Ancient metamorphosed basalts show a sulfur isotopic fingerprint of surface sediment, suggesting volatile cycling by a subduction-like process was occurring more than 3.8 billion years ago.

Planetary differentiation had a profound influence on the geochemical signature of the Earth ' s silicate reservoirs. Some of the early created complementary reservoirs dissipated with time ( e.g., Bennett et al. , 2007) and only remnants can be observed. Here, we apply the short lived isotopic system 146 Sm- 142 Nd to an alternative archive - marine chemical sediments - and show that alternating Fe- and Si-rich bands from the 2.7 billion -year -old Temagami banded iron formation (BIF), Canada, display significantly different 142 Nd isotopic compositions. The Fe-rich bands yield a depleted signature (expressed as deviation from the standard in mu notation) with an average mu 142 Nd of & thorn; 7.02 +/- 0.71, while the Si-rich bands display modern mantle-like signatures (average mu 142 Nd - 2.83 +/- 2.32) likely being the results of mixing between different sources. These complementary signatures reflect the dominant, locally derived source of Nd in the seawater at the time of deposition. Our results promote that layering in BIFs is a syn-depositional feature, and that BIFs are unique geochemical archives capable of recording silicate reservoirs that formed during the Hadean but were still extant during the Neoarchean.

Besides the accretion from the solar nebular and the degassing from magma oceans, the main source of the atmospheres of terrestrial planets is magmatic volatile release from the interior. The atmosphere on early Earth is crucial for the emergence and evolution of life. It´s build-up and composition is largely influenced by magmatic outgassing. This outgassing process includes the well-studied extrusive as well as the often neglected intrusive volatile release. However, it is assumed that the intrusive magma production rates - at least on Earth - are significantly higher compared to extrusive rates, which makes the investigation and quantification of possible volatile exsolution processes even more important.We simulate the crystallization of an intrusive magma body emplaced at different depths within the lithosphere. As the solubility of volatiles like H2O and CO2 increases with pressure, they usually do not exsolve from the melt. However, through the precipitation of nominally dry minerals, the remaining melt is enriched in incompatible elements and volatiles. They accumulate until a saturation level is reached and the volatiles exsolve. The composition of the resulting volatile phase depends on the solubility of the volatile species, the pressure and temperature, the initial composition of the melt, the partition coefficient and the oxygen fugacity. We consider these parameters in our model and benchmark our results with literature values. Additionally, we investigate the likelihood of reactions with the surrounding mantle, to form water-bearing minerals, during the ascent of volatiles. Finally, we quantify the impact of intrusive degassing on the build-up and composition of the atmosphere.

We present petrological data and seven Lu-Hf garnet-amphibole-whole rock ages obtained from a single garnet-hornblende-mica schist sample from the Isua supracrustal belt (West Greenland). Garnets grew during prograde metamorphism toward regional amphibolite-facies peak conditions, and a mylonitic foliation formed during and after garnet growth. Garnet crystals show typical prograde zoning with no visible traces of a relict garnet generation. They do show various degrees of retrogression. While some crystals are perfectly euhedral with only minor chemical alteration along cracks, others are elongated in the foliation and either grew in this shape or were deformed. Six garnet splits were separated from crushed single crystals and one from a crushed bulk sample. Individual three-point garnet-horn-blende-whole rock ages scatter between 2.603 +/- 0.018 Ga and 2.432 +/- 0.059 Ga for single garnets. The garnet split from the bulk sample defines an age of 2.463 +/- 0.031 Ga, the data point farthest from the regression line for all data points (2.551 +/- 0.074 Ga, mean square of weighted deviates = 25). We interpret these data to indicate partial retrogression of a Neo-archean garnet population not significantly older than the oldest obtained three-point age. Well-preserved garnet zoning, regional peak temperatures well below the closing temperature of the Lu-Hf system, and the small scatter of Lu-Hf ages preclude an interpretation of the observed metamorphism and deformation as being Eoarchean in age.

Stable zirconium (Zr) isotope of magmatic zircons is a promising new tracer to understand magma dif-ferentiation in the continental crust. However, magmatic processes controlling zircon Zr isotopic varia-tions remain poorly constrained. Here we present high-spatial-resolution in-situ methods on magmatic zircons for U-Pb age, trace elements, Hf isotopes, and stable Zr isotopes (894/90Zr relative to IPGP-Zr) as well as bulk rock 894/90Zr for a large granite batholith (SiO2 =-73 wt%) in the Jiaodong Peninsula, eastern North China Craton. Magmatic zircons are classified into high-luminance Type-I and low-luminance Type-II zircons in the cathodoluminescence images. Both types show indistinguishable U-Pb ages and initial Hf isotopic compositions, indicating their same magma source. Yet, they differ in chemical compositions and 894/90Zr values. Type-I zircons display lower 894/90Zr values (-0.35%0 to 0.15%0) than Type-II zircons (0.16-0.54%0). The 894/90Zr values overall increase with decreasing Zr/Hf, Th/U ratios, Ti-in-zircon temperature, and increasing U abundances in zircons, implying that zircon 894/90Zr values becomes heavier with the enhanced magma differentiation. Such concomitant correlations resulted from closed-system magma crystallization without noticeable segregation of feldspar and zir-con, as revealed by high Sr and Ba content, limited Eu anomalies, and mantle-like 894/90Zr in the bulk rocks (-0.01 +/- 0.07%0 and 0.02 +/- 0.04%0). Thus, Type-I zircons incorporating light Zr isotopes crystallized at an early stage of magma solidification, while Type-II zircons grew from more evolved residual melts with elevated 894/90Zr values. Zoned zircon grains with Type-I cores and Type-II rims record the pro-longed crystallization history covering both stages with contrasting melt compositions; whereas oscilla-tion zircon grains of Type-I or Type-II, crystallizing at the stable melt composition, display the restricted intragrain variations of 894/90Zr, Zr/Hf, and Th/U ratios. These results demonstrate that closed-system magmatic crystallization plays a critical role in zircon Zr isotopic variations. We further propose that the variability of 894/90Zr values and multiple types of Zr isotopic profiles in zircons are predominantly driven by the compositional effect of adjacent melts from which zircons crystallize. The composition -related 894/90Zr variations provide a fundamental framework for understanding Zr isotopic evolution in the silicic igneous system and can be used for exploring open-system magmatic processes in the mushy pluton bodies, which are important for continental crust evolution. (c) 2022 Elsevier Ltd. All rights reserved.

The timing and formation of Earth's first continents during the Archean are subjects of significant debate. By examining titanium isotope variations in Archean Tonalite-Trondhjemite-Granodiorite (TTG) rocks and using advanced thermodynamic modelling, we can narrow down the processes involved and emphasise the role of mafic precursor compositions. In our study of Eoarchean Isua metabasalts and Itsaq tonalites in southern West Greenland, we observed a pattern of increasing Ti isotope enrichment with higher SiO2 content, resembling the compositions found in modern subduction zone rocks. Our modelling suggests that the Ti isotope variations in TTGs can be best explained by a combination of partial melting of low TiO2 metabasalts and subsequent crystallisation of tonalitic magmas, resulting in heavier Ti isotopes. This means that Ti isotopes help us distinguish the contributions of various mafic sources and fractional crystallisation during TTG formation. In the case of Itsaq tonalites and many other Eoarchean TTGs, low TiO2 tholeiitic metabasalts with arc-like characteristics likely represent the mafic source rocks, suggesting the formation of some of Earth's earliest continental crust within a proto-subduction zone setting.

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.

An interlaboratory comparison (ILC) was organised to characterise 87Sr/86Sr isotope ratios in geological and industrial reference materials by applying the so‐called conventional method for determining 87Sr/86Sr isotope ratios. Four cements (VDZ 100a, VDZ 200a, VDZ 300a, IAG OPC‐1), one limestone (IAG CGL ML‐3) and one slate (IAG OU‐6) reference materials were selected, covering a wide range of naturally occurring Sr isotopic signatures. Thirteen laboratories received aliquots of these six reference materials together with a detailed technical protocol. The consensus values for the six reference materials and their associated measurement uncertainties were obtained by applying a Gaussian, linear mixed effects model fitted to all the measurement results. By combining the consensus values and their uncertainties with an uncertainty contribution for potential heterogeneity, reference values ranging from 0.708134 mol mol‐1 to 0.729778 mol mol‐1 were obtained with relative expanded uncertainties of ≤ 0.007 %. This study represents an ILC on conventional 87Sr/86Sr isotope ratios, within which metrological principles were considered and the compatibility of measurement results obtained by MC‐ICP‐MS and by MC‐TIMS is demonstrated. The materials characterised in this study can be used as reference materials for validation and quality control purposes and to estimate measurement uncertainties in conventional 87Sr/86Sr isotope ratio measurement.

A greater quantity of halogens (F, Cl, Br, and I) appear to be subducted globally than are erupted at magmatic arcs, requiring either an increase in the mantle halogen budget through time or an additional output pathway or reservoir. The sub-continental lithospheric mantle (SCLM) is one such reservoir. SCLM can be enriched in volatile elements after metasomatism by fluids or melts from subducting oceanic lithosphere. We analyzed the bulk halogen content (F, Cl, Br, and I) of 28 variably metasomatized spinel and garnet peridotite xenoliths from the Navajo Volcanic Field (NVF; Central Colorado Plateau) to constrain the effects of the subducting Farallon plate-derived metasomatism on the halogen content of the western North American SCLM. We also analyzed 33 anhydrous spinel peridotites from various localities on and around the Colorado Plateau, as well as xenoliths from Oahu, Hawaii, and Eifel, Germany to compare them to the modally hydrated NVF xenoliths. Cl, Br, and I are enriched in NVF xenoliths relative to the depleted mantle, correlating with olivine oxygen isotope values and indices of metasomatism. F is less enriched, indicating preferential retention in the slab residue. Br/Cl and I/Cl are similar to partially dehydrated serpentinite, indicating that the source of these fluids is consistent with serpentinized oceanic lithosphere of the Farallon plate. Anhydrous xenoliths from the southwestern United States have more depleted mantle-like Cl and F contents but have highly enriched Br contents similar to the NVF xenoliths. Similar to NVF xenoliths, anhydrous xenolith Br/Cl and I/Cl suggest a Farallon derived serpentinite source of halogen enrichment. These results indicate that the Farallon slab sequestered halogens in the North American SCLM of the central and south Colorado Plateau and the southern Rio Grande Rift. Therefore, halogen sequestration in the SCLM may be a critical component in the global halogen cycle.

Measurements of Nd-142 isotope signatures in Archean rocks are a powerful tool to investigate the earliest silicate differentiation events on Earth. Here, we introduce a new analytical protocol that allows high precision radio -genic and mass-independent Nd isotope measurements by MC-ICP-MS. To validate our method, we have measured well-characterized-3.72 to-3.8 Ga samples from the Eoarchean Itsaq Gneiss Complex and associated supracrustal belts, as well as Mesoarchean greenstones and a Proterozoic dike in SW Greenland, including lithostratigraphic units that were previously analyzed for Nd142-143 isotope systematics, by both TIMS and MC-ICP-MS. Our mu Nd-142 values for-3.72 to-3.8 Ga rocks from the Isua region range from +9.2 +/- 2.6 to +13.2 +/- 1.1 ppm and are in good agreement with previous studies. Using coupled Nd-142,Nd-143/Nd-144 isotope systematics from our data for-3.8 Ga mafic-ultramafic successions from the Isua region, we can confirm previous age constraints on the earliest silicate differentiation events with differentiation age of 4.390(-0.060)(+0.045) Ga. Moreover, we can resolve a statistically significant decrease of Nd-142/Nd-144 isotope compositions in the ambient mantle of SW Greenland that already started to commence by Eoarchean time, between-3.8 Ga (mu Nd-142 = +13.0 +/- 1.1) and -3.72 Ga (mu Nd-142 = +9.8 +/- 1.0). Even lower but homogeneous mu Nd-142 values of +3.8 +/- 1.1 are found in-3.4 Ga mantle-derived rocks from the Ameralik dike swarms. Our study reveals that epsilon Nd-143(i) and epsilon Hf(i) values of Isua rocks scatter more than it would be expected from a single stage differentiation event as implied from nearly uniform mu Nd-142 values, suggesting that the previously described decoupling of Hf and Nd isotopes is not a pri-mordial magma ocean signature. Instead, we conclude that some of second stage processes like younger mantle depletion events or recycling of subducted material affected the (Sm-143Nd)-Sm-147 isotope systematics. The preser-vation of pristine whole-rock isochrons largely rules out a significant disturbance by younger alteration events. Based on isotope and trace element modelling, we argue that the temporal evolution of coupled Nd-142,Nd-143/Nd-144 isotope compositions in the ambient mantle beneath the Isua rocks is best explained by the progressive admixture of material to the Isua mantle source that must have had present-day-like mu Nd-142 compositions. In contrast, Mesoarchean mafic rocks from the-3.08 Ga Ivisaartoq greenstone belt and the 2.97 Ga inner Ameralik Fjord region as well as a 2.0 Ga Proterozoic dike within that region all have higher mu Nd-142 values as would be expected from our simple replenishment model. This argues for reworking of older Isua crustal material that carried elevated mu Nd-142 compositions.

Extracting information about past tectonic or climatic environmental changes from sedimentary records is a key objective of provenance research. Interpreting the imprint of such changes remains challenging as signals might be altered in the sediment-routing system. We investigate the sedimentary provenance of the Oligocene/Miocene Upper Austrian Northern Alpine Foreland Basin and its response to the tectonically driven exhumation of the Tauern Window metamorphic dome (28 ± 1 Ma) in the Eastern European Alps by using the unprecedented combination of Nd isotopic composition of bulk-rock clay-sized samples and partly previously published multi-proxy (Nd isotopic composition, trace-element geochemistry, U-Pb dating) sand-sized apatite single-grain analysis. The basin offers an excellent opportunity to investigate environmental signal propagation into the sedimentary record because comprehensive stratigraphic and seismic datasets can be combined with present research results. The bulk-rock clay-sized fraction εNd values of well-cutting samples from one well on the northern basin slope remained stable at ∼−9.7 from 27 to 19 Ma but increased after 19 Ma to ∼−9.1. In contrast, apatite single-grain distributions, which were extracted from 22 drill-core samples, changed significantly around 23.3 Ma from apatites dominantly from low-grade (<upper amphibolite-facies) metamorphic sources with Permo-Mesozoic and late Variscan U-Pb ages and εNd values of −4.4 to dominantly high-grade metamorphic apatites with late Variscan U-Pb ages and εNd values of −2.2. The change in apatite single-grain distributions at 23.3 Ma is interpreted to result from the exposure of a new Upper Austroalpine source nappe with less negative εNd values triggered by the ongoing Tauern Window exhumation. Combining these data with the clay-sized bulk-rock εNd values reveals that the provenance changed 4–5 Myrs later at 19 Ma in the clay-sized fraction. Reasons for the delayed provenance-change recording are rooted in the characteristics of the applied methods. Whereas single-grain distributions of orogen-wide sediment-routing systems can be dominated by geographically small areas with high erosion and mineral fertility rates, bulk-rock methods integrate over the entire drainage basin, thus diminishing extreme values. Hence, by combining these two methods, spatial information are uncovered, enabling a previously unattained understanding of the underlying environmental change.

Much of the continental lithosphere developed during the Archean, which was an Eon of change in terms of global geodynamics and geochemical cycles. Uncovering the causal links between crust forming processes and prevailing geodynamic mechanisms is crucial for understanding the origins and composition of the present-day continental lithosphere. Pristine Archean crust is scarce yet can be found in cratons worldwide. Many of these occurrences comprise rocks of the tonalite-trondhjemite-granodiorite (TTG) suite, which represent a prevalent component of the Archean continental crust. TTGs are generally considered to have formed by partial melting of amphibolite or eclogite source rocks that had basaltic precursors originally extracted from a depleted mantle (e.g., [1]). The age of the source rocks (i.e., the time between the basalt extraction from the mantle and TTG formation) can be determined from the initial radiogenic isotope compositions of TTGs, provided that the P/D ratio of the source can be reliably estimated and is significantly different from that of the depleted mantle. Based on this principle, we estimated the age of basaltic sources of TTGs from cratons of different age and paleogeography from initial 87Sr/86Sr compositions determined by in-situ Sr isotope analysis of primary igneous apatite (LA-MC-ICPMS). The 87Sr/86Sr of these apatites show that prior to 3.4 Ga TTGs were derived from relatively old mafic sources and that the average time between formation of basaltic material from the mantle and subsequent remelting under amphibolite to eclogite facies conditions decreased drastically during the Paleoarchean. This secular change indicates a rapid global increase in the efficiency of TTG production or the emergence of a new TTG-forming process at c. 3.4 Ga [2]. In this contribution we explore this hypothesis by comparing the 87Sr/86Sr signature of the TTGs with their trace-element compositions, as well as with 176Hf/177Hf zircon data for these rocks and contemporary TTGs from other studies. This combined geochronological, isotope and geochemical analyses will provide new constraints on the age of TTG sources during the Archean and will allow investigation into the nature and probable causes of the apparent rejuvenation at 3.4 Ga, as indicated by Sr isotopes. [1] Hoffmann, J.E. et al. (2011) Geochim. Cosmochim. Acta 75, 4157-4178. [2] Caton, S., et al., (in review) Chem. Geol.

Radiogenic isotopes provide an important means towards elucidating Archean crustal evolution. The global Hf and Nd isotope record of Archean crustal fragments has been instrumental to unveiling the history of ancient crustal growth and differentiation. The Rb-Sr system could provide valuable complementary constraints in this regard, as this system is particularly sensitive to magmatic fractionation processes, and the chemical and isotopic evolution of magma sources. Application of this system has so far been complicated, however, by its suscepti-bility to isotope re-equilibration or alteration of the Rb/Sr parent-daughter ratio. In-situ Sr isotope analysis of primary igneous minerals with very low Rb/Sr, such as apatite, provides a new means to determine the initial 87Sr/86Sr (87Sr/86Sri) values for igneous rocks directly. In this study, we apply in-situ Sr isotope analysis of apatite by LA-MC-ICPMS to tonalite-trondhjemite-granodiorite (TTG) rocks and end-member sanukitoids from Archean cratons worldwide. The 87Sr/86Sri values of sanukitoids are relatively radiogenic, supporting the model in which such rocks are formed by flux melting of a mantle strongly enriched by metasomatism, possibly by slab -derived fluids. The 87Sr/86Sri values for TTGs formed between 3.72 and 3.45 Ga are generally radiogenic, indicating aged amphibolite sources. The 87Sr/86Sri values of younger TTGs are systematically lower and were derived from mafic sources that had an average age of <= 0.2 Gyr. This evolution matches with observations from Hf isotopes for TTGs of similar age and indicates a systematic change in the nature or efficiency of TTG crust formation during the Paleoarchean. In-situ Sr isotope analysis of apatite provides a useful method to uncover the Sr record of the early continental crust, and enables constraints on local source evolution and the general two-step evolutionary process of Archean crust formation.