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Pressure solution is inferred to be a significant contributor to sediment compaction and lithification, especially in carbonate sediments. For a sediment deforming primarily by pressure solution, the compaction rate should be directly related to the rate of calcite dissolution, transport along grain contacts, and calcite reprecipitation. Previous experimental work has shown that there is evidence that deformation in wet calcite grain packs is consistent with control by pressure solution, but considerable ambiguity remains regarding the rate limiting mechanism. We present the results of laboratory compaction experiments designed to directly measure calcite dissolution and precipitation rates (recrystallization rates) concurrently with strain rate to test whether measured rates are consistent with predicted rates both in absolute magnitude and time evolution. Recrystallization rates are measured using trace element chemistry (Sr/Ca, Mg/Ca) and isotopes (87Sr/86Sr) of fluids flowing slowly through a compacting grain pack as it is being triaxially compressed. Imaging techniques are used to characterize the grain contacts and strain effects in the post-experiment grain pack. Our data show that calcite recrystallization rates calculated from all three geochemical parameters are in approximate agreement and that the rates closely track strain rate. The geochemically inferred rates are close to predicted rates in absolute magnitude. Uncertainty in grain contact dimensions makes distinguishing between surface reaction control and diffusion control difficult. Measured reaction rates decrease faster than predicted from standard pressure solution creep flow laws. This inconsistency may indicate that calcite dissolution rates at grain contacts are more complex, and more time-dependent, than suggested by geometric models designed to predict grain contact stresses.

The first detailed data are obtained on the Sr‒Nd‒Pb isotope systematics and geochemistry of Quaternary intraplate hauyne basanites and ordanshites in the Lesser Caucasus. The parental magmas of the rocks were found out to have been generated by mixing material from at least two regional sources: one relatively depleted and the other significantly enriched in incompatible elements. One of these sources of the hybrid magmas was most likely a mildly depleted regional plume–asthenospheric source of the CAUCASUS OIB type, whose isotopic-geochemical signatures were close to those of the COMMON and PREMA mantle reservoirs. The other source of the material for the rocks was relatively enriched in radiogenic Sr and Pb and depleted in radiogenic Nd and was most probably enriched subcontinental lithospheric mantle of the EM II type. [ABSTRACT FROM AUTHOR]

The Early Cretaceous gold deposits in the North China Craton are known as Jiaodong-type gold deposits. Here, we summarize a quantity of reported (including this study) pyrite trace element, δ34S, and Pb isotope data from the Jiaodong, Xiaoqinling, and Central Taihangshan gold fields to comprehensively reveal the characteristics of the ore-forming fluids in Jiaodong-type gold deposits. The results show that the Au concentrations in the pyrites from the Jiaodong-type gold deposits are typically less than 8.12 ppm and do not correlate with As but have significant positive correlations with Bi and Te, implying that Bi and Te may govern Au enrichment in pyrite. The overall As concentrations in the pyrites are relatively low, and only the Jiaodong gold field is significantly higher, which may be caused by fluid flowing through As-rich metamorphic sedimentary rocks. In Jiaodong-type gold deposits, Au is dominantly found as visible gold, followed by invisible gold. Invisible gold generally occurs as a solid solution (Au+), and only the proportion of nanoparticles (Au0) in the Xiaoqinling gold field is slightly higher (20%). Sulfidation and fluid immiscibility or boiling were the key mechanisms leading to visible gold precipitation. The Co/Ni ratio, δ34S, and Pb isotopes indicate that the ore-forming fluids in the Jiaodong-type gold deposits exhibit remarkable magmatic features, and the ore-forming materials are primarily derived from a mixture of lower crust and mantle sections. Among them, the ore-forming materials from the lower crust of the Central Taihangshan gold field are slightly higher. [ABSTRACT FROM AUTHOR]

The article provides new data on the structure of the Laptev Sea flank of the Gakkel Ridge. The intensive supply of clastic material from the Laptev Sea shelf leads to the development of a thick alluvial fan at the continental rise, which determines the structure of the bottom topography. In the northwestern direction, the influence of the fan decreases and tectonics becomes the main relief-forming factor. The bathymetric survey traced the asymmetrical rift valley of the Gakkel Ridge, the western flank of which is complicated by terraces. The presence of fault structures, bottom subsidence, extensive sediment supply, and the widespread development of subaqueous slump processes indicate the high neotectonic activity of the Laptev Sea flank of the Gakkel Ridge. For the first time in this region, numerous carbonate rocks have been discovered, the authigenic cement of which is represented by magnesian calcite or aragonite with an admixture of terrigenous material. The palynological and micropaleontological analysis of the carbonate rocks indicates the Quaternary formation of authigenic carbonate cement. An important role in the formation of authigenic carbonates was played by diagenetic solutions coming from the sedimentary cover together with methane and oxidation products of gases and organic matter. The authigenic carbonates were precipitated mainly in an isotopic equilibrium with bottom water at a temperature of about 0°C. The negative correlation between 87Sr/86Sr and δ13C indicates the presence of at least two different sources of carbonate-forming solutions. [ABSTRACT FROM AUTHOR]

Fragments of marble revetment and floor slabs as well as some broken statuary and vessels were recovered from the excavation of a Roman temple in the harbor town of Berenike on the Red Sea coast of Egypt. Petrographic analyses, including optical, cathodoluminescence, and scanning electron microscopy as well as isotopic analyses (δ13C, δ18O, 87Sr/86Sr), were conducted to determine the provenance of the marble. The aim was to reconstruct the commercial ties that led to this prized building stone being brought to Berenike. Most, if not all, of the slabs are of banded gray to white marble showing properties indicative of a Prokonnesian origin. This marble, exploited on Marmara Island (Sea of Marmara, Turkey) and extensively utilized throughout the Mediterranean, including Egypt from at least the second century A.D., might have been procured from the marble depots in Alexandria. This could have involved engaging a team of Bithynian master craftsmen for the project, presumably to embellish the main temple of the city during the reign of the Roman emperor Hadrian. The statuary and vessel finds are composed of white marble representing several sources. Some coarse‐grained specimens were surely extracted in Prokonnesos. For others, the source is uncertain and the likely candidates are Prokonnesos, Paros (Cyclades, Aegean Sea), and Ephesos (Aegean coast of Asia Minor). The fine‐grained varieties represented high‐quality Dokimian (Afyon region, Asia Minor) and most likely expensive Parian (lychnites type) marble. Marble from the ancient Gebel Rokham quarries in Egypt was also examined for comparison, but its properties have excluded this source in the case of the marble artifacts from Berenike analyzed in this work. [ABSTRACT FROM AUTHOR]

Abstract Shell ring archaeological sites are one of the most visible site types along the lower South Atlantic Coast of the United States. These cultural sites are large, circular to arcuate piles of mollusk shells with some reaching over three meters in elevation and over 100 m in diameter. They are comprised largely of mollusk shells (e.g., Eastern oyster, Crassostrea virginica), but also contain early pottery, nonhuman faunal remains, and other artifacts. Our work establishes that they represent the earliest widespread Native American villages occupied year-round in the Eastern Woodlands of North America. Significantly, our results from sea-level modelling and isotope geochemistry on mollusks establish that the inhabitants of these earliest villages (ca. 5000–3800 yrs. BP) lived within a fluctuating coastal environment, harvested certain resources year-round, and targeted diverse habitats across the estuaries. Both the growth and decline of these earliest villages are associated with a concomitant rise and lowering of sea level that impacted the productivity of the oyster reef fishery along the South Atlantic Coast. Despite these large-scale environmental changes, this research indicates that Native American fishing villages persisted along the coast for over 1000 years.

We review published studies characterizing the Thamama‐B reservoir zone in the upper Kharaib Formation (late Barremian) in Abu Dhabi oilfields and at outcrops in Oman. Available data for oxygen and carbon isotope compositions, fluid inclusion measurements, cement abundance and formation water composition are interpreted in terms of a paragenetic model for the Thamama‐B in field F in Abu Dhabi where the interval is deeply buried. The present synthesis provides a useful basis for understanding and predicting reservoir quality in static models and undrilled prospects, as well as for planning promising directions for further research. The goals of this study were to summarize the geologic setting and petrology of the Thamama‐B reservoir and its surrounding dense zones, and to examine how sedimentology, stratigraphy and diagenesis have interacted to control porosity and permeability. Results that may have useful applications for similar microporous limestone reservoirs in general include: the depositional environments and stratigraphy of the subject strata;a model for how porosity variations result mainly from calcite cementation sourced from stylolites, with little dependence on lithofacies other than the localization of chemical compaction by depositional clay linked to sequence stratigraphy;the use of solidity (rock thickness with porosity removed) as a check on porosity creation by burial dissolution;observations linking high‐permeability streaks with storm lag beds and fractures;the concept of strata being gradually buried through a relatively static salinity‐stratified water column;integration of conventional and clumped stable‐isotope data with petrologic observations to constrain the timing of porosity evolution. [ABSTRACT FROM AUTHOR]

Determining the mechanisms by which the earliest continental crust was generated and reworked is important for constraining the evolution of Earth's geodynamic, surface, and atmospheric conditions. However, the details of early plate tectonic settings often remain obscured by the intervening ~4 Ga of crustal recycling. Covariations of U, Nb, Sc, and Yb in zircon have been shown to faithfully reflect Phanerozoic whole-rock-based plate-tectonic discriminators and are therefore useful in distinguishing zircons crystallized in ridge, plume, and arc-like environments, both in the present and in deep time. However, application of these proxies to deciphering tectonic settings on the early Earth has thus far been limited to select portions of the detrital zircon record. Here, we present in situ trace-element and oxygen isotope compositions for magmatic zircons from crystalline crustal rocks of the Acasta Gneiss Complex and the Saglek-Hebron Complex, Canada. Integrated with information from whole-rock geochemistry and zircon U-Pb, Hf, and O isotopes, our zircon U-Nb-Sc-Yb results reveal that melting of hydrated basalt was not restricted to a single tectonomagmatic process during the Archean but was operative during the reworking of Hadean protocrust and the generation of juvenile crust within two cratons, as early as 3.9 Ga. We observe zircon trace-element compositions indicative of hydrous melting in settings that otherwise host seemingly differing whole-rock geochemistry, zircon Hf, and zircon O isotopes, suggesting contemporaneous operation of stagnant-lid (oceanic plateau) and mobile-lid (arc-like) regimes in the early Archean. [ABSTRACT FROM AUTHOR]

Since the mid-1970s, groundwater resources in Bermuda have been explored to supplement growing potable water demand on the island. Much of this work has focused on modeling the shape and size of freshwater lenses beneath the island's surface, mainly the Devonshire Lens. Less attention has been paid to how these freshwater lenses interact with surrounding coastal seawater, a process that may grow in importance as sea levels rise. Due to isotopic differences between aquifer water and seawater, these interactions can be tracked using the oxygen isotopic composition of water (δ18Ow) samples collected from coastal and subterranean areas. A pilot study found more temporal variation in coastal seawater δ18Ow along Bermuda's South Shore (the section of the coast closest to the Devonshire Lens) compared to elsewhere around the island and suggested that freshwater was discharging into coastal seawater fromthe Devonshire Lens in significant quantities. However, this study was limited by its small dataset so could not quantify the full spatial and temporal variability of δ18Ow in this area. Here, we present salinity and δ18Ow measurements from seawater samples collected around Bermuda and in wells tapping the Devonshire Lens on timescales ranging from hourly to monthly to better visualize the dynamic interaction between coastal seawater and aquifersourced freshwater. We find tight correlation between salinity and δ18Ow in well waters, indicating a simple linear mixing relationship between seawater and aquifer water in the subsurface. We confirm previous findings of larger variability in δ18Ow along the South Shore compared to elsewhere and relate observed changes to tidal height on hourly to monthly timescales. Surprisingly, South Shore seawater salinity does not vary in accordance with δ18Ow, implying additional mechanisms, such as the addition of salt spray, must be acting to mute salinity changes. These findings also demonstrate the potential in using δ18Ow to study submarine groundwater discharge, as salinity measurements alone did not detect as much variability. As sea levels rise and interactions between ocean and aquifer waters change, coastal and well water δ18Ow measurements may be helpful in tracking these processes, and in particular, changes in aquifer size. [ABSTRACT FROM AUTHOR]

The Jurassic–Cretaceous boundary is the only Phanerozoic period-level boundary that lacks a golden spike on the geological timescale despite significant global geological and environmental change during this time related to the opening of the Atlantic Ocean. Paleoenvironmental proxy profiles (total organic carbon, δ34S, δ15N, Fe, Mn, Ce/Ce*, Th/U, δ13Corg, P, Ni, Zn, Cu, and B/Ga) for core 3 of the Baccalieu I-78 well in the Flemish Pass Basin, offshore eastern Canada, exhibit a geochemical anomaly between 3288.5 and 3289 m, overlapping with the biostratigraphic placement of the Jurassic–Cretaceous boundary. Collectively the geochemical analyses are interpreted to indicate that the anomaly is associated with a fall in relative sea level, followed by a rise, which led to restricted circulation, stratification, and widespread anoxia. This anoxia, coupled with an arid climate, further resulted in reduced weathering, limited nutrient supply, and an overall reduction in primary productivity. The results of this study, in conjunction with previous biostratigraphic studies on core 3, suggest that the Jurassic–Cretaceous boundary in Baccalieu I-78 likely falls within the geochemical anomaly, specifically between 3228.5 and 3288.85 m. Furthermore, the paleoenvironmental interpretations derived in this study agree with published reports on global sea level and climate trends around the Jurassic–Cretaceous boundary, implying the influence of global, rather than regional, factors on deposition. This suggests that geochemical proxies may be useful in providing additional paleoenvironmental insights and helping to constrain stratigraphic boundaries, particularly in intervals that lack significant lithological or biological change. [ABSTRACT FROM AUTHOR]

The incremental construction of plutons characterises magmatic activity in arc settings, where new continental crust is produced. This polyphasic growth entails interactions with one or more crustal components, which modulate the geochemical and isotopic compositions of the newly formed crust. However, the early stages of magmatism are not always preserved due to obliteration by later magmatic pulses. Spatial migration of magmatism during the construction of the Adamello batholith (Northern Italy) enables the examination of the early pulses of pluton formation, thus allowing a time-integrated study of the relative importance of crystallisation-differentiation and contamination in a continental arc setting. We conducted a detailed textural, major and trace element and Sr isotopic study of plagioclase from the first intrusive pulses of the Adamello batholith, combined with new major, trace element and Sr–Nd isotopic analyses of bulk rock samples across the entire Adamello batholith. We selected well-characterised samples with published CA-ID-TIMS 206Pb-238U ages and Hf isotopic composition for zircons. Strontium isotopes in plagioclase from the same samples were determined by laser ablation multi-collector ICP-MS. The tonalitic samples in the early magmatic stages show elevated but constant Sr isotopic compositions despite large variations in anorthite contents (An90 to An13), indicating that crustal contamination occurred before significant differentiation. Invariant bulk-rock 87Sr/86Sr with variable SiO2 in all superunits of the Adamello batholith further supports contamination preceding significant melt differentiation. Contamination by lower crustal basement lithologies is due to the increasing thermal anomaly triggered by consecutive magmatic injections coupled with the heterogeneous and less restitic nature of the basement in the early stage of the magmatic system (i.e. before consumption of fusible components). In addition, we observe significant variability in crustal contamination proxies (e.g. 87Sr/86Srplag, 87Sr/86Srbulk, εNdbulk, εHfzircon) during the initial phases of magmatism. This variability likely reflects the uneven distribution of positive thermal anomalies in the lower crust during early magmatic stages as well as the diverse lithological and isotopic makeup of the lower crust. The processes identified in our case study are pertinent to continental arc magmatism, particularly where magmas interact with a metapelitic lower crust. [ABSTRACT FROM AUTHOR]

Geochronological (U-Pb zircon, ID-TIMS), isotope-geochemical (Nd, Sr, Pb), and geochemical studies of rocks of the Amanan and Amudzhikan intrusive complexes and volcanic rocks of the Ukurey Formation in the eastern part of the West Stanovoy superterrane of the Central Asian Orogenic Belt were performed. The assignment of granitoids of these complexes to high-potassium C-type adakites is substantiated. It is established that the studied rocks are cogenetic and can be ascribed to a single Amudzhikan volcano-plutonic association formed in the age range of 133 ± 1–128 ± 1 Ma. The igneous complexes of this association belong to the Stanovoy volcano-plutonic belt, which extends in the sublatitudinal direction from the Pacific Ocean inward the North Asian continent for more than 1000 km, subparallel to the Mongol-Okhotsk suture zone, and assembles the tectonic structures of the Dzhugdzhur-Stanovoy and West-Stanovoy superterranes. The formation of the Stanovoy Belt is related to the closure of the Mongolo-Okhotsk Ocean and the collision between North Asian and Sino-Korean continents at ~140 Ma. The subsequent collapse of the collisional orogen, which was accompanied by large-scale lithospheric extension and delamination of the lower part of the continental lithosphere, led to upwelling of asthenospheric mantle. This caused melting of the lithospheric mantle and continental crust and, as a consequence, the formation of both mafic (shoshonitic) melts and anatectic crustal melts of the adakite type. The mixing of these melts led to the formation of the parental magmas of the Amudzhikan magmatic association. The crustal component in the source was of heterogeneous nature and finally formed as a result of the Early Cretaceous collision event. It is characterized by the upper-crustal isotopic signatures: increased Rb/Sr and U/Pb ratios and a decreased Sm/Nd ratio in the source. The mantle component is represented by enriched lithospheric mantle of the Central Asian Orogenic Belt, the formation of which is associated with subduction processes and closure of the Mongol-Okhotsk paleoocean. Metasomatic transformation of the mantle with the introduction of melts and fluids with isotopic parameters of an EMII-type source or upper crust occurred at this stage. [ABSTRACT FROM AUTHOR]

Zinc (Zn) is an essential trace element that is involved in both biotic and abiotic processes in Earth's surface environments. Over the last 20 years, advances in mass spectrometry instrumentation have enabled unprecedented high-precision Zn isotope abundance ratio determinations in natural and anthropogenic samples. Supported by a solid theoretical background inherited from the traditional non-metal stable isotopes (C, N, H, O, S), the understanding of the controlling factors of Zn isotope fractionation has rapidly evolved. In this article, we review the main applications and findings of Zn isotopes in a variety of scientific domains, including metal contamination, magmatic differentiation, plant uptake, weathering, global climate change, dietary and trophic chains, and biomedicine. The analytical aspects of Zn isotope determination in solid and water samples and the principles and mechanisms of Zn isotope fractionation are also reviewed. This work aims to provide a general yet in-depth panorama of Zn isotope chemistry and to demonstrate the versatility and potential of this isotope system for studying the biological, geological and chemical cycling of Zn. [ABSTRACT FROM AUTHOR]

Summary: To reveal the stratigraphic age of the Shiqianfeng Formation in the eastern continental basin of the North China Craton and the provenance of its sediments from the Late Carboniferous to the Early Triassic, six sandstone samples from the Puyang area were selected for zircon U-Pb dating. The result show that the Shiqianfeng Formation in the eastern North China Craton belongs to the Early Triassic. According to the age clusters of six samples, considering the regional geological setting and the distribution of zircon ages in the potential provenance area, it can be inferred that the Inner Mongolia Paleo-uplift provided continuous provenance supply for the study area during the Late Carboniferous-Early Triassic. It is also suggested that the Inner Mongolia Paleo-uplift originated during the Devonian and received denudation to provide provenance for inland basins. The second and third tectonic uplift occurred during the middle-late Permian, and the early-middle Triassic, respectively.

Since the mid-1970s, groundwater resources in Bermuda have been explored to supplement growing potable water demand on the island. Much of this work has focused on modeling the shape and size of freshwater lenses beneath the island’s surface, mainly the Devonshire Lens. Less attention has been paid to how these freshwater lenses interact with surrounding coastal seawater, a process that may grow in importance as sea levels rise. Due to isotopic differences between aquifer water and seawater, these interactions can be tracked using the oxygen isotopic composition of water (δ18Ow) samples collected from coastal and subterranean areas. A pilot study found more temporal variation in coastal seawater δ18Ow along Bermuda’s South Shore (the section of the coast closest to the Devonshire Lens) compared to elsewhere around the island and suggested that freshwater was discharging into coastal seawater from the Devonshire Lens in significant quantities. However, this study was limited by its small dataset so could not quantify the full spatial and temporal variability of δ18Ow in this area. Here, we present salinity and δ18Ow measurements from seawater samples collected around Bermuda and in wells tapping the Devonshire Lens on timescales ranging from hourly to monthly to better visualize the dynamic interaction between coastal seawater and aquifer-sourced freshwater. We find tight correlation between salinity and δ18Ow in well waters, indicating a simple linear mixing relationship between seawater and aquifer water in the subsurface. We confirm previous findings of larger variability in δ18Ow along the South Shore compared to elsewhere and relate observed changes to tidal height on hourly to monthly timescales. Surprisingly, South Shore seawater salinity does not vary in accordance with δ18Ow, implying additional mechanisms, such as the addition of salt spray, must be acting to mute salinity changes. These findings also demonstrate the potential in using δ18Ow to study submarine groundwater discharge, as salinity measurements alone did not detect as much variability. As sea levels rise and interactions between ocean and aquifer waters change, coastal and well water δ18Ow measurements may be helpful in tracking these processes, and in particular, changes in aquifer size.

[Significance] Carbonate factories provide the foundation for forming carbonate depositional systems. They are closely related to marine evolution, elemental cycling, and earth surface processes and are an essential part reflecting the evolution of the Earth system. The transition of carbonate factories often coincides with biological and environmental changes. Over geological time, the change of carbonate factories frequently occurs along with biological or environmental crises such as mass extinction or the initiation of new life forms such as life explosion or biological recovery after crisis. Therefore, quantifying the characterization of carbonate factories and their controlling factors is for a deeper understanding of the geological information recorded in carbonate rocks. [Progress] However, most studies on carbonate factories, particularly those from the geological records, are qualitative based on the lithological and microfacies analysis. This study summarizes the research progress in the semi-quantitative to quantitative characterization of carbonate factories, combining the introduction of the methods for forward modelling of sedimentary processes to provide a perspective for the detailed characterization of carbonate factories from a quantitative reconstruc-tion perspective. In addition to providing information on rock components that indicate the ingredients of carbonate factories, statistical analysis of carbonate grains can offer insights into the sedimentary environment by examining parameters such as size, roundness, and sorting. These shape characteristics can serve as quantitative indicators of water energy and grain transportation processes. Elemental geochemical proxies enable the assessment of environmental parameters such as redox conditions, nutrient levels, and climatic conditions. Isotopic geochemical proxies play a crucial role in reconstructing the evolution of environmental factors such as temperature and seawater carbonate saturation. By a combination of multiproxies and sedimentary process modelling, a comprehensive analysis can identify the production process, controlling factors, and evolution of carbonate factories. [Prospects] Based on traditional carbonate sedimentology, studying carbonate factories should deepen our understanding of their controlling factors, particularly the quantitative assessment of factors directly impacting ecosystems. When applying quantitative analysis methods such as sediment transport patterns or hydrodynamic analysis that are established in siliciclastic sedimentary systems, the differences caused by the biogenic nature of certain carbonate sediments compared to siliciclastic sediments need to be considered. Furthermore, models and analysis methods applicable to carbonate grains should be further refined. In addition, when quantitatively evaluating the development of carbonate factories in ancient marine using quantitative carbonate grains statistics or geochemical indicators, there should be a strengthened focus on developing quantitative assessment methods for the level of diagenetic alteration. Further efforts should be directed toward developing and applying in-situ elemental and isotopic testing methods to reduce the impact of diagenesis on geochemical signals. While developing and applying new geochemical proxies for carbonate rocks, the mechanisms of occurrence or fractionation need to be clearly understood to interpret the reflected paleoclimate and paleoenvironmental information accurately. Simultaneously, when studying deep-time evolution and production mechanisms of carbonate factories through sedimentary process forward modelling, it is necessary to consider the applicability of parameters obtained from modern environments in deep-time records and account for the impact of syndepositional-early diagenesis and chemical evolution of seawater geochemical evolution in the modelling process. [ABSTRACT FROM AUTHOR]

Petrological, geochemical and zircon U–Pb and Hf isotope studies were carried out on the Hajseyran pluton, along the Tarom–Hashtjin metallogenic zone, as part of the Alborz–Azerbaijan magmatic belt, which is located in the central part of the Alpine–Himalayan orogenic belt. The Hajseyran pluton, which is made up of syenite, monzonite, quartz-monzonite and granite, yields a zircon U–Pb age of 39.20 ± 0.56 Ma (for a quartz-monzonite sample) with shoshonitic features. Enrichment in large ion lithophile elements, depletion in high-field-strength elements and negative anomalies of Nb, Ta and Ti in Chomalou samples suggest a subduction-related arc magmatic setting. The Chomalou epithermal Pb–Zn–Cu deposit occurs close to the Hajseyran pluton with the quartz–base metal sulfide veins predominantly hosted by Eocene volcanic rocks. The ore-forming processes include chalcopyrite and sphalerite–galena formation, with the latter the major mineralisation in this region. Microthermometric results from the liquid–vapour fluid-inclusion assemblages show that the homogenisation temperatures in the first-stage quartz range from 230 to 310 °C, in the sphalerite and second-stage quartz from 161 to 293 °C and in the late-stage quartz from 175 to 262 °C. The salinities of fluids decrease from early-stage quartz to late-stage quartz. The calculated stable isotope values of ore–fluid components (δ18Owater = +3.28‰ to −3.68‰; δ34SH2S = +5.5‰ to +7.8‰) show that magmatic fluids have played a significant role during mineralisation. The Chomalou deposit is interpreted as a volcanic-hosted intermediate-sulfidation type of epithermal mineralisation formed through shallow-level emplacement of the Hajseyran pluton, which formed via partial melting of phlogopite–amphibole-bearing sub-continental lithospheric mantle. The Neotethyan slab roll-back and concomitant asthenospheric upwelling led to the decompression melting of metasomatised sub-continental lithospheric mantle and the formation of several K-rich plutons and associated epithermal deposits in the Alborz–Azerbaijan magmatic belt. The late Eocene Hajseyran pluton shows a shoshonitic, arc-related signature. The Chomalou Pb–Zn–Cu deposit is an intermediate-sulfidation style of epithermal mineralisation. Fluid inclusion and stable isotope data suggest the evolution of ore-fluid system from magmatic to meteoric. Decompression melting of metasomatised sub-continental lithospheric mantle via slab roll-back led to the formation of Hajseyran pluton. [ABSTRACT FROM AUTHOR]

The Panzijian gold deposit is located in the Jiaobei uplift on the eastern margin of North China Craton. It is a quartz vein-type gold deposit in the southern end of the Qixia-Penglai ore belt. In order to explore the source and properties of ore-forming fluids and materials in the Panzijian gold deposit, explore the ore-forming process and reveal the genesis of the deposit, this work has carried out petrographic observation and temperature measurement of gold-bearing quartz fluid inclusions, laser Raman experiment, gold-bearing quartz H–O isotope study, and gold-bearing pyrite Pb isotope study. The Panjian gold deposit is divided into four metallogenic stages and the metallogenic stage Ⅲ is the main gold mineralization stage. Fluid inclusions show that the ore-forming fluids at the Panzijian gold deposit belong to a CO2–H2O–NaCl system with low temperature (172–341 °C), salinity (1.57–10.49 wt% NaCl), and density (0.79–0.96 g/cm3). Gold-bearing Quartz H–O isotopic data (δD = −79.8 to −65.1‰, δ18OH2O = 1.33–2.63‰) show that the ore-forming fluid was derived from the mixing of magmatic water and meteoric water. Gold-bearing Pyrite Pb isotopes with crustal signature (206Pb/204Pb = 16.06–16.943, 207Pb/204Pb = 15.337–15.858, 208Pb/204Pb = 37.143–38.081, and 206Pb/207Pb = 1.025–1.105) support that some ore-forming materials were crust-derived. We proposed a metallogenic model for the Panzijian gold deposit: Stress transition of Jiaobei uplift tectonic system inducing asthenospheric upwelling. The lithostatic pressure dropped and fluids were exsolved from the magma. The ore-forming fluid ascended along local faults and the pressure further dropped, resulting in fluid immiscibility and gold deposition along structural traps (e.g., faults).

Magnetite-(apatite) ore deposits are interpreted as being formed by the crystallization of iron-rich ultrabasic melts, dominantly generated by the interaction of silicate melts with oxidized P-F-SO4-bearing sedimentary rocks. This hypothesis is supported by geologic evidence, experimental studies, numerical modeling, stable and radiogenic isotope geochemistry, mineralogy, and melt- and mineral-inclusion data. Assimilation of crustal rocks during ascent promotes separation from a silicate magma of Fe-rich, Si-Al-poor melts with low solidus temperatures and viscosities, allowing coalescence, migration, and emplacement at deep to subaerial crustal environments. When the iron-rich melt attains neutral buoyancy, fractional crystallization leads to melt immiscibility similar to that observed in industrial blast furnaces, which promotes separation of massive magnetite ore overlain by different types of "slag" containing actinolite or diopside ± phosphates ± magnetite ± feldspar ± anhydrite ± scapolite, commonly enriched in high field strength elements. The mineralogy and morphology of this iron-depleted cap strongly depend on the depth of emplacement and composition of the iron-rich magma. Most of these systems exhibit high oxygen fugacity, which inhibits the precipitation of significant sulfide mineralization. The initially high fO2 of these systems also promotes the formation of low-Ti (< 1 wt%) magnetite: Ti acts as an incompatible component and is enriched in the iron-poor caps and in the hydrothermal aureole. High fluid-phase pressures produced during massive crystallization of magnetite from the melt further facilitate the exsolution of magmatic-hydrothermal fluids responsible for the formation of aureoles of alkali-calcic-iron alteration with hydrothermal replacement-style iron mineralization. On the whole, these systems are dramatically different from the magmatic-hydrothermal systems related to intermediate to felsic igneous rocks; they are more akin to carbonatite and other ultramafic rocks. [ABSTRACT FROM AUTHOR]

Terrestrial‐marine dust fluxes, pedogenic carbonate δ13C values, and various paleovegetation proxies suggest that Africa experienced gradual cooling and drying across the Pliocene‐Pleistocene (Plio‐Pleistocene) boundary (2.58 million years ago [Ma]). However, the timing, magnitude, resolution, and relative influences of orbitally‐driven changes in high latitude glaciations and low latitude insolation differ by region and proxy. To disentangle these forcings and investigate equatorial eastern African climate across the Plio‐Pleistocene boundary, we generated a high‐resolution (∼3,000‐year) data set of compound‐specific n‐alkane leaf wax δ2H values—a robust proxy for atmospheric circulation and precipitation amount—from the HSPDP‐BTB13‐1A core, which spans a ∼3.3–2.6 Ma sequence in the Baringo‐Tugen Hills‐Barsemoi Basin of central Kenya. In combination with the physical sedimentology, our data indicate that precipitation varied strongly with orbital obliquity, not precession, during the late Pliocene, perhaps imparted by variations in the cross‐equatorial insolation gradient. We also observe a marked shift toward wetter conditions beginning ∼3 Ma that corresponds with global cooling, drying in western Australia, and a steepening of the west‐east zonal Indian Ocean (IO) sea surface temperature (SST) gradient. We propose that northward migration of the Subtropical Front reduced Agulhas current leakage, warming the western IO and causing changes in the IO zonal SST gradient at 3 Ma, a process that has been observed in the latest Pleistocene‐Holocene but not over longer timescales. Thus, the late Cenozoic moisture history of eastern Africa is driven by a complex mixture of low‐latitude insolation, the IO SST gradient, and teleconnections to distal high‐latitude cooling. Key Points: We present new high resolution (3,000‐year) leaf wax δ2H data from central Kenya spanning 3.3–2.6 million years before present (Ma)Pronounced 41,000‐year variability throughout is potentially attributable to the cross‐equatorial insolation gradientLong‐term (>200,000‐year) variability in eastern African hydroclimate tracks the zonal Indian Ocean surface temperature gradient [ABSTRACT FROM AUTHOR]

This paper presents the first geochemical, isotope-geochemical (Sm–Nd) and geochronological (U–Pb, LA–ICP–MS) data on acid volcanic rocks collected in the Bogdanikha River basin of the Priamursky fragment of the Nora–Sukhotino terrane in the northeastern South Mongolia–Khingan orogenic belt. In terms of the contents of rock-forming components, the studied volcanic rocks correspond to high-silica and high-alumina rhyolites. The elevated contents of alkalis, Ga, Zr, Nb, and Y, lower concentrations of Ba, Sr, Ti, and Eu, and mantle values of εNd(t) = +3.0...+3.6 allow the rhyolites from the Bogdanikha River basin to be classified as A2-type rhyolites. The concordant age of the youngest zircon population from the rhyolite, according to geochronological (U–Pb, LA—ICP–MS) studies, is 301 ± 4 Ma, which corresponds to the Late Carboniferous. Taking the geochemical features of the studied rhyolites and the existing models for the formation of the South Mongolia–Khingan orogenic belt into account, it is most likely that they formed in a collisional setting as a result of slab break-off. [ABSTRACT FROM AUTHOR]

This paper describes the first finding of authigenic carbonates on the southern flank of Gakkel Ridge in its junction with the continental margin of the Laptev Sea of the Russian Federation. The samples are represented by compact magnesian calcites and aragonites, including rounded and angular fragments of terrigenous material, as well as microphytoplankton and spores and pollen of terrestrial and aquatic plants of various ages. The elemental and organochemical characteristics are indicative of the predominant oxidation conditions or those intermediate between oxidation and reduction conditions of carbonate crystallization likely due to the fact that carbonates were formed near the bottom surface. The O, C, and Sr isotopic compositions make it possible to conclude that diagenetic carbonates of Gakkel Ridge were deposited mainly in isotopic equilibrium with bottom water at a temperature of about 0°C, corresponding to measurements from the research vessel. A wide range of δ13С (from –23.5 to –37.3) is indicative of the fact that methane was an important, but not the sole source of carbon in carbonates. Based on wide variations in 87Sr/86Sr (0.70906–0.70933) correlated with δ13С values, the carbonate-forming fluid was not only modern seawater, but also diagenetic solutions coming from the sedimentary cover together with methane and methane and organic matter oxidation products. The active discharge of heterogeneous methane-bearing fluids can be related to the high modern tectonic activity of the study region. [ABSTRACT FROM AUTHOR]

The Jinying gold deposit is located in southern Jilin Province in northeast China and is representative of the large Early Cretaceous gold deposits in this area. To better understand ore genesis of this deposit, a multi-isotope integrated analysis of U–Pb–Rb–Sr–He–Ar–S has been carried out. Laser ablation inductively coupled plasma–mass spectrometry (LA–ICP–MS) dating of zircons from the granodiorite porphyry and dioritic porphyrite in the study area yields ages of 172.1 ± 1.2 Ma and 122.5 ± 0.8 Ma, suggesting that corresponding intrusion occurred in the Middle Jurassic and the Early Cretaceous. Rb–Sr dating of the pyrite yields an isochron age of 120 ± 3 Ma, suggesting that gold mineralization occurred in the Early Cretaceous. The fluid inclusions in pyrite yield 3He/4He ratios clustered within a small range from 0.08 to 0.13 Ra, 40Ar/36Ar ratios between 331.6 and 351.3, and mantle He in the range of 1.0–1.6%, indicating that the ore-forming fluids originated from a mixed crustal and mantle source. The in situ S isotopic values of pyrite vary between + 0.1 ‰ and + 2.8 ‰, suggesting that the ore-related sulphur came from the deep magmatic source. Combined with the geological history of the study area, it can be concluded that the gold mineralization was possibly related to the extensional setting associated with the rollback of the Palaeo-Pacific Plate. [ABSTRACT FROM AUTHOR]

The Murchison meteorite is a well-studied carbonaceous chondrite with relatively high concentrations of amino acids thought to be endogenous to the meteorite, in part because they are characterized by carbon isotope (δ13C) values higher than those typical of terrestrial amino acids. Past studies have proposed that extraterrestrial amino acids in the Murchison meteorite could have formed by Strecker synthesis (for α-amino acids), Michael addition (for β-amino acids), or reductive amination, but a lack of constraints have prevented confident discrimination among these possibilities, or assignment of specific formation pathways to each of several specific amino acids. Position-specific carbon isotope analysis differentiates amongst these mechanisms by relating molecular sites to isotopically distinct carbon sources and by constraining isotope effects associated with elementary chemical reactions. Prior measurements of the position-specific carbon isotopic composition of α-alanine from the Murchison CM chondrite demonstrated that alanine's high δ13C VPDB value is attributable to the amine carbon (δ13C VPDB = +142 ± 20‰), consistent with Strecker synthesis drawing on 13C-rich carbonyl groups in precursors (Chimiak et al., 2021). Here, we measured the δ13C composition of fragment ions generated by electron impact ionization of derivatized ⍺-alanine, β-alanine, and aspartic acid from Murchison via gas chromatography-Fourier transform mass spectrometry. α-Alanine's amine carbon yielded δ13C VPDB = +109 ± 21‰, which is consistent with the previously measured value and with formation from 13C-rich precursors. β-Alanine's amine carbon presents a lower δ13C VPDB = +33 ± 24‰, which supports formation from 13C-rich precursors but potentially via a Michael addition mechanism rather than Strecker synthesis. Aspartic acid's amine carbon has δ13C VPDB = −14 ± 5‰, suggesting synthesis from precursors distinct from those that generated the alanine isomers. These measurements indicate that Murchison amino acids are a mixture of compounds made from different synthesis mechanisms, though some subsets likely drew on the same substrates; this conclusion highlights the complexity of extraterrestrial organic synthesis networks and the potential of emerging methods of isotope ratio analysis to elucidate the details of those networks. [ABSTRACT FROM AUTHOR]

The Guandi and Banshigou iron deposits of southern Jilin Province, China, are Algoma-type banded iron formations (BIFs) located in the Eastern Block of the North China Craton (NCC). LA–ICP–MS U–Pb dating shows the magmatic zircons in plagioclase amphibolite from the Guandi BIF (PA–GD) and plagioclase hornblende gneiss from the Banshigou BIF (PHG–BSG) were crystallised at 2556 ± 17 Ma and 2545 ± 27 Ma, respectively, representing the formation age of the BIFs. Metamorphic overgrowth zircons from both samples gave two U–Pb ages of 2452 ± 23 Ma and 2446 ± 70 Ma, indicating the age of metamorphism. The zircon εHf(t) values of PA–GD (–1.3 to +2.8) and PHG–BSG (–1.5 to +2.7) indicate that the magma source was derived from depleted mantle with contamination of crustal material. According to our study, the PA–GD and PHG–BSG were formed in an island arc setting and support previously proposed subduction zone tectonic models for the northeastern NCC during the Neoarchean. The magmatic zircons from the PA–GD and PHG–BSG were crystallised at 2556 ± 17 Ma and 2545 ± 27 Ma, which represents the formation age of the BIFs. The metamorphic overgrowth zircons from the PA–GD and PHG–BSG gave two ages of 2452 ± 23 Ma and 2446 ± 70 Ma, which represent the age of metamorphism. Major-element and REE data indicate that BIFs precipitated in a mixture of seawater and hydrothermal fluids in an anoxic environment. Geochemical and Hf isotope characteristics of BIFs' wall rock indicate that the source magma was derived from a depleted mantle wedge metasomatised by subduction-slab melts and contaminated by ancient crust, formed in an island arc setting. [ABSTRACT FROM AUTHOR]

Complex interpretation of the distribution of δ13C and δ18О values in carbonates, as well as δ34S and 87Sr/86Sr values, in gypsum from the lower Eifelian Osveya horizon (Belarus) showed that significance of the diagenetic isotope signals is low and the isotope variations can be explained consistently within a sedimentation model. Along with the section intervals with standard marine δ13C values, there are negative excursions of the parameter (up to –7...–11‰) marking segments with carbonate–sulfate rocks and smaller sulfate manifestations. The excursions correspond to evaporitic episodes when the basin became shallower and, probably, disintegrated into separate depressions, leading to increase in the role of continental water enriched with soil carbon in the geochemical sedimentation system due to the continental runoff activation and/or shallowing. The waters could enter both from the prolonged exposed land areas where the Eifelian rocks are absent until now and from the periodically existing islands. The oxygen isotope composition does not respond to negative δ13C excursions by similar shifts due to the possible absence of significant difference between the δ18О values of the atmospheric precipitation generating the land water and the seawater at low latitudes where the Belarus region was situated in the Devonian. In 40% of the studied samples, the δ18О values range from –4 to –2‰, corresponding to the Eifelian "plateau" (approximately –3‰) in the generalized chemostratigraphic curve based on calcite of brachiopod shells from several regions of the world. The δ18О values higher than –2‰ (44% of samples), probably, are related to water evaporation, whereas values lower than –2‰ (16% of samples), which can decrease to –7.0...–9.5‰ at the peaks of evaporation episodes, are caused by the water heating (sometimes very significant) during the basin shallowing. Activation of the role of continental water accompanying the evaporation episodes is supported by the following fact: the 87Sr/86Sr ratio in the Osveya gypsum (0.708402–0.708742) is much higher than in the Eifelian seawater according to a global estimate (0.70772), whereas the δ34S value in gypsum (15.5–21.2‰) in more than one-half of the analyzed samples is lower than typical values in the Middle Devonian seawater sulfate (19–20‰). [ABSTRACT FROM AUTHOR]

The Montecristo district, northern Chile, is one of the few places worldwide where there is a direct relationship between magnetite-(apatite) (MtAp) mineralization and iron oxide-copper–gold (IOCG) mineralization. The MtAp mineralization includes Ti-poor magnetite, fluorapatite, and actinolite and is crosscut and partially replaced by a younger IOCG mineralization that includes a second generation of actinolite and magnetite with quartz, chalcopyrite, pyrite, and molybdenite. The MtAp stage at Montecristo is interpreted as the crystallized iron-rich melts that used the pre-existing structures of the Atacama Fault System as conduits. These rocks later acted as a trap for hydrothermal IOCG mineralization. Geochronology data at Montecristo indicate that the host diorite (U–Pb zircon 153.3 ± 1.8 Ma, 2-sigma), MtAp mineralization (40Ar-39Ar in actinolite, 154 ± 2 Ma and 153 ± 4 Ma, 2-sigma), and the IOCG event (Re-Os on molybdenite, 151.8 ± 0.6 Ma, 2-sigma) are coeval within error and took place in a time span of less than 3.4 Ma. The εHfi and εNdi values of the host diorite are + 8.0 to + 9.8 and + 4.3 to + 5.4, respectively. The whole-rock 87Sr/86Sri values of the IOCG mineralization (0.70425 to 0.70442) are in the lower end of those of the MtAp mineralization (0.70426–0.70629). In contrast, εNdi values for the IOCG mineralization (+ 5.4 and + 5.7) fall between those of the MtAp rocks (+ 6.6 to + 7.2) and the host diorite, which suggests that the IOCG event was related to fluids having a more crustal Nd (εNdi < + 5.7) composition than the MtAp mineralization. This likely reflects the mixing of Nd from the MtAp protolith and a deep magmatic-hydrothermal source, very likely an unexposed intrusion equivalent to the host diorite. Sulfur isotope compositions (δ34S, + 0.3 to + 3.4‰) are consistent with a magmatic source. [ABSTRACT FROM AUTHOR]

Breccia pipe deposits of the Grand Canyon region contain ore grade copper and uranium. Horn Creek is located near the Orphan Mine mineralized breccia pipe deposit, and groundwater emerging from the bedrock in the headwaters of Horn Creek has the highest uranium concentrations in the region. Uranium decreases an order of magnitude between the groundwater at the top of the watershed and the groundwater emerging from the alluvial material lower in the watershed. Horn Creek water has low sulfur and uranium isotopic ratios which may suggest interaction with sulfide and uranium minerals found in mineralized breccia pipe deposits. Per- and polyfluoroalkyl substances were found in low concentrations in groundwater from the bedrock and may be related to mining process materials or other anthropogenic activities. PHREEQC modelling suggests that water that is elevated in uranium emerging from the bedrock in the upper watershed may mix with other groundwater and atmospheric precipitation infiltrated into the alluvial material in the lower watershed. Tritium is elevated in Horn Creek groundwaters, suggesting a component of modern water, some of which may have interacted with Orphan Mine workings. Additional studies could build on this understanding of chemistry changes in the waters of Horn Creek to provide more direct evidence of the contribution of water moving through the Orphan Mine. Supplementary material: Chemical data for this paper are available at https://doi.org/10.5066/F7P55KJN, PHREEQC geochemical simulations are available at https://doi.org/10.5066/P9X17FKG and groundwater chemistry from south of Grand Canyon, AZ is available at https://doi.org/10.6084/m9.figshare.c.6747638 Thematic collection: This article is part of the Geochemical processes related to mined, milled, or natural metal deposits collection available at: https://www.lyellcollection.org/topic/collections/geochemical-processes-related-to-mined-milled-or-natural-metal-deposits [ABSTRACT FROM AUTHOR]

For the present study, geochemical ages were derived from radiocarbon and radiokrypton age calibration with ground-water chemical contents (Na+, K+, Mg2+, Ca2+, Cl−, SO42−, HCO3−). Geochemical ages may fill the dating gap (40–150 ka) between the isotope techniques mentioned. A case study of groundwater in the Baltic Artesian Basin has involved geochemical age calibration, data filtering (such as regional subdivision of the basin for more accurate results) and geochemical dating of groundwater of unknown age. Various approaches to interpretations of geochemical age results could be used. Bicarbonate and sulphate are sensitive to the hydrochemical environment and should be omitted from geochemical age calculations. Modern fresh groundwater samples should also be excluded from calibration in order to obtain more reliable trend lines. Calcium-sodium cation exchange occurs in deep aquifers and may be used for geo-chemical age determination of fossil groundwater.

The Tuotuohe region is a highly prospective area for Pb and Zn mineral exploration. This paper contributes to our comprehension of the ore-controlling structures, fluid inclusions, and C–H–O–S–Pb isotope geochemistry of Pb–Zn deposits in this region. These deposits are generally hosted by carbonates and controlled by fractures. The principal homogenization temperatures of quart- and calcite-hosted inclusions ranged predominantly between 120 and 220 °C, with salinities varying from 6 to 16 wt.% NaCl equivalent. The Pb isotope compositions of the ore deposits are comparable to those of Cenozoic volcanic rocks in the region but differ significantly from those of the host rocks, indicating that the Pb within these deposits was derived from the mantle. The C, O, and S isotope compositions of samples exhibit a bimodal distribution based on whether they were derived from magma or host rocks, implying that magma-derived fluids underwent an isotopic exchange with the host rocks. The H-O isotope compositions of samples also indicate that ore-forming fluids were originally magmatic but were depleted by combining with meteoric water. These findings are also supported by variations in fluid inclusion homogenization temperatures and salinities. Taken together, these findings suggest that the Pb–Zn deposits of the Tuotuohe region developed from magma to hydrothermal fluids at medium–low temperatures. [ABSTRACT FROM AUTHOR]

Stable isotope ratios of nitrogen and oxygen (15N/14N and 18O/16O) of nitrate (NO3–) are excellent tracers for developing systematic understanding of sources, conversions, and deposition of reactive atmospheric nitrogen (Nr) in the environment. Despite recent analytical advances, standardized sampling of NO3–) isotopes in precipitation is still lacking. To advance atmospheric studies on Nr species, we propose best-practice guidelines for accurate and precise sampling and analysis of NO3– isotopes in precipitation based on the experience obtained from an international research project coordinated by the International Atomic Energy Agency (IAEA). The precipitation sampling and preservation strategies yielded a good agreement between the NO3– concentrations measured at the laboratories of 16 countries and at the IAEA. Compared to conventional methods (e.g., bacterial denitrification), we confirmed the accurate performance of the lower cost Ti(III) reduction method for isotope analyses (15N and 18O) of NO3– in precipitation samples. These isotopic data depict different origins and oxidation pathways of inorganic nitrogen. This work emphasized the capability of NO3– isotopes to assess the origin and atmospheric oxidation of Nr and outlined a pathway to improve laboratory capability and expertise at a global scale. The incorporation of other isotopes like 17O in Nr is recommended in future studies. [ABSTRACT FROM AUTHOR]

The magnitude of isotopic fractionation during sublimation of ice remains poorly constrained. Field and laboratory studies that span decades have persistently shown conflicting results. A better understanding of fractionation during sublimation is needed to improve interpretation of alpine hydrology, glaciology, paleoclimate and planetary histories that rely on stable isotopic records stored in icy reservoirs. At the core of the problem is the question of whether sublimation occurs as a layer-by-layer process with no fractionation or whether diffusion within the ice and vapor-ice exchange generate fractionation. We present results from an experiment where we suspended ice spheres in temperatures ranging from -25 to -10 °C in an unsaturated atmosphere and used aRayleigh distillation model to estimate fractionation of the spheres. A small, yet statistically significant and repeatable, isotope fractionation (103lnα18O of ∼ −0.6 ‰ and 103lnα2H between −3.0 and − 4.0 ‰ or α = 0.999, α = 0.9940 to 0.9970, respectively) was found during the sublimation of ice. The results indicate the presence of fractionation yet the values are an order of magnitude smaller than would be predicted for equilibrium fractionation at this temperature. By assuming a porosity for the ice of 0.0005 % - which is typical for ice frozen under these conditions, we estimate an increase in diffusivity relative to solid ice consistent with the observed fractionation values. The results help to reconcile how fractionation estimates during sublimation could vary between experimental and observational studies where porosity is not controlled for and can vary substantially across a continuum from porous firn layers to low porosity ice deep in glaciers. • Closed porosity within ice can increase the diffusivity generating a small but observable isotope fractionation. • Secondary processes such as ice compaction can affect porosity, thus the magnitude of isotope fractionation may vary depending on ice type. • Isotope fractionation during sublimation is much lower than equilibrium fractionation predictions, yet statistically significant. [ABSTRACT FROM AUTHOR]

Here we present in situ Rb Sr and Pb isotopic analysis of K-feldspar from the Shap Granite, (Cumbria, UK) and detrital K-feldspar from the associated Shap Wells Conglomerate Formation, to investigate the potential of the detrital K-feldspar record as an archive of crustal composition. We use a unique, collision cell – multi collector inductively coupled plasma tandem mass spectrometer to make the in situ isotope measurements, using 'chemical resolution' of 87Rb+ and 204Hg+ isobaric interferences on 87Sr+ and 204Pb+, achieved with SF 6 and NH 3 reaction gases, respectively. Using this technique, we successfully demonstrate that the majority of detrital K-feldspar Rb Sr ages, as well as initial Sr and Pb isotope ratios, from the Shap Wells Conglomerate are within uncertainty of those for parental Shap Granite K-feldspar (398 ± 1 Ma, n = 6). Some detrital K-feldspar grains record perturbed Rb Sr ages, reflecting post depositional alteration events. The majority of samples with disturbed Rb Sr ages carry distinct petrographic features evident in SEM imaging, prior to in situ dating, which indicates a means to help screen for reliable ages. We further illustrate the potential value of combined Rb Sr and Pb isotopic information preserved in K-feldspar to estimate the timing and chemical composition of juvenile continental crust formed in the past. Where U Pb has been fractionated during juvenile crust formation, the initial Pb isotope ratio provided by the K-feldspar yields model crustal U/Pb (diagnostic of tectonic setting) and extraction age. The contrast in the U/Pb composition of juvenile crust formed in intraplate or subduction settings allows the model U/Pb ratios of the detrital K-feldspars to be used to constrain the style of juvenile crust formation. Additionally, the initial 87Sr/86Sr isotope ratio measured in detrital K-feldspar can be combined with the calculated crustal extraction age and Rb Sr K-feldspar age to model the Rb/Sr of the juvenile crustal protolith. • Magmatic Rb Sr age and initial Pb isotopic compositions can be preserved in detrital K-feldspars. • Model age and U/Pb composition of crustal protolith determined from coupled Rb Sr and Pb analysis of K-feldspars. • U/Pb composition of crustal protolith can be used to infer tectonic setting of its formation. • Protolith age and K-feldspar initial 87Sr/86Sr ratios used to model protolith 87Rb/86Sr and degree of differentiation. [ABSTRACT FROM AUTHOR]

Serpentinites record processes that redistribute major and trace elements between mantle and crust. Platinum Group Elements (PGEs) are trace elements in serpentinites hosted in sulphides and alloys. Alloys are challenging to find, and most analytical techniques lack the spatial resolution to analyse them. This research adopts automatic mineral mapping technique to detect PGM grains in a sample from the Wadi Tayin (Oman) peridotite and uses atom probe tomography, a nanoscale quantitative analytical technique, to analyse the grain. This work applies and assesses the applicability of atom probe tomography to measure the 187Os/188Os isotopic ratio of natural alloys and uses the ratio to constrain the source of Os. A novel algorithm is used to automatically determine the number of counts of the 187Os and 188Os peaks, to calculate the isotopic 187Os/188Os ratio and the analytical uncertainty. The 187Os/188Os ratio is 0.126 ± 0.003, consistent with the isotopic composition reported by literature in the dunite of the Main Mantle Section of the Wadi Tayin ophiolite. The analytical uncertainty is one order of magnitude higher than conventional bulk rock techniques, such as negative-thermal ionisation mass spectrometry (N-TIMS) and inductively coupled plasma mass spectrometry (ICP-MS). However, the precision is sufficient to conclude that the non-radiogenic 187Os/188Os ratio is compatible with a mantle origin for the alloy. Decreasing whole-rock Re with increasing LOI and the overprinting of magmatic pentlandite by magnetite demonstrate that progressive serpentinisation may have modified the Re budget. The results indicate that atom probe tomography can analyse 187Os/188Os ratio quantitatively in micron-sized natural alloys and provide insights into natural processes. • Atom probe tomography can quantitatively analyse 187Os/188Os in natural alloys. • Atom probe tomography allows the isotopic composition analyses of nanoscale particles, overlooked by bulk rock techniques. • A novel algorithm ranges the isotopic peaks in the ToF spectrum from the APT analysis, testing the data robustness. • Serpentinisation modifies platinum group minerals. [ABSTRACT FROM AUTHOR]

The establishment of extensive carbonate platforms characterized the Ediacaran period during CaCO3 oversaturation events and the exceptional creation of accommodation space associated with the aftermath of the Marinoan glaciation (∼635 Ma). Carbonate deposits in the Araras Group record the early Ediacaran period, stage 1, in the Amazon Craton. The Serra do Quilombo Formation is an intermediate unit characterized by heavily fractured and faulted dolomites, as well as the presence of dolomite-cemented breccias (CB) overlying thick limestone packages associated with diagenetic and hydrothermal modifications. These features are commonly attributed to structurally controlled hydrothermal dolomitization (HTD) and are of significant economic importance as hydrocarbon reservoirs and Mississippi Valley-type (MVT) lead-zinc mineralization hosts. This study aims to unravel the origin of cemented breccias and the diagenetic/burial processes within the unit, focusing on dolomitization processes. Dolomite samples were analyzed using petrographic, scanning electron microscopy, microprobe, micro-Raman, cathodoluminescence, and isotopic analyses (δ13C, δ18O, 87Sr/86Sr) to unravel their burial history. CBs are sub-vertical to sub-horizontal bodies with complex geometries, generally cutting bedding at high angles, indicating hydrofracturing processes related to vertical flows of hydrothermal fluids (hydraulic breccia) and present the typical cockade texture of expansion breccias in dilatational faults. The substitutive matrix RD1 is the main constituent of the Serra Quilombo Formation, its low correlation between δ13C and δ18O (R2 = 0.009), the well-preserved fabric, and the similarity with the isotopic values (C and Sr) documented for Ediacaran carbonates, suggest that the syndepositional dolomitization. The first generation of dolomite cement (DC1) and the last phase of dolomitic cementation (saddle dolomite - SD) occur, filling pores, CBs, and fractures. The cockade texture of the breccias evidences a low precipitation rate or a pause in precipitation between DC1 and SD. Concurrently, DC1 has isotopic signals of δ18O = −4.34 ± 1.32‰ (n = 18) and 87Sr/86Sr = 0.708831 (n = 2), while SD has values of δ18O = −9.57 ± 2.51‰ (n = 15) and 87Sr/86Sr = 0.711464 (n = 3). The large isotopic fractionation between DC1 and SD suggests different dolomitizing fluids. This relationship shows an increase in 87Sr in the fluid as the temperature increases; moreover, the enrichment in 87Sr of the fluid is explained by the interaction of this fluid with rocks from the crystalline basement. Thus, the main conduit for the ascent of this radiogenic fluid would be faults with deep roots spatially close to tectonically active zones. Lastly, the presence of tectonic stylolites cutting cemented breccias and rotated zebra-like strata-bound structures suggests that brecciation occurred before the installation of fragile post-Ordovician transtensional structures, preceding the establishment of Paleozoic Basins on the South American Platform. • Seismicity favoring hydrothermal, fault-controlled systems and brecciation. • Dolomitization fronts led to breccia formation in Serra do Quilombo Formation. • Fine-dolostone and isotopic values suggest seawater involvement in dolomitization. • Cockade breccias resulted seismic reactivation and isotopic fluid composition shifts. • Structurally controlled hydrothermal dolomitization with involvement of deep radiogenic fluids. [ABSTRACT FROM AUTHOR]

The Pliensbachian-Toarcian (Pl-To) boundary was marked by an extinction event in marine organisms, and localised ocean anoxia – resulting in the deposition of black shales. Negative isotopic excursions in bulk organic carbon in many of these black shales, are widely believed to indicate that a global carbon cycle disruption accompanied this extinction event. The Pl-To preceded a period of more intense global carbon cycle disruption that occurred during the Toarcian Oceanic Anoxic Event (T-OAE) by around a million years. It is evident from targeted carbon isotopic analyses of marine and terrestrial organic matter that simultaneous disruptions to the marine and terrestrial carbon cycles occurred during the T-OAE. However, it remains a matter of debate whether the main source of carbon emissions was a climate-sensitive methane reservoir, or volcanic processes. No records of terrestrial carbon cycle disruption exist for the latest Pliensbachian, and so the causal mechanisms behind localised anoxia in this stage of the Lower Jurassic are poorly constrained. We present a record of concomitant isotopic depletion in short and long-chain n -alkanes derived from a thin black shale (the Lower Sulphur Band – LSB) deposited during the latest Pliensbachian (located in Yorkshire, UK). A key argument is that simultaneous isotopic depletions in these different compound classes implies the presence of a brief global hyperthermal event in the latest Pliensbachian, with a timescale too short to have been captured by previous analyses of the Yorkshire section. We discuss the relevance of our data to the stratigraphic record of the Lower Jurassic sediments of Yorkshire, highlighting, in particular, the need for better constraint on the ammonite biostratigraphy of the study section. We further argue that the brief climate disruption that occurred in the latest Pliensbachian made the shallow marine environment vulnerable to the development of more widespread marine anoxia, during the succeeding Toarcian stage. [Display omitted] • For a 10 Kyr period in the Early Jurassic, both marine and terrestrial carbon reservoirs became isotopically depleted. • Carbon cycle disruption, exhausted stabilizing mechanisms in the earth system, presaging later climate change. [ABSTRACT FROM AUTHOR]