Fragments of Proto-Tethyan oceanic lithosphere are well-preserved along the southern belt of the North Qilian suture, and the origin and emplacement of these ophiolites have become subjects of intense debate. In this study, we integrate field observations, mineralogical and geochemical analyses, zircon U-Pb dating, and isotopic data to investigate the Yanglong ophiolite. The Yanglong ophiolitic rocks are found as tectonic slices resting on the Neoproterozoic sedimentary and volcanic rocks. These rocks are composed of Cambrian serpentinized peridotite, gabbro, dolerite, and rodingite. The spinels in the serpentinized peridotites have variable Cr # values（21, 38–46, and 59–61） and display affinity to those in abyssal and forearc peridotites. The dolerites show slight enrichment in Th and have elevated（La/Sm） N ratios（1.19–2.01）, indicating a subduction-related geochemical affinity. The Yanglong ophiolitic rocks have positive zircon ε Hf （t） values（+10.3 to +18.4） and whole-rock ε Nd （t） values（+5.3 to +6.7） indicating derivation from partial melting of a depleted mantle source. These results, together with the regional geology, collectively suggest that the Yanglong ophiolite was generated in a forearc setting during the Early Cambrian northward intra-oceanic subduction. It was emplaced onto the Central Qilian Block during the subsequent arc–continent collision, no later than the Early Ordovician.

Late Paleozoic sedimentary environments and the associated paleogeography of the SW Yangtze block of South China are critical for understanding the formation of bauxite and clay-type Li deposits, which in turn provide insights into the tectonic evolution of East Asia. However, there is a lack of consensus on the sedimentary environments and provenance of these deposits. Analysis of rock assemblages and sedimentary structures shows that Devonian to Permian sediments in the Central Yunnan basin are dominated by siliciclastic and carbonate rocks that are indicative of deposition in coastal tidal environments. Permian bauxite and bauxitic claystone exhibit variable but elevated Li2O contents ranging from 0.35% to 1.62%, with an average Al2O3 content of 60.46%. The lithium (Li) content in these bauxitic claystones is strongly influenced by sedimentary environments, texture, and postdepositional weathering and leaching. Geochemical data suggest that the sediments are highly mature in composition, with sources primarily from felsic igneous rocks and minor contributions from mafic rocks of an uplifted basement within a passive margin setting that underwent significant recycling and intense weathering. Detrital zircon U-Pb age determinations indicate that Devonian and Carboniferous sediments share a primary source, with ages of ca. 832−808 Ma, and minor input from Paleoproterozoic rocks. In contrast, Lower Permian sediments exhibit age distributions similar to those of Ordovician sediments, with key age peaks at ca. 964 Ma, 812 Ma, 624 Ma, and 546 Ma. Regionally, Middle to Upper Devonian coastal−tidal deposits unconformably interfinger with pre-Devonian and Carboniferous shallow-marine sediments. Additionally, Lower Permian tidal lagoon sediments of the Daoshitou Formation unconformably overlie the Carboniferous deposits. These findings suggest that both lithium and aluminum oxides in the Daoshitou Formation originated primarily from the weathering and recycling of ancient sedimentary and felsic primary rocks, and subsequently accumulated in a tidal lagoon environment within an extensional basin. This basin, located in the southwestern Yangtze block, was associated with the late Paleozoic opening of the Paleo-Tethyan Ocean.

Identification and anatomy of oceanic arcs within ancient orogenic belt are significant for better understanding the tectonic framework and closure process of paleo-ocean basin. This article summarizes the geological, geochemical, and geochronological characteristics of upper crust of Proto-Tethyan Lajishan intra-oceanic arc and provides new data to constrain the subduction evolution of the South Qilian Ocean. The intra-oceanic arc volcanic rocks, including intermediate–mafic lava, breccia, tuff, and minor felsic rocks, are distributed along southern part of the Lajishan ophiolite belt.Geochemical and isotopic compositions indicate that the intermediate–mafic lava were originated from depleted mantle contaminated by sediment melts or hydrous fluids, whereas the felsic rocks were likely generated by partial melting of juvenile mafic crust in intra-oceanic arc setting. Zircons from felsic rocks yield consistent and concordant ages ranging from 506 to 523 Ma, suggesting these volcanic rocks represent the relicts of upper crust of the Cambrian intra-oceanic arc.Combined with the Cambrian forearc ophiolite and accretionary complex, we suggest that the Cambrian intra-oceanic arc in the Lajishan ophiolite belt is belonging to the intra-oceanic arc system which was generated by south-directed subduction in the South Qilian Ocean at a relatively short interval between approximately 530 and 480 Ma.

Abstract The possibility that the Proto‐Tethys Ocean may have undergone intra‐oceanic subduction during ocean closure remains poorly constrained due to a lack of geological evidence for a mature intra‐oceanic arc. Here we present new geochemical and geochronological data for potential arc‐related volcanic rocks adjacent to the accretionary complex and forearc basin in the North Qaidam collisional belt, northern Tibetan Plateau. The volcanic rocks are dominated by foliated basalt, andesite, tuff, and minor dacite with zircon U‐Pb ages ranging from 517 to 497 Ma. They show distinctive geochemical characteristics and can be subdivided into three groups: island‐arc intermediate‐basic volcanic rocks, back‐arc basin basalts (BABB), and dacites with intra‐oceanic arc affinity. The island‐arc volcanic rocks have variable εNd(t) values (+1.6 to +7.5) that decrease northward and were generated by partial melting of depleted mantle wedge modified by hydrous fluid and sediment melt. The BABBs have high εNd(t) values (+5.3 to +6.6) and formed through the melting of MORB‐like mantle, whereas the nearby dacites have positive εNd(t) values (+1.9 to +3.6) similar to the surrounding island‐arc volcanic rocks and were derived from partial melting of intra‐oceanic arc crust as a result of BABB underplating. Integrated analysis of the spatial‐temporal distribution of these volcanic rocks and the reconstructed intra‐oceanic arc‐trench system confirms the existence of the earliest Phanerozoic intra‐oceanic arc formed in response to north‐directed intra‐oceanic subduction. This unrecognized subduction of the Proto‐Tethys Ocean in the North Qaidam belt initiated at ca. 530 Ma, matured ca. 520 Ma, and terminated by ca. 480 Ma.

Late Mesoproterozoic to early Neoproterozoic metamorphic and magmatic events related to the assembly of Rodinia are identified in microcontinents (such as North Wulan terrane, Qaidam block, Central Qilian terrane, Quanji Massif, and Hualong terrane) from the northeastern Tibetan Plateau. However, the peak P-T conditions, P-T paths, and timing of the metamorphic events are still controversial. In this contribution, we integrate petrography, phase equilibrium modelling, mineral chemistry and zircon geochronology to develop a detailed metamorphic history of felsic paragneiss and garnet amphibolite from the North Wulan terrane. Zircon U-Pb geochronology reveals two stages of metamorphism at 1.2-1.0 Ga and - 0.9 Ga. The earlier metamorphic event caused granulite-facies metamorphism with peak P-T conditions of 800-850 degrees C at 8-10 kbar. The second metamorphic event (-0.9 Ga) reached amphibolite-facies conditions at 700-750 degrees C and 6-7 kbar. Granulitefacies metamorphism probably took place in an arc-related setting, whereas amphibolite-facies metamorphism was likely associated with tectonic extrusion during the collision between the North Wulan terrane and unknown continental fragments. The North Wulan terrane and surrounding continental blocks/fragments in the northeastern Tibetan Plateau share a similar evolution that includes long-lived oceanic subduction from 1.2 to 1.0 Ga followed by continental collision at - 0.9 Ga at the periphery of Rodinia. Our results improve the understanding of the tectonic processes responsible for microcontinent evolution in the northeastern Tibetan Plateau during the assembly of Rodina, and provide important constraints on the reconstruction of Rodinia.

The Early Paleozoic (Silurian to Devonian interval) is the main stage for the closure of the Proto-Tethys Ocean and collisional orogenesis in the East Kunlun. Abundant rocks, including eclogites, A-type granites, mafic-ultramafic rocks, as well as the associated mineral deposits, such as the Xiarihamu Ni deposit and Baiganhu W-Sn deposit, were formed during this period. However, the detail collisional orogenic process and exhumation mechanism of eclogites in the Early Paleozoic remain unclear. The discovery of the Early Paleozoic adakitic intrusive rocks in the Kunlun River area may provide the important evidence for the solution to these questions. LA-ICP-MS zircon U-Pb dating indicates that there are Late Ordovician (446Ma) and Late Silurian (427 similar to 425Ma) adakitic intrusive rocks in the Kunlun River area. The Late Ordovician adakitic rocks are granodiorites and exhibit high SiO2 (67.55% similar to 68.21%), Al2O3 (14.59% similar to 15.89%), and Na2O (4.91% similar to 5.15%), and low (K)2O (1.54% similar to 1.64%). They are depleted in heavy rare earth elements with low Y (7.76x10(-6) similar to 8.61x10(-6)) and Yb (0.67x10(-6) similar to 0.93x10(-6)) and high Sr (484x10(-6) similar to 621x10(-6)), Sr/Y ratios (56 similar to 80), Cr (31.2x10(-6) similar to 38.3x10(-6)), and Ni (19.0x10(-6) similar to 22.5x10(-6)). They have relatively depleted whole-rock Nd isotopic compositions with positive epsilon(Nd)(t) values (+1.1 similar to +1.2). The magmatic zircons of the Late Ordovician (446Ma) adakitic granodiorites have two groups of eHf(t) values: +2.2 similar to +10.6 for most of magmatic zircons and -11.5 similar to -1.3 for some of them. The Late Silurian adakitic intrusive rocks consist of granodiorites and granites. They contain high SiO2 (66.36% similar to 71.14%), Al2O3 (15.5% similar to 19.65%) and Na2O (5.65% similar to 7.68%), but low K2O (0.68% similar to 1.47%). They are strongly depleted in heavy rare earth elements with low Y (1.90x10(-6) similar to 5.02x10(-6)), Yb content (0.16x10(-6) similar to 0.51x10(-6)), high Sr (362x10(-6) similar to 1100x10(-6)), and Sr/Y ratios (130 similar to 514). They have relatively enriched whole-rock Nd isotopic compositions with negative epsilon(Nd)(t) values (-1.45 similar to -1.24). The magmatic zircons from Late Silurian (427 similar to 425Ma) adakitic intrusive rocks have variable epsilon(Hf)(t) values ranging from -10.2 to +9.3. We suggest that the Late Ordovician adakitic intrusive rocks were most likely formed by the mixing between coeval subducted ocean crust and ancient continental crust-derived magams during ascent, whereas the Late Silurian adakitic intrusive rocks were generated by partial melting of the thickened lower crust. Taking into account regional geological data, we suggest that, in the East Kunlun, the subduction and partial melting of oceanic crust happened during Late Ordovician (446Ma), and several other processes including the continental collision, slab break-off, exhumation of the high pressure-ultra high pressure (HP-UHP) metamorphic rocks occurred simultaneously during 436 similar to 425Ma, which triggered the generation of adakitic, mafic-ultramafic, and A-type granitic magmas

The North Qaidam belt is an important polymetallic metallogenic belt in the northwestern region of China. However, the tectonic setting and age of related VMS deposits remain debated. Here we performed an integrated analysis of field relationship, geochemistry, and geochronology for hosting rocks of the Lüliangshan VMS-type Cu deposit and surrounding mafic-ultramafic rocks. These rocks, including serpentinite, pyroxenite, chromitite, mafic dykes with associated meta-plagiogranite, lava, chert, and limestone, constitute a relatively complete ophiolite complex, indicating that the Lüliangshan Cu deposit can also be introduced as an ophiolite-hosted VMS deposit. Geochemical data show that the meta-dolerite and ore-hosting lava exhibit geochemical features similar to tholeiitic forearc basalt and are probably generated by partial melting of a depleted mantle source metasomatized by hydrous fluids. Some lavas have boninitic compositions and are formed by partial melting of residual mantle after extraction of forearc basalt. Some ore-hosting lavas also have geochemical affinities to island arc tholeiites as a result of more SSZ components involved in their magma source. The chert samples have remarkably high Fe2O3T contents and are classified as iron-rich one of hydrothermal origin, which is deposited in a ridge-proximal environment. These rocks, together with chromitites with subducted-related geochemical features, collectively indicate that the ophiolite-hosted VMS-type Cu deposit was formed in the forearc setting. Meta-gabbros intruding the ore-hosting lavas yield zircon U-Pb ages mainly ranging from 527 Ma to 518 Ma. The new ages of forearc ophiolite and the oldest age of island-arc rocks (514 Ma) suggest that the Lüliangshan Cu deposit formed in the early Cambrian during early-stage subduction of Proto-Tethys Ocean.

AbstractThe North Qaidam tectonic belt is characterized by the development of high-pressure to ultrahigh-pressure eclogite formed during deep subduction of the continental lithosphere. However, the tectonic processes that occurred prior to continental collision/subduction are relatively poorly studied and this leads to controversy over the evolutionary history of the North Qaidam tectonic belt. In this contribution, we present an integrated study of field observations, petrography, geochronology, and geochemistry (whole-rock major elements, trace elements, and Sr–Nd isotopes as well as zircon Lu–Hf isotopes) of continental arc mafic rocks in the North Wulan metamorphic complex to track Proto-Tethyan oceanic subduction and the nature of metasomatism of the mantle wedge. Zircon U–Pb geochronology demonstrates that continental arc mafic rocks crystallized at ca. 483–472 Ma. Mafic intrusions are enriched in light rare earth elements and large ion lithophile elements but are depleted in high field strength elements; these are typical features of arc-related magmatic rocks. They have relatively radiogenic Sr–Nd–Hf isotope compositions, with relatively high initial 87Sr/86Sr ratios of 0.710363 to 0.719404, low εNdt values of -7.77 to -2.30, variable zircon εHft values ranging from -8 to +2.8, and the single-stage Hf model ages of ca. 1.4–1.0 Ga. These features suggest that the mafic intrusions were sourced from ancient subcontinental mantle that was modified by subducted oceanic slab-derived components. The modified mantle source was generated by the interaction between subcontinental lithospheric mantle peridotite in the overlying mantle wedge and hydrous fluid and felsic melt that were derived from a subducted oceanic slab and seafloor sediments with ancient terrestrial origin in the rutile stability field. Crust-mantle interaction transferred the subducted crustal geochemical signatures to the mantle source during subduction of the Proto-Tethyan oceanic lithosphere. Retreat and rollback of the Proto-Tethyan oceanic slab triggered asthenosphere upwelling and the partial melting of metasomatized and enriched fertile lithospheric mantle to form continental arc mafic magmas in the North Qaidam tectonic belt. Combined with the coeval LP-HT metamorphism, the North Wulan metamorphic complex records the early Paleozoic tectonic evolution of a continental arc-back-arc system, and these continental arc mafic rocks record the subduction of the Proto-Tethyan oceanic lithosphere.

The South Qilian suture in the Qilian Orogen is an early Paleozoic belt that developed as a result of closure of the southern branch of the Proto-Tethyan Ocean. It is characterized by widespread Cambrian intermediate-basic volcanic rocks which record the early-stage evolution of the paleo-ocean basin. However, Cambrian evolution of the paleo-ocean basin remains controversial due to the lack of research on the age and tectonic affinity of these volcanic rocks. In this study, we identified rhyolites from the intermediate-basic volcanic rocks in the South Qilian suture. They occur as pebbles in the breccias, or as veins and interlayers within the intermediate-basic volcanic rocks. Zircon U-Pb datings yield ages of 514.0 +/- 2.8 Ma, 521 +/- 4 Ma, 523 +/- 5 Ma, and 513 +/- 9 Ma for four rhyolites, respectively. The Cambrian rhyolites show variable La/Sm ratios and Rb contents and positive zircon epsilon Hf(t) values (+6.8 to +14.6) and whole-rock epsilon Nd(t) values (+2.1 to +4.6), suggesting that they were derived from partial melting of juvenile mafic crust. They also have high Al2O3 and CaO contents, as well as low K2O and trace element concentrations, which are similar to those of oceanic arc rhyolite. These early Cambrian oceanic arc rhyolites, along with the SSZ-type ophiolite (ca. 530-520 Ma) to the north and late-stage granitoid intrusions (ca. 474-450 Ma), indicate that the southern branch of the Proto-Tethyan Ocean experienced southward intra-oceanic subduction during the early Cambrian-early Ordovician period.

Accurate lithostratigraphy framework of the Central Qilian belt is key to understand subduction-collision of the Proto-Tethyan Ocean in the NE Tibetan Plateau. The Dongchagou and the Moshigou formations share similar detrital zircon age populations with youngest age peak at ca. 1.15-1.21 Ga, which is consistent with the granitoid gneiss of the Liujiatai Formation. In combination with rock assemblages, metamorphic facies, and associated oldest granitoid plutons, we revised Precambrian lithostratigraphy of the Central Qilian belt as the >1.2 Ga Huangyuan Group and the ca. 1200-930 Ma Huangzhong Group in this study. The former is the same as the Liujiatai Formation, whereas the later includes the Dongchagou and Moshigou formations. Siliciclastic turbidites of the Qingshipo Formation gradually pass upward into carbonates of the Huashishan Group, we therefore ascribe them to the Huashishan Group. This group unconformably overlies the Precambrian basement of the Central Qilian belt and consists of continental slope to coastal plain deposits with a bi-direction of the S- and N-ward paleocurrent. These sediments contain abundant metamorphic, magmatic, and minor ophiolitic detritus with main age populations of ca. 910 Ma, ca. 487 Ma, and ca. 447 Ma detrital zircons, probably derived from the Central and South Qilian belts. The basement of the Huangzhong Group experienced 440-430 Ma continent-continent collision-related metamorphism and deformation. These results and regional geology demonstrate that the Huashishan Group was formed by arc-continent collision deposition during culmination of the Proto-Tethyan Ocean closure in the Qilian orogenic belt, NE Tibetan Plateau.

Volcano-sedimentary system of the Cambrian-Ordovician Tanjianshan Group in the northern margin of Qaidam basin was formed by the subduction of the Proto-Tethys Ocean during Early Paleozoic and hosted massive sulfides and orogenic gold deposits in western China. Much attention had been paid to geochemistry and isotopic dating of the volcanic Formation of the Tanjianshan Group, but the sedimentary sequence and facies of the associated clastic rocks received less care. Systemic studies on the sedimentary sequence and facies in the processes of the geological mapping demonstrate that the clastic Formation in the Tuomoerrite area consists of pebbly sandstone, sandstone, siltstone, mudstone, tuffite, siliceous tuff, chert and minor conglomerate. This formation can be subdivided into two lithologic units. The lower unit is mainly dominated by tuffite deposited in the lower submarine fan environment, whereas the upper unit is deposited in the upper, mid, and lower fan environments. In contrast, the rock assemblages of the upper unit are mainly composed of the mid-fan deposits. The upper unit is characterized by fining-upward sequence and increasing abundance of volcanic composition northwestward, but the thickness of sandstones decreases and conglomerate disappears to northwest. Sandstones mainly comprise lithic greywacke. Lithic fragments contain andesite, basalt, dacite, and minor tuff and limestone. Feldspar fragments are dominated by plagioclase grains, and less monocrystalline quartz grains with an igneous origin occur in several samples. Clasts of conglomerates are dominated by angular andesite, chert and minor limestone and tuff. Irregular basal erosional surface, normal grading, parallel laminations and ripples are widespread show typical of turbidite. Slumping folds and wave marks can also be observed in the local outcrops. Regionally, volcano-clastic rocks distributed in the southern margin of Cambrian-Ordovician Keke island arc with a southwestward paleocurrent. These results demonstrate that the clastic formation is closely related to the Cambrian-Ordovician island arc.

Early Paleozoic magmatic rocks are widely distributed in the Saishiteng area of the North Qaidam, which not only recorded the evolution of the Proto-Tethyan Ocean but also provided important information for further understanding of the accretionary and collisional orogenic processes of the Qinling-Qilian-Kunlun orogens. In this paper, we report zircon U-Pb ages, zircon Lu-Hf isotopic data, whole rock major- and trace-element geochemistry and Sr-Nd isotopic data of a set of granidiorite, meta-dolerite and meta-gabbro from the Early to Middle Ordovician magmatic rocks in the Saishiteng area of the North Qaidam. LA-ICP-MS zircon U-Pb dating results show that the ages of granidiorite, meta-dolerite and meta-gabbro are 485Ma, 473Ma and 470 similar to 464Ma, respectively. The granidiorites show similar geochemical features with the weakly peraluminous calc-alkaline type granite: they have a strong fractionation of the light rare earth elements (La/Yb = 18.0 similar to 25.1; (La/Yb)(N) = 12.9 similar to 18.0) and high Sr/Y ratios (30.0 similar to 44.8) with slightly negative Eu anomalies; their whole-rock epsilon(Nd) (t) values and initial Sr-87/Sr-86 ratios varied within +1.1 similar to +3.4 and 0.7048 similar to 0.7060, respectively; and the zircon epsilon(Hf) (t) values of the measured samples ranged in +9.4 similar to +11.3. The meta-dolerites belong to the tholeiitic series, and they have high MgO (5.31% similar to 8.79%), Al2O3 (14.5% similar to 18.07%) and CaO (7.79% similar to 11.92%) contents, Mg-# values (47 similar to 58), and low TiO2 contents (0.41% similar to 0.83%) and rare earth elements (26.0 x 10(-6) similar to 62.5 x 10(-6)) with a weak fractionation of the light rare earth elements ((La/Yb)(N) = 3.3 similar to 4.0); they also have negligible Eu anomalies (delta Eu = 0.9 similar to 1.1); the whole-rock E-Nd (t) values and initial Sr-87/Sr-86 ratios of them varied within +2.2 similar to +5.5 and 0.7049 similar to 0.7055, respectively; and the zircon epsilon(Hf) (t) values of of the measured samples varied within +7.3 similar to +9.1. The meta-gabbros belong to the tholeiitic series, and they have high FeOT (11.79% similar to 15.45%) and TiO2 (1.06% similar to 1.57%) contents, and low MgO (3.41% similar to 5.23%), me values (31 similar to 44), and total rare earth elements (59.2 x 10(-6) similar to 121.6 x 10(-6)) with a weak fractionation of the light rare earth elements ((La/Yb)(N) = 3.2 similar to 5.7); they also display negligible Eu anomalies (delta Eu = 0.9 similar to 1.1); the whole-rock epsilon(Nd) (t) values and initial Sr-87/Sr-86 ratios of them varied within +1.4 similar to +1.9 and 0.7042 similar to 0.7044, respectively; and the zircon epsilon(Hf) (t) values of the samples varied within +7.5 similar to +13.9. These results suggest that the granites may be generated by partial melting of the nascent lower crust of island arc with some degree of thickening, and the meta-gabbro and meta-dolerite are likely to have originated from a depleted mantle wedge in a subduction-related magmatic arc setting. Combined with previous research results, the Early Paleozoic magmatic rocks can be subdivided into three stages of similar to 514Ma, 484 similar to 464Ma and 444 similar to 437Ma, respectively. The integrated analyses further indicate that the Early Paleozoic magmatic rocks in the Saishiteng area were formed during the Proto-Tethyan subductions within ocean basin and continental margin (514 similar to 450Ma) and the afterwards continental collision (445 similar to 420Ma).

Lajishan suture in the Qilian Orogen records subduction process of the southern branch of the Proto-Tethyan Ocean. However, when and where the subduction started remain controversial issues. We present a study of the Cambrian volcanic rocks from the Lajishan suture. These volcanic rocks are coherent and composed of basalt, andesite, and volcanic breccia with minor interlayers or veins of dacite and rhyolite. Zircons from the dacite and rhyolite yield concordant Early-Middle Cambrian ages ranging from 521 to 510 Ma. Basalt and andesite exhibit subduction-related geochemical signatures with enrichment in large ion lithophile elements and depletion in high field strength elements. They have evolved REE, LREE, epsilon(Nd)(t) (+2.6 to +8.2), and (La/Sm)N ratios, sug-gesting derivation from depleted mantle wedge with addition of hydrous fluid or various amounts of sediment-derived melts. Dacite and rhyolite have positive zircon epsilon(Hf)(t) values (+6.1 to +11.6) and whole-rock epsilon(Nd)(t) values (+1.7 to +4.2). They were generated by partial melting of juvenile mafic crust resulting from magma under -plating. These Cambrian volcanic rocks in the Lajishan suture are exposed to the south of the accretionary complex and therefore are likely to be relicts of Cambrian oceanic arc built on the oceanic crust during south-ward subduction of the South Qilian Ocean. Considering the Cambrian-Ordovician intra-oceanic trench-arc-basin system reconstructed in the North Qilian suture, it is suggested that both southern and northern branches of the Proto-Tethyan Ocean have experienced intra-oceanic subduction process which initiated at ca. 530 Ma.

Most porphyry Cu deposits are formed in magmatic arc settings, but some occur in non-arc environments, such as intracontinental settings. The petrogenesis of fertile magmas for porphyry Cu deposits formed in intracontinental settings is still ambiguous. To address this issue, we performed an integrated study of the late Mesozoic porphyry Cu deposits in the South Qinling Orogenic Belt. Zircon U–Pb ages indicate that these late Mesozoic porphyry Cu deposits were formed at 149–142 Ma, in a postcollisional intracontinental setting. εNd(t) (− 4.5 to − 2.7), initial 87Sr/86Sr (0.7046 to 0.7084), and zircon εHf(t) values (− 3.8 to + 2.2) of the late Mesozoic ore-forming and barren rocks suggest that both originate from Meso-Neoproterozoic juvenile lower crust. Whole-rock geochemical and isotopic characteristics indicate that the ore-forming rocks could be formed by the delamination of thickened juvenile lower crust or by the reaction of mantle with normal juvenile lower crust. The barren rocks could be formed by the partial melting of thickened or normal juvenile lower crust. Whole-rock petrochemistry and reversed anorthite contents and Sr isotope data of zoned plagioclase crystals indicate that the mafic magma was recharged into the ore-forming magma chamber. Due to the injection of mafic magma, the ore-forming rocks obtained higher oxygen fugacity, volatiles, water, sulfur, and Cu contents than the barren rocks. According to the regional tectonic evolution, the late Mesozoic porphyry Cu deposits in the South Qinling Orogenic Belt were formed in an extensional environment due to transformation of the tectonic regime. Large-scale lithospheric extension caused asthenospheric mantle upwelling and crust-mantle interaction, providing the crucial metallogenic conditions. Moreover, the injection of mantle-derived mafic magma into the normal magma is a key factor in the formation of the late Mesozoic porphyry Cu deposits in the SQB and similar porphyry systems in an intracontinental setting.

A crustal‐scale detachment system, linking cooler hanging wall basins and the hotter footwall Yiwulüshan metamorphic core complex (MCC), is located in the Fuxin area of NE China. The relationship between detachment tectonism and sedimentation along supra‐detachment basins remains a challenging topic, and the effect of detachment tectonism on basin‐fill and thermal histories is poorly understood. Based on the detailed sedimentological, seismic, and geochemical analysis, we reconstruct the sedimentation and thermal history of the Fuxin Basin in the context of detachment tectonism. Two depositional systems, including a fan delta–shore‐shallow lake and a subaqueous fan–semi‐deep lake, developed during the early Cretaceous. The sedimentation history reveals that the lake‐basin scale started with expansion, and then gradually declined toward the eastern depocenter. During the early Cretaceous, a reconstructed dynamic model for basin‐range evolution reveals the three evolution phases of proto‐rift, fault subsidence, and transpression in the Fuxin area. We infer that the evolution of the supra‐detachment basin, sedimentation, and thermal records were controlled by detachment tectonism associated with the uplift and exhumation of the Yiwulüshan MCC. Thermal parameters and burial history indicate a general increase in the maximum paleotemperature toward the eastern part of the basin. Effects of sedimentary fill, shear heating, transpression, and fault displacement from detachment tectonism dominated the thermal evolution of this basin. Our results illustrate the importance of the dynamic evolution of the MCC in characterizing the sedimentation and thermal history of supra‐detachment basins that contribute to the understanding of subduction systems and their resource development.

The Zongwulong belt is sandwiched in the Proto-Tethyan tectonic domain of Chinese Central Orogenic Belt and contains Tianjunnanshan ophiolite which formed during the evolution of the Paleo-Tethyan Ocean. The Tianjunnanshan ophiolite is the key geological unit to study the transition process from Proto-Tethyan to Paleo-Tethyan. It is composed of ultramafic rocks, doleite, basalt, and chert. Spinets from the serpentinite have high Mg-# values (58. 6 similar to 64. 5) and low Cr-# values ( 38. 9 similar to 43. 9 ). The basalt and dolerite belong to tholeiitic series and are characterized by left-inclined LREE, flat HREE, enrichment in Th, and depletion in Ti. Their chondrite-normalized REE and N-MORB-normalized trace element patterns are consistent with those of back-arc basin lavas. In addition, the mafic rocks have relatively high Th/Yb and low epsilon(Nd) (t) values ( + 7. 5 similar to + 9. 6) , suggesting a depleted mantle source contaminated by subducted sediment. New LA-ICP-MS zircon U-Pb dating of dolerite yields a weighted mean Pb-206/U-238 age of 509 +/- 4Ma. Combined with field occurrences, it is concluded that some ophiolitic rocks in the Zongwulong belt formed during the Cambrian Period and prior to the unconformably overlying Carboniferous flysch and the granite vein (444. 9 +/- 4. 7Ma) . These Cambrian ophiolitic rocks occur as a remnant ocean basin overlain unconfromably by the Carboniferous flysch. They are structurally injected into the overlying strata during closure of the ocean basin in Trassic. These results indicate that the Zongwulong belt is not a Late Paleozoic to Early Messozoic orogenic belt but an Early Paleozoic to Early Messozoic composite orogenic belt formed after the closure of the ProtoTethyan Ocean and Paleo-Tethyan Ocean.

AbstractAs the remnant of the South Qilian Ocean, the South Qilian suture zone recorded abundant information on the Cambrian–Ordovician subduction history of the southern branch of the Proto-Tethyan Ocean. However, the closure timing of the South Qilian Ocean and subsequent collision are poorly constrained. In this study, we report early Silurian (433–435 Ma) U–Pb ages of felsic subvolcanic rocks from Lianhuashan, Ayishan and Shihuiyao of the Lajishan district within the South Qilian suture zone. They intruded the Late Ordovician – Silurian sedimentary or Late Ordovician volcanic rocks and have high SiO2(61.43–73.06 wt%), Sr/Y ratios with significant different rare earth elements (REEs) and trace-element spider diagrams, and Sr–Nd isotopic compositions, probably implying that they were formed through distinctly different generation mechanisms. Geochemistry of the Lianhuashan dacites reveals compositions typical of adakitic rocks derived from partial melting of lower crust in a thickened setting. The Ayishan dacites were derived from partial melting of crustal materials with the involvement of minor peridotite mantle, and the Shihuiyao rhyolites were derived from partial melting of felsic crust. The similar geochemical characteristics of coeval post-collisional igneous rocks in the Central Qilian and South Qilian blocks indicates that the lower Silurian subvolcanic rocks were generated in a thickened crust of post-collisional setting. Considering their intrusive contacts with Late Ordovician – Silurian retro-foreland basin and Late Ordovician collisional volcanic rocks, we propose that the South Qilian suture zone was at a transitional stage from collisional to post-collisional during the early Silurian Period.

The accretionary complex (AC) in the North Qilian belt comprises coherent and chaotic units consisting of bedded cherts, pelagic mudstone, shale, turbidites, basalt, limestone, blueschist, eclogite lenses and ophiolitic mélange. Cherts from the Donggoukou and Biandukou outcrops in the north of the blueschist belt contain abundant Middle Ordovician radiolarians together with rare conodonts. Well-preserved radiolarians also occur in cherts associated with high-pressure/low-temperature rocks in the Baijingsi AC outcrop. Conodonts of Floian–Dapingian age and Middle Ordovician radiolarians also occur in the Shihuigou AC. Geochemical analysis of 23 cherts reveals variable SiO 2 contents (74.56–97.16 wt%) and high mean Al/(Al + Fe + Mn) ratios ranging from 0.35 to 0.85, indicating a non-hydrothermal origin. Ce/Ce* and La N /Yb N ratios of 0.70–1.22 and 0.67–1.59 respectively are high and variable, similar to those of associated muddy siltstone (0.59–0.96 and 1.14–1.55, respectively), suggesting near-trench deposition with associated terrigenous input. Together with the metamorphic ages of blueschists and eclogites, the North Qilian belt AC formed by accretion of ocean plate stratigraphic successions in response to subduction of the Proto-Tethyan Ocean prior to 450 Ma. Supplementary material: Appendices 1-6 are available at: https://doi.org/10.6084/m9.figshare.c.5418275 Thematic collection: This article is part of the Fold-and-thrust belts collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-belts

Table S1: Spinel compositions of serpentinites from the Saibagou ophiolite complex; Table S2: Whole-rock major (wt%) and trace elements (ppm) compositions for the Luofengpo ophiolitic rocks; Table S3: LA-ICP-MS zircon U-Pb data for various rocks from the ophiolite complex and ocean plate stratigraphy within the North Qaidam belt; Table S4: Zircon Lu-Hf isotopic compositions for various rocks from the ophiolite complex and ocean plate stratigraphy within the North Qaidam belt; Table S5: Whole-rock Rb-Sr and Sm-Nd isotopic compositions for the Luofengpo ophiolitic rocks.

This supporting information includes tables that provide zircon U-Pb age, mineral chemical, geochemical, zircon Lu-Hf and Sr-Nd isotopic data of ophiolitic rocks from the North Qaidam belt. Table S1. Spinel compositions of serpentinites from the Saibagou ophiolite complex. Table S2. Whole-rock major (wt.%) and trace elements (ppm) compositions for the Luofengpo ophiolitic rocks. Table S3. LA-ICP-MS zircon U-Pb data for various rocks from the ophiolite and accretionary complex within the North Qaidam belt. Table S4. Zircon Lu-Hf isotopic compositions for various rocks from the ophiolite and accretionary complex within the North Qaidam belt. Table S5. Whole-rock Rb-Sr and Sm-Nd isotopic compositions for the Luofengpo ophiolitic rocks.