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We report on the quantitative nondestructive analysis of the natural isotopic abundances of hafnium and tungsten elements using nuclear resonance fluorescence. Metallic samples of hafnium and tungsten were irradiated to six quasi-monochromatic γ -ray beams generated by laser Compton scattering in the energy range of 2.4–3.2 MeV. Multiple nuclei were simultaneously excited at each of the six γ -ray beam energies. A high-purity germanium detector array detected deexcitations of the nuclei. In total, 51 transitions were unprecedentedly employed to estimate the isotopic abundances of heavy elements nondestructively. The estimated abundances of three hafnium isotopes and three tungsten isotopes are consistent with standard known natural abundances within the experimental uncertainties. The deviation from the standard values ranges from 0.18 % to 1.36 %. [ABSTRACT FROM AUTHOR]

Zircon trace element geochemistry has become an increasingly popular tool to track crustal evolution through time. This has been especially important in early-Earth settings where most of the crust has been lost, but in some fortuitous instances detrital zircons derived from that lost crust have been preserved in younger sediments. To study the formation and geochemical evolution of continental crust from the Hadean to the Paleoarchean, the 3.6 to 3.2 Ga Barberton Greenstone Belt in southern Africa is an excellent target due to its outstanding preservation and presence of detrital zircons that span almost a billion years. Here, we use trace elements, in combination with hafnium and oxygen isotopes, of 3.65 to 3.22 Ga detrital and tuffaceous zircons of the Moodies and Fig Tree groups and compare their geochemistry to previously studied 4.2 to 3.3 Ga detrital zircons from the Green Sandstone Bed of the Onverwacht Group. The major detrital zircon age clusters in the former at 3.55 Ga, 3.46 Ga, and 3.26–3.23 Ga overlap with episodes of TTG emplacement and felsic volcanism in the Barberton area, suggesting a local provenance. In contrast, age clusters at 3.65 Ga and 3.29 Ga of the Moodies and Fig Tree groups as well as 4.2 to 3.3 Ga detrital zircons from the Green Sandstone Bed do not have known intrusive sources and were likely derived from outside the present-day Barberton belt. This indicates that more than half of the felsic igneous events in the detrital zircon record do not have a whole-rock representation that can be directly studied. The similar compositions and inferred crustal evolution histories recorded in zircons from the Fig Tree and Moodies groups, as well as from the Green Sandstone Bed, suggest that they were derived from connected terranes experiencing similar crustal processes diachronously. Together, they show three phases of felsic continent formation, reflecting different crustal processes: (1) long-lived protocrust formed in the Hadean from undepleted mantle sources. These zircons are vastly different from younger zircons and, hence, Barberton TTGs are not good analogues of Hadean crust formation. (2) At 3.8 Ga, onset of significant crustal growth though cyclic juvenile additions and hydrous melting, possibly within a volcanic plateau setting but an arc-like setting cannot be excluded based on this data. (3) Between 3.4 and 3.3 Ga, felsic crust is generated through a previously unrecognized episode of crustal growth by shallow melting of mafic, mantle-derived sources. This is immediately followed by the onset of crustal thickening through the transport of surface-altered, hydrated materials to deep crustal levels. Since there is geological evidence for extension and shortening at that time this may reflect the onset of horizontal movement. Whether this last geodynamic setting reflects modern-style plate tectonics or not, continent formation and the onset of plate tectonics in the Barberton area occurred through complex multi-stage processes spanning almost a billion years, most of which is only accessible through the detrital zircon record. [ABSTRACT FROM AUTHOR]

The volcanic rocks of the Chon Aike Silicic Large Igneous Province (CASP) are recognized as magmas dominantly produced by crustal anatexis. Investigating the zircon of the CASP provides an opportunity to gain further insight into geochemical and isotopic differences of the potential magmatic sources (i.e., crust versus mantle), to identify crustal reservoirs that contributed to the felsic magmas during anatexis, and to quantify the contributions of the respective sources. We present a combined zircon oxygen and hafnium isotope and trace element dataset for 16 volcanic units of the two youngest volcanic phases in Patagonia, dated here with LA-ICP-MS U–Pb geochronology at ca. 148–153 Ma (El Quemado Complex, EQC) and ca. 159 Ma (western Chon Aike Formation, WCA). The EQC zircon have 18O-enriched values (δ18O from 7 to 9.5‰) with correspondingly negative initial εHf values (− 2.0 to − 8.0). The WCA zircon have δ18O values between 6 and 7‰ and εHf values ranging between − 4.0 and + 1.5. Binary δ18O-εHf mixing models require an average of 70 and 60% melt derived from partial melting of isotopically distinct metasedimentary basements for the EQC and WCA, respectively. Zircon trace element compositions are consistent with anatexis of sedimentary protoliths derived from LIL-depleted upper continental crustal sources. The overlap between a high heat flux environment (i.e., widespread extension and lithospheric thinning) during supercontinental breakup and a fertile metasedimentary crust was key in producing voluminous felsic volcanism via anatexis following the injection and emplacement of basaltic magmas into the lower crust. [ABSTRACT FROM AUTHOR]

This study compares three zircon synthesis techniques (synthesis, high-temperature and high-pressure sintering and fast hot-pressing sintering) for the preparation of reference materials for Hf isotope analysis of zircon by laser ablation multi-collector inductively-coupled plasma mass spectrometry (LA-MC-ICP-MS). Ultrafine milled zircon powder particles doped with Yb2O3 produced by wet milling were used to synthesize zircon samples by using high-temperature and high-pressure sintering and fast hot-pressing sintering techniques. Li–Mo flux was necessary to obtain synthetic zircon grains. Zr signals for synthetic zircon grains and high-temperature and high-pressure sintered zircon are consistent with those of natural zircons but higher than that of fast hot-pressing sintered zircon, indicating that high-temperature and high-pressure sintered zircon has approximated the theoretical maximum density due to high pressure. The Hf isotopic compositions of high-temperature and high-pressure sintered and fast hot-pressing sintered zircon are comparable to those of the initial starting materials, whereas the Hf isotopes in synthetic zircon grains deviate slightly from those of the initial Hf solution. Compared with Hf isotope ratios obtained by SN-MC-ICP-MS, all preparation techniques give reliable LA-MC-ICP-MS results, suggesting that all synthetic zircon samples have great potential as both tools for in situ method development and isotopic reference materials. [ABSTRACT FROM AUTHOR]

Clay mineral authigenesis at continental margins plays an important role in global marine element cycles. However, despite being increasingly used as tracers for both modern and past oceanographic conditions, the behavior of the rare earth elements (REEs) and their isotopes during marine clay authigenesis still remains poorly known. In this study, we report on a detailed geochemical investigation of glauconite from the West African continental shelf, near the mouth of the Congo River. Elemental, neodymium, and hafnium isotope analyses were conducted on both acid leachate and separated clay-size fractions of glauconite pellets, in order to investigate the behavior of REE during the formation of authigenic clays. Our data indicate that kaolinite dissolution and subsequent Fe-bearing clay authigenesis act as a net source of REEs to seawater. We show that enhanced glauconitization, as inferred from increasing Fe and K contents, is accompanied by significant decoupling of the REE toward markedly LREE-enriched shale-normalized patterns in neoformed clay separates. Using both Nd and Hf isotopes and SEM observations, we rule out any seawater influence and argue that this shift primarily reflects the progressively overwhelming presence of insoluble nanocrystals of detrital LREE-rich phosphates, which are known to occur in close association with kaolinite in tropical soils. Due to their marked insolubility in surface environments, such nanocrystals can be preserved during kaolinite dissolution and subsequently incorporated into the aggregates of authigenic green clays forming the peloids. Most strikingly, we show that the combined influence of net REE loss (due to kaolinite dissolution) and decoupling (due to subsequent entrapment of inherited LREE-bearing accessory phases into neoformed clay minerals) is accompanied by preferential release of a dissolved REE fraction characterized by seawater-like distribution patterns. These findings reinforce the emerging view that clay mineral dissolution and authigenesis at continental margins possibly play a major role in marine REE cycling. [ABSTRACT FROM AUTHOR]

Radiogenic Hf isotope disequilibrium during crustal anatexis complicates petrogenetic studies that link sources to sinks in granitoid systems and hinders the applications of Hf isotopes to evaluating long-term crustal growth and evolution. Garnet can be a dominant host of radiogenic Hf in crustal rocks, and its behavior in granitoid sources may play a crucial role in isotopic decoupling between residue and melt. We document covariation between (Gd/Lu)N ratios and εHf(t) in post-collisional granitoids from the Dabie orogen (central China). This covariation reflects different garnet modal contents in the residue during anatexis. Quantitative modeling further confirms the dominant role of mixing between melts derived from garnet-rich and garnet-poor residua in producing the observed covariation patterns, but results are inconsistent with the entrainment of garnet rich in radiogenic Hf in the melt. Our results demonstrate that the garnet effect on Hf isotope ratios during crustal anatexis is a crucial factor in elucidating the granitoid source and complicates interpretations of crustal growth from the global zircon archive. [ABSTRACT FROM AUTHOR]

Nine Paleozoic sedimentary formations from western Tasmania and two from the Lachlan Orogen—one in northeast Tasmania and one in Waratah Bay in Victoria—contain detrital zircons that fall into major U–Pb age clusters at 2.0–1.4, 1.25–0.95 and 0.62–0.49 Ga. The zircon Th/U ratios and rare earth element (REE) patterns suggest a magmatic origin for detrital zircons in all these rock sequences. The REE geochemical signatures on bivariate discrimination diagrams indicate that most of the zircons originated in continental orogenic settings. The oldest group of zircons have a southwest Laurentian signature previously recognised from Proterozoic metasedimentary rocks in Tasmania. The 1.25–0.5 Ga zircons from all the samples have very similar εHfi values. They are not statistically different from those of typical Lachlan Orogen sandstones and resemble those in Rodinia and early Gondwana orogenic belts. The εHfi values of the Cambrian zircons within the Pioneer Sandstone are similar to the Mount Read Volcanics but cannot be distinguished on εHfi values from other sources in East Gondwana. The detrital zircon provenance of the Bear Gully Chert Bed at the base of the Digger Island Marlstone at Waratah Bay includes the west Tasmanian Proterozoic, the East Gondwana margin and the Macquarie Arc. This mixed provenance provides evidence for the late Cambrian docking of VanDieland with East Gondwana. New zircon Hf isotope data are reported for early Paleozoic sedimentary rocks in Tasmania and Waratah Bay, southern Victoria. The western Tasmania basement was the dominant source for Tasmanian sandstones and a minor source for the Lachlan Orogen sandstones on the northeast margin of VanDieland. The mixed provenance of the Bear Gully Chert supports a late Cambrian accretion of VanDieland to the East Gondwana margin. The youngest zircons in the Bear Gully Chert at Waratah Bay were potentially sourced from the Macquarie Arc. [ABSTRACT FROM AUTHOR]

New zircon reference materials for in situ zircon radiogenic Hf isotope and stable Zr isotopic determinations made by laser ablation multi‐collector inductively coupled plasma‐mass spectrometry (LA‐MC‐ICP‐MS) are required due to high data productivity and consequently high reference material consumption rate. This study examines a new natural zircon for Zr isotope ratios by double spike thermal ionisation mass spectrometry (TIMS), and for Hf isotopes by bulk solution nebuliser (SN)‐MC‐ICP‐MS with both Zr and Hf determined by LA‐MC‐ICP‐MS. A total of five zirconium isotope measurements from drilled zircons, determined by TIMS, yield a mean δ94/90ZrIPGP‐Zr value of ‐0.09 ± 0.06‰ (2s). Five and eight hafnium isotope measurements for powders from the drilled zircons and Ban‐1‐4 by SN‐MC‐ICP‐MS, yield mean 176Hf/177Hf ratios of 0.282985 ± 0.000011 (2s) and 0.282982 ± 0.000007 (2s), respectively. The mean δ94/90ZrIPGP‐Zr value and 176Hf/177Hf ratio determined by LA‐MC‐ICP‐MS analyses are ‐0.06 ± 0.09‰ (2s, n = 504) and 0.282985 ± 0.000035 (2s, n = 327), respectively. The isotopic homogeneities suggest that the Ban‐1 zircon is a suitable reference material for microbeam Zr and Hf isotopic measurements. [ABSTRACT FROM AUTHOR]

Extensive crustal anatexis is common during the decompressional exhumation of deeply subducted continental crust and the delamination of a collision‐thickened orogenic lithosphere, indicating that determining the timing of partial melting can provide insights into the possible tectonic evolution during orogenic processes. An integrated study of petrology, zirconology and whole-rock geochemical compositions from migmatites and pegmatites in the Nageng, Langmuri and Wulonggou area of the East Kunlun Orogenic Belt, is presented in this study. The protoliths of these migmatites include Tonian sedimentary rocks and ca. 440 Ma arc-related dioritic rock. Together with previous studies, an extensive crustal anatexis event recorded by anatectic zircons occurred after ca. 410 Ma. In addition, hafnium isotope analyses indicate that the anatectic zircons may or may not inherit their Hf isotope compositions from protolith zircons during partial melting, depending on whether or not the garnet Hf contributes to the Hf budget of anatectic melt. Thus, the most reasonable method to trace the source of granite is to compare the Hf isotope composition of anatectic zircon in migmatite and magmatic zircon in contemporaneous granite. By such method, anatectic melt produced by migmatites in this study could account for both penecontemporaneous A- and I-type granites with high magmatic zircon εHf(t) values and S-type granites with low magmatic zircon εHf(t) values. As the extensive crustal anatexis is later than both metamorphic peak and amphibole-facies retrogression of high-pressure and ultrahigh-pressure (HP-UHP) metamorphic rocks, it is reasonable that post-collision orogenic collapse of the collision‐thickened orogenic lithosphere as a result of delamination and asthenospheric upwelling occurred after ca. 410 Ma, which is also supported by contemporaneous granulite-facies metamorphism, molasse deposition, and magmatic events including Xiarihamu mafic-ultramafic intrusions, A-type granites, and mafic dykes formed in the continental rifting setting. [ABSTRACT FROM AUTHOR]

The correlations of the reduced hindrance factor Fν of the K-isomers in Ta and Hf isotopes with respect to NpNn (the product of valence nucleons), EK − ER (the isomer excitation energy referred to a rigid rotor), and EK(Nn)−EK(Nn−max) (the energy difference between the same configuration at Nn and Nn−max (middle of a shell), at given spin and isotopic chain) have been re-examined. The analysis is performed in the valence regionsdivided into particle–particle (p–p), particle–hole (p–h), and hole–hole (h– h) regions, based on the NpNn phenomenology. The Ta and Hf isotopes are considered, given the availability of the same spin configuration in the different sectors of the valence regions. In our study, we observe that the parameter EK(Nn)−EK(Nn−max) shows a significant correlation with Fν, within an isotopic chain. [ABSTRACT FROM AUTHOR]

The supercontinent cycle has been the focus of researchers for many years, but the parameters of its cyclicity remain a central debate; thus, prediction of the occurrence of the next supercontinent remains elusive. In this research, a mathematical point of view is adopted, based on the assumption that the supercontinent Columbia assembled at – 2000 Myr X - 2 and the supercontinent Rodinia assembled at – 1000 Myr X - 1 . The younger supercontinents are calculated following this mathematical equation: X n = 2 ∗ X n - 1 - X n - 2 - 540 3 n , where X n represents the assembly and n is the position of the supercontinent in the sequence. Therefore, Gondwana X 0 amalgamated at -540 Myr, Pangea X 1 at – 260 Myr, Eurasia X 2 at – 40 Myr and Pangea Proxima X 3 might form at + 160 Myr. Moreover, two logarithmic regressions give fairly similar results, confirming that a constant acceleration of the supercontinent cycle is probable. The detrital zircon, metamorphic and hafnium isotope records support the assemblies' hypotheses that produce the mathematical equation. However, a recent supercontinent or "megacontinent" called Eurasia lacks strong geological evidence in the three datasets. These findings might reconcile the paradox brought about by the closer ages in time for the Earth's more recent supercontinental assemblies and the assumed constant cyclicity of the cycle. [ABSTRACT FROM AUTHOR]

The hafnium isotopes of zircon have recently been identified as a new means of detecting magmatic cyclicity. A hierarchy of possible magmatic cycles has been verified, ranging from the ∼600 Myr supercontinent cycle to 10–20 Myr plutonic cycles. While the supercontinent cycle is well-established, the shorter mantle convective and plutonic cycles require further work to understand how magmatic dynamics may give rise to such cyclicity. In this study, we analyze in detail the long-lived orogenic system of the Australian Tasmanides, and a hierarchy of cycles is visible, including a ∼ 290 Myr accretionary/orogenic cycle, a ∼ 65 Myr upper mantle cycle, and 20–10 Myr magmatic and plutonic cycles. These cycles correlate with the evolution of the orogens and episodic continental growth of eastern Gondwana. The surprising similarity in period length between the opening/closing of a typical Atlantic-like Wilson cycle to the case here of the lifecycle of a West Pacific-type arc system may imply that the two distinct tectonic settings have a similar mantle convective effect, which requires further empirical testing and theoretical study. Similar to magmatic cycles identified in the Hadean and in modern arc settings, the hierarchy of cycles in the Tasmanides implies a uniformitarian similarity in arc magmatism throughout Earth history. • A hierarchy of magmatic cyclicity has been identified in the Australian Tasmanides. • Geological processes of the cycles have been systematically addressed. • Mechanisms of cyclicity and episodic continental growth have been proposed. • Geological significance of modulation of the cycles has been proposed. • The hierarchy of cycles displays a uniformitarian affinity throughout Earth history. [ABSTRACT FROM AUTHOR]

Amphibole- and clinopyroxene-bearing monzodiorites were emplaced at 340 Ma (CA-ID-TIMS zircon age), suggesting the formation of hydrous and dry magmas closely related in space and time in the NE Bohemian Massif. Hafnium and oxygen isotopes of zircon in less evolved rocks (<55 wt% SiO2) are similar between Amp and Cpx monzodiorites (εHf = −3.3 ± 0.5 and − 3.5 ± 0.8; δ18O = 6.4 ± 1.0 and 6.8 ± 0.7, respectively), consistent with a common source—a contaminated mafic magma derived from an enriched mantle. At the same time, the conditions of crystallization are distinct and zircon appears to be an excellent tool for distinguishing between hydrous and anhydrous crystallization conditions, a process that may be more ambiguously recorded by whole rock and major mineral chemistry. In particular, elements fractionated by either amphibole or plagioclase crystallization, such as Hf, Dy, and Eu, differ in zircon from amphibole- and clinopyroxene-bearing rocks, and Zr/Hf, Yb/Dy, and Eu/Dy are therefore useful indices of crystallization conditions. We show that the composition of zircon from hydrous dioritic magmas is not comparable with that of typical zircon from dioritic-granitic suites worldwide, suggesting a specific process involved in their formation. Here, we propose that fluid-present remelting of a mafic underplate is necessary to explain the rock textures as well as the composition of the whole rock, zircon, and other minerals of amphibole-bearing monzodiorites and that a similar process may control the formation of amphibole-rich dioritic rocks worldwide, including appinitic suites. Overall, we show that dioritic rocks represent snapshots of differentiation processes that occur in the early stages of magma evolution before the magma is homogenized into large-scale batholiths. [ABSTRACT FROM AUTHOR]

Interpretation of Earth's oldest preserved crustal archive, the Jack Hills zircon of Western Australia, has been controversial in terms of the onset of plate tectonics. We conduct timeseries analysis on hafnium isotopes of the Jack Hills zircon and reveal an array of statistically significant cycles that are reminiscent of plate-tectonic subduction. At face value, such cycles may suggest early Earth conditions similar to those of today--the uniformitarian hypothesis that plate tectonics was essentially operational since "day one". On the other hand, in the context of expected secular changes due to planetary evolution and geological observations, the cycles could instead imply that modern plate-tectonic subduction inherited mantle convective harmonics already facilitated by an early phase of stagnant-lid delamination--the "lid-toplates" hypothesis. Either way, any model for the nature of plate tectonics must incorporate conditions operating during Hadean time, either by initiation of plate tectonics then or by later inheritance of preexisting cycles of mantle convection. [ABSTRACT FROM AUTHOR]

Hafnium (Hf) isotopes in zircon are important tracers of granite petrogenesis and continental crust evolution. However, zircon in granites generally shows large Hf isotope variations, and the reasons for this are debated. We applied U-Pb geochronology, traceelement, and Hf isotope analyses of zircon from the Miocene Himalayan granites to address this issue. Autocrystic zircon had εHf values (at 20 Ma) of -12.0 to -4.3 (median = -9). Inherited zircon yielded εHf values (at 20 Ma) of -34.8 to +0.3 (median = -13); the majority of εHf values were lower than those of autocrystic zircon. The εHf values of inherited zircon with high U concentrations resembled those of autocrystic zircon. Geochemical data indicates that the granites were generated during relatively low-temperature (<800 °C) partial melting of metasedimentary rocks, which, coupled with kinetic hindrance, may have led to the preferential dissolution of high-U zircon that could dissolve more efficiently into anatectic melt due to higher amounts of radiation damage. Consequently, Hf values of autocrystic zircon can be biased toward the values of U-rich zircon in the source. By contrast, literature data indicate that granites generated at high temperatures (>820-850 °C) generally contain autocrystic and inherited zircons with comparable Hf isotope values. During highertemperature melting, indiscriminate dissolution of source zircon until saturation is reached will result in near-complete inheritance of Hf isotope ratios from the source. Our results impose an extra layer of complexity to interpretation of the zircon Hf isotope archive that is not currently considered. [ABSTRACT FROM AUTHOR]

This paper synthesizes available and original U-Pb geochronological and hafnium and oxygen isotope data on zircon from gabbro and peridotites in the oceanic core complexes (OCC) of the Mid-Atlantic Ridge (MAR) extending for 2000 miles along its crest zone. We attempted to reproduce the evolution of MAR magmatism and to determine the geochemical and geodynamic nature of zircon protolith in OCC. We show that the relicts of old continental lithosphere have been preserved locally beneath the axial ridge zone and were involved in the partial melting of a shallow mantle during the entire magmatic evolution of the MAR rift valley. Age variations of zircon from plutonic rocks of the oceanic basement of fracture zones at some distance from the rift valley suggest young magmatism that differs in age from established magnetic anomalies. During the geological history of the Atlantic Ocean, the evolution of the melt originated in the rift valley of MAR, with zircon crystallization at the final stages, was influenced by aqueous (or aqueous–saline) fluid. Obtained conclusions confirm the fundamental significance of the interaction between hydrothermal and magmatic systems in the slow-spreading mid-ocean ridges. [ABSTRACT FROM AUTHOR]

• Nd-Hf isotope investigation of river clays from the Niger River basin. • Saharan dust accounts for ∼40 ± 20 % of the fine sediment exported by the Niger River. • Wet dust deposition controls regional chemical weathering patterns. • Phosphorus release in soils linked to dissolution of windblown phosphate minerals. Huge amounts of mineral dust are produced in northern Africa, representing the largest source of aerosols worldwide. Transatlantic dust transport is known to fertilize soils as far as in the Amazon Basin. Yet, the influence of Saharan dust on chemical weathering fluxes and associated nutrient release in West Africa remains largely overlooked. To address this issue, we analysed clay fractions (<2 µm) of river sediments (n = 37) from across the Niger River basin - the largest river system in West Africa - using neodymium and hafnium isotope compositions as proxies for provenance (ε Nd) and chemical weathering (Δε Hf CLAY). Compared to previously published data for corresponding sand fractions, measured ε Nd values indicate significant size-dependent decoupling for Nd isotopes in most samples, with ε Nd differences between clay and sand fractions yielding values as great as ∼26 ε-units. Using mixing models, we show that this discrepancy reflects the overwhelming presence in the studied clay fractions of Harmattan dust blown from the Bodélé Depression in Chad, which we estimate to account for about 40 % of the fine-grained sediment load exported to the Gulf of Guinea. Additionally, significant Δε Hf CLAY variability occurs across the Niger catchment, partly explained by the presence of zircon in clay-size fractions, but also by preferential alteration of dust-borne accessory phosphate minerals in the subtropical regions of the watershed. Based on these results, we propose that Saharan dust plays a major role in controlling regional patterns of chemical weathering in West Africa, suggesting that enhanced wet deposition of mineral dust in shield areas dominated by transport-limited weathering regime can result in a large increase in weatherability and associated release of phosphorus. These findings have general implications for the importance of mineral aerosols in controlling sediment yield and the supply of weathering-derived nutrients to continental areas bordering large subtropical deserts worldwide. [ABSTRACT FROM AUTHOR]

Alkaline-silicate complexes host some of the world's largest resources of rare-earth elements and high-field-strength elements (REE & HFSE) and represent the most fractionated magmatic systems on our planet. Geochemical evidence indicates that they are mantle melts, but while various studies highlight a role for lithospheric mantle, we do not know the precise origin of their contained REE and HFSE, and whether enrichment of the mantle source for these magmas can be attributed to specific geodynamic processes or events. We present new Nd-Hf isotope measurements (▪/▪ &▪/▪) made by LA-MC-ICP-MS, as well as a compilation of existing isotopic data for a suite of alkaline igneous rocks from the Gardar Province, a Mesoproterozoic continental rift in southern Greenland. Neodymium and hafnium isotopes are unaffected by crystal fractionation and can directly fingerprint the source of REE and HFSE. The dataset covers both phases of Gardar magmatism (1325–1261 and 1184–1140 Ma) and incorporates mafic dyke swarms and km-scale intrusive complexes, including Ilimmaasaq (Ilímaussaq) and Motzfeldt, which host some of the world's largest REE and HFSE deposits. The majority of Gardar complexes have a narrow range of positive median initial ε Nd (0 to +3.3) and ε Hf values (+0.2 to +6.0). Only two granite intrusions and the Eriksfjord basaltic lavas have crustally contaminated Nd-Hf isotope compositions, with the vast majority of Gardar igneous rocks preserving the isotope signature of their mantle source. Considering the diversity of rock types in the Gardar Province, initial ε Nd - ε Hf compositions are remarkably homogeneous, indicating a derivation of the Gardar's REE and HFSE from a laterally-extensive mantle melt source. Several Gardar systems have low initial ε Hf for a given ε Nd (▪ ε Hf to -9.7), a distinctive signature as few geological processes decouple the Nd and Hf isotope systems. The decoupled Nd-Hf isotope signatures are consistent with contributions from isotopically-matured phlogopite-bearing metasomatic veins (commonly known as PIC: phlogopite-ilmenite-clinopyroxene) in the lithospheric mantle. The metasomatising fluids that formed these source rocks were introduced via Palaeoproterozoic subduction, but the Gardar isotopic signatures indicate that REE and HFSE enrichment of these metasomes was not derived from subducted sediment; instead it is likely that metals were scavenged from the mantle wedge overlying the ancient subduction zone. The Gardar Nd-Hf isotope evolution trends overlap with a global compilation of kimberlites through time and allow us to tie the origin of the PIC metasomes to the regional geodynamic history of South Greenland. We identify PIC metasomes as a key metal source for the Gardar and by extension perhaps other REE-mineralised igneous provinces globally. • Nd Hf isotopes reported for alkaline rocks from REE rich Gardar continental rift. • Negative ▪ ε Hf discounts enrichment of mantle source by subducted sediment. • REE & HFSE derive from isotopically matured metasomatic veins in lithospheric mantle. • Origin of enriched source tied to regional geodynamic history. • Provides conceptual basis for distribution of REE HFSE provinces globally. [ABSTRACT FROM AUTHOR]

The separation of zirconium and hafnium isotopes from the early actinides and rare earth elements (REE) with Eichrom's Pb resin has been studied. Batch studies were performed to characterize the behavior of actinium, thorium, zirconium, hafnium, lutetium, and yttrium on Pb resin from HCl solutions (0.001 M to 11 M). The early actinides and REE had no affinity for the resin at any concentration of HCl, but zirconium and hafnium showed a moderate uptake at high concentrations of HCl with a maximum extraction at 11 M HCl. Several column separations were tested, including with only tracer isotopes and with mass. Rapid, simple separations of zirconium from actinium, thorium, protactinium, and the REE with high yields and low elution volumes are presented with applications for tracer isotope production and fission product separations. The resin is less suitable for hafnium separations as hafnium tends to bleed off the resin even at high concentrations of HCl. [ABSTRACT FROM AUTHOR]

The continental crust that dominates Earth's oldest cratons comprises Eoarchaean to Palaeoarchaean (4.0 to 3.2 Ga) felsic intrusive rocks of the tonalite-trondhjemite-granodiorite (TTG) series. These are found either within high-grade gneiss terranes, which represent Archaean mid-continental crust, or low-grade granite-greenstone belts, which represent relic Archaean upper continental crust. The Palaeoarchaean East Pilbara Terrane (EPT), Pilbara Craton, Western Australia, and the Barberton Granite-Greenstone Belt (BGGB), Kaapvaal Craton, southern Africa, are two of the best exposed granite-greenstone belts. Their striking geological similarities has led to the postulated existence of Vaalbara, a Neoarchaean-Palaeoproterozoic supercraton. Although their respective TTG domes have been compared in terms of a common petrogenetic origin reflecting a volcanic plateau setting, there are important differences in their age, geochemistry, and isotopic profiles. We present new zircon Hf isotope data from five granite domes of the EPT and compare the geochemical and isotopic record of the Palaeoarchaean TTGs from both cratons. Rare >3.5 Ga EPT evolved rocks have juvenile Hf(t) requiring a chondritic source. In contrast, younger TTG domes developed via 3.5 to 3.4 and 3.3 to 3.2 Ga magmatic supersuites with a greater range of Hf(t) towards more depleted and enriched values, trace element signatures requiring an enriched source, and xenocrystic zircons that reflects a mixed source to the TTGs, which variously assimilates packages of older felsic crust and a more juvenile mafic source. EPT TTG domes are composite and record multiple pulses of magmatism. In comparison, BGGB TTGs are less geochemically enriched than those of the EPT and have different age profiles, hosting coeval magmatic units. Hafnium isotopes suggest a predominantly juvenile source to 3.2 Ga northern Barberton TTGs, limited assimilation of older evolved crust in 3.4 Ga southern Barberton TTGs, but significant assimilation of older (Hadean-Eoarchaean) crust in the ca. 3.6 Ga TTGs of the Ancient Gneiss Complex. The foundation of the EPT is younger than that for the oldest components of the Eastern Kaapvaal. Although the broader prevailing Palaeoarchaean geologic framework in which these two cratons formed may reflect similar a geodynamic regime, the superficial similarities in dome structures and stratigraphy of both cratonic terranes is not reflected in their geochemical and age profiles. Both the similarities and the differences between the crustal histories of the two cratons highlights that they are formed from distinct terranes with different ages and individual evolutionary histories. Vaalbara sensu lato represents typical Palaeoarchaean cratonic crust, not in the sense of a single homogeneous craton, but one as diverse as the continents are today. [ABSTRACT FROM AUTHOR]

• First dissolved Nd/Hf isotope and REE data from the Congo River Plume. • High REE and Hf fluxes from the Congo River to the southeast Atlantic. • Conservative river and surface seawater mixing of Nd/Hf isotopes and REEs/Hf at S > 23. • Congo River particles impact intermediate and deep water signals of NE Angola Basin. The Congo River is the second largest river by discharge in the world and a major source of element inputs into the South Atlantic Ocean. Yet, the element fluxes and transport mechanisms across and beyond its estuary and their impacts on the marine distribution and cycling of many major and trace elements are not well understood. We present the first combined dissolved neodymium (Nd) and hafnium (Hf) isotope and rare earth element (REE) concentration distributions following the Congo River plume along its flow path off the West African coast and along a connected offshore latitudinal section at 3°S. The Congo River freshwater itself is characterized by extraordinarily high Nd and Hf concentrations of up to 4000 pmol/kg and 54 pmol/kg, and by Nd (ε Nd) and Hf (ε Hf) isotope compositions that range between −15.6 and −16.4 and between 0.35 and −1.4, respectively. Our near- and offshore data indicate that at salinities above 23 conservative mixing of Congo-derived Nd and Hf concentrations and isotopic signatures with ambient surface seawater occurs for at least 1000 km to the northwest of the river mouth. This demonstrates a large spatial extent of the influence of the Congo plume on trace metal distributions in the eastern south Atlantic surface waters. A comparison between dissolved Nd and Hf fluxes from the Congo River and the shelf zone estimated based on radium isotope compositions indicate that release from Congo-derived particulate phases likely balances strong estuarine REE and Hf removal in the low salinity zone. The combined riverine and shelf zone flux for Nd is almost twice as high as that estimated for the Amazon River, despite that the Amazon discharge is about five times higher than that of the Congo River. Even the offshore Nd flux estimated for the 3 °S transect based on radium isotope compositions still corresponds to ∼40% of the Congo-shelf-zone flux and reaches 150 ± 50 Mg/year for Nd. Moreover, intermediate waters below the plume are strongly affected by exchange with particulate inputs from the Congo River given that Nd isotope signatures are inconsistent with values expected from large-scale water mass mixing and instead support unradiogenic Nd release either from sinking or deposited Congo-derived detrital material. Deep and bottom water isotopic signatures are also slightly affected by interaction with particles and benthic Nd release. [ABSTRACT FROM AUTHOR]

Polycyclic caldera complexes hold clues to understanding why some magmatic systems develop into supersized magma bodies and how they can recover to produce several caldera-forming eruptions. However, the geologic records of the transitions between successive caldera events are very often inaccessible due to limited preservation of eruptive products of inter-caldera activity, prompting the search for alternative archives of magma evolution such as accessory minerals. Here we applied multiple geochemical tools to study one of the most active caldera centres of the Quaternary, the Toba caldera complex in Sumatra (Indonesia), which produced at least four caldera-forming eruptions in the last 1.6 My, including the iconic Youngest Toba Tuff at 74 ka. We combined feldspar 40Ar/39Ar and zircon U–Pb geochronology of proximal pyroclastic deposits with glass and mineral chemistry of both the tuffs and distal marine tephra to revise the eruption chronology of Toba, obtaining new eruption ages of 1417 -31/+14 ka (zircon) or 1339 ± 39/39 ka (plagioclase, internal/full external 2 σ uncertainty) for the Haranggaol Dacite Tuff, 783.81 ± 0.85/1.32 ka (sanidine) for Oldest Toba Tuff, and 503.61 ± 1.36/1.50 ka (sanidine) for Middle Toba Tuff. Isotope dilution thermal ionisation mass spectrometry (ID-TIMS) U–Pb crystallisation ages, trace element contents and Hf isotopic ratios of zircons illuminate changes in the shallow magma reservoir which saw near-continuous zircon crystallisation over 1.6 My. Prolonged build-ups to each eruption with highly scattered zircon trace element compositions reflect a complex, heterogeneous character of the shallow reservoir, without a clear temporal trend or indications of the eruption trigger. In contrast, hafnium isotopes in zircon display a pronounced shift towards unradiogenic values immediately after the OTT caldera collapse, followed by a gradual recovery to a baseline value of ε Hf = -7 at the time of YTT eruption, interpreted as a reflection of the shift in magma reservoir position corresponding to change in the character of assimilated crust. We can show in unprecedented detail how a large caldera collapse affects magma geochemistry; however, identification of patterns in the behaviour of the Toba system and making geochemistry-based predictions about its future development remain a challenge. • 40Ar/39Ar dating and tephra correlations reveal four, not five major Toba eruptions. • Zircon compositions sample a heterogeneous magma reservoir prior to each eruption. • Abrupt shift in zircon ε Hf, bulk 87Sr/86Sr after Oldest Toba Tuff caldera collapse. • Geochemical changes linked to shifting locus of magma accumulation. [ABSTRACT FROM AUTHOR]

The Huashan Group preserves Neoproterozoic volcanic‐sedimentary sequences in the northern Yangtze Block and is an ideal target for determining the provenance and characteristics of Neoproterozoic sedimentary basins and the Precambrian crustal evolution of the Yangtze Block. Here, we report LA‐ICP‐MS detrital zircon U–Pb–Hf isotopes from four metamorphic clastic rock samples in the Huashan Group. Detrital zircons ages yield four major peaks at ca. 2,670, 2,040, 940, and 840 Ma and five subordinate peaks at greater than or equal to ca. 2,850, 2,490, 1,840, 1,600, and 1,240 Ma. The provenance of the Huashan Group includes Archean to mid‐Neoproterozoic magmatic rocks, and reworked sedimentary rocks from the northern Yangtze Block. The Huashan Group was deposited from ca. 830 to 800 Ma and represents sedimentation accompanying the development of a mid‐Neoproterozoic continental rift basin in Yangtze Block associated with the breakup of the Rodinia supercontinent. Hafnium isotope analyses of detrital zircon from the Huashan Group suggest that most crustal growth in the northern Yangtze Block occurred during the Late‐Mesoproterozoic and early to Middle Neoproterozoic and crustal reworking occurred from the Archean to the Neoproterozoic. [ABSTRACT FROM AUTHOR]

Several orogenies have shaped the bedrock of southern Sweden. While mafic intrusions represent significant sources of information for reconstructing geodynamics and crustal evolution, the characterization of the various generations of such intrusions in Sweden remains limited. We report in situ zircon U–Pb ages and Hf isotope data from a Fe-Ti eclogite and a coronitic metagabbro from the Eastern Segment in southern Sweden. Crystallisation ages at 1683 ± 17 Ma of the eclogite suggest affiliation with the surrounding 1730–1660 Ma Transscandinavian Igneous Belt intrusions that dominate the Eastern Segment. Secondary zircon growth and Pb-loss in the eclogite sample at 1459 ± 44 Ma and the crystallisation of the metagabbro at 1431 ± 26 Ma overlap and are related to magmatic activity during the Hallandian orogeny. Zircon Hf isotope signatures with chondritic and sub-chondritic values at ~1683 Ma and ~1431 Ma, respectively, correspond to an enriched (or mildly depleted) source in line with a "Mixed Svecofennian Crustal Reservoir". These isotope signatures are more enriched than those in the surrounding gneisses. Zircon isotope data from the herein analysed zircon grains indicate that the eclogite and metagabbro had an enriched mafic source in the mid to lower crust, or within the subcontinental lithospheric mantle below Fennoscandia. [ABSTRACT FROM AUTHOR]

Archaeological glass contains information about the movement of goods and ancient economies, yet our understanding of critical aspects of the ancient glass industry is fragmentary. During Roman times, distinct glass types produced in coastal regions of Egypt and the Levant used evaporitic soda (natron) mixed with Nile-derived sands. In the Levant, furnaces for producing colourless Roman glass by addition of manganese have been uncovered, whereas the source of the desirable antimony-decolourised Roman glass remains an enigma. In the Edict of Diocletian, this colourless glass is listed as "Alexandrian" referring to Egypt, but its origin has been ambiguous. Previous studies have found overlapping strontium and neodymium isotope ratios for Levantine and Egyptian glass. Here, we confirm these findings and show for the first time, based on glasses from the ancient city of Gerasa, that hafnium (Hf) isotopes are different in Egyptian and Levantine natron glasses, and that Sb Roman glass is Egyptian. Our work illustrates the value of Hf isotopes in provenancing archaeological glass. We attribute the striking difference in Hf isotopes of Egyptian versus Levantine glasses to sorting of zircons in Nile sediments during longshore drift and aeolian transport along the south-eastern Mediterranean coast leaving behind a less juvenile fraction. [ABSTRACT FROM AUTHOR]

In view of the fact that the fast-neutron experimental cross-section data of hafnium which is an important structural material of fusion reactor are few and there are the great differences in their evaluation values, several activation cross sections of (n, 2n), (n, p), (n, a) and (n, n′) reactions on hafnium isotopes have been investigated by neutrons generated from the T(d, n)4He reaction at the K-400 Neutron Generator at China Academy of Engineering Physics (CAEP). The gamma activities of the product nuclei were measured by a high-resolution gamma-ray spectrometer with a coaxial high-purity germanium detector. The 93Nb(n, 2n)92mNb reaction was used as neutron fluence standard, these experimental cross sections of the 174Hf(n, 2n)173Hf, 176Hf(n, 2n)175Hf, 178Hf(n, α)175m+gYb, 178Hf(n, p)178gLu, 178Hf(n, p)178mLu, 180Hf(n, 2n)179m2Hf, 180Hf(n, α)177m+gYb and 180Hf(n, n′)180mHf reactions were obtained in the neutron energy range of 13.5–14.8 MeV. These measured cross sections were discussed and compared with some previous experimental results from the literature and with the evaluation data from ENDF/B-VIII.0, CENDL-3.1, JEFF-3.3 and the theoretical results by using the computer code system Talys-1.9. [ABSTRACT FROM AUTHOR]

Measurements of U–Th–Pb, Lu–Hf and oxygen isotopes as well as selected trace and rare earth elements were carried out on zircon grains from high-grade metasedimentary rocks from the Albany–Fraser Orogen in southwest Australia. Oxygen isotopes from detrital zircon domains yield δ18O (VSMOW) values ranging from 5.8 to 8.0‰ and exhibit coupled Hf- and O-isotope compositions. In contrast, metamorphic zircon domains show considerably less variability in O-isotope compositions with a median δ18O of 5.6 ± 0.5‰ and exhibit decoupled Hf- and O-isotope compositions. 176Hf/177Hf isotope ratios of metamorphic zircon grains are within the evolutionary trend defined by the detrital grains implying negligible input from external sources during their growth. In addition, the relatively low δ18O value of the metamorphic zircons implies crystallisation from a relatively 18O depleted crustal melt. Such δ18O values are lower than those typically observed in most metamorphic zircon, including those preserved in partial melts of metasediments (10–12‰) and suggest that the sedimentary protolith was hydrothermally altered by meteoric fluids prior to high-temperature metamorphism. We suggest that alteration of the sedimentary protolith is related to the proximity to the Fraser Shear Zone, a major crustal scale structure within the orogen, which may represent an old reactivated structure. Occurrences of low δ18O metamorphic zircon, and potentially also low δ18O igneous rocks, in ancient collisional settings may, therefore, delineate long-lived fluid pathways within the crust. [ABSTRACT FROM AUTHOR]

The first ever search for α decays to the first excited state in Yb was performed for six isotopes of hafnium (174, 176, 177, 178, 179, 180) using a high purity Hf sample of natural isotopic abundance with a mass of 179.8 g. For 179 Hf, also α decay to the ground state of 175 Yb was searched for thanks to the β -instability of the daughter nuclide 175 Yb. The measurements were conducted using an ultra-low-background HPGe-detector system located 225 m underground. After 75 days of data taking no decays were detected but lower bounds for the half-lives of the decays were derived on the level of lim T 1 / 2 ∼ 10 15 - 10 18 a. The decay with the shortest half-life based on theoretical calculation is the decay of 174 Hf to the first 2 + 84.3 keV excited level of 170 Yb. The experimental lower bound was found to be T 1 / 2 ≥ 3.3 × 10 15 a. [ABSTRACT FROM AUTHOR]

The U–Pb age and oxygen and hafnium isotope ratios of zircon from rocks of oceanic core complexes along the Mid-Atlantic Ridge have been studied using SHRIMP and MC-LA-ICP-MS techniques. The U–Pb dating revealed four groups of zircon: (1) 0.6–1.7 Ma, (2) 6.7–11.2 Ma, (3) 12.9–17.6 Ma, and (4) ≥ 200 to 2044 Ma. The δ18O values range from 4.74 to 7.2‰ and are distinct for zircon grains of different ages. The hafnium isotope ratio for zircon with an age from 0.6 to 17.6 Ma corresponds or is close to that of the MORB from the Central Atlantic. The oxygen and hafnium isotope compositions of zircon older than 280 Ma correspond to those of the sialic continental crust. The hypothesis of involvement of the ancient "pre-Atlantic" sialic (≥280 Ma) and "old Atlantic" (7–17 Ma) crusts in the generation of the contemporary ("juvenile") oceanic crust during the formation of the slow-spreading Mid-Atlantic Ridge has been proposed. [ABSTRACT FROM AUTHOR]

Mid-heavy nuclei offer unique opportunities to study the collective and single-particle aspects of nuclear structure. This mass regime is a dynamic area where protons and neutrons generally occupy different orbitals, giving rise to complex structures with a wide variety of shapes, shape evolution and shape coexistence. To that end, measurements of nuclear lifetimes and electromagnetic moments (µ,Q) can be invaluable. Recent experimental activities of the NuSTRAP group in Athens have focused on γ-spectroscopy studies employing the RoSPHERE array in Magurele, Romania. In recent studies [1, 2], the neutron-rich 144-146Ba isotopes have exhibited octupole degrees of freedom. Similar questions exist for the lighter 140Ba isotope, which is located at the onset of octupole collectivity. In addition, understanding the structure of heavier, even-even hafnium isotopes requires more data regarding shape coexistence and shape evolution. Preliminary results on lifetimes in this area pave the way to understand dynamical phenomena prior to studying more exotic species in the future. [ABSTRACT FROM AUTHOR]

Coupled oxygen-hafnium isotope and trace element geochemical data were obtained using thirty eight previously dated zircon grains extracted from five mafic to intermediate crustal xenoliths of the Wyoming Craton (Montana, USA). Xenoliths include mid to lower crustal (642–817 °C and 3.5–9.4 kbar) mafic granulites and amphibolites with dominantly Mesoproterozoic (1772–1874 Ma) and minor Paleoproterozoic to Late Archean (2004–2534 Ma) 207Pb/206Pb zircon ages. Zircon oxygen isotope data indicate derivation from melts in equilibrium with a mantle source that interacted with limited supracrustal material (δ18O = 4.4–5.7‰), as well as the incorporation of supracrustal fluids or melts into mantle source regions (δ18O = 6.0–8.1‰). The small within-sample isotopic variability suggests that primary zircon did not exchange with isotopically distinct fluids or melts after initial formation. Initial zircon Hf isotopic values are highly variable across all xenoliths (ε Hf = +3.7 to −17.6), consistent with protolith derivation from mantle sources that incorporated evolved, unradiogenic material or were modified by subduction-related fluids. Within a single granulite xenolith, two zircon types are recognized based on CL imagery, Hf isotopes and U-Pb ages (Type I and Type II). Type I magmatic zircons show dispersed ages (ca. 1700–2534 Ma) and unradiogenic initial Hf (ε Hf = −17.6 to −1.5, 176Hf/177Hf = 0.281074–0.281232). The spread in ages and initial ε Hf , but narrow range in initial 176Hf/177Hf, points to variable Pb loss in response to dissolution-recrystallization of pre-existing zircon. Type II metamorphic zircon yields a younger Proterozoic population (ca. 1700–2155 Ma) with more radiogenic initial Hf relative to Type I zircon (ε Hf = −7.9 to +1.4, 176Hf/177Hf = 0.281427–0.281578); this type represents newly grown metamorphic zircon that formed in the solid-state and incorporated Zr and Hf from pre-existing zircon and silicate matrix/metamorphic phases. REE patterns from all xenoliths are steep and positively sloping without discernible HREE depletion relative to LREE, implying zircon crystallization/recrystallization in the absence of garnet. Negative Eu anomalies signify simultaneous zircon and feldspar crystallization. Solid-state recrystallization may have lead to variations in LREE, Eu and Ce in certain xenoliths. Xenoliths containing magmatic zircon (1834 ± 19 Ma) with mantle-like δ18O (4.4–5.5‰) and radiogenic initial ε Hf (−2.3 to +3.7) likely formed through crystallization of melts derived from a mantle source that incorporated minor amounts of subducted sedimentary/supracrustal material. Proterozoic (1874 ± 8 Ma) xenoliths with elevated δ18O (6.0–7.0‰) and unradiogenic initial ε Hf (−8.2 to −9.6) within magmatic zircon represent melt products of subduction-induced melting and metasomatism of the overlying mantle wedge in the vicinity of the northern GFTZ. Older (ca. 2534 Ma) xenoliths containing zircons with elevated δ18O (6.4–7.2‰) and unradiogenic ε Hf (up to −17.6) represent crystallization of protolith magmas extracted from a mantle source metasomatized by subduction-derived fluids and melts in the Late Archean or earlier. Zircon geochronology and isotope systematics within Mesoproterozoic xenoliths support a model of ocean-closure and subsequent continental collision between the Medicine Hat Block and Wyoming Craton, resulting in the formation of subduction-related melts at ca. 1834–1874 Ma, followed by ca. 1770 Ma collision-related metamorphism thereafter. • Zircon from crustal xenoliths of the Wyoming Craton was investigated using Hf, O and REE isotopic analyses. • Mantle-like δ18O (4.4–5.7‰) and radiogenic εHf (−2.3 to +3.7) in zircon imply mantle-derived protolith magmas. • Elevated zircon δ18O (6–8‰) and unradiogenic εHf (−8.2 to −9.6) are products of subduction-related mantle metasomatism. • Data are consistent with ocean-closure between the Medicine Hat Block and Wyoming Craton at ca. 1.8 Ga. • Collisional metamorphism at ca. 1.7 Ga may recrystallize xenoliths to amphibolite/granulite facies. [ABSTRACT FROM AUTHOR]

Here, a two‐stage column separation scheme is developed for the concomitant isolation of Sr, Pb, Nd, and Hf from geological samples. The first column, which consists of three resin layers (AG50W‐X8 ion exchange resin + Ln specific resin + Sr specific resin), separates the high field strength element + rare earth element, Sr and Pb from the matrices. Subsequently, Nd and Hf are further separated from the high field strength element + rare earth element fraction on the second column using 1 mL of Ln specific resin. The two‐stage column process can be completed within about seven and a half hours for a batch of samples (20–30). The separated Sr fraction was ready for isotope ratio measurements by thermal ionization mass spectrometry. The Pb, Nd, and Hf fractions were converted to nitrate prior to isotopic analyses by multi‐collector inductively coupled plasma mass spectrometry. The feasibility of this new procedure is confirmed by the analyses of four international rock standards (BCR‐2, AGV‐2, BHVO‐2, and JB‐3), which yielded isotope ratios that were in good agreement with other published data. [ABSTRACT FROM AUTHOR]

The timing for the onset of plate tectonics, along with the secular changes in the tectonic settings of continental crust formation, continue to be debated. Recent interpretations based on the increase in zircon 176Hf/177Hf ratios at the time of crystallisation (expressed as εHf (t) with respect to chondritic evolution) have been used to ascertain changes in geodynamic settings in the early Earth, specifically in the 3.8–3.6 Ga interval. This increase is widely interpreted as a change in magma generation, from source(s) dominated by ancient crust to source(s) dominated by juvenile inputs from the mantle. At issue, Hf isotope variations remain limited in the early Earth due to the long decay of the Lu Hf system. This feature, along with the scarcity of rocks and minerals of Eo/Mesoarchaean and Hadean ages, generate large uncertainties over the nature and the timing of the interactions between mantle and crustal reservoirs. The distinction between mantle and crustal sources becomes much clearer in the Palaeoproterozoic, and the study of ancient terranes with several billion years of protracted crustal evolution may hold the key to unlock complex mantle–crust interactions. Here we investigate high-grade metamorphic rocks from the Anabar shield, which contain zircons that crystallised between the Eoarchaean (oldest core at 3814 ± 16 Ma) and the Palaeoproterozoic (youngest core at 2251 ± 15 Ma and youngest rim at 1910 ± 21 Ma). The combination of in situ U Pb and Hf isotope analyses in zircon indicates the formation of the continental crust in the Siberian Craton in the Eoarchaean, and a conspicuous metamorphic event at 2.0–1.9 Ga. We demonstrate that 2.0–1.9 Ga zircon ages reflect recrystallisation processes under subsolidus conditions, involving the breakdown of high-Lu/Hf minerals (i.e. garnet and pyroxene). The εHf (t) shift at 2.0–1.9 Ga towards more radiogenic values may not be related to a change in magmatic style and sources, but rather to resetting of the Lu Hf system in response to heating and metamorphic reactions on a mineral scale. Our findings challenge the widely-evoked mechanism of changes in tectonic style and magma sources to account for vertical arrays in the εHf (t) versus crystallisation age space. This calls for considering alternative options, including those based on petrographic data, when interpreting Hf isotope variations in the Hadean/Archaean detrital zircon record. [Display omitted] • Evidence for the oldest crust formation in the Siberian Craton at ∼3.8 Ga. • Hf isotope data show two main evolution stages of the Anabar shield: i) decreasing εHf (t) (0 to −15) from 3.5 to 2.0 Ga; and ii) a large εHf (t) variation (−25 to 10) at ∼1.9 Ga. • The breakdown of high-Lu/Hf minerals during high-grade metamorphism releases radiogenic Hf, which is incorporated into new or recrystalised zircon to produce a large εHf (t) range. • Metamorphic breakdown reactions are a complementary mechanism for 'vertical shifts' in εHf (t) , typically attributed to mixing of ancient crust and mantle-derived magmas. • Changes in geodynamic settings in the early Earth are not necessarily a direct cause of abrupt shifts in εHf (t) in detrital zircon datasets. [ABSTRACT FROM AUTHOR]

• The maximum depositional age of the Suoi Chieng Formation is 1769 Ma. • The U-Pb age and Hf isotopes indicate sources originate from local basement rocks and the Rae craton of North Laurentia. • Distinct crustal evolutionary histories for the SW Yangtze and N Yangtze before their assembly in the late Paleoproterozoic. • The Yangtze Block was situated between southern Siberia and northern Laurentia within Nuna supercontinent. New U-Pb ages and Hf isotopic data for detrital zircons from the late Paleoproterozoic sedimentary rocks (Suoi Chieng Formation) in the Phan Si Pan Zone of northwest Vietnam constrain their depositional ages, provenance, and tectonic setting. The weighted average age of the youngest coherent zircon population is 1769 ± 31 Ma (MSWD = 1.3, n = 8), which provides a maximum depositional age for the Suoi Chieng Formation. The detrital zircons obtained from six Paleoproterozoic samples exhibit various ages, showing multiple magmatic and metamorphic events. The detrital zircon age pattern shows that magmatic activities in the source areas occurred at 2650 Ma, 2350–2150 Ma, and 2050 Ma, as well as minor activities at 2850 Ma, 1850 Ma, and 1780 Ma. Additionally, a prominent metamorphic age peak is observed around ca. 1850 Ma, while a few metamorphic zircons exhibit ages ranging from 2600 to 2500 Ma and 2100 Ma. This pattern indicates that the primary source of these zircons is the local basement rocks of the Phan Si Pan Zone and SW Yangtze. However, contributions from other adjoining cratonic blocks are also possible and these likely included the Rae craton of North Laurentia. Our new data verifies and expands earlier results, showing that the SW Yangtze and north Yangtze have distinct Archean-Paleoproterozoic crustal evolutionary histories prior to their assembly in the late Paleoproterozoic. Regional correlations based on detrital zircon spectra, stratigraphic and tectono-thermal histories show strong similarities between the SW Yangtze and the Rae craton of north Laurentia throughout the Paleoproterozoic, suggesting the proximity of the two blocks before or during the formation of the Nuna supercontinent. We further suggest that the north Yangtze adjoined southern Siberia in the Archean to late Paleoproterozoic as supported by their identical tectono-thermal histories and detrital zircon age spectra. In combination with published data, we propose that the Yangtze Block was located between north Laurentia and south Siberia during the Nuna assembly. [ABSTRACT FROM AUTHOR]

• A combined submarine hydrothermal and terrigenous sources for REY and iron to Late Neoarchean ambient seawater. • A continent-derived riverine flux being the main source of silica to ambient seawater at Neoarchean. • Decoupled Nd and Hf isotopes in BIFs suggest terrestrial weathering had significant effects on oceanic geochemistry at the Neoarchean eon. • A weak to moderate chemical weathering conditions for Neoarchean continents. We here present trace element and coupled Sm-Nd and Lu-Hf isotope data for both pure and detritus-rich BIF samples collected from the ∼2.51 Ga Zhalanzhangzi BIF, North China Craton to investigate sources of BIF-forming materials to the ambient seawater, and to evaluate factors controlling the decoupling of Hf and Nd isotope systems in Late Neoarchean seawater. Both pure and detritus-rich BIFs exhibit positive Eu anomalies, positive correlation between ε Nd(2.51Ga) values and Fe 2 O 3 contents, and moderate negative to positive ε Nd(2.51Ga) values, revealing a combined submarine hydrothermal and terrigenous sources for REY and iron to ambient seawater. Instead of interpreting the correlation between Ge/Si ratio and iron (or silica) content of BIFs as the mixing of hydrothermal and terrigenous sources of silica, we preferred a terrigenous source for silica to Neoarchean seawater. Moreover, by compiling published Ge/Si data, we argue that although hydrothermal fluids might be the dominant source of silica to early Archean oceans, a continent-derived riverine flux was expected to be the main source of silica to ambient seawater, following the substantial increase in land mass during Neoarchean. The ε Nd(2.51Ga) and ε Hf(2.51Ga) values of pure BIFs reveal decoupling of Nd and Hf isotopes in ambient seawater, and suggest that incongruent terrestrial weathering had significant effects on oceanic geochemistry at the end of Archean eon. In addition, based on the observation that Neoarchean seawater was characterized by more radiogenic ε Hf values when compared to its modern counterpart, we posit a weak to moderate chemical weathering conditions for Neoarchean continents. [ABSTRACT FROM AUTHOR]

Eoarchean peridotite enclaves found in southern West Greenland's Itsaq Gneiss Complex (IGC) represent an important and valuable record of Earth's early geodynamic history. However, the origins of these rocks and the processes acting on them in the Eoarchean remain a subject of debate. Some researchers have proposed that these peridotites represent the oldest preserved pieces of Earth's mantle, while others have suggested that they represent ultramafic cumulates. Similarly, the geodynamic context in which they formed and were emplaced is subject to multiple interpretations. Some researchers argue that only vertical tectonic processes operated in the Eoarchean and others contend that these peridotites were embedded in the crust by horizontal tectonic processes. We present multiple sulfur isotope data from IGC peridotite enclaves, offering new insights into these rocks' origins and tectonic processes in the early Earth. Generally small but significant nonzero Δ33S values of 0.04 to 0.21‰ were detected in the studied peridotites. Peridotites with almost no petrographic signs of metasomatic alteration have on average slightly higher Δ33S values, whereas peridotites with clear petrographic and geochemical signatures of melt metasomatism were found to have slightly lower Δ33S values. These Δ33S values point to incorporation of surface-derived material of Archean age or older. Correlations between Δ33S values and previously published major and trace element data support the view that these peridotites were subject to hydrous melt depletion of incompatible elements, followed by variable melt re-enrichment. Notably, a distinct correlation also exists between previously published Hf isotope data and Δ33S values, indicating a depleted mantle source for melt percolating through the peridotites in the Eoarchean. The sulfur isotope data demonstrate that these processes included the introduction of surface-derived sulfur, pointing to an early onset of crustal recycling. These findings point to the existence of depleted mantle domains in the Hadean and suggest that crustal recycling processes operated during the Eoarchean or earlier. • 3.81 Ga peridotites from southern West Greenland contain a MIF-S signal • Sulfur isotope values indicate incorporation of surface-derived S in the Archean • Sulfide minerals crosscut by amphiboles show that sulfides predate metamorphism • Correlation between εHf and Δ33S values indicate mantle depletion and re-enrichment • This is evidence for Eoarchean recycling of surface material into the mantle [ABSTRACT FROM AUTHOR]

This study evaluates for the first time Hf-isotope characteristics of zircon from dunite of the Kondyor massif, which is closely related to an economic platinum placer deposit. The significant range in εHf(t) values (from –8.4 ± 0.8 to 10.5 ± 1.3) in Mesozoic zircons indicates the interaction of a "juvenile" mantle source (εHf(t) = +15) with distinct magma sources, equivalent to a subcontinental lithospheric mantle and/or a continental crust. The peculiarities of the Hf-isotopic composition of Precambrian zircons (εHf(t) from –2.3 to +0.3) is consistent with their xenogenic origin and inheritance from basement rocks of the Siberian Craton. [ABSTRACT FROM AUTHOR]

Megacrystic zircon grains from alkaline basaltic fields are rare but can provide fundamental insights into mantle metasomatic processes. Here, we report in-situ U-Pb ages, trace element concentrations and hafnium and oxygen isotopes for fourteen zircon megacrysts from two intraplate alkaline basalt locations in New Zealand. U-Pb ages indicate the zircons crystallised between 12.1 and 19.8 Ma. Zircon oxygen isotopic compositions range from low to mantle-like compositions (grain average δ18O = 3.8–5.1‰). Hafnium isotopes (εHf (t) = +3.3 to +10.4) mostly overlap with intraplate mafic rocks and clinopyroxene in metasomatized peridotitic mantle xenoliths but show no correlation with most trace element parameters or oxygen isotopes. The zircons are interpreted to have formed by the reaction between low-degree melts derived from pre-existing mantle metasomes and the depleted mantle lithosphere prior to eruption and transport to the surface. The low Hf concentration, an absence of Eu anomalies, and elevated U/Yb compared to Nb/Yb in the megacrystic zircons are interpreted to show that the source metasomes comprised subduction- and carbonatite-metasomatised lithospheric mantle. As these trace element characteristics are common for megacrystic zircon in intra-plate basaltic fields globally, they suggest the prevalence of subduction- and carbonatite-metsasomatised mantle under these intraplate volcanic regions. The unusually low δ18O was likely present prior to metasomatic enrichment and may have resulted from high-temperature hydrothermal alteration during initial mantle lithosphere formation at a mid ocean ridge or, possibly, during subduction-related processes associated with continent formation. The combination of proportionally varied contributions from carbonatite- and subduction-metasomatised lithospheric melts with asthenospheric melts may explain the variety of primitive intraplate basalt compositions, including low δ18O reported for some local intraplate lavas. [ABSTRACT FROM AUTHOR]

Abstract We report a Hf isotope investigation of zircons from four Eoarchaean orthogneisses from the Godthåbsfjord region of southern West Greenland by laser ablation MC-ICPMS, to elucidate crust-mantle differentiation processes in the early Earth. Zircon crystals of all samples record a complex, multi-stage growth and disturbance history, and these discrete growth phases also exhibit disparate Lu-Hf isotope systematics. The oldest (3.84–3.82 Ga) zircon cores have tightly clustered 176Hf/177Hf ratios that are consistent with derivation of their tonalitic precursors from chondritic mantle at this time, with no evidence of input from older crustal or depleted mantle sources. Younger (3.67–3.62 Ga) zircon overgrowths have subchondritic Hf and plausibly grew from small fraction partial melts of the tonalitic host, involving variable dissolution of the older zircon cores. The Neoarchean (ca. 2.7 Ga) zircon component in some samples extends to significantly higher 176Hf/177Hf than the >3.65 Ga zircon, a feature that is interpreted to reflect addition of radiogenic Hf from the rock matrix during metamorphic zircon growth and recrystallisation at 2.7 Ga. The strongly positive ε Hf (3.82 Ga) values obtained by dissolution of GGU110999 zircons are interpreted to be an artifact of calculating ε Hf values at ages that are too old, and also from the inclusion of radiogenic younger domains in the analysed multi-grain fractions, rather than to a contribution from depleted Eoarchean mantle. Such data – from zircon grains with multiple age and isotopic components – should not be used to define the evolution of crust-mantle reservoirs. A re-interpretation of the existing Pb isotope data, incorporating the new Hf isotope constraints, posits that the protoliths to the Godthåbsfjörd gneisses were influenced by radiogenic Pb introduced as a fluid mobile component during recycling of a high-μ stagnant basaltic lid at ≥3.8 Ga. The destruction of this mafic protocrust, with attendant fluid release into chondritic mantle, may have been instrumental for the generation of stable Eoarchean tonalitic crust from ca. 3.8 Ga. [ABSTRACT FROM AUTHOR]

Abstract The Yizuomao area, located in the south segment of Lesser Xing'an Range–Zhangguangcai Range, is an important part of ore-concentrated area in the east of Ha'erbin. The Yizuomao Complex comprises medium- to coarse-grained, medium- to fine-grained and fine-grained biotite-bearing alkali feldspar granite, and the results show 206Pb/238U ages of 195.3 ± 1.8 Ma, 200.6 ± 3.2 Ma and 205.2 ± 4.1 Ma, respectively. The geological characteristics for these deposits indicate that a genetic link between the emplacement of granite porphyries and skarn-type mineralization. The ages of regional mineralization and crystallization of the granite porphyrie suggest that skarn mineralization in the Yizuomao area occurred during the late Early–early Middle Jurassic. The Yizuomao Complex and associated granite porphyries have similar characteristics, as both comprise high–K calc–alkaline rocks containing high concentrations of SiO 2 and K 2 O + Na 2 O, and low concentrations of Ti, Fe, Mn and Ca. The magmatic rocks are depleted in Ba, Nb, Sr, and Ti, and enriched in Rb, Th, U, K and Pb, and have high Rb/Sr ratios, characteristic of highly fractionated I-type granites. Moreover, all display positive ε Hf (t) values from +5.6 to +14.3, and young zircon Hf single-stage and two-stage model ages, suggesting a significant contribution of juvenile material. Based on the geochronology, geochemistry and Hf isotopic data, we suggest that the Yizuomao Complex and associated granite porphyries were derived from partial melting of juvenile crust. The Yizuomao Complex was emplaced in the transformation period from the post-collision extension of the NCC and the Jiamusi-Khanka Massif to the subduction of Paleo-Pacific Plate. The granite porphyries that are intimately associated with the mineralization were the result of magmatic activity along an active continental margin related to subduction of the Paleo-Pacific Plate. Graphical abstract Unlabelled Image Highlights • There is a genetic link between the emplacement of granite porphyry and skarn-type mineralization. • The skarn mineralization in the Yizuomao area occurred in the Early to Middle Jurassic. • The Yizuomao Complex and associated granite porphyry were derived from partial melting of juvenile crust. [ABSTRACT FROM AUTHOR]

Highlights • Supercontinents assemble alternatively through introversion and extroversion mechanisms. • Only an extroversion supercontinent assembly leads to the formation of a new subduction girdle and a complete reorganization of mantle structure. • The ca. 600 Myr supercontinent cycle is modulated by a longer superocean cycle. Abstract The supercontinent cycle of episodic assembly and breakup of almost all continents on Earth is commonly considered the longest period variation to affect mantle convection. However, global zircon Hf isotopic signatures and seawater Sr isotope ratios suggest the existence of a longer-term variation trend that is twice the duration of the supercontinent cycle. Here we propose that since ∼2 billion years ago the superocean surrounding a supercontinent, as well as the circum-supercontinent subduction girdle, survive every second supercontinent cycle. This interpretation is in agreement with global palaeogeography and is supported by variations in passive margin, orogen, and mineral deposit records that each exhibits both ∼500–700 million years periodic signal and a 1000–1500 million years variation trend. We suggest that the supercontinent cycle is modulated by an assembly that alternates between dominantly extroversion after a more complete breakup, and dominantly introversion after an incomplete breakup of the previous supercontinent. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • P-T conditions of 650–730 °C/5.8–9.1 kbar from the MQC and 680–770 °C/6.0–7.7 kbar from the JFC. • The 2.67–2.61 Ga magma of the MQC sourced from 3.82 to 3.42 Ga crustal components. • 2.38 Ga and 2.05–1.96 Ga arc magma of the JFC sourced from ∼3.45 Ga crust and juvenile components. • Ca. 600 Ma continental arc magmatism of the JFC sourced from recycled ancient crustal components. • 590–560 Ma high-grade metamorphism by the collision of the Congo and São Francisco Cratons. Abstract The Mantiqueira and the Juiz de Fora Complexes (MQC and JFC) in the Araçuaí-Ribeira orogenic system, southeastern Brazil, have been regarded as parts of the Neoproterozoic to Cambrian Brasiliano Orogeny formed by a series of collisions of the São Francisco and the Congo Cratons. Here we report new petrological, geochemical, and zircon U-Pb and Lu-Hf isotopic data on felsic to mafic orthogneisses from the complexes with a view to evaluate the timing and P-T conditions of the collisional event as well as protolith formation. Metamorphic P-T estimates for orthogneisses indicate amphibolite-facies conditions of 650–730 °C and 5.8–9.1 kbar from the MQC, whereas slightly higher (upper amphibolite- to lower granulite-facies) conditions of 680–770 °C and 6.0–7.7 kbar were obtained from the JFC. Geochemical, zircon U-Pb geochronological, and Lu-Hf isotopic data of felsic orthogneisses indicate that the MQC was formed by a series of Neoarchean (ca. 2.67 and 2.61 Ga) volcanic arc magmatisms with magma sourced from Eoarchean to Paleoarchean (ca. 3.82–3.42 Ga) crustal components. In contrast, slightly younger U-Pb ages of ca. 2380 Ma and ca. 2050–1960 Ma were obtained from the JFC marking the timing of volcanic arc magmatism as Early to Middle Paleoproterozoic, with magma sourced from Paleoarchean (∼3.45 Ga) crust with addition of juvenile crustal components. The recycled ancient crustal components were also supplied for late Neoproterozoic (ca. 600 Ma) continental arc magmatism of the JFC. The high-grade metamorphism is possibly related to the final collision of the Congo and São Francisco Cratons at 590–560 Ma, which broadly compares with the formation of the Kuunga Orogen. [ABSTRACT FROM AUTHOR]

Abstract Volcanic activity around the time of the Permian-Triassic boundary (PTB) has been proposed as a trigger for the associated biocrisis. Multiple claystone beds are prominent near the PTB sections in South China. Twenty one PTB ash beds from three sections at Shangsi, Jianshi and Meishan in South China were sampled and analyzed. Volcanic ash geochemistry indicate dacite and rhyolite compositions. Zircons from the ash layers yield comparatively low Nb/Hf and high Th/Nb ratios, falling in the range of arc/orogenic-related settings. Zircon Hf-isotope compositions show that ε Hf (t) values vary from −11.7 to 1.8, indicating involvement of both juvenile and ancient crustal components. The ash beds (SS27a, JS129, JS130, JS133,MS25, MS26) near the biotic extinction horizon display a large variation in ε Hf (t) and relatively positive average values, indicating input of juvenile mantle or crust, and implying rapid transit through the older basement of the South China Craton. Spatial and temporal distribution of ash beds from thirty one PTB sections worldwide reveal that volcanic ash beds occur mainly in, or proximal to, the Tethys region and were sourced locally. Integration of Hf-isotope and trace-element compositions from magmatic zircons suggests that the PTB volcanism occurred along the convergent continent margin in, or near, southwestern South China as a result of the closure of the Paleo-Tethys Ocean. Highlights • Volcanic ash beds covering the PTB in South China were derived from felsic magma emplaced into continental crust. • Volcanic ashes formed in a magmatic arc associated with subduction of Tethyan oceanic lithosphere and assembly of Asia. • Ash beds near the extinction horizon show increased input of juvenile mantle material. [ABSTRACT FROM AUTHOR]

Abstract The amalgamation of five Paleo- to Mesoarchean protocontinent blocks [Singhbhum, Bastar, Dharwar, Aravalli and Bundelkhand] resulted in the present-day tectonic configuration of India. The Dongargarh Supergroup is a major volcano-sedimentary sequence in the Bastar craton, central India. For nearly six decades, it was presumed that the extensive lava pile in the Dongargarh Supergroup has accumulated over a protracted duration of magmatic eruptions spanning from early Paleoproterozoic (~2462 Ma) to mid-Mesoproterozoic (~1367 Ma). However, in the absence of any age information, this time-window remained speculative. The detrital zircon U-Pb depositional ages acquired for the three intercalated sedimentary units do not provide any such evidence of significantly prolonged magmatism in the Dongargarh Supergroup. The close proximity between the depositional ages and the similarities between the geochemical attributes of the basalts in the four volcanic formations [Pitapani, Sitagota, Mangikhuta and Kotima] of the Dongargarh Supergroup, suggest contemporaneous evolution spanning few tens of million years around ca. 2.5 Ga. The negative initial εNd (t =2.5 Ga) isotopic compositions in the bulk-rock basalt samples of Pitapani (−0.36 to +0.41) and Mangikhuta (−0.62 to −0.49) suggest interaction with ~3.5 Ga continental crust in the Bastar craton. On the contrary, near chondritic to positive initial εNd (t =2.5 Ga) isotopic compositions in the Kotima (+0.01 to +0.92) and Sitagota (+1.75 to +2.24) basalts are inconsistent with any significant crustal assimilation. Overall, the initial εHf (t =2.5 Ga) isotopic compositions in the four volcanic formations are positive and range from +0.31 to +6.26, which is consistent with their generation from juvenile mantle sources. On the basis of Nb concentrations and rare earth element systematics, the basalts in the Dongargarh Supergroup can be subdivided into two geochemical groups comprising of Sitagota + Kotima with Nb < 4.5 ppm, and Pitapani + Mangikhuta with Nb > 4.5 ppm. The Zr/Nb and Nb/Yb systematics in these basalts suggest that their mantle sources were relatively fertile and enriched in high field strength elements, which is comparable to the source region of mid-oceanic ridge basalts, and basalts that are generated in the back-arc basins. Collectively, the Dongargarh basalts exhibit negative Nb and Ti anomalies on a primitive mantle normalized incompatible trace element variation diagram. The geochemical signatures in combination with the initial isotopic compositions in these basalts are inconsistent with their origin in a continental-rift setting, or from a mantle plume, as hypothesised by the previous evolutionary models proposed for the Dongargarh Supergroup. Moreover, it cannot be attributed to crustal assimilation sensu stricto. Instead, we interpret the evolution of the volcanic sequences in the Dongargarh Supergroup by the subduction of an oceanic spreading ridge beneath the continental lithosphere, presumably in a back-arc or marginal sea basin that has witnessed contemporaneous sedimentation, which led to the development of an Andean-type magmatic arc around ca. 2.5 Ga in the Bastar craton, central India. Highlights • We report detrital zircon U-Pb ages for the intercalated sedimentary units. • We report εHf (t = 2.5 Ga) and εNd (t = 2.5 Ga) in thirty-three bulk-rock basalt samples. • Magmatism and sedimentation were apparently contemporaneous. • Isotopic signatures and geochemical attributes are consistent with an arc setting. • Dongargarh volcano-sedimentary Supergroup represents an Andean-type arc. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Seamount basalts in the SCS show that they have variably mixed sources with depleted and enriched mantle. • The enriched mantle components may be originated from the Hainan mantle plume. • A model has been presented for indicating the Cenozoic tectonic evolution of the SCS region. Abstract Post-spreading intraplate volcanism has widely affected the South China Sea (SCS) region including Indochina, the northern margin of the SCS, and the SCS basin itself. In the SCS basin, several off- and on-fossil spreading center seamounts formed between 3.8 and 7.9 Ma. Based on previously published geochemical and Sr-Nd-Pb isotopic data, the intraplate volcanism is widely related to the Hainan mantle plume, whose existence has been evidenced by recent geophysical studies. To test this petrogenetic model, new Hf isotope data have been obtained from volcanic rocks from a suite of compositionally representative seamounts in the SCS basin. Compared to published Nd isotope ratios (0.512675–0.512965, 5 εNd units), 176Hf/177Hf ratios span a much larger range (0.282876–0.283097, 8 εHf units), even within individual seamounts (e.g., Zhangzhong seamount). These features, combined with previous studies, clearly confirm mantle heterogeneity beneath the SCS region. Similar to the trends in Sr-Nd-Pb isotope space, Nd-Hf isotope ratio show a relatively narrow, elongate mixing trend between a depleted Indian MORB-type mantle endmember and an enriched EMII-type mantle end member. We propose that this narrow trend is inconsistent with the origin of the enriched end member from a heterogeneous sub-continental lithospheric mantle (SCLM) and instead suggests a plume-related origin. As a conceptual model for the post-spreading tectonic scenario of the Hainan plume affecting the SCS region, we propose that a plume ascends to the bottom of the lithosphere beneath Hainan and its northern Leizhou peninsula at the northern margin of SCS, from where it migrates along sloping rheologic boundary layers to lithospheric faults under an extensional setting towards the central SCS where the magmas erupt at the young spreading centers. [ABSTRACT FROM AUTHOR]

Piaoac granites exposed in the Cao Bang region, northern Vietnam, are S-type granite, which are associated with W-Sn-Mo-Be-F mineralization. Zircon U-Pb ages, major and trace elements, mineral chemical and Hf isotopic compositions of the W-Sn-bearing granites from the Piaoac District have been investigated in detail. LA-ICP-MS U-Pb dating of zircon grains from these granites yielded ages of 82.5±2.3 and 82±1.8 Ma, representing an episode of Late Cretaceous magmatic event. These granites are characterized by high peraluminous and have typical S-type geochemical signatures with high SiO2 (72.37 wt.%-73.07 wt.%), high A/CNK values (1.61-1.65) and Аl2О3 (14.4 wt.%-15 wt.%). They are enriched in Rb, U, K, Th, Ta and Pb and display pronounced negative Ba, Sr, Nb, Ti and Eu (Eu/Eu*=0.19-0.24) anomalies. The high degree of fractional crystallization is characterized by low Rb, Sr, Ba and Eu concentrations with high ratios of La/Sm and Eu/Eu*. Zircon grains show εHf(t) values from -9.69 to -0.9 and the corresponding TDm2 range from 1.2 to 1.7 Ga, indicating that these granites could be derived from the Proterozoic basement rocks with minor input from mantle-derived magmas. The calculation of Fe3+ and Fe2+ of biotites indicates a low oxygen fugacity condition (log fO2 ranging from 10-17 to 10-18 bars, below MH), which is favorable for the W-Sn mineralization. Tungsten and tin have been enriched in granitic magmas through fractionation, and low oxygen fugacity conditions have promoted the accumulation and transportation of W-Sn in the hydrothermal fluids, leading to deposition of mineral phases. The geochemical data suggest that Piaoac granites formed in an extensional setting related with the Late Cretaceous magmatism occurring large-scale lithospheric extensional in South China Block. [ABSTRACT FROM AUTHOR]

The Truong Son metallogenic belt in central Laos and Vietnam is an important Fe-Cu-Sn-Au polymetallic ore district. The Pha Lek Fe deposit is closely related to Late Carboniferous- Early Permian I-type granitic magmatism, and contains >50 Mt @ 45% to 50% of Fe ore. Ore minerals occur mainly as magnetite and hematite in the skarn alteration zone between a granitic pluton and metamorphosed Middle-Upper Devonian carbonates. The granitic pluton comprises granodiorite and granite, with zircon U-Pb dating indicating synchronous emplacement at 288.2±1.3 and 284.9±1.2 Ma, respectively. Zircons from these granitoids have εHf(t) values of 2.9-11.2 and relatively young TDM2 ages (<1.0 Ga), indicating an origin by partial melting of depleted mafic crust or magma mixing. Previous studies have shown that these granitoids have high Y, Yb, and K2O contents, and low Sr and Na2O contents, which are interpreted as the melting of mafic continental crust. Pyrite of the main mineralization stage yields an 187Re/188Os-187Os/188Os isochron age of 287±17 Ma, indicating that mineralization is associated with Pha Lek granitic magmatism. A Late Carboniferous-Early Permian subduction-related skarn-type Fe mineralization model is proposed for the Pha Lek deposit. More evidence is needed to verify a hypothesis of volcanic overprinting during Late Triassic post-collisional extension. [ABSTRACT FROM AUTHOR]

Abstract The effect of hafnium on the microstructure of as-hot isostatically pressed nickel-based powder metallurgy superalloy FGH4097 has been investigated. It is shown that when adding 0.3 wt.% hafnium, the statistical annealing twin boundary length fraction of the hafnium-free superalloy decreases from 0.35 ± 0.01 to 0.30 ± 0.01 and its interaction events of annealing twins are considerably reduced. The main reason is found to be the increase of MC (where M = metal atom) carbide density caused by micro-addition of hafnium, which could effectively lower the annealing twin nucleation probability and impede its growth into grains by retarding the movement of Shockley dislocation in the end of non-coherent twin boundary. Graphical abstract Image 1 Highlights • Effect of Hf on annealing twin formation in a nickel-based superalloy was studied. • With adding 0.3 wt.% hafnium, the annealing twin boundary fraction is decreased. • Minor addition of hafnium yields increased amounts of MC carbides. • MC carbides could effectively lower the annealing twin nucleation probability. • MC carbides could effectively impede the growth of annealing twin into grains. [ABSTRACT FROM AUTHOR]