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Strontium isotopic characterization of the Palmottu hydrosystem (Finland): Water-rock interaction and geochemistry of groundwaters
Geofluids
Abstract
The Palmottu hydrosystem is located in a granitic host rock in southern Finland. Along well-defined pathways in the fractured crystalline rock, strontium isotopes are used to trace the degree of water–rock interaction (WRI) and mixing processes in groundwaters.
The 87Sr/86Sr ratios range between 0.716910 and 0.735606 in the surface waters and between 0.719991 and 0.750787 in the groundwaters, but are between 0.720 and 0.735 in most of the samples. Moreover, the results show a lack of correlation between the water chemistries determining the classification into different water-types (Na–Cl, Na–SO4, etc.) and the results of the strontium (Sr) contents and Sr isotopic ratios. From a WRI standpoint, this implies that the Sr behaviour is independent of the water chemistry; the occurrence of large 87Sr/86Sr variations is site specific and mainly dependent on the lithology. A model to determine the 87Sr/86Sr ratio of water after interaction with granite was developed. This model is based on the assumption that Sr was derived from three minerals: plagioclase, K-feldspar and biotite. The results of the calculation indicate that around half of the water analysed within the Palmottu hydrosystem can be explained by the weathering of the granites. However, clearly lower 87Sr/86Sr are observed in waters when compared to the calculated 87Sr/86Sr and other sources of Sr, with low 87Sr/86Sr, rather than the calculated granite–water interaction, which may be suspected.
When comparing the 87Sr/86Sr and ion ratios (Ca/Na, Mg/Na, Sr/Na, Cl/Na), the scattering of the data can be explained by the presence of four end-members: a brine component (low 87Sr/86Sr and Ca/Na ratios…), a deep granitic component (high 87Sr/86Sr ratios and low Ca/Na ratios…), a subsurface component (intermediate 87Sr/86Sr ratios associated with high Ca/Na ratios…) and a surface end-member:snow and river drainage (low 87Sr/86Sr and low Ca/Na ratios…). These extreme end-members define a series of WRI-mixing line within a rather complex hydrosystem.
... Chemical weathering models have been developed by many authors to investigate ecosystem sensitivity to acidic deposition (Christoffersen and Seip, 1982;April et al., 1986;Fritz et al., 1992;. These models are usually based on the assumption that the most abundant minerals like plagioclase, K-feldspar, biotite and muscovite in granite bedrock are the major cation sources (Blum et al., 1994;Bullen et al., 1997;Négrel et al., 2001Négrel et al., , 2003. Trace minerals such as calcite or apatite are often not taken into account. ...
... Trace minerals such as calcite or apatite are often not taken into account. However, there is now increasing evidence that plagioclase is not the predominating geochemical Ca source in many acid rock catchments in spite of being the predominant Ca-bearing mineral Jacobson and Blum, 2000;Négrel et al., 2003;. Thus, an additional Ca source is required to explain the observed chemical composition of the weathering solution. ...
... pointed out the role of disseminated calcite in the chemical weathering of granitoid rocks, using Ca/Na ratios compared to plagioclase stoichiometries and flow-through experiments. Likewise, , , Jacobson and Blum (2000) and Négrel et al. (2003) emphasized the contribution of calcite present in trace amounts in silicate bedrock (gneiss, granite) to the chemical composition of the weathering solution. attribute more than 90% of the Ca export from high elevation watersheds in the Pyrenees (France) to the dissolution of apatite and other trace Ca-rich minerals, representing less than 1% of the total rock volume. ...
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.
... The zone where meteoric waters dominate is relatively shallow (50-200 m) in the coastal areas, which is certainly owing to influence from the Baltic Sea and its precursors, but may attain several hundreds of metres farther inland. By combining isotopic data from the literature for Baltic sea water, deep-saline and shallow groundwaters, and surface water, with new data obtained by Négrel et al. (2003) in Palmottu (south Finland), by Casanova et al. (1999Casanova et al. ( , 2000 in Äspö (Sweden) and the Baltic Sea, we have compiled an overview of saline groundwater in the Fennoscandian Shield. ...
... Fifty-four water samples have been analyzed for the Palmottu site, including surface water, groundwater in the overburden, and deep groundwater from different boreholes; data used for this study are from Négrel et al. (2003). The chemical and Sr isotope data for Äspö groundwater were taken from the hydrochemical investigation databases of the Swedish Nuclear Fuel and Waste Management Company. ...
... Figure 3 illustrates the depth distribution for Sr contents, showing a strong increase with increasing depth. In Palmottu, as demonstrated by Négrel et al. (2003), the evolution of Sr contents versus depth shows (a) an increase of Sr contents with increasing depth that can be related to an increase of the water-rock interaction, and (b) a decrease of Sr contents, which could be explained through a mixing with highly diluted waters (HCO 3 water type, Négrel et al. 2003) as saturation indexes are not supersturated with respect to Sr phases (celestite, strontianite) or Ca-Sr phases (calcite…). At Outokumpu and Parainen, a three-step evolution for Sr, in a pattern similar to that of other elements, was described by Smalley et al. (1988) and Nurmi et al. (1988). ...
High salinity CaNaCl brines occur in Sweden and Finland. The complex geological history of the Fennoscandian Shield is reflected by the wide range of saline waters whose chemical compositions have been explained by local waterrock interaction, simple evolution of relict sea water, or freezing of sea water during glacial periods. This study deals with the present knowledge of Sr isotopes in groundwater from the Fennoscandian Shield to better constrain the origin of their deep saline component. Two different mixing trends are seen between Äspö Island groundwater and the Baltic Sea. The first trend links the North Sea to rivers through various dilution levels in the Baltic; the second trend is a simple linear relationship through Äspö groundwaters, agreeing with a binary mixing between a Baltic end-member and a highly Sr-concentrated fluid. Strontium isotope compositions are presented for precipitation in Finland and Sweden, the Baltic Sea, and the river waters draining the Fennoscandian Shield, and for groundwaters from several sites in the Fennoscandian Shield. At least six mixing lines between rain-and-snow input and surface waters can be drawn in each region around the Baltic Sea, reflecting a first step of waterrock interaction. A second series of calculated lines links the surface end-members and the deep brines, and defines a range of 87Sr/86Sr ratios for the deep brines at each site. All sites show a specific 87Sr/86Sr signature and the large 87Sr/86Sr variations is site specific. The well-constrained 87Sr/86Sr signatures in deep brines should correspond to a large, well-mixed, and homogeneous water reservoir.
... Trace minerals such as calcite or apatite are often not taken into account. However, there is now increasing evidence that plagioclase is not the predominating geochemical Ca source in many acid rock catchments in spite of being the predominant Ca-bearing mineral (Clow et al., 1997; White et al., 1999; Jacobson and Blum, 2000; Négrel et al., 2003; Oliva et al., 2004 ). Thus, an additional Ca source is required to explain the observed chemical composition of the weathering solution. ...
... Now they are increasingly used to identify Ca sources due to the similar chemical behaviour of Sr and Ca (Åberg et al., 1989; Gosz and Moore, 1989; Wickman and Jacks, 1992; Miller et al., 1993; Bailey et al., 1996; Clow et al., 1997 Clow et al., ). Åberg et al. (1989, Wickman and Jacks (1992), Bain and Bacon (1994), Clow et al. (1997), Probst et al. (2000, Harrington and Herczeg (2003) studied weathering processes and Frape et al. (1984), Kay and Darbyshire (1986), Négrel et al. (2003) and Gosselin et al. (2004) water–rock interactions in watersheds using Sr isotope ratios. The impact of atmospheric inputs on water quality in watersheds was investigated by Graustein and Armstrong (1983), Gosz and Moore (1989) and Probst et al. (2000). ...
... Several authors have found that disseminated calcite, a very soluble trace mineral (e.g. Hodson et al., 1996), can have an important influence on the chemical composition of surface waters and groundwaters in crystalline catchments and can explain excess Ca (Clow et al., 1997; Blum et al., 1998; White et al., 1999; Jacobson and Blum, 2000; Négrel et al., 2003). Clow et al. (1997) showed that weathering of calcite, present in trace amounts in silicate bedrock (Loch Vale, Colorado) can account for between 43 and 59% of the total Ca flux in stream water. ...
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.
... Sr isotopes have been used extensively in hydrological/hydrochemical studies to trace water origin and mixing, in surficial waters [1,2], at the boundary between surficial water and groundwater [3,4], in groundwaters of sedimentary basins [5], and in groundwaters of deep crystalline rock fractures [6][7][8]. 87 Sr/ 86 Sr values have also been used for sedimentary carbonates and carbonate shells to understand ocean water evolution, such as salinity variations and freshwater input from glaciations [9][10][11][12][13][14][15]. In bedrocks such as crystalline rock settings, the bulk rock 87 Sr/ 86 Sr signature evolves over time due to the decay of 87 Rb in K-bearing minerals like biotite and K-feldspar [16]. ...
... The Forsmark calcites overall show significantly lower 87 Sr/ 86 Sr values in the youngest calcite growth zones compared to the corresponding groundwaters. This "disequilibrium" between the calcites and the present-day groundwaters can be explained by different scenarios [1,61]: (1) The calcites may be of greatly different ages from the water, with 87 Sr/ 86 Sr calcite values reflecting the temporal 87 Sr/ 86 Sr evolution in the host rock [7,16]. Radiogenic 87 Sr in deep groundwaters is continuously produced by the decay of 87 Rb (half life 4.9 × 1010a, [74,75]) through water rock interaction processes involving Rb-bearing minerals such as K feldspar and biotite [23,76]. ...
The strontium isotope signature (87Sr/86Sr) of calcite precipitated in rock fractures and faults is a frequently used tool to trace paleofluid flow. However, bedrock fracture networks, such as in Precambrian cratons, have often undergone multiple fracture reactivations resulting in complex sequences of fracture mineral infillings. This includes numerous discrete calcite crystal overgrowths. Conventional 87Sr/86Sr analysis of dissolved bulk samples of such crystals is not feasible as they will result in mixed signatures of several growth zonations. In addition, the zonations are too fine-grained for sub-sampling using micro-drilling. Here, we apply high spatial resolution 87Sr/86Sr spot analysis (80 µm) in transects through zoned calcite crystals in deep Paleoproterozoic granitoid fractures using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) to trace discrete signs of paleofluid flow events. We compare the outermost calcite growth zone with 87Sr/86Sr values of the present-day groundwater sampled in the same boreholes to distinguish potential modern precipitates. We then connect our results to previously reported radiometric dating and C and O isotope signatures to understand the temporal history and physicochemical evolution of fluid flow within the fractures. Comparisons of modern calcite precipitated in a borehole over a period of 17 years with modern waters prove the concept of using 87Sr/86Sr as a marker for fluid origin in this environment and for how 87Sr/86Sr changed during marine water infiltration. Intermittent calcite precipitation over very long time spans is indicated in calcite of the currently open fractures, showing an evolution of 87Sr/86Sr from ~0.705–0.707—a population dated to ~1.43 billion years—to crystal overgrowth values at ~0.715–0.717 that overlap with the present-day groundwater values. This shows that high spatial resolution Sr isotope analysis of fine-scaled growth zonation within single calcite crystals is applicable for tracing episodic fluid flow in fracture networks.
... Groundwater in the fracture porosity of crystalline rocks shows a wide range of chemical composition varying from weakly mineralized Ca–HCO 3 waters to highly saline brines (Frape et al. 2004; Fritz and Frape 1987; Bucher and Stober 2000). The solutes have different origins including the reaction of recharge water with the rock matrix, fossil seawater and sedimentary waters imported from cover sequences of the basement (Frape et al. 2004; Bottomley et al. 1993; Edmunds et al. 1987; Stober and Bucher 1999; Louvat et al. 1999; Casanova et al. 2001; Negrel et al. 2003 ). In general, the permeability of fractured crystalline basement is relatively high and permits groundwater advection and large-scale fluid flow (Manning and Ingebritsen 1999; Caine and Tomusiak 2003; Stober and Bucher 2007). ...
... In general, the permeability of fractured crystalline basement is relatively high and permits groundwater advection and large-scale fluid flow (Manning and Ingebritsen 1999; Caine and Tomusiak 2003; Stober and Bucher 2007). The information on chemical properties of groundwater in the basement comes from shallow near surface wells (Banks and Banks 1993 ), scientific deep drilling (Möller et al. 1997), research for nuclear waste disposal (e.g., Nordstrom et al. 1989 ), prospection for geothermal energy (e.g., Stober and Bucher 2004) and deep mines (Fritz and Frape 1987; Negrel and Casanova 2005). In this paper, we present water composition data and observations from the 700 m deep Clara mine in the crystalline basement of the Black Forest (Germany). ...
The chemical composition of water sampled in a 700 m deep underground barite-fluorite mine in the crystalline basement of
the Black Forest area (SW Germany) varies systematically with depth and the length of flow paths trough, the fracture porosity
of the gneiss matrix. Calcium and sulfate increase as a result of a combined sulfide oxidation and plagioclase alteration
reaction. The gneiss contains andesine–plagioclase (An20–An40) and is rich in primary sulfide. As an effect of Ca and SO4 release by the prime water–rock reaction, dissolved oxygen decreases and the waters become more reduced. The waters have
Cl/Br mass ratios of about 50, which is very close to that of experimentally leached gneiss powders indicating that the rock
matrix is the source of the halogens. The waters are undersaturated with respect to calcite in the upper parts of the mine.
With increasing reaction progress, calcite saturation is reached and carbonate forms as a reaction product of the prime reaction
that also controls the partial pressure of CO2 to progressively lower values. The chemical evolution of groundwater in fractured basement of the Clara mine suggests that
the partial pressure of CO2 is an internally buffered parameter rather than a controlling external variable.
... Seventy groundwater samples from the Canadian and Fennoscandian crystalline Shields were selected for δ 37 Cl and δ 81 Br analyses. Twenty of these samples were also analyzed for 87 Sr/ 86 Sr ratios to expand a previously published dataset and allow a comparison with an isotopic parameter used as an indicator of water-rock interaction in crystalline environments McNutt et al., 1984;Franklyn, 1987;McNutt, 1987;McNutt et al., 1987;Smalley et al., 1988;McNutt et al., 1990;Franklyn et al., 1991;Negrel et al., 2003;Frape et al., 2004;Negrel et al., 2005). Fig. 1 displays sample locations across the Canadian and Fennoscandian Shields, and a summary of major rock units, mineralogy (where available), and sample type is provided in Table 1. ...
... Water-rock interactions in the Canadian and Fennoscandian Shields have been previously investigated utilizing 87 Sr/ 86 Sr ratios McNutt et al., 1984;Franklyn, 1987;McNutt, 1987;McNutt et al., 1987;Smalley et al., 1988;McNutt et al., 1990;Franklyn et al., 1991;Negrel et al., 2003;Frape et al., 2004;Negrel et al., 2005). In crystalline shield groundwaters, strontium is a proxy for calcium, and correlates positively with Br (McNutt et al., 1984. ...
Chlorine and bromine are two major anionic components of most brines, and typically behave conservatively in groundwater systems. Chlorine isotopes have been utilized to determine brine evolution during water rock evolution, very few investigations have analyzed for bromine isotopes. In this paper, brines and fluids from the Canadian and Fennoscandian Shields are characterized through a survey of chlorine and bromine stable isotopes. Stable chlorine and bromine isotopic values in Fennoscandian Shield fluids were more positive, and a greater range of values than was observed for Canadian Shield fluids. For the Fennoscandian Shield, isotopic values for δ37Cl varied between − 0.54‰ and + 1.52‰ SMOC, while δ81Br values ranged between + 0.26‰ and + 2.04‰ SMOB, while values in the Canadian Shield varied between − 0.78‰ and + 0.98‰ SMOC and + 0.01‰ and +1.29‰ SMOB, respectively. A weak positive correlation between chlorine and bromine isotopes was also observed. At one site with serpentinite rocks, a large variation in δ37Cl isotopic values compared with minimal variation in δ81Br values is attributed to ion filtration through serpentinite, which affected the Cl but not Br ions. Comparisons with other isotopic systems, such as 87Sr/86Sr, indicate water–rock interactions at some sites are likely to influence halogen isotopic composition (δ37Cl, δ81Br). The δ37Cl and δ81Br values of the investigated samples do not support a marine origin for these brines. However, if a seawater origin were to be considered for the fluids, a process or combination of processes significantly altered chlorine and bromine isotopic signatures. A positive correlation between the fluid halide isotopic composition (δ37Cl, δ81Br) and methane gas isotopic composition (δ2H, δ13C) may be due to changes in redox, pH, temperature and pressure conditions, as well as diffusion over geologic time. Although overlap occurs, the differences between the chlorine and bromine stable isotope ranges and behaviors for crystalline shields and sedimentary basins presented in this paper are significant, which indicates either different sources or different evolutionary processes in the two different environments. This could have implications to several shield evolutionary pathways published in the present literature.
... Strontium isotopes are also widely used in hydrogeology to characterize weathering processes conditioned by waterrock interactions (Ettayfi et al. 2012;Negrel et al. 2003;Negrel and Pauwels, 2004;Negrel et al. 2018;Santoni et al. 2016;Shand et al. 2007;Wang et al. 2006). As Sr isotopes rarely fractionate in the water environment and the 87 Sr/ 86 Sr ratio signature of atmosphere input is always quickly replaced by the rock signatures, the 87 Sr/ 86 Sr ratios are more sensitive to water sources than other traditional hydrogeochemical analyses and are constrained by mineral and weathering processes (Bickle et al. 2003). ...
As one of the most representative forms of groundwater, mineral water provides a critical understanding of regional hydrogeochemical features and rock weathering processes. However, current studies have mostly focused on the quality of mineral water and have rarely addressed the weathering process during its formation. Therefore, a multi-tracer approach combines chemical parameters, major ions, selected trace elements, and ⁸⁷Sr/⁸⁶Sr ratios for mineral water samples in Changbai Mountain during 2020–2021. First, we determined the hydrogeochemical characteristics of different types of mineral water. Secondly, the water-rock interaction processes governing the water mineralization were described to fix the hydrogeochemical background. Thirdly, the chemical weathering rate was calculated. The total dissolved load generated by rock weathering was around 6.76 tons/km²/year in the mineral water catchment area; 44.6% and 36.9% of the dissolved load were derived from silicate and carbonate weathering, respectively. The trace carbonates also played an important role in the overall rock weathering. Finally, after fully considering various influencing factors, we concluded that lithological characteristics and the soil environment rich in organic acids were the most important factors affecting rock weathering in the Changbai Mountain area. Overall, this study highlights the mineral water’s role in the fluxes of CO2 in local area and reveals possible influence of the unique ecological and geological environment on rock weathering in Changbai Mountain. It can provide a reference for the subsequent assessment of environmental stability for basalt areas and the possibility of sustainable water resources development.
... While F1 is negatively correlated to As and SiO 2 (hydrothermal elements) and positively correlated with Sr and E.C. This axis discriminates magmatic influences, with its high As-content related to the presence of geothermal fluids [63], from mixing flows involving different flow pattern with high Sr-content due to the increase in combined sedimentary and granitoid rocks hydrolysis [69]. The Figure 6 highlights the main reservoirs involved in the mineralisation of cold waters (except ACQ and CAM-F), which are flowing mainly through sedimentary rocks and are influenced by shallow waters mixing, while thermal waters (except VIGN) flow mainly through magmatic rocks without shallow water mixing and dilution. ...
Understanding hydrogeological processes at the origin of thermal and mineral groundwater are necessary to ensure their sustainable management. However, many processes are involved in their genesis and often only one or two processes are investigated at the same time. Here, we propose to use an innovative combination of geochemical, isotopic (34S, 14C, 18O, 2H) and geothermometry tools to identify, for the first time in a multi-composite geological context, all processes at the origin of diversified thermo-mineral waters. 19 springs covering a wide range of temperature and chemical composition emerging on a restricted area of Corsica Island (France) were selected.
Geochemical results highlight five geochemical provinces, suggesting a common origin for some of them. Geothermometry tools show the unexpected involvement of a common deep groundwater reservoir within this non-active zone. Water stable isotopes highlight a contrasted altitude in recharge areas supplying lowland springs. This suggests that different flow patterns have to be involved to explain the wide geochemical diversity observed and to allow the design of a very first conceptual groundwater-flow model. This paper demonstrates the efficiency of the combination of the selected tools as tracers of water–rock interaction, independently of flow depth, intrinsic water properties, geological conditions and interaction time disparities.
... With relatively high Sr concentrations (i.e., 2.9 μmol·l −1 ) compared to river waters (i.e., 0.5 to 1.2 μmol·l −1 ), SGDs represent an unradiogenic Sr source that can account for 13-30% of the global Sr ocean budget (Basu et al., 2001;Krabbenhöft et al., 2010;Beck et al., 2013). Depending on their geochemical and hydrodynamical characteristics related to the age and nature of weathered rocks but also oceanic intrusions, meteoric recharges, and water residence time in the aquifers (e.g., Négrel et al., 2003;Fadili et al., 2015Fadili et al., , 2016Santoni et al., 2016), their impact on the elemental and isotopic Sr budgets are, however, highly variable in coastal domains (e.g., Beck et al., 2013;Trezzi et al., 2017;Shao et al., 2018). This is illustrated by comparing the Salses-Leucate and Oualidia lagoons. ...
To better constrain the Sr isotope budget in marginal domains without any fluvial inputs, we analyzed the chemical composition and 87Sr/86Sr ratio of waters and shells from four locations: two coastal lagoons, one hemipelagic platform and one open marine shelf. Our results highlight homogeneous 87Sr/86Sr ratios typical of oligotrophic oceanic waters (OOW) (i.e., 0.709172 ± 0.000023) in the Pacific Tatakoto atoll and along a Mediterranean shore to offshore transect (~25 km off Banyuls-sur-Mer, BSM). This attests that oceanic inputs from oligotrophic areas remain the main Sr source in open shelf areas compared with submarine groundwater discharges (SGD) or particulate dissolution influences. In BSM, only foreshore data are more radiogenic, possibly due to rainwater mixing, local groundwater springs or more efficient particle dissolution in the intertidal zone. In restricted areas, we report variable 87Sr/86Sr ratios between the Salses-Leucate (France) and Oualidia (Morocco) lagoons. The first one has homogeneous 87 Sr/ 86 Sr ratio typical of OOW except close to SGD. In Oualidia, 87Sr/86Sr ratios decrease by 1.2 × 10 −3 from OOW values close to the Atlantic inlet to progressively less radiogenic ones upstream within the interior of the lagoon. These differences depend on several factors including the leaky, restricted or choked morphology of lagoons modulating the oceanic Sr inputs, but also SGD fluxes whose 87 Sr/ 86 Sr ratios and Sr concentrations are highly variable according to the nature of rocks leached in karstic aquifer. In Oualidia, the low 87 Sr/ 86 Sr ratios correspond to high Sr concentrations (up to 150 μmol·l −1) issued from the dissolution of Mesozoic evaporites, leading to SGD fluxes accounting for 60% of the local Sr budget. Through data compilation, we show that similar 87 Sr/ 86 Sr gradients and processes prevail at the whole Mediterranean scale. Finally, we postulate that high coastal water retention times can also account for anomalous coastal 87 Sr/ 86 Sr ratios and that the combination of water mass restriction, SGD, bioadsorption and early diagenetic processes could decrease seawater Sr concentrations in some marginal areas.
... The average 87 Sr/ 86 Sr ratio in the rivers on the Precambrian shield of Fennoscandia is estimated to be 0.730 (Löfvendahl et al. 1990). Negrel et al. (2003) report values between 0.720 and 0.735 in most of the samples from a lake in southwest Finland. In general, 87 Sr/ 86 Sr values around 0.730 would appear to be common in Finland. ...
Isotopic analysis of strontium in human tooth enamel from 15 burials from the medieval St. Clement Church cemetery at the Russian site of Staraya Ladoga identified at least five non-local individuals with isotopic signatures that match the Malaren region of east-central Sweden. These were medieval Christian graves dating approximately to the eleventh to twelfth centuries AD. Staraya Ladoga, located 128 km east of St. Petersburg, was an important trading center during the Viking period in Scandinavia. Historical documents describe the town as a melting pot of local Russians, Slavs, and Scandinavians. The identification of individuals of Scandinavian origin among the burials confirms the historical and archeological record of an important Scandinavian presence at the site.
... The chemical composition of waters is controlled by several identifiable processes (i.e. water-rock interaction, calcite dissolution and precipitation, brackish groundwaters with distinct glacial isotopic signatures…) (Négrel et al., 2003). ...
Several radionuclides of the 238U decay series (234Th, 234mPa, 234U, 222Rn and 210Pb), 235U and 232Th have been measured through gamma spectrometry in surface water and four dug wells in two successive years, in order to study the effect of flash flood event of 18th January 2010 on radionuclides distribution in Wadi Naseib, southwestern Sinai, Egypt. Variation of 238U/235U activity ratio by flash flood is observed in surface water sample and increased with time. This is due to that the 238U activity was determined indirectly from the gamma rays emitted by its daughter products (234Th and 234mPa), while 235U activity was determined directly by its own gamma ray peaks. The surface water sample reached secular equilibrium between 238U and its daughter products (234Th and 234mPa) after about one hundred days. The water-rock interactions during the journey of flash flood (April 2010) in the studied area changed the chemistry and the specifications of the groundwater. The cations and anions results are varied with time of collecting water and place of the wells. The activity concentrations of 238U, 210Pb and 232Th in groundwater samples collected in 2011 are found lower than that collected in 2010 while that of 234U and 222Rn are higher in 2011 than that in 2010. The groundwater residence time of two samples, collected from (Well-Zeid) in two successive years (2010 and 2011) were 27.93 and 42.44 ky, respectively, which show the young date just after the flash flood and gain of uranium with the new added water while after one year with the decrease of U-concentrations, the residence time increased. The last date may be coincide with the last wet period in Egypt.
... dissolution, suggesting stable hydrogeological conditions in many of these fractures since the Proterozoic. Hydrothermal calcites from Simpevarp/Laxemar () and the Palmottu site in Finland (Negrél et al., 2003 and references therein) show similar 87 Sr/ 86 Sr ratios as those in Forsmark, whereas those at Stripa are much more radiogenic (N0.7814) (Clauer et al., 1989). However, it is difficult to interpret whether the 87 Sr/ 86 Sr ratios in hydrothermal fracture filling calcite from areas with different bedrock geology could be related to the same tectonothermal event due to the high influence on the 87 Sr/ 86 Sr of the calcite from fluid–rock interaction. ...
In this paper, we show how studies of fracture mineral paragenesis, their orientation and 40Ar/39Ar geochronology can be applied in order to recognise the brittle tectonothermal evolution in an area. Samples were selected from nearly 18 km of drill cores from the upper 1 km of the Fennoscandian Shield obtained during the site investigation for a repository of spent nuclear fuel in Forsmark, central Sweden. Four major events of fracturing and/or reactivation of fractures associated with fracture mineralisation have been distinguished. The first event was characterised by precipitation of epidote, quartz and chlorite, along preferably sub-horizontal and gently-dipping fractures or steep, WNW–ESE to NW–SE fractures. Precipitation occurred between 1.8 and 1.1 Ga, possibly during the late stage of the Svecokarelian orogeny close to 1.8–1.7 Ga. The second event is associated with precipitation of hematite-stained adularia and albite, prehnite, laumontite, calcite and chlorite, preferably along steep, ENE–WSW to NNE–SSW and NNW–SSE fractures. Precipitation occurred around 1107±7 to 1034±3 Ma, probably due to effects from the Sveconorwegian orogeny. This event was followed by a period with dissolution of fracture minerals and subsequent precipitation of mainly calcite, quartz, pyrite and asphaltite during the Palaeozoic. The formation fluid emanated from an overlying organic-rich sedimentary cover. Precipitation occurred during reactivation of Proterozoic fractures, but formation of new fractures is also inferred, possibly due to far-field effects of the Caledonian orogeny, or elevated hydrostatic pressure due to its foreland basin. The latest event is dominated by clay minerals, chlorite and calcite along hydraulically conductive fractures. These minerals are prominent along sub-horizontal and gently-dipping fractures, but also occur in sets of steeply-dipping fractures. It is inferred that the hydraulically conductive fractures are Proterozoic structures in which mineral precipitation has occurred during a long period. However, some of the near-surface, sub-horizontal fractures may be Quaternary in age.
... dissolution, suggesting stable hydrogeological conditions in many of these fractures since the Proterozoic. Hydrothermal calcites from Simpevarp/Laxemar () and the Palmottu site in Finland (Negrél et al., 2003 and references therein) show similar 87 Sr/ 86 Sr ratios as those in Forsmark, whereas those at Stripa are much more radiogenic (N0.7814) (Clauer et al., 1989). However, it is difficult to interpret whether the 87 Sr/ 86 Sr ratios in hydrothermal fracture filling calcite from areas with different bedrock geology could be related to the same tectonothermal event due to the high influence on the 87 Sr/ 86 Sr of the calcite from fluid–rock interaction. ...
Drilling through the Palaeoproterozoic bedrock at Forsmark, central Sweden, during the site investigation for a potential geological repository of highly radioactive nuclear waste has provided high quality drill-core material from the upper 1 km of the Fennoscandian Shield. Analyses of stable isotopes (δ13C, δ18O, δ34S, 87Sr/86Sr), rare earth elements and fluid inclusions in fracture filling calcite and pyrite from these drill cores have resulted in the discrimination of several episodes of fracture mineralisations. These events represent migration of fluids during a wide range of conditions, ranging from high-temperature hydrothermal to present-day groundwater circulation. Four major events have been distinguished: 1) Precipitation of epidote, chlorite and quartz under hydrothermal conditions (T > 150–200 °C) during the Proterozoic, sometime between 1.8 and 1.1 Ga. 2) Hydrothermal circulation at temperatures close to 200 °C with precipitation of adularia, albite, prehnite, laumontite, calcite and chlorite. Most of these minerals precipitated during a tectonothermal event between 1.1 and 1.0 Ga, possibly in response to far-field effects of the Sveconorwegian orogeny. 3) Precipitation of mainly quartz, calcite, pyrite and asphaltite occurred during the Palaeozoic, at temperatures between 60 and 190 °C (mainly at < 100 °C). Mixing of a fluid emanating from an organic rich overlying sedimentary cover and a deep basinal fluid from the crystalline bedrock is suggested to have caused this precipitation, possibly as a far-field response to the Caledonian orogeny and/or the development of the Caledonian foreland basin. 4) The youngest generation of fracture minerals is associated with formation of clay minerals and calcite with minor occurrences of pyrite and goethite. These minerals have probably precipitated episodically during a long time period (possibly from the Late Palaeozoic to the present) from various fluids at low temperature conditions (< 50 °C). Few calcites in equilibrium with the present groundwater suggest that the ongoing precipitation of calcite is very limited.
... Hence, the Sr isotope ratio in Kalix vendace caviar is a product of mixing between these two end-points. Also data for Finnish caviar are within the reported range for 87 Sr/ 86 Sr ratios in the surface waters of Finland (between 0.71691 and 0.73561) [29]. ...
Different analytical approaches for origin differentiation between vendace and whitefish caviars from brackish- and freshwaters were tested using inductively coupled plasma double focusing sector field mass spectrometry (ICP-SFMS) and multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). These approaches involve identifying differences in elemental concentrations or sample-specific isotopic composition (Sr and Os) variations. Concentrations of 72 elements were determined by ICP-SFMS following microwave-assisted digestion in vendace and whitefish caviar samples from Sweden (from both brackish and freshwater), Finland and USA, as well as in unprocessed vendace roe and salt used in caviar production. This data set allows identification of elements whose contents in caviar can be affected by salt addition as well as by contamination during production and packaging. Long-term method reproducibility was assessed for all analytes based on replicate caviar preparations/analyses and variations in element concentrations in caviar from different harvests were evaluated. The greatest utility for differentiation was demonstrated for elements with varying concentrations between brackish and freshwaters (e.g. As, Br, Sr). Elemental ratios, specifically Sr/Ca, Sr/Mg and Sr/Ba, are especially useful for authentication of vendace caviar processed from brackish water roe, due to the significant differences between caviar from different sources, limited between-harvest variations and relatively high concentrations in samples, allowing precise determination by modern analytical instrumentation. Variations in the 87Sr/86Sr ratio for vendace caviar from different harvests (on the order of 0.05-0.1%) is at least 10-fold less than differences between caviar processed from brackish and freshwater roe. Hence, Sr isotope ratio measurements (either by ICP-SFMS or by MC-ICP-MS) have great potential for origin differentiation. On the contrary, it was impossible to differentiate between Swedish caviar processed from brackish water roe and Finnish freshwater caviar based solely on 187Os/188Os ratios.
Les reconstitutions passées de la composition isotopique en Sr (87Sr/86Sr) des squelettes carbonatés d'organismes marins (MCS) sont très largement utilisées par les chimiostratigraphes et les paléoenvironnementalistes car elles permettent de reconstituer les variations du rapport 87Sr/86Sr de l'océan au cours des temps géologiques. Les reconstitutions paléoenvironnementales et les datations chimiostratigraphiques reposent sur le consensus que les MCS précipitent leurs tests carbonatés à l'équilibre isotopique avec l'eau de mer qui est homogène à l'échelle globale en raison d'un temps de résidence du Sr (2 Ma) supérieur au temps de brassage océanique (1600 ans). Leur fiabilité en tant qu'outils chimiostratigraphiques peut être remise en question, notamment parce qu'aucune évaluation formelle des biais biologiques et environnementaux n'a été réalisée à l'échelle mondiale. Cette étude propose donc une réévaluation à l'échelle globale de la signature isotopique en Sr des MCS et de l'eau de mer d'environnements côtiers. La signature isotopique des MCS et de l'eau côtière est largement influencée par des apports continentaux qui peuvent modifier les signatures isotopiques de ces derniers. De fait, au vu de ces hétérogénéités cette étude a recalculé le temps de résidence du Sr à plusieurs échelles spatiales. Elle propose de façon générale une meilleure compréhension des processus côtiers sur la signature isotopiques de l'eau et des MCS.
Isotopic proveniencing has been applied to human inhumations and cremations as well as fauna from the Viking Age site of Birka and the surrounding Mälaren region, located in east-central Sweden. Human enamel from inhumations has been measured for strontium, oxygen, and carbon isotope ratios (petrous bone from cremations was measured for strontium only) to obtain information on mobility and diet. Seven graves from the larger Mälaren region and several at Birka had distinctive grave goods thought to have originated in Finland. The isotopic values from these graves indicate that they may have been local individuals. The faunal remains from the Mälaren region corresponded closely with samples from Birka providing a baseline for strontium isotopic ratios in this area. At the site of Birka, two distinct groups of burials can be identified among the measured values, along with several outliers. The data suggest that Birka was a multi-ethnic settlement in the Viking period, consistent with historical sources and concomitant with its role as an important center of economy and trade on the east coast of Sweden.
The debate on the origin and evolution of the fluids in crystalline rocks is very much an ongoing research topic. A number of experimental and research sites, such as the ones discussed in this article, will continue to produce hydrogeochemical information well into the middle of this century as researchers around the globe attempt to understand the hydrogeology and geochemistry of crystalline rock environments.
A multi-isotope approach in combination with hydrochemical data and borehole logging is applied to identify the source of brackish groundwater in a borehole in the well field of Nekso Municipal Waterworks in Bornholm, Denmark. The aquifer lithology consists of fractured Lower Cambrian sandstones resting on Proterozoic crystalline basement. The water body in the studied borehole is significantly stratified with respect to the hydrochemical and isotopic signatures and reveal a Na-Ca-Cl-HCO(3) water type and TDS values.1,000 mg/L below a halocline at 40-55m below measurement point (bmp). The occurrence of brackish groundwater is remarkable for this aquifer, which otherwise yields potable groundwater of good quality. The stable isotope ((18)O and (2)H) compositions indicate a meteoric origin of the brackish groundwater, which rules out seawater intrusion into the aquifer. (14)C activities show apparent (14)C ages of the brackish groundwater in the range 2200-4300 yr (BP), whereas the freshwater samples above the halocline indicate modern age. Hydrochemical (Cl/Br and Sr) and isotopic studies ((18)O, (2)H and (87)Sr/(86)Sr) of the brackish groundwater point to a well-mixed and homogeneous water body reflecting long water-rock interaction and suggest a contribution of palaeowater from the fractured crystalline basement which has intruded into the Lower Cambrian sandstone aquifer.
The glacigenic Virttaankangas aquifer in SW Finland is characterized by groundwaters with high pH values of up to 9.5. High pH values exceeding 9 are uncommon for shallow groundwaters from unconsolidated glacigenic formations on crystalline bedrock. To evaluate the geochemical evolution of groundwater, water samples were collected from 17 sites. The samples were analysed for the isotopic composition of oxygen, hydrogen, dissolved inorganic carbon (DIC) and strontium, the activities of radiocarbon and tritium, and for the basic chemical composition. Groundwaters in the Virttaankangas aquifer system show a considerable range in water pH from 6.4 to 9.5. The isotopic and chemical characteristics of the groundwater in the aquifer units were observed to vary depending on the aquifer mineralogy, groundwater residence time and the openness of the system to CO(2) exchange. The pH values were noted to increase in parallel with the contents of Ca and DIC and delta(13)C(DIC). In higher pH values, the groundwaters had attained saturation with respect to calcite. These chemical changes were interpreted to result from dissolution of calcite, present in trace amounts in the Virttaankangas sediments. Specifically, the highest pH values were attributed to calcite dissolution under closed system conditions at a low partial pressure of CO(2).
The safe disposal of high-level nuclear wastes requires its isolation from the humanly accessible e nvironment until radioactive decay reduces the toxicity to low levels. This requires periods of many thousands of years (up to 10 5
Results from cryogenic column experiments are compared with the geochemical data collected in the Canadian and Fennoscandian Shields over the past 25 years to investigate the relative influence of the glacial–interglacial cycle; specifically, the impact of continental glaciers, permafrost, and methane hydrate, on the evolution of groundwater from crystalline shield environments. Several different geochemical indicators of freezing processes (either glacial or permafrost-related) were utilized: comparisons of Na/Cl and Br/Cl ratios, δ18O and δ2H values, and δ18O values and Cl− concentration. During freezing, fluids with different dominant cations follow distinctly different linear trends when Na/Cl and Br/Cl ratios are compared. Significantly, none of the freezing trends follows the trend hypothesized by Herut et al. (1990) for the evolution of seawater chemistry during freezing. Intrusion of glacial meltwater and in situ freezing (i.e., permafrost formation) result in a similar end-member when comparing δ18O values and Cl− concentration. The geochemical influence of a freezing process on fresh, brackish, and some saline fluids was identified at some, but not all Canadian Shield sites, regardless of site location with respect to modern-day permafrost. Appreciably, physical and geochemical data do not support the formation of brines through any freezing process in the Canadian and Fennoscandian Shields, as hypothesized by Starinsky and Katz (2003). Rather, on all diagnostic freezing plots, brines are an end-member, indicating a different evolutionary pathway. Significant depletions in 18O with respect to modern precipitation, an indication of either glacial meltwater or a freezing process, were identified at depths of up to 1 km at some sites in the Canadian Shield, and to shallower depths in the Fennoscandian Shield. The potential of this fluid to reach such depths could be attributable to artificial gradients and mixing, glacial recharge, permafrost or paleo-permafrost formation, or methane hydrate or paleo-methane hydrate formation. At most locations it was not possible to distinguish between the different scenarios using the current geochemical database.
A synthesis of Sr isotope data from shallow and deep groundwaters, and brines from the Fennoscandian and Canadian Shields is presented. A salinity gradient is evident in the water with concentrations varying from approximately 1–75 g L−1 below 1500 m depth in the Fennoscandian Shield and from 10 up to 300 g L−1 below 650 m depth in the Canadian Shield. Strontium isotope ratios were measured to assess the origin of the salinity and evaluate the degree of water–rock interaction in the systems. In both shields, the Sr concentrations are enriched relative to Cl, defining a positive trend parallel to the seawater dilution line and indicative of Sr addition through weathering processes. The depth distribution for Sr concentration increases strongly with increasing depth in both shields although the variation in Sr-isotope composition does not mirror that of Sr concentrations. Strontium-isotope compositions are presented for surface waters, and groundwaters in several sites in the Fennoscandian and Canadian Shields. Numerous mixing lines can be drawn reflecting water–rock interaction. A series of calculated lines links the surface end-members (surface water and shallow groundwater) and the deep brines; these mixing lines define a range of 87Sr/86Sr ratios for the deep brines in different selected sites. All sites show a specific 87Sr/86Sr signature and the occurrence of large 87Sr/86Sr variations is site specific in both shields. In Canadian Shield brines, the Sr isotope ratios clearly highlight large water rock interaction that increases the 87Sr/86Sr ratio from water that could have been of marine origin. In contrast to the Canadian Shield, groundwater does not occur in closed pockets in the Fennoscandian, and the well-constrained 87Sr/86Sr signatures in deep brines should correspond to a large, well-mixed and homogeneous water reservoir, whose Sr isotope signature results from water–rock interaction.
The Palmottu uranium ore deposit, located within a granitic host rock in southern Finland, is an excellent setting for conducting analogue studies to assess radionuclide transport from the uranium deposit fractured crystalline host rock. In this context, Nd isotope ratios are used to establish the degree of water–rock interaction (WRI) and to clarify mixing processes within the groundwaters. Variations in Nd isotopes in selected water types from the Palmottu hydrosystem provide new information on the mixing history.
The Fennoscandian Shield has been subjected to several glaciations over the past million years, the last of which (Weichselian Ice Age) ended only at about 10Ka. Here we used boron isotopes and B contents to (a) establish the degree of water-rock interaction (WRI) and (b) clarify freezing processes within groundwaters from the Aspo site in Sweden and from various sites in Finland. The high delta(11)B values recorded by all groundwaters (up to 51.9 per thousand) including diluted, boron-poor, inland groundwaters suggest selective uptake of (10)B into ice related to freezing processes under permafrost conditions. According to co-existing ice and residual brines in a Canadian frozen mine, this fractionation process, enhanced by Rayleigh fractionation, can generate a natural field of isotopic variation around 60 per thousand and provides a new application of B isotope that makes possible to easily characterise groundwaters that underwent past permafrost conditions.
Groundwaters collected at deep levels in the granitic body of Stripa in central Sweden, are of a saline type. Our results clearly discard a marine origin for the primary waters, but they do not definitely address the alternative possibility which is a leaching of fluid inclusions.-from Authors
Atmospheric acidic deposition introduces hydrogen ions to terrestrial and aquatic ecosystems, which become partially neutralized by chemical weathering. In the southern Alps of Switzerland, small catchments containing little or no soil and lacking carbonate minerals represent sensitive hydrological settings in which the relationship between alteration of granitic gneiss by acid deposition and the resulting composition of lake waters can be studied. Mass balance calculations and the stoichiometry of suitable chemical reactions representing the weathering processes were used to derive a plausible reaction sequence on the interaction of the predominant reactive rock minerals with acid precipitation that accounted for the measured chemical composition of the acid lakes. -from Authors
The RbSr isotope systematics of bedrock, soil digests, and the cation exchange fraction of soils from a granitic glacial soil chronosequence in the Wind River Mountains, Wyoming, USA, were investigated. Six soil profiles ranging in age from 0.4 to ∼300 kyr were studied and revealed that the ratio of exchangeable strontium in the B-horizons decreased from 0.7947 to 0.7114 with increasing soil age. Soil digests of the same samples showed much smaller variation in from 0.7272 to 0.7103 and also generally decreased with increasing soil age. Elevation of the ratios of Sr released by weathering over the soil digest and bedrock values results from the rapid weathering of biotite to form hydrobiotite and vermiculite in the younger soils. Biotite is estimated to weather at aaproximately eight times the rate of plagioclase (per gram of mineral) in the youngest soil profile and decreases to a rate of only ∼20% of that of plagioclase in the oldest soil. ratios of the soil cation exchange fraction are estimated to be depleted by factors of up to 11 over the ratios released by weathering, due to ion exchange partitioning. This study demonstrates that the ratio released by weathering of crystalline rocks can deviate significantly from bedrock values, and that in soils less than ∼20 kyr in age which contain biotite in the soil parent material, weathering-derived values can be elevated so dramatically that this factor must be considered in estimations of weathering rates based on strontium isotopes.
Based upon dissolution of feldspars under controlled laboratory conditions, we conclude that Sr release, at pH 3, is neither consistently stoichiometric nor constant for the feldspars measured. Bytownite, microcline, and albite all initially release Sr at rates which are 5 (bytownite) to 160 (microcline) times faster than steady-state release rates. The Sr/Si ratios in the early effluents are significantly elevated compared to the bulk mineral values. The 87Sr/86Sr measured in effluent early in dissolution is higher than the bulk mineral 87Sr/86Sr for bytownite, but lower than bulk mineral ratios for microcline and albite. 87Sr/86Sr ratios for the feldspar powders also changed markedly during dissolution of the three phases. In part, nonstoichiometric release of Sr can be explained by the presence of secondary phases (exsolution lamellae or minute quantities of accessory phases) or by surface leaching. Although we infer that these feldspars eventually release Sr with isotopic composition roughly equal to that of the bulk mineral at steady-state, the feldspars dissolve at extremely different rates (bytownite releases Sr at a steady-state rate ∼102 to 103 times faster than albite and microcline, at pH 3). Therefore, a mixture of these feldspars, or of other minerals exhibiting vast differences in dissolution rate, will release 87Sr/86Sr ratios distinctly different from the bulk whole rock. In addition, initial Sr release rates of the minerals (bytownite > microcline > albite) differ from steady-state release rates (bytownite > albite > microcline), complicating analysis of weathering solutions. Log (rate constants) for bytownite, albite, and microcline decrease from −13.5 to −16.4 to −17.2 (mol Sr cm−2 s−1). Interpretation of catchment scale riverine 87Sr/86Sr ratios on the basis of whole-rock Sr isotopes is, therefore, problematic at best, and would require normalization of bulk isotopic ratios by relative rates of dissolution of Sr-contributing phases.
Canadian Shield brines are characterized by high concentrations of both
stable iodine and 129I, the former reflecting its
concentrated but diagenetically modified seawater origin, and the latter
its long subsurface residence time within its host shield rocks. Stable
iodine concentrations in the Yellowknife brine are as high as 18 mg/L,
requiring the contribution of iodine from an external marine reservoir.
This reservoir likely comprised organic-rich marine sediments in the
basin where the brine was produced. Diagenesis of these sediments
released iodine to the brine during its infiltration into the
subsurface. 129I concentrations in the Yellowknife brine are
as high as 3.4 × 108 atom/L and are due to the fission
of 238U in the rock matrix and subsequent diffusion of the
radiogenic 129I into the fracture fluids. This concentration
is close to the predicted secular equilibrium concentration for a fluid
in basaltic rock with a uranium concentration of 1 mg/kg after the
residence time of ˜80 m.y. required for secular equilibrium has
been attained. This time period is interpreted as the minimum residence
time of the Yellowknife brine in the shield, but it may be much greater,
possibly dating back to Middle Devonian time when most of the
present-day shield was covered by seawater. Similarly high stable iodine
and 129I concentrations measured in the Sudbury brine support
a generic, ancient marine hypothesis for the origin of shield brines.
Stable iodine and 129I concentrations in the shallower mine
waters are the result of mixing between the brine and low-iodine modern
meteoric recharge that is enriched in 129I due to global
fallout from nuclear fuel waste reprocessing activities.
The growing understanding of the molecular basis of carcinogenesis has revolutionized the field of cancer genetics.The discovery of genes that, when somatically altered, are involved in tumor development and in the progression of a variety of cancers has led to entirely new avenues of research to identify molecular targets for therapeutic interventions and management of cancer patients.27 The process of gene discovery has been greatly enhanced by the study of families with hereditary cancer to identify and characterize the molecular basis of susceptibility to cancer.14 This research strategy has resulted in the identification of dozens of cancer genes associated with a variety of hereditary cancer syndromes.34Table 1 summarizes some of the better known syndromes for which genetic testing may improve cancer risk management of patients and their families.
The results of subsequent studies that link mutational and molecular data with clinical phenotypes among patients and families have been even more intriguing. For example, mutation in the APC gene was found to be the genetic basis for the autosomal dominant colorectal cancer syndrome, familial adenomatous polyposis (FAP). It was subsequently discovered that Gardner's syndrome (in which additional extracolonic manifestations occur, such as osteomas and desmoid tumors) was caused by mutations in the same gene and could be clinically categorized with FAP on molecular grounds.35 On the other hand, in some patients Turcot's syndrome, once thought to be an autosomal recessive condition featuring colon tumors and brain tumors, 52 has been found to result from mutations in the APC gene (which cause FAP), but in other patients Turcot's syndrome is caused by mismatch repair genes associated with autosomal dominant hereditary nonpolyposis colorectal cancer (HNPCC) syndrome.20 Thus, molecular genetic testing can enhance clinical diagnoses. It has also been learned that, depending on the location of a mutation within a gene, there may be variation in phenotype severity. The location of the mutation in the APC gene may cause attenuated polyposis or dense polyposis. 47 and 48 A gene can give rise to different syndromes altogether. For example, multiple endocrine neoplasia type 2A and type 2B, familial medullary thyroid cancer, and Hirschsprung's disease are all caused by mutations involving different regions of the RET gene. 9, 13, 22, 33 and 44 The ability of molecular genetic testing to distinguish among various forms of inherited cancer will prove valuable as genetic knowledge and technology are incorporated into clinical practice.
We propose an experimental evaluation of the simultaneous dissolution rate of K-feldspar, biotite and plagioclase during the interaction between a granite and a fluid artificially enriched in the less abundant strontium and potassium isotopes. Experiments were carried out at 453 K and 10 bars, for a time of 6 months, putting powered granite in contact with fluids, spiked in 39K and 84Sr, and saturated with respect to kaolinite, low-temperature albite, prehnite, calcite, adularia and quartz. The evolution of the (Rb/39K)sol vs. (41K/39K)sol and (87Sr/86Sr)sol vs. (84Sr/86Sr)sol ratios allows us to identify a single rock end-member from the first month of interaction. This indicates that the dissolving mineral assemblage remains constant during the remaining 5 months of interaction. Associating the mass conservation law to the isotopic mixing equations for both Sr and K, we evaluate that the mass of dissolved plagioclase is 3–4 times higher the mass of dissolved biotite and 10–20 times higher the mass of dissolved sanidine. The rate of potassium dissolution is estimated assuming that the (41K/39K)sol ratio is continuously in equilibrium with the ratio in neogenic phases. Coupling the proportion of dissolved minerals to the overall rate of potassium dissolution and normalising to the mineral surface area, we finally estimate that, in our experimental conditions, plagioclase and biotite dissolve with a rate of, respectively, 3±1×10−12 and 6±2×10−13 mol m−2 s−1, while the K-feldspar dissolution rate is 4±2×10−13 mol m−2 s−1.
The East Bull Lake pluton is a 2.48 Ga-old, layered mafic intrusion located on the southern margin of the Superior Province, Precambrian Shield in Ontario, Canada. The groundwaters have been studied as part of a detailed geological mapping and geochemical study of the pluton for the Canadian Nuclear Fuel Waste Management Program.All groundwater samples are dilute—the most concentrated NaCl type water contains 3.1 g/l total dissolved solids. Present day87Sr/86Sr values of the rock samples varies from 0.705 to 0.714 and the groundwaters from 0.711 to 0.720. The CaHCO3 recharge waters show the greatest range in values, in contrast to the deeper NaHCO3 and deep NaCl waters where a narrow range of 0.712–0.713 is found. Fracture-filling laumontite, calcite and gypsum have the same isotopic signature as the deep water.The CaHCO3 water is the youngest component of the groundwater system and its spread in isotopic values reflects local conditions at the surface. The NaCl water is considered to be the oldest component and its Sr isotopic ratio value indicates equilibration with silicate fracture mineral phases. The isotopic data suggest that laumontite, calcite, and gypsum fracture phases have either crystallized from this water or are currently controlling its isotopic composition by dissolution. No age can be assigned to the deep waters, except that the NaCl component may date from the Early Paleozoic, based on geological arguments or, more likely, be 104–106 years old based on kinetic studies of rock-water interaction and other isotopic data.If seawater was one component of the NaCl water history, there is no record of this in the87Sr/86Sr ratios.
The recent literature on the kinetics of water-rock interactions is reviewed. The data are then extended to provide a quantitative framework for the description of weathering and alteration. The available experimental data on dissolution of silicates verifies quantitatively the usual mineral stability series in sedimentary petrology. The rate of hydration of carbonic acid is shown to be a possible limiting factor in water-rock interactions. The framework is developed to enable use of laboratory dissolution experimental results and thermodynamics to arrive at a rate law applicable up to equilibrium and therefore applicable to natural systems. The kinetic justification for the significance of a water-rock ratio is discussed. With a proper treatment of fluid flow, the equations are applied to the weathering profile leading to the development of bauxites from nepheline syenites.
Saline Ca-Na/Cl type groundwaters and brines sampled in deep mines over an extensive area of the Canadian Precambrian Shield have elevated Br / Cl ratios which may indicate that the chlorinity of these waters was derived from the infiltration of residual evaporitic brines, remnants of the great marine incursions of the Paleozoic era. Boron concentrations in these waters are generally low (i.e., < ~2 mg/ L) relative to seawater or Alberta Basin Devonian formation waters. However, the 11 B / 10 B ratios of these waters are significantly greater than the average value for continental crustal rocks with the highest values (~4.19) approaching that of present-day seawater (4.20). Moreover, the boron isotopic ratios generally trend to higher values with increasing chlorinity which supports the conclusion from the Br-Cl relationship that most of the chloride in shield brines is of marine origin, rather than a product of water/rock interactions. If this is correct, crystalline rocks must then be sufficiently permeable on a regional scale to have allowed the brine to infiltrate to depths of several kilometers where it now resides.
Atmospheric acidic deposition introduces hydrogen ions to terrestrial and aquatic ecosystems, which become partially neutralized by chemical weathering. In the southern Alps of Switzerland, small catchments containing little or no soil and lacking carbonate minerals represent sensitive hydrological settings in which the relationship between alteration of granitic gneiss by acid deposition and the resulting composition of lake waters can be studied. Transmission and scanning electron microscopy, coupled with X-ray powder diffraction of lake sediments from such areas showed mainly unaltered minerals from parent rocks and no secondary silicate minerals. Element mapping indicated noncrystalline aluminum hydroxide as a product of the chemical weathering of silicates. Noncrystalline iron hydroxide was also observed. Mass balance calculations and the stoichiometry of suitable chemical reactions representing the weathering processes were used to derive a plausible reaction sequence on the interaction of the predominant reactive rock minerals with acid precipitation that accounted for the measured chemical composition of the acid lakes.
The Carnmenellis granite and its aureole contain the only recorded thermal groundwaters (up to 52 °C) in British granites. They occur as springs in tin mines at depths between 200 and 700 m and most are saline (maximum mineralization 19 310 mg 1 ⁻¹ ). Mining activity has disturbed the groundwater circulation pattern developed over a geological time-scale and levels of bomb-produced tritium (> 4 TU) indicate that a significant component (up to 65 %) of the most saline waters are of recent origin. All components of all the mine waters are of meteoric origin. Radiogenic ⁴ He contents, ⁴⁰ Ar/ ³⁶ Ar ratios, and uranium series geochemistry suggest that the thermal component has a likely residence time of at least 5 × 10 ⁴ years and probably of order 10 ⁶ years.
The thermal waters have molar Na ⁺ /Cl ⁻ ratios considerably less than 1 but they are enriched relative to sea water in all major cations except Mg. The groundwater is also particularly enriched in Li with contents ranging up to 125 mg 1 ⁻¹ . The groundwater salinity, which may reach a maximum of 30 000 mg 1 ⁻¹ , is shown to result from weathering reactions of biotite (probably through a chloritization step) and plagioclase feldspar, to kaolinite. On volumetric considerations, fluid inclusions cannot contribute significantly to the groundwater salinity, and stable isotope ratios rule out any contribution from sea water.
Groundwater silica contents and molar Na ⁺ /K ⁺ ratios suggest that the likely equilibration temperature is 54°C, which would imply a depth of circulation of about 1.2 km.
The most important weathering reaction that neutralizes incoming atmospheric acidity in the South Cascade Lake basin is weathering of calcite, which occurs in trace amounts in veins, on joint surfaces, and as a subglacial surficial deposit. Although the basin is underlain by igneous and high-grade metamorphic rocks, weathering of plagioclase is quantitatively negligible; the principal silicate weathering reaction is alteration of biotite to vermiculite. These conclusions are based on mass-balance calculations involving runoff compositions and on mineralogical observations. For predictive modeling of the effects of increased acid deposition, it is essential to identify the relevant weathering reactions. Feldspar weathering is commonly not an important source of solutes in alpine basins underlain by granitic rocks. *Present address: Bureau of Reclamation, Pecos River Projects Office, P.O. Box 1356, Carlsbad, New Mexico 88220
A Sr isotopic study combined with stable isotope determinations ( 18 O and 13 C ), petrographic observations and speciation calculations suggests that the Stripa granite (Sweden) contains at least three different types of calcite veins. One type with 18 O = -18 to -24%. (PDB) and 87 Sr / 86 Sr = 0.7814 to 1.0696 probably formed at temperatures above 200°C, together with chlorite and epidote, during one or two metamorphic events which are recorded in the Rb-Sr systematics of some minerals of the granite at 1.4 and 0.8 Ga. Another type with 18 O = -12 to -18%. (PDB) and 87 Sr / 86 Sr = 0.7406 to 0.7536 and mainly associated with chlorite, is most likely in equilibrium with the presentday groundwaters, which probably have reacted with the fracture minerals of the granitic body for a long time without any supply of external fluids. The third type of calcite with 18 O = -12 to -18%. (PDB), 13 C = -5 to -45%. (PDB) and 87 Sr / 86 Sr = 0.7266 to 0.7406, could have formed from reactions involving methane oxidation or sulphate reduction in the presence of bacteria.
The chemical and isotopic compositions of groundwaters in the crystalline rocks of the Canadian Shield reflect different degrees of rock-water interactions. The chemistry of the shallow, geochemically immature groundwaters and especially of the major cations is controlled by local rock compositions, whereby dissolution reactions dominate. Conservative constituents, such as chloride and bromide, however, are not entirely a result of such reactions but appear to be readily added from leachable salts during the initial stages of the geochemical evolution of these waters. Their concentration changes little as major cations increase, until concentrations of Total Dissolved Solids (TDS) reach 3000 to 5000 mg 1−1. The isotopic composition of these shallow waters reflects local, present day precipitations.In contrast to the shallow groundwaters, the isotopic and chemical compositions of the deep, saline waters and brines are determined by extensive, low-temperature rock-water interactions. This is documented in major ion chemistries, 18O contents and strontium isotopic compositions. These data indicate that the deep brines have been contained in hydrologically isolated “pockets”. The almost total loss of primary compositions make discussions on the origin of these brines very speculative. However, all brines from across the Canadian Shield have a very similar chemical composition, which probably reflects a common geochemical history. The concentrations of some major and most minor elements in these fluids appear to be governed by reactions with secondary mineral assemblages.
We have determined the concentration and isotopic composition of Sr and Nd in waters from the Baltic Sea. The Baltic Sea is an intracontinental, stratified, brackish water, estuarine-like system, and the rivers emptying into it drain a suite of terranes ranging from Proterozoic-Archean in the north to Phanerozoic in the south. The sampled brackish waters range in salinity from seawater (SW) at 35.289‰ to a minimum of 2.460‰ at the surface in the innermost part of the Gulf of Bothnia. The Sr concentrations show generally conservative behavior, indicating a simple two-component mixing. However, small deviations (3–70 ‰) from a perfect mixing line reveal that the imprints from rivers with different Sr concentrations are preserved in the blending. Strontium concentrations from a depth profile across the redoxcline in the Baltic proper indicate that vertical particle transport alters the Sr concentration in the water. Our estimated concentration of Sr in the average freshwater input to the Baltic is ∼ 0.03 ppm, which is only about 0.4% of the SW concentration. The Sr isotopic data range from ε^(Sr)(SW) = 0 in seawater to ε_(Sr)^(BW)(SW) = 7.8 in the least saline Baltic water (BW) sample in the Gulf of Bothnia. The isotopic composition of Sr versus 1/Sr in the Baltic Sea follows an almost perfect mixing line, which shows that seawater Sr is mixed with much more radiogenic components. Calculated end-member values of ε_(Sr)^*(SW) for each sample show that the riverine input into the Gulf of Bothnia has ε_(Sr)^*(SW) = 120–200 and 10–50 ε units in the Baltic proper. These values are in general agreement with direct measurements of river waters in each region. However, the calculated values in the Gulf of Bothnia are lower than the measured river water input in this region, which indicates the presence of less radiogenic Sr, presumably originating from the river waters draining the southern part of the basin which are partially transported northward and mixed with Sr from the Gulf of Bothnia rivers.
The Nd concentration in the Baltic Sea is not conservative, varying between 5 and 45 ppt, with the highest concentrations in the bottom waters due to vertical particulate transport. A plot of ε_(Nd)(O) in Baltic water yields a good correlation with the calculated freshwater end member ε_(Sr)^*(SW). The data show that it is possible to unravel the different freshwater sources into the Baltic and to identify the zones of particulate removal of both non-conservative species such as the REE and of quasi-conservative species such as Sr. The use of isotopic tracers in this estuarine environment may provide a much better insight into mixing and element transport. It should also be possible to trace lateral movements of freshwater inputs.
The mixing equation applied by Vollmer [1] to Pb and Sr isotope ratios is shown to be a general equation applicable to consideration of element and isotope ratios. The mixing equation is hyperbolic and has the form:Ax + Bxy + Cy + D = 0where the coefficients are dependent on the type of plot considered: i.e. ratio-ratio, ratio-element, or element-element. Careful use of this equation permits testing whether mixing is a viable process, places constraints on end member compositions, allows distinction between mixing of sources and mixing of magmas, and should allow distinction between recent mixing and long-term evolution of sources.The available chemical data for postglacial basalts from Iceland and along the Reykjanes Ridge are not consistent with either mixing of magmas or simple mixing of an enriched ocean island source with a depleted ocean ridge source. If the available analyses for basalts are representative of the source regions, the data are consistent with at least two models neither of which can be properly tested with the available data.(1) There are two separate mixing trends: one beneath Iceland with the alkali basalt source and a depleted Iceland source as end members; the second along the Reykjanes Ridge with a heterogeneous ocean ridge basalt source and a source similar to that for intermediate basalts on Iceland as end members. The depleted Iceland source and the depleted ocean ridge source are not the same.(2) The chemistry of the basalts is not determined by mixing. Instead the basalts are derived from a multiplicity of sources with a similar history which have been isolated for hundreds of millions of years.
Surface and mineral waters from a geothermal area (Cézallier) in the centre of the Massif Central, France, were analysed for Sr isotopes, Sr and major elements in order to use Sr isotopes to investigate the discharge of a mineralised water area, especially in the case of disseminate mineralised water emergences.The 87Sr86Sr ratios of mineralised waters ranged from 0.715541 to 0.716773. The variation in 87Sr86Sr values was small for the 5 mineral springs sampled over two periods (5 × 10−6–14 × 10−6). Regarding the reproductivity of the 87Sr86Sr ratio measurements, no differences can be seen and the 87Sr86Sr ratio of mineral waters can be considered to be constant with time. The 87Sr86Sr ratios of surface waters collected along the Zagat River ranged from 0.705303 to 0.715091. The lowest values were always observed in the headwaters. The difference in the 87Sr86Sr ratios between the two sampling periods was ∼ 22 × 10−4 and can be related to the hydrological situation (low or high flow). The 87Sr86Sr ratios of surface waters collected in the drain ranged from 0.715072 to 0.716585. The difference in the 87Sr86Sr ratios between the two sampling periods is ∼ 11 × 10−4 for the drain headwaters and ∼ 13 × 10−5 at the outlet of this area. Likewise, these variations can also be related to the hydrological situation.Plots of 87Sr86Sr vs. 1Sr ratios show two distinct binary mixing trends and the existence of at least four end-members. A mixing parameter f giving the proportions of the two components can be estimated for assumed 87Sr86Sr ratio and Sr content values of the pure end-members.An estimate of the mineral water discharge can be calculated using the results of the mixing model and the measured flow. In the drain area, the mixing model gives an estimate ∼ 0.5–1 l s−1, or 10–13% of mineral water in the total flow. A similar calculation was done for the river where the mineral water flow was ∼ 0.96 l s−1 (3.5 m3 h−1 100 m downstream from the bridge in April 1994, and 6 m3 h−1 20 m downstream from the bridge in September 1994.
Twenty-four groundwater samples from seven operating mines at Sudbury, Yellow-knife and Thompson (Ontario, North West Territories and Manitoba, resp.), all from depths greater than 1 km and ranging in total dissolved solids (TDS) from 1900 to 250,000 mg l−1, were measured for their values. Each geographic location gives a limited range in values and each location is distinct from the others. This is interpreted as the result of extensive water-rock interaction on a local scale. For most of the time, these brines were isolated and only recently have been exposed to surface water as a result of the mining operations. The extent of the isolation is shown by the contrasting isotopic values of two “pockets” of water (0.711 vs. 0.716) located on opposite sides of the same fault system on the North Range at Sudbury. The exchange at all sites probably has continued until the present, as indicated by the close agreement between water and present-day whole-rock values. If so, it suggests that there is no single age for such brines, but it may be possible to date stages in the water's evolution by determining the age of secondary minerals that equilibrated with the water.
Strontium isotope ratios are used to identify end-member ground-water compositions at Äspö in southeastern Sweden where the Hard Rock Laboratory (HRL) has been constructed to evaluate the suitability of crystalline rock for the geologic disposal of nuclear waste. The Hard Rock Laboratory is a decline (tunnel) constructed in 1.8 Ga-old granitic rock that forms islands in an archipelago along the Swedish coast. Ground-water samples were obtained for isotopic analyses from boreholes drilled from the surface and from side boreholes drilled within the HRL. Infiltration at Äspö occurs primarily through fractures zones in the granitic bedrock beneath thin soils throughout the area. Because of extremely low Sr concentrations, rain and snow are not important contributors to the Sr isotope budget of the ground-water system. At shallow levels, water percolating downward along fractures and fracture zones acquires a δ87Sr between +9.5 and +10.0‰ and maintains this value downward while Sr concentrations increase by two orders of magnitude. Ground-water samples from both boreholes and from in the HRL show the effects of mixing with saline waters containing as much as 59 mg/L Sr and δ87Sr values as large as +13.9‰. Baltic Sea water is a potential component of the groundwater system with δ87Sr values only slightly larger than modern marine values (+0.3‰) but with much lower concentrations (1.5 mg/L) than ocean water (8 mg/L). However, because of large Sr concentration differences between the saline groundwater (59 mg/L) and Baltic Sea water (1.5 mg/L), δ87Sr values are not particularly sensitive indicators of sea-water intrusion even though their δ87Sr values differ substantially.
Dissolution of minerals by water is an important Earth surface geochemical process. Notable examples include weathering in soils and dissolution of planktonic tests in the deep sea. Although much work has been done in predicting, from thermodynamic calculations, whether or not dissolution can occur, little attempt has been made to elucidate how dissolution occurs under natural conditions. The purpose of this paper is to point out some of the factors that control the rate of dissolution of minerals and to give the reader a better idea of the applicability of chemical kinetics to the solution of geochemical problems.
In late February 1988, fresh snow was sampled at eight stations along a 450 km long transect, spanning the Scandinavian Peninsula from the Atlantic Ocean in the west to the Gulf of Bothnia in the east. The elements Na, Mg, Ca, S, Cl, Sr, Al, Fe, Mn and Zn were analyzed, and the nuclide pairs 87Sr86Sr, 18O16O and 2H1H measured.The concentrations of Na, Mg, Cl and Sr decrease rapidly with distance from the Atlantic coast. The other elements studied reflect more complicated patterns, caused by addition of terrigeneous matter and anthropogenic pollution.Stable oxygen and hydrogen isotopic compositions follow the general precipitation pattern, with values close to seawater in the west, becoming isotopically progressively lighter eastwards.The 87Sr/86Sr ratio in snow varies from 0.7098 near the Atlantic Ocean to 0.7194 at the easternmost station. Mixing calculations reveal that seawater contributes about 90% of the Sr at the westernmost stations, decreasing to 10–30% some 300 km eastwards. The increase in the 87Sr/86Sr ratio inland is controlled by Sr fractions more radiogenic than seawater, but strongly heterogeneous. The easternmost station is distinctly influenced by pollution, giving enhanched concentrations of S, Ca and Sr and the highest 87Sr/86Sr ratio.
We present a continuous Sr-isotope depth profile of waters, sampled in situ in the deepest borehole in Finland (˜1.1 km). The waters, all with a meteoric oxygen- and hydrogen-isotope signature, are compositionally stratified; a recent fresh-water zone (0.05 mg/L Sr, 87Sr/86Sr >0.730) ˜400 m thick is underlain by two saline-water zones, the upper with ˜25 mg/L Sr and 87Sr/86Sr = ˜0.724, the lower with 45 mg/L Sr and 87Sr/86Sr = ˜0.723. The Sr-isotope data show that the stratification is not due merely to upward dilution of saline water by fresh surface waters; two discrete saline waters are present. The two saline-water components are homogeneous in composition, apparently unaffected by local variations in rock composition either within the borehole or between neighboring boreholes. The implication is that the saline waters did not develop in isolated pockets but, rather, in large, well-mixed bodies. Most likely salinization mechanisms involve breakdown of low-Rb/Sr minerals (e.g., plagioclase feldspar) and/or leaching of fluid inclusions.
This is a text in isotope geology/geoscience that integrates material taught in various courses into a unified picture of the earth sciences. It presents an exposition of the principles used in the interpretation of isotopic data and shows how such interpretations apply to the solution of geological problems. References up to 1985 are included with chapters in this edition. New chapters on Sm-Nd, Lu-Hf Re-Os, and K-Ca decay schemes and cosmogenic radionuclides have been added. Data summaries and references have been expanded.
Analyses of saline waters, fracture minerals, and host rocks from seven localities on the Canadian Shield demonstrate the utility of the ratio in the study of groundwater systems in crystalline rocks. The ratios range from 0.704 to 0.753 and have obtained their signatures by mineral/rock interactions, primarily involving the feldspars. We have identified brines from isolated pockets in the same mines where extensive flow regimes exist. There is mixing of different brines as well as mixing with meteoric waters.The isotopic results on calcites from fractures and shear zones show more than one generation of mineral growth in a given fracture. The ratios of the calcites vary from values identical to the present-day brine in the fracture zone to ratios with Archean signatures. This implies that activity may occur in fault zones over a very long time.The brines are very rich in Sr (up to 2400 mg/1), very low in Rb, and have relatively radiogenic ratios. They are ubiquitous in Shield rocks and, if they were present throughout geological time, they may be one reason why ages of felsic plutons are commonly younger than associated ages.
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.
Fluid-granite interaction at near-equilibrium conditions was investigated by doping an experimental system with 84Sr. Reactions were performed at 453 K, saturated vapour pressure, and fluid/rock ratio of 20. The initial composition of the experimental fluid corresponded to the theoretical saturation with respect to kaolinite, quartz, laumontite, low-temperature albite, calcite and adularia. Sr was used to trace parent-mineral dissolution, neogenic phase precipitation, and to identify the reactions at Sr2+ steady state.The interaction is described, initially, by the isotopic mixing of the solution ratio and the granite ratio. However, in the rock end-member every main mineral has a different ratio. The evolution of ratio in solution as a function of showed that in the early stage of the interaction (where the dissolution of the rock is the dominant reaction) 87Sr-enriched phases, such as biotite, strongly influence the isotopic budget. After some time, the ratio of the fluid approaches the Sr isotopic ratio of the bulk rock, suggesting that fluid-granite isotopic equilibration is attained. When the dissolution of the granite is stopped and once the Sr2+ concentration reached steady state, variations of the ratio with time can be interpreted by an isochemical dissolution-precipitation of neogenic phases.
Using radioactive Eu as a tracer for rare-earth elements (REE), simple experiments were carried out to determine if an re-adsorption artifact occurs during the chemical leaching of marine sediments. Fourteen commonly used chemical leaching solutions were used with and without (controls) the presence of Buzzards Bay (Massachusetts, U.S.A.) sediment. All controls show 100% recovery of soluble 152Eu, indicating no adsorption or precipitation during handling. In contrast, almost all chemical leaching solutions show poor recoveries even at low (2–4) pH. Even for HCl and HNO3, recoveries ranged from 25% to 85% at ≤ 0.2 M. Hydroxylamine hydrochloride in acetic acid, for example, shows only 33% and 57% recoveries for 0.02 M and 0.04 M concentrations, respectively.The results show that large-scale re-adsorption of REE onto sediments occurs even at low pH associated with mineral acids, organic chelators and reductive solutions. Given their large hydrolysis constants, a case is made that one would expect that REE, like Pb and Th, to exhibit significant re-adsorption onto sediments following their dissolution from specific phases. This result reinforces concerns in the literature that chemical leaching techniques have major artifacts associated with non-selectivity and re-adsorption of trace metals. Interpretations of REE diagenesis and authigenesis, based on chemical leaching data, should be viewed with caution.
The Eye-Dashwa Lakes pluton is a Sr-rich felsic intrusive of the sanukitoid suite located in NW Ontario in the Superior Province of the Canadian Shield. The 87Sr/86Sr values of the CaNaCl-type saline, deeper groundwaters fall in the narrow range of 0.7057–0.7070, similar to the 87Sr/86Sr value in plagioclase but not to that in K-feldspar, biotite, or the whole rock. This suggests that the water isotopic composition is the result of plagioclase-water interaction. The fracture minerals gypsum and calcite have similar 87Sr/86Sr ratios, indicating that they have crystallized from waters similar to the present deep groundwaters. The shallow, CaHCO3-type, dilute groundwaters show a wider spread in the Sr ratio of 0.7065–0.7278, reflecting their derivation from minerals in the overlying soil.The results for the saline groundwaters are consistent with thermodynamic and kinetic models that demonstrate the relatively rapid dissolution of plagioclase with respect to other rock-forming silicates, and should have application to most brines located in silicate host rocks.
Sr isotope data from surface, shallow and deep groundwaters from the granitoids of the Vienne District (France) are presented in this paper. In surface waters, the Sr contents in the rocks and groundwaters agree with previous data for groundwaters sampled from granitic and sedimentary rocks in France where a large range in 87Sr/86Sr ratios is observed. After correction for the Sr input from rain, the surface water samples plot within a mixing field that can be explained by three end-members, one anthropogenic (low 87Sr/86Sr and high Cl/Sr ratio) and two end-members characterised by low Cl/Sr ratios and a large range in 87Sr/86Sr ratios (from around 0.707–0.720).For deep groundwaters, the 87Sr/86Sr ratios and Sr contents are also determined by applying a correction to account for the influence of cleaning waters during drilling operations. The results are scattered amongst five different groups and the lack of a direct linear relationship between any of the samples implies that, as found for the shallow groundwaters, the results are due to mixing between more than two end-members.A model to determine the 87Sr/86Sr ratio (Irf) of groundwater after interaction with an actively weathering granite is developed. The results yield a low Irf value for waters associated with weathering of the tonalite (0.70463) and a higher one for waters associated with weathering of the monzogranite (0.70704). Given the much higher Irf values derived from the deep groundwater samples, these results indicate that the deep groundwaters analysed within the Vienne hydrosystem cannot be directly related to weathering of either tonalite or monzogranite. It is speculated that this high 87Sr/86Sr source originated from marine incursions during the Jurassic and have been diluted by mixing with former groundwaters produced by water–rock interaction (WRI) with the granites.
A small watershed (89 km2) underlain by granite or granite-gneiss in the Margeride mountains, southern Massif Central (France), has been studied using the chemical and isotopic composition of its dissolved load, bed sediments and soils. Dissolved concentrations of major ions (Cl, SO4, NO3, HCO3, Ca, Na, Mg, K, Al and Si), trace elements (Rb and Sr) and strontium isotopes have been determined for three different hydrologic periods in the main stream of the Desges river and its tributaries.
The aim was to characterize the chemical and isotopic signatures of each reservoir in the watershed; signature changes are interpreted as fluctuations in the different influencing components: rainwater, weathering products and anthropogenic addition. In the study area, as in other watersheds in granite environments, the only source for input of chemical species into the dissolved load at high altitude is chemical weathering and atmospheric deposition, whereas at lower altitude, human influence plays a non-negligible role.
As precipitation is a major vehicle for the addition of dissolved chemical species into the hydrosystem, a systematic rainwater study using an automatic collector was carried out over one year in order to better constrain rain elemental input. Corrections for rainwater addition, using chloride as an atmospheric-input reference, were computed for selected elements and for 87Sr/86Sr ratios. After these correction, the geochemical budget of the watershed was determined and the role of anthropogenic addition was evaluated based on strontium isotope relationships.
For particulate matter, we used the normalization of chemical species relative to parent rocks and the element ratios which reflect the depletion or enrichment in soils and sediments. Both the immobile- and mobile-element approaches have been tested, using Ti/Zr and La/Ce ratios for the former and Ca/Sr, K/Rb, and K/Fe ratios for the latter.
The 87Sr/86Sr ratios of precipitation, throughfall, groundwater, streamwater and mineral matter were analyzed. Precipitation strontium ratios are around 0.71; throughfall, which is affected by strontium from the mineral soil, has ratios of 0.72–0.73; and shallow groundwater in a drug well and runoff have ratios around 0.73–0.74. There is a tendency for this relationship to be reversed for discharge. Higher ratios are associated with lower discharges. Water from a fracture zone gave the highest value (0.78), approaching the value of the bedrock (around 0.85).A calcium budget, which reflects the mean conditions over a few years, has been calculated. This budget indicates that weathering should be of the order of 8 kg Ca ha−1yr−1 to maintain the pool of exchangeable calcium at a constant level. The major anion in the runoff is suphate, which has entered the system in the form of “acid rain”. Sulphur deposition has been rather constant over the last two decades. If acidification had an effect on weathering of silicates this would have shown up in a tendency of the strontium isotope ratios toward higher values in the soil pool and in runoff water. Thus its seems from the observed ratios that at least a major portion of the excess calcium export resulting from sulphur deposition is taken from the soil pool, resulting in a gradual acidification of the soil.
The use of strontium isotopes to evaluate mineral weathering and identify sources of base cations in catchment waters requires an understanding of the behavior of Sr in the soil environment as a function of time. Our approach is to model the temporal evolution of 87Sr/86Sr of the cation exchange pool in a soil chronosequence developed on alluvium derived from central Sierra Nevada granitoids during the past 3 Ma. With increasing soil age, 87Sr/86Sr of ammonium-acetate extractable Sr initially decreases from values typical of K-feldspar to those of plagioclase and hornblende and then remains constant, even though plagioclase and hornblende are absent from the soils after approximately 1 Ma of weathering. The temporal variation of 87Sr/86Sr of exchangeable Sr is modeled by progressively equilibrating Sr derived from mineral weathering and atmospheric deposition with Sr on exchange sites as waters infiltrate a soil column. Observed decreases in quartz-normalized modal abundances of plagioclase, hornblende, and K-feldspar with time, and the distinct87Sr/86Sr values of these minerals can be used to calculate Sr flux from weathering reactions. Hydrobiotites in the soils have nearly constant modal abundances, chemistry, and 87Sr/86Sr over the chronosequence and provide negligible Sr input to weathering solutions. The model requires time and soil horizon-dependent changes in the amount of exchangeable Sr and the efficiency of Sr exchange, as well as a biologic cycling term. The model predicts that exchangeable Sr initially has 87Sr/86Sr identical to that of K-feldspar, and thus could be dominated by Sr leached from K-feldspar following deposition of the alluvium. The maximum value of 87Sr/86Sr observed in dilute stream waters associated with granitoids of the Yosemite region is likewise similar to that of the K-feldspars, suggesting that K-feldspar and not biotite may be the dominant source of radiogenic Sr in the streams. This study reveals that, when attempting to use Strontium isotopes to identify sources of base cations in catchment waters and biomass, both preferential leaching of Sr from minerals during incipient soil development and changing Sr exchange efficiency must be considered along with chemical contributions due to mineral dissolution.
We have measured and Rb and Sr concentrations in several minerals, primarily sulfides, spanning the paragenesis of hydrothermal mineralization in the Viburnum Trend in southeast Missouri. Separate measurements were made for fluid inclusions opened by crushing or thermal decrepitation and for the solids. For comparison, measurements were also made on samples of probable local aquifers, the Bonneterre Formation and the Lamotte Sandstone. For some of the samples, concentrations of K, Ca, Cl, Na, and Mg are also reported.In several cases are different (higher) in the solids than in the fluid inclusions. We have investigated the possibility that either type of sample gives spurious results, e.g., that the fluid inclusions are secondary or contaminated by host dolomite, or that Sr in the solids reflects a detrital rather than an authigenic source. Consideration of mass balance, overall solute chemistry, and examination of non-sulfide dissolution residue, however, suggests that both types of sample reflect primary fluid Sr composition. We thus adopt the working hypothesis that Sr isotopic composition in fluids at the time of hydrothermal mineralization was highly variable.The observed results for the Viburnum Trend do not conform well to expected trends for Mississippi Valley-type (MVT) mineralization based primarily on analyses of gangue carbonates, barite, and fluorite. Fluid inclusion Sr in some of the Viburnum Trend samples is more radiogenic than in the host dolomite but only moderately so; in other samples, notably main-stage octahedral galena, fluid inclusion Sr composition is within the range observed for the host dolomite. In contrast, Sr in some of the sulfides is very radiogenic, much more so than previously reported for MVT minerals, and is very radiogenic early in the paragenesis (pyrite, chalcopyrite, sphalerite), less radiogenic during main-stage ore deposition, and again more radiogenic in later paragenetic stages.
Na-Ca-Cl groundwaters with salinities of 1 to 30% discharge from natural springs and artesian wells in Mississippian carbonates and Ordovician sandstones and carbonates in central Missouri. Carbonate saturation and quartz supersaturation are maintained throughout the salinity range. Major and trace element and isotopic variations in the waters are used to place constraints on models for rock-water interaction and regional hydrology.
The groundwaters have δD values that range from −108 to −45‰ and δ^(18)O values that range from −14.7 to −6.5‰ (SMOW). These data lie approximately along the meteoric water line, ranging from values similar to local recharge in Missouri, to significantly lower values that are similar to δ^(18)O and δD for meteoric recharge in high altitude and high latitude regions of North America. The more saline samples have the lowest ^(18)O and D contents, a trend that is opposite to that observed in most other studies of saline waters. The H-O isotopic correlation and the range in salinity and several major and trace element concentrations in central Missouri groundwaters are readily explained by a saline-dilute water mixing model. 87Sr/86Sr ratios for the groundwaters range from 0.7155 to 0.7161. These values are significantly higher than previously published values for: 1) estimates of ^(87)Sr/^(86)Sr in Phanerozoic seawater (0.7068–0.7092); and 2) carbonates of the Mississippian Burlington-Keokuk Fm. (0.7075–0.7105), through which some of the waters migrate as they pass to the surface. ϵNd(0) values in the groundwaters range from −10.9 to −8.1, and ^(147)Sm/^(144)Nd ratios range from 0.108 to 0.128. These values are similar to or lower than previously published analyses of carbonates and other authigenic phases from the Burlington-Keokuk Fm. (mean ϵNd(0) = −7.8 ± 0.8 (1σ); mean ^(147)Sm/^(144)Nd = 0.141).
The H, O, Sr and Nd isotopic data and the results of model calculations preclude: 1) models involving the modification of ancient seawater for the origin of the saline waters, and 2) extensive interaction between the groundwaters and their host carbonates. The waters apparently acquired their δ^(18)O and δD values as meteoric recharge and their 87Sr/86Sr and rare earth element signatures from extraformational crustal sources (high ^(87)Sr/^(86)Sr; low ϵNd(0); low 147Sm/144Nd) and largely preserved these isotopic signatures during subsequent migration through the carbonates. Chemical exchange via rock-water interaction is required for isotopic exchange to occur. Therefore, the present state of chemical equilibrium between the groundwaters and carbonate aquifer minerals may serve to limit rock-water interaction, and hence preserve the extraformational isotopic signatures in the waters.
The integration of geochemical, isotopic and hydrologic data on a local and regional scale suggests a history for the central Missouri groundwaters involving: 1) meteoric recharge in the Front Range of Colorado; 2) dissolution of Permian halite in the subsurface of Kansas; 3) interaction with predominantly silicate mineral assemblages in Paleozoic strata (and possibly Precambrian basement), with aquisition of crustal Sr and REE signatures; 4) dilution and migration to shallow aquifer levels in central Missouri; and 5) mixing with local meteoric recharge through Mississippian carbonates with no significant change of the isotopic signatures acquired in stage (3).
Application of the thermodynamic principles of chemical petrology and solution chemistry to the study of geochemical processes permits prediction of the consequences of reaction between aqueous solutions of electrolytes and typical igneous, metamorphic, and sedimentary mineral assemblages. A given geochemical process can be represented by a set of reversible and irreversible chemical reactions that corresponds to an array of linear differential equations relating partial equilibrium and nonequilibrium in thermodynamic systems. Simultaneous evaluation of these equations defines the nature and extent of the compositional change and redistribution of species in the aqueous phase, the order of appearance of stable and metastable phases, and the mass transfer resulting from irreversible reactions between the minerals and the aqueous solution.
The isotopic composition of Sr has been measured in brine samples from the Upper Jurassic Smackover Formation in southern Arkansas; ratios range from 0.7071 to 0.7101. With one exception, the 32 Smackover brines contain Sr which is significantly more radiogenic than the Sr in Late Jurassic sea water, indicating sizable Sr contributions from detrital sources. Isotopic analyses of core samples from rock units associated with the brines and regional stratigraphic relationships suggest that the radiogenic Sr was released from detrital minerals in Bossier shale to interstitial fluids expelled from the underlying Louann Salt in the North Louisiana salt basin. These fluids migrated through the Bossier Formation updip to the South Arkansas shelf, where they entered the upper Smackover carbonate grainstone. The radiogenic fluids mixed with Sr-rich interstitial marine waters that had the isotopic composition of Late Jurassic sea water; mixing in variable proportions resulted in the random distribution pattern of variable ratios that is observed in Smackover brines within the 5000 km2 study area. Isotopic analyses of nonskeletal carbonate grains and coexisting coarse calcspar cement from the upper Smackover grainstone imply that the grains were diagenetically stabilized in the presence of interstitial marine waters, whereas the calcspar cement is a relatively late diagenetic phase precipitated after the arrival of radiogenic fluids.
The stoichiometries of activated complexes responsible for controlling the kinetics of mineral dissolution can be inferred from experimental rate data. Constraints are provided by adsorption equilibria, surface ion exchange reactions, and the pH-dependence of the steady-state rates of surface detachment. Adsorption equilibria may lead to accelerated or decelerated rates of hydrolysis due to formation of surface species. They may also result in pH-independent dissolution rates at low pH as a consequence of hydrogen ion surface saturation. Surface exchange reactions of H+ or H3O+ for M(2) site cations in pyroxenes, Ca2+ in wollastonite, and alkali cations in feldspars go essentially to completion for dissolution in solutions that are appreciably undersaturated with respect to the reactant mineral. The rate of surface exchange is proportional to the fraction of exchangeable cations on the reacting surface, which leads to an integrated exponential relation for mass transfer as a function of time. The independence of detachment rates on the degree of surface exchange indicates approximately equivalent formation of activated complexes at both exchanged and unexchanged sites. The degree of hydration or protonation of activated complexes formed from surface species at active sites can be inferred from the dependence of the steady-state hydrolysis rates on pH.
The 87Sr/86Sr ratios of dissolved strontium in six Sierra Nevada streams at base flow are 0.00070 to 0.00175 higher than the average whole-rock value for the granodiorite bedrock underlaying the drainage basins. We suggest that the strontium isotope ratios and major cation compositions of the stream waters are controlled predominantly by the weathering reactions: plagioclase ⇒ kaolinite and biotite ⇒ vermiculite. Stream drainages that were glaciated ∼10 kyr ago (exposing fresh bedrock surfaces) have 87Sr/86Sr ratios 0.00036 to 0.00105 higher than drainages that were not glaciated in the past ∼100 kyr. We interpret the 87Sr/86Sr ratios of the stream water to indicate that biotite is weathering ∼6 times and ∼4 times more rapidly than plagioclase in the recently glaciated and nonglaciated drainages, respectively. Our results suggest that continental glaciation may have the effect of accelerating biotite weathering, significantly elevating riverine 87Sr/86Sr ratios in regions draining silicate bedrock for periods of ∼100 kyr.
Chemical and isotopic analyses of water from drill holes and mines throughout the Fennoscandian Shield show that distinct layers of groundwater are present. An upper layer of fresh groundwater is underlain by several sharply differentiated saline layers, which may differ in salinity, relative abundance of solutes, and O, H, Sr and S isotope signature. Saline groundwater can be classified into four major groups based on geochemistry and presumed origin. Brackish and saline waters from 50–200 m depth in coastal areas around the Baltic Sea exhibit distinct marine chemical and isotopic fingerprints, modified by reactions with host rocks. These waters represent relict Holocene seawater. Inland, three types of saline groundwater are observed: an uppermost layer of brackish and saline water from 300–900 m depth; saline water and brines from 1000–2000 m depth; and superdeep brines which have been observed to a depth of at least 11 km in the drill hole on the Kola Peninsula, U.S.S.R. Electrical and seismic studies in shield areas suggest that such brines are commonly present at even greater depths. The salinity of all inland groundwaters is attributed predominantly to water-rock interaction. The main solutes are Cl, Ca, Na and Mg in varying proportions, depending on the host rock lithology. The abundance of dissolved gases increases with depth but varies from site to site. The main gas components are N2, CH4 (up to 87 vol.%) and locally H2. The δ13C value for methane is highly variable (−25 to −46%), and it is suggested that hydrothermal or metamorphic gases trapped within the surrounding rocks are the most obvious source of CH4. The uppermost saline water has meteoric oxygen-hydrogen isotopic compositions, whereas values from deeper water plot above the meteoric water line, indicating considerably longer mean residence time and effective low temperature equilibration with host rocks. Geochemical and isotopic results from some localities demonstrate that the upper saline water cannot have been formed through simple mixing between fresh water and deep brines but rather is of independent origin. The source of water itself has not been satisfactorily verified although superdeep brines at least may contain a significant proportion of relict Precambrian hydrothermal or metamorphic fluids.
Dissolved and suspended load river material represents the integrated products of the erosion of drainage basins. To enlarge the study of erosion processes we have determined87Sr/86Sr ratios and the Cl, Na, Mg, Ca and Sr contents for the main tributaries of the Congo River Basin, both for water and suspended sediment. We have also analyzed 30 streams draining monolithological terranes.A systematic study of precipitation has permitted the estimation of a good rain correction factor. Sr isotopic ratios have shown that the seawater input correction based on riverine Cl content is not valid in the Congo Basin because a large part of the Sr, Ca and Mg come from a terrestrial source. The conventional atmospheric input correction by reference to the marine ratios underestimates the real atmospheric input because of the crustal elements carried by rainwaters.Different erosion source parameters have been obtained for carbonates, evaporites and silicates. An inversion scheme has been developed to compute the multimixing equations and allows the quantification of the input of each main reservoir (atmosphere, carbonates, evaporites and silicates) for each tributary and each element. For Ca and Mg, rainfall and carbonate dissolution are the main inputs. For Sr, the input is mainly controlled by rains and silicate weathering.By using Sr isotopic systematics we have calculated the Sr isotopic composition of the silicate weathered crust for each of the main tributaries of the Congo Basin. We obtain uniform values for the main tributaries ranging between87Sr/86Sr= 0.7195 ± 0.001 and 0.7251 ± 0.005. These results allow the calculation of strontium model agesTSr, which differ from neodymium model agesTNd. UsingTNd, we have calculated the87Rb/86Sr of the silicate weathered crust. We obtain homogeneous values close to 0.75, which is in agreement with estimates for the average silicate crust. The discrepancy betweenTSr andTNd may be linked to the vegetation impact which fractionates Rb and Sr.
A study was conducted of the isotopic composition and concentration of Sr and of major elements in dissolved and suspended loads of fresh and brackish waters. The purpose was to establish the contributions of different parent rocks and minerals to Sr during weathering and transport and to identify the role of FeMn oxyhydroxides in the redistribution of Sr in the water column during the sedimentary cycle. Studies were conducted on a profile across an oxic-anoxic boundary in the Baltic and on rivers covering behavior over an annual cycle. In general, the 87Sr/86Sr ratios differ between particulate and dissolved loads, with more radiogenic Sr in the particulate loads. These differences are attributed to differential weathering of minerals, where high Rb/Sr minerals dominate the particulate load and low Rb/Sr the dissolved load. There is broad correlation of 87Sr/86Sr with K/Al in the suspended load. The differences in 87Sr/86Sr between suspended and dissolved load are highly variable and are related to the Fe or Mn concentration on the particulates. In samples with high Fe/Al, the difference becomes small. A good correlation was found between Sr/Al and Fe/Al or Mn/Al in the particulates both in brackish and fresh waters. Sr is removed from solution both in rivers and in the Baltic Sea whenever there is formation of FeMn oxyhydroxide particulates. This precipitation greatly diminishes the difference in isotopic composition of the dissolved and suspended loads. As the particles containing FeMn oxyhydroxides settle, they dissolve in anoxic zones and release Sr. This provides a mechanism for Sr redistribution in the water column. Sr is thus only quasi-conservative in environments where FeMn oxyhydroxides form or dissolve. From consideration of the isotopic differences in Sr between dissolved and suspended loads, it follows that the net Sr input depends upon weathering characteristics of the contributing mineral phases. Changes in weathering mechanisms due to climate change may cause Sr isotopic shifts in the marine environment.
We present major and trace element data on the suspended and dissolved phases of the Amazon River and its main tributaries. The Sr isotopic composition of the dissolved load is also reported. Special attention is paid to the abundances of REE and to their fractionation between the dissolved and suspended phase. The rivers of the Amazon Basin are among the richest in dissolved REE and are similar to the rivers of the Congo system. However a greater range of fractionation between LREE and HREE is reported here. At a global scale the rivers have intermediate patterns between those of the Congo system and those of high pH rivers such as the Indus and Mississippi rivers. Only few elements (Rb, U, Ba, K, Na, Sr and Ca) are mobilized by silicate weathering. These elements are strongly depleted in the suspended phase with respect to upper continental crust. In the dissolved load, these elements are controlled by atmospheric inputs and the weathering of the main lithologies. We propose a model based on mass budget equations, that allow the proportions derived from the different sources to be calculated. As a consequence silicate, carbonate and evaporite weathering rates can be estimated as well as the consumption of CO2 by weathering of each of these lithologies. Physical weathering rates can be estimated by two complementary approaches. On the one hand, the multi-year average of suspended sediments yields can be used to estimate physical denudation. On the other hand, we have developed a steady-state model of erosion that allows us to calculate physical erosion rates on the basis of the dissolved load of rivers. A mean crustal composition is assumed in this model for the rock sources of the drainage basins. Comparison of the rates predicted by the model to the observed rates shows good agreement for the lowland rivers, but a strong discrepancy for the rivers derived from the Andes. Andean rivers (Solimoes, Madeira and Amazon) have observed sediment yields much greater than those predicted according to the steady-state model of chemical and physical weathering. Two interpretations can account for this inconsistency. The first is that these rivers are not in steady state and hence that the soils are being destroyed. The second requires that the local continental crust is different from the average continental crust of Taylor and McLennan, and contains a large proportion of sedimentary rocks. Using the measured sediment yields, and assuming a steady state, we can estimate the amount of sediment recycling for each drainage basin. For the Amazon at Santarem, we find that at least 25% of the mass of the upper continental crust of the Amazon drainage basin is constituted of recycled material.
The Palmottu uranium ore deposit, located within a granitic host rock in southern Finland, is an excellent setting for conducting analogue studies to assess radionuclide transport from the uranium deposit fractured crystalline host rock. In this context, Nd isotope ratios are used to establish the degree of water–rock interaction (WRI) and to clarify mixing processes within the groundwaters. Variations in Nd isotopes in selected water types from the Palmottu hydrosystem provide new information on the mixing history.
Surface water and soil samples were collected from a series of small catchments on granitic gneiss in the Canton of Ticino in southern Switzerland. Elevations of the sampling points ranged from 220 to 2400 m; vegetation varied correspondingly from deciduous forest through coniferous forest to alpine pasture and essentially unvegetated rock and talus. Annual precipitation averaged 1.9 to 2.4 m.The concentrations of the major cations and silica in surface waters decreased more or less exponentially with elevation. The cationic denudation rate decreased from about 500 meq/m2 · y at the lower elevations to about 20 meq/m2 · y at the highest. Alkalinity decreased from 250 to about −7 μeq/1. Although total concentrations decreased with elevation, there were no clear systematic trends in the ratios of the concentrations of the major cations and silica. This suggests that the nature of the secondary minerals formed during weathering in the area does not change with elevation, despite great changes in soil type and environmental conditions.The clay mineralogy of the soils is dominated by unweathered and slightly weathered bedrock minerals: mica and chlorite, hydrobiotite, and poorly characterized mixed-layer material. Small amounts of kaolinite and smectite were observed in a few samples, but there do not appear to be any systematic trends in clay mineralogy with elevation. Mass-balance arguments suggest that the major (in terms of solute generation) weathering product is either kaolinite or a mixture of A1(OH)3 and 2:1 clays.The lack of dependence of weathering stoichiometry on elevation (a surrogate for several environmental variables) or solute concentrations perhaps reflects the importance of local relief, which did not vary systematically with elevation.
Nuclear science and technology EUR 18202
We have analyzed a suite of seventy-four formation-water samples from Mississippian and Pennsylvanian carbonate and siliciclastic strata in the Illinois basin for major, minor, and trace element concentrations and for strontium isotopic composition. A subset of these samples was also analyzed for boron isotopic composition. Data are used to interpret origin of salinity and chemical and Sr isotopic evolution of the brines and in comparison with a similar data set from an earlier study of basin formation waters from Silurian-Devonian reservoirs. Systematics of Cl-Br-Na show that present Mississippian-Pennsylvanian brine salinity can be explained by a combination of subaerial seawater evaporation short of halite saturation and subsurface dissolution of halite from an evaporite zone in the middle Mississippian St. Louis Limestone, along with extensive dilution by mixing with meteoric waters. Additional diagenetic modifications in the subsurface interpreted from cation/Br ratios include K depletion through interaction with clay minerals, Ca enrichment, and Mg depletion by dolomitization, and Sr enrichment through CaCO3 recrystallization and dolomitization. Ste. Genevieve Limestone (middle Mississippian) formation waters show 87Sr/86Sr ratios in the range 0.70782-0.70900, whereas waters from the siliciclastic reservoirs are in the range 0.70900-0.71052. Inverse correlations between 87Sr/86Sr and B, Li, and Mg concentrations suggest that the brines acquired radiogenic 87Sr through interaction with siliciclastic minerals. Completely unsystematic relations between 87Sr/86Sr and 1/Sr are observed; Sr concentrations in Ste. Genevieve and Aux Vases (middle Mississippian) waters appear to be buffered by equilibrium with respect to SrSO4. Although there are many similarities in their origin and evolution, these formation waters are distinguished from Silurian-Devonian brines in the basin by elevated Cl/Br and Na/Br ratios and by unsystematic Sr isotope relationships. Thus waters from these two major segments of the Illinois basin stratigraphic column form distinct geochemical regimes which are separated by the New Albany Shale Group (Devonian-Mississippian) regional aquitard. Geochemical evolution appears to have been influenced significantly by Paleozoic and Mesozoic hydrologic flow systems in the basin. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/31001/1/0000676.pdf
86 Sr values of Canadian Shield brines and fractures minerals with applications to groundwater mixing, fracture history, and geochronology
- Sr Mcnutt Rh
- M Gascoyne
- Kamineni
- Dc
Sr/ 86 Sr values of Canadian Shield brines and fractures minerals with applications to groundwater mixing, fracture history, and geochronology. Geochimica et Cosmochimica Acta, 54, 205±15. McNutt RH, Gascoyne M, Kamineni DC (1987) 87 Sr/ 86 Sr values in groundwaters of the East Bull Lake pluton, Superior Province, Ontario, Canada. Applied Geochemistry, 2, 93±101.