 | Chondritic osmium isotope composition of early Earth mantle Abstract: The Ujaragssuit Intrusion, North Atlantic Craton (NAC), Greenland, is thought to host the oldest chromitites (>3.8 Ga) on Earth, showing evidence of both Hadean mantle depletion events and nucleosynthetic isotopic heterogeneities. We set out to verify the age of the intrusion and identify the Os isotope composition of the Ujaragssuit mantle source. Here, we show that the only minimum age constraint is 2970 ± 8 Ma, provided by cross-cutting leucogranites. Concordant Re-Pt-Os isotope ages are consistent with formation of the intrusion from a chondritic primitive mantle source at 3246 ± 120 Ma; mean Pt-depletion ages of 3437 ± 587 Ma offer no direct evidence for Hadean mantle depletion. No nucleosynthetic Os isotopic anomalies could be identified, consistent with large scale Os homogeneity in the presolar nebular. The new ‘young’ age for Ujaragssuit means that nucleosynthetic anomalies occur repeatedly between ∼3.8 and >3.0 Ga in the NAC, suggesting its unique mantle source was repeatedly tapped over ∼600 Myr without significant mixing with the rest of Earth’s mantle. |
 | Corrigendum to “Sulfur solubility in a deep magma ocean and implications for the deep sulfur cycle” by Steenstra et al., 2022. |
 | Subduction of sedimentary carbonate in the Mariana trench Abstract: Calcium carbonate is a major component of shallow marine sediments but is rarely preserved in deep sea environments below the calcite compensation depth (CCD). In this study, we present evidence of sedimentary carbonate on the subducting Pacific plate of the Mariana Trench at a water depth ranging from 6675 to 10,813 m, far surpassing the local CCD of 4800 m. These deposits consist of well-preserved calcareous nannofossils, planktonic foraminifera, and siliceous radiolarians. Fossil assemblages and isotope stratigraphy analyses constrain the age of carbonate sediments to 17.6–13.5 Ma. We propose that the calcareous sediments originated from rapid deposition and burial on the seafloor above the CCD during the Miocene. Subsequently, they were transported into the hadal zone with the subduction of the Pacific Plate and exposed due to the excavation of extensive subducting-related normal faults within the subducting plate. This study implies that sedimentary carbonate may be a key component of subducting carbon at the hadal subduction zones, which has important implications for evaluating global carbon input fluxes at these zones. |
 | Barium isotope evidence for a magmatic fluid-dominated petrogenesis of LCT-type pegmatites Abstract: Understanding the petrogenesis of granitic pegmatites associated with Li mineralisation is fundamental in constraining rare metal enrichment mechanisms. However, there is still significant controversy surrounding the central issue of the nature of pegmatite-forming liquids. Here, we report Ba isotope data for a 3000 m borehole in the Jiajika pegmatite field that hosts the largest hard rock-type Li deposit in Asia. The pegmatites exhibit markedly lower δ138/134Ba than the wall rocks and the average upper continental crust, which cannot be attributed to low degree anatexis of metasedimentary or crystal fractionation of highly evolved granitic magmas. Instead, modelling suggests that their low δ138/134Ba most likely results from substantial involvement (10–40 %) of isotopically light hydrothermal fluids exsolved from the underlying magmatic reservoirs. In the context of transcrustal magmatic system, these magmatic fluid components may be a key medium in extracting, concentrating, and transporting Li to provide a material source for mineralisation in granitic pegmatites. |
 | Corrigendum 2 to “Inferred pyrite growth via the particle attachment pathway in the presence of trace metals” by Domingos et al., 2023 |
 | Australasian microtektites: early target-projectile interaction in large impacts on Earth Abstract: Microtektites are microscopic impact glass spherules produced by the melting and vapourisation of the Earth’s crust upon hypervelocity impact of large asteroidal/cometary bodies. They are distal ejecta distributed in strewn fields extending for thousands of kilometres. We studied the geographic distribution of the impactor signature in microtektites from the Australasian strewn field using Ni contents as a proxy. Although still unidentified, geological evidence suggests an impact location in southeast Asia. Based on this assumption, the impactor signature (Ni concentrations of up to 678 μg/g; one order of magnitude higher than continental crust values) decreases with ejection distance and is not detected in the most distal microtektites from Antarctica. This evidence, coupled with trends versus launch distance in the concentrations of cosmogenic nuclides, volatile elements, Fe isotopes, and compositional homogeneity documented in the literature, suggests the following constraints for tektite formation models: the parent melts of the microtektites launched further away formed first, experienced the highest thermal regimes and record no impactor-target materials interaction, whereas those microtektites ejected closer formed later, experienced lower thermal regimes and record variable impactor-target materials interaction. The lack of impactor contamination in the most distal microtektites suggests that the early formed tektite/microtektite melts originated shortly before touchdown, possibly through thermal radiation in a compressed air front preceding the incoming fireball. |
 | Solubility of calcium carbonate hemihydrate (CCHH): Where does CCHH occur? Abstract: Recently, calcium carbonate hemihydrate (CCHH, CaCO3·1/2H2O) was discovered in a laboratory synthesis experiment. Because CCHH can form from aqueous solutions comprising ubiquitous components under ambient conditions, it is expected to exist in nature and may play an important role in carbon cycling at the Earth’s surface. Here, to constrain its possible formation environments; we investigated the solubility of CCHH for the first time by monitoring the evolving solution and mineralogical compositions of CaCl2-MgCl2-Na2CO3 solutions at 25 °C. During the experimental runs, CCHH formed from amorphous calcium carbonate and transformed to aragonite over time. When CCHH was present as a single reactive solid phase, a constant ionic activity product was reproducibly obtained. The solubility product (log Ksp) was −6.80 ± 0.05, between those of ikaite and monohydrocalcite, and near the upper limit of ionic activity products of calcium carbonates observed in alkaline lakes around the world. These results suggest that CCHH can form in alkaline lakes under evaporative conditions. |
 | In situ determination of NaCl-H2O isochores up to 900 oC and 1.2 GPa in a hydrothermal diamond-anvil cell Abstract: NaCl-H2O is a typical binary system solution in geologic environments. However, its available PVTX properties (e.g., isochores) are primarily applicable in the pressure-temperature (P−T) range of <600 MPa and <700 oC. Here, we performed 53 experiments in a hydrothermal diamond-anvil cell (HDAC) to determine NaCl-H2O isochores by using the newly defined α-β quartz P−T transition boundary as a pressure calibrant (Li and Chou, 2022 Li, S.H., Chou, I-M. (2022) Refinement of the α-β quartz phase boundary based on in situ Raman spectroscopy measurements in hydrothermal diamond-anvil cell and an evaluated equation of state of pure H2O. Journal of Raman Spectroscopy 53, 1471–1482. https://doi.org/10.1002/jrs.6367 ). The refined isochores fitted with our data are expressed by: P (bar) = A1 + A2 × T (oC) andA1 = 0.0061 + (0.2385 − a1) × Th − (0.002855 + a2) × Th2 − (a3 × Th + a4 × Th2) × m A2 = a1 + a2 × Th + 9.888 × 10−6 × Th2 + (a3 + a4 × Th) × m where m is the NaCl molality (mole/kg H2O), Th (°C) is the liquid-vapour homogenisation (to the liquid phase) temperature, and al, a2, a3, and a4 are constants (27.21, −0.05956, −0.3095, and 0.003232, respectively). The isochores have better applicability for the salinity range of 5−25 wt. % NaCl, 100 oC < Th <450 oC, and P−T range up to ∼1.2 GPa and ∼900 oC. Compared with previous data, these isochores are more precise above 600 MPa, and are particularly suitable for the geological applications involving saline fluids in the deep Earth. |
 | Correcting for vital effects in coral carbonate using triple oxygen isotopes Abstract: Carbonate oxygen isotopes (18O/16O) are a valuable tool for estimating palaeotemperatures, but their accuracy can be limited by so called vital effects that influence the isotope composition of biomineralised hard parts. In this study, we analysed the triple oxygen isotope composition (18O/16O and 17O/16O) of cold- and warm-water corals to demonstrate how such data can be used to identify and correct for vital effects. We found that the observed slopes in triple oxygen isotope space between the measured and expected equilibrium compositions are mainly controlled by CO2 absorption, although there is a possibility of additional isotope fractionation effects from processes such as CO2 (aq) diffusion through the cell membrane. We corrected these effects using an empirical vital effect slope and obtained accurate coral growth temperatures. The precision of reconstructed temperatures, considering the measurement error only, is ±5 °C. |
 | Dissecting the complex Ne-Ar-N signature of asteroid Ryugu by step-heating analysis Abstract: Samples returned from the carbonaceous asteroid (162173) Ryugu show mineralogical, chemical, and isotopic similarities with Ivuna-type (CI) carbonaceous chondrites, which likely contributed to Earth’s volatile inventory. To better understand the complex Ne-Ar-N signature of CI-type material, we analysed a single, mg-sized Ryugu particle by multi-step (n = 85) heating. Noble gases (Ne, Ar) are a mixture between implanted Solar Wind (SW), presolar component(s), and the carbonaceous phase Q, with negligible cosmogenic contributions. The δ15N variations observed during progressive heating reflect the presence of various N-bearing phases. The large number of heating steps provide key insights into the effect of thermal processing on the N abundance and isotopic ratio, and indicate that low temperatures can result in extensive N loss from CI-type material, without significantly affecting the bulk N isotopic composition. Nitrogen isotopes, therefore, remain a reliable and powerful tool for tracing volatile sources in the Solar System. |
 | Copper isotope fractionation during asteroid core solidification Abstract: Moderately volatile elements (MVE) and their isotopic compositions are powerful tools to understand the origin of volatiles on terrestrial planets, including Earth. The 65Cu/63Cu ratio of Cu, one of the MVEs, has been found to be relatively high in the bulk silicate Earth (BSE), which potentially was caused by either evaporative loss or partitioning into Earth’s inaccessible core. Iron meteorites are the accessible cores of differentiated planetesimals whose creation involved processes similar to Earth’s in the early Solar System. Measurements of their Cu isotope composition currently yield a large range of values that reveal little about core-forming processes. Here, we determine the equilibrium Cu isotope fractionation between solid and liquid metal and quantify the partitioning of Cu between troilite and metal, showing that the latter is a more significant factor in fractionating the Cu isotopes when planetesimal cores cool. Our experiments also call for verification of existing data for equilibrium Cu isotope fractionation between silicate–sulphide and silicate–metal to support current models using sulphide segregation to explain the heavy Cu isotope enrichment in bulk silicate Earth and Moon. |
 | Ocean mixing timescale through time and implications for the origin of iron formations Abstract: Our study examines whether the ocean mixing timescale has remained constant throughout Earth’s history. If varied, it could have affected the distribution of geochemical tracers in ancient seawater, complicating interpretations of sedimentary archives. For example, the modern ocean mixing timescale is similar to the neodymium (Nd) residence time, allowing distinct Nd isotopic compositions (𝜀Nd) to coexist in different oceanic basins. However, it is unknown whether the Archean ocean was more or less isotopically heterogeneous, and how this was recorded by banded iron formations (BIFs). We use an Earth system model to investigate the sensitivity of ocean mixing dynamics to variations in day length, surface pressure, continental configuration, and tidal dissipation. Our experiments indicate that the ocean mixing timescale fluctuated between a few hundred and a couple of thousand years since the Archean. Coupling our mixing model with a Nd cycling model in the Archean ocean, our simulations suggest that hydrothermal fluids could have mixed with other water masses carrying Nd from sediments and rivers before reaching the continental shelf. The large range of 𝜀Nd in some BIFs might therefore reflect the weathering of exposed juvenile and ancient igneous rocks, challenging prevailing views on the hydrothermal source of iron in BIFs. |
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