The Cryogenian Period included at least two long-lived global Snowball glaciations, the Sturtian and Marinoan, which were separated by a non-Snowball interval that lacks evidence for persistent ice cover. Non-Snowball Cryogenian sediments record the earliest possible rise of chlorophyte algae, high magnitude perturbations to the carbon cycle, and possible evidence for a substantial increase in atmospheric oxygen. The shallow marine Datangpo Formation and the correlative, deep-marine Xiangmeng Formation document continuous, shale-dominated sequences that were deposited in the Nanhua Basin on the Yangtze Craton (South China) during the non-Snowball interval. Previous studies have extrapolated estimates of seawater molybdenum isotope (delta 98Mo) compositions for the non-Snowball using data from the lower Datangpo Fomation and the Arena Formation of east Greenland, which either constitute only a small portion of the total thickness of non-Snowball deposits, or are difficult to assess based on the likelihood of isotopic fractionation during non-quantitative Mo drawdown. To address these limitations, we report bulk rock Fe speciation data in combination with published redox sensitive trace element (Mo and U) concentration data from euxinic marine sedimentary rocks that were deposited throughout the non-Snowball interval. Local syn-depositional and diagenetic effects during Mn-carbonate precipitation are considered during interpretations of regional redox datasets, and these insights provide a base framework for the robust interpretation of new delta 98Mo data from euxinic sediments. The result is a better constrained and continuous record of global ocean palaeoredox change throughout the non-Snowball interval. The global Mo dataset shows an increase in delta 98Mo from +0.67 +/- 0.06%o to +1.12 +/- 0.09%o, and a contemporaneous decrease in maximum Mo concentrations in euxinic sediments. Using these data, we employ a single reservoir model to evaluate the evolving spatial extent of different oceanic redox states. When assuming a post-Sturtian decrease in weathering input, the model results suggest that substantial anoxic seafloor was maintained throughout the non-Snowball, while euxinic seafloor area decreased, mirroring trends in regional redox proxy data. Our geochemical data and modelling further support the proposal that both temperature and redox conditions in marine environments may have been more hospitable in the latter part of the non-Snowball interlude, broadly contemporaneous with the earliest possible evidence for the emergence of animal life.

To elucidate the geochemical behavior and fractionation mechanisms of titanium (Ti) isotopes during granitic magma evolution, we conducted a systematic Ti isotopic analysis of I-type granodiorites, quartz diorites, and their associated mafic microgranular enclaves (MMEs), along with major Ti-bearing minerals biotite, hornblende, and titanite from the Early Cretaceous Fangshan pluton, North China Craton (NCC). The granodiorites and quartz diorites exhibit a narrow range of S49/47Ti values (+0.14 %o to +0.25 %o; average + 0.18 + 0.07 %o, 2SD, n = 15), comparable to that of the upper continental crust (UCC, S49/47Ti = +0.18 + 0.07 %o; 2SD). These values show no discernible correlation with conventional magmatic differentiation indices (e.g., SiO2, TiO2, MgO), suggesting limited Ti isotope fractionation during I-type granite differentiation. Thermodynamic modeling and mass balance calculations indicates that the isotopically enriched Ti signatures of the Fangshan granodiorites and quartz diorites result from partial melting (5-20 %) of rutile-bearing eclogitic sources in a thickened lower crust. In contrast, the MMEs display a wider range of S49/47Ti values (+0.04 %o to +0.33 %o) that correlates with SiO2, TiO2, and MgO contents, consistent with mixing between mantle-derived mafic and crustal-derived felsic magma, coupled with fractional crystallization. Mineral separates reveal clear intra-mineral Ti fractionation: titanite is consistently enriched in lighter Ti isotopes (S49/47Ti =-0.09 %o to +0.09 %o) relative to coexisting biotite (+0.22 %o to +0.44 %o) and hornblende (+0.16 %o to +0.35 %o), consistent with differences in the Ti coordination environments between the melt and crystallizing mineral. Taken together with previous studies, our results demonstrate that although Ti isotopes alone offer limited discrimination between I-and S-type granites, they act as a reliable tracer of A-type granites, where extensive fractional crystallization produces pronounced Ti isotope fractionation. Overall, these findings advance our understanding of Ti isotope behavior in granitic systems and highlight their potential as a tracer for granite petrogenesis and crustal evolution.

Graptolites were abundant and cosmopolitan zooplankton in Early Paleozoic oceans, but a prominent change in species occurred across the Late Ordovician mass extinction. We use ocean redox, iron isotope (δ56Fe), and phosphorus phase partitioning records from shelf and deep-ocean settings to evaluate the drivers behind this major reshaping of the pelagic marine ecosystem. A marked decrease in mesopelagic graptolites coincided with a stepwise negative δ56Fe shift on the shelf, driven by partial seawater Fe drawdown resulting from episodic intensification of mid-depth euxinia. Subsequently, a positive δ56Fe shift in both deep-ocean and shelf sediments reflects extensive seawater Fe removal during the development of more widespread euxinia. This led to enhanced sedimentary phosphorus recycling from sediments, which ultimately fueled the radiation of epipelagic graptolites. Thus, wide-scale changes in Fe cycling, linking the global oceanic redox state to phosphorus cycling, were ultimately responsible for the initial demise and subsequent radiation of select graptolite species.

High precision magnesium isotope data have been widely used in geological and astrochemical research. Previous studies used cation-exchange resins (e.g., AG50W-X8, AG50W-X12, AGMP-50) for Mg purification of routine geological samples, and these Mg purification protocols yield solutions meeting multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) analytical requirements, but one problem with the reported protocols is that the elution procedure is complex and time-consuming. In addition, some manganese nodule and shale samples have high Mn/Mg mass ratios. Previous studies have used highly concentrated HCl (e.g., 9-12 mol.L-1 HCl) or acetone (95%) to separate Mg from Mn and other elements. However, a low Mn removal efficiency, alongside the toxicity of acetone, may limit the purification of Mg in high-Mn samples (Mn/Mg >16), suggesting that further improvements should be made to the protocol. Here, we developed an efficient, user-friendly, and highly robust protocol for Mg isotope purification and analysis by MC-ICP-MS. Briefly, to isolate Mg from high-Mn matrices, an initial separation from matrix elements (e.g., Mn, Cu, Zn) was performed using AGMP-1M resin (100-200 mesh) eluted with 4.5 mL of 10 mol.L-1 HCl. A subsequent purification step using AG50W-X12 resin (200-400 mesh) was applied to remove major residual matrix elements with a mixed HNO3-HF solution, and Mg was finally collected by elution with 8 mL of 2 mol.L-1 HNO3. With this method, the yield during Mg purification was similar to 100%, and after one column or a two-column pass, most geological samples were suitable for high-precision Mg isotope analysis. We demonstrate that our method yields accurate Mg isotope ratios with a precision of +/- 0.07 parts per thousand for delta Mg-26, based on analyses of seawater, basalt, granodiorite, shale, manganese nodule, and carbonate reference materials.

As an important global sources of iron, the origin of iron oxide-apatite (IOA) deposits, whether magmatic or hydrothermal, has been a matter of persistent scholarly debate. To explore this issue, we conducted a detailed study of clinopyroxene in ore-hosting andesite, high-temperature hydrothermally altered andesite, and veined magnetite-apatite-clinopyroxene ore from the enigmatic Pliocene El Laco iron deposit in northern Chile, which is recognized as the youngest and best-preserved IOA deposit in the world. New data presented here show that clinopyroxene in magnetite-apatite-clinopyroxene ore at El Laco exhibits exceptionally high Sc concentrations, reaching up to 1476 mu g/g (average 476 +/- 666 mu g/g, 2SD). These data contrast sharply with clinopyroxene from the host andesite and the high-temperature alkali-calcic hydrothermally altered andesite, which exhibit Sc concentrations of 72-174 mu g/g (average 128 +/- 46 mu g/g, 2SD) and predominantly <10 mu g/g (average 0.5 +/- 0.7 mu g/g for clinopyroxene in early-stage alkali-calcic altered andesite and 4.3 +/- 20 mu g/g for pristine clinopyroxene in late-stage alkali-calcic altered andesite), respectively. In combination with comprehensive statistical analyses of Sc concentrations in clinopyroxene from global magmatic and hydrothermal systems, and the occurrence of abundant fluorapatite and anhydrite +/- magnetite inclusions in fluorapatite from veined magnetite-apatite-clinopyroxene ore at El Laco, we propose that the extremely Sc-enriched clinopyroxene, along with its host magnetite ore, precipitated at magmatic temperatures from a magmatic-hydrothermal fluid wherein Sc was dissolved and transported as Sc-sulfate and Sc-fluoride complexes. Notably, magnetite-apatite-clinopyroxene ore and the pervasive alkali-calcic alteration at El Laco likely formed from paragenetically distinct pulses of magmatic-hydrothermal fluids evolved from a common underlying magma plumbing system. This study provides compelling evidence for a magmatic-hydrothermal origin for IOA deposits, invoking multiple pulses of magmatic-hydrothermal fluids, and suggests that IOA deposits could be prospective targets for Sc exploration.

A study on Pb isotopes was conducted within the soil-plant-aerosol system. The results indicate that Pb isotopes serve as a suitable tool not only for tracing atmospheric pollution sources but also for tracking the Pb transfer process into and within plants. The main findings are as follows: 1) Pb isotopes in plants are a powerful tool for tracing Pb sources. When plants are removed from their original location, Pb isotopes in the whole plant or roots are suitable for tracing their growth sites; Pb isotopes in leaves are suitable for tracing aerosol particles in the surrounding environment; however, Pb isotopes in stems are not suitable for tracing Pb sources. 2) Pb isotopic fractionation occurs during the growth process of E. splendens Nakai (delta 208Pbplant-soil =-4.31 to 0.30 parts per thousand), and the extent of fractionation is larger than that of most mineral nutrients. This study also demonstrates that Pb isotopes in plants are a powerful tool for tracing the absorption and transport processes of Pb into and within the plant. Regardless of whether Pb is absorbed through the roots or leaves, lighter isotopes tend to be preferentially enriched in the subsequent tissues (from soil to root, from root to stem, and from leaf to stem within the plant), indicating non-selective absorption of Pb through ion channels. This is consistent with the diffusion effect on isotope ratio variation. Pb absorbed through the roots constitutes the main source of Pb in the plant. 3) The correlation between Pb isotope ratios could verify Pb pathways. Whether the correlation conforms to the principle of mass fractionation depends on whether Pb comes from one path or multiple pathways. This provides a new insight into understanding Pb sources in any physicochemical process or geological sample. 4) The addition of ethylene diamine disuccinic acid (EDDS, C10H16N2O8) promotes the uptake of Pb in the plant. However, it only affects the Pb concentration in the root and stem, but not in the leaf. This shows that altering soil state and promoting plant absorption are not ideal for reducing Pb pollution in soil for non-accumulator plants. The addition of EDDS in the soil also affects the variation in Pb isotope ratios within the plant. Compared with CK plants, heavier Pb isotopes were enriched in the EDDStreated plants, which suggests a plant protection mechanism whereby heavier Pb isotopes are stored in biological macromolecules such as Pb-proteins/ligands to mitigate toxicity.

Iron formations (IFs), as extremely Fe-rich chemical deposits, play an important role in the global steel industry and the investigation of Precambrian ocean chemistry. However, the controlling factors of IF generation remain enigmatic, particularly during the Mesoproterozoic era when large-scale IFs are scarce. Here we report rare earth element (REE) results of a recently confirmed large-scale Mesoproterozoic-aged IF, the Jingtieshan IF in Northwest China, which could provide new insights into this issue. REE systematics is instrumental in understanding the origins of IFs and ancient ocean chemistry. However, interpretations derived from prior REE studies remain ambiguous due to the analytical challenges posed by the unusually high concentrations of Ba in the Jingtieshan IF. In this study, we present robust REE analyses using a novel method consisting of coprecipitation of REE with Fe, followed by chromatographic purification. This method enables accurate determination of REEs in samples rich in Fe and Ba matrices with ICP-MS. Our results reveal significant positive Eu anomalies (1.52-3.43) in the Jingtieshan IF, demonstrating substantial high-temperature hydrothermal contributions. Asynchronous Eu anomalies across three close IF sections formed during the same period imply that Fe was sourced from different local hydrothermal activities rather than a unified source of deep seawater upwelling. The variable Ce anomalies (0.76-1.62) and subchondritic Y/Ho ratios (18.1-28.4) indicate that the Jingtieshan IF was deposited in anoxic-suboxic waters between Mn and Fe chemoclines within a stratified ocean. Furthermore, global compilations of carbonate Ce anomalies and Fe isotope data in IFs indicate that redox conditions during the mid-Proterozoic allowed large-scale IF deposition under prevalent ferruginous oceans. Growing evidence also highlights strong hydrothermal signatures in mid-Proterozoic IFs worldwide. Collectively, these findings suggest that the scarcity of Mesoproterozoic IFs was the result of reduced hydrothermal Fe flux due to prolonged tectonic quiescence during the transition between the Columbia and Rodinia supercontinents, rather than shifts in ocean redox conditions. We emphasize that the local hydrothermal activities associated with regional rifting played a crucial role in the generation of Mesoproterozoic large-scale IFs.

Superior-type iron formations (IFs) represent a globally significant source of iron ore; yet, their origin remains a subject of ongoing debate. Early models proposed a continental weathering source for the iron, whereas later interpretations—mainly supported by positive europium (Eu) anomalies—favored a hydrothermal source. However, the hydrothermal model largely relies on REE systematics, and whether iron and REEs in Superior-type IFs share the same source remains uncertain. As iron isotopes directly trace the sources and fractionation history of iron, a spatial co-variation between Fe isotopes and Eu anomalies would shed new light on the iron source issue of IFs. In this study, we present new Fe isotope and REE data from the drill core WILDD004 at Wilgena Hill and integrate them with reported data for two additional drill cores: HKDD4 (Hawks Nest) and GWDD1 (Giffen Well). All three cores are stratigraphically equivalent to the Wilgena Hill Jaspilite Formation but span a lateral distance of ~100 km across the Gawler Craton, South Australia. While the Hawks Nest and Giffen Well samples exhibit both positive Eu anomalies and elevated δ56Fe values, the Wilgena Hill samples show positive yet smaller Eu/Eu* (1.17–2.41) and negative δ56Fe values (−0.60‰ to −1.63‰). The consistent presence of Eu anomalies and the systematic spatial correlation between δ56Fe and Eu/Eu* across all three locations provide direct, Fe-based geochemical evidence for a hydrothermal source of iron in this Superior-type IF.

Barium (Ba) isotopes have emerged as powerful tracers in geochemical, environmental, and cosmochemical studies. However, achieving high-precision Ba isotope measurements remains challenging due to matrix removal, procedural blanks, isotopic ratio measurement uncertainties, and accurate mass bias correction. Here, we develop a robust analytical protocol for delta 137/134Ba determination using a 130Ba-135Ba double spike on a Nu Plasma II MC-ICP-MS. Our method employs an in-tandem micro-column chromatography (AG50-X12 cation-exchange resin followed by Sr-Spec (TM) resin) to efficiently purify Ba from matrix elements with minimal acid consumption. By eliminating intermediate evaporation and re-dissolution steps, we achieve rapid purification of Ba with a procedural blank of only 278 pg, negligible for most geological samples. Both MATLAB simulations and experimental validation suggested an optimal of similar to 20% double-spike proportion in the spike-sample mixture. Additionally, we found that a 200 ppb Ba concentration balances sample consumption, signal intensity and Faraday cup performance. To further refine sampling strategies and minimize isobaric interferences, we mapped the spatial distributions of Ba and Xenon (Xe) ion intensities, and isotope ratios in the ICP both in wet and dry plasma conditions, identifying a stable plasma region where Ba isotope ratios show minimal variability and Xe interference is low. We demonstrate that even trace matrix elements (a few millivolts in intensity) can significantly impact the precision in isotope ratio measurements. The method achieves a long-term external reproducibility better than 0.03 parts per thousand (2SD). Analyses of twelve geological reference materials (AGV-2, BCR-2, BHVO-2, BIR-1a, COQ-1, DTS-2B, GSO-2, GSP-2, GSR-8, JF-1, RGM-2, and SCo-1) yield delta 137/134Ba values consistent with published data except for three previously unreported materials (DTS-2B, JF-1, and SCo-1), confirming the reliability of the proposed method. This protocol provides a robust foundation for the mechanism of ion interaction in the ICP and contributes to high-precision Ba isotope applications across diverse geological processes.

Recycled oceanic crust and sediments play a crucial role in generating the chemical and lithological heterogeneity of the Earth's mantle. However, unequivocally identifying the lithological properties of these recycled crustal materials in the mantle sources of basalts remains a challenge, despite its significant implications for mantle dynamics and the generation of magma diversity. Here, we explore titanium (Ti) stable isotopes as a novel method for tracing eclogite melting in the source of intraplate basalt. We present new Ti isotope data for a suite of well-characterized intraplate basalts from northeast (NE) China, which were thought to be formed through interaction between primitive low-MgO melts derived from eclogitic recycled crust and the local lithospheric mantle peridotite. Results show that these basalts display large Ti isotopic variation, with delta Ti-49/47 values ranging from -0.05 parts per thousand to 0.14 parts per thousand. The delta Ti-49/47 values are well correlated with radiogenic Sr-Nd-Pb isotopes and stable Fe isotopes, suggesting the mixing of two endmembers with distinct Ti isotopic compositions. The low-delta Ti-49/47 endmember exhibits depleted Sr-Nd isotopic compositions that resemble those of the local lithospheric mantle peridotite. The high-delta Ti-49/47 endmember (delta Ti-49/47 >= 0.14 parts per thousand) is characterized by an elevated delta Fe-57/54 value (>= 0.3 parts per thousand) and low values of MgO (<= 5 wt.%), CaO/Al2O3 (<= 0.4), Nb/Nb* (<= 0.7), and Ti/Ti* (<= 0.6), which require an eclogite melt component in equilibrium with residual rutile in the source. Our thermodynamic modeling and mass balance calculations further suggest that such a melt can be produced by partial melting of a rutile-bearing eclogite, which has a protolith of mixed recycled oceanic crust and sediments. Therefore, this study highlights that Ti isotopes can serve as a novel tool for identifying the contribution of rutile-bearing eclogite to intraplate basalts.

The Cryogenian Sturtian (717-660 Ma) and Marinoan glacial deposits (∼650-635 Ma), typically consisting of alternating layers of glaciogenic diamictite and clast-free lithofacies, indicate dynamic glaciers or glacial-interglacial cycles during the global glaciations. This may result from ice sublimation in tropics under a Snowball Earth condition. However, this model fails to explain the deposition patterns observed in mid-latitude continents. We propose the presence of unfrozen oceans while the continents are covered, i.e., the icy-continents. The open-ocean condition requires low atmospheric pCO2 level. We argued that the mantle CO2 degassing could be counterbalanced by a growing pool of dissolved organic carbon (DOC) in the deep ocean, maintaining a small marine dissolved inorganic carbon (DIC) pool and a low atmospheric pCO2 level. The persistent marine productivity in the open ocean would support the expanded DOC pool due to reduced ocean ventilation and limited terrestrial inputs of oxidants. However, the global glaciation with open oceans was climatically unstable. The fluctuation of the DOC pool on a local or regional scale likely contributed to the frequent glacial-interglacial oscillations recorded in the rock records. Additionally, the expansion of the DOC pool removed seawater nutrients, e.g., phosphorus (P), and insufficient nutrient supply prevented the transfer of mantle-degassing carbon as DOC, ultimately leading to the termination of global glaciation. The turnover of the DOC pool, caused by deep ocean ventilation in the deglacial period, significantly increased the atmospheric pCO2 level. This event was followed by intense continental weathering, increased seawater pH, recovery of primary productivity, cap carbonate precipitation, and eventually, the emergence of new life forms and innovations in the biosphere.

The Tarim Craton is an ancient Precambrian continental block, and detailed knowledge of its thermo-tectonic history is crucial for understanding the early history of continental evolution. Abundant layered mafic rocks, which have commonly been regarded as basalts, occur within the Ediacaran Sugetbrak Formation(Fm.) in the Aksu region of the northwestern Tarim Craton. Clear intrusive features have now been discovered, including mafic rocks truncating Ediacaran sedimentary layers, exhibiting an intrusion-baked margin where they interact with both the overlying and bottom wall rocks, and displaying a fine-grained transition zone from their interior to their margins. The new findings demonstrate that these mafic rocks within the Aksu Ediacaran strata were not erupted basalts but instead are intrusive diabase dykes. Therefore, these mafic rocks cannot be used to constrain the timing of the Sugetbrak Fm. in the Aksu area, nor as marker layers for regional stratigraphic correlation. Furthermore, the Ediacaran thermo-tectonic evolution in this region, deduced from the assumption that the mafic rocks are lavas, needs to be revised.

The Gaobanhe deposit is one of the most typical Mesoproterozoic SEDEX polymetallic sulfide deposits in China. However,the types of its mineralization and the dominant mineralization process of its different ore types and their genetic relationships are still controversial. Here,we focus on the sulfur isotope characteristics of typical ore types,i. e.,the laminated/ banded pyrite ores and the massive and vein.type sulfide ores,in the Gaobanhe deposit to study their sulfur isotope compositions. The laminated/ banded pyrite ores are closely associated with Mn-rich pyritic black shales,while the massive and vein.type sulfide ores are mainly hosted in dolomite. A bimodal distribution of the sulfur isotope compositions occurred in these two types of ores:the fine-grained pyrites corresponding to the bedding-parallel layers or laminations are significantly enriched in heavy sulfur isotopes (delta S-34 = + 6. 7%similar to + 27. 1%),while the coarse-grained,anhedral pyrites corresponding to main stage of sulfide mineralization (pyrite mounds,massive mineralization)have significantly lower sulfur isotope compositions (mostly between - 10. 0% and + 5. 0%). Unlike the traditional SEDEX model,which emphasizes the sulfate.limited water environment,we suggest that the Gaobanhe sulfide mineralization is a product of the enhanced hydrothermal activity during the transition of the transgressive. regressive sequence. Geological evidence,such as the presence of dolomitic nodules in the lower part of the black shale overlying on the shallow carbonates,indicates that this set of manganese.rich black shale belongs to the product of a large.scale marine transgressive event which led to the formation of a local sulfidic water environment. In this scenario,the complete reduction of seawater sulfate makes the bedding.parallel layers or laminations significantly enriched in heavy sulfur isotopes whose average value is generally consistent with the previously reported sulfur isotopic composition of coeval seawater sulfate. In contrast,the presence of a large number of stromatolites in manganese.bearing carbonate rocks and the "heterochronic"characteristics of the layered ore body indicate a transition of their sedimentary facies. The higher sulfate concentration in the sedimentary. early diagenetic environment of shallow.water carbonates,which underwent thermochemical reduction under locally enhanced hydrothermal activity,accounted for formation of massive and vein ores with lower sulfur isotopes compared to seawater sulfates. In summary, the Gaobanhe deposit is a product of both syn.sedimentary mineralization and hydrothermal replacement,which is accompanied by changes of sedimentary facies during the transition from transgressive to regressive sequences, and that the difference in sulfur isotope composition is mainly caused by the difference in sulfate concentration of seawater at different depths. These results provide important implication for the Gaoyuzhuang sulfide and Mn mineralization

During the interglacial period of the Cryogenian glaciation, the extensive "Datangpo-type" manganese ores were deposited in the Nanhua Basin. However, there has been significant controversy over the precipitation mechanism of manganese for decades. Based on iron and nitrogen isotope data from the manganese ores of the Datangpo Formation in Chongqing (South China), combined with previous research, we propose that the manganese ores of the Datangpo Formation precipitated directly in an anoxic bottom-water environment in the form of rhodochrosite. The delta 56Fe values in the Bijiashan manganese ore (delta 56Fe = -0.19 +/- 0.13 parts per thousand) are close to those of modern marine hydrothermal iron, and there is a strong positive correlation between the delta 56Fe value and iron concentration (R2 = 0.81), indicating that the precipitation of manganese ore could be mainly affected by hydrothermal input. After comprehensively comparing the delta 56Fe values of the whole rock and pyrite in the manganese ore of the Datangpo Formation, we believe that iron from hydrothermal sources directly and quantitatively combined with sulfides to form pyrite. Additionally, the bottom seawater of the basin was mainly anoxic. The nitrogen isotope composition indicates the presence of a stable nitrate reservoir in the ocean at that time, and manganese ore deposition may have been influenced by the input of high-salinity water from the open ocean. Due to the supply of NO3- from the open ocean to the graben basin, the delta 15N in manganese ore is significantly higher than that in black shale. The input from the open ocean led to an increase in alkalinity in the bottom water of the basin, which favored the precipitation of rhodochrosite. Considering that the oxidation potential required for manganese oxidation precipitation is higher than that required for iron oxidation precipitation, it is most reasonable to conclude that under alkaline anoxic conditions in the bottom water layer, Mn2+ directly precipitated in the form of rhodochrosite.

Mass-independent fractionation during Zn isotope analysis by MC-ICP-MS is identified, which is responsible for the sensitive DS ratio effect. Using the correction method proposed, the results obtained are consistent with theoretical predictions.

Previous studies have reported that even low concentrations of Sn can lead to biased Cd isotopic measurements using MC-ICP-MS. In this paper, we propose a novel method of Cd isotopic analysis involving use of a Cd-106-Cd-111 double spike. To eliminate isobaric interference from Sn-114, we use Cd-113 together with Cd-106, Cd-110, and Cd-111 to obtain delta Cd-113/110, and then calculate delta Cd-114/110 as 1.33 x delta Cd-113/110. We find that when Sn/Cd is <= 2.5 in sample solutions, delta Cd-114/110 values are not affected by Sn, which behaves as a matrix element rather than causing isobaric interference. Cd isotopic measurements are not sensitive to the molarities of diluted HNO3 or the Cd concentration. Additionally, when Mo/Cd, Ni/Cd, and Se/Cd are <= 1 in sample solutions, Cd isotopic measurements are not significantly affected. Instead, when Zn/Cd is >0.1, In/Cd > 0.05, and Pd/Cd > 5 x 10(-3), the measured delta Cd-114/110 values deviate significantly from zero. However, Zn and In can be eliminated completely, and Pd was not detected in any Cd eluents. The delta Cd-114/110 values of three standard solutions (Spex-CUGB, BAM I012, and M & uuml;nster) and four geochemical reference materials (SGR-1b, BCR-2, GSD-7a, and NIST 2711a) were measured and found to be in close agreement with published results (with 2SD and ranges for all data of less than 0.090 and 0.120, respectively). This indicates that the data obtained by our double spike method are precise and reliable. Additionally, our new technique can help to simplify separation procedures, thus saving time and reducing the quantities of acid required.

Iron formations (IFs) represent an economically important iron-rich rock type in the Precambrian geologic record. It is generally assumed that after ca. 1.85 Ga, large-scale IFs were not deposited for approximately 1.1 Gy. However, substantial IFs, including over 15 large- to small-scale iron deposits, have been identified recently in Northwest China, and they would constitute the largest Mesoproterozoic IFs globally if their Mesoproterozoic ages can be confirmed. Field observations reveal that these iron deposits are dominantly stratiform and stratoid within the thick clastic-carbonate and volcanic-sedimentary succession. The ores mainly comprise Fe-rich (specularite, hematite, and siderite) and Si-rich (jasper and quartz) minerals with banded or massive structures. Geochemical investigations of typical iron ores show high SiO2 and TFe2O3 and relatively low Al2O3 and TiO2 contents, indicating that they are primary chemical sediments with high hydrothermal and low detrital contributions. These features suggest that these iron deposits in the NQOB are typical IFs, which resemble the Archean and Paleoproterozoic IFs worldwide. New zircon U-Pb dating and lithostratigraphic correlations indicate that these IFs were deposited at ca. 1.1 Ga. The sizable ore reserves and Mesoproterozoic ages confirm that these IFs are the largest reported IFs for the billion years between 1.8 and 0.8 Ga. The large-scale Mesoproterozoic-aged IFs help fill the longest gap in Earth history where the IFs were thought absent from the geologic record and provide an unusual perspective to understand the reappearance mechanism of Precambrian IFs.

Carbon-stable isotopes of diamonds provide clues regarding their growth processes. Thus, an accurate, efficient, and affordable method to determine the carbon isotope ratio is extremely urgent. Accurate and precise determination of the carbon isotope ratio with LA-MC-ICP-MS is limited by the high background intensity of 12C+ and instrumental settings. Hence, laser parameters were gradient-changed to investigate their influences on carbon isotope analysis. Besides, high-resolution spatial distributions of 12C+ and 40Ar3+ intensities coupled with the 13C/12C value in the ICP were investigated in detail to elucidate the ionization kinetics of 40Ar3+ and to determine the most stable zone for carbon isotope analysis in the ICP. Finally, two types of diamonds (a natural diamond (D-N-1) and synthetic diamond (D-HTHP)) were measured to verify their homogeneity and flexibility for in situ analysis of the carbon isotope on diamonds with LA-MC-ICP-MS. The signal-to-noise ratio (SINR) greatly affects precision, which could be significantly improved by optimizing laser parameters. The internal precision of in situ C isotope analysis is better than 0.2 parts per thousand (2SE) when the SINR is more than 4. The ionization efficiency of 40Ar3+ was found to be controlled by the catalysis of C ions and the thermodynamic parameters of the ICP. The most stable zone for carbon isotope analysis in the ICP was found to be located at approximate to 1.4 mm ahead of the 12C+ signal-maximum point. Hence, the precision of 13C/12C could be improved when the torch was retreated approximate to 1.4 mm from the maximum 12C+ intensity point axially. The natural and synthetic diamonds exhibited similar down-hole fractionation behaviors of the C isotope during laser ablation, indicating that they can be used to correct each other with LA-MC-ICP-MS. The accuracy of the carbon isotope was validated by comparing the data with those of nano-scale secondary ion mass spectrometry (NanoSIMS) and laser ablation-isotope ratio mass spectrometry (LA-IRMS). This study suggested that in situ LA-MC-ICP-MS is a rapid, precise and accurate way to measure the carbon isotope of diamonds. The interactive influence of the ionization process of nuclides leads to elemental and isotopic fractionations, which is one of the mechanisms of the matrix effect.

Mantle xenoliths entrained in a newly discovered Cenozoic basalt at Houtuancun within the Yilan-Yitong fault zone, situated beneath the Xing'an Mongolian Orogenic Belt in Northeast China, provide a unique opportunity to constrain the nature and evolution of the lithospheric mantle beneath this region. The mantle xenoliths are predominantly spinel lherzolite, with rare occurrences of harzburgite, wehrlite, and websterite. The Houtuancun spinel lherzolite and harzburgite are characterized by high forsterite contents in olivines (89.3-91.1), and their clinopyroxene rare earth element patterns range from slightly light rare earth element (LREE)-depleted to LREE-enriched, reflecting variable degrees of partial melt extraction (up to 20%) overprinted by later metasomatism. Despite this, the Fe isotopic composition of the Houtuancun lherzolite and harzburgite exhibits little variation (delta Fe-57/54 = - 0.05-0.09 parts per thousand), with an average of 0.02 +/- 0.09 parts per thousand (2SD, n = 9), close to the suggested delta Fe-57/54 value of 0.04 +/- 0.04 parts per thousand for the upper mantle, and there is no significant inter-mineral disequilibria. In contrast, the wehrlite has a slightly lower Mg# [=100 x Mg2+/(Mg2+ + Fe2+)] (88.4) and delta Fe-57/54 (-0.05 parts per thousand) compared to the spinel lherzolite and harzburgite, reflecting kinetic iron fractionation during melt-rock interaction. The websterite exhibits the lowest MgO (20.6-24.8 wt%), highest Al2O3 content (5.8-7.3 wt%), and the highest delta Fe-57/54 (0.25-0.28 parts per thousand) among the studied xenoliths, suggesting an episode of subduction-related silicate melt circulation through the upper mantle. The results demonstrate compositional heterogeneity of the mantle beneath the Xing'an Mongolian Orogenic Belt in Northeast China. The observed heterogeneity may result from a combination of varying degrees of melt extraction of the subcontinental lithospheric mantle and metasomatism by melts related to the subduction of the (Paleo)-Pacific plate.