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International audience; It is well-established that lanthanide rare earth elements (REEs) have the potential to record the nature and source characteristics of their host magmas, in both whole-rock and their minerals. Accessory minerals that concentrate REEs are especially useful in crustal evolution studies, both for their elemental and isotopic information; the classic and unrivalled example being zircon. Approaches using a single radiogenic isotopic system, or one radiogenic and one stable isotope system (e.g., Hf and O) in one REE-bearing mineral (usually zircon) are common, but those involving multiple isotopes in several minerals remain scarce despite offering many advantages. Importantly, the latter approaches also allow comparing different techniques and provide evidence on whether isotopic systems were disturbed by secondary processes. This contribution documents several isotopic systems within the abundant accessory mineral of Caledonian high Ba-Sr granitoids from Northwest Scotland. We present a multi-isotope study of titanite, zircon and apatite from two localities (Strontian and Rogart), which were selected for their contrasting whole-rock isotopic signatures-the former deriving from a depleted mantle source, whereas the latter derived from a strongly enriched mantle source. New in-situ Sm-Nd in titanite and apatite and Hf in zircon isotope data are discussed and compared with in-situ 2 oxygen isotope data previously published for the same samples. An internal consistency is observed for Nd isotopes in apatite and titanite. Nd isotopes values for both minerals strongly correlate with Hf isotopes in zircon. Isotopic data at the mineral scale confirm the Strontian and Rogart source characteristics previously defined from whole-rock isotope data, with the Rogart having a more enriched signature than the Strontian source along the "Caledonian Parental Magma Array"(CPMA). In contrast, a significant discrepancy exists between whole-rock and REE-mineral oxygen isotope data as the latter can be affected by post emplacement alteration and hence can be misinterpreted. Importantly, the contribution of sediments in the CPMA source(s) can be estimated from a diagram combining Sm-Nd isotopic signatures and (La/Sm)N in apatite and titanite. Overall, we demonstrate that detailed petrogenetic records are not only available in zircons but also in magmatic titanite and apatite, and we suggest that integrated multi-mineral approaches have potential to maximise constraints from in-situ mineral isotope geochemistry.

Floods are among the most destructive natural hazards on Earth. In paleohydrology, sediments are generally considered as one of the best archives to extend flood records to pre-historical timescales. Doing so requires being able to identify flood deposits from sediment archives and decipher between flood types. The latter is particularly important in glacierized regions, where meteorological floods frequently co-occur with glacial lake outburst floods (GLOFs). In Patagonia, results from a recent study suggest that GLOFs are recorded in downstream fjord sediments as fine-grained and organic-poor layers, representing the high amount of glacier rock flour transported during lake outbursts, whereas meteorological floods are represented by coarser and more organic deposits. However, not all fine-grained organic-poor deposits could be associated with historical GLOFs. Here, we reconstruct the provenance of these Baker River flood deposits using Sr-87/Sr-86 and epsilon Nd, taking advantage of the clear lithological differences that exist between both sides of the watershed. Our results show that both Sr-87/Sr-86 and epsilon Nd are suited to reconstruct sediment provenance in the Baker River watershed but that epsilon Nd is the most effective and the least affected by grain-size variations. Our provenance results confirm that the 21st-century fine-grained and organic-poor deposits represent GLOFs and that the largest winter meteorological flood on record has a distinct coarse and organic-rich signature. However, our results show that rain-on-snow events that occur in summer, and therefore primarily affect the western glacierized part of the watershed, have the same fine-grained organic-poor signature as GLOFs. Therefore, this study shows that the sedimentary signature of rain-on-snow floods in partially glacierized watersheds depends on the season during which they occur. We anticipate that our findings will contribute to a better interpretation of flood records from partially glacierized watersheds.

The role of Quaternary ice sheet fluctuations in driving meltwater pulses and ocean circulation perturbations is widely acknowledged. What is less clear is the role of these processes in driving changes in past atmospheric dust activity, and possible wider links between dust and climate. Terrestrial windblown dust (loess) deposits along the northern fringe of the European loess belt potentially record past atmospheric dust emission from regions close to the former Eurasian Ice Sheet (EIS) and provide a means to evaluate the role of ice sheet fluctuations in the past dust cycle. Numerical loess chronologies across this region generally agree on greatly enhanced dust deposition rates during MIS 2, when the EIS reached its maximum extent. Yet, uncertainties over the sources of this material prevent understanding of the precise causes of this greatly enhanced atmospheric dustiness, and any potential link to ice sheet fluctuations and climate. In southeast England, loess accumulation dominantly occurred in two phases centered on 25– 23.5 ka and 20–19 ka, matching the timing of coalescence of the Fennoscandian and British-Irish ice sheets and specifically advances and retreats of nearby ice lobes in the western North Sea. As such, these deposits provide an ideal test of the role of ice sheet fluctuations in atmospheric dust dynamics. Here we undertake such a test through a detailed provenance study of loess in southeast England and potential dust source sediments across the North Sea region. We group extensive new and published data sets of detrital zircon U–Pb ages from basement rocks and Cenozoic sediments in the North Sea area, which not only provide new insight into both loess source, but also the nature of sediment transport over NW Europe into the North Sea basin more widely. Multi-proxy evidence allows us to unambiguously identify ice sheet derived sediments in the exposed North Sea basin as the dominant source of loess in southeast England, while fluvial sediments delivered by rivers draining Continental Europe possibly contributed additional source material to the first loess accumulation phase. We propose that sudden retreats of the North Sea Lobe released substantial amounts of sediment rich meltwater into the southern North Sea and Channel basins, driving accelerated dust emission, loess deposition and provenance variability in NW Europe during MIS 2. Moreover, we propose that this model of dust activity driven by proglacial sediment availability may be applicable for EIS marginal regions more widely, even where resultant loess cover is rarely preserved due to extensive erosion and reworking along the ice marginal spillway. This implies the role of ice sheets in controlling wider dust emission may be underestimated. In addition to driving changes in ocean circulation through meltwater pulses, ice sheet dynamics in the Quaternary may have also driven substantial and abrupt changes in atmospheric dust activity. This mechanism may in part explain the coupling between dust and climate events widely seen in Quaternary dust sediment records and suggests a possible major role of high latitude dust emission in MIS 2 dustiness across Europe and beyond.

International audience; Hafnium and neodymium isotopes provide robust tool tracers for tracking the mechanisms of crustal generation and differentiation, from mantle extraction to the late geological processes undergone by the studied rocks. Though these two isotope systems commonly behave similarly and define a positive correlation between 143 Nd/ 144 Nd and 176 Hf/ 177 Hf referred to as the "terrestrial array", they may differ in terrains having a complex geological history, such as Archean cratons. This study presents the first combined whole-rock Hf and Nd isotopic analyses of Archean mafic and felsic igneous rocks from the Sangmelima terranes in the Ntem Complex (located in the Northwest of Congo Craton (NW CC) in southern Cameroon). It mainly consists of Mesoarchean charnockites and tonalite-trondhjemite-granodiorite (TTG) suites, greenstone belts, mafic enclaves or dykes, and potassic granitoids. Mesoarchean charnockite and TTG suites have subchondritic initial 176 Hf/ 177 Hf and 143 Nd/ 144 Nd ratios with a mean initial (suffix (i)) ε 176 Hf (i) and ε 143 Nd (i) of-3.30 ± 1.40 and-3.85 ± 0.65 (2SD) respectively, implying the involvement of Eo-to Paleoarchean components in their petrogenesis. The bulk rock initial Hf and Nd isotope compositions of the gabbro and gabbronorites are suprachondritic (ε 176 Hf (i) = +3.4 to + 8.2; ε 143 Nd (i) = +0.9 to + 1.6), indicate that they were derived from a depleted mantle source. Coupled with pre-existing data from the literature, these new Hf-Nd isotopic data indicate that two episodes of mantle-derived mafic magmatism in the Ntem Complex occurred during the Mesoarchean period (i.e., at ~ 3.1 and 2.86 billion years (Ga)). Neoarchean dolerite dykes show broadly chondritic to supra-chondritic ε 176 Hf (i) and ε 143 Nd (i) values of-0.28 to + 4.53 and T CHUR ages of 2.74-2.76 Ga, suggesting the derivation of doleritic magma from a depleted mantle source with either none or limited crustal residence time. Considering other Archean domains of the NW CC, there were multi-stage magmatism events and crustal growth events occurred at ~3.75-3.31 Ga, ~3.26-3.0 Ga, ~2.92-2.85 Ga, and ~2.75-2.72 Ga from Eoarchean to Neoarchean in the NW Congo Craton.

International audience; An ongoing debate concerns what initiated the Great Oxidation Event (GOE) and associated glaciation between ~ 2.45 and 2.2 Ga. One possibility is the emergence of continental landmasses and the increase of subaerial igneous province weathering during the Late Archean. We test this hypothesis in the Hamersley Basin by reporting Nd-isotope data from a succession of iron formations (IFs), mudstone/siltstones and glacial diamictites from the Boolgeeda Iron Formation and overlying Turee Creek Group deposited during the GOE. In a 147Sm/144Nd - εNd(t) diagram, the data define a negative trend indicating the contribution of a high εNd(t) ~ +3 hydrothermal component and a strongly negative εNd(t) ~ -9 crustal component, which is compatible with the Nd-isotope composition of the upper continental crust but also of the underlying felsic volcanics of the Woon-garra Rhyolite and crustally-contaminated mafic volcanics of the Fortescue Group. A less pronounced negative trend originating from the same hydrothermal source but correlated with non-contaminated ultramafic Fortescue volcanics (εNd(t) ~ -2) is observed for the older Joffre, Dales Gorge and Marra Mamba IFs. As Nd-isotopes are not sensitive to redox conditions, the major shift of Nd-isotopic compositions at ~ 2.45 Ga cannot be linked to a change in the weathering regime, rather to a change in the nature of the continental surface exposed to weathering. One explanation is that the Sm-Nd sources for sediments deposited before and during the GOE were locally derived from the underlying subaerial LIPs, reflecting a change in the geodynamic context of deposition and/or hydrographic network and catchment areas. Another explanation could be a significant change in the nature of fluid–rock interactions due to the increase role of weathering processes associated with the emergence of continental landmasses. Additional Nd isotope data from different cratons worldwide are needed, however, to infer as to whether or not the marked shift in Nd isotope compositions recorded in the Turee Creek Group reflect a change in the global hydrological cycle. Our data support the role of large subaerial magmatic provinces as triggers of the rise of atmospheric oxygen and the onset of glaciations at the beginning of the Proterozoic.

Radiogenic lead (Pb) and neodymium (Nd) isotope compositions extracted from authigenic phases in marine sediments are sensitive tracers to reconstruct past ocean circulation and water mass mixing. Chemical reductive leaching of hydrogenetic ferromanganese oxyhydroxides from bulk sediments is the most practical way to recover past seawater Pb and Nd isotope signatures in the Southern Ocean, due to the scarcity of alternative archives. However, the leached signal could be compromised if substantial quantities of Pb and Nd were released from non‐hydrogenetic sediment fractions during chemical extraction. Here we developed a very short 10‐s leaching method to extract reliable seawater Pb and Nd isotope signals from sediments in the Atlantic sector of Southern Ocean. The effect of a previously recommended MgCl2 pre‐wash, the role of chelate ligands in the leaching solution and length of leaching time were investigated. The results show that 10‐s exposure time of sediments to reductive leaching extracted sufficient and more reliable hydrogenetic Pb and Nd compared with the commonly used 30‐min leaching approaches. The robustness of our improved leaching method was validated via direct comparison of Pb and Nd isotope signatures with actual seawater, porewater, and corresponding sediment leachates from three stations in front of the Antarctic Filchner‐Rønne Ice Shelf. Our findings also indicate that in contrast previously studied sites on the West Antarctic continental shelf, the bottom seawater Nd concentration is less elevated through benthic fluxes in the area of the southern Weddell Sea shelf., Plain Language Summary: Individual modern ocean water masses can often be identified by the isotopic signature of dissolved trace metals lead (Pb) and neodymium (Nd) supplied from surrounding continents. By analyzing past seawater Pb and Nd isotope ratios preserved in the sedimentary archives, we can understand how the ocean circulation changed. In the Southern Ocean, archives preserving past seawater Pb and Nd isotope compositions are very scarce. Thus, the chemical extraction of Pb and Nd from seawater‐derived ferromanganese oxyhydroxides within deep marine sediments becomes the most practical way to recover past seawater signal. However, Southern Ocean sediments commonly contain substantial quantities of Antarctic continental fine‐grained sediment, which easily partially dissolve during extraction, thereby releasing Pb and Nd, which did not originate from past ambient seawater. Here we established a gentle and efficient extraction method to obtain reliable past Southern Ocean seawater signatures. In addition, via analysis of regional seawater‐derived Pb and Nd signatures in the Atlantic sector of Southern Ocean, we found that the sediments further away from Antarctica and volcanically active regions are better suited to preserve unaltered seawater Pb and Nd isotope signals, which strongly supports the unique possibility of tracing past water mass sourcing in the Southern Ocean with our analytical approach., Key Points: 10‐s reductive leaching is capable of reliably extracting seawater Pb and Nd isotope signals from Southern Ocean sediments. Natural porewater Pb isotopic compositions are analyzed for the first time in front of the Antarctic Filchner‐Rønne Ice Shelf. Identify potential sites for extracting seawater Pb and Nd isotopic signatures from bulk sediments in the Atlantic sector of Southern Ocean., China Scholarship Council (CSC)

The ability to trace and quantify sediment provenance in northwestern Patagonia is increasingly needed to properly understand modern sediment erosion and transport processes in this rapidly changing environment, and to accurately interpret sediment records from adjacent basins in terms of climate and environmental change. Nonetheless, no study so far has systematically evaluated the effectiveness of different tracers to reconstruct sediment provenance in this region. To fill this gap, we assess the effectiveness of commonly-used provenance indicators, including bulk mineralogy, major and rare earth element (REE) geochemistry, and Sr and Nd isotopes, to reconstruct sediment provenance in northwestern Patagonia. First, the ability of these tracers to discriminate between the main sources of sediment in the region is investigated, mostly using data compiled from the literature. Then, the potential of these tracers for provenance reconstruction is assessed by comparing the composition of sediments from six major Chilean rivers between 44 and 48°S to lithological proportions in their respective watersheds. The results suggest that mineralogy, major element geochemistry, and REE geochemistry can be used as qualitative tracers of sediment provenance. However, the compositional overlap between the sources and the relatively large variability within them prevent quantitative reconstructions. By comparison, 87Sr/86Sr and εNd allow to clearly differentiate between the sources, most likely due to significant age differences between the main lithologies, and to estimate the relative contribution of each source. End-member mixing results based on Sr and Nd isotopes show that the relative source contributions are in general agreement with the lithological proportions in the river watersheds. Differences between estimated contributions and lithological proportions in the watersheds are interpreted as the result of the high regional precipitation gradient and unequal glacier distribution, which lead to variable erosion rates across the study area. Our results demonstrate the suitability of 87Sr/86Sr and εNd for quantitative provenance reconstruction in northwestern Patagonia. They constitute a strong basis for the interpretation of sediment archives from the Patagonian fjords and from the eastern South Pacific, and they should be particularly useful to quantitatively investigate modern and past earth-surface processes., SCOPUS: ar.j, info:eu-repo/semantics/published

Financial support to DJW, TS, and TvdF was provided by the Natural Environment Research Council (NE/N001141/1), the Leverhulme Trust (RPG-398), the Grantham Institute for Climate Change and the Environment, and a Marie Curie Reintegration grant (IRG 230828). LFR acknowledges support from the Natural Environment Research Council (NE/N003861/1) and the European Research Council (278705). The sequence of deep ocean circulation changes between the Last Glacial Maximum and the Holocene provides important insights for understanding deglacial climate change and the role of the deep ocean in the global carbon cycle. Although it is known that significant amounts of carbon were sequestered in a deep overturning cell during glacial periods and released during deglaciation, the driving mechanisms for these changes remain unresolved. Southern Ocean sea-ice has recently been proposed to play a critical role in setting the global deep ocean stratification and circulation, and hence carbon storage, but testing such conceptual and modelling studies requires data constraining past circulation changes. To this end, we present the first deglacial dataset of neodymium (Nd) isotopes measured on absolute-dated deep-sea corals from modern Lower Circumpolar Deep Water depths in the Drake Passage. Our record demonstrates deglacial variability of 2.5 εNd units, with radiogenic values of up to during the Last Glacial Maximum providing evidence for a stratified glacial circulation mode with restricted incorporation of Nd from North Atlantic Deep Water in the lower cell. During the deglaciation, a renewed Atlantic influence in the deep Southern Ocean is recorded early in Heinrich Stadial 1, coincident with Antarctic sea-ice retreat, and is followed by a brief return to more Pacific-like values during the Antarctic Cold Reversal. These changes demonstrate a strong influence of Southern Ocean processes in setting deep ocean circulation and support the proposed sea-ice control on deep ocean structure. Furthermore, by constraining the Nd isotopic composition of Lower Circumpolar Deep Water in the Southern Ocean, our new data are important for interpreting deglacial circulation changes in other ocean basins and support a spatially asynchronous return of North Atlantic Deep Water to the deep southeast and southwest Atlantic Ocean. Postprint Postprint

International audience; The Iberian Pyrite Belt (IPB), located in the South Portuguese Zone of the Iberian Massif (Spain), is a world-class VHMS province containing numerous, huge mineral deposits hosted by bimodal volcanic sequences. The province can be subdivided in several domains, which differ from each other both in the nature and relative abundance of their volcanic sequences, and in the distribution of associated VHMS deposits. In spite of its geological and economic interest, information available for the northern part of the province is still relatively scarce. We present a new dataset of geochemical and Nd isotopic analyses on the Paymogo Volcano-Sedimentary Alignment (PVSA), an area that is considered to be representative of this northern segment of the IPB.Volcanic sequences in the PVSA contain very scarce mafic rocks. In contrast, felsic rocks are abundant and have been classified in two groups: (i) the Paymogo rhyolitic sequence, hosting most of the VHMS deposits and (ii) a dacitic sequence. Although approximately coeval, these groups of felsic rocks clearly differ in geochemical features and ƐNd signature. In view of these differences, it is suggested that felsic rocks were produced from different mid-crustal domains during a major event of partial melting related to a regional, late Devonian/Early Carboniferous transtensional event. It is further suggested that some volcanic rocks previously described as andesites, are better interpreted as dacites.The age (347.3 ± 0.8 Ma), geochemical features, (Zr

12 pages, 6 figures, 2 tables, supplementary material https://doi.org/10.1016/j.pocean.2020.102340, Seawater rare earth element (REE) concentrations and Nd isotopic composition (εNd) are increasingly applied as valuable tracers of oceanographic processes such as water mass mixing and lithogenic inputs to seawater. However, their measurements are basically lacking in the Mediterranean Sea water column. This study analyzes 9 seawater stations around the central Mediterranean Sea to clarify the relative importance of external sources, vertical (biogeochemical) processes and lateral water mass transport in controlling REE and εNd distributions. Concentrations of REE do not show nutrient-like profiles with depth, likely indicative of relatively young waters with limited accumulation of remineralized REE. Light REE (LREE) present a non-conservative behavior, which largely peak at surface waters and rapidly decrease with depth. The negative correlation of surface LREE enrichment with offshore distance highlights the influence of continental input from the western Italian coast to the Tyrrhenian surface waters. In contrast to other regions with reported boundary exchange, this process does not modify the εNd values here. On the other side, distributions of dissolved heavy REE (HREE) and εNd display a conservative behavior that can be explained by mixing of western- (MAW and WMDW) and eastern- (LIW and EMDW) originated waters. We test this hypothesis with an Optimum Multi-Parameter Analysis (OMPA) including HREE and εNd parameters. Even though the limited data set, consistent results of water mass fractions are obtained for the four main water masses although with some particularities. While LIW takes on major importance when considering HREE in the model, EMDW fractions are preferentially detected with εNd. This latter finding implies a noticeable deep water flux across the Sicily Strait into the Western Mediterranean that was not clearly evidenced before, This research has been financially supported by the TIMED Project funded by the European Commission (ERC Consolidator Grant to I. Cacho; ID: 683237). The authors thank financial support from the CHIMERA Project (CTM2016-75411-R), Generalitat de Catalunya-Grups de Recerca Consolidats (2017 SGR 315) and the Project of Strategic Interest NextData PNR 2011-2013 (www.nextdataproject.it). [...]. E. Garcia-Solsona acknowledges support from a post-doctoral fellowship (FPDI-2013-15660) and L.D. Pena from the Ramón y Cajal program (MINECO, Spain). I. Cacho thanks the ICREA-Academia programme from the Generalitat de Catalunya. J.N. Pérez-Asensio has been funded by a Beatriu de Pinós postdoctoral fellowship from AGAUR (Generalitat de Catalunya) and the European Commission (Marie Curie-COFUND), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

The Miocene is a key interval in the geodynamic and oceanographic evolution of the Mediterranean marking the transition from a wide open basin to the modern closed basin. We used the Sr and Nd isotope records of two Miocene carbonate successions in the Adriatic to document that the evolution of the Mediterranean Basin controlled its seawater chemistry. During the late Aquitanian (similar to 21Ma), a time of glaciation and sea level lowstand, increased runoff affected the Sr isotope ratios of Mediterranean waters, whereas during the Burdigalian (20.44-15.97Ma) volcanism in the circum-Mediterranean area mainly influenced the Sr isotopic signature. During the Langhian (15.97-13.82Ma), a time of sea level highstand associated with the Middle Miocene Climatic Optimum, the Nd isotope values indicate that waters exchanged between the Paratethys and the Central Mediterranean. The Central Mediterranean was well connected with the Atlantic Ocean between the Langhian and the early Tortonian (15.97-11.5Ma), but exchange of water with the Paratethys declined. In the Messinian (6.3Ma), connections between some marginal Mediterranean basins, for example, the proto-Adriatic basin, and the Central Mediterranean, became restricted. In this basin, the Sr isotope values fell below the global reference line, while Nd isotope ratios show a strong affinity with the Atlantic Ocean and also indicate freshwater input. We conclude that the Mediterranean Nd isotope signature differs from that in the open oceans and reflects the basin physiography, reflecting a mix of signals derived from the adjacent oceans and local signals.

The recurrent deposition of organic-rich sapropel layers in the eastern Mediterranean Sea (EMS) has been attributed to deep-water stagnation and enhanced biological production. However, the underlying climatic interactions, paleoceanographic processes, and associated ventilation dynamics are still debated. Here, we present a basin-wide reconstruction of circulation systematics during sapropel S1 formation (∼10.8–6.1 kyr BP), using the Nd isotope composition ( e Nd ) as paleo-seawater tracer. Our e Nd data from fish debris and foraminifera tests are remarkably radiogenic compared to today, and spatially and temporally constant. These results predominantly reflect enhanced Nile versus Atlantic contributions, and indicate that EMS deep-water stagnation prevailed below ∼800 m water-depth during S1 formation. Additional e Nd records obtained from bulk sediment leachates show that such stagnation was preconditioned thousand(s) of years prior to S1 initiation by intensified Nile flooding, whereas it terminated with a basin-wide, deep-water renewal. In addition, decoupling of deep waters between the EMS and western Mediterranean Sea (WMS) is evident for the S1-period. Using a box-model for Nd in the EMS, the observed e Nd distribution can be most adequately explained by a 2-fold increase in Nile discharge, and a 50% decrease in the EMS–WMS exchange that was mostly limited to the surface waters alone. The corresponding circulation during S1 was more sluggish and shallow for the EMS, but largely unaffected for the WMS. This implies that deep-water stagnation is a prerequisite for sapropel formation.

International audience; Sedimentary basins are, in many cases, the only preserved record of the geological processes active through geological time. These deposits preserve age, isotopic and geochemical signatures of the source rocks, providing insights into tectonic setting. In this context, we investigate the lithostratigraphy, provenance and tectonic environment of the Carrancas Group, a meta-sedimentary sequence characterised by a basal psammitic unit (Lower Unit) passing up into interbedded psammo-pelites (Intermediate Unit), which are overlain by a further psammitic unit (Upper Unit). This succession, along with the Canastra, Paranoá and Vazante groups (Brasília orogen), comprises a mature passive margin developed at the western-southern margin of the São Francisco craton during the Neoproterozoic. Detrital zircon U-Pb ages and Nd-Hf isotope data enable revised stratigraphic correlations across the basin, highlighting variations in the source of detritus. Deposition began after 0.92 Ga, with the sedimentation of the Lower Unit, with input of juvenile ∼2.1 Ga detritus (εNdt = −0.1 to +3.2) derived from the São Francisco craton. A marine transgression characterises the transition to the Intermediate Unit, which gradually covered over juvenile ∼2.1 Ga terrains and rendered them unavailable as possible source rocks for detrital zircons. Evolved Archaean-Palaeoproterozoic basement rocks, the Espinhaço Supergroup and evolved Neoproterozoic granitoids, all belonging to the São Francisco craton, acted as sources for the Intermediate and Upper units (U-Pb = 2.7 Ga to 0.9 Ga; εNdt = −10.4 to +7.1). The Goiás massif might also have acted as a source, providing juvenile Mesoproterozoic detritus. The sediments of the Upper Unit register a significant shift in source, with incoming of juvenile Mesoproterozoic and crustal 1.9 – 1.7 Ga detritus. This change in the ages of the detrital material may be related to exhumation of the Espinhaço Supergroup during the evolution of the passive continental margin basin. The whole-rock Nd TDM model ages become progressively younger from the base to the top of the sequence (Nd TDM = 2.6–1.8 Ga). The collisional events between Amazonian and São Francisco cratons and the Paranapanema block set the minimum age of deposition along this passive continental margin at around 0.67 Ga.

Resolving the possible mantle and crustal sources for shergottite meteorites is crucial for understanding the formation and early differentiation of Mars. Orbiter and rover characterization of the martian surface reveal that the major element composition of most of its surface does not match the shergottites (McSween et al. 2009) leaving the relationship between them poorly understood. The identification of the meteorite NWA 7034 and its pairs as a Mars surface rock (Cartwright et al. 2014) provides access to a representative sample of Mars' crust (Agee et al. 2013; Humayun et al. 2013). Utilizing the short-lived 146Sm–142Nd, and long-lived 147Sm–143Nd and 176Lu–176Hf chronometers, which are sensitive to silicate differentiation, we analyzed three fragments of NWA 7034. The very negative mean isotopic compositions for this breccia, μ142NdJNdi-1=−45±5 (2SD), ε143NdCHUR=−16.7±0.4 (2SD) and ε176HfCHUR=−61±9 (2SD) point to an ancient origin for this martian crust. However, modeling of the data shows that the crust sampled by NWA 7034 possesses a Hf/Nd ratio and coupled ε143Nd–μ142Nd model age that are incompatible with this crustal reservoir being an end-member that generated the shergottite source mixing array. In addition, this crust is not juvenile, despite its rare earth element profile, but has had a multistage formation history. Therefore, early crustal extraction alone was not responsible for the creation of the reservoirs that produced the shergottites. Instead mantle reservoirs formed via other early differentiation processes such as in a Mars magma ocean must be responsible for the trace element and isotopic signatures present in shergottites., SCOPUS: ar.j, info:eu-repo/semantics/published

During the production of natron glass most features of the raw materials are lost and only some bulk geochemical characteristics have potential as provenance indicators. To determine the primary origin of archaeological glass artefacts, suitable sand raw materials have to be accurately characterised. In this respect, information about the possible variation in geochemical properties within a silica source is also vital to account for potential (partial) overlap of different sources. In this study, it is shown that the variation in major and minor elemental composition of beach sand on a local scale is smaller than the variation in Roman natron glass. Therefore, a single sand deposit can be seen as a relatively homogeneous source of silica for glass production. Nd isotopic signatures are identical for all samples analysed. The isotopic composition of Sr however varies considerably due to local variations in the relative proportions of carbonates and silicates (mostly feldspar). ispartof: STAR: Science & Technology of Archaeological Research vol:1 issue:2 pages:115-124 status: published

The Mediterranean Outflow (MOW) is generated by deep and intermediate waters from different basins in the Mediterranean Sea. Despite the number of studies on Mediterranean water masses, little work has been done on the source and properties of intermediate waters in the westernmost Mediterranean Sea and their links with MOW. Here we examine three marine sediment records spanning the last 20 kyr, located at key depths to trace intermediate waters along the Alboran Sea. We use a combination of redox-sensitive elements, which can serve as proxies to reconstruct variations in the water column oxygenation and the Nd isotopic composition of foraminiferal ferromanganese coatings, in order to reconstruct water mass provenance of Eastern/Western Mediterranean waters. As measured, eNd < − 9.2 and a low U/Th ratio during glacial periods can be attributed to the presence of Western Mediterranean Deep Water (WMDW) at the study sites. During deglaciation, higher Nd isotopic compositions and U/Th ratios point to an enhanced contribution of the modified Levantine Intermediate Water (LIW). The comparison between our data and other LIW and MOW records suggests that i) the lower branch of MOW is linked to WMDW during the glacial period, ii) the middle MOW branch follows LIW activity during deglaciation, while iii) the upper branch is more active during late Holocene, coinciding with LIW formation increase after sapropel deposits. This reconstruction has significant implications for an understanding of the MOW evolution.

Neodymium isotope data on exhalites and tuffs from the Cambrian Lemarchant volcanogenic massive sulphide (VMS) deposit provide insights into the tectonic environment of the Tally Pond group, Canada. New data from exhalites from the Lemarchant area show evolved values of εNd513 = 6.0 to 1.8, whereas the associated volcanic rocks have εNd513 of +0.4 to +1.4. The Lemarchant exhalite εNd compositions overlap the underlying Ganderian Neoproterozoic Sandy Brook Group (εNdt = 6.5 to 1.9) and Crippleback Intrusive Suite (εNdt = 5.9 to 5.2). The evolved Nd isotopic signatures suggest that the volcanic rocks of the Tally Pond group were formed upon Ganderian arc basement, which itself was possibly built upon, or proximal to, the Gondwanan Amazonian margin. Erosion of older crustal material and Tally Pond group volcanic rocks, together with coeval eruption of the volcanic rocks, released Nd-rich detritus into the water column. Uptake of eroded detrital and scavenged Nd resulted in mixed Nd sources (juvenile and evolved), which are archived in the exhalites. The results of this study are of significance not only for occurrences of exhalites within the Tally Pond group, but also have exploration implications for VMS districts globally. Postprint

Arc lavas form from melting of mélange rocks; sediment melts and slab-derived fluids are not major contributors., In subduction zones, sediments and hydrothermally altered oceanic crust, which together form part of the subducting slab, contribute to the chemical composition of lavas erupted at the surface to form volcanic arcs. Transport of this material from the slab to the overlying mantle wedge is thought to involve discreet melts and fluids that are released from various portions of the slab. We use a meta-analysis of geochemical data from eight globally representative arcs to show that melts and fluids from individual slab components cannot be responsible for the formation of arc lavas. Instead, the data are compatible with models that first invoke physical mixing of slab components and the mantle wedge, widely referred to as high-pressure mélange, before arc magmas are generated.

International audience; Neodymium isotopic compositions (143Nd/144Nd or εNd) have been used as a tracer of water masses and lithogenic inputs to the ocean. To further evaluate the faithfulness of this tracer, we have updated a global seawater εNd database and combined it with hydrography parameters (temperature, salinity, nutrients and oxygen concentrations), carbon isotopic ratio and radiocarbon of dissolved inorganic carbon. Archive εNd data are also compiled for leachates, foraminiferal tests, deep-sea corals and fish teeth/debris from the Holocene period (< 10,000 years).At water depths ≥ 1500 m, property-property plots show clear correlations between seawater εNd and the other variables, suggesting that large-scale water mass mixing is a primary control of deepwater εNd distribution. At ≥ 200 m, basin-scale seawater T-S-εNd diagrams demonstrate the isotopic evolution of different water masses. Seawater and archive εNd values are compared using property-property plots and T-S-εNd diagrams. Archive values generally agree with corresponding seawater values although they tend to be at the upper limit in the Pacific. Both positive and negative offsets exist in the northern North Atlantic. Applying multiple regression analysis to deep (≥ 1500 m) seawater data, we established empirical equations that predict the main, large-scale, deepwater εNd trends from hydrography parameters. Large offsets from the predicted values are interpreted as a sign of significant local/regional influence. Dominant continental influence on seawater and archive εNd is observed mainly within 1000 km from the continents. Generally, seawater and archive εNd values form gradual latitudinal trend in the Atlantic and Pacific at depths ≥ 600 m, consistent with the idea that Nd isotopes help distinguish between northern/southern sourced water contributions at intermediate and deep water depths.

The history of the Amazon River is a much-discussed subject, and the timing of the development of a transcontinental system in particular is a matter of some controversy, with estimations varying between the Early Miocene and the Pliocene or even the Pleistocene. To shed further light on this, we studied the sediment provenance of an Oligocene to Late Pleistocene marine sedimentary section from the Ceara Rise (ODP Site 925), a topographic high in the central Atlantic Ocean, using major element concentrations and Nd isotopic composition in 85 samples. In addition, the carbon isotopic composition of bulk organic matter and changes in the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) were used to identify periods of increased river outflow. On the basis of these results, we suggest that the history of the development of the Amazon River is characterized by specific steps. During the late Oligocene/Early Miocene (30–18.3 Ma), the terrigenous mass accumulation rates (TARs) were high, and sediment and GDGT compositions suggest that a large river system existed, which at times received weathering products from a younger and probably Andean sediment source. A shift to a younger Andean sediment provenance after 8.7 Ma indicates that the Amazon River became permanently connected with the Andes. Between 18.3 and 4.5 Ma, TARs were generally low, and GDGTs were derived for the most part from in situ production in marine waters. Around 4.5 Ma, the river expanded, probably due to ongoing tectonic activity, and uplift in the Andes increased Andean rock erosion. This led to a strong increase in terrigenous sediment deposition and enhanced organic matter preservation on the Ceara Rise, and the delivery of terrestrial (both soil and riverine) branched GDGTs to the Ceara Rise.

Antarctic Intermediate Water (AAIW) is a key player in the global ocean circulation, contributing to the upper limb of the Atlantic Meridional Overturning Circulation (AMOC), and influencing interhemispheric heat exchange and the distribution of salinity, nutrients and carbon. However, the deglacial history of AAIW flow into the North Atlantic is controversial. Here we present a multicore-top neodymium isotope calibration, which confirms the ability of unclean foraminifera to faithfully record bottom water neodymium isotopic composition ( e Nd ) values in their authigenic coatings. We then present the first foraminifera-based reconstruction of e Nd from three sediment cores retrieved from within modern AAIW, in the western tropical North Atlantic. Our records reveal similar glacial and interglacial contributions of AAIW, and a pronounced decrease in the AAIW fraction during North Atlantic deglacial cold episodes, Heinrich Stadial 1 (HS1) and Younger Dryas (YD). Our results suggest two separate phases of reduced fraction of AAIW in the tropical Atlantic during HS1, with a greater reduction during early HS1. If a reduction in AAIW fraction also reflects reduced AMOC strength, this finding may explain why, in many regions, there are two phases of hydrologic change within HS1, and why atmospheric CO2 rose more rapidly during early than late HS1. Our result suggesting less flow of AAIW into the Atlantic during North Atlantic cold events contrasts with evidence from the Pacific, where intermediate-depth e Nd records may indicate increased flow of AAIW into the Pacific during the these same events. Antiphased e Nd behavior between intermediate depths of the North Atlantic and Pacific implies that the flow of AAIW into Atlantic and Pacific seesawed during the last deglaciation.

The oxygen (O) and neodymium (Nd) isotopic composition of monazite provides an ideal tracer of metamorphism and hydrothermal activity. Calibration of the matrix effect and monitoring of the external precision of monazite O&ndash, Nd isotopes with microbeam techniques, such as secondary ion mass spectrometry (SIMS) and laser ablation-multicollector-inductively coupled plasma-mass spectrometry (LA-MC-ICPMS), require well-characterized natural monazite standards for precise microbeam measurements. However, the limited number of standards available is impeding the application of monazite O&ndash, Nd isotopes. Here, we report on the RW-1 monazite as a potential new working reference material for microbeam analysis of O&ndash, Nd isotopes. Microbeam measurements by electron probe microanalysis (EPMA), SIMS, and LA-MC-ICPMS at 10&ndash, 24 &micro, m scales have confirmed that it is homogeneous in both elemental and O&ndash, Nd isotopic compositions. SIMS measurements yield &delta, 18O values consistent, within errors, with those obtained by laser fluorination techniques. Precise analyses of Nd isotope by thermal ionization mass spectrometry (TIMS) are consistent with mean results of LA-MC-ICPMS analyses. We recommend &delta, 18O = 6.30&permil, &plusmn, 0.16&permil, (2SD) and 143Nd/144Nd = 0.512282 &plusmn, 0.000011 (2SD) as being the reference values for the RW-1 monazite.

International audience; Major, trace element concentrations and Nd, Sr isotopic data are reported for Neoproterozoic high-pressure (HP) mafic granulites from the Agou Igneous complex (AIC), which marks the suture zone of the Pan-African Dahomeyide orogen in southwestern Togo. The main rock types consist of garnet-free and garnet-bearing metagabbronorites (GFM and GBM) that are cross cut by subordinate leucocratic to melanocratic veins and dykes of garnet-bearing microgabbroic rocks. Geochemical data suggest that the HP granulites may have preserved the geochemical imprints of their igneous protoliths. They display either cumulitic features or liquid compositions varying from primitive to evolved basalts and andesites and then to more differenciated dacitic magmas as supported by major and trace element contents. Primary basalts display LREE and LILE enriched patterns and no Eu anomaly, but are depleted in Y and Yb suggesting a slightly enriched mantle source or a weak crustal contamination. Mafic veins and dykes display REE flat patterns (LaN/YbN = 0.58-1.7) and a slightly negative Eu anomaly and ∑REE content ranging between 10 and 20. These features are consistent with protoliths of N- to E-MORB affinities. Mafic cumulates and andesitic basalts are characterized by various REE patterns which could be compared to those of the primary and/or the evolved basalts, probably identifying various igneous suites. The fractionated REE patterns (Ce/YbN ≈ 11.0-17.9) with slight LREE enrichment (Ce/SmN ≈ 3.1-3.8) and HREE depletion (Sm/YbN ≈ 3.6-4.8) could be induced by a garnet residue in the melt source. Neodymium isotopic data show that most mafic cumulative rocks have similar 143Nd/144Nd ratios between 0.5127 and 0.51289, corresponding to initial εNd(T) values between +2.26 and +6.33 that yielded TDM ages from 1.2 to 0.94 Ga. The mafic mesocratic vein displays 143Nd/144Nd values of 0.51227, corresponding to initial εNd(T) values of +6.87 that yielded TDM = 0.94 Ga, and constrains the minimum age. However primitive basalts samples A17 (GFM) and other mafic cumulate Ag224 (GBM) give an older depleted mantle source derivation age of 2.31 and 1.68 Ga respectively, suggesting crustal contamination by the surrounding gneissic Paleoproterozoic basement. The Nd isotopic compositions suggest that the parental magmas of the Agou Igneous Complex in southern Togo were derived from time-integrated depleted mantle source. Such geochemical features are consistent with an active continental margin environment and suggest that the AIC represents a magmatic body emplaced and cooled at the base of a continental crust above a subduction zone.

International audience; Hydroclimate variability has exerted a fundamental control on the alternating deposition of organic-lean marl and organic-rich sapropel sediments in the eastern Mediterranean Sea (EMS). However, the exact mechanisms regarding the freshwater sources and related changes are still debated. Here, Sr and Nd isotopes and high-resolution elemental data are used to constrain different riverine and eolian supplies to the central Mediterranean over the past 9.8 l

International audience; The stratoid granites of Madagascar are sheet-like granite sills emplaced conformably to the schistosity of the Antananarivo and Ikalamavony domains of the Precambrian basement. Most of them are fine-grained rocks with A-type affinities. They belong to two different plutonic suites: the Kiangara Suite north of Antananarivo and the Imorona–Itsindro Suite recognized in the whole central Madagascar. Stratoid granites are everywhere characterized by the same structural pattern evidencing two deformation events. The first event (D1 characterized by foliations mildly dipping to the west and lineations trending WSW) was coeval with synkinematic magma emplacement. The second one, responsible for local reworking in ductile conditions, is regarded as the result of late Pan-African transcurrent tectonics along N–S striking shear zones. New in situ U–Pb zircon dating from both suites yields similar results evidencing two group of ages: upper intercept ages of 790–780 Ma regarded as crystallization ages, and younger ages of ca. 555 Ma corresponding to a metamorphic overprint. These new data suggest that both plutonic suites in central Madagascar were emplaced at 790–780 Ma. New Sm–Nd isotopic data from the Kiangara Suite support the existence of two granite groups. The first group has εNd(t) at −15 and is likely derived from partial melting of the late Archaean crust. The second group made of granites with a more pronounced A-type nature and comagmatic syenites has εNd(t) at −12 evidencing the contribution of mantle melts. Mafic enclaves with εNd(t) ranging from −5 to −11 encompass the Nd isotopic signature of coeval Itsindro gabbros, which are regarded as derived from a subcontinental lithospheric mantle source. The interpretation of both structural and isotopic data is consistent with crustal thinning and extension during a Cryogenian Rodinia rifting stage at 790–780 Ma, that left a major imprint in central Madagascar. Separation from a conjugage margin represented by the North China craton is suggested. The Pan-African influence is limited to reheating, tectonic reworking and fluid transfer in the vicinity of late-Neoproterozoic (∼550 Ma) shear zones.

A. Westin and M.C. Campos Neto acknowledge support from São Paulo Research Foundation (FAPESP) through grants 2011/13311-9, 2013/13530-8 and 2013/19095-1. A. Westin is a grant holder at FAPESP and M. C. Campos Neto is a CNPq researcher. P. A. Cawood, C. J. Hawkesworth and H. Delavault acknowledge support from Natural Environment Research Council grant NE/J021822/1. Early Proterozoic sedimentary basins are an important record of crust generation processes and consequently a fundamental key to unravelling Earth's evolution through geological time. Sediments within the basins are typically deformed and metamorphosed by subsequent tectonothermal events, which can obliterate their links to source terranes. Nd-whole-rock and detrital zircon U-Pb and Lu-Hf isotopic analyses are among the most reliable tools to be used in provenance investigations, since zircon is a resilient mineral and the Sm-Nd system is not extensively modified during metamorphism. These methods have been applied to a study of the provenance and tectonic setting of the São Vicente Complex, preserved in a Neoproterozoic passive margin related allochthon within the Southern Brasilia Orogen. The complex consists of siliciclastic and calc-silicate gneisses with mafic and minor ultramafic rocks, which were deformed and metamorphosed during late Neoproterozoic collision between the Paranapanema Block and the São Francisco-Congo plate. Detrital zircons indicate derivation from a juvenile Paleoproterozoic source terrane (peaks of crystallisation ages of ca. 2130 Ma, 2140 Ma and 2170 Ma; ɛHft between +0.1 and +6.0; NdTDM = 2.31-2.21 Ga; ɛNdt = +1.6 to +2.8), with a minor contribution from older continental crust. Interlayered amphibolite rocks, with juvenile signatures (ɛHft = +5.8 to +8.2; NdTDM = 2.14 and 2.30 Ga; ɛNdt = +2.2 and +3.2), yielded similar ages of 2136 ± 17 and 2143 ± 14 Ma, suggesting syn-sedimentary magmatism. Thus, the maximum age of deposition at around 2130 Ma represents the best estimate of the depositional age of the complex. The dominance of detrital zircons ages close to the age of deposition, along with syn-sedimentary magmatism, imply a convergent margin basin tectonic environment for the São Vicente Complex, with similarities to fore arc basin and trench deposits. Amphibolite and meta-sedimentary rocks point to important juvenile magmatism around 2.14 Ga. Juvenile Rhyacian (ca. 2.1 Ga) granite-granodiorite-tonalite orthogneisses with arc-related geochemical signatures (Pouso Alegre Complex) that override the São Vicente Complex, are the probable main source of detritus within the complex. Both basin and source were part of the southern edge of the São Francisco plate during the assembly of West Gondwana, and served as sources for early Neoproterozoic passive margin related basins. The age of intrusive anorogenic A-type Taguar granite indicates that by 1.7 Ga the São Vicente Complex was in a stable tectonic environment. Postprint

International audience; In the Sudetes, northeastern Bohemian Massif, three groups of (meta-)granitoids occur: 1) Cadomian orthogneisses, with a protolith c. 600-540 Ma old, 2) Early Ordovician (~500 Ma) orthogneisses, and finally 3) Variscan (~300 Ma) granitoids. The three groups exist together in the Karkonosze-Izera Massif in the West Sudetes and in the Strzelin Massif in the East Sudetes.In the Strzelin Massif, the ~600 Ma old granitoids belong to the Strzelin Complex ascribed to the Brunovistulian microcontinent, whereas the ~500 Ma orthogneisses are part of the allochtonous Stachów Complex, correlated with the Saxo-Thuringian Zone. During the Variscan Orogeny, the Stachów Complex was thrust onto the Strzelin Complex. Subsequently, both complexes were intruded by Variscan granitoids.Trace-element data support the crustal affinity of the three generations of granitoids but they do not provide evidence for their mutual relationships. Neodymium isotope data suggest that, while the 600 Ma orthogneisses were produced from ancient, purely crustal source materials, the genesis of the Ordovician metagranites involved protoliths that were isotopically less mature. Finally, Variscan granitoids required a significant contribution of juvenile (mantle-derived) components.The general increase of initial εNd values with decreasing age is reflected by the younging average crustal residence ages of the source materials to each particular group of granitoids in the Strzelin Massif. Although they are allochtonous in the massif, the 500 Ma gneisses fit very well to the scheme: the younger granites, the less negative values of the εNdi.The zircon inherited-core ages suggest that the protoliths of the 600 Ma and 500 Ma gneisses originated from different sources derived from Avalonia- and Armorica-type terranes, respectively.

The Gawler Craton forms the bulk of the South Australian Craton and occupies a pivotal location that links rock systems in Antarctica to those in northern Australia. The western Gawler Craton is a virtually unexposed region where the timing of basin development and metamorphism is largely unknown, making the region ambiguous in the context of models seeking to reconstruct the Australian Proterozoic. Detrital zircon data from metasedimentary rocks in the central Fowler Domain in the western Gawler Craton provide maximum depositional ages between 1760 and 1700 Ma, with rare older detrital components ranging in age up to 3130 Ma. In the bulk of samples, εNd(1700 Ma) values range between −4.3 and −3.8. The combination of these data suggest on average, comparatively evolved but age-restricted source regions. Lu–Hf isotopic data from the ca 1700 Ma aged zircons provide a wide range of values (εHf(1700 Ma) +6 to −6). Monazite U–Pb data from granulite-grade metasedimentary rocks yield metamorphic ages of 1690–1670 Ma. This range overlaps with and extends the timing of the widespread Kimban Orogeny in the Gawler Craton, and provides minimum depositional age constraints, indicating that basin development immediately preceded medium to high grade metamorphism. The timing of Paleoproterozoic basin development and metamorphism in the western Gawler Craton coincides with that in the northern and eastern Gawler Craton, and also in the adjacent Curnamona Province, suggesting protoliths to the rocks within the Fowler Domain may have originally formed part of a large ca 1760–1700 Ma basin system in the southern Australian Proterozoic. Provenance characteristics between these basins are remarkably similar and point to the Arunta Region in the North Australian Craton as a potential source. In this context there is little support for tectonic reconstruction models that: (1) suggest components of the Gawler Craton accreted together at different stages in the interval ca 1760–1680 Ma; and (2) that the North Australian Craton and the southern Australian Proterozoic were separate continental fragments between 1760 and 1700 Ma. Refereed/Peer-reviewed

The 618 Ma Curral de Cima tonalite and 577 Ma Lourenco monzodiorite, northeastern Brazil, are magmatic epidote-bearing plutons that carry ferrohornblende, biotite, titanite, and epidote. Major, trace, and isotope chemistry suggests that the major magmas of the two plutons followed similar differentiation trends but derived from source rocks that differed in age and isotopic composition. The mineral phases of the Curral de Cima tonalite, the presence of amphibole-rich clots, and juvenile component (average eNd = −3.55) point to an I-type source for these rocks. These data and high calculated δ 18 O(w.r.) (10.0‰) for the tonalite and high δ 18 O value for a clot (9.3‰) argue that the clots are fragments of a metabasaltic source rock that has been hydrothermally altered at a low temperature. In contrast, average calculated δ 18 O(w.r.) for the Lourenco monzodiorite = 7.8‰, 87 Sr/ 86 Sr = 0.7083, eNd = −14.6, and T DM = 1.92 Ga. These data are compatible with a long crustal residence time of lower crust amphibolites source. Epidote in the Curral de Cima pluton crystallized close to the NNO buffer, and hornblende chemistry, due to Al reequilibration, yielded sub-solidus temperature and pressure. In contrast, in the Lourenco pluton epidote crystallized close to the HM buffer and Al-in-hornblende points to near-solidus solidification (685 °C) around 4.4 Kbar. This study confirms that magmatic epidote in granitic plutons can crystallize at pressures lower than 5.5 Kbar under higher f O 2 as experimentally foreseen. Rapid magma transportation through hot continental crust during the peak of metamorphism in early stages of an orogenic cycle prevents epidote dissolution.

Devonian-Carboniferous granites are widespread in Tasmania. In eastern Tasmania, Devonian granites intrude Ordovician-Early Devonian quartz-rich turbidites of the Mathinna Supergroup. The earliest (*400 Ma) I-type granodiorites may be arc-related. Following the Tabberabberan Orogeny (*389 Ma), more felsic and, finally, strongly fractionated I- and S-type granites were emplaced until *373 Ma. In contrast, western Tasmania granites intrude a more diverse terrane of predominantly marine shelf successions, with depositional ages as old as Late Mesoproterozoic. They are mostly felsic and fractionated I- and S-types emplaced from *374-351 Ma, possibly in response to post-collisional crustal extension following juxtaposition of the eastern and western Tasmanian terranes. Granites from the two terranes are readily distinguishable by the age spectra of their inherited zircon, which are noticeably similar to those of the detrital zircon from sedimentary successions in their respective terranes. Furthermore, within each terrane, both I and S-types yield similar inheritance patterns. This suggests a pivotal role for the sedimentary successions in the petrogenesis of both types. Western Tasmanian granites are also enriched in *1600 Ma zircon, which is essentially unrepresented in the exposed supracrustal succession. Subtle differences between the inheritance and detrital age spectra in eastern Tasmania probably relate to unrepresentative sampling of the supracrustal rocks. Nd, Sr and Pb isotopic characteristics of the granites are consistent with their derivation by mixing of magmas derived from the mantle, possibly the lower crust, and from supracrustal rocks. Systematic isotopic trends in some eastern Tasmanian I-types, particularly in the Scottsdale Batholith, correlate well with major and trace element geochemistry and age. The isotopes are inconsistent with simple restite unmixing or crystal fractionation in a closed magma chamber, and indicate progressive contamination by the Mathinna Supergroup, or similar rocks. The isotopic characteristics of late, strongly fractionated granites, although sometimes obscured by hydrothermal alteration, are also consistent with concurrent assimilation-fractional crystallisation processes. Together with the close association of some strongly fractionated I- and S-types, this suggests that such granites were generated directly in the lower crust, and were not derived from unfractionated parental granite magmas.

The 1690–1670 Ma felsic Tunkillia Suite was generated through the central Gawler Craton, southern Australia, during or after the waning stages of the 1730–1690 Ma Kimban Orogeny. Previous models for the generation of the Tunkillia Suite used trace element tectonic discrimination diagrams to suggest a subduction-related petrogenesis. Subsequently, Tunkillia Suite magmatism was used to infer an active plate margin in paleotectonic reconstruction models. In part, this led to the suggestion of a long-lived active margin on the southern edge of paleo-Australia that was correlated with the long-lived active margin of south-western Laurentia. The more detailed geochemical and isotopic analyses used in this study highlight the shortcomings of analysis based upon simple application of trace-element tectonic discrimination diagrams. The combination of detailed geochemical assessment and new geochronology demonstrates that some intrusions previously used to characterise the tectonic setting of the Tunkillia Suite are in fact unrelated. Tunkillia Suite intrusions are typically high-K, alkali-calcic and magnesian and are dominantly felsic (>70 wt% SiO2), moderately peraluminous granitoids. Trace and rare earth element abundances display large variations. Sr and Y concentrations range from 40 to 550 ppm and from 4.7 to 41 ppm, respectively. Eu/Eu* values range from 0.2 to 1.6 and combined with REE patterns demonstrate the varying composition of restite associated with melt generation of the Tunkillia Suite. The majority of the Tunkillia Suite display chemical characteristics typical of a plagioclase- or hornblende-dominated restite with only three samples demonstrating garnet-rich restite composition. Nd-isotope characteristics of Tunkillia Suite intrusions suggest a crustal column of variable age exists in the Gawler Craton, as variation in ɛNd(T) values (−6.3 to +2.6) cannot be accounted for simply through assimilation and fractional crystallisation processes. The limited SiO2 compositional range of the Tunkillia Suite inhibits unequivocal tectonic classification due to the inability to determine mantle melt composition and infer mantle melting conditions leading to the generation of the Tunkillia Suite. Geochemical, isotopic and mineralogical characteristics of the Tunkillia Suite are most consistent with a ‘late- to post-tectonic’ setting for petrogenesis. The term ‘late- to post-tectonic’ is used in this instance as a genetic descriptor based upon the comparison with Phanerozoic granitoid suites formed in such a setting after collisional orogenesis. Contrary to the suggestion of previous studies, a subduction-related arc setting is not readily reconcilable with the chemical and mineralogical characteristics of the Tunkillia Suite. Refereed/Peer-reviewed

Dust deposition provides rock-derived nutrients such as phosphorus (P) to terrestrial ecosystems. Over pedogenic timescales, as bedrock sources of P are depleted, dust sources of P may support productivity in certain ecosystems, but controls on the spatial variability of dust in montane forested systems are largely unknown. Here, we use neodymium (Nd) isotope ratios in 31 ridgetop surface soils to evaluate the spatial variability of dust contributions to soil across ~ 100 km 2 in the Luquillo Mountains, Puerto Rico. Dust from the Sahara–Sahel region of Africa carries a distinct isotopic signature of − 12 e Nd . Local bedrock, in contrast, has a e Nd value of ~+ 7. End-member mixing calculations based on e Nd reveal a wide range in dust influence on surface soils, with between 0% and 92% of the top 20 cm of ridgetop soil Nd derived from African dust. Using e Nd paired with both dust and soil Nd content, the current soil dust content was calculated, ranging from 0 to 8%. There were no correlations between current dust content of soil and 10 Be-based denudation rate, elevation, rainfall, longitude, or forest type. Current soil dust content in the Luquillo Mountains is significantly higher in soils developed on volcaniclastic sandstone, breccia and mudstone than in soils developed on quartz diorite bedrock, which we attribute to greater retention capacity in the volcaniclastic soils. Current soil dust content also increases with increasing ridge-width, implying that small-scale topographic effects and other factors such as wind speed and turbulence influence local dust deposition rates. Higher current dust content of soil is also positively correlated with biologically cycled fractions of soil P on quartz diorite bedrock (r 2 = 0.24 and p = 0.002 for sum of extractable NaHCO 3 -P + NaOH-P), suggesting that atmospheric dust inputs contribute to the fertility of Luquillo Mountain ecosystems on the relatively P-poor quartz diorite bedrock.

International audience; A high-resolution peat record from Eastern Belgium reveals the chronology of dust deposition for the last 2500 years. REE and lithogenic elements in addition to Nd and Pb isotopes were measured in a 173 cm age-dated peat profile and provide a continuous chronology of dust source and intensity. Calculated dust flux show pronounced increases c. 300 BC, 600 AD,1000 AD, 1200 AD and from 1700 AD, corresponding to local and regional human activities combined with climate change. The Industrial Revolution samples (1700-1950 AD) are characterised by a significant enrichment in Sc-normalised REE abundance (sum REE/Sc > 25) due to intensive coal combustion. For the pre-Industrial Revolution samples, the Sc-normalised REE abundance (10 < Sum REE/Sc < 25) and the eNd variability (-13 to -9) are interpreted by a mixing between dust particles from local soils and long-range transport of desert particles. Three periods characterised by dominant-distal sources (c. 320 AD, 1000 AD and 1700 AD) are consistent with local wetter-than-average intervals as indicated by a lower degree of peat humification. Local erosion prevails during the drier (higher humification) intervals (100 AD,600 AD). On a global scale, more distal supplies are driven during colder periods, in particular during the Oort and Maunder minima, suggesting a potential link between dust deposition and global climate. Combining REE abundance, fractionation between Light REE and Heavy REE and Nd isotope data in ombrotrophic peat allows one to distinguish between dust flux changes related to human and climate forcings.

International audience; The relationship between law-grade metasedimentary and high-grade paragneissic Precambrian rock units in the Bras d'Or terrane of central Cape Breton Island is a long-standing geological problem. Whole­ rock geochemical and Nd isotopie data from representative components of these units in the Kellys Mountain area, the Glen Tosh formation and Kellys Mountain Gneiss, show strong similarity. Major and trace element characteristics suggest that protolith sediments for both units were wackes derived from felsic igneous sources and deposited at an active continental margin. Samarium-Nd isotopie data in combination with previously published detrital zircon ages show that the sediments contained an ancient (ca. 2 Ga) end-member of recycled continental crust mixed with a juvenile component of Late Neoproterozoic age. The similarities suggest that the rocks represent the same sedimentary unit at different grades of metamorphism, implying a major crustal break under the area of mixed dioritic and granitic rocks that separates the gneissic and lower grade rocks.

International audience; Metamorphosed during the Variscan orogeny, sediments of the ca. 560 Ma Młynowiec Formation and ca. 530 Ma Stronie Formation in the Bystrzyckie and Orlickie Mountains (Central Sudetes, Poland) contain metabasites with a range of basaltic compositions. Immobile trace element and Nd isotope features allow distinction of dominant, either E-MORB-like (Group 1: Zr/Nb 9-20, εNd530 +2.6 to +6.7) or mildly enriched N-MORB-like tholeiites (Group 2: Zr/Nb 21-27, εNd530 +0.2 to +6.7), and scarce but genetically important OIB-like alkaline (Group 3: Zr/Nb 5, εNd530 +2.2) or depleted tholeiitic rocks (Group 4: Zr/Nb 67, εNd530 +7.9). Neither the radiogenic age nor age relationships between these four groups are known. However, field evidence suggests that the metabasites are younger than the Młynowiec Formation and that their emplacement must have been coeval with the accumulation of the Stronie Formation sediments. The OIB affinity of Group 3 is interpreted to reflect an enriched mantle (EM)-type asthenopheric source whilst the groups of tholeiitic rocks indicate involvement of depleted (locally slightly residual) MORB-type mantle (DMM). Several geochemical signatures, the decoupling between Nd isotope and trace element characteristics, and melting models indicate variable enrichment of the DMM-like source, here ascribed to asthenosphere-derived OIB-like melts (Group 1 and 2) and a contribution from a supra-subduction zone (Group 2 and 4). Based on contrasting back-arc basin (BAB)- and within-plate-like affinities of the metabasites, and on petrogenetic constraints from the spatially related infill of the Stronie Formation rift basin, the studied magmatic episode is suggested be related to cessation of the supra-subduction zone activity, presumably induced by ridge-trench collision. This event might have led to slab break-off, the development of a transform plate boundary, opening of a slab window and upward migration of sub-slab enriched asthenosphere. Decompression melting of the upwelling asthenosphere could then have produced OIB-like melts which segregated and infiltrated into the mantle of the former subduction zone, with randomly distributed slab-derived components. In an extensional regime, magmas generated at shallow levels from heterogeneous mantle regions were emplaced within sedimentary rocks of the overlying rift basin. The vestiges of subduction-related processes and within-plate style of mantle enrichment suggest that the metabasites could be related to final stages of the Cadomian orogeny and incipient Early Palaeozoic rifting of Gondwana that heralded the opening of the Rheic Ocean.

International audience; We present SIMSU-Pbzircon ages andNdisotope data for the felsic volcanic rocks from seven Neoarchean greenstone belts of the Eastern Dharwar craton (EDC) and from the Chitradurga greenstone belt in the Western Dharwar craton (WDC). Zircon ages show bimodal age distribution of felsic volcanism. The ca. 2.70-2.65 Ga felsic volcanic event is contemporaneous with 2.7 Ga mafic greenstone volcanism and emplacement of juvenile tonalitic to granodioritic crust, while 2.58-2.54 Ga felsic volcanics are coeval and spatially (and probably genetically in some cases) linked to the major episode calc-alkaline magmatic accretion in the EDC. The Chitradurga and Veligallu greenstone belts host felsic volcanics of the first generation, the latter showing inheritance at ca. 2.95 Ga. Four of the five greenstone belts hosting the second generation of felsic volcanics (Chitradurga, Kolar, Kadiri, Hutti) show crustal inheritance at ca. 2.6, 2.7, 2.9, 3.0, 3.1 and 3.3 Ga. åNdt indicate derivation of the felsic volcanics from juvenile sources or short-lived crustal sources with minor influence of older crust. The new and existing data are consistent with two-stage growth of the Dharwar craton in the Neoarchean. First-stage accretion led to the growth of a 2.7-2.6 Ga juvenile crustal province of mafic volcanics and felsic plutons along the eastern margin of the WDC. Second-stage accretion (2.58-2.52 Ga) led to the emplacement of TTG and calc-alkaline plutons and felsic volcanics throughout the Eastern Dharwar craton. An active margin context could apply for the two-stage accretion scenario considering a west-dipping subducting slab beneath the craton in the framework of long-lived ultra-hot accretionary orogen. But the great width of influence of magmatic accretion and/or reworking, particularly during the second stage, would suggest large-scale mantle flow reorganization that would have generated large plume(s).

In this study, we compare the major- and trace-element compositions of olivine, garnet, and clinopyroxene that occur as single crystals (142 grains), with those derived from xenoliths (51 samples) from six kimberlites in the Lucapa area, northeastern Angola: Tchiuzo, Anomaly 116, Catoca, Alto Cuilo-4, Alto Cuilo-63 and Cucumbi-79. The samples were analyzed using electron probe microanalysis (EPMA) and laser-ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS). The results suggest different paragenetic associations for these kimberlites in the Lucapa area. Compositional overlap in some of the macrocryst and mantle xenolith samples indicates a xenocrystic origin for some of those macrocrysts. The presence of mantle xenocrysts suggests the possibility of finding diamond. Geothermobarometric calculations were carried out using EPMA data from xenoliths by applying the program PTEXL.XLT. Additional well calibrated single-clinopyroxene thermobarometric calculations were also applied. Results indicate the underlying mantle experienced different equilibration conditions. Subsequent metasomatic enrichment events also support a hypothesis of different sources for the kimberlites. These findings contribute to a better understanding of the petrogenetic evolution of the kimberlites in northeastern Angola and have important implications for diamond exploration. Fil: Robles Cruz, Sandra E.. Universidad de Barcelona; España Fil: Melgarejo, Joan Carles. Universidad de Barcelona; España Fil: Galí, Salvador. Universidad de Barcelona; España Fil: Escayola, Monica Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina

International audience; We present the first combined Sm-146.147-Nd-142,Nd-143 and Lu-176-Hf-176 study of mafic rocks (amphibolites) from the western part of the Isua Supracrustal Belt (ISB, SW Greenland). Sm-Nd and Lu-Hf whole-rock isochrons yield identical ages within error: 3.72 +/- 0.08 and 3.67 +/- 0.07 Ga, respectively. Nd-142 measurements confirm and extend the database of Nd-142 excesses in Isua samples (mu Nd-142 = 7-16 ppm relative to the terrestrial Nd standard), indicating that early-differentiated reservoirs escaped complete homogenization by mantle convection until the Archean. Combined Sm-146,Sm-147-Nd-142,Nd-143 systematics suggest differentiation of the Isua amphibolite reservoir at maximum ages of similar to 4.53, similar to 4.47, and similar to 4.32 Ga. These ages are relative to, respectively, ordinary-chondritic, enstatite-chondritic, and higher-than-chondritic mantle compositions. The intercept of the Sm-Nd whole-rock isochron is in accordance with Nd-142 results and consistent with a superchondritic initial Nd-143/Nd-144 ratio (epsilon Nd-143(3.7Ga) = +1.41 +/- 0.98). In contrast, the corresponding initial epsilon Hf-176(3.7Ga) = -1.41 +/- 0.57 is subchondritic. Since Lu/Hf and Sm/Nd fractionate similarly during mantle processes, the Sm-Nd and Lu-Hf isotope systems display incongruent relative parent-daughter behavior in the source of Isua amphibolites. Based on high-pressure and -temperature phase partition coefficients, we propose a model that satisfies Sm-147-Nd-143, Lu-176-Hf-176, and Nd-142 results, as well as trace element characteristics. A deep-seated source composed largely of magnesium perovskite (98% MgPv) and containing 2% calcium perovskite satisfactorily explains the Nd and Hf isotopic discordance observed for Isua amphibolites. The negative HFSE anomalies characterizing Isua basalts likewise could have been inherited from such an early (4.53-4.32 Ga) deep mantle cumulate. Since the similar to 4 Ga old Acasta Gneisses (Northwest Territories, Canada) have radiogenic Hf-176/Hf-177 (Scherer et al., 2010), dissociation of the Lu-Hf and Sm-Nd isotope systems may not be a ubiquitous feature of the Hadean mantle, but rather reflects that a deep-seated source was involved in the formation of ISB lavas

International audience; This work provides five new U-Pb zircon dating and the corresponding Nd isotope data for felsic granulites from the south Itabuna-Salvador-Curaçá Block (ISCB), in the São Francisco Craton, Brazil. Three major sets of felsic granulites can be recognised. The oldest set is tonalitic in composition and of TTG affinity. It is Archaean in age with magmatic zircon cores dated at 2675 ± 11 Ma by LA-ICPMS and up to ca 2.7-2.9 Ga by SHRIMP on an other sample. It exhibits epsilon Nd values between −8 and −11 at 2.1 Ga. This Nd signature is similar to that of granulites found in the western Archaean Jequié Block. Cartographically, this set of Archaean terrains represents at least 50% of the granulites in the studied area. The second set corresponds to a Palaeoproterozoic calc-alkaline tonalitic suite with zircon ages from 2019 ± 19 Ma to 2191 ± 10 Ma and epsilon Nd values between −3 and −4 at 2.1 Ga, corresponding partially to a newly formed crust. The third set of granulites is also Palaeoproterozoic. It is shoshonitic to monzonitic in composition and synchronous with the high grade metamorphism dated by metamorphic zircons at 2086 ± 7 Ma (average of five samples). The Nd isotope signature for this alkaline set is similar to that of the Palaeoproterozoic calc-alkaline one. Nd isotopes appear to be a very efficient tool to distinguish Archaean from Palaeoproterozoic felsic protoliths in granulitic suites of the Itabuna-Salvador-Curaçá Block (ISCB). Finally, the southern part of the ISCB is composed of a mixture of Archaean and Palaeoproterozoic protoliths, in similar amounts, suggesting that it was probably an active margin between 2.1 and 2.2 Ga located on the eastern border of the Archaean Jequié Block. A major crustal thickening process occurred at ca 2.09 Ga in the ISCB and seems significantly younger towards the west, in the Jequié granulites, where an average of 2056 ± 9 Ma is determined for the high grade event.

The Tamazert Eocene alkaline complex of the Central High Atlas Range of Morocco hosts the largest outcropping occurrences of carbonatites in northern Africa. The complex consists of carbonatites and undersaturated ultramafic to syenitic alkaline to peralkaline silicate rocks. Mineralogically and geochemically the Tamazert carbonatites are classified as calciocarbonatites, magnesiocarbonatites and silicocarbonatites. They are enriched in light rare earth elements and large ion lithophile elements (Cs, Rb, Ba, U, Th), but depleted in high field strength elements (particularly, Ti, Nb and Ta). Stable and radiogenic isotope ratios vary in the range of delta C-13(PDB) = -5 center dot 8 to 1 center dot 8 parts per thousand, delta O-18(SMOW) = 6 center dot 9-23 center dot 5 parts per thousand, initial Sr-87/Sr-86 = 0 center dot 7031-0 center dot 7076, Nd-143/Nd-144 = 0 center dot 5125-0 center dot 5129 and Pb-206/Pb-204 = 18 center dot 29-19 center dot 89. Calciocarbonatites intruding Jurassic limestones have the highest delta C-13 and delta O-18 values and the most radiogenic initial Sr-87/Sr-86, but least radiogenic Nd-143/Nd-144, Pb-206/Pb-204 and Pb-208/Pb-204 isotope ratios, and are interpreted to have interacted with the limestones (crustal components). The magnesio- and silicocarbonatites have Sr, Nd and Pb isotope ratios that are nearly identical to those of low-Sr-87/Sr-86 calciocarbonatites. The isotope signature of the high-Sr, low-Sr-87/Sr-86 calciocarbonatites with mantle-type O and C isotopic compositions indicates the presence of HIMU- and EMI-type components in the mantle source of the Tamazert carbonatites, similar to what has been proposed for the Cape Verde and Canary Islands. The close similarity in carbonatite composition between the Cape Verde and Canary Islands and Tamazert suggests a common sublithospheric source for these carbonatites. We therefore propose that the Tamazert carbonatites originated through melting of Canary plume material that may have flowed through a sub-lithospheric corridor extending from the Atlantic near the Canary Islands to the Middle Atlas, formed by the delamination of the subcontinental lithosphere in response to Africa-Europe collision at c. 42 Ma. Seismic tomography data suggest that the common source may be within the lower mantle at depths > 1000 km.

Nd isotope and geochemical data are presented for biotite tonalite, hornblende tonalite, hornblende granodiorite, biotite granite and peraluminous granite from the Archean Berens River subprovince of the Superior province in northwestern Ontario, Canada. The older tonalitic suites were synchronous with greenstone belt volcanism and were followed by granodioritic and granitic intrusions. The suites vary from 57 to 74% SiO 2 , are light rare-earth element (REE) enriched, with variable Eu and Nb anomalies and heavy REE depletion among the tonalites. The Nd isotope compositions for the granitoids vary from depleted values of ɛ Nd = +1.5 (tonalites) to enriched values of −1.5 (peraluminous granite). The range of isotopic composition supports a model where the granitoids were emplaced into, contaminated by, and locally melted an older pre-existing Archean crust (ca. 3.0 Ga). The Nd isotope compositions of the granites and the tonalites decrease towards the north (increased crustal contamination) away from the greenstone belts that form the southern margin. This implies a thickening of the crust towards the north and is consistent with an Andean-style convergent margin in which oceanic crust subducted northwards beneath an older Archean crustal plate. Crustal contamination increased heavy REE contents in the tonalites and decreased the Sr/Y ratios for all granitoids. Failure to account for this crustal contamination can lead to errors in estimating the degree of partial melting based on the Sr/Y ratio. Compositional differences between the biotite tonalites and hornblende tonalites likely reflect different degrees of partial melting of a garnet-bearing amphibolite source.