Strontium Isotopic Composition Research Articles

Magmatic Fluids Implicated in the Formation of Propylitic Alteration: Oxygen, Hydrogen, and Strontium Isotope Constraints from the Northparkes Porphyry Cu-Au District, New South Wales, Australia

AbstractIn porphyry ore deposit models, the propylitic alteration facies is widely interpreted to be caused by convective circulation of meteoric waters. However, recent field-based and geochemical data suggest that magmatic-derived fluids are likely to contribute to development of the propylitic assemblage. In order to test this hypothesis, we determined the oxygen and hydrogen isotope compositions of propylitic mineral separates (epidote, chlorite, and quartz), selected potassic mineral separates (quartz and magnetite), and quartz-hosted fluid inclusions from around the E48 and E26 deposits in the Northparkes porphyry Cu-Au district, New South Wales, Australia. In addition, the strontium isotope composition of epidote was determined to test for the potential contribution of seawater in the Northparkes system given the postulated island-arc setting and submarine character of some country rocks.Oxygen isotope geothermometry calculations indicate potassic alteration occurred between ~600° and 700°C in magmatic/mineralized centers, persisting to ~450°C upon lateral transition into propylitic alteration. Across the propylitic facies, temperature progressively decreased outward to <250°C. These temperature estimates and additional data from chlorite geothermometry were utilized to calculate the oxygen and hydrogen isotope composition of the fluid in equilibrium with the sampled minerals. Results show that propylitic fluids spanned a range of compositions with δ18O between 0.5 and 3.7‰ and δD between –49 and –17‰. Comparison of these results with the modeled compositions of meteoric and/or magmatic fluids during their evolution and isotopic exchange with local country rocks shows that a magmatic fluid component must exist across the propylitic halo during its formation. Strontium isotope data from propylitic epidote provide initial (based on formation at ~450 Ma) 87Sr/86Sr values in the range of 0.704099 to 0.704354, ruling out the presence of seawater as a second fluid in the system. Although we cannot exclude magmatic-meteoric mixing, especially toward the fringes of the system, our results support a model in which magmatic-derived fluid is the primary driver of propylitic alteration as it undergoes cooling and chemical equilibration during outward infiltration into country rocks. This is consistent with chemical mass transfer calculations for Northparkes and published chemical-thermodynamic models that only require a magmatic fluid for the production of propylitic assemblages. In view of this and supporting data from other deposits, we suggest that magmatic fluids are essential drivers of propylitic alteration in porphyry systems.

Diamondiferous and barren eclogites and pyroxenites from the western Kaapvaal craton record subduction processes and mantle metasomatism, respectively

Mineral major and trace elements combined with Sr isotopes of clinopyroxene are used to unravel the origins and evolution of mantle eclogite and pyroxenite xenoliths from the Doornkloof-Sover orangeite dike (western Kaapvaal craton), and to investigate the generation and destruction of diamond in these rocks. Two different eclogite types are present: (1) MgO-poor eclogites (MgO = 7.3 to 14.5 wt%; n = 43) with accessory diamond ± corundum and kyanite, high garnet grossular content (median Ca# = 0.25) and clinopyroxene jadeite content (0.39). Reconstructed bulk rocks are LREE-depleted (median La 0.29 ppm) and have low median Cr2O3 (0.06 wt%) and incompatible trace-element contents (e.g. Sr, Zr, Ba, Pb, Th), and high Li and transition metal abundances. Some are characterised by stepped REE patterns or steep slopes in the MREE, similar to eclogites affected by interaction with dehydration fluids generated in subduction zones. These fluids may also have deposited diamond in typically reducing eclogite assemblages at diamond-stable pressures. (2) MgO-rich eclogites and pyroxenites (MgO = 14.0 to 20.0 wt%; n = 29), which are barren and enriched in LREE (median La 1.39 ppm), Cr2O3 (0.25 wt%) and incompatible trace elements, with lower Li and transition metal abundances than the MgO-poor group. These are typical signatures of carbonated ultramafic melt metasomatism in the mantle lithosphere. Strontium isotopic compositions vary widely in both groups, but high Cr2O3 and Ba contents are dominantly associated with 87Sr/86Sr > 0.7055. This reflects interaction with metasomatic agents remobilised from ancient lithospheric metasomes, which eventually gave rise to regional orangeite magmatism. The presence of strong positive Eu anomalies in both groups, including two pyroxenites, requires low-pressure igneous protoliths, presumably derived from a ca. 3 Ga spreading ridge, as reported for other eclogite materials from the western Kaapvaal craton.Based on the proportions of MgO-poor and –rich eclogites and pyroxenites, approximately 40% of the diamond inventory were destroyed by mantle metasomatism centred at ~135 ± 15 km depth, overlapping a low-velocity anomaly (mid-lithospheric discontinuity). Two diamondiferous orangeites ≤20 km from Doornkloof-Sover contain significantly different eclogite xenolith populations: At Newlands, MgO-poor diamondiferous eclogites are present in addition to barren MgO-rich ones and pyroxenites, suggesting that the host orangeite sampled a source region equally affected by diamond-destructive mantle metasomatism, whereas at Bellsbank, all eclogites are MgO-poor and LREE-depleted. This may explain higher diamond grades reported for this locality compared to Newlands or Doornkloof-Sover.

Geochemical variations in the Upper Kazanian (Middle Permian) stratotype section, Russia

The present paper shows elemental and carbon and strontium isotope composition of the Upper Kazanian (Middle Permian) stratotype section Pechishchi, Russia. A new version of Noinsky’s cycles scheme has been obtained for Martinet and Sougy’s Diagram types of carbonates, with the geochemical indices values changing within marine, evaporate and clastic beds. The δ13Ccarb values vary within interval 0 − +10‰ V-PDB with a mean value 6.2 ‰ V-PDB. The negative excursions of δ13Ccarb values (with amplitudes 2-8 ‰) are assigned as significant land-derived sedimentary inputs. The values of 87Sr/86Sr ratio in the data set of 17 samples change from 0.707267 to 0.707417 (mean value 0. 70734). On standard 87Sr/86Sr curve these values correspond to the interval 273 – 268 Ma.

Phased evolution and variation of the South Asian monsoon, and resulting weathering and surface erosion in the Himalaya–Karakoram Mountains, since late Pliocene time using data from Arabian Sea core

AbstractWe investigate the phased evolution and variation of the South Asian monsoon and resulting weathering intensity and physical erosion in the Himalaya–Karakoram Mountains since late Pliocene time (c.3.4 Ma) using a comprehensive approach. Neodymium and strontium isotopic compositions and single-grain zircon U–Pb age spectra reveal the sources of the deposits in the east Arabian Sea, and show a combination of sources from the Himalaya and the Karakoram–Kohistan–Ladakh Mountains, with sediments from the Indian Peninsula such as the Deccan Traps or Craton. We interpret shifts in the sediment sources to have been forced by sea-level changes that correlate with South Asian monsoon rainfall variation since late Pliocene time. We collected 908 samples from the International Ocean Discovery Program Hole U1456A, which was drilled in the east Arabian Sea. Time series of hematite content and grain size of the sediments were examined downcore. We found South Asian monsoon precipitation and weathering intensity experienced three phases from late Pliocene time. Lower monsoon precipitation, with a lower variability and strong weathering intensity, occurred during 3.4–2.4 Ma; an increased and more variable South Asian monsoon rainfall, along with strengthened but fluctuating weathering intensity, occurred at 1.8–1.1 Ma; and a reduced rainfall with lower South Asian monsoon precipitation variability and moderate weathering intensity marked the period 1.1–0.1 Ma. Maximum entropy spectral analysis and wavelet transform show that there were orbital-dominated cycles of periodsc.100 andc.41 ka in these proxy-based time series. We propose that the monsoon, sea level, global temperature and insolation together forced the weathering and erosion in SW Asia.

Isotopic-geochemical features of thermal water of the Kyndyg deposit (Republic of Abkhazia)

Subject. The aim of the work is to study the mechanism and sources of water formation, as well as the peculiarities of carbonate mineralization in the aquifer of the Kyndyg thermal water deposit. Materials and methods. The samples of water (8) and deposited carbonates (15), collected at different seasons at three sites, characterized by different temperatures and distances from the source, were investigated. pH, Eh, and electrical conductivity were determined by an electrochemical method. For the determination of HCO3 – , Cl– , SO4 2–, titrimetric, mercurymetric and turbidimetric methods were used. Trace element composition was determined by ICP-MS (NexION 300S); strontium isotopic composition – by MC-ICP-MS (Neptune Plus) using the bracketing technique after Sr chromatographic separation. Results. The chloride-calcium hydrochemical type prevails in the studied waters. A number of trace elements in water exceeds the clarke concentrations for groundwater in the supergene zone of mountain landscapes. 87Sr/86Sr isotope ratios (0.7065–0.7072) in thermal waters suggest that their composition is determined rather by the isotopic characteristics of the rocks through which water drains than by the influence of sea water. Among the newly formed carbonates, aragonite prevails. In contrast to thermal water, the concentrations of most metals in carbonates are below the clarke values; only Sr and Se are increased, which content is significantly increased in water as well. Deposited carbonates are characterized by 87Sr/86Sr values (0.7028–0.7074), which are lower than in the source thermal waters. Conclusions. On the basis of hydrogeological, hydrochemical and geochemical data, it can be assumed that the waters of this aquifer complex are formed mainly due to fresh fractured karst waters of lower Cretaceous limestones with submerged monocline dipping into the zone of slow circulation and mixing with sedimentogenic sodium chloride waters. The geochemical data and the presence of scandium anomaly suggest that the underlying Jurassic volcanogenic rocks also participate in water exchange.

Determination of Stable Strontium Isotopic Compositions by MC-ICP-MS

Determination of Stable Strontium Isotopic Compositions by MC-ICP-MS

Oligocene incursion of the Paratethys seawater to the Junggar Basin, NW China: insight from multiple isotopic analysis of carbonate

The Cenozoic retreat of the Paratethys Sea, as well as uplift of the Tibet plateau and global cooling, have been considered as the main mechanisms for the onset of the Asian monsoon. However, due to the weak constraints on the time and path of the Paratethys Sea, the relative contribution of each of the three factors to the onset of the Asian monsoon remains debatable. Previous studies on the retreat process of the Paratethys suggested that its east coastline had already withdrawn from the Chinese Tianshan area to the west by the Oligocene. Here, we provide a new perspective on this discussion through the study of the Oligocene Anjihaihe dolomite from the northern Chinese Tianshan. Through the comparisons of carbon, oxygen, magnesium, and strontium isotope compositions between the dolomite beds and their interlayered precursor lacustrine limestone beds, we show that the Anjihaihe dolomites were formed at the end of the Oligocene from dolomitization by a fluid characterized by high δ18O, low δ26Mg, low temperature, relatively poor in carbon and Sr. This fluid was likely derived from seawater from the close-by Paratethys Sea at the time. This discovery suggests a larger Paratethys Sea during the Oligocene than previously thought and may have important implications to understand the evolution of the palaeogeography in the Chinese Tianshan region and the onset of the Asian monsoon.

Distinction of strontium isotope ratios between water-soluble and bulk coal fly ash from the United States

Coal ash is one of the largest industrial waste streams in the United States and contains elevated concentrations of hazardous elements that could pose environmental and human health risks. Due to the relatively high strontium concentrations in coal ash and the distinctive 87Sr/86Sr ratios, strontium isotopes have been utilized to trace coal ash contaminants in impacted water resources. While previous studies have characterized the Sr isotope ratios for the water-soluble Sr derived from coal ash, the strontium isotopic composition of the bulk coal ash has not been systematically evaluated. In the current study, we report the 87Sr/86Sr ratios of bulk and water-soluble Sr in fly ash derived from coals of the three major coal-producing basins in the U.S., the Appalachian Basin, Illinois Basin, and Powder River Basin. The data show a wide range of 87Sr/86Sr ratios in the bulk fly ash samples (0.710788–0.722311), with the most radiogenic 87Sr/86Sr ratios in fly ash originating from Illinois Basin coals (0.718029 ± 0.003365; n = 16), followed by those from Appalachian Basin coals (0.712641 ± 0.000860; n = 16), and those from Powder River Basin coals (0.711663 ± 0.000489; n = 7). The 87Sr/86Sr ratios in the water leachates are significantly lower than the 87Sr/86Sr ratios of the bulk fly ash for Illinois Basin and Appalachian Basin (0.711660 ± 0.001172 and 0.710694 ± 0.000317, respectively, p-value < 0.01), whereas there is no significant difference for the Powder River Basin fly ash (0.711666 ± 0.000456, p-value = 0.13). These isotopic differences most likely reflect the different mineralogical compositions of the studied fly ash and the differential solubility of carbonate phases with low 87Sr/86Sr ratios relative to more radiogenic silicate phases. Overall, the distinction between the strontium isotope ratios of bulk fly ash versus water-soluble fly ash is important, as it refines the application of strontium isotopes as a forensic tracer for tracking coal ash spills and contamination in the environment.

Strontium Isotopic Composition in Carbonate from Breccias of Mud Volcanoes of Azerbaijan

In 13 out of 14 samples of carbonate xenoliths from mud volcanic breccias of Azerbaijan, the 87Sr/86Sr values (0.70675–0.70823, 87Sr/86Srmd = 0.7073 ± 0.0005) are within the same limits as in the volcanic waters (Bujakaite et al., 2019). Genetically, they can be associated both with Mesozoic carbonate and saline deposits or with Cenozoic volcanosedimentary strata. Similarity of the Sr isotopic composition with isotopic values in carbonate extracts from terrigenous rocks of the Maikop Formation was noted only in the calcite sample from the Cheildag Volcano (87Sr/86Sr = 0.71047). The most interesting results with the lowest Sr ratios were obtained for carbonate fragments from breccias of the Byandovan Volcano. The combination of low δ13C values (down to –49.2‰), high Sr contents (up to 3108 μg/g) and 87Sr/86Sr (0.70675‒0.70690) values typical of the Late Jurassic brings them closer to caprocks of salt domes of Jurassic oil-bearing formations in the western United States.

The spatial distribution and geochemical variation of fault and fracture hosted calcite and gypsum cements in the eastern Bristol Channel Basin

Abstract The spatial distribution and geochemical variation of fault- and fracture-hosted cements can be used to reconstruct the evolution and migration of pore fluids in sedimentary basins. Geochemical data, from stable oxygen and carbon isotope and strontium isotope analyses, of calcite and gypsum cements provide valuable insights into the source of pore fluids and their evolution in the eastern Bristol Channel Basin. Overall, at both an outcrop-scale and a basin-scale there were no observable relationships between the dip angle and direction of fractures with the oxygen and carbon isotopic composition of calcite cements, indicating that the movement and distribution of fluids in fractures is not controlled by the orientation of fracture opening. Radiogenic strontium isotopic compositions of calcite and gypsum cements indicate at least two different mineralising fluid compositions that are strongly controlled by the lithologies (fossiliferous limestones and shales, and marls with gypsum nodules, respectively) in which they occur. These fluids originated as connate pore fluids that were altered during the diagenesis of their host lithologies. Mineralising fluids within the Lower Jurassic Lias Group are characterised by enriched oxygen and strontium isotopic compositions and relatively depleted carbon isotopic compositions, associated with the alteration of labile minerals and carbonaceous fossils. Mineralising fluids within the Triassic Mercia Mudstone Group have enriched strontium isotopic compositions as a result of the interaction of fluids with evaporitic intervals. The mineralising fluids were redistributed through migration along faults and their associated damage zones. This study highlights the importance of integrating a range of geochemical analyses when attempting to understand the source of fluids and their evolution through time. The findings from this study can also be applied to nearby petroleum producing basins, e.g. the Wessex Basin, where equivalent rocks are economically significant source rocks and caprocks and have experienced similar structural histories.

Strontium Isotope Compositions of Hydrothermal Barite from the Yonaguni IV: Insight into Fluid/Sediment Interaction and Barite Crystallization Condition

Hydrothermal barite is a typical low-temperature mineral formed during the mixing of hydrothermal fluid and seawater. Because of its extremely low solubility, barite behaves as a close system after crystallization and preserves the geochemical fingerprint of hydrothermal fluid. In this study, the elemental contents and Sr isotope compositions of hydrothermal barites from the Yonaguni IV were determined using electron microprobe and LA-MC-ICP-MS respectively. On these bases, the fluid/sediment interaction during the hydrothermal circulation and physicochemical condition of barite crystallization were discussed. Results show that the 87 Sr/ 86 Sr values of hydrothermal barites from the Yonaguni IV are apparently higher than those of the seawater and associated volcanic rocks, indicating the sufficient interaction between the hydrothermal fluid and overlying sediment. Monomineral Sr abundance shows large variations, reflecting the changes in barite growth rate during the fluid mixing. The mineralization condition in the Yonaguni IV was unstable. During the crystallization of barite, hydrothermal fluid and seawater mixed in varying degrees, with the proportions of hydrothermal fluid varied from 36% to 72%. The calculated crystallization temperatures range from 109 to 220°C. Sediment plays a critical role during the mineralization process in the Yonaguni IV and incorporation of sediment component into hydrothermal system was prior to barite crystallization and sulfide mineralization.

Comparative Fe and Sr isotope study of nephrite deposits hosted in dolomitic marbles and serpentinites from the Sudetes, SW Poland: Implications for Fe-As-Au-bearing skarn formation and post-obduction evolution of the oceanic lithosphere

Nephrites belonging to both the dolomite-related and serpentinite-related genetic types, from the Złoty Stok deposit, and Jordanów Śląski and Nasławice prospects in the Ślęża Ophiolite, respectively, were analyzed for Fe and Sr isotope compositions. These deposits in the Central Sudetes (SW Poland), are unusually situated relatively close to each other. This study is a first attempt to perform combined Fe and Sr isotope study of nephrites. Our results show that Fe in the Fe-As-Au-bearing skarn samples from Złoty Stok (2.77–7.00 wt% Fe, δ56Fe +0.07 to +0.14‰, and δ57Fe +0.12 to +0.21‰), to which the dolomite-related nephrite belongs, is not inherited from the host dolomitic marbles (ca. 0.4 wt% Fe; δ56Fe −0.08 to −0.07‰, and δ57Fe −0.12 to −0.09‰), but derived from the nearby, ca. 340 Ma granite intrusion (2.64–5.64 wt% Fe). In contrast, iron in the serpentinite-related nephrites (2.06–3.88 wt% Fe, δ56Fe +0.41 to +0.45‰, and δ57Fe +0.59 to +0.66‰) was likely inherited from host serpentinites (5.27–4.81 wt% Fe), rather than metasomatically derived from adjacent granite intrusions (0.13–0.45 wt% Fe). Moreover, both the marble transformation into a dolomite-related nephrite (and Fe-As-Au-bearing skarn), and the abyssal serpentinite – through ophiolite – towards serpentinite-related nephrite transformation, are accompanied by a progressive increase of δ56Fe and δ57Fe. This increase is regardless of changes in the bulk Fe content, increasing during the dolomite-related nephrite formation, and decreasing during serpentinite-related nephrite formation. This phenomena may be caused by one of the below listed factors, or combinations: a) preferential incorporation of heavy iron by tremolite and diopside; b) preferential incorporation of the heavy iron in the Fe3+-bearing phases, crystallizing during nephrite formation; c) preferential incorporation of the heavy Fe from migrating granite-derived fluids (positive fractionation between aqueous Fe-bearing fluid, and tremolite/diopside); d) positive isotope fractionation between dolomite/antigorite precursor, and newly formed amphibole/clinopyroxene; e) change of the Fe oxidation state. Furthermore, Fe in the rock-forming tremolite from the serpentinite-related nephrites is isotopically heavier than Fe in tremolite from the dolomite-related ones. In contrast to the iron, the isotopic composition of strontium, combined with its content and structural evidence, suggest multiple sources for this element. In the case of the dolomite-related nephrite (ca. 3–4 ppm Sr; initial 87Sr/86Sr = 0.7085), Sr inheritance from the host-dolomitic marble (ca. 90 ppm Sr; initial 87Sr/86Sr = 0.7081), as well as its derivation from intrusions of both the syn- to late-tectonic, ca. 340 Ma granites (ca. 400–440 ppm Sr), and post-tectonic ~305 Ma granites (86.4 ppm Sr), is suggested. In the case of the serpentinite-related nephrite (6.3–61.7 ppm Sr; initial 87Sr/86Sr 0.7037 to 0.7081), the situation is similar, i.e., Sr in the most primitive samples tends to be sourced from ophiolitic rocks (up to 2.4 ppm Sr in serpentinite), whereas in the more evolved types, it was likely delivered from the adjacent, ca. 340 Ma partially rodingitized granites (8.8–102.6 ppm Sr), as well as ~305 Ma granites (ca. 80 ppm Sr). Moreover, these granites caused the fluid-flow, responsible for Sr-bearing clinozoisite vein formation; these veins are likely related with nephrite formation, and with a metallic mineralization.

К оценке мобильности жителей Суздальского Ополья X – первой половины XII века

Становление Северо-Восточной Руси X-XI вв. традиционно рассматривается как процесс, сопряженный с активным мультикультурным взаимодействием и продвижением в Волго-Окский регион выходцев из Поднепровья, северо-западных земель Руси и Скандинавии, а густая сеть сельских поселений XI-XIII вв., документированная в центральных районах Северо-Восточной Руси в последние десятилетия, и реконструкции средневековых ландшафтов однозначно свидетельствуют о том, что подъем региона во многом обеспечивался его сельскохозяйственным потенциалом, благосостоянием и устойчивостью сел. Вопрос об уровне мобильности населения Северо-Восточной Руси X-XII вв. представляет исключительный интерес. Перспективным является его изучение с использованием данных об изотопном составе стронция в эмали зубов и костной ткани индивидов из средневековых погребений. По материалам некрополя крупной сельской агломерации X- начала XIII в. Шекшово-9 ее население предстает многокомпонентным в культурном отношении, состоятельным и включенным в сеть торговых связей. В основу обсуждения миграционной активности обитателей этого большого сельского поселения положены данные масс-спектрометрических исследований 24 индивидов и трех животных из могильников Шекшово-2 и -9. Проведенные реконструкции указывают на высокий по сравнению с аналогичными восточно-европейскими памятниками процент местных уроженцев в шекшовской палеопопуляции. Не выявлена непосредственная связь между присутствием инокультурных предметов и изотопной «меткой» мигранта первого поколения. Полученная картина местного происхождения основной части населения не находит пока прямых аналогий среди памятников Восточной и Северной Европы XXI вв., исследованных с использованием данных об изотопном составе стронция в скелетных останках.

The Strontium Isotope Composition of Vein Calcite in Prospective Oil- and Gas-Bearing Deposits of the Flysh Formation, North-Western Part of the Krosno Zone, Ukrainian Carpathians

The Strontium Isotope Composition of Vein Calcite in Prospective Oil- and Gas-Bearing Deposits of the Flysh Formation, North-Western Part of the Krosno Zone, Ukrainian Carpathians

Towards a biologically available strontium isotope baseline for Ireland

Strontium isotopes are used in archaeology, ecology, forensics, and other disciplines to study the origin of artefacts, humans, animals and food items. Strontium in animal and human tissues such as bone and teeth originates from food and drink consumed during life, leaving an isotopic signal corresponding to their geographical origin (i.e. where the plants grew, the animals grazed and the drinking water passed through). To contextualise the measurements obtained directly on animal and human remains, it is necessary to have a sound baseline of the isotopic variation of biologically available strontium in the landscape. In general, plants represent the main source of strontium for humans and animals as they usually contain much higher strontium concentrations than animal products (meat and milk) or drinking water. The observed difference between the strontium isotope composition of geological bedrock, soils and plants from the same locality warrants direct measurement of plants to create a reliable baseline. Here we present the first baseline of the biologically available strontium isotope composition for the island of Ireland based on 228 measurements on plants from 140 distinct locations. The isoscape shows significant variation in strontium isotope composition between different areas of Ireland with values as low as 0.7067 for the basalt outcrops in County Antrim and values of up to 0.7164 in the Mourne Mountains. This variability confirms the potential for studying mobility and landscape use of past human and animal populations in Ireland. Furthermore, in some cases, large differences were observed between different types of plants from the same location, highlighting the need to measure more than one plant sample per location for the creation of BASr baselines.

Controls on the provenance of late Eocene to Quaternary Mozambique Channel shales (DSDP 25 Site 242)

Provenance determination of late Eocene to Quaternary sediments deposited at the DSDP 25 Site 242 may help to evaluate the mechanisms that have controlled the sediment deposition in the Mozambique Channel. To determine the provenance of the clay fraction, we measure major and trace element concentrations as well as strontium (87Sr/86Sr) and neodymium isotopic compositions (expressed as ƐNd(0)) of thirty-six sedimentary samples from DSDP 25 Site 242 on the eastern flank of the Davie Fracture Zone. Light Rare Earth Element (LREE) enrichment and Heavy REE (HREE) depletions against Post Archean Australian Shales (PAAS) associated with Ce anomalies higher than or equal to 0.90 for all the analyzed samples suggest very little influence of authigenic smectite incorporation. The absence of correlation of Al/Si and CIA with REE content, Eu/Eu*, Cr/Th, Th/Sc, and 87Sr/86Sr and ƐNd(0) suggests that chemical weathering has not modified these provenance proxies. Slight increase of Eu/Eu*, Cr/Th ratios, ƐNd(0) values associated with slight decrease in 87Sr/86Sr and Th/Sc ratios from the late Eocene to the Quaternary point to input of less differentiated and younger detritus to the DSDP 25 Site 242 with age. Based on variations in ƐNd(0) and Nd concentrations, we estimate an overall decrease of the Southeast African rivers (Congo/Zambezi) contribution from ~65.7% (Standard Deviation (S.D.) ~13.2) in the late Eocene to ~28.5% (S.D. ~10.0) in the early Pliocene. The causes for the low ƐNd(0) values and high Southeast African contribution between the late Eocene and the early Oligocene remain to be determined. It could record the onset of modern sedimentation in the Zambezi delta or the discharge of the Paleo Congo river in the Indian Ocean. The decrease of Zambezi contribution between the late Oligocene and early Pliocene is attributed to the cumulative effect of increasing tectonic activity of the Davie Fracture Zone and intensification of the Mozambique Current. The late Pliocene to Quaternary glacial-interglacial cycles promoted higher Zambezi contribution during glacial sea-level lowstands and in turn lower ƐNd(0) detrital values, whereas low Zambezi contributions are favored during interglacial highstand causing higher ƐNd(0) values. Hence, the modern dispersal pattern of fine-grained sediments within the Mozambique Channel is no younger than late Pliocene.

Shallow retardation of the strontium isotope signal of agricultural liming - implications for isoscapes used in provenance studies

An intensified debate centers on the use of strontium isotopes in surface water run-off as archive for bioavailable signatures in prehistoric provenance studies. Its use has been challenged by a recent suggestion that modern agricultural liming of farmlands exerts a serious imprint on the strontium isotope compositions of these waters. We here present results from a soil profile beneath agricultural farmland in the glaciogenic outwash plain of central West Jutland, Denmark, which show that strontium and its isotope composition derived from lime products is efficiently retained near the surface. Pore waters and bioavailable strontium from the acidic zone below the surface soil depict strontium isotope signatures that can best be explained by a mixture of silicate-derived and relic natural (not agriculturally added) carbonate-derived strontium. We therefore argue that agricultural liming does not contaminate groundwaters and groundwater-supported surface waters, rendering reference maps based on them relevant for modern and past provenance studies.

A strontium isotope baseline of Cyprus. Assessing the use of soil leachates, plants, groundwater and surface water as proxies for the local range of bioavailable strontium isotope composition

In this study, a strontium isotope baseline for Cyprus is presented. The aim of the study was two-fold; first to provide an environmental multi-proxy-based baseline (water/plants/soil leachates) suitable for archaeological provenance and mobility studies, food source authentication, and forensic investigations; and second, to contribute to the debate around which proxy (or combination of proxies) might be most suitable to define bioavailable fractions of strontium in geologically complex areas also exposed to sea-spray and other Sr-bearing aerosols. Lowest bioavailable strontium isotope signatures range is found within terranes dominated by ophiolites, where 87Sr/86Sr ratios range from 0.7055 to 0.7081, however, results reveal a high degree of variability in bioavailable 87Sr/86Sr ratios, both spatially, along depth profiles and amongst the different proxies. A narrower range of bioavailable Sr isotope signatures is observed within the Circum Troodos Sedimentary Successions (C.T.S.S.), both in spatial distribution and between different proxies. Observed range is 87Sr/86Sr = 0.7079 to 0.7089 in areas dominated by pre-Quaternary C.T.S.S., and 87Sr/86Sr ratios = 0.7076 to 0.7086 in areas covered by Quaternary C.T.S.S., revealing the lithologies to be very homogenous with respect to bioavailable strontium ratios. Intra-site variations in three archaeological sites (multiple samples from each site from within a 500 m radius) within the pre-Quaternary and Quaternary C.T.S.S. are smaller than inter-site variations, suggesting that tracing studies inferred from baselines sampled within a limited spatial area could lead to erroneous conclusions regarding provenance. The study points to the necessity for conducting multi-proxy, spatially extensive sampling to adequately characterize complex geological areas, if these should serve as reliable reference areas in provenance studies.

Effect of cold and hot water injection on the chemical and microbial composition of an aquifer and implication for its use as an aquifer thermal energy storage

A Triassic, siliciclastic aquifer was hydraulically tested for its suitability as aquifer thermal energy storage in the city of Berlin (Germany). This study investigates the effects of groundwater mixing, change of temperature, and water-rock interactions on the chemical and microbial water composition. The water chemistry was monitored during a step rate test and two subsequent tracer push pull tests (one conducted with aquifer water and the second with heated aquifer water). Apart of the main ions and physicochemical parameters, the microbial community were determined. In addition, molecular size distribution of dissolved organic carbon as well as the stable isotope compositions of strontium and water were measured in selected samples. This comprehensive monitoring resulted in the following main findings:The chemical water composition of all analysed samples was similar to seawater with main cations and anions correlating well with each other. Although the total element content varied over time, the produced water was homogenously mixed as evidenced by constant ratios of stable water isotopes. The most remarkable observation was an extremely high aluminium concentration (up to 4.7 mM) measured in the flowback after cold water injection. This can be explained by a hydraulic connection between the Triassic Formation and an overlaying Tertiary sand. Water-rock interactions between oxygen dissolved in the injected water and the pyrite-containing Tertiary sand eventually mobilized the aluminum.The measured effect of injecting hot water into the aquifer on the chemical and microbial composition was relatively small. However, temperature-dependent reactions might still be of relevance due to (I) the generally high microbial cell numbers that could trigger microbial enhanced reactions and (II) a calculated oversaturation of calcite that might result in mineral precipitation.

Ore Formation During Jurassic Subduction of the Tethys Along the Eurasian Margin: Constraints from the Kapan District, Lesser Caucasus, Southern Armenia

AbstractThe Kapan mining district in the southernmost Lesser Caucasus is one of the few locations along the central Tethyan metallogenic belt where ore-forming processes were associated with magmatic arc growth during Jurassic Tethys subduction along the Eurasian margin. Three ore deposits of the Kapan district were investigated in this study: Centralni West, Centralni East, and Shahumyan. The ore deposits are hosted by Middle Jurassic andesitic to dacitic volcanic and volcaniclastic rocks of tholeiitic to transitional affinities below a late Oxfordian unconformity, which is covered by calc-alkaline to transitional Late Jurassic-Early Cretaceous volcanic rocks interlayered with sedimentary rocks.The mineralization consists of veins, subsidiary stockwork, and partial matrix replacement of breccia host rocks, with chalcopyrite, pyrite, tennantite-tetrahedrite, sphalerite, and galena as the main ore minerals. Centralni West is a dominantly Cu deposit, and its host rocks are altered to chlorite, carbonate, epidote, and sericite. At Centralni East, Au is associated with Cu, and the Shahumyan deposit is enriched in Pb and Zn as well as precious metals. Both deposits contain high-sulfidation mineral assemblages with enargite and luzonite. Dickite, sericite, and diaspore prevail in altered host rocks in the Centralni East deposit. At the Shahumyan deposit, phyllic to argillic alteration with sericite, quartz, pyrite, and dickite is dominant with polymetallic veins, and advanced argillic alteration with quartz-alunite ± kaolinite and dickite is locally developed.The lead isotope composition of sulfides and alunite (206Pb/204Pb = 18.17–18.32, 207Pb/204Pb = 15.57–15.61, 208Pb/204Pb = 38.17–38.41) indicates a common metal source for the three deposits and suggests that metals were derived from magmatic fluids that were exsolved upon crystallization of Middle Jurassic intrusive rocks or leached from Middle Jurassic country rocks. The δ18O values of hydrothermal quartz (8.3–16.4‰) and the δ34S values of sulfides (2.0–6.5‰) reveal a dominantly magmatic source at all three deposits. Combined oxygen, carbon, and strontium isotope compositions of hydrothermal calcite (δ18O = 7.7–15.4‰, δ13C = −3.4−+0.7‰, 87Sr/86Sr = 0.70537–0.70586) support mixing of magmatic-derived fluids with seawater during the last stages of ore formation at Shahumyan and Centralni West.40Ar/39Ar dating of hydrothermal muscovite at Centralni West and of magmatic-hydrothermal alunite at Shahumyan yield, respectively, a robust plateau age of 161.78 ± 0.79 Ma and a disturbed plateau age of 156.14 ± 0.79 Ma. Re-Os dating of pyrite from the Centralni East deposit yields an isochron age of 144.7 ± 4.2 Ma and a weighted average age of the model dates of 146.2 ± 3.4 Ma, which are younger than the age of the immediate host rocks. Two different models are offered, depending on the reliability attributed to the disturbed 40Ar/39Ar alunite age and the young Re-Os age. The preferred interpretation is that the Centralni West Cu deposit is a volcanogenic massive sulfide deposit and the Shahumyan and Centralni East deposits are parts of porphyryepithermal systems, with the three deposits being broadly coeval or formed within a short time interval in a nascent magmatic arc setting, before the late Oxfordian. Alternatively, but less likely, the three deposits could represent different mineralization styles successively emplaced during evolution and growth of a magmatic arc during a longer time frame between the Middle and Late Jurassic.