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The principal possibility of using high-uranium metamict zircon with a high self-irradiation α-dose for U–Pb geochronological studies (ID-TIMS) is demonstrated. The application of the optimal parameters of “chemical abrasion,” accompanied by preliminary high-temperature annealing, allowed us to estimate the age of Li–F granites of the Turga massif (Eastern Transbaikalia) (146 ± 4 Ma and 141 ± 1 Ma).

The structural and chemical properties of zircon inclusions in garnet megablasts from the Dora Maira Massif (Western Alps, Italy) were characterized in detail using charge contrast imaging, Raman spectroscopy, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The aim of this work is to determine to what extent the degree of metamictization, metamorphic recrystallization, inherent structural heterogeneity, chemical composition, and zoning, along with the elastic stress imposed by the host mineral, can influence the Raman peak position of the zircon inclusion and hence, the residual pressure estimated via Raman geo-thermobarometry. We show and confirm that metamictization and inherent structural heterogeneity have a major influence in the Raman spectra of zircon in terms of peak position and peak width. We suggest that, for spectral resolution of 2 cm−1, the peak width of the B1g mode near 1008 cm−1 of reliable grains must be smaller than 5 cm−1. The method can be applied to both inherited igneous and newly formed Alpine metamorphic crystals. By coupling structural and chemical information, we demonstrate that there are no significant differences between the Raman spectra of zircon with oscillatory-zoned texture, formed during magmatic crystallization, and those formed by fluid-induced Alpine (re)crystallization. The discrimination between magmatic and metamorphic zircon based only on micro-textural constraints is not robust. Finally, our results allow establishing a protocol devoted to the selection of reliable buried zircon inclusions, relying only on Raman spectroscopic measurements, to use for elastic thermobarometry applications.

The U–Pb isotopic system in zircon is the tool of choice to interrogate high-temperature geological processes, yet this system has potential to investigate lower temperature fluid–rock interaction as well. In some cases, removal of radiogenic Pb is incomplete, potentially allowing regression of discordant U–Pb data on a concordia diagram to determine both the age of crystallization and the timing of fluid-driven isotopic disturbance. However, in rocks preserving more complex histories, simple regression is not effective at resolving multiple Pb loss events. Here, we use a ‘concordant–discordant comparison’ (CDC) test to establish the times of U–Pb disturbance in the Acasta Gneiss Complex (AGC), Canada. AGC c. 4.03 to c. 3.40 Ga orthogneisses experienced a long and complex post-crystallization history, for which U–Pb zircon data reflects not only the heterogeneous nature of the rock, but also the varying degrees and duration of crustal reworking that inevitably involved open system processes. The CDC test calculates the similarity between the concordant age structure and a modelled age structure, the latter inferred from discordant analyses, over a wide range of potential disturbance times. Our analysis reveals concordant zircon components implying new growth and/or recrystallization at 3992 ± 5, 3501 ± 6, 3442 ± 5 and 3126 ± 6 Ma. In addition, we establish episodes of radiogenic-Pb loss driven by fluid–rock interaction at 3150 ± 50 Ma, and probably at 2875 ± 50 Ma and c. 2590 Ma. These Pb-loss episodes correlate with previously recognised events recording growth of zircon rims during metamorphism, granite emplacement, and unroofing. Pb-loss within the AGC shows an antithetic relationship in different samples that are in close geographic proximity. We suggest that zircon alteration and associated new growth effectively rendered those grains that underwent Pb-loss at a particular time less susceptible to alteration during the next episode of fluid interaction.

High-resolution electron backscattered diffraction (EBSD) and correlated in situ secondary ion mass spectrometry (SIMS) U–Pb geochronology have been conducted on impact-metamorphosed zircon, titanite, and apatite grains from the 453 Ma Lac La Moinerie impact structure of Quebec, Canada. Building on previous work, our new U–Pb results highlight the challenges associated with SIMS dating of low U, common Pb-rich accessory phases (apatite and titanite) within terrestrially shocked impact lithologies. Unlike zircon, microstructurally controlled Pb loss is limited in apatite and titanite, providing evidence that the mechanisms governing impact resetting in these phases are distinct from high U, low common Pb phases (zircon, monazite, baddeleyite). EBSD mapping reveals internal complexity within all three phases, providing new insights into their microstructural evolution during impact-related metamorphism. Correlated EBSD and Raman analysis of Former Reidite In Granular Neoblastic (FRIGN) zircon provides the first documented case of post-recrystallization radiation damage of individual zircon neoblasts. Two modes of recrystallization are recorded in apatite: systematic (Type I), wherein strain-free domains are preferentially oriented along specific crystallographic planes, and non-systematic (Type II), where strain-free domains exhibit no preferred orientation. A new shock twin is observed in titanite that has a disorientation relationship of 74°/ , interpreted to be the result of strain-induced misorientation of pre-existing $$\left\{ {1\overline{1}1} \right\}$$ shock twins. We document the first case of impact-recrystallized titanite, which is intergrown with granular rutile and partially preserves former $$\left\{ {1\overline{1}1} \right\}$$ shock twins along boundaries of strain-free subdomains. Based on our EBSD observations, we provide a microstructural framework outlining the sequential evolution of zircon, titanite, and apatite during shock and thermal metamorphism.

Obtaining reliable petrochronological and geochemical data from metamict zircon may be challenging. Metamict zircon and crystalline apatite from the Meiwu granodiorite and its microgranular enclaves from the Paleo-Tethys belt are examined to constrain their crystallization ages and the genetic mechanism of related skarn mineralization. The metamict zircon yields highly disturbed 206Pb/238U dates. Transmission electron microscopy shows that radiation damage forms nanoscale-banded damaged zones, leading to spurious dates. The coexisting apatite has not accumulated radiation damage, and apatite crystals from the granodiorite and its enclaves yield reasonably precise LA-ICPMS U–Pb Tera–Wasserburg concordia lower intercept dates of 240.2 ± 3.8 and 239.9 ± 4.0 Ma (2σ), with MSWDs of 1.0 and 2.1. Considering the fast cooling of the granite, the U–Pb dates effectively represent crystallization ages for these rocks. Compositional analysis shows that there are no Ce anomalies in apatite in either the granodiorite or enclave, indicating low oxygen fugacities. Apatite crystals from enclaves have weaker negative Eu anomalies, higher Sr, and lower HREE and Y contents than those in granodiorite. The compositions confirm enclaves as products of water-rich melts, resulting in amphibole fractionation and suppression of plagioclase crystallization. The hydrous magma induced production of hydrothermal-fluids that mobilized metals dispersed in dry magma and concentrated them into mineralization traps, which contributed to the formation of widespread skarns in Paleo-Tethys belt. This study demonstrates that apatite is effective in tracing the evolution of magmatic systems containing metamict zircon.

The Guangshigou deposit is the largest pegmatite-type uranium deposit in the Shangdan domain of the North Qinling Orogenic Belt, which is characterized by the enrichment of uraninite hosted in biotite granitic pegmatites. At Guangshigou, uraninite commonly occurs as mineral inclusions in quartz, K-feldspar and biotite or in interstices of these rock-forming minerals with magmatic characteristics (e.g., U/Th &lt, 100, high ThO2, Y2O3 and REE2O3 contents and low concentrations of CaO, FeO and SiO2). It crystallized at 407.6 ± 2.9 Ma from fractionated calc-alkaline high-K pegmatitic melts under conditions of 470–700 °C and 2.4–3.4 kbar as deduced by the compositions of coexisting peritectic biotite. The primary uranium mineralization took place during the Late Caledonian post-collisional extension in the North Qinling Orogen. After this magmatic event, uraninite has experienced multiple episodes of fluid-assisted metasomatism, which generated an alteration halo of mineral assemblages. The alteration halo (or radiohalo) was the result of the combined effects of metamictization and metasomatism characterized by an assemblage of goethite, coffinite and an unidentified aluminosilicate (probably clay minerals) around altered uraninite. This fluid-assisted alteration was concomitant with the albitization of K-feldspar subsequently followed by the coffinitization of uraninite during the major period of 84.9–143.6 Ma, as determined by U-Th-Pb chemical ages. Further investigations revealed that the metasomatic overprinting on uraninite initially and preferentially took place along microcracks or cavities induced by metamictization and promoted their amorphization, followed by the release of U and Pb from structure and the incorporation of K, Ca and Si from the fluids, finally resulting in various degrees of uraninite coffinitization. The released U and Pb were transported by alkali-rich, relatively oxidizing fluids and then re-precipitated locally as coffinite and an amorphous U-Pb-rich silicate under low to moderate temperature conditions (85–174 °C). The compositional changes in primary uraninite, its structure amorphization together with the paragenetic sequence of secondary phases, therefore, corroborate a combined result of intense metamictization of uraninite and an influx of alkali–metasomatic fluids during the Late Mesozoic Yanshanian magmatic event in the region. Hence, the remobilization and circulation of uranium in the North Qinling Orogen was most likely driven by post-Caledonian magmatism and hydrothermal activities related to large-scale tectonic events. In this regards, Paleozoic pegmatite-type uranium mineralization may represent a significant uranium source for Mesozoic hydrothermal mineralization identified in the Qinling Orogenic Belt.

The Hadean Jack Hills zircons represent the oldest known terrestrial material, providing a unique and truly direct record of Hadean Earth history. This zircon population has been extensively studied via high-spatial-resolution high-throughput in situ isotopic and elemental analysis techniques, such as secondary ionization mass spectrometry (SIMS), but not by comparatively destructive, high-temporal-precision ( % two-sigma) thermal ionization mass spectrometry (TIMS). In order to better understand the lead loss and alteration history of terrestrial Hadean zircons, we conduct stepwise chemical abrasion–isotope dilution–thermal ionization mass spectrometry with trace element analysis (CA-ID-TIMS-TEA) on manually microfractured Hadean Jack Hills zircon fragments previously dated by SIMS. We conducted three successive HF leaching steps on each individual zircon fragment, followed by column chromatography to isolate U–Pb and trace element fractions. Following isotopic and elemental analysis, the result is an independent age and trace element composition for each leachate of each zircon fragment. We observe ∼50 Myr of age heterogeneity in concordant residues from a single zircon grain, along with a protracted history of post-Hadean Pb loss with at least two modes circa ∼0 and 2–4 Ga. Meanwhile, stepwise leachate trace element chemistry reveals enrichments of light rare earth elements, uranium, thorium, and radiogenic lead in early leached domains relative to the zircon residue. In addition to confirming the efficacy of the LREE-I alteration index and providing new insight into the mechanism of chemical abrasion, the interpretation and reconciliation of these results suggest that Pb loss is largely driven by low-temperature aqueous recrystallization and that regional thermal events may act to halt – not initiate – Pb loss from metamict domains in the Hadean Jack Hills zircons.

This study examines the oxidation and coordination of lead (Pb) in the uranium (U) minerals uraninite (UO2), coffinite (USiO4), and brannerite (UTi2O6), and minerals that have U as a minor constituent, zircon (ZrSiO4) and titanite (CaTiSiO5). The characterization of Pb was conducted through a combination of micro-synchrotron X-ray fluorescence mapping (µSXRF) and micro-X-ray absorption spectroscopy (µXAS), collected at the Pb LII and LIII edge on characterized grains (electron microscopy and X-ray diffraction) from a range of geological settings and ages. For all minerals considered in this study, Pb LII and LIII X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data indicate that Pb exists as Pb2+. In the case of uraninite, DFT structure optimization calculations suggest that the substitution of Pb2+ for U4+ is facilitated by the stereochemically active electron lone pair indicative of Pb2+, which effectively takes the place of an oxygen vacancy (coupled substitution Pb2+ + □ = U4+ + O2−). In detail, however, the EXAFS and XANES data, supported by first principle calculations of the XANES associated with Pb2+ replacing U4+ in the crystal lattice of uraninite, indicate that Pb2+ is present in a less distorted coordination than suggested by DFT, which may reflect a yet to be characterized link between interstitial oxygen defects and Pb2+ incorporation, rather than a simple oxygen vacancy. For coffinite, the XANES data demonstrate that Pb exists mainly as Pb2+ in the form of galena, indicating limited stability of the isomorphous substitution in coffinite. In contrast, Pb is homogeneously distributed in the metamict mineral brannerite, which displays a distinct XANES spectrum suggestive of Pb2+ bonded to oxygens in a highly distorted coordination environment. Pb LII XANES indicate that radiogenic Pb exists predominantly as Pb2+ within the crystal lattice of zircon and as distinct mineral PbO nano-scale inclusions or domains. Additionally, Pb LII XANES measurements also indicate that Pb2+ exists within titanite although the coordination environment is unclear. Overall, these data suggest that the previous indications of the presence of Pb4+ in radioactive minerals need to be reconsidered. The nature of radiogenic Pb2+ incorporation in U-bearing minerals controls the mobilization of Pb in hydrothermal fluids and the utility of a mineral as a geochronometer. The Pb valence and coordination data presented in this study provide fundamental constraints imperative for our understanding of the controls governing the mobilization of radiogenic Pb during water-rock interaction and metamorphism.

Annealing is commonly used in the recrystallization of metamict minerals in an attempt to reconstruct the original structure. Annealing at 750 °C of Nb-rich chevkinite-(Ce) from the Biraya rare-metal deposit, Russia, resulted in the structural transformation C2/m → P21/a, which defines chevkinite stability in different environments. This transformation seems to be a rapid version of a naturally occurring process that possibly involves twinning of the crystals. Nb-rich chevkinite-(Ce) occurs naturally as two polymorphs, one with the C2/m space group and the other with P21/a. The latter is the stable form under ambient conditions. There are some distinct differences in the values of the structural parameters, such as the average M-O distances or site scattering values of particular sites for both space groups, which can be associated with the redistribution of some lighter cations, mainly Mg2+, within the crystal lattice. The use of complementary experimental techniques (electron probe microanalysis, X-ray diffraction, and photoelectron spectroscopy) has delivered information on the structure and transformation of a very complex, highly zoned and partially metamict solid solution. It should be useful in determining the structure of any mineral where cation disorder is present.

This work presents a detailed investigation on zircon crystals of a Mesoproterozoic granite from the SW Amazonian Craton using a combination of back scattered electron (BSE) imaging, thermal ionisation mass spectrometry (TIMS) and Raman scattering spectroscopy. Six zircon grains were analysed. The results plotted in the Concordia diagram yielded an upper intercept age of 1423.0 ± 3.8 Ma, which is interpreted as the crystallization age of the rock. The scattering of the analyses in such diagram indicates that U-Pb isotopes are volume-dependent in the studied zircon grains. BSE reveals zonation in the zircon crystals, and Hf is the main element causing the variability in the BSE intensity and U has a secondary effect. Both elements have much higher atomic number than the principal constituents of zircon (Zr, Si and O), so the substitution of Zr by U and Hf results in increasing image brightness. BSE images from the zircon grains exhibit a euhedral external shape and fine-scale euhedral oscillatory zoning. The predominance of magmatic zoned crystals points out that the granite has not suffered metamorphic heating or any other processes that induce the formation of new phases. The results of the Raman scattering technique indicate that a SiO 4 tetrahedral internal vibrational structure is sufficiently sensitive to determine the increasing degree of metamictization. Furthermore, evidence for metamictization is given by the heterogeneity of the half-width values of the Raman scattering peaks, which exhibit a decreasing trend from the core to the rims of the analysed grains. We concluded that the combination of the three techniques provides information on the Pb loss and that the degree of U-Pb isotopic discordance correlates closely with the volume of the zircon grain. The data, in addition to the lateral degree of metamictization detected by the Raman scattering technique, indicate that the loss of radiogenic Pb may be linked to the continuous diffusion of this element. The correlation of the U-Pb discordance and metamictization emphasizes the importance of the Raman scattering spectroscopy analysis to performing zircon dating. Indeed, it is a helpful tool for geochronologists.

The ultrahigh-pressure (UHP) whiteschists of the Brossasco-Isasca unit (Dora-Maira Massif, Western Alps) provide a natural laboratory in which to compare results from classical pressure (P)–temperature (T) determinations through thermodynamic modelling with the emerging field of elastic thermobarometry. Phase equilibria and chemical composition of three garnet megablasts coupled with Zr-in-rutile thermometry of inclusions constrain garnet growth within a narrowP–Trange at 3–3.5 GPa and 675–720 °C. On the other hand, the zircon-in-garnet host-inclusion system combined with Zr-in-rutile thermometry would suggest inclusion entrapment conditions below 1.5 GPa and 650 °C that are inconsistent with the thermodynamic modelling and the occurrence of coesite as inclusion in the garnet rims. The observed distribution of inclusion pressures cannot be explained by either zircon metamictization, or by the presence of fluids in the inclusions. Comparison of the measured inclusion strains with numerical simulations shows that post-entrapment plastic relaxation of garnet from metamorphic peak conditions down to 0.5 GPa and 600–650 °C, on the retrograde path, best explains the measured inclusion pressures and their disagreement with the results of phase equilibria modelling. This study suggests that the zircon-garnet couple is more reliable at relatively low temperatures (P–Tpaths.

In the current study, different heavy minerals typical of gold placer deposits were identified by means of micro-Raman spectroscopy, and their chemical composition analyzed and discussed (garnet, kyanite, staurolite, zircon, allanite, monazite, xenotime, rutile, anatase, cassiterite, titanite, barite). Even complex solid solution series, such as those of garnets, can be deciphered with the aid of systematic trends observed in Raman line frequencies. The &nu, 1 mode in garnets will shift from high to low frequencies as a function of the ionic radius of the X2+ cation, from Mg2+, to Fe2+ and Mn2+, while the presence of Ca2+ will make the band to be shifted strongly to even lower wavenumbers. This approach has successfully been taken to differentiate between polymorph triplets such as kyanite-sillimanite-andalusite and rutile-anatase-brookite. Minerals under consideration with high contents of REE, U and Th are affected by intensive metamictization, particularly zircon and titanite. Raman peak features, such as shape, symmetry and intensity, respond to this radiation damage of the lattice and enable fine-tuning of these heavy minerals, such as in the case of fluorite (fetid fluorite).

This study investigates the variations of structural parameters and chemistry of a partially metamict and seven detrital zircon samples from different localities using single-crystal X-ray diffraction, synchrotron high-resolution powder X-ray diffraction, and electron-probe micro-analysis techniques. The unit-cell parameters for the eight zircon samples vary linearly with increasing unit-cell volume, V. A zircon sample from the Canadian Arctic Islands has the smallest unit-cell parameters, bond distances, ideal stoichiometric composition, unaffected by &alpha, radiation damage, and is chemically pure. A zircon sample from Jemaa, Nigeria has the largest unit-cell parameters because of the effect of &alpha, radiation doses received over a long time (2384 Ma). All the samples show good correlations between Zr and Si apfu (atom per formula unit) versus unit-cell volume, V. The &alpha, radiation doses in the samples are lower than ~3.5 &times, 1015 &alpha, decay events/mg. Substitutions of other cations at the Zr and Si sites control the variations of the structural parameters. Relatively large unit-cell parameters and bond distances occur because the Zr site accommodates other cations that have larger ionic radii than the Zr atom. Geological age increases the radiation doses in zircon and it is related to V.

U Pb zircon geochronology is one of the most widely used techniques in sedimentary provenance analysis. Unfortunately, the ability of this method to identify sediment sources is often degraded by sediment recycling and mixing of detritus from different source rocks sharing similar age signatures. These processes create non-unique zircon U Pb age signatures and thereby obscure the provenance signal. We here address this problem by combining detrital zircon U Pb geochronology with Raman spectroscopy. The position and width of the Raman signal in zircon scales with its degree of metamictization, which in turn is sensitive to temperature. Thus, combined U-Pb + Raman datasets encode information about the crystallization history of detrital zircons as well as their thermal history. Using three borehole samples from Mozambique as part of a source-to-sink study of interest for hydrocarbon exploration, we show that zircon populations with similar U Pb age distributions can exhibit different Raman signatures. The joint U-Pb + Raman analysis allowed us to identify three different annealing trends, which were linked to specific thermal events. Thus we were able to differentiate a dominant Pan-African U Pb age peak into several sub-populations and highlight the major effect of Karoo tectono-magmatic events. In our case study, we used Raman also as a means to systematically identify all zircon grains in heavy-mineral mounts, resulting in considerable time savings. Raman spectroscopy is a non-destructive and cost-effective method that is easily integrated in the zircon U Pb dating workflow to augment the resolution power of detrital zircon U Pb geochronology.

Radioactivity monitoring post-cold war has become more complex due to the nuclear fallout and the surge in use of radioactive materials. This requires novel methods to detect, trace and distinguish natural and anthropogenic radioactive sources in the environment. We explored the feasibility of using ZrSiO4 (Zircon), as a reference signature for radioactivity monitoring due to the unique phenomenon of metamictization. We investigated the variations in microstructural properties of Zircon samples collected from a proposed Uranium site to identify these signatures using analytical techniques such as Gamma-ray Spectroscopy, XRD and Raman spectrum analysis. Besides elevated levels of radioactivity, the samples exhibited distinct properties such as increased lattice parameters observed from the XRD analysis and dramatic broadening of A1g (439 cm−1) and B1g (1008 cm−1) vibrational modes in the Raman spectrum. Structural parameters were further analyzed by modeling the crystal from experimentally observed lattice parameters. Ab-initio calculations were then performed on the modeled structure providing more insight into the microstructural variations. Samples collected from proposed Uranium mines indicate an increase of 1.226% and 0.9389% in Si–O and Zr–O bond lengths of the Zircon crystal signifying the ongoing process of metamictization from radiation damage. By correlating radioactivity levels with the lattice parameters variations of the collected samples, the study establishes a linear relation between the degree of damage to a mineral's crystal structure and the amount of radioactivity. We propose to use the variations in damage found in a mineral's structure as a nuclear forensic signature for advanced assessment of accumulated radioactivity in a particular geographical location.

The results of isotope U–Pb dating of zircons from lherzolite and vein olivine orthopyroxenite composing the Roseta ultramafic massif are presented. The zircons differ in their morphological, optical, and geochemical properties and in their age. Lherzolite samples that are almost deprived of cathodoluminescence are represented by two age clusters 788 ± 15 and 638.2 ± 5.4 Ma. The zircons from the first cluster are relict. A later event recorded in the zircons from the second cluster was manifested in an intense metamict mineral transformation. The age of the zircons from vein olivine orthopyroxenite conforms to 608.9 ± 3.4 Ma. These zircons are considered to be syngenetic; therefore, their age is determined by the time of crystallization of olivine orthopyroxenites.

Lamellae of 1.5 µm thickness, prepared from well-crystallised monazite–(Ce) and zircon samples using the focused-ion-beam technique, were subjected to triple irradiation with 1 MeV Au+ ions (15.6% of the respective total fluence), 4 MeV Au2+ ions (21.9%) and 10 MeV Au3+ ions (62.5%). Total irradiation fluences were varied in the range 4.5 × 1012 – 1.2 × 1014 ions/cm2. The highest fluence resulted in amorphisation of both minerals; all other irradiations (i.e. up to 4.5 × 1013 ions/cm2) resulted in moderate to severe damage. Lamellae were subjected to Raman and laser-induced photoluminescence analysis, in order to provide a means of quantifying irradiation effects using these two micro-spectroscopy techniques. Based on extensive Monte Carlo calculations and subsequent defect-density estimates, irradiation-induced spectroscopic changes are compared with those of naturally self-irradiated samples. The finding that ion irradiation of monazite–(Ce) may cause severe damage or even amorphisation, is in apparent contrast to the general observation that naturally self-irradiated monazite–(Ce) does not become metamict (i.e. irradiation-amorphised), in spite of high self-irradiation doses. This is predominantly assigned to the continuous low-temperature damage annealing undergone by this mineral; other possible causes are discussed. According to cautious estimates, monazite–(Ce) samples of Mesoproterozoic to Cretaceous ages have stored only about 1% of the total damage experienced. In contrast, damage in ion-irradiated and naturally self-irradiated zircon is on the same order; reasons for the observed slight differences are discussed. We may assess that in zircon, alpha decays create significantly less than 103 Frenkel-type defect pairs per event, which is much lower than previous estimates. Amorphisation occurs at defect densities of about 0.10 dpa (displacements per lattice atom). Electronic supplementary material The online version of this article (10.1007/s00269-018-0975-9) contains supplementary material, which is available to authorized users.

The effect of selective preservation during transportation of zircon grains on the detrital age spectrum is difficult to quantify and could potentially lead to systematic bias in provenance analysis. Here we investigate whether the shape of detrital zircon grains holds provenance information and if the grain shape can assist in understanding preservation. We applied multiple linear regression analysis to identify significant shape properties in detrital zircons from Proterozoic metasediments of the Capricorn and Amadeus basins and their Archean and Proterozoic sources in the Yilgarn Craton and the Musgrave Province in Western Australia. Digital images and isotopic data from 819 SIMS U–Pb dated zircons were examined for correlation between grain shape, age, U and Th content. Out of twelve shape descriptors measured, Minor Axis , the width of zircon grains perpendicular to the crystallographic c-axis, consistently shows the most significant correlation with isotopic age. In the studied population Archean grains are narrower than Proterozoic grains: the probability that grains wider than 75 μm are Archean is less than 30%. Calculations of the proportions of source material in sedimentary rocks relative to the proportions of source material in the overall catchment area (erosion parameter ‘ K ’ calculated based on age spectra) produced values typical for mature river systems, with K = 6 for the Yilgarn-Capricorn and K = 5.5 for the Musgrave-Amadeus source-sink system. For the Yilgarn-Capricorn system, we also calculated ‘ K ’ based on Minor Axis , to determine whether grain width can be linked to age populations. Results of the shape-based K of 5.3 suggest a similarity between age-based and shape-based ‘ K ’ values, demonstrating that zircon grain width may be a useful discriminator of provenance. Contrary to commonly applied qualitative shape classifications, we found no consistent correlations between shape descriptors of magmatic zircons and the composition of their host rock. While metamict zircons were preferentially removed during transport, the similarities in grain shape and age distribution of magmatic and detrital populations suggest that hydraulic sorting did not have a significant effect. We conclude that transport of zircon grains from magmatic source to sedimentary sink affects their width less than their length.

Zircon- and bulk-rock Zr-based thermometric parameters have become fundamental to petrogenetic models of magmatism, from which broader geochronological and tectonic implications are being made. In particular, petrogenetic models have become increasingly reliant on Ti concentration in zircon geothermometry (T ZircTi ) and zircon saturation temperature (T Zircsat ). A feature of many of these studies is an implicit assumption that all zircons present in the host igneous rock are autocrystic, that is, crystallised from the surrounding melt. However, it has long been recognised that zircons present in an igneous rock can be inherited either from the surrounding country rock or source region (xenocrysts), or from earlier phases of magmatism or the magmatic plumbing system (antecrysts). Distinguishing these different origins for zircon crystals or domains within crystals is not straightforward. Here, we first review the utility and reliability of zircon-based thermometers for petrogenetic studies and show that T Zircsat is a theoretical temperature and cannot be used to constrain magmatic or partial melting temperatures. It is a dynamic variable that changes during magma crystallisation, and essentially increases as fractional crystallisation proceeds, whereas true magmatic temperatures (T Magma ) decrease. Generally, in Temperature-SiO2 space, the cross-over point of these two temperatures is magmatic system dependent, and also affected by the type of calibration used for the T Zircsat calculations. Consequently, each magmatic system needs to be evaluated independently to assess the validity and usefulness of T Zircsat . A fundamental conclusion of T Zircsat and T Magma relationships assessed here is that new zircon generally only crystallises in silicic (granitic/rhyolitic) melt compositions, and thus autocrystic zircons should not be assumed to be present in igneous rocks with bulk compositions Zircsat and T Magma ) to estimate whether the magma was zircon-saturated or undersaturated. To test this new protocol, we use as examples, several Phanerozoic granitic rocks intersected by drilling in Queensland where contextual information is limited, and show how antecrystic and xenocrystic zircons and monazites can be distinguished. In contrast, where zircons are metamict (for example, high U and Th-rich zircons), much of the ability to discriminate is impacted because such zircons have suffered Pb loss and have modified compositions (e.g., higher T ZircTi ). We recommend an integrated approach incorporating whole-rock chemistry, independent geothermometric constraints, zircon composition, textures and ages obtained by routine cathodoluminescence and LA-ICP-MS or ion microprobe analysis to provide increased confidence for the discrimination of inherited zircons from autocrystic zircons and determination of the emplacement age.

A strongly altered zircon-xenotime intergrowth in pegmatite from the Pilawa Gorna (the Gory Sowie Block, SW Poland) was studied with transmission electron microscopy (TEM) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Distinct domains demonstrate features related to fluid-induced coupled dissolution-reprecipitation processes resulting in microscale to nanoscale porosity in the zircon and in xenotime, and diffusion-reaction processes in the metamict core of the zircon. The inclusions of secondary phases include fluorapatite, unknown layered Fe-silicate, fibrous Fe-oxides, solid solutions of coffinite-thorite and uraninite-thorianite, uraninite and secondary U-rich zircon. The fluid had high concentrations of Ca and Fe, transporting these nonformula elements through the zircon and xenotime structure while mobilizing U, Th and Pb even in robust xenotime, thus forming small inclusions in nanopores. Nanoinclusions of galena in the zircon represent major Pb mobilization that may cause disturbance during U Pb geochronological analysis. The trace element composition of zircon matches patterns typical of altered zircon. The differentiation of geochemical characteristics between the metamict core and the altered rim of zircon implies different alteration mechanisms, with a stronger role of fluids in the alteration of the rim. Nanoscale observations complement trace element microanalysis and serve as an important and necessary tool to further understand the alterations of geochronometers in the presence of alkaline-rich fluid, especially in the complex environments of pegmatites.

Detrital zircon studies can suffer from selective loss of provenance information due to U-Pb age discordance, metamictization, metamorphic overprinting and fluviatile transport processes. The relationship between isotopic composition and zircon grain shape, and how grain shape is modified during transport, is largely unknown. We combine X-ray tomography with U-Pb geochronology to quantify how fluvial transport affects 3-D zircon shape, detrital age signature, and grain density along the Murchison River, whose catchment comprises Eoarchean to Early Paleozoic source rocks in Western Australia. We acquired tomographic volumes and isotopic data from 373 detrital zircons to document changes in size, shape and density in transport direction, and explore how grain shape, age spectra and the proportion of discordant material vary along the channel. Results show that shape characteristics are sensitive to transport distance, stream gradient, proximity to source material, and whether the source consists of primary or recycled zircons. With increasing transport distance, grain lengths decrease more than their widths. Furthermore, the loss of metamict grains occurs at a near constant rate, resulting in a linear increase of mean calculated zircon density by ca. 0.03 g/cm3 per 100 km transport distance. 3-D grain shape is therefore strongly linked to detrital age signature, and mean grain density is a function of the absolute transport distance. 3-D shape characteristics provide valuable information on detrital zircon populations, including the interaction between source materials with fluvial transport processes, which significantly affects preservation bias and, by inference, the representativeness of the sampled data.

The isotopic composition of lead ( 207 Pb/ 206 Pb, 208 Pb/ 206 Pb, and 210 Pb) in a recently formed galena from burning heaps after coal mining in Radvanice, Markousovice, and Rybnicek, the Lower Silesian basin, Czech Republic, was studied in detail. 210 Pb activity in galena varied from 135 ± 9 to 714 ± 22 Bq/g and calculated integral doses ranged from 2.21 × 10 11 to 6.11 × 10 11 α/g. The radioactivity of the galena causes micro-deformations in its crystal structure as indicated by the Williamson-Hall graphs, showing that the level of micro-strain depends on the length of time that galena samples were exposed to the radiation. However, the crystal structure of galena is affected very inhomogenously; according to TEM investigations there are domains of fully crystalline, polycrystalline, and fully metamict galena within one crystal. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to determine the isotopic composition of the studied galena. The stable isotope ratios of Pb varied for 207 Pb/ 206 Pb from 0.8402 to 0.8435 and for 208 Pb/ 206 Pb from 2.0663 to 2.0836. The average ratios 207 Pb/ 206 Pb = 0.8312 and 208 Pb/ 206 Pb = 2.0421 were obtained for coal from the same localities. These isotope ratios show that there is no isotopic fractionation taking place during the coal burning and subsequent galena crystallization from hot gases.

We present a microstructural and Usingle bondPb systematics study comparing pristine, thermally annealed (TA) and chemically abraded (CA) ~ 3500 Ma zircon from a quartz-dioritic gneiss, with the aim to improve pre-analytical workflows for more accurate and precise LA-ICP-MS Usingle bondPb dating of ancient zircon. Four zircon domains are identified: i) low- to medium-U concentric-oscillatory zoned cores, ii-iii) two porous high-U outer alteration domains, and iv) low-U narrow inward growing recrystallization rims. Raman spectroscopy on the pristine zircon reveals a positive correlation between increasing structural damage and U content. The porous high-U outer domains show a drastic increase in non-formula Ca above estimated amorphous fractions of ~ 0.8, which we ascribe to hydrothermal alteration of high-damage zircon characterized by percolating networks of amorphous areas. Upon treatment (TA, CA), hyper-spectral CL and Raman spectroscopy suggest structural recovery of point defects, but not full repair of high-damage amorphous areas. Calculated Raman radiation damage ages suggest that natural annealing affected all domains at ~ 500 Ma, consistent with negligible laser ablation matrix effects comparing pristine and treated cores. We show that reverse discordance in pristine and TA cores is not an analytical artifact. High-U alteration domains are normal discordant and were partially reset at ca. 3410 Ma. Upon CA, Usingle bondPb discordance and scatter are reduced in the cores, yielding intercepts of 3503 ± 14 Ma and 560 ± 550 Ma (MSWD = 1.0). The lower intercept matches the timing of Pb-loss recorded in the alteration domains and the Raman radiation damage age. We argue that short distance Pb redistribution within the cores, which led to reverse discordance, was controlled by Usingle bondPb systematics recording both the crystallization age and the timing of Pb redistribution. Some excess Pb was redistributed from the partially re-set alteration domains into the cores, leading to mixed Usingle bondPb systematics and further reverse discordance. Removal of the latter excess Pb upon CA suggests that radiogenic Pb from the alteration domains accumulated within distinct damage sites accessible for CA leaching. We conclude that standardization of pre-analytical treatment is not recommended; we propose to investigate the structural state of unknown specimen by means of Raman spectroscopy, in combination with commonly applied CL imaging. During LA-ICP-MS analyses, co-measurement of non-formula and selected trace elements is deemed highly valuable in detecting ablations for use in reliable Usingle bondPb age determination.

In the Scotian Basin, offshore eastern Canada, an unusual combination of high heat flow in the Cretaceous and the abundance of halite has resulted in unusual diagenetic minerals such as sphalerite. The Newburn H-23 well is the most distal well in the basin with good core samples and has two previously unknown diagenetic mineral occurrences: fluorine-rich ferroan calcite and diagenetic zircon. This study uses SEM backscattered electron images and EDS analyses, EMP WDS mineral analyses and Raman spectroscopy to determine mineral chemistry and textures to investigate the diagenetic and thermal significance of these minerals. Late diagenetic Fe-calcite contains 1–2.5 wt% fluorine, mostly from adsorption, but rarely as small fluorite crystals. Fluoride is also adsorbed on the surfaces of some framework minerals and chlorite. Fluoride was transported in highly saline formation brines derived from the Argo salt Formation. Zircon grains, 20–40 μm in size, have crystal outlines that are straight adjacent to pores, partially lobate filling porosity, and cross cutting other grains: these may be diagenetic. Some zoned detrital zircon grains show 1–3 μm wide diagenetic outgrowths. Neoformation of diagenetic zircon requires temperatures of >250 °C. Transport of zirconium is favored by ligands in low-pH solution, principally fluoride and phosphate anions, with zirconium mobilized during the alteration of metamict detrital zircon under low-grade metamorphic conditions. The presence of diagenetic sphalerite and the documented mid-Cretaceous thermal event in the Scotian Basin indicate conditions that could have been suitable for the formation of diagenetic zircon in this well. Suitable geological conditions for such diagenetic formation of zircon will be found in a subsiding rift basin with early evaporites that are affected by a subsequent phase of volcanism due to new rifting or subduction.

This work was supported by National Science Centre, Poland, through grant no. PW-0415-003., The preliminary results of 57Fe Mössbauer spectroscopy and X-ray diffraction (XRD) of fully metamict samarskite dated at ~1500 Ma, which absorbed α-dose of 6.5 × 1017 α-decay mg-1, are reported after one-hour annealing at 673, 873, 1173 and 1373 K in argon atmosphere. Metamict minerals contain radioactive elements that degrade their crystal structures over geological time. All the Mössbauer spectra obtained can be fitted to two quadrupole doublets assigned to Fe2+ and Fe3+ in octahedral positions. The relative contribution of Fe2+ (Fe2+/Fe) reaches a minimum of 0.10 at 1173 K., NCN

Magmatic zircon from altered gabbros adjacent to the ∼1.07 Ga Lala Fe-Cu deposit, SW China was modified by NaCl-rich brines related to the Fe-Cu mineralization. The modified zircon grains are composed mostly of both inclusion-free and porous domains, and some grains also have overgrowth/rims. The inclusion-free domains, commonly overgrown by the porous domains, are roughly homogeneous under BSE imaging but display oscillatory or sector zoning under CL imaging. In contrast, the porous domains are distinctly mosaic-like under CL imaging, and contain abundant pores and mineral inclusions such as thorite, xenotime, REE-rich phases, actinolite, albite, biotite and calcite. The inclusion-free domains have concentrations of “non-formula” elements (for example Al, Ca, and Fe) much higher than the magmatic zircon, and are thus interpreted to be products of interaction between magmatic zircon (possibly metamictized) and the fluids via a diffusion-reaction process. However, these resultant domains have retained the Th and U contents, REE patterns, U-Pb ages and Hf isotopes of the precursor, magmatic zircon. On the other hand, the porous domains have stoichiometric end-member compositions (that is lowered Th, U, REE, Y, and P), and given that they are porous and inclusion-rich, we proposed that they have formed from the precursor, element-rich inclusion-free domains or magmatic zircon via a fluid-induced dissolution-reprecipitation process. It is notable that the porous domains retained the 177Hf/176Hf ratios of the precursors, but possess modified and meaningless U-Pb ages. Instead, a meaningful U-Pb age (1006 ± 62 Ma), similar to the timing of the Lala deposit, is well recorded by the overgrowth/rims with distinctly high LREEs (La = 50–700 ppm) and elevated Hf isotopic ratios. Our new results reveal that in the presence of the NaCl-rich brines, the nature of the precursor, magmatic zircon (that is high element budgets and/or metamictization) plays a key role on hydrothermal alteration of zircon.

In ceramic industry, zircon sand is widely used in different applications because zirconia plays a role as common opacifying constituent. In particular, it is used as a basic component of glazes applied to ceramic tiles and sanitary ware as well as an opacifier in unglazed bulk porcelain stoneware. Natural zircon sands are the major source of zirconium minerals for industrial applications. In this paper, long, medium, and short range studies were conducted on zirconium minerals originated from Australia, South Africa, and United States of America using conventional and less conventional techniques (i.e., X-Ray Diffraction (XRD), Positron Annihilation Lifetime Spectroscopy (PALS), and Perturbed Angular Correlations (PAC)) in order to reveal the type and the extension of the regions that constitute the metamict state of zircon sands and themodifications therein produced as a consequence of the industrial milling process and the thermal treatment in the production line. Additionally, HPGe gamma-ray spectroscopy confirms the occurrence of significant levels of natural radioactivity responsible for metamictization in the investigated zircon samples. Results from XRD, PALS, and PAC analysis confirm that the metamict state of zircon is a dispersion of submicron disordered domains in a crystalline matrix of zircon., Facultad de Ciencias Exactas

He+ ion implantation at 4.0 MeV, equivalent to energy of α particles from natural radioactive nuclei 238U and 232Th, has been conducted for undoped synthetic zircon. The cathodoluminescence (CL) of implanted samples was measured to clarify the radiation-induced effects. Unimplanted synthetic zircon shows pronounced and multiple blue emission bands between 310 nm and 380 nm, whereas the implanted samples have an intense yellow band at ~550 nm. The blue emission bands can be assigned to intrinsic defect centers formed during crystal growth. The yellow band should be derived from induced-defect centers by He+ ion implantation, which might be related to the metamicitization originated from a self-induced radiation in natural zircon. The yellow band may be separated into two emission components at 1.96 eV and 2.16 eV. The emission component at 2.16 eV is recognized in both unimplanted and implanted samples, and its intensity increases with an increase in the implantation dose. The CL of zircon can be used as the geodosimeter.

We report the result of a SIMS U–Th–Pb and O–OH study of 44 ancient zircons from the Jack Hills in Western Australia with ages ranging from 4.3 Ga to 3.3 Ga. We have investigated the behaviour of oxygen isotopes and water in the grains by determining δ18O and OH values at a number of locations on the polished surfaces of each grain. We have divided the zircons into five groups on the basis of their U–Th–Pb and OH-oxygen isotopic behaviour. The first group has concordant U–Th–Pb ages, minimal common Pb, δ18O values consistent with zircons derived from mantle source rocks and no detectable OH content. U–Th–Pb systems in zircons from Groups 2, 3 and 4 vary from concordant to extremely discordant where influenced by cracks. Discordia intercepts with concordia at approximately zero Ma age are interpreted as disturbance of the zircon U–Th–Pb systems by weathering solutions during the extensive, deep weathering that has affected the Archean Yilgarn Craton of Western Australia since at least the Permian. Weathering solutions entering cracks have resulted in an influx of Th and U. δ18O values of Group 2 grains fall approximately within the “mantle” range and OH is within background levels or slightly elevated. δ18O values of Group 3 grains are characterised by an initial trend of decreasing δ18O with increasing OH content. With further increase in OH this trend reverses and δ18O becomes heavier with increasing OH. Group 4 grains have a distinct trend of increasing δ18O with increasing OH. These trends are explained in terms of the reaction of percolating water with the metamict zircon structure and appear to be independent of analytical overlap with cracks. Group five zircons are characterised by U–Pb systems that appear to consist of more than one age but show only minor U–Pb discordance. Nevertheless trends in δ18O versus OH in this group of grains resemble trends seen in the other groups. The observed trends of δ18O with OH in the Jack Hills zircons are similar to those reported in a previous study of zircons from an Archean granite from south-western Australia.

International audience; High purity synthetic silica glass (Suprasil F300) samples were densified by High Pressure/High Temperature (HP-HT) using three different pressure/temperature/duration values. Their relaxation process was studied by applying 2.5 MeV electron irradiation with doses varying from 1 MGy up to 11 GGy. At very high dose (11 GGy), all the densified silica samples exhibit the same density value (∼2.26 g/cm3) regardless of the densification conditions, referring to an equilibrium value known as an amorphous silica metamict phase. In detail, the HP-HT silica samples were progressively dedensified from 1 GGy irradiation dose until reaching this equilibrium. Whatever the initial topological disorder revealed through Raman spectra, all silica samples present identical Raman spectra at 11 GGy, with high intensities of D1 and D2 components, attesting they reach one unique silica polymorph. Regarding the irradiation at high temperature (600 MGy, 600 K), the results show that the thermal annealing during irradiation “accelerates” somehow the relaxation kinetics of both macroscopic density and vibrational signature. Furthermore, it seems that such high irradiation temperatures lead to increase the Non-Bridging Oxygen Hole Center point defects generation.The National Network EMIR was acknowledged for supporting the irradiation experiments in SIRIUS (No. 18-6129). The authors would like to thank l'Ecole Polytechnique for the junior postdoctoral grant. DEFI CNRS “Instrumentation aux Limites” was thanked for funding the Ultra-Bragg project.

In situ U–Pb geochronology has been performed via laser ablation inductively coupled mass spectrometry on shocked apatite, titanite and zircon from the ~ 8-km-diameter Lac La Moinerie impact structure, Canada. The three analyzed phases are inherited from target rocks that were transformed to impact melt-bearing breccias and clast-laden impact melts. Apatite yields an array of U–Pb ratios populating a region between a younger regression with a refined age of 453 ± 5 Ma, and an older regression with a lower intercept age of 1708 ± 10 Ma. Titanite defines a younger regression with an age of 444 ± 15 Ma, and an older array with a lower intercept at 1844 ± 24 Ma. Zircon yields an upper intercept age of 1810 ± 13 Ma and a lower intercept age of 433 ± 21 Ma, within error of apatite and titanite. The oldest ages from all three phases define Paleoproterozoic igneous–metamorphic events in granitoid target rocks of the De Pas Suite. Isotopic resetting in apatite and titanite, with relatively high Pb-diffusion rates, was controlled by a combination of proximity to impact-generated superheated melt and the formation of fast diffusion pathways facilitated by shock effects and dynamic recrystallization. Zircon resetting was controlled by shock effects and metamictization, which resulted in significant Pb loss. We outline an approach for discriminating ‘true’ impact ages from metamict zircons with high common Pb that have experienced post-impact Pb loss. Lower intercept ages of all phases constrain the age of formation for the Lac La Moinerie impact structure, with apatite yielding the most precise age of 453 ± 5 Ma. With an age of 453 Ma, Lac La Moinerie joins a growing cluster of more than 12 terrestrial impact structures formed in the Middle-to-Late Ordovician, with potential connection to the L-chondrite parent body breakup event and a period of enhanced bombardment on Earth.