Pb Isotope Signatures Research Articles

Sr-Pb isotope differences in pre- and post-burial human bone, teeth, and hair keratin: implications for isotope forensics.

The isotopic signatures of human tissues can provide valuable information on geographic origin for medicolegal investigations involving unidentified persons. It is important to understand the impact of diagenetic processes on isotopic signatures, as alterations could result in incorrect estimation of geographic origin. This study examines alterations in isotope signatures of different tissues of five human body donors studied throughout decomposition at the Forensic Anthropology Research Facility (FARF), San Marcos, TX. Two body donors were buried, two were placed in open pits, and one was first allowed to naturally mummify and then buried. Remains were recovered after a period of 7-34months. The preplacement and post-recovery Sr-Pb isotope data of scalp hair, bone (iliac and tibia), and tooth enamel and dentine were compared. The hair samples record significant shifts in Sr-Pb isotope compositions, with hair keratin Pb isotope composition shifting towards the Pb signature of local soil samples. Hair keratin Sr isotope compositions were altered by the burial environment and possibly also by the lab sample cleaning method. The spongy iliac bone samples show inconsistencies in the recoverability of the preplacement Sr-Pb isotope signatures. The post-placement signatures of the buried donors show slight elevation over preplacement signatures. The post-placement signatures of donors placed in open pits are significantly elevated. The tibia and dental samples record the most consistent isotopic data with the least alteration. These more densely mineralised elements show good recoverability of the preplacement isotope signatures in burials and open pits and are thus deemed better targets for forensic investigative purposes.

Sources and historical records of metal(loid)s in river sediments from an agricultural tributary of Tuojiang river: Evidence from geochemical analyses and Pb isotope

Clarifying the sources and historical variation of metal(loid)s in agricultural river sediments is vital for watershed contamination control and environmental improvements. In this study, a systematical geochemical investigation of Pb isotopic characteristics and the spatial-temporal distribution of metal(loid)s abundances was conducted to delineate the origins of metal(loid)s (Cd, Zn, Cu, Pb, Cr, and As) in sediments from an agricultural river, Sichuan Province, Southwest China. The results showed significant enrichment of Cd and Zn in the whole watershed, with substantial anthropogenic contributions of 86.1% and 63.1% for the surface sediments, and 79.1% and 67.9% for the core sediments, respectively. As was mainly derived from natural sources. Cu, Cr, and Pb were originated from the mixing sources of natural and anthropogenic processes. The anthropogenic origin of Cd, Zn, and Cu in the watershed was closely correlated with agricultural activities. The profile of EF-Cd and EF-Zn displayed an increasing trend from the 1960s–1990s, and then kept a high value, which was consistent with the development of national agricultural activities. Pb isotopic signatures suggested multiple sources of the anthropogenic Pb contamination, including industrial/sewage discharge, coal combustion, and vehicle exhaust. The average anthropogenic 206Pb/207Pb ratio (1.1585) approximated that of local aerosols (1.1660), suggesting aerosol deposition was a crucial pathway of anthropogenic Pb input to sediment. Furthermore, the anthropogenic Pb percentages (mean of 52.3 ± 10.3%) from the EF approach were in line with that from the Pb isotopic method (mean of 45.5 ± 13.3%) for sediments under intense anthropogenic impacts.

Slight transition in Chinese atmospheric Pb isotopic fingerprinting due to increasing foreign Pb

Atmospheric lead (Pb) pollution negatively affects human health and ecosystem, and extensive research is required to identify its sources and develop robust mitigation methods. In this study, the concentration and isotopic composition of Pb in fine particulate matter (PM2.5) at five sites in the China's Beijing-Tianjin-Hebei (BTH) region were analyzed. The results showed that the Pb concentration in the BTH region declined along the northwest direction in winter owing to the East Asian monsoon. Pb isotopic signatures confirmed that anthropogenic activities significantly contributed to Pb pollution, compared with natural sources. With the increasing import of foreign Pb (with a relatively lower 208Pb/206Pb ratio) to China, we hypothesized that the unique isotopic signature of Pb in Chinese aerosols may decline over time. Therefore, the application of the isotopic approach for quantifying Pb transported from China should be carefully appraised in future research to provide a realistic estimate of the contribution of local sources and the transboundary effect consistent with air mass trajectories analysis. This study provides a theoretical reference for supporting the utilization of Δ208Pb values for better clarify the transboundary impact of Pb pollution and to reduce international disputes.

Archean Pb isotope variability tracks crust-mantle fractionation, granite production, and ore deposit formation

Various geological processes that affect Earth's crust may be encoded into isotopic tracers preserved in rocks and minerals. The enhanced sensitivity of U, Th, and Pb to crustal fractionation processes allows Pb isotopes to complement information from the Nd and Hf isotope systems. However, melt fractionation, crustal contamination and recycling, hydrothermal fluid flow and fluid-rock interaction, and other processes in the continental crust can lead to mixing of Pb isotopic signatures. Here, we report new Pb isotopic data from granite-K-feldspar and integrate these data with published Pb isotope ratios from granite K-feldspar and Pb-rich ores across the Yilgarn Craton in Western Australia. The aim of this study is to explore how the variability of Pb isotope ratios and derivative parameters can be used to gain information on specific geological processes occurring throughout the crustal column. We develop a model that subdivides different sampling media into chemical process groups and links their initial Pb signatures to Pb source regions and fractionation processes at various locations within the crust and upper mantle. Equilibration of Pb signatures with a primary mantle source reservoir (in part represented by volcanic-hosted massive sulfides) is contrasted with granite formation in the mid to lower crust (granite K-feldspar), and mineralization of ore deposits in the mid to upper crust (Pb-rich ores). Spatial trends similar to those in Nd and Hf isotopic data are recorded by Pb isotopic derivative parameters (μ = source 238U/204Pb, ω = 232Th/204Pb, and Δt - the difference between true sample age and Pb model age) calculated for komatiite-hosted Ni sulfide ores, granite K-feldspar, and volcanic-hosted massive sulfide (VHMS) ores. The significance of subtle differences in absolute values of derivative parameters is supported by the diversity of Pb isotope ratios, Pb model ages, and ∆t as tracked by a statistical metric, quantifying the variability of Pb sources involved in the formation of different chemical process groups. Generally greater variety in an older terrane (Youanmi) documents more ancient and recycled continental crust as compared with more homogeneous Pb isotopic signatures in a younger terrane (Eastern Goldfields Superterrane). The Pb signatures are interpreted, in part, to relate to the timing of source fractionation in the upper mantle with a legacy of this source signal preserved through various depths in the lithospheric section. The least radiogenic VHMS ore samples appear to provide a good approximation of mantle Pb signatures, indicated for example by a deficit in 206Pb and 208Pb relative to the other process groups. A significant heterogeneity recorded in Pb isotopic data from Pb-rich gold ores is explained by the interplay of hydrothermal fluids with diverse sources leading to the mineralization of gold deposits (e.g., leaching of Pb from surrounding rocks or fluid mixing). Such gold ore Pb signatures are distinct from other process groups, which together track sources less heterogeneous in age and/or U and Th.

Carboniferous mafic-ultramafic intrusions in the Eastern Pontides (Pulur Complex): Implications for the source of coeval voluminous granites

This study deals with the age and petrogenesis of mafic-ultramafic intrusions ranging in size from a few meters to 10 km within the Early Carboniferous high-grade gneisses of the Pulur Complex in the Eastern Pontides. The intrusions comprise dunite, wehrlite, gabbronorite, leucogabbro, anorthosite and ilmenite-bearing gabbronorite of cumulus origin, and are crosscut by dikes of ilmenite-bearing gabbronorite, leucogranite and microdiorite. U Pb dating on zircons from gabbronorite, anorthosite and leucogranite yielded igneous crystallization ages of 322–326 Ma, indicating that the intrusions were emplaced ca. 5–7 Ma after the peak of high-grade metamorphism, and form part of the Late Carboniferous high-volume magmatism in the region. In most cumulate rocks, Cr Al spinel, olivine and plagioclase were early crystallizing phases, followed by orthopyroxene, clinopyroxene and hornblende. Whole rock geochemical data suggest that wehrlite, gabbronorite, leucogabbro and anorthosite stem from a common magma, and ilmenite-bearing gabbronorite and dikes of leucogranite and microdiorite from different magmas. Application of mineral/melt partition coefficients to trace element compositions of clinopyroxene and hornblende in cumulate rocks suggests that the main cumulate body was derived from middle- to high-K calc-alkaline basic melts, and relatively late ilmenite-bearing gabbronorites from hypersthene-normative Ca-rich melts. All the rock types display radiogenic Sr and Pb isotopic signatures, and unradiogenic Nd isotopic ratios, which are indistinguishable from those of the coeval voluminous high-K calc-alkaline I-type granites in the region; the isotopic ratios are probably related to the metasomatism of the lithospheric mantle by sediment-derived melts. We suggest that the parental melts of the mafic-ultramafic intrusions and those of the high-K calc-alkaline granites were genetically related, and melts of the high-K calc-alkaline granites were probably derived from the melting of newly underplated calc-alkaline basic material at lower crustal depths, that were compositionally comparable to the parental magmas of the mafic-ultramafic intrusions. • The Pulur mafic-ultramafic intrusions (NE Turkey) formed at 326–322 Ma. • They are part of the Late Carboniferous high-volume magmatism. • Parental melts of the mafic-ultramafic intrusions were middle- to high-K calc-alkaline basic melts. • The high-volume magmatism probably resulted from the convective thinning of the lithosphere.

Petrogenesis of Early Mesozoic volcanic rocks in southeastern NE China: Geochemical and Sr–Nd–Pb–O isotopic evidences

This paper reports a study of whole-rock geochemical, Sr–Nd–Pb isotopic compositions and zircon UPb ages and O isotopic compositions of Late Triassic to Early Jurassic volcanic rocks of the Yanbian–Dongning area, northeastern China. The obtained data are used to constrain the petrogenesis of these rocks and to provide new insights into the timing of transition from the Paleo-Asian to the Paleo-Pacific tectonic regime. The studied Late Triassic to Early Jurassic volcanic rocks can be divided into two periods: Late Triassic–early Early Jurassic (212–198 Ma) and late Early Jurassic (ca. 181 Ma). The former rocks display high SiO2 and total alkalis contents, high Ga/Al ratios, depleted SrNd and highly radiogenic Pb isotopic signatures, and low zircon δ18O values. The former rocks have a genetic relationship with coeval intrusions, and their primitive melt was derived from juvenile crustal materials and underwent subsequent differentiation and assimilation of low-δ18O rocks. In contrast, the latter rocks have SiO2 contents of 49.00–63.30 wt%, are classified as calc-alkaline, and display arc-type trace-element features. Their geochemical and Sr–Nd–Pb–O isotopic compositions imply derivation from the partial melting of depleted mantle wedge metasomatized by oceanic slab-derived fluid and sediment melt. Combining these new results with published data, the Late Triassic–early Early Jurassic volcanic rocks are inferred to have formed in a rift-like extensional setting, whereas the late Early Jurassic volcanic rocks were generated in a subduction-related setting. The transition from the Paleo-Asian to the Paleo-Pacific tectonic regime occurred during the Early Jurassic.

Determining the geochemical fingerprint of the lead fallout from the Notre-Dame de Paris fire: Lessons for a better discrimination of chemical signatures

On 2019, the fire of Notre-Dame de Paris cathedral (“NDdP”) spread an unknown amount of lead (Pb) dust from the roof of the cathedral over Paris. No data describing the geochemical fingerprint of the roof lead, as well as no particle collected during the fire, were available: a post-hoc sampling was performed. To discriminate the potential environmental impact of the fire from multiple Pb sources in Paris, it was mandatory to define unequivocally the fire dust geochemical signature. A dedicated and in hindsight geochemistry-based strategy was developed to eliminate any source of potential contamination due to sampling substrates or previously deposited dust. Radiogenic Pb isotopic signatures (206Pb/207Pb and 208Pb/206Pb ratios) and elemental ratios were determined in 23 Pb-rich samples collected inside NDdP. We determined that the dust collected on wood substrates on the first floor was most representative of fire emissions. These samples were the analyzed for the 4 Pb isotopes (204, 206, 207, 208) and the fire dust signature is characterized by ratio values of 206Pb/207Pb: 1.1669–1.1685, 208Pb/206Pb: 2.0981–2.1095, 208Pb/204Pb: 38.307–38.342, 207Pb/204Pb: 15.633–15.639 and 206Pb/204Pb: 18.242–18.275. In addition, the fire dust presents typical element-to-Pb ratio. This fingerprint was compared to the signatures of the known local Pb sources. The geochemical fingerprint of the fire is significantly different from that of the dominant urban Pb source. This will allow future evaluation of the contribution of the fire to Paris Pb pollution and of the real extent of the area affected by the Pb-containing dust plume. Moreover, the geographical origin of Pb used for the roof restauration and the spire building was identified. These findings open new ways to study the Pb sources in historical monuments for environmental impacts evaluation, as well as for historical perspectives.

High contribution of vehicular exhaust and coal combustion to PM2.5-bound Pb pollution in an industrial city in North China: An insight from isotope

Although industrial emissions are the major pollution source of PM2.5-bound Pb, which affects air quality in cities, their influence has gradually decreased with the enhancement of industrial control in recent years. Thus, at present, the source of PM2.5-bound Pb is unclear, especially in an industrial city in North China. In this study, by incorporating the stable Pb isotopic compositions into a Bayesian isotope mixing model (MixSIAR), source apportionment of PM2.5-bound Pb was conducted during autumn and winter in 2017, and summer in 2018 in Changzhi. The daily average concentrations of PM2.5 and PM2.5-bound Pb during the study period were lower than the second-grade limit value of China (75 μg m−3) and the Chinese National Ambient Air Quality Standard (1 μg m−3), respectively. The pollution sources of PM2.5-bound Pb were fully distinguishable using Pb isotopes. In Changzhi, the 206Pb/207Pb ratio in soil (average: 1.0891) and exhaust dust from gasoline (average: 1.0832) and diesel (average: 1.0814) showed low levels of Pb isotope signature in Changzhi, whereas the rest of the source exhibited Pb isotope signature levels. The source apportionment results revealed that in an industrial city with many steel and coking plants, the primary source of PM2.5-bound Pb were motor vehicle emission (29.7%) and coal combustion (26.9%), rather than industrial emission (26.5%). Moreover, seasonal variations in PM2.5 of Pb sub-sources were observed: soil dust (21.7% and 18.4%) and diesel motor vehicles emission (16.4% and 15.6%) in summer and autumn; domestic coal combustion (17.1%) and coal-fired power plant emission (15.5%) in winter. The carcinogenic risk from motor vehicle emission in autumn was higher than that from industrial and coal sources in winter, and higher than that from motor vehicle sources in summer. This finding is a critical evidence of an anomalistic enrichment of PM2.5-bound Pb in an industrial city. These results obtained through Pb isotopic composition and MixSIAR model also improved the accuracy of source apportionment of atmospheric PM2.5-bound Pb, representing a high scientific significance and reference value for Pb pollution control in North China.

A Practical Procedure for Analysis of Lead Isotopes in Bivalve Shells Using Laser Ablation Multicollector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS).

Lead, like other trace elements, is incorporated in the growing bands of bivalve shells. The chemicals stored into the shells can provide valuable information about seawater conditions during the period of shell formation. In this study, we present a practical approach to determine Pb isotopic signatures in bivalve shells as a tool for evaluating lead pollution in coastal waters. To demonstrate the applicability of the method, Pb isotopic fingerprinting in bivalve shell layers were investigated using laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). Lead isotope ratios (208Pb/206Pb and 206Pb/207Pb) were measured along distinct sections of the maximum growth axis of the shells. Calibration and quantification of Pb isotopes were performed using NIST 612 as reference material. Our results demonstrated that Pb isotope ratios in the shells ranged from 1.143 to 1.201 for 206Pb/207Pb and from 2.061 to 2.161 for 208Pb/206Pb. The isotopic signatures recorded in the sample shells correspond to similar ranges of Pb signatures reported for marine sediments from the same study area. In general, this work shows that LA-MC-ICP-MS is a suitable technique for determining spatially resolved lead isotopic signatures in bivalve shells and that it can be used to estimate the origin of Pb pollution in aquatic environments.

Seasonal variation of atmospheric Pb sources in Singapore - Elemental and lead isotopic compositions of PM10 as source tracer

Southeast Asia has become a hotspot of anthropogenic particulate matter (PM) emissions due to increased coal combustion, high-temperature industrial operations, vehicular traffic, and agricultural biomass burning. Lead (Pb), a criteria pollutant, bound to such PM can be hazardous when inhaled, even at extremely low concentrations. Precise and accurate source apportionment of atmospheric Pb is thus, critical in order to minimize its exposure. This study investigates the sources of atmospheric Pb in Singapore aerosol samples (PM10) using Pb isotopes and elemental composition as tracers of contamination sources. PM10 aerosol sampling was conducted over a period of 1 year from June 2017 to May 2018 to capture the seasonal variations in sources of atmospheric Pb. Elemental concentrations reveal particularly high enrichment factors for Pb, Cu, V, Ni and Zn, especially when under the influence of southwest (SW) and inter monsoon (IM) winds. Pb isotopic ratios across the three seasons (206/207Pb = 1.147˗1.150 and 208/207Pb = 2.420˗2.428) are not significantly different. The Pb isotopic signatures and V/Ni ratios for all three seasons overlap with those of gasoline, diesel and ship emissions. Moreover, V/Pb values of more than unity for SW and IM winds suggest influence of transboundary coal combustion emissions particularly from Indonesia. Consequently, using Pb isotopic fingerprints and elemental ratios, we find that the primary sources of atmospheric Pb are vehicular & ship emissions, heavy oil combustion, transboundary coal combustion emissions, waste incineration and recirculation of historic leaded gasoline.

Lead isotopic fingerprinting of 250-years of industrial era pollution in Greenland ice

Emissions from mid-latitude industrial activities (e.g., mining, smelting , coal combustion) result in long-range atmospheric transport of lead (Pb) to the Arctic. While previous measurements of elemental concentrations and Pb isotopic ratios in ice and sediments have been used to suggest potential sources of toxic heavy metal pollution in these regions, high resolution Pb isotope records are largely unavailable due to the low Pb concentrations found in Arctic ice. Here we present and interpret a high-resolution, 1759–2008 record of Pb isotopes measured in a central Greenland ice core; the first high-resolution Pb isotope record for Greenland to include the First Industrial Revolution. Records of past industrial activities coupled with Pb isotopic signatures for regional ores and coals suggest Pb pollution prior to the mid-19th century was dominated by emissions from mining and combustion of coals in England, Scotland, and Wales. Rapid 1860s increases in Pb levels and decreases in 206 Pb/ 207 Pb ratios coincided with expansion of coal consumption in Europe and North America. Significant influence of 20th century smelting of Australian Broken Hill Pb ores in Europe resulted in a less radiogenic Pb isotope signature. The phase-out of leaded gasoline and other emissions reductions following passage of air-quality legislation in the United States had a pronounced effect on 206 Pb/ 207 Pb ratios, with values falling from 1.187 in 1978 to 1.154 in 1983. Increasing 208 Pb/ 207 Pb ratios through the 1990s and 2000s indicate rising influence of long-range transport from Asia countering declines in European emissions. This 250-year high-resolution Pb isotope reconstruction allows attribution of Pb sources to central Greenland with unprecedented detail. • 250-year high resolution Pb isotopic ice core record from central Greenland. • > 95% of Pb in the ice originated from pollution; U.S. pollution Pb peaked in 1968. • Following 1980 s U.S. Pb pollution declines, Pb from Asia dominated. • British Isles emissions lead as the Pb source from 1759 to 1817. • Smelting of Australian Broken Hill Pb ore in Europe seen beginning in the 1890s

Laurentide Ice Sheet extent over the last 130 thousand years traced by the Pb isotope signature of weathering inputs to the Labrador Sea

Understanding the history of continental ice-sheet growth on North America, and in particular that of the Laurentide Ice Sheet (LIS), is important for palaeoclimate and sea-level reconstructions. Information on ice-sheet extent pre-dating the Last Glacial Maximum (LGM) is heavily reliant, though, on the outputs of numerical models underpinned by scant geological data. Important aspects of LIS history that remain unresolved include the timing of its collapse during Termination 2, the first time that it expanded significantly during the Last Glacial Cycle, and whether its volume was significantly reduced during marine isotope stage (MIS) 3. To address these issues and more, we present authigenic iron-manganese (Fe–Mn) oxyhydroxide-derived high-resolution records of Pb isotope data and associated rare earth element profiles for samples spanning the past ∼130 kyr from northwest North Atlantic Labrador Sea, IODP Site U1302/3. We use these new data to track chemical weathering intensity and solute flux to the Labrador Sea associated with LIS extent on the adjacent highly radiogenic (high Pb isotope composition) North American Superior Province (SP) craton since the Penultimate Glacial Maximum (PGM). Our new records show that relatively high (radiogenic) values characterise warm marine isotope stages (MIS) 5, 3 and 1 and the lowest (most unradiogenic) values occurred during cold stages MIS 6, 4 and 2. The radiogenic Pb isotope excursion associated with Termination 2 is short-lived relative to the one documented for Termination 1, suggesting that LIS retreat during the PGM was relatively fast compared to the LGM and that its collapse during the last interglacial occurred ∼125 ka. Highly radiogenic inputs to the Labrador Sea during MIS 5d-a, ∼116–71 ka, most likely reflect a spin-up in Labrador Current vigour, incipient glaciation and renewed glacial erosion of high grounds of the eastern SP craton by localised wet-based ice-caps. A large decrease in Pb isotope values towards unradiogenic LGM-like compositions between ∼75–65 ka across the MIS 5/4 transition likely reflects a slow-down in Labrador Current vigour, an increase in subaerial deposition of aeolian dust and a significant advance of the LIS across Hudson Bay caused a strong reduction or even abandonment of Pb sourcing from the SP. The relatively radiogenic Pb isotope composition of bottom-waters bathing our study site during MIS 3, 57–29 ka, is unlikely to support a recently proposed major reduction in LIS extent for this time. Instead, we argue these values are better explained by southern Greenland Ice Sheet retreat, increased chemical weathering of the Ketelidian Mobile Belt and subsequent Pb runoff from Greenland.

Quaternary Collision-Zone Magmatism of the Greater Caucasus

Abstract The Greater Caucasus mountains (Cavcasioni) mark the northern margin of the Arabia–Eurasia collision zone. Magmatism in the central part of the Greater Caucasus began in the Pleistocene, up to ~25 Myr after initial collision. This paper presents bulk-rock and Sr–Nd–Pb isotope geochemistry from 39 Quaternary volcanic rock samples (<450 Ka) recovered from the Mt. Kazbek (Kasbegui) region of the Greater Caucasus, Georgia, to assess the sources and magmatic evolution of these lavas and the possible triggers for melting in the context of their regional tectonics. Compositions are dominantly calc-alkaline basaltic andesite to dacite (57–67 wt % SiO2). Although the lavas were erupted through thick continental crust, there is little evidence for extensive modification by crustal contamination. Trace element and isotopic systematics indicate that the lavas have supra-subduction zone signatures, most likely reflecting derivation from a lithospheric source that had been modified by melts and/or fluids from material subducted before and during the collisional event. Mass-balance modelling of the Sr–Nd isotope data indicates that the lavas require significant input from a subducted slab, with deep-sourced fluids fluxing the slab into the source region. In contrast with published data from Lesser Caucasus magmatism, data from the Mt. Kazbek region suggest that a compositionally distinct sediment source resides beneath the Greater Caucasus, producing characteristic trace element and Pb isotopic signatures. Two distinct compositional groups and therefore primary liquids can be discerned from the various volcanic centres, both derived from light rare-earth element enriched sources, but with distinct differences in Th/Yb and Dy/Yb ratios and Pb isotopes. Rare-earth element modelling of the lava sources is consistent with 3–4% melting starting in the garnet peridotite and continuing into the spinel facies or, potentially, sited in the garnet-spinel transition zone. Small-scale convection related to mantle upwelling provides a plausible mechanism for Greater Caucasus magmatism and explains the random aspect to the distribution of magmatism across the Arabia–Eurasia collision zone.

Contribution of recycled sediments to the mantle reservoir beneath Hainan Island: Evidence from Sr, Nd, Pb, Hf, and Mg isotopic analyses of Late Cenozoic basalts

Magnesium isotopes are a useful tool for constraining the origin of basalts with EM-like isotopic signatures in relation to ancient subducted slabs and recycled materials incorporated in mantle plumes. In this study, we present new SrNdPbHf and Mg isotopic data that were used to determine the origin of the basalt on Hainan Island and investigate the EM mantle reservoir beneath the island. Cenozoic basalts from northern Hainan Island are mainly tholeiitic, with a small amount of alkaline basalts. The Hainan basalts exhibited depleted SrNd isotopic compositions and EM2-like Pb isotopic signatures. The δ26Mg values of the Hainan basalts ranged from −0.40‰ to −0.28‰. The origin of the low δ26Mg signature can be attributed to carbonate sediments from recycled oceanic slab. Hainan basalts show a negative concave curve relationship between 87Sr/86Sr and εNd values, a positive relationship between 206Pb/204Pb and 207Pb/204Pb values and exhibit an evolution trend from depleted mantle towards marine sediments. This indicates that Hainan Island basalts can be explained by the mixing between depleted mantle and marine sediments. Most Hainan basalts have higher K/U × 10−3 and Ba/Th ratios than primitive mantle (K/U × 10−3 ≈ 11.8, Ba/Th ≈ 83), moreover, display highly correlated K/U × 10−3 and Ba/Th compositions with low-pressure (6–8 GPa) carbonated melt released from initial sediments. Therefore, we speculate that the primitive mantle peridotite, coupled with the low-pressure carbonated melt, ultimately became the mantle source of Hainan Island basalts.

Effects of forest fires on soil lead elemental contents and isotopic ratios

This study described the behavior of Pb and its isotopes in forest soils affected by different temperature wildfires. We collected samples of burned (and unburned) soil and ash in Abiul, central Portugal, in areas affected by different temperatures. The different soil burned severities were assessed in situ.The high-temperature fires consumed all organic matter in the topsoil (down to 5 cm), while lower temperatures did not. All the soil and ash samples were analyzed for their lead (Pb) contents and Pb isotopic compositions using inductively coupled plasma mass spectrometry.The average Pb elemental concentration in the unburned topsoils was 10.7 mg kg−1, and the isotopic composition ranged from 206Pb/207Pb = 1.167 to 1.178. No significant accumulation of Pb was observed in the topsoil (and ash) affected by the high-temperature fire, but their respective ratios increased (soil 206Pb/207Pb = 1.197; ash 206Pb/207Pb = 1.180). However, there was a significant accumulation of Pb (15.3 mg kg−1) in the topsoil and especially in the ash (Pb avg. = 21.8 mg kg−1), affected by the low-temperature fire. The soil 206Pb/207Pb isotopic ratios remained stable but decreased in the ash (206Pb/207Pb = 1.174 and 1.166, respectively).According to the isotopic composition, Pb in the topsoils was of mixed origin (natural and anthropogenic). We assumed that lithogenic Pb (206Pb/207Pb > 1.19) occurred in stable mineral forms while anthropogenic Pb mainly originated from leaded gasoline (206Pb/207Pb < 1.16). Anthropogenic Pb was more easily mobilized due to the volatile nature of the emitted compounds of vehicular Pb (oxyhalogenides). Hence, during the high-temperature burning of the soil, Pb with a lower isotopic signature would be preferentially released from the soil Pb pool. Consequently, resulting soils and ash exhibited an increase in 206Pb/207Pb isotopic ratios. However, ash and soils affected by low temperatures, which did not volatilize anthropogenic Pb, retained their isotopic signatures.This work suggests that it may be possible to determine the temperature of a forest fire from the Pb isotopic signatures of the burned materials.

Deciphering multiple ore-forming processes of the Shuangqishan orogenic gold deposit, Southeast China by in situ analysis of pyrite

Gold deposits are characteristically formed via multiple mineralization and remobilization events. Inferences on the complex formation history of such deposits from ore textures can be ambiguous in the lack of chemical and isotopic evidence as exemplified by the Shuangqishan orogenic gold deposit in Southeast China. We, therefore, conducted LA-ICP-MS spot analysis coupled with LA-MC-ICP-MS sulfur and lead isotope analysis on texturally complex gold-bearing pyrite from the Shuangqishan deposit. Gold distribution in different syn- to late-ore pyrite generations indicate initial evenly deposition of nano- to micro-inclusions of Au-Ag-Pb-Bi tellurides within pyrite grains and subsequent Au remobilization following brittle deformation and fluid-mediated coupled dissolution-reprecipitation (CDR) reactions. Gold dissolved from the pyrite during the reworking event became re-concentrated and re-precipitated as visible gold either as inclusions in pyrite or larger free gold grains within microfractures of pyrite. The distribution of Bi-Te-Pb-Ag assemblage is comparable to that of Au, illustrating that these trace metals became redistributed in a similar fashion. Early, undeformed pyrite has the least radiogenic Pb isotopic compositions. Late, porous and inclusion-rich pyrite, brecciated pyrite, and recrystallized Te-Bi minerals have variable but in general more radiogenic Pb isotope ratios (higher 206Pb/204Pb and 207Pb/204Pb ratios), which are attributed to modification and precipitation from a more evolved crustal fluid during the re-precipitation of native gold. The Pb isotopic signature of the younger pyrite generations was likely inherited from Pb released during modification of earlier proto-pyrite and a second, crustal lead source that was involved in the hydrothermal system during later remobilization. The δ34S values for the early proto-pyrite and the reworked pyrite generations within the individual vein stage are broadly similar. The variations in sulfur isotope compositions reflect the change in physicochemical conditions (temperature and oxygen fugacity) during proto-ore formation. Our study highlights the importance of metal recycling from early proto-auriferous pyrite during later reworking and gold remobilization, which led to visible gold and high-grade ore shoot formation. The extensive variations of trace element concentrations and S-Pb isotope compositions of proto and reworked pyrites record the complicated Au mobilization and deposition processes and help to understand how gold ores evolved.

Applications of Pb isotopes in granite K-feldspar and Pb evolution in the Yilgarn Craton

The isotopic composition of Pb in a mineral or rock at the moment it formed – often referred to as common Pb – provides an important tool to track geological processes through time and space. There is a wide range of applications of common Pb isotopes including understanding magma sources, melt production, fractionation, contamination, and crystallization in the crust. Pb but not U is incorporated into the structure of K-feldspar during crystal growth, which, together with its widespread occurrence as a framework mineral, makes it an excellent common Pb tracer. Consequently, common Pb isotopes in granite K-feldspar crystals provide a potential signature of source composition and a link to crustal growth processes in the mid to lower crust. Hence, combining common Pb isotopes with Sm-Nd (or Lu-Hf) isotopic signatures from the same dated rocks allows assessment of the degree of isotopic communication from deep fractionation systems to those higher in the crustal column. In this contribution, we analyze common Pb isotopic signatures in K-feldspar from a granite sample transect through the Archean Yilgarn Craton in Western Australia. This transect crosses the major crustal-scale Ida Fault that is apparent on Nd and Hf isotopic maps and interpreted as a fundamental lithospheric boundary across which magma sources change. Our results yield a difference in median values of the Pb isotope derivative parameters µ (238U/204Pb) and ω (232Th/204Pb) across the Ida Fault, with higher µ and ω associated with more evolved Nd and Hf isotopic signatures on the western side of the fault. Pb evolution in the Yilgarn Craton is distinct from the widely applied Stacey & Kramers (1975) model. New Yilgarn-specific Pb evolution models are developed with implication for common Pb correction. A correlation in the spatial trends of granite K-feldspar common Pb signatures with those of upper crustal Pb ores and also the Sm-Nd and Lu-Hf systems reveals geochemical communication all the way through the crustal column, implying a common source for the entire lithospheric section on each side of the Ida Fault. Pb isotopes in granite K-feldspar are not an independent geochronometer but may yield important source context on major phase silicate growth that helps refine U-Pb geochronology interpretations (e.g., distinguishing magmatic versus metamorphic zircon growth).

Deciphering anomalous Ag enrichment recorded by galena in Dayingezhuang Au(-Ag) deposit, Jiaodong Peninsula, Eastern China

Texture, geochemistry, and in-situ Pb isotope of galena were investigated to probe the origin of anomalous Ag enrichment in the DayingezhuangAu(-Ag) deposit. Silver enrichment postdates the main Au mineralization and occurs in the south of the Dayingezhuang deposit. It is primarily associated with galena and the exsolution of Ag-rich sulfosalts (e.g., matildite) in distal vein-ores related to steeply dipping brittle fractures. Silver-rich galena is characterized by the least radiogenic Pb isotope signature (206Pb/204Pb 17.195–17.258 and 208Pb/204Pb 37.706–37.793), possibly indicating a metasomatized lithospheric mantle or modified lower crustal source for Pb and Ag. Both of these mafic and ultramafic source regions have been previously suggested as Au reservoirs for other Jiaodong Au deposits, implying that the metal reservoir has only a weak control on the uneven Ag-enrichment. Since the Ag-enrichment areas are located in the footwalls of both the Dayingezhuang and Zhaoping faults, the enrichment was most likely dominated by local rotational stress during coeval movements of the two faults in a NE–SW compression and NW−SE extension regime. This work highlights the shallow-crust structural deformation responsible for controlling the flow of late ore-forming fluid resulting in local anomalous metal enrichment.

Constraints on the behaviour and content of volatiles in Galápagos magmas from melt inclusions and nominally anhydrous minerals

Despite their relatively low concentration in most oceanic basalts, volatile species (e.g. H2O, CO2 and S) have a disproportionately large influence on a wide range of mantle and magmatic processes. Yet, constraining the concentration of H2O (and other volatiles) in basaltic magmas is not straightforward as submarine glass analyses are influenced by assimilation of hydrothermal brines, and the melt inclusion record is often reset by post-entrapment processes. Nevertheless, in this study we show that it is possible to reconstruct a detailed history of the volatile content of basaltic magmas through integration of multiple discreet volatile records and careful consideration of secondary processes. We present new analyses of volatiles in olivine-hosted melt inclusions, melt embayments and nominally anhydrous minerals (NAMS, clinopyroxene and orthopyroxene) found in basalts erupted on Floreana Island in the south-eastern Galápagos Archipelago. Our results indicate that the Floreana magmas, which are characterised by the most radiogenic Pb and Sr isotope signatures in the Galápagos Archipelago, contain H2O concentrations between 0.4 and 0.8 wt% (at a melt Mg# of 0.65, where Mg# = Mg/(Mg + Fe) molar). These are marginally greater than the H2O contents of magmas beneath Fernandina in the western Galápagos Archipelago (cf. 0.2–0.7 wt% H2O at Mg# = 0.65). However, while the volatile content of magmas from the western archipelago follow trends defined by concurrent mixing and crystallisation, NAMs from Floreana reveal the presence of rare, volatile-rich magmas (∼2 wt% H2O) that form as a consequence of reactive porous flow in mush-dominated magmatic systems beneath the south-eastern Galápagos. Furthermore, the Floreana magmas have similar H2O/light Rare Earth Element ratios to basalts from the western Galápagos but contain F/Nd and Cl/K ratios that are ∼ 2–3 times greater, indicating that the mantle source of the Floreana lavas might represent an important halogen reservoir in the Galápagos mantle plume.

Evolution of mafic lavas in Central Anatolia: Mantle source domains

Abstract We present new Sr-Nd-Pb-Hf isotopic data on mafic lavas from the Sivas, Develidağ, Erciyes, and Erkilet volcanic complexes in central Turkey and Tendürek in eastern Turkey to evaluate the mantle sources for volcanism in the context of the geodynamic evolution of the Anatolian microplate. Early Miocene through Quaternary volcanism in Western Anatolia and latest Miocene through Quaternary activity in Central Anatolia were dominated by contributions from two distinct source regions: heterogeneous metasomatized or subduction-modified lithosphere, and roughly homogeneous sublithospheric ambient upper mantle; we model the source contributions through mixing between three end members. The sublithospheric mantle source plots close to the Northern Hemisphere reference line (NHRL) with radiogenic 206Pb/204Pb of ∼19.15, while the other contributions plot substantially above the NHRL in Pb isotope space. The lithospheric source is heterogeneous, resulting from variable pollution by subduction-related processes likely including direct incorporation of sediment and/or mélange; its range in radiogenic isotopes is defined by regional oceanic sediment and ultrapotassic melts of the subcontinental lithospheric mantle. The geochemical impact of this contribution is disproportionately large, given that subduction-modified lithosphere and/or ocean sediment dominates the Pb isotope signatures of mafic Anatolian lavas. Subduction of the Aegean or Tethyan seafloor, associated with marked crustal shortening, took place throughout the region until ca. 16–17 Ma, after which time broad delamination of the thickened lower crust and/or the Tethyan slab beneath Central Anatolia allowed for sediment and/or mélange and slab-derived fluids to be released into the overlying evolving modified mantle. Aggregation of melts derived from both mantle and lithospheric domains was made possible by upwelling of warm asthenospheric material moving around and through the complexly torn younger Aegean-Cyprean slab that dips steeply to the north beneath southern Anatolia.