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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.

Much of the global picture of crustal evolution has been constructed using zircon. While this has revealed a rich and complex history, this view is necessarily incomplete because of the lithology-specific affinity of zircon and the high temperatures needed to reset the U-Pb and Lu-Hf systems inherent within it. Here we use a five mineral, multi-isotope system approach to compare the record of crustal evolution recorded by zircon versus the picture provided by monazite, titanite, apatite, and rutile from the Yong-Ding and Luan rivers, northern China. These other minerals sample more diverse lithologies and temperature-pressure conditions that reflect additional tectonothermal events to those recorded solely by zircon. Zircon from both studied rivers predominantly reflects magmatic features, yielding age peaks at 2.6–2.3, 2.0–1.8, and 0.38–0.13 Ga, corresponding to the major magmatic events in their catchments. However, the detrital zircon record from both catchments fails to record and detail several important tectonothermal events. Specifically, the detrital monazite U-Pb ages cluster into two Paleoproterozoic peaks of ca. 1.95 and 1.85 Ga, while detrital apatite and rutile ages document unimodal and protracted U-Pb age peaks at 1.9–1.6 Ga. The different U-Pb closure temperatures of monazite, apatite, and rutile likely record two metamorphic events and the subsequent cooling history—key details that are absent from or obscured in the zircon record. The Phanerozoic mineral U-Th-Pb ages correspond to multiple magmatic events between 0.40 and 0.24 Ga and subsequent 0.24–0.20 Ga metamorphism. The 0.60–0.25 Ga rutile U-Pb ages along with 0.33–0.24 Ga U-Pb ages in some zircon grains with radiogenic Hf isotope compositions from the Luan River do not match the geological records in the North China Craton, but instead reflect the protracted subduction-accretionary history of the Central Asian Orogenic Belt. In addition to their U-Th-Pb ages, Nd model ages of monazite, titanite, and apatite, plus zircon Hf model ages provide additional constraints on regional crustal evolution. The Nd model age information is blurred by the fact that the relationship between the Sm/Nd of these minerals and their former host rocks is not precisely known. Taken at face value, the monazite Nd model ages have two Neoarchean peaks at 2.9–2.7 and ca. 2.5 Ga, that may correspond to two crustal growth episodes, while the titanite Nd model ages with predominant peaks at 2.2–1.8 and 1.5–1.3 Ga broadly correspond with those derived from the whole-rock analyses of the wide spread Phanerozoic granitoids, and hence record extensive crustal reworking. In contrast, the zircon Hf model ages are strongly skewed to a 2.9–2.7 Ga period and fail to record the post-Archean evolution of this region. These data highlight the power of integrating the U-Th-Pb age and Lu-Hf/Sm-Nd isotope compositions of multiple detrital minerals, with a broad range in geochemical behavior and closure temperatures, to gain a more complete understanding of tectonothermal history and crustal evolution than zircon alone.

An integrated study of zircon U–Pb geochronology and O–Hf isotope compositions, and whole-rock geochemistry was carried out for Dashimen rhyolites from the Tongbai orogen in the northern Yangtze Block. Zircon grains from two rhyolite samples show oscillatory zoning and moderate U (498–1612 and 216–668 ppm) and Th (319–1144 and 161–452 ppm) contents with relatively high Th/U ratios (0.57–0.75 and 0.50–1.31), indicating their magmatic origin. Zircon U–Pb dating yielded consistent U–Pb ages of 906 ± 7 Ma (2σ; MSWD = 0.48) and 908 ± 4 Ma (2σ; MSWD = 0.68), representing the formation ages of the Dashimen rhyolites. The Dashimen rhyolites have relatively high SiO2 (74.85–76.56 wt%), K2O (5.40–6.56 wt%) and Fe2O3T (1.61–2.33 wt%), and moderate Al2O3 (11.48–12.32 wt%) and Na2O (1.76–2.47 wt%), but low MgO (0.15–0.24 wt%) and CaO (0.08–0.10 wt%) contents. They show strong enrichments of almost all incompatible elements, except for the notable depletions in Ba, Sr, Eu, and P. The volcanic rocks have high zircon saturation temperatures of 846 to 876 °C with an average of 862 °C. These features suggest that the Dashimen rhyolites are high-temperature, ferroan, A-type magmatism. The zircons from the two studied samples show δ18O values of 3.6 to 5.0‰ and 3.9 to 4.5‰ with weighted averages of 4.30 ± 0.18‰ and 4.23 ± 0.10‰, respectively. These δ18O values are obviously lower than those of the normal mantle zircons and thus suggest the zircons crystallized from low-δ18O magmas. The rhyolites have negative whole-rock eNd(t) (−2.11–−0.28) and subtly positive zircon eHf(t) (0.01–3.35) values, with corresponding two stage depleted mantle model ages of 1.73–1.58 Ga and 1.69–1.66 Ga, respectively. The low-δ18O magmas were therefore suggested to be generated by re-melting of meteoric-hydrothermally altered continental crustal rocks. The finding of the high-temperature, ferroan, and low-δ18O A-type Dashimen rhyolites indicates that there existed a back-arc rift of a Grenvillian accretionary orogen in the northern part of the Yangtze Block.

The precise timing, petrogenesis, and geodynamic significance of the Paleozoic magmatic rocks in the southern Qinling–Tongbai Orogenic Belt (QTOB), Central China, are poorly constrained. We performed an integrated study of petrology, zircon U Pb ages, geochemistry, and Hf–O–Nd isotopic compositions of the Huangyangshan pluton from the southern QTOB to constrain its genesis and tectonic implications. A granite sample from the pluton yields a weighted mean zircon 206Pb/238U age of 445 ± 6 Ma, representing the age of the pluton. The Huangyangshan pluton is dominated by alkaline granite and quartz syenite, has a peralkaline signature (A/NK = 0.82–0.96), and belongs to the shoshonite and high-K calc-alkaline series. Both the alkaline granite and quartz syenite have geochemical signatures similar to A-type granite, with high SiO2 and total alkali (Na2O + K2O) contents, high Fe-numbers and TiO2/MgO and Ga/Al ratios, and high field-strength elements (HFSEs), along with low MgO, CaO, and P2O5 contents. These samples are enriched in light rare earth elements (LREEs) and have flat heavy rare earth element (HREE) patterns and strongly negative Eu anomalies. They are enriched in most large-ion lithophile elements (LILEs) and HFSEs, with significant negative Eu, Ba, Sr, and Ti anomalies in primitive-mantle-normalized trace-element diagrams. The samples have relatively high Zr contents (175–776 ppm), yielding minimum magmatic temperatures of 768 °C–891 °C. The Huangyangshan pluton has initial zircon eHf(t) values of +6.6 to +10.0 and whole-rock eNd(t) values of +2.86 to +3.62. The analyzed zircons yield a mean δ18O value of 5.14‰ ± 0.26‰, indicating negligible incorporation of hydrothermally altered crustal materials. The geochemical signatures of the Huangyangshan pluton indicate that the magmas were derived from prompt partial melting of juvenile crust rocks. Combined with previous results, we suggest that the Paleozoic Huangyangshan peralkaline A-type granites resulted from the rifting of a passive continental margin in the northern South China Block, followed by the opening of the Paleotethyan Ocean.

Coexistence of baddeleyite and zircon is rarely documented in metacarbonate rocks and poorly understood. In this study, metamorphic baddeleyite and zircon were recognized in marbles from the Tongbai orogen, central China. We carried out high spatial resolution analysis of trace element geochemistry and U‒Pb‒Lu‒Hf‒O isotope systematics for the zircon and baddeleyite. SIMS (Secondary Ion Mass Spectroscopy) U‒Pb analysis yields weighted average 207Pb/206Pb ages of 1848.0 ± 3.3 Ma (MSDW = 1.2, n = 12) for baddeleyite and 1840 ± 13 Ma (MSWD = 1.7, n = 13) for zircon. The baddeleyite grains have relatively low REE (Rare Earth Element) contents (ΣREE = 1.30–47.3 ppm) with flat chondrite-normalized patterns and moderate contents of HFSE (High Field Strength Element), which are ascribed to the nature of its host metacarbonate rock and mineral assemblage. The zircon grains have low Ti contents (1.63–3.56 ppm), positive Ce anomalies (Ce/Ce* = 1.91–6.96), and mineral inclusions of hematite, calcite, dolomite, lizardite and H2O. These characteristics indicate zircon formation in a relatively low-temperature setting under oxidizing and water-rich conditions. The baddeleyite and zircon have similar ranges of eHf(t) values of – 7.7 to – 10.5 and – 7.8 to – 11.6, respectively, which suggest their derivation from a relatively uniform Hf source. The high δ18O values of these zircon grains (20.0–21.0‰) preclude any percolation of external meteoric fluids during their crystallization. Therefore, a “detrital-zircon-dissolution” reaction is preferred to provide the Zr for the metamorphic zircon and baddeleyite in this study. The O isotope disequilibrium between whole-rock (δ18O = 16.2–16.3‰) and metamorphic zircon is most likely caused by metamorphic devolatilization or interaction with an H2O-dominant fluid during later metamorphism. On the other hand, the baddeleyite grains yield δ18O values ranging from 4.5 to 8.7‰, which is in disequilibrium with metamorphic zircon at the temperature of “detrital-zircon-dissolution” reaction (ca. 660–710 °C; Zircon + Dolomite → Baddeleyite + Forsterite + Calcite + CO2). The genesis of metamorphic zircon can be interpreted by a baddeleyite-to-zircon reaction of ZrO2 + SiO2 → ZrSiO4 at a retrograde stage, consistent with the low Ti-in-Zircon temperatures. The results highlight the importance of integrating trace element and multiple isotopic compositions in studying the genesis of metamorphic baddeleyite and zircon. Additionally, the U–Pb geochronology data also indicate that the protoliths of the marble were deposited in the early Paleoproterozoic and experienced a metamorphism at 1.85 Ga. The ca. 1.85 Ga high-grade metamorphic event might have been induced by the coeval magmatism in an extensional setting.

In recent years, the melange model has been increasingly considered as an important way to transfer slab components to arc sources in modern subduction zones. This model differs from the classic slab fluid/melt metasomatism model in that it invokes physical mixing of bulk sediment, altered oceanic crust (AOC), serpentinite, and mantle wedge at the slab-mantle interface. However, due to the lack of subducted sediment compositions, the melange model has not been applied to any significant extent in paleo-subduction zones. The lack of evidence for bulk AOC and serpentinite components in melange sources also hinders our understanding of any melange origin for arc-type magmas. Here, we report Mg-Ba-Sr-Nd isotope compositions of the early Paleozoic Fushui mafic rocks in the Qinling orogen of central China, to trace their origin and constrain slab component transfer. The Fushui mafic rocks show typical arc-type geochemical features and enriched Sr-Nd isotope compositions, indicating the likely contribution of subducted sediments. They have low Rb/Ba ratios ( δ 138 / 134 Ba values of −0.38 to +0.10‰, similar to those of sediments (−0.2 to +0.1‰) but lower than those of MORBs (+0.03 to +0.14‰), indicating that these low δ 138 / 134 Ba values are most likely derived from sediment components. One Fushui sample has a high δ 138 / 134 Ba of +0.31‰, similar to that of AOC (up to +0.4‰). This high δ 138 / 134 Ba is not correlated with fluid input; instead, it results from the contribution of bulk AOC. The Fushui rocks exhibit variable δ 26 Mg values (−0.23 to −0.11‰), slightly higher than those of MORBs. This most likely reflects 26Mg-enriched subducted serpentinite components in their source. Our results not only identify the variable slab components (sediment, AOC, and serpentinite) in the arc source, but also suggest that these slab components may be transferred to their arc source by the melange process. This study therefore provides solid evidence for the generation of arc magmas by melange processes in paleo-subduction zones, which confirms an important role for the melange model in slab material transport.

Granites generated by anatexis are ideal crustal probes to decipher the differentiation processes within deep continental crust. In this study, the successive emplacement of granites, including the porphyries and the coarse-grained granites, was found in the nucleus (the Kongling Complex) of the Yangtze Craton. The porphyries, intruding at 1840 ± 17 Ma (SHRIMP ages), occur as veins and contain phenocrysts of K-feldspar (∼15%), quartz (∼5%), plagioclase (∼4%) and garnet (∼1%) setting in a fine-grained groundmass (∼75%) of K-feldspar, plagioclase, quartz and biotite. The coarse-grained granites, emplacing at 1821 ± 8 Ma (SHRIMP ages), are outcropped as pluton and comprise K-feldspar (∼60%), quartz (∼30%), biotite (∼5%), plagioclase (∼5%). They are similar to A-type granites with relatively high SiO2 (69.2–71.5 wt%, 72.6–74.5 wt%), high Fe2O3T/MgO (21.5–27.7, 5.9–19.5), 104*Ga/Al ratios (3.6–4.3, 2.7–3.5) respectively and enriched HFSEs (Th, U, Pb, Ga). The porphyries contain higher total trace element contents and zirconium saturation temperature (mean 892 °C) than those of the coarse-grained granites (mean 803 °C). Magmatic zircons from the porphyries and coarse-grained granites have eHf(t) values of −17.6 to −11.7 and −21.0 to −14.8, which yield two-stage Hf model ages of 3.6–3.3 Ga and 3.8–3.4 Ga respectively, both falling into the evolutionary trend of the 2.9–2.8 Ga Kongling TTGs. It implies both granites are anatectic (crustal reworking) derivatives from partial melting of the Archean TTGs under sustaining extension in Paleoproterozoic. Applying trace element modelling, we further identify a unique tonalitic source for both granites which is analogous to the exposed natural Kongling tonalite, and find the porphyries slightly affected by the juvenile crust. Based on the intrusion of porphyry veins into granitic gneisses, we envisage the crustal structure beneath the craton is layered from older (∼2.94 Ga) tonalites upward to younger (∼2.87 Ga) granitic gneisses. Such hierarchical structure could shed new light on the imperceptible vertical differentiation process as cratonization.

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.

Post-collisional granites are generally generated by partial melting of continental crust during orogenic extension. The occurrence of normal calc-alkaline granites following adakitic granites in a collisional orogen is frequently supposed as a sign of tectonic regime transition from compression to extension, which has been debated yet. In this paper, we present a comprehensive study of zircon U–Pb ages, Hf–O isotopes, as well as whole-rock major and trace elements and Sr–Nd isotopes, for Tongbai and Jigongshan post-collisional granitic plutons in the Tongbai orogen. Zircon U–Pb dating yields intrusion ages of ca. 140 and 135 Ma for the Tongbai and Jigongshan plutons, respectively, suggesting they are post-collisional granites. These granites are high-K calc-alkaline series, metaluminous to weakly peraluminous with A/CNK ratios of 0.85–1.08. The Tongbai gneissic granites are normal calc-alkaline granite, having variable SiO2 (61.93–76.74 wt%) and Sr/Y (2.9–38.9) and (La/Yb)N (1.7–30.1) ratios with variably negative Eu anomalies (0.41–0.92). They have relatively high initial Sr isotope ratios of 0.707571 to 0.710317, and low eNd(t) (− 15.74 to − 11.09) and eHf(t) (− 17.6 to − 16.9) values. Their Nd and Hf model ages range from 2.2 to 1.8 Ga and 2.3 to 2.2 Ga. On the contrary, the Jigongshan granites show higher SiO2 (66.56–72.11 wt%) and Sr/Y (30.1–182.0) and (La/Yb)N (27.4–91.4) ratios with insignificant Eu anomalies (0.73–1.00), belonging to adakitic granite. They have Isr = 0.707843–0.708366, eNd(t) = − 19.83 to − 17.59, and eHf(t) = − 26.0 to − 23.5. Their Nd and Hf model ages vary from ca. 2.5 to 2.4 Ga and ca. 2.8 to 2.6 Ga. The Tongbai and Jigongshan granites are characterized by mantle-like zircon δ18O values (5.17–5.46‰). These geochemical features suggest that the Tongbai and Jigongshan granites were derived from partial melting of Paleoproterozoic and Archean continental crust, respectively. Fractional crystallization affected the geochemical compositions of the Tongbai gneissic granites, while the compositions of the Jigongshan granites were mainly controlled by partial melting. The adakitic signatures of the Jigongshan granites were either inherited from their source or ascribed to more garnet in their residues. The voluminous post-collisional granites might form by the collapse of the thickened Tongbai orogenic root. The normal Tongbai gneissic granites occurred slightly earlier than the Jigongshan adakitic granites in the Tongbai orogen, suggesting that it is not a mandate to sign the tectonic transition from adakitic to normal calc-alkaline granites in post-collisional settings. Therefore, this study provides another example supporting the burst of voluminous post-collisional granites with different compositions as a consequence of the collapse of the thickened orogenic roots of collisional orogens.

The crustal structure of collisional orogen is critical for deciphering the crustal evolution and geodynamics of an orogen. Metamorphic rocks and post-collisional magmatic rocks are the key subjects to probe the crustal structure. In this study, we conducted an integrated study of zircon U Pb age, Hf and O isotopes for migmatites and post-collisional granites in the southern segment of the Tongbai orogen. Zircon U−Pb dating yields protolith ages of 755 ± 55 to 713 ± 6 Ma and metamorphic ages of 162 ± 11 Ma to 138 ± 2 Ma for the migmatites and intrusion ages of 137 ± 2 Ma for the post-collisional granites. The inherited magmatic cores in the migmatites exhibit similar Hf isotopic compositions to the metamorphic zircons. Their eHf(t) values range from 13.5 to −9.5 with crust Hf model ages of 787 Ma to 2233 Ma, indicating that the protoliths were derived from reworking of Paleoproterozoic crust with the addition of juvenile components during the Neoproterozoic. Zircon δ18O of inherited magmatic cores are of −1.45‰ to 5.90‰, signifying the protoliths were formed by remelting of hydrothermally altered low δ18O rocks. By comparison, the post-collisional granites mostly show normal mantle-like O zircon isotope compositions and have lower eHf(t) and eNd(t) values than the migmatite rocks. These features suggest that the granites were formed by fusion of the ancient crust that might have suffered insufficient water-rock interaction. The discrepancies in O–Hf–Nd isotopic compositions of the studied migmatites and granites might be inherited from their precursors. It is thus inferred that the precursors of the granites might lie at the shoulder of the Neoproterozoic rift and thus might have experienced slight water-rock hydrothermal alteration and crust-mantle interaction; whereas the protoliths of the metamorphic rocks might be located at or near the rift center and thus had suffered intensive water-rock hydrothermal alteration and crust-mantle interaction. Prior to the late Mesozoic magmatism, the Tongbai orogen would have an uncoupled double-layered crust, where the upper layer consists of the metamorphic rocks and the lower is the sources of the post-collisional granites. They were stacked by the Permian-Triassic orogeny. The final architecture of the Tongbai orogen might be constituted by the emplacement of the voluminous granites from the deeper crust and the formation of the migmatites in the Tongbai complex. This configuration might widespread for other collisional orogens.

Plagiogranites are a volumetrically minor component of oceanic crust and ophiolites, but offer an opportunity to probe the processes and mechanisms by which felsic crusts were produced from the mafic oceanic crusts. The Qinling-Tongbai orogenic belt in central China is a typical composite orogenic belt that records the amalgamation processes between the North China Block and the South China Block. The Erlangping unit represents an accretionary oceanic unit in the Qinling-Tonbai orogenic belt and contains minor plagiogranites, which have received little attention. In this study, we carried out an integrated study of U–Pb geochronology and Hf–O isotopes in zircon, as well as whole-rock isotope and geochemical analyses for felsic rocks in the Erlangping unit. These rocks occur as dikes to stocks intruding ambient basalts. They have relatively high Na2O and Al2O3, moderate MgO and low K2O contents, and are classified as oceanic plagiogranites. Zircon U–Pb geochronology yielded formation ages of ca. 465 Ma. Zircon δ18O compositions (4.4–5.1‰) are lower than or similar to those of zircons from normal mantle. The low TiO2 content, elevated Zr/Hf, and light rare-earth element (LREE) enrichments in these rocks indicate that these plagiogranites were generated by partial melting of hydrothermally altered oceanic crust. These samples have more depleted whole-rock eNd(t) (+4.4 to +5.1) and zircon eHf(t) (+10.5 to +12.8) values than the basaltic wall-rocks, implying they were derived from a newly accreted oceanic arc. Taking into account the tectonic framework of the broader Qinling Orogenic belt, a subduction-induced magma flare-up in the Ordovician could have triggered the anatexis of the existing Erlangping oceanic arc, and in turn generated these plagiogranites. Partial melting of oceanic crust that has been enriched in a subduction system may be an important mechanism for the formation and maturation of continental crust in oceanic arc settings.

An integrated study of whole-rock elements, Sr–Nd isotopes, and zircon U–Pb ages and Hf-O isotopes was carried out for the “Grenvillian” granites from the North Qinling unit, central China. The results not only place clear constraints on the petrogenesis of these granites, but also give insights into the geodynamic evolution of the Qinling orogen during the assemblage of supercontinent Rodinia. LA-ICPMS zircon U–Pb dating of three representative granites from the Dehe, Fangzhuang, and Zhaigen outcrops yielded formation ages of ca. 940–900 Ma. These muscovite-bearing granites have high silica contents (72–79 wt%) and are weak to strong peraluminous (ASI = 1.01–1.15). They exhibit arc-like trace element distribution patterns with enrichment of LREE and LILE (e.g., Rb, K, Pb) but depletion in HFSE (e.g., Nb, Ta, Ti). Besides, they show variable initial 87Sr/86Sr ratios of 0.704 to 0.729 and relatively low eNd(t) values of −3.2 to −6.1, as well as variable zircon eHf(t) and δ18O values (−8.1–+2.6, 7.9‰–12.0‰). These results suggest their derivation from partial melting of a heterogeneous source that dominated by supracrustal components. Furthermore, a few inherited grains give negative eHf(t) values of −9.4 to −18.4 with two-stage Hf model ages up to 2.9 Ga, suggesting the involvement of minor Archean crustal components. Along with their peraluminous features, high zircon δ18O values, and enriched Sr–Nd isotope compositions, these granites were unambiguously derived from partial melting of metasedimentary rocks and thus are of S-type affinity. Geothermometric and compositional approaches suggest these S-type granites were likely generated by dehydration melting of metagraywacke- and/or metapelite-dominated sources. They might be formed in an accretionary orogen associated with the Rodinia-assembly during the early Neoproterozoic, through which the outboard North Qinling terrane was eventually adjacent to the South China Block.

The Shangdan Ocean represents the eastern branch of the Proto-Tethys Ocean, which is important to decipher the evolution of the Central China Orogenic Belt. However, its evolution is still in debated. In this contribution, we carried out an integrated study of zircon U Pb ages, whole-rock geochemistry, as well as zircon Hf O isotope compositions for the Lajimiao mafic complex in the Shangdan Suture Zone in the North Qinling orogen. The Lajimiao mafic complex is composed of coarse-grained gabbros to norite-gabbros (Group 1) in the inner and fine-grained diorites (Group 2) in the outer part. The Group 1 samples are comprised predominantly of salite to augite (Mg# = 75–80), magnesi-hornblende (Mg# = 65–67) and Ca-rich plagioclase (An = 45–67); the Group 2 samples are comprised predominantly of magnesi-hornblende (Mg# = 60–66) and plagioclase (An = 28–53). New SIMS and LA-ICP-MS U Pb dating of zircon grains from a gabbro and a diorite sample yielded similar weighted mean ages of 412 ± 4 Ma and 414 ± 2 Ma, indicating that they were formed simultaneously. The Group 1 samples have relatively low SiO2 (49.56–50.78 wt%), high MgO (6.67–7.70 wt%) and Fe2O3T (7.46–9.61 wt%) contents, while the Group 2 samples have relatively high SiO2 (57.74–59.53 wt%), low MgO (3.28–3.42 wt%) and Fe2O3T (5.76–7.01 wt%) contents. They both belong to calc-alkalic series and enriched in large ion lithophile elements (LILEs), light rare earth element (LREEs) and depleted in high field strength elements (HFSEs), which are typical of arc-related rocks. The Group 2 diorites exhibit relative enrichment in light rare earth element (LREE) ((La/Yb)N = 10.9–13.1) with slightly negative Eu anomalies (Eu/Eu⁎ = 0.82–0.93), compared to the Group 1 samples ((La/Yb)N = 5.2–9.6; Eu/Eu⁎ = 0.91–1.43). Both of them have enriched initial Sr (0.7049–0.7054), and chondritic to slightly depleted Nd (ƐNd(t) = −0.09 ~ +1.50), but depleted whole-rock and zircon Hf isotopic compositions (ƐHf(t) = 7.81–8.10 and 8.2–9.1). The Hf Nd isotopic systems are decoupled with positive △ƐHf values (5.22 to 5.92) (△ƐHf = ƐHf(t) – (1.59 × ƐNd(t) + 1.28)). The zircon grains display higher δ18O values of 6.3 to 6.5‰ than those of the normal mantle zircon. Whole-rock Pb isotopic compositions of the studied samples are of 15.610–15.624 for 207Pb/204Pb, 38.027–38.178 for 208Pb/204Pb, and 18.100–18.269 for 206Pb/204Pb. These geochemical features indicate that the Lajimiao mafic complex was derived from relatively depleted mantle that had been metasomatized by 2–5% subducted zircon-barren oceanic sediments. Combining with regional geological, geochronological, mineralogical, and geochemical data, the Lajimiao mafic complex was suggested to be generated by partial melting of a phlogopite-bearing mantle source at relatively low pressure in an arc setting. We suggested that the generation of the Lajimiao mafic complex was induced by the subduction of Shangdan Ocean during the early Devonian and thus the eastern branch of Proto-Tethys Ocean might have not been closed until that time.

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.

Understanding the rheological behavior of the Tibetan Plateau and its response to geodynamic processes requires a clear knowledge of the composition, evolution and lithological properties of the deep crust. Here we present U–Pb–Hf isotopes of zircons, bulk-rock geochemistry and mineral compositions for seven intermediate gneiss xenoliths and their host Early Mesozoic granites (205 ± 6 Ma) in the central Lhasa terrane to probe the deep crust beneath Southern Tibet. The xenoliths contain plagioclase, amphibole, titanite, allanite, quartz, biotite and muscovite, with accessory Fe–Ti oxides, apatite and zircon. Bulk-rock and mineral geochemistry suggests that these xenoliths have a magmatic origin and experienced deformation and amphibolite-facies metamorphism (equilibration at pressures of 0.46–0.83 GPa and temperatures of ~ 650 °C), before they were captured by the host granite at ~ 205 Ma. Zircons in these xenoliths show complex microstructures, including inherited cores, magmatic or metamorphic bands, and high U–Th hydrothermal rims. Inherited zircon cores record U–Pb ages from 2277 Ma to 517 Ma. Igneous zircons show a range of concordant U–Pb ages, suggesting a protracted magmatism from 236 Ma to 203 Ma. Metamorphic zircon zones record the timing of amphibolite-facies metamorphism from 224 to 192 Ma, while the high U–Th hydrothermal rims show a subsequent fluid activity until ~ 150 Ma. Unradiogenic Hf isotopic compositions of both xenoliths and host granites [xenolith e Hf (t) = − 11.2 to 0; host granite e Hf (t) = − 17.3 to − 3.3] indicate that the Early Mesozoic deep crust in the central Lhasa terrane originated mainly from ancient (i.e., Proterozoic) crust, with little or no interaction with juvenile magmas. This study suggests a possible continental differentiation mechanism during crustal reworking; progressive melting may initiate from the lower mafic crust (at ca. 236 Ma) and gradually migrate into the sediment-rich upper crust (until ca. 203 Ma). The reworking results in the transition from small fluxes of intermediate magmas to voluminous peraluminous S-type granite in a convergent depth.

Detrital zircon U-Pb age and Hf isotope studies are useful for identifying the chemical evolution of the continental crust. Zircon, however, is typically a magmatic mineral and thus often fails to document the timing of low-grade metamorphism, and its survival through multiple sedimentary cycles potentially biases the crustal evolution record toward older events. In contrast, monazite typically records metamorphic events and is less likely to survive sedimentary recycling processes, thus providing information not available by zircon. Here, we demonstrate that monazite apparently faithfully records the Sm-Nd isotope composition of the bulk rock and can therefore track the record of crustal evolution and growth, similar to Hf isotopes in zircon. We examine the utility of detrital zircon and monazite for studies of crustal evolution through a comparison of age and tracer isotope information using sediments from two large rivers draining the South China block (SCB). Monazite and zircon grains yield mostly Mesozoic and Paleozoic U-Pb ages and depleted mantle model age peaks at ca. 1900–1300 Ma, indicating that both minerals preserve similar, yet critical, information on the crustal evolution of the catchment area. In contrast, zircon yields abundant Neoproterozoic and older U-Pb ages with a very large spread of model ages, preserving a history strongly skewed to older ages. Based on the lack of known rocks of this age in the catchments, ancient zircon was likely sourced from sedimentary rocks within the catchment area. This combined data set presents a more complete history of crustal evolution and growth in the SCB and demonstrates the advantages of an integrated approach that includes both detrital monazite and zircon.

Subduction of oceanic slabs can physically and chemically modify mantle wedges, but how mantle wedges are temporally evolved is difficult to be constrained. In this study, we use in situ zircon U–Pb ages and Hf–O isotopes of mafic intrusions to examine a coupled evolution of magmas and mantle sources above a subduction zone. Neoproterozoic mafic intrusions in the western margin of the Yangtze Block are mostly composed of gabbros that were formed in an arc system during 870–750 Ma followed by generation of voluminous slab-derived granitoids. The mantle wedge was progressively modified by slab fluids, sediment melts and altered oceanic crust (AOC) melts. Gabbros from the 870-Ma intrusion have normal δ18O (4.79‰ to 6.07‰), high eHf (+ 10.4 to + 15.0) and eNd (+ 4.0 and + 6.4) and were derived from a mantle source enriched by slab fluids. Gabbros from the 860–840-Ma intrusions have overall relatively high δ18O (5.61‰ to 7.42‰), but variable eHf values (− 3.5 to + 15.0) that are decoupled from eNd (+ 1.85 to + 3.87). These features are clearly suggestive of a mantle source modified by sediment melts. However, gabbros from the 820–780-Ma intrusions have relatively low δ18O (4.22‰ to 5.49‰), and constant eHf (+ 4.7 to + 9.6) that are decoupled from eNd (− 0.52 to + 1.92). Such features can be explained by a mantle source contaminated by 18O-depleted AOC melts. The widespread younger TTG-type granitoids were partial melts of the subducted oceanic slab and terminated the mafic magmatism in the region, indicating that slab break-off probably resulted in slab melting after a long period of subduction. Similar Neoproterozoic magmatism also occurred in Greater India and Madagascar, suggesting a giant Andean-type arc system along the western margin of Rodinia. In this arc system, mantle-derived magmas were dominated by an arc affinity in the earlier stage before 820 Ma and became rift-related after that, reflecting regional slab tearing and break-off. Our study also provides evidence for the linkage between the marginal subduction and the internal rifting in Rodinia, and suggest that slab break-off probably triggered its break-up.

International audience; We analyze Magnetospheric Multiscale Mission observations of whistler waves and associated electron field-aligned crescent distribution in the vicinity of the magnetotail near-Earth X-line. The whistler waves propagate outward from the X-line in the neutral sheet. The associated field-aligned streaming electrons exhibit a crescent-like shape, with an inverse slope (df/d|v|||>0) at 1-5 keV. The parallel phase velocity of the waves is in the range (1-5 keV) of the inverse slope of the field-aligned crescents in the velocity space. We demonstrate that the observed whistler waves are driven by the electron field-aligned crescents through Landau resonance. The cyclotron resonance is at the high-energy tail with negligible free energy of pitch angle anisotropy in these events.

Marble-hosted eclogite is volumetrically minor in collisional orogens, but its geochemistry has great bearing on the origin of deeply subducted crustal rocks and the fluid mobility of subduction zones. This paper presents a combined study of whole-rock major-trace elements and Sr Nd isotopes, mineral O isotopes, carbonate C and O isotopes, and zircon U Pb ages and Lu Hf isotopes for marble-hosted ultrahigh-pressure metamorphic eclogites from Rongcheng and Sanqingge in the Sulu orogen. The results provide insights into the protolith nature of eclogites and the fluid mobility of subduction zones. Zircon U Pb dating yields consistent middle Triassic ages for the two occurrences of eclogites, indicating new growth of metamorphic zircon during continental collision. The Sanqingge eclogite shows LREE-enriched patterns and negative eNd(t) of − 16.6 to − 14.3 for whole-rock and negative eHf(t) of − 27.1 to − 15.2 for metamorphic zircon. A few relict zircon domains show middle Neoproterozoic U Pb ages and negative eHf(t) of − 35.2 to − 15.5. Thus, the Sangqingge eclogite was metamorphosed from a mafic rock that was derived from partial melting of an anciently enriched mantle source. In contrast, the Rongcheng eclogite exhibits flat or even LREE-depleted patterns with negative eNd(t) values of − 12.2 to − 1.0 for whole-rock but positive eHf(t) values of 5.4 to 10.4 for zircon. The occurrence of interstitial and highly cuspate plagioclase along grain boundaries indicates the presence of partial melting in the eclogite. Thus, its positive zircon eHf(t) values are ascribed to the eclogite protolith of juvenile origin, whereas the LREE depletion is due to extraction of LREE-rich anatectic melt from the eclogite during the Triassic continental collision. As such, the Rongcheng eclogite was metamorphosed from a mafic rock that was derived from partial melting of a less enriched mantle source. All the eclogites from both areas show variably high δ18O values of 9.4‰ to 19.5‰. Oxygen isotope fractionations between mineral pairs mostly yield eclogite-facies temperature of 600 to 800 °C, suggesting that the high δ18O signature was inherited from their protoliths before the Triassic subduction. In combination with the field relation between the eclogite and marble, it is inferred that the eclogite protolith is probably basaltic tuff and its high δ18O value would be acquired together with the marble protolith during their deposition from the surface water. Therefore, there would be the limited isotopic exchange between marble and eclogite during continental collision.

Geochemical analysis of the 14.4-m-thick lacustrine succession of the Lower Cretaceous Yixian Formation (Jehol Group) has yielded new insights concerning vertebrate mass mortality events in the Lake Sihetun volcanic caldera in western Liaoning Province (northeastern China) that produced the Jehol Biota fossil lagerstatten. The long-term evolution of the caldera system resulted in a shift from felsic to mafic magma chemistry, accompanied by a reduced frequency of pyroclastic eruptions, declining hydrothermal activity, and lower lacustrine productivity. The basal Tetrapod Beds exhibit strong hydrothermal influence, as indicated by enrichments of boron (B), certain alkalis (Rb, Cs), rare-earth elements (REEs), yttrium (Y), and many metals (e.g., Co, Cr, Cu, Ge, Mo, Ni, Sb, U, V, and W), and by strongly negative molybdenum isotope compositions (δ98Mo to –2.50‰) that may record large fractionations between molybdate and thiomolybdate species in the Sihetun caldera hydrothermal system. In contrast, the overlying Fish Beds and Non-Fossiliferous Beds have an elemental and Mo-isotopic composition similar to calc-alkaline basalts (δ98Mo = –0.29 ± 0.04‰) in the surrounding watershed, suggesting weathering of Yixian Formation volcanic rocks as the major source of sediment. During its

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 Archean Kongling Terrane preserves voluminous Paleoarchean-Paleoproterozoic granitoids, recording the early formation and evolution history of the Yangtze Craton, South China. We present petrography, geochemistry, zircon U–Pb geochronology and Lu–Hf isotopes of twelve gneissic granitoids from this terrane, including trondhjemites, biotite-granites, and two-mica granites. Magmatic zircons in these granitoids yield emplacement ages of 3.31–3.29 Ga for trondhjemites, 2.81–2.78 and 2.66 Ga for biotite-granites, as well as 2.70–2.64, 2.42, and 2.00 Ga for two-mica granites. The 2.8–2.6 Ga granites contain minor 3.4–2.9 Ga inherited zircons and 2.0 Ga metamorphic zircons that formed mainly by recrystallization. Major and trace element compositions of the trondhjemites suggest a garnet amphibolite-facies low-K mafic source, similar to the typical Archean medium-pressure trondhjemite-tonalite-granodiorites (TTGs), whereas those of the biotite- and two-mica granites indicate tonalitic and tonalitic-sedimentary sources, respectively. The Lu–Hf data (chondritic ɛHf(t) values −0.8 to 0 and Eoarchean two-stage Hf model ages 3.75–3.70 Ga) for the trondhjemites support partial melting of a long-lived ancient depleted-mantle-derived or a juvenile lower-mantle-derived mafic crust. The Lu–Hf data and inherited zircon ages also suggest that the 2.8 Ga granites were derived from the local 3.4–2.9 Ga TTGs. Together with previously addressed 3.2 and 3.0–2.9 Ga TTG magmatism, a remarkable change is observed at 2.8 Ga in the petrology, geochemistry, and petrogenesis of the episodic 3.3–2.0 Ga granitoid magmatism from TTG- to granite-dominated in the Kongling Terrane, which may reflect a transition from subduction- to collision-related tectonics. In addition, we note that the 2.70–2.64 Ga biotite- and two-mica granites (this study) as well as 2.67–2.62 Ga A-type granites (published data) were emplaced shortly after a 2.75–2.72 Ga high-grade metamorphic event (published data) in the Kongling Terrane. These granites could be generated as a result of orogenic root collapse and subsequent mantle upwelling, implying a 2.7 Ga orogenic event in the Yangtze Craton.

Granitoids widely occur in collisional orogens, which are a critical target for probing the nature of deep crust and mantle-crust interaction. In this study, we present an integrated study of in situ zircon U–Pb dating and Hf–O isotopes, in combination with whole-rock geochemistry, for the Mangling complex in the eastern Qinling orogen. The Mangling complex is composed mainly of monzogranites with some mafic microgranular enclaves (MMEs) and subordinate diorites. Zircon U–Pb dating yields identical crystallization ages of 141–143 Ma for the diorites and monzogranites, suggesting that they are formed simultaneously and belong to post-collisional magmatism. The Mangling diorites have relatively low SiO2 but high MgO, Cr and Ni contents and Mg# values. They are characterized by enrichment of large ion lithophile elements (LILEs) but depletion of high field-strength elements (HFSEs). They show initial Sr isotope (ISr) of 0.706491 to0.706622, eNd(t) of −10.82 to −10.38, and zircon eHf(t) of −10.8 to −7.9 and δ18O values of 6.48–7.18‰. These geochemical features indicate that the diorites were derived from an enriched lithospheric mantle source. In contrast, the Mangling monzogranites have high silica and low Mg# values. They exhibit more variable isotopic compositions: Isr = 0.707191–0.708310, eNd(t) = −13.74 to −8.10, and zircon eHf(t) = −17.2 to −7.0 and δ18O = 5.83–7.08‰. Some inherited zircon cores have been observed in the monzogranite samples with U–Pb ages of 1773–1791 Ma. These inherited cores have δ18O values of 5.42–5.69‰ and eHf(t) values of −7.8 to −5.9. Their U–Pb ages and Hf–O isotopic compositions are similar to those of the Xiong'er Group in the southern margin of the North China Craton (NCC), which have underthrusted the juvenile (in terms of isotopes) Kuanping unit where the Mangling complex has been emplaced. Isotopic modeling shows that the monzogranites were likely produced by fusion of the Kuanping unit and Xiong'er Group, with the involvement of enriched mantle-derived materials. The crustal rocks as well as the enriched sub-lithospheric mantle were both contributed to the Mangling complex, and some of the crustal components show more juvenile isotopic fingerprints. Therefore, it is not a mandatory to involve a depleted juvenile mantle-derived component to recognize mantle-crust interaction during granitoid generation, especially in which the preceded juvenile arcs were superimposed on ancient crust and/or enriched mantle. The ‘inverse’ isotopic compositions in crust and mantle components imply that a detailed petrochemical and isotopic study should be conducted to address the issue about crust-mantle interaction during granitoid generation.

The temperature dependence of anomalous magnetoresistance and weak antilocalization (WAL) is studied in HgTe/CdTe (111) quantum wells (QWs). An anomalous positive to negative magnetoresistance transformation dependent on temperature is observed in HgTe/CdTe QWs grown at 157 °C, but not in those grown at 160 °C. The Hikami–Larkin–Nagaoka model is employed to analyze the WAL effect. A high-resolution transmission electron microscopy investigation of the HgTe–CdTe interface supports the transport results. For HgTe topological insulators, the anomalous magnetoresistance may be caused by temperature-induced fluctuations in conduction, which could transform the inverted energy band to a normal energy band. At high temperature, the negative magnetoresistance may be due to scattering of the interface defective states under the normal energy band.

Partial melting of high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks in subduction zones has great influence on both the chemical and physical properties of deeply subducted continental crust. Felsic veins in HP-UHP metamorphic rocks are products of partial melting and thus would be a key target to trace partial melting in HP-UHP terranes. This contribution is an integrated study of petrology, zircon and titanite U-Pb ages, as well as zircon Hf-O and major minerals O isotope compositions for a felsic vein and its host granitic gneiss in the Sulu UHP terrane to decipher the timing and mechanism of partial melting. Zircon U-Pb dating for the inherited magmatic zircon cores of the granitic gneiss constrains the protolith age at ca. 750 Ma. The inherited zircons had an average δ18O value of 0.03 ± 0.15‰ and yielded a weighted mean eHf(t) value of −1.16 ± 0.54 and two-stage Hf model ages of 1707 ± 65 Ma. These results suggest that the protolith was derived from reworking of Paleoproterozoic crust in a Neoproterozoic rift. In the two samples, broad garnet core/mantle domains are of metamorphic origin and narrow garnet rims of peritectic origin. There are large differences in δ18O values between the protolith magmatic zircon (δ18O = 0.03 ± 0.15‰) and metamorphic garnet (−4.14 ± 0.21‰ for the felsic vein and −4.13 ± 0.11‰ for the host granitic gneiss), suggesting that the negative δ18O fingerprints might result from hydrothermal alteration or multi-episodes of rift magmatism after the formation of the protolith. Zircon from the felsic vein yielded a U-Pb age of 212 ± 3 Ma. Titanites from the two studied samples show undistinguishable U-Pb ages of 227 ± 14 Ma and 212 ± 6 Ma within the analytical uncertainties. These ages register the timings of the partial melting. The approximately consistent δ18O values of the metamorphic zircon (−4.78 ± 0.15‰) and metamorphic garnet indicate that the melt was sourced from the surrounded gneiss in a closed system, which might be triggered by breakdown of phengite. According to a compilation of partial melting in the Sulu UHP terrane, there exists a clear spatio-temporal variation. The ca. 237-224 Ma partial melting in the northern UHP zone might be due to its relatively high temperature metamorphism; the most extensive partial melting occurred at ca. 220-215 Ma in both the southern and northern UHP zones, which might be triggered by the detachment of the preceding subducted slab; and partial melting of the northern UHP zone continued to ca. 210 Ma due to heat supply from the underneath mantle. Such a variation might be dictated by the tectonic evolution of the different UHP slices. Accordingly, the whole partial melting process of UHP rocks in the Sulu UHP terrane might have lasted for about 27 Myr with two major episodes at ca. 230–224 and 220-215 Ma.

The North Qaidam UHPM (ultra-high pressure metamorphism) belt is a typical continental subduction-collision belt containing continental crust deep subduction metamorphic products and oceanic crust relics, And it is an ideal region to study the ocean-continent transition and exhumation mechanism of oceanic UHP rocks during continental deep subduction process. In this paper, we report integrated in situ U-Pb, Lu-Hf and O isotope analyses of zircons from a serpentinized harzburgite as well as U-Pb dating for zircons from a kyanite eclogite from the North Qaidam Dulan UHPM terrane, and use these data to discuss the ocean-continent transition and exhumation mechanisms of oceanic UHP rocks during continental deep subduction. The serpentinized harzburgite was dated at 448±9 Ma, consistent with 455±5 Ma age for the kyanite eclogite within analytical errors. Zircons from the serpentinized harzburgite have uniform 176Hf/177Hf values ranging from 0.282 842 to 0.282 883 and e Hf(t) values from 11.6 to 13.3. Zircon δ18O values of the serpentinized harzburgite vary from 4.47‰ to 5.29‰, slightly lower than the value of 5.3‰±0.6‰ for the normal mantle zircon. These Hf-O isotopic features indicate that the protolith of the serpentinized harzburgite was derived from depleted-mantle source, and might have experienced high-temperature rock-water interaction. Therefore, the serpentinized harzburgite was possibly located in the lower part of an oceanic section. The serpentinized harzburgite and kyanite eclogite were both formed due to the subduction of oceanic crust. The UHP metamorphism occurred successively from the oceanic crust to continental crust rocks of the North Qaidam UHP terrane. Low-density serpentinized peridotite and continental rocks possibly have negative buoyancy and play a key effect on preservation and exhumation of high-density oceanic eclogite.

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.

Continents are underlain by thick, cold thermal boundary layers. Thermal contraction should render these boundary layers negatively buoyant and unstable; this is why old, cold oceanic lithospheres subduct. However, the ancient lithospheric roots of many continents appear to have existed for billions of years. In the common view, this preservation is due to the fact that the thermal boundary layers are compositionally distinct from the ambient mantle in that they are highly melt-depleted and dehydrated; the former provides positive buoyancy and the latter provides strength. Here, we show using mantle xenoliths that the Precambrian South China Block originally was underlain by highly depleted mantle, but has been refertilized via silicate melts generated from the asthenosphere. It is now more fertile than the ambient convecting mantle and is intrinsically denser by more than 1.5%. Achieving sufficient melt generation for refertilization is only possible if the lithosphere is thin enough to provide “headspace” for decompression melting. Thus, continental boundary layers thinner than the maximum depth of melting should experience refertilization, whereas thicker continents would altogether suppress melting and hence the potential for refertilization. We propose that refertilization, once initiated, will destabilize the base of the continent; this in turn will increase the amount of “headspace” and promote further refertilization, resulting in a positive feedback that could culminate in lithospheric destruction. By contrast, continents that are thick enough may not experience significant refertilization. This suggests that initial lithospheric thickness, as well as lithospheric composition, may be important for defining the fate of continents.

The ChahJam–Biarjmand complex (CJBC), flanked by the Alborz Mountains in the north and the Lut–Tabas block to the south, is part of Central Iranian block, where the oldest continental crust of Iran is found. This complex contains granitic to tonalitic orthogneissic rocks (old plutons) and associated metasediments, amphibolites and paragneisses. Metamorphosed granitic and granodioritic dikes intrude orthogneisses as well as metasediments and are abundant close to the plutons (orthogneissic rocks). Based on the results of bulk rock trace and rare earth elements, the orthogneissic rocks are inferred to have crystallized from subduction-related melts. Amphibolites also have subduction-related signatures and are inferred to have formed both as metamorphosed volcanoclastic sediments and as attenuated basic dikes. The presence of para-amphibolites associated with paragneisses and metasediments (mica schists) could represent a sedimentary basin filled with magmatic arc erosional products. U–Pb zircon dating of the ChahJam–Biarjmand rocks yielded 238U/206Pb crystallization ages of ca. 550 to 530 Ma (Ediacaran–early Cambrian). Sr–Nd isotope systematics on whole rocks (eNd(t) = − 2.2 to − 5.5) and zircon Hf isotope results indicate that CJBC Cadomian granitic rocks contain older, possible Mesoproterozoic, continental crust in their source. The ChahJam–Biarjmand granitic–tonalitic gneissic rocks are coeval with other similar-aged metagranites and gneisses within Iranian basement exposed in Central Iran, the Sanandaj–Sirjan Zone and the Alborz Mountains, as well as in the Tauride–Anatolide platform in western Anatolia and in NW Turkey. All these dispersed Cadomian basement rocks are interpreted to show fragments of Neoproterozoic–early Cambrian continental arcs bordering the northern active margin of Gondwana.

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.

Titanite U–Pb isotopic and major and trace element compositions of one mafic garnet granulite from a rare suite of lower crustal xenoliths (e.g., eclogite, garnet pyroxenite, and mafic garnet granulite) hosted in Early Cretaceous dioritic porphyries in the Xu–Huai area along the southeastern margin of the North China Craton (NCC) were analyzed by laser ablation ICP-MS. Titanite occurs as granular grains or coronary rims on rutile. The coronary titanite is clearly a secondary product of rutile decomposition. The granular titanite exhibits zonation in U–Pb age and chemical composition. Petrographic and geochemical evidence suggests that the zonation was formed by thermal diffusion and later fluid-assisted recrystallization. Occurrences of granular titanite between garnet grains point to a pressure of > 10 kbar, while inclusions of rutile inside granular titanite rims imply that the pressure might have reached 15 kbar. Granular titanite cores give U–Pb ages of 237–241 Ma and Zr-temperatures of 794–831 °C at 10 kbar and 850–892 °C at 15 kbar, indicating high-pressure granulite-facies metamorphism. Together with previous P–T estimates of coeval eclogite-facies xenoliths, a geotherm of above 60 mW m− 2 is implied. The geotherm plots below the temperature field of amphibole dehydration melting, consistent with presence of abundant amphibole. This geotherm is similar to that of the Kohistan arc, which has preserved a 12-km-thick dense lower crust, but significantly cooler than the geotherm of the Talkeetna arc, where most of the dense lower crust has been foundered. Our results provide new evidence for Triassic thickened dense lower crust along the southeastern margin of the NCC. By comparison with the Kohistan and Talkeetna arc crusts, we suggest that this dense lower crust was not hot enough to be foundered in the Triassic. Foundering must have occurred in the Jurassic–Cretaceous in order to explain the present-day seismic velocity structure characterized by a sharp Moho, overall slow velocities in the lower crust, and a thin crustal thickness in the Xu–Huai area and other parts of the eastern NCC. We suggest that the Jurassic–Cretaceous foundering was related to the Pacific subduction. On one hand, the Jurassic subduction may have further thickened the southeastern margin of the NCC prior to Cretaceous extension, leading to greater instability of the lower crust. On the other hand, the subduction-related magma provided heat and water that weakened the lower crust, resulting in the final foundering. The large contrast in mineralogy between the Xu–Huai eclogite-facies xenoliths and nearby Nushan garnet-free granulite xenoliths entrained by Quaternary basalts indicates > 20 km removal of the lower crust along the southeastern margin of the NCC.

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.

Zircon U–Pb–Lu–Hf–O isotopic compositions of two granitic gneisses from the Kongling Terrain in the Yangtze Craton, South China were determined by SIMS, LA-ICP-MS and LA-MC-ICP-MS. Whole rocks of the two samples were analyzed for major and trace element compositions. The SIMS and LA-ICP-MS data reveal similar five zircon age groups of 3.4, 3.3, 2.9, 2.7, and 2.0 Ga for both gneisses. Three groups (magmatic Group A, metamorphic Group B, and overgrowth Group C) of the 3.4 Ga zircons were identified based on their CL images. These three groups have indistinguishable ages and Th/U ratios. Groups A and B show identical 176Hf/177Hf (t), although Group C was too thin to be analyzed by LA-ICP-MS. Taken together, zircons from the two samples with 98–102% age concordance give weighted average SIMS ages of 3434.3 ± 9.6 Ma (2σ, MSWD = 13, n = 8) for Group A, 3446.0 ± 8.8 Ma (2σ, MSWD = 10.7, n = 15) for Group B, and 3479 ± 26 Ma (2σ, MSWD = 0.49, n = 2) for Group C. Groups A and B together yield an upper intercept age of 3457 ± 14 Ma (2σ, MSWD = 0.85, n = 23). The LA-ICP-MS data yield weighted average ages of 3442 ± 19 Ma (2σ, MSWD = 0.17, n = 7) for Group A and 3435 ± 11 Ma (2σ, MSWD = 0.44, n = 16) for Group B. They yield an upper intercept age of 3443 ± 13 Ma (2σ, MSWD = 0.63, n = 23). These SIMS and LA-ICP-MS ages are consistent. We propose that the above SIMS and LA-ICP-MS ages of Groups A and B are the best estimates of the granitic magmatism and the subsequent metamorphism. The metamorphism must have occurred after the granitic magmatism within a few tens of million years, as constrained by their age errors. Accordingly, these two granitic gneisses represent the oldest rocks currently known in South China. They predate the previously reported 3300-Ma-old trondhjemitic gneiss from the Kongling Terrain by 150 Ma. The 3.4 Ga zircons show near chondritic ɛHf (t) (−0.7 ± 1.0, 2σ, MSWD = 1.14, n = 8), which is below the coeval value of the depleted mantle. This suggests that the granitic magma contained materials of pre-existing continental crust. Their higher-than-mantle δ18O values (6.1–6.4‰) imply that such materials must have been interacted with surface water. Crust formation ages (TDM2) of the 3.4 Ga zircons vary from 3.9 to 3.6 Ga with a weighted average of 3703 ± 27 Ma (2σ, MSWD = 1.05, n = 7). Our results support previous studies that the Yangtze Craton may have contained the continental crust as old as 3.8 Ga. Among the younger age groups, the 3.3 Ga zircons exhibit 176Hf/177Hf (t) and δ18O values similar to the 3.4 Ga zircons, suggesting that they were altered from the 3.4 Ga zircons. The 2.9 and 2.7 Ga zircons in both samples are rare and magmatic. Their 176Hf/177Hf (t) ratios are distinct from the 3.4 Ga zircons, indicating different sources. These two age groups are consistent with the 2.9 Ga trondhjemitic–tonalitic–granodioritic and the 2.7 Ga A-type granitic magmatism in the Kongling Terrain. The 2.0 Ga metamorphic zircons, regardless of being concordant or discordant, have 176Hf/177Hf (t) ratios overlapping those of the 2.7 Ga zircons, suggesting a common source. In contrast, δ18O of the 2.0 Ga zircons is strongly variable and positively correlated with age concordance. The low δ18O (down to 3.1‰) requires interaction with hydrothermal fluid. These results suggest that at least some of the 2.0 Ga zircons were likely to have been altered from the 2.7 Ga zircons by hydrothermal fluid.