A New Symmetrodont Mammal with Fur Impressions from the Mesozoic of China

Western Liaoning of northeastern China is world-renowned for the Mesozoic Jehol biota, especially for yielding many feathered dinosaurs, primitive birds, mammals and fossil angiosperm. This paper describes a complete specimen of a symmetrodont mammal with well-preserved hairs and soft tissue from the basal part of the Yixian Formation in the Sihetun area, Beipiao, western Liaoning. It is significant for understanding the morphology, osteology, phylogeny and life habits of Mesozoic symmetrodont mammals.     

Ascalochrysidae – a new lacewing family from the Mesozoic of China (Insecta: Neuroptera: Chrysopoidea)

Ascalochrysa megaptera gen. et sp. nov. is described from the Yixian Formation (Lower Cretaceous) of China. It is treated as belonging to the new family Ascalochrysidae fam. nov., closely related to Mesochrysopidae but easily distinguished from it in the hindwing venation features: e.g., numerous subcostal crossveins; branches of Rs widely, irregularly spaced and deeply branched; crossvenation rich, irregular; convex vein-like fold (‘M5’) before concave CuA present. The presence of well-developed ‘M5’ in the hind wing is interpreted to be plesiomorphic condition within the order. Ascalochrysidae are considered the sister group of Mesochrysopidae (s.l.).     

Palaeoproterozoic magmatic–metamorphic history of the Quanji Massif,Northwest China: implications for a single North China-Quanji-Tarim craton within the Columbia supercontinent?

The Quanji Massif (QM), in the northeast part of Tibet, consists of Palaeoproterozoic metamorphic rocks, granitoids, and mafic dikes. U–Pb dating of a diorite gneiss and a mafic dike in the QM yielded a crystallization age of 2272 ± 15 Ma and a metamorphic age of 1928 ± 11 Ma, respectively. Although some post-emplacement alteration has occurred, the mafic dikes display a sub-alkaline signature with slight light rare earth element-enrichment, depletion in Th, Nb, Ta, and Ti, and have a rare earth element pattern consistent with volcanic arc basalts. Based on the geochronology and field relationships, we conclude that the mafic dikes formed in an extensional setting within either a fore-arc or back-arc environment. We argue that the metamorphism that affected the dikes occurred shortly after intrusion. Our diorite gneiss and monzodiorite samples are characterized by relatively high Mg# (47–56) and Sr contents (367–1070 ppm), low-to-moderate Sr/Y (10–90), low Rb/Sr (0.03–0.28) and high K/Rb (179–775). These felsic melts likely originated from partial melting of a mafic source. Our new data, combined with results from previous studies, indicate that the QM formed between 2.50 and 2.30 Ga and underwent metamorphism around 1.95–1.75 Ga that may relate to the dispersal of Neoarchaean ‘Kenorland’ and the formation of the Columbia supercontinent. The similarity between the Palaeoproterozoic events in the Tiekelik, North Altyn–Dunhuang, Alashan blocks, and QM suggests that QM was part of either the Tarim or the North China Craton in the late Archaean and Palaeoproterozoic. If the model is correct, then there was a single ‘North China–Quanji–Tarim Craton’ that was later disrupted by Neoproterozoic to Phanerozoic tectonic events.     

U–Pb and Hf-isotope analysis of zircons in mafic xenoliths from Fuxian kimberlites: evolution of the lower crust beneath the North China craton

Mafic xenoliths from the Paleozoic Fuxian kimberlites in the North China craton include garnet granulite, and minor pyroxene amphibolite, metagabbro, anorthosite and pyroxenite. The formation conditions of the amphibolites are estimated at 745–820 °C and 7.6–8.8 Kb (25–30 km); the granulites probably are derived from greater depths in the lower crust. LAM-ICPMS U–Pb dating of zircons from four granulites reveals multiple age populations, recording episodes of magmatic intrusion and metamorphic recrystallisation. Concordant ages and upper intercept ages, interpreted as minimum estimates for the time of magmatic crystallisation, range from 2,620 to 2,430 Ma in three granulites, two amphibolites and two metagabbros. Lower intercept ages, represented by near-concordant zircons, are interpreted as reflecting metamorphic recrystallisation, and range from 1,927 to 1,852 Ma. One granulite contains two metamorphic zircon populations, dated at 1,927±55 Ma and 600–700 Ma. Separated minerals from one granulite and one amphibolite yield Sm–Nd isochron ages of 1,619±48 Ma (¹⁴³Nd/¹⁴⁴Nd)i=0.51078), and 1,716±120 Ma (¹⁴³Nd/¹⁴⁴Nd)i=0.51006), respectively. These ages are interpreted as recording cooling following metamorphic resetting; model ages for both samples are in the range 2.40–2.66 Ga. LAM-MC-ICPMS analyses of zircon show a range in ¹⁷⁶Hf/¹⁷⁷Hf from 0.28116 to 0.28214, corresponding to a range of _Hf from –34 to +12. The relationships between ²⁰⁷Pb/²⁰⁶Pb age and _Hf show that: (1) the granulites, amphibolites and metagabbro were derived from a depleted mantle source at 2.6–2.75 Ga; (2) zircons in most samples underwent recrystallisation and Pb loss for 100–200 Ma after magmatic crystallisation, consistent with a residence in the lower crust; (3) metamorphic zircons in several samples represent new zircon growth, incorporating Hf liberated from breakdown of silicates with high Lu/Hf; (4) in other samples metamorphic and magmatic zircons have identical ¹⁷⁶Hf/¹⁷⁷Hf, and the younger ages reflect complete resetting of U–Pb systems in older zircons. The Fuxian mafic xenoliths are interpreted as the products of basaltic underplating, derived from a depleted mantle source in Neoarchean time, an important period of continental growth in the North China craton. Paleoproterozoic metamorphic ages indicate an important tectonic thermal event in the lower crust at 1.8–1.9 Ga, corresponding to the timing of collision between the Eastern and Western Blocks that led to the final assembly of the North China craton. The growth of metamorphic zircon at 600–700 Ma may record an asthenospheric upwelling in Neoproterozoic time, related to uplift and a regional disconformity in the North China craton.     

Assessing the ‘wicked problems’ associated with the quality of groundwater used in irrigation: a case study from the North China Plain

Studies on the quality of groundwater have moved beyond the physical realm of contamination and purification, towards the economic concerns of choice and the management of the problem. With these approaches the complex biophysical processes are assessed from the users’ perspective and the policy outcomes that could be used to resolve the problems of groundwater contamination are evaluated. However, in a set of unrelated studies, it has been found that attempts by governments to resolve the problems of groundwater contamination in agriculture have a poor record of success. This could be because the problem is too extensive and diverse to handle or it could be a case of poor policy selection. Taking an example from the North China Plain to illustrate some of the major issues raised in this study, it is concluded that the problem itself is unresolvable on a large scale. In other words, groundwater contamination can be defined as a ‘wicked problem’, i.e. unresolvable by applying pure science, closely linked with social issues, and for which there are no optimal solutions. In this situation, the best solution is possibly to encourage farmers to live with and handle the problem as they best see fit.     

Crust-mantle interaction during the tectono-thermal reactivation of the North China Craton: constraints from SHRIMP zircon U–Pb chronology and geochemistry of Mesozoic plutons from western Shandong

Chronological, geochemical and Sr–Nd–Pb isotopic analyses have been carried out on the Mesozoic plutons in western Shandong with the aim of characterizing crustal–mantle evolution during the tectono-thermal reactivation of the craton. Detailed SHRIMP zircon U–Pb dating reveals two main periods of Mesozoic activity with contrasting compositions. The older magmatic pulse is manifested by monzonites and monzodiorites from Tongshi for which zircon rims yield a concordant age of 177±4 Ma and the cores have a discordant age of ca. 2.5 Ga. Low MgO and Cr, high Na₂O contents and especially their isotopic compositions (⁸⁷Sr/⁸⁶Sr < 0.7042, ²⁰⁶Pb/²⁰⁴Pb < 16.8 and _Nd ~ –12) are consistent with derivation from late Archean–Paleoproterozoic lower crust. Relatively high HREE contents in these Jurassic plutons indicate a garnet-free source (<32 km), in contrast to the garnet-bearing source (>40 km) of the late Mesozoic high Sr and low Y granitoids from the same region. Distinctively different depths of crustal melting suggest dynamic thickening of the crust by magmatic underplating during the Jurassic and Cretaceous. The younger dioritic plutons from Laiwu and Yinan were emplaced at 132–126 Ma and show relatively high MgO and Cr contents and large isotopic variability. They were likely derived from enriched lithospheric mantle source and were subjected to crustal contamination during magma evolution. Early Cretaceous mantle melting is coeval with the widespread late Yanshanian granitic magmatism in North China. Early Cretaceous time may correspond to a critical period when a temperature increase due to lithospheric thinning allowed the intersection of the local geotherm and the wet peridotite solidus. While some mantle-derived magmas were erupted, most were trapped at variable crustal depths, triggering large-scale concomitant melting of the crust. Lithospheric thinning must have continued until the late Cretaceous because of the change in the source of mafic magmas from lithospheric to asthenospheric at that time. It is proposed that removal of the lithospheric keel beneath the North China craton may have been initiated as early as the Jurassic, but with the most intense period in the Cretaceous between 130–75 Ma. Such a relatively long timescale (~100 Ma) emphasizes the role of thermomechanical erosion by convective mantle in lithospheric thinning beneath this region.     

Paleoproterozoic gabbronoritic and granitic magmatism in the northern margin of the North China craton: Evidence of crust–mantle interaction

Paleoproterozoic Xuwujia gabbronorites in the northern margin of the North China craton occur as dykes, sills and small plutons intruded into khondalite (aluminous paragneisses, sedimentary protoliths deposited at ca. 2.0–1.95 Ga), and as numerous entrained bodies and fragments of variable scales in the Liangcheng granitoids (ca. 1.93–1.89 Ga). These gabbronoritic dykes are present at all locations where ca. 1.93–1.92 Ga ultra-high-temperature metamorphism is recorded in the khondalite. A gabbronorite sample from the Hongmiaozi dyke gives zircon ²⁰⁷Pb/²⁰⁶Pb mean ages of 1954 ± 6 Ma (core domains) and 1925 ± 8 Ma (rim domains). These ages, as well as previously reported ages, constrain the age of mafic magmatism to be at ca. 1.96–1.92 Ga (∼1.93 Ga). One sample from the Xigou gabbro intruded by the Liangcheng granitoids gives a zircon ²⁰⁷Pb/²⁰⁶Pb mean age of 1857 ± 4 Ma, which is interpreted as the age of a metamorphic overprint. The Xuwujia gabbronorites comprise mainly gabbronorite compositions, as well as some norite, olivine gabbronorite, monzonorite, quartz gabbronorite, and quartz monzonorite. Chemically, they are tholeiitic and can be divided into two groups: a high-Mg group (6.2–22.9 wt.% MgO) and a relatively low-Mg group (2.2–5.7 wt.% MgO). The high-Mg group shows negative Eu-anomalies (Eu/Eu* = 0.53–0.72), slight light rare earth element enrichment (La/Yb_N = 0.56–1.53), and small negative anomalies in high field-strength elements. The ?Nd (t = 1.93 Ga) values vary from +0.3 to +2.4. The low-Mg group shows varied Eu-anomalies (Eu/Eu* = 0.48–1.05), and is enriched in light rare earth elements (La/Yb_N = 1.51–11.98). The majority shows negative anomalies in high field-strength elements (e.g., Th, Nb, Zr, and Ti). Initial ?Nd (at 1.93 Ga) values for low-Mg gabbronorites vary from −5.0 to 0. The Xuwujia gabbronorites possibly experienced assimilation of crust, and fractional crystallization of initially olivine and hypersthene (the high-Mg group), and then olivine, clinopyroxene, and plagioclase (the low-Mg group). The slightly younger Liangcheng granitoids consist of garnet-bearing granite, granodiorite and quartz-rich granitic compositions. They are intermediate to felsic calc-alkaline rocks, thought to be derived from surrounding metasedimentary crust. Xigou gabbro could represent early cumulates. The granitoids have relatively high-Mg numbers (up to 54), and show some chemical affinities with the gabbronorites, which could have resulted from incorporation of gabbronoritic melts. The occurrence and chemical variations of the Xuwujia gabbronorites and Liangcheng granitoids can be interpreted to have resulted from crust–mantle interaction, with mingling and partial mixing of mantle (gabbronoritic) and crustal (granitic) melts. The Xuwujia gabbronorites originated from a mantle region with high potential temperatures (∼1550 °C), possibly associated with a plume or more likely a ridge-subduction-related mantle upwelling event. They could have had extremely high primary intrusion temperatures (up to 1400 °C). Emplacement of these magmas was likely responsible for the extensive crustal anatexis (Liangcheng granitoids) and the local ultra-high-temperature metamorphism. These sequences may have followed ca. 1.95 Ga continent–continent (arc?) juxtaposition and were themselves followed by significant regional uplift and exhumation in the northern margin of the North China craton.     

Origin of two contrasting latest Permian–Triassic volcanic rock suites in the northern North China Craton: implications for early Mesozoic lithosphere thinning

New geological, geochronological, and geochemical results on volcanic rocks and cobbles from early Mesozoic sedimentary rocks identify two contrasting latest Permian–Triassic volcanic rock suites in the northern North China Craton (NCC). The early rock suite erupted during the latest Permian–Early Triassic at ca. 255–245 Ma and was probably widely distributed in the northern NCC prior to the Early Jurassic. It comprises rhyolitic welded tuff, rhyolite, and tuffaceous sandstone and is characterized by high contents of SiO₂ and K₂O, moderate initial ⁸⁷Sr/⁸⁶Sr, low negative ε_Nd(t) and ε_Hf(t) values, and old Nd-Hf isotopic model ages. It was likely produced by fractional crystallization of lower crustal-derived magmas due to underplating by lithospheric mantle-derived magmas near the crust–mantle boundary in syncollisional to post-collisional/post-orogenic tectonic settings. The late rock suite, erupted during the Middle–Late Triassic at ca. 238–228 Ma, displays adakitic geochemical signatures and consists of intermediate volcanic rocks such as andesite, trachyandesite, and autoclastic trachyandesite breccia, with minor felsic rocks. This suite is characterized by high Al₂O₃, MgO, Sr, Ba, Cr, V, and Ni concentrations; high Mg# values; low Y and Yb concentrations and high Sr/Y ratios; low initial ⁸⁷Sr/⁸⁶Sr; high negative ε_Nd(t) and ε_Hf(t) values; and young Nd-Hf isotopic model ages. The younger suite was generated by mixing of magmas derived from melting of upwelling asthenosphere, with melts of ancient lower crust induced by underplating of basaltic magmas in an intraplate extensional setting. Strong upwelling of asthenospheric mantle and significant involvement of the asthenospheric mantle materials indicate that the lithospheric mantle beneath the northern NCC was partially delaminated during Middle–Late Triassic time, representing the initial destruction and lithospheric thinning of the northern NCC. Lithospheric thinning and delamination are likely the most important reasons for the Triassic tectonic transition and change of magmatism and deformation patterns in the northern NCC.     

The Taihua group on the southern margin of the North China craton: further insights from U–Pb ages and Hf isotope compositions of zircons

The "Taihua Group" is a collective term for a series of old terranes scattered along the southern margin of the North China Craton. The timing of formation and thermal overprinting of the Taihua Group have long been contentious, and its relationship with the Qinling orogenic belt has been unclear. In this study, new data from integrated in-situ U–Pb dating and Hf isotope analysis of zircons from an amphibolite (from the Xiong’ershan terrane) and a biotite gneiss (from the Lantian-Xiaoqinling terrane) indicate that the Upper Taihua Group formed during the Paleoproterozoic (2.3–2.5 Ga) and thus was originally part of the southern edge of North China Craton, detached during the Mesozoic Qinling orogeny and displaced about 100 km north from its original location. This suggests that the Taihua Group became part of the tectonic terrane associated with the Qinling orogeny and now forms part of the overthrust basement section of the Qinling belt. Before the Qinling orogeny, the Taihua Group was metamorphosed at 2.1 Ga. The initial Hf-isotope compositions of zircons, together with positive εNd(t) values for the whole-rocks, imply that the original magmas were derived from a juvenile source with some assimilation of an Archean crustal component.     

Re–Os isotope evidence from Mesozoic and Cenozoic basalts for secular evolution of the mantle beneath the North China Craton

The mechanism and process of lithospheric thinning beneath the North China Craton (NCC) are still debated. A key criterion in distinguishing among the proposed mechanisms is whether associated continental basalts were derived from the thinning lithospheric mantle or upwelling asthenosphere. Herein, we investigate the possible mechanisms of lithospheric thinning based on a systematic Re–Os isotopic study of Mesozoic to Cenozoic basalts from the NCC. Our whole-rock Re–Os isotopic results indicate that the Mesozoic basalts generally have high Re and Os concentrations that vary widely from 97.2 to 839.4 ppt and 74.4 to 519.6 ppt, respectively. They have high initial ¹⁸⁷Os/¹⁸⁸Os ratios ranging from 0.1513 to 0.3805, with corresponding variable γ_Os(t) values (+20 to +202). In contrast, the Re–Os concentrations and radiogenic Os isotope compositions of the Cenozoic basalts are typically lower than those of the Mesozoic basalts. The lowest initial ¹⁸⁷Os/¹⁸⁸Os ratios of the Cenozoic basalts are 0.1465 and 0.1479, with corresponding γ_Os(t) values of +15 and +16, which are within the range of ocean island basalts. These new Re–Os isotopic results, combined with the findings of previous studies, indicate that the Mesozoic basalts were a hybrid product of the melting of pyroxenite and peridotite in ancient lithospheric mantle beneath the NCC. The Cenozoic basalts were derived mainly from upwelling asthenosphere mixed with small amounts of lithospheric materials. The marked differences in geochemistry between the Mesozoic and Cenozoic basalts suggest a greatly reduced involvement of lithospheric mantle as the magma source from the Mesozoic to the Cenozoic. The subsequent lithospheric thinning of the NCC and replacement by upwelling asthenospheric mantle resulted in a change to asthenosphere-derived Cenozoic basalts.     

Geochemical characteristics of the coal gangues from the Du’erping coal mine,Xishan coalfield,North China

Inductively coupled plasma mass spectrometry, inductively coupled plasma optical emission spectroscopy, hydride generation-atomic fluorescence spectrometry, emission spectrometry, X fluorescence spectrometry, and X-ray diffraction were employed to study the geochemistry and mineralogy of coal gangues from Nos. 2, 3, and 8 coal seams of the Du’erping coal mine, Xishan coalfield, Taiyuan, Shanxi Province. The study revealed that compared with the sedimentary cover, upper continent crust, Carboniferous-Permian coal from North China, as well as most coal in China, coal gangues from Nos. 2 and 3 coal seams are rich in Li, Be, Sc, Cr, Cu, Ga, Ba, Th, Nb, Cd, Pb, Ta and rare-earth elements, and coal gangues from No. 8 coal seam are rich in Li, Sc, V, Cr, Ga, U, and rare-earth elements. Compared with the Carboniferous-Permian coal from North China and most coal in China, coal gangues from Nos. 2, 3 and 8 seams are rich in Rb, V, Cs and Sr. Therefore, The Du’erping coal gangues in the Xishan coalfield are rich in most hazardous trace elements and rare-earth elements, wherein the contents of Ga and Li reach the industrial grade and have significance for industrial utilization. On the whole, coal gangues of the Shanxi Formation from the Permian are rich in more trace elements than those of the Carboniferous Taiyuan Formation. The distributions of REE show obviously dipping rightwards with negative Eu anomalies. The contents of rare-earth elements in the three seams are quite different. All of the above indicate that the source of the rare-earth elements is terrigenous debris. Minerals in No. 2 seam identified by X-ray diffraction mainly include quartz, kaolinite, in addition to calcite, pyrite, apatite, epidote, and epsomite. No. 3 seam mainly contains quartz, kaolinite, in addition to a small amount of sodium feldspar, calcium nitrate, iron ore, gypsum, and vivianite. No. 8 seam mainly contains kaolinite, dickite, quartz, illite, and a small amount of hematite and U. The correlations between major elements and trace elements in coal gangues of the Du’erping coal mine analyzed by using SPSS (Statistical Product and Service Solutions) indicate that the trace alkali elements and rare-earth elements occur mainly in such clay minerals as kaolinite.     

Metallogenic ‘factories’ and resultant highly anomalous mineral endowment on the craton margins of China

The current margins of the North China and Yangtze Cratons provide arguably the best examples globally of anomalously high mineral endowment within a 100 km buffer zone, hosting 66 diverse world-class to giant ore systems that help explain China’s premier position as a producer of multiple metal and mineral commodities. After the cratonization of these crustal blocks during the Neoarchean-Paleoproterozoic, with incorporation of iron ores on assembled micro-block margins, the margins of the cratons experienced multiple convergence and rifting events leading to metasomatism and fertilization of their underlying sub-continental lithospheric mantle. The rifted margins with trans-lithosphere faults provided pathways for Cu-Au (Mo-W-Sn)-bearing felsic to Ni-Cu-bearing ultrabasic intrusions and REE-rich carbonatite magmas, and for the development of marginal sedimentary basins with both Cu-Pb-Zn-rich source units and reactive carbonate or carbonaceous host rocks. There was diachronous formation of hydrothermal orogenic gold, antimony, and bismuth systems in the narrow orogenic belts between the cratons. Complexity in the Mesozoic Paleo-Pacific subduction systems resulted in asthenosphere upwelling and lithosphere extension and thinning in the North China Craton, leading to anomalous heat flow and formation of orogenic gold deposits, including those of the giant Jiaodong gold province on its north-eastern margin. These gold deposits, many of which formed from fluids liberated by devolatilization of previously metasomatized sub-continental lithospheric mantle, helped propel China to be the premier gold producer globally. The thick sub-continental lithospheric mantle of the cold buoyant cratons helped the preservation of some of the world’s oldest porphyry-skarn and epithermal mineral systems. Although craton margins globally control the formation and preservation of a diverse range of mineral deposits, China represents the premier example in terms of metal endowment due to the anomalous length of its craton margins combined with their abnormally complex tectonic history.     

A Possible Long-tailed Bird with a Pygostyle from the Late Mesozoic Yixian Formation, Western Liaoning, China

AbstractAn incomplete caudal vertebral series (IVPP Vl1309) from the Yixian Formation of late MesozoicJianshangou area of Beipiao, western Liaoning Province, may represent a new bird. The tail is composed of at least 12 free caudal vertebrae and the most distal 5 caudal vertebrae co-ossified into a pygostyle. The pygostyle is plate-like and slightly curved dorsally. The anterior free caudals are amphiplatyan. The anterior caudal surfaces of the last three free caudals are concave, but their posterior articular surfaces are convex. The pygostyle is regarded as the first appeared flight apparatus during the evolutionary process from Archaeopteryx to neornithes. The pygostyle appeared in most early fossil birds and almost all the modem birds. Although their morphologies are different, they are basically formed by at least four last caudal vertebrae. The specimen V11309 is regarded as a bird rather than a non-avian theropod dinosaur based on the following characters: short caudal vertebrae, numerous pits present on the surfaces of the centra and, a foramen present between the basal part of the fused neural spines, which is similar to that of Struthio camelus. The discoveries of pygostyles from the therizinosauroids and oviraptorosaurs may provide strong evidence for supporting the origin of birds from small theropod dinosaurs. The structure of the pygostyle in specimen Vl1309 is different from those of Beipiaosaurus (Therizinosauroid) and Nomingia (oviraptorosaur). The most parsimonious interpretation is that these pygostyle-like structures are independently acquired by Beipiaosaurus and Nomingia during their evolutionary process.     

Analysis of historical drought and flood characteristics of Hengshui during the period 1649–2018: a typical city in North China

Natural Hazards - The objective of this study was to reconstruct the long-term drought and flood time series to analyze their changing characteristics in Hengshui City of North China. Disaster...     

Petrogenesis of the Mesozoic intrusive complexes from the southern Taihang Orogen,North China Craton: elemental and Sr–Nd–Pb isotopic constraints

A geochemical and isotopic study was carried out for three Mesozoic intrusive suites (the Xishu, Wuan and Hongshan suites) from the North China Craton (NCC) to understand their genesis and geodynamic implications. The Xishu and Wuan suites are gabbroic to monzonitic in composition. They share many common geochemical features like high Mg# and minor to positive Eu anomalies in REE patterns. Initial Nd–Sr isotopic compositions for Xishu suite are _Nd(135 Ma)=–12.3 to –16.9 and mostly I_Sr = 0.7056–0.7071; whereas those for Wuan suite are slightly different. Pb isotopic ratios for Xishu suite are (²⁰⁶Pb/²⁰⁴Pb)_i = 16.92–17.3, (²⁰⁷Pb/²⁰⁴Pb)_i=15.32–15.42, (²⁰⁸Pb/²⁰⁴Pb)_i=37.16–37.63, which are slightly higher than for Wuan suite. The Xishu–Wuan complexes are considered to originate from partial melting of an EM1-type mantle source, followed by significant contamination of lower crustal components. The Hongshan suite (mainly syenite and granite) shows distinctly higher _Nd(135 Ma) values (–8 to –11) and slightly higher Pb isotopic ratios than the Xishu–Wuan suites. It was formed via fractionation of a separate parental magma that also originated from the EM1-type mantle source, with incorporation of a small amount of lower crustal components. Partial melting of the mantle sources took place in a back-arc extensional regime that is related to the subduction of the paleo-Pacific slab beneath the NCC.     

Source characteristics of the ∼2.5 Ga Wangjiazhuang Banded Iron Formation from the Wutai greenstone belt in the North China Craton: Evidence from neodymium isotopes

Here we first present samarium (Sm)–neodymium (Nd) isotopic data for the ∼2.5 Ga Wangjiazhuang BIF and associated lithologies from the Wutai greenstone belt (WGB) in the North China Craton. Previous geochemical data of the BIF indicate that there are three decoupled end members controlling REE compositions: high-T hydrothermal fluids, ambient seawater and terrigenous contaminants. Clastic meta-sediment samples were collected for major and trace elements studies in an attempt to well constrain the nature of detrital components of the BIF. Fractionated light rare earth elements patterns and mild negative Eu anomalies in the majority of these meta-sedimentary samples point toward felsic source rocks. Moreover, the relatively low Th/Sc ratios and positive ε_Nd(t) values are similar to those of the ∼2.5 Ga granitoids, TTG gneisses and felsic volcanics in the WGB, further indicating that they are derived from less differentiated terranes. Low Chemical Index of Weathering (CIW) values and features in the A-CN-K diagrams for these meta-sediments imply a low degree of source weathering. Sm–Nd isotopes of the chemically pure BIF samples are characterized by negative ε_Nd(t) values, whereas Al-rich BIF samples possess consistently positive ε_Nd(t) features. Significantly, the associated supracrustal rocks in the study area have positive ε_Nd(t) values. Taken together, these isotopic data also point to three REE sources controlling the back-arc basin depositional environment of the BIF, the first being seafloor-vented hydrothermal fluids (ε_Nd(t) < −2.5) derived from interaction with the underlying old continental crust, the second being ambient seawater which reached its composition by erosion of parts of the depleted landmass (likely the arc) (ε_Nd(t) > 0), the third being syndepositional detritus that received their features by weathering of a nearby depleted source (likely the arc) (ε_Nd(t) > 0).     

Provenance analyses of early Mesozoic sediments in the Ningwu basin: Implications for the tectonic–palaeogeographic evolution of the northcentral North China Craton

This paper reports results from detrital zircon U–Pb geochronology, Hf isotopic geochemistry, sandstone modal analysis, and palaeocurrent analysis of the early Mesozoic strata within the Ningwu basin, China, with the aims of constraining the depositional ages and sedimentary provenances and shedding new light on the Mesozoic tectonic evolution of the northcentral North China Craton (NCC). The zircons from early Mesozoic sandstones are characterized by three major populations: Phanerozoic (late Palaeozoic and early Mesozoic), late Palaeoproterozoic (with a peak at approximately 1.8 Ga), and Neoarchaean (with a peak at approximately 2.5 Ga). Notably, three Phanerozoic zircons in the Early Triassic Liujiagou Formation were found to have positive ε_Hf(t) values and characteristics typical of zircons from the Central Asian Orogenic Belt (CAOB). Therefore, the CAOB began to represent the provenance of sediment in the sedimentary basins in the northern NCC no later than the Early Triassic (261 Ma), implying that the final amalgamation of the NCC and CAOB occurred before the Early Triassic. The U–Pb geochronologic and Hf isotopic results show that the Lower Middle Triassic sediments were mainly sourced from the Yinshan–Yanshan Orogenic Belt (YYOB), and that a sudden change in provenances occurred, shifting from a mixed YYOB and CAOB source in the Middle Jurassic to a primarily YYOB source in the Late Jurassic. The results of the sandstone modal analysis suggest that the majority of the samples from the Lower Middle Jurassic rocks were derived from either Continental Block or Recycled Orogen sources, whereas all the samples from the Upper Jurassic rocks were derived from Mixed sources. The change in source might be ascribed to the southward subduction and closure of the Okhotsk Ocean and the resulting intense uplift of the YYOB during the Late Jurassic. This uplift likely represents the start of the Yanshan Orogeny.     

Geochemistry of 1.78 Ga A-type granites along the southern margin of the North China Craton: implications for Xiong'er magmatism during the break-up of the supercontinent Columbia

The Palaeoproterozoic Luoling granites occur along the southern margin of the North China Craton. They are rich in silica and total alkalis with SiO₂ contents ranging from 65.18 to 72.72 wt.%, K₂O from 4.68 to 6.62 wt.%, and Na₂O from 1.35 to 4.88 wt.%. They have high Fe*[FeO_t/(FeO_t + MgO)] ranging from 0.84 to 0.95 wt.% and low MnO (0.03–0.09 wt.%), MgO (0.27–1.55 wt.%), CaO (0.36–2.04 wt.%), TiO₂ (0.4–1.12 wt.%), and P₂O₅ (0.04–0.36 wt.%). Geochemically, they show typical characteristics of A-type granites, such as high contents of alkalis (i.e. high K₂O + Na₂O, with K₂O/Na₂O > 1), Rb, Y, Nb, and REEs (except for Eu); high FeO_t/MgO and Ga/Al ratios; and low CaO, Al₂O₃, and Sr contents. New secondary ion mass spectroscopy (SIMS) zircon U–Pb ages reveal that the Luoling granites were emplaced at 1786 ± 7 Ma and thus were approximately coeval with Xiong'er volcanic rocks in the area. Their negative bulk-rock initial Nd and zircon initial Hf isotopic ratios suggest that they have affinities to EM-I-type mantle and both are the products of Xiong'er magmatism during the Palaeoproterozoic. We regard them as produced under a continental rift setting during the Palaeoproterozoic, genetically related to the break-up of the Columbia supercontinent.     

Mesozoic Volcanism Surrounding Songliao Basin,China: Implication for the Relationship with Evolution of Basin

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Geochemistry and Os–Nd–Sr isotopes of the Gaositai Alaskan-type ultramafic complex from the northern North China craton: implications for mantle–crust interaction

We report petrological, chemical and Os–Nd–Sr isotopic data for the Gaositai ultramafic complex from northern North China craton (NCC) to reveal its petrogenesis. The complex shows features of Alaskan-type intrusions, including (1) the concentric zoning from dunite core, to clinopyroxenite and hornblendite in the rim, and the common cumulative textures; (2) the abundance of olivine, clinopyroxene and hornblende, and the scarcity of orthopyroxene and plagioclase, and (3) the systematic decrease in Mg# of ferromagnesian phases from core to rim, accompanied by the Fe-enrichment trend of accessory spinel. The different rock types show highly varied, radiogenic Os isotopic ratios (0.129–5.2), and unradiogenic Nd isotopic composition (ε_Nd(t) = −8 to −15), but are homogeneous in I_Sr ratios (0.7054–0.7066). The (¹⁸⁷Os/¹⁸⁸Os)_i ratios are found to be anti-correlated with ε_Nd(t) values and whole-rock Mg# as well. These data suggest significant crustal contamination during magma evolution. The crustal contaminants are dominantly Archean mafic rocks in the lower crust, and subordinate TTG gneisses at shallower crustal levels. The parental magma was hydrous picritic in composition, derived from an enriched lithospheric mantle source above a subduction zone. The zoned pattern of the complex formed probably through “flow differentiation” of a rapidly rising crystal mush along a fracture zone that was developed as a result of lithospheric extension in a back-arc setting in the northern margin of the NCC at ca. 280 Ma.