Pb Isotopic Compositions Research Articles

An innovative isotopic method to identify the volcanic source of distal tephra

Identifying the sources of distal tephra in marine sediments or polar ice provides clues on the dynamic and large-scale impact of major volcanic eruptions. However, determination of the volcanic source of distal tephra is challenging due to size-dependent fractionation during atmospheric transport that modifies the mineral, chemical and even isotope composition of the transported and settled tephra. The composition of distal fine ash may thus be different from the coarser proximal products of the same eruption. Identifying the volcanic source of distal ash using the compositional data may therefore prove difficult. To get around this modification of distal composition, we propose here a new isotopic method to identify the source of distal tephra that is not based on raw transport-dependent isotope ratios but on two-dimension Pb isotope mixing lines, which account for atmospheric fractionation processes. To demonstrate the robustness of our method, we used the extensive database of Pb isotope compositions of volcanic products from the Northern Andean arc, to which we append 68 new Pb isotopic analyses obtained on proximal and distal eruptive tephra. We show for the first time that proximal products define a straight line in the 208Pb/206Pb-207Pb/206Pb space, whose equation is specific to each volcanic source. We then show that distal co-genetic tephra plot on the same line as proximal products, implying that the isotopic lines are robust fingerprints of volcanic sources that do not depend on the age, mineral assemblage, and nature of the emitted products. This new method uses bulk rock analyses and therefore provides a new perspective on distal tephra correlation and source identification in the Andes and probably other volcanic arcs with significant Pb isotopic variations.

Geochemical comparison between oceanic and continental arc volcanic rocks: Insights to arc magmatism

Compositional differences between continental and oceanic arc volcanic rocks have long been recognized; however, our understanding of them is incomplete. This study presents a comprehensive geochemical comparison, including major, trace and Sr–Nd–Pb isotope compositions, between global continental and oceanic arc volcanic rocks. Our data compilation reveals that volcanic rocks from a single oceanic arc occupy basaltic to basaltic–andesitic average lithochemical compositions, except for volcanic rocks from the Lesser Antilles arc, which occupies an andesitic average lithochemical composition, similar to the bulk composition of volcanic rocks from single continental arcs. The composition of the average continental arc volcanic rocks, the average Lesser Antilles arc volcanic rocks and the average oceanic arc volcanic rocks are different in many ways, which span the entire compositional range from basalts to rhyolites, and are reflected in major, trace element and Sr–Nd–Pb isotope compositions. Qualitative geochemical analyses and semi‐quantitative modelling suggest that the compositional differences in mafic arc volcanic rocks can be accounted for by differences in source mixing between mantle wedge peridotite and slab‐derived crustal components. Slab melts‐peridotite source mixing governs most of the lithochemical features of the continental arc and the Lesser Antilles arc mafic volcanic rocks, which is especially true for Sr–Nd–Pb isotopes. On the other hand, such source mixing occurred to a lesser extent in the petrogenesis of oceanic arc mafic volcanic rocks. Magma evolution processes such as fractional crystallization may further modify the lithochemical composition of the arc volcanic rocks, especially the felsic ones, but this is not the governing factor.

Multi-Isotopic Compositions of Ores from the Shizishan Cu–Au–Mo Orefield in the Tongling Region, Eastern China: Implications for Ore Genesis

The Middle–Lower Yangtze Metallogenic Belt (MLYMB) hosts abundant porphyry–skarn–stratabound-type Cu–Au–Mo deposits. Despite extensive research, the origin of the stratabound-type deposits, which developed at the unconformity interface between the Devonian and Carboniferous strata in the MLYMB, remains controversial. The primary debate centers on whether these deposits are the result of Carboniferous sedimentary exhalative mineralization or Mesozoic magmatic–hydrothermal mineralization. In this paper, we examine three representative deposits in the Shizishan orefield: the Chaoshan skarn-type Au deposit, the Hucun porphyry–skarn-type Cu–Mo deposit, and the Dongguashan Cu–(Au) deposit, which has a disputed genesis of its stratiform orebodies. Economically important ore minerals, such as chalcopyrite, molybdenite, and pyrrhotite, and their associated quartz and calcite, were focused on, rather than the extensively studied pyrite in the Tongling region. The ore genesis and sources of mineralized elements in the Shizishan orefield were investigated using H, O, C, S, Pb, and Cu isotopes. The H–O isotopic compositions of hydrothermal quartz from the Chaoshan, Dongguashan, and Hucun deposits indicate that the ore-forming fluids were mainly magmatic water with some meteoric water input. The C–O isotopic compositions of calcite show a large difference from the local sedimentary carbonates. The S isotopic compositions of sulfides reveal a magmatic sulfur signature. The Pb isotopic compositions in the three deposits are similar to those of the Shizishan intrusions, suggesting a magmatic source for Pb. The Cu isotopic compositions of chalcopyrite and pyrrhotite demonstrate that Cu, the primary ore-forming element, was mainly derived from magmatic–hydrothermal fluids. The stratiform orebodies display H–O–C–S–Pb–Cu isotopes consistent with the porphyry orebodies in the Dongguashan deposit, as well as in the Chaoshan and Hucun deposits, indicating a common ore genesis. From these, we conclude that the porphyry–skarn–stratabound-type Cu–Au–Mo deposits in the Shizishan orefield can be classified as a unified Mesozoic magmatic–hydrothermal metallogenic system. The stratabound-type copper sulfide deposits and the porphyry–skarn-type copper deposits in the MLYMB have a strong similarity in the source and genesis of their ore-forming elements.

Ore-forming process of the Huize super-large Pb-Zn deposit, SW China: Constraints from in situ elements and S-Pb isotopes

Study on the ore-forming process is crucial for comprehending the mechanisms of metal enrichment and facilitating mineral exploration. The Huize deposit in southwestern China is characterized by significant Pb and Zn resources, as well as economic coproducts of Ge and Ag. In spite of extensive studies, the key factors for ore deposition remain controversial. Mineral textures, in situ trace elements of dolomite, and S and Pb isotopes of sphalerite and galena from the contact zone between ore body and wall rocks were used to decipher this issue. The contact zone samples are further divided into three parts at the thin section scale: ore, transitional zone, and wall rock dolostone. In the ore part, dolomite is characterized by irregular replacement. In the transitional zone, dolomite displays a core-rim texture with dolomite in the core and Fe- and Mn-rich dolomite in the rim. In the wall rock part, the Fe- and Mn-rich dolomite occur as veins. From the ore, through the transitional zone, to the wall rock, the contents of Ca, Mg, and rare earth elements in dolomite increased, whereas the contents of Mn, Fe, In, and V decreased, indicating interaction between ore-forming fluids and dolostone. The LREE depletion of hydrothermal dolomite in three zones is caused by fluid-rock interaction and retention of Cl- complexes. Negative Eu and Ce anomalies indicate that fluids evolve from alkaline to weakly acidic at relatively low temperatures. The δ34S values of sphalerite generally decrease from the ore to the transitional zone, consistent with the kinetic fractionation of sulfur isotopes due to the precipitation of sulfides. The Pb isotopic composition of galena generally increases from the ore, transitional zone, to the wall rock, reflecting increased involvement of dolostone. The detailed ore-forming process can be summarized as follows. When hydrothermal fluids, with higher ore elements, higher δ34S value, and low Pb isotope composition, enter the wall rock that has relatively high Pb isotopic composition, intense fluid-rock interaction occurs, and elements and isotopes are exchanged, forming dolomite-dominated alteration and Pb-Zn sulfides. During this process, the fluids evolve from alkaline to neutral and weakly acidic. Therefore, we suggest that the change in the pH due to the replacement of dolostone has played an important role in ore deposition.

Lead and lead isotopes as tracers of soil contamination in southwestern Nigeria

The association of soil Pb levels has received considerable attention in recent times in developing countries like Nigeria due to its human health and environmental effect. Unfortunately, the sources of the pollutant has not been resolved for environmental health interest. Therefore, the aim of this study is to trace the sources of Pb contamination using the isotopic composition of Pb in the soil. Thirty (30) soil samples were collected at 0-20 cm depth in 3 different land-use zones, industrial area (IDA, n=10), municipal solid waste facility (MSW, n=10), and traffic section (TRS, n=10). In addition, 3 rock (gneisses) and 3 blacksmith dust samples were collected in the study area for comparison. Properties of the soil such as physico-chemical parameters (pH, organic content, and soil texture) and mineralogical composition were determined to understand the distribution of Pb in the soil of the study area. Similarly, the samples were analyzed for their Pb concentrations and Pb isotopic compositions using inductively coupled plasma mass spectrometry. The soil pH, organic matter, and texture were slightly acidic (4.9-6.9), average organic content (7.9-19.1%), and sandy clay loam in nature, respectively. Therefore, the Pb distribution was enhanced by the physico-chemical parameters. However, the mineral constituent of the soil in order of their abundance include quartz, feldspars, illite-muscovite, kaolinite, Biotite, goethite, and hematite. Consequently, there is no Pb-rich primary mineral in the soil. The environmental assessment of Pb in the study area showed that all the zones were contaminated on the basis of the average contamination factor and geoaccumulation index values. Similarly, the ecological risk factor estimation of Pb showed that the three zones had moderate potential ecological risk factors (41-54). The isotopic compositions of 208Pb/207Pb, and 206Pb/207Pb of the contaminated soil were lower than the corresponding component in gneisses, while the composition of 208Pb/206Pb was higher than the gneisses. Furthermore, the standard plot of (208Pb/207Pb) vs (206Pb/207Pb) showed clearly that the source of Pb in the contaminated soil was mainly from anthropogenic sources.Therefore, from the Pb concentration and isotopic composition acquired, the Pb contamination was mainly sourced from anthropogenic activities from the study area. These sources mainly include scrap metal recycling industry, vehicle emission and domestic and industrial waste. So, more effective remediation strategies need to be developed to reduce the contamination.

Winter-time pollution in Central European cities shifts the 208Pb/207Pb isotope ratio of atmospheric PM2.5 to higher values: Implications for lead source apportionment

Atmospheric lead pollution has adverse health effects on humans. Identification of anthropogenic Pb sources is thus crucial for understanding of pollution-related risks and for formulation of efficient abatement strategies. We analyzed concentrations and isotope ratios of Pb in fine air-borne particulate matter (PM2.5) in three Central European cities. Aerosol sampling in 12-h intervals was performed during summer and winter in Hradec Králové, Olomouc and Brno, regional centers of highly industrialized Czech Republic, each with a population of more than 90 thousand. Lead analysis was complemented with concentration measurements of Zn, Cu, Cd, As, Sb, and S. Trace element and PM2.5 concentrations were higher in winter than in summer in all studied cities, on average by 47%. The overall mean concentration of PM2.5 in urban air was 21 μg m−3, similar to that in Bern (Switzerland) and Vienna (Austria). Across the sites, 206Pb/207Pb ratios ranged from 1.142 to 1.178 in summer and from 1.143 to 1.173 in winter. The mean 206Pb/207Pb ratios were statistically indistinguishable in all three studied cities (1.165 in Hradec Králové, 1.163 in Olomouc, and 1.160 in Brno). In the 206Pb/207Pb vs.208Pb/207Pb graph, Pb isotope composition of summer samples formed a straight line, whereas Pb isotope composition of winter samples was shifted toward higher 208Pb/207Pb ratios. A Pb isotope inventory of regional pollution sources indicated that winter-time Pb pollution was not caused solely by household heating and increased electricity production in coal-burning power plants. Recycling of industrial Pb originating from Variscan ores and waste incineration could have shifted the 208Pb/207Pb ratio of PM2.5 to higher values, however, such sources do not emit more Pb in winter than in summer. Remobilization of legacy alkyl-Pb from gasoline additives and Pb emissions from current unleaded gasoline and diesel could have shifted both Pb isotope ratios to lower values.

A method to produce low lead blank silicon dioxide gel as an emitter for isotopic analysis of sub-nanogram lead sample

Lead (Pb) isotopes have been widely used in isotopic dating and geochemical tracing. The rapid development in Earth sciences requires high precision and accuracy of isotopic measurements of low Pb contents or small amounts of samples. However, low ionization efficiency can significantly affect the sensitivity and precision of the measurement. Emitters, such as silicon dioxide (SiO2) gel used in the thermal ionization mass spectrometer (TIMS) measurement of Pb isotopes, can reduce Pb loss at the low-temperature stage and improve Pb ionization efficiency at the high-temperature stage, but they inevitably introduce Pb blank and affect the quality of the results. Therefore, the emitters should possess the features of both high ionization efficiency and low Pb blank. In the present study, a SiO2 gel solution was produced via a double-bottle method and then purified by the Sr-spec® resin. We further measured Pb blank value of this emitter using the isotopic dilution method and examined its ionization efficiency via measuring isotopic composition of standard reference materials of Pb solution and rock powders using different amounts of Pb. Analytical data show that Pb blank values of the twice-purified SiO2 gel solution are lower than 1 pg/μL (lowest value of ∼0.3 pg/μL). Moreover, it can effectively improve Pb ionization, and maintain high and stable ion signal intensity during the measurement runs. Analytical results of Pb isotopic compositions, obtained from nano- to subnano-gram Pb amounts of reference materials, all fall in the ranges of their reference values, meeting the requirements in precision and accuracy for the measurements on micro-samples. This emitter is useful for Pb isotopic measurement of micro-samples and predictable to promote the application of Pb isotopic geochemistry.

Analytical workflow to trace lead sources in fill-derived soils in Turku, Southwest Finland

We present an analytical workflow scheme to trace the source of lead and to estimate risks to lead contaminated soil and demonstrate the methods with test sites from the city of Turku. This workflow includes lead concentration, sequential extractions, mineralogical characterization, and isotope composition. Lead concentrations higher than 100 mg/kg were found in 16 out of 219 urban topsoil samples in the city of Turku during soil geochemical baseline mapping. Ten samples were selected for detailed geochemical and mineralogical studies. Most of the elevated Pb concentrations were measured from fill-derived soils. Mineralogical investigations using FE-SEM-EDS demonstrated that Pb exists in various types of particles and compounds in the Turku topsoil samples. Most of the particles appear to be of anthropogenic origin. The Pb isotopic compositions measured on individual Pb-bearing particles using laser ablation MC-ICP-MS in Turku soil rule out their origin from Finnish and Swedish bedrock. Thus, Pb in the fill-derived soils must have been imported from other regions. Based on the combined use of traditional geochemical study and advanced micro-analytical techniques, it was found that Pb in urban fill-derived soils is bound to various carrier phases and has several pollution sources. When Pb-containing urban soil is reused in city constructions, care should be taken to prevent direct contact with the Pb-containing soil and dust generation at such sites.

An isotopically enriched mantle component in the source of Rodrigues, Réunion volcanic hotspot

The Mascarene Islands in the western Indian Ocean, encompassing La Réunion, Mauritius, and Rodrigues, are the recent (<10 Ma) surface expressions of the Réunion hotspot. Ocean island basalts (OIB) from these islands exhibit a remarkably homogeneous long-lived radiogenic isotopic composition, coinciding with the convergence field of many global OIB trends in the mantle array. Réunion plume-related OIB therefore provide one of Earth’s most pristine representations of this “focal zone” component, which may have a primordial heritage. Besides this signature, Mascarene lavas have been suggested to retain contributions from sources with distinct compositions, including: (1) Archaean-aged zircons assimilated from continental crust within the oceanic lithosphere by trachytic magmas from Mauritius; (2) more deeply recycled continental crust components preserved by elevated 87Sr/86Sr and 208Pb/206Pb in lavas from the Piton des Neiges volcano of Réunion; and (3) an isotopically depleted mantle component resulting from interaction with Central Indian Ridge material.In this study we use Sr-Nd-Pb isotope systematics, along with major and trace element compositions of basaltic lavas from all three Mascarene Islands to investigate the relationship of their sources to well-characterized mantle endmembers. Among the Mascarene Islands, Rodrigues lavas are the most enriched in highly incompatible elements, likely reflecting shallower and lower degrees of partial melting than Réunion or Mauritius. Combined Sr-Nd-Pb isotope compositions indicate that lavas from the Older Series of Mauritius resemble those from Réunion, whereas lavas from the Younger and Intermediate Series, together with Rodrigues, are consistent with contributions from an isotopically depleted component. In addition, the Pb isotopic compositions of Rodrigues samples require an additional contribution from a component with a long-term enrichment in its Th/U ratio. Based on isotope mixing models, direct assimilation of continental crust embedded within the oceanic lithosphere is unlikely to account for the Pb isotopic variation of Rodrigues. A metasomatized mantle component, previously envisaged as a “fossil” Réunion plume near the Central Indian Ridge, is partially able to reproduce the trace element signature, but not the observed Sr-Nd-Pb isotopic compositions of Rodrigues. Instead, small proportions (<5%) of an EM1-like component provide a preferred endmember. The composition and origin of this component, which is exclusively reflected within Rodrigues lavas, may constitute a new geochemical feature of the Mascarene Islands and is consistent with geodynamical predictions that small-scale enriched mantle domains may be widespread in the source regions of hotspot volcanoes.

Genesis of the Giant Huoshaoyun Non-Sulfide Zinc–Lead Deposit in Karakoram, Xinjiang: Constraints from Mineralogy and Trace Element Geochemistry

The Huoshaoyun zinc–lead deposit, a giant non-sulfide deposit in Xinjiang, is one of the most significant discoveries of zinc–lead deposit in China and globally in recent years. The deposit is dominated by zinc–lead non-sulfides, with minor occurrences of sulfides such as sphalerite, galena, and pyrite. The non-sulfide minerals include smithsonite, cerussite, anglesite, and Fe-oxide. This study focuses on the mineralogical characteristics of sulfide and non-sulfide ores, as well as the trace element characteristics of sphalerite, smithsonite, and Fe-oxide. Mineralogical analysis reveals that smithsonite is derived from the oxidation of primary sulfide minerals and can be classified into three types that are generated during different stages of supergene oxidation. The three types of smithsonite are formed through replacing the sphalerite and host limestone, as well as directly precipitating in the fissures and vugs. Trace element analysis of sphalerite indicates that it is rich in Cd, Tl, and Ge, but poor in Fe and Mn. The ore-forming temperature, calculated using the GGIMFis geothermometer, is mostly within the range of 100~150 °C. Moreover, the trace element characteristics, ore-forming temperature, and S and Pb isotope compositions of the sulfide ores of the Huoshaoyun deposit are similar to those of the Jinding and Duocaima MVT lead–zinc deposits, which are also located in the Eastern Tethyan zinc–lead belt. This suggests that the sulfide orebody in the Huoshaoyun Zn-Pb deposit could also be the MVT deposit. Study of the trace element of the non-sulfide minerals shows that the Mn and Cd are relatively enriched in smithsonite, while Ga, Ge, and Pb are enriched in Fe-oxide. This can be attributed to distinct geochemical properties of the trace elements in the non-sulfide minerals of the Huoshaoyun deposit and is consistent with those of the other oxidized MVT deposits, thus indicating the supergene oxidation process of this deposit.

Occurrence, Chemical, and Pb-isotopic Composition of Uraninite: A Verification of the Effective Source of Uranium in a Granite Aquifer of the Daejeon Area, South Korea

Occurrence, Chemical, and Pb-isotopic Composition of Uraninite: A Verification of the Effective Source of Uranium in a Granite Aquifer of the Daejeon Area, South Korea

Petrogenesis, tectonic setting and geodynamic implications of keziergayin granites in the kelan basin (Chinese Altai): constraints from geochemistry, zircon U-Pb geochronology and Nd‒Hf‒Pb‒O isotopes

The Chinese Altai is characterized by abundant granitoids, which not only are indicators of the interaction between crust and mantle but also provide critical constraints on the tectonic evolution of the orogen. This study presents zircon U‒Pb‒O isotopes, whole-rock major and trace element and Nd‒Hf‒Pb isotopes data for granite porphyries from the Keziergayin region in the Kelan Basin. The granite porphyries intrude in the Kangbutiebao Formation with zircon U‒Pb dating of 394 ± 3 Ma. They have the characteristics of subalkaline and metaluminous to weakly peraluminous and show geochemical affinity with I-type granite. The granite porphyry samples display negative εNd(t) (−1.9 to −1.4), positive εHf(t) (+4.3 to +11.4) values, with Nd–Hf decoupling; low Pb isotope compositions; δ18OV-SMOW (6.38‰–8.45‰) is less than 10‰, within the range of O isotopes of medium-basic igneous rocks. These geochemical signatures indicate that the granite porphyries originated from lower crust medium−basic igneous rocks extracted from the lithospheric mantle metasomatized by subducted melt. They are characterized by high SiO2 contents and Rb/Sr ratios; low CaO contents and K/Rb ratios, hinting that they were formed by highly evolved magmas, with fractionation crystallization of feldspar, apatite, garnet, allanite and/or monazite. The granite porphyries possess positive Rb, Th, U, Nd, Zr, Pb and light rare Earth elements (LREEs) anomalies with strong negative Ba, Nb, Ta, Sr, P, Ti and Eu anomalies, implying that their formation were related to an island arc. Combined with previous studies, it is suggested that the existence of the Early Devonian arc-basin system associated with subducting slab rollback in the Chinese Altai, which belongs to the Siberian active continental margin system.

Global warming induces the succession of photosynthetic microbial communities in a glacial lake on the Tibetan Plateau

As an important freshwater resource in the Qinghai-Tibet Plateau, glacial lakes are being immensely affected by global warming. Due to the lack of long-term monitoring data, the processes and driving mechanisms of the water ecology of these glacial lakes in a rapidly changing climate are poorly understood. This study, for the first time, reconstructed changes in water temperature and photosynthetic microbial communities over the past 200 years in Lake Basomtso, a glacial lake on the southeastern Tibetan Plateau. Temperatures were reconstructed using a paleotemperature proxy based on branched glycerol dialkyl glycerol tetraethers (brGDGTs), the cell membrane lipids of some bacteria, and photosynthetic microbial communities were determined by high-throughput DNA sequencing. The reconstructed mean annual air temperature (MAAT) at Lake Basomtso varied between 6.9 and 8.3 °C over the past 200 years, with a rapid warming rate of 0.25 °C /10 yrs after 1950s. Carbon isotope of sediment and n-alkane analyses indicate that ≥95% of the organic matter in Lake Basomtso is derived from a mixture of terrestrial C3 plants and endogenous organic matter inputs, and the proportion of endogenous organic matter in the sediments has gradually increased since the 1960s. The sedimentary DNA analyses of the sediment core reveal that Chloracea is the most dominant prokaryotic photosynthetic microbial group (84.5%) over the past 200 years. However, the relative abundance of Cyanobacteria has increased from ≤6.8% before the 1960s to 15.5% nowadays, suggesting that warmer temperatures favor the growth of Cyanobacteria in glacial lakes. Among eukaryotic photosynthetic microorganisms, the Chlorophyceae have been gradually replaced by Dinoflagellata and Diatomacae since the 1980s, although the Chlorophyceae still had the highest average relative abundance overall (30–40%). The Pb isotopic composition, together with the total phosphorous concentration, implies that human activity exerted a minimal impact on Lake Basomtso over the past 200 yrs. However, the synchronous fluctuations of total organic carbon (TOC), total nitrogen (TN), and metal elements in sediments suggest that temperature appears to have a strong influence on nutrient input to Lake Basomtso by controlling glacial erosion. Global warming and the concurrent increase in glacial meltwater are two main factors driving changes in nutrient inputs from terrestrial sources which, in turn, increases the lake productivity, and changes microbial community composition. Our findings demonstrate the sensitive response of glacial lake ecology to global warming. It is necessary to strengthen the monitoring and research of glacial lake ecology on the Tibetan plateau, so as to more scientifically and accurately understand the response process and mechanism of the glacial lake ecosystem under global warming.

Pb and O isotopic characteristics of single minerals in the Jianggang radial sand ridges of the southwestern Yellow Sea: Implications for provenance and pathways of silt-size sediments

Understanding the sediment provenance of the Jianggang radial sand ridges (RSRs) along the Jiangsu coast in the southwestern Yellow Sea is crucial for sustainable coastal development and land resource management. In this study, the provenance and transport patterns of silt-size sediments in the Jianggang RSRs were explored using Quartz oxygen (O) and K-feldspar lead (Pb) isotopic compositions and their large ion lithophile elements (LILEs) concentrations. The Pb-O isotopic compositions and concentrations of most LILEs in RSRs sediments were between those of the Yangtze River Mouth (YTZ), Old Yellow River Delta (OYR), and Modern Yellow River Mouth (MYR). The Pb-O isotopic compositions and typical elemental ratios were similar between the onshore and northwest offshore RSRs sediments, implying shoreward transport of offshore silt-size sediments. Through multidimensional scaling and graphic methods, it was found that the sediments of onshore and offshore RSRs originate mainly from the YTZ and OYR. Furthermore, the MixSIAR model showed that the contributions of the YTZ to onshore and offshore RSRs reached 33 ± 4 % and 36 ± 3 %, respectively. Followed by the OYR with contributions of 36 ± 3 % and 25 ± 8 %, respectively, and the contributions of the MYR and Korean Peninsula were <21 % and 8 %, respectively. Meanwhile, contributions from the Northern Chinese Deserts (approximately 10 %) deserved attention. Through the distribution of indicators, the transport patterns of silt-size sediments were proposed and compared with those of other fractions for the first time. According to the correlation analysis, the change in the area of central Jiangsu coast was mostly affected by terrestrial river supply and coastal mariculture. Therefore, it was necessary to control the scale of river reservoir construction and strengthen mariculture for sustainable land development and management. In future, comprehensive interdisciplinary and large temporal–spatial scales are suggested to further understand the coastal development.

Effects of crustal assimilation on 238U-230Th disequilibria in continental arc settings

Compositions of arc magmas depend on several factors and are often thought to reflect conditions in the mantle wedge and at the slab-mantle interface. However, in continental arc settings, magmas are also influenced by assimilation of continental crust. Here, we present measurements and modeling of 238U-230Th activity ratios, Sr, Nd, Hf, and Pb isotopic compositions, and major and trace element concentrations in young, historic lavas erupted from Reventador, an active stratovolcano in the Ecuadorian Andes. In arc lavas, 238U-230Th disequilibria are often assumed to reflect processes occurring in the mantle wedge, as U and Th behave differently in this relatively oxidized and fluid-rich environment. Enhanced mobility of hexavalent U in aqueous fluids results in (230Th/238U) < 1 and elevated (238U/232Th), which are common in arc lavas. However, the majority of Reventador lavas have (230Th/238U) = 1.0–1.1 and (238U/232Th) = 0.94–1.12, the latter of which is considerably lower than the depleted mantle ((238U/232Th) ∼ 1.5, Sims and Hart, 2006). While this Th enrichment could be due to melting of subducted oceanic crust, approximately linear trends between (230Th/232Th), wt. % SiO2, and radiogenic isotope ratios indicate otherwise. We argue that crustal assimilation lowers long-term, or time-integrated, (238U/232Th) in Reventador magmas. To quantify the effects of assimilation we modeled stepwise assimilation and fractional crystallization. Observed trends between (230Th/232Th), 87Sr/86Sr, εNd, εHf, and 208Pb/206Pb can be reproduced by up to 10% assimilation, which is consistent with previous regional studies. However, reproducing the full spectrum of isotopic diversity among Reventador lavas requires heterogeneous basalt compositions. In a broader context, this study emphasizes the need to consider crustal processes when examining continental arcs. While 238U-230Th disequilibria develop in the mantle wedge, they can be overwritten by subsequent interaction with continental crust.

Lead isotope fingerprinting techniques help identify and quantify 3000 years of atmospheric lead pollution from Laguna Roya, northwestern Iberia

Legacy pollution research has established that over the past 3000 years, mining and metallurgical activities have resulted in widespread deposition of lead (Pb) pollution. However, there is still a limited understanding of how humans have impacted the long-term cycling of Pb in the environment. We present a 4,000-year lake sediment Pb isotope record from Laguna Roya, northwestern Iberia, that identifies and quantifies the predominant sources of atmospheric Pb pollution. For the first time, Pb isotopic compositions of ancient slag samples dated (∼600 BCE–200 CE) from a mining district in the southwest of the Iberian Peninsula are compared to Pb isotope ratios of Pb pollution deposited contemporaneously in lake sediments. In addition, literature Pb isotope ratios of ores from mining regions throughout Iberia are compared with those of leaded gasoline and coal to identify additional sources of anthropogenic Pb. Deposition of atmospheric Pb pollution begins after 950 BCE, and until 1750 CE, the Pb isotopic composition most resembles the southwestern slag deposits, containing a mixture of Pb ores from southeast Iberia (up to 36%) and southwest Iberia (∼74%). Between 1750 and 1960 CE, Pb pollution is attributed to Pb mining in southcentral Iberia. After 1960 CE, the dominant Pb pollution source (∼85%) is again metal refining in southwestern Iberia, and only ∼15% is from leaded gasoline. Provenance and reconstruction of the temporal and spatial distribution of legacy Pb pollution further our understanding of how humans have affected the biogeochemical cycle of this toxic element in the environment over time.

Petrogenesis and Geodynamic Evolution in the Northern Westfjords, Iceland, Elucidated by Iceland's Oldest Silicic Rocks

AbstractIceland's oldest silicic rocks provide unique insight into the island's early crustal evolution. We present new zircon U‐Pb ages bolstered with zircon trace element and isotopic compositions, and whole rock Nd, Hf, and Pb isotope compositions, from three silicic magmatic centers—Hrafnsfjörður, Árnes, and Kaldalón—to understand the petrogenesis of large silicic volcanic centers in the northern Westfjords, Iceland. Our data confirm Hrafnsfjörður as the oldest known central volcano in Iceland (∼14 Ma) and establish an older age for Árnes (∼13 Ma) than previously estimated. We also report the first U‐Pb zircon dates from Kaldalón (∼13.5 Ma). Zircon oxygen isotope compositions range from δ18O∼+2 to +4‰ and indicate involvement of a low‐18O component in their source magmas. Hrafnsfjörður zircon Hf (mean sample εHf ∼ +15.3–16.0) and whole rock Hf and Nd (εHf = +14.5 to +15; εNd = +7.9 to +8.1) isotopic compositions are more radiogenic than those from Árnes (zircon sample εHf ∼ +11.8–13; whole rock εHf = +12.8 to +15.1; εNd = +7.3 to +7.7), but Hrafnsfjörður whole rock Pb isotope compositions (208/204Pb = 37.95–37.96; 206/204Pb = 18.33–18.35) are less radiogenic than those from Árnes (208/204Pb = 38.34–38.48; 206/204Pb = 18.64–18.78). Kaldalón has zircon Hf isotope compositions of εHf∼+14.8 and 15.5 (sample means). These age and isotopic differences suggest that interaction of rift and plume, and thus the geodynamic evolution of the Westfjords, is complex. Isotopic compositions of Hrafnsfjörður and Árnes support involvement of an enriched mantle (EM)‐like mantle component associated with a pulsing plume that resulted in variable spreading rates and magma fluxes and highlight the heterogeneity of the Icelandic mantle.

Genesis of the Sinongduo Carbonate‐hosted Pb‐Zn‐Ag Deposit in the Central Lhasa Terrane, Tibet

AbstractThe Sinongduo mining region includes two types of mineralizations: the epithermal and the carbonate‐hosted Pb‐Zn‐Ag deposits. Despite being studied for many years, the ore formation process and genesis of the carbonate‐hosted Pb‐Zn‐Ag deposits remain poorly understood. The Pb‐Zn‐Ag ore bodies occur as veins and are hosted by limestone and dolostone of the Permian Xiala Formation. Three sulfide mineralization substages have been identified at the Sinongduo carbonate‐hosted deposit. Indium coupled with Cu, Co and Sn was incorporated into sphalerite as substitutions: 2Zn2+ ↔ Cu+ + In3+, (3n/2 + 1)Zn2+ ↔ Co2+ + nIn3+ or (2n + 1)Zn2+ ↔ Co2+ + n(Cu+ + In3+) (n &gt; 1) and 4Zn2+ ↔ Sn2+ + 2In3+. Sphalerite and pyrite in the mineralization stage display δ34S values in a narrow range of +5.7‰ to +11.3‰, which are similar to those of Palaeocene igneous rocks, indicative of a magmatic source of sulfur. We present systematic carbon‐hydrogen‐oxygen isotope results that further support a magmatic source for the ore‐forming fluids that were influenced by meteoric water. Furthermore, the Pb isotope compositions of sulfide minerals in the Sinongduo carbonate‐hosted deposit overlap with the values of coeval Linzizong volcanic rocks and are similar to those of Indian Ocean sediments, indicating upper crustal sources of metals. We conclude that the Sinongduo carbonate‐hosted Pb‐Zn‐Ag deposit is a medium‐ to low‐temperature magmatic‐hydrothermal deposit related to Linzizong magmatism.

Sources of Metals for the Rudny Altai VMS Deposits: Results of High-Precision MC-ICP-MS Lead Isotope Study

The Rudny Altai metallogenic province, which is concordant to the structures of the eponymous terrane and located in the Central Asian orogenic belt (CAOB), is one of the largest volcanic massive sulfide (VMS) provinces in the world. Lead isotopic composition of galena (61 samples in total) was measured for the first time with high accuracy (±0.02%, SD) for 20 sulfide base metal deposits representing the dominant Kuroko type in the Rudny Altai. They are enclosed in the Early–Middle Devonian volcano-sedimentary sequence in association with volcanic rocks of the bimodal basalt-rhyolite series. We studied the large and superlarge deposits of this type: Ridder-Sokol’noe, Tishinskoe, Novo-Leninogorskoe, Zyryanovskoe, Zmeinogorskoe, and Korbalikha. In the province, the isotope ratios 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb vary within narrow limits. At average values of 206Pb/204Pb = 17.820, 207Pb/204Pb = 15.517 and 208Pb/204Pb = 37.669, the root mean square variations (variation coefficient, %) are 0.22, 0.038 and 0.063% respectively. Even more homogeneous composition is observed within ore districts of the province (0.054, 0.012 and 0.020%) and especially within deposits (0.025, 0.010 and 0.013%), where the scale of variations of lead isotope ratios reaches their measurement error (±0.02%). The lead isotopic composition in the province shows no isotopic “signatures” of juvenile (asthenospheric) origin. The evolutionary characteristics of the lead source (its depletion in uranium, the old model Pb-Pb age, and moderate values of the µ2 parameter) together with the persistent isotopic composition allow us to regard the lithospheric mantle consisting of metasomatized and recycled rocks as its source. This source was of regional significance, chemically (U-Th-Pb) and isotopically (Pb-Pb) homogeneous, and common for all deposits. Among other CAOB terranes, including the Chinese Altai, the 206Pb, 207Pb and 208Pb isotopes in the ore lead of the Rudny Altai terrane have the least radiogenic composition. The previously noted (Chiaradia et al., 2006) systematic decrease of radiogenic isotope content in the lead of ores and rocks of the CAOB terranes from the southwest to the northeast correlates with a decrease in the lower crustal contribution in the same direction in their composition, where fragments and blocks of Precambrian crust are also involved. The peculiarity of the Pb isotopic composition of the Rudny Altai terrane is largely determined by the absence of Precambrian crustal blocks in its composition.

Geology, Fluid Inclusions, and C–H–O–S–Pb Isotope Geochemistry of Pb–Zn Deposits within the Tuotuohe Region of the Tibetan Plateau: Implications for Ore Genesis

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.