Sr Source Research Articles

Geochemistry and petrogenesis of late Miocene granitoids, Cyclades, southern Aegean: Nature of source components

Neogene igneous activity in the Aegean region comprised both extrusive volcanism and intrusive granitoid plutonism. Granitoid plutonism in the Cyclades was established in the mid-Miocene period and lasted until late Miocene (18 to 9 Ma). The timing of granitoid intrusion was associated with the initiation of extensional tectonics in the Aegean. These intrusions form a broad belt about 200 km long running from the west (Lavrium and Serifos) to the eastern Aegean. Both S-type and I-type granitoids are present, the former generally being emplaced earlier than the I-types (~ 15 to 8.3 Ma). Major and trace element variations reveal that three end-member components are involved in the granitoids, but the proportions of these vary in the different plutons. Initial isotopic compositions of all the granitoids are typical of crust-derived magmas from heterogeneous metasedimentary sources (I-type: 87Sr/86Sr = 0.7091–0.712, εNd = − 6.4 to − 10.4; S-type: 0.710–0715, εNd = − 7.5 to − 10.1). Three end-member sources have been identified: 1) One end-member appears to be a metasedimentary biotite-gneiss (greywacke-type) such as that forming the metamorphic core complexes (Naxos and Paros); this is a dominant (but not the only) component in the S-types. 2a) Major, trace element and Sr–Nd isotopic composition correlations of the S-type granitoids with basement gneiss require an extra source of Sr and Ca, having lower initial 87Sr/86Sr indicating a more depleted metasedimentary source at depth, due to possible interaction, of metamorphic fluids with marbles and amphibolites and infiltration through the gneissic units, at mid-crustal levels. 2b) A possible second end-member could be the marble component, as indicated by the buffered values of the Initial Sr isotopic ratios. Major element variation of the mafic microgranular (quartz diorites and tonalites) enclaves are compatible with dehydration melting of a mafic source similar to the amphibolites (island arc tholeiites) at medium pressure (~ 8 kb) conditions. 3) Amphibolite is another end-member which may contribute mostly to the source of the younger intrusions, along the western flank of the arc.

Strontium isotopes in Chilean rivers: The flux of unradiogenic continental Sr to seawater

Analyses of Chilean river waters indicate that the average yield of unradiogenic Sr (~ 517 mol Sr km − 2 yr − 1 , 87Sr/ 86Sr ~ 0.7057) from western South America (1,220,853 km 2) into the southeastern Pacific Ocean is ~ 2–4 times higher than that from Iceland (~ 110 mol Sr km − 2 yr − 1 , 87Sr/ 86Sr ~ 0.7025) and the Deccan traps, but lower than fluxes of unradiogenic Sr from ocean islands in the Lesser Antilles and Réunion. The Sr flux from western South America accounts for about 1.8% of the annual dissolved Sr delivered to the ocean via rivers. If Chilean rivers analyzed in this study accurately characterize runoff from western South America, active convergent continental margins release about as much unradiogenic Sr to seawater as a 0–1 Myr old mid-ocean ridge segment of equivalent length. Modulations of the flux of unradiogenic Sr from active margins over geologic time scales have to be considered as an additional driving force of change in the marine Sr isotope record, supplementing temporal variations in the submarine hydrothermal flux as a source of unradiogenic Sr to seawater. Such modulations can be driven by changes in the surface exposure of volcanic arc terrains, changes in climate, ocean currents and geographic latitude due to plate tectonics, as well as topographic changes that can affect local rainfall, runoff and erosion.

Deglacial variations of Sr and 87Sr/ 86Sr ratio recorded by a stalagmite from Central China and their association with past climate and environment

A low-resolution strontium isotopic ratio ( 87Sr/ 86Sr) record coupled with a high-resolution Sr concentration profile covering the last deglacial period were obtained for a stalagmite, SJ3, collected from Songjia Cave, northeast Sichuan province, Central China. Both Sr and 87Sr/ 86Sr display significant variations during the period between 20 and 10 ka, which correlate well with oxygen isotope records from Greenland ice cores and speleothems in the East Asian summer monsoon regime, with higher Sr and more radiogenic 87Sr/ 86Sr values occurring during cold-dry climatic phases and vice versa. The Sr in SJ3 shows a negative linear relationship between 87Sr/ 86Sr and 1/Sr, suggesting the binary mixing of two end-members, the host rock of Late Permian limestone with a relatively lower 87Sr/ 86Sr ratio (∼ 0.7071) and an exotic Sr source with a relatively radiogenic 87Sr/ 86Sr ratio (∼ 0.7109 deduced from the 87Sr/ 86Sr-1/Sr correlation). Atmospheric dust activity was suggested to be the most probable factor influencing the two indices. Because the carbonate fraction in wind-blown dust is enriched in Sr and has a more radiogenic 87Sr/ 86Sr ratio, enhanced atmospheric dust activity under stronger Asian winter monsoon which is associated with cold-dry climate would lead to higher Sr concentrations and more radiogenic 87Sr/ 86Sr ratios in SJ3 and vice versa. This interpretation is supported by the general parallelism of the two Sr indices to winter monsoon proxy from East Asia such as the dust flux and quartz median diameter in Luochuan loess profile during the same period. This study suggests that the speleothem 87Sr/ 86Sr ratio and Sr concentration, especially the former in northeastern Sichuan Province can be used to investigate the atmospheric dust activity and Asian winter monsoon.

Chemical and strontium isotope characterization of rainwater at an urban site in Loess Plateau, Northwest China

Major ion concentrations and strontium isotopic ratios ( 87Sr/ 86Sr) were measured in rainwater samples collected at the urban site of Lanzhou, a city located on the Loess Plateau in the arid and semi-arid areas of northwest China. The rainwater samples possessed alkaline pH, at a reference level of 5.6, with a range of 6.82 to 8.28 and a volume-weighted mean (VWM) pH value of 7.70. The alkaline character of rainwater in Lanzhou is due to the result of neutralization caused by the alkaline soil dusts which contain large amount of CaCO 3. It was observed that Ca 2+ was the most abundant cation with a VWM value of 886 µeq l − 1 (115–2184 µeq l − 1 ), accounting for 87.8% of the total cations. Without considering HCO 3 −, SO 4 2− and NO 3 − were dominant among the anions, accounting for 64.2% and 23.0%, respectively, of the total measured anions. Using Na as an indicator of marine origin and Al for terrestrial inputs, the proportions of sea salt and non-sea-salt elements were estimated from elemental ratios. The precipitation in this region has typical continental characteristics. The Sr concentrations varied from 0.004 to 0.885 µmol l − 1 , and strontium isotopic ratios ( 87Sr/ 86Sr) lay in the range of 0.71025–0.71302, with an average of 0.71143. The 87Sr/ 86Sr ratios of Lanzhou rainwater are higher than that of seawater, which reflects contributions from the radiogenic Sr sources of the aerosols. The most suitable candidate for the source would be the soil dust originating from local and distant loess and desert areas. The 87Sr/ 86Sr ratios were used to characterize different sources of base cations in rainwater, suggesting that the samples could be interpreted in terms of combinations of at least three components: soil dust derived from the Loess Plateau and desert areas in northwest China (with 87Sr/ 86Sr ~ 0.7130), seawater (with 87Sr/ 86Sr ~ 0.70917), and anthropogenic inputs (with 87Sr/ 86Sr ~ 0.7103). The high 87Sr/ 86Sr ratio and Ca and Sr content in the rainwater from Lanzhou can be attributed to the dissolution of calcium carbonate in soil dust.

Silicon Carbide for High Signal to Noise Ratio MIPs Detection From Room Temperature to 80$^{\circ}$C

The relatively low value of the number of electron-hole (e-h) pairs per micron for Minimum Ionizing Particles (MIPs) in SiC against the value for Si, imposes severe constrains on the crystallographic quality, the thickness and the doping concentration of the SiC epitaxial layer used as detection medium. In this work, a 85 mu m thick 4H-SiC epitaxial layer with a low doping concentration, N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> les 1 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , was used in order to have a high number ( ap 4700) of e-h pairs generated by a MIP in the active region. We present experimental data on the charge spectrum for beta MIPs from a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sup> Sr source, collected in a temperature range from room temperature up to 81degC.

Early to middle Eocene history of the Arctic Ocean from Nd‐Sr isotopes in fossil fish debris, Lomonosov Ridge

Strontium and neodymium radiogenic isotope ratios in early to middle Eocene fossil fish debris (ichthyoliths) from Lomonosov Ridge (Integrated Ocean Drilling Program Expedition 302) help constrain water mass compositions in the Eocene Arctic Ocean between ∼55 and ∼45 Ma. The inferred paleodepositional setting was a shallow, offshore marine to marginal marine environment with limited connections to surrounding ocean basins. The new data demonstrate that sources of Nd and Sr in fish debris were distinct from each other, consistent with a salinity‐stratified water column above Lomonosov Ridge in the Eocene. The 87Sr/86Sr values of ichthyoliths (0.7079–0.7087) are more radiogenic than Eocene seawater, requiring brackish to fresh water conditions in the environment where fish metabolized Sr. The 87Sr/86Sr variations probably record changes in the overall balance of river Sr flux to the Eocene Arctic Ocean between ∼55 and ∼45 Ma and are used here to reconstruct surface water salinity values. The ɛNd values of ichthyoliths vary between −5.7 and −7.8, compatible with periodic (or intermittent) supply of Nd to Eocene Arctic intermediate water (AIW) from adjacent seas. Although the Norwegian‐Greenland Sea and North Atlantic Ocean were the most likely sources of Eocene AIW Nd, input from the Tethys Sea (via the Turgay Strait in early Eocene time) and the North Pacific Ocean (via a proto‐Bering Strait) also contributed.

Conceptual design of Hefei advanced light source

The conceptual of Hefei Advanced Light Source, which is an advanced VUV and Soft X-ray source, was developed at NSRL of USTC. According to the synchrotron radiation user requirements and the trends of SR source development, some accelerator-based schemes were considered and compared; furthermore storage ring with ultra low emittance was adopted as the baseline scheme of HALS. To achieve ultra low emittance, some focusing structures were studied and optimized in the lattice design. Compromising of emittance, on-momentum and off-momentum dynamic aperture and ring scale, five bend acromat (FBA) was employed. In the preliminary design of HALS, the emittance was reduced to sub nm · rad, thus the radiation up to water window has full lateral coherence. The brilliance of undulator radiation covering several eVs to keVs range is higher than that of HLS by several orders. The HALS should be one of the most advanced synchrotron radiation light sources in the world.

First experience with G-APDs in [formula omitted] instrumentation

Muon spin spectroscopy ( μ SR ) is an experimental technique which utilizes the muon as a fully polarized spin probe to study the properties of condensed matter. The operation of a μ SR spectrometer is based on the detection of muons entering the sample and the corresponding decay positrons. For this purpose traditionally scintillation detectors based on photomultiplier tubes (PMTs) are used. Multipixel Geiger-mode Avalanche Photodiodes (G-APDs) are recently developed solid state photodetectors competitive to PMTs in terms of gain and photon detection efficiency, but insensitive to magnetic fields. They are most suited for compact, finely segmented detectors intended for operation in the presence of high magnetic fields. In this work we demonstrate the potential of G-APD based detectors for the development of the μ SR technique. For the 5 T Avoided Level Crossing instrument located at the Swiss Muon Source of the Paul Scherrer Institut (PSI, Villigen, Switzerland) we are building a completely new detector system using as a basic element a tile-fiber scintillation counter with a G-APD readout. For the planned 10 T high magnetic field spectrometer we are carrying out feasibility tests aiming at the highest possible time resolution. A counter constructed as a G-APD directly coupled to a fast plastic scintillator was tested at detection of minimum ionizing electrons from a 90 Sr source. With about 0.33 MeV deposited energy the time resolution of σ = 35 ps has been measured.

Strontium isotopes and major ion chemistry in the Chambal River system, India: Implications to silicate erosion rates of the Ganga

The dissolved concentrations of major ions and Sr isotopes ( 87Sr/ 86Sr) were measured in the headwaters of the Chambal river and its tributaries draining the Deccan Trap basalts and the Vindhyan sediments of peninsular India. The total dissolved solids (TDS) ranged from 181 to 547 mg L − 1 ; much higher than the global “mean” river water. A significant fraction of solute abundance in the Chambal river is derived from sodium salts, unlike the Himalayan rivers which exhibit dominance of (Ca + Mg) salts. It is estimated that the Chambal river supplies about one-third of sodium via the Yamuna to the Ganga at Rajshahi (Bangladesh), with only ∼ 6.5% of water discharge. The presence of Na salts not associated with chloride in the Chambal headwaters constraints the application of Na⁎ (Na corrected for Cl) as an index of silicate derived component. This finding brings out the need to revisit the estimates of silicate erosion rate (SER) and associated CO 2 consumption in the Ganga basin, downstream Allahabad, based on Na⁎ as an index. The Sr concentration in the Chambal tributaries varied from 1.9 µM to 5.9 µM and 87Sr/ 86Sr ratio from 0.70923 to 0.71219. Unlike the Himalayan Rivers, Sr isotope composition in the Chambal river is far less radiogenic as the major sources of Sr to the Chambal are the Deccan Trap basalts and the Vindhyan sediments, which are low in 87Sr/ 86Sr. The Sr isotope budget of the Ganga, based on available data of the Chambal, Betwa, Ken, Yamuna and the Ganga shows that, weathering of the Deccan Trap basalts and the Vindhyan sediments (the drainage basin of the Chambal, Betwa and the Ken) contribute ∼ 70% of the dissolved Sr to the Ganga at Varanasi. This study highlights the key role of peninsular rivers draining the Deccan and the Vindhyan regions in the major ion and Sr budget of the Ganga.

Sr fluxes and isotopic compositions in the headwaters of the Yangtze River, Tongtian River and Jinsha River originating from the Qinghai–Tibet Plateau

Water and sediment samples were collected from the headwaters (the Tuotuo River and Chumaer River) of the Yangtze River, Tongtian River and Jinsha River (HTJR) originating from the Qinghai–Tibet Plateau (QTP). Sr and 87Sr/ 86Sr have been measured to analyze temporal and spatial variation characteristics and determine relative contributions from atmospheric inputs, anthropogenic activities and rock weathering. These results show that Sr in the HTJR waters ranges from 1.37 to 11.07 µmol L − 1, and 87Sr/ 86Sr from 0.70948 to 0.71409. The headwaters Tuotuo River and Chumaer River receive ~ 95% of their Sr from evaporite dissolution. The influence of evaporite decreases gradually downwards from source area as increase in discharge. Silicate weathering contributes 4.9%–28.2% of dissolved Sr to the Jinsha River mainstream and 11.5%–42.4% to the tributaries. 87Sr/ 86Sr ranges from 0.71034 to 0.71177 in the Jinsha River mainstream, which is higher than those in other reaches of the Yangtze River. In the Jinsha River suture belt, granitoids and metamorphic rocks with relatively high 87Sr/ 86Sr are exposed. Moreover, carbonate weathering is another important source of Sr in the Jinsha River waters. It is estimated that 15.9%–46.8% of Sr in the mainstream and 37%–64.5% of Sr in the tributaries are derived from carbonate weathering. Contribution from atmospheric precipitation to the Sr in the HTJR is from 0.75% to 6.1% and influence of anthropogenic activities is slight. The 87Sr ex flux forcing changes in seawater Sr isotopic composition is 1.13 × 10 6 mol a − 1 for the HTJR at Yibin, being far lower than those in the Ganges and Brahmaputra and merely accounting for 1.36% of the total carried by the global rivers. Therefore, impact of the HTJR on steady increase of seawater 87Sr/ 86Sr ratio since 40 Ma may be very small.

Use of foliar Ca/Sr discrimination and 87Sr/86Sr ratios to determine soil Ca sources to sugar maple foliage in a northern hardwood forest

Calcium/strontium and 87Sr/86Sr ratios in foliage can be used to determine the relative importance of different soil sources of Ca to vegetation, if the discrimination of Ca/Sr by the plant between nutrient sources and foliage is known. We compared these tracers in the foliage of sugar maple (Acer saccharum) to the exchange fraction and acid leaches of soil horizons at six study sites in the White Mountains of New Hampshire, USA. In a previous study, sugar maple was shown to discriminate for Ca compared to Sr in foliage formation by a factor of 1.14 ± 0.12. After accounting for the predicted 14% shift in Ca/Sr, foliar Ca/Sr and 87Sr/86Sr ratios closely match the values in the Oie horizon at each study site across a 3.6-fold variation in foliar Ca/Sr ratios. Newly weathered cations, for which the Ca/Sr and 87Sr/86Sr ratios are estimated from acid leaches of soils, can be ruled out as a major Ca source to current foliage. Within sites, the 87Sr/86Sr ratio of the soil exchange pool in the Oa horizon and in the 0–10 cm and 10–20 cm increments of the mineral soil are similar to the Oie horizon and sugar maple foliar values, suggesting a common source of Sr in all of the actively cycling pools, but providing no help in distinguishing among them as sources to foliage. The Ca/Sr ratio in the soil exchange pool, however, decreases significantly with depth, and based on this variation, the exchange pool below the forest floor can be excluded as a major Ca source to the current sugar maple foliage. This study confirms that internal recycling of Ca between litter, organic soil horizons and vegetation dominate annual uptake of Ca in northern hardwood ecosystems. Refinement of our understanding of Ca and Sr uptake and allocation in trees allows improvement in the use of Ca/Sr and 87Sr/86Sr ratios to trace Ca sources to plants.

Interaction between different water bodies in a small catchment in the Paris basin (Brévilles, France): Tracing of multiple Sr sources through Sr isotopes coupled with Mg/Sr and Ca/Sr ratios

Abstract Intensive monitoring of the Cuise Sands Aquifer in a small agricultural catchment (3 km2, where agricultural practices are well documented) over nearly 5 a showed significant disparities for major element concentrations, Sr concentrations, isotopic compositions and 3H values, depending on the groundwater sampling locations. Lower 87Sr/86Sr values (0.7079–0.7085) associated with low NO 3 - concentrations, low Mg/Sr molar ratios ( 0.7085) and higher Mg/Sr molar ratios (>250) suggest a contribution of Sr from anthropogenic sources. Strontium isotopes coupled with Mg/Sr and Ca/Sr ratios of groundwater in this catchment successfully demonstrated the capacity to trace fertilizer contributions, which significantly modify the natural Sr isotopic signature of groundwater. The specific geochemical signature of groundwater revealed by Sr isotopes, in addition to major and trace element concentrations (in particular Mg/Sr and Ca/Sr molar ratios), demonstrated the partial isolation of groundwater bodies in this catchment. Compartmentalisation of the aquifer is compatible with fault distribution as defined by geological and geophysical investigations. Thus, the Sr isotopic tool coupled with Mg/Sr and Ca/Sr ratios has been applied with success to trace water pathways and recharge and to provide scenarios for the hydrological functioning of the system.

Comparison of irradiated stFZ silicon sensors using LHC speed front-end electronics

Results from irradiated detector modules assembled with sensors made out of standard p-in-n FZ silicon will be presented. The modules were read out using LHC speed front-end electronics and characterised with different techniques. Two complementary methods to generate the charge inside the sensor were used: An IR laser set-up with a wavelength of λ = 982 nm and a β set-up utilising a 90 Sr source allowing for both relative and absolute CCE measurements. As the aim of our measurement programme is to develop silicon detectors able to operate at the sLHC, these modules were irradiated with three different fluences with the highest corresponding roughly to the fluence expectations for an LHC luminosity upgrade at a radial distance of r ≈ 35 cm [M. Huhtinen, First CMS Upgrade Workshop, CERN, February 26–27, 2004. 〈 http://agenda.cern.ch/fullAgenda.php?ida=a036368 〉 ]. The sensors were characterised before and after irradiation with 26 MeV protons. After irradiation the modules were stored at temperatures below - 40 ∘ C and operated at temperatures around - 5 ∘ C to limit the leakage current and annealing effects. The full depletion voltage V fd and the charge collection efficiency have been measured.

An acoustic sensor system for localizing RF breakdown in warm copper accelerating structures

X-band accelerator structures meeting the Next Linear Collider (NLC) design requirements have been found to suffer damage due to Radio Frequency (RF) breakdown when processed to high gradients [F. Le Pimpec, et al., in: LINAC 2002, Korea, SLAC-PUB-9526, 2002 [1]]. Improved understanding of these breakdown events is desirable for the development of structure designs, fabrication procedures, and processing techniques that minimize structure damage. Acoustic sensors attached to an accelerator structure can detect both normal and breakdown RF pulses [M. Gangeluk, et al., Acoustic monitoring system of RF breakdowns inside the electrodynamics structure at Kurchatov SR source accelerator, in: EPAC, P.1986, 1994 [2]]. Using an array of acoustic sensors, we have been able to pinpoint both the cell and azimuth location of individual breakdown events. This permits studies of breakdown in time and in space, so that underlying causes can be determined. This technique provided a significant understanding of breakdown in the structure input coupler.

A normalised seawater strontium isotope curve: possible implications for Neoproterozoic-Cambrian weathering rates and the further oxygenation of the Earth

The strontium isotope composition of seawater is strongly influenced on geological time scales by changes in the rates of continental weathering relative to ocean crust alteration. However, the potential of the seawater 87 Sr/ 86 Sr curve to trace globally integrated chemical weathering rates has not been fully realised because ocean 87 Sr/ 86 Sr is also in- fluenced by the isotopic evolution of Sr sources to the ocean. A preliminary attempt is made here to normalise the seawa- ter 87 Sr/ 86 Sr curve to plausible trends in the 87 Sr/ 86 Sr ratios of the three major Sr sources: carbonate dissolution, sili- cate weathering and submarine hydrothermal exchange. The normalised curve highlights the Neoproterozoic-Phanerozoic transition as a period of exceptionally high continental influ- ence, indicating that this interval was characterised by a tran- sient increase in global weathering rates and/or by the weath- ering of unusually radiogenic crustal rocks. Close correlation between the normalised 87 Sr/ 86 Sr curve, a published seawa- ter 34 S curve and atmospheric pCO2 models is used here to argue that elevated chemical weathering rates were a ma- jor contributing factor to the steep rise in seawater 87 Sr/ 86 Sr from 650 Ma to 500 Ma. Elevated weathering rates during the Neoproterozoic-Cambrian interval led to increased nutri- ent availability, organic burial and to the further oxygenation of Earth's surface environment. Use of normalised seawater 87 Sr/ 86 Sr curves will, it is hoped, help to improve future geo- chemical models of Earth System dynamics.

The hydrochemical response of cave drip waters to sub-annual and inter-annual climate variability, Wombeyan Caves, SE Australia

A thorough understanding of cave seepage waters is necessary to interpret geochemical variations in speleothem calcite in terms of changing surface climatic conditions at a particular site. Here we present the hydrochemistry of ten cave drip waters from a karst system in SE Australia based on up to 5.5 years of monitoring. Discharge was continuously measured at six sites and manually at the other sites. Dripwater samples were analysed for pH, electrical conductivity, cations and anions at all sites at monthly or more frequent intervals. Each drip possesses a unique chemistry, and not all drip waters responded to antecedent short-term hydrological variations. For example, the hydrochemical behaviour of three adjacent drips at a bedrock depth of 45 m was completely different to that of shallower sites, and was apparently un-related to surface hydrology throughout the investigation. Based on modelled calcite precipitation vectors, prior calcite precipitation was demonstrated at several sites but can only be linked directly to changes in surface recharge at the shallowest sites. At extremely low flow, shallow drip waters accessed a high Mg, Sr and Ba source, thought to be the overlying soil. High-frequency sample collection allows for the calculation of predicted Mg/Ca calcite and Sr/Ca calcite values, highlighting that the sites with the greatest potential to record high-resolution palaeohydrological records are those situated at shallow depth. Longer temporal-resolution palaeohydrological records may be recorded at deeper sites but longer-term monitoring is required to identify probable time scales. Inherent system non-linearities, dissolution of secondary calcite in pore spaces of the aquifer, changes in the source of trace elements, and the presence of multiple reservoirs confirm the need for the use of multiple speleothems and a multi-proxy approach to gain accurate palaeohydrological records from this site.

Salinization of groundwater in the North German Basin: results from conjoint investigation of major, trace element and multi-isotope distribution

Conjoint consideration of distribution of major, rare earth elements (REE) and Y (combined to REY) and of H, O, C, S, Sr isotopes reveals that four types of groundwater are distinguishable by their chemical composition presented by spider patterns. REY patterns indicate thermo-saline deep water and two types of shallow saline groundwaters. Presence of connate waters is not detectable. Sr isotope ratios distinguish three sources of Sr: fast and slow weathering of biotite and K-feldspar in Pleistocene sediments, respectively, and dissolution of limestones. δ13C(DIC) indicate dissolution of limestone under closed and open system conditions. Numerous samples show δ13C(DIC) > 13‰ which is probably caused by incongruent dissolution of calcite and dolomite. The brines from below 1,000 m represent mixtures of pre-Pleistocene seawater or its evaporation brines and infiltrated post-Pleistocene precipitation. The shallow waters represent mixtures of Pleistocene and Recent precipitation salinized by dissolution of evaporites or by mixing with ascending brines. The distribution of water types is independent on geologic units and lithologies. Even the Tertiary Rupelian aquiclude does not prevent salinization of the upper aquifer.

Sr and Nd isotopic compositions and sources of basalts of southern Primorye

Sr and Nd isotopic compositions and sources of basalts of southern Primorye

Constraints on paleowater dissolved loads and on catchment weathering over the past 16 ka from 87Sr/ 86Sr ratios and Ca/Mg/Sr chemistry of freshwater ostracode tests in sediments of Lake Constance, Central Europe

Sr isotope and Ca/Mg/Sr chemical compositions of freshwater ostracode tests separated from a sediment core represent the last 16 ka of sedimentation in Lake Constance, Central Europe. The chemical evolution of the paleowater's dissolved load of Lake Constance was estimated by correcting the ostracode data for Ca/Mg/Sr fractionation due to biogenic calcification. Since the Late Pleistocene deglaciation, the Ca/Sr molar ratios of paleowaters increased systematically from about 100 (a near marine signature) to about 200. Ca/Mg molar ratios varied in the range of 1–25. The 87Sr/ 86Sr ratios indicate Late Pleistocene paleowater compositions of 0.7086–0.7091, significantly more radiogenic than present day waters (0.7085). Sr isotopes and Ca/Mg/Sr chemical data together show that weathering of Mesozoic evaporites consistently dominated the dissolved Sr load (80–90%). Carbonate and silicate weathering were less important (1–10%). Trends of Sr dissolved loads were therefore not related to Mg which was mainly mobilized by carbonate weathering. Biotite weathering was an important source of radiogenic Sr in the paleowaters. The short-term release (duration about 600–800 years) of radiogenic Sr during glacier retreat started 15.2 ka ago and was due to enhanced biotite weathering at the glacier base. Long-term release of radiogenic Sr was due to biotite weathering in glacial soils and silicate rocks, and has gradually declined since the Late Pleistocene/Holocene transition.

Geochemistry of bedded barite of the Mesoproterozoic Aggeneys-Gamsberg Broken Hill-type district, South Africa

Stratiform and stratabound barite ± magnetite beds are intimately associated with the polymetallic Broken Hill-type (BHT) massive sulfide deposits of the Aggeneys-Gamsberg Pb–Zn–Cu ± Ag–Ba district in the Northern Cape Province, South Africa. Barite samples were collected and studied from four localities in the district. Although metamorphic water–rock interaction processes have partially altered the chemical and to a lesser degree the isotopic composition of barite, samples identified as being the least altered display distinctly different isotopic compositions that are thought to reflect different modes of origin. All barite samples are marked by low concentrations of SrO (0.5 ± 0.2 wt%), highly radiogenic 87Sr/86Sr ratios, elevated δ 34S and δ 18O values compared to contemporaneous Mesoproterozoic seawater. Radiogenic 87Sr/86Sr signatures (0.7164 ± 0.0028) point to an evolved continental crustal source for Sr and Ba, while elevated δ 34S values (27.3 ± 4.9‰) indicate that contemporaneous seawater sulfate, modified by bacterial sulfate reduction, was the single most important sulfur reservoir for barite deposition. Most importantly, δ 18O values suggest a lower temperature of formation for the Gamsberg deposit compared with the occurrences in the Aggeneys area, i.e. Swartberg-Tank Hill and Big Syncline. The obvious differences in temperature of formation are in good agreement with the Cu-rich, Ba-poor nature of the sulfide mineralization of the Aggeneys deposits vs the Cu-poor, Ba-rich character of the Gamsberg deposit. In conjunction with this, isotopic and petrographic arguments favor a sub-seafloor replacement model for the stratabound barite occurrences of the Aggeneys deposits, while at Gamsberg, deposition at the sediment–water interface as a true sedimentary exhalite appears more likely.