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Ages radiométriques de quelques granites des Vosges moyennes
... Apatite data in the literature exhibit a high variance of element concentration and Sr isotope ratios that renders a clear interpretation difficult (Bonhomme, 1967;Van Gaans et al., 1995;Sun and Higgins, 1996;Tilton et al., 1997;Charoy, 1999;Sha and Chappell, 1999;Négrel et al., 2001). However, the apatite leachates analysed by Irber (1996) could be regarded as a missing endmember for the deep groundwater samples (Figs. 4, 6 and 8). ...
... These samples were taken from granite in the Ore Mountains, but of the same age as the Lehstenbach catchment granite. The low Sr isotope ratio of 0.711416 is comparable with the value of 0.709 given by Bonhomme (1967) for the Brézouard granite apatite in the Vosges mountains (France) and of 0.70679 by Négrel et al. (2001) for the Monzogranite apatite in the Vienne District (west of the french Massif Central). All these rocks are about the same age between 288 and 315 Ma. ...
From a biogeochemical perspective, catchments can be regarded as reactors that transform the input of various substances via precipitation, deposition, or human activities as they pass through soils and aquifers towards receiving streams. Understanding and modeling the variability of solute concentration in catchment waters require the identification of prevailing processes, determining their respective contributions to the observed transformation of substances, their interplay with hydrological processes, and the determination of anthropogenic impacts. However, numerous biogeochemical processes often interact in a highly non-linear way and vary on temporal and spatial scales, resulting in temporally and spatially varying water chemistry in catchments. This is particularly true for riparian wetlands. Processes in this catchment area often superimpose the influence of the hill slope (and largest) area of the catchment on surface water quality. Accordingly, the first part of this thesis (Study 1 and 2), focuses on the temporal and spatial variability of biogeochemical processes at the catchment scale. Therefore, the first aim was to identify the prevailing biogeochemical processes which affect the quality of catchment waters in two forested granitic catchments. Based on these results, (i) the long-term behavior of these processes was determined (Study 1) and (ii) hot spots of these processes at the catchment scale along different flow paths were identified (Study 2). The second part (Study 3) focuses on the interplay between hydrological and biogeochemical processes in a riparian wetland, with the aim of systematically tracing back the temporal patterns of stream water chemistry to different biogeochemical processes and antecedent hydrological boundary conditions in the wetland. The third part (Study 4 and 5) focuses on weathering processes with the goal (i) of identifying the mineralogical sources of the groundwater’s buffer capacity against acid atmospheric deposition in a forested granitic catchment and (ii) determining the mineralogical sources of the high cation loads in surface water, induced by intensive agricultural activities in two agricultural granitic catchments. To reach these aims, multivariate statistical methods of dimensionality reduction (linear Principal Component Analysis, non-linear Isometric Feature Mapping), a low-pass filtering of time-series, a Cluster analysis, and major and trace element ratios and strontium isotopes were used. A small number of biogeochemical process bundles explained 94% and 89% of the variance of the data set in Study 1 and 2, respectively. In Study 1, redox and topsoil processes, road salt and sulfate contamination were identified as predominating processes influencing water chemistry in the respective catchments. Low-pass filtered time series of component scores revealed a different long-term behavior at different sampling sites in both catchments, which could be traced back to the fraction of wetland area in the respective subcatchments as well as by the varying thickness of the regolith. Study 2 revealed that the upper 1 m topsoil layer could be considered as a biogeochemical hot spot for redox processes, acid-induced podsolization, and weathering processes along different flow paths. Up to 97% of the biogeochemical transformation of the chemical composition of soil solution, groundwater and stream water in the Lehstenbach catchment was restricted to this soil layer representing less than 2% of the catchment’s regolith. Wetland stream water, mobilized in the topsoil layer being considered a biogeochemical hot spot, showed a highly dynamic temporal pattern of component scores. Study 3 revealed four different types of wetland stream water chemical status, depending on the interplay between discharge dynamics, biological activity, and the water table position in the wetland. The sequence of different stream water types roughly followed a seasonal pattern, albeit being heavily modified by the respective hydrological boundary conditions for different years. Extended periods of low groundwater level in the second half of the growing season drastically changed the chemical boundary conditions, becoming evident in a drastic reoxidation of reduced species like sulfides and corresponding effects. Weathering processes are one of the predominating biogeochemical process bundles influencing water chemistry in forested catchments. Study 4 showed that the mineralogical sources of the groundwater’s buffer capacity against acid atmospheric deposition were dominated by the release of base cations from apatite dissolution, preferential cation release from feldspars and biotite, and feldspars weathering. In Study 5, determining the mineralogical sources of the high cation loads in surface water induced by intensive agricultural activities revealed a dominant manure contribution in the topsoil, and enhanced mineral dissolution (plagioclase and biotite) by fertilizer application in subsoils, becoming the unique source of base cations in the saprolite. Stream water chemistry differed from that of soil water, suggesting that stream water chemistry was dominated by elements issued from enhanced mineral and rock weathering. Soil acidification induced by agriculture allows the mobilization of cations stored in soil layers, enhances the rock weathering and accelerates plagioclase dissolution, which can highly influence stream water quality. Numerous biogeochemical, hydrological, and anthropogenic processes were found to interact with each other, mostly with non-linear patterns, influencing catchment water chemistry. The integral approach used in this thesis would be a useful prerequisite to develop accurate and parsimonious models commonly used for water management purposes by distinguishing between short- term and long-term shifts, reducing the number of processes to the predominating ones ultimately to be included in the model, focusing on hot spots and including spatial patterns where necessary and appropriate.
... Values of elements content and 87 Sr/ 86 Sr ratios compiled from (a)Altherr et al., 1990; Bonhomme, 1967; Brenot et al., 2008; (d) English et al., 2001; (e) Faure, 1986; (f)Goede et al., 1998; Grupe et al., 2011; (h) Hodell et al., 2004; Koepnick et al., 1985; Kudo et al., 1972; Laughlin et al., 1971; (l) Probst et al., 2000; (m) Rich et al., 2012; (n) Rich et al., 2015; (o) Shaw et al., 2003; (p) Song et al., 2015; (q) Stein and Hofmann, 1992; (r) Stueber et al., 1987; (s) van der Hoven and Quade, 2002; (t) Weinstein, 2000; (u) Weinstein et al., 2006; (1) Andrews et al., 2016; (2) Bullen and Chadwick, 2016; (16) Shalev et al., 2017. Values of d 88/86 Sr (‰) compiled from (1) Andrews et al., 2016; (2) Bullen and Chadwick, 2016; (3) Chao et al., 2015; (4) Charlier et al., 2012; (5) de Souza et al., 2010; (6) Halicz et al., 2008; (7) Krabbenh€ oft et al., 2010; (8) Kramchaninov et al., 2012; (9) Ma et al., 2013; (10) Moynier et al., 2010; (11) Ohno and Hirata, 2007; (12) Ohno et al., 2008; (13) Pearce et al., 2015a; (14) Raddatz et al., 2013; (15) Rüggeberg et al., 2008; (16) Shalev et al., 2017 (17) Stevenson et al., 2014; (18) Stevenson et al., 2016; (19) Vollstaedt et al., 2014. ...
... The 87 Sr/ 86 Sr ratio of rainwater samples from different countries and range of variation of the values. Data compiled from (a) Åberg et al., 1989; (b) Aubert et al., 2002; (c) Bedel et al., 2016; (d)Gosz et al., 1983; (e)Graustein and Armstrong, 1983; (f)Herut et al., 1993; Probst et al., 2000; (h) N egrel, 1992; (i) N egrel and Roy, 1998; (j) N egrel et al., 1993; Pearce et al., 2015a; Pearce et al., 2015b;(m) Wickman, 1996. ...
Different approaches are used to study wood provenance, but most of them are based on tracers in wood that are generally controlled by climatic factors. The strontium isotopic ratio ⁸⁷Sr/⁸⁶Sr in trees and soils is related to the signature of the local bedrock. Despite being used in diverse archaeological studies, Sr isotopes have rarely been used to trace the provenance of archaeological wood and especially wood from shipwrecks. In addition, recent analytical advances have allowed the detection of mass-dependent fractionation of Sr isotopes during biogeochemical processes, as reflected in the variation of δ88/86Sr values between different environmental materials. The δ88/86Sr values could be used in conjunction with the ⁸⁷Sr/⁸⁶Sr isotope ratio to improve constraints on the sources of Sr in the archaeological materials being studied. This paper discusses the potential and limitations of using both of these Sr isotope ratios to trace the provenance of wood from shipwrecks. We review the ⁸⁷Sr/⁸⁶Sr and δ88/86Sr variations in rocks, waters, soils, plants and other living organisms and discuss how to determine the local Sr isotopic signature of potential sites. We also compile a list of known wood post mortem modifications in seawater. Possible implications in terms of the modification of the original Sr isotope ratios of wood during storage in seawater are illustrated through preliminary observations. This paper points out some limitations and perspectives for using Sr isotopes in provenancing wood from shipwrecks, and suggests future research to test and apply this approach for tracing the origin of archaeological wood.
... In the silicate (Vosgian) part of the basin, river waters are characterized by 87 Sr/ 86 Sr ratios (0.7128–0.7249) that are intermediate between values for mean local precipitation (0.7102 and 0.7128; Probst et al., 2000; Chabaux et al., 2005) and values for mineral separates and granites from the Vosges mountains (0.71612–5.865, Bonhomme, 1967; France-Lanord, 1982; Probst et al., 2000; Aubert et al., 2001; Aubert et al., 2004). Bonhomme, 1967; Probst et al., 2000; Aubert et al., 2001) (Fig. 3). A similar correlation is observed between 87 Sr/ 86 Sr and K/Sr, which also supports the preferential weathering of other mineral phases such as K-feldspars ( 87 Sr/ 86 Sr = 0.7827–0.79 ...
... Sr/ 86 Sr ratios (0.7128–0.7249) that are intermediate between values for mean local precipitation (0.7102 and 0.7128; Probst et al., 2000; Chabaux et al., 2005) and values for mineral separates and granites from the Vosges mountains (0.71612–5.865, Bonhomme, 1967; France-Lanord, 1982; Probst et al., 2000; Aubert et al., 2001; Aubert et al., 2004). Bonhomme, 1967; Probst et al., 2000; Aubert et al., 2001) (Fig. 3). A similar correlation is observed between 87 Sr/ 86 Sr and K/Sr, which also supports the preferential weathering of other mineral phases such as K-feldspars ( 87 Sr/ 86 Sr = 0.7827–0.7975, Probst et al., 2000; Aubert et al., 2001). The range of 87 Sr/ 86 Sr shown by the silicate rivers ...
Magnesium and strontium isotope signatures were determined during different seasons for the main rivers of the Moselle basin, northeastern France. This small basin is remarkable for its well-constrained and varied lithology on a small distance scale, and this is reflected in river water Sr isotope compositions. Upstream, where the Moselle River drains silicate rocks of the Vosges mountains, waters are characterized by relatively high 87Sr/86Sr ratios (0.7128–0.7174). In contrast, downstream of the city of Epinal where the Moselle River flows through carbonates and evaporites of the Lorraine plateau, 87Sr/86Sr ratios are lower, down to 0.70824.
... Apatite data in the literature exhibit a high variance of element concentration and Sr isotope ratios that renders a clear interpretation difficult (Bonhomme, 1967; Van Gaans et al., 1995; Sun and Higgins, 1996; Tilton et al., 1997; Charoy, 1999; Sha and Chappell, 1999; Négrel et al., 2001 ). However, the apatite leachates analysed by Irber (1996) could be regarded as a missing endmember for the deep groundwater samples (Figs. 4, 6 and 8). ...
... These samples were taken from granite in the Ore Mountains, but of the same age as the Lehstenbach catchment granite. The low Sr isotope ratio of 0.711416 is comparable with the value of 0.709 given by Bonhomme (1967) for the Brézouard granite apatite in the Vosges mountains (France) and of 0.70679 by Négrel et al. (2001) for the Monzogranite apatite in the Vienne District (west of the french Massif Central). All these rocks are about the same age between 288 and 315 Ma. ...
The role of different minerals in base cation release and thus the increase of buffering capacity of groundwater against acid deposition is controversially discussed in the literature. The ⁸⁷Sr/⁸⁶Sr ratios and base cation concentration were investigated in whole rock leachates, mineral separates, precipitation, soil solution, groundwater and stream water samples in the Lehstenbach catchment (Germany) to identify the weathering sequence of the granite bedrock. Three different approaches were followed in parallel. It was assumed that the contribution of different minerals to base cation supply of the groundwater with increasing weathering intensity would be observed by investigating (1) unweathered rock leachates, deep groundwater and shallow groundwater, (2) groundwater samples from new groundwater wells, reflecting the initial weathering of the drilled bedrock, and groundwater from wells that were drilled in 1988, (3) stream water during baseflow, dominated by deep groundwater, and stream water during high flow, being predominantly shallow groundwater. Whereas the first approach yielded consistent patterns, there was some evidence that groundwater from the new wells initially reflected contamination by the filter gravel rather than cation release in an initial stage of weathering. Time series samples of stream water and groundwater solute concentrations and isotope ratios turned out to reflect varying fractions of soil water and precipitation water at baseflow and high flow conditions rather than varying contributions of different minerals that prevail at different stages of granite weathering.
... The bedrock is a base-poor leucogranite (Brézouard granite). Its Rb-Sr whole rock isochron age is 315 Ϯ 7 Ma (Bonhomme, 1967). This coarse grained granite has been affected by postintrusive hydrothermal fluids. ...
... The Sr isotope ratios of the most important rock-forming minerals of the "fresh" and hydrothermally not strongly altered Brézouard granite (HPT) define a reference line in the Sr isochron diagram whose slope corresponds to an age of 311 Ma (not shown), which is in agreement with an earlier published Rb-Sr isochron age of 315 Ϯ 7 Ma (Bonhomme, 1967). How-ever, this age dates only approximately the intrusion of the granite because some of the data points plot off the reference line, indicating that even the so-called fresh granite has already been altered. ...
Very few studies deal with REE (rare earth element) mobility within the system soil–soil solution–streamwater. In this article, we try to characterize the fractionation and the migration of the REE in a granite-derived soil system located in a small catchment of the Vosges mountains. ICP-MS and TIMS measurements were performed on both solid samples (“fresh” granite, soil, and suspended load of the stream) and waters (soil solutions, springwater, and streamwater) to determine their respective REE concentrations and Sr and Nd isotopic compositions. The PAAS-normalized REE pattern of the bedrock is characterized by a strong depletion in HREE (heavy REE) and a negative Eu anomaly (0.46). Similarly, the granite-normalized REE distribution patterns of the soil samples show HREE depletions that become more important with decreasing depth. The correlative behavior between P2O5, Th, and REE with depth indicates that, besides apatite, other phosphate minerals such as monazite are the most important phases controlling the Th and REE budget in the soil profile. On the other hand, at greater depth, zircon seems to be another important mineral phase controlling especially the HREE enrichment as shown by the positive relationship between Zr content and the Yb/Ho ratio. Different grain size fractions show similar REE distribution patterns and are only weakly fractionated, compared with bulk soil sample. However, the finest fraction (0–20 μm) is more enriched in Sr and REE, suggesting a stronger concentration of REE-carrying minerals in this fraction. The suspended and dissolved load of the stream show as a whole an enrichment in HREE if compared with the granite or with the different soil samples. However, compared with the uppermost soil samples, the suspended load is significantly more enriched in HREE. Its REE distribution pattern is more similar to that of the finest fraction of the deeper soil sample and to the “fresh” granite. Thus, most probably the REE of the suspended load originated from a source with REE characteristics found in the deep soil horizons. This source might have been situated in the uppermost soil profile, which is actually REE depleted. The weathering process can be compared with a leaching experiment where the waters correspond to the leachate and the soil to the residual phase of the granite. The Sr isotope data indicate that the suspended load originates from the finest soil fraction. The Sr and Nd isotopic data of the suspended load suggest that it contains up to 3% Sr and Nd from apatite and up to 97% from feldspar. Most of the Sr and Nd in the waters originate from apatite leaching or dissolution.
... The main bedrock of the catchment is a Hercynian base-poor granite (cordieritic granite) with low Ca and Mg contents (Bonhomme, 1967). The summit of the north slope is composed of gneiss bodies enriched in Mg due to the presence of biotite and chlorite Fichter et al., 1998b). ...
Les forêts sont soumises à de nombreuses perturbations naturelles et/ou anthropiques, à court et à long terme. Une meilleure compréhension des interactions sol/eau/plante et des réponses des écosystèmes aux modifications devient de plus en plus cruciale pour une meilleure gestion des ressources naturelles et renouvelables. Dans un environnement granitique, comme dans les Vosges (NE de la France), le déclin des forêts peut être lié au lessivage des nutriments du sol par les pluies acides et par les processus naturels d’acidification des sols qui peuvent être plus importants avec des résineux qu’avec des feuillus. L’acidification peut modifier la disponibilité des nutriments dans le sol et l'équilibre entre les différents réservoirs de nutriments.Avec cette étude, nous développons une approche expérimentale afin de reproduire et d'analyser en laboratoire le lessivage des sols à plus petite échelle. Les résultats montrent un comportement chimique très variable selon l'élément, le type de sol, les horizons et le type d'acide. De plus, nous avons observé des résultats inattendus pour le calcium : la quantité totale de Ca extraite après 150 jours correspond à une très faible proportion du calcium échangeable obtenu avec la cobaltihexamine, soulignant une biodisponibilité complexe de ce nutriment dans le sol.
... The main bedrock of the catchment is a Hercynian base-poor granite (cordieritic granite) with low Ca and Mg contents (Bonhomme, 1967). The granite on the northern slope is more hydrothermally altered than that on the southern slope (El Gh'Mari, 1995). ...
The global demand for wood is growing and the sustainability of forests has become an increasingly important issue. The first metre of soil represents the reserve of nutrients cations (K, Ca, Mg) for trees. The depletion of these elements in the soil gradually leads to a decrease in soil fertility, which can have a strong impact on the development and health of forests.
The aim of this study was to better understand the source and dynamics of nutrients in forested soils from a base poor environment by combining mineralogic, chemical, isotopic and numerical tools through an experimental approach. We designed batch experiments to follow the leaching of soils from two experimental plots (under spruce and under beech from the Strengbach catchment, Vosges Mountain, NE France). The studied elements show highly contrasting behaviours. Mg release results from a mixing between cationic exchange, mineral dissolution (mainly smectite) and organic matter mineralization. The dynamics of K are underestimated by modelling, which may be attributed either to an unknown source of K or to an overestimation of the secondary phase precipitation. The Sr isotopic approach, used as a proxy to identify the sources of Ca, shows that the exchangeable complex supplies nutrients first and rapidly to the solution, followed by the clay compartment and at the very end, the bulk soils. Na is mainly controlled by albite dissolution.
The release of Ca is significantly lower than that of other cations as Mg or K. Our results suggest that the exchangeable Ca, estimated through classical extractions, is only partly available for plants, due to strong chemical binding with organic matter and/or the occurrence of Ca-chemical bridges between clay and organic matter. Sustainable management should thus consider that exchangeable Ca, conventionally determined, does not necessarily provide an accurate picture of the real availability of Ca and therefore of the fertility of soils, with a risk of overestimation of nutrient reservoir for trees. Calcium tree nutrition at these sites has to rely on the long term on atmospheric deposition and an efficient recycling through biological cycling. This is also true for the other nutrient cations, but to a lesser extent since soil intrinsic fluxes (i.e., weathering, mineralisation of OM…) are not null and may thus supply the exchangeable pools and participate substantially to tree nutrition. Harvesting and biomass exportation could rapidly impact the biological cycle and threaten the sustainability of these ecosystems, similar to changing tree species that may influence the nature of the litter, its turnover and the input of nutrients to the soil.
... The main bedrock of the catchment is a Hercynian base-poor granite (cordieritic granite) with low Ca and Mg contents (Bonhomme, 1967). The granite on the northern slope is more hydrothermally altered than that on the southern slope (El Gh'Mari, 1995). ...
... C'est un granite à grain très grossier, pauvre en cations basiques et de teinte claire gris-rosâtre typique d'un leucogranite. C'est un des granites intrusifs les plus récents des Vosges Moyennes (Bonhomme, 1967). L'histoire géologique de ce granite est complexe et intègre une succession d'évènements dont la datation précise reste encore mal connue. ...
Lors de ce travail de thèse, la combinaison des méthodes de la géochimie analytique et isotopique avec les approches modélisatrices a permis d’apporter de nouvelles connaissances à la compréhension de la zone critique et du régolithe. Pour l’étude du régolithe, ce travail présente une méthodologie permettant de réaliser sur un même profil d’altération les analyses de la géochimie élémentaire, de la minéralogie, ainsi que des isotopes de la série de l’uranium (U-Th-Ra) et de l’isotope cosmogénique du 10Be in situ. Les résultats obtenus montrent l’importance de la bonne résolution spatiale de l’échantillonnage pour pouvoir pleinement exploiter les outils de la série U-Th-Ra et du 10Be in situ, notamment pour déterminer d’une manière indépendante les paramètres clés que sont les taux de production et de dénudation du régolithe à long terme. Les deux profils d’altération réalisés dans cette étude montrent de plus que (1) la structure du régolithe est relativement simple sur les positions sommitales et permet une interprétation continue des données géochimiques et minéralogiques et (2) les processus de pente tendent à augmenter l’hétérogénéité spatiale du régolithe et des processus d’altération. D’une façon complémentaire, le suivi et la modélisation hydrogéochimique des eaux de surface permettent d’étudier les processus d’altération actuels, et de comprendre les mécanismes impliqués dans leurs variabilités récentes. Ce travail a notamment montré le lien pouvant exister entre les modifications enregistrées en surface dans les solutions de sol et l’évolution temporelle des certaines propriétés chimiques des eaux de source (pH, concentration en calcium). Les simulations réalisées ont également permis de comprendre la faible variabilité des flux d’altération globaux exportés par les sources, en relation avec la relative stabilité des concentrations de sodium et de silice dissoute sur la période récente allant de 1990 à 2010. Cette étude a finalement montré l’importance du couplage des méthodes apportant des informations sur les processus d’altération et d’érosion à différentes échelles de temps et d’espace, en particulier pour évaluer correctement la dynamique du régolithe et pour replacer le fonctionnement actuel d’un bassin versant vis-à-vis de son évolution à long terme.
... The Strengbach catchment bedrock is a base poor leucogranite (the Brezouard granite) aged 315 ± 7 Ma (Bonhomme, 1967). The apatite has the lowest 87 Sr/ 86 Sr ratio of the minerals from this catchment (Aubert et al., 2001) and is also the less enriched in K. ...
Calcium is the fifth most abundant element of the silicate Earth. Its interest results from its abundance in the Earth crust and from the existence of a huge quantity of minerals containing it. A maximal fractionation of 1.3 ‰ per a.m.u was recorded up to now. The work realised during the Ph-D deals with new studies on Ca isotopes.
First, a measurement protocol was developed at the Centre de Géochimie de la Surface to avoid instrumental fractionation. After chemical separation on ion exchanging resins, the Ca isotopic compositions were measured on a thermo-ionisation mass spectrometer, using a double-spike technique. The Ca isotopic ratios were expressed in a delta notation. To do this, a reference material is needed. No international standard presently exists for Ca isotopes. For that reason, we proposed to use the SRM 915a carbonaceous standard from the NIST. Seawater, the only common sample of most of previous studies has also been used: it was calibrated against the carbonaceous standard and used in present study.
This protocol was then applied to study the Ca oceanic budget. The isotope data of continental waters allowed to constrain the Ca flux to the ocean. A limited variability of δ44Ca (0.5 ‰) was recorded at the outlet of main rivers or for hydrothermal vents. Moreover, no relationship was observed between δ44Ca and the lithology or the climate of the studied watersheds. This allowed to determine the mean Ca isotopic composition of the Ca flux to the ocean (-1.1 ± 0.2 ‰) and to suggest that this value remains rather constant through time. A consequence of this value is that present-day seawater is at steady-state with regard to Ca isotopes. The δ44Ca study of marine phosphates from Miocene and Pleistocene, which reflect the paleo-seawater variations through time, has shown that this was not necessarily the case in the past. At 22 Ma, a deviation in δ44Ca through more positive values suggests that the intensity of the incoming and outcoming fluxes changed, but not their isotopic composition.
... The Sr data are measured values of the minerals from the Brezouard granite in the Strengbach catchment Data fromBlum et al. 1994 .Assigned value equal to the zero 87 Rbr 86 Sr intercept of the Ž . isochron determined on the Brezouard graniteBonhomme, 1967 . ...
This paper determines the weathering and atmospheric contributions of Ca in surface water from a small spruce forested silicate catchment (N–E France) receiving acid atmospheric inputs. The bedrock is a granite with K-feldspar and albite as dominant phases. The calcium content in plagioclase is low and the Ca/Na ratio in surface water is high, reflecting other sources of calcium from those expected from the weathering of major mineral phases. The biotite content is low. Only traces of apatite were detected while no calcite was found in spite of a major hydrothermal event having affected the granite. The strontium isotopic ratio 87Sr/86Sr and Sr content was used as a tracer of weathering and was determined in minerals and bulk bedrock, open field precipitation, throughfall, soil solution, spring and stream water. The Sr isotopic ratio of the reacting weathering end-member was predicted by simulating the alteration of the granite minerals by incorporating strontium into the water–rock interaction kinetic code KINDIS. In the early stages of water–rock interaction, K-feldspar and biotite strongly influence the isotopic composition of the weathering solution whereas, the Na-rich plagioclase appears to be the main long-term reactive weathering end-member. Approximately 50% of dissolved Sr in streamwater are atmospherically derived. The 87Sr/86Sr ratios of exchangeable Sr in the fine fraction at 1-m depth from a soil profile indicate that the amount of exchangeable Sr seems essentially controlled by atmospheric inputs. The exception is the deep saprolite where weathering processes could supply the Sr (and Ca). Na-Plagioclase weathering obviously control the chemistry and the isotopic composition of surface waters. The weathering of trace mineral plays a secondary role, the exception is for apatite when plagioclase is absent. Our hydrochemical, mineralogical and isotopic investigations show that a major part of the strong Ca losses detected in catchment hydrochemical budgets that result from the neutralization of acid precipitation has an atmospheric origin. Consequently, in the long term, in such areas, the availability of such an exchangeable base cation might be strongly limited and surface waters consequently acidified.
... The important lithological units in the source region of the investigated Vosges streams are granitic Ž rocks e.g., the Brezouard granite in the Strengbach catchment with an initial 87 Srr 86 Sr isotopic compo-. sition of 0.795; Bonhomme, 1967 . Thus, the high 87 Srr 86 Sr isotopic ratio of 0.725 at the sources of the Vosges streams is controlled by a silicate end-member. ...
The aim of this study is to characterize the evolution of the rare earth elements (REE) in non-mature streams from small catchment areas in the Vosges mountains downstream to more mature plain rivers including the river Rhine. The dissolved load REE distribution patterns of the low-pH Vosges streams are very different from those of high-pH plain rivers indicating that different physico-chemical parameters control REE transport in these different water systems. The plain rivers and groundwater show similar REE distribution patterns with a strong negative Ce anomaly and heavy rare earth element (HREE) enrichment. In addition, the river Rhine has a positive Gd anomaly which is of anthropogenic origin. Similar to the world's major rivers the light rare earth element (LREE) enrichment in the plain rivers is mainly pH controlled. Their Sm/Nd and isotope ratios are close to average continental crust values. This is not the case for the less evolved, non-mature and low pH Vosges streams. Their high Sm/Nd and ratios but low ratios suggest that chemical alteration of accessory middle rare earth element (MREE) enriched minerals such as apatites from rocks in the catchment area control the REE abundances of these waters. A comparison of the dissolved load REE distribution patterns with those of the principal lithologies in the corresponding drainage basins illustrates that especially the Eu anomalies of the Vosges streamlets are strongly lithology dependent. Leaching experiments indicate that the suspended load is isotopically very inhomogeneous. The REE distribution patterns of the suspended load leachates have no similarities with those of the corresponding dissolved load indicating that the leachable reservoir not only contains adsorbed REE but also REE from leachable mineral phases. Their , Sm/Nd and ratios support this suggestion being always higher and lower, respectively, than those of their corresponding dissolved loads. They rather point to the presence of relic primary apatite in the leachable portion of the suspended load. The flat PAAS normalized REE distribution patterns, the high and low isotopic ratios of the corresponding residues suggest secondary silicate phases such as clay minerals in the residual phase of the suspended load. Leachates and corresponding residual phases define alignments in the Sm/Nd isochron diagram whose slopes define ages ranging between 200 and 390 Ma indicating that the mineral phases in the suspended load retain some memory of their primary precursor minerals in the Hercynian granitic source rocks.
... Tributaries and springs from several regions in the Vosges mountains above the Rhine valley have especially been collected (Strengbach, Ohmbach, Lisbeth). These samples have been analysed previously using the ( 234 U/ 238 U) activity ratio and the 87 Sr/ 86 Sr isotopic composition [17,66]. Four pit water samples have also been collected in the Alsatian plain, between Colmar and Mulhouse. ...
Calcium isotope ratios relative to seawater were studied in natural waters in order to constrain the Ca isotopic flux to the oceans and to discuss the oceanic Ca budget. This study includes the analysis of (1) Ca isotopes in continental waters at the regional scale of the Upper Rhine valley and (2) the determination of the δ44Ca values of some major rivers and hydrothermal vents. The data indicate that the global δ44Ca variability of the studied waters, with a maximal range of 1‰, is limited and must be linked to mass fractionation processes. At the scale of a small watershed (Aubure, Vosges, France), the δ44Ca river flux changes due to the variation of the proportion of waters resulting from chemical alteration of rocks and biologically fractionated soil solutions. Ca isotopes could therefore be an important tool to quantify the impact of the plants and the biosphere on the river water chemistry. At the regional scale of the Rhine valley as well as at the global scale of world rivers, the δ44Ca variability of river samples ranges from 0.5 to 1‰ without any relationship with the lithology of the watershed or the climate. Similarly, the δ44Ca value of hydrothermal vents is also uniform and close to the mean value of river waters. Consequently, the δ44Ca flux to the ocean should remain rather constant through time with a mean of −1.1±0.2‰. This value confirms that the Ca budget of the present-day seawater is in steady-state. This was not necessarily the case in the past. Non-steady-state periods should have been due to intensity variations of incoming and outcoming Ca fluxes rather than to the variations in their isotopic signatures.
... The total runoff reached 853 mm for the 1986-1995 period (Probst et al., 1995a), which corresponds to a mean annual discharge of 21.7 l/s. The bedrock is a base poor leucogranite (The Bre´zouard granite) aged 315 AE7 Ma (Bonhomme, 1967). This granite is coarse-grained and has undergone hydrothermal alteration, which is particularly obvious on the south-facing slope of the catchment (Fig. 1, El Gh'Mari, 1995). ...
Strontium and particularly 87Sr/86Sr ratios in stream water have often been used to calculate weathering rates in catchments. Nevertheless, in the literature, discharge variation effects on the geochemical behavior of Sr are often omitted or considered as negligible. A regular survey of both Sr concentrations and Sr isotope ratios of the Strengbach stream water draining a granite (Vosges mountains, France) has been performed during one year. The results indicate that during low water flow periods, waters contain lower Sr concentrations and less radiogenic Sr isotope ratios (Sr=11.6 ppb and 87Sr/86Sr=0.7246 as an average, respectively) than during high water flow periods (Sr= 13 ppb and 87Sr/86Sr=0.7252 as an average, respectively). This is contrary to expected dilution processes by meteoric waters which have comparatively lower Sr isotopic ratios and lower Sr concentrations. Furthermore, 87Sr/86Sr ratios in stream water behave in 3 different ways depending on moisture and on hydrological conditions prevailing in the catchment. During low water flow periods (discharge < 9 l/s), a positive linear relationship exists between Sr isotope ratio and discharge, indicating the influence of radiogenic waters draining the saturated area during storm events. During high water flow conditions, rising discharges are characterized by significantly less radiogenic waters than the recession stages of discharge. This suggests a large contribution of radiogenic waters draining the deep layers of the hillslopes during the recession stages, particularly those from the more radiogenic north-facing slopes. These results allow one to confirm the negligible instantaneous incidence of rainwater on stream water chemistry during flood events, as well as the existence in the catchment of distinct contributive areas and reservoirs. The influence of these areas or reservoirs on the fluctuations of Sr concentrations and on Sr isotopic variations in stream water depends on both moisture and hydrological conditions. Hence, on a same bedrock type, 87Sr/86Sr ratios in surface waters can be related to flow rate. Consequently, discharge variations must be considered as a pre-requisite when using Sr isotopes for calculating weathering rates in catchments, particularly to define the range of variations of the end-members.
... The total runoff averages 853 mm for the 1986-1995 period (Probst et al., 1995), which corresponds to a mean annual discharge of 21.7 L/s. The bedrock is a base poor leucogranite (the Brézouard granite) aged of 315 ± 7 Ma (Bonhomme, 1967). This granite is coarse grained and has undergone hydrothermal alteration 183.9 ...
A numerical model of chemical weathering in soil horizons and underlying bedrock (WITCH) has been coupled to a numerical model of water and carbon cycles in forest ecosystems (ASPECTS) to simulate the concentration of major species within the soil horizons and the stream of the Strengbach granitic watershed, located in the Vosges Mountains (France). For the first time, simulations of solute concentrations in soil layers and in the catchment river have been performed on a seasonal basis. The model is able to reproduce the concentrations of most major species within the soil horizons, as well as catching the first-order seasonal fluctuations of aqueous calcium, magnesium and silica concentrations. However, the WITCH model underestimates concentrations of Mg2+ and silica at the spring of the catchment stream, and significantly underestimates Ca2+ concentration. The deficit in calculated calcium can be compensated for by dissolution of trace apatite disseminated in the bedrock. However, the resulting increased Ca2+ release yields important smectite precipitation in the deepest model layer (in contact with the bedrock) and subsequent removal of large amount of silica and magnesium from solution. In contrast, the model accurately accounts for the concentrations of major species (Ca, Mg and silica) measured in the catchment stream when precipitation of clay minerals is not allowed. The model underestimation of Mg2+ and H4SiO4 concentrations when precipitation of well crystallized smectites is allowed strongly suggests that precipitation of well crystallized clay minerals is overestimated and that more soluble poorly crystallized and amorphous materials may be forming. In agreement with observations on other watersheds draining granitic rocks, this study indicates that highly soluble trace calcic phases control the aqueous calcium budget in the Strengbach watershed.
Ce travail propose d'identifier et de quantifier dans le temps et dans l'espace l'origine de l'eau et de certains éléments dissous sur le bassin versant amont de la Moselle en utilisant trois familles de traceurs isotopiques. La singularité du bassin étudié réside dans la diversité des lithologies drainées et une occupation des sols variée. Un fort contraste réside entre les Vosges cristallines avec des sols principalement forestiers en amont et le plateau lorrain carbonaté dominé par les activités agricoles en aval. Un premier volet de ce travail a permis d'apporter des éléments à la compréhension du fonctionnement hydrologique du bassin versant de la Moselle. L'analyse de la composition isotopique de l'H et de l'O de l'eau a permis de décrire une dynamique des eaux et un temps de réponse au signal des eaux météoriques variable suivant le compartiment hydrologique étudié et la période de l'année. Les temps de réponse estimés sont de quelques jours pour les eaux de sols collectées par drainage en période de haut régime hydrique, à plusieurs semaines pour les eaux de rivières, jusqu'à plusieurs mois pour les eaux de sols collectées par bougies poreuses et les eaux de sources. Un deuxième volet de ce travail a permis d'identifier l'origine spatiale et temporelles des sulfates dissous dans les eaux de rivières. Trois sources principales de sulfates ont été identifiées: les apports atmosphériques, le lessivage d'évaporites et le lessivage d'engrais soufrés. L'apport de sulfates provenant d'engrais soufrés est saisonnier et n'apparaît qu'en période de haut régime hydrique (octobre 2003 à mars 2004), lorsque le lessivage des sols agricoles est le plus intense et peut représenter jusqu'à 13% des sulfates exportés annuellement par le Madon à Mirecourt. La composition isotopique du Sr de la phase dissoute des rivières indique que le Sr des eaux de la Moselle provient d'un mélange simple entre le pôle silicate et le pôle carbonate/évaporite définis localement, témoignant d'une relative simplicité du système étudié. Nous avons donc abordé l'utilisation du Mg comme traceur isotopique en hydrochimie. Les compositions isotopiques en Mg sur le bassin de la Moselle sont parmi les premières valeurs mesurées pour le Mg dissous dans des eaux de rivières et de sols. Les eaux de rivières drainant uniquement des silicates ( 26Mg=-1,2 à -0,7 ) présentent un appauvrissement systématique en isotopes lourds par rapport aux roches silicatées ( 26Mg=0,22 à 0,94 ) et à leurs sols associés ( 26Mg=0,36 à 1,68 ). Ce résultat suggère un fractionnement isotopique du Mg lors de l'altération. Les eaux de rivières drainant le plateau lorrain à dominante carbonatée ont une gamme de valeurs ( 26Mg=-1,6 à -1,2 ) significativement plus basse que celle du bassin silicaté. En plus d'être contrastées selon la lithologie drainée, les valeurs de 26Mg du Mg dissous sont bien corrélées avec les rapports 87Sr/86Sr et Sr/Mg témoignant clairement de la capacité des isotopes du Mg à tracer la source de Mg dissous dans ces rivières. Enfin un important excès de Mg et de Sr par rapport au Ca a été mis en évidence pour les rivières drainant les roches sédimentaires du plateau lorrain et seule la perte de Ca dissous par précipitation de calcite permet de rendre de cet excès
The scientific objective of this work is to better understand the riverine carbon transfers to the oceans and to identify the different biogeochemical processes controlling these transfers using carbon isotopic signature (δ13C). In order to do that, 25 watersheds have been investigated in the world, going from small catchments to large river basins. The results emphasize the major control of CO2 degassing to the atmosphere and of organic carbon oxidation (allochtonous and autochtonous) on the riverine δ13CDIC. The average isotopic signature δ13CDIC of the inorganic carbon riverine flux into the oceans has been estimated in this study to be -11,8‰. Finally, a first approach of a numerical model (δ-Carb) has been developed to simulate the δ13CDIC evolution in rivers.
The assessment of the environmental impacts of CO2 geological storage requires the investigation of potential CO2 leakages into fresh groundwater, particularly with respect to protected groundwater resources. The geochemical processes and perturbations associated with a CO2 leak into fresh groundwater could alter groundwater quality: indeed, some of the reacting minerals may contain hazardous constituents, which might be released into groundwater. Since the geochemical reactions may occult direct evidence of intruding CO2, it is necessary to characterize these processes and identify possible indirect indicators for monitoring CO2 intrusion. The present study focuses on open questions: Can changes in water quality provide evidence of CO2 leakage? Which parameters can be used to assess impact on freshwater aquifers? What is the time scale of water chemistry degradation in the presence of CO2? The results of an experimental approach allow selecting pertinent isotope tracers as possible indirect indicators of CO2 presence, opening the way to devise an isotopic tracing tool.
Initial 87Sr/86Sr ratios have been plotted against time of formation for various rock-types in the Schwarzwald and Vosges basement areas. These data exhibit strong positive correlations between the two variables.
The Schwarzwald data define two distinct trend lines on the diagram, for the time span 500 to 250 Ma ago. The first comprises the data from orthogneisses, diatexites and pre-tectonic granites and documents the Sr isotope evolution in the crust underlying the Sehwarzwald. This region of the crust had a 87Rb/86Sr ratio of about 1. The other is delineated by data points from the post-tectonic plutons. These form a band corresponding to the development of closed systems with 87Rb/86Sr ratios of between 10 and 20 as indicated by the slope of the band. The second trend is interpreted as resulting from the formation of large, stable, deep-seated magma chambers formed by segregation of anatectic melts during a phase of tectonism 330Ma ago. The high 87Rb/86Sr ratios of these magmas arose by fractional crystallization, in response to tectonic decompression, during the coalescence of the presumedly water-saturated melts.
Data for rocks from the Vosges, taken from the literature, form a single development line. Its slope corresponds to a 87Rb/86Sr ratio of about 5 and the line is analogous to the second trend line defined by the Schwarzwald data.
The differences in the Rb/Sr systematics between the two areas can be explained as resulting from the deeper level of erosion in the Vosges.
An important implication for Rb/Sr studies is that co-magmatic rocks can have very different initial 87Sr/86Sr ratios so that discrepancies in this ratio between rock-types cannot be used to divide plutons into genetic suites. On the other hand essential information is contained in the Rb/Sr systematics of orogenic magmatic rocks, such as the Variscan plutons in the Schwarzwald, that cannot be obtained from geochemical and petrological studies alone.
In the Saxothuringian part of the Vosges (France), a first series of Variscan plutonic rocks (diorites to granites) has been intruded by several younger granites. Rocks of both the older generations have been cross-cut by the late orogenic Kagenfels granite. The averages of the hitherto published mineral ages of the earlier rock generations are 331 and 334 Ma, respectively, whereas Rb-Sr and K-Ar dates around 290 Ma have been reported for the Kagenfels granite. Because of the unlikely large age hiatus, a redetermination of the intrusion age of the Kagenfels granite formation appeared to be irrevocable. The newly obtained mineral ages on the Kagenfels granite (K-Ar and 40Ar/39Ar biotite ages as well as single zircon radiogenic 207Pb/206Pb data: 331 5 Ma) are about 40 Ma older than the previous results. They are interpreted as giving the time of emplacement of the Kagenfels granite during the latest Visan. The mineral ages of the earlier plutonic rocks in this part of the Variscan Orogeny in all probability are not significantly different from their ages of intrusion. Therefore the age concordance of all three granitoid generations constrains a rather narrow time interval of orogenic magmatism close to the Lower-Upper Carboniferous boundary.
In the Central Vosges Mts. (France) of the Variscan belt, Mg---Cr garnet peridotite bodies occur within the uppermost tectonometamorphic unit (Leptynitic granulites) as lenses in low-pressure/high-temperature metamorphic rocks. Neglecting late-stage serpentinization, the metamorphic evolution of these rocks was characterized by four stages. During stage I, the rocks were equilibrated at high pressures and temperatures (> 4.9 GPa/ > 950°C, in most cases > 1100°C), either within or near to the stability field of diamond. Stage II is documented by the formation of coronas around relict garnet with the assemblage orthopyroxene ± clinopyroxene ± amphibole + spinel ± plagioclase. During stage III, the remaining garnet was transformed to very fine-grained kelyphite consisting of orthopyroxene + amphibole + spinel ± plagioclase. Small relict garnet grains are preserved in one peridotite only. Stage IV corresponds to the late formation of tremolitic hornblende and chlorite which partially replaced the pseudomorphs after garnet or occur along cracks in the matrix of some rocks. Compositional zoning patterns of pyroxene porphyroclasts suggest that initial decompression was either accompanied by a moderate increase in temperature or nearly isothermal. Garnet breakdown textures and compositions of minerals grown during stages II and III also suggest rapid decompression at still elevated temperatures (1000-720°C).
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