Arc magmatism plays a critical role in continental crustal growth and the formation of significant metal deposits, including granite-related tin (Sn) systems. However, the mechanisms governing Sn transport and isotopic fractionation at convergent margins remain poorly constrained due to a lack of systematic studies across spatial variations (arc-front to rear-arc) and magmatic-hydrothermal transitions. In this study, we present high-precision Sn isotopic data for lavas, pumices, and hydrothermal products from Whakaari (arc-front) and Taranaki (rear-arc) in the Kermadec system, alongside magmatic H2O concentrations estimated from clinopyroxene. Whakaari lavas exhibit significant variation (δ122/118Sn = –0.241‰ to 0.361‰). The heaviest values are attributed to extensive shallow degassing (>40%), with Rayleigh modeling indicating the preferential partitioning of light Sn isotopes into the vapor phase—a process corroborated by low magmatic water contents (avg. 0.83 wt.%). In contrast, Taranaki samples show limited variation (δ122/118Sn = 0.124 to 0.235‰). While amphibole and titanomagnetite fractionation may lower bulk-rock values, these processes cannot explain why both volcanoes are isotopically lighter than MORB (0.367 ± 0.087‰).We propose that this light Sn signature originates from the subducted slab. Simulations suggest that the addition of 5–20% reduced, Cl-rich fluids derived from altered oceanic crust (AOC) can effectively lower arc magma δ122/118Sn. Regardless of the specific redox mechanism, slab-derived fluids dominate the Sn budget of the mantle wedge and the resulting arc magmas. Our results suggest that widespread light Sn isotope signatures serve as a diagnostic feature of fluid-mediated mass transfer in subduction zones. By combining spatial variations from arc-front to rear-arc, this study provides a robust geochemical framework to decipher slab-mantle interactions and the dynamic cycling of metals at convergent margins.

The identification of subducted materials and the mechanisms by which they were transported into the mantle wedge remain incompletely understood. To address this issue, we here present zinc (Zn) isotopic compositions, integrated with major-trace elements and radiogenic isotopes, for 22 lava samples from seven Lesser Antilles island arcs and 50 marine sediment samples from the Deep Sea Drilling Project (DSDP) Sites 543 and 144. Sediments display significant Zn isotopic variations (delta 66Zn = - 0.15 %o to 0.50 %o). Their delta 66Zn values positively correlate with CaO/TiO2 ratios and negatively correlate with Rb/Sr ratios, suggesting that sediment mineralogy predominantly dominates the Zn isotopic variations. Clay-rich sediments from Site 543 show relatively light Zn isotopic compositions with delta 66Zn (-0.15 %o to 0.22 %o) negatively correlating with weathering indices (e.g., MgO/Na2O and CIW) but positively with Zn contents, indicating that the Zn isotopic variations most likely result from chemical weathering. In contrast, carbonate-rich sediments from Site 144 have relatively high delta 66Zn values (0.17-0.50 %o) and high CaO/TiO2 ratios, indicating that biogenic carbonates archive the Zn isotopic compositions of deep seawater. Arc lavas display delta 66Zn values ranging from 0.17%o to 0.39%o, which cannot be attributed to alteration, crustal contamination, and/or magmatic processes. Their variable Zn isotopic compositions reflect the contribution of recycled slab-derived materials into the mantle wedge. Combined analyses of major-trace element data with SrNd-Zn isotopic compositions support a model that bulk sediments and altered oceanic crust (AOC, potentially including serpentinites) were recycled into the mantle wedge via melange diapirism. This study highlights Zn isotopes as a novel tool to trace sediment recycling and the physicochemical mechanisms of material transfer in subduction zones.

As a redox-sensitive and volatile-chalcophile tracer, Sn isotopes provide unique insights into the origin and transport mechanisms of Sn at convergent margins, yet the drivers of their fractionation remains poorly understood due to a lack of integrated spatial and process-oriented studies. We present high-precision Sn isotopic compositions of lavas (pumices) and hydrothermal products and clinopyroxene-inferred H2O concentrations from Whakaari (arc-front) and Taranaki (rear-arc) in the Kermadec- Hikurangi subduction system.Our results reveal that Whakaari lavas exhibit significant Sn isotopic variations (δ122/118Sn = –0.241‰ to 0.361‰), where the heaviest value can be best explained by extensive shallow degassing (>40%). Rayleigh modelling and light signatures in hydrothermal products such as crater lake water (δ122/118Sn = –0.09‰ to 0.11‰, Sn = 0.48–3.4 ppm) suggests preferential partitioning of Sn and light Sn isotopes into vapour, leaving residual lavas isotopically heavy. This is corroborated by extremely low magmatic water concentrations inferred from clinopyroxene phenocrysts (H2Omagma = 0.29–2.67 wt%, average = 0.83 wt%). In contrast, Taranaki samples show limited variations (δ122/118Sn = 0.124‰ to 0.235‰) without experiencing significant degassing and have H2O = 0.08–3.85% (average = 1.67 wt%). Fractionation of amphibole and titanomagnetite phenocrysts in Taranaki samples may have contributed in lowering bulk-rock Sn isotopic compositions. However, neither of these processes nor mantle partial melting can account for the isotopically light Sn signature of the majority of the Whakaari (0.16 ± 0.06‰) and Taranaki lavas/pumices (0.19 ± 0.06‰) relative to mid-ocean ridge basalts (δ122/118Sn = 0.367 ± 0.087‰).Combined with previously published data from Sunda Arc (0.26 ± 0.06‰), this pervasive light isotope signature can be attributed to input of slab-derived fluids that dominate Sn budget in arc magmas. This is likely achieved either through the transport of light Sn by inherently reduced (fO2 ≤ nickel-nickel oxide buffer), Cl-rich fluids from altered oceanic crust (AOC), or via redox-driven reduction Sn4+ to Sn2+ during the infiltration of oxidised slab fluids into the reduced mantle wedge. These findings not only establish a primary Sn isotopic baseline for arc magmas but also demonstrate that slab-derived fluids—rather than sediment melts—are the primary carriers of Sn to the sub-arc mantle.

The nature of Earth's crust during the Hadean eon [≥4.03 billion years ago (Ga)] is uncertain. Numerical models of early Earth geodynamics emphasize the control of mantle temperature but generally consider only internally derived heat, despite empirical evidence for an intense Hadean impact flux. Using a stochastic model of that flux, we show that the time-integrated heat due to impacts would have dwarfed that produced internally throughout the Hadean. Earth's Hadean crust would have been extensively molten at depths below a few kilometers, causing gravitational segregation of dense, iron- and magnesium-rich material and driving average crustal compositions to become increasingly silica rich. Globally, impact heating would have become much less important after 3.9 Ga, allowing the crust to thicken. That enduring continental crust appeared around this time is likely not a coincidence.

The Mo stable isotope system is a promising tracer of crustal recycling. As subduction zones play a major role in returning crustal material back to the Earth's mantle, understanding the Mo isotope behavior during processes operating at these settings is paramount. The Mo isotope compositions of arc lavas are highly variable and despite recent advances in this field, questions remain about Mo isotope fractionation and mobilization during slab processes and the relative effect of magmatic differentiation on the Mo isotope compositions (598/95Mo) of arc lavas. The Tonga-Kermadec arc is well suited to assess and disentangle crustal and source processes in intraoceanic arc settings owing to widespread felsic volcanism and along-arc source variations, characterized by increasing proportions of a metasedimentary component from the northern Tonga to the southern Kermadec arc. In the pursuit of these objectives, we analyzed a set of basaltic to dacitic tholeiitic arc lavas from volcanoes covering the whole length of the Tonga-Kermadec arc and sediments from DSDP site 204. Tonga-Kermadec arc lavas have highly variable Mo concentrations (0.21 and 2.35 mu g/g) and 598/95Mo values (-0.29 to +0.34 parts per thousand). At some volcanoes, considerable 598/95Mo variations in samples as primitive as basalt are correlated with indices of differentiation and Sr-Nd radiogenic isotopes, indicating an impact of crustal assimilation on Mo isotope compositions. However, the 598/95Mo of the most primitive lavas analyzed for each volcano appear to have preserved primary melt signatures, since they form an along-arc trend mirroring those of Pb isotope averages, a proxy that is controlled by source processes in the Tonga-Kermadec arc. Using these data, a north-south decrease in 598/ 95Mo of the sources of arc magmas is resolved. This is interpreted to reflect the competing signals of isotopically heavy slab-fluids (598/95Mo higher than D-MORB values) with that of an increasing contribution of a metasedimentary component that is lighter than the DMM toward the south. Our data suggest that crustal assimilation can significantly distort primitive 598/95Mo even in mafic magmas from simple intra-oceanic arcs. The induced intra-volcano 598/95Mo scatter has the potential to obscure along-arc variability as well as systematics with typical chemical and isotopic proxies used to characterize arc lava sources (e.g., Ba/Th, radiogenic isotopes). However, we also show that a careful evaluation of these effects can, at least in the Tonga-Kermadec arc, allow the assessment of arc lava source compositions.

Phase equilibrium experiments were used to determine conditions of melt evolution and phenocryst growth in high-Mg andesite magmas that were erupted at Whakaari (White Island) in New Zealand between 1976 and 2000. The high-Mg andesites are both mafic (7.21–10.3 wt

Spheroidal carbonaceous particles (SCPs) are formed from the incomplete, high-temperature combustion of fossil fuels. They are transported to a variety of depositional environments downwind of their sources and thus have the potential to be used to measure human activity on a regional scale. Composed mainly of elemental carbon, these fly ash particles are chemically inert and survive acid treatment, including HF. However, unlike microcharcoal, SCPs are typically overlooked during palynological analysis. Both types of black carbon are common in palynological preparations of varved sediments from Crawford Lake, Ontario, Canada where they can be correlated with the historic record of land use over the past two centuries. Increases in microcharcoal concentration correlate with historic records of land clearing in the early-mid nineteenth century and logging and lumber milling between 1885 and 1957 CE. The rapid increase in SCP concentration during the mid-twentieth century is attributed to the global increase in fossil fuel combustion and industrial activity (the Great Acceleration) and the decline during the early 1980s records increasingly stringent air quality standards as well as decreased demand for steel (and coking coal) in nearby Hamilton. Palynologists are urged to pay attention to these useful proxies of fossil fuel combustion in their slides.

Subduction zones are key regions of mass exchange between the Earth’s crust and mantle, and magmas in the sub-arc mantle form as a result of the release of volatiles from the subducting slab, i.e. fluid-flux melting. Introducing unique geochemical tracers (e.g., Large Ion Lithophile Elements) into the depleted mantle wedge allows tracing of the flow of material underneath the island arcs. Back arc spreading centres form as a result of slab-rollback, and here melts form due to decompression melting similar to those forming at mid-ocean ridges. Back arc systems situated angular to their adjacent island arc encompass a range of slab depths and provide a unique means to assess the compositional changes as a function of distance to the active arc and above the subducting slab. The Valu Fa Ridge (VFR), Eastern Lau (ELSC) and Central Lau (CLSC) spreading centres are situated at an increasing distance from the active Tonga arc from south to north. Here, we present new major, trace and volatile element data along with radiogenic isotope and U-Th-Ra disequilibria along the VFR and ELSC and across the VFR. A systematic change of, e.g., Ba/Nb, Nb/La, H2O contents and Pb isotopes with increasing distance between the back arc and the Tonga arc could be interpreted to reflect the slab-related metamorphic dehydration reactions. However, we do not observe a gradual change in geochemical compositions at a distance 100 km between the arc and back arc, the occurrence of (230Th/238U) excess suggests that melting is due to decompression and that the systematic decrease in subduction influence observed with increasing distance is likely the result of melting of hydrous, ancient slab remnants during rollback. We conclude that the melting regimes between the ELSC and Tonga island arc separate at ~100 km total distance, as evident from the stepwise change in trace element and isotope geochemistry. The decrease in subduction-related signatures along the VFR and ELSC results from an overlap of the melting regimes and melt mixing between the arc and back arc in which the melting of the depleted mantle underneath the back arc becomes more prominent with increasing distance.

Although Earth, together with other terrestrial planets, must have had an early-formed protocrust, the chemical composition of this crust has received little attention. The protocrust was extracted from an extensive magma ocean formed by accretion and melting of asteroidal bodies1. Both experimental and chronological data suggest that the silicate melt ascending from this magma ocean formed in equilibrium with, or after, metal was extracted to form Earth's core. Here we show that a protocrust formed under these conditions would have had incompatible (with respect to silicate minerals) trace-element characteristics remarkably similar to those of the current average continental crust. This has major implications for subsequent planetary evolution. Many geochemical arguments for when and how plate tectonics began implicitly assume that subduction is required to produce the continental trace-element signature. These arguments are severely compromised if this signature was already a feature of the Hadean protocrust.

The Anthropocene was introduced to denote a dramatic, ongoing, planetary shift from prolonged relative Holocene stability, driving the Earth system into a new functional state outside its natural variability. Now stratigraphically-grounded, the Anthropocene is de facto a new epoch, not the subjective filtering of all anthropogenic impacts in Earth history.

There is increasing evidence for the presence of microplastics within terrestrial soils, but little is known about their distributions at smaller spatial scales. This study investigated the small-scale distribution and characteristics of microplastics (500 µm—5 mm) in Epping Forest, an ancient woodland in London, UK. Soil samples were taken along transects within an open area and an adjacent forested area, at depths of 0–5 cm and 5–10 cm. Microplastics were found in all soil samples. Surface soil microplastic concentrations were significantly higher (p = 0.004) in the forested area (350—8000 particles kg−1; mean 2937 particles kg−1) than in the open area (133—900 particles kg−1; mean 543 particles kg−1) and exceed those that have been reported in more remote locations, as well as some agricultural soils. Elevated microplastic concentrations deeper into the forest suggest that this sheltered environment creates a preferential accumulation zone, whereas no clear spatial pattern was found in the open area. No significant difference in microplastic concentrations was found between soil depths. In both areas, fibres were the most common microplastic shape, and larger size classes (3–5 mm) were most abundant. Polyethylene terephthalate (PET) was the most common polymer identified by micro-FTIR analysis. Recreation, littering and diffuse atmospheric deposition are thought to be the main sources of microplastic pollution within the study area. These data represent, to our knowledge, the first recorded presence of microplastic pollution within UK woodland soils, and demonstrate that urban forest soils could represent significant sinks for microplastic pollution.

This is the Executive Summary of a report produced by the membership of the Anthropocene Working Group as part of a submission to the Subcommission on Quaternary Stratigraphy to seek formalisation of the Anthropocene as an epoch of geological time. It summarises the content of two reports and their associated appendices which provide a background to: the history of usage of the term Anthropocene, when the proposed epoch started, the characterisation of the Anthropocene geological deposits and their stratigraphic value, the recognition of the Anthropocene in different sedimentary environments, the rank and duration of the Anthropocene, the proposed Global boundary Stratigraphic Section and Point and supporting Standard Auxiliary Boundary Sections.

Oxidation of the sub-arc mantle driven by slab-derived fluids has been hypothesized to contribute to the formation of gold deposits in magmatic arc environments that host the majority of metal resources on Earth. However, the mechanism by which the infiltration of slab-derived fluids into the mantle wedge changes its oxidation state and affects Au enrichment remains poorly understood. Here, we present the results of a numerical model that demonstrates that slab-derived fluids introduce large amounts of sulfate (S6+) into the overlying mantle wedge that increase its oxygen fugacity by up to 3 to 4 log units relative to the pristine mantle. Our model predicts that as much as 1 wt.% of the total dissolved sulfur in slab-derived fluids reacting with mantle rocks is present as the trisulfur radical ion, S3-. This sulfur ligand stabilizes the aqueous Au(HS)S3- complex, which can transport Au concentrations of several grams per cubic meter of fluid. Such concentrations are more than three orders of magnitude higher than the average abundance of Au in the mantle. Our data thus demonstrate that an aqueous fluid phase can extract 10 to 100 times more Au than in a fluid-absent rock-melt system during mantle partial melting at redox conditions close to the sulfide-sulfate boundary. We conclude that oxidation by slab-derived fluids is the primary cause of Au mobility and enrichment in the mantle wedge and that aqueous fluid-assisted mantle melting is a prerequisite for formation of Au-rich magmatic hydrothermal and orogenic gold systems in subduction zone settings.

The formalisation of the Anthropocene as a subdivision of the Geological Time Scale has been under debate. Its stratigraphic boundary has been proposed as a precise Global boundary Stratotype Section and Point (GSSP) in the mid-20th century, but it is part of an episode of human-induced changes to the Earth System that have unfolded over millennia. Here we attempt to identify stratigraphical patterns of the Anthropocene from a previously well studied lake sedimentary archive from the English Midlands, located in one of the most heavily human-modified landscapes in the UK, and the birthplace of the Industrial Revolution. Our analysis is predicated on the sedimentary succession of Groby Pool, a small lake situated to the immediate northwest of Leicester. We have found that whilst proxy signals for biotic change are indicative of significant landscape and consequent ecological changes prior to the 20th century, the signal from radiogenic fallout and rapid increase in spheroidal carbonaceous particles indicative of fossil-fuel combustion yield a clear mid and later 20th century stratigraphical signature that corresponds with the Great Acceleration of the post-WWII period. We therefore demonstrate clear stratigraphical signatures in the oldest Industrial Revolution landscape on Earth that are consistent with a mid-20th century start point for the Anthropocene.