Lu Hf Research Articles

Geochemical and zircon 18O–Hf–U/Pb isotopic study of volcanic rocks from Lutao Island in the northern Luzon magmatic arc

AbstractLutao is an islet off the eastern coast of the main island of Taiwan and is composed of pyroclastic agglomerates, volcanic breccias, lava flows, and dykes. There have been no reports of SIMS zircon oxygen isotopic data from Lutao Island so far, which has significantly hampered further understanding of its magmatic processes, such as crystallization, evolution, and generation of magma. In this study, we use zircon U–Pb dating, Lu–Hf and O isotopic analysis to constrain the age, origin, and magmatic processes of the volcanic rocks from Lutao Island. Integration of our new U–Pb and Hf–O isotope data with available published data allows us to better assess the timing and magmatic processes of Lutao Island in the context of the northern Luzon arc system. This work is the first report of SIMS zircon oxygen isotopic data of volcanic rocks from Lutao island. This study shows that the volcanic rocks from Lutao Island were generated by mantle-derived magma associated with high-T° hydrothermal alteration by seawater-derived fluids.

Geological position of the Junggar terrane (Southern Kazakhstan) in the structure of Rodinia supercontinent: results of research of the late-precambrian metasedimentary complexes

The results of studying of the Precambrian metasedimentary sequences of the Junggar terrane located in South Kazakhstan are given in the article. In the structure of the Junggar terrane, we studied the rocks of the Sarychebyn group and Kosagash formation. Petrogeochemical data combined with the results of U‒Pb and Lu‒Hf isotope-geochronological studies of the detrital zircons showed that the Sarychebyn Group and the Kosagash formation represent a similar stratigraphic level that accumulation occurred in the Late Mesoproterozoic to Early Neoproterozoic (~1026‒~920 Ma). The main sources of the detrital zircon age populations were the Mesoproterozoic and Paleoproterozoic complexes. Among these complexes can be identified metabasites and metapelites of intermediate and high metamorphic grades, as well as felsic igneous rocks formed with the participation of various sources, can be distinguished. The Junggar terrane exhibits a close tectonic affinity with the Aktau-Mointy, Yili, Issyk-Kul, Chinese Central Tien-Shan, and the Northern Kazakhstan terranes in the Late Precambrian. They were probably located near the Sveconorwegian orogen in the western Baltica within the Rodinia supercontinent structure.

The formation and recycling of Neoproterozoic granitoids in the Jiangnan Orogen, South China: Implications for Mesozoic rare metal mineralization

In the era of energy transition on the Earth, rare metal mineralization has attained increased significance for various energy sectors and understanding their formation and evolution in various tectonic settings is of great importance for formulating exploration strategies. The Neoproterozoic Jiangnan Orogen in South China marks the assembly zone of the Yangtze and Cathaysia blocks and carries numerous rare metal deposits. In this contribution, we investigate the Neoproterozoic Jiuling composite batholith to understand the formation of rare metal mineralization. We present new in-situ zircon U–Pb ages and Lu–Hf isotopes, and whole-rock geochemistry and Sm–Nd isotopes of the Banbei biotite granodiorite and the associated rare metal-mineralized Baishawo granite in the western portion of the Jiuling batholith suite. Zircon U–Pb dating indicates that the Banbei biotite granodiorite, and the Baishawo two-mica granite and muscovite granite formed at ca. 820 Ma, 153 Ma, and 142 Ma, respectively. The εHf(t) values of the biotite granodiorite, two-mica granite and muscovite granite are –4.4 to +5.8, –11.8 to –7.0, and –10.5 to –7.3, respectively. The εNd(t) values of the biotite granodiorite, two-mica granite and muscovite granite are –3.88 to –2.73, –10.6 to –10.2, and –9.23 to –9.16, respectively. Zircon Hf isotopes and whole-rock Sm–Nd isotopes suggest that the granite suite was sourced from the Mesoproterozoic crust. Geochemical modeling suggests that the Banbei biotite granodiorite was derived from partial melting of Meso- to Neoproterozoic metasedimentary rocks, whereas the Baishawo two-mica granite and muscovite granite were derived from assimilation–fractional crystallization of the Neoproterozoic Banbei biotite granodiorite and Mesozoic magma with low degrees of differentiation. Combined with previous studies on the granite suites in the Jiangnan Orogen, we suggest that collision between the Yangtze and Cathaysia blocks ceased at least 820 Ma, and that Precambrian rocks might have contributed significantly to the enrichment of rare metal mineralization in Mesozoic granite through reworking.

Provenance of the He 8 Member of the Upper Paleozoic Shihezi Formation, Ordos Basin, China: Insights from Heavy Minerals, Paleocurrents, Detrital Zircon Chronology, and Hf Isotopes

The Ordos Basin is located in the western part of the North China Craton. The Upper Paleozoic Shihezi Formation, particularly the He 8 Member, is one of the main gas-bearing strata. However, the source areas for the north and south sections have not been clearly distinguished, which has constrained oil and gas exploration to some extent. Therefore, understanding the source rock evolution of He 8 Member in both the south and north basins will provide a favorable theoretical basis for oil and gas exploration. The provenance of the He 8 Member of the Shihezi Formation in the Ordos Basin has not been well defined until now. Seven wellbore sandstone samples and three field outcrop sandstone samples from the He 8 Member in the Ordos Basin were analyzed. Based on zircon U–Pb dating and Lu–Hf isotope analyses, zircon assemblages of 520–386 Ma and 350–268 Ma in the southern Ordos Basin might have originated from the North Qinling Orogenic Belt (NQinOB) and the North Qilian Orogenic Belt (NQiOB); the 350–268 Ma age group of zircons from the NQinOB, and a large number of ~320–260 Ma detrital zircons supplied to the southern Ordos Basin by the NQinOB suggest that NQinOB magmatic and/or metamorphic events may have occurred in the NQinOB during the ~320–260 Ma period. From ~320–260 Ma, the NQinOB might have experienced significant tectonic activity that has not been fully revealed thus far. The zircons from 2600–2300 Ma, 2000–1600 Ma, and 450–300 Ma in the northern Ordos Basin might have been derived from the Trans-North China Orogenic Belt (TNCO), the Khondalite Belt, the Yinshan Belt, and the Alxa Belt. The paleocurrent and heavy mineral analyses determined that there are certain differences between the northern Ordos Basin and southern Ordos Basin, with unstable minerals such as barite and pyrite, as well as moderately stable minerals such as garnet, showing an increasing trend from south to north. There are also differences in the dominant paleocurrent directions between the south and north parts of the basin, and the Hf isotope data in the Ordos Basin show two-stage Hf model ages (TDM2) ranging from 918 Ma to 3574 Ma. As a result, the He 8 Member deposits in the southern Ordos Basin and northern Ordos Basin had different sources. The southern Ordos Basin might have derived from the NQinOB, the NQiOB, and the TNCO, and the northern Ordos Basin might have derived from the TNCO, the Khondalite Belt, the Yinshan Belt, and the Alxa Belt.

Detrital zircon and apatite reveal Paleoproterozoic rifting along the eastern margin of the Yilgarn Craton

Detrital minerals within Proterozoic basins are commonly an extant record of now-destroyed crust and provide valuable constraints on ancient paleogeography and tectonic processes. However, reconstructing basin histories depends on discriminating potentially exotic, far-travelled (allochthonous) versus locally sourced (autochthonous) detritus. Detrital zircon from the Woodline Formation, a component of the Proterozoic Barren Basin at the margin of the Yilgarn Craton, Western Australia, closely matches the age and Hf isotopic signatures of magmatic units in the Paleo- to Mesoproterozoic Albany–Fraser Orogen (AFO). However, the provenance of some 2300–2000 Ma zircon detritus is not readily accounted for by known magmatism in the AFO nor the wider Western Australian Craton. To help resolve this enigmatic source, we present isotopic data (U–Pb, Lu–Hf) and trace element geochemistry for zircon and limited U–Pb data for scarce apatite collected from sand and rocks of the Woodline Formation. Based on Hf isotopic signatures, some of the detritus appears to be derived from the recently identified 2030–2010 Ma felsic-igneous Moonyoora Suite, representing the oldest known magmatic components of the AFO. Moreover, the isotopic data imply an earlier ca. 2250 Ma episode of mafic rift-related magmatism, potentially offering a glimpse into the earliest rifting stages along the Yilgarn Craton’s eastern margin. While Paleoproterozoic detritus is omnipresent in Woodline rocks, it is conspicuously absent from overlaying regolith, demonstrating that cover atop the Woodline Formation is imported and not locally derived. This disparity is important as it highlights that ongoing exploration efforts analysing unconsolidated regolith may not fully capture basement signatures.

Late Ordovician Bentonites From the Southern Ordos Basin: Response to the Subduction of the Proto‐Tethys Ocean

ABSTRACTThe connection between the Ordovician bentonites on the southern margin of the Ordos Basin and the Early Palaeozoic volcanic rocks of the North Qinling Orogenic Belt is crucial for understanding the subduction and collisional closure of the Shangdan Ocean during the Early Palaeozoic. This paper investigates zircon U–Pb ages, geochemistry and Lu–Hf isotopic compositions of zircons in the Upper Ordovician Zhaolaoyu Formation bentonites located on the southern margin of the Ordos Basin. U–Pb dating of zircon indicates a coeval age of 453.3 ± 1.4 Ma (MSWD = 0.99), which represents the crystallisation age during the Late Ordovician Katian stage. The bentonites exhibit higher SiO2 (57.94–77.95 wt.%) and Al2O3 (9.21–14.33 wt.%), classifying them within the low‐potassium alkali basalt to medium‐potassium calc‐alkaline series. The parent rock of the bentonites is likely intermediate to felsic volcanic rocks. The rare earth element partitioning curves of the bentonites are right‐dipping, with a more pronounced negative Eu anomaly (δEu = 0.48–0.67). The zircons in the bentonites yield two‐stage model ages ranging from 546 to 956 Ma, along with εHf(t) values between 5.56 and 13.55. These results indicate that the bentonites are products of volcanic arc magma formed in a subduction–collision environment. The interbedded bentonites in the Upper Ordovician limestones of the southern margin of the Ordos Basin may be associated with the northward subduction of the Shangdan Oceanic crust, reflecting the subduction and consumption of the Proto‐Tethys Ocean along the southern margin of the North China Block.

SOURCES OF MAGMAS OF PERMIAN GABBROS OF THE KHANGAI MOUNTAINS (Western Mongolia)

We present Sm–Nd and Rb–Sr isotope composition data on mafic–ultramafic massifs in the Khangai Mountains of Western Mongolia: Oortsog-Uul, Nomgon, and Yamaat-Uul. The U–Pb age of zircon and its Lu–Hf isotope and trace-element compositions were determined by LA–ICP–MS. New and previous geochronological data obtained by SIMS and LA–ICP–MS support the Permian age of the studied gabbros. The trace-element composition of zircon, characterized by strong HREE enrichment ((Lu/Gd)n > 7) and cerium positive (Ce/Ce* > 6.6) and europium negative (Eu/Eu* = 0.16–0.49) anomalies, indicates its magmatic genesis and the possibility of using isotope characteristics to assess the origin of mafic magmas. The formation of zircon from a residual mafic melt is inferred from the enrichment of zircon in U and Th with increasing Th/U, reflecting the accumulation of these highly incompatible elements in the residual melt, and from the crystallization temperature of zircon (810–880 °С). The geochemical characteristics of the rocks, their isotopic composition, the absence of xenogenic ancient zircons, and the lack of correlation between εNd(T) and major indices of crustal contamination indicate that crustal contamination did not influence the composition of the gabbros. Isotopic data on rocks and zircon indicate the involvement of two mantle sources in the formation of the mafic–ultramafic massifs of the Khangai Mountains: (a) depleted, predominant for the Nomgon and Yamaat-Uul massifs (εHf = 16.1–2.0; εNd = 4.5–0.0; and ISr = 0.70385–0.70537), and (b) enriched, predominant for the second phase of the Oortsog-Uul massif (εHf = 1.4–0.2; εNd = –3.6… –5.7; and ISr = 0.70704–0.70933).

Zircon U-Pb Age and Hf-O Isotope Evidence of the Taihua Complex on the Southern Margin of the North China Craton: Implications for Its Magmatic Process During the Early Paleoproterozoic

The Xiaoqinling is the largest terrane of the Taihua Complex and records Paleoproterozoic silicic magmatism, which is one of the most potential areas for understanding secular changes in tectonic processes during the Tectono-Magmatic Lull (TML). In this study, we use zircon U–Pb dating, Lu–Hf and O isotopic analysis to constrain the age, provenance, and magmatic processes of the protoliths for the Paleoproterozoic granitic gneiss, tonalitic gneisses, and migmatitized tonalitic gneiss from the Xiaoqinling area. The isotopic composition of zircon provides a key proxy for querying the crustal record. Integration of our new U–Pb and Hf–O isotope data with available published data from other regions of the North China Craton (NCC), allows us to better assess the secular changes of the North China Craton during the magmatic lull at ∼2.3 Ga. This study shows that the protolith of the tonalitic gneisses in the study area have crust-like Hf–O isotopic compositions with slightly negative to positive εHf(t) (−3.0− +2.1) and low to moderately elevated δ18O values (2.71–7.87‰), indicating a mixed origin of continental crust assimilated by mantle-derived magmas.

Discovery of Late Cretaceous basalts in the Asuo area, Central Tibet: Implications for orogenic root removal beneath the Lhasa-Qiangtang orogenic belt

Post-collisional mafic rocks provide valuable insights into the mantle properties and evolution of orogenic belts. However, their origins remain unknown. In this study, comprehensive age, elemental, and zircon Lu–Hf isotopic data are presented for mafic dikes from the Asuo area of the Central Tibetan Plateau. The Asuo mafic dikes exhibit typical arc-related characteristics such as enrichment in large-ion lithophile elements and depletion in high-field-strength elements. This sodium-rich calc-alkaline mafic rocks has low K2O contents (0.98–1.26 wt%) and high Na2O/K2O ratios (2.55–2.97). The presence of xenolith zircons and varying zircon Hf isotopic composition [εHf(t): 1.33–8.32] indicate that the mafic magma assimilated juvenile crust. Zircon U-Pb dating results suggest that the Asuo mafic rocks were emplaced contemporaneously with the adakite-like rocks during ∼ 95–75 Ma. However, no genetic link between Asuo mafic rocks and the adakite-like rocks in the Lhasa–Qiangtang Orogenic belt was observed. The primary contribution of mantle-derived mafic magmas to the formation of coeval intermediate–felsic magmas is the provision of additional heat. The mass exchange between them may be limited. We suggest a geodynamic scenario in which the orogenic root may have been removed during the post-collisional period via repeated and localized lithospheric dripping. In this model, the formation of mafic and adakite-like intrusions occurred in two stages, that is, (1) partial melting of metasomatized lithospheric mantle generated mafic melts, and (2) underplating of these mafic melts beneath the thickened juvenile lower crust, which resulted in partial melting of the juvenile mafic lower crust and generation of adakite-like melts. Our results provide new insights into the magmatism in the terminal stage of an orogenic system.

Petrogenesis and tectonic implication of the Triassic monzogranite from the central segment of the East Kunlun Orogen, NW China

The Triassic granitoids in the East Kunlun Orogenic Belt (EKOB) are crucial for understanding the tectonic evolution of the Paleo-Tethys Ocean. This study presents zircon U–Pb ages, Lu–Hf isotopes, whole-rock major and trace elements, and Sr–Nd isotope compositions from monzogranite plutons in the central segment of EKOB to constrain their petrogenesis and tectonic evolution. These monzogranites are dominant composed of mineral assemblages of K-feldspars, plagioclase, minor biotite and accessory minerals. U–Pb dating of zircons from the Xinle South (XLS), Nanshankou (NSK) and Changgou South (CGS) plutons yield ages of 251 Ma, 232 Ma and 221 Ma, respectively. The studied monzogranites have relatively high SiO2 and Al2O3, but have low contents of TiO2, Fe2O3T, MgO relative to the coeval granodiorites. These monzogranites are classified as fractionated I-type granites, ranging from calc-alkaline to high-K calc-alkaline compositions. Their negative εNd(t) values (−4.2 to −6.3) and zircon εHf(t) values (−6.1 to −9.3) suggest that magma generation occurred through partial melting of ancient lower crust, followed by extensive fractional crystallization. Integrating our new data with regional geological evidence, we propose that the Early Triassic XLS monzogranite emplaced in a localized extensional environment linked to the northward subduction of the Paleo-Tethys oceanic plate. In contrast, during the post-collisional extensional phase of the Late Triassic, the formation of the NSK and CGS monzogranite plutons was directly influenced by asthenospheric upwelling, lower crust delamination, and subsequent continental rifting.

In situ Lu–Hf dating of allanite by LA-ICP-MS/MS: Implications for geochronology

Allanite is a common REE-rich accessory mineral found in various igneous and metamorphic rocks, and can record a variety of geological processes. Therefore, allanite geochronology has the potential to answer a range of important geological questions. Allanite U–Th–Pb geochronology is hampered by common open-system behavior in the system. In this study, we demonstrate the feasibility of in situ allanite Lu–Hf dating by LA–ICP–MS/MS. A total of nine allanite samples from different rock types (e.g., granite, pegmatite) were investigated. These allanite samples have ages ranging from ca. 2650 to ca.100 Ma, and Lu contents ranging from several to hundreds of μg g−1 levels and relatively high Lu/Hf ratios (> 30). At a mass shift of +82, the isobaric interferences 176Lu and 176Yb have extremely low reaction rates of ∼0.003 % and ∼ 0.0003 %, respectively, indicating the isobaric interference corrections are insignificant for the allanite samples (mean 175Lu/177Hf = ∼814; mean 172Yb/177Hf = ∼719). A two-step calibration strategy was proposed for the 176Lu/176Hf and 177Hf/176Hf ratio corrections using NIST SRM 610 (for instrument drift) and LE2808 (for matrix effect). The nine allanite samples contain common Hf contents (f176Hf) of ∼5 % to >90 %, and the data are plotted in inverse isochron diagrams. Unanchored inverse isochron ages exhibit a large deviation in accuracy (5–10 %), whilst anchored isochron ages have a better accuracy of <5 %. The uncertainty of anchor initial 176Hf/177Hf values was investigated and, in general, was insignificant (< 2.8 %) for samples with f176Hf < 80 %. Our results demonstrate that in situ allanite Lu–Hf dating by LA-ICP-MS/MS is feasible and can yield precise and accurate ages (< 5 %). Lu–Hf geochronometer captures the high-temperature process and may be more resistant during the late thermal event. Thus, it provides an alternative solution for those samples which are suffered by open-system behavior in U-Th-Pb system.

Petrogenesis and Geodynamic Mechanisms of Porphyry Copper Deposits in a Collisional Setting: A Case from an Oligocene Porphyry Cu (Au) Deposit in Western Yangtze Craton, SW China

The Xifanping deposit is a distinct Cenozoic porphyry Cu (Au) deposit located in the Sanjing porphyry metallogenic belt 100–150 km east of the JinshajFiang fault in the western Yangtze craton. We present new zircon U–Pb–Lu–Hf isotopic studies and geochemical data of the ore-bearing quartz monzonite porphyry from the Xifanping deposit to determine their petrogenesis and geodynamic mechanisms. LA–ICP–MS zircon U–Pb dating yielded precise emplacement ages of 31.87 ± 0.41 Ma (MSWD = 0.86) and 32.24 ± 0.61 Ma (MSWD = 1.8) for quartz monzonite porphyry intrusions, and 254.9 ± 5.1 Ma (MSWD = 1.7) for inherited zircons of the monzonite porphyry. The ore-bearing monzonite porphyry is characterized by high-K calc–alkaline to shoshonite and peraluminous series, relatively enriched in light over heavy REEs, with no distinct Eu anomalies, as well as enrichment in LILEs and depletion of HFSEs, with adakitic affinities. The zircon Lu–Hf isotope data ranged from εHf(t) values of −2.94 to +3.68 (average −0.47) with crustal model (TDM2) ages ranging from 0.88 to 1.30 Ga, whereas the inherited zircons displayed positive εHf(t) values ranging from +1.83 to +7.98 (average +5.82), with crustal model (TDM2) ages ranging from 0.77 to 1.17 Ga. Results suggest that the Xifanping porphyry Cu (Au) deposit is related to two periods of magmatic activities. Early magmas were generated from the Paleo-Tethys oceanic subduction during the Late Permian. The subsequent porphyry magma was likely formed by the remelting of previously subduction-modified arc lithosphere, triggered by the continental collision between the Indian and Asian plates in the Cenozoic. The deep magmas and late hydrothermal fluids took advantage of the early magma transport channels along tectonically weak zones during the transition from an extrusive to an extensional–tensional tectonic environment. Early dikes from remelted and assimilated crust contributed to the two age ranges observed in the porphyry intrusions from the Xifanping deposit. The juvenile lower crust materials of the early magmatic arc were potential sources of the Cenozoic porphyry magmas, which has significant implications for mineral exploration and the geological understanding of porphyry Cu deposits in this region.

Accretion of microcontinents and arcs in the southern Central Asian Orogenic Belt: insights from provenance analyses of early Paleozoic sedimentary records in Beishan

The Central Asian Orogenic Belt involves amalgamation of numerous magmatic arcs, accretionary complexes and continental fragments during long-lived subduction and accretion. However, the nature of key microcontinental terranes, as well as their continuity, remains unclear. This study conducted outcrop observation, heavy mineral assemblage, whole-rock geochemistry, detrital zircon U–Pb dating and Lu–Hf isotope analysis on sandstones in the Beishan orogenic belt. The findings from field observations, petrographic analysis and weathering indices show that the tectonic setting of the sandstone is a forearc sedimentary basin. The maximum depositional ages (MDAs) of sandstones are 503.8 ± 6.9 Ma and 431.9 ± 6.0 Ma. The provenance of the sandstone is complex, which probably originates from the Shuangyingshan and Hanshan blocks. By comparing the detrital zircon U–Pb ages with adjacent terranes such as Central Tianshan, Dunhuang and Tarim, it was observed that the Shuangyingshan block shares similar provenance with the Dunhuang terrane, while the Mazongshan–Hanshan shows affinity to the Central Tianshan terrane. This study highlights the complex nature of sediment provenance in the Beishan orogenic belt, influenced by tectonic processes involving thrusting, accretionary complexes and the presence of multiple terranes.

Early-stage intracontinental rifting in the Neoproterozoic Centralian Superbasin: Systematic U–Pb and Lu–Hf isotopes in detrital and inherited zircons from the Yeneena Basin, northwest Australia

Detrital zircons from different lithostratigraphic units of Supersequence 1 across the Neoproterozoic northwest Officer and Yeneena basins were investigated using LA-ICPMS U−Pb and Lu − Hf isotope analyses to understand the source of detritus and potential links to regional tectono-magmatic events, as well as the crustal evolution of the sedimentary sources terranes. All data show that Proterozoic detritus dominate the age spectra of samples from the Yeneena Basin and northwest Officer Basin, with signatures varying in the heights of peaks rather than the presence or absence of age groups in different formations. The Archean and Proterozoic ages overlap with known magmatic events in the Pilbara Craton, Fortescue Basin, Rudall Province, Capricorn Orogen, Musgrave Province, Madura Province, and the Coompana Province suggesting these terranes are possible sources of the detritus. The detrital zircon population of the samples have main age peaks in the range 1300 to 1000 Ma, suggesting magmatic rocks of the Rudall and Musgrave provinces are the main sources of detrital zircons, which can be differentiated by Hf signature. The distal Musgrave Province persistently dominates the provenance of detritus in the northwestern Officer and Yeneena basins, while detritus from the proximal Rudall Province contributes to a lesser extent. This suggests that the distal Musgrave Province remained emergent during the evolution of the northwestern Officer Basin and the Yeneena Basin, whereas the proximal Rudall Province potentially became buried by the accumulating sedimentary rocks and contributed less detrital zircons. The 833.6 ± 1.4 Ma maximum depositional age obtained in this study for the sedimentary rocks of the northwestern Officer and Yeneena basins point to the approximate time of the start of basins development. The extensional event in this age period is related to emplacement and extrusion of the ca. 830 Ma Willouran Large Igneous Province (LIP). The Duke gabbro sills observed in the Yeneena Basin are part of this LIP, which extends from the Adelaide Rift Complex, through the Musgrave Province, central–northwest Officer Basin and into the Yeneena Basin. The sediment source terranes suggest a southeast–northwest oriented depositional system between central and Western Australia, possibly because of intracontinental rifting related to widespread mafic–ultramafic magmatic events that could include the earlier Ngaanyatjarra Rift formed by the 1090–1040 Ma Warakurna LIP as well as the ca. 830 Ma Willouran LIP, synchronous with the breakup of Rodinia in the mid-Neoproterozoic.

Archaean multi-stage magmatic underplating drove formation of continental nuclei in the North China Craton

The geodynamic processes that formed Earth’s earliest continents are intensely debated. Particularly, the transformation from ancient crustal nuclei into mature Archaean cratons is unclear, primarily owing to the paucity of well-preserved Eoarchaean–Palaeoarchaean ‘protocrust’. Here, we report a newly identified Palaeoarchaean continental fragment—the Baishanhu nucleus—in northeastern North China Craton. U–Pb geochronology shows that this nucleus preserves five major magmatic events during 3.6–2.5 Ga. Geochemistry and zircon Lu–Hf isotopes reveal ancient 4.2–3.8 Ga mantle extraction ages, as well as later intraplate crustal reworking. Crustal architecture and zircon Hf–O isotopes indicate that proto-North China first formed in a stagnant/squishy lid geodynamic regime characterised by plume-related magmatic underplating. Such cratonic growth and maturation were prerequisites for the emergence of plate tectonics. Finally, these data suggest that North China was part of the Sclavia supercraton and that the Archaean onset of subduction occurred asynchronously worldwide.

In Situ Lu–Hf Garnet Dating of Archean Deep Crust Granulites from the Polymetamorphic Grenville Front Tectonic Zone

Abstract Recent advances in geochronological techniques now make it possible to efficiently decipher the timing and duration of geological processes in complex high-grade polymetamorphosed orogenic terranes. This is the case of the Grenville Front Tectonic Zone, which truncates the Superior Craton to the southeast. The zone exposes parautochthonous Archean rocks that underwent mid- to high-pressure granulite facies metamorphism of uncertain age. The metamorphic assemblages have been either interpreted as Archean and associated with the final stages of the Superior Craton assembly or as the result of Mesoproterozoic Grenvillian metamorphism, based on cross-cutting relationships and traditional geochronology methods such as U–Pb zircon and 40Ar–39Ar mica dating. Herein, we revisit the extent of the Grenvillian metamorphic overprint in the parautochthonous domain and provide new age constraints for granulite-facies metamorphic assemblages through in situ garnet dating within migmatitic paragneiss, migmatitic orthogneiss, and mafic granulites, combined with in situ trace element mapping. Six samples, which show bell-shaped and occasionally sharp and oscillatory lutetium growth zoning in garnet, yield garnet Lu–Hf isochrons with identical Archean dates of c. 2.6 Ga. Sparse analyses of the material trend towards Grenvillian ages (c. 1 Ga) in one sample from which garnet shows lutetium zoning consistent with post-growth fluid-assisted disturbance. Overall, our results indicate that the widespread granulite-facies metamorphism within the Grenville Front Tectonic Zone is dominantly late Neoarchean in age, unveiling a rare exposure of Archean lower crust in the southeastern Superior Craton. Our results also point towards a limited Grenvillian metamorphic overprint, though the spatial extent and precise thermal conditions of this metamorphism are still unknown. The results presented herein demonstrate the potential of in situ isotopic geochronology on rock-forming minerals like garnet in polymetamorphic terranes.

Thermal evolution of the North China Craton revealed by microsampling garnet geochronology on single xenoliths

Granulite xenoliths, sourced from the lower cratonic crust and brought to the Earth's surface within volcanic rocks, offer unique insights into the formation and destruction of cratons. Age determinations are essential for constructing the thermal history of cratons. However, accurate dating is complicated by the xenoliths' extended exposure to high temperatures and their complex thermal histories. Specifically, the effects of extended lower crust residency and entrainment heating on coupled Sm–Nd and Lu–Hf systematics remain to be explored. Six xenoliths hosted in the Mesozoic dioritic porphyry from the eastern North China Craton were sampled from center to edge using micro-drilling/sawing techniques. From each xenolith, two to four concentric zones were successfully extracted for coupled Lu–Hf and Sm–Nd geochronological analysis. These xenoliths predominantly exhibit a granoblastic texture, with minerals that are mostly unzoned. Textural and chemical analyses of minerals indicate a decompression process following the granulite-facies metamorphism, with subsequent multiple reheating events. Thermobarometric calculations suggest granulite-facies equilibration at temperatures of ∼750 °C and pressures of 1.2–2.0 GPa. Consistent Lu–Hf and U–Pb ages of ca. 1.7 Ga, obtained from garnet, zircon, and titanite in chemical and textural equilibrium, are attributed to granulite-facies metamorphism. The Paleoproterozoic Lu–Hf ages and the Neoproterozoic Sm–Nd dates are indistinguishable across all concentric zones within each xenolith, whereas Sm–Nd ages are consistently ∼1.0 Ga younger than the corresponding Lu–Hf ages. This discrepancy suggests a complex history for this section of the lower cratonic crust, marked by a granulite-facies metamorphic event around 1.7 Ga, followed by prolonged cooling. A significant heating event during the Tonian, likely due to regional mantle plume activity, is inferred to have partially or completely reset the Sm–Nd isochrons. This thermal event and subsequent thermal relaxation on the samples at different residence depths thereby decoupled the Sm–Nd system from the Lu–Hf system, signifying a thermal pulse at the southern margin of North China Craton. The Mesozoic entrainment heating event appears to have had minimal impact on the Lu–Hf/Sm–Nd systematics of garnet and U–Pb of zircon/titanite. Our data highlight the potential of coupled microsampling Lu–Hf and Sm–Nd geochronology on individual xenoliths to reveal tectonic episodes within the lower crust that might be undetected by accessory mineral U–Pb geochronology.

Paleo-to-Mesoarchean crustal evolution in the Uauá Block, Northeastern São Francisco Craton, Brazil: New insights from petrography, U–Pb geochronology, Lu–Hf isotopes and trace elements in zircon

The timing of Earth's initial crustal growth and reworking through collisional settings remains an issue of extensive debate. Here, we report a Paleo-to Mesoarchean migmatite-gneiss, temporally- and spatially-associated with a convergent plate boundary in the Uauá Block, Brazil. This rock records an amphibolite-bearing tonalitic residue and pyroxene-bearing granitic leucosome. Orthopyroxene indicates high-temperature metamorphism during leucosome generation, while the widespread retrogressed hornblende in the residue indicates conditions corresponding to amphibolite facies. Zircon grains display LREE-depleted magmatic cores characterized by distinct zoning, crystallized at 3325 ± 70 and 3245 ± 8 Ma. They are enclosed by LREE-enriched metamorphic overgrowth zones and rims formed at 3120 ± 7 and 3069 ± 9 Ma, accompanied by an increase in Ti content. The εHf(t) values decrease with time from +1.55 to −7.06 and Lu/Hf ratios (0.001–0.011) are consistent with the evolution of the Paleo-to Eoarchean crustal sources with TDM Hf model ages between 3.56 and 3.73 Ga. Our findings provide direct evidence of crustal reworking, implicating a Paleoarchean protolith submitted, during early Mesoarchean, to a high-temperature metamorphism spatially-associated with a regional collisional setting in the São Francisco Craton. Further, we surmise that convergent tectonic processes may have played an important role in crustal reworking during the Paleo-to Mesoarchean transition. These observations allowed a comparison between the crustal evolution of the Uauá and Gavião Blocks in the northern São Francisco Craton, as well as with other Archean cratons.

Devonian plutons in the eastern Meguma terrane, Nova Scotia, Canada: zircon U–Pb, Lu–Hf, and O isotopic compositions, age, and petrogenetic implications

Abundant granitic plutons intruded the eastern Meguma terrane of Nova Scotia in the middle- to late Devonian. Less voluminous diorite–tonalite and gabbro intrusions are associated with the granitic plutons along the northern margin of the terrane adjacent to the Cobequid–Chedabucto fault zone. All plutons contain metasedimentary xenoliths, and the mafic plutons show magma mingling textures with their adjacent granitic plutons. New U–Pb zircon data from autocrystic zircon in 13 samples indicate coeval emplacement of mafic and granitic plutons between ca. 382 and 368 Ma. However, the zircon grains contain numerous inherited domains that range in age from Palaeoproterozoic to Devonian. These inherited ages correspond to detrital zircon U–Pb dates from the Cambrian to Ordovician metasedimentary host rocks. Zircon oxygen isotopic data (δ18O) are between +7.4 ± 0.2‰ and +9.3 ± 0.3‰ indicating significant involvement of the crust as the magma source or contaminant. If the high δ18Ozrn values are a result of contamination, the contaminant was likely the metasedimentary rocks of the Meguma terrane. Hafnium isotopic data from autocrystic zircon have εHf( t) between −6.0 ± 1.5 and +2.1 ± 2.5. The new zircon U–Pb, O, and Hf isotopic data from plutons in the eastern Meguma terrane are indistinguishable from published data from the South Mountain Batholith. The data suggest that Devonian magmatism in the Meguma terrane post-dated the main orogenic event that caused folding and regional metamorphism and involved the same magma source and/or contaminants throughout the terrane.

Correction to: Garnet–Quartz Inclusion Thermobarometry and Lu–Hf Chronology Detail the Pre-Ultra-High Pressure Metamorphic History of the Grapesvare Nappe, Scandinavian Caledonides

Correction to: Garnet–Quartz Inclusion Thermobarometry and Lu–Hf Chronology Detail the Pre-Ultra-High Pressure Metamorphic History of the Grapesvare Nappe, Scandinavian Caledonides