Lu Hf Isotope Research Articles

Multiproxy provenance analyses in the Devonian Villavicencio Formation of the Mendoza Precordillera, Argentina: correlation and geotectonic implications for the SW Gondwana margin

Abstract This work focuses on the sedimentary provenance of the Villavicencio Formation of the Mendoza Precordillera and integrates the information obtained with previous work on other coeval units of the Precordillera Central of San Juan province (Gualilán Group: Talacasto and Punta Negra formations) in western Argentina. Multiproxy provenance analyses are carried out from different applied methodologies (petrography, geochemistry, morphological, and cathodoluminescence studies of detrital zircon grains, and analysis of U-Pb and Lu-Hf isotopes). The Villavicencio Formation is mostly composed of pelites and very fine-grained psammites. The major components are quartz, both monocrystalline and polycrystalline, and metamorphic lithics that associate this unit with a recycled orogen. Regarding geochemistry, the Chemical Index of Alteration (CIA) values are similar to the Post-Archean Australian Shales (PAAS), indicating a null to incipient degree of weathering. The ratios between different trace elements and rare earth elements (REEs) suggest the felsic composition of the source area. Th/U ratios differ, but a secondary uranium enrichment is inferred. The morphological analysis of the zircon grains reveals their mainly plutonic origin. The integration of U-Pb data with Lu-Hf data shows a juvenile-mantle origin in which the populations are dominantly Mesoproterozoic and ɛHf of positive values (up to 12), indicating poor differentiation. The Villavicencio Formation would be the product of deltaic deposits in which its components are dominantly from the Western Pampean Sierras associated with the Grenville orogen, assuming exhumation and erosion of the Mesoproterozoic basement. The data support the hypothesis of equivalence and correlation with the Punta Negra Formation in the Devonian depocenters of the south-central region of the San Juan Precordillera.

Three episodes of Triassic volcanism in the Eastern Kunlun Orogen, NW China: constraints for evolution of the Palaeo-Tethys Ocean

ABSTRACT The Eastern Kunlun Orogenic Belt (EKOB), located north of the Qinghai-Tibetan Plateau, recorded voluminous late Palaeozoic – early Mesozoic intermediate-acid volcanic rocks. The tectonic evolution of the Palaeo-Tethys Ocean from initial subduction and final closure and post-collision extension has been hotly debated. This study examines the petrogenesis of Palaeozoic to Early Mesozoic volcanic rocks at six locations: Xiahe, Elashankou, Jirimai, Harizha, Nagengkangqieer, and Yazigounan. The investigation involves detailed field observations, petrology, zircon U-Pb geochronology, Lu-Hf isotopes, and whole-rock geochemical analysis. The rocks analysed represent three episodic volcanic events. The ca. 257–245 Ma volcanic rocks were derived from magma mixing response to the subduction. The ca. 227–220 Ma highly fractionated I-type volcanics were derived from partial melting of the ancient lower crust, with varying contribution proportions of mantle materials. The ca. 216 Ma A-type volcanic rocks derived from partial melting of the juvenile crust. In this study, using existing regional geological data and spatiotemporal distribution of the magmatic region, combined with our new data, we attempt to propose more rational models to reveal the tectonic evolution of the Palaeo-Tethys Ocean, and we recognize three significant time nodes: (1) Ca. 240 Ma marks the final closure time of the Palaeo-Tethys Ocean. (2) Ca. 230 Ma indicates the vital tectonic regime transition from compression to extension response to slab break-off and continued lithospheric delamination. (3) Ca. 216 Ma mark the beginning of the final stage of orogeny in the EKOB, and mild magmatism lasts to ca. 200 Ma in response to the mountain collapse.

Paleozoic tectonic evolution of the proto-Korean Peninsula along the East Asian continental margin from detrital zircon U-Pb geochronology and Hf isotope geochemistry

Detrital zircon geochronology and Hf isotope analysis can be used for inferring provenance characteristics, and to evaluate the tectonic evolution of sedimentary basins and their link with regional orogenesis. The Paleozoic sequences of the Okcheon Belt consist of the Lower Paleozoic Joseon and the Upper Paleozoic Pyeongan supergroups with Middle Paleozoic hiatus locally on top of the Neoproterozoic bimodal volcanic rocks, reflecting an intracontinental rift setting between the two basements (viz. Gyeonggi and Yeongnam massifs) at southern part of the Korean Peninsula. Our detrital zircon U-Pb ages and Lu-Hf isotope results show that all these Paleozoic strata commonly have Paleoproterozoic and Paleozoic zircon ages with rare Meso- to Neoproterozoic ages. The individual zircon populations display following features, allowing estimation of their sedimentary provenances: (i) The Paleoproterozoic zircons (ca. 1.85 Ga and 2.50 Ga) with similar ranges of εHf(t) values are most common in the basement rocks of the Korean Peninsula, and were sourced from both the Gyeonggi and Yeongnam massifs. (ii) The Meso- to Neoproterozoic zircons, preserved only in the Middle to Late Cambrian clastic sedimentary rocks within the carbonate sequences probably reflect proximal provenance. (iii) The youngest Paleozoic zircons of each formation, almost coincident with their deposition ages, suggest presence of syndepositional magmatism, indicating proximal magmatic sources during their deposition. (iv) The Cambrian–Ordovician zircons, from the Lower Paleozoic sequences, but rare in the successive Upper Paleozoic sequences, suggest a provenance change after the hiatus between the two sedimentary successions. (v) The Permian zircons showing different εHf(t) values indicate that detrital sources were varied at that time. The integrated results in our study suggest provenance variability linked to diverse tectonic environments, reflecting prolonged subduction-related crustal evolution of the proto-Korean Peninsula during the Paleozoic.

Response of Sm–Nd isotope systematics to complex thermal histories: A case study from 3.58 Ga gneisses of the Pilbara Craton

In felsic igneous rocks, the parent and daughter elements in the widely used Sm–Nd and Lu–Hf isotope tracer systems are mainly hosted in accessory phases. Recrystallisation and/or breakdown of these minerals during metamorphism, deformation and weathering potentially compromises the chemical and isotopic composition of the respective whole rocks, impeding the utility of such information for deducing the timing, rates and processes of crust-mantle differentiation in the early Earth. The different abilities of zircon and REE-rich minerals to withstand metamorphism have been suggested as a reason for the decoupling of the Lu–Hf and Sm–Nd isotope systems observed in a number of ancient gneiss terranes. The controls on element mobility and subsequent isotopic disturbance during recrystallisation and breakdown of LREE-rich accessory minerals are, however incompletely understood. Here, we use petrography, element mapping, and microanalysis of accessory minerals, in tandem with whole rock Sm–Nd data, to assess the reliability of the Sm–Nd system in the 3.59–3.58 Ga Mount Webber Gabbros, the oldest rocks in the Pilbara Craton (Western Australia). We show that despite multiple thermal events, which reset the mineral Sm–Nd systematics, and decomposition of the REE-rich mineral allanite, the Mount Webber rocks retained the Sm–Nd isotope signatures of their magmatic protoliths at the whole-rock scale. We show that the allanite breakdown occurred during modern, near-surface weathering processes at low temperature, such that the REE were sequestered into secondary minerals rather than escaping in higher temperature metamorphic fluids. The whole rock Sm–Nd, and zircon O–Hf signatures, together with new 142Nd isotope data, suggest derivation of the Mount Webber rocks from undifferentiated mantle sources that preserve no evidence for Hadean silicate Earth differentiation. This study highlights the benefits of a combined analytical approach using both in-situ and whole-rock isotope analyses to obtain a more complete record of the source and thermal evolution of ancient, highly metamorphosed igneous rocks.

Xenocrystic zircon in Central New York State Kimberlites record Neoproterozoic disturbance of Grenville Basement rocks

Zircon grains from two central New York State (USA) Mesozoic kimberlite dikes intruding Middle and Upper Devonian sedimentary rocks were analyzed for UPb and LuHf isotopes, and trace elements, and were derived from different parts of the continental crust and/or upper mantle. Zircon from the Six Mile Creek (SMC) kimberlite has variable physical properties and “felsic” chondrite normalized REE patterns, and yields dates (321–1732 Ma) compatible with entrainment of sedimentary xenoliths during accent through the upper crust. In contrast, zircon from the Taughannock Creek (TAG) kimberlite have near concordant UPb dates that are distributed between intercept ages of 572 ± 25 and 960 ± 20 (2σ) Ma (MSWD = 0.61) with homogeneous LuHf systematics and 176Lu/177Hf ratios <0.0001. Examination in CL reveal TAG zircon grains vary in internal zoning and structures, but they are geochemically and isotopically similar. Their evolution includes early Neoproterozoic (ca. 950 Ma) granulite-facies metamorphism in equilibrium with garnet growth (flat to negative sloping HREE patterns and Ti-in-zircon temperatures >900 °C) during the final assemblage of the supercontinent Rodinia, followed by subsequent Pb-loss, resulting in a discordant array and decoupling of the UPb and LuHf isotopic systems prior to entrainment. Concordant zircon UPb dates, anchoring the lower intercept, yield an age of 596 ± 7 (2σ) Ma for the timing of Pb-loss. This most likely occurred in a zone of rifting and mafic magmatism beneath Central New York and Pennsylvania during the opening of the Iapetian Ocean.

Miocene lamprophyre and felsic volcanics in the outer zone of SW Japan: arc building through multiple sources in an active convergent margin

ABSTRACT Subduction-related magmatism is a significant contributor to arc building and continental growth. In the active convergent margin of the SW Japan arc, voluminous volcanic rocks and mafic dykes formed through subduction and back-arc rifting during Miocene. In this study, we investigate a suite of felsic volcanic rocks (rhyolite and dacite) and lamprophyres from central Shikoku Island, which occur in the north-central part of the Chichibu belt and Sanbagawa belt in the Outer zone of the SW Japan arc. Whole-rock geochemistry results show that the rhyolite and dacite samples are peraluminous, belong to the high-K calc-alkaline series, show LREE and LILE enrichment, HREE and HFSE depletion that suggest arc volcanic affinity. The lamprophyre samples belong to alkali lamprophyre, show LREE and HFSE enrichments, and display OIB (oceanic island basalt)-like geochemical features. The 206Pb/238U weighted mean ages of the zircons from the rhyolite and dacite samples range from 14.39 ± 0.21 Ma to 13.92 ± 0.30 Ma, whereas the lamprophyre shows 206Pb/238U weighted mean age of 12.21 ± 0.35 Ma. Zircon Lu-Hf isotope data suggest that the rhyolite and dacite were derived from the remelting of the arc crustal rocks and that the lamprophyre was derived from depleted mantle sources and was contaminated by crustal materials. The felsic volcanic rocks (rhyolite and dacite) can be correlated to Miocene (15.5 Ma to 13.5 Ma) magmatism in the Outer Zone of the SW Japan arc. The formation of lamprophyre dykes in the SW Japan arc may be related to the subhorizontal mantle flows beneath the SW Japan arc associated with the opening of the Japan Sea back-arc basin or asthenosphere upwelling through the slab-tear of the Philippine Sea Plate beneath the SW Japan arc. Our study shows that the SW Japan Arc was built by multiple magmatism from diverse sources in an active convergent margin.

Deciphering the parent-daughter relationship between Ediacaran high-silica ignimbrites and their complementary silicic cumulates: Insights from zircon trace element composition

The Ediacaran Campo Alegre-Corupá Basin (CACB) comprises a rare and excellent exposure of caldera-forming pyroclastic rocks and their cogenetic underlaying plutons. The CACB experienced at least two major episodes of bimodal volcanic activity. The Basin Stage (∼605–590 Ma), characterized by transitional OIB-like basaltic lava flows with minor trachydacites and rhyolites, interbedded with surge-like, silicic pyroclastic deposits, and the Caldera Stage (∼583–577 Ma), marked by at least one cycle of silicic alkaline, caldera-forming eruption, dominated by rhyolitic to trachytic ignimbrites and lava flows/domes with subordinate IAB-like basalts. During the Caldera Stage, granitoid plutons were emplaced at shallow crustal levels (∼5–8 km deep), correlating with the depth of the magma chamber responsible for the contemporaneous large silicic eruption(s). Previous studies have suggested a genetic connection between the post-collisional volcanic and plutonic rocks based on their similar ages, composition, and Sr-Nd-Hf isotopic signatures. In this study, we analyze zircon trace elements from the volcanic rocks of both stages in the CACB to constrain their evolutive compositional patterns, redox conditions, and Ti-in-zircon saturation temperatures. We compare our results with zircon compositions of the cogenetic granitoids, focusing on the Corupá Pluton, which likely supplied the magma for the caldera-forming eruption(s). By examining whole-rock and zircon chemical compositions, we establish a petrogenetic link between the volcanic rocks and their potential remnant magma reservoir. Our findings indicate that the silicic volcanic rocks from the Caldera Stage represent highly evolved compositions extracted from a crystal mush that solidified as a syenitic intrusion. During the evolution of the volcanic-plutonic system, zircon crystals tracked compositional changes associated with the extraction of residual silicic liquids from crystal mushes and the formation of intermediate-silicic cumulates. Unique variations in zircon compositions of volcanic and plutonic rocks, such as Eu/Eu*, Zr/Hf, and Th/U ratios support such a connection and suggest crystal-melt segregation processes at relatively low crystallinities (< 30 vol%). Additionally, our trace element data supports the occurrence of intense hydrothermal-induced recrystallization of zircon within the caldera structure, as suggested by the morphologic aspects of crystals previously analyzed for UPb and LuHf isotopes.

Constraining mixing and mingling processes from zoned magmatic enclaves: An example from the Taejongdae granite in Busan, Korea

Zoned magmatic enclaves (MEs) within granitic intrusions provide valuable insights into the pre-intrusive processes involved in the formation of granitic magmas. This study focuses on the Taejongdae granite in Busan, Korea, which features uniquely zoned MEs, and aims to constrain the processes involved in their formation. Through a whole-rock geochemistry analysis, SHRIMP U-Pb zircon dating, and Lu-Hf isotope data, we investigated the geochemical characteristics and origin of the two magmas responsible for the zoned MEs (that is, dioritic and host granite magmas). Our findings have shown that the host granite aligns with the Bulguksa granites in the Gyeongsang Basin, which represent the I-Type magma resulting from the fractionation of magma generated through partial melting of the continental crust. In contrast, the dioritic magma exhibits a low K2O composition, high Sr content, and a positive-to-no Eu anomaly, indicating its formation via amphibole-dominated fractional crystallization under different pressure–temperature conditions. Both magmas share the same Cretaceous age and Hf ratios. The zoned MEs in the study area provide compelling evidence of magma mixing processes that occur between the outer dioritic zone and mafic core of the enclaves. However, the relationship between the outer dioritic zone and the host granite suggests limited interaction between the enclaves and host granite. This implies that mixing within the zoned enclaves occurred prior to enclosure in the host granite. By highlighting the significance of zoned magmatic enclaves, this case study advances our understanding of the pre-intrusive processes involved in the formation of granitic magmas, including magmatic mixing, mingling, and fractionation. These results offer important insights into the origin and geochemical characteristics of the two magmas and their interactions, thus contributing to a broader understanding of crustal evolution in subduction-related settings.

Petrogenesis and tectonic setting of Early Permian–Late Triassic granitoids in the Qinling Orogenic Belt: Constraints from petrology, geochemistry and zircon U–Pb–Hf isotopes

The widely distributed Late Hercynian–Indosinian granites in the West Qinling Orogenic Belt are keys to better understand the tectonic–magmatic evolution of the West Qinling Orogenic Belt. In this paper, granitoids from the Zhacanggou area of Guide Basin in the western section of the West Qinling Orogenic Belt were studied on petrography, geochemistry, zircon U–Pb dating, and Lu–Hf isotopes. Zircon U–Pb dating yield granitoids in the Zhacanggou area were emplaced at 228.3 ± 4.4 Ma, 265.2 ± 2.2 Ma and 277.8 ± 2.5 Ma, respectively. The whole-rock geochemical compositions of these granitoids belong to the weakly peraluminous calc-alkaline to metaluminous high-K calc-alkaline series, and exhibit different degrees of negative Eu anomalies, loss of high-field strength elements (Nb, P and Ti), and enrichment of large ion lithophile elements (Rb, Th, U and Sr). The εHf (t) values of Early–Middle Permian and Late Triassic granitoids range from −12.0 to 5.3 and –10.6 to −5.0, and corresponding two-stage model ages (TDM2) of 956 to 2051 Ma and 1581 to 1936 Ma, respectively. A summary of geochronology for granitoids formed in the West Qinling Orogenic Belt during the Late Hercynian–Indosinian indicating magmatic activities concentrated in the Late Triassic (210–230 Ma) and Permian–Middle Triassic (235–277 Ma). These granitoids were both formed by partial melting of ancient crust, which then mixed with enriched lithospheric mantle, and the former has a higher mantle contribution than the latter. The early granitoids were associated to northward subduction of the Mianlue oceanic slab, while the late granitoids were formed in the transition from collision to extension.

Petrogenesis and tectonic environment of the Middle Permian Luerma igneous complex in the southern Lhasa subterrane, Tibet: Evidence from geochemistry; Rb–Sr, Sm–Nd, and Lu–Hf isotopes; and zircon U–Pb geochronology

Due to the lack of corresponding magmatic records, the timing of the opening of the Yarlung–Tsangpo Neo‐Tethyan Ocean remains controversial. The Middle Permian Luerma igneous complex, which is situated in the western Gangdese magmatic belt of the southern Lhasa subterrane, western Tibet, can be divided into four or more rock types, including foid gabbro, amphibole gabbro, monzogabbro, and pyroxene‐bearing monzodiorite. Through zircon U–Pb dating using laser ablation–inductively coupled plasma–mass spectrometry, the age of the Luerma igneous complex is determined to be ~261 Ma. The complex is rich in titanium, iron, magnesium, and total alkalis, with medium to high levels of calcium, potassium and aluminium, as well as low levels of silicon. Therefore, it is classified as a shoshonite–latite rock series. The complex is relatively enriched in light rare earth elements and high‐field‐strength elements, without obvious Eu and Ce anomalies. These rocks exhibit relatively low (87Sr/86Sr)i values, high εNd(t) values, and high εHf(t) values. The geochemical and isotopic characteristics indicate that the magmas are derived from partial melting of the upper mantle in an intraplate tectonic environment. The new data presented here provide supplementary evidence for the initial rifting of the Lhasa terrane from the northern margin of Gondwana during the Middle Permian. These data also confirm that the opening of the Yarlung–Tsangpo Neo‐Tethyan Ocean occurred in the Middle Permian.

The robustness of the Lu-Hf and Sm-Nd isotopic systems during metamorphism – A case study of the Åker metabasite in southern Sweden

While whole-rock Lu-Hf isotope analysis remains one of the only ways to obtain initial Hf isotope signatures of old mafic rocks, Hf isotope analyses of more robust accessory zircon in intermediate to silicic rocks have largely replaced whole-rock analyses during the last decade. This has led to a discrepancy in the amount of existing data from mafic and felsic lithologies. However, especially in mafic, Si-poor rocks with a metamorphic imprint, Hf isotope data rely on whole-rock analysis since baddeleyite, commonly used for U-Pb age analyses of mafic rocks, is sensitive to alteration and metamorphism. Hence, to accurately evaluate the trace element and isotope signatures of altered mafic rocks, it is important to understand the mechanisms of element mobility during metamorphism. Here, we report whole-rock trace element compositions, Lu-Hf and Sm-Nd isotope data from variably deformed and metamorphosed samples of a mafic intrusion in southern Sweden, the Åker metabasite. These data suggest that trace elements were undisturbed on a whole-rock sample scale during deformation at upper amphibolite facies (at least 1000 MPa and 600 °C) metamorphism under hydrated conditions. Despite redistribution of Zr associated with the breakdown of baddeleyite and other igneous phases, the Åker metabasite has retained its chemical and isotopic integrity since igneous crystallisation at ca. 1565 Ma. This study demonstrates and strengthens the feasibility of whole-rock analyses of (meta-)mafic rocks for determining initial εNd and εHf values, despite deformation and metamorphism under hydrated amphibolite-grade metamorphic conditions. Testing the coherence of the calculated initial Nd and Hf isotope ratios by examining variably deformed and metamorphosed varieties of a rock in a single outcrop, could be used as a model for research on more complex Archean rocks.

Petrogenesis and Geodynamic Significance of the Early Triassic Nanpo Adakitic Pluton of the Luang Prabang-Loei Tectonic Belt (Northwestern Laos) in the East Tethys Domain: Constraints from Zircon U-Pb-Hf Isotope Analyses and Whole-Rock Geochemistry

Adakites are magmatic rocks with specific geochemical characteristics and specific dynamics that provide important clues to understanding the magmatic-tectonic evolution of orogenic belts. We studied the Early Triassic Nanpo adakitic pluton of the Luang Prabang-Loei tectonic belt in the Eastern Tethys domain (Laos Sarakan) using detailed petrological, zircon U-Pb chronological, whole-rock geochemical, and zircon Lu-Hf isotope studies to constrain their petrogenesis. The rocks are predominantly diorites and granodiorites with Early Triassic zircon U-Pb emplacement ages ranging from 247.9 ± 1.0 to 249.0 ± 2.4 Ma. Moderate SiO2 (56.26–65.95 wt%) and Na2O (3.24–5.00 wt%) contents, with Na2O/K2O values between 1.76 and 2.51 and A/CNK values between 0.81 and 0.94, indicate that the rocks belong to the metaluminous calc-alkaline rock series. The high Sr content (590–918 ppm), low Y (6.30–11.89 ppm) and Yb (1.99–3.44 ppm) contents, intermediate Mg# (42–50) values, and high Sr/Y and (La/Yb) N ratios (Sr/Y = 24–41, (La/Yb) N = 6.84–13.8) are typical for adakites. Zircon Hf isotope analysis shows a significant variation in the εHf(t) values (6.7–12.0), with a mean value of 9.4 and a TDM2 of 512–845 Ma. Geochemical evidence indicates that the Nanpo adakitic rock was formed by the partial melting of the thickened lower crust in the plate-breaking environment and has an important contribution to the underplated mantle-derived magma. We propose that the Early Triassic adakites in the Luang Prabang-Loei tectonic belt formed during the transition from subduction to a continental collision, and the mixing of crust- and mantle-derived magmas is the main mechanism for the growth of continental crust in the Paleo-Tethys orogenic belt of southeastern Asia.

Neoproterozoic tectonic transition from subduction to back-arc extension along the western Yangtze Block, South China: Petrological evidence of Nb-enriched basalts and arc-type intrusive rocks

Identifying the tectonic transition process from persistent slab subduction to back-arc extension is vital for the systematical study of arc magmatic evolution in a temporal perspective. Although Neoproterozoic subduction setting along the western Yangtze Block has been widely documented, the detailed tectonic transition from subduction to back-arc extension was not systematically constrained. The coexistence of Nb-enriched rocks and normal arc-type rocks can generally provide unique insights into back-arc extension background under subduction setting. Herein we therefore present combined data of petrology, mineralogy, zircon U-Pb geochronology, whole-rock major and trace elements, and Sr-Nd isotopes as well as zircon Lu-Hf isotopes for the Neoproterozoic Nb-enriched basalts and arc-type intrusive rocks (i.e., gabbros and diorites) from the Luding area along the western Yangtze Block (South China), to characterize back-arc extension setting of Neoproterozoic continental magmatic arc. Zircon U-Pb ages suggest that the Nb-enriched basalts and arc-type gabbros-diorites formed coevally at ca. 780 Ma. The Nb-enriched basalts have much clinopyroxene phases and display higher TiO2, P2O5, Nb, Nb/La, and Nb/U values than normal arc volcanics. They are weakly enriched in Rb and Ba, and slightly depleted in Nb, Ta, Zr, and Hf, and show decoupled Nd-Hf isotopes with highly positive whole-rocks εNd(t) (+5.79 ∼ +7.39) and relatively low zircon εHf(t) (+1.09 ∼ +9.05) values, indicating an origination of subduction slab melts-metasomatized mantle wedge source, resembling with the genesis of those typical Nb-enriched mafic rocks in a back-arc setting. Compared with Nb-enriched basalts, the arc-type gabbros and diorites contain more hornblende minerals, and are characterized by variably high MgO (3.10–5.71 wt%) contents and Mg# values (51.5–57.2), and enriched LREEs and LILEs (e.g., Rb, Ba, Sr, and K) as well as depleted Nb, Ta, and Ti. Considering their relatively depleted and coupled Nd-Hf isotopes, these arc-type gabbros and diorites were formed by partial melting of hydrous mantle wedge modified by subduction fluids. The co-occurrence of Nb-enriched basalts and arc-type gabbros-diorites studied here therefore reveal Neoproterozoic back-arc extension background under the subduction setting. Combined with ca. 810–780 Ma mafic rocks showing Nb-enriched signatures and ca. 860–740 Ma normal arc-type mafic-intermediate rocks in the western Yangtze Block, we support that Neoproterozoic geodynamic transition from continuing subduction to back-arc extension initially occurred at ca. 820–810 Ma. The Neoproterozoic back-arc extension is thus significant for geochemical changes of subduction-related metasomatized agents and arc magmatic types.

Geochemistry, Detrital Zircon U-Pb Geochronology, and Lu-Hf Isotopes of the Metasedimentary Rocks (Xinghongpu Formation, Late Devonian) in the Central South Qinling Orogenic Belt: Implications for Provenance and Tectonics

The Xinghongpu Formation is very important for understanding the Devonian tectonic evolution of the South Qinling orogenic belt. Geochemical, detrital zircon U-Pb-Hf isotopic studies were carried out on the Late Devonian metasedimentary rocks of the Xinghongpu Formation to constrain the depositional age, the provenance, and the tectonic setting. The detrital zircon U-Pb dating results revealed that the depositional age of the Xinghongpu Formation of the Late Devonian was not earlier than 363.2 Ma. The whole-rock geochemistry suggested that (1) this suite of metasedimentary rocks was mainly derived from quartzose sediments of mature continental provenance, with a small contribution from mafic and intermediate igneous provenance, and (2) the metasedimentary sandstone of the Xinghongpu Formation from the Late Devonian was deposited in an active continental margin to continental arc setting. The detailed detrital zircon U-Pb dating showed that the age spectra of detrital zircon could be divided into four groups: (1) 416–480 Ma, accounting for about 23%; (2) 740–850 Ma, accounting for about 19%; (3) 889–1017 Ma, accounting for about 19%; and (4) 1072–1146 Ma, accounting for about 12%. It also contained a group of Early Proterozoic zircons. The age and Hf isotope of the detrital zircons suggested that the clastic sediment deposited in the Xinghongpu Formation mainly came from the South Qinling Orogenic Belt and the North Qinling Orogenic Belt. The detrital zircon Lu-Hf isotopes indicated that most zircons were the products of the ancient crustal remelting, and the mantle-derived magmatic sources contributed to the provenance. The Xinghongpu Fm. formed in an oceanic basin in a continental margin environment with arc systems.

Petrogenesis of the Granitic Dykes in the Yangshan Gold Belt: Insights from Zircon U-Pb Chronology, Petrography, and In-Situ Hf Isotope Analysis

The Yangshan gold belt is renowned for its igneous rock formations, particularly dykes that form in tectonically weak zones. Some of these rock formations exhibit a close spatial relationship with gold mineralization, and a tiny portion of the granitic dykes serve as gold ore bodies by themselves. In order to investigate the nature of granitic dykes and their association with gold mineralization, we conducted a comprehensive study consisting of zircon U-Pb chronology, petrography, and in situ Hf isotope analysis of 25 granitic dyke samples collected from east to west across the belt. According to LA-ICP-MS zircon U-Pb dating results, the granitic dykes inherited zircon ages that are concentrated between 745.0 and 802.0 Ma, and magmatic intrusion ages that mainly fall between 201.0 and 213 Ma. Moreover, the granitic dykes display a calc-alkaline to high-K calc-alkaline peraluminous series, which is relatively enriched in light over heavy REE, with moderate Eu anomalies. These dykes are rich in large-ion lithophile elements and poor in high-field-strength elements. The zircon Lu-Hf isotope data range from εHf(t) values of −1.5 to 0.1, mantle model (TDM1) ages range from 859 to 937 Ma, and crustal model (TDM2) ages range from 1111 to 1218 Ma. The granitic dykes found in the Yangshan gold belt were formed between 200 and 213 Ma ago, during a period of intracontinental extension following the late collision between the Yangtze plate and Qinling microplates. These dykes originated from the volcanic basement of the Mesoproterozoic Bikou Group, which was formed by the melting of the upper crust under the crustal thickening caused by the subduction and collision of the Qinling microplate. Subsequently, the dykes were transported along a tectonically weak zone, assimilating surrounding rocks and undergoing a transformation from “I”-type to “S”-type granite before finally evolving into granite with specific “A”-type characteristics. Our study provides new insights into the petrogenesis of granitic dykes in the Yangshan gold belt, as well as the relationship between gold mineralization and magmatic activity, which has significant implications for mineral exploration and the geological understanding of gold mineralization in this region.

Implications of Nd isotopic mapping for crustal composition and metallogenesis in the Sanjiang orogenic belt (SW China)

The Sanjiang orogenic belt, located in southwestern China and the southeastern Tibetan Plateau, includes a variety of economically important metal deposits. Previous studies have focused on Lu-Hf isotopic mapping to suggest its lithospheric architecture and mineralization. In this study, we provide the results of Nd isotopic mapping and compare them with the results of Hf isotopic mapping based on the similarity of Sm-Nd and Lu-Hf isotope systems, which indicate three juvenile domains with high εNd(t) and young Nd model ages within the Eastern Qiangtang-Simao terrane, while presenting negative εNd(t) values over the entire horizon. The very negative εNd(t) and old Nd model ages found in the Tengchong-Baoshan terrane and Changning-Menglian suture suggest that these terranes are old and might be reworked. The Nd isotopic mapping of the Sanjiang orogenic belt also suggests a relationship between different lithospheric architectures and the locations of distinct ore deposits. Porphyry-skarn Cu–Mo–(Au) deposits occur in the juvenile crust, which has relatively high εNd(t) (−3.3–5.1) and young TDM ages, whereas skarn and hydrothermal vein-type W–Sn deposits and Pb‒Zn‒Cu‒Ag deposits are located in the low-εNd(t) area.

Early Cretaceous tectonic transition in South China: Insights from felsic igneous rocks and mafic dikes, eastern Guangdong Province

Large‐scale magmatic activity and associated mineralization in South China are linked to the subduction of the palaeo‐Pacific Plate, although specific processes have remained controversial including the timing of subduction initiation and lithospheric extension. We present new geochemical data and zircon U–Pb and Lu–Hf isotope measurements on volcanic rocks, granites and mafic dikes from coastal south‐eastern China along the Eurasian continental margin. The biotite monzogranites show I–type granitoid affinity and fractional crystallization with zircon εHf(t) values ranging from −10.15 to +0.50, suggesting magma derivation from the melting of lower crust with the addition of juvenile crustal or mantle components. The biotite granites are typical of highly fractionated A‐type granites with εHf(t) values ranging from −3.63 to +1.35, indicating magma hybridization between anatectic granitic and mantle‐derived mafic magmas. The diabase dikes have zircon εHf(t) values ranging from −2.99 to +1.71, with high La/Nb and La/Ta ratios. This suggests derivation from partial melting of a lithospheric mantle metasomatized by fluid from a subducting–slab, with contributions of depleted asthenospheric mantle components. Our data, combined with those from previous studies, suggest that the shallow subduction of the palaeo–Pacific Plate beneath the Eurasian continent had begun by ca. ~170 Ma at least and the subduction orientation changed to oblique with respect to the continental margin. Steepening of the subduction angle likely caused a slab rollback during the Early Cretaceous, resulting in a tectonic transition from compression to extension in South China at ca. 145 Ma.

Late Cryogenian–Ediacaran magmatism in southern Borborema Province, NE Brazil: Ages, sources, petrogenesis, and tectonic setting

The Sergipano Orogenic System (SOS) in southern Borborema Province (NE Brazil) hosts voluminous Neoproterozoic plutonism related to the Brasiliano/Pan-African Orogeny. This paper presents comprehensive whole-rock geochemical data, titanite U-Pb ages, and the first combined zircon U-Pb and Lu-Hf isotope results for plutonic rocks from the Macururé Domain to constrain their sources, petrogenesis, and tectonic setting. Three magmatic episodes are recognized and record the evolutionary stages of the orogen. (i) Early-collisional magmatism (643–628 Ma) comprises gabbros and diorites with minor tonalites characterized by well-developed tectonic foliation and evidence of solid-state deformation. These rocks are magnesian, high-K calc-alkaline, LILE- and LREE-enriched and provide subchondritic εHf(t) values (−6.5 to −4.7) and Orosirian Hf-TDMC model ages (1.83–1.94 Ga). Such features indicate derivation from a lithospheric mantle source metasomatized by incorporating crustal components through subduction processes prior to magma generation, possibly related to the Rhyacian Orogeny (2.20–1.96 Ga). Extensive mixing/mingling between basaltic and crust-derived magmas took place at lower crustal depths, producing coeval hybrid diorites and quartz-diorites. (ii) Syn-collisional magmatism (630–624 Ma) encompasses biotite- and muscovite-bearing granodiorites and monzogranites, preserving their structures parallel to the schistosity of the country rocks. These rocks are leucocratic, weakly metaluminous to peraluminous, and contain abundant surmicaceous enclaves. Petrographic features and geochemical composition suggest an origin related to the partial melting of graywacke protoliths with a subordinate igneous component. (iii) Late-collisional magmatism (625–600 Ma) includes undeformed and isotropic monzonites and granodiorites, which truncate the regional foliation. These rocks are consistently metaluminous and magnesian, showing affinities with the high-K calc-alkaline to shoshonite series. Trace element modeling with subchondritic εHf(t) values (−8.3 to −4.1) and Paleoproterozoic Hf-TDMC model ages (1.77–2.03 Ga) demonstrate that reworking of ancient lower mafic crust played an important role at this time. The integration of our data with previously published results leads us to conclude that the geodynamic evolution of the SOS along the western Gondwana margin is better explained by large-scale lithospheric extension followed by basin inversion and continental collision.

Provenance of multi-stage volcanic ash recorded in the Late Carboniferous coal in the Jungar Coalfield, North China, and their contribution to the enrichment of critical metals in the coal

The origins of partings within the Late Carboniferous No. 6 coal in the Jungar Coalfield, North China, and their relationship to the enrichment of critical metals in the coal, is poorly understood. This study combines UPb ages and LuHf isotope data of zircon, whole-rock geochemistry, LA–ICP–MS elemental mapping, and selective chemical extraction experiments to investigate the provenance of the partings and the occurrence mode of critical metals in the partings collected from the exploration area in the northwest of the Jungar Coalfield. It was found that the zircons in the kaolinite-dominant partings yielded a single age group of ca. 300 Ma at the latest Carboniferous (Gzhelian), indicating that the partings are alteration products of air-fall volcanic ash (tonsteins). The zircons are characterized by negative εHf(t) values and a continental arc tectonic setting, suggesting a genetic connection between the volcanic ash and the Late Paleozoic continental arc that existed in the Inner Mongolia Paleo-Uplift, related to the southward subduction of the Paleo-Asian oceanic plate beneath the northern margin of the North China Block. During the devitrification of volcanic glasses to kaolinite in the mires, the incompatible elements, such as Nb, Ta, Zr, Hf, and rare earth elements (REEs and Y, REY), preserved in the volcanic glasses were leached out as they are incompatible with the crystal lattice of kaolinite. Niobium and Ta, similar to Ti in ionic radii, were preferentially incorporated into fine-grained Ti oxides as reprecipitated products in the alteration process of volcanic ash. The enrichment of Nb, Ta, and Ti in organic matter in the tonsteins suggests that they have some mobility during alteration of volcanic ash and could be, to some extent, transported into the enclosing peats. Zirconium, Hf, and REY were fixed by organic matter admixed with the volcanic ash after their deposition in the mires. Meanwhile, they could also be transported into the enclosing peats, as no secondary minerals formed could substantially retain them. Although Li and Ga were able to be incorporated into the crystal lattice of kaolinite during their crystallization, they could also be transported into the enclosing peats due to their fluid-mobile nature. Both the leaching of a voluminous amount of volcanic ash contacting with the peats and the input of the volcanic ash as an admixture into the peats contributed to the enrichment of critical metals in the Late Carboniferous coal in the Jungar Coalfield.

Closure of the Eastern Paleo-Asian Ocean: Evidence from Permian–Triassic Volcanic Rocks in the Northern Margin of the North China Craton

The Central Asian Orogenic Belt (CAOB) is the world’s largest accretionary orogenic belt, and its formation is related to the closure of the Paleo-Asian Ocean (PAO). However, the closure time and style of the PAO remain controversial. To address these issues, this paper presents zircon U-Pb dating, whole-rock geochemistry and zircon Lu-Hf isotope analyses of the volcanic rocks in the Faku-Kaiyuan area on the northern margin of the North China Craton. The results show that the Bachagou andesites formed in the Early Permian (287 ± 2 Ma), while the Chaijialing andesites and dacites formed in the Late Permian (253.3 ± 3.7 Ma) and Middle Triassic (244.3 ± 1.3 Ma), respectively. The Bachagou andesites and Chaijialing andesites are enriched in LILEs and LREEs and depleted in HFSEs and HREEs, indicating that they formed in the active continental margins. The Chaijialing dacites show similar geochemical signatures to adakite and formed in a syn-collisional setting. Geochemistry and isotopic analysis indicates that the Bachagou andesites were derived from a partial melting of the mantle wedge that was metasomatized by subduction fluids. The Chaijialing andesites were generated from a metasomatized mantle by slab-derived and sediment fluids. The Chaijialing dacites formed by a partial melting of thickened lower crust. Combined with previous research results, we can conclude that the Eastern PAO closed by a scissor-like movement from west to east during the Late Permian–Middle Triassic.