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The Qingchengzi Pb–Zn–Au–Ag–Mo polymetallic ore field located in the Liaodong Peninsula, Liaoning Province, China, is spatially associated with multiple magmatism, which provide a classic example for studying the multiple tectonic and metallogenetic events. In this paper, we report some new geochemical and geochronological data of igneous rocks in the Qingchengzi ore field, including diabase, lamprophyre, microdiorite, granite porphyry, and quartz porphyry. Zircon U–Pb dating yielded the formation ages of these rocks as Triassic, Jurassic, and Early Cretaceous. Low‐Mg adakitic granite porphyries formed at 233 Ma have zircon εHf(t) values of −17.7 to −14.5, suggesting that they were mainly derived from partial melting of thickened lower crust. Mafic dykes formed during 226–203 Ma have zircon εHf(t) values of −28.6 to −12.8, suggesting that they were mainly derived from partial melting of ancient lithospheric mantle. Zircons from the 168Ma Jurassic diabase have high Nb/Ta and low Nb/Th ratios, with zircon εHf(t) values of −25.2 to −18.5. This suggests that ancient lithospheric mantle was influenced by melts/fluids from the subducted Palaeo‐Pacific Plate. The Early Cretaceous microdiorites (126 Ma) are high‐Mg adakite rocks, with zircon εHf(t) values of −27.3 to −19.6. Melting of delaminated eclogitic lower crust might produce these high‐Mg adakitic microdiorites. The upwelling asthenosphere could heat the residual lower crust to form the quartz porphyries. The Early Cretaceous diabase (100 Ma) shows low Nb/Ta and high Nb/Th ratios, with zircon εHf(t) values of −0.7 to 5.8, implying a depleted mantle source. The characteristics of Triassic–Cretaceous intermediate‐mafic intrusions show that the lithospheric mantle evolved from enriched ancient mantle to depleted juvenile mantle. This transformation of the lithospheric mantle might have resulted from the delamination of the lower crust that was caused by subduction of the Palaeo‐Pacific Plate. Based on the field observation and geochemical data, Au, Pb–Zn–Ag, Mo mineralization in the Qingchengzi ore field show closely spatial and genetic relationship with intrusive rocks, indicating that the Mo, Pb–Zn–Ag mineralization might be related to the Jurassic magmatic activity, whereas Au mineralization related to the Early Cretaceous magma. [ABSTRACT FROM AUTHOR]

Petrological, geochronological, and geochemical analyses of mafic rocks in northern Liaoning were conducted to constrain the formation age of the Proterozoic strata, and to further study the source characteristics, genesis, and tectonic setting. The mafic rocks in northern Liaoning primarily consist of basalt, diabase, gabbro, and amphibolite. Results of zircon U-Pb chronology reveal four stages of mafic magma activities in northern Liaoning: the first stage of basalt (2209 ± 12 Ma), the second stage of diabase (2154 ± 15 Ma), the third stage of gabbro (2063 ± 7 Ma), and the fourth stage of magmatic protolith of amphibolite (2018 ± 13 Ma). Combined with the unconformity overlying Neoproterozoic granite, the formation age of the Proterozoic strata in northern Liaoning was found to be Paleoproterozoic rather than Middle Neoproterozoic by the geochronology of these mafic rocks. A chronological framework of mafic magmatic activities in the eastern segment of the North China Craton (NCC) is proposed. The mafic rocks in northern Liaoning exhibit compositional ranges of 46.39–50.33 wt% for SiO2, 2.95–5.08 wt% for total alkalis (K2O + Na2O), 6.17–7.50 wt% for MgO, and 43.32–52.02 for the Mg number. TiO2 contents lie between 1.61 and 2.39 wt%, and those of MnO between 0.17 and 0.21 wt%. The first basalt and the fourth amphibolite show low total rare earth element contents. Normalized against primitive mantle, they are enriched in large ion lithophile elements (Rb, Ba, K), depleted in high field strength elements (Th, U, Nb, Ta, Zr, Ti), and exhibit negative anomalies in Sr and P, as well as slight positive anomalies in Zr and Hf. The second diabase and the third gabbro have similar average total rare earth element contents. The diabase shows slight negative Eu anomalies (Eu/Eu* = 0.72–0.88), enrichment in large ion lithophile elements (Ba), depletion in Rb, and slight positive anomalies in high field strength elements (Th, U, Nb, Ta, Zr, Hf, Ti), with negative anomalies in K, Sr, and P. The gabbro is enriched in large ion lithophile elements (Rb, Ba, K), depleted in high field strength elements (Th, U, Nb, Ta, Zr, Hf), and exhibits positive anomalies in Eu (Eu/Eu* = 1.31–1.37). The contents of Cr, Co, and Ni of these four stages of mafic rocks are higher than those of N-MORB. The characteristics of trace element ratios indicate that the mafic rocks belong to the calc-alkaline series and originate from the transitional mantle. During the process of magma ascent and emplacement, it is contaminated by continental crustal materials. There are residual hornblende and spinel in the magma source of the first basalt. The other three magma sources contain residual garnet and spinel. The third gabbro was formed in an island arc environment, and the other three stages of mafic rocks originated from the Dupal OIB and were formed in an oceanic island environment. The discovery of mafic rocks in northern Liaoning suggests that the Longgang Block underwent oceanic subduction and extinction in both the north and south in the Paleoproterozoic, indicating the possibility of being in two different tectonic domains. [ABSTRACT FROM AUTHOR]

The Lanong ophiolitic mélange is a typical ophiolitic mélange in the middle section of the Bangong–Nujiang suture zone in northern Tibet. It mainly consists of ultramafic and mafic rocks, and its tectonic setting and formation age remain poorly constrained. In this paper, new geochemical and LA–ICP–MS (laser ablation–inductively coupled plasma mass spectrometer) zircon U–Pb age data obtained from gabbro, gabbro–dolerite, dolerite and basalt of the Lanong ophiolitic mélange are provided. The pillow basalts exhibit N-MORB (normal mid-ocean ridge basalt)-like geochemical features with a zircon U–Pb age of 147.6 ± 2.3 Ma. They were generated by ~ 20–30% partial melting of a depleted mantle source composed of spinel lherzolite. The gabbro, massive basalt and gabbro–dolerite samples are characterised by more depleted and “V”-shaped REE (rare earth element) patterns, and they exhibit variable degrees of boninite-like geochemical characteristics, with a zircon U–Pb age of 149.1 ± 1.2 Ma (gabbro-dolerite). They were derived from the remelting of a significantly refractory mantle source following one or more episodes of previous basaltic melt extraction. Geochemical data of these mafic rocks indicate that they were developed in a continental fore-arc setting, and magmas were derived from depleted mantle sources modified by subducted slab-derived fluids and melts with minor crustal contamination. On the other hand, the dolerites show distinct OIB (oceanic island basalt)-like geochemical features, with a zircon U–Pb age of 244.1 ± 3.0 Ma. They were formed in a rift setting on a continental shelf-slope and originated from a low degree of partial melting of a depleted asthenospheric magma source mixed with some ancient sub-continental lithospheric mantle materials. The signatures presented here, combined with the results of previous studies, suggest that the Lanong ophiolitic mélange probably developed in a convergent plate margin under the southward subduction of the Bangong–Nujiang Tethys Ocean beneath the Lhasa terrane during the Middle Triassic–Early Cretaceous. Namely, the OIB-like dolerites likely reflect an extensional rift setting featuring thin continental crust in the Middle Triassic, and the gabbros, gabbro–dolerites and basalts represent a later stage of a fore-arc basin during the Late Jurassic–Early Cretaceous. [ABSTRACT FROM AUTHOR]

Dolerite dykes are common in the southern margin of Alxa Block which is the westernmost part of North China Craton. The ages and petrogenesis of the dolerite dykes, which are important for a better understanding of tectonic–magmatic evolution in the region, are uncertain. This paper reports the results of an integrated geochronological and geochemical study of the dolerite dykes in the Jinchuan area. Previously, these dolerite dykes were considered to be coeval with the ∼831 Ma Jinchuan ultramafic intrusion by some researchers, despite a cross-cutting relationship for the dykes. Our new zircon U–Pb dating indicates that the dolerite dykes were emplaced at ∼424 Ma, >400 Ma younger than the Jinchuan intrusion. The Jinchuan dolerite dykes contain 5–9 wt.% MgO and 47–51 wt.% SiO 2 , and are characterized by light REE (rare earth elements) enrichments relative to heavy REE, pronounced negative Nb anomaly, elevated initial 87 Sr/ 86 Sr from 0.7056 to 0.7068, negative εNd from −2 to −5, and zircon εHf from −2 to −20. The trace element and isotope data are consistent with an asthenosphere-derived parental magma that experienced 10–25% crustal contamination prior to final emplacement. Since the Jinchuan dolerite dykes are 20–40 Ma younger than the subduction-related basaltic volcanic rocks, blueschists and eclogites in the nearby North Qilian orogenic belt to the south, we propose that the Jinchuan dolerite dykes are the products of basaltic magmatism induced by delamination of previously subducted oceanic lithosphere and the associated asthenosphere upwelling in a post-subduction setting. The occurrence of ∼424 Ma post-subduction dolerite dykes in the Jinchuan area and the ∼450 Ma arc basalts to the south indicate that the southwestern margin of North China Craton was an active plate margin in Early Paleozoic. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Subashi ophiolite in West Kunlun Orogenic Belt was formed at ca. 455–446 Ma. • Geochemical features indicate the Subashi ophiolite formed in a MOR setting. • Mazha-Kangxiwa mélange zone with Subashi ophiolite marks a Proto-Tethys suture. The West Kunlun Orogenic Belt (W-KOB) in the northwestern Tibetan Plateau retains critical information about the tectonic evolution of the Proto- and Paleo-Tethys during the Early Paleozoic to Mesozoic. Although a trench-arc-back arc basin model was used to address the tectonic evolution of Proto-Tethys, records about the evolution of this ocean basin remain ambiguous, particularly no studies about ages and tectonic affinities of ophiolites in the W-KOB are available. In this paper, we present new results on whole-rock elemental and Sr-Nd isotopic composition of basalts, and U-Pb zircon ages of gabbro, diabase and basalt from the Subashi ophiolite. The basalts are characterized by low REE concentrations, depleted LREEs in the chondrite normalized REE patterns, and unfractionated HFSEs in the primitive mantle normalized trace element spider diagrams, resembling normal mid-ocean ridge basalts. They have constant 87Sr/86Sr(i) values of 0.70472–0.70590 and positive ε Nd values of +7.5 to +7.9. Accordingly, it can be concluded that the Subashi ophiolite was derived from a depleted spinel lherzolite mantle source in a mid-ocean ridge setting. Zircon grains separated from basalt, diabase and gabbro have 206Pb/238U ages of 455 ± 4 Ma, 451 ± 6 Ma, and 446 ± 6 Ma, respectively, which are taken to be the crystallization ages of these rocks. Together with previously published data, our new data propose that the Mazha-Kangxiwa-Subashi ophiolitic mélange zone marks the existence of the Proto-Tethys ocean basin during the Early Paleozoic. [ABSTRACT FROM AUTHOR]

Diabase swarms widely intrude the late Paleoproterozoic to Mesoproterozoic sedimentary rocks in the northern margin of the North China Craton (NCC). In this paper, we present new baddeleyite SIMS Pb–Pb ages and whole-rock geochemical data for representative samples of the diabase swarms intruding the Mesoproterozoic Wumishan and Xiamaling formations in the western Liaoning region. Our aim is to elucidate the age and origin of the diabase swarms and their relationship to the fragmentation of the Columbia supercontinent. The baddeleyite SIMS Pb–Pb dating results show emplacement ages varying from 1325.9 ± 4.1 Ma to 1318.6 ± 3.7 Ma, indicating voluminous basic magmatism leading to the generation of the diabase swarms during the Mid-Mesoproterozoic time. Geochemically, the Mesoproterozoic diabasic rocks have relatively low REEs contents and show weak positive Eu anomalies. Moreover, these diabase samples are characterized by enrichment in light rare earth elements (LREEs), large ion lithophile elements (LILEs; e.g., Rb and Pb) and some high field strength elements (HFSEs; e.g., Th, U, Zr, Ti and Hf), and depletion in heavy rare earth elements (HREEs) and several high field strength elements (HFSEs; e.g., Nb, Sm, Gd and P), with affinities to basalts belonging to within-plate tholeiite series. Taken together, these geochemical characteristics suggest that the primary magmas of the diabases in the western Liaoning region could have been derived by partial melting of a transitional mantle or slightly enriched mantle in a continental extensional setting. In the context of assembly, growth and breakup of the Columbia supercontinent, together with the recognition of large volumes of ∼1.32 Ga diabase swarms in the northern NCC as well as the nearly coeval rift-related anorogenic magmatism recorded elsewhere on the globe, such as Africa, Baltica, Siberia, North America and Greenland, we conclude that the northern margin of NCC experienced the global-scale Mid-Mesoproterozoic rifting events, corresponding to the final breakup of the Columbia supercontinent, probably at around 1.32 Ga. [ABSTRACT FROM AUTHOR]

Mesozoic mafic dykes in the Litun ore district provide an opportunity to study the nature of the Mesozoic lithospheric mantle beneath the Luxi area of the North China Craton. U–Pb dating of zircon from the Litun diabase using laser ablation inductively coupled plasma mass spectrometry yields an age of 124.6 ± 1.7 Ma, indicating an Early Cretaceous emplacement age. Samples from the Litun diabase display a medium‐ to fine‐grained texture, consisting of plagioclase (60–65 vol%), clinopyroxene (30–35 vol%), and minor biotite (~2 vol%). They are characterized by enrichment of large‐ion lithophile elements (LILEs, such as Rb, Ba, Th, and U) and light rare‐earth elements (LREEs) without significant Eu anomalies (0.83–1.07), depletion of high‐field‐strength elements (HFSEs, such as Nb, Ta, and Ti). The Litun diabase has relatively high initial 87Sr/86Sr ratios (0.7049–0.7060) and negative εNd(t) values (−11.7 to −9.7). The Litun diabase also shows high MgO (10.52–13.84 wt%), Cr (956–1,162 ppm), Co (26.5–65.6 ppm), and Ni (240–514 ppm) contents and low Rb/Sr ratios (0.01–0.03). These geochemical features suggest that the Litun diabase may have originated from an enriched lithospheric mantle source with amphibole as an essential phase, and that the Litun diabase was not significantly affected by fractional crystallization and crustal contamination. In combination with the Sr–Nd isotopic compositions of mafic rocks in the Luxi area (such as the Mengyin mafic dykes and Jinan gabbro), our results suggest that the lithospheric mantle beneath the Luxi area may have been rapidly enriched between ~144 and ~124 Ma, which was induced by sequential hybridization of sinked lower crust. [ABSTRACT FROM AUTHOR]

The Zhangguangcai Range in the Xing'an Mongolian Orogenic Belt, NE China, contains Early Jurassic (c. 188 Ma) Dabaizigou (DBZG) porphyritic dolerite. Compared with other island-arc mafic rocks, the DBZG dolerite is characterized by high trace-element contents, relatively weak Nb and Ta enrichments, and no Zr, Hf or Ti depletions, similar to OIB-type rocks. Analysed rocks have (87Sr/86Sr)i ratios of 0.7033–0.7044, relatively uniform positive ɛNd(t) values of 2.3–3.2 and positive ɛHf(t) values of 8.5–17.1. Trace-element and isotopic modelling indicates that the DBZG mafic rocks were generated by partial melting of asthenospheric mantle under garnet- to spinel-facies conditions. The occurrence of OIB-like mafic intrusion suggests significant upwelling of the asthenosphere in response to lithospheric attenuation caused by continental rifting. These processes occurred in an incipient continental back-arc environment in the upper plate of a palaeo-Pacific slab subducting W–NW beneath East Asia. [ABSTRACT FROM AUTHOR]

Mafic dyke swarm is widely developed in Proterozoic continental lithosphere. The Gangou diabase dyke from the Xixia area, intruded into the Douling complex of the South Qinling belt, yields zircon UPb age of 731 Ma. It has low SiO2 content (49.02 wt.%-49.37 wt.%) and Mg# (34.0–37.7) and shows characteristics of subalkaline tholeiite series. They show high ΣREE (155.5×10 6–184.7×106), weak negative Eu anomaly (SEu=0.88-0.93), slight depletion of Nb and Ta, and enrichment of LILE. Their major and trace element, Sr-Nd-Pb isotope and clinopyroxene compositions indicate that it originated from the partial melting of the asthenospheric mantle within-plate extension setting and was slightly contaminated by crust compositions. The similarities of formation age, petrogenesis, source characteristic and tectonic setting for Gangou diabase with mafic dykes in Wudang Block and mafic volcanic rocks in Yaolinghe Group indicate that the South Qinling belt underwent strong continental extension in Neoproterozoic during 796–685 Ma most likely correspondence to the breaking-up of the Rodinia supercontinent. [ABSTRACT FROM AUTHOR]

The ages and source of Late Cretaceous mafic dolerite dykes of the Songliao Basin were determined using geochronological, geochemical, zircon Hf, whole‐rock Sr–Nd isotopic, and zircon fission tract. The results show that (a) petrographic data reveal doleritic, poikiloblastic textures, and amygdale structures of the dolerite dykes. (b) LA‐MC‐ICP‐MS U–Pb analysis of zircons yielded an age of 70.0 ± 3.0 Ma of one of these mafic dykes in agreement with the zircon fission track age (69–68 Ma) of host rocks within uncertainty, placing them within the Late Cretaceous. (c) Geochemical researches indicate that the dykes are classified as the alkaline and tholeiitic series according to their major elements and characterized by high Na2O (2.79–4.89 wt.%), TiO2 (1.63–2.71 wt.%), and low K2O (0.46–2.45 wt.%). And they have enrichment of incompatible elements (e.g., K, Ti, Rb, Ba, Th, U, Nb, Ta, and REEs), high Rb/Sr (0.026–0.066), LaN/YbN (3.83–15.93), near‐chondritic HREEs ([Gd/Yb]N = 1.78–3.37), low Sm/Nd (0.202–0.282) ratios, and with negligible Eu anomalies (Eu/Eu* = 0.98–1.06). The dykes contain relatively low amounts of radiogenic Sr, as shown by (87Sr/86Sr)i values (0.7037–0.7045), and have positive values of εNd(t) (3.66–5.40) and εHf (t) (2.66–7.45), suggesting that the mafic dykes have been derived from partial melting of the depleted lithospheric mantle and contaminated by crust in the source region and formed in back‐arc rift settings caused by the subduction of the Pacific Oceanic Plate. All the above indicate large‐scale extensional event in Songliao Basin NE China at about 70 Ma. [ABSTRACT FROM AUTHOR]

Mafic magmatic rocks formed between ca. 615 and 560 Ma along the Neoproterozoic margins of Baltica and Laurentia are classically attributed to continental rifting heralding the opening of the Iapetus Ocean. We report new data for the Kebnekaise Intrusive Complex (KIC) exposed in the Seve Nappes in northern Sweden. The KIC consists of sheeted dolerite dykes and gabbroic bodies with mutually intrusive relations. Major and trace element data exhibit a transitional- to normal-mid-ocean-ridge basalt-type geochemical signature. Differentiation processes and late-stage liquid immiscibility of a tholeiitic melt are considered to account for the compositional range exhibited by the KIC igneous rocks. U/Pb SIMS geochronological data from zircon rims yield an emplacement age of 578 ± 9 Ma. The KIC is thus younger and more depleted than coeval mafic rocks found in the Seve Nappe, and is interpreted to represent a high-level magma plumbing system in a late-stage continental rift. The composition and volume of rift-related igneous rocks in the Seve Nappes are inconsistent with a mantle plume origin, but are thought to record progressive lithospheric thinning and increasing involvement of an asthenospheric mantle component. [ABSTRACT FROM PUBLISHER]

The U–Pb measurements of youngest, coherent group of zircons from the Mielnik IG1 dolerite at the Teisseyre-Tornquist margin (TTZ) of East European Craton (EEC) in Poland yielded age of 300 ± 4 Ma. Zircon dated an evolved portion of magma at the late stage crystallization. It is shown that this isolated dyke from the northern margin of the Lublin Podlasie basin (Podlasie Depression) and regional dyke swarms of close ages from the Swedish Scania, Bornholm and Rügen islands, Oslo rift, Norway, and the Great Whine Sill in northeastern England, were coeval. They have been controlled by the same prominent tectonic event. The Mielnik IG1 dolerite is mafic rock with Mg-number between 52 and 50 composed of the clinopyroxene, olivine-pseudomorph, plagioclase, titanite, magnetite mineral assemblage, indicating relatively evolved melt. This hypabyssal rock has been affected by postmagmatic alteration. The subalkaline basalt composition, enrichment in incompatible trace elements, progressive crustal contamination, including abundance of zircon xenocrysts determines individual characteristics of the Mielnik IG1 dolerite. The revised age of dolerite, emplaced in vicinity of TTZ provides more evidences documenting the reach of the Permo-Carboniferous extension and rifting accompanied by magmatic pulses, that were widespread across Europe including the margin of the EEC incorporated that time into the broad foreland of the Variscan orogen. [ABSTRACT FROM AUTHOR]