after the final closure of the North Altyn Ocean. In contrast, some ca. 470–460 Ma detrital zircons were probably derived from the coeval intermediate- to felsic-magmatic rocks in the Central Altyn Tagh terrane during the exhumation stage of the deep continental collision after the final closure of the South Altyn Ocean. Combination of provenance study and magmatic record provides potential to establish complicated orogenic evolution. [ABSTRACT FROM AUTHOR]

The Neoproterozoic Jiangnan orogenic belt records the accretion and collision between the Yangtze and Cathaysia blocks in South China. The orogen is divisible into three units: a northeastern domain (also referred to as the Huaiyu or Shuangxiwu domain), a central domain (Jiuling domain) and an undifferentiated southwestern domain. Detrital zircons from the oldest sequences (Shuangqiaoshan, Lengjiaxi, Fanjingshan and Sibao groups) in the central and southwest domains yield similar age spectra with major age populations at c. 875–820 Ma, along with minor Palaeo- to Mesoproterozoic and Archaean ages. The dominance of detrital ages close to the deposition ages of the units, along with juvenile zircon Hf isotopic compositions and arc-like whole-rock compositional data, indicate the sedimentary units accumulated adjacent to a convergent plate margin magmatic arc. The presence of Mesoproterozoic and older zircons, both as detritus in the units and as xenocrysts within igneous rocks displaying a subduction-related signature, along with the compositional data, place the magmatic arc along a continental margin. In the northeastern domain, the oldest coeval sequence (Shuangxiwu and Qigong groups) and arc igneous suites are dated at c. 970–850 Ma, and lack older detritus and xenocrysts, indicating they represent an accreted oceanic arc system. [ABSTRACT FROM AUTHOR]

The Neoproterozoic Jiangnan orogenic belt delineates the suture zone between the Cathaysia and Yangtze blocks of the South China Craton. The western part of the belt, in the Longsheng region, consists of a disrupted mafic-ultramafic assemblage of pillow basalt, gabbro, diabase, and peridotite along with siliceous marble, ophicalcite, and jasper mixed with basalt. Significant talc deposits occur on the margins of the ultramafic bodies as well as in the transition zone between marble and basalt. Primary rock relations are largely overprinted by pervasive shearing, resulting in disruption of the assemblage into series of discontinuous blocks within a phyllite matrix. West-dipping thrust faults mark the eastern contact of blocks, and the overall succession has the appearance of a tectonic mélange. U-Pb zircon age data from the gabbros and diabases yield crystallization ages of 867 ± 10, 863 ± 8, and 869 ± 9 Ma, with positive εHf(t) values. The gabbro, basalt, serpentinite, and some talc samples display minor light rare earth element–enriched patterns with obvious depletion of Nb and Ta, indicating a subduction-related setting. The tuffaceous phyllite shows similar geochemical features. A few mafic rocks and the altered ultramafic rocks display mid-ocean ridge basalt (MORB) affinity. Overall lithostratigraphic relationships, age data, and geochemical signatures suggest a forearc setting that was imbricated and disrupted within an accretionary prism environment to form an ophiolitic mélange. The pillow basalt, red jasper, and MORB-type mafic-ultramafic rocks within the mélange occur as exotic blocks derived from the subducting oceanic plate, whereas the arc-type mafic rocks occur as autochthonous blocks, which are all exposed in a matrix of sandy and tuffaceous phyllite. [ABSTRACT FROM AUTHOR]

The Jiangshan-Shaoxing fault zone lies along the SE margin of the Jiangnan belt, and delineates the northeastern margin of the Cathaysia Block of the South China Craton. At Shijiao in NE Zhejiang, the fault zone consists of hornblende schist intruded by migmatized quartz diorite. It constitutes a shear zone delineating the welded boundary between the Neoproterozoic Shuangxiwu Group of Jiangnan belt to the north and the Chencai Complex of Cathaysia Block to the south. The Shuangxiwu Group is composed mainly of basalt, andesite and flysch, whereas the Chencai Complex contains magmatic and sedimentary rocks that experienced amphibolite facies metamorphism. Zircons from quartz diorite and gabbro from the fault zone at Shijiao yield ages of 854 ± 6 Ma, 857 ± 5 Ma and 860 ± 5 Ma, with positive ɛHf( t ) values of 7.81–11.8 and 4.57–10.39. The quartz diorite and mafic-ultramafic rock samples display minor LREE enriched pattern with obvious depletion of Nb, Ta, Rb, Ba and Ti, compared to their neighboring elements and plot in the volcanic arc field on geochemical diagrams, similar to that of volcanic rocks from Shuangxiwu Group. Overall relationships within the Jiangshan-Shaoxing fault zone at Shijiao suggest the ca. 860–850 Ma rock suites were generated in a convergent plate margin and are part of the Jiangnan belt, and not the Cathaysia Block, thus constraining the location of the suture between the two lithotectonic units in NE Zhejiang area during Neoproterozoic. [ABSTRACT FROM AUTHOR]

The Jiangnan orogenic belt in South China defines a subduction-collisional zone between the Yangtze and the Cathaysia blocks. The eastern part of this belt comprises the oceanic Huaiyu terrane, the northeast Jiangxi suture zone and the continental Jiuling terrane. We report zircon U–Pb and Hf isotope data and whole rock geochemistry on the arc magmatic rocks of andesite and basalt occurring as olistostromal blocks, as well as conglomerate in the Dengshan Group above the unconformity between cover sequence and the volcanic arc units. The andesites yield weighted mean ages of 864 Ma, 868 and 871 Ma, whereas the detrital zircons from the conglomerate yield a major age population of 863–810 Ma (peak of 833 Ma), with two minor ones of 1120–940 Ma (peak at 960 Ma) and 1780–1560 Ma (1670 Ma). A post-ca. 810 Ma depositional age is thus suggested for the Dengshan Group. The influx of olistostromal deposits into the Dengshan Group must post-date the youngest detrital zircon age of 810 Ma and is possibly related to the widespread Nanhua rifting associated with the breakup of Rodinia. Furthermore, the age distribution of detrital zircons from the phyllite associated with the arc units compared to its depositional age also suggest a convergent setting, and those from the conglomerate are plotted into a similar field. The andesite and basaltic trachyandesite have LREE enriched patterns, with minor negative Eu anomaly, and negative Nb, Ta, Cs and Ti anomalies. However, the basalt displays only minor LREE enrichment, with no Eu anomaly, and almost flat spidergram trace element patterns, except for a minor positive Sr, Ba and Ti anomaly and negative Rb anomaly. The andesite and basaltic trachyandesite are all plotted in the field of volcanic arc, suggesting an arc setting. The basalt is plotted between EMROB and volcanic arc domains, suggesting magma generation from metasomatised sub-arc sources with subducted oceanic components. The Hf isotopic data on zircons from the andesite yield positive ɛ Hf( t ) values of 2.79–15.51 and late Mesoproterozoic model ages, suggesting that the Neoproterozoic arc sources include reworking of subducted late Mesoproterozoic materials. Our results show that the amalgamation of the Yangtze and Cathaysia blocks in the eastern part occurred at some time between ca. 864 Ma and ca. 810 Ma. [ABSTRACT FROM AUTHOR]

Highlights: [•] N-MORB type basalts are identified from the west Jiangnan orogenic belt. [•] Ca. 863Ma Mafic suites in the eastern and western segments of the belt show arc related signatures. [•] Amalgamation of Yangtze and Cathaysia Blocks in the eastern part after ca. 863Ma, followed by breakup at ca. 790Ma. [ABSTRACT FROM AUTHOR]

The Neoproterozoic Jiangnan accretionary orogenic belt recorded the accretion and collision of the Yangtze and Cathaysia blocks to form a stablized South China Block, but related geometry and kinematics is poorly constrained, leading to largely varied tectonic models. Here, we present detailed field investigation and kinematic analysis of the plutonic-metamorphic complexes in the Yuanbaoshan and Sanfang areas of the west Jiangnan orogenic belt, which enables identification of extensional granite-cored domes. In the dome margins, down-dipping lineations display a radial pattern and dome dominated foliations are extensively developed. The shearing structures within the plutonic-metamorphic complexes display extensional shearing surrounding the Yuanbaoshan and Sanfang granitic dome cores. Gneissic granites and massive ones from both the Yuanbaoshan and Sanfang plutons yield comparable crystallization ages of ca. 835–823 Ma that are within age errors of each other, as are the sheared recrystallized asymmetric quartz veins and mylonites dated at 831 Ma. Overall ages of the deformed Sibao Group and the undeformed overlying Danzhou Group, along with those of the granite plutons and mylonites, suggest formation of the granite-cored domes at ca. 835–823 Ma, coeval to the timing of emplacement of the granitic plutons. Locally, top-to-the-E thrusting structures are also observed in the west Yuanbaoshan and Sanfang areas and are inferred as at ca. 860–835 Ma, coinciding well with E- or SE- directed structures developed elsewhere in the Jiangnan orogenic belt, but in contrast with doming extensional shearing structures. Therefore, overall geometry and kinematics in the west Jiangnan belt indicate development of granitic dome related extensional ductile shearing deformation dated at ca. 835–823 Ma and a possible top-to-the-E compressional ductile thrusting deformation within 860–835 Ma. Given the previously inferred regional geology observations, along with age and chemical data across the Jiangnan orogenic belt, the dominant extensional shearing deformation in the region argue for a slab roll-back event within an accretionary belt, typical of domes-and-basins structures formed in accretionary convergent continental margin. The top-to-the-E thrusting is here interpreted as corresponding to compressional regime generated by the west directed subduction of oceanic crust beneath the northern Guangxi continental margin arc in the west Jiangnan orogenic belt. • Two stages of Neoproterozoic ductile deformation identified in the west Jiangnan accretionary orogenic belt. • The ca. 835–823 Ma extensional domes-and-basins were generated by a slab roll-back event in an accretionary belt. • The ca. 860–835 Ma top-to-the-E thrusting indicates west directed subduction beneath the western Jiangnan belt. [ABSTRACT FROM AUTHOR]

• Recognition of middle Mesoproterozoic sedimentary rocks in the northeastern Altyn Tagh orogen, southeast of the Tarim craton. • Detrital zircon U-Pb ages and Hf isotopes in the Altyn Tagh resemble those from the southern Central Asian orogenic belt. • Mesoproterozoic basements in the southern Central Asian orogenic belt show an affinity with western Amazonia associated with the peripheral accretion of Supercontinent Nuna. The Central Asian orogenic belt (CAOB) is one of the largest Phanerozoic accretionary orogens in Earth's history with myriad metal deposits. Mesoproterozoic basements are sporadically preserved along the southern CAOB. Their tectonic affinity remains controversial, which hampers us from better understanding the basic architecture and Phanerozoic tectonic evolution of the CAOB. This study identified Mesoproterozoic sedimentary rocks in the northeastern Altyn Tagh, southeast of the Tarim craton, from which detrital zircons have remarkable U-Pb age peaks at ca. 1.7 and 1.4 Ga and highly variable ε Hf (t) values from −9 to + 14, resembling those from the southern CAOB. Based on provenance tracing and comparison of available geological records, the Mesoproterozoic basements in the southern CAOB show an affinity with the Rondonian-San Ignacio Province in western Amazonia associated with the peripheral accretion of the Nuna supercontinent and were subsequently fragmented and dispersed over 3000 km in distance. Predominately juvenile 1.8–1.3 Ga magmatic rocks with a scarcity of ca. 1.4 Ga ones in southern Laurentia and southwestern Baltica preclude a possible link. Likewise, a paucity of ca. 1.4 Ga zircons and incomparable isotope signatures in North China, India, and Australia challenge their affinities with the CAOB's basements. This work focuses on the tectonic attribution of the Mesoproterozoic basements in the southern CAOB and highlights the energetic Mesoproterozoic era, during which the accretionary orogeny was intensely operative along the periphery of the Nuna supercontinent. [ABSTRACT FROM AUTHOR]

The South China Block is situated in the Eastern Asian margin. Since the Neoproterozoic, its tectonic evolution was constrained by successive consumption-closure processes of the Paleo-South China, Proto-Tethys, Paleo-Tethys, and Paleo-Pacific oceans. Studies suggest that this block was initially formed by the Neoproterozoic assembly of the Yangtze and Cathaysia blocks following the subduction-accretion of the Paleo-South China Ocean. Then after, it experienced three tectonic-magmatic events in the Phanerozoic. Among these events, the Late Mesozoic tectonism-magmatism was linked with the consumption of the Paleo-Pacific Ocean, while the Silurian and Early to Middle Triassic events took place in intracontinental settings that were related to far-field effects of the closure of the remote Proto-Tethys and Paleo-Tethys oceans, respectively. The subduction-accretion of the Paleo-South China Ocean, and collision at 980–820 Ma between the Yangtze and Cathaysia blocks formed the Jiangnan Orogenic Belt and the Proto-South China Continent, followed by a rifting tectonics and bimodal volcanism at 810–760 Ma. From 760 Ma to 460 Ma, the South China Block was situated under shore, shallow sea to slope depositional environments. During Late Ordovician to Early Devonian (460–400 Ma), an intracontinental orogeny occurred mainly in the Cathaysia Block as a response to the closure of the Proto-Tethys Ocean. Shortly afterwards, this block underwent a stable carbonate deposition during Early Devonian- Middle Triassic (400–230 Ma) and was thus under a shore or shallow sea environment. In the Middle-Late Triassic (240–220 Ma), the South China Block was affected by the closure of the Paleo-Tethys Ocean, intracontinental deformation and S-type granitic magmatism. During the Cretaceous, a multi-stage basin-and-range framework occurred in the western shore of the Paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

The Neoproterozoic Jiangnan Orogen in South China records a succession of arc-trench-basin assemblages culminating in accretion of the bounding Yangtze and Cathaysia blocks to form the stabilized South China Craton. The orogen can be traced over some 1500 km and extends up to 100 km across strike. It is divisible into three domains: the northeast domain (also referred to as the Huaiyu or Shuangxiwu Terrane), the central domain (Jiuling Terrane), and an undifferentiated southwest domain. The northeast domain contains arc type volcanic suites and I-type granitoids dated at ca. 970–850 Ma. It is interpreted as an intra–oceanic terrane based on the juvenile radiogenic isotopic signature of the igneous rocks, the absence of older detritus and inherited xenocrysts, and the presence of ophiolites along its southwestern and western margins. The central and southwest domains contain trench-arc-basin assemblages of clastic sedimentary units, mappable magmatic arc suites and ophiolitic mélanges (Sibao and equivalent groups) that range in age from ca. 880 to 820–815 Ma. The presence of old zircon grains within these two domains, both as detritus within sedimentary units and as inherited zircon in arc basalt, suggest they formed at convergent continental margins. S-type granites dated at 845–815 Ma are a distinctive element of the central and southwest domains. The ages of these granites overlap with convergent plate magmatism in the two domains, arguing against previous models for plume-rift and post-collisional geodynamic settings. Instead, these bodies likely formed in an accretionary orogenic margin setting in which granitic magmatism occurred in an extensional regime triggered by slab rollback. The slab-rollback process triggered mantle-sourced thermal input and partial melting of the older and buried arc-bounding basin sediments. Early Paleozoic S-type granites in the Lachlan and New England belts in eastern Australia and Jurassic ones in the Cordillera belt of the western US provide analogous geodynamic environments. Isotopic data indicate that the central Jiangnan domain experienced significant crustal growth, whereas in the southwest domain there was a greater degree of crustal reworking. The character and distribution of the early Neoproterozoic sedimentary and igneous succession in the orogen suggests it represents a ca. 970–820 Ma accretionary orogen. Upper age limits on the Jiangnan Orogen are provided by a regional angular unconformity in the central and southwest domains at ca. 810–805 Ma, and in the northeast domain at ca. 825 Ma, along with the overlying bimodal volcanic and clastic sedimentary successions mostly dated at ca. 810–730 Ma. Thus, timing of final assembly of South China displays variations across the Jiangnan Orogen, from ca. 825 Ma in the northeast to ca. 820–805 Ma in the central and southwest of the orogen. Post-assembly successions are parts of the Nanhua Basin and are interpreted to have formed during regional lithospheric extension across the eastern and central South China Craton. The age patterns across the South China Craton are indicative of northwest directed accretion of fragments and suggest an external rather than an internal position of the craton within the assembled Rodinia supercontinent. Paleomagnetic data, regional correlations and sedimentary records are consistent with a position along the northern margin of Rodinia, adjacent to India and Australia. The Jiangnan Orogen recorded the accretion of trench-arc assemblages and ultimately the Yangtze Block to the Cathaysia Block that was already located on the margin of Rodinia. The Panxi-Hanan belt, which lies along the western and northwestern margin of the Yangtze Block, formed on the upper plate to a subduction system that both overlaps with, and is younger than, the Jiangnan Orogen. The belt provides a record of ongoing accretion on the Rodinia margin until the mid-Neoproterozoic. [ABSTRACT FROM AUTHOR]

The Trans-North China Orogen is a major Neoarchean Paleoproterozoic collisional orogenic belt above the North China Craton, formed due to prolonged and complex processes. Even though many Neoarchean-Paleoproterozoic magmatic and metamorphic activities have been reported, due to the Huozhou Complex's small outcropping range, little attention has been paid to the origin of various igneous rocks of the Huozhou Complex in the center of the Trans-North China Orogen. The Huozhou Complex, located south of the Lüliang, Wutai, and Hengshan complexes, is an important window into the Early Precambrian structure and evolution of the North China Craton. Its magma and metamorphism are crucial to understanding the development of the structural evolution of the Trans-North China Orogen. The Huozhou metamorphic complex area exposes a range of Precambrian metamorphic rocks, among which the most extensively dispersed is felsic biotite plagioclase gneiss. In this study comprehensive geological field survey, micropetrology, chronology, geochemistry, and Hf isotope analysis were carried out for the Qinggangping and Anziping gneiss in the north of the Huozhou Complex. The results show that the magmatic zircon age of the Qinggangping gneiss is 2196 ± 14 Ma, and its protolith is I-type granite, formed by partial melting of igneous rocks in the absence of weathering. Its source is mainly the juvenile crust from depleted mantle dating 2431–2719 Ma, with a small amount of mantle-derived material. The Anziping gneiss has a metamorphic zircon age of 1931 ± 13 Ma with an S-type granite protolith belonging to peraluminous granite. The Anziping gneiss is formed by recycling pre-existing crustal components at 2613–2848 Ma. A minor quantity of mantle-derived magma is also introduced to the crust simultaneously. The samples of Qinggangping gneiss and Anziping gneiss show the characteristics of obvious negative Nb, Ti, and P elements in the spider diagram of primitive mantle standardization. This implies that the rocks have the characteristics of magmatic rocks in an island arc or subduction environment, which could have formed in the tectonic environment of the continental margin arc. [ABSTRACT FROM AUTHOR]

• Firstly reported the metapelite and metagraywacke in the Chengde Complex. • Metapelite and metagraywacke preserve different peak metamorphic P-T conditions and clockwise P-T paths with ITD process. • The metamorphism occurred at ∼ 1.91–1.80 Ga. • The Chengde Complex records a Paleoproterozoic collisional event formed by a subduction channel. Metasedimentary rocks can provide important information for reconstructing tectonic evolution of an orogen. In this study, we report the newly identified metapelite and metagraywacke samples from the Chengde Metamorphic Complex, the Trans-North China Orogen in the North China Craton. The garnet-bearing paragneiss generally occurs as country rocks of mafic granulite and amphibolite, and displays compositional layering with distinct gneissosity. The metapelite mainly consists of garnet, sillimanite, biotite, muscovite, plagioclase, and quartz, while the metagraywacke commonly comprises garnet, plagioclase, K-feldspar, quartz, and biotite/chlorite. Application of conventional geothermobarometers and phase equilibrium modelling constrains diverse peak metamorphic pressure–temperature (P-T) conditions (CD35, ∼800 ℃/10.5 kbar determined by phase equilibrium modelling; CD37, 677−716 ℃/9.6−9.8 kbar determined by geothermobarometers; CD45, 665−691℃/9.1−9.6 kbar and ∼ 745 ℃/11.2 kbar determined by geothermobarometers and phase equilibrium modelling respectively). The metapelite sample CD35 also records two retrograde stages, defining a clockwise P-T path with isothermal decompression (ITD) process. U-Pb dating of zircon and monazite yields metamorphic ages of 1910−1796 Ma, implying the timing of subduction to the lower crust. Combining previous studies in the Chengde Metamorphic Complex, we conclude that this complex is composed of imbricate rocks with different peak metamorphic P-T conditions, metamorphic grades, metamorphic ages, protolith origins, or protolith ages, indicating that these rocks were subducted to different depths in the subduction channel and then exhumed together to shallower crustal levels. [ABSTRACT FROM AUTHOR]

The dynamic evolution of the Paleo-Tethys Ocean from continental rift-drift and seafloor spreading to initial subduction and final closure has been hotly debated. This paper tries to bring new constraints to this longstanding debate based on the compiled the latest data and investigations into Carboniferous-Triassic magmatism in the westernmost segment of the Eastern Kunlun orogenic belt, North Tibetan Plateau. New results indicate that the ca. 335 Ma appinite stocks were derived from the asthenosphere mantle wedge slightly modified by slab-derived materials. The ca. 244 Ma dioritic appinite stocks were sourced from the partial melting of hydrothermally altered upper oceanic crust following the closure of the Paleo-Tethys Ocean. The ca. 231 Ma adakitic granite stock originated from the partial melting of the thickened eclogitic lower crust in the syn -collisional setting, and the ca. 219–215 Ma granite batholith had a mafic source in the post-collisional setting. By integrating records available, new scenarios of the evolution of the Paleo-Tethys Ocean in Eastern Kunlun were established. The ca. 390–380 Ma continental rifting leading to the opening of the Paleo-Tethys Ocean is attributed to the post-collisional gravitational instability subsequent to the closure of the Proto-Tethys Ocean and the far-field extensional stress induced by the retreating subduction of the Paleo-Asian Oceanic lithosphere along the northern margin of Tarim-Qaidam. The Paleo-Tethys Oceanic lithosphere initially northward subducted at ca. 366–335 Ma. The closure of the Paleo-Tethys Ocean leading to the "soft" collision between the Eastern Kunlun and Bayanhar terranes occurred at ca. 235–225 Ma followed by the ca. 225–200 Ma post-collisional extension. • The ca. 390–380 Ma opening of the PTO due to gravitational instability and retreating subduction. • The initial northward subduction of PTO occurred at ca. 366–335 Ma. • The closure occurred at 235–225 Ma followed by 225–200 Ma post-collisional extension. [ABSTRACT FROM AUTHOR]

The closure time of the Karamaili Ocean is the key to understand the accretionary history of the East Junggar at the southern Central Asian Orogenic Belt in the Paleozoic. In this study, we report geochronology, whole-rock elemental and Sr-Nd isotopic data and zircon Lu-Hf isotopic data of four Late Carboniferous to Early Permian I- and A-type granitic plutons in the Karamaili region in East Junggar, NW China. The Carboniferous Hongliuxia gneissic granite and the Hongliugou granodiorite yield zircon 206Pb/238U ages of 324 ± 1 Ma and 306 ± 1 Ma, respectively, and both of them are high-K calc-alkaline and belong to I-type granitoids. These granites show (87Sr/86Sr) i values from 0.7034 to 0.7046, ɛ Nd (t) values from 4.4 to 6.3, with Nd T DM2 model ages of 559–727 Ma; and ɛ Hf (t) values from 9.4 to 12.8, with Hf T DM2 model ages of 481–710 Ma. The variable positive Nd-Hf isotopic signature and young T DM2 model ages suggest that the I-type granitoids were derived from partial melting of juvenile crustal source, probably earlier arc intrusion. The Early Permian Daliugou and Mawangmiao plutons have 206Pb/238U ages of 297 ± 1 Ma and 284 ± 2 Ma, respectively, show high-K calc-alkaline to shoshonitic characteristics and belong to A 2 -type granite. They exhibit (87Sr/86Sr) i values from 0.7040 to 0.7065, ɛ Nd (t) values from 2.1 to 5.4, with Nd T DM2 model ages of 612–887 Ma; and ɛ Hf (t) values from 5.2 to 11.5, with Hf T DM2 model ages ranging from 548 Ma to 955 Ma, and the Nd-Hf isotope data also suggest that they were derived from juvenile crustal source. Mafic microgranular enclaves in the Daliugou pluton yield zircon 206Pb/238U age of 299 ± 2 Ma, and show similar geochemistry affinity with the granite host. The presence of enclaves and reverse zoning K-feldspars indicate that the magma mixing may have played an important role in the evolution of the Daliugou pluton. In this study, only the Hongliuxia gneissic granite was deformed, and a Nd-Hf isotopic transition occurred at ~300 Ma. Furthermore, the Late Carboniferous I-type granitoids from the Hongliuxia and the Hongliugou plutons show an arc affinity, and the Early Permian A-type granitoids from the Mawangmiao and the Daliugou plutons show post-collisional affinity. These lines of evidence enable us to argue that the Karamaili Ocean probably closed at a period between 324 Ma and 306 Ma. The post-collisional Early Permian magmatism in East Junggar was independent from the Tarim mantle plume. [Display omitted] • The Late Carboniferous granitic magmatism along the Karamaili ophiolite belt is I-type. • The Early Permian granitic magmatism along the Karamaili ophiolite belt is A-type. • Magma mixing may have played an important role in the East Permian A-type magmatism. • The closure of the Karamaili Ocean probably occurred between 324 Ma and 306 Ma. • The Early Permian magmatism was independent from the Tarim mantle plume. [ABSTRACT FROM AUTHOR]

High-grade metamorphic complexes are critical for the understanding of regional crustal configuration and accretionary history of the Altai orogenic belt. The orthogneissic rocks from the Northern Fuyun Complex, southern Chinese Altai, are investigated in this study. Zircon U Pb isotopic analysis yields ages of ca. 411–398 Ma, arguing against previous views that these rocks represent old Precambrian basement. All the samples are calc-alkaline, metaluminous to weakly peraluminous (ASI = 0.80–1.06), and can be classified as I-type granitoids. They have low to medium Al 2 O 3 and relatively high ferromagnesian compositions, and most of them exhibit weak heavy rare-earth element (HREE) fractionation and variably negative Eu anomalies. The above geochemical compositions are consistent with dehydration melting of meta-basaltic or amphibolitic crustal rocks followed by later fractional crystallization for their derivation. In addition, their positive zircon εHf(t) (average = 2.58–8.38) and mantle- to CHUR (chondritic uniform reservoir)-like whole-rock εNd(t) (−1.6 to +2.9) values indicate a relatively juvenile signature of their source rocks, which suggests that the deep crustal section of the Chinese Altai may be dominated by juvenile mantle-derived materials. The high MgO contents (2.06–3.66 wt%) of some samples and the occurrence of the mafic microgranular enclave may reflect the involvement of mantle materials in their petrogenesis, implying possible anatexis of the lower crust driven by basaltic underplating. By synthesizing magmatic, metamorphic, and structural geological evidence, we interpret that the Chinese Altai experienced a lithospheric-scale extensional event in the Devonian, which resulted in massive heat influx, emplacement of juvenile magmas, syn-orogenic crustal anatexis, and formation of mature and layered continental crust. The available data further suggest that alternating contraction and extension have probably operated on the Chinese Altai in the Early-Middle Paleozoic, which is possibly critical for the evolution of accretionary systems worldwide. • Orthogneisses from the southern Chinese Altai were Devonian I-type granitoids. • Precursor magmas were produced by dehydration melting of juvenile mafic lower crust. • No Precambrian but juvenile materials dominated the lower continental crust. • The Chinese Altai underwent a lithospheric-scale extensional event in the Devonian. • Tectonic switching between compression and extension may happen in the Paleozoic. [ABSTRACT FROM AUTHOR]