Sr Isotopic Data Research Articles

Epidote dissolution–precipitation during viscous granular flow: a micro-chemical and isotope study

Abstract. Deformation of polymineralic aggregates can be accommodated by viscous granular flow, a process mediated by the interplay among intracrystalline plasticity and dissolution–precipitation, each active in specific minerals under given P–T conditions. Some rock-forming minerals like quartz and feldspars have been intensively studied in terms of deformation processes. Instead, the deformation behavior of epidote and its role during viscous granular flow is not well investigated, although this mineral is ubiquitous in granitic rocks deforming under greenschist-facies conditions. In this contribution, we provide microstructural and geochemical evidence for the occurrence of dissolution–precipitation of epidote during deformation of an epidote–quartz vein. The main part of the vein is deformed, producing a fold, which is visible due to relicts of primary-growth layering inside the vein. The deformation mechanisms active during deformation include dynamic recrystallization of quartz by subgrain rotation recrystallization, producing grain size reduction in the primary vein quartz. Recrystallization occurs contemporaneously with dissolution and (re)precipitation of epidote and quartz grain boundary sliding, leading to a combined process described as viscous granular flow. The combination of grain boundary sliding and dissolution locally and repeatedly produces creep cavities. These represent not only loci for nucleation of new epidote grains at the expense of dissolved ones, but they also allow fluid-mediated transport of elements. The same trace element patterns between old epidote relicts and newly formed grains, with much narrower variability in the latter, indicate a process of chemical homogenization. The nature of the fluid that mediates deformation is investigated using Pb–Sr isotope data of epidote, which suggest that deformation is assisted by internally recycled fluids with the addition of a syn-kinematic external fluid component.

Major and rare earth element mineral chemistry of low-grade assemblages inform dynamics of hydrothermal ocean-floor metamorphism in the Dinaridic Neotethys

AbstractThis contribution provides insights into ocean-floor hydrothermal metamorphism of the fast-evolving Dinaridic Neotethys. Mineralogical, geochemical and Sr isotope data collected from altered ophiolites and non-ophiolite basalts/andesites and tuffs of the active continental margin are consistent with hydrothermal alteration trajectories that reflect the host-rock composition. This suggests that hydrothermal fluxes were restricted within a simple closed seawater-fed system. Based on the initial isotopic ratios of Sr, two fluid–rock interaction trends are established: (a) low-to-medium degrees of metasomatism in pre-Middle Jurassic anorogenic ophiolites that progressively abated, and (b) increased intensities of metasomatism in post-Middle Jurassic orogenic ophiolites. This agrees with chlorite thermometry and Ca-Al-(Fe)-silicate phase chemistry. The metamorphic assemblages belong to the zeolite, prehnite-pumpellyite, prehnite-actinolite and greenschist facies. The facies is reliant on the temperature of hydrothermal systems and their fluid chemistry. Rare earth element (REE) phase geochemistry shows (a) variable fluid–rock ratios in chlorite and pumpellyite dependent on fluid temperatures, (b) prominent Eu and Ce anomalies that reflect the fluid oxidation state, (c) light REE/heavy REE mobilization attributed to prevalent ligand complexation, and (d) multi-phase fluid percolation across reaction zones of heterogeneous permeability. This study proposes initiation of simple hydrothermal system(s) at or near a spreading centre(s) in the infancy of the Dinaridic Neotethys. Such a system became more complex during Middle Jurassic and Early Cretaceous time with reactive hydrothermal fluids passing the recharge area and reaching the hot reaction zone. An abrupt obliteration of the established high-temperature regime ensued, following the final closure of the Neotethys.

Concurrent magma mixing and crystallization processes revealed by clinopyroxene macrocrysts from Lamont guyot lavas in NW Pacific

Minerals in volcanic rocks have been commonly used to reconstruct the physicochemical conditions of crystallization and magma chamber processes (magma mixing and recharge) prior to eruption which are fundamental to deduce the petrogenesis of volcanic rocks. Here we present mineral chemistry including in situ major-trace element and Sr isotopic data for clinopyroxene (Cpx) and plagioclase macrocrysts from lavas collected from Lamont guyot in the Wake seamount group, NW Pacific. The Cpx macrocrysts display normal and reverse zoning or complex zoning (e.g., combination of reverse, normal, sector and/or patchy zoning). The normally-zoned Cpx macrocrysts are euhedral and in Fe Mg equilibrium with the host rock compositions. In contrast, the cores of reversely- and complexly-zoned Cpx macrocrysts are in textural (e.g., resorption texture) and chemical (very low Mg#) disequilibrium with their host rock compositions. These reversed cores, however, form coherent compositional trends with and display parallel trace element patterns to the normally zoned Cpx crystals, suggesting that these resorbed cores are most likely antecrysts which crystallized from progenitor melts. The continuously changing major-trace element contents with Cpx Mg# values can be explained by crystallization of these Cpx crystals from melts that progressively fractionate Cpx, plagioclase and Fe Ti oxides. Together with those of the complexly-zoned plagioclase, the complex zoning patterns and large ranges of La/Yb and Sm/Yb ratios at a restricted Cpx Mg# range record magmatic processes of fractional crystallization and mixing in the magma plumbing system. The Cpx crystals from a single lava sample have various 87 Sr/ 86 Sr ratios (0.7025–0.7042) extending from HIMU (high μ = 238 U/ 204 Pb) to FOZO (focal zone) mantle components suggesting that the large 87 Sr/ 86 Sr variation in Cpx could be explained by mixing between HIMU and FOZO components. Our data suggest that frequent recharging of melts derived from different mantle sources and concurrent mixing and crystallization are important processes that shape the currently observed compositional variation of Lamont guyot lavas. • Textural and compositional zoning of Cpx from Lamont seamount lavas, NW Pacific • Cpx shows large trace element and 87 Sr/ 86 Sr variations at a restricted Mg# range. • Reverse and complex zoning textures of Cpx record magma recharge and mixing. • Mixing of multiple batches of HIMU- and FOZO-derived melts. • Concurrent mixing and crystallization played a key role in forming the Cpx crystals.

The timing and tectonic context of Pan-African gem bearing pegmatites in Malawi: Evidence from Rb–Sr and U–Pb geochronology

The Pan-African belts of Malawi contain a largely unexplored endowment of gem bearing pegmatites. We present U–Pb in zircon (LA-ICPMS) and Rb–Sr mineral isochron geochronological and isotope data from pegmatites across Malawi. The pegmatites contain tourmaline, beryl, aquamarine, zircon, amethyst and sunstone as gemstone species. Two zircon bearing pegmatites in southern Malawi intruded early in the Pan-African orogenic cycle at 719 ± 5 Ma and 729 ± 4 Ma and are associated with the emplacement of alkaline rocks that formed during an intra-continental rifting episode in the eastern part of former Rodinia. One further zircon pegmatite containing inherited zircon of a similar age (746 ± 44 Ma) was emplaced at 598 ± 15 Ma, after the assembly of Western and Eastern Gondwana and the formation of the East African Orogen (EAO). The majority of the analysed pegmatites, however, are significantly younger. The ∼550 Ma pegmatites were emplaced during the Kuunga Orogeny, correlating with the collision of northern and southern Gondwana cratonic entities. During a prolonged post-collisional period, possibly related to crustal collapse and extension, further gem-mineralised pegmatites formed at ∼520 ± 6 Ma and ∼500–485 Ma. The youngest pegmatite intruded in the southern Malawian Ntcheu area in the Middle Ordovician at ∼460 Ma. A large spread in 87Sr/86Sr initial isotopic ratios between 0.70556 and 0.79018 suggests a variety of magma sources for the Kuunga-related pegmatites with a variably strong crustal affinity.

Rare earth elements and neodymium and strontium isotopic constraints on provenance switch and post-depositional alteration of fossiliferous Ediacaran and lowermost Cambrian strata from Arctic Norway

The Digermulen Peninsula in northeastern Finnmark, Arctic Norway, comprises one of the most complete Ediacaran–Cambrian transitions worldwide with a nearly continuous record of micro- and macrofossils from the interval of the diversification of complex life. Here, we report on the provenance and post-depositional alteration of argillaceous mudstones from the Digermulen Peninsula using rare earth elements and Sm–Nd and Rb–Sr isotopic systematics to provide an environmental context and better understand this important transition in Earth’s history. The studied sections comprise a mid-Ediacaran glacial–interglacial cycle, including the Nyborg Formation (ca. 590 Ma) and Mortensnes Formation (related to the ca. 580 Ma-old Gaskiers glaciation), and the Stáhpogieddi Formation (ca. 560–537 Ma), which yields Ediacara-type fossils in the Indreelva Member and contains the Ediacaran–Cambrian boundary interval in the Manndrapselva Member and basal part of the informal Lower Breidvika member (ca. 537–530 Ma). Three sample groups, (1) Nyborg and Mortensnes formations, (2) the lowermost five samples from the Indreelva Member and (3) the remaining samples from the Indreelva as well as from the Manndrapselva and Lower Breidvika members, can be distinguished, belonging to distinct depositional units. All samples have negative εNd(T) values (−6.00 to − 21.04) indicating a dominant input of terrigenous detritus with an old continental crust affinity. Significant shifts in Sm–Nd isotope values are related to changes in the sediment source, i.e. Svecofennian province vs Karelian province vs Svecofennian province plus in addition likely some juvenile (late Neoproterozoic volcanic) material, and probably reflect palaeotectonic reorganisation along the Iapetus-facing margin of Baltica. The combined Rb–Sr isotopic data of all samples yield an errorchron age of about 430 Ma reflecting the resetting of the Rb–Sr whole-rock isotope systems of the mudstones during the Scandian tectono-metamorphic event in the Gaissa Nappe Complex of Finnmark. Preservation of palaeopascichnids coincides with the sedimentation regimes of sample groups 2 and 3 while other Ediacara-type fossils, e.g. Aspidella-type and frondose forms, are limited to the sample group 3. Our results are similar to those of earlier studies from the East European Platform in suggesting oxic seafloor conditions during the late Ediacaran.

Rare Earth Element Mobility and Sr Isotope Systematics of Altered Volcanic Rocks from Seawater-Based and Magmatically Influenced Hydrothermal Systems: Brothers Volcano, Kermadec Arc (IODP Expedition 376)

AbstractIn 2018, International Ocean Discovery Program (IODP) Expedition 376 successfully drilled into seawater-based and magmatically influenced hydrothermal systems within and on the wall of the caldera of Brothers volcano, an active submarine volcano in the Kermadec arc. We report rare earth element (REE) abundances and ratios for altered volcanic material recovered from three holes to assess mobility and partitioning under the different conditions of fluid-rock reactions. We combine these with loss on ignition (LOI) and X-ray diffraction (XRD) data to document the extent of alteration, and with Sr concentration and isotope data to evaluate water/rock (W/RSr) ratios and provide constraints on hydrothermal exchange and conditions of alteration. Rocks recovered from the seawater-based NW Caldera hydrothermal system show variable extents of alteration (LOI values of 1–11 wt %) at low W/RSr ratios (1–14) to chlorite- and quartz-rich alteration mineral assemblages. We attribute the limited changes observed in total REE content (ΣREE) and chondrite-normalized REE patterns to a combination of their incorporation into secondary minerals such as chlorite and smectite and complexation with chloride ligands in the reacting fluids. Rocks recovered from the magmatically influenced Upper Cone hydrothermal field (and from an older interval deep beneath the NW Caldera wall) are more extensively altered (LOI values of 4 to >22 wt %), although at similar low W/RSr ratios (~1–16) to heterogeneous natroalunite- and pyrophyllite-bearing assemblages. The REEs exhibit considerably greater mobility with lower ΣREE contents, particularly in the middle and heavy REEs (LaN/YbN ratios up to 4). We suggest that accommodation in secondary minerals is unlikely to play a role in REE behavior due to their lack of substitution sites for the REEs. We attribute enhanced mobility of all the REEs to increased solubility due to the very low pH, and interpret fractionation of the middle and heavy REEs as likely due to complexation with fluoride, which enhances their solubility relative to the light REEs.

Geochemical and Sr-Isotopic Study of Clinopyroxenes from Somma-Vesuvius Lavas: Inferences for Magmatic Processes and Eruptive Behavior

Somma-Vesuvius is one of the most dangerous active Italian volcanoes, due to the explosive character of its activity and because it is surrounded by an intensely urbanized area. For mitigating the volcanic risks, it is important to define how the Somma-Vesuvius magmatic system worked during the past activity and what processes took place. A continuous coring borehole drilled at Camaldoli della Torre, along the southern slopes of Somma-Vesuvius, allowed reconstructing its volcanic and magmatic history in a previous study. In this work, the wide range of chemical (Mg# = 92–69) and isotopic (87Sr/86Sr = 0.70781–0.70681) compositions, collected on single clinopyroxene crystals separated from selected lava flow units of the Camaldoli della Torre sequence, have been integrated with the already available bulk geochemical and Sr-isotopic data. The detected chemical and isotopic signatures and their variation through time allow us to better constrain the behavior of the volcano magmatic feeding system, highlighting that mixing and/or assimilation processes occurred before a significant change in the eruptive dynamics at Somma-Vesuvius during a period of polycyclic caldera formation, starting with the Pomici di Base Plinian eruption (ca. 22 ka).

Advances in in-situ Rb-Sr dating using LA-ICP-MS/MS: applications to igneous rocks of all ages and to the identification of unrecognized metamorphic events

Age determinations of rocks by in-situ Rb-Sr dating of minerals has the advantage of providing spatially resolved analysis without time-consuming preparation, but is hampered by isobaric and polyatomic interferences on Sr isotopes, especially 87Rb. LA-ICP-MS/MS using N2O as a reaction gas allows online chemical separation of 87Rb from 87Sr by measuring SrO+. Here, the method for in-situ Rb-Sr is optimized and applicability demonstrated for geological samples ranging from late Archean to 20 Ma in age.Rb-Sr isotopes of multiple reference materials and geological samples have been analyzed by LA-ICP-MS/MS to evaluate the method for dating rocks throughout the geological record. The quality of Sr isotopic data can be greatly improved by external calibration of mass bias. For internal calibration, better accuracy is obtained with the addition of H2 as a trace molecular gas. The elemental fractionation of Rb and Sr during LA-ICP-MS/MS analysis varies for different reference materials. We find that the matrix of NIST SRM 610 renders it unsuitable for correction of 87Rb/86Sr. The Mica-Mg reference material is preferred for calibration of 87Rb/86Sr of micas despite showing significant Rb-Sr fractionation.In-situ Rb-Sr ages were determined for igneous samples ranging in age from 20 Ma to Mesoproterozoic, confirming accurate application of the method to samples of widely differing ages. The most accurate isochron ages were obtained with 87Rb/86Sr calibrated against Mica-Mg. Application to two metamorphic gneisses with late Archean protoliths from Labrador and Finland reveal thermal events at 1.66–1.70 Ga when they were part of a large Paleoproterozic active margin along the southern edge of Laurentia-Baltica. Data collected for minerals with differing closure temperatures for the Rb-Sr system allow detection of thermal events not recorded by other geochronological systems, indicating a huge potential of this technique not only for accurately dating samples, but also for providing previously inaccessible information on metamorphic histories.

Insights into the temporal evolution of magma plumbing systems from compositional zoning in clinopyroxene crystals from the Agnano-Monte Spina Plinian eruption (Campi Flegrei, Italy)

The complex sequential compositional zoning of clinopyroxene crystals erupted <5 ka during the Agnano-Monte Spina (A-MS) eruption, which is considered to be the reference event for a future large-scale explosive eruption at Campi Flegrei caldera (Italy), has been characterized in detail. Concentration profiles (20–800 μm long, spacing 2.5–10 μm) of major (Si, Ti, Al, Fe, Mg and Ca) and minor (Mn, Na, Ni and Cr) elements were measured along different directions in the clinopyroxene crystals. The zoning patterns of Fe–Mg and selected elements (e.g., Al, Ti) often consist of two or more compositional plateaus with both sharp and/or slightly diffuse boundaries between the plateaus. Each compositional population results from a growth stage in a distinct Magmatic Environment (ME), which is identified as a defined set of intensive thermodynamic variables (pressure, temperature, bulk composition and fugacity of fluids including oxygen). The large range of chemical compositions of clinopyroxenes reveals the existence of at least four MEs that are characterized by different compositional populations; two of these are dominant. The variation in zoning pattern from one plateau composition to another fingerprints the transfer of the crystal from one ME to another. In combination with Sr isotopic data and thermobarometric estimates, our systematic characterization of clinopyroxene zoning patterns suggests recharge by deep mafic magmas (ME0: Mg# = 85–92) of an evolved shallow reservoir (ME2: Mg# = 70–78). Such a process also led to the formation of a compositionally intermediate environment (ME1: Mg# = 84–80), that is detected in the clinopyroxene zoning pattern.A new method has been developed in this work to evaluate the effective diffusive modifications that affect the concentration profiles of zoned crystals. The application of different diffusion modeling methods indicates that deep and shallow reservoirs beneath the Campi Flegrei caldera were connected to each other over several tens of years until the amount of mafic recharge increased during the last 10–15 years before the A-MS eruption. This study highlights the complex relationships between events of magma recharge and the onset of eruption. Our results provide a contribution to the knowledge of timescales of magmatic processes that have recently occurred beneath the Campi Flegrei caldera, which is useful for risk assessment.

PTE and multi-isotope assessment of spring water used for human consumption in the historical mining region of Taxco de Alarcón in southern Mexico

The concentration of potentially toxic elements (PTE) and the isotope compositions (87Sr/86Sr, δ34S, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios) were determined in spring water, sulfide minerals, and rocks samples to evaluate spring water used for human consumption in the historical mining region of Taxco de Alarcón, southern Mexico. The springs samples were collected from the most representative rock units of the study area, from older to younger, to the Taxco Schist, Morelos, Mexcala, Balsas, and Tilzapotla formations. The spring water samples were classified as HCO3–Ca and HCO3–Ca–Na–Mg. The concentrations of Cd, Pb, Sb, Ni, Cu, Zn, Mn, Ba, and Al in the spring water samples were below the recommended values for human consumption according to Mexican and international agencies. However, Al, Ba, Mn, Li, Tl, and Ga concentrations may represent adverse health effects. The average concentrations in the springs followed the decreasing order Tl > Cd > Pb > Sb > Ni > Cu > Li > Zn > Ga > Mn > Ba > Al. This order is similar to that of the rocks rather than the sulfide mineralization, which suggests a major water-rock interaction, and therefore, a genetic link with the rocks. The water-rock interaction is supported by the Sr isotope data, mainly with the rocks belonging to the Tilzapotla Fm. According to the S isotope composition of the springs, two groups were identified: (1) springs characterized by lighter δ34S values, similar to those of the disseminated pyrite hosted in rocks from the Mexcala Fm; and (2) springs with heavier δ34S values, which were within the compositional range of the sulfide mineralization and Morelos Fm rocks. The Pb isotope compositions and mixing models indicated that the rock formations, particularly the Morelos Fm rocks, and the sulfide mineralization, influenced the composition of the spring water. This type of research is crucial to assess PTE contents and sources of spring water used for human consumption, particularly in developing countries, where the lack of infrastructure is common in rural areas.

3-D seismic chronostratigraphy of reefs and drifts in the Browse Basin, NW Australia

Abstract In its subsurface, the Browse Basin on the Australian Northwest Shelf accommodates one of the largest Miocene–Pliocene carbonate platform provinces on Earth. This study presents a comprehensive three-dimensional (3-D) documentation and investigation of the Neogene Browse Basin carbonates based on the analysis of 15 3-D seismic reflection volumes covering ca. 33,000 km2 and 22 industry boreholes. Eight basin-wide seismic marker horizons tied to Sr isotope and biostratigraphic data provide a robust 3-D chronostratigraphic framework that (1) newly documents the occurrence of Miocene to recent carbonate systems in vast inboard basin areas; (2) presents the 3-D distribution and dynamic development of carbonate platforms through time constrained by absolute ages; and (3) supports the detailed 3-D interpretation of Miocene to recent depositional processes and key stratigraphic controls. Around 18.6 Ma, the extent of all Browse Basin carbonate platforms was ca. 8600 km2, rising to &amp;gt;10,000 km2 between 15.6 Ma and 12 Ma. By ca. 9.7 Ma, the total platform extent had decreased to ca. 5700 km2, waning to &amp;lt;2800 km2 in the Pliocene. The observed reef demise is less abrupt than previously thought and comprises two steps, with the first in the late Miocene on the outer shelf and the second in the Pliocene on the middle and inner shelf. The Miocene outer-shelf platform demise coincided with (1) strong subsidence that outpaced sedimentation, (2) an increase in NW–SE-oriented tidal current activity, (3) the development of NNE–SSW-oriented bottom currents, and (4) the onset of drift sedimentation. The Pliocene demise of middle-shelf reefs coincided with (1) an increase of clastic sediment input from land and (2) stalling of the Indonesian Throughflow around 3.7 Ma. The basin-wide, 3-D seismic chronostratigraphic analysis presented supports a re-evaluation of the key controls for Miocene and Pliocene reef growth and decay on the NW Shelf and highlights the complexity of interacting global, regional, and local processes and peculiarities in carbonate platform development.

Pleistocene volcanism along the margins of the Canal de Ballenas transform fault, Gulf of California

Pleistocene subaerial volcanism along the margins of the Ballenas Channel, northern Gulf of California, is represented by two morphologically young dacite dome complexes exposed at the opposite edges of sheared continental crust: Isla Coronado in coastal Baja California, and the Lobera volcanic complex in west-central Isla Ángel de la Guarda. Single crystal zircon U-Pb crystallization ages of Coronado and Lobera volcanoes range between ca. 250 and 1000 ka, indicating maximum ages for the eruptions. Eruption ages are directly constrained by an 40Ar/39Ar whole-rock age of 692 ± 164 ka for one of the lava units in the Lobera volcanic complex. Trace elements in Pleistocene zircon indicate continental affinity, which supports radiogenic (Nd, Sr) isotopic data that were modeled using different mixing and AFC scenarios indicating a MORB-type primary magma with significant (~10–20 %) crustal assimilation involving tonalitic basement of the eastern Peninsular Ranges Batholith.

Geochronology, geochemistry and petrology of the oligocene magmatism in SE segment of the UDMB, Iran

Despite diverse geochronological-geochemical studies on Cenozoic igneous rocks from the SE segment of the Urumieh-Dokhtar Magmatic Belt (UDMB) of Iran, the nature of the Oligocene magmatic rocks from the farthermost end of the SE segment- where it is linked to the Makran magmatic belt- has been ignored due to the difficulty of access. In this study, we focus on syn-collisional mafic to felsic igneous rocks of calc-alkaline and high-K calc-alkaline affinities from the SE segment of the Urumieh-Dokhtar Magmatic Belt (UDMB) near Nagisun, south of Bam. The Nagisun rocks have low Sr/Y and La(n)/Yb(n), similar to igneous rocks from typical arcs. Zircon UPb ages show comparable ages for plutonic (~ 34–25 Ma) and volcanic (~34–27 Ma) rocks. The εHf(t) values for zircons from plutonic rocks range from −0.3 to +12.8, whereas the εHf(t) values for the volcanic rocks vary from −2.6 to +13. Modelling of trace elements compositions using Nagisan basaltic samples indicate that an 87:2:11 mixture of the depleted MORB mantle, subducting (trench)-sediments and altered oceanic crust with 5% aggregated fractional melting closely matches the trace-element abundances of the Nagisun basaltic rocks. Indeed, the modelling of Sr and Nd isotopic data emphasizes that the Nagisun magmatic rocks could be products of bulk mixing between a depleted MORB mantle and/or a mixed, fertilized mantle with the Cadomian lower and upper continental crust. Furthermore, our compiled data display that the magmatism in the SE segment of the UDMB changed through time from normal calc-alkaline magmatism to adakitic magmatism at ~20 Ma, after the collision with Arabia began ca 27 Ma.

Strontium Isotope Systematics of Tenerife Wines (Canary Islands): Tracing Provenance in Ocean Island Terroir

The production of fraudulent goods remains widespread and economically damaging. The high value of the wine industry makes it particularly vulnerable, and a number of geochemical methods have been developed to ensure traceability and identification of origin. Here, strontium (Sr) isotope data on wines from five defined regions in Tenerife (Canary Islands, Spain) show that the young volcanic geology imparts a clearly identifiable low 87Sr/86Sr signature (&lt;0.7072). These values discriminate Tenerife wines from mainland Spanish and continental European produce, as these are much more radiogenic in general. However, unlike continental wine regions, wines from Tenerife show small but ubiquitous enrichments in 87Sr/86Sr above what is expected in the soils. Bentonite addition has not affected the 87Sr/86Sr signatures, with white wines at lower Sr concentrations than red wines in all regions. A number of natural contributions to the terroir are evaluated in relation to Tenerife’s unique combination of geology and geography. Atmospheric precipitation (rainfall) is likely a dominant influence on Sr isotope systematics in northern Denominación de Origen regions, and evaporation may play a role in buffering signatures in southern regions. Other natural additions of 87Sr are not precluded at a local scale, given the large range in climatic conditions of island terroir and known input of mineral dust from Africa. Despite natural explanations affecting the overall small shift observed, there are clear outliers with considerably higher 87Sr/86Sr and Sr concentration. This confirms the utility of Sr isotope systematics for oceanic-island viticulture and demonstrates the use of young volcanic soils for tracing natural inputs that may be masked in other regions.

Elemental and isotopic tracing of mineral infillings from various microstructures of a fault system into fine-grained sediments: which interacting fluids?

Elemental contents and Sr isotopic data of calcite and celestite infillings from various tectonic microstructures of the so-called “Main Fault” that occurs in the Opalinus Clay Formation (Switzerland) were used to elaborate on the geochemical impact of this structural system on the fine-grained host sediments. The chemical data of the leachates from vein, slickenside and gouge infillings are significantly different from those of leachates from diffuse calcite of the undeformed and of the highly deformed Opalinus Clay rock matrix called scaly clays. For instance, the fluids flowing within the microstructural veins and slickensides could not derive from pore waters of the host sediments, as the data show that the flowing waters diffused from veins into the matrix. The fluid/rock interactions in the gouges were also different from those in the veins and the slickensides, probably due to an additional pressure-solution impact in the former, complemented by a further local supply of organics from very close sediments. The infillings of the vein and slickenside micro-features and of some scaly clays that precipitated from bi-carbonated and/or sulfated flowing fluids yield an almost constant 87Sr/86Sr ratio of 0.70774 ± 0.00001 (2\(\upsigma\)). This constrained Sr isotopic value points to a unique homogeneous external source for the tectonic-related fluids that were of probable marine origin, signing those of the early, but also of the late faulting event. Notably different from those seeping presently throughout the host rocks, the initial flowing fluids were apparently related to a late-Eocene marine invasion into the Delémont Basin that occurred during the contemporaneous rifting of the Rhine-Graben tectonic system. The flowing fluids induced by the late Main-Fault system obviously used, at least, some if not most of these earlier tectonic microstructures, as they yield the Sr isotopic signature of their infillings. The regional evolution includes then an initial Rhine-Graben tectonic episode with fluids resulting from a flooding of the deposited sediments and into the faults of the regional active Rhine-Graben rifting by contemporaneous seawater. These fluids precipitated precisely calcite and celestite infillings in the microstructures induced by the rifting that remained then unaffected until the renewed tectonic activation during the late Eocene in the Mont Terri and its fault system. This new tectonic–thermal episode created a new generation of microstructures during the thin-skinned deformation of the Jura Belt within and around the Main Fault, in addition to those from earlier Rhine-Graben event that already existed in the host rocks. Connections between the two generations of veins could be observed at the wall of a new gallery in the rock laboratory. The flowing fluids involved in this late belt event moved apparently along these newly created tectonic microstructures, as well as along older ones when accessible. This duality allowed the preservation of the same initial Sr isotopic signature by partial dissolution of the initial infillings that precipitated about 30 million years earlier in the initial drains of the Rhine-Graben fault system.

Formation of the Chah-Gaz iron oxide-apatite ore (IOA) deposit, Bafq District, Iran: Constraints from halogens, trace element concentrations, and Sr-Nd isotopes of fluorapatite

The textures, chemistry and Sr-Nd isotopic compositions of apatite from the Chah-Gaz iron-oxide apatite (IOA) deposit in the Bafq metallogenic belt, central Iran, were studied to investigate the formation of this ore deposit. Two generations of apatite were recognized based on Cl/F and Cl/OH ratios. Primary fluorapatite, which is coeval with magnetite in the massive ore bodies, is chemically homogeneous and characterized by Cl/F < 0.05 and Cl/OH in the range of 0.01–0.07. By contrast, F-depleted apatite rims are present in apatite hosted in veinlets that crosscut the massive ore bodies and are disseminated in the igneous host rocks, and have Cl/F and Cl/OH-apatite ratios of 0.08–0.12 and 0.15–0.79, respectively. The F-depleted rims are also depleted in LREEs, Th and U, consistent with the presence of secondary monazite, xenotime and thorite that formed by coupled dissolution-reprecipitation. The whole-rock Nd–Sr isotopic data ((87Sr/86Sr)(I) = 0.7052 to 0.7064 and ɛNd(t) = +1.3 to + 2.7) of gabbro-diorite indicate an mantle source, while the high -K, calc-alkaline-shoshonitic volcanic host rocks have εNd(t) = − 5.5 to − 7.6, clearly reflecting mixing between mantle-derived mafic magmas and assimilated Proterozoic basement. The initial 87Sr/86Sr ratios and ɛNd values of both F-rich and -depleted apatites (0.7038 to 0.7050 and −0.3 to + 6.5, respectively) are similar to gabbroic rocks and support a magmatic source for primary fluorapatite, with minimal or no crustal contribution, and indicate that the magmatic event with negative ɛNd values did not affect the whole-rock Sm-Nd signature of the ore. Petrography plus geochemical and Nd-Sr isotopic data of both studied fluorapatite, which come from iron oxide stage, are consistent with a combined igneous/magmatic-hydrothermal genesis for the Chah-Gaz IOA deposit, with low degrees of hydrothermal overprint, as evidenced by the formation of F-depleted (Cl-rich) apatite rims. The relatively constant Sr-Nd data in apatite are consistent with superimposed, episodic hydrothermal fluids from the same, evolving, magmatic-hydrothermal system.

Source and evolution of the ore-forming fluid of the Cuonadong Sn-W-Be polymetallic deposit (southern Tibet, China): Constraints from scheelite trace element and Sr isotope geochemistry

The Cuonadong Sn-W-Be polymetallic deposit is the first rare-metal deposit with an extraordinary metallogenic potential that has been discovered in the Tethyan Himalayan metallogenic belt. The deposit shows a wide range of different mineralization types, including greisen-, pegmatite-, skarn-, and hydrothermal vein-type mineralization. Of these mineralization types, the skarn-type has the largest inferred resources. In order to constrain the source and evolution of the ore-forming fluid, we conducted a detailed study of the skarn-hosted scheelite, including cathodoluminescence imaging, in-situ trace elemental analysis, and bulk Sr isotope analysis. In addition, bulk Sr isotope analysis of fluorite, phlogopite 40Ar-39Ar dating, and marble whole-rock geochemical analysis were also conducted. Phlogopite 40Ar-39Ar dating indicates that the skarn was formed at ca. 15 Ma, which is close to the formation age of the Cuonadong muscovite granite reported in previous studies. Cathodoluminescence images indicate that skarn-hosted scheelite can be subdivided into an older type 1 scheelite and a younger type 2 scheelite. Type 1 scheelite is characterized by a negative Eu anomaly, whereas type 2 scheelite shows a positive Eu anomaly. Considering the close temporal and spatial relationship between the Cuonadong Miocene leucogranite and the ore-bearing skarn, and their similar lanthanide tetrad effect as observed in the REE patterns, we propose that the negative Eu anomaly was inherited from the Cuonadong Miocene leucogranite, while the positive Eu anomaly resulted from the addition of Eu2+ to the ore-forming fluid during greisenization. Sr isotope data show that the fluorite (87Sr/86Sr)i value of 0.728885 is within the range of the Cuonadong Miocene leucogranite (87Sr/86Sr)i values, while scheelite (87Sr/86Sr)i values (0.709717–0.713480) are similar to those of the Cuonadong marble (0.709525–0.712146). Since scheelite is intergrown with fluorite, we propose that the hydrothermal fluid that exsolved from the Cuonadong Miocene leucogranite is responsible for formation of both fluorite and scheelite. Water-rock interaction between this magma-derived fluid and the marble is responsible for the loss of the scheelite magmatic Sr isotopic signature.

Sr isotope-salinity modelling constraints on Quaternary Black Sea connectivity

Reconstruction of the Black Sea's connectivity history during the Quaternary is based on high-resolution isotope data and longer-term biotic records. These demonstrate that the Black Sea experienced rapidly changing hydrologic configurations involving, at different times, isolation from and/or connection with the Mediterranean and Caspian seas. Here, we simulate these connectivity scenarios using a numerical box model of Black Sea hydrography. This allows us to explore the magnitude of the different water fluxes and their consequences for Black Sea salinity and Sr isotope ratio; parameters that we can measure today and reconstruct in the past. We show that the model is able to replicate the present-day hydrography using new Sr isotopic data measured on modern Black Sea water (0.709143 ± 0.000008) and that the Black Sea has a homogenous Sr isotope ratio despite its strongly stratified water column. We then create a 1.2 Myr record of paired Sr isotope (ostracods) and palaeosalinity (dinoflagellate cysts) data, using samples from DSDP Site 379. We also provide the first constraints on the Sr isotope ratio of the Amu Darya River, a substantial fluvial system that previously fed the Caspian Sea and therefore influenced the Black Sea when the two basins were connected. Modelling the different connectivity scenarios and incorporating both new and previously published geochemical and biotic data indicates that influx from the Caspian Sea dominated Black Sea hydrography between 1.2 to around 0.5 Ma. In contrast, Mediterranean input has exerted increasing influence since 0.6 Ma, particularly during interglacial periods. The hypothesis that an interval of anomalously high Sr isotope ratios in the Black Sea during the late Saalian deglaciation (MIS 6) was caused by input from the Amu Darya is demonstrably unrealistic. Instead the high Sr ratios may have been driven by variations in glacial extent within the Dnieper catchment and the resultant erosion of Sr from granitic basement rocks. Our new combined model-data approach tests and refines interpretations of the glacio-hydrographic development of the Black Sea during the second half of the Quaternary.

Cleaning up the record – revised U-Pb zircon ages and new Hf isotope data from southern Sweden

ABSTRACT Ten samples of felsic plutonic rocks from the Eastern Segment of the Sveconorwegian Orogen in southern Sweden, previously dated by ID-TIMS on zircon, have been dated anew using SIMS spot analysis of individual zircon grains, leading to more reliable and in most cases also more precise revised magmatic crystallization ages. A gneissic monzonite within the Protogine Zone in Småland yields a revised U-Pb age of ca. 1725 Ma, four samples of orthogneiss from Skåne all yield revised ages between 1700 and 1690 Ma, while two samples of coarse-grained granitic gneiss in the same region yield ages between 1690 and 1680 Ma. These revised ages are between 15 and 250 m.y. older than previously obtained TIMS ages. Two samples of the Gumlösa-Glimåkra granite along the Protogine Zone in northern Skåne and one sample of related syenite yield ages around 1220 Ma, similar but more precise compared to the previous ages. The U-Pb zircon data have been complemented by Hf isotope analysis by LA-ICP-MS on the same grains, and previously obtained initial Sr and Nd whole-rock isotope data have been recalculated to the revised crystallization ages. The Sr isotope data scatter, while the revised initial εNd values fall between +1 and +2 for the older rocks, and close to 0 for the younger intrusives along the Protogine Zone. Initial εHf in magmatic undisturbed zircons shows relatively little spread within each sample, between 2 and 4 Epsilon units, disregarding a few outliers, with average values for the 1725 to 1680 Ma rocks between +3 and +5.5 and for the 1220 Ma rocks at ca. +1.5. Covariation between initial εNd and initial εHf in the older rocks suggests either mixing between two isotopically distinct magma sources or one magma source which was isotopically heterogeneous. The isotopic signatures of the 1220 Ma intrusive rocks along the Protogine Zone are indicative of juvenile mantle input to their magmas, rather than pure crustal melting.

Zircon trace elements and oxygen fugacities of parental magma of Maher abad and Khopik Cu porphyries, Lut block

The Maher abad and Khopik porphyry Cu deposits occurred in the Upper Eocene (39-37 Ma) in Lut block. All of them associated with intermediate (mostly monzonite) rocks. Porphyry deposits are closely associated with oxidized magmas. Oxygen fugacity (fO2) is a key factor that controls the formation of porphyry Cu deposits. The composition of the major and trace elements of zircon grains related to several ore-bearing monzonite were measured in Maher abad and Khopik porphyry copper indices. Zircon grains show moderate to low Ce4+/Ce3+ with a range of 19 to 610 and an average of 155. The average of oxygen fugacity (logfO2) values of Meher abad and Khopik ore-bearing magmas, range ∆FMQ -3.2 to MFMQ -1.3 with mean ∆FMQ -2.2, indicate formation under moderate oxidation conditions (between Ni-NiO (NNO) and Faylite magnetite-quartz (FMQ) buffers, but magnetite-hematite (HM) buffer, which ), which is not ideal for the formation of porphyry deposits. This is supported by whole-rock and Sr-isotopic data, and absence of high oxidation minerals such as hematite, and the poor adakitic charactristic of rocks in both deposits, which are due to factors involved in magma origin such as rock type and partial melting rate (possibly peridotite with low participation of slab).