Isotopic Studies Research Articles

Acid-base synergistic effect towards catalytic transfer hydrogenation reactions

Catalytic transfer hydrogenation (CTH) of aldehydes/ketones by using alcohols as hydrogen donors is an attractive and environmentally friendly hydrogenation technology, which has evoked widespread attention in synthesis of fine chemicals from biomass resources. In this work, a Co-Al mixed metal oxide catalyst (Co1Al2-MMO-200) was obtained through structural topological transformation process of layered double hydroxides, which was used in the CTH reaction of furfural with isopropanol. Notably, the reaction rate achieves 0.023 mol g−1 h−1, which is preponderate to acid-base catalysts earlier reported. The joint research based on CO2-TPD, NH3-TPD and poisoning experiment substantiates that the synergy effect of acid-base sites plays an essential role in this catalytic system. Isotopic labelling MS, in-situ FT-IR and DFT studies further verify that the CTH reaction of furfural occurs via the Meerwein-Ponndorf-Verley (MPV) route, in which the basic site promotes the deprotonation of isopropanol whilst the acid site facilitates the formation of a six-membered ring transition state. This work demonstrates an acid-base synergetic catalysis for the CTH reaction by revealing the structure-property correlation and exploring reaction route, which is instructive for designing high-performance heterogenous catalysts.

Insights on long-term ecosystem changes from stable isotopes in historical squid beaks

BackgroundAssessing the historical dynamics of key food web components is crucial to understand how climate change impacts the structure of Arctic marine ecosystems. Most retrospective stable isotopic studies to date assessed potential ecosystem shifts in the Arctic using vertebrate top predators and filter-feeding invertebrates as proxies. However, due to long life histories and specific ecologies, ecosystem shifts are not always detectable when using these taxa. Moreover, there are currently no retrospective stable isotopic studies on various other ecological and taxonomic groups of Arctic biota. To test whether climate-driven shifts in marine ecosystems are reflected in the ecology of short-living mesopredators, ontogenetic changes in stable isotope signatures in chitinous hard body structures were analysed in two abundant squids (Gonatus fabricii and Todarodes sagittatus) from the low latitude Arctic and adjacent waters, collected between 1844 and 2023.ResultsWe detected a temporal increase in diet and habitat-use generalism (= opportunistic choice rather than specialization), trophic position and niche width in G. fabricii from the low latitude Arctic waters. These shifts in trophic ecology matched with the Atlantification of the Arctic ecosystems, which includes increased generalization of food webs and higher primary production, and the influx of boreal species from the North Atlantic as a result of climate change. The Atlantification is especially marked since the late 1990s/early 2000s. The temporal patterns we found in G. fabricii’s trophic ecology were largely unreported in previous Arctic retrospective isotopic ecology studies. Accordingly, T. sagittatus that occur nowadays in the high latitude North Atlantic have a more generalist diet than in the XIXth century.ConclusionsOur results suggest that abundant opportunistic mesopredators with short life cycles (such as squids) are good candidates for retrospective ecology studies in the marine ecosystems, and to identify ecosystem shifts driven by climate change. Enhanced generalization of Arctic food webs is reflected in increased diet generalism and niche width in squids, while increased abundance of boreal piscivorous fishes is reflected in squids’ increased trophic position. These findings support opportunism and adaptability in squids, which renders them as potential winners of short-term shifts in Arctic ecosystems.

Evolution of Devonian and Carboniferous pre-Andean arc magmatism in the Frontal Cordillera (27°-35°S), Argentina: Insights from U–Pb zircon and isotopic studies

We propose a conceptual model for the magmatic system that gave rise to the Devonian and Carboniferous subduction-related magmatism in the Frontal Cordillera of Argentina, (representing the pre-Andean margin of SW Gondwana), integrating previous geochronological studies with new geochronological data from granitoids and subvolcanic dikes, which include reported petrological, geochemical, and isotopic data. This conceptual magmatic system postulates an extended magmatic activity, similar to that reported in a previous study for the Devonian foreland magmatism located in the present-day Sierras Pampeanas of Argentina. The geochronological data play a central role in the model, and lead us to postulate the presence of a deep mush reservoir, where a prolonged magmatic activity, permitted the extended crystallization of Devonian (ca. 400 ± 3 and 414 ± 3 Ma) and Carboniferous antecrysts (334 ± 2 Ma, 341 ± 2, and 348 ± 2, where the age of 348 Ma maybe considered as derived from the source, i.e. xenocrysts). Migration of the parental magma from the mush reservoir zone occurred near the time of emplacement and culminated in the formation of an ephemeral magma chamber located in shallow levels, where Devonian and Carboniferous zircon autocrysts crystallized (382 ± 5 Ma and 325 ± 2 Ma, respectively). Age spectra reported within individual sample, favors the idea of a massive migration of magma when conditions were favorable (e.g., thermally matured crust). Notably, the Carboniferous geochronological data is strongly consistent with previous geochronological data recently reported for the granitic rocks of the Tabaquito batholith. Although this model supports a protracted magmatic system for the Devonian and Carboniferous subduction-related magmatism, previous and new isotopic data reveal a significant difference in the petrogenetic processes. While the Carboniferous arc magmatism shows significant juvenile material contribution, this is not the case for the Devonian magmatic arc, where isotopic data suggest an older continental lithosphere as the dominant source. These different sources are attributed to two contrasting geodynamic settings, with advancing and retreating oceanic slabs, respectively.

One Thousand Years of Mediterranean Silver Trade to the Levant: A Review and Synthesis of Analytical Studies

AbstractSilver exchanged by weight for its intrinsic value was the most important measure of value and means of payment in the southern Levant, starting from the Middle Bronze Age II–III through the Iron Age (~1700/1650‒600 BC). Since silver is not available locally in the Levant, its ongoing use as currency in the region triggered long-distance trade initiatives, and its availability or lack thereof had a direct impact on the economy. The continued use is evidenced in 40 silver hoards found in various sites across the region. A comprehensive study of lead isotopes and chemical analyses of samples obtained from 19 hoards enabled us to trace the origin of silver in the millennium during which it was extensively used as currency in the southern Levant and to identify constantly changing silver sources and concomitant trade routes. The results indicate that silver originated initially in Anatolia and Greece (~1700/1650–1600 BC) and shortly after from an unknown location in the Aegean/Carpathian/Anatolian sphere (~1600–1200 BC). After the collapse of Late Bronze Age Mediterranean trade routes, during Iron Age I (~1200–950 BC), there was a period of shortage. Silver trade was revived by the Phoenicians, who brought silver to the Levant from Sardinia and Anatolia (~950–900 BC), and later from Iberia (~900–630 BC). Further change occurred after the Assyrian retreat from the Levant, when silver was shipped from the Aegean (~630–600 BC). Following the devastation caused by the expanding Babylonian empire, silver consumption in the Levant practically ended for a century. Considering the isotopic results, combined with a detailed study of the context, chronology, and chemical composition, we demonstrate that all these factors are essential for the reconstruction of developments in the supply of silver in the southern Levant, and more generally. The changes in trade routes closely follow political and social transformations for over a millennium; exchange in this case was not only, not even mainly preconditioned by the environmental/geographic circumstances, as has often been argued for the Mediterranean. From an analytical point of view, we offer a protocol for the provenance of silver in general.

Differences in Non-heme Iron Absorption Between Healthy Adults of East Asian and Northern European Ancestry: A Stable Iron Isotope Study

Differences in Non-heme Iron Absorption Between Healthy Adults of East Asian and Northern European Ancestry: A Stable Iron Isotope Study

Tin-polymetallic mineralization and granitic rocks in the Nanling daping mining area: Geochemical and geochronological constraints

The Daping polymetallic deposit in the Nanling is a recently discovered deposit with significant potential in the Dayishan area. High-precision geochronological studies indicate that the emplacement ages of two fine-grained porphyritic (containing tourmaline) biotite granite units are 153.2 ± 0.9 Ma and 152.3 ± 1.0 Ma, representing products of the fifth magmatic activity in the Dayishan intrusion. The cassiterite U-Pb ages from the residual skarn type and greisen-type tin ores are 153.4 ± 3.6 Ma and 150.22 ± 0.37 Ma, respectively, and they are consistent within the error range, both belonging to the Yanshanian Early period. Petrogeochemical analyses of the granite reveal characteristics of high silica content (73.56 ∼ 75.91 %), alkali (K2O = 4.04 ∼ 5.58 %, Na2O = 2.22 ∼ 3.67 %), low calcium (0.42 ∼ 0.80 %), low magnesium (0.075 ∼ 0.29 %), and peraluminous nature (A/CNK = 1.26 ∼ 1.35). The rare earth element (REE) contents range from 35.78 × 10-6 to 111.57 × 10-6, with δEu values between 0.006 and 0.026, LREE/HREE ratios of 2.23 ∼ 3.41, and (La/Yb)N values of 1.20 ∼ 2.42. The granite is enriched in elements such as Rb, K, Th, U, Nd, Hf, and depleted in Ba, Sr, P, Nb, Ti, indicating strong crystal differentiation in the area. Sr, Nd, and Hf isotope studies show that the granite samples have ISr values of 0.67612–0.70040, εNd(t) values of −5.83 ∼ -8.23, εHf(t) values of −6.1 ∼ -1.9, (Nd)TDM2 values ranging from 1361 to 1573 Ma, and (Hf)TDM2 values ranging from 1147 to 1408 Ma. It is proposed that the Dayishan intrusion originated from the mixing of a mid-Paleoproterozoic mafic rock and a metamorphic sedimentary source region, with the latter being predominant. The detachment of source rocks from the mantle reservoir occurred in the mid-Paleoproterozoic. Combining lithological, petrogeochemical, and comparative analyses, it is classified as a highly fractionated A-type granite formed in a local extensional setting related to the subduction of the Pacific Plate. Additionally, this paper constructs a ore-forming model for the Daping tin deposit, aiming to provide reference for regional rare metal ore exploration.

The Kharbei Amphibolite–Gneiss Complex (Polar Urals): P–T Evolution and Results of U–Pb LA-ICP-MS Isotopic Study of Metamorphic Zircon

The Kharbei Amphibolite–Gneiss Complex (Polar Urals): P–T Evolution and Results of U–Pb LA-ICP-MS Isotopic Study of Metamorphic Zircon

Toward mending the marine mass balance model for nickel: Experimentally determined isotope fractionation during Ni sorption to birnessite

In fewer than fifteen years, the study of Ni stable isotopes has advanced from early method development to application of a powerful tool for resolving a long-standing question: why does it appear that output fluxes of Ni from the global oceans far exceed input fluxes? The seawater concentration of Ni, a bioessential trace metal, is almost certainly at steady state on timescales comparable to its residence time of ∼20 kyr, so some of the current flux estimates must be inaccurate. Just as the input and output fluxes should balance, so should the flux-weighted isotopic compositions of the inputs and outputs. Thus, isotopic characterization of inputs and outputs provide an additional constraint on a balanced model of the marine Ni budget. Here, we report on experiments designed to elucidate fractionation mechanisms and magnitudes for sorption of Ni to Mn oxyhydroxide (birnessite), because Mn-rich sediments accumulating on abyssal plains represent the largest sink flux of Ni from seawater to marine sediments. Our results show remarkably large fractionations at low ionic strength (average Δ60/58Nidissolved-sorbed = +1.38 ‰). Neither closed-system equilibrium trends nor Rayleigh curves fit the data well. Fractionations are even larger at high ionic strength (Δ60/58Nidissolved-sorbed ranging from +2.0 to +4.0 ‰), and they decrease with experimental duration from 2 d (49 h) to 27 d. The high ionic strength data fit Rayleigh trends well. Here, we use X-ray absorption fine-structure spectroscopy (EXAFS) and results from previous studies to support interpretation of our data as combinations of kinetic and equilibrium isotope effects that vary in their proportional contributions to the total fractionation with time and with surface loading. One important consequence of this study is that none of the experimental results reported thus far, including ours, are directly applicable to building steady-state models of the Ni cycle. Even our longest duration experiments did not achieve equilibrium, which is likely to be manifest in the very slowly accumulating sediments on abyssal plains. Our work constrains further the mechanisms of Ni sorption to birnessite and clearly indicates that determination of equilibrium fractionation in this system, although challenging, will be a crucial step toward resolving the apparent marine Ni imbalance.

Assessing a standardized method to identify optimal baselines for trophic position estimation in stable isotope studies of stream ecosystems

Assessing a standardized method to identify optimal baselines for trophic position estimation in stable isotope studies of stream ecosystems

Elemental differentiation and isotopic fractionation during space weathering of Chang’E-5 lunar soil

To investigate the chemical variation during space weathering of young mare basalts, here we report elemental, radiogenic Sr-Nd and stable Fe-Mg-Ca isotopic data of Chang’E-5 sieved soils and breccias. From the coarse fraction to the fine one, the sieved soils display increasing Al2O3 (10.34 wt%–13.36 wt%) and Sr (248 ppm–307 ppm) but decreasing FeO (23.50 wt%–20.22 wt%), MgO (6.88 wt%–5.78 wt%), FeO/Al2O3 (2.27–1.51) and MgO/Al2O3 (0.67–0.43). The contents of rare earth elements (except Eu) and high field strength trace elements do not vary with particle size but correlate with P2O5 contents. Given the limited contribution from contamination by meteorites and exotic materials ejected far away from the landing site, these elemental variations can be explained by differential comminution and distribution behaviors of plagioclase and mesostasis phases. These sieved soils yield a Sm-Nd isochron age (1.84 ± 0.83 Ga) comparable to that of basaltic clasts obtained by U-Pb dating (∼2.0 Ga). However, their Rb-Sr isotopic system is disturbed as indicated by their relatively homogeneous 87Sr/86Sr (0.701425–0.701592) despite variable Rb/Sr (0.017–0.028). These results suggest the Sm-Nd isotopic system is more robust to impact disturbance during space weathering compared to the Rb-Sr isotopic system. Given that the bulk soil still plots on the 2.03 Ga Rb-Sr reference isochron from the pristine plagioclases in CE-5 basalts, this disturbance did not affect the Rb-Sr isotopic system on the bulk scale. The CE-5 bulk soil has higher Mg# (33.6), 87Rb/86Sr (0.06) and present-day 87Sr/86Sr (0.701542) than the mean composition of reported basaltic clasts (Mg#: ∼28; 87Rb/86Sr: ∼0.038; 87Sr/86Sr: ∼0.700941), possibly implying that the bedrocks in CE-5 landing site consist of multiple magma pulses. The δ56Fe (0.122 ± 0.002 ‰ to 0.199 ± 0.008 ‰) and δ26Mg (−0.204 ± 0.016 ‰ to −0.109 ± 0.006 ‰) of sieved CE-5 soils increase with decreasing particle sizes but their δ44/42Ca (0.38 ± 0.04 ‰ to 0.44 ± 0.02 ‰) are relatively homogeneous. Mass balance modelling indicates that differential comminution has limited influence on the Fe-Mg-Ca stable isotopic compositions. We further dismiss the role of solar-wind sputtering, as Ca and Mg are more susceptible to sputtering and thus would be expected to show larger isotope fractionations compared to Fe, which is inconsistent with the observations. Free evaporation may explain the elevated δ56Fe and δ26Mg in fine fractions at given very limited depletion in FeO and MgO. The observed positive correlation between δ56Fe and δ26Mg, however, is much steeper than the slope expected for free evaporation, indicating also other mechanisms (e.g., Fe-Mg inter-diffusion). Since the CE-5 soil has a unique composition compared with Apollo and Luna soils, the chemical differentiation identified in this study provides new insights for establishing a connection between the chemistry and reflectance spectral properties of lunar soil. Our combined Fe-Mg-Ca isotopic study also provides a paradigm to distinguish the role of solar-wind sputtering and impact evaporation, and shows that the inter-particle diffusion process may be an important mechanism for the isotope fractionation among lunar soil components.

Isotope studies of presolar silicon carbide grains from supernovae: new constraints for hydrogen-ingestion supernova models

ABSTRACT We report isotope data for C, N, Al, Si, and S of 33 presolar SiC and Si3N4 grains (0.3–1.6 $\mu$m) of Type X, C, D, and N from the Murchison CM2 meteorite of likely core-collapse supernova (CCSN) origin which we discuss together with data of six SiC X grains from an earlier study. The isotope data are discussed in the context of hydrogen ingestion supernova (SN) models. We have modified previously used ad-hoc mixing schemes in that we considered (i) heterogeneous H ingestion into the He shell of the pre-SN star, (ii) a variable C-N fractionation for the condensation of SiC grains in the SN ejecta, and (iii) smaller mass units for better fine-tuning. With our modified ad-hoc mixing approach over small scales (0.2–0.4 M⊙), with major contributions from the O-rich O/nova zone, we find remarkably good fits (within a few per cent) for 12C/13C, 26Al/27Al, and 29Si/28Si ratios. The 14N/15N ratio of SiC grains can be well matched if variable C-N fractionation is considered. However, the Si3N4 isotope data point to overproduction of 15N in hydrogen ingestion CCSN models and lower C-N fractionation during SiC condensation than applied here. Our ad-hoc mixing approach based on current CCSN models suggests that the O-rich O/nova zone, which uniquely combines explosive H- and He-burning signatures, is favourable for SiC and Si3N4 formation. The effective range of C/O abundance variations in the He shell triggered by H ingestion events in the massive star progenitor is currently not well constrained and needs further investigation.

On the Nature of the Kharamatolou Structure and the Ratio of the Amount of Ultramafic Rocks of the Voykar-Synya Massif to That of the Ray-Iz Massif, Polar Urals

There have been petrographic, geochemical, geochronological (Rb-Sr, Ar-Ar) and isotopic (Sm-Nd) studies done on the metamorphic formations of the Kharamatolou structure of the Polar Urals, which were usually assigned to the Precambrian. The temperatures of metamorphism have been shown to range from 450 to 626 °C, and the pressures – from 3.7–9.1 kbar once PT-conditions reached the amphibolite facies. The amphibolites of the Kharamatolou formation are geochemically divided into two groups. According to the distribution spectra of lanthanides and Nd isotope composition, one group has the characteristics similar to depleted N-MORB basalts εNd(0)=+7.0, and another group – those similar to moderately enriched E-MORB basalts εNd(0)=+(4.5–2.4). It has been found that the Kharamatolou structure is probably composed of the Early to Middle Paleozoic continental rise deposit of the Russian Platform, which passed the main stage of folding and metamorphism in the Late Devonian (Rb-Sr, 366±11 Ma). The gabbro-ultrabasic Ray-Iz and Voykar-Synya massifs have been shown to be one during most of their Pre-Triassic history. Now these ultrabasite massifs are separated by the young (Triassic) Kharamatolou uplift which is an erosive-tectonic semi-window where ultrabasic rocks of the Polar-Ural belt are exposed at the base of the thrust fault. The Kharamatolou structure is one of the transverse uplifts of the Urals which probably resulted from the Middle to Late Triassic compression therealong. As a result of the Middle to Late Triassic uplift of the Haramatolou metamorphites, the overlying ultrabasites were washed away by erosion. The mélange serpentinites observed in the center of the Kharamatolou structure are uneroded remnants of the link that once existed between the Ray-Iz and Voikar-Synya massifs. This significantly increases the metallogenic potential of the Voikar-Synya massif, as the Ray-Iz hosts the largest known chromite deposits in Russia.

A mineralogical and isotopic study of the historic monomict eucrite Padvarninkai

AbstractThe Padvarninkai meteorite is a relatively understudied eucrite, initially misclassified as a shergottite given its strong shock characteristics. In this study, a comprehensive examination of the petrology; mineral composition; major, minor, and trace element abundances; and isotopic composition (C, O) is presented. Padvarninkai is a monomict eucrite consisting of a fine to coarse‐grained lithology and impact melt veins. Pyroxene grains are typically severely fractured and mosaicked whilst plagioclase is either partially or totally converted to maskelynite. Based on shock features observed in pyroxene, plagioclase, and apatite, Padvarninkai can be given a shock classification of M‐S4/5. Despite the high shock experienced by this sample, some of the original igneous textures remain. Compositionally, Padvarninkai is a main group eucrite with a flat REE pattern (~10–12 × CI) and elevated Ni abundances. Whilst both new and literature oxygen isotopes are similar to other eucrites, however, Padvarninkai displays an anomalously high δ13C value. To reconcile the high Ni and δ13C value, impact contamination modeling was conducted. These models could not reconcile both the high Ni and δ13C value with the eucritic δ18O values, arguing against impact as a source for these anomalies.

SCLEROCHRONOLOGICAL EVIDENCE OF LIFE HISTORY AND AMBIENT TEMPERATURE FROM MODERN AND EARLY PLEISTOCENE GLYCYMERIS AMERICANA (MOLLUSCA:BIVALVIA) OF THE U.S. EASTERN SEABOARD

Abstract Growth-increment and isotopic studies of shells of the marine bivalve Glycymeris americana are a potential source of information bearing on its life history and preferred environment over the late Cenozoic on the U.S. eastern seaboard. We demonstrate that the ages of shells can be determined from growth bands and ontogenetic profiles of oxygen isotope (δ18O) composition, and that shell aragonite is deposited in oxygen isotopic equilibrium with seawater, enabling calculation of ambient temperatures by means of a generic transfer function. Modern specimens from North Carolina rarely reach the large size commonly attained by modern forms from Florida and Early Pleistocene forms from both states, and modern populations from North Carolina probably include fewer old individuals, the most certain disparity being with Early Pleistocene populations from the state. The temporal change in age structure in North Carolina may be an effect of recent scallop trawling but earlier non-anthropogenic environmental change cannot be ruled out as the cause. Maximum and minimum temperatures calculated from the δ18O profiles of Early Pleistocene shells indicate a larger seasonal range than now in both Florida and North Carolina, due to cooler winters. This may reflect greater southward penetration of cool northern waters, with transport along the shelf supplemented by upwelling of water brought south at depth.

Individual from the kurgan burial of the XII century in the Middle Oka — experience of complex archaeological and genetic research

For the first time, this paper presents a complex study of the burial of the ancient Russian woman from the classic “Vyatich” mound from the Kremenyie burial site (Moscow region). The mounds and synchronized ground cremation burials are combined at this unique 12th-century burial site. The aim of this research is to examine the historical details of the person from the mound using conventional archaeological, anthropological, and archae-oparasitology methodologies along with modern paleogenetics methods. The burial site is characterized by a general “archaic” rite, manifested in the late preservation of the cremation rite along with the burial. According to anthropological data, an elderly woman, over forty, was buried there. She was identified as a member of the local population by radiogenic strontium isotope (87Sr/86Sr) study. Rich grave content and the fact that the body was buried in the middle of the mound indicate the woman's high social standing in the community. According to ar-chaeoparasitological data, the eating habits of the woman appear to be characterized by the consumption of un-cooked or insufficiently thermally prepared freshwater fish. The complete mtDNA sequence reconstruction indi-cates that it belongs to haplogroup V1a1, one of the Western Eurasian haplogroup V branches. To date, this represents the first case of the V1a1 mitogroup being found in the Russian Plain during ancient times. A repre-sentative of the Danish Viking clan from the Oxford burial site of the XI century was the closest of the ancient samples to the mtDNA of the studied woman, which indicates a genetic relationship on the maternal lineage with the medieval Northwestern European population. Single nucleotide substitution A7299G in the mitogenome of the woman clusters her with present-day Russians from the Belgorod and Pskov regions and shows the continuity of the modern Russian population with the Ancient Russians. Thus, the results of our study demonstrate the private details of the individual as common historical features, which include the ceremonial side of burial and belonging to the maternal genetic lineage preserved in the modern gene pool of the Russian population.

Camelids in the hyperarid core of the Atacama desert 12,000–11,000 years ago? A stable isotope study and its consequences for early human settlement

How did hunter-gatherers initially settle and move across extreme environments? We conducted a multi-disciplinary study to tackle this question, focusing on how Paleoindigenous populations inhabited the hyperarid core of the Atacama Desert. Particularly, we examined the stable isotopic values of ∼12,000–11,200-year-old camelid and rodent bones and hair samples retrieved from low-elevation archaeological sites (Pampa del Tamarugal basin - PdT, 800–1200 masl). By integrating novel and existing data into a regional stable isotope ecology, we offer a baseline for interpreting our results. δ13C and δ15N values on archaeological remains show animals with different geographical origins. A first group includes camelids and rodents with lower δ15N values and δ13C values indicating a dominantly C3 diet, corresponding to animals either local to the PdT or from the Andean Steppe, at least ∼80 km away and between 4000 and 4500 masl. Most of these remains, however, come from residential sites and belong to young camelids, indicating a local origin. A second group presents a higher δ15N signal and δ13C values indicative of a mixed C3–C4 based diet. These animals were not local but source to the Puna at least ∼60 km away between 3200 - 4000 masl. We hypothesize that the first would correspond to animals associated with hunter-gatherer bands settled around a wetland and grove environment in the PdT. The second group could correspond to remains brought by humans from the Puna to the PdT. Our results demonstrate that during the Late Pleistocene/Early Holocene the Atacama was very different than today, supporting life that included large and mid-size game. These results also show that the core of the Atacama attracted animals and people and counters the notion of this ecosystem as a barren passageway from the Andes to the coast.

Recycling carbonated hydrous sediments into the mantle source of carbonatite-associated rare-earth-element deposits

Decoding the petrogenesis of carbonatites is of great importance for our understanding of the Earth’s deep carbon cycling and formation of rare-earth-element (REE) deposits. Among global carbonatites, the Cenozoic Mianning-Dechang (MD) carbonatites in the western Yangtze Craton are unique because of their development in a post-collisional zone and host numerous giant-large REE deposits. However, most of previous studies have focused on the late magmatic to hydrothermal stages, while the nature of the mantle source and early-stage magmatic evolution remain largely unexplored. Here we present a combined petrographic, chemical and Sr-Nd-Pb isotopic study on the MD lamprophyres to address these issues. A genetic linkage is revealed between these lamprophyres and the MD carbonatites and syenites by their geochemical similarities and close spatial and temporal associations. Our data suggest a phlogopite-rich carbonated subcontinental lithospheric mantle (SCLM) source metasomatized by subducted carbonated hydrous sediment-derived melts/fluids. Significant fractional crystallization of olivine, clinopyroxene and biotite (±Ti-Fe oxides) from hydrous, K-rich and carbonated primary melts caused the carbonate–silicate liquid immiscibility in the highly evolved melts and thus formation of the MD carbonatites and syenites at shallow depths. Melting of subducted carbonated hydrous sediments not only provides carbonatitic liquids for the SCLM carbonation, but also supplies sufficient water and alkalis that are critical for accumulating and transporting REE in carbonatitic fluids. Post-collisional lithospheric thinning also played a critical role in the formation of carbonatites via triggering the melting of the carbonated SCLM. This study provides new insights into the deep processes during the formation of carbonatites and associated REE deposits in post-collisional zones.

Tune and turn the pyrolysis of metal organic frameworks towards stable supported nickel catalysts for the dry reforming of methane

Dry reforming of methane (DRM) is an inimitable approach for eliminating both greenhouse gases, methane and CO2, while producing synthesis gas which further can be converted to added-value fuels. However, the industrialization of DRM has been limited due to sintering and coking to the catalysts under the harsh reaction conditions. Here, we propose a new methodology for producing tunable supported nickel-based catalysts for DRM using metal organic frameworks (MOFs) as precursors of the catalyst components. In particular, Ni- and La-MOFs were coalesced using sonication and then calcined at different temperatures to produce catalysts with tailored Ni metal size (5–20 nm) and tuned strong metal-support interactions (SMSI). Here, the synthesis of nickel and nickel oxide nanoparticles embedded on lanthanum-based supports by controlled calcination of the MOF structures is demonstrated; the Ni supported catalysts were then used for DRM reaction. Among the developed catalysts, the catalyst produced following calcination at 500 °C (Ni-La-500) has shown stable and high CH4 conversion rates under DRM conditions at 800 °C with negligible carbon formation at elevated gas hourly space velocities. Further, the catalytic performance of Ni-La-500 catalyst (sonicated) was compared to the physically mixed MOFs derived catalyst (Ni-La-500-PM), conventional wetness impregnated catalyst (Ni-La-500 WI), Ni-MOF derived unsupported catalyst (Ni-500), and lower Ni concentration catalyst (sonicated, 10Ni-La-500). The observed CH4 conversion rates at 50,000 mL·gcat–1·h−1 GHSV are 81.8, 67.9, 85.4, 34.7, and 57.9 % for Ni-La-500, Ni-La-500 PM, Ni-La-500 WI, Ni-500, and 10Ni-La-500 catalysts, respectively after 24 h of DRM reaction. With isotopic studies, it was found that the 18O exchange rate was higher in case of Ni-La-500-PM catalyst (8.1 mmol·g−1) as compared to Ni-La-500 catalyst (5.5 mmol·g−1). Prior interaction between MOFs, calcination temperatures, reaction conditions, and the carbon pathways during catalytic activity dictates the conversion rates and selectivity of the products. Overall, with the herein proposed approach of MOF-derived supported catalysts exceptional conversion rates and stability during the DRM reaction with nominal coking and sintering were demonstrated, solving the two major challenges faced by conventional and unsupported catalysts.

U–Pb zircon, zircon Hf and whole-rock Sm[sbnd]Nd isotopic signatures on the evolution of Late paleozoic bimodal magmatism in Gharebagh area, NW Iran

The Gharebagh area consists of a suite of mafic to acidic rocks located in northwestern Iran, in the Sanandaj-Sirjan zone (SSz), which is part of the Zagros orogenic belt. In this paper, we present a detailed petrological, geochronological, and isotopic study of representative rocks of Late Paleozoic igneous activity in NW Iran. LA-ICP-MS dating of zircons shows that the Gharebagh intrusive body (GIB) was formed in a tight time frame of 300 Ma. Geochemical analyses as well as isotopic studies of LuHf on zircon and SmNd on whole-rock were used to determine the petrogenesis of these rocks and develop a tectonic model. Crustal-model ages (Hf-tNC) of 0.57 to 1.02 Ga indicate the contribution of older Neoproterozoic crust to the formation of these rocks. The partially melted lower crust was one part of the magma together with a mafic melt formed by differentiation of the depleted mantle. The GIB suite was presumably formed by an anorogenic magmatic event (continental rift) that included extensive mantle upwelling and partial melting of the lower crust. So the gabbroid and granitoid rocks are coeval with the 300 Ma but not co-magmatic origin.

Early Mississippian global δ13C excursion is not a diagenetic artifact

Shallow-water platform carbonate δ13C may provide a record of changes in ocean chemistry through time, but early marine diagenesis and local processes can decouple these records from the global carbon cycle. Recent studies of calcium isotopes (δ44/40Ca) in shallow-water carbonates indicate that δ44/40Ca can be altered during early marine diagenesis, implying that δ13C may also potentially be altered. Here, we tested the hypothesis that the platform carbonate δ13C record of the Kinderhookian-Osagean boundary excursion (KOBE), ∼353 m.y. ago, reflects a period of global diagenesis using paired isotopic (δ44/40Ca and clumped isotopes) and trace-element geochemistry from three sections in the United States. There is little evidence for covariation between δ44/40Ca and δ13C during the KOBE. Clumped isotopes from our shallowest section support primarily sediment-buffered diagenesis at relatively low temperatures. We conclude that the δ13C record of the KOBE as recorded in shallow-water carbonate is consistent with a shift in the dissolved inorganic carbon reservoir and that, more generally, ancient shallow-water carbonates can retain records of primary seawater chemistry.