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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]

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. [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]

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]

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]

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]

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]

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 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]

Geochemical and isotopic fluid signatures from a 2.9–3.2 km deep, 45–55 °C temperature, hypersaline brine from Moab Khotsong gold and uranium mine in the Witwatersrand Basin of South Africa were combined with radiolytic and water–rock isotopic exchange models to delineate brine evolution over geologic time, and to explore brine conditions for habitability. The Moab Khotsong brines were hypersaline (Ca-Na-Cl) with 215–246 g/L TDS, and Cl− concentrations up to 4 mol/L suggesting their position as a hypersaline end-member significantly more saline than any previously sampled Witwatersrand Basin fluids. The brines revealed low DIC (∼0.266–∼1.07 mmol/L) with high (∼8.49–∼23.6 mmol/L) DOC pools, and several reduced gaseous species (up to 46 % by volume H 2) despite microoxic conditions (Eh = 135–161 mV). Alpha particle radiolysis of water to H 2 , H 2 O 2 , and O 2 along with anhydrous-silicate-to-clay alteration reactions predicted 4 mol/L Cl− brine concentration and deuterium enrichment in the fracture waters over a period > 1.00 Ga, consistent with previously reported 40Ar noble gas-derived residence times of 1.20 Ga for this system. In addition, radiolytic production of 7–26 nmol/(L × yr) H 2 , 3–11 nmol/(L × yr) O 2 , and 1–8 nmol/(L × yr) H 2 O 2 was predicted for 1–100 μ g/g 238U dosage scenarios, supporting radiolysis as a significant source of H 2 and oxidant species to deep brines over time that are available to a low biomass system (102–103 cells/mL). The host rock lithology was predominately Archaean quartzite, with minerals exposed on fracture surfaces that included calcite, pyrite, and chlorite. Signatures of δ 18O calcite , δ 13C calcite , Δ33S pyrite, δ 34S pyrite and 87Sr/86Sr obtained from secondary ion mass spectrometry (SIMS) microanalyses suggest several discrete fluid events as the basin cooled from peak greenschist conditions to equilibrium with present-day brine temperatures. The brine physiochemistry, geochemistry, and cellular abundances were significantly different from those of a younger, shallower, low salinity dolomitic fluid in the same mine, and both were different from the mine service water. These results indicate the discovery of one of few long-isolated systems that supports subsurface brine formation via extended water–rock interaction, and an example of a subsurface brine system where abiotic geochemistry may support a low biomass microbial community. [ABSTRACT FROM AUTHOR]

We applied field structural data and isotope geochemical (δ13C, δ18O and 87Sr/86Sr) analyses to understand the relationship among calcite veins, fault damage zones and carbonate host rocks in a thrust fault damage zone in the Achado quarry, Irecê Basin in the São Francisco Craton, NE Brazil. Our results reveal three hydrological packages with different rheological behaviours in a stratified carbonate succession. The upper package includes the Achado fault damage zone that is characterised by interlayered dolomitised grainstones and mudstones. These rocks display high positive δ13C values (10‰–13‰), negative δ18O values (mean −6.34‰) and radiogenic (87Sr/86Sr) isotope values (0.70885–0.71519). A second package is marked by a cataclastic brittle shear zone lateral parallel to dolograinstones bedding. These rocks show low to positive δ13C values (−3.41‰ to +8.85‰), more positive δ18O values (mean −3.73‰) and radiogenic (87Sr/86Sr) isotope values (0.71039–0.71373). The lower package is characterised by well‐preserved pristine limestone succession that shows δ13C values ranging between −0.46‰ and +3.17‰, mean δ18O = −5.41‰ and less radiogenic 87Sr/86Sr values (0.70762–0.70818). In contrast to the upper and intermediate packages, rocks from the lower one exhibit very low permeability and behaved as a seal for fluid migration. Fluid flow occurred several times during basin evolution, for example along syn‐rift fault damage zones, bedding‐parallel carbonate breccia, thrust faults, cataclastic shear zones, synorogenic conjugate shear fractures or joints and opening mode I fracture‐fill calcite veins. These fractures allowed pervasive fluid flow in the porous intermediate cataclastic shear zone where fluids flowed and formed veins, as diffuse fluid flow in randomly oriented fracture swarms, or channelised fluid flow in aligned fracture corridors. They record significant centimetre‐scale to km‐scale hydrological behaviour within carbonate layers. Most carbonates that are associated with veins, fault damage zones and hydraulic breccia were formed by fluids of the same origin with low δ13C (−6.0 to −2.0‰) and δ18O (−6.0 to −8.5‰) values, and more radiogenic 87Sr/86Sr values compared to the carbonate host rocks. [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. [ABSTRACT FROM AUTHOR]

Zinc and Cd isotope compositions are presented for a comprehensive suite of terrestrial rocks to constrain the extent of Zn and Cd isotope fractionation during igneous processes and better define the δ66Zn and δ114Cd values of the silicate Earth (the δ values denote per mille deviations of 66Zn/64Zn from JMC Lyon Zn and of 114Cd/110Cd from NIST SRM 3108 Cd). Analyses of spinel lherzolites provide a bulk silicate Earth (BSE) δ114Cd BSE value of –0.06 ± 0.03 ‰ (2SD). For Zn, the peridotite data of the current and previous studies define a mean δ66Zn BSE = 0.20 ± 0.05 ‰ (2SD). Komatiite analyses of this and published investigations yield similar mean values, which suggests that the Zn and Cd isotope compositions of the mantle remained fairly constant since the Archean. Data for loess provide upper continental crust compositions of δ114Cd = 0.03 ± 0.10 ‰ and δ66Zn = 0.23 ± 0.07 ‰. The Zn isotope and abundance data for peridotites and oceanic basalts are in accord with the previous observation of a mantle array, with basalts having higher Zn concentrations and δ66Zn values than the peridotites. To a first order, this reflects slightly incompatible behaviour of Zn during mantle melting and melt differentiation with associated enrichment of heavy Zn isotopes in the melt phase. Cadmium is marginally more incompatible than Zn during igneous processes and the oceanic basalts also display a minor enrichment of heavy Cd isotopes relative to peridotites. However, secondary processes produce significant Cd isotope variability in both mantle melts and peridotites, obscuring the primary igneous array. The δ66Zn BSE estimates of this and previous studies resemble the Zn isotope compositions of CV and CO carbonaceous and some enstatite chondrites. In contrast, the BSE has a lower δ114Cd BSE value than enstatite and carbonaceous chondrites. This implies that the Cd isotope composition of the BSE was either fractionated during accretion or that Earth's Cd inventory was not exclusively acquired from material related to carbonaceous and enstatite chondrites. Importantly, delivery of Zn and Cd to the BSE solely by CI and CM chondrites is not in accord with the meteorite and terrestrial stable isotope data of these elements. [ABSTRACT FROM AUTHOR]

Apatite is a useful geochronological tool due to its common occurrence and incorporation of a variety of radioactive parent isotopes during crystallisation. However, an understanding of the geological conditions recorded by each of these isotopic systems in apatite is necessary for their effective application to geological problems. In this study, U–Pb, Sm–Nd, and Lu–Hf dates for apatite grains from samples of ∼ 3.0 Ga TTG gneisses in the Akia terrane of the North Atlantic Craton (south-western Greenland) were obtained in order to better understand the conditions under which isotopic re-equilibration in apatite is achieved. This isotopic data records at least two thermotectonic events subsequent to the initial magmatic crystallisation of these rocks. Whereas the Lu–Hf and Sm–Nd isotopic systems in these apatites record a regional high temperature metamorphic event at ∼2.7 Ga, the U–Pb system records a milder thermal event at ∼ 1.7 Ga. This decoupling of the U–Pb from the Sm–Nd and Lu–Hf systems in apatite reflects a difference in closure temperature. The regional thermal effects of the ∼ 1.7 Ga Nagssugtoqidian orogeny in adjacent parts of the North Atlantic Craton resulted in partial to complete reequilibration of the U–Pb systems in apatite across the Akia terrane but were insufficient to cause open system behaviour of Sm–Nd or Lu–Hf. The indistinguishable apatite Sm–Nd and Lu–Hf ages produced in each analysed sample suggest that these systems are similarly susceptible to isotopic re-equilibration. The older ages produced by the Sm–Nd and Lu–Hf systems relative to U–Pb in apatite demonstrate that the former are more robust and thus more likely to faithfully record high temperature events than the U–Pb system. [ABSTRACT FROM AUTHOR]

The paper presents data on granites and gneisses recovered by Kulindinskaya-1 hole drilled in the central part of the Siberian Craton. The biotite granites retain a porphyritic texture, correspond to I-type according to their compositional features, are enriched in LREE and moderately depleted in HREE, and have negative Eu, Sr, and Nb and positive Zr anomalies. The U−Pb zircon age of the granites is Neoarchean (2525 ± 10 Ma), with single cores of zircon grains dated at about 2.6 Ga, which likely suggests a crustal source of the granitic magmas. The model age TNd(DM) = 2.77 Ga of the granite shows that the crust from which the initial melts were derived had been formed shortly before the melting episode. In terms of age and all characteristics, the granites are close to those of the Yurubchen massif, which was drilled through in the western part of the Tunguska superterrane. The biotite gneiss was apparently derived from sedimentary rocks and was heavily reworked when the granites were emplaced. The enrichment of the gneiss in Cr and Ni is probably inherited from the sedimentary protolith, whereas the REE, HFSE, and LILE concentrations and distribution in the gneiss are similar to those of the granite. The concordant (D < 1%) U−Pb zircon ages (according to LA-ICP-MS data) broadly vary from 3284 to 2620 Ma, with two major peaks at 2717 and 2678 Ma. The model age of the gneiss TNd(DM) = 2.91 Ga confirms a contribution of the ancient crustal component to the sedimentary protolith of the rock. The minimum age of the detrital zircon, 2.62 Ga, determines the maximum age limit for sedimentation, and the minimum age limit is set by the age of the granite intrusions at 2.53 Ga. According to our data, the Archean gneisses and granites recovered by the Kulindinskaya-1 drillhole probably compose the eastern part of the Neoarchean Tunguska superterrane. Ereminskaya-101 drillhole, which was drilled 20 km northeast of Kulindinskaya-1, recovered gneisses with model ages TNd(DM) from 2.30 to 2.37 Ga, which belong to the adjacent Taimyr−Baikal suture zone with widespread Paleoproterozoic rocks. The contrasting crustal history of the adjacent complexes provides grounds to suggest that they were tectonically combined, which is an additional reason to consider the Taimyr−Baikal suture zone as a Paleoproterozoic collisional orogen. [ABSTRACT FROM AUTHOR]

The Central Asian Orogenic Belt experienced a complex subduction accretion–collision history, forming the Irtysh gold belt. The Doranasai deposit is a typical gold deposit in the Irtysh gold belt, but its genesis is still unclear. The Doranasai gold deposit occurs in the east wing of the Aksay syncline. The orebodies are controlled by the NS-trending fault. The main ore types are quartz vein type and altered rock type. Wall rock alteration is represented by albitization, pyritization, sericitization, silicification, chloritization and carbonation. The ore-forming process includes three stages: albite–quartz–pyrite stage, quartz–polymetallic sulfide stage and barren quartz–carbonate stage. The fluid inclusions in the early- and middle-stage quartz are mainly aqueous inclusions and CO2–H2O inclusions, while only aqueous inclusions are developed in the late-stage quartz. The homogenization temperature of fluid inclusions has evolved from up to 300 °C in the early stage, 180–280 °C in the middle stage to lower than 200 °C in the late-stage, and the salinities have evolved from 4.2–9.6 wt% NaClequiv. in the early stage and 4.3–10.9 wt% NaClequiv. in the middle stage to 2.1–6.9 wt% NaClequiv. in the late stage. The coexistence of different types of inclusions in middle-stage quartz indicates that the fluid is not uniformly trapped, and fluid phase separation is the main mechanism of gold precipitation. The isotopic compositions of quartz from the Doranasai gold deposit show some variation but are generally comparable to those of other orogenic gold deposits. Fluids trapped in early-stage quartz have a δ18Owater range of 12.5–7.6‰, δD of − 101‰ and δ 13 C CO 2 of − 12.9‰, and the isotopic compositions of fluids trapped in middle-stage quartz have δ18Owater values of 11.4‰ to 4.4‰, δD of − 112‰ to − 102‰ and δ 13 C CO 2 of − 11.7‰ to − 9.5‰. In contrast, isotopic compositions of fluids trapped in late-stage quartz have δ18Owater values of 7.6‰ to 1.8‰, δD of − 108‰ to − 90‰ and δ 13 C CO 2 of − 12.4‰ to − 11.1‰. The early-stage fluids are probably derived from metamorphic decarbonation of the sedimentary host rock at depth, leading to the precipitation of barren quartz veins. In the middle stage, a decrease of the regional pressure and temperature may lead to the incorporation of meteoric water into the ore-forming system. Late-stage fluids trapped by calcite veins show isotopic compositions similar to meteoric water, indicating the cessation of hydrothermal fluid circulation. The geological and fluid inclusion characteristics of the Doranasai gold deposit are consistent with those of the orogenic gold deposit, indicating that it is an orogenic gold deposit formed in the collisional setting. [ABSTRACT FROM AUTHOR]

Wide variations of 87Sr/86Sr (0.70825‒0.70924) have been established at the Porozhinsk deposit in manganese ores and carbonates ascribed to the Pod"emsk Formation. These data, together with variations in the carbon (δ13C = –14.6...2.0‰, PDB) and oxygen (δ18О = 19.4...28.3‰, SMOW) isotope composition indicate different conditions of the formation of the studied rocks. The 87Sr/86Sr values in the studied dolomites of the Porozhinsk deposit are much higher than those of carbonate rocks (dolomites, limestones) of the Pod"emsk Formation from the Chapa River section. The position of the 87Sr/86Sr values of dolomites from the Porozhinsk deposit on the secular 87Sr/86Sr variation curve for Late Proterozoic ocean (Kuznetsov et al., 2014) suggests that the carbonate rocks attributed to the Pod"emsk Formation at the Porozhinsk deposit have younger age than carbonates of the Pod"emsk Formation from the Chapa River section. The Mn/Sr values usually taken as a criterion for the degree of secondary alteration of carbonates (in interpreting 87Sr/86Sr variations and discussing the suitability of the material for chemostratigraphic constructions) are not suitable for rocks formed in manganese ore sedimentation basins. [ABSTRACT FROM AUTHOR]

This paper reviews the results of fundamental importance achieved by the Institute of Volcanology and Seismology (IV&S), Far East Branch (FEB), Russian Academy of Sciences (RAS) for the period 1962‒2021. We consider the most important achievements classified under the following headings: Volcanological research includes petrologic and geochemical features of ejecta by volcanoes in the Kuril–Kamchatka region; the age of volcanoes and the phases of volcanogenic catastrophism in Kamchatka; hydrothermal systems and geothermal reserves of Kamchatka; hydrothermal metasomatism and volcanogenic mineral generation and mineralization; Geophysical research includes the seismology of volcanoes; deformation at active volcanoes; tectonic earthquakes and tsunamis; the internal structure of volcanic systems. [ABSTRACT FROM AUTHOR]

Benthic foraminifera δ18O increased by 5.4 ‰ through the Cenozoic Era, the past 65 million years of Earth's history. This increase is attributed to growth of global ice sheets and global ocean cooling. On the other hand, δ18O measurements of planktonic foraminifera do not exhibit significant change. These measurements initially were interpreted to suggest cool tropical and subtropical temperatures and introduced the concept of the "cool tropics paradox", in which global bottomwater temperatures were significantly warmer but tropical surface temperatures were not during the early Cenozoic. This lack of change in δ18O of planktonic foraminifera was explained by secondary postburial alteration of the primary planktonic isotope signal. We provide an alternative record of sea surface water characteristics of Cenozoic Era by measuring δ18O of siliceous microfossils. This scarce phase of marine silica, unaltered biogenic opal-A, composed of diatoms, radiolaria and sponge spicules, was separated and purified from deep-sea Cenozoic sediments. We measured δ18O of siliceous microfossils from a set of drilled cores: DSDP 278 from the South Pacific, DSDP 513 from the South Atlantic, and ODP 1050–1053 and DSDP 391 from the subtropical North Atlantic. The purity of the biogenic opal and its mineralogical phase was assessed with SEM, SEM/EDS, XPS, and XRD. The δ18O of biogenic opal-A fluctuates around an average value of 43.0 ‰ through the Cenozoic Era, comparable to the Southern Ocean average of 43.2 ‰ of diatoms and radiolaria from the last 30,000 years which represent the last glacial and interglacial period and suggesting cold surface temperatures of 2–7 °C, both in the subtropical and polar latitudes. Taking into consideration changes in δ18O associated with bottomwater interaction with the lower crust and changes in sea level associated with waxing and waning of ice sheets, we conclude lack of or minimal change in the surface water temperature through the Cenozoic Era. This revives the original idea of the "cool tropics" paradox with a carbonate independent δ18O record and without issues associated with diagenesis of benthic and planktonic foraminifera. [ABSTRACT FROM AUTHOR]

Along the Central Indian Ridge (CIR), the geochemical and isotopic signature of mid-ocean ridge basalts (MORB) from three segments between 8° and 12°S show a FOZO-like enrichment with elevated 3He/4He (R/R A) (> 10 R A), suggesting small-scale upwelling with a deep primordial mantle component. Based on complementary major and trace elements analysis as well as Sr, Nd and Pb radiogenic isotope compositions of MORB samples from the same location, we confirm the presence of a FOZO/C-like enriched signature characterized by high Pb isotope ratios (206Pb/204Pb = 18.1134–19.1481; 207Pb/204Pb = 15.4710–15.6146 and 208Pb/204Pb = 37.8625–39.0332), relatively low 87Sr/86Sr (0.702767–0.702974) and high 143Nd/144Nd (0.512989–0.513118). In agreement with recent seismological studies highlighting an asthenospheric anomaly centered under the Mascarene Basin and flowing beneath the CIR, we propose that this plume-like anomaly named Mascarene Basin Asthenosphere Reservoir (MBAR) is the source of the enriched FOZO/C-like signature observed along this portion of the CIR. Furthermore, our analyses reveal that the source of the MBAR anomaly may have a unique geochemical signature in the Indian Ocean, distinct from other Indo-African plumes such as the Réunion plume. Moreover, the primordial characteristics, and the location of the MBAR (next to the margin of the African LLSVP) suggest that this plume-like anomaly may be a disconnected blob/proto-plume of a broad mantle structure formed by different Indo-African plumes/upwelling (e.g., Afar and Bouvet plumes) and anchored in the lower mantle. • Sr-Nd-Pb isotope and trace element confirm a FOZO/C-like signature for CIR MORB. • Interaction between Mascarene Basin Asthenosphere Reservoir (MBAR) and CIR. • MBAR may be an aborted plume branch from the deep mantle, from the African LLSVP. • MBAR unlikely originated from the same plume branch conduit as the Réunion plume. • MBAR component may show a unique geochemical signature in the Indian Ocean. [ABSTRACT FROM AUTHOR]

The amethyst and agate geodes from the Los Catalanes Gemmological District in Uruguay represent one of the main deposits of its kind worldwide. The geometry of the deposit is horizontal, with an irregular distribution of amethyst geodes within the upper level of the basalt lava flows and shows strong variations in their abundance, as well as quality, geometry, and shape. Reliable exploration guides are scarce, and the limited knowledge of the geological parameters controlling its occurrence makes exploration unpredictable, leading to inaccurate reserve estimation. Based on cutting-edge methods including nucleation-assisted microthermometry of one-phase fluid inclusions and determination of triple oxygen isotope in silicates and carbonates, as well as analysis of geode-hosted water and groundwater, we estimate the crystallisation temperatures in the range between 15 and 60 °C. These low temperatures point to amethyst crystallisation after the emplacement of the complete basalt pile. The mineralising fluid shows isotopic signatures consistent with meteoric water and very low salinities from pure water up to rarely over 3 wt% NaCl-eq., likely sourced from the groundwater hosted in the aquifers in the basaltic sequence and underlying units. Based on the insights provided by the new data, we propose the combination of open- and closed-system crystallisation inside pre-existing cavities due to the episodic infiltration of meteoric water in a rather stable geological context. [ABSTRACT FROM AUTHOR]

Understanding changes in redox conditions in the Earth's geological record is fundamental to unravelling some of the major events of our planet's history, such as the Great Oxidation Event (G.O.E.), biological changes through time related to mass extinctions, or the formation of ore deposits for primordial metal resources. Rocks from uranium deposits are ideal candidates to examine the coupled isotopic fractionation of Tl, Mo and U, as they are fundamentally caused by redox processes, occur in a wide variety of geological settings throughout much of geological history (from about 3 Ga), and result from the interplay between fluids and rocks of variable redox states. Herein we measure δ97Mo (−10.2 to +6.1 ‰), ε205Tl (−9.5 to +5.0 ε-units), and δ238U (−0.72 to 0.30 ‰) for 34 samples from granite-related, intrusive, metamorphic, and Proterozoic unconformity related U deposits. Collectively, these results suggest: 1) in metamorphic and unconformity-related contexts, samples with decreasing ε205Tl values also have decreasing δ238U values, indicative of change in redox conditions, 2) ε205Tl values in the sulfide-rich samples likely reflect the affinity of 205Tl for these minerals, 3) Tl undergoes significant isotopic fractionation during the reduction of U-bearing fluids to precipitate uraninite, and 4) Tl isotopes do not fractionate during secondary remobilization of elements within these systems, and thus retain a record of the conditions of formation, whereas Mo isotopes are heavily fractionated by secondary remobilization. We suggest that the study of U, Mo, and Tl isotopes in U-ore deposits conveys new information related to building blocks of life on Earth and shows great potential for the study of past oxygenation events, thus potentially allowing us to reconstruct the geological and chemical history of our planet. • Uranium and thallium isotopes show potential as proxies for redox reactions in U-ore deposits. • Thallium isotopes do not seem to be affected by alteration and secondary remobilization of uranium. • Molybdenum isotopes in U-ore deposit samples are strongly affected by secondary processes. [ABSTRACT FROM AUTHOR]

The Harla gold deposit is located on the eastern segment of the Kanggur-Huangshan ductile shear belt in Eastern Tianshan, on the southern margin of the Central Asian Orogenic Belt. The orebodies show close spatial association with NEE-trending faults and are hosted in volcanic rocks of the Lower Carboniferous Xiaorequanzi Formation. Three mineralization stages were recognized: an early stage characterized by specularite–pyrite–quartz mineralization, an intermediate stage with pyrite–chalcopyrite–gold–quartz genesis, and a late stage defined by sulfide-poor calcite and quartz veins. Three types of fluid inclusions (FIs) were recognized: daughter mineral-bearing triphase FIs (S-type), liquid-dominated biphase FIs (LV-type), and liquid-only monophase FIs (L-type). S- and LV-type FIs entrapped in the early stage show similar homogenization temperatures (Th) at 216–229 °C and 199–222 °C. However, they display contrasting salinities of 32.2–33.4 and 6.7–8.9 wt.% NaCl eqv., respectively. LV-type FIs entrapped in the intermediate stage display Th of 163–191 °C, with salinities of 5.6–7.4 wt.% NaCl eqv. LV-type FIs occur in the late stage display Th of 135–258 °C and salinities of 3.7–5.6 wt.% NaCl eqv. Insights from hydrogen, oxygen, and carbon isotope analyses (δ18OH2O = −10.7 to 3.3‰, δDH2O = −88.1 to −61.4‰, δ13CH2O = −8.9 to −6.2‰), combined with FI characteristics, indicate that the ore-forming fluids were derived from a hybrid source of magmatic and meteoric water, with the latter becoming dominant in the later stage. Sulfide and lead isotopic compositions (δ34Spyrite = 0.2 to 2.5‰, 206Pb/204Pb = 17.709–18.273, 207Pb/204Pb = 15.483–15.569, 208Pb/204Pb = 37.533–37.754) suggest that ore-forming materials were mainly derived from wall rocks (Xiaorequanzi Formation rocks and plagiogranite). By integrating geological background work and fluid inclusion analyses, as well as isotope data, we conclude that the Harla gold deposit is an epithermal-type deposit. [ABSTRACT FROM AUTHOR]

The Tissint strewn field has produced over 16 kg of material that has minimal terrestrial weathering and/or contamination. Tissint, along with 16 other incompatible trace element (ITE)-depleted shergottite specimens with igneous crystallization ages spanning 327–2403 Ma, were ejected together from Mars 1.1 m.y. ago. Despite the geochemical similarities of fragments from the Tissint strewn field, there are reported discrepancies in age determinations from different fragments that raise the possibility that the strewn field may be heterogenous. There are also questions about whether the shock ejection event incorporated martian soil components into impact glass, and the sources of radiogenic Sr and Pb that have been measured from leachate fractions in previous studies. An impact melt-rich fragment of Tissint was analyzed by LA-ICPMS for rare-earth element (REE) and highly siderophile element (HSE) concentrations and Pb isotopic compositions. Leachate and residues from 8 specimens representing separate individual fragments collected from the strewn field were analyzed for Rb-Sr. Unleached fractions of the 8 specimens were also analyzed for Sm-Nd and Lu-Hf. The measured REE and HSE concentrations of impact melt glass and associated sulfide measured by LA-ICPMS are consistent with bulk rock compositions of Tissint and show no evidence for incorporation of more ITE-enriched martian surface components. Measured Pb isotopic compositions confirm that the impact melt glass and associated sulfide contain no evidence for incorporation of more radiogenic materials than the Pb compositions inherited from the primary magma. In situ Pb isotopic data from sulfide likely represents the most robust method for constraining initial Pb isotopic compositions of shergottites whereas approaches that rely on leaching and digestion may not remove all mineral and/or crack surface contaminants. Rubidium-strontium analyses of the 8 Tissint specimens indicate that labile components hosting HCl-soluble Rb and Sr are not in isotopic equilibrium with the igneous assemblage and that the washed residues are in isotopic equilibrium with the igneous assemblage. The Sr isotopic compositions of the leachate are within the range of 'more ITE-enriched' depleted shergottites, perhaps indicating sources from the igneous pile on Mars. The radiogenic Sr component could represent crack and mineral surface coatings of volatilized materials derived from nearby depleted shergottite rock units during the impact ejection process but are not radiogenic enough to represent ITE-enriched crust or mantle components. The Lu-Hf isotopic data from the specimens indicate no evidence of contamination or element mobility, whereas the Rb-Sr and Sm-Nd isotopic systems show evidence for element mobility and potential mixing with an isotopic component not in equilibrium with the igneous phases. The calculated ages using data compiled from Brennecka et al. (2014) , and Grosshans (2013) for Lu-Hf, Rb-Sr, and Sm-Nd are 571 ± 84 Ma, 590 ± 49 Ma and 559 ± 39 Ma, respectively. These data indicate that the specimens analyzed here are cogenetic and the Tissint strewn field appears to be homogeneous. [ABSTRACT FROM AUTHOR]

We present new Sr, Nd, Hf and Pb isotope data for Early Miocene shoshonitic and high-K lavas dredged from seamounts in the South Fiji Basin, southwest Pacific Ocean. Our analyses provide a useful reference dataset for this distinctive compositional suite. The shoshonitic lavas formed in an intra-oceanic back-arc basin setting and are broadly coeval with nearby arc and back-arc basin lavas. Further work in the region will be needed before the tectonic implications of the shoshonitic and high-K lavas are fully understood. [ABSTRACT FROM AUTHOR]

To addresshow parent materials are affecting organic carbon dynamics in a soil profile, soils from a lithosequence comprising six parent lithologies under a rangeland ecosystem have been explored at three depth intervals for soil organic carbon (SOC) content and its 13C depth trends. Studied parent materials ranged from metamorphic (foliated: FM and non-foliated: NFM) to sedimentary (clastic carbonate: CCS) to plutonic (intermediate: IP, felsic: FP and intermediate felsic: IFP) geological contexts. The relationship between SOC concentration and its isotopic signatures to a depth of 50 cm in FM, NFM, FP and IFP profiles was well described by the kinetic fractionation of SOC during biodegradation. For CCS and IP lithologies, strong divergence from the Rayleigh equation was observed suggesting that the 13C enrichments in these soils resulted from both mixing different SOC pools and isotope fractionation related to the C mineralization. Results suggest that SOC across the lithosequence goes through different isotopic evolutions resulting from different 13C-enriched inputs and pedogenic properties as described by the extended Rayleigh equation (0 ≤ βC ≤ 0.80). These are presumably caused by the bedrock lithology implying that parent material affects C storage and dynamics. [ABSTRACT FROM AUTHOR]

Stable isotope-based dietary information on the tenth century CE Hungarian population serves as a valuable comparative tool to other dietary stable isotope studies in the region. This study presents a multiproxy approach involving skeletal samples with the least diagenetic alteration and the best-preserved primary signals. Dental and bone samples collected from three cemeteries in northeastern Hungary were investigated using a combination of Fourier-transform infrared spectroscopy (FTIR), stable isotope geochemistry, and strontium isotope analysis. FTIR measurements were used to detect the addition of secondary carbonate to the skeletal apatite carbonate component and to differentiate diagenetically altered samples. Our results suggest that all but the bone apatite carbonate stable isotope values and 87Sr/86Sr ratios are trustworthy and may be used to interpret the diet and migration of the researched individuals. We also determined that the inhabitants of the three tenth century CE Hungarian settlements relied primarily on C3 plants, but that C4 plants, most likely broomcorn millet (P. miliaceum), comprised a moderate portion of their plant-based diet and that animal products were generally consumed in moderate-high amounts. Coupled analyses of carbonate oxygen and strontium isotope compositions revealed that most of the bone apatite carbonate was heavily altered, whereas enamel apatite carbonate samples largely preserved their primary compositions. The bones showing the least amount of diagenetic alteration may partially preserve their primary apatite carbonate compositions, as well as show a combination of primary and secondary signals, which should be taken into consideration when bone apatite carbonate data are interpreted. [ABSTRACT FROM AUTHOR]

Sodium nitrate ores from the Atacama Desert in South America were economically important as they represented huge natural resources for the fertilizer and explosives industries during the early nineteenth to early twentieth centuries. Nitrogen and oxygen isotope ratios (δ15N and δ18O) of these desert nitrates generally show unique compositions (from close to 0 and up to ca. +50 ‰, respectively). The nitrates indicate the provenance as atmospheric in origin due to the mass-independent photochemical reaction of nitric oxide (NO) with ozone (O3) in the atmosphere to produce nitrate (NO3–). This paper examines the previously existing isotope data for specimens acquired from the Atacama Desert. It then reports new data from dual isotope analysis of historic nitrate specimens archived in museums in the UK. In the stable isotope signatures for nitrates from two areas of the Atacama Desert, Tarapacá in the north and Antofagasta in the south, were examined, and this analysis enabled a more detailed definition of their isotopic compositional ranges. This improved database is useful for tracing the provenance of the historic nitrates used in gunpowder and saltpetre, and also the cause of nitrate pollution in natural environments for which routine chemistry alone cannot provide the definite evidence for the origin. [ABSTRACT FROM AUTHOR]

The Shenshuitan gold deposit is located within the Eastern Kunlun Orogen in northwest China. The gold mineralization here occurs primarily within the ductile fault XI. The sulfide mineral assemblage is dominated by pyrite and arsenopyrite, with minor pyrrhotite, chalcopyrite, galena, and sphalerite. Host rocks predominantly consist of Ordovician silicic slate and late Silurian granites, and their alterations include silicification and sericitization. The measured δD and δ18O values of quartz and sericite range from −113.9‰ to −93.1‰ and from 4.6‰ to 12.0‰, respectively. Bulk and in situ δ34S values of sulfides range from −7.3‰ to +9.6‰ and from −3.92‰ to 11.04‰, respectively. Lead isotope compositions of sulfides show 206Pb/204Pb ratios from 18.071 to 19.341, 207Pb/204Pb ratios from 15.530 to 15.67, and 208Pb/204Pb ratios from 37.908 to 38.702. Collectively, the isotope (H, O, S, and Pb) geochemistry suggests that the ore-forming fluids were of a metamorphic origin mixed with meteoric water and that the sulfur and lead were sourced from a mixture of host rocks and original ore-forming metamorphic fluids. Lastly, this deposit can be classified as an orogenic gold deposit associated with the final collision between the Bayan Har–Songpanganzi Terrane and the Eastern Kunlun Orogen during the Later Triassic. [ABSTRACT FROM AUTHOR]

The Plio-Quaternary post-collisional volcanism in the Karapınar area is represented by two occurrences: (1) Karacadağ Volcanic Complex (KCVC) and (2) Karapınar Volcanic Field (KPVF). The investigated volcanic units are the southwestern part of the Neogene to Quaternary Cappadocia Volcanic Province (CVP) in Central Anatolia. The CVP generally displays calc-alkaline affinity in the Late Miocene to Pliocene rocks, but both calc-alkaline and sodic alkaline affinity in the Plio-Quaternary rocks, all of which have an orogenic geochemical signature. Such a volcanic activity contradicts the Western and Eastern Anatolian volcanism characterized by anorogenic OIB-like sodic alkaline volcanic rocks postdating early orogenic calc-alkaline ones. We hypothesize that such temporal and geochemical variations in the investigated rocks result from crustal contamination and present major and trace element chemistry and Sr-Nd-Pb-O isotope geochemistry, coupled with 40Ar/39Ar geochronology data to restrict the genesis and evolution of the rocks. The Neogene Karacadağ volcanic rocks are represented by lava flows, domes and their pyroclastic equivalents constituting a stratovolcano, and dated by new 40Ar/39Ar ages of 5.65 to 5.43 Ma. They are mainly composed of andesitic, rarely basaltic, dacitic and trachytic rocks and have a calc-alkaline character. Constituting a monogenetic volcanic field, the Quaternary Karapınar volcanic rocks are typically formed by cinder cones, maars and associated lavas, including xenoliths and xenocrysts plucked from the Karacadağ rocks. They comprise basaltic to andesitic rocks with a transitional affinity, from sodic alkaline to calc-alkaline. Both the Karacadağ and Karapınar volcanic rocks display incompatible trace element patterns rather characteristic for orogenic volcanic rocks. The Sr, Nd and Pb isotopic systematics of both units show a relatively narrow range, but their d18O values are markedly different. The Karacadag volcanic rocks have d18O values ranging from 7.5 to 8.9 ‰, resembling those of subduction-related basalts, but the Karapınar volcanics have d18O ratios between 5.7 and 6.5 ‰ corresponding to OIB-like rocks. Additionally, d18O values and 87Sr/86Sr ratios correlate positively with SiO2 in the rocks, indicating that contamination played an important role during differentiation processes. All the data obtained suggest that the Karacadağ basaltic rocks stemmed from a subduction-modified lithospheric mantle source. On the other hand, the origin of the Karapınar basaltic rocks can be explained in terms of OIB-like melts contaminated with the Karacadağ volcanic rocks to gain orogenic geochemical signature, which may be an alternative model for the origin of the CVP sodic alkali basalts. [ABSTRACT FROM AUTHOR]

Eocene intermediate to felsic subvolcanic rocks of the Torud-Ahmad Abad magmatic belt (TAMB), in the northern part of the Central Iran zone, are exposed between the Torud and Ahmad Abad regions in South-Southeast Shahrood. These igneous rocks include hypabyssal dacite, trachyte, andesite, trachy-andesite, and basaltic andesite; they are mainly composed of phenocrysts and microcrystalline groundmass of pyroxene, amphibole, and plagioclase, with minor biotite and titanomagnetite; they form domal structures (plugs and stocks), dikes, and sills that intruded into Neoproterozoic to cogenetic Eocene volcano-sedimentary sequences. Based on isotopic analysis of these intermediate to acidic rocks, initial ratios of 143Nd/144Nd range from 0.512 775 to 0.512 893 and initial ratios of 87Sr/86Sr range from 0.703 746 to 0.705 314, with quite positive εNd(i) values of +3.69 to +6.00. They are enriched in light rare earth elements and large ion lithophile elements and depleted in heavy rare earth elements and high-field strength elements, the SiO2 content is (52–62) wt.%, and Na2O content >3 wt.%, Al2O3 content >16 wt.%, Yb <1.8 ppm, and Y <18 ppm. These geological, geochemical, and Sr and Nd isotopic data are consistent with adakitic signatures originating by partial melting of the subducted Neo-Tethys oceanic slab (Sabzevar branch) and lithospheric suprasubduction zone mantle. The mantle signatures typifying the rapidly emplaced adakitic rocks (slab (high-silica adakite) and suprasubduction zone (low-silica adakite) melts) together with their locally voluminous extent are evidences that support a locally extensional geodynamic setting; and the evidence is consistent with an evolution to local transpression in the Late Eocene in this convergent margin arc environment to rifting (basalts to adakites) towards submarine conditions in the Neogene. [ABSTRACT FROM AUTHOR]

Gas samples were collected from 25 m long horizontal boreholes drilled into the excavation field at 10° inclination to the longwall face in two mining areas, Pesje and Preloge, in the Velenje Coal Mine, Slovenia, from 2013 to 2018. The degassing mechanism of coalbed gas and its stable isotopic composition (δ13CCO2, δ13CCH4, and δ2HCH4) were investigated in boreholes in advance of eight working faces. The major coalbed gas constituents were CO2 and methane. Gas concentrations and isotope values revealed that the methane is biogenic in origin with δ13CCH4 values of −69.4 to −29.5 ‰, δ2HCH4 values of −301 to −222 ‰, and a fractionation factor (αCO2-CH4) of 0.998–1.073, suggesting that methane derives from microbial acetate fermentation and CO2 reduction. The carbon dioxide methane index values ranged from 50.0–98.3 vol.% and δ13CCO2 values from −11.8 to −0.5 ‰, indicating that CO2 is biogenic and endogenic in origin. The degassing mechanism results in isotope fractionation of methane and CO2 for carbon isotopes up to 39.9 ‰ and up to 8.5 ‰, respectively, depending on the position of the excavation fields in space, e.g. under pre-mined coal area, fresh overburden. [ABSTRACT FROM AUTHOR]

• Absence of Os isotope and highly siderophile element evidence of extraterrestrial input for the Younger Dryas sediments. • Unradiogenic Os isotope ratios and highly siderophile element concentrations fingerprint volcanic aerosols. • Correlated unradiogenic Os peaks supports the proposed distant and episodic volcanic mechanisms for the Younger Dryas event. One of the prevailing hypotheses for the origin of the Younger Dryas (YD) cooling event is that it resulted from a bolide impact or airburst. Purported impact markers peak at or near the YD basal boundary layer at Northern Hemisphere locations. In this study, the 187Os/188Os ratios and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundances in a well-dated sediment section through the Younger Dryas at the Debra L. Friedkin site, Texas are reported. Unradiogenic 187Os/188Os peaks, which could be mantle-derived or extraterrestrial, have been found above, within, and below the YD basal boundary layer. Mass balance mixing models using chondrites or iron meteorites with upper continental crust fail to duplicate the chondrite-normalized HSE patterns of the sediment samples. These HSE signatures in the Friedkin site section replicate those found in Hall's Cave, Texas. The new results here thus independently confirm that the HSE abundances in the unradiogenic Os layers are likely a fingerprint of volcanic gas aerosols derived from large Plinian eruptions and not extra-terrestrial materials. To better constrain the lithological origins of YD sediments from the Friedkin and Hall's Cave sites, Texas, trace elements are presented here. The rare earth elements (REE) patterns and Ir, Ni, Ti and Zr abundances are also characterized with terrestrial signatures as opposed to impact melt rocks. An age profile correlation between the two study sites, further shows that three unradiogenic Os peaks overlap in time. The results are inconsistent with the extraterrestrial hypothesis and support instead an episodic and volcanic origin for the observed geochemical anomalies at the Debra L. Friedkin and Hall's Cave sites, Texas. [ABSTRACT FROM AUTHOR]