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The final assembly of Gondwana, known as the late Pan-African orogeny, is characterized by Ediacaran–early Cambrian ultrahigh temperature (UHT) metamorphism, which is widely identified within reconstructed East Gondwana. This distinctive feature likely provides a reliable criterion for identifying new Gondwanan terranes that lack paleo-geomagnetic data. Here we present zircon U–Pb geochronology and phase equilibria calculations for a variety of granulite types newly recognized from western Qaidam, China, which provide the first evidence that the Qaidam block, at least western Qaidam, experienced high-grade metamorphism in excess of 900 °C before/at 540–520 Ma. These UHT metamorphic rocks, similar to many well-known Pan-African UHT metamorphic terranes, is inferred to evolve along a clockwise P–T path that is usually related to collisional orogens. Comparison between new metamorphic zircon U–Pb ages from western Qaidam and the published age data from the UHT metamorphic terranes within East Gondwana suggests that the UHT metamorphic rocks found in western Qaidam similarly records the final assembly of Gondwana. Although the exact paleo-geographical location of the Qaidam block during the Gondwana period is unknown yet because of lacking paleo-geomagnetic data, new Pan-African UHT metamorphic record found in western Qaidam indicates, for the first time, that the Qaidam block is a Gondwanan terrane that split from this semi-supercontinent after the Pan-African orogeny.

The granulitized eclogites from the Luliangshan terrane of the North Qaidam UHP metamorphic belt occur as lenses within pelitic gneisses and orthogneisses. Combined petrologic data and phase equilibrium modeling indicate a multi-stage metamorphic history of the granulitized eclogites: (1) an earlier eclogite facies metamorphism (P>18.5 kbar, T> 830 °C) is deduced from omphacite relics in the matrix and rare omphacite inclusions within garnet. The possible assemblage is garnet+omphacite+rutile+ quartz; (2) the early stage of high pressure granulite facies assemblages (garnet+clinopyroxene+ plagioclase+rutile+quartz+liquid) developed in the early decompression process has a P-T regime of 17.5 kbar and 852–858 °C, constrained by plagioclase and clinopyroxene inclusions in garnet. The late stage of high pressure granulite assemblages (garnet+clinopyroxene+amphibole+plagioclase+rutile+quartz+liquid) records an isothermal decompression process with the pressure successively declining from 17.5 to 14.7 kbar and to 11.3 kbar at 858 °C; (3) the later medium pressure granulite facies assemblage (garnet+ orthopyroxene+ clinopyroxene+amphibole+plagioclase+ilmenite+liquid+quartz) indicates a drop in pressure and rise in temperature at P-T conditions of 7.6–7.7 kbar and 878–883 °C; (4) retrogressive amphibolite facies stage, which is represented by amphibole+plagioclase kelyphitic rims around garnet, formed under conditions of

As the products of early Paleozoic continental collision, widespread eclogite facies rocks crop out in the Yuka terrane, western North Qaidam Mountains, NW China. Eclogites commonly reach ultrahigh pressure (UHP) metamorphic conditions. However, whether the associated metapelitic rocks also experience UHP metamorphism has not been thoroughly elucidated to date. In this contribution, we chose two eclogite samples and one metapelite sample to investigate their metamorphic evolution. Combining with petrographic observation and P–T pseudosections, similar clockwise P–T paths with peak stages at 25–34 kbar, 580–633 °C were obtained for eclogites and metapelites. Eclogite ZM871 records a prograde metamorphic condition at 21.6 kbar/552 °C, defined by the assemblage garnet + omphacite + epidote + lawsonite + talc (+quartz + phengite + rutile) and a peak metamorphic condition at 34.0 kbar/633 °C by the assemblage garnet + omphacite + lawsonite + talc (+coesite + phengite + rutile). Eclogite ZM641 records a prograde metamorphic condition at 21.5 kbar/520 °C, defined by the assemblage garnet + omphacite + glaucophane + lawsonite (+quartz + phengite + rutile) and a peak condition at 30 kbar/616 °C by the assemblage garnet + omphacite + lawsonite + talc (+quartz + phengite + rutile). Metapelite ZM8–1 records a prograde metamorphic condition at 18.2 kbar/530 °C defined by the assemblage garnet + chloritoid + chlorite (+quartz + phengite + rutile), a peak condition at 25 kbar/580 °C by the assemblage garnet + kyanite + chloritoid (+quartz + phengite + rutile), and a retrograde condition at 16.2 kbar/595–598 °C by the assemblage garnet + kyanite + chloritoid + chlorite (+quartz + phengite + rutile). Combined with previous data from orthogneiss and impure marble in the Yuka terrane, which also recorded UHP metamorphic conditions, the Yuka eclogite–bearing unit commonly underwent UHP metamorphism, although further investigation is warranted to verify whether the Yuka unit represents a single coherent UHP metamorphic terrane or a collage of different UHP metamorphic slices.

The Hutuo Group, as one of the classic examples of Paleoproterozoic strata, plays an important role in establishing evolutionary processes in the Trans-North China Craton. In this contribution, we present petrologic, detrital zircon U-Pb ages and Lu-Hf isotopes from three subgroups of the Hutuo Group. Sandstones in the Doucun and Dongye Subgroups are dominated by Q (monocrystalline and polycrystalline quartz) and F (K-feldspar and plagioclase) with minor lithic fragments, suggesting that the detrital components were mainly derived from both the continental block and recycled orogen. In contrast, clastic components in the Guojiazhai Subgroup are mainly Q and lithic fragments, indicating they were derived predominantly from the recycled orogen. The ages of detrital zircons from sandstones in the Doucun and Dongye Subgroups are mainly concentrated at ca. 2.5 Ga and 2.2–2.1 Ga with minor 2.7 Ga zircons also present which indicates they were dominantly sourced from 2.5 Ga Wutai, Fuping and Zanhuang Complexes, and Paleoproterozoic intrusives. The Guojiazhai Subgroup displays a different zircon age population of ca.2.4 Ga, 2.2–2.1 Ga and 2.0–1.9 Ga, which indicates likely derivation from Paleoproterozoic intrusives in the Wutai, Luliang and Hengshan areas. Based on the observation that sandstone clastic components in the Doucun and Dongye Subgroups are dominantly quartz, feldspar and sedimentary lithic fragments, but not volcanic lithics, we propose that they were deposited in a rift-related setting. Zircons from the lower sequence of the Hutuo Group yielded a young population of 2140 Ma. Considering the volcanic rocks of 2140 ± 14 Ma at the base of the group and 2.2–2.0 Ga magmatism along the TNCO, we propose that Doucun and Dongye Subgroups formed at 2.2–2.0 Ga. The youngest, ca. 1.9 Ga, zircons in the Guojiazhai Subgroup indicate this Group was deposited during closure of the rift at 1.9–1.8 Ga. The two stage model ages of the detrital zircons mainly range from 2.6 to 2.9 Ga with a minor ∼2.5 Ga contribution. Therefore, we infer that 2.6–2.9 Ga represents a period of intensive crustal growth in the Trans-North China Orogen, but that some degree of crustal growth continued to ∼2.5 Ga.

In the northern West Qinling orogen (WQO), granulite-facies metamorphic rocks are recognized within the Qinling Complex. These rocks are composed of amphibole-bearing two-pyroxene granulite and garnet-sillimanite gneiss with widespread migmatitization. We investigate three granulite-facies samples and one leucosome sample from the Qinling Complex, which are suitable for U-Pb analyses of zircon and monazite. SHRIMP and LA-ICPMS U-Pb age dating of zircon and monazite from two pelitic granulites provides weighted mean ages of 430±4 Ma (MSWD=0.88) and 433±4 Ma (MSWD=0.27), respectively. Based on the petrographic characteristics and zircon CL imagery, we postulated a ca. 430 Ma metamorphic timing for the pelitic granulites. LA-ICPMS zircon U-Pb data from an amphibole two-pyroxene granulite sample reports two weighted mean age groups: 424±3 Ma (MSWD=0.45) and 402±3 Ma (MSWD=1.4), which were interpreted as granulite-facies metamorphic and retrograde ages, respectively. LA-ICPMS U-Pb dating of zircons from the leucosome sample yields a weighted mean age of 426±2 Ma (MSWD=0.3), which is interpreted as the crystallization age of the leucosome. These data indicate that the West QOB experienced early Paleozoic granulite-facies metamorphism and anatexis similar to the East QOB. However, it remains unclear whether the early Paleozoic granulite facies metamorphism resulted from an arc setting created by the northward subduction of the Shangdan ocean or from a continental collisional orogenic event.

The Gantaohe Group, located in the Zanhuang area, contains typical North China Craton Paleoproterozoic strata, and is one of the best-preserved examples of these rocks. It is therefore a significant area for deciphering evolutionary process in the trans-North China Orogen. In this paper, we present petrologic, detrital and volcanic zircon U–Pb ages and Lu–Hf isotopes from three formations of the Gantaohe Group. The zircons from a conglomerate at the base of the Gantaohe Group yielded a young population of ca. 2.1 Ga. Dacite from the upper section of the Nansizhang Formation yielded zircon 207 Pb/ 206 Pb ages of 2090 ± 14 Ma. Thus, the initial deposition of the Gantaohe Group occurred at ∼2.1 Ga. The Group underwent greenschist to low amphibolite facies metamorphism, identical to regional 1.87–1.85 Ga metamorphism in Zanhuang Complex. Therefore, we propose that the Gantaohe Group was deposited in the period between 2.1 Ga and 1.9 Ga. Sandstones in the Gantaohe Group are dominated by Q (monocrystalline and polycrystalline quartz) and F (K-feldspar and plagioclase) with only minor lithic fragments, suggesting that detrital components were mainly derived from a cratonic source. Detrital zircons from sandstones exhibit a dominant population of 2.55–2.5 Ga grains with minor contributions of ∼2.7 Ga and ∼2.1 Ga grains, which further indicate they were dominantly sourced from ∼2.5 Ga TTG gneisses, late Archean Zanhuang and late Archean to Paleoproterozoic Guandu Groups, with subordinately input from ∼2.7 Ga TTG gneisses and the Paleoproterozoic Xuting granite. Given that the sandstone clastic components chiefly comprise quartz and feldspar, there is a lack of volcanic lithics, and the major detrital zircons are 400 Ma older than the initial deposition age, we propose that the Gantaohe Group was deposited in a rift-related setting far from any back-arc basin at ∼2.1 Ga or 1880–1810 Ma syn-collisional processes. A few 2.5–2.7 Ga zircons have positive e Hf ( t ) values identical with the contemporaneous depleted mantle and the 207 Pb/ 206 Pb ages are similar to their single stage model ages ( T DM1 ), which suggests some degree of 2.5–2.7 Ga crustal growth. Most ∼2.5 zircons, however, show 207 Pb/ 206 Pb ages that are much younger than the Hf single stage model ages, which indicates intensive crustal reworking in the late Neoarchean. The zircons collectively present two stage model ages ranging from 2.6 to 2.9 Ga. Therefore, we suggest that the 2.6–2.9 Ga periods represents a time of intensive crustal growth in the Zanhuang Complex.

The Xuting pluton, located at the north section of the Zanhuang Complex, contains potassic and sodic granite in both of which shallow level emplacement is shown by graphic texture feldspar and quartz intergrowth. Two potassic granite and one sodic granite samples yielded zircon 207 Pb/ 206 Pb ages of 2066 ± 17 Ma, 2092 ± 14 Ma, and 2071 ± 14 Ma, respectively, suggesting that the Xuting pluton emplaced between 2070 Ma and 2090 Ma, which is coeval with the Paleoproterozoic Gantaohe Group dominated by mafic volcanic and sedimentary rocks. The potassic granite is enriched in SiO 2 , total FeO, REEs (except Eu), Zr, Nb, Ga and Y, and depleted in MgO, CaO, Al 2 O 3 , Sr, V, Cr and Ni, with high TFeO/MgO ratios, consistent with the features of A-type granite. Except for the high MgO and low K 2 O contents, the sodic granite also presents most of the features of A-type granites. The zircon saturation temperatures from the potassic and sodic granites range from 855 to 998 °C and 853 to 933 °C respectively, indicating that they are from the high temperature magma. The potassic granites have the e Hf (t) ranging from − 5.9 to + 1.33 and Hf model ages of 2.5–2.8 Ga, which are identical with the ages of Neoarchean TTG gneisses in the Zanhuang Complex. We propose that the potassic granite in the Xuting pluton derived from the partial melting of Neoarchean TTG gneisses. The sodic granites also present negative e Hf (t) values from − 4.81 to − 0.76 and Hf model ages of 2.5–2.8 Ga, suggesting that they come from the partial melting of the Neoarchean crust. However, with relative enrichment in MgO and total FeO, and lower K 2 O and Rb, the sodic granite was derived from a mafic source in the lower crust. The likely heat source was high heatflow associated with mantle upwelling. The A-type Xuting pluton and mafic volcanic rocks in the Gantaohe Group constitute a bimodal lithologic association from a Paleoproterozoic continental rift environment. 2.2–2.0 Ga magmas are widely distributed along the Trans-North China Orogen (TNCO), and also present a bimodal character. We propose that 2.2–2.0 Ga bimodal magmas throughout the TNCO were likely formed in a Paleoproterozoic rifting setting. Considering the widespread 2.2–2.0 Ga magmatic rocks in the North China Craton (NCC), we infer that the magmatism likely occurs in tensional environment after the initial amalgamation of the NCC in the late Archean.

The Hutuo Group, located in the Wutai Mountains area, is characteristic of Paleoproterozoic strata in the North China Craton, and plays an important role in establishing evolutionary processes in the Trans-North China Orogen. We present petrological observations along with geochemical and Nd isotopic data for basalts in the Qingshicun and Hebiancun Formations of the Hutuo Group. These basalts are enriched in TFeO (11.97−18.01 wt.%), consistent with occurrences of iron-rich basalt world-wide. They also display relatively high MgO (4.95−12.25 wt.%), Ni (79−121 ppm) and Cr (37−101 ppm) and low in SiO 2 (41.37−51.95 wt.%). Therefore, the iron-rich character of the Hutuo Group basalts originated with their parental magma rather than via shallow crustal fractionation at low oxygen fugacity, as inferred for many high iron basalts. The Hutuo Group basalts exhibit weak to moderate differentiation of light REE over heavy REE ((La/Lu) cn = 2.61−6.79) with minor or slight Eu anomalies (Eu/Eu* = 0.77−1.41), and also show the Nb and Ti troughs without obvious Zr and Hf anomalies. The ɛ Nd ( t ) values of the basalts range from −1.23 to +0.81 with T DM of 2489−2664 Ma. The basalts most plausibly originated from the fertile subcontinental lithosphere mantle and, in the case of the Qingshicun Formation basalts, also underwent the crustal contamination. Basalts in the Hutuo Group also have the high Zr/Hf ratios, and present high Ti/V values of 24−55 and Zr/Y ratios ranging from 4.6 to 13.6, suggesting that they were emplaced in a within-plate setting. Considering the sedimentary associations and detrital fragments in the Hutuo and Gantaohe Groups, and bimodal magmatism along the Trans-North China Orogen, we propose that 2.2−2.0 Ga geological events within the orogen were rift-related, but did not result from subduction or island arc processes.

The Qinling Orogen, which was formed by long-lived subduction and collision between the North and South China blocks, can be divided into the South Qinling orogenic belt (SQOB) and the North Qinling orogenic belt (NQOB) by the Shangdan suture zone. Orogen-scale shear zones developed on the boundaries within the NQOB can be used to enhance our understanding of collisional orogeny that occurred during the Paleozoic in the Qinling Orogen. Previous studies have identified several ductile shear zones on boundaries between different lithotectonic units in the eastern NQOB. However, ductile shear zones related to orogenic processes in the western NQOB have attracted relatively little attention. Herein, we present structural and chronological data for the ductile shear zones in the Tianshui region, western NQOB. Three sub-parallel ductile shear zones (DSZ-1, DSZ-2, and DSZ-3) are recognised in the southern Qinling Complex or as boundaries between the Qinling Complex and adjacent lithotectonic units in the Huamiao area, Tianshui City. Microstructural and fabric analyses indicate that these shear zones have kinematics of transpressive sinistral strike-slip. Zircon U-Pb and 40Ar-39Ar dating data suggest that these ductile shear zones experienced a prolonged period of deformation from 420 to 370 Ma during exhumation, which was related to oblique convergence between the SQOB and the NQOB. Combining with the synchronous Xinyang-Yuanlong dextral shear zone in the northern Qinling Complex, we suggest that the transpressive sinistral shearing and dextral transpressive ductile shearing on both sides of the Qinling Complex subjected it to orogen-parallel oblique-slip extrusion during the middle Paleozoic. Our results, together with previously published data in the eastern NQOB, indicate the occurrence of orogen-scale strike-slip shearing along the whole NQOB during the Paleozoic orogeny.

Cathodoluminiscence imagery of zircons revealing 206Pb/238U ages and Th/U ratios (Table S1) and analysis of biotite from mylonitized paragneiss yielding Ar–Ar plateau and isochron ages (Table S2)