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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 new data set of ca. 500 LA–ICP-MS U–Pb detrital zircon ages for six metasedimentary units from the Tuscan basement (Apuan Alps, Monti Pisani, Monticiano-Roccastrada), along with a precise SHRIMP U–Pb crystallization age of a metavolcanic unit (Apuan Alps) have been collected to determine their depositional ages and provenance. These results have been integrated with the recently published ca. 900 U–Pb detrital zircon ages from Elba Island to draw a complete picture of the Paleozoic journey of the Tuscan basement. A major change in the sources supplying sediments to the Tuscan basins is shown to occur during this journey. Detrital zircon ages of early Cambrian to middle Ordovician metasediments mirror those of coeval northern Africa sediments: most samples were sourced in western Africa, while one sample is derived material from central northern Africa. The Tuscan block was therefore located at the peri-Gondwana margin, close to central northern Africa. The prominent mid-Ordovician magmatic arc activity (ca. 460 Ma) at the northern Gondwana margin and its detritus, characterise the zircon age distribution of Ordovician and Silurian volcano-sedimentary rocks, that were therefore generated at the northernmost Gondwana margin during subduction and subsequent initial Paleotethys rifting. The Carboniferous–Permian metasediments are dominated by populations of Ordovician and Variscan-age zircons, with a minor occurrence of Neoarchean and Paleoproterozoic zircons that is best explained by recycling of European Neoproterozoic–Cambrian metasediments. In summary, the main sources supplying the Tuscan basins were located in northern Africa throughout Cambrian–Ordovician times, shifting to the volcanic arc active at the northern Gondwana margin during the middle Ordovician. During Variscan and post-Variscan times, detrital zircon sources were mostly located in European terrains, witnessing the shift of Tuscany from Africa to Europe.

The LA-ICP-MS U-(Th-)Pb geochronology international community has defined new standards for the determination of U-(Th-)Pb ages. A new workflow defines the appropriate propagation of uncertainties for these data, identifying random and systematic components. Only data with uncertainties relating to random error should be used in weighted mean calculations of population ages; uncertainty components for systematic errors are propagated after this stage, preventing their erroneous reduction. Following this improved uncertainty propagation protocol, data can be compared at different uncertainty levels to better resolve age differences. New reference values for commonly used zircon, monazite and titanite reference materials are defined (based on ID-TIMS) after removing corrections for common lead and the effects of excess 230Th. These values more accurately reflect the material sampled during the determination of calibration factors by LA-ICP-MS analysis. Recommendations are made to graphically represent data only with uncertainty ellipses at 2s and to submit or cite validation data with sample data when submitting data for publication. New data-reporting standards are defined to help improve the peer-review process. With these improvements, LA-ICP-MS U-(Th-)Pb data can be considered more robust, accurate, better documented and quantified, directly contributing to their improved scientific interpretation. La communauté internationale de la géochronologie LA-ICP-MS U-(Th-)Pb a défini les nouvelles normes pour la détermination des âges U-(Th-)Pb. Un nouveau flux de travail définit la propagation adéquate des incertitudes pour ces données, en identifiant les composants aléatoires et systématiques. Seules les données avec des incertitudes relatives à l'erreur aléatoire devraient être utilisées dans les calculs des moyennes pondérées des âges de la population; les composantes de l'incertitude pour les erreurs systématiques sont propagées après cette étape, empêchant leur réduction erronée. En suivant ce protocole amélioré pour la propagation de l'incertitude, les données peuvent être comparées à différents niveaux d'incertitude pour mieux résoudre les différences d’âge. Les nouvelles valeurs pour les matériaux de référence zircon, monazite et titanite sont définies (basée sur ID-TIMS) après les corrections du plomb commun et les effets de l'excès en 230Th. Ces valeurs reflètent plus fidèlement le matériau échantillonné lors de la détermination des facteurs d’étalonnage par analyse LA-ICP-MS. Des recommandations sont faites pour représenter graphiquement des données avec seulement des ellipses d'incertitude à 2s et pour soumettre ou pour citer des données de validation avec les données de l’échantillon lors de la soumission des données pour publication. Les nouvelles normes de déclaration des données sont définies pour améliorer le processus d'évaluation par les pairs. Grâce à ces améliorations, les données LA-ICP-MS U-(Th)-Pb peuvent être considérés comme plus solides, exactes, mieux documentées et quantifiées, contribuant ainsi à une meilleure interprétation scientifique.

Accepted manuscript version. Published version available at https://doi.org/10.1016/j.precamres.2017.06.017. Detrital zircon provenance study of a metamorphosed sedimentary succession in the eastern part of the Kaoko Belt in Namibia has revealed two distinct sources for the Neoproterozoic sedimentation along the southwestern Congo Craton margin. The lower part of the succession shows detrital zircon ages consistent with erosion of Paleoproterozoic basement of the Congo Craton with an inferred Mesoproterozoic volcano-sedimentary cover. Within the middle part of the succession, which includes glaciogenic sediments correlated with the Sturtian (717–660 Ma) glaciation, the Mesoproterozoic zircon grains disappear and the signal is dominated by ages known from the Congo Craton basement. The sedimentation in these parts of the succession is interpreted as related to the early Neoproterozoic rifting. The sedimentary rocks in the top part of the profile contain only subordinate proportion of the Paleoproterozoic–Archaean zircon grains and the populations are dominated by three age groups of ca. 1.0–1.2 Ga, ca. 800–750 Ma and ca. 650 Ma, consistent with erosion of the Punta del Este–Coastal Terrane exposed in the centre of the Kaoko–Dom Feliciano–Gariep orogen. An associated glaciogenic horizon interpreted as reflecting the Marinoan (645–635 Ma) glaciation constrains the sedimentation in the upper part of the succession and suggests a short time span between the high-grade metamorphism/magmatism in the Punta del Este–Coastal Terrane and its exhumation. Sedimentary rocks with such detrital zircon pattern appear also in the Damara and Gariep belts. Their source in the western part of the Kaoko–Dom Feliciano–Gariep orogen suggests that they represent an early orogenic flysch that originated during early collision in the western part of the orogen. The short time span between the metamorphism/magmatism in the Punta del Este–Coastal Terrane and deposition of the early orogenic flysch derived from it suggests that the Coastal Terrane was never separated from the Congo Craton by an oceanic domain. The estimated time span between the end of lithospheric stretching and sedimentation of the early flysch suggests that the hypothetical Adamastor Ocean separating the western and eastern forelands of the Kaoko–Dom Feliciano–Gariep orogen must have been small.

Zircon ages (U–Pb, LA-ICP-MS) obtained from skarns in the Kutna Hora and Svratka units and in the Moldanubian Zone (Bohemian Massif) show significant variations between the lithotectonic units as well as among samples from individual localities. The ages fall between 310 Ma and 3.1 Ga. We suggest that such large spread is a result of both different zircon clastic grain sources and subsequent metamorphic histories. The oldest Neoarchaean to Neoproterozoic ages are interpreted as detrital zircon grains from pre-Cadomian basement. Pronounced age maxima between 600 and 520 Ma (late Neoproterozoic to early Cambrian) were found in skarn samples from the Moldanubian Zone, Svratka and Kutna Hora units. We interpret these as maximum ages of skarn precursor deposition. Apparent Cambrian–Ordovician– Silurian to early Devonian zircon ages were obtained from non-mineralized samples of the Moldanubian Zone and also in the Kutna Hora Unit. This wide temporal interval could reflect maximum ages of skarn precursors related to disintegration of abundant early Palaeozoic magmatic rocks, provided the zircons were not modified by later metamorphism or fluid circulation. The early Carboniferous ages are interpreted to result from strong Variscan HT metamorphism and subsequent circulation of post-metamorphic fluids. Zircons of this age are dominant in skarns with massive magnetite mineralization, while the non-mineralized samples preserve the older ages.

Discontinuous and kinematically unrelated C-S fabrics have been recognized along the contact between the Gemeric and Veporic Units in the Western Carpathians. The formation of S and C fabrics within orthogneiss, quartzite and chloritoid-kyanite schist of the Veporic Unit is associated with Cretaceous syn-burial orogen-parallel flow and subsequent exhumational unroofing. The formation of the two fabrics characterized by distinct quartz deformation microstructure and metamorphic assemblage is separated by an inter-tectonic growth of transversal chloritoid-, kyanite-, ± monazite-bearing assemblage. The monazite U-Th-Pb concordia age of 97 ± 4 Ma was obtained by the laser ablation ICP-MS dating method. The age of this inter-tectonic metamorphic stage together with existing 40Ar/39Ar ages on exhumation of the Veporic Unit indicate that despite the similar appearance to shear bands or C-S mylonites there is a time span of at least 10 Myr between the formation of homogeneous S fabrics and superposed discrete C fabrics in the studied rocks

Accepted manuscript version. Published version at http://doi.org/10.1016/j.precamres.2016.05.011. License CC BY-NC-ND 4.0. The match of geological units of the dissected Kaoko-Dom Feliciano-Gariep orogenic system exposed along the coasts of the South Atlantic is poorly understood. Two suites of intrusive rocks crop out in the Angra Fria Bay area, a part of the Coastal Terrane of the Kaoko Belt in Namibia. U–Pb zircon dating of three samples from the younger suite provided ages of 574 ± 6, 586 ± 3 and 584 ± 7 Ma, similar to the ages of the oldest syn-collisional granitoids in the area. Three samples of the older suite gave ages of 626 ± 5, 622 ± 5 and 620 ± 6 Ma respectively, which have not previously been recorded in intrusive rocks of the Kaoko Belt, but which coincide with those from the Florianópolis Batholith in the Dom Feliciano Belt in Brazil. Zircon ages, Sr–Nd isotopic composition and tectonic position of these granitoids suggest that this magmatic complex could be a continuation of the Florianópolis Batholith on the African side of the Atlantic Ocean. Consequently, the Angra Fria intrusions and the Florianópolis Batholith may represent suitable localities for spatial reconstruction of the Gondwana supercontinent in the area, where the robust pre-Mesozoic connecting points are scarce.

The postcollisional tectonic development of northeast Mozambique and subsequent cooling from high-temperature metamorphism is delineated with an extensive new set of U-Pb titanite, 40Ar/39Ar hornblende, and 40Ar/39Ar mica analyses. The complex data suggest a polyphase metamorphic history from the late Neoproterozoic to the Ordovician within the East African–Antarctic Orogen (EAAO), with marked differences between the major constituent blocks. In all the data sets, samples from the basement south of the Lu´ rio Belt show generally younger ages than those from the north, resulting from a late metamorphic event and slow cooling between ca. 520 and 440 Ma. The ages north and south of the Lu´ rio Belt are consistently offset by ca. 30–70 Ma, a difference that is maintained and even appears to increase during cooling from very high temperatures to ca. 350C. Based on the first-order assumption that all the ages are cooling ages, cooling rates in the south are estimated at ca. 7–8C/Ma, while those north of the Lu´ rio Belt are faster at ca. 16C/Ma. The data are consistent with previous geochronological, petrographic, and field data and suggest a late high-temperature/low-pressure metamorphic event that affected only the basement rocks south of the Lu´ rio Belt and portions of the latter. This late metamorphism and subsequent delayed, slower cooling agree well with a model of elevated heat flow following lithosphere delamination in the southern part of the orogen, which also explains the observed widespread granitoid magmatism, migmatization, and renewed deformation in the southern basement.

*Corresponding author The Guacimal Pluton is situated in the Cordillera de Tilaran in the northwestern Costa Rica. It forms an oval-shaped body strongly elongated in the NW–SE direction. Its dimensions are ~15 × 4–6 km with an exposed surface of 60–70 km 2 . The pluton intruded basic volcanic rocks of the Aguacate Group (Miocene–Pliocene) and is surrounded by a wide thermal aureole of calc-silicate metasomatic rocks. The pluton is mainly formed of monzogranites to granodiorites, which strongly prevail over more basic types occuring scarce and relatively thin dykes and enclaves. The dominant magmatic minerals of this felsic suite are quartz, plagioclase, and K-feldspar with subordinate Mg-rich biotite, amphibole I, and magnetite. Orthopyroxene, Mn-rich ilmenite, Al-poor titanite, rutile, apatite, zircon, thorite, and chalcopyrite are accessories. Secondary minerals, which occur as fillings of miarolitic cavities and interstices, are quartz II, K-feldspar II, epidote, chlorite, actinolite, ilmenite II and Al-rich titanite II. The much less frequent mafic suite (mainly quartz diorite to quartz monzodiorite/monzogabbro) is composed of plagioclase, pargasite, actinolite, K-feldspar, quartz and magnetite, with accessory amounts of opaque minerals, epidote, chlorite, and titanite. The pluton was emplaced at a depth of c. 3 km, crystallized at temperature of c. 760–800 °C under a relatively high oxygen fugacity (1.6–2.1 log units above the NNO buffer). Increased activities of volatiles (H 2 O, F) upon cooling are indicated by the presence of highly aluminous, F-rich titanite and other hydrous silicates in miarolitic cavities. The prevailing, felsic rocks of the Guacimal Pluton are high-K calc-alkaline, whereas the mafic suite is nearly exclusively medi um-K calc-alkaline in nature. Laser ablation ICP-MS dating of zircons from two granite samples yielded statistically identical U–Pb ages of 6.3 ± 0.5 and 6.0 ± 0.4 Ma, respectively. The Sr–Nd isotopic compositions are rather primitive ( 87 Sr/ 86 Sr 6 = 0.70380–0.70413, e 6 Nd ~ +7.3 to +7.9). Narrow range of these values rules out open-system processes such as magma mixing or assimilation of isotopically contrasting upper continental crust. Instead, the felsic suite is interpreted as either having crystallized from a highly fractionated melt extracted from a plagioclase–amphibole-dominated crystal mush in a putative deep crustal reservoir or a product of partial melting of older arc-related rocks, such as intermediate lavas or volcaniclastics or immature psammitic sediments rich in volcanic material. The observed variation in the felsic suite was most likely produced by low degrees of closed-system fractional crystallization of an assemblage dominated by feldspars. At least some of the rocks of the volumetrically subordinate mafic suite may represent litholo gies rich in the complementary cumulates.

*Corresponding author Skarns in the Svratka Unit, in the neighbouring part of the Moldanubian Zone and in the Kutna Hora Complex were studied with respect to their metamorphic evolution, major- and trace-element geochemistry, oxygen isotopic composition and zircon ages. Skarns form competent lenses and layers in metamorphosed siliciclastic rocks and preserve some early deformation structures and several equilibrium assemblages representing the products of successive metamorphic reactions. The main rock-forming minerals, garnet and clinopyroxene, are accompanied by less abundant magnetite, amphibole, plagioclase, epidote ± quartz. In the Svratka Unit the early prograde M 1 , prograde/peak M 2 , and retrograde M 3 metamorphic stages have been distinguished. Metamorphic conditions in skarns of the Moldanubian Zone are limited to a relatively narrow interval of amphibolite facies. The prograde and retrograde events in the Kutna Hora Complex skarns probably took place under amphibolite-facies conditions. The presence of magnetite and the increasing proportion of the andradite component in the garnet indicate locally increased oxygen fugacity. Skarn geochemistry does not show systematic differences in the skarn composition among the three units. The regional variations are exceeded by differences among samples from individual localities. The Al 2 O 3 /TiO 2 , Al 2 O 3 /Zr, TiO 2 /Nb ratios point to the variable proportion of the detrital material, combined in skarn protoliths with CaO and FeO, the major non-detrital components. The skarns exhibit elevated abundances of Cu, Zn, Sn and As. The Eu/Eu* ratio varies in the range of 0.5–8.6, the total REE contents vary from 8 to 345 ppm. The lowest ΣREE values (< 100 ppm) occur in skarns with magnetite mineralization. The wide intervals of ΣREE and Eu/Eu* values are interpreted to indicate variations in the temperature and redox conditions among layers of the same locality and at various localities. The oxygen isotope compositions of garnets, pyroxenes and amphiboles from skarns of the Svratka Unit exhibit a range of δ 18 O = 0.1 to 4.1 ‰. In situ (laser-ablation ICP-MS) U-Pb dating of zircon from one of the Svratka Unit skarn bodies yielded a wide range of ages (0.5–2.6 Ga), supporting the detrital origin of this zircon population. The skarn protoliths were probably rocks of mixed detrital-exhalative origin deposited on the sea floor . The geological position of skarns, with their structural and metamorphic record, probably reflect tectono-metamorphic evolution shared with that of their host rocks. The geochemical characteristics, including oxygen isotopic compositions and the presence of detrital zircons with a wide range of ages exclude metasomatic, and point to a sedimentary-exhalative mode of origin for the studied skarns.

The Pinjarra Orogen, stretching along the western coast of Western Australia, is one of the least understood orogens on the continent. Exposure is limited to fault-bound basement blocks within the Phanerozoic Perth Basin, which have been interpreted as either remnants of a Mesoproterozoic orogen or as allochthonous blocks within a Neoproterozoic orogen. Thus even the timing of orogenesis is controversial. However, since the orogen is in a critical position for reconstructions of both Rodinia and Gondwana, a better understanding is highly desirable. New U–Pb ages of detrital zircon cores, metamorphic zircon rims and metamorphic monazites from the Northampton Complex, the northernmost and largest of the exposed basement blocks, provide better insights into the sedimentary provenance and metamorphic history of the metasediments exposed in this part of the orogen. Both the monazite ages and the youngest metamorphic zircon rims constrain metamorphism in the Northampton Complex to 1090–1020 Ma. Additionally, a large number of older metamorphic zircon rims pre-date this event and were inherited from the Albany-Fraser Orogen in southwestern Australia, which is also identified as the main source region for the detrital zircon cores. Additional sources of detrital zircons are the Mawson Continent (the South Australian Craton and parts of East Antarctica) and possibly the North Australian Craton, as well as synsedimentary volcanic rocks. However, the combination of ages from the cores and inherited metamorphic rims shows that zircons from the Mawson Continent/North Australian Craton were not directly transported to the Northampton Complex but arrived there after being incorporated into the Albany-Fraser Orogen and then eroded from there. The dataset records therefore two orogenic cycles: (1) erosion of the Mawson Continent/North Australian Craton, deposition along the craton margins, collision between the Mawson Continent and North-West Australian Craton and metamorphism in the Albany-Fraser Orogen and (2) erosion of the Albany-Fraser Orogen, deposition along Australia's western margin and metamorphism during the Pinjarra Orogeny. This highlights the care that must be taken in detrital zircon studies, since many of the detrital cores record a second-order provenance. It also explains how zircons from the Mawson Continent could be transported across the Albany-Fraser Orogen that should normally have been a barrier to northwest-directed sediment transport. Finally, in light of these new and previously published data, we support the interpretation that the Pinjarra Orogen is a Mesoproterozoic orogen formed along Australia's western margin.

International audience; LA-ICP-MS U-Pb analyses performed on zircon grains from the Lizio granite yielded an emplacement age of 316 6 Ma. Typical S-C structures show that the Lizio granite was emplaced contemporaneously with dextral shearing along the northern branch of the South Armorican Shear Zone and that it was therefore active at that time. 40Ar/39Ar analyses performed on muscovite grains yielded plateau dates ranging between 311.5 and 308.2 Ma. Muscovite chemistry is typical of primary magmatic muscovite, which precludes a late fluidsinduced resetting of the K-Ar isotopic system. 40Ar/39Ar dates thus likely correspond to the cooling ages below the argon closure temperature. Considering the uncertainties on the measured ages, we can propose that either the Lizio granite cooled down quickly in less than a million of years or that it remained in a hot environment for several millions of years after its emplacement. This latter scenario could have been sustained by shear heating during dextral shearing along the northern branch of the South Armorican Shear Zone.

The Letovice Complex, composed of metamorphosed enriched mid-ocean ridge basalts with trondhjemitic sheets, as well as gabbroic and ultrabasic bodies, is exposed within an important Variscan suture separating the Moldanubian Domain (to the west) from the Brunovistulicum (to the east) in the eastern part of the Bohemian Massif, Czech Republic. A polyphase tectonic evolution of the study area was connected with underthrusting and subsequent exhumation of the former oceanic realm, which resulted in three deformation phases (D 1 –D 3 ). New U–Pb laser ablation inductively coupled plasma mass spectrometry dating of magmatic zircons from amphibolite and trondhjemite yielded statistically identical concordia ages of 530 ± 6 Ma and 529 ± 7 Ma (2σ), respectively. These are interpreted as dating intrusions of the Early Cambrian protoliths of the studied rocks. Based on this age as well as whole-rock geochemical and Nd isotopic data, the Letovice Complex is interpreted as a vestige of an incipient oceanic basin developing on attenuated crust. The most likely geotectonic setting was a post-Cadomian extensional regime at the northern margin of Gondwana that marked the onset of its break-up. Supplementary material: Photomicrographs of microstructures, sample locations, descriptions of analytical techniques, and selected electron microprobe analyses of the main rock-forming minerals are available at http://www.geolsoc.org.uk/SUP18424.

(Fe–Zn–Mg)-spinel-bearing assemblages in the high-grade rocks from three localities in the Moldanubian domain of the Bohemian Massif (Variscan belt of Central Europe) have been studied to monitor the partition behaviour of zinc along the pressure–temperature path followed by the host rock and to discuss the role of Zn in spinel stabilization. Spinels in two studied samples are characterized by low gahnite content (max. 0.09 Zn p.f.u), they crystallized only under silica-undersaturated conditions and the presence of zinc is thus assumed to be insignificant for their stabilization. One sample contains spinels that are gahnite-rich (up to 0.58 Zn p.f.u) leading to their stabilization within a quartz-bearing matrix. All spinel-bearing domains reflect late re-equilibration corresponding to decompression. However, in samples with preserved relics of a high-pressure mineral assemblage, changes in the zinc content attributed to prograde garnet growth were observed in the garnet cores. In order to monitor the distribution of zinc along the pressure-temperature path, textural observations have been combined with electron-microprobe and laser ablation ICP-MS data. The results point to preferential partitioning of zinc into biotite during the spinel-absent early stages of decompression and suggest that biotite was the main source of zinc for spinel crystallizing at low pressures.

The Huqf Supergroup in Oman contains an exceptionally well-preserved and complete sedimentary record of the Middle to Late Neoproterozoic Era. Outcrops of the Huqf Supergroup in northern and central Oman are now well documented, but their correlation with a key succession in the Mirbat area of southern Oman, containing a sedimentary record of two Neoproterozoic glaciations, is poorly understood. Integration of lithostratigraphic, chemostratigraphic and new U–Pb detrital zircon data suggests that the Mirbat Group is best placed within the Cryogenian ( c . 850–635 Ma) part of the Huqf Supergroup. The c . 1 km thick marine deposits of the Arkahawl and Marsham Formations of the Mirbat Group are thought to represent a stratigraphic interval between older Cryogenian and younger Cryogenian glaciations that is not preserved elsewhere in Oman. The bulk of detrital zircons in the Huqf Supergroup originate from Neoproterozoic parent rocks. However, older Mesoproterozoic, Palaeoproterozoic and even Archaean zircons can be recognized in the detrital population from the upper Mahara Group (Fiq Formation) and Nafun Group, suggesting the tapping of exotic sources, probably from the Arabian–Nubian Shield.

Hf isotopic data of minerals in a mafic pyroxene granulite from the southern Bohemian Massif, together with their major and trace element composition and petrological observations were used to decipher the metamorphic history and behaviour of zircon in the granulite. The Hf isotopic composition in the minerals was used to estimate whether the decompression reaction, namely the consumption of garnet and rutile, could have provided Zr for the formation of newly grown metamorphic zircon. The age of the decompression reaction indicated by the evolution of Hf isotopes in garnet and orthopyroxene is between 333 and 331 Ma, i.e. ca. 7 Ma younger than the available U–Pb zircon ages from the Moldanubian granulites and than the newly obtained 343 ± 2 Ma laser ablation ICP-MS U–Pb age of zircons. The combination of bulk and in-situ Hf isotopic data, major and trace element composition and petrological modeling of P–T evolution revealed that the formation of zircons can not be related to the decompression phase of the evolution of the mafic granulites.

The chemical and phase compositions of particles produced by laser ablation (266 nm Nd:YAG) of silicate NIST glasses and zircon were studied by SIMS and HR-TEM techniques. The data suggest that the formation of phases of different mineralogy and/or chemical composition from the original sample at the ablation site can result in elemental fractionation (non-stoichiometric sampling) in material delivered to the ICP-MS for quantitative analysis. Evidence of the element fractionation is preserved in chemically zoned ejecta deposited around the ablation pit. The chemical composition and mineralogy of particles varies with particle size so that the efficiency of transport of particles also plays a role in elemental fractionation. During the first 250 pulses in a typical ablation experiment using a 266 nm laser, particle sizes are mainly

U-Pb isotopic data obtained by laser ablation ICPMS analysis of nine zircons with centre to margin oscillatory growth zones from a K-feldspar-rich augen gneiss in the allochthonous Lower Crystalline Nappe of the Erzgebirge domain of the western part of the Bohemian Massif yield a concordia age of 524 ± 10 Ma (2 sigma). This Early Cambrian age represents the time of magmatic crystallization of the protolith of a representative, from near Měděnec, of the allochthonous “Red gneiss” whose igneous nature is shown by the presence of (deformed) xenoliths. Data from TIMS analysis of zircons with variable proportions of unzoned xenocrystic cores surrounded by oscillatory-zoned overgrowths point to magma derivation from upper Proterozoic, or older, rocks. Data obtained for five zircon grains from another “Red gneiss” in the Lower Crystalline Nappe (in the Klinovec anticline) plot below the concordia with the age of the one point that is near concordant being 519 ± 26 Ma (2 sigma). These data, together with internal features of the zircons, are consistent with Early Cambrian granitic plutonism also in this part of the Erzgebirge but with later Pb loss, possibly associated with considerable fluid movement during thrust nappe development. Another sample of a coarse-grained orthogneiss from the autochthonous St Catherine9s dome yielded a significantly younger Early Ordovician age of 480 ± 10 Ma (2 sigma) calculated from eight zircon analyses. However, three zircon grains from the same sample gave a significantly older near-concordant Late Proterozoic age of ca. 620 Ma. Provided that the age difference of ca . 40 Ma between orthogneisses from Měděnec - Klinovec and St Catherine9s dome holds also for other orthogneisses in the Erzgebirge, zircon U-Pb age data could be used to discriminate between allochthonous and autochthonous units in this region. The ca. 25 Ma difference between the Early Cambrian protolith age of the augen gneiss from near Měděnec determined by the laser ablation ICPMS technique and a previously reported older age of 550 ± 9 Ma for a nearby sample determined by the Pb-Pb evaporation technique is accounted for on the basis of the latter not being adequate for dating zircons with a small xenocrystic component. This study demonstrates the importance of high spatial resolution dating techniques, such as SHRIMP or laser ablation ICPMS, in dating zircons with complex growth history that are common in crustally-derived melts.

Nous avons acquis des donnees geochronologiques (systeme U-Th-Pb) par ablation au laser avec un plasma a couplage inductif et spectrometrie de masse (LAM-ICP-MS) afin de preciser in situ l'âge de l'allanite et du zircon dans une seule lame mince polie du granite de October Harbour, au Labrador. C'est la premiere fois que l'allanite est ainsi etudiee pour datation Th-Pb par methode LAM-ICP-MS, avec verification des resultats par datation du zircon dans le meme echantillon. Des cristaux atteignant a peine 20 X 20 μm ont meme pu etre analyses dans une lame mince polie d'une epaisseur de 100 μm. Au prealable, les cristaux de zircon ont ete examines avec des images d'electrons retrodiffuses afin d'evaluer la presence de coeurs herites, de surcroissances, et de croissance oscillatoire. Nous avons effectue 45 analyses LAM-ICP-MS de 35 cristaux de zircon. Selon les donnees U-Th-Pb obtenues sur zircon, l'âge du granite serait 1657 ′ 10 Ma (MSWD = 0.77, moyenne ponderee des âges 2 0 7 Pb/ 2 0 6 Pb telle que determinee avec 25 points concordants). Les donnees indiquent la presence de zircon herite ayant un âge de 1800-1850 Ma, et des signes de pertes repetees de plomb dans plusieurs grains. L'allanite se presente en gros cristaux idiomorphes. Elle fait preuve de teneurs elevees en U et en Th. Vingt-six analyses de deux cristaux d'allanite ont donne seize points concordants, provenant surtout du noyau a faible teneur en Th d'un seul cristal, et une moyenne ponderee de l'âge 2 0 8 Pb/ 2 3 2 Th de 1635 ′ 17 Ma (MSWD = 2.1). Quoique les signes d'une perte complexe de plomb sont aussi presents dans certaines portions de l'allanite, il n'y a aucun signe d'un coeur herite. L'âge du granite de October Harbour serait d'environ 1640-1660 Ma, ce qui est passablement plus jeune que ce que l'on avait propose anterieurement suite a une analyse conventionelle U-Pb de plusieurs grains de zircon pris de la suite intrusive de Strawberry, soupconnee d'etre liee genetiquement, ce qui avait donne un âge de 1719 ′ 3 Ma. La suite de Strawberry pourrait donc etre plus complexe qu'une simple suite de roches mise en place il y a environ 1720 Ma, et contenir des roches d'âges tres differents.

Laser-ablation quadrupole ICP-MS analyses of molybdenite samples from Preissac, Quebec, and Mokrsko, Belcice and Kasperske Hory gold deposits in the Bohemian Massif, Czech Republic, for Re and radiogenic 187 Os suggest the presence of strong zoning in Re and in 187 Os/ 187 Re values within grains. The zoning patterns indicate decoupling of daughter 187 Os from parent 187 Re after molybdenite crystallization. Whereas Re is not homogeneously distributed in the molybdenite grains studied, the lack of correlation between the calculated 187 Os/ 187 Re value and the Re content also reflects the mobility of 187 Os within individual grains of molybdenite. Such decoupling of Re and Os could affect the accuracy of Re-Os ages if disturbed portions of molybdenite are sampled for dating by conventional isotope-dilution N-TIMS or ICP-MS techniques. The results re-emphasize the critical need for homogenization of quantities of molybdenite sufficiently large to capture the bulk Os/Re of the sample to be dated by these methods. Laser-ablation sampling, when used with a multicollector magnetic-sector ICP-MS instrument, is able to produce Re-Os ages with a precision better than 2% (1 � m) from single spots in certain old and Re-rich molybdenite grains, but would be difficult to use as a dating tool given the extreme 187 Os/ 187 Re heterogeneity seen in individual grains.

Thermal breakdown of zircon during laser ablation sampling for ICP-MS analysis results in decoupling of Si from Zr, and Pb from U + Th, following the reaction ZrSiO4(U, Th, Pb) = ZrO2(U, Th) + SiO2(Pb). The rate of the laser-induced elemental fractionation can be linked to the concentration of oxygen in the ambient He sample carrier gas. Deposition of ZrO2 and SiO2 on the walls of the ablation craters is enhanced by the presence of oxygen during ablation, and the composition of the deposit is dominated by ZrO2. This study shows that even a small amount of oxygen (e.g., 500 ppm) added to the sample carrier gas can shift the U–Pb ages of zircon by as much as 9%, which is well beyond the typical analytical uncertainty of LA-ICP-MS zircon dating. Addition of up to 2000 ppm oxygen to the sample carrier also increases the instrument sensitivity by as much as 3 times for light elements and ca. 1.5 times for heavy elements. The increase in sensitivity is accompanied by an increase in the U and Th oxide formation, suggesting that the signal enhancement is not related to the concomitant M+ and MO+ ion formation, but rather to the improved atomization and ionization capabilities of the mixed gas ICP. The study shows that maintaining a constant level of O2 throughout the ablation cell over an analytical session at the time of analysis is a prerequisite for further improvements in the repeatability of U–Pb LA ICP-MS dating of zircon.

Laser ablation multi-collector inductively coupled plasma mass spectrometry (LA MC ICP-MS) and secondary ion mass spectrometry (SIMS) were used to determine the boron isotopic compositions of several natural tourmaline group minerals (elbaite, schorl and dravite). This study reports on the effects of instrument parameters of LA MC ICP-MS and the composition of sample matrix on data accuracy, reproducibility and repeatability. We demonstrate that the tourmaline matrix has a significant effect on the obtained δ11B values and impacts on data accuracy, with a bias of up to ca. 2.5‰ if a non matrix-matched reference material is used to calibrate the measurements. In the case of a matrix-matched calibration, the boron isotopic data obtained by LA MC ICP-MS are comparable to the reference TIMS values, with typical repeatability for δ11B results between 0.2 and 0.5‰ (1s). This is somewhat better compared to the repeatability of 0.8–1.3‰ (1s) for small format single collector SIMS.

Xenotime overgrowths on detrital zircon in siliciclastic sediments have been reported in numerous studies. However, in natural samples, solid solution of zircon and xenotime is limited to near-end-member compositions. In order to characterize the interface region between both minerals and to draw inferences on the growth mechanisms of authigenic xenotime, we studied xenotime overgrowths on detrital zircon grains from two Phanerozoic sandstone samples with contrasting post-depositional histories. In one sample, the small (≤10 μm), pyramidal xenotime overgrowths are of diagenetic origin and grew without major discontinuity on the detrital zircon grain. The second sample shows up to >50-μm-wide, porous and inclusion-rich, hydrothermal xenotime overgrowths on detrital zircon, whereas the transition zone between both minerals is accompanied by large pore volume. Chemical compositions of the xenotime precipitates from the two samples differ particularly in Y, REE, Th and Sc concentrations, whereas high MREE availability in the diagenetic sample and the presence of Sc in the hydrothermal sample, respectively, appear to have promoted xenotime growth. Transmission electron microscopy on electron-transparent foils cut from the interface region shows that both the diagenetic xenotime and the hydrothermal xenotime are crystalline and grew in optical and crystallographic continuity to their detrital zircon substrata. Only a narrow transition zone (≤90 nm—diagenetic sample, 200–300 nm—hydrothermal sample) between zircon and xenotime is in part made up of nanometre-scale crystalline domains that are slightly distorted and may have formed from dissolution–re-precipitation processes at the zircon rim along with precipitation from the respective fluid.

[1] We investigated some of the sampling and mineral separation biases that affect the accuracy of detrital zircon provenance studies. The study has been carried on a natural catchment in the Scottish Highlands that represents a simple two-component source system and on samples of synthetic sediment prepared for this study to test the effects of heavy mineral separation on the resulting zircon age spectra. The results suggest that zircon fertility of the source rocks and physical properties of zircon represent the most important factors affecting the distribution of zircon age populations in the stream sediments. The sample preparation and selection of zircons for analysis may result in preferential loss of information from small zircon grains. Together with the preference for larger crystals during handpicking, it can result in several-fold difference compared to the real age distribution in the sediment sample. These factors appear to be more important for the reproducibility of zircon age spectra than is the number of zircon grains analyzed per sample.

Lithospheric thickening during protracted Ediacaran supercontinent assembly was dissipated in various ways along the “Pan-African” East African–Antarctic Orogen. In NE Mozambique, late-tectonic extension and plutonism south of the Lurio Belt has been modelled in terms of lithosphere delamination, although rigorous testing of the hypothesis by structural analysis has not yet been undertaken. This study presents the first analyses of late-tectonic structures in both the Mesoproterozoic basement and the Cambrian cover sequences in the Nampula Complex, NE Mozambique, supported by, and integrated with, new geochronological data. Both late compressional and extensional fabrics overprint the main Pan-African collisional structures to a variable degree in identified structural domains. The long-lived northern boundary of the Nampula Complex, the Lurio Belt high-strain zone, initiated in the Ediacaran, was reactivated and segmented during these later phases, with boundary-parallel shortening. U–Pb SIMS ages from selected latest-tectonic units in the Nampula Complex and the Lurio Belt give consistent ages between 518 ± 2 and 514 ± 5 Ma. They are coeval with migmatisation and granitoid plutonism in the Nampula Complex. U–Pb titanite (471 ± 9 Ma) and 40 Ar/ 39 Ar biotite (431 ± 3 Ma) data suggest subsequent slow cooling rates in the Nampula Complex, consistent with basal heating by asthenosphere uprise following lithosphere delamination. Consequently, we believe the new data suggest that the observed intense late polyphase deformation has preferentially occurred where the delaminated lithosphere was doubly weakened by loss of the mantle root and the resulting long-lived elevated temperature regime.

Advances in the chemical and isotopic characterisation of geological and environmental materials can often be ascribed to technological improvements in analytical hardware. Equally, the creation of novel methods of data acquisition and interpretation, including access to better reference materials, can also be crucial components enabling important breakthroughs. This biennial review highlights key advances in either instrumentation or data acquisition and treatment, which have appeared since January 2010. This review is based on the assessments by scientists prominent in each of the given analytical fields; it is not intended as an exhaustive summary, but rather provides insight from experts of the most significant advances and trends in their given field of expertise. In contrast to earlier reviews, this presentation has been formulated into a unified work, providing a single source covering a broad spectrum of geoanalytical techniques. Additionally, some themes that were not previously emphasised, in particular thermal ionisation mass spectrometry, accelerator-based methods and vibrational spectroscopy, are also presented in detail.

Microbial activity in volcanic glass within the oceanic crust can produce micron sized pits and tunnels. Such biogenic textures have been described from the recent oceanic crust and mineralized equivalents in pillow lavas as old as 3.47–3.45 Ga from the Barberton Greenstone Belt (BGB) of South Africa. In meta-volcanic glasses these microbial traces are preserved by titanite mineralization (CaTiSiO5) and on the basis of morphological, textural and geochemical evidence have been argued to represent Earth's oldest trace fossils. Here we report the results of in-situ U–Pb dating of titanite that infills trace fossils from the Hooggenoeg Complex of the BGB using laser ablation MC-ICP-MS (multi-collector inductively coupled, plasma mass spectrometry). This yields a titanite age of 3.342 ± 0.068 Ga demonstrating the antiquity of the BGB trace fossils. This radiometric age confirms that a sub-seafloor biosphere was already established in the PaleoArchean and that it likely represented an important habitat for the emergence and evolution of early microbial life on the Earth.

In order to address the correct reporting and therefore comparison of isotopic measurements across different instrument types and instrumental techniques a prepared set of synthetic standards was sent to 28 laboratories for boron (B) isotopic analyses. Standards were prepared from enriched and purified isotopic salts to avoid any sample preparation fractionation. The range in uncertainties of the analyses between different instrumental analytical techniques is as large as the differences within an instrumental analytical technique obscuring any systematic offset. We conclude that uncertainties in the measurement of d11B values were often underestimated and a procedure is suggested to allow a better comparison of the different techniques. Two new standards (JABA and JABB) have been quantified and these are available to all laboratories for testing their analyses. The d11B values of these new standards are 10.0& and 23.7&. The results from this exercise impact on the way all isotope measurements are performed and reported. Guidelines are defined to aid the comparison of measurements between different laboratories., JRC.E.8-Nuclear safeguards and Security

We introduce and propose zircon M257 as a future reference material for the determination of zircon U-Pb ages by means of secondary ion mass spectrometry. This light brownish, flawless, cut gemstone specimen from Sri Lanka weighed 5.14 g (25.7 carats). Zircon M257 has TIMS-determined, mean isotopic ratios (2s uncertainties) of 0.09100 ± 0.00003 for 206pb/238U and 0.7392 ± 0.0003 for 207pb/235U. Its 206pb/238U age is 561.3 ± 0.3 Ma (unweighted mean, uncertainty quoted at the 95% confidence level); the U-Pb system is concordant within uncertainty of decay constants. Zircon M257 contains ∼ 840 μg g−1 U (Th/U ∼ 0.27). The material exhibits remarkably low heterogeneity, with a virtual absence of any internal textures even in cathodoluminescence images. The uniform, moderate degree of radiation damage (estimated from the expansion of unit-cell parameters, broadening of Raman spectral parameters and density) corresponds well, within the “Sri Lankan trends”, with actinide concentrations, U-Pb age, and the calculated alpha fluence of 1.66 × 1018 g−1. This, and a (U+Th)/He age of 419 ± 9 Ma (2s), enables us to exclude any unusual thermal history or heat treatment, which could potentially have affected the retention of radiogenic Pb. The oxygen isotope ratio of this zircon is 13.9%o VSMOW suggesting a metamorphic genesis in a marble or calc-silicate skarn. Nous presentons et proposons a la communaute le zircon M257 qui pourrait devenir un materiau de reference pour la determination des âges U-Pb sur zircon par spectrometrie de masse a ions secondaires (SIMS). Ce specimen scie d'une gemme brun clair, sans defauts, provenant du Sri Lanka, pese 5.14 g (25.7 carats). Les moyennes des rapports isotopiques (et les incertitudes associees 2s) mesurees par TIMS sur ce zircon M257 sont 0.09100 ± 0.00003 en 206pb/238U et 0.7392 ± 0.0003 en 207pb/235U. Son âge 206pb/238U est de 561.3 ± 0.3 Ma (moyenne non ponderee, incertitude: 95% intervalle de confiance); le systeme U-Pb y est concordant, aux erreurs sur les constantes de desintegration pres. Le zircon M257 contient ∼ 840 μg g−1 U (Th/U ∼ 0.27). Ce materiel montre de tres faibles heterogeneites, avec une quasi absence de textures internes, meme a I'examen par cathodoluminescence. Le degre de dommage lie aux radiations (estime par I'expansion des parametres de la cellule unitaire, I'elargissement des parametres des spectres Raman et la densite) est modere et uniforme. II se correle bien, (sur I'alignement “Sri Lanka”) avec les concentrations en actinides, I'âge U-Pb et la fluence calculee de 1.66 × 1018 g−1 Ceci, couplea son âge (U+Th)/He de 419 ± 9 Ma (2s), nous permet d'exclure I'existence d'evenement thermique passe, ou de traitement par la chaleur, qui aurait potentiellement pu affecter le processus de retention de Pb radiogenique. Le rapport isotopique de I'oxygene de ce zircon est 13.9%o VSMOW, suggerant une genese par metamorphisme, au sein d'un marbre ou d'un skarn calco-silicate.

Matrix-matched calibration by natural zircon standards and analysis of natural materials as a reference are the principle methods for achieving accurate results in inicrobeam U-Pb dating and Hf isotopic analysis. We describe a new potential zircon reference material for laser ablation ICP-MS that was extracted from a potassic granulite facies rock collected in the southern part of the Bohemian Massif (Plesovice, Czech Republic). Data from different techniques (ID-TIMS, SIMS and LA ICP-MS) and several laboratories suggest that this zircon has a concordant U-Pb age with a weighted mean (206)Pb/(238)U date of 337.13 +/- 0.37 Ma (ID-TIMS, 95% confidence limits, including tracer calibration uncertainty) and U-Pb age homogeneity on the scale used in LA ICP-MS dating. Inhomogeneities in trace element composition due to primary growth zoning prevent its use as a calibration standard for trace element analysis. The content of U varies from 465 ppm in pristine parts of the grains to similar to 3000 ppm in actinide-rich sectors that correspond to pyramidal faces with a high degree of metamictization (present in ca. 30% of the grains). These domains are easily recognized from high intensities on BSE images and should be avoided during the analysis. Hf isotopic composition of the Plesovice zircon (>0.9 wt.% Hf) is homogenous within and between the grains with a mean (176)Hf/(177)Hf value of 0.282492 +/- 0.000013 (2SD). The age and Hf isotopic homogeneity of the Plesovice zircon together with its relatively high U and Pb contents make it an ideal calibration and reference material for laser ablation ICP-MS measurements, especially when using low laser energies and/or small diameters of laser beam required for improved spatial resolution.

Elemental fractionation poses serious difficulties in obtaining accurate concentration and isotope ratio data when using laser ablation sampling. One of the factors that control the extent of laser-induced elemental fractionation is the composition of sample carrier gas in the sample cell. This study demonstrates that the presence of small amounts of oxygen in the He carrier gas has a significant effect on elemental fractionation during the ablation of silicate (NIST 612 glass and zircon 91500) and sulphide (NiS fire assay) samples. The extent of elemental fractionation for a given amount of ablated material and concentration of oxygen in the He carrier gas was related to the volume of the plasma plume that forms above the sample surface. This indicates that an oxidation reaction takes place in the plasma plume. It has been reported that oxidation can affect the particle size distribution during laser sampling and hence change the extent of elemental fractionation. The purity of the carrier gas used in laser ablation–ICP-MS, as well as the amount of oxygen released from silicate and oxide samples during the ablation in "oxygen-free" ambient gas, is shown to contribute significantly to elemental fractionation.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) uranium-thorium-lead (U-Th-Pb) dating is an increasingly popular approach for determining the age of mineral grains and the timing of geological events. The spatial resolution offered by this technique allows detailed investigations of complex igneous and metamorphic processes, and the speed of data capture allows vast amounts of information to be gathered rapidly. Laser ablation U-Th-Pb dating is therefore becoming an increasingly influential technique to the geochronology community, providing cost-effective and ready access to age data for laboratories and end users worldwide. However, complications in acquiring, processing, and interpreting data can lead to inaccurate age information entering the literature. With the numbers of practitioners expanding rapidly, the need to standardize approaches and resolve difficulties (particularly involving the subjectivity in processing laser ablation U-Th-Pb data) is becoming important.

Data on elemental fractionation of alkali elements during laser ablation ICP-MS analysis of silicate reference glasses (NIST-610, BCR-2G, alkali element-doped andesite glasses) and crystalline mineral albite (NaAlSi3O8) are reported. Laser ablation ICP-MS and SIMS were used to determine differences in sample composition before and after laser interaction with the samples. The fractionation trends of the alkali elements are different from those of other lithophile elements, such as Ca and the rare earth elements (REEs). The rate of fractionation varies for different sample matrices and for different alkali elements in the same matrix. Data from SIMS analyses of the ejecta blanket deposited adjacent to the laser ablation crater in silicate NIST-610 glass and crystalline albite suggest a matrix dependent fractionation of alkali elements for different particle size fractions in the ablated aerosol. The extent of fractionation varies for different alkali elements and is independent of their ionic radii. Ion probe depth profiling into the bottom of laser craters showed laser ablation-induced chemical changes in the sample that involved alkali elements and major matrix elements including Si and Ca. This suggests that a combination of thermally-driven diffusion and size-dependent particle fractionation are responsible for the observed fractionation of alkali elements during laser ablation of silicate samples.