High-precision Pb Isotope Data Research Articles

High-precision Pb isotopes of drinking water lead pipes: Implications for human exposure to industrial Pb in the United States

Millions of lead (Pb) pipes are still used in the drinking water distribution systems in many regions in the world. Human exposure to Pb from contaminated drinking water continues to be of concern in the United States (U.S.), as illustrated by the widely publicized “Flint Water Crisis” in 2015. The Pb isotopic composition of Pb-pipes potentially can be useful to identify human exposure to Pb from lead service lines (LSLs). In addition, as the LSLs were likely manufactured from similar industrial Pb sources as other Pb objects and materials in the USA, the Pb-pipes isotope data can provide information about the overall isotopic composition of the U.S. industrial Pb.In this work we present high-precision Pb isotope data from Pb-pipes excavated from different U.S. municipalities. The Pb-pipes show an extremely wide range of Pb isotopic compositions, with 206Pb/204Pb ranging from 17.004 to 22.010, 207Pb/204Pb from 15.460 to 15.921, and 208Pb/204Pb from 36.687 to 41.120. The wide isotope range is observed even in a single town, suggesting that no regional Pb isotope patterns can be expected within the continental USA. However, the high-precision MC-ICP-MS Pb data form a clear linear trend that, depending on the context, can be used to identify human Pb exposure. Furthermore, as the linear trend is a result of utilization of Pb ores from different domestic and international sources and secondary recycling of metallic Pb, it is likely representative of the overall isotopic composition of the U.S. industrial Pb pool. Therefore, the identified trend is the most accurate isotope representation of the U.S. anthropogenic Pb at present and can be used as first-order evaluation to determine if a person with elevated blood Pb levels was exposed to U.S. industrial Pb sources.

The significance of galena Pb model ages and the formation of large Pb-Zn sedimentary deposits

In an attempt to clarify the significance of Pb model ages in Pb-Zn sedimentary deposits, we report high-precision Pb isotopic compositions for 64 galenas and 52 K-feldspars, the former from ores and the latter separated from granites. All samples are from Spain and the French Pyrenees. Lead from galena ores is of unequivocal continental origin. With few exceptions, Pb model ages systematically exceed emplacement ages by up to 400 Ma, a gap which is well outside the uncertainties of ~ 30 Ma assigned to the model. The histogram of the new high-precision Pb isotope data shows prominent peaks of galena Pb model ages at 94 ± 38 Ma and 392 ± 39 Ma. When the data are consolidated with literature data and examined in 3-dimensional Pb isotope space, cluster analysis identifies five groups. The model ages of the peaks occur, in order of decreasing peak intensity, at 395 ± 40 (Middle Devonian), 90 ± 34 Ma (Middle Cretaceous), and 613 ± 42 Ma (Neoproterozoic), with two minor peaks at 185 + 26 Ma (Jurassic) and 313 ± 41 (Upper Carboniferous). To a large extent, the model ages centered around these peaks correspond to distinct localities. The ages of the peaks do not coincide with any of the Betic, Variscan, or Pan-African tectonic events, which are the main tectonic episodes that shaped Iberian geology, but instead match well-known global oceanic anoxic events. It is argued that surges of metals weathered from continental surfaces scorched during anoxic events accumulated and combined in anoxic water masses with unoxidized marine sulfide released by submarine hydrothermal activity to precipitate the primary Pb-Zn stock. Frozen Pb isotope compositions require that galenas from black shales are the source of the final ores. The sulfides were later remobilized by large-scale convective circulation of basinal and hydrothermal fluids. The peaks of K-feldspar Pb model ages are distinct from those of galenas and do not correlate with magmatic emplacement ages. It is suggested that they instead reflect local circulation in Paleozoic sediments surrounding individual plutons. While Pb isotopes can be used as a regional provenance tool, such an approach requires that the data are considered in a fully 3-dimensional space.

Geochemical Evolution of Arc and Slab Following Subduction Initiation: a Record from the Bonin Islands, Japan

AbstractVolcanism following the initiation of subduction is vital to our understanding of this specific magma-generation environment. This setting is represented by the first development of the Izu–Bonin–Mariana arc system as subduction commenced along the Western Pacific margin in the Eocene. A new collection of volcanic rocks recovered from the islands and exposed crustal sections of the Bonin Ridge spans the first 10 Myr of arc evolution. An elemental and radiogenic isotope dataset from this material is presented in conjuction with new 40Ar/39Ar ages and a stratigraphic framework developed by a detailed mapping campaign through the volcanic sections of the Bonin Islands. The dating results reveal that both the locus and type of magmatism systematically changed with time in response to the progressive sinking of the slab until the establishment of steady-state subduction at around 7–8 Ma. Following initial mid-ocean ridge basalt (MORB)-like spreading-related basalt magmatism, volcanic centres migrated away from the trench and changed from high-Si boninite to low-Si boninite or high-Mg andesite, then finally tholeiitic or calcalkaline arc magma. Subducting pelagic sediment combined with Pacific-type igneous ocean crust dominates the slab input to the shallow source of high-Si boninites at 49 Ma, but high-precision Pb isotope data show that this sediment varies in composition along the subducting plate. At around 45 Ma, volcanism switched to low-Si boninite and the pelagic sediment signature was almost entirely replaced by volcanic or volcaniclastic material originating from a HIMU ocean island source. These low-Si boninites are isotopically consistent with a slab component comprising variable proportions of HIMU volcaniclastic rocks and Pacific MORB. In turn, this signature was replaced by a Pacific MORB-dominated flux in the post 45 Ma tholeiite and calcalkaline volcanic rocks. Notably, each change in slab-derived flux coincided with a change in the magma type. Fluctuations in the slab-derived geochemical signature were superimposed on a change in the mantle wedge source from highly depleted harzburgite to a depleted MORB-type mantle-type source. In turn, this may correspond to the increasing depth of the leading edge of the slab through this 5 Myr period.

Lead isotopes as tracers of crude oil migration within deep crustal fluid systems

Although Pb, U, and Th may be fractionated between crude oil and formation waters, Pb isotopes are not. This unique property makes Pb isotopes a particularly useful marker of hydrocarbon generation and migration. Here we show that Pb isotopes offer a new vision of long-range (secondary) oil migration relevant to the formation of oil fields. North Sea oils are largely generated from Jurassic black shales, yet their Pb isotopes are mixtures of Cenozoic to Proterozoic end-members. The same observation is made for crude oils from the Paris Basin, the Barents Sea, Libya, Kuwait, Kazakhstan, and Australia. Bulk Pb in crude oil therefore, for the most part, is foreign to its source rock(s). Our high-precision Pb isotope data on 195 crude oils worldwide, the first such data set in the published literature, and 17 Northern European black shales indicate that deep-seated Pb components originating beneath the source rocks are ubiquitous in crude oil. This implies that oil fields are embedded in basinal convective systems of hydrous fluids heated from below. Plumes of hot fluids rise from the lower thermal boundary layer, which Pb isotopes require douse the basement, into the core of the porous-flow convective cell where they dissolve the newly formed hydrocarbons sequestered in the source rocks. The fluids finally unload unmixed formation waters and crude oil at the base of the upper (conductive) boundary layer where they can be trapped in favorable sites. Based on these new insights we argue that Pb isotopes in crude oil constitute a good tracer of oil migration.

Pb and Hf isotope evidence for mantle enrichment processes and melt interactions in the lower crust and lithospheric mantle in Miocene orogenic volcanic rocks from Monte Arcuentu (Sardinia, Italy)

Miocene (ca. 18 Ma) subduction-related basalts and basaltic andesites from Monte Arcuentu, southern Sardinia, Italy, show a remarkable correlation between 87Sr/86Sr (from ~0.705 to ~0.711) over a small range of SiO2 (~51–58 wt%) that contrasts with most other orogenic volcanic suites worldwide. New high-precision Pb and Hf isotope data help to constrain the petrogenesis of these rocks. The most primitive Monte Arcuentu rocks (MgO >8.5 wt%) were sourced from a mantle wedge metasomatized by melts derived from terrigenous sedi­ment, likely derived from Archean terranes of northern Africa. This gave rise to magmas with high 87Sr/86Sr (0.705–0.709) and 207Pb/204Pb (15.65–15.67) with moderate eHf (–1 to +8) and eNd (–6 to +1), but it does not account for the full range of compositions observed. More evolved rocks (MgO <8.5 wt%) have higher 87Sr/86Sr (up to 0.711) and 207Pb/204Pb (up to 15.68), with eHf and eNd as low as –8 and –9, respectively. Mixing calculations suggest that evolved rocks with low Rb/Ba and low 206Pb/204Pb interacted with lower crust similar compositionally to that exposed today in Calabria, Italy, which was formerly in crustal continuity with Sardinia. High Rb/Ba and high 206Pb/204Pb magmas interacted with lithospheric mantle similar to that sampled by Italian lamproites. Partial melting of lower crustal and upper mantle lithologies was facilitated by the rapid extension, and subsequent passive mantle upwelling, that occurred as Sardinia drifted away from the European plate during the Oligo-Miocene (ca. 32–15 Ma). Fractional crystallization under these PT conditions involved ­olivine + clinopyroxene with little or no plagioclase, such that differentiation proceeded without significant increase in SiO2. The Monte Arcuentu rocks provide insights into assimilation process in the lower crust and lithospheric mantle that may be obscured by upper crustal assimilation–fractional crystallization (AFC) processes in other orogenic suites.

Molybdenum mobility and isotopic fractionation during subduction at the Mariana arc

The fate of crustal material recycled into the convecting mantle by plate tectonics is important for understanding the chemical and physical evolution of the planet. Marked isotopic variability of Mo at the Earth's surface offers the promise of providing distinctive signatures of such recycled material. However, characterisation of the behaviour of Mo during subduction is needed to assess the potential of Mo isotope ratios as tracers for global geochemical cycles. Here we present Mo isotope data for input and output components of the archetypical Mariana arc: Mariana arc lavas, sediments from ODP Sites 800, 801 and 802 near the Mariana trench and the altered mafic, oceanic crust (AOC), from ODP Site 801, together with samples of the deeper oceanic crust from ODP Site 1256. We also report new high precision Pb isotope data for the Mariana arc lavas and a dataset of Pb isotope ratios from sediments from ODP Sites 800, 801 and 802. The Mariana arc lavas are enriched in Mo compared to elements of similar incompatibility during upper mantle melting, and have distinct, isotopically heavy Mo (high 98Mo/95Mo) relative to the upper mantle, by up to 0.3 parts per thousand. In contrast, the various subducting sediment lithologies dominantly host isotopically light Mo. Coupled Pb and Mo enrichment in the Mariana arc lavas suggests a common source for these elements and we further use Pb isotopes to identify the origin of the isotopically heavy Mo. We infer that an aqueous fluid component with elevated [Mo], [Pb], high 98Mo/95Mo and unradiogenic Pb is derived from the subducting, mafic oceanic crust. Although the top few hundred metres of the subducting, mafic crust have a high 98Mo/95Mo, as a result of seawater alteration, tightly defined Pb isotope arrays of the Mariana arc lavas extrapolate to a fluid component akin to fresh Pacific mid-ocean ridge basalts. This argues against a flux dominantly derived from the highly altered, uppermost mafic crust or indeed from an Indian-like mantle wedge. Thus we infer that the Pb and Mo budgets of the fluid component are dominated by contributions from the deeper, less altered (cooler) portion of the subducting Pacific crust. The high 98Mo/95Mo of this flux is likely caused by isotopic fractionation during dehydration and fluid flow in the slab. As a result, the residual mafic crust becomes isotopically lighter than the upper mantle from which it was derived. Our results suggest that the continental crust produced by arc magmatism should have an isotopically heavy Mo composition compared to the mantle, whilst a contribution of deep recycled oceanic crust to the sources of some ocean island basalts might be evident from an isotopically light Mo signature.

Deciphering petrogenic processes using Pb isotope ratios from time-series samples at Bezymianny and Klyuchevskoy volcanoes, Central Kamchatka Depression

The Klyuchevskoy group of volcanoes in the Kamchatka arc erupts compositionally diverse magmas (high-Mg basalts to dacites) over small spatial scales. New high-precision Pb isotope data from modern juvenile (1956–present) erupted products and hosted enclaves and xenoliths from Bezymianny volcano reveal that Bezymianny and Klyuchevskoy volcanoes, separated by only 9 km, undergo varying degrees of crustal processing through independent crustal columns. Lead isotope compositions of Klyuchevskoy basalts–basaltic andesites are more radiogenic than Bezymianny andesites (208Pb/204Pb = 37.850–37.903, 207Pb/204Pb = 15.468–15.480, and 206Pb/204Pb = 18.249–18.278 at Bezymianny; 208Pb/204Pb = 37.907–37.949, 207Pb/204Pb = 15.478–15.487, and 206Pb/204Pb = 18.289–18.305 at Klyuchevskoy). A mid-crustal xenolith with a crystallization pressure of 5.2 ± 0.6 kbars inferred from two-pyroxene geobarometry and basaltic andesite enclaves from Bezymianny record less radiogenic Pb isotope compositions than their host magmas. Hence, assimilation of such lithologies in the middle or lower crust can explain the Pb isotope data in Bezymianny andesites, although a component of magma mixing with less radiogenic mafic recharge magmas and possible mantle heterogeneity cannot be excluded. Lead isotope compositions for the Klyuchevskoy Group are less radiogenic than other arc segments (Karymsky—Eastern Volcanic Zone; Shiveluch—Northern Central Kamchatka Depression), which indicate increased lower-crustal assimilation beneath the Klyuchevskoy Group. Decadal timescale Pb isotope variations at Klyuchevskoy demonstrate rapid changes in the magnitude of assimilation at a volcanic center. Lead isotope data coupled with trace element data reflect the influence of crustal processes on magma compositions even in thin mafic volcanic arcs.

The Dupal isotopic anomaly in the southern Paleo-Asian Ocean: Nd–Pb isotope evidence from ophiolites in Northwest China

It has been suggested that the Dupal isotopic anomaly in the mantle can be traced in the Paleozoic ophiolites from the Neo- and Paleo-Tethyan Ocean (275–350Ma). The Karamaili ophiolite (KO) and Dalabute ophiolite (DO) in the eastern and western corners, respectively, of the Junggar basin in NW China represent remnants of the relatively older (>350Ma) Paleo-Asian Ocean (PAO) crust. Thus, these ophiolites can provide additional constraints on the long-term composition and evolution of the Paleozoic suboceanic mantle. We present new major-trace element and Sr, Nd and high-precision Pb isotope data for the basalts, gabbros and a plagioclase separate from the KO and DO. Our results indicate that the PAO crust indeed has a Dupal-like isotopic signature. In detail, all samples have relatively low εNd(t) and high 208Pb/204Pb(t) for given 206Pb/204Pb(t) ratios (i.e., positive Δ8/4 values), similar to the Dupal isotopic characteristics of Indian Ocean mid-ocean ridge basalts (MORB). The trace element signature of DO mafic rocks is similar to that of normal- and enriched-MORB whereas that of the KO is transitional between MORB and arc basalt. Therefore, the DO mantle domain reflects the PAO asthenosphere and the KO domain additionally shows the influence of the subduction process. Geochemical modeling using Th/Nd as well as Nd and Pb isotopic ratios indicates that up to 2% subduction component had been added to a depleted Indian MORB-type mantle to produce the bulk of KO rocks. The subduction component in the KO rocks consisted of variable proportions of ≤1% partial melt of unradiogenic sediment similar to modern Izu–Bonin trench sediment and hydrous fluid dehydrated from the subducted altered oceanic crust. The Devonian asthenospheric mantle beneath the southern PAO is isotopically heterogeneous, but lends support to the idea that the Dupal isotopic anomaly existed prior to the opening of the Indian Ocean. Finally, plate tectonic reconstruction indicates that the anomaly was present in the Neo- and Paleo-Tethyan oceans in the southern hemisphere and in the southern part of PAO in the northern hemisphere during the late Paleozoic.

Subduction zone dynamics in the SW Pacific plate boundary region constrained from high-precision Pb isotope data

This study presents high-precision Pb isotope data obtained by MC-ICP-MS for lavas from the Solomon island arc that covers ca. 1000 km of the SW Pacific plate boundary. Following a reversal of subduction polarity, the presence of the old subducted Pacific oceanic crust, and the presently subducting Indian–Australian plate beneath the entire island arc is confirmed by geophysical and geochemical evidence. New high-precision Pb isotope data now permit to distinguish more clearly between Indian and Pacific-type subduction components in this complex plate tectonic constellation. The values range from 206Pb/ 204Pb = 18.345 to 18.845, 207Pb/ 204Pb = 15.498 to 15.545, and 208Pb/ 204Pb = 38.120 to 38.372, indicating the absence of pelagic sediments in the sub-arc mantle. These data reveal a predominance of subduction components derived from ancient subduction of the Pacific plate. In contrast, lavas with Indian-type Pb isotope signatures are confined to the central New Georgia Group of the Solomon Islands, where the young Woodlark Ridge spreading centre is currently subducting. All other Solomon arc segments with a lower geothermal gradient have apparently not yet been overprinted by younger subduction components over the past 6 Myrs. Moreover, trace element and Pb isotope data for Woodlark Ridge basalts show that subduction components from the fossil Pacific slab have locally modified the source of Woodlark Basin lavas. Altogether, our study highlights the potential of high-resolution Pb isotope measurements to distinguish between Indian and Pacific-type subduction components along the SW Pacific plate boundary.

Evolution of shield-building and rejuvenescent volcanism of Mauritius

We report chemical and isotopic analyses of 68 samples and 40Ar/ 39Ar ages of 47 samples from Mauritius undertaken to understand the compositional evolution of the volcano and its causes through time. New 40Ar/ 39Ar ages show that construction of the Mauritius shield was well underway by 8.9 Ma, 1.1 m.y. earlier than previously thought and that the hiatus between the Intermediate and Younger Series was shorter than previously thought, as eruption of the rejuvenescent Intermediate Series continued through at least 1.66 Ma and Younger Series volcanism began by at least 1.0 Ma. Eruption frequency over the last 50 ka has been rather typical of Younger Series volcanism over the last 400 ka and future eruptions are possible. Although outcrops of the Intermediate Series lavas are confined to the Southwest, Intermediate Series are present beneath Younger Series flows in drill cores throughout the island. We estimate the total volume of rejuvenescent lavas at ~ 35 km 3 or about 0.05% of the volume of the volcano, similar to rejuvenescent volume fractions on Hawaiian volcanoes. As earlier studies found, Older Series lavas, which on average are slightly normatively silica-saturated, are somewhat more incompatible-element enriched than are the Intermediate and Younger Series, which are both slightly silica-undersaturated on average. Mean Sr and Nd isotope ratios of the Intermediate and Younger Series are nearly identical, but mean Pb isotope ratios, La/Sm, Nb/Y, and Nb/Zr of the Intermediate Series are higher than in the Younger Series. New high precision Pb isotope data, which shows considerably less scatter than previously published data, plot between the Older Series and basalts of the Central Indian Ridge, allowing the possibility that the source of the rejuvenescent lavas is a mixture of this plume and depleted mantle. We propose two possible explanations for the composition of rejuvenescent lavas. The first is that plume-derived melts reacted with deep lithosphere to form pyroxenite veins during the early shield-building stage. Later, these veins melted as a consequence of conductive heating of the lithosphere by the plume to produce the rejuvenescent lavas. Alternatively, rejuvenescent lavas may be derived from a sheath of thermally entrained mantle that surrounds the plume and is a mixture of plume material and depleted upper mantle.

Compositional Characteristics and Spatial Distribution of Enriched Icelandic Mantle Components

We present compositional data on a suite of 18 primitive neovolcanic alkali basalts from three flank-zone regions in Iceland (Vestmannaeyjar in the south, Snaefell in the east, and Snaefellsnes in the west) that are peripheral to the main rift zones that are dominated by tholeiitic basalts. This study integrates He isotope data with radiogenic isotope data (Sr–Nd–Pb–Hf), stable isotope data (δ18O), and trace element data to characterize the compositional features of the trace element enriched components of the Icelandic mantle. We also present high-precision Pb isotope data on an additional 57 lava samples from the flank zones (including Oraefajokull in the SE) and the Northern and Eastern rift zones. Most Icelandic lavas have negative Δ207Pb (–4 to –1), with higher values (–1 to +4) found only in samples from Oraefajokull, Snaefell, and parts of the Reykjanes Peninsula. At Snaefell, this EM1-type component is characterized by a low δ18Oolivine signature (+4·1‰ to +4·6‰), moderate 206Pb/204Pb values (18·4–18·6) and mid-ocean ridge basalt (MORB)-like 3He/4He (6·9–7·5 R/RA). Samples from Vestmannaeyjar and Snaefellsnes have mantle-like δ18Oolivine (+4·9‰ to +5·0‰), and radiogenic 206Pb/204Pb values (18·9–19·3) that fall on the Northern Hemisphere Reference Line for 208Pb/204Pb (Δ208Pb –5 to +5). Compared with the Vestmannaeyjar lavas, Snaefellsnes lavas have higher La/YbN (5–11 vs 3–5), lower eNd (5·5–6·5 vs 6·8–7·6) and lower 3He/4He (6·3–8·6 R/RA vs 11·4–13·5 R/RA). Therefore, the most trace element enriched components in the Icelandic mantle are not the carriers of the high 3He/4He values (>15 R/RA) found in some lavas on Iceland and the adjacent ridges, and instead are consistent with degassed, recycled components. Even after excluding the EM1-type high Δ207Pb samples, high-precision Pb isotope data produce a kinked array on a 206Pb/204Pb vs 208Pb/204Pb plot, which is not consistent with simple binary mixing between two end-members. This requires significant lateral heterogeneity within the Icelandic mantle and the presence of more than just two compositionally distinct local mixing end-member components. Samples from each of the main axial rift zones define different trends. Despite the tectonic continuity between the Northern Volcanic Zone and the Eastern Volcanic Zone, lavas from these two rift zones define separate sub-parallel linear arrays. Lavas from the adjacent Western Volcanic Zone and the Eastern Volcanic Zone define oblique linear arrays that converge on a common local end-member that is not involved in the magmatism of the Northern Volcanic Zone. Therefore, there is a distinct NE–SW compositional heterogeneity within the Icelandic mantle.

A 5 million year record of compositional variations in mantle sources to magmatism on Santiago, southern Cape Verde archipelago

High-precision Pb isotope data and Sr–Nd–Hf isotope data are presented together with major and trace element data for samples spanning the 4.6 Ma history of volcanism at Santiago, in the southern Cape Verde islands. Pb isotope data confirm the positive Δ8/4 signature of the southern islands indicating that the north–south compositional heterogeneity in the Cape Verde archipelago has persisted for at least 4.6 Ma. The Santiago volcanics show distinct compositional differences between the old, intermediate and young volcanics, and suggest greater involvement of an enriched mantle (EM1)-like source over time. Isotopic variations in the Santiago volcanics indicate convergence towards a homogeneous EM1-like end-member and distinct temporal variations in the FOZO-like end-member. Santiago and Santo Antao (a northern island, Holm et al. 2006), show a simultaneous decrease in 208Pb/204Pb of the high 206Pb/204Pb FOZO-like source with time. Such systematic archipelago-wide variations in the FOZO-like component suggest that this component is more likely to be present as a coherent package of recycled ocean crust rather than as multiple small heterogeneities dispersed in the upwelling mantle. The temporal variations in 208Pb/204Pb reflect minor lateral variations in Th/U of this recycled ocean crust package entering the melting zone beneath the islands. The location of the EM1-like component is more equivocal. A shallow lithospheric location is possible, but this would require a coincidence between spatial compositional variations in the lithosphere (EM1 is spatially restricted to the southern islands) and flow lines in the upwelling mantle revealed by seismic anisotropy. Therefore, we favour a deeper asthenospheric mantle source for the EM1-like source.

High-precision Pb isotopic measurements of teeth and environmental samples from Sofia (Bulgaria): insights for regional lead sources and possible pathways to the human body

High-precision Pb isotopic measurements on teeth and possible sources in a given area can provide important insights for the lead (Pb) sources and pathways in the human body. Pb isotopic analyses on soils from the area of Sofia, Bulgaria show that Pb is contributed by three end-members represented by two natural sources and leaded gasoline. Sequential leaching experiments reveal that the alumosilicate fraction of the soils is mainly controlled by natural Pb derived from two mountain massifs bordering the city. Around 1/3 to a half of the Pb in the soil leachates, however, can be explained by contamination from leaded gasoline. Contemporary teeth from Sofia residents show very similar Pb isotopic compositions to the soil leachates, also indicating that around 1/3 to a half of the Pb can be explained by derivation from leaded gasoline. The remarkable isotopic similarities between the teeth and the most labile fractions of the local soils suggest that the lead can be derived from the latter. Pb incorporation in the human body via soil-plant–human or soil–plant–animal–human chains is unlikely due to the fact that no significant farming occurs in the city area. The isotopic compositions of the local soil labile fractions can be used as approximation of the bioaccessible lead for humans. Considering all possible scenarios it appears that soil and/or soil-born dust inhalation and/or ingestion is the most probable pathway for incorporation of local soil lead in the local population. The high-precision Pb isotope data presented in this work indicate that apparently the local soil is what plays major role in the human Pb exposure.

Pb isotope variations among Bandelier Tuff feldspars: No evidence for a long-lived silicic magma chamber

Research Article| June 01, 2003 Pb isotope variations among Bandelier Tuff feldspars: No evidence for a long-lived silicic magma chamber J.A. Wolff; J.A. Wolff 1 Department of Geology, Washington State University, Pullman, Washington 99164, USA Search for other works by this author on: GSW Google Scholar F.C. Ramos F.C. Ramos 1 Department of Geology, Washington State University, Pullman, Washington 99164, USA Search for other works by this author on: GSW Google Scholar Geology (2003) 31 (6): 533–536. https://doi.org/10.1130/0091-7613(2003)031<0533:PIVABT>2.0.CO;2 Article history received: 27 Nov 2002 rev-recd: 21 Feb 2003 accepted: 24 Feb 2003 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation J.A. Wolff, F.C. Ramos; Pb isotope variations among Bandelier Tuff feldspars: No evidence for a long-lived silicic magma chamber. Geology 2003;; 31 (6): 533–536. doi: https://doi.org/10.1130/0091-7613(2003)031<0533:PIVABT>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We report, for the first time, high-precision Pb isotope data from a high-silica rhyolite. Prior work on Sr isotopes in the 1.6 Ma Otowi Member of the Bandelier Tuff (Valles caldera, New Mexico) established that large 87Sr/86Sr variations exist among Otowi glasses and sanidine phenocrysts. While the glasses display unequivocal evidence for wall-rock contamination of the Otowi magma following sanidine growth, a positive correlation between 87Sr/86Sri and 87Rb/86Sr among the feldspars could be interpreted as either a mixing line or an in situ magmatic isochron dating a differentiation event ∼270 k.y. prior to eruption. The 206Pb/204Pb and 87Sr/86Sr ranges for Otowi sanidines are 17.790 ± 0.002 to 17.831 ± 0.002 and 0.7074–0.7052, respectively. This Pb isotope range cannot be produced by radiogenic ingrowth at the U/Pb ratios of the host magma on any geologically reasonable time scale, and hence is unequivocal evidence for open-system behavior of the Otowi magma prior to and/or concurrent with feldspar growth. Open-system behavior is predicted to control Sr isotope variations due to much higher concentrations of Sr, relative to Pb, in the country rock than in the magma. These observations therefore undermine any age significance of the Rb-Sr isotope variations. In the absence of supporting data, Rb-Sr relations alone do not impart any information about residence times of high-silica rhyolite magmas with subchondritic concentrations of Sr. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geographic control on Pb isotope distribution and sources in Indian Ocean Fe-Mn deposits

High-precision Pb isotope data have been obtained on Indian Ocean Fe-Mn deposits with a large geographic coverage. These data reveal a strong geographic control on the distribution of Pb isotopes as well as sources of Pb within this basin. The provinciality of Pb isotopes at the scale of the whole Indian Ocean, as well as that of individual basins, broadly matches the pattern of deepwater flow.The existence of several sources of Pb is best illustrated by the presence of three well-defined Pb isotopic arrays, each of which is confined to clear-cut geographic domains. These arrays imply a dominance of binary mixing of Pb sources within each of these domains. The domains consist of the North-Indian (N-Indian; north of 20°S), Southwest-Indian (SW-Indian; 20°S to 50°S, west of 45°E), South-Indian (S-Indian; 20°S to 50°S, east of 45°E) and Antarctic-Indian (A-Indian; south of 50°S), and clearly exhibit a strong control by latitude. The S-Indian domain and Mozambique Channel samples form a cluster, suggesting that there are more than just two sources contributing in these regions.We show that the N-Indian is dominated by sources of Pb derived from the High Himalayas and the Trans-Himalayan Complex, and most likely inherited from interaction at the water interface with Bengal and Indus Fan sediments. The SW-Indian and A-Indian domains share a common unradiogenic component, represented by circumpolar waters derived from the Pacific Ocean and flowing through the Drake Passage into the Atlantic and Indian Oceans. However, the radiogenic sources of Pb in these two domains are clearly distinct. In the SW-Indian, the radiogenic Pb signal reflects the tongue of North Atlantic Deep Water flowing around the tip of South Africa, while in the A-Indian, the source of radiogenic Pb is less certain, but quite probably originates in the Weddell Sea region.These data illustrate the complexity of the spatial Pb isotopic distribution, and Pb sources, within a single ocean basin at the present day, which should be borne in mind when interpreting long-term radiogenic isotope paleorecords from Fe-Mn crusts.