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The Bressanone (Brixen) pluton, cropping out at the culmination of the Southalpine indenter between the North Giudicarie and the Pustertal-Gailtal faults, is mainly composed of Permian granodiorite to granite, with minor gabbros and diorites in its southern part. New U–Pb SHRIMP zircon ages reveal two distinct crystallization episodes at 289.7 ± 3.2 and 280 ± 2.2 Ma, respectively. The pluton is affected by a hydrothermal potassic to sodic + Cu metasomatic alteration, which has long been ascribed to a late phase of the Permian magmatism. In contrast with this hypothesis, we report new 39Ar–40Ar data for different generations of metasomatic K-feldspar, which indicate formation ages between 35.3 ± 0.3 and 27.8 ± 0.5 Ma. This interval overlaps with the ages of the widespread 'Periadriatic' calc-alkaline magmatism, which extends from the Western to the Eastern Alps straddling the Periadriatic Fault System. The observed hydrothermalism has geochemical characteristics compatible with those of the coeval calc-alkaline Periadriatic magmatism. These data altogether suggest the release of fluids from a hidden intrusion during the main stage of the Alpine orogenic magmatism. Our results provide the first evidence of Oligocene magmatic activity in the Southern Alps east of the Giudicarie Line, bridging the gap between the western-central and eastern Alpine magmatic plutons. A fairly continuous Oligocene magmatic belt straddling the Periadriatic Fault System is consistent with a triggering of the magmatism by slab steepening or slab break-off, either of which are considered to be an essential driver for the Miocene lithospheric rearrangement in the Eastern Alps. Our finding is particularly relevant given that the outcropping area of the Bressanone pluton is centred above the imaged subducting lithosphere gap that separates the Western-Central and the Eastern Alps, hence at a location where mantle upwelling should have been easier although no relevant magmatism was found to date. [ABSTRACT FROM AUTHOR]

The article presents a study which showed that modern global mean sea level (GMSL) rise is anomalous relative to any natural variability in ice volumes over the past 4000 years. Topics discussed include the need for an accurate record of preindustrial sea level to contextualize modern GMSL rise with respect to natural variability, modern sea-level elevation measurements, and predicted sea-level change in Mallorca.

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 at given P-T conditions. Common rock-forming minerals like quartz, feldspars and sheet silicates 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 at 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 of the primary vein quartz. This occurs contemporaneously with dissolution and (re)precipitation of epidote, and grain-boundary sliding, leading to a combined process described as viscous granular flow. The combination of intracrystalline plasticity, grain boundary sliding and dissolution locally and repeatedly produce creep cavities. These represent not only loci for nucleation of new epidote grains at the expenses of dissolved one, 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, indicate a process of chemical homogenization. The nature of the fluid mediating 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. [ABSTRACT FROM AUTHOR]

Abstract: In the Kharta area, east of Mount Everest, the Greater Himalayan Crystallines are significantly richer in mafic rocks than the surrounding areas, Sikkim–West Bhutan and Makalu–Cho Oyu. These rocks are lenses with a complex metamorphic history. The mafic lenses of Shao La, in the Greater Himalayan Sequence south of Kharta, are here considerated as dismembered dykes apparently escaped the Himalayan high-temperature metamorphism and only record a low-grade metamorphic event. They are calc-alkaline medium-K basalts to basaltic andesites, consisting of plagioclase (core 62% An and rim 55% An), augite (Wo43–47En3636–37Fs16–20), hypersthene (Wo1.6–3.3En50–52Fs46–48), and minor brown hornblende, biotite and ilmenite. They show strong enrichment in low ionic potential elements relative to high-field-strength elements, and only minor Ce and P enrichment with respect to MORB. Combined Sr–Nd systematics suggest contamination of a basic magma from a subcontinental mantle source with a small amount of crust (about 4 vol.%). This in turn indicates that the Shao La basalts and basaltic andesites have the geochemical fingerprint of a supra-subduction zone magma. U–Pb dating of zircon from one sample yielded an age of 457±6Ma for the crystallisation of the Shao La basic rocks, assigning them to the Cambro-Ordovician Bhimphedian orogenic event. The age and geochemical characteristics of the Shao La rocks are similar to those of the basic rocks of the Cambro-Ordovician Mandi pluton further west. This suggests the existence of an extensive supra-subduction zone magmatism along the Indian margin of Gondwana. Like the bimodal granite-gabbro magmatism in the Mandi-Kaplas area, the Shao La basic rocks are contemporaneous with the emplacement of granitic plutons in the Everest-Kharta area. This acid plutonism is interpreted as crustal melt triggered by the upwelling of metasomatised mantle in a back-arc setting. The age of basic and acidic plutonism in the Everest-Kharta area is evidence that the Bhimphedian Orogeny was still active as late as the Late Ordovician [Copyright &y& Elsevier]

A technique combining 40Ar/39Ar step-heating analyses, in situ UV laserprobe dating and electron microprobe chemical characterization has been developed to unravel the relationships between microstructures, metamorphism and K/Ar systematics. This technique has been applied to white micas of a discrete shear zone in the Roffna metarhyolite in the Suretta nappe (SE Switzerland). Neoformed phengites from the Roffna metarhyolite crystallised in shear zones during Tertiary Alpine deformation under blueschist- and greenschist-facies conditions. In situ 40Ar/39Ar UV laser dating of white micas defining the schistosity and C-planes yield systematically younger isotopic dates in the C-planes, which are also correlated with decreasing celadonite content (i.e., Si/Al ratio). These results suggest that the timing of the high-pressure deformation event is preserved in the schistosity; high-Si micas appear to have lost no Ar. Later deformation was localised preferentially in C-planes giving younger 40Ar/39Ar dates probably related to a later period of phengite growth. The age sequence is broadly consistent with the textural constraints and geological field relations. [Copyright &y& Elsevier]

The Itremo region in Central Madagascar comprises a deformed metasedimentary sequence (Itremo Group) that has undergone greenschist to lower amphibolite facies metamorphism. During a first phase of deformation (D1) Itremo Group sediments were deformed into a fold-and-thrust belt and transported toward the E to NE on top of migmatitic gneisses rocks of Anatananarivo block. A second phase of deformation (D2) affected both the fold-and-thrust belt and structurally underlying units, and formed large-scale N-S trending folds with steeply dipping axial planes. A Late Neoproterozoic Th–U–Pb XRF monazite age (565±17 Ma) dates the emplacement of a granite that truncates first-phase structures in the Itremo Group, and indicates that the fold-and-thrust belt formed prior to ≈565 Ma. Th–U–Pb electron microprobe dating was applied to elongated monazites that lie within the first-phase foliation of Itremo Group metapelites. The detrital cores of zoned monazites reveal two distinct age populations at ∼2000 and 1700 Ma, the latter age giving a maximum depositional age for the Itremo Group. Statistical analysis of ages determined from the rims of zoned monazites and from unzoned monazites indicates three Late Proterozoic–Early Paleozoic monazite growth events at about 565–540, 500 and 430 Ma. The oldest age population is contemporaneous within error, with the intrusion of the dated granite. The two younger age populations are found both in the Th–U–Pb and Ar–Ar data; together with the perturbation of the Rb–Sr system we interpret both ages as due to alteration related to fluid circulation events, possibly connected to the emplacement of pegmatite fields in Central Madagascar. Syn-D1 tectonic growth of contact metamorphism minerals such as andalusite has been observed locally in metapelites along the margin of Middle Neoproterozoic (≈800 Ma) granites, suggesting that D1 in the Itremo Group is contemporaneous with the intrusion of granites at ≈800 Ma. The N-S trending D2 folds are associated with ≈E-W shortening during the final assembly of Gondwana in Late Neoproterozoic–Early Cambrian times. [Copyright &y& Elsevier]

The degree of early Archaean terrestrial differentiation into mantle and crust is long debated. A number of studies rely on bulk rock Hf and Nd isotope data to gain further insight. Here we present Hf-Nd data from two igneous basements suites of Barberton Mountain Land, namely a tonalite-trondhjemite-granodiorite (TTG) and granodiorite-granite-monzogranite (GGM) suite to further decipher crust formation and its timing in the Archaean. TTG show high initial ε(Hf) and ε(Nd) if corrected using their respective U/Pb zircon ages that can be interpreted in two ways: (i) early differentiation of bulk silicate Earth or (ii) overcorrection of these data caused by decoupling of zircon from the 'zircon-free' bulk rock due to metamorphic overprint. Indeed, regional metamorphism affected the early TTG ca. 250 Ma after their emplacement and disturbed their bulk rock Hf and Nd systematics. Correction of bulk rock Hf and Nd data to the age of metamorphism yields values between +0.9 and − 6.2 and from −1.3 to −4.3, respectively, thus indicating open-system behaviour. Lu-Hf and Sm-Nd mineral isochron ages of two TTG plutons are significantly younger than their corresponding U/Pb zircon age, but agree within uncertainty perfectly with external age constraints for the age of the metamorphic overprint. The same accounts for the 40Ar-39Ar systematics of the investigated plutons. Amphibole samples consist of a mixture of heterochemical generations that yield ages that are both older and younger than the metamorphic overprint at 3.2 Ga. The metamorphic minerals in each plutons provide a highly divergent age information from the coexisting zircon. Hence, the positive ε(Nd) and ε(Hf)-values that resulted from age-correction to the respective U/Pb zircon age are most probably over-corrected. Finally, if all data is age-corrected to the metamorphic overprint all samples agree with models for the Nd-Hf isotopic evolution in the mantle that do not require a large-scale early differentiation of Earth into enriched and depleted reservoirs. Mantle extraction ages (T DM) of TTG are interpreted as minimum ages for the generation of felsic Archaean crust whereas T DM of GGM are interpreted as maximum ages for the last major crust growth episode in the Barberton Mountain Land. [ABSTRACT FROM AUTHOR]

Vorticity estimates based on porphyroclasts analysis are limited by the extrapolation to three dimensions of two‐dimensional data. We describe a 3D approach based on the use of X‐ray micro‐computed tomography that better reflects the real 3D geometry of the porphyroclasts population. This new approach for kinematic vorticity analysis in the Munsiari Thrust mylonites, the lower boundary of the Main Central Thrust zone (MCTz) in Indian Himalaya, indicates a large pure shear component during non‐coaxial shearing. 40Ar/39Ar ages of micas along the mylonitic foliation of the Munsiari and Vaikrita thrusts (the upper boundary of the MCTz) constrain thrust activity to 5–4 and 8–9 Ma, respectively. Available kinematic vorticity analyses of the Vaikrita mylonites suggest the dominance of a simple shear component. Combining these data, we suggest that the southward and structurally downward shift of deformation along the MCTz was accompanied by a progressive increase in the pure shear component in a general shear flow. [ABSTRACT FROM AUTHOR]

Abstract The Singhbhum Craton in eastern India, one of the four major Archean cratons of the Indian Shield, is underlain by Paleoarchean granitoids (trondhjemite-tonalite-granodiorite i.e. TTGs, and potassic granites) that are encircled by greenstone belts rich in banded iron formation known as Iron Ore Group. This study presents whole rock major-trace element geochemistry, Sr and Nd isotopes, K-feldspar common Pb isotopes, along with in-situ zircon U–Pb ages and Hf isotope data from the granitoids and the greenstone volcanic rocks to characterize their source(s) and to constrain the evolution of the Paleoarchean continental crust. Zircon U–Pb ages show that these granitoids were emplaced during two magmatic episodes at ca. 3.47–3.44 Ga and 3.36–3.28 Ga. The greenstone volcanic rocks in the eastern part of the craton are basalts and basaltic andesites with rare komatiites, whereas those in the western part are basaltic-andesites and andesites. Whole rock Sm–Nd isotope regression lines for volcanic rocks from the eastern (including komatiites) and western regions yield ages of 3746 ± 340 Ma (MSWD = 169) and 2961 ± 420 Ma (MSWD = 3.3), respectively. The major and trace element data show that the volcanic rocks of the eastern and western greenstone belts had a different petrogenesis. The granitoids are highly evolved with SiO 2 contents up to 76 wt%. The major and trace element data indicate that the granitoids of the Singhbhum Craton were derived by partial melting of a mafic crust at variable depths (ca. 10–15 kbar). The isotopic compositions of Pb measured on leached K-feldspars from the granitoids show undepleted mantle-like characteristics and negate the possible involvement of much older evolved crust in the formation of these rocks. The whole rock initial Nd isotopic compositions (εNd i = −0.3 to +2.2) and zircon in-situ initial Hf isotopic compositions (εHf i = −0.3 to +2.0) of the granitoids calculated using zircon crystallization ages indicate that they were derived from a near-chondritic reservoir. These data suggest that only a limited volume of continental crust formed prior to ca. 3.5 Ga, and major crust extraction from the mantle started at ca. 3.5 Ga. Using this time as the start of major crustal growth and concomitant mantle depletion, Nd and Hf mantle depletion histories are proposed for the Singhbhum Craton that can be described by the equations εNd t = −2.85 × (t Ga) + 10, and εHf t = −4.68 × (t Ga) + 16.4. These curves do not change the model ages for young rocks, but they make a significant difference for the Archean rocks. Highlights • Granitoids of the Singhbhum Craton were emplaced in two magmatic episodes at ca. 3.47–3.44 Ga and ca. 3.36–3.28 Ga. • Hafnium and Nd isotope data of most of these granitoids indicate their derivation from a near-chondritic source. • Lead isotopes in K-feldspars show no evidence for much older evolved crustal material in petrogenesis of these granitoids. • Major continental crust formation started at ca. 3.5 Ga. [ABSTRACT FROM AUTHOR]

Detrital thermochronology is often employed to assess the evolutionary stage of an entire orogenic belt using the lag-time approach, i.e., the difference between the cooling and depositional ages of detrital mineral grains preserved in a stratigraphic succession. The impact of different eroding sources to the final sediment sink is controlled by several factors, including the short-term erosion rate and the mineral fertility of eroded bedrock. Here, we use apatite fertility data and cosmogenic-derived erosion rates in the Po river catchment (Alps–Apennines) to calculate the expected percentage of apatite grains supplied to the modern Po delta from the major Alpine and Apenninic eroding sources. We test these predictions by using a cutting-edge dataset of trace-element and Nd-isotope signatures on 871 apatite grains from 14 modern sand samples, and we use apatite fission-track data to validate our geochemical approach to provenance discrimination. We found that apatite grains shed from different sources are geochemically distinct. Apatites from the Lepontine dome in the Central Alps show relative HREE enrichment, lower concentrations in Ce and U, and higher 147 Sm/ 144 Nd ratios compared to apatites derived from the External Massifs. Derived provenance budgets point to a dominant apatite contribution to the Po delta from the high-fertility Lepontine dome, consistent with the range independently predicted from cosmonuclide and mineral-fertility data. Our results demonstrate that the single-mineral record in the final sediment sink can be largely determined by high-fertility source rocks exposed in rapidly eroding areas within the drainage. This implies that the detrital thermochronology record may reflect processes affecting relatively small parts of the orogenic system under consideration. A reliable approach to lag-time analysis would thus benefit from an independent provenance discrimination of dated mineral grains, which may allow to proficiently reconsider many previous interpretations of detrital thermochronology datasets in terms of orogenic-wide steady state. [ABSTRACT FROM AUTHOR]

This study presents static measurements of the Ca isotopic composition of standard reference materials SRM 915 a/b on a Triton Plus ™ thermal ionization mass spectrometer with a specially developed Faraday cup array allowing simultaneous measurement of 40 Ca and 48 Ca. The total amount of Ca in all analyses was kept <1 μg. With this setup the measurement uncertainties were 0.06‰ for 40 Ca/ 44 Ca and 0.12‰ for 48 Ca/ 40 Ca. Measuring all isotopes simultaneously better allows to test the internal consistency of different Ca isotope abundances reported in the literature. The exponential law was observed to correct incompletely instrumental mass fractionation. An improved fractionation correction based on the exponential law is proposed. It changes the 40 Ca/ 44 Ca ratio of SRM 915a (corrected relative to 42 Ca/ 44 Ca = 0.31221; 48 Ca/ 44 Ca = 0.08871) from 47.1635 ± 0.0028 to 47.1649 ± 0.0047. The measurements of SRM 915b were performed with different analytical conditions (runs were prolonged till complete filament load depletion). Even if the 40 Ca/ 44 Ca ratio of SRM 915b, when corrected with the simple exponential law, appears different (47.1532 ± 0.0038) from that of SRM 915a, it becomes coincident (47.1613 ± 0.0028) when corrected with a second-order refinement. This supports the use of the improved exponential law to obtain internally consistent Ca isotope ratio for natural samples. [ABSTRACT FROM AUTHOR]

Abstract: This study presents an integrated mineralogical–geochemical database on fine-grained sediments transported by all major rivers of southern Africa, including the Zambezi, Okavango, Limpopo, Olifants, Orange and Kunene. Clay mineralogy, bulk geochemistry, Sr and Nd isotopic signatures of river mud, considered a proxy of suspended load, are used to investigate the influence of source-rock lithology and weathering intensity on the composition of clay and silt produced in subequatorial to subtropical latitudes. Depletion in mobile alkali and alkaline-earth metals, minor in arid Namibia, is strong in the Okavango, Kwando and Upper Zambezi catchments, where recycling is also extensive. Element removal is most significant for Na, and to a lesser extent for Sr. Depletion in K, Ca and other elements, negligible in Namibia, is moderate elsewhere. The most widespread clay minerals are smectite, dominant in muds derived from Karoo or Etendeka flood basalts, or illite and chlorite, dominant in muds derived from metasedimentary rocks of the Damara Orogen or Zimbabwe Craton. Kaolinite represents 30–40% of clay minerals only in Okavango and Upper Zambezi sediments sourced in humid subequatorial Angola and Zambia. After subtracting the effects of recycling and of local accumulation of authigenic carbonates in soils, the regional distribution of clay minerals and chemical indices consistently reflect weathering intensity primarily controlled by climate. Bulk geochemistry identifies most clearly volcaniclastic sediments and mafic sources in general, but cannot discriminate the other sources of detritus in detail. Instead, Sr and Nd isotopic fingerprints are insensitive to weathering, and thus mirror faithfully the tectonic structure of the southern African continent. Isotopic tools thus represent a much firmer basis than bulk geochemistry or clay mineralogy in the provenance study of mudrocks. [Copyright &y& Elsevier]

Recent improvements in the precision of mass spectrometric measurements have reduced the uncertainty of K–Ar and 39Ar–40Ar ages measured on geological materials. Now the major sources of uncertainty are the uncertainties on the 40K decay constant and the absolute abundance of 40K. In order to improve on this situation we determined the abundance of the 40K isotope in terrestrial standards. A ThermoFischer Triton+ thermal ionization mass spectrometer was used for K isotope ratio measurements of the NIST K standard reference materials SRM 918b and SRM 985. Ion beams were measured in Faraday cups with amplifiers equipped with 1010, 1011 and 1012 Ω resistors. Three measurement protocols were used: (A) dynamic measurement with in-run fractionation correction by normalization to the IUPAC recommended isotope ratio 41K/39K=0.072 1677; (B) total evaporation; (C) a modified total evaporation with interblock baseline measurements. Different measurement protocols were combined with different loading procedures. The best results were obtained by loading samples on single oxidized tantalum filaments with 0.1M H3PO4. The total ion yields (ionization+transmission) were tested for the evaporation procedures (B) and (C) and ranged up to 48%. The resulting best estimate for the 40K/39K ratio is 0.000125116±57 (2σ), corresponding to an isotopic abundance 40K/K=(1.1668±8)×10−4. [ABSTRACT FROM AUTHOR]

Abstract: Detrital studies that utilize zircon U–Pb geochronology and fission-track (FT) thermochronometry are subject to a range of potential sources of bias that should be properly evaluated and minimized. Some of them are common to any single-grain mineral analysis (e.g., variable bedrock mineral fertility, hydraulic sorting during transport, selective grain loss during sample processing), whereas others are intrinsic to zircon, and are related to radiation damage and age discordance. In this article, we quantify the impact of intrinsic bias on detrital studies thanks to the analysis of modern detritus shed from the European Alps, and illustrate the general implications on geological interpretations. We show that detrital zircon U–Pb age distributions based on statistically robust datasets are highly reproducible and representative of the parent bedrock ages in the catchment. Arbitrary or selective removal of discordant grain ages can be minimized by using the Kolmogorov–Smirnov test to identify an appropriate cutoff level. Loss of metamict (α-damaged) zircon has a minor impact on data representativeness, and is mainly controlled by regional metamorphism rather than by mechanical abrasion during river transport. Zircon FT grain-age distributions were found to have poor reproducibility, although age spectra are consistent with bedrock data. However, unlike the U–Pb datasets, U-rich zircon grains (>1000ppm) are systematically missed, and undatable grains may exceed 50%. We identify two major sources of distribution bias specific to zircon FT datasets: (i) sediment sources dominated by U-rich zircon grains are markedly underrepresented in the detrital record, because such grains often have uncountable high densities of fission tracks (“U concentration bias”); (ii) sediment sources that shed zircon grains with high levels of α-damage are underrepresented, because these grains are lost during chemical etching for FT revelation (“etching bias”). In the case of multimethod dating on the same grains (e.g., FT and U–Pb double dating), bias affecting detrital zircon FT dating propagates to the entire dataset. These effects may not impact on exhumation-rate studies that utilize the youngest grain ages (i.e., lag-time approach). However, they represent a limiting factor for conventional provenance studies, and generally preclude application of zircon FT dating to sediment budget calculations. [Copyright &y& Elsevier]

Fissure ridge travertines grown from geothermal springs of Denizli Basin, southwestern Turkey, are investigated through stratigraphic, structural, geochemical, and geochronological methods, with the aim of understanding the growth of these elongate mound-shaped structures. Two main types of travertine deposits are recognized: (1) bedded travertines, which grew as flowstone on sloping surfaces and form the bulk of fissure ridges, and (2) banded travertines, which grew as veins within the bedded travertine chiefly along its central feeding conduit. Stratigraphic and structural observations shed light on the bedded-banded travertine relationships, where the banded features grew through successive accretion phases, crosscutting the bedded travertine or forming sill-like structures. The bedded and banded travertines alternated their growth, as demonstrated by complicated crosscutting relationships and by the upward suture, in places, of banded travertine by bedded travertine that was, in turn, crosscut by younger banded travertine. The bedded travertine is often tilted away from the central axis of the fissure ridge, thus leaving more room for the central banded travertine to form. U-series ages confirm the bedded-banded travertine temporal relationships and show that the growth of the studied fissure ridges lasted up to several tens of thousands of years during Quaternary time. The banded travertine was deposited mainly during cold events, possibly in coincidence with seismic events that might have triggered the outflow of deep geothermal fluids. C and O stable isotope and rare earth element data indicate a shallow feeding circuit for the studied structures with a fluid component deriving from a deeper geothermal circuit. A crack-and-seal mechanism of fissure ridge growth is proposed, modulated by the interplay of local and regional influencing factors and mechanisms such as geothermal fluid discharge, paleoclimate, tectonics, and the progressive tilting of bedded travertine limbs over a soft substratum creating the necessary space for the central veins to grow. [ABSTRACT FROM AUTHOR]

Abstract: We analyzed the molybdenum (Mo) isotope compositions (IC) of 59 samples from two molybdenite mineralizations (Alpjahorn and Grimsel) and from a Mo-rich hydrothermal breccia (Grimsel) from the Aar Massif, Switzerland. The formation temperature of the Late Paleozoic Mo mineralizations (300–600°C) is much higher than that of the Pliocene breccia (100–160°C). The Mo IC of the molybdenites varies over 1.35‰. Even in a single hand specimen it spans 0.45‰, indicating that fractionation processes during molybdenite precipitation can vary on a cm scale. The Mo IC of most molybdenites analyzed here are significantly heavier than that of the host rock (δ 98/95Mo=(0.05±0.1)‰) and show a bimodal distribution centered around δ 98/95Mo≈1.1‰ and 0.2‰. This result rules out single stage Rayleigh fractionation as the relevant formation mechanism and instead, redox variations are suggested to be a main factor controlling the Mo IC of the studied high-temperature Mo deposits. The range of the Mo IC in one single deposit, the Alpjahorn, overlaps with the variation range of almost all other published values for Mo IC in Mo deposits. Compared to the molybdenites, the breccia shows an even wider variation of 3.0‰ (δ 98/95Mo between −1.6‰ and +1.4‰). In contrast to the high-T molybdenite deposits, here the Mo was transported via oxidized surface waters into the breccia system, where it was reduced and precipitated. This indicates that oxidation and reduction of Mo complexes may lead to highly variable Mo IC in hydrothermal systems. [Copyright &y& Elsevier]

Abstract: Ten Early Bronze Age (BzA1, 2200–2000 BC) copper artefacts from the central Valais region from Switzerland were studied for their elemental composition and lead isotope ratios. In order to answer the archaeological question of a local copper supply, a database for copper minerals across the Valais (Switzerland) has been established. This database contains 69 data on lead isotope ratios as well as additional information on the minerals and geochemical associations for copper minerals from 38 locations in the Valais. Comparisons of the artefacts were also made with data pertaining to minerals from various deposits from Europe and Anatolia taken from the literature. The provenance of the materials is very diverse. Some of the data are compatible with the data from the copper mineral deposits of the Valais region. Moreover, three copper lunulae were identified as possibly Tuscan, which suggests contacts between Italy and the Valais region. This pattern also establishes a multiplicity of provenances for the metal and cultural influences in the Alpine environment of the Rhone Valley of Switzerland at the beginning of the Early Bronze Age. [Copyright &y& Elsevier]

Abstract: The integration of structural analyses with 40Ar/39Ar dating of fault-related pseudotachylytes provides time constraints for the reconstruction of the Alpine evolution of the central portion of the South Alpine orogenic wedge. In the northern sector of the belt a Variscan basement is stacked southward on the Permian to Mesozoic cover along regional faults (Orobic and Porcile thrusts). Fault zones, slightly postdating a first folding event of Alpine age, experienced a complex evolution through the ductile and brittle deformation regime, showing greenschist facies mylonites overprinted by a penetrative cataclastic deformation. Generation of fault-related pseudotachylyte veins marks the onset of brittle conditions, lasting up to the youngest episodes of fault activity. 40Ar/39Ar dating of the pseudotachylyte matrix of 9 samples give two separated age clusters: Late Cretaceous (80–68Ma) and latest Palaeocene to Middle Eocene (55–43Ma). These new data provide evidence that the pre-Adamello evolution of the central Southern Alps was characterised by the superposition of different tectonic events accompanying the exhumation of the deepest part of the belt through the brittle–ductile transition. The oldest pseudotachylyte ages demonstrate that south-verging regional thrusting in the central Southern Alps was already active during the Late Cretaceous, concurrently with the development of a synorogenic foredeep basin where the Upper Cretaceous Lombardian Flysch was deposited. Our reconstruction provides direct evidence for an important Cretaceous “EoAlpine” orogenic event which was nearly coeval to the HP metamorphism affecting the Austroalpine units of the eastern Alps. In our view, the Upper Cretaceous Southern Alps can be interpreted as the south-verging retrobelt, which formed during subduction phenomena active to the north in the Austroalpine realm. [Copyright &y& Elsevier]

Abstract: The present paper refers to research conducted in the tectonic-karst depression of Campo Felice in the central Apennines (Italy), in which glacial, alluvial and lacustrine sediments have been preserved. Stratigraphic interpretations of sediments underlying the Campo Felice Plain are based on evidence obtained from nine continuous-core boreholes. The boreholes reach a depth of 120m and provide evidence of five sedimentation cycles separated by erosion surfaces. Each cycle is interpreted as an initial response to a mainly warm stage, characterized by low-energy alluvial and colluvial deposition, pedogenesis, and limited episodes of marsh formation. In turn, a mainly cold stage follows during which a lake formed, and glaciers developed and expanded, leading to deposition of glacial and fluvioglacial deposits. The chronological framework is established by eleven accelerator mass spectrometer 14C ages and three 39Ar–40Ar ages on leucites from interbedded tephra layers. These age determinations indicate five glacial advances that respectively occurred during marine oxygen isotope stages 2, 3–4, 6, 10 and 14. [ABSTRACT FROM AUTHOR]

This investigation reports on the comparison between ICP-MS U-Th and AMS 14C ages of Phreatic Overgrowths on Speleothems (POS) from two different caves on the island of Mallorca (Spain). These speleothem encrustations form at the water table of coastal caves in a low-amplitude tide-controlled microenvironment and are used to reconstruct past sea level changes. The aim of this study is to evaluate if this particular type of speleothem is datable using 14C method and to investigate possible problems connected with the incorporation of dead carbon inherited from the dissolution of 14C-free limestone. The results show that 14C ages are strongly site dependent and appear related to local residence time of water infiltration through the soil and epikarst. When short transit time and limited interaction with soil and bedrock, as in Cova de Cala Varques A, the so-called "reservoir" effect is negligible and 14C and U-Th ages corresponds within the error range. When the residence time is longer, as in Cova des Pas de Vallgornera, 14C ages are steadily 2,300-2,400 years older than the U-Th data, as shown by the mean value (25%) of estimated percent dead carbon proportions and by higher and better correlated contents of major and trace elements in the vadose support of this speleothem encrustation. The potential use of this multi-method approach to paleoenvironmental studies is also suggested. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the redox-sensitive isotope system of molybdenum (Mo) in marine carbonates to evaluate their potential as archive of the Mo isotopic composition of coeval seawater. We present Mo isotope data (δ 98/95Mo) of modern skeletal and non-skeletal carbonates as well as a variety of precipitates from the mid and late Carboniferous. The external reproducibility is determined by repeated analyses of two commercially available carbonate standards. The resulting uncertainty of the low concentration samples is ±0.1‰ (2σ). Analysis of modern ooid sands from the Bahamas shows a consistently heavy Mo isotopic composition (δ 98/95Mo between 2 and 2.2‰), approaching modern mean seawater values (δ 98/95Mo=2.3‰±0.1‰ (2σ)). This suggests that isotope fractionation during Mo uptake into non-skeletal carbonate precipitates is small. In contrast, modern skeletal carbonates show variable isotopic compositions (0.1 to 2.2‰) which suggests a biologically controlled fractionation process. The varying Mo signatures found in Carboniferous cement phases point to a strong response to local changes in fluid composition from which they precipitated. Overall, we recognized three important factors to cause an offset relative to ocean water: Mo derived from skeletal components, input of detrital Mo and admixture of light, hydroxide derived Mo via diagenetic fluids. All of these factors cause a lighter Mo isotopic composition relative to seawater. Due to the apparent small isotope fractionation during Mo uptake into non-skeletal carbonates, their δ 98/95Mo closely reflects the ambient fluid composition. From these results we conclude that carbonates represent a promising new tool to characterize the water mass Mo isotopic composition of marine paleo-environments. [Copyright &y& Elsevier]

Abstract: Combining Lu–Hf garnet geochronology with in situ trace element analyses in garnet allowed us to gain new insight into the metamorphic evolution of UHP–UHT rocks in the Stary Gierałtów region, in the Polish Sudetes. Prograde garnet growth recorded by Rayleigh-type heavy REE (HREE) zoning in the felsic granulites indicates that the obtained 386.6±4.9 Ma Lu–Hf age represents the time of garnet crystallization on a prograde UHP metamorphic path. The surrounding rocks were metamorphosed at the same time as indicated by 381.2±6.7 Ma Sm–Nd garnet age obtained for the mid-crustal metapelites. The second metamorphic episode, which affected most of the lower crust in the Orlica–Śnieżnik Massif (OSM) occurred at ca. 340 Ma as determined by U–Pb zircon and Sm–Nd garnet dating of granulites in this and previous studies is interpreted as a high temperature event, which took place on a retrograde path. Trace element distribution in garnets from the layered granulites showed significant differences in distribution of medium and HREE in garnets from mafic and felsic protoliths over the course of the metamorphic evolution. This had strong impact on the isotopic dating results and led to “decoupling” of the Sm–Nd and Lu–Hf clocks, which recorded timing of the two different metamorphic episodes separated by as much as 40 Ma. Moreover, the preservation of the HREE growth zonation profile in garnets from the felsic granulites whose minimum metamorphic temperature was established at 900 °C implies that the Lu–Hf system under relatively dry conditions does not undergo significant diffusional re-equilibration even at such extreme temperatures and therefore it sill provides the age of prograde garnet growth. Under hydrous conditions, at least some resetting will take place, as documented by the partially relaxed HREE zonation profile in the amphibolitised mafic granulite, which yielded a 10 Ma younger age. The HREE distribution study appeared to be a particularly valuable and essential tool, which allowed us to distinguish garnet growth from post-growth complexities and hence, provide improved age interpretation. Medium REE, on the other hand, did not show any obvious correlation with the isotopic signature of garnet. Two distinct metamorphic episodes recorded in the Stary Gierałtów region show that buoyancy-driven uplift of UHP rocks can be arrested at the base of a continental crust if not supported by any additional force. In our case study, the UHP rocks would have never reached the surface if their uplift had not been resumed after a long pause under a different tectonic regime. The multistage, discontinuous uplift revealed by the UHP rocks of the OSM provides a new scenario for the exhumation of continental crust from mantle depths distinct from the fast-track exhumation histories recognized in UHP terranes elsewhere. [Copyright &y& Elsevier]

Abstract: We present 39Ar–40Ar dating of phengite, muscovite and paragonite from a set of mafic and metasedimentary rocks sampled from the high-pressure (HP) metaophiolites of the Voltri Group (Western Alps) and from clasts in the basal layer conglomerates from the Tertiary molasse which overlie the high-pressure basement. The white mica-bearing rocks display peak eclogitic and blueschist-facies parageneses, locally showing complex greenschist-facies replacement textures. The internal discordance of age spectra is proportional to the chemical complexity of the micas. High-Si phengites from eclogite clasts record a 39Ar–40Ar age of ca. 49 Ma for the eclogite stage and ca. 43 Ma for the blueschist retrogression; phengites from a blueschist basement sample yield an age of ca. 40 Ma; low-Si muscovite from a metasediment dates the formation of the greenschist paragenesis at ca. 33 Ma. Our data indicate that the analyzed samples reached high-pressure conditions at different times over a time-span of c.a. 10 Ma. Subduction was continuing during exhumation and blueschist retrograde re-equilibration of higher-pressure, eclogite-facies rocks. This process kept the isotherms depressed, allowing the older HP-rocks to escape thermal re-equilibration. Our results, added to literature data, fit a tectonic model of a subduction–exhumation cycle, with different tectonic slices subducted at different times from Early Eocene until the Eocene–Oligocene boundary. [Copyright &y& Elsevier]

The Erongo subvolcanic center in Namibia is the largest composite, bimodal complex in the Mesozoic Etendeka igneous province of Namibia. This study of 40Ar/39Ar and high spatial resolution U–Pb zircon dating demonstrates that emplacement of the various igneous units at Erongo took place within a time span equivalent to or shorter than geochronologically resolvable age differences (ca. 2 Ma), and at the peak of regional flood-basalt activity in the Etendeka–Parana´ province. The Erongo complex comprises a series of felsic volcanic and intrusive units that overlie or intrude basaltic lavas attributed to the Etendeka Group. The stratigraphically oldest rhyodacite (Erongorus unit) yielded U–Pb zircon ages of 131.8±1.1 Ma (1σ). The overlying Ombu rhyodacite was previously dated at 135.0±1.6 Ma and our new ages for a resurgent intrusion of the same magma type (Ombu granodiorite) in the vent area are 132.6±1.1 Ma (40Ar/39Ar) and 132.3±1.9 Ma (U–Pb zircon) respectively. The youngest felsic magmas at Erongo are the high-silica Ekuta rhyolite and compositionally equivalent Erongo granite. These units yielded U–Pb zircon ages of 131.9±2.9 and 130.3±1.4 Ma, respectively. Concordant 40Ar/39Ar biotite ages from two samples of the granite average 132.2±0.8 Ma. The final stage of magmatism at Erongo involved emplacement of basic alkaline plugs and dikes. Phlogopite and kaersutite from foidite plugs of this series yielded 40Ar/39Ar ages of 130.8±1.0 and 132.0±1.0 Ma. In a regional context, these age results indicate that silicic magmatism in the largest complexes of the Damaraland (Erongo, Brandberg, Paresis, Messum) began simultaneously with the peak of flood-basalt effusion at about 132 Ma throughout the Etendeka province and ceased by about 130 Ma. The silicic magmas are hybrid, with varying contributions of crustal and mantle-derived melts, and the age constraints suggest that crustal melting was caused by a short-lived thermal pulse related to the main flood-basalt event. Basic magmatism in the Damaraland complexes continued sporadically thereafter to about 123 Ma, but lacked the power to create further crustal melting. [Copyright &y& Elsevier]

The chronology of the crustal evolution of the granulite facies fault-bounded Epembe Unit south of the anorthositic Kunene Intrusive Complex (KIC) in NW Namibia is presented. U–Pb zircon ages by ion microprobe (SHRIMP II) from a heterogeneous set of granulite facies rocks from the Epembe Unit reveal Mesoproterozoic ages between 1520 and 1510 Ma for prograde zircon growth. Cathodoluminescence (CL) imaging clearly shows metamorphic growth of zircon grains and zircon rims around igneous cores. Zircon core analyses obtained by SHRIMP yield ages between 1635 and 1810 Ma. These ages are comparable to those of the Epupa basement and indicate derivation of the inherited zircon cores from Palaeoproterozoic protoliths. Pb–Pb stepwise leaching (PbSL) TIMS ages on peak-metamorphic garnet and retrograde sapphirine reflect granulite facies conditions at ca. 1490 to 1447 Ma.Our combined age data from the granulite facies Epembe Unit reveal a complete early Mesoproterozoic orogenic cycle between ca. 1640 and 1450 Ma. The cycle begins with erosion of the Palaeoproterozoic Epupa basement and involves sedimentation, burial down to the crust–mantle boundary leading to high-grade metamorphism and rapid exhumation. An orogenic cycle of this age matches in time with events dated in the Pinwarian (Grenville Province, Canada), in the Amazonian craton (Brazil) and in the Gothian (Baltic Shield, Sweden) but has not been reported in southwestern Africa before. [Copyright &y& Elsevier]

• Pb isotopic variations exceed uncertainties by up to 2 orders of magnitude both at 10m and cm scales. • Pb isotope diagrams require at least seven isotopically well distinct fluid circulation episodes. • S isotopic compositions show heterogeneities. • Leaching of country rocks can produce observed Pb isotope composition and trace element patterns. • Different end-members identified by the Pb isotope correlation can be linked to different country rocks. The Janggun lead-zinc-(silver) deposit in South Korea was formed by hydrothermal-metasomatic processes. We collected 12 samples over a 100 m transect in one of the five orebodies recognized in the deposit and analyzed a total of 68 sulfide minerals. Detailed mineralogical observations show successive modifications and overprint of pristine sulfide by replacement reactions, suggesting several distinct petrogenetic events. We distinguished four different phase assemblages, which occur in contiguous zones of the transect. This suggests multiple alteration fronts. Major and minor element concentrations of sulfide phases were measured for the different sulfide generations. Milligram-sized sulfide mineral samples were micro-drilled for Pb and S isotope analyses with a resolution of 200 µm to 1 mm. Pb and S isotopic compositions (206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb and δ34S) are variable, showing 206Pb/204Pb ranges from 18.334 to 18.879, 207Pb/204Pb; 15.667 to 15.692, and 208Pb/204Pb; 38.682 to 38.899, and δ34S ranges from + 4.4 to + 6.2‰. Although Pb isotopic compositions and δ34S data are similar to literature data from different areas of the Janggun deposit, the Pb isotopic variations between the different samples (at the 10 m scale), and within individual polished sections (at the cm scale) are well over 100 times larger than the analytical uncertainty. The scatter in sulfur isotopic compositions confirms the Pb isotopic heterogeneity at both the cm and 10 m scales. At least seven isotopically well distinct fluid circulation episodes are required in the study area to explain different projections of common-denominator Pb isotope diagrams. This suggests that fluid pulses of distinct chemical and isotopic compositions circulated in distinct spatial and temporal episodes. To investigate the role of country rocks as sources of the metals transported by the ore-forming fluids, we leached 13 samples of country rocks (Janggun limestone, Chunyang granite, granophyre, and dyke) with dilute acid and analyzed both leachates and residues. Correlations are observed between Pb isotopic compositions and trace ratios (e.g. Co/Ni, Cu/Ag, and Zn/Cd). The Pb isotopic compositions of country rocks and Precambrian basement suggest that leaching of country rocks by circulating fluids is able to produce the observed Pb isotope and trace elements variations in the sulfide minerals, whereby different end-members in the isotope correlation diagrams can be linked to different country rocks. [ABSTRACT FROM AUTHOR]

Microscale oxygen isotope analysis (18O/16O) of minerals can identify distinct events of fluid-rock interaction. This method is, however, still limited to a few major and accessory minerals of which most are anhydrous minerals. We present the systematic study of oxygen isotope distribution in white mica by Secondary Ion Mass Spectrometry (SIMS). Texturally and chemically distinct white mica populations in granitic and contact metamorphic rocks from the Larderello-Travale geothermal field (LTGF), Italy, record stages of magmatic crystallization, metamorphic-hydrothermal replacement and fluid-rock interaction. The large range in intra- and inter-grain white mica δ18O values between 1 and 14‰ reflects varying protoliths and degrees of fluid-mineral interaction at variable temperatures (180–450 °C present-day temperatures; p.d.T.). This variability reflects the large-scale circulation of both (1) magmatic, syn -intrusive to early contact metamorphic hydrothermal fluids with high-δ18O values, and (2) meteoric fluids with δ18O values of −7‰ during a post-intrusive, late hydrothermal stage. Metasedimentary rocks from the upper reservoir contain distinct white mica populations occurring in close proximity (μm-scale), including detrital grains (δ18O = 12–14‰; high Na, low Mg), partially altered white mica (δ18O = 8–9‰) and late hydrothermal white mica (1–6‰; low Na, mid Mg). The late hydrothermal white mica has similar δ18O values to other secondary minerals and is in equilibrium with meteoric-dominated fluids with a δ18O of −6 to 0.5‰, which circulated in the late hydrothermal stage. Downhole towards the lower reservoir, white mica from two contact metamorphic micaschist samples shows either (1) homogeneous δ18O values of ca. 9‰ likely due to recrystallization in the contact metamorphic hydrothermal stage (T ca. 600 °C), or (2) a large spread in δ18O from 2 to 12‰ within and across grains of variable texture and chemistry in the host rock and a cross-cutting quartz-white mica vein (ca. 300 °C, present day temperature; hereafter p.d.T.). This contrasting δ18O signature of white mica is also recorded in granite cored at up to 4.6 km depth. The Carboli granite contains white mica with a homogeneous magmatic δ18O of 10 ± 0.6‰, whereas older granite samples from Radicondoli have magmatic to hydrothermal white micas that vary in δ18O from 4 to 10‰. A pronounced intra-grain δ18O variability of up to 6‰ occurs in white mica domains with higher Fe-Mg-Ti halos around inclusions of chloritized biotite, as a result of interaction with dominantly meteoric fluids that infiltrated to depths of at least 4.6 km. In the Porto Azzurro granite on Elba, Italy, altered white mica has δ18O values of 2.6‰ down from 10‰ in unaltered grains. The distribution of oxygen isotope ratios in white mica is thus firstly a result of pervasive versus selective fluid alteration (at depth, sample and grain scale). Secondly, the actual preservation of these μm-scale variabilities indicates that volume diffusion is not detectable at microscale at p.d.T at or below 350 °C where most of the heterogeneous white mica is found. Selective, sample- and grain-scale fluid penetration occurs episodically and anisotropically, on micro- and megascale, along faults, fractures and cleavages, producing lower δ18O white mica at various times in zones of higher secondary permeability and active hydrothermal fluid circulation. [ABSTRACT FROM AUTHOR]

The lunar meteorite Sayh al Uhaymir 169 consists of an impact melt breccia extremely enriched with potassium, rare earth elements, and phosphorus [thorium, 32.7 parts per million (ppm); uranium, 8.6 ppm; potassium oxide, 0.54 weight percent], and adherent regotith. The isotope systematics of the meteorite record four lunar impact events at 3909 ±13 million years ago (Ma), ∼2800 Ma, ∼200 Ma, and <0.34 Ma, and collision with Earth sometime after 9.7 ±1.3 thousand years ago. With these data, we can link the impact-melt breccia to Imbrium and pinpoint the source region of the meteorite to the Lalande impact crater. [ABSTRACT FROM AUTHOR]

The Montecristo district, northern Chile, is one of the few places worldwide where there is a direct relationship between magnetite-(apatite) (MtAp) mineralization and iron oxide-copper-gold (IOCG) mineralization. The MtAp mineralization includes Ti-poor magnetite, fluorapatite, and actinolite and is crosscut and partially replaced by a younger IOCG mineralization that includes a second generation of actinolite and magnetite with quartz, chalcopyrite, pyrite, and molybdenite. The MtAp stage at Montecristo is interpreted as the crystallized iron-rich melts that used the pre-existing structures of the Atacama Fault System as conduits. These rocks later acted as a trap for hydrothermal IOCG mineralization. Geochronology data at Montecristo indicate that the host diorite (U-Pb zircon 153.3 ± 1.8 Ma, 2-sigma), MtAp mineralization ( 40 Ar- 39 Ar in actinolite, 154 ± 2 Ma and 153 ± 4 Ma, 2-sigma), and the IOCG event (Re-Os on molybdenite, 151.8 ± 0.6 Ma, 2-sigma) are coeval within error and took place in a time span of less than 3.4 Ma. The εHf i and εNd i values of the host diorite are + 8.0 to + 9.8 and + 4.3 to + 5.4, respectively. The whole-rock 87 Sr/ 86 Sr i values of the IOCG mineralization (0.70425 to 0.70442) are in the lower end of those of the MtAp mineralization (0.70426-0.70629). In contrast, εNd i values for the IOCG mineralization (+ 5.4 and + 5.7) fall between those of the MtAp rocks (+ 6.6 to + 7.2) and the host diorite, which suggests that the IOCG event was related to fluids having a more crustal Nd (εNd i  <  + 5.7) composition than the MtAp mineralization. This likely reflects the mixing of Nd from the MtAp protolith and a deep magmatic-hydrothermal source, very likely an unexposed intrusion equivalent to the host diorite. Sulfur isotope compositions (δ 34 S, + 0.3 to + 3.4‰) are consistent with a magmatic source., Supplementary Information: The online version contains supplementary material available at 10.1007/s00126-023-01172-0., Competing Interests: Competing interestsThe authors declare no competing interests., (© The Author(s) 2023.)

Multiple sulfur (δ 34 S sulfate , Δ 33 S sulfate , & Δ 36 S sulfate ), nitrogen and oxygen (δ 15 N nitrate & δ 18 O nitrate ) and strontium ( 87 Sr/ 86 Sr) isotope compositions of precipitation collected from Seoul, South Korea were analyzed to study the sources, transportation and deposition of air pollutants in East Asia. The δ 34 S sulfate values (from 1.9 to 14.6‰ with a median of 4.7‰) and the δ 15 N nitrate values (from -2.0 to 13.3‰ with a median of 1.0‰) suggest that fossil fuel use (emission from coal combustion and vehicle exhaust) is a predominant source for sulfur and nitrogen, but other natural sources including biogenic contributions of DMS also add to their total budget. The seasonal variations are observed in δ 34 S sulfate and δ 15 N nitrate values (both higher in winter season), which is likely to result from the increase of coal use for domestic heating in China. The δ 18 O nitrate values also varied seasonally depending on the NO x oxidation pathway, being about 20‰ higher in winter than in summer season. The Δ 33 S sulfate and Δ 36 S sulfate values are not anomalous, showing the absence of MIF signals in precipitation of Seoul. The 87 Sr/ 86 Sr ratio of the precipitation samples range from 0.70988 to 0.71487 with a median of 0.71073, indicating the influence of at least three end-member (silicate dust, carbonate dust and anthropogenic emission). Ionic ratios such as (K + +NH 4 + )/(Ca 2+ +Mg 2+ ) and Cl - /Na + suggest the overwhelming effect of anthropogenic input rather than carbonate dust on the end-member with lower 87 Sr/ 86 Sr ratios., (Copyright © 2021 Elsevier Ltd. All rights reserved.)