Animal proxies to characterize the strontium biosphere in the northeastern Nile Delta

Strontium (⁸⁷Sr/⁸⁶Sr) isotope analysis is a potent tool for reconstructing the residential mobility of humans and animals in the past but is reliant on knowledge of strontium isotope variation within the expanded physical environment. This paper aims to contribute to the isoscape in the northeastern Nile Delta with faunal samples from the site of Tell el-Dab‘a (Avaris), believed to be the capital of the so-called Hyksos kings. Mapping the available ⁸⁷Sr/⁸⁶Sr ratios from Egypt and the Sudan highlights major research gaps outside the Nile region. e current corpus of knowledge also shows that the Nile River region yields a homogenous range of isotopic values (median and IQR 0.7076 0.0003). Strontium isotope ratios from human dental enamel, which record childhood residence, will provide evidence of non-locals from outside the Nile area with confidence but these values suggest that identifying movement along the Nile River in the past will be difficult without the use of supplementary evidence (e.g. oxygen stable isotope analysis). We present ⁸⁷Sr/⁸⁶Sr ratios of archaeologically-derived faunal bone samples (n=6) from the site of Tell el-Dab‘a (Avaris) in the northeastern Nile Delta. e ⁸⁷Sr/⁸⁶Sr ratios fit within the expectations of the wider Nile values (mean 0.70769 0.00003) and serve as the first archaeologically-derived values reported for this area of Egypt

Osmium isotope compositions of detrital Os-rich alloys from the Rhine River provide evidence for a global late Mesoproterozoic mantle depletion event

We report osmium isotopic compositions for 297 mantle-derived detrital Ru–Os–Ir alloy grains found in gold and platinum-group mineral bearing placers of the Rhine River. These alloys were likely formed as a result of high degree melting in the convective mantle and derived from residual Paleozoic mantle peridotites in the Alps of Central Europe that were accreted as part of a collage of Gondwana-derived ‘Armorican’ terranes before the Variscan Orogeny. The 187Os/188Os isotope ratios of the Os-rich alloys show a wide distribution, with two modes at 0.1244 and 0.1205. These two modes correspond to rhenium depletion ages, interpreted to correspond with episodes of high-degree mantle melting, at ∼0.5 and ∼1.1 Ga. The data confirm the ability of the oceanic mantle to preserve evidence of ancient melting events. Our new data, in combination with published data on Os-rich alloys from the Urals and Tasmania and with data for abyssal peridotites, indicate a geographically widespread record of a major global Late Mesoproterozoic (1.0–1.2 Ga) high-degree melting event in Paleozoic oceanic mantle rocks. This model age peak is essentially absent from the crustal record of Central-Western Europe, but does coincide with the apparent peak in global continental crust zircon ages at this time. Thus, high-degree mantle melting peaking in the 1.0–1.2 Ga interval may have affected a large part of Earth's mantle. This interval occurred during a period of relative super-continental stability, which may have been accompanied in the oceanic realm by rapid seafloor spreading and extensive subduction, and by unusually high activity of mantle plumes forming two active mantle superswells

Paragenesis of multiple platinum-group mineral populations in Shetland ophiolite chromitite: 3D X-ray tomography and in situ Os isotopes

Chromitite from the Harold’s Grave locality in the mantle section of the Shetland ophiolite complex is extremely enriched in Ru, Os and Ir, at µg/g concentrations. High-resolution X-ray computed tomography on micro-cores from these chromitites was used to determine the location, size, distribution and morphology of the platinum-group minerals (PGM). There are five generations of PGM in these chromitites. Small (average 5 µm in equivalent sphere diameter, ESD) euhedral laurites, often with Os-Ir alloys, are totally enclosed in the chromite and are likely to have formed first by direct crystallisation from the magma as the chromite crystallised. Also within the chromitite there are clusters of larger (50 µm ESD) aligned elongate crystals of Pt-, Rh-, Ir-, Os- and Ru-bearing PGM that have different orientations in different chromite crystals. These may have formed either by exsolution, or by preferential nucleation of PGMs in boundary layers around particular growing chromite grains. Thirdly there is a generation of large (100 µm ESD) composite Os-Ir-Ru-rich PGM that are all interstitial to the chromite grains and sometimes form in clusters. It is proposed that Os, Ir and Ru in this generation were concentrated in base metal sulfide droplets that were then re-dissolved into a later sulfide-undersaturated magma, leaving PGM interstitial to the chromite grains. Fourthly there is a group of almost spherical large (80 µm ESD) laurites, hosting minor Os-Ir-Ru-rich PGM that form on the edge or enclosed in chromite grains occurring in a sheet crosscutting a chromitite layer. These may be hosted in an annealed late syn- or post magmatic fracture. Finally a few of the PGM have been deformed in localised shear zones through the chromitites. The vast majority of the PGM – including small PGM enclosed within chromite, larger interstitial PGM and elongate aligned PGM – have Os isotope compositions that give Re-depletion model ages approximately equal to the age of the ophiolite at ∼492 Ma. A number of other PGM – not confined to a single textural group – fall to more or less radiogenic values, with four PGM giving anomalously unradiogenic Os corresponding to an older age of ∼1050 Ma. The 187Os/188Os isotopic ratios for PGM from Cliff and Quoys, from the same ophiolite section, are somewhat more radiogenic than those at Harold’s Grave. This may be due to a distinct mantle source history or possibly the assimilation of radiogenic crustal Os

190Pt-186Os geochronometer reveals open system behaviour of 190Pt-4He isotope system

Platinum Group Minerals are typically dated using the 187Re-187Os and 190Pt-186Os isotope systems and more recently using the 190Pt-4He geochronometer. The 187Re-187Os and 190Pt-186Os compositions of Pt-alloys from the Kondyor Zoned Ultramafic Complex (ZUC) analysed here reveal overprinting for both geochronometers except in one alloy exhibiting the most unradiogenic 187Os/188Os and most radiogenic 186Os/188Os signatures. These signatures argue for an Early Triassic mineralisation, when silicate melts/fluids derived from the partial melting of an Archean mantle crystallised to form the Kondyor ZUC while the 190Pt-4He chronometer supports an Early Cretaceous mineralisation. We propose that Kondyor ZUC represents the root of an alkaline picritic volcano that constitutes the remnants of an Early Triassic island arc formed during the subduction of the Mongol-Okhotsk ocean seafloor under the Siberia craton. After the Early Cretaceous collision of Siberia with the Mongolia-North China continent, the exhumation of deep-seated structures - such as the Kondyor ZUC - allowed these massifs to cool down below the closure temperatures of the Pt-He and K-Ar, Rb-Sr isotope systems, explaining their Early to Late Cretaceous ages for the Kondyor ZUC

Titanium stable isotope investigation of magmatic processes on the Earth and Moon

We present titanium stable isotope measurements of terrestrial magmatic samples and lunar mare basalts with the aims of constraining the composition of the lunar and terrestrial mantles and evaluating the potential of Ti stable isotopes for understanding magmatic processes. Relative to the OL–Ti isotope standard, the δ49Ti values of terrestrial samples vary from −0.05 to +0.55‰, whereas those of lunar mare basalts vary from −0.01 to +0.03‰ (the precisions of the double spike Ti isotope measurements are ca. ±0.02‰ at 95% confidence). The Ti stable isotope compositions of differentiated terrestrial magmas define a well-defined positive correlation with SiO2 content, which appears to result from the fractional crystallisation of Ti-bearing oxides with an inferred isotope fractionation factor of View the MathML source. Primitive terrestrial basalts show no resolvable Ti isotope variations and display similar values to mantle-derived samples (peridotite and serpentinites), indicating that partial melting does not fractionate Ti stable isotopes and that the Earth's mantle has a homogeneous δ49Ti composition of +0.005 ± 0.005 (95% c.i., n=29). Eclogites also display similar Ti stable isotope compositions, suggesting that Ti is immobile during dehydration of subducted oceanic lithosphere. Lunar basalts have variable δ49Ti values; low-Ti mare basalts have δ49Ti values similar to that of the bulk silicate Earth (BSE) while high-Ti lunar basalts display small enrichment in the heavy Ti isotopes. This is best interpreted in terms of source heterogeneity resulting from Ti stable isotope fractionation associated with ilmenite–melt equilibrium during the generation of the mantle source of high-Ti lunar mare basalts. The similarity in δ49Ti between terrestrial samples and low-Ti lunar basalts provides strong evidence that the Earth and Moon have identical stable Ti isotope compositions

No V-Fe-Zn isotopic variation in basalts from the 2021 Fagradalsfjall eruption

The Earth’s mantle is chemically heterogeneous in space and time, which is often reflected by variable isotopic compositions of mantle derived basalts. Basalts from the first 40 days of the 2021 Fagradalsfjall eruption, Reykjanes Peninsula, Iceland, display systematic temporal variations in the ratios of incompatible elements alongside resolvable variations in Sr, Nd and Pb radiogenic isotopes. These variations reflect progressive influx of magma derived from melting of a deeper, more enriched and potentially lithologically distinct source. We use this eruptive time series to conduct the first combined V-Fe-Zn isotope study, exploring the sensitivity of the combined isotopic approach, with particular focus on fingerprinting source lithological heterogeneity. We find no analytically resolvable change in V (δ51VAA between −0.95 ± 0.09 ‰ 2 s.d. and −0.86 ± 0.07 ‰ 2 s.d.), Fe (δ56FeIRMM-524 between +0.047 ± 0.042 ‰ 2 s.d. and +0.094 ± 0.049 ‰ 2 s.d.) and Zn (δ66ZnAA-ETH between −0.042 ± 0.003 ‰ 2 s.d. and +0.013 ± 0.027 ‰ 2 s.d.) isotopic compositions. The lack of variability in V-Fe-Zn isotopes, despite the evolving trace element and radiogenic isotope ratios, suggests there is no significant contribution of melts from a lithologically distinct (pyroxenite) mantle component under the Reykjanes Peninsula

Generation of the Mt Kinabalu granite by crustal contamination of intraplate magma modelled by Equilibrated Major Element Assimilation with Fractional Crystallisation (EME-AFC)

New geochemical data are presented for the composite units of the Mount Kinabalu granitoid intrusion of Borneo and explore discrimination between crustal- and mantle-derived granitic magmas. The geochemical data demonstrate that the units making up this composite intrusion became more potassic through time. This was accompanied by an evolution of isotope ratios from a continental-affinity towards a slightly more mantle-affinity (87Sr/86Sri ∼0.7078; 143Nd/144Ndi ∼0.51245; 206Pb/204Pbi ∼18.756 for the oldest unit compared to 87Sr/86Sri ∼0.7065, 143Nd/144Ndi ∼0.51250 and 206Pb/204Pbi ∼18.721 for the younger units). Oxygen isotope ratios (calculated whole-rock δ18O of + 6.5–9.3‰) do not show a clear trend with time. The isotopic data indicate that the magma cannot result only from fractional crystallisation of a mantle-derived magma. Alkali metal compositions show that crustal anatexis is also an unsuitable process for genesis of the intrusion. The data indicate that the high-K units were generated by fractional crystallisation of a primary, mafic magma, followed by assimilation of the partially melted sedimentary overburden. We present a new, Equilibrated Major Element – Assimilation with Fractional Crystallisation (EME-AFC) approach for simultaneously modelling the major element, trace element, and radiogenic and oxygen isotope compositions during such magmatic differentiation; addressing the lack of current AFC modelling approaches for felsic, amphibole- or biotite-bearing systems. We propose that Mt Kinabalu was generated through low degree melting of upwelling fertile metasomatised mantle driven by regional crustal extension in the Late Miocene

Precise and accurate 186Os/188Os and 187Os/188Os measurements by multi-collector plasma ionisation mass spectrometry (MC-ICP-MS). Part 1, solution analyses

We present new high precision Os isotope data obtained by solution-mode MC-ICP-MS for 4 different Os isotope reference materials and compare the data to that obtained by the N-TIMS method. Mass fractionation effects for MC-ICP-MS are evaluated and we demonstrate excellent adherence to the exponential law. An improved and robust method for the derivation of interfering element isotope ratios is presented and evaluated via analysis of solutions with widely varying interfering element/analyte ratios. We show experiments that illustrate the extent of memory with a conventional solution introduction system and establish a protocol that reduces washout time and memory effects to the same level as those common for other elements typically analysed at high precision by MC-ICP-MS. Data for 4 Os Reference material solutions show excellent agreement between MC-ICP-MS and N-TIMS for all Os isotope ratios except 186Os/188Os and 184Os/188Os which are consistently lower by 100 ppm and 3–5‰ respectively for MC-ICP-MS. These differences are highly unlikely to arise from problems relating to Faraday cup or amplifier efficiency variations, residual mass fractionation effects or inaccuracies in the applied W interference corrections on 186Os and 184Os for MC-ICP-MS analyses. These issues require further investigation if the Pt–Os system is to find routine application as a geochemical tracer