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A combination of U-Pb zircon ages and geochemical and Sr-Nd-Hf isotopic data are presented for the Early Paleozoic granodiorites from the Haoquangou and Baimawa plutons in order to probe the crustal thickness variation of the eastern North Qilian and the diachronous evolution of the North Qilian orogen. The granodiorites formed at 436–435 Ma and have high Sr/Y ratios (63–117). Elemental and isotopic data combined with geochemical modeling and comparisons with experimental data suggest that they were produced from the melting of relatively juvenile mafic rocks in the thickened lower crust. Together with other petrological and geochemical data and the calculation of variation in crustal thickness, this indicates that the eastern North Qilian experienced clear crustal thickening and thinning from the Late Ordovician to Late Silurian. Based on available data, we suggest that diachronous collision from east to west, which probably resulted in the distinct intensity of orogenesis between eastern and western North Qilian, can well account for the differential distribution of Early Paleozoic high Sr/Y magmatism and other geological differences between the eastern and western parts of the North Qilian. Our study also implies that diachronous collision may lead to, apart from distinct metamorphic, structural and sedimentary responses, the large differences in magmatism and deep crustal processes along the orogenic strike.

Identification of slab window process is important for understanding the nature of the accretionary orogenesis. In this study, we report detailed petrological, geochronological, geochemical, Sr–Nd isotopic, and mineral chemical data for two dyke-like gabbroic intrusions from the South Tianshan belt of Tajikistan, southwestern margin of the Central Asian Orogenic Belt. Both intrusions are composed of coarse- and fine-grained gabbros. U–Pb zircon dating shows that they were emplaced at 431±5 Ma. The gabbroic rocks show relatively large variation in elemental and isotopic compositions, with SiO2 of 40.62–53.97 wt.%, Sr of 333–1261 ppm, and εNdt of +2.5 to +5.8. Especially, the fine-grained gabbros show lower SiO2 and higher MgO but more evolved isotopes than the coarse-grained gabbros for each of the intrusions. All the rocks display OIB-like or transitional OIB-/E-MORB-like geochemical characteristics with no obvious Nb-Ta depletion, indicative of an intraplate affinity. Combined with their mineral chemical compositions, we suggest that these gabbroic rocks were generated by partial melting of asthenospheric mantle in the transitional spinel-garnet stability field, followed by different degrees of fractional crystallization of olivine, clinopyroxene, and plagioclase and mixing with carbonatitic melts. The available data indicate that roll-back of the subducting Turkestan oceanic slab occurred during the Late Ordovician to Early Silurian period. Asthenosphere upwelling due to the opening of slab window resulted from localized slab tearing during slab roll-back may have been responsible for the generation of the studied dyke-like gabbroic intrusions.

Neoproterozoic intrusions are widespread in the northwestern margin of the Yangtze Block, and their petrogenesis was closely related to the assembly and breakup of Rodinia supercontinent. A combined study of zircon U–Pb dating, geochemistry and Sr–Nd–Hf isotopes was carried out for three types of intrusive rocks from the Hannan region, including the Beiba gabbros, the Tianpinghe and Taojiaba I-type granites and the Tiechuanshan and Huangguan A-type granites. LA-ICP-MS zircon U–Pb dating results show that the studied intrusions have crystallization ages ranging from ca. 880 to 770 Ma. The ca. 880 Ma Beiba gabbros have variable contents of MgO, Al2O3, Cr and Ni and extremely low high field strength elements (HFSE) concentrations that indicate a cumulate origin. These gabbros display subduction-related geochemical signatures with whole-rock initial 87Sr/86Sr (ISr) = 0.704–0.705, eNd(t) = −0.4 to +0.6 and zircon eHf(t) = +6.9 to +8.4, suggesting that they were derived from the partial melting of an enriched lithospheric mantle that had been modified by slab-derived materials. The ca. 860 Ma Tianpinghe I-type granites have high ISr (> 0.704) and negative eNd(t) (−5.6 to −3.5) values and zircon eHf(t) = −1.9 to +1.6, indicating their sources were mixtures of Neoproterozoic juvenile mafic crust and minor Paleoproterozoic crustal components, whereas the ca. 770 Ma Taojiaba I-type granites have relatively low ISr (

Early Paleozoic boninites occur in the Central Qilian orogenic belt, Northwest China. Their petrogenesis provides insights into lithosphere process and tectonic evolution of the Qilian block. In this paper, we carry out a study of geochronological, geochemical and Sr-Nd isotopic compositions for the Early Paleozoic boninites in the Lajishan area of the Central Qilian block. The Lajishan boninites (∼483 Ma) have high Al2O3/TiO2 (36.7–64.7) and CaO/TiO2 (31.1–49.6) ratios, and high MgO (7.86–10.47 wt%), Cr (439–599 ppm) and Ni (104–130 ppm) contents, indicating that the boninites result from a refractory mantle source. They are depleted in high field-strength elements (HFSE) and enriched in large ion lithophile elements (LILE), coupled with slightly high initial 87Sr/86Sr values of 0.7059–0.7074 and low eNd(t) values of −1.05 to +2.66, indicating that the mantle source was metasomatized by subducted slab-derived components. We found that an assemblage of low-Ca group and high-Ca group boninites occurred in the Lajishan belt. The high-Ca group boninites were derived from relatively fertile mantle with slightly higher melting degree, whereas the low-Ca group boninites were generated by partial melting of more refractory mantle wedge peridotites with slightly lower melting degree. The assemblage of low-Ca group and high-Ca group boninites reveals that the low-Ca group boninites were generated by the further melting of the more refractory mantle source after the segregation of the high-Ca group boninitic magmas in response to the back-arc basin opening. In the light of reported boninites worldwide, a diagram of Zr/Y vs. CaO/Al2O3 is used to identify boninites in fore-arc and back-arc regions. We suggest that the Lajishan boninites represent the products of back-arc basin development in response to the northward subduction of the Qaidam-West Qinling ocean slab.

The role of the mantle in generating ultrahigh-temperature metamorphism and peraluminous S-type granites, and the extent of crust−mantle interaction are topics fundamental to our understanding of the Earth's evolution. In this study we present geochronological, geochemical, and Sr–Nd–Hf isotopic data for dolerites and mafic volcanic rocks from the Darongshan granite complex belt in western Cathaysia, South China. LA–ICP–MS U–Pb zircon analyses yielded magma crystallization ages of ca. 250–248 Ma for the dolerites, which are coeval with eruption of the mafic volcanic rocks, ultrahigh-temperature metamorphism, and emplacement of S-type granites in the Darongshan granite complex belt. The mafic volcanic rocks are high-K calc-alkaline or shoshonitic, enriched in Th, U, and light rare earth elements, and depleted in Nb, Ta and Ti. The dolerites are characterized by high Fe2O3tot (11.61–20.39 wt%) and TiO2 (1.62–3.17 wt%), and low MgO (1.73–4.38 wt%), Cr (2.8–10.8 ppm) and Ni (2.5–11.4 ppm). Isotopically, the mafic volcanic rocks have negative whole-rock eNd(t) values (−6.7 to −9.0) and high ISr values (0.71232 to 0.71767), which are slightly depleted compared with the dolerite samples (eNd(t) = −10.3 to −10.4 and ISr = 0.71796 to 0.71923). Zircons in the dolerites have eHf(t) values of −7.6 to −10.9. The mafic volcanic rocks are interpreted to have resulted from the partial melting of an enriched lithospheric mantle source with minor crustal contamination during ascent, whereas the dolerites formed by late-stage crystallization of enriched lithospheric mantle-derived magmas after fractionation of olivine and pyroxene. The formation of these mantle-derived mafic rocks may be attributed to transtension along a NE-trending strike-slip fault zone that was related to oblique subduction of the Paleo-Pacific plate beneath South China. Such underplated mafic magmas would provide sufficient heat for the generation of ultrahigh-temperature metamorphism and S-type granites, and act as a mafic end-member for S-type granite genesis.

This paper presents an integrated study of petrology, geochronology, and geochemical and Sr–Nd–Hf isotopic compositions for the Jishishan medium- and fine-grained diorites and the Bamishan gabbroic and quartz dioritic dykes from the eastern Qilian orogen, to address their petrogenesis and the lithospheric evolution of the Qilian orogen. Laser ablation inductively coupled plasma mass spectrometry U–Pb zircon analyses show that they formed at c. 472–432 Ma. Geochemical and isotopic data suggest that the Jishishan diorites were derived from amphibole-bearing garnet-facies lithospheric mantle metasomatized by slab-derived fluids, whereas the Bamishan gabbroic dyke was derived from phlogopite-bearing garnet-facies lithospheric mantle enriched by sediment-derived melts. The Bamishan quartz dioritic dykes are high-potassic calc-alkaline and were predominantly derived from mafic lower crust. Based on available data, we suggest that the Jishishan diorites were generated during northward subduction of the South Qilian oceanic slab, whereas the Bamishan mafic–intermediate dykes formed in a post-collisional setting related to slab break-off. Moreover, we propose an integrated model for the Early Paleozoic tectonomagmatic evolution of the eastern Central Qilian, in which fluid-induced mantle metasomatism and melting characterized the oceanic subduction stage, whereas melting of varied sources (including subducted oceanic crust and overlying sediments, sediment melt-modified lithospheric mantle and the continental crust) was involved at the post-collisional stage. Supplementary material: Analytical methods, whole-rock geochemical and Sr–Nd isotopic compositions and zircon U–Pb and Lu–Hf isotopic data are available at https://doi.org/10.6084/m9.figshare.c.3975447

Post-collisional granitoids are widespread in the North Qilian and southern margin of the Alxa block and their petrogenesis can provide important insights into the lithospheric processes in a post-collisional setting. This paper carries out an integrated study of U-Pb zircon dating, geochemical and Sr-Nd-Hf isotopic compositions for five early Paleozoic intrusive plutons from the North Qilian to southern margin of the Alxa block. The geochronological and geochemical results show that their magmatism can be divided into three periods with distinct geochemical features. The early-period intrusive rocks (~ 440 Ma) include the Lianhuashan (LHS) and Mengjiadawan (MJDW) granodiorites. Both of them display high Sr/Y ratios (52–91), coupled with low Y and HREE contents, implying that they were derived from partial melting of thickened lower crust, with garnet in the residue. The middle-period intrusive rocks (~ 430 Ma), including the MJDW quartz diorites and Yangqiandashan (YQDS) granodiorites, are high-K calc-alkaline with low Sr/Y values. The geochemical and isotopic data suggest that they are generated from partial melting of lower crust without garnet in the residue. The late-period intrusive rocks (414–422 Ma), represented by the Shengrongsi (SRS) and Xinkaigou (XKG) plutons, are A-type or alkali-feldspar granites. They are possibly derived from partial melting of felsic crustal material under lower pressure condition. Our data show decreasing magma crystallization ages from MJDW pluton in the north and LHS pluton in the south to the SRS and XKG plutons in the central part of the study area. We suggest that such spatial and temporal variations of magmatic suites were caused by lithospheric delamination after the collision between the Central Qilian and the Alxa block. A more plausible explanation is that the delamination propagated from the margin part of the thickened lithosphere to inward beneath the North Qilian and southern margin of the Alxa block.

The petrogenesis of high Sr/Y-type magmas is still open to debate. Usually, such magmas could result from melting under high-pressure settings (> 12 kbar). In this paper, we gave an example that some high Sr/Y-type magmas could originate from melting of crustal materials at pressure of 10–12 kbar. We carried out a study of petrogenesis for Devonian high Sr/Y granites from the Beidashan batholith (397–411 Ma), southwestern Alxa Block, Northwest China. The Beidashan granites have SiO 2 (69.21–74.60 wt.%) and Al 2 O 3 (14.01–16.20 wt.%) with A/CNK ratios of 0.99–1.08. According to their trace element compositions and whole-rock zirconium saturation temperatures ( T Zr ), the Beidashan granites can be divided into two groups: Group I ((Dy/Yb) N = 1.2–3.0, Eu/Eu* = 0.77–1.3, T Zr = 761–856 °C), resulted from fluid-absent partial melting of mafic to intermediate crustal materials leaving garnet residuum at pressure of ~ 12 kbar, and Group II ((Dy/Yb) N = 0.76–2.16, Eu/Eu* = 1.7–5.3, T Zr = 651–785 °C), formed by fluid-present melting of mafic to intermediate crustal materials with residual amphibole in the source at pressure of ~ 10 kbar. Both Group I and Group II show high Sr/Y and (La/Yb) N features. They show I Sr = 0.7134–0.7180, e Nd ( t ) = − 6.61 to − 9.71, T 2DM = 1.7–1.9 Ga; e Hf ( t ) = − 5.6 to − 9.9 and T DM C = 1.7–2.0 Ga, indicating that the Beidashan high Sr/Y granites were derived from melting of crustal basement materials. Our results suggest that some high Sr/Y-type granites formed under relatively lower pressure conditions (~ 10–12 kbar), and they could not be an indicative of partial melting of thickened crust.

Early Paleogene granitoids in Southern Lhasa subterrane have been widely investigated and many petrogenesis and geodynamic models have been proposed in the past few years. However, contemporaneous granitoids in the Motuo tectono-magmatic belt, southeast Lhasa terrane, are still limitedly studied. Here we present the petrology, zircon U–Pb geochronology, whole-rock geochemistry, and Sr–Nd–Hf isotope data of the Damu and 52 K quartz–monzonite in the Motuo area. LA-ICP-MS U–Pb zircon dating shows that they have magma crystallization ages of 49 and 69 Ma, respectively. The Damu quartz–monzonite (SiO2 = 63.76–68.33 wt.%) is high-K calc-alkaline (K2O = 2.54–4.02 wt.% with K2O/Na2O = 0.59–1.09) and metaluminous to weakly peraluminous (A/CNK = 0.99–1.07). The 52 K quartz–monzonite (SiO2 = 61.12–66.12 wt.%) shows slightly higher K2O contents (3.80–5.28 wt.% with K2O/Na2O = 1.03–1.45) and metaluminous series (A/CNK = 0.96–1.00). The analyzed samples are characterized by high Ba (850–2573 ppm), Sr (534–986 ppm) contents, and fractionated REE patterns ((La/Yb)N = 22–72 and (Sm/Yb)N = 4.55–8.24). These geochemical features are comparable with those of high Ba–Sr granite. They display weakly evolved Sr–Nd–Hf compositions (whole-rock (87Sr/86Sr)0 = 0.7068 to 0.7086, eNd(t) = − 4.20 to − 3.41, and zircon eHf(t) = − 5.2 to − 0.9). Geochemical and Sr–Nd–Hf isotopic data reflect that the Damu and 52 K quartz–monzonite represent residual magma from AFC processes of lithospheric mantle-derived mafic melts. The over-thickened lower crust in the eastern Lhasa terrane had been delaminated during ca. 83–70 Ma, which led to the replacement of ancient lithospheric mantle by the juvenile lithospheric mantle. The juvenile mantle wedge in the study area was suspected to be metasomatized by melts that were derived from the foundering arc root, rather than the subducted sediments. Thus, the early Paleogene high Ba–Sr magmas from the SE Lhasa terrane may provide evidence for recycling of continental lithosphere by density destruction.

Mafic intrusive rocks are widely exposed in the Motuo tectono-magmatic belt, southeast Lhasa terrane. LA–ICP-MS U–Pb zircon dating shows that they have magma crystallization ages of 69 and ca. 50 Ma. These mafic intrusive rocks are characterized by variable SiO 2 (44.60–57.60 wt.%), high Al 2 O 3 (17.19–20.86 wt.%), and low MgO (1.85–5.38 wt.%) with Mg# of 31–55. Their chemical composition is comparable with low-MgO high-Al basalts to basaltic andesites. They are enriched in LILEs (Rb, Ba, K) and LREE and depleted in HFSEs (Nb, Ta, Zr, Hf, Ti), with weakly evolved Sr–Nd–Hf compositions (whole-rock ( 87 Sr/ 86 Sr) 0 = 0.7064 to 0.7086, e Nd ( t ) = − 3.41 to + 1.22, and zircon e Hf ( t ) = − 3.8 to + 6.4). The mafic rocks were derived from partial melting of metasomatized lithospheric mantle. Geochemical and Sr–Nd–Hf isotopic data show that they were insignificantly modified during magma emplacement. We provide a different secular evolution of the lithospheric mantle beneath the eastern part relative to the central part of the southern Lhasa terrane. Sr–Nd isotopic composition of the Motuo Late Cretaceous–Eocene mafic rocks argues that they were derived from partial melting of a relatively homogeneous and depleted lithospheric mantle. We propose that the Late Cretaceous delamination resulted in the replacement of ancient lithospheric mantle by the juvenile homogeneous lithospheric mantle in the eastern Lhasa terrane. The foundered ancient materials may subsequently re-fertilize the lithospheric mantle not only in the eastern Lhasa terrane but also in the surrounding areas.

Late Cretaceous (~ 106–76 Ma) adakite-like intrusive rocks in the middle-eastern Gangdese belt occur in an E–W trending belt paralleling the Indus–Yarlung suture, south Tibet. Their petrogenesis and geodynamic processes have been a subject of debate. We report here U–Pb zircon ages, geochemical and Sr–Nd–Hf isotopic data for adakite-like intrusive rocks as well as the normal arc rocks (gabbros and gabbroic diorites) in the middle Gangdese belt. LA-ICPMS U–Pb zircon analyses yielded an identical age of ~ 88 Ma for two adakite-like rocks, which are slightly younger than the gabbro and gabbroic diorite (ca. 94–90 Ma). Both the adakite-like rocks and the normal arc rocks have similar whole-rock Sr–Nd and zircon Hf isotope compositions, indicating that they have been derived from a common source. Similarly, the adakite-like and normal arc intrusive rocks in the eastern Gangdese belt also show similar Sr–Nd–Hf isotope compositions. In the middle-eastern Gangdese belt, the > 85 Ma Late Cretaceous intrusive rocks consist of a magma series from gabbro to granodiorite, including both normal arc rocks and adakite-like rocks. These rocks overlap in space and time that conform to a normal arc differentiation trend. In terms of major and trace elements, they also show a clear evolution from the normal arc magmatic into adakitic field. Thus, we suggest that these > 85 Ma Late Cretaceous intrusive rocks were ultimately derived from melting of the hydrated mantle wedge and the adakite-like rocks can be generated in normal arc magmas by amphibole-dominated fractionation. Taking into accounting for the spatial and temporal distribution of the Cretaceous magmatic rocks in the Lhasa terrane, we prefer a model of early Late Cretaceous rollback following Early Cretaceous low-angle oceanic slab subduction. At intermediate pressure and H2O-rich conditions, fractionation of amphibole changes the major and trace element compositions of arc magmas, and will efficiently drives basaltic composition to andesitic composition in arc magmas.

Voluminous Early Paleozoic intrusive rocks occur in the Qilian orogenic belt, northeastern margin of the Tibetan Plateau. Their petrogenesis can provide insights into the tectonic evolution of Qilian and its adjacent areas. This paper carries out an integrated study of U–Pb zircon dating, geochemical and Sr–Nd–Hf isotopic compositions for the Bamishan and Heishishan plutons in the eastern Qilian orogen. Both the Bamishan and Heishishan plutons consist of mafic, intermediate and felsic intrusive rocks. U–Pb zircon dating yielded the magma crystallization ages of 459–449 Ma for the Bamishan pluton and 447–438 Ma for the Heishishan pluton. Their geochemical and Sr–Nd–Hf isotopic data show that the parental magmas of the Bamishan monzogranites and quartz diorites were generated by slab (MORB and overlying sediments) melting. The Bamishan hornblende gabbros have extremely high Cr (1159–1163 ppm), Ni (220–353 ppm) and Mg# (73–74), indicating a cumulate origin. The Heishishan granodiorite–granite has adakitic geochemical signatures and they were produced by partial melting of the mafic lower crust. The Heishishan hornblende gabbro and quartz diorites were derived from the enriched lithospheric mantle metasomatized by subduction-related fluid/melt. In light of the available data, we propose that there was an Early Paleozoic ocean basin between the Central-South Qilian and Qaidam–West Qiling belts. The northward closure of this basin and subsequent continental collision and post-collisional processes resulted in the generation of the Early Paleozoic magmatism in the eastern Central Qilian. The Late Ordovician to Early Silurian (~ 460–440 Ma) intrusive rocks in the eastern Central Qilian formed in a post-collisional setting. A slab break-off model may account for the magma generation.

Whole-rock geochemistry, Sr–Nd isotope and zircon U–Pb isotope data are reported for seven granitoid intrusions from the eastern Lhasa terrane. Our zircon U–Pb data exhibit three periods of magmatism: 164–125 Ma, 83 Ma, and 71–45 Ma. Granitoids from the Middle Jurassic to Early Cretaceous (164–125 Ma) display evolved Nd isotope composition, with eNd(t) = − 8.6 to − 15.5 and T2DM = 1.6 to 2.2 Ga. In contrast, the Late Cretaceous (83 Ma) granitoids with adakitic characteristics (high Sr/Y ratios) display less evolved Nd isotopic composition, with eNd(t) = − 0.3 to − 3.0 and T2DM = 0.9 to 1.1 Ga. Geochemical and Sr–Nd isotopic data indicate that the Middle Jurassic to Early Cretaceous granitoids were derived from partial melting of Proterozoic crustal basement and the Late Cretaceous adakitic granitoids were derived from partial melting of over-thickened lower crust. Geochemical and Sr–Nd isotopic data of granitoids from the Latest Cretaceous to Eocene period (71–45 Ma) reveal that they result from diverse magma sources including both juvenile and reworked mature crustal materials. Our compilation of new and published data from the eastern Lhasa terrane show a marked variation in Sr/Y ratios and a step change in Sr–Nd isotope compositions during the Late Cretaceous. We suggest that the Middle Jurassic to Early Cretaceous granitoids resulted from the northward Neo-Tethyan ocean slab subduction. The increasing Sr/Y ratios from the Middle Jurassic to Late Cretaceous granitoids and northeastward migration of arc magmatism in the eastern Lhasa terrane during the interval ca. 125–95 Ma are attributed to the shallowing angle of subduction of the Neo-Tethyan ocean slab. The Late Cretaceous magmatism in the eastern Lhasa terrane probably resulted from the Neo-Tethyan mid-ocean ridge subduction and subsequent delamination of the arc root. The Latest Cretaceous to Eocene granitoids could be interpreted as a magmatic response to roll-back and/or break-off of the subducted Neo-Tethyan slab.

The Qinling–Dabie–Sulu orogenic belt is the junction between the North and South China blocks, which resulted from the final amalgamation of China continents during the Indosinian. Indosinian granitoids are widespread in the Qinling orogen, and their geneses can thus constrain the evolution of China continent. We carried out a combined U–Pb zircon dating and geochemical study for the Shuangpengxi granodiorite pluton and the Xiekeng diorite–granodiorite pluton in the middle part of the West Qinling orogen. U–Pb zircon dating shows that the magma crystallization ages of 242 ± 3 Ma for the Shuangpengxi pluton and ~244–242 Ma for the Xiekeng pluton. Geochemical and Sr–Nd–Hf isotopic compositions reveal that the magma of the Shuangpengxi granodiorite was derived from partial melting of crustal materials. The Xiekeng diorites can be divided into high-Al diorite and high-Mg diorite. Both of them resulted from partial melting of enriched lithospheric mantle, but their mantle source had been modified by previous slab-derived melt. The high-Al diorite was formed by fractional crystallization of olivine, pyroxene and/or preferential accumulation of plagioclase, and the high-Mg diorite was formed by fractional crystallization of olivine and/or preferential accumulation of pyroxene. The Xiekeng granodioritic porphyry was formed by mixing of crust-derived and mantle-derived melts. We propose that the Early Indosinian magmatism resulted from break-off of subducted oceanic slab after collision. The slab break-off model can well explain the linear distribution of the Early Indosinian plutons and rapid crustal uplift during the Middle Triassic in the West Qinling.