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The Dom Feliciano Belt of southern Brazil and Uruguay represents part of a larger Neoproterozoic orogenic system formed during the amalgamation of Western Gondwana. The hinterland and foreland domains in parts of the belt preserve deformation structures and metamorphic assemblages that developed during early crustal thickening from c. 650 Ma. However, the metamorphic history of the southern foreland, in Uruguay, and its relationship with the hinterland, is not so well understood. We show that metamorphism in the southern hinterland is characterized by near-isothermal decompression from ~10 kbar (~770°C) down to ~6 kbar, reflecting exhumation from depths of ~40 km during convergent thrusting and crustal thickening. This metamorphic event and associated magmatism is constrained by garnet Lu–Hf and zircon U–Pb dating to c. 655–640 Ma, supporting age and P–T constraints from previous studies. In contrast, prograde metamorphism in the foreland supracrustal rocks reached maximum lower-amphibolite facies conditions (~6–7 kbar and ~550–570°C) and is constrained by garnet Lu–Hf dating to 582 ± 23 Ma. An exposed sheet of imbricated foreland basement rocks reached partial melting at upper-amphibolite facies conditions, and metamorphism is similarly constrained to c. 585–570 Ma by monazite U–Pb dating. The data indicate that metamorphism in the foreland occurred during a sinistral transpressional event c. 55–85 Ma after the start of crustal thickening recorded in the hinterland, whereby strain partitioning during sinistral transpression led to imbrication in the foreland and oblique thrusting of the basement over more distal supracrustal rocks. This event is coeval with transpressional deformation in the Kaoko and Gariep belts, indicating a distinct two-stage tectonic history driven by the three-way convergence between the Congo, Kalahari, and South American cratons.

The Dunhuang block in NW China preserves Archean to Paleoproterozoic basement rocks that are exposed alongside Paleozoic magmatic and metamorphic rocks. Although both subduction-accretion and collisional processes have been proposed for the formation of Paleozoic metamorphic rocks, links between their metamorphic ages, P−T evolution and deformational history remains ambiguous. Here we present zircon and in-situ monazite U−Pb geochronology linked to P−T modelling of metapelites from the Hongliuxia belt in the southern Dunhuang block. Oriented inclusion trails in garnet from metapelites reveal rare relics of an S1 fabric. The earliest continuous metamorphic fabric is an originally steep N-S striking foliation S2. This fabric was further reworked by upright folds F3 associated with development of an ubiquitous steep, mainly south-dipping, E-W striking axial planar foliation S3. The Bt−Ms−St−Pl−Qz−Tur−Ilm assemblage forming inclusions in garnet is assigned as the D1-M1a event whereas the foliation S1b in metapelites is associated with Grt–Ky–St–Bt–Ms–Pl–Qz–Rt assemblage. The Grt−Ky−St aligned parallel to the S2 matrix in low-strain domains are considered as remnants of a dismembered M1 assemblage, while the S2 foliation is characterized by the Grt–Sil–Bt–Pl–Qz–Rt–Liq in high-strain domains. The S3 foliation is associated with the Grt–Sil–Bt–Ms–Pl–Qz–Kfs–Chl–Ilm assemblage. Altogether, metapelites record similar clockwise P–T evolution an early prograde (M1a) stage starting at 4.5–5 kbar and 500–550°C, metamorphic peak (M1b) stage at ~8 kbar and 700–725°C, decompressional heating to ~6 kbar and ~750°C (M2) and a retrograde stage to 4.5–5.5 kbar and 500–550°C (M3). Zircon U−Pb geochronological investigations suggest that metapelites from the basement record metamorphic ages of 1847 ± 11 Ma and 404 ± 15 Ma. In-situ U–Pb dating of monazite combined to monazite trace-element composition analysis further suggest that the rock burial most likely started at c. 410 Ma, peak-P conditions M1b were reached at 400–395 Ma, M2 heating occurred at c. 390 Ma and M3 retrogression occurred between c. 384 and 353 Ma. The D1-M1 burial event reflects either underthrusting of the basement below the supra-subduction active margin system or propagation of the deformation front to the south of the Dunhuang block. The D2-M2 event is a consequence of thermal relaxation following crustal thickening, possibly accompanied by convective lithospheric thinning, whereas D3-M3 reflects exhumation during shortening of the system. Combined with the available regional data, it is suggested that the Devonian multi-stage tectono-metamorphic evolution described in the study area corresponds to a polyphase Andean-type deformation of the active margin of the Dunhuang block. Such a process can be regarded as a response to a progressive relocation of the Dunhuang block alongside with the Tarim-North China Collage in the Devonian. Funding: This research is part of the project No. 2021/43/P/ST10/02996 co-funded by the National Science Centre and the European Union Framework Program for Research and Innovation Horizon 2020 under the Marie Skłodowska-Curie grant agreement No. 945339, as well as the President’s International Fellowship Initiative for Postdoctoral Researchers of the Chinese Academy of Sciences, grant No. 2021PC0013.

Refereed/Peer-reviewed Multi-mineral petrochronology can effectively track changes in the thermochemical environment experienced by rocks during metamorphism. We demonstrate this concept using garnet–chlorite schists from the Walter-Outalpa Shear Zone of the southern Curnamona Province, South Australia, which reveal a cryptic and protracted (c. 39 Myr) record of high thermal gradient metamorphism. Petrochronological data including in situ monazite U–Pb and garnet Lu–Hf and Sm–Nd dating suggest elevated geotherms were persistent between at least c. 519–480 Ma, throughout the duration of garnet growth. Additional in situ xenotime U–Pb dating implies that partial garnet breakdown occurred between c. 480–440 Ma, likely induced by fluid-rock interaction or exhumation. Although metamorphism temporally overlaps with the timing of the regional Delamerian Orogeny (c. 520–480 Ma), the thermal mechanism to sustain elevated temperatures has remained enigmatic. One-dimensional thermal models are used to appraise the role of radiogenic heat production in driving the observed high thermal gradient metamorphism. The models reveal that with only modest crustal thickening during orogenesis, the endogenous radiogenic heat production hosted within the basement rocks could plausibly provide the thermal impetus for metamorphism.

We thank Prof. Buttner for his comments on our paper (van Schijndel et al., 2020), which allow us to clarify our work and the tectonic model we proposed for the eastern margin of the Namaqua Sector of the Namaqua Natal Metamorphic Province. The Kaaien Terrane forms a tectonic transition between the Kaapvaal Craton, Rehoboth Province, Kheis belt and the Archeachap Terrane of the Namaqua Sector and forms part of an NW-vergent foreland thrust sequence in the Namaqua Front (e.g. Cornell et al., 2006). The exact tectonic extent of the Kaaien Terrane is still unclear and it has recently been proposed to be part of the newly defined Kheis Terrane (Van Niekerk and Beukes, 2019). Buttner (2020) states that the tectonic model for the Mesoproterozoic evolution of Namaqua Sector which envisages the collision of multiple exotic terranes after the subduction of multiple oceanic basins (e.g. Miller 2012, and references therein) is outdated and newer tectonic models have been discussed in the literature in recent years. Bial et al. (2015a, 2015b, 2016) and Macey et al. (2018) propose a continental back-arc mobile belt setting to explain the high temperature and low pressure history of several terranes of the Namaqua Sector. For example, Pressure-Temperature time (P-T-t) paths describing the crustal evolution for the Kakamas Terrane by Bial et al. (2015a) suggest along-lasting high-temperature history (>650°C) at pressure not exceeding 5.5 kbar between ∼1350 Ma and

We studied the petrographical characteristics and bulk chemical composition along with the age of detrital zircon grains from quartzites exposed in the western part of the Orlica-Śnieżnik dome in the Saxothuringian zone. Age spectra of detrital zircons were obtained by U–Pb laser ablation inductively coupled plasma mass spectrometry dating. The zircon ages define a few clusters of which the most numerous are Cambro-Ordovician and Neoproterozoic, and less frequent are Paleoproterozoic and Archean. A distinctive feature of the investigated samples is the lack of Mesoproterozoic zircon grains. The youngest age cluster documented in the investigated quartzites points to a Late Cambrian maximum depositional age and detritus derivation from erosion of Cambro-Ordovician metagranitoids. Bulk chemical composition of the quartzites indicates that they originated owing to erosion of granite within sedimentary basins developed on a passive continental margin. Presented data prove the similarity of the examined rocks to quartzites known from the eastern part of the Orlica-Śnieżnik dome and quartz metasandstones documented in other parts of the Variscan Belt of Europe known as the Armorican quartzites or their equivalents exposed in the Saxothuringian zone. Our results support the suggestion that the Orlica-Śnieżnik dome has an affinity to the West African Craton of the Gondwana margin and represents a fragment of the Saxothuringian zone.

Metamorphic provinces such as the ∼1 ​Ga Grenvillian, ∼400 ​Ma Caledonide and Triassic Qinling Provinces often contain rocks with high-pressure assemblages such as eclogites, which formed at mantle depths in subduction zones. These are evidence of the accretion of terranes by subduction of oceans and collision to form large tectonostratigraphic provinces. The Mesoproterozoic Namaqua-Natal Province comprises a number of terranes thought to have been assembled by plate-tectonic processes, but they have generally yielded metamorphic pressures below 5 ​kbar, corresponding to

Determining pressure and temperature variations between high-pressure/low-temperature (HP–LT) eclogite blocks is crucial for constraining end-member exhumation models; however, it has historically been challenging to constrain eclogite pressures due to the high variance associated with this bulk-rock composition. In this work, we utilize quartz-in-garnet elastic barometry to constrain formation pressures of eclogites from the northern (Junction School, Ring Mountain, Jenner Beach) and southern Franciscan Complex (Santa Catalina Island). Multiple eclogite blocks from Jenner Beach are analyzed, and a single eclogite from the other localities. By comparing garnet growth conditions from within a single outcrop and between distinct outcrops, we evaluate the local and regional spatial distribution of P conditions recorded by eclogites. We compare the mean, median, and max pressures between different garnet zones and eclogites. Pressures sometimes exhibit systematic changes across garnet zones; however, some eclogites exhibit no systematic pressure variations across garnet zones. Pressures from northern Franciscan eclogites range from ∼1.4–1.8 GPa, at an estimated temperature of 500 degrees C; pressures from the Catalina eclogite range from ∼ 1.2–1.5 GPa, at an estimated temperature of 650 degrees C. Mean and maximum pressures of different eclogites from the northern Franciscan exhibit negligible differences (< 0.1 GPa). The results are inconsistent with models that propose exhumation of metamorphic blocks from different structural levels, and suggest that now exposed HP–LT eclogites from the northern Franciscan Complex may represent rocks that were coherently underplated, and exhumed from similar structural levels., Contributions to Mineralogy and Petrology, 177 (1), ISSN:0010-7999, ISSN:1432-0967

The Dom Feliciano Belt in southern Brazil and Uruguay represents the western half of a Neoproterozoic orogenic belt located in the southern portion of the South Atlantic Neoproterozoic Orogenic System. Current interpretations are divided as to the nature of orogenesis in this belt, in part owing to lacking geochronological constraints. Metamorphosed and deformed supracrustal sequences of the Brusque Complex in the northern Dom Feliciano Belt, representing part of the orogenic foreland, record the onset and duration of crustal thickening. Structural analysis and pressure–temperature estimates indicate that the complex reached peak regional metamorphic conditions of 540–570°C and 5.5–6.7 kbar during thrusting and burial, consistent with orogenic metamorphism and early crustal thickening. Garnet–whole rock Lu–Hf and Sm–Nd isochron ages date this event to between circa 660–650 Ma. Ar–Ar dating of mica suggests thrust-controlled exhumation and partial cooling by circa 635 Ma, and that localised deformation occurred into the late Ediacaran. Our results show that the orogenic foreland reached metamorphic conditions typical for crustal thickening 20–30 million years prior to the onset of massive magmatic activity in the hinterland. Such a delay is typical of hot, internal parts of orogens, which supports interpretations that hinterland magmatism in the northern Dom Feliciano Belt represents post-collisional magmatism and not arc magmatism above a subduction zone. Instead, we suggest that orogenesis in the northern Dom Feliciano Belt was initiated by rift-basin inversion driven by far-field forces transmitted through the crust in an intracontinental rift or back-arc rift setting.

The Teschenite Association Rocks (TAR) in the Outer Western Carpathian (OWC) flysch form a classic suite of alkaline intrusions where teschenite and picrite were first defined. They represent continental intraplate volcanism that produced a wide range of melano- to mesocratic rocks emplaced during the Early Cretaceous rifting within the southern margin of the European Plate. Geochemical modelling indicates that they may be a product of ~2–5 % partial melting of the metasomatised, asthenospheric mantle. The variations in REE (low / heavy REE content, LaN/YbN = 11–34) are consistent with deep melting of garnet peridotite. Initial ε(Nd)i = 5.0–6.3 and ε(Hf)i = 4.9–10.0 preclude the significant mature crust involvement. Instead, a linear array formed by the 143Nd/144Nd and 176Hf/177Hf isotopic ratios points to a genesis from the mixed, HIMU–OIB source with the more depleted, MORB-type component. Mantle metasomatism was most likely caused by the Variscan subduction–collision processes as indicated by the depleted mantle Nd model ages. The isotope and trace element ratios of the TAR resemble the European Asthenospheric Reservoir (EAR) — the common mantle end-member for the widespread Cenozoic volcanic rocks in Europe. This confirms a long-term existence of the EAR mantle component beneath the Central Europe, at least since the Early Cretaceous. In situ laser-ablation ICP-MS U–Pb dating of titanite indicates short duration of mafic alkaline magmatism in the OWC, lasting from 123.7 ± 2.1 to 117.9 ± 1.8 Ma. Emplacement of the TAR is correlated with the maximum lithospheric thinning that triggered adiabatic decompression and partial melting of the upwelling asthenospheric mantle. Magmatism ceased most likely due to transition to the dominantly compressive regime associated with the major stress field reorganization directly preceding the Carpathian– Alpine Orogeny.

Metamorphic minerals in the Brusque Complex of the northern Dom Feliciano Belt, Brazil, provide new insights into the timing and mode of regional convergence, challenging a long-lived subduction-collision model for orogenesis. The key evidence for subduction is an extensive linear belt of granitic rocks (the Granite Belt) that intruded the length of the hinterland of the Dom Feliciano Belt between ~630─580 Ma, and that is inferred to represent arc magmatism above the subducting Adamastor Ocean prior to continental collision. The study area comprises supracrustal units of a foreland fold-and-thrust belt outcropping along the western edge of the symmetric Kaoko─Dom Feliciano orogenic system. The integrated study of primary metamorphic mineral assemblages and associated deformation fabrics support the interpretation of a fold-and-thrust belt environment, with early tectonic movement top-to-NW away from the hinterland. P─T estimates constrained by garnet compositions indicate peak metamorphic conditions of 540─570°C and 5.5─6.5kbar, in line with typical geothermal gradients associated with orogenic metamorphism. The timing of early garnet growth, and by inference the early stages of crustal thickening in the foreland, is constrained by Lu─Hf garnet geochronology at ~660─650 Ma. The data indicate that the onset of metamorphism and deformation in the orogenic foreland occurred ~20–30 m.y. prior to intrusion of extensive granitic magmatism into the orogenic hinterland. The timing of early orogenic thickening in the foreland precludes the interpretation of the Granite Belt as an arc above a large-scale subduction zone in the lead up to orogenesis. Instead, it is interpreted to represent syn-orogenic magmatism typical for hinterland domains in other ancient and recent orogenic systems.We appreciate financial support from Diku Norway and CAPES Brazil (project UTF-2018-10004), and from the Czech Science Foundation (project no. 18-24281S). This work was partly supported by the Research Council of Norway through the funding to The Norwegian Research School on Dynamics and Evolution of Earth and Planets, project number 249040/F60.

The relations between Barrovian- and Buchan-type metamorphic series in the Chinese Altai remain obscure, and hence a representative region of the central part of the Chinese Altai was investigated to address this issue, using combined microstructural, petrological and geochronological methods. In the region, Barrovian-type garnet, staurolite, kyanite and sillimanite zones are locally overprinted by Buchan-type andalusite- and cordierite-bearing domains. Microstructural analysis shows that Barrovian garnet, staurolite and kyanite grew synchronously with the earliest regional metamorphic foliation S1B. A sillimanite-bearing assemblage locally overprinted the assemblage of the staurolite zone in a foliation parallel with S1B, assigned as S1M. The originally subhorizontal S1B-M foliation, metamorphic zones and mineral isograds were folded by F2 upright folds, leading to their inclination and juxtaposition to upper crustal levels. Subsequent D3 deformation affected heterogeneously all previous structures producing vertical high-strain zones around low-strain domains. The D3 high-strain zones in the vicinity of Permian pegmatites are associated with Buchan-type metamorphism, and are characterized by syn-D3 growth of andalusite and cordierite. Phase equilibria modelling of the staurolite-kyanite-bearing assemblages suggests a prograde P-T path with an apparent thermal gradient of ~ 23 °C/km associated with the S1B fabric. The partial reequilibration occurred in the sillimanite stability at ~ 670 °C, corresponding to an apparent thermal gradient of ~ 34 °C/km in the S1M fabric. Garnet to sillimanite metamorphic zones were subsequently exhumed without apparent reequilibration during the D2 event. The interpreted pressure−temperature (P−T) evolution of the Buchan-type metamorphism on the basis of thermobarometry and phase equilibria modelling suggests significant heating processes, corresponding to apparent thermal gradient of 41 °C/km or more. In situ U-Pb dating of monazite inclusions in staurolite revealed predominantly 280−260 Ma ages and minor older ages scattering between 350 and 290 Ma, interpreted as important monazite recrystallization during the D3 event. Monazite in andalusite and cordierite yielded only ages of 280−260 Ma, interpreted as dating the growth of these minerals. Lu-Hf garnet-whole rock isochron of a garnet-cordierite-chlorite schist gave an age of ca. 262 Ma, overlapping in time with the age of monazite in the cordierite. Combined with available regional data, the results suggest that the Barrovian-type metamorphic cycle reflects a continued burial-heating followed by decompression, probably connected with the Devonian suprasubduction tectonic switching between shortening and extension events. In contrast, the Permian Buchan-type metamorphism documents an important heat input associated with regional NE-SW shortening, probably related to the Early Permian collision between the Chinese Altai and the southerly Junggar arc system.

International audience; The aim of this paper is to determine the composition and age of high-temperature (HT) hydrothermal fluids in Closepet granites (Dharwar craton, India). The magmatic origin of the Neoarchaean Closepet batholith has been recognized and dated many times, whereas a HT fluid system, strong evidence for which has been partly investigated, has never been dated. Titanite was chosen for a geochemical study on its pristine and altered domains to illustrate the fluid composition; the domains were dated to recognize the timing of fluid activity. Titanite presents distinct trace element enrichments in non-altered domains and strong depletions in trace elements in marginal, irregular, patchy zones. The high total rare earth element (REE) concentrations and the marked negative Eu anomalies suggest crystallization from a residual melt. The negative Eu anomalies diminish progressively in the REE patterns of altered parts and become positive. Trace element ratios (Nb/Ta, Y/Ho, and U/Th) indicate fluid-crystal interactions. Strong U/Th fractionation might be linked to the presence of CO2 and Cl-. Zr-in-titanite thermometry yields a crystallization/recrystallization temperature of ~700 °C for both magmatic and altered domains. The titanite factor Ti+4/(Al+3 + Fe+3) reveals an affinity with significant mantle input to the fluid system. Pristine and altered titanite domains have been successfully dated by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Reversely discordant apparent ages suggest interaction with fluids, which modified the Pb composition of the magmatic titanite. The oldest semi-concordant analyses of titanite cores indicate an age of approximately 2500 Ma, which we interpret as the minimum age of magmatic titanite crystallization. Narrow dark rims of titanite with considerably lower Th/U ratios form a more coherent group of analyses defining an upper concordia intercept age of 2345 ± 0.016 Ma, interpreted as the best estimate for the time of complete titanite resetting associated with the metasomatic event. The HT fluid system appears to have remained active into the Palaeoproterozoic. Confirmation by dating that the tested fluids belonged to the Archaean hydrothermal system gives us information about this system at the time, but the information that it worked at least until the Palaeoproterozoic provides additional valuable information about the hydrothermal systems during the Neoarchaean-Palaeoproterozoic transition.

Mobility of people and goods during the Upper Paleolithic has proven difficult to reconstruct given the relative rareness of remains. Nevertheless, archaeological contexts like the Late Pleistocene horizon of Borsuka Cave (Southern Poland) represent a unique opportunity to explore patterns of objects’ transportation across Central Europe. We investigated the origin of four ornaments made of European elk (Alces alces L.) incisors recovered at Borsuka Cave – the oldest known burial site in Poland, possibly a child grave. Laser-ablation plasma source mass spectrometric analyses of trace elements and Sr isotopic compositions revealed that one elk was roaming within a geologically uniform area while the others changed their pastures during their lifetimes. The non-local origin of the elk teeth is inferred from their exotic Sr isotopic compositions and the lack of evidence for the presence of elk in this territory during the Pleistocene. Instead, the elks’ Sr isotopic composition show good agreement with sites near the Austria-Slovakia border region and northern Hungary, ~250 km away from the study site. We argue that the artefacts were most likely brought to Borsuka Cave by humans or by a network of exchange, so far never reported in the time range 32.5–28.8 ka cal BP for Southern Poland.

Ultra-high temperature (UHT) metamorphism is a thermal regime that can be attained by the lower continental crust in exceptional contexts and that is usually accompanied by fluid-absent dehydration melting. Such conditions are observed in the Gruf Complex, a 12 x 10 km migmatitic body located in the Central Alps, which is characterized by the presence of UHT granulitic schlieren and enclaves within migmatitic orthogneisses and charnockites. Two types of granulites, both with a massive and melanocratic texture, were investigated. The first granulite contains sapphirine, garnet, orthopyroxene, K-feldspar and biotite in the peak mineral assemblage, whereas the second type displays garnet, orthopyroxene, sillimanite and biotite. In both granulites, garnets are porphyroblastic and can reach up to 2 cm in size. These garnets are almost pure almandine-pyrope solid solutions and are zoned, showing pyrope-richer rims (Alm43-54Prp43-55Sps0-2Grs1-6) compared to cores (Alm47-62Prp32-48Sps0-3Grs2-9). A clear zoning is also observed in the rare earth elements (REE), with garnet cores showing the highest REE concentrations. Moreover, the porphyroblastic garnets are characterized by the presence of numerous melt inclusions (MI), which can be noticed both in garnet cores and rims. The MI occur as polycrystalline (nanogranitoids) and glassy inclusions, and dominantly display a peraluminous, rhyolitic composition, suggesting that they were originated, along with the host garnet, by incongruent, fluid-absent melting reactions during crustal anatexis. Lu-Hf ages obtained for the MI-bearing garnet cores of both granulites indicate that they formed at about 41 ± 4 Ma, which therefore can be interpreted as the time that crustal anatexis generated the UHT granulites. Considering the granulites in the context of the alpine framework, it is also inferred that UHT conditions in the lower crust were achieved as a consequence of asthenospheric upwelling, probably related to slab steepening or slab breakoff.

This research concerned radioactivity of lichens and mosses from coastal zones of the Canadian Arctic and Alaska. Over 50 samples were collected from 7 positions during two scientific expeditions in 2012 and 2013. The tundra contamination caused by anthropogenic radionuclides was relatively low, reaching mean values with SD's of: 17.4 ± 3.5 Bq/kg for 90Sr, 14.0 ± 2.9 Bq/kg for 134Cs, 38.4 ± 7.5 Bq/kg for 137Cs, 0.86 ± 0.24 Bq/kg for 239+240Pu, 0.065 ± 0.017 Bq/kg for 238Pu and 0.50 ± 0.13 Bq/kg for 241Am. The increase of activity concentration with increasing latitudes was noticed mostly in regard to 90Sr, Pu isotopes and 241Am. The analysis of isotopic ratios exhibited dominant contribution of the global fallout (+SNAP 9A satellite re-entry fallout) for the presence of plutonium isotopes and 241Am. The Fukushima fallout signature was identified in a few lichens from Alaska. However, the influence of additional unknown factor on the occurrence of 90Sr and 137Cs has been detected in western part of Canadian Arctic. Natural radioisotopes of thorium and uranium were found throughout the entire investigated region and the average values of activity concentration with SD's were as follows: 2.92 ± 0.47 Bq/kg for 230Th, 2.61 ± 0.48 Bq/kg for 232Th, 4.32 ± 0.80 Bq/kg for 234U and 3.97 ± 0.71 Bq/kg for 238U. Examined Western Arctic tundra was not affected with any technically enhanced natural radioactivity.

The paper presents results of the radioecological investigation carried out in south-western Greenland shoreline. There were examined over 50 samples of lichens and mosses collected from 7 locations during two scientific expeditions conducted in the summer of 2012–2013. The levels, trends and the most likely origin were determined for following natural and artificial radionuclides: 90Sr, 137Cs, 230, 232Th, 234, 238U, 238, 239+240Pu and 241Am. The radioactive pollution was found as relatively low, reaching the maximum values at: 25.3 ± 2.04 Bq/kg for 90Sr, 293 ± 27 Bq/kg for 137Cs, 4.01 ± 0.13 Bq/kg for 239+240Pu, 0.1381 ± 0.0070 Bq/kg for 238Pu and 1.90 ± 0.21 Bq/kg of 241Am, 9.15 ± 0.48 Bq/kg for 230Th, 25.1 ± 1.2 Bq/kg for 232Th, 7.5 ± 1.5 Bq/kg for 234U and 7.26 ± 0.80 Bq/kg for 238U. Both activity and mass isotopic ratio assays revealed dominant contribution of the global fallout + SNAP 9A on the presence of plutonium isotopes and 241Am in Greenland tundra. However, noticeable deviations of 241Am/239+240Pu and to a lesser extend of 240Pu/239Pu ratios from the GF level have been observed. The origin of 137Cs was evidently connected with the coexistence of global and Chernobyl fallout, while the presence of 90Sr was caused by nuclear weapon tests and affected by leaching process. The seaborne signature of uranium isotopes was manifested in research material as well.

Accurate dating of eclogite-facies metamorphism is of paramount importance in order to understand the tectonic evolution of an orogen. An eclogite sample from the Najac Massif (French Massif Central, Variscan belt) displays a zircon-bearing garnet-omphacite-amphibole-rutile-quartz peak assemblage. Pseudosection modeling suggests peak pressure conditions of 15–20 kbar, 560–630 °C. Eclogite-facies garnet displays Lu-enriched cores and Sm-rich rims and yields a Lu-Hf age of 382.8 ± 1.0 Ma and a Sm-Nd age of 376.7 ± 3.3 Ma. The ages are interpreted as marking the beginning of the prograde garnet growth during the initial stages of the eclogite-facies metamorphism, and the high-pressure (and temperature) peak reached by the rock, respectively. Zircon grains display chondrite-normalized REE spectra with variably negative, positive or no Eu anomalies and are characterized by either enriched or flat HREE patterns. However, they yield a well constrained in situ LA-ICP-MS U-Pb age of 385.5 ± 2.3 Ma, despite this REE pattern variability. Zr zonation in garnet, Y content in zircon and the diversity of zircon HREE spectra may suggest that zircon crystallized prior to and during incipient garnet growth on the prograde P-T path, recording the initial stages of the eclogite-facies conditions. Consequently, the zircon age of 385.5 ± 2.3 Ma, comparable within error with the Lu-Hf age obtained on garnet, is interpreted as dating the beginning of the eclogite-facies metamorphism. Accordingly, the duration of the prograde part of the eclogite-facies event is estimated at 6.1 ± 4.3 Myr. Subsequent exhumation is constrained by an apatite U-Pb age at 369 ± 13 Ma.

Foreland basins associated with collisional mountain belts undergo postdepositional deformation in response to compressive stress exerted from the evolving orogen. The low thermal regime of such processes requires sensitive methods to unravel the structural evolution of such regions. In this study, we conducted apatite fission track (AFT) and (U Th)/He thermochronology on the sedimentary succession of the Subathu basin in the Himalayan foreland of the Himachal Pradesh region in India, an area preserving the sedimentary record of the India-Asia collision since the late Paleocene-early Eocene. The results show that the Subathu basin exposes a fossilised apatite partial annealing zone (APAZ) depicted by incompletely reset AFT ages and shortened track lengths in the Paleocene-middle Miocene pre-Siwalik units and unreset ages in the Neogene Siwalik Group. We associate the partial annealing of the pre-Siwalik rocks with thickening due to internal imbrication and nappe stacking triggered by shearing along the Main Boundary Thrust and its splays since the middle Miocene. Thermal modelling of the Siwalik rocks projects a rapid heating up to approximately 90–100 °C reached between 4 and 1 Ma. Following the thermal peak, the Siwalik rocks cooled rapidly, as indicated by 2.6–1.2 Ma AHe ages. We associate this recent cooling event with SW-directed thrusting along the Main Frontal Thrust, which placed the foreland basin over the Gangetic Plains. Our results are similar to those obtained for the foreland basin in Nepal, indicating that the movement along the youngest major discontinuity of the Himalaya is synchronous along the orogen.

Garnet and zircon geochronology combined with trace element partitioning and petrological studies provide tight constraints on evolution of the UHT-(U)HP terrain of the Orlica-Śnieznik Dome (OSD) in the NE Bohemian massif. Lu-Hf dating of peritectic garnet from two mesocratic granulites constrained the time of its initial growth at 346.9 ± 1.2 and 348.3 ± 2.0 Ma recording peak 2.5 GPa pressure and 950 °C temperature. In situ, U-Pb SHRIMP dating of zircon from the same granulite gave a younger age of 341.9 ± 3.4 Ma. Ti-in-zircon thermometry indicates crystallization at 810–860 °C pointing to zircon formation on the retrograde path. Lu partitioning between garnet rim and zircon suggest equilibrium growth and thus U-Pb zircon age constrain the terminal phase of garnet crystallization which lasted about 6 Ma. All Sm-Nd garnet ages obtained for mesocratic and mafic granulites are identical and consistently younger than the corresponding Lu-Hf dates. They are interpreted as reflecting cooling of granulites through the Sm-Nd closure temperature at about 337 Ma. The estimated PTt path documents the ca. 10 Ma evolution cycle of the OSD characterized by two distinct periods: (1) 347 - > 342 Ma period corresponds to nearly isothermal decompression resulting from crustal scale folding and vertical extrusion of granulites, and (2) at > 342–337 Ma which corresponds to a fast, nearly isobaric cooling.

A study is conducted to supplement the uppermost Lower Jurassic–lowermost Cretaceous marine strontium isotope dataset and to present new statistical fits of the Middle–Late Jurassic seawater strontium isotope curve based on a numerical time scale and a detailed biostratigraphical zonal scheme. The use of the stratigraphical scheme allows reduction of dating errors related to uncertainty of numerical age determinations. The presented correlation charts enable direct calibration between strontium isotope stratigraphy and regional biostratigraphical frameworks. New strontium isotope data have been obtained from well-preserved Lower Bajocian, uppermost Callovian, Oxfordian, Kimmeridgian, and Upper Volgian belemnite rostra. The presented seawater 87 Sr/ 86 Sr curve is characterized by reliable 95% confidence limits (mean width of ± 0.000007), which take into account precision of dating of particular data points. A decrease of seawater 87 Sr/ 86 Sr ratio, from ca. 0.70730 to ca. 0.70683, is observed throughout the Middle Aalenian–Early Oxfordian (172.1–160.8 Ma ago). The steepest Phanerozoic fall of the ratio, with a rate of change of up to 0.00015 per 1 Ma, is recorded in the Bajocian segment of the strontium isotope curve. The Phanerozoic minimum of the marine 87 Sr/ 86 Sr ratio occurred at the Early–Middle Oxfordian transition. The 87 Sr/ 86 Sr ratio increased starting from the Middle Oxfordian till the end of the Jurassic (160.8–145.7 Ma) reaching a value of ca. 0.70720 at the Jurassic–Cretaceous transition. The Middle–earliest Late Jurassic decrease in seawater 87 Sr/ 86 Sr ratio is interpreted as a result of the increased hydrothermal activity of the seafloor during the breakup of Gondwana, and the formation of new Atlantic–Tethyan oceanic basins. The successive rise of the ratio is probably related to the decelerated hydrothermal venting of the oceanic crust although a partial increase in radiogenic strontium input from continental weathering cannot be excluded.

International audience; The late Carboniferous accretionary system of the South Tianshan orogen (North-Western China) underwent complex structural and polymetamorphic evolution. Combined petrological, geochronological and microstructural analysis of (ultra)high-pressure (UHP) metabasites (eclogites and blueschists) enclosed in metapelites show a relict coarse-grained eclogitic fabric S2 surrounded by a dominant fine-grained eclogite and blueschist facies retrograde fabric S2. The S2 fabric is reworked by upright folds F3 that are responsible for a major shortening of the whole accretionary system. For both the eclogite and blueschist, peak and retrograde P–T conditions have been thermodynamically constrained at 25–26 kbar and 425–500 °C and 10–13 kbar and 500−550 °C respectively, suggesting a shared exhumation history. The garnet-whole rock-amphibole isochron in the blueschist yielded Lu–Hf and Sm–Nd ages of 326.0 ± 2.9 Ma and 318.4 ± 3.9 Ma respectively, interpreted to date the prograde to peak metamorphic assemblage. The retrograde path of the eclogite is characterized by heterogeneous omphacite recrystallization into a mylonitic fine-grained matrix and crystallization of blue amphibole. Microstructures in both pristine porphyroclastic and recrystallized fine-grained domains in the eclogite indicate a gradual evolution from constriction-dominated (L>S-type) to flattening-dominated (S>L-type) type of deformation, increase of fabric intensity reflected by gradually growing M-indexes and the development of lattice preferred orientation (LPO) typical for dislocation creep under slightly hydrated conditions. Recrystallization of the matrix in the blueschist is homogeneous, which indicates a matrix dominated channel flow during exhumation. These LPOs evolutions suggest a significant mechanical coupling with the upper plate concomitant with oroclinal bending of the Kazakh orocline. Lock up of Kazakh orocline is responsible for further stress increase resulting in horizontal shortening of South Tianshan accretionary wedge and development of D3 upright folding and steepening of the whole sequence.

The Main Central Thrust (MCT) is a prominent continental-scale fault within the Himalaya. Its definition has been the topic of some debate in the literature. After a brief consideration of the state of discussion to clarify the definition we use in this work, we report features from the field- to the microstructural- scale of a particularly well-exposed section in Sikkim, NE India. The nature of the protoliths as well as the overlying and underlying rocks is characterized in terms of e-Nd. The dates of motion on the fault are constrained using U–Pb geochronology of zircon and monazite from pegmatitic dikes that cross-cut the deformation fabric. It is found that the mechanism of deformation recorded in the fault zone rocks is different compared to that found in the overlying Greater Himalayan (GH) or the underlying Lesser Himalayan (LH) rocks. The GH and LH have different protolith characteristics as well. Combined with existing data on P–T history, dates of metamorphism, and cooling- and exhumation-rates of the GH and the LH, our measurements show that major motion on this fault occurred before 20 Ma at 450–700 °C but after peak metamorphism of rocks (750–800 °C) in this zone. Isolated events occurred in this zone as late as 11 Ma, possibly in the brittle domain. This underscores the pulsed nature of movement over an extended period on such major faults, and the related difficulties in dating fault movement, determination of the rates of movement, and designating a fault plane as in- or out-of-sequence within a propagating deformation front.

One of the enduring debates in the study of the Himalayan orogen (and continental collision zones in general) is whether the salient observed features are explained (a) by localized deformation along discrete, narrow fault zones/ductile shear zones separating individual blocks or slices (e.g. critical taper or wedge tectonic models), or (b) by distributed deformation dominated by wide zones of visco-plastic flow in the solid or a partially molten state (e.g. channel flow models). A balanced cross-section from Sikkim in the eastern Himalaya that is based on structural data and is drawn to satisfy petrological and geophysical constraints as well, is used in combination with information from petrology, geochronology, geospeedometry and microstructural data to address this question. We discuss that any tectonic model needs to be thermally, rheologically, geometrically and temporally viable in order to qualify as a suitable description of a system; models such as channel flow and critical taper are considered in this context. It is shown that channel flow models may operate with or without an erosional porthole (channel with tunnel and funnel mode vs. channels with only the tunnel mode) and that the predicted features differ significantly between the two. Subsequently, we consider a large body of data from Sikkim to show that a channel flow type model (in the tunneling without funneling mode), such as the ones of Faccenda et al. (2008), describes features formed at high temperatures very well, while features formed at lower temperatures are more consistent with the operation of localized, fault-bounded, slice tectonics, (LFBST, be it in the form of critical taper, wedge tectonics, or something else). Thus, the two modes are not competing, but collaborating, processes and both affect a given rock unit at different points of time during burial, metamorphism and exhumation. A transitional stage separates the two end-member styles of tectonic evolution. The proposed models bear similarities to those suggested by Mallet (1875) and Auden (1935) and mechanisms proposed by Beaumont and Jamieson (2010). We conclude by discussing some of the implications of such a model for motion on the major Himalayan faults, and by considering which features of any given rock are likely to record signatures of a particular style of tectonic evolution. Some directions for future research are suggested in the end.

The ca. 2 Ga retrogressed eclogites in the Usagaran Belt in central Tanzania are among the oldest documented eclogites in the world. As such, they have been used to pinpoint the thermal conditions of the onset of modern style subduction on Earth. Two samples of retrogressed mafic eclogite have been interrogated to reconstruct the metamorphic history of the subducted crust. The samples are several kilometres apart, separated by a mylonitic upper amphibolite-transitional granulite foliation. Lu–Hf garnet geochronology pinpoints eclogite metamorphism at 1994 ± 9 Ma, supported by rutile U–Pb geochronology. Zircon U–Pb geochronology supports subduction metamorphism at ca. 2000 Ma. Mineral equilibria modelling and Zr in rutile thermometry suggests the retrogressed eclogites reached a minimum pressure of 18 kbar at approximately 800 °C, consistent with a warm subduction thermal gradient. These conditions were followed by amphibolite-granulite-facies overprinting. Proposed tectonic models for the formation of the eclogites involve either east-dipping subduction of the Tanzanian Craton margin, or west-dipping subduction of oceanic crust under the Tanzanian Craton. The retrogressed eclogites were likely exhumed via slab breakoff driven buoyancy of the oceanic crust and transferred to shallow crustal levels in a back arc position. This data, combined with data from eclogites from the Eburnian-Transamazonian and Ubende orogens, demonstrate the possible existence of a large subduction system on the margin of west Africa from ca. 2.1–1.9 Ga. This system has led to the preservation of several eclogitic rocks, which suggests that modern style subduction was operating on significant geographic and temporal scales at this time. Refereed/Peer-reviewed

This paper reports evidence of Pu isotopes in the lower part of the troposphere of Central Europe. The data were obtained based on atmospheric aerosol fraction samples collected from four places in three countries (participating in the informal European network known as the Ring of Five (Ro5)) forming a cell with a surface area of about 200,000km(2). We compared our original data sets from Krakow (Poland, 1990-2007) and Bialystok (Poland, 1991-2007) with the results from two other locations, Prague (Czech Republic; 1997-2004) and Braunschweig (Germany; 1990-2003) to find time evolution of the Pu isotopes. The levels of the activity concentration for (238)Pu and for ((239+240))Pu were estimated to be a few and some tens of nBqm(-3), respectively. However, we also noted some results were much higher (even about 70 times higher) than the average concentration of (238)Pu in the atmosphere. The achieved complex data sets were used to test a new approach to the problem of solving mixing isotopic traces from various sources (here up to three) in one sample. Results of our model, supported by mesoscale atmospheric circulation parameters, suggest that Pu from nuclear weapon accidents or tests and nuclear burnt-up fuel are present in the air.

The lesser- and greater- Himalayan sequences (LH and GH) in Sikkim have been studied in detail recently. The LH consists mainly of pelitic lithologies with detrital zircon ages > 1800 Ma and εNd(0) of -27.7 to -23.4 (with intercalated calc-silicates, metabasites and a sheared granite gneiss – the Lingtse gneiss). The metamorphic sequence is characterized by (i) a remarkably continuous and systematic metamorphic field gradient (~ 60–70 °C kbar-125 ), (ii) peak pressures as well as temperatures of metamorphism increasing at higher metamorphic grades (~ 5 kbar, 500 °C at the garnet zone to ~ 8 kbar, 700 °C at the sillimanite–muscovite zone), (iii) clockwise P–T paths of a tight “hairpin” shape with aprograde slope of 20–30 °C kbar-129 , (iv) initiation of garnet growth (Lu–Hf chronometry) at systematically older ages at higher grades (10.5–11 Ma at garnet zone to 16.8 Ma at sillimanite–K-feldspar zone), (v) peak of metamorphism simultaneously at all grades (11–13 Ma), (vi) deformed and folded metapelitic rocks but with little evidence of pervasive shearing, and (vi) duration of melt formation and segregation on the order of a few 100,000 years. Degree of melting was low, as indicated by the presence of muscovite all through the sequence. These evidence indicate that the LH behaved as a coherent block, and thermomechanical models quantitatively reproduce many of these features as well as explain the formation of inverted metamorphic sequence in such a coherent block. The greater Himalayan sequence (GH), also largely metapelitic, has different protoliths (with components as young as 800 Ma) and a different metamorphic history (extensive migmatisation at higher grades ~ 8–12 kbar, 750–850 °C at an older age of largely > 20 Ma along a different clockwise P–T path characterized by sharp, isothermal decompression followed by near isobaric cooling). Geochronological data (monazite, zircon, garnets) as well as cooling rate calculations (geospeedometry) reveal that the GH is made up of at least two blocks with distinct, complex and multistage P–T–t histories. Different stages of the high temperature cooling were rapid (100’s °C Ma-1 to 10’s °C Ma-1 at different stages) and at 45 least some of it was unrelated to exhumation; synthesis of these results with low temperature thermochronometry allows the detailed multistage cooling and exhumation history of this block to be reconstructed. The reconstructed cooling and exhumation histories show that a number of interlinked processes operating on a hierarchy of timescales leads to the overall evolution. The P–T history with rapid cooling can be reproduced by thermomechanical models that consider conductive as well as advective heat transport and there is no need to invoke additional processes (such as the role of fluids). Metabasic inclusions within both the LH and the GH appear to record a different (? older in part) history. The role of these in the overall evolution, as well as the difference in metamorphic ages of the LH and GH remain open questions that need to be addressed in future research.

Late orogenic andesites and basaltic andesites in the Pieniny Klippen Belt (PKB) in the Western Carpathians display atypical isotope systematics, strongly departing from those observed among other Neogene–Quaternary calc-alkaline rocks in the Carpathian–Pannonian region. Low eNd values (− 10.6 to − 5.2) and low eHf values (− 19.6 to − 5.2) are accompanied by unusually low 87 Sr/ 86 Sr ratios (0.7052 to 0.7059). Major, trace element, isotope and geochronological data presented in this study indicate two magma sources evolving with low Rb/Sr ratio from which the PKB calc-alkaline rocks originated. Basaltic andesites showing less enriched signature and wider range of isotope compositions (eNd = − 7.7 to − 5.2, eHf = − 11.3 to − 5.2 and 87 Sr/ 86 Sr = 0.7052–0.7059) are interpreted as having originated from the partial melts derived from an ancient metasomatized, sub-continental lithospheric mantle which during emplacement were contaminated by the upper crustal material. Andesites, whose precise timing of emplacement was constrained by in situ LA ICP-MS U–Pb zircon dating at 11.2 ± 0.2 to 12.1 ± 0.3 Ma, show more enriched signature and narrow range of Nd and Hf isotope compositions (eNd = − 10.6 to − 10.1, eHf = − 19.6 to − 18.3) accompanied by low 87 Sr/ 86 Sr (0.70531–0.70541). U–Pb dating of the inherited domains in zircons revealed the presence of late Paleozoic, Precambrian and Archean age components which support crustal origin of the PKB andesites. In situ Hf isotope analyses of zircons suggest that andesites could have been derived from enriched (initial eHf = − 13 to − 10) Permian igneous domains in the lower crust. Generation of the calc-alkaline magmas in the upper lithospheric mantle and in the thickened crust was triggered by decompression or crustal delamination following Middle Miocene collision of the Alcapa block with southern margin of the European platform. The PKB fault zone and its splays acted as conduits which enabled ascent of small volumes of andesitic magmas into the upper crust of the Western Carpathians.

The paper summarizes results of investigation of the current state of radioactive contamination on site being under consideration for planned nuclear power plant in northern Poland. Thanks to use of sequential procedure it was possible to determine activity concentrations for radioisotopes of nine elements, both natural and artificial. Results show that observed levels of radioactive contamination are rather typical for central Europe and global fallout is dominant factor of presence of artificial radionuclides. The total deposition for artificial radionuclides revealed maxima equal to 1747 ± 121 Bq/m2 for 137Cs, 3854 ± 158 Bq/m2 for 90Sr, 101 ± 23 mBq/m2 for 237Np, 57.7 ± 6.0 Bq/m2 for 241Am, 3.27 ± 0.80 Bq/m2 for 238Pu and 68.5 ± 5.0 Bq/m2 for 239+240Pu.

Voluminous felsic volcanic magmas were formed in Central Europe at the Carboniferous/Permian boundary in numerous pull-apart basins; one of which is the Saale Basin, which holds the Halle Volcanic Complex (HVC), the focus of this study. The rhyolites in the HVC formed laccoliths and scarce lavas, and occur in two different textural types: fine and coarse porphyritic. Zircon isotope and trace element composition was analysed in four units, two per each textural type. Zircon from the different units shows similar ranges in eHf (− 4.1 to − 8.1) and δ 18 O values (6.51–8.26), indicating similar sources and evolution processes for texturally diverse rhyolites from the HVC. Scarce inherited zircon ranges from ~ 315 Ma to ~ 2100 Ma with the major groupings around 315–550 Ma. These ages are typical for Devonian arc magmatic activity (350–400 Ma) and Cadomian igneous rocks (500–600 Ma), which occur in the basement presently underlying the HVC. Therefore, the source of the rhyolites was multicomponent and probably represented by a basement composed of various crystalline rocks. Trace elements in zircon show similar distributions in all analysed samples, which is broadly consistent with zircon cores crystallizing in a less evolved magma undergoing limited fractional crystallization, whilst the zircon rims crystallized from a magma undergoing extensive fractional crystallization of major and accessory minerals. Interestingly, comparison of the zircon composition in HVC rhyolites and other rhyolites worldwide shows that the observed trends are similar in such rhyolites despite the values being different. This may suggest that most of the zircon in rhyolites crystallizes at a similar stage in the rhyolite magma evolution, from magmas undergoing extensive crystallization of major phases and apatite. The implication is that most of the zircon represents late stage crystallization, but also that antecrystic component may be present and preserve information on the development of precursor magmas, probably within mush-rich magma bodies.

Apatite is a key mineral whose Sr-isotope record has a wide range of applications including palaeofluid flow studies from inorganic apatite, and past faunal/human mobility or palaeoecology using bioapatite. The incremental growth of mammalian enamel bioapatite potentially allows extraction of Sr isotopic compositions at sub-annual time-resolution using laser-ablation plasma mass spectrometry (LA-MC-ICPMS). However, existing apatite LA-MC-ICPMS Sr-isotope data have yielded mixed results. Here we assess the achievable accuracy/precision of (bio)apatite LA-MC-ICPMS Sr-isotope analysis and evaluate sources of inaccuracy. Using robust plasma conditions (ThO+/Th+ < 0.2%), we obtain long-term (4 year) accurate and precise Sr-isotope data for modern shark teeth for both radiogenic 87Sr/86Sr (0.709171 ± 0.000053, 2 SD), and naturally invariant 84Sr/86Sr (0.056500 ± 0.000040, 2 SD). Based on our accurate 84Sr/86Sr-results also for low-Sr enamel, we deduce that interferences are successfully corrected (Kr) or negligible (Ca-argide/dimer), leaving 87Rb and 40Ca31P16O isobaric interferences as key potential sources for 87Sr/86Sr inaccuracy. Our (pseudo)high-resolution mass scans using a virtually Rb–Sr-free, concentrated Ca–P-solution simulating apatite LA analysis show no evidence for 40Ca31P16O at the required intensities to explain previously observed 87Sr/86Sr offsets. Rather, using the same Ca–P solution with varying Rb + Sr isotope standard additions, we accurately constrain the mass bias-corrected 85Rb/87Rb-ratio, and using apatite glasses assess the extent of Rb/Sr elemental fractionation during laser-ablation. Finally, we present concordant LA-MC-ICPMS and microsampled-TIMS 87Sr/86Sr results for low-Sr tooth enamel with highly variable inter & intra-87Sr/86Sr ratios and comparatively high Rb/Sr-ratios. This archaeological example also illustrates well the problem of defining equivalent sample volumes that allow unequivocal comparison between LA and TIMS data.

International audience; Precise and accurate investigation of geochronometers in the light of a detailed petrologi- cal context is the best way to fully understand the evolution of metamorphic rocks. Eclogite-facies rocks highlight the early stages of orogenesis; constraining their P-T-t evolution is then of paramount importance to any geodynamic interpretation. An eclogite sample from the Najac Massif (south French Massif Central) displays a zircon-bearing garnet-omphacite-amphibole-rutile-quartz peak assemblage. Pseudosection modelling suggests peak pressure conditions of 15–20 kbar, 560–630°C. Eclogite-facies garnet displays Lu-rich cores and Sm-enriched rims and yields a Lu-Hf age of 382.8 ± 1.0 Ma and a Sm-Nd age of 376.7 ± 3.3 Ma. These ages are interpreted as marking the beginning of the prograde garnet growth during the initial stages of the eclogite-facies metamorphism, and the high-pressure (and temperature) peak reached by the rock, respectively. Zircon grains display chondrite-normalized REE spectra with variably negative, positive or no Eu anomalies and are characterized by either enriched or flat HREE patterns. However, they yield a well constrained in situ LA-ICP-MS U-Pb age of 385.5 ± 2.3 Ma, despite this REE pattern variability. Zr zonation in garnet, Y content in zircon and the diversity of zircon HREE spectra may suggest (i) that zircon crystallized prior to and during incipient garnet growth on the prograde P-T path, in numerous pulses, or (ii) that local REE equilibria were recorded and preserved in zircon. The zircon age of 385.5 ± 2.3 Ma, comparable within error with the Lu-Hf age obtained on garnet, is interpreted as dating the beginning of the eclogite-facies metamorphism. Accordingly, the duration of the prograde part of the eclogite-facies event is estimated at 6.1 ± 4.3 Myr. Coarse crystals of apatite, that formed late in the metamorphic history at significantly lower pressure, yield a U-Pb age of 369 ± 13 Ma interpreted as the timing of the subsequent exhumeation. Combined with the HP dating results obtained, via a similar petrochronological approach, in the adjacent Lévézou Massif (Lotout et al., same volume), constrained at ca. 358 Ma, these results allow to discuss not only the age of the HP metamorphism but also the geodynamics of the French Massif Central.

International audience; To unravel the evolution of metamorphic rocks, the understanding of the mineral growth through time is required. However, dating early metamorphic stages is a challenge, due to subsequent retrograde overprinting. This is particularly true for HP metamorphism that highlights the early stages of orogenesis.A perfectly fresh eclogite and a former eclogite retrogressed under amphibolite facies from the southern French Massif Central (Lévézou massif, Variscan Belt), were investigated with a large panel of geochronometers (U-Pb on zircon, rutile and apatite, Lu-Hf and Sm-Nd on garnet) in a petrological context tightly constrained by petrographic observation, trace element analyses and phase equilibrium modelling.Both samples recorded similar HP conditions at 18-23 kbar and 680-800°C, while the retrogressed eclogite later equilibrated at 8-9.5 kbar and ca. 620°C. In the retrogressed sample, most of the zircon grains are characterized by negative Eu anomalies and HREE enrichment, and yield an Ordovician U-Pb date of 472.3 ± 1.7 Ma. This is interpreted as the emplacement age of the mafic protoliths and, in agreement with other data available for the Variscan belt, is considered to represent the extreme thinning of continental margins during a rifting event or a back-arc extension. Few zircon rims show a weaker HREE enrichment and yield a date of 378 ± 5.7 Ma, interpreted as a prograde, pre-eclogitic, age. Lu-Hf garnet dating from both samples yields identical dates of 357 ± 13 Ma and 357.5 ± 4 Ma, that approximate the age of the high pressure metamorphic peak. Fresh and retrogressed samples respectively yield 350.4 ± 7.7 Ma and 352 ± 20 Ma dates for Sm-Nd garnet dating, and 367.8 ± 9.1 Ma and 354.9 ± 9.5 Ma for U-Pb rutile dating. Apatite grains from the retrogressed sample give a mean age of 351.8 ± 2.8 Ma. All these ages are identical within error and, when combined with P-T estimations, highlight a major decompression ranging from 8.5 to 15 kbar in less than 6 My, suggesting exhumation rates in excess of 5 mm/yr up to more than 1 cm/yr. Decompression is nearly adiabatic with gradient ranging from 7.8 to 1.3°C/km, followed by cooling rates after major decompression exceeding 50°C/Ma.

The aim of the article was to verify the hypothesis concerning the diversification of plutonium sources in the natural environment of Antarctica. Plutonium activity and atom ratios were analyzed in two groups of biological samples: terrestrial and marine. Both isotopic ratios in the terrestrial set were consistent with global radioactive fallout ratios. The average activity ratio in the marine ecosystem was lower than global radioactive fallout. At the same time mass ratio values in this group turned out to be surprisingly varied. Analysis of the results showed statistically significant differences between the marine and terrestrial ecosystems. Electronic supplementary material The online version of this article (10.1007/s10967-018-6274-6) contains supplementary material, which is available to authorized users.

Lu-Hf and Sm-Nd garnet-whole rock geochronology combined with petrographic observations, minero-chemical variations, thermodynamic modelling and structural data was used to constrain the P–T–t–d evolution of eclogites from the Marianske Lazně Complex (Bohemian Massif). Boudins of mostly isotropic eclogite with relict steep eclogite-facies fabric are affected by steep migmatitic foliation, which is followed on a regional scale by the development of almost pervasive, predominantly SE-dipping, extensional foliation. The structural succession shows continuous transition from eclogite to garnetiferous migmatitic amphibolite and to amphibolite migmatite. A least retrogressed sample of eclogite shows clusters of fine-grained inclusion-poor garnet, omphacite relicts surrounded by a fine-grained clinopyroxene-plagioclase symplectite with minor amphibole, biotite-plagioclase intergrowths after white mica, kyanite with plagioclase-spinel coronas and accessory rutile. Rare potassic white mica occurs as inclusions in omphacite. A more retrogressed eclogite, with no omphacite or kyanite relicts, contains inclusion-poor garnet surrounded by amphibole-plagioclase corona in a matrix dominated by plagioclase-amphibole symplectite with minor clinopyroxene. In places, the symplectite is overgrown by coarse-grained amphibole. Peak P–T conditions, inferred from combined conventional thermobarometry and phase-equilibria modelling and based on inclusions of white mica (up to 3.33 Si p.f.u.), matrix omphacite (Jd33–36) and garnet core (Alm33–38Prp38–42Grs22–25Sps1) compositions are ~25 kbar at 650–750 °C. A HT overprint occurred at ~14–18 kbar and >800 °C based on coexisting clinopyroxene (Jd18–24), plagioclase (An18–35), and amphibole (Na(B) Lu-Hf and Sm-Nd garnet geochronology has been applied to both samples, an older age (c. 390 Ma) obtained by the Lu-Hf method is interpreted as the timing of HP metamorphism, while c. 15 Ma younger ages were obtained by the Sm-Nd method. As temperatures for the HT overprint exceed the empirically and experimentally determined closure temperature of the Sm-Nd system the Sm-Nd ages are interpreted to date cooling following the HT overprint. Combined together, contrasting eclogite and amphibolite-facies migmatite fabrics, the mineral textures, calculated P–T conditions, and distinct Lu-Hf and Sm-Nd ages, provide a complete P–T–t–D path characterised by rapid (~15 Ma) transition from HP subduction, crustal thickening to extensional HT shearing. This unconventional exhumation path does not fit to models of monocyclic exhumation in a subduction channel proposed for the Munchberg and ZEV Devonian HP units to the west. In contrast, the post-peak extensional low angle shearing shortly after subduction and collision resembles more the geodynamic model typical for the Iberian subduction system both in time scales and sequence of tectonic events.

Accepted manuscript. Final version published in Journal of the Geological Society, 176(3), 492-504, is available at https://doi.org/10.1144/jgs2018-173. Isotopic dating of monazite and garnet from high-pressure metamorphic rocks exposed in the northern part of the Saxothuringian palaeo-suture in the Bohemian Massif revealed a diachronous metamorphism of various rock types that are now closely associated within allochthonous units representing the Devonian–Carboniferous subduction–accretionary complex. Mafic blueschists of the middle unit yielded a Lu–Hf garnet age of 363.9 ± 1.3 Ma. The blueschists occur within high-pressure, garnet-free phyllites. Monazite extracted from this rock type yielded a U–Pb isotope dilution thermal ionization mass spectrometry age of 336.5 ± 0.5 Ma. Garnet-bearing micaschist of the lower unit contains monazite with a U–Pb secondary ion mass spectrometry age of 341 ± 3 Ma, consistent with Lu–Hf garnet–whole-rock ages of 344.5 ± 1.3 and 342 ± 7 Ma obtained from the same rock type. Existing tectonic models of the Bohemian Massif, and particularly of its northern part, assume that the period of oceanic subduction was terminated at c. 380–375 Ma by the arrival of an attenuated Saxothuringian continental crust, which was partly subducted and partly relaminated underneath the overriding Teplá–Barrandian Domain. However, our data, as well as data from mafic high-pressure rocks in the southern part of the Saxothuringian Domain, suggest that the initial collision was probably caused by the arrival of a smaller crustal block present within the Saxothuringian oceanic domain. After its subduction and relamination, the oceanic subduction was re-established and terminated by continental subduction and later collision of the Saxothuringian passive margin at c. 345–335 Ma

Strontium isotope compositions of ancient sulphate deposits not only provide chemostratigraphic information but also offer insight into the system in which the evaporites precipitated. Primary gypsum from two Middle Miocene (Badenian) sections in southern Poland shows steadily higher 87Sr/86Sr ratios than those expected from a marine-derived formation. The ratios are interpreted as the result of increasing inflow into the basin at the time of gypsum precipitation. Palaeogeographic reconstructions suggest that riverine runoff sources were situated in the West and East European platforms (to the north and east, respectively) and the Carpathians (to the south), which are mostly composed of Mesozoic sedimentary rocks; their dissolution cannot be responsible for the higher 87Sr/86Sr ratios recorded. We conclude that Archaean and Palaeoproterozoic igneous and supracrustal rocks of the Ukrainian Shield were the source of the higher 87Sr/86Sr ratios recorded in the Badenian primary gypsum. A distinctive decreasing trend of 87Sr/86Sr ratios from western Ukraine to southern Poland is explained by a consistent direction of brine inflow during gypsum crystallization (typical cyclonic circulation controlled by the Coriolis effect).

We investigated Lu–Hf isotopic systematics in garnets from gradually higher grade metamorphic rocks from the first appearance of garnet at c. 500 °C to biotite dehydration melting at c. 800 °C in the Sikkim Himalaya, India. Exceptionally precise Lu–Hf ages obtained for the Barrovian metasedimentary sequence in the Lesser Himalaya (LH) correspond to the time of early garnet formation on a prograde path and show remarkable correlation with increasing metamorphic grade and decreasing structural depth. The youngest age is reported for the garnet zone ( 10.6 ± 0.2 Ma ) and then the ages become progressively older in the staurolite ( 12.8 ± 0.3 Ma ), kyanite ( 13.7 ± 0.2 Ma ) and sillimanite ( 14.6 ± 0.1 Ma ) zones. The oldest age of 16.8 ± 0.1 Ma was recorded at the top of the sequence in the zone marking the onset of muscovite dehydration melting, directly below the Main Central Thrust (MCT). These ages provide a tight constraint on the timing and duration of the Barrovian sequence formation which lasted about 6 Ma. The age pattern is clearly inverted with respect to structural depth but shows “normal” correlation with the metamorphic grade, i.e. earlier garnet growth in higher grade rocks. The timing of the peak metamorphic conditions estimated for the garnet and kyanite zones suggests that thermal climax occurred in all zones within a relatively short time span about 10–13 Ma ago. The metamorphic inversion in the Sikkim Himalaya must therefore have occurred after the metamorphic peak was attained in all grades. Lu–Hf garnet ages in the overthrust Higher Himalaya (HH) continue to be older but do not show a clear progression. There is about 6 Ma jump to 22.6 ± 0.1 Ma within the MCT zone and even older ages of 26–28 Ma were obtained for migmatites from the lower part of the HH. The Lu–Hf system in garnets from the HH records the time of melting at or near the thermal peak rather than dates initial garnet growth as in the LH. The age pattern obtained in this study provides precise time constraints on the continental collision models which must take into account early and prolonged anatexis in the HH, progressive delay in initial garnet growth in different Barrow zones in the LH, nearly contemporaneous metamorphic peak in all grades and post peak inversion of the coherent LH block during exhumation.

Although the polar regions have not been industrialised, numerous contaminants originating from human activity are detectable in the Arctic environment. This study reports evidence of 240Pu/239Pu atomic ratios in the tundra and initial soils from different parts of west and central Spitsbergen and recognizes possible environmental inputs of non-global fallout Pu. The average atomic ratio of 240Pu/239Pu equal to 0.179 (ranging between 0.129 and 0.201) in tundra soils are comparable to the characteristic ratio for global fallout (0.180). However, the 240Pu/239Pu atomic ratios in the initial soils from proglacial zone of glaciers change within wide range between 0.1281 and 0.234 with the mean value of 0.169. By combining alpha and mass spectrometry, the three-sources model was used to identify the Pu sources in initial soils. Our study indicated that the main source of Pu is nuclear tests and that a second source with lower Pu ratio may come from weapons grade Pu (unexploded weapons grade Pu ie. material from bomb which didn't undergo nuclear explosions for example for security tests). Additionally, we found samples with high 238Pu/239+240Pu activity ratios and with typical global fallout 240Pu/239Pu atomic ratios, which are associated with separate sources of pure 238Pu from the SNAP-9A satellite burn up in the atmosphere.

International audience; In the absence of other indicators, the link between the growth of a specific zircon crystal (or part of it) and the eclogite-facies part of the P–T evolution of a rock is commonly validated using the analysis of its REE signature (e.g. Rubatto, 2002). The absence of an Eu anomaly and a flat HREE pattern are considered to reflect a growth in a plagioclase-free garnet-bearing assemblage, typical for the eclogite facies. The ages obtained using this approach can reveal, however, to be in conflict with other geological evidence. Using two eclogite samples from the south of the French Massif Central, we argue that this approach should be used with caution. (1) Zircon grains from an eclogite embedded in massive amphibolite in the Najac-Carmaux Klippe yield a well-constrained U/Pb age of 386.0 ± 1.2 Ma (MSWD = 1.5) consistent with the Lu/Hf age of 382.8±1.0 Ma (MSWD = 0.61) and the Sm/Nd age of 377.8 ± 1.1 Ma (MSWD = 1.4) obtained on garnet. Yet, chrondrite-normalized REE spectra of the dated zircon crystals display variably negative, positive or no Eu anomaly, and their HREE patterns are either enriched or flat. (2) U/Pb zircon data from an eclogite wrapped in a cordierite-bearing migmatite in the Montagne Noire Dome, yield two ages at 339.9 ± 3.4 Ma (MSWD = 0.093) and 315.3 ± 1.4 Ma (MSWD =0.13). With the exception of one analysis, all the REE spectra display neither Eu anomaly nor HREE enrichment, which should suggest that the zircon grains crystallized during the HP metamorphism. The younger age is identical, however, to the ages found in the LP-HT cordierite-bearing migmatite host (320-300 Ma, Poujol et al., 2017). We question therefore the link between the U/Pb age and REE patterns in zircon and suggest that they can be disconnected: “magmatic” spectra (strong negative Eu anomaly and HREE enrichment) can correspond to eclogitic zircon and conversely “eclogitic” spectra can be found in zircon that (re)crystallized after the HP event. Resetting of the U/Pb system does not necessarily go hand in hand with the resetting of the REE system. We propose that REE spectra in zircon may fossilize the REE budget of the rock at the time of the zircon growth: REE patterns in zircon reflect the successive crystallization of the different mineral assemblages in the rock. A U/Pb date, even if obtained on zircon grains yielding an “eclogite-like” REE spectrum cannot be automatically interpreted as the age of the eclogite-facies metamorphic stage, unless its significance is supported by other methods. Poujol, M., Pitra, P., Van den Driessche, J., Tartèse, R., Ruffet, G., Paquette, J.L., Poilvet, J.C. (2017) Two-stage partial melting during the Variscan extensional tectonics (Montagne Noire, France). IJES 106: 477-500. Rubatto, D. (2002) Zircon trace element geochemistry: partitioning with garnet and the link between U–Pb ages and metamorphism. Chemical geology 184:123-38.