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Significance The Jehol Biota is well known for producing exceptionally preserved specimens of feathered dinosaurs, early birds, mammals, as well as insects and early flowering plants, thus providing key evidence for understanding the early evolution of birds and for reconstructing the Early Cretaceous terrestrial ecosystem. Here, we present eight SIMS U-Pb zircon ages from the Huajiying Formation, the lowest Jehol fossil-bearing deposits in northern China, which have placed stringent age controls on the early phase of the Jehol Biota, and have extended the temporal range of the Jehol Biota to over 15 My. Our findings will shed light on the evolutionary radiation of the Jehol Biota as well as the origins of major vertebrate groups in the Early Cretaceous., The Lower Cretaceous Huajiying Formation of the Sichakou Basin in northern Hebei Province, northern China contains key vertebrate taxa of the early Jehol Biota, e.g., Protopteryx fengningensis, Archaeornithura meemannae, Peipiaosteus fengningensis, and Eoconfuciusornis zhengi. This formation arguably documents the second-oldest bird-bearing horizon, producing the oldest fossil records of the two major Mesozoic avian groups Enantiornithes and Ornithuromorpha. Hence, precisely determining the depositional ages of the Huajiying Formation would advance our understanding of the evolutionary history of the Jehol Biota. Here we present secondary ion mass spectrometry (SIMS) U-Pb zircon analysis results of eight interbedded tuff/tuffaceous sandstone samples from the Huajiying Formation. Our findings, combined with previous radiometric dates, suggest that the oldest enantiornithine and ornithuromorph birds in the Jehol Biota are ∼129−131 Ma, and that the Jehol Biota most likely first appeared at ∼135 Ma. This expands the biota’s temporal distribution from late Valanginian to middle Aptian with a time span of about 15 My.

Reactive nitrogen (N) deposition from human activity significantly impacts temperate vegetation in areas where low natural N availability limits vegetative productivity. However, the ecosystem response to anthropogenic N deposition remains elusive owing to the scarcity of long-term empirical observations. Here a N isotope of a pyrogenic material was used to investigate long-term N availability evolution in a forest-steppe ecosystem in North China. The N availability was found to have significantly increased since circa 7,400 years BP when primitive agriculture began. Different N availability changes were observed under primitive agriculture (6,600-3,500 cal. years BP) and Sui-Tang traditional agriculture (AD 581-907), implying dependency on the agricultural mode. A 220-year N availability recovery period after Sui-Tang agriculture was observed. On this basis, a minimum of several hundred years is projected for the restoration of the temperate ecosystem if the modern N cascade were to be stopped. Plain Language Summary The manner in which a temperate ecosystem responds to continuous anthropogenic nitrogen (N) deposition remains an open question. The lack of long-term empirical observation has limited the understanding of this ecological issue. Agricultural practices over the past several thousand years in North China may be an ancient reference for the modern use of N fertilizer. In the present study, we used a geochemical method to reconstruct a 10,000-year history of N changes in the plant-soil system of the Daihai Lake region in North China. The reconstructed N history was then compared with archeological evidences of early agriculture in the region. We found that early agriculture significantly influenced N changes in the plant-soil system about 7,400 years ago and that 220 years were required for the plant-soil system to recover from the N disturbance caused by agricultural activity during the Sui-Tang dynasty (AD 581-907). On this basis, it is predicted that several hundred years would be required to reverse the effects of modern N disturbance on a temperate ecosystem.

In this contribution, we carry out an integrated study of petrology, whole-rock geochemistry, as well as zircon morphology, trace element, U–Pb and Lu–Hf isotopes for granitic gneisses and leucogranites from the Yudongzi complex, a poorly studied Archean outcrop in the northwestern Yangtze Block. The granitic gneisses have the TTG affinity characterized by relatively high Na2O/K2O and Sr/Y ratios, and fractionated REE pattern with relatively high LREE but low HREE concentrations. Zircon grains in the granitic gneisses show magmatic cores and metamorphic rims. U–Pb dating on zircon core of four granitic gneiss samples yielded their formation ages as 2660–2632 Ma with a weighted average of 2650 ± 21 Ma (MSWD = 1.6; n = 4). Their average eHf (t) values range from −0.6 to 0.5 and two-stage model ages from 3.20 to 3.10 Ga, suggesting that the granitic gneisses were likely generated by remelting of thickened Mesoarchean proto-mafic crust. The metamorphic zircon rims have relatively high Th/U ratios and identical Hf isotope compositions to their corresponding cores, indicating that the rims were formed via solid-state recrystallization process. The metamorphic zircons recorded a metamorphic event at ca. 2.5 Ga. U-Pb dating and Lu-Hf isotopes on magmatic zircons from a leucogranite sample revealed a magmatic event at 2477 ± 18 Ma. The recognization of the 2.65 Ga TTG magmatism and the 2.48 Ga intercrustal remelting event in the Yudongzi complex demonstrates the widespread Neoarchean magmatism in the Yangtze Block. Combined with the age spectra of previous detrital zircons, we show that the Yangtze Block has experienced a major tectonothermal event in the late Archean. The Yudongzi complex has a distinct crustal evolution history compare with the Paleoarchean continent nucleus in the eastern part of the Yangtze Block, suggesting that the continent nucleus might have subjected to lateral growth by accretion processes.

This study discussed the petrological classification, petrogenesis, and tectonic significance of early Paleozoic high-Mg granodiorite from the Erlangping unit, in the North Qinling orogen. To achieve this target, we conducted integrated investigation of in situ zircon U–Pb dating, whole-rock geochemical, as well as Sr-Nd-Hf-O isotopic compositions for the Kanfenggou pluton from the Erlangping unit. LA-ICP-MS zircon dating for the Kanfenggou samples yields U–Pb ages of 442.9 ± 6.2 and 438.0 ± 6.7 Ma, suggesting that the pluton was emplaced at ca. 440 Ma. Whole-rock geochemical compositions of the samples display intermediate SiO 2 (60.48–64.67 wt%) and K 2 O (1.21 to 2.10 wt%), but high Al 2 O 3 (15.44 to 16.51 wt%) and Na 2 O (4.01 to 4.81 wt%) contents. The granodiorite samples are characterized by elevated MgO ranging from 2.30 to 3.44 wt% and Mg# values of 53.35to 56.66, implying they are high-Mg granodiorites. They are characterized by very high Ba (524–1132 ppm) and Sr (684–980 ppm) contents, but depleted in HREE, and high (La/Yb) N ratios of 6.34 to 16.5 and slightly negative to weak positive Eu anomalies (Eu/Eu* = 0.68–1.09). These evidence that the Kanfenggou pluton belongs to the sanukitoid series. The high-Mg granodiorite samples exhibit a mantle signature with high Mg# values (53.35–56.66), Cr (45.8 to 93.3 ppm) and Ni (28.2 to 48.2 ppm) contents, but enriched in LILE, pointing to an enriched mantle source. The samples show relatively depleted radiogenic isotopic compositions with initial 87 Sr/ 86 Sr ratios varying from 0.7044 to 0.7047, e Nd (t) values from 0.31 to 4.21, and zircon e Hf (t) values from 7.3 to 8.3. The zircons have a mean δ 18 O value of 5.20 ± 0.17 ‰. Based on the trace element geochemical features, the metasomatic agent was suggested to be the fluids generated from dehydration of subducted slab. Therefore, we suggest two-stage processes for the formation of the Erlangping high-Mg granodiorites: (1) interaction between slab fluids and mantle peridotite; (2) partial melting of metasomatized mantle peridotite caused by the asthenosphere mantle upwelling and the initial back-arc opening resulted from the oceanic slab rollback.

Ascertaining the petrogenesis of granitoid rocks in subduction zones holds the key for understanding the processes of how continental crust is produced. The synchronous Taoyuan and Huanggang plutons occur in two different geological units of the Paleozoic Tongbai orogen of central China. They provide an optimal opportunity for a study to address the role of the crustal basement in generating voluminous granitoid magmatism in subduction zones. The Taoyuan and Huanggang plutons have identical U–Pb zircon crystallization ages of 440–444 Ma, which are temporally related to northward subduction of the Paleotethyan Ocean. The Taoyuan samples show high SiO 2 (73.36–79.16%) and low Al 2 O 3 (12.00–13.45%) contents, Mg numbers (20.6–38.2), and Sr/Y (2.04–10.1) and (La/Yb) N (2.34–7.32) ratios with negative Eu anomalies (Eu/Eu* = 0.33–0.93). They yielded positive e Nd (t) (+ 3.0 to + 6.7) and e Hf (t) (+ 11.8 to + 13.2) values, elevated initial Sr isotopic ratios (0.7040–0.7057) and relatively low zircon δ 18 O values of 4.62–5.39‰. These suggest that they were produced through partial melting of hydrothermally altered lower crust of the accreted Erlangping oceanic arc. In contrast, the Huanggang samples exhibit variable whole-rock geochemical and isotopic compositions with SiO 2 contents of 57.01–64.42 wt.%, initial Sr isotopic ratios of 0.7065–0.7078, and e Nd (t) values of − 5.7 to − 9.4. Additionally, they have high zircon δ 18 O values of 7.57–8.45‰ and strongly negative zircon e Hf (t) values of − 14.4 to − 10.5. They were suggested to have been mainly derived from ancient continental crust of the Kuanping crustal unit with the addition of 20–40% juvenile, mantle-derived material. Accordingly, the granitoids in both oceanic and continental arcs are likely to be mainly derived from intracrustal melting of their crustal basement. It is revealed by the Huanggang pluton that little net continental crust growth occurs in continental arcs, and addition of new volume of continental crust may be balanced by the loss of old mafic lower continental crust. Continental growth was likely achieved through the accretion and subsequent differentiation of oceanic arcs, as manifested by the Taoyuan pluton.

An integrated study of petrography, zircon U-Pb ages, Hf-O isotope compositions, as well as whole rock geochemistry was carried out for a Paleoproterozoic granite complex in the northern Yangtze Block, to investigate its petrogenesis and geological significances. Petrographically, the Huashanguan complex is a granite complex comprised of monzogranite in the marginal facies and K-feldspar granite in the central facies. U-Pb dating of magmatic zircons from the monzogranite and K-feldspar granite yielded ages of 1816 ± 50 Ma and 1843 ± 9 Ma respectively. The more precise age of 1843 ± 9 Ma is suggested to represent the formation age of the Huashanguan complex. The granites have uniform negative zircon e Hf (t) values of −20.2 to −15.8, with corresponding T DM2 ages of ca. 3.6–3.5 Ga. The δ 18 O values average at 6.80 ± 0.09‰. These indicate that the granites were generated by partly melting of Archean rocks, implying the widespread of Archean basement in the Yangtze Block. The monzogranites display low FeO T and MgO contents and evolved trace element features, suggesting their formation by more fractional crystallization from similar parent magma of the K-feldspar granites. The occurrence of the Huashanguan granite complex indicates that the Yangtze Block has experienced a tectonic transition from tectonic convergence to extension at ca. 1.85 Ga, possibly due to the collapse of the ca. 2.0 Ga orogeny.

In comparison with previous studies on the Ni-Mo-PGE ore deposits within the deep water Lower Cambrian black shales of the Niutitang Formation around Hunan and Guizhou provinces, this study focused on the shallow water Ni-Mo-PGE enriched layer of the Niutitang Formation around Hubei Province by means of an integrated geochronological, PGE, REE and trace element geochemical study. The results suggest the Ni-Mo-PGE enriched layer has a dominant seawater origin, whereas the Ni-Mo-PGE ore deposits have mixed seawater, hydrothermal and terrigenous origins. Trace metals precipitated from ambient seawater under anoxic-suboxic settings at exceedingly slow sedimentation rates with episodic injections of fresh oxidized seawater. Organic matter played an important role in sourcing, transporting and precipitating trace metals. However, decay of organic material by means of sulfate reducing reactions and/or fluid reworking overprinted primary relationships with trace metal contents. However, the positive linear relationships are clearly shown between organic carbon and trace metal contents. New SIMS U-Pb ages constrained the depositional age of the Ni-Mo-PGE enriched layer to be 532–527 Ma, which argues against previous assumption that the anoxic event recorded in the Ni-Mo-PGE took place at the Ediacaran–Cambrian boundary. Furthermore, new radiometric ages suggest the Shuijingtuo/Niutitang Formation could be correlated with Shiyantou Formation, Dahai and upper Zhongyicun members, whereas Yanjiahe Formation correlated with Daibu and lower Zhongyicun members in Yunnan Province, respectively.

Adakitic rocks are often considered as a key to deciphering the genesis of Archean TTGs and the early crustal growth. Granites from the Huichizi pluton in the North Qinling (NQ) unit have high Sr/Y and (La/Yb) N ratios similar to adakites. Their relatively high SiO 2 , K 2 O, and Na 2 O and very low MgO, Cr, and Ni contents are in the range of high-SiO 2 adakites and early Archean TTGs and are compositionally similar to experimental melts derived from metabasalt sources. New SIMS zircon U–Pb dating constrains the emplacement age of the Huichizi pluton at 422 ± 5 Ma. Rock samples from the Huichizi pluton have e Nd (t) and zircon e Hf (t) values similar to the Neoproterozoic metabasalts in the NQ unit. In combination with their normal mantle-like δ 18 O zir values, these adakites are best explained by partial melting of the Neoproterozoic mafic crustal root due to subduction of the Shangdan ocean. Regional geological data suggest that the crust was probably thickened by a ca. 490 Ma arc-collision process prior to the emplacement of the Huichizi pluton. Our results confirm that underplating of mafic magma and its subsequent fusion triggered by slab subduction under high pressure conditions could be an important mechanism for the formation of early continental crust.

The presence of old residual continental crustal rocks in cratons is crucial for investigation of their early evolution. Due to the poor exposure of Archean rocks, the early evolution of the Yangtze Craton has not been well constrained yet. In this study, a combined study of zircon U–Pb and Hf–O isotopes, as well as whole rock major and trace elements and Nd isotopes have been conducted for a granite pluton at Huji town, in the northern part of the Yangtze Craton. U–Pb dating for magmatic zircons yielded a weighted mean age of 2656 ± 6 Ma, revealing another Archean outcrop in the Yangtze Craton besides the Kongling terrane. The granite samples show relatively evaluated (K 2 O + Na 2 O)/CaO, TFeO/MgO ratios, and Zr, Nb, Ce, Ga and Y contents, sharing the same features as the A-type granite. They have pronounced Eu, Sr and Ba negative anomalies on the primitive mantle-normalized trace element spidergram, implying the residual of plagioclase in the magma sources. Their high Zr contents of 440–529 ppm correspond to initial magma temperatures of 930–962 °C. The zircons have negative ɛ Hf ( t ) values of −2.7 to 0.1, and Hf model ages of ca. 3.2 Ga, respectively. The δ 18 O values of the zircons range between 4.94 and 5.72‰ and give an average of 5.26 ± 0.14‰, suggesting no contribution of supracrustal rock into the host magma. Therefore, the Hf model ages indicate the generation of the Huji granite by reworking of ca. 3.2 Ga juvenile crustal rocks. Combined with previous studies, the finding of the Neoarchean Huji granites with ca. 3.2 Ga Hf model ages suggests the widespread of Archean basement in the Yangtze Craton. The occurrence of the ca. 2.65 Ga Huji granites likely records the thermally stable lithosphere and thus heralds the craton stabilization of the eastern part of the Yangtze Block.

Geochemical features of island arc rocks require two slab-derived components of a melt and a fluid added to their sources. These two liquids may unite to an intermediate aqueous melt at the base of volcanic arc. Direct evidence of this process has been scarce yet. Here we present an integrated study of in situ U–Pb age, trace element, and O–Hf isotope for zircons from a suite of a quartz vein, a felsic vein, their host eclogite, and surrounding gneiss at the Xitieshan UHP terrane of the North Qaidam metamorphic belt (NQMB). Oscillatory zoned zircons from the quartz vein are enriched in U, Li, Nb, and REE, with a formation age of 442 ± 6 Ma, consistent with the timing of the peak UHP metamorphism. This demonstrates there is no temporal gap between the UHP metamorphism and fluid flow in the Xitieshan terrane. In particular, the oscillatory zoned zircons of the quartz vein have similar Hf isotope compositions to zircons from the surrounding gneiss, but variable O isotope compositions between the host eclogite and surrounding gneiss. The fluid from surrounded gneiss was thus an aqueous melt with high transport ability for Lu and Hf and O, while the fluid from the host eclogite was an aqueous fluid only with the ability to transport O. According to the similar behaviors of granitic rock and sediment, it is inferred that a channelized hydrous melt can be formed in the downgoing sediment layer, where an aqueous fluid can be formed from underlying basalt and/or peridotite layers at the sub-arc depth. The two types of fluid are fed to the overlying mantle wedge from subducting slab to form island arc rock. By contrast, the zircons in the felsic vein yield a weighted mean 206Pb/238U age of 420 ± 4 Ma, which can be regard as the timing of partial melting during the exhumed stage for the Xitieshan UHP rocks. The zircon O and Hf isotopic features of the felsic vein are between the country gneiss and host eclogite, compatible with their emanating from hydrous melt of both the eclogite and gneiss during the exhumation stage of the UHP rocks. This indicates that hydrous melt would be released from both the sediment and basalt or peridotite layers of the subducting slabs at relatively shallow depth.

The Yangtze Craton is one of the most important cratonic blocks in eastern Asia. However, its early evolution has not been well constrained yet, because of the poor exposure of Archean basement rocks. In this contribution, a combined study of zircon U–Pb age, Hf–O isotope compositions, as well as whole rock element compositions was carried out for gray gneiss rocks from the Douling complex in the northwestern part of the Yangtze Craton. Zircon U–Pb dating for two gneiss samples yielded weighted mean ages of 2509 ± 21 and 2496 ± 15 Ma. The gray gneisses have high SiO2 (63.64–73.74%), Na2O (3.66–6.21%), but low K2O (0.76–2.93%) contents, and belong to the trondhjemite, tonalite and granodiorite series rocks. They are characterized by enrichments of LILEs and LREEs, but notable depletions in Nb–Ta and Ti, as well as heavy REEs and Y. All the samples plot into the fields of typical Archean TTG rocks in the (La/Yb)N vs. (Yb)N and Sr/Y vs. Y diagrams. Therefore, the gray gneisses in the Douling complex are Neoarchean TTG rocks. The relatively high Nb/Ta and Zr/Sm ratios of 19.6–46.0 and 14.5–143.4 suggest their formation under eclogite-facies conditions. They have low ɛHf(t) values of −3.21 and −3.39 and Hf model ages of 3194 ± 26 and 3205 ± 24 Ma, indicating their derivation from ca. 3.2 Ga juvenile mafic rocks. Their δ18O values of 6.41 ± 0.12 and 5.44 ± 0.12‰ suggest that surface rocks were differently recycled into their sources. Collectively, the TTG rocks in the Douling complex were generated by partial melting of thickened mafic crust rather than direct partial melting of oceanic crust in a convergent plate boundary. A compilation of available zircon U–Pb and Hf isotope compositions of the Yangtze Craton reveals that there are quite differences of Hf isotope compositions in Archean. The ca. 3.8–3.4 Ga zircons exhibit ɛHf(t) values of −5.8 to 0.0. These chondritic to slightly enriched hafnium isotope compositions imply that their host rocks were formed by protracted intra-crustal reworking of ancient protoliths without juvenile input. By contrast, zircons with ages younger than ca. 3.2 Ga register both negative and positive ɛHf(t) values up to the depleted mantle, providing clear evidence for the addition of juvenile materials. These imply that the subduction-driven plate tectonics might have been operated since ca. 3.2 Ga in the Yangtze Craton.

S-type peraluminous granite can crop out in various tectonic settings. The Paleozoic Piaochi granitic intrusion is a large S-type peraluminous intrusion located in the North Qinling orogen, and has important implication for its tectonic evolution. Though intensively studied, the age and tectonic setting of this intrusion are still controversial. In this study, we carried out an integrated study of zircon U–Pb age, major and trace elements, and Sr–Nd–Hf–O isotope compositions for the Piaochi intrusion, with aims to constrain its petrogenesis and tectonic significance. SIMS and LA-ICPMS U–Pb zircon data obtained from magmatic zircons indicate that the Piaochi intrusion was emplaced at 473 ± 4 Ma, and contained ca. 490 Ma inherited zircons. The granite samples from the Piaochi intrusion show typical S-type characteristics, such as the relatively moderate aluminum saturation index (1.00–1.08), low zirconium saturation temperatures, occurrences of muscovite, and high zircon δ 18 O values (8.70 to 9.54‰). The relatively low Sm/Nd (0.13–0.20) and FeO T /MgO ratios (2.21–3.9) suggest that the granites are unfractionated. The geochemical compositions reveal that they were derived from partial melting of a clay-poor, but plagioclase- and biotite-rich psammitic source, similar to metasedimentary rocks outcropping in the North Qinling unit. Moreover, the Piaochi granites are moderately depleted in Eu and heavy rare earth elements, and have relatively high (La/Yb) N values (22.8–56.8), implying a high-pressure, plagioclase-poor and garnet-rich residual assemblage. The Piaochi granites have high and variable initial 87 Sr/ 86 Sr ratios (0.72167–0.72511) and low e Nd (t) (from − 10.23 to − 8.71) values with two-stage Nd model ages (T DM2 ) of 1.91–2.03 Ga, which are comparable with those of supracrustal materials in the North Qinling unit. In addition, our results show that the ca. 470 Ma magmatic zircons display a narrow e Hf (t) array within those of the inherited cores. These imply that the Piaochi granites inherited their isotopic characteristics wholly from their sources, and the Hf isotopes might have been differently homogenized during the partial melting. Our new zircon U–Pb ages indicate that the Piaochi granites were emplaced after the climax of the UHP metamorphism, coeval with later retrograde metamorphism during exhumation. Therefore, we suggest that the formation of the early Paleozoic Piaochi intrusion was triggered by the exhumation of the UHP rocks.

Migmatites are predominant in the North Qinling (NQ) orogen, but their formation ages are poorly constrained. This paper presents a combined study of cathodoluminescence imaging, U–Pb age, trace element and Hf isotopes of zircon in migmatites from the NQ unit. In the migmatites, most zircon grains occur as new, homogeneous crystals, while some are present as overgrowth rims around inherited cores. Morphological and trace element features suggest that the zircon crystals are metamorphic and formed during partial melting. The inherited cores have oscillatory zoning and yield U–Pb ages of c. 900 Ma, representing their protolith ages. The early Neoproterozoic protoliths probably formed in an active continental margin, being a response to the assembly of the supercontinent Rodinia. The migmatite zircon yields Hf model ages of 1911 ± 20 to 990 ± 22 Ma, indicating that the protoliths were derived from reworking of Palaeoproterozoic to Neoproterozoic crustal materials. The anatexis zircon yields formation ages ranging from 455 ± 5 to 420 ± 4 Ma, with a peak at c. 435 Ma. Combined with previous results, we suggest that the migmatization of the NQ terrane occurred at c. 455–400 Ma. The migmatization was c. 50 Ma later than the c. 490 Ma ultra-high-P (UHP) metamorphism, indicating that they occurred in two independent tectonic events. By contrast, the migmatization was coeval with the granulite facies metamorphism and the granitic magmatism in the NQ unit, which collectively argue for their formation due to the northward subduction of the Shangdan Ocean. UHP rocks were distributed mainly along the northern margin and occasionally in the inner part of the NQ unit, indicating that they were exhumed along the northern edge and detached from the basement by the subsequent migmatization process.

Eclogites in an orogen, serving as a credible marker for deep subduction of oceanic or continental crust, are a key to decipher the process and fate of plate subduction. The nature of eclogite precursors bears important information on orogenic mechanism and pre-subducted geological history. Despite their importance, the nature of ultra-high pressure (UHP) eclogites in the North Qinling (NQ) terrane is still poorly constrained, which leads to conflicting tectonic scenarios for the evolution of the Qinling orogenic belt. In this paper, we provide a combined study of zircon U–Pb ages, major and trace element data, and Sr–Nd–Pb–Hf isotope compositions for eclogites from the NQ terrane. U–Pb age determinations on magmatic zircon cores of two eclogite samples yield similar ages of ca. 800 Ma, indicating that the protoliths of the NQ UHP eclogites formed in the Neoproterozoic. The NQ eclogites have tholeiitic compositions and are characterized by high TiO 2 (1.40–2.40%), and low P 2 O 5 (0.09–0.22%), Na 2 O (1.10–2.49%) and K 2 O (0.17–1.04%) contents. They are moderate fractionation in REEs (La N /Yb N = 2.31–4.20) and show negligible Nb, Ta, Ti, and Eu anomalies (Eu/Eu* = 0.82–1.10). The eclogites have high positive whole-rock ɛ Nd ( t ) (2.81–5.53) and zircon ɛ Hf ( t ) (10.5–11.9) values, indicating their derivation from a relatively depleted mantle source. On geochemical discriminant diagrams based on immobile element ratios, the NQ eclogites fall in the field of continental basalts. Moreover, both the geochronological and geochemical features of the eclogite protoliths are quite different from those of the Erlanpging basaltic rocks, but comparable to those of the coeval continental basalts in South Qinling (SQ) orogen and the northern margin of the South China Block (SCB). As the mid-Neoproterozoic basaltic rocks in the SQ orogen and the northern margin of the SCB were well documented to form in a continental rift setting in response to the global-scale breakup of the Rodinia supercontinent, it is inferred that the NQ eclogite precursors might also form in a continental rift setting at ca. 800 Ma, which resulted in the splitting of the NQ terrane from the SCB. As the protoliths of the NQ eclogites have a continental property, we suggest that the ca. 490 Ma UHP metamorphism of the NQ unit might result from its northward subduction beneath the Erlangping arc and thus manifested an arc-continent collision process.

The Dabie–Sulu orogen in east-central China is the largest UHP belt in the world. Many studies have dealt with detrital minerals from sedimentary basins surrounding the Dabie belt in order to constrain the tectonic unroofing of this terrane. On the other hand, still few are the works focused on detritals from the basins associated with the Sulu belt. The Jiaolai basin, adjacent to the Sulu belt, is made of Mesozoic sedimentary rocks. Two sandstone samples collected from the Early Cretaceous Laiyang Group in the northern and southern margins of the Jiaolai basin were selected for zircon U–Pb dating and trace element analysis. The zircons show main U–Pb age clusters at ca. 2500–2400, 2000–1700, 850–700, and 330–130 Ma, with a minor peak at ca. 1100 Ma and a few Archean ages. Most zircons show texture features reflecting a magmatic origin, whereas several late Paleoproterozoic and Triassic zircons show homogeneous CL images and low Th/U ratios, indicating a metamorphic origin. The Neoproterozoic ages are consistent with the protolith ages of the metamorphic rocks in the Sulu terrane, implying that the Sulu tarrane may be a major source for this component. Whereas most Neoproterozoic zircons are euhedral to subhedral or angular in shape and are not surrounded by overgrowths, this implies that low-grade metamorphic Neoproterozoic metaigneous rocks ocurring along the northern margin of the Sulu terrane or metasediments overlying the HP–UHP rocks in the Sulu terrane might provide source materials to these detrital zircons. The late and early Paleoproterozoic age peaks are consistent with the thermal events occurred in the Jiaobei terrane, slightly younger than those in the Yangtze Block. These suggest that the Jiaobei terrane was a potential source for the Paleoproterozoic to Archean detrital zircon components. Only two early Paleozoic zircon grains were found in the studied samples, indicating the early Paleozoic arc did not extend into the Sulu terrane. According to the distribution of different kinds of rock adjacent to the Sulu terrane, the Early Cretaceous detrital zircons may be potentially derived from Cretaceous plutons from the Sulu belt. Eight detrital zircons including six metamorphic grians and two metamorphic overgrowth rims yield the Triassic ages, which might be derived from HP–UHP rocks from the Sulu terrane. A metamorphic overgrowth rim yields a metamorphic age of 246 ± 3 Ma, probably recording the timing of the prograde metamorphism of the Sulu terrane. One metamorphic grain yields an age of 212 ± 2 Ma, which is interpreted to record a retrograde metamorphic event. Based on the REE patterns, the remaining six Triassic analyses can be subdivided into two groups. Four of them record a weighted mean age of 230 ± 6 Ma and show nearly flat HREE patterns and slight negative or positive Eu anomalies. The last two grains are enriched HREE; considering their ages and the REE patterns, it is suggested that they may originate from other diverse UHP rocks. The Triassic metamorphic zircons were detected in the Laiyang Group, indicating that the Sulu UHP rocks were exposed to the surface before the Early Cretaceous.

Here we report an integrated study of zircon U-Pb age and Hf isotope composition for a gneiss sample from the Kongling terrain in the Yangtze Craton. CL imaging reveals that most zircons are magmatic, and a few of them have thin metamorphic rims. The magmatic zircons gave a weighted mean U-Pb age of 3218±13 Ma, indicating the gneiss is the oldest basement rock in the Yangtze Craton found to date. They have e Hf( t) value of -2.33±0.51, and two-stage Hf model age of 3679±49 Ma, indicating that the gneiss was derived from partial melting of >3.6 Ga crustal rock. The metamorphic rims yielded an age of 2732±16 Ma, implying that the metamorphic event occurred in the Neoarchean era, which may be also a major tectono-thermal event in the Yangtze Craton.

In this paper, we report U-Pb age and Hf isotope composition of hydrothermal zircons from a quartz vein within an UHP eclogite outcrop from the Hong’an area, western Dabie orogen. These data are used to decipher the age, formation conditions and source of fluid flow during the exhumation of UHP rock. Zircons from the vein have perfect euhedral shape, oscillatory zoning or weak zoning, and very low Th/U ratios (0.03―0.07), indicating that they precipitated from the aqueous fluid responsible for the vein formation. The weighted mean 206Pb/238U age of 224.7 ± 1.3 Ma of these zircons is taken as the best estimated age of the quartz vein formation, and records aqueous fluid flow during the early exhumation stage of the UHP rocks. The zircons in the quartz vein show low Lu/Hf ratios and have similar Hf compositions to those in the host eclogite, indicating an internal source and small-scale fluid transport for veining. Therefore, the Hf isotope composition of hydrothermal zircon from quartz vein can constrain on the nature, forming condition, and origin of high-pressure metamorphic fluids.

Quartz veins in high-pressure (HP) to ultrahigh-pressure (UHP) rocks are the products of fluid-rock interaction, and thus provide insight into fluid processes in subduction zones. In this paper, we report an integrated study of mineral inclusion, trace-element, U-Pb age, and Lu-Hf isotope compositions of hydrothermal zircon grains from a quartz vein within an UHP eclogite outcrop from the Hong’an area, western Dabie Mountains. These data are used to decipher the age, conditions of formation, and source of fluid for zircon formation during the exhumation of UHP rocks. Zircon grains from the vein have perfect euhedral shape, and show sector zoning or weak zoning, indicating that they precipitated from the aqueous fluid responsible for the vein formation. Raman spectroscopy analysis reveals that the zircon grains contain inclusions of garnet, omphacite, rutile, quartz, and H2O, implying that they crystallized from aqueous fluid under HP eclogite-facies conditions. The zircon grains show low Th/U and Lu/Hf ratios, nearly flat HREE patterns, absent Eu anomalies and low LREE contents. These characteristics are consistent with their precipitation in the presence of garnet and epidote, and absence of feldspar, and thus suggest that trace-element concentrations in hydrothermal zircon are controlled by co-precipitation of mineral assemblages. Crystallization temperatures of 670 to 712 °C, which were calculated using the Ti content of zircon, are consistent with their formation under eclogite-facies conditions and may correspond to the temperature of the infiltrating fluid. The weighted mean 206Pb/238U age of 224.7 ± 1.3 Ma is taken as the best estimate for the age of quartz-vein formation and records aqueous fluid flow during the early exhumation stage of UHP rocks. The zircon grains in the quartz-vein have Hf compositions similar to those in the host eclogite, which demonstrates isotopic equilibrium between fluid and rocks and that the fluid-rock ratio was likely low.

Mafic dyke is a sign of regional extension, and thus has important tectonic significance. A great amount of mafic dykes occur in the Kongling terrain of the Yangtze Craton, which have great bearing on the early evolution of the Yangtze Craton. Their ages, however, have not been well constrained. In this paper we report an integrated study of zircon U-Pb age and Hf isotope compositions for a mafic dyke in the Kongling terrain. The zircons yielded a weighted mean 207Pb/206Pb age of 1852±11Ma, which represents its intrusion age. They have ɛ Hf(t) values of −6.3 to 0.5, with a weighted mean of −3.06±0.88, suggesting that the mafic dyke came from metasomatic mantle. The results indicate that the Yangtze Block had transformed into post-collisional extensional regime at ca. 1850 Ma. In the same period, the Yangtze Craton shows enough rigidity to produce brittle rupture, and thus has the characteristics of a craton.

The Hong’an area (western Dabie Mountains) is the westernmost terrane in the Qinling-Dabie-Sulu orogen that preserves UHP eclogites. The ages of the UHP metamorphism have not been well constrained, and thus hinder our understanding of the tectonic evolution of this area. LA-ICPMS U–Pb age, trace element and Hf isotope compositions of zircons of a granitic gneiss and an eclogite from the Xinxian UHP unit in the Hong’an area were analyzed to constrain the age of the UHP metamorphism. Most zircons are unzoned or show sector zoning. They have low trace element concentrations, without significant negative Eu anomalies. These metamorphic zircons can be further subdivided into two groups according to their U–Pb ages, and trace element and Lu–Hf isotope compositions. One group with an average age of 239 ± 2 Ma show relatively high and variable HREE contents (527 ≥ LuN ≥ 14) and 176Lu/177Hf ratios (0.00008–0.000931), indicating their growth prior to a great deal of garnet growth in the late stage of continental subduction. The other group yields an average age of 227 ± 2 Ma, and shows consistent low HREE contents and 176Lu/177Hf ratios, suggesting their growth with concurrent garnet crystallization and/or recrystallization. These two groups of age are taken as recording the time of prograde HP to UHP and retrograde UHP–HP stages, respectively. A few cores have high Th/U ratios, high trace element contents, and a clear negative Eu anomaly. These features support a magmatic origin of these zircon cores. The upper intercept ages of 771 ± 86 and 752 ± 70 Ma for the granitic gneiss and eclogite, respectively, indicate that their protoliths probably formed as a bimodal suite in rifting zones in the northern margin of the Yangtze Block. Young Hf model ages (TDM1) of magmatic cores indicate juvenile (mantle-derived) materials were involved in their protolith formation.