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Detrital zircon U-Pb studies of mudstone provenance are rare but may preferentially fingerprint distal zircon sources. To examine this issue, Pierre Shale and Trinidad Sandstone deposited in a Late Cretaceous deltaic environment in the Raton Basin, Colorado (USA), were measured for detrital zircon U-Pb age by laser ablation–inductively coupled plasma–mass spectrometry. Two major detrital zircon age peaks at ca. 70 and 1690 Ma are found in both Pierre Shale and Trinidad Sandstone but in inversely varying proportions: 68% and 16%, respectively, for the finest zircon fraction (~15–35 μm) in the shale, and 25% and 32%, respectively, for the coarsest zircon fraction (~60–80 μm) in the sandstone. Proximal sources in the Sangre de Cristo Mountains, directly west of the Raton Basin, contain coarse-grained, ca. 1690 Ma zircon, whereas distal sources in Laramide uplifts and basins in Colorado, New Mexico, and Arizona contain fine-grained, ca. 70 Ma zircon. The results indicate that U-Pb zircon provenance of mudstone reflects availability of volcanic and other fine-grained source rocks rather than simply distal sources. U-Pb zircon provenance studies should routinely include mudstone units because these units may identify fine-grained zircon sources more reliably than sandstones alone.

A number of hydrocarbon discoveries have been made recently in the Flemish Pass Basin and Central Ridge, offshore Newfoundland, Canada, but there is only limited geological information available. The primary goal of this study was to determine the sedimentary provenance and paleodrainage patterns of mudstones and sandstones from the Upper Jurassic Rankin Formation, including the Upper and Lower Kimmeridgian Source Rock (organic-rich shale) members and Upper and Lower Tempest Sandstone Member reservoirs, in this area. A combination of heavy mineral analysis, whole-rock geochemistry and detrital zircon U-Pb geochronology was determined from cores and cuttings from four offshore wells in an attempt to decipher provenance. Detrital heavy minerals in 20 cuttings samples from the studied geologic units are dominated by either rutile + zircon + apatite ± chromite or rutile + apatite + tourmaline, with minor zircon, indicating diverse source lithologies. Whole rock Zr-Th-Sc trends suggest significant zircon recycling in both mudstones and sandstones. Detrital zircon U-Pb ages were determined in two mudstone and four sandstone samples from the four wells. Five major U-Pb age groups of grains were found: A Late Jurassic group that represents an unknown source of syn-sedimentary magmatism, a Permian–Carboniferous age group which is interpreted to be derived from Iberia, a Cambrian–Devonian group derived from the Central Mobile Belt of the Newfoundland–Ireland conjugate margin, and two older age groups (late Neoproterozoic and &gt, 1 Ga) linked to Avalonia. The Iberian detritus is abundant in the Central Ridge and southern Flemish Pass region and units containing sizable populations of these grains are interpreted to be derived from the east whereas units lacking this population are interpreted to be sourced from the northeast and possibly also the west. The Upper Tempest Sandstone contains Mesozoic zircons, which constrain the depositional age of this unit to be no older than Late Tithonian.

Use of small spots (≤20 μm) for laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb zircon geochronology is of increasing interest in the Earth sciences because the temporal record of geologic processes is often preserved on a fine scale within zircon grains. However, the systematic biases and external sources of uncertainty of U–Pb ages is poorly defined when measured on small spots by LA-ICP-single-collector-sector-field (SF)-MS instrumentation. This study addresses the accuracy and precision for small spots and specifically the extent to which short ablation times limit Pb/U Down-Hole Fractionation (DHF), which largely controls the accuracy of the U–Pb ages. Six zircon reference materials (91500, FC-1, R33, Temora 2, Plesovice, and Fish Canyon Tuff) were measured on spot sizes of 20, 15, 10, and 7 μm diameter. Laser fluence was increased from 3 to 6 J cm−2 with decreasing spot size to compensate partially for decreasing U and Pb signals. 91500 zircon was the calibration reference material. Raw count rate data were processed using Iolite version 3.63 software with the U–Pb common approach data reduction scheme and smoothed cubic spline DHF correction model. Samples were ablated for 30 seconds and results processed for the first 28, 15, 10, and 7 seconds of ablation (masking the initial 2 seconds) in order to assess the accuracy and precision of U–Pb ages as a function of ablation time. Measured 206Pb/238U ratios for the six zircon reference materials increase steadily with ablation time, reflecting DHF, but exhibit somewhat different patterns of increase for different zircons, producing the major source of uncertainty for the U–Pb ages. A secondary source of uncertainty is differences between the 206Pb/238U (normalized to their accepted values) for different zircons near the start of ablation, which may reflect matrix-dependent instrumental mass bias in the ICP. Nonetheless, processing data from only the first 10 to 15 seconds of ablation (50 to 75 laser pulses) restricts the extent of DHF and time-resolved Pb/U variations between different zircons to a sufficient degree to give concordant U–Pb ages on 20 to 7 μm spots that are accurate and precise to better than 1.4% using LA-ICP-single-collector-SF-MS instrumentation.

This GGR biennial critical review covers developments and innovations in key analytical methods published since January 2014, relevant to the chemical, isotopic and crystallographic characterisation of geological and environmental materials. In nine selected analytical fields, publications considered to be of wide significance are summarised, background information is provided and their importance evaluated. In addition to instrumental technologies, this review also presents a summary of new developments in the preparation and characterisation of rock, microanalytical and isotopic reference materials, including a précis of recent changes and revisions to ISO guidelines for reference material characterisation and reporting. Selected reports are provided of isotope ratio analyses by both solution-nebulisation MC-ICP-MS and laser ablation-ICP-MS, as well as of radioactive isotope geochronology by LA-ICP-MS. Most of the analytical techniques elaborated continue to provide new applications for geochemical analysis, however it is noted that instrumental neutron activation analysis has become less popular in recent years, mostly due to the reduced availability of nuclear reactors to act as a neutron source. Many of the newer applications reported here provide analysis at increasingly finer resolution. Examples include atom probe tomography, a very sensitive method providing atomic scale information, nanoscale SIMS, for isotopic imaging of geological and biological samples, and micro-XRF, which has a spatial resolution many orders of magnitude smaller than conventional XRF.

Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) has been used for more than 30 years to determine the elemental composition of natural and synthesized objects. A focused laser beam ablates a small volume of target material, and the aerosol produced is transferred in a gas stream to an ICP–MS for elemental and/or isotopic analysis. Through the increasing use of deep ultraviolet lasers and ultra-sensitive mass spectrometers, the technique has evolved towards higher sampling resolution and to generating 2-D (and 3-D) images of compositional variations. The future is likely to see femtosecond lasers and simultaneous mass spectrometers in common use, making new research areas possible.

Sedimentary basins provide an archive of magmatic and tectonic events in their detrital zircon record, which can be dated and coupled with Hf isotopic data to reveal secular changes in the production of juvenile and evolved magmatism and track the history of orogenic events. The Rae craton, which forms a substantial portion of the northern Canadian Shield, experienced successive orogenic events along its margins during most of the Paleoproterozoic Era. Yet, some of these orogenic events are poorly defined and their details remain controversial. We present coupled detrital zircon U–Pb age and e Hf data from Paleoproterozoic metasedimentary successions of the eastern Rae craton. The zircon preserve an archive of ∼600 million yr of magmatic and tectonic history on the Rae craton and its periphery. The U–Pb and Hf isotopic data indicate that zircon provenance was dominantly from the northern and western Rae craton, where magmatic and tectonic activity was focused during the ∼2.5 to 2.3 Ga Arrowsmith orogeny and the ∼2.0 to ∼1.93 Ga Taltson and Thelon events. Our detrital zircon dataset holds a more complete record of these Proterozoic orogenic events than is currently defined from known and dated crustal rocks on the Rae craton and shows that juvenile magmatism is more common than current models for either event suggest. Notably, an inverted U or horseshoe-shaped e Hf array (−15.5 to +5.0) in our zircon dataset reflects a Wilson cycle that began in the earliest Paleoproterozoic on the Rae craton.

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.

The Ming deposit in the northwestern Canadian Appalachians is a metamorphosed, bimodal-mafic, precious-metal (Au, Ag)-bearing and Cu-rich volcanogenic massive sulfide (VMS) deposit consisting of several, spatially proximal lenses in a sericite- to chlorite-altered rhyodacitic footwall. The various lenses (1807 Zone, 1806 Zone, Ming South Up Plunge, Ming South Down Plunge, and the Lower Footwall Zone) have variations in Cu, Au, Ag, and Zn grades that reflect varying physico-chemical conditions of ore formation. This study describes the complex ore mineralogy of the orebodies and constrains the genesis of the deposit using field methods, mineralogy, whole rock sulfide geochemistry, and micro-analytical methods. The orebodies are predominantly pyrite, chalcopyrite, with lesser sphalerite, pyrrhotite, and trace galena and arsenopyrite, with the exception of the Lower Footwall Zone, which consists of a high temperature (> 320 °C) chalcopyrite–pyrrhotite–pyrite ± cubanite assemblage. The other orebodies (1806, 1807, Ming South Up Plunge and Down Plunge) contain trace amounts of tellurides (hessite, altaite, tsumoite, unnamed bismuthtelluride), sulfosalts (Ag-poor and Ag-rich tennantite–tetrahedrite, meneghinite, AgSb phases, stannite), and precious metal phases (electrum, AgHg ± Au alloys). The 1807 Zone is enriched in Te, Bi, and Se, whereas the 1806 Zone is telluride-free and contains As, Sb, Hg, Au, and Ag. Mineral chemistry of sphalerite shows strong variations in Fe content (1.12–11.04 wt.%). Intermediate Fe (4.33–6.33 wt.% Fe) and Fe-rich (7.327–11.04 wt.% Fe) sphalerite are common in all orebodies, whereas Fe-poor sphalerite (1.12–3.57 wt.% Fe) occurs exclusively in the 1807 and 1806 zones. Tennantite-tetrahedrite is typically Ag-poor (0.25–2.19 wt.%) in the 1807 Zone, but is significantly enriched in Ag (up to 29.3 wt.%) in the 1806 Zone. Galena in the 1807 Zone and Ming South orebodies is commonly myrmekitically intergrown with tellurides and has high concentrations of Te, Bi, Se, and Ag. In contrast, galena in the 1806 Zone is less enriched in Te, Bi, and Se, but high in Ag. Variations in mineralogy, epithermal elements (As, Bi, Hg, Sb, Se, Sn, Te) and precious metal (Ag, Au) content, and mineral chemistry between the different orebodies indicate that they were formed from predominantly reduced, acidic hydrothermal fluids with varying ƒTe2/ƒS2, ƒSe2/ƒS2, and mBi/mSb ratios as temperatures steadily decreased from > 300 °C to

Sixteen nonporphyritic chondrules and chondrule fragments were studied inpolished thin and thick sections in two enstatite chondrites (ECs): twelve objects fromunequilibrated EH3 Sahara 97158 and four objects from equilibrated EH4 Indarch. Bulkmajor element analyses, obtained with electron microprobe analysis (EMPA) and analyticalscanning electron microscopy (ASEM), as well as bulk lithophile trace element analyses,determined by laser ablation inductively coupled plasma?mass spectrometry (LA-ICP-MS),show that volatile components (K2O + Na2O versus Al2O3) scatter roughly around the CIline, indicating equilibration with the chondritic reservoir. All lithophile trace elementabundances in the chondrules from Sahara 97158 and Indarch are within the range ofprevious analyses of nonporphyritic chondrules in unequilibrated ordinary chondrites(UOCs). The unfractionated (solar-like) Yb/Ce ratio of the studied objects and the mostlyunfractionated refractory lithophile trace element (RLTE) abundance patterns indicate anorigin by direct condensation. However, the objects possess subchondritic CaO/Al2O3 ratios;superchondritic (Sahara 97158) and subchondritic (Indarch) Yb/Sc ratios; and chondriticnormalizeddeficits in Nb, Ti, V, and Mn relative to RLTEs. This suggests a unique nebularprocess for the origin of these ECs, involving elemental fractionation of the solar gas by theremoval of oldhamite, niningerite, and/or another phase prior to chondrule condensation. Alayered chondrule in Sahara 97158 is strongly depleted in Nb in the core compared to therim, suggesting that the solar gas was heterogeneous on the time scales of chondruleformation. Late stage metasomatic events produced the compositional diversity of thestudied objects by addition of moderately volatile and volatile elements. In the equilibratedIndarch chondrules, this late process has been further disturbed, possibly by apostaccretional process (diffusion?) that preferentially mobilized Rb with respect to Cs inthe studied objects. Fil: Varela, Maria Eugenia. Consejo Nacional de Investigaciones Cienti­ficas y Tecnicas. Centro Cientifico Tecnologico San Juan. Instituto de Ciencias Astronomicas de la Tierra y del Espacio; Argentina Fil: Sylvester, P.. Memorial University Of Newfoundland; Canadá Fil: Brandstätter, F.. Naturhistorisches Museum. Mineralogisch-Petrographische Abteilung; Austria Fil: Engler, A.. University of Graz. Department of Mineralogy and Petrology. Institute of Earth Sciences; Austria

We carried out an integrated rock magnetic and paleomagnetic study of the ∼36 Ma Mistastin Lake (Labrador, Canada) meteorite impact structure in order to investigate whether energy from the collision influenced the geodynamo and to assess the effects of shock on the magnetic properties of the target basement rocks. Stepwise demagnetization of 114 specimens isolates a well-defined magnetization component throughout the crater whose overall mean deviates slightly from the expected direction for North America at the time of impact. Paleointensity results from seven samples meeting stringent selection criteria show no significant difference with a global compilation from 40 to 30 Ma. The combined results, including those from a ∼80 m-thick profile of an impact melt unit (Discovery Hill), lend no support that the impact caused an aberration of the geodynamo within a few centuries of a bolide collision that created the ∼28 km-diameter crater. Both titanium-rich and titanium-poor titanomagnetite carry the magnetic remanence in the impact melt rocks; their relative proportions, compositions and domain states are cooling rate dependent. Magnetic hysteresis parameters of the magnetite-bearing anorthositic basement rocks reveal systematic changes as a function of distance from the crater's center with an increasing prevalence of single domain-like grains toward the center. Changes with radial distance are also found in the character of the Verwey transition in magnetite. Basement rocks were thermally overprinted when lying less than a meter from the impact melt rocks; Mesoproterozoic basement rocks more than a meter below the impact melt rocks hold similar magnetization directions to those expected from a 1500 Ma result for Laurentia. No evidence exists that shock heating of the basement rocks exceeded 200 °C at distances of 6–7 km from the crater's center.

Avalonia, the largest accreted crustal block in the Appalachian orogen, consists of Neoproterozoic magmatic arc sequences that represent protracted and episodic subduction-related magmatism before deposition of an Ediacaran–Ordovician cover sequence including siliciclastic rocks. Zircon crystals were obtained from arc-related magmatic rocks and from clastic sedimentary sequences and analyzed in situ for their Hf-isotope composition. The majority of magmatic and detrital zircons are dominated by initial 176Hf/177Hf values that are more radiogenic than chondritic uniform reservoir (CHUR) with calculated crust formation Hf–TDM model ages that range from 0.84 to 1.30 Ga. These results suggest formation by partial melting of juvenile mantle in a Neoproterozoic continental arc. Some zircons have Hf–TDM model ages ca. 1.39–3.09 Ga with εHf values of –33.9 to –0.5 and more clearly indicate involvement of older lithosphere in their petrogenesis. Whole-rock Sm–Nd isotopic compositions from felsic volcanic rocks are characterized by positive initial εNd values with Mesoproterozoic depleted mantle model ages consistent with juvenile extraction. Results suggest a dominant mantle component with long-term light rare earth element (LREE) depletion mixed with an older crustal component with long-term LREE enrichment. The pattern of TDM model ages and variations in Lu–Hf and Sm–Nd isotopic character are compatible with a ca. 1.0–1.2 Ga igneous tectonomagmatic event that formed basement to Neoproterozoic magmatic arcs in Avalonia. The presence of evolved isotopic signatures, however, indicates that significant older Proterozoic crust is present locally beneath Avalonia, suggesting that Avalonia formed in a single Neoproterozoic arc system that generated juvenile mantle-derived crust, coupled with lesser anatectic reworking of significantly older crust.

The Ming deposit, Baie Verte, Newfoundland, Canada, is an Early Ordovician bimodal-mafic, Cu-Au-(Zn-Ag) volcanogenic massive sulfide (VMS) deposit. The deposit consists of a number of ore lenses that are stacked in the uppermost part of the Rambler rhyolite. One of the uppermost lenses, the 1806 zone, is enriched in Au and Ag. The deposit has been affected by Silurian-Devonian greenschist to amphibolite grade metamorphism and polyphase deformation and this has led to debates as to whether the Au-Ag enrichment in the deposit is syngenetic or a product of a later metamorphic and structural overprint. The 1806 zone consists predominantly of discordant sulfide stringer, stratabound semimassive to massive sulfides and a weakly mineralized silicified cap zone. The ore is largely hosted within the footwall Rambler rhyolite that is strongly altered to quartz-sericite ± green mica with sporadic chlorite-biotite. Base and precious metal zoning is developed from the down-plunge portion (Cu-Au) to the up-plunge portion (Cu-Zn-Au-Ag-Pb) of the 1806 zone. The ore mineralogy and mineral chemistry are complex and are interpreted to be of an intermediate sulfidation type. Pyrite and chalcopyrite are the dominant sulfide species with minor to accessory sphalerite, galena, pyrrhotite, and arsenopyrite. Sulfosalts including Ag-bearing tennantite-tetrahedrite, stannite, boulangerite, and loellingite, and precious metal-rich phases are common throughout the deposit. Precious metals occur as (1) mercurian electrum (7.93–20.57 wt % Hg) and (2) various Ag phases (miargyrite, pyrargyrite, mercurian stephanite, unnamed AgCuFeS phase, Ag-Hg ± Au alloys) that are more abundant in the up-plunge portion of the 1806 zone. Tellurides and bismuthides are present in trace amounts. Oxides (cassiterite and magnetite) are present exclusively in the down-plunge portion of the 1806 zone. The deposit geometry, metals distribution, complex ore assemblages, abundant sulfosalts, and the significant concentration of the epithermal suite of elements (e.g., Au, Ag, As, Hg, Sb, Bi) in the ore strongly contrast with those of orogenic Au deposits and support a syngenetic or synvolcanic origin for precious metals in the Ming VMS deposit, including a possible magmatic input into the 1806 zone ore-forming system. Evidence for a late, syndeformation precious metal emplacement via orogenic overprinting is lacking at the 1806 zone and all data point to a syngenetic origin for precious metal enrichment, indicating that Ordovician Appalachian VMS deposits are favorable targets for Au. Nevertheless, Silurian-Devonian metamorphism and deformation have resulted in textural recrystallization and local remobilization of precious metals and the main fabrics largely control the current geometry of the host succession and of the Ming orebody.

Despite several decades of research on growth of the continental crust, it remains unclear whether the production of juvenile continental crust has been continuous or episodic throughout the Precambrian. Models for episodic crustal growth have gained traction recently through compilations of global U–Pb zircon age frequency distributions interpreted to delineate peaks and lulls in crustal growth through geologic time. One such apparent trough in zircon age frequency distributions between ∼2.45 and 2.22 Ga is thought to represent a pause in crustal addition, resulting from a global shutdown of magmatic and tectonic processes. The ∼2.45–2.22 Ga magmatic shutdown model envisions a causal relationship between the cessation of plate tectonics and accumulation of atmospheric oxygen over the same period. Here, we present new coupled U–Pb, Hf, and O isotope data for detrital and magmatic zircon from the western Churchill Province and Trans-Hudson orogen of Canada, covering an area of approximately 1.3 million km2, that demonstrate significant juvenile crustal production during the ∼2.45–2.22 Ga time interval, and thereby argue against the magmatic shutdown hypothesis. Our data is corroborated by literature data showing an extensive 2.22–2.45 Ga record in both detrital and magmatic rocks on every continent, and suggests that the operation of plate tectonics continued throughout the early Paleoproterozoic, while atmospheric oxygen rose over the same time interval. We argue that uninterrupted plate tectonics between ∼2.45 and 2.22 Ga would have contributed to efficient burial of organic matter and sedimentary pyrite, and the consequent rise in atmospheric oxygen documented for this time interval.

The Camamu basin is related to the breakup of Gondwana and belongs to the group of sedimentary basins that are part of the eastern Brazilian passive margin. We have determined the provenance of the precursor sediments by investigating the petrography of fluvial and eolian units from the early-rift Brotas Group and syn-rift Almada Group, coupled to in situ laser ablation MC-ICPMS U–Pb and Lu–Hf isotopic analyses of the detrital zircon grains. Detrital zircon grains from the Sergi Formation, Brotas Group, have a main population of U–Pb ages of 480–600 Ma with smaller populations of ages of 900–1000 Ma, 1900–2100 Ma, 2500–2800 Ma and 3000–3200 Ma. The Almada Group zircon grains are characterized by a distribution of ages predominantly in the Paleoproterozoic and Archean. The Hf T DM model ages of the Brotas and Almada Group zircon grains range from ca. 1.1 to 4.0 Ga, and the e Hf (t) values vary from − 31.4 to + 9.6, providing evidence that some detrital zircon grains in the Camamu Basin were derived from juvenile sources but that the majority have reworked crustal sources or formed from juvenile magmatic rocks that were contaminated by older crustal material. Whole rock Sm–Nd isotope data collected previously are largely consistent with the new U–Pb, Lu–Hf zircon data but do suggest that zircon-poor detritus from the Neoproterozoic to Eopaleozoic Brasiliano Aracuai-West Congo Belt contributed to particularly the Brotas Group sediments more than would be indicated by the zircon data alone. Thus, integrated petrographic, U–Pb, Lu–Hf zircon and Sm–Nd whole rock studies provide very important clues to the provenance history of the initial sedimentation on Camamu basin passive margin, where the early-rift phase is marked by the input of detritus from the Aracuai-West Congo belt situated south of the basin, whereas syn-rift sedimentation received major contributions from Paleoproterozoic (Transmazonian cycle) to Archean (Jequie cycle) Sao Francisco craton units, located to the west.

Inter-laboratory comparison of laser ablation ICP-MS and SIMS U-Pb dating of synthetic detrital zircon samples provides an insight into the state-of-the art of sedimentary provenance studies. Here, we report results obtained from ten laboratories that routinely perform this type of work. The achieved level of bias was mostly within ± 2% relative to the ID-TIMS U-Pb ages of zircons in the detrital sample, and the variation is likely to be attributed to variable Pb/U elemental fractionation due to zircon matrix differences between the samples and the reference materials used for standardisation. It has been determined that ~ 5% age difference between adjacent age peaks is currently at the limit of what can be routinely resolved by the in situ dating of detrital zircon samples. Precision of individual zircon age determination mostly reflects the data reduction and procedures of measurement uncertainty propagation, and it is largely independent of the instrumentation, analytical technique and reference samples used for standardisation. All laboratories showed a bias towards selection of larger zircon grains for analysis. The experiment confirms the previously published estimates of the minimum number of grains that have to be analysed in order to detect minor zircon age populations in detrital samples. Une comparaison inter-laboratoires de datation U-Pb d'echantillons de zircons detritiques de synthese par les methodes d'ablation laser ICP-MS et SIMS donne un apercu de l'etat de l'art des etudes de provenance sedimentaire. Nous presentons ici les resultats obtenus par dix laboratoires qui effectuent regulierement ce type de travail. Le niveau de biais atteint etait compris dans l'intervalle ± 2% par rapport aux âges U-Pb ID-TIMS des zircons de l'echantillon detritique et la variation peut certainement etre attribue a un fractionnement elementaire Pb/U variable relie a des differences de matrices entre les zircons des echantillons et les zircons de reference utilises pour la normalisation. Il a ete determine qu'environ 5% de difference d'âge entre les pics d'âge adjacents est actuellement a la limite de ce qui peut etre resolu en mode routine par la datation in situ d'echantillons de zircons detritiques. La precision de la determination de l'âge de zircon individuel reflete principalement la reduction des donnees et les procedures de mesure de la propagation de l'incertitude, et elle est largement independante de l'instrumentation, de la technique d'analyse et des echantillons de reference utilises pour la standardisation. Tous les laboratoires ont montre un biais vers la selection des plus gros grains de zircon pour l'analyse. L'experience confirme les estimations precedemment publiees sur le nombre minimum de grains qui doivent etre analyses afin de detecter les populations mineures d'âge de zircons dans les echantillons detritiques.

The platinum-group elements (PGE) are exceptional tracers of planetary differentiation and therefore are useful discriminants of different high-temperature processes. Many of the initial efforts to understand how PGE behave during mantle melting involved experiments where PGE solubility in silicate melt was measured. The results of these experiments showed that PGE dissolve in silicate melts as oxide species, and that their saturation depends on oxygen partial pressure (pO 2 ). However, the majority of these experimental studies were conducted on FeO and sulfur-free melt compositions that little resemble natural magmas. In particular, the role of sulfur has been downplayed because of its lower availability as a ligand to the PGE in silicate melt when compared to oxygen. However, magmatic sulfides from oceanic basalts and layered intrusions are greatly enriched in the PGE relative to the silicate melts in equilibrium with them, suggesting that the PGE are strongly chalcophile. The question then is whether the PGE are actively scavenged into sulfide melt after it exsolves from a silicate melt; or if the PGE are already associated with S 2− in a silicate melt prior to sulfide saturation. Here we report the results of experiments where the solubilities of Ru and Pd have been measured in natural picritic melt, as a function of pO 2 and in the presence of sulfur. Results show that the presence of sulfur in the silicate melt enhances the solubility of Ru in picrite by over an order of magnitude. These results can be used to quantify the preference that PGE have to associate with sulfur relative to oxygen. For example, Ru was found to be 880 ± 410 times more likely to associate with sulfur than with oxygen at pO 2 around the fayalite–magnetite–quartz redox equilibrium. The preferential association of the PGE with S 2− ligand indicates that once a sulfide melt exsolves, it will already be enriched in PGE precluding the need for it to actively scavenge PGE from a silicate melt.

The Sittampundi Anorthosite Complex (SAC) in southern India is one of the well exposed Archean layered anorthosite-gabbro-ultramafic rock associations. Here we present high precision geochemical data for the various units of SAC, coupled with zircon U-Pb geochronology and Hf isotopic data for the anorthosite. The zircon ages define two populations, the older yield a concordia age of 2541 ± 13 Ma, which is interpreted as the best estimate of the magmatic crystallization age for the Sittampundi anorthosite. A high-grade metamorphic event at 2461 ± 15 Ma is suggested by the upper intercept age of the younger zircon population. A Neoproterozoic event at 715 ± 180 Ma resulted in Pb loss from some of the metamorphic zircons. The magmatic age of the anorthosite correlates well with the timing of crystallization of the arc-related ~ 2530 Ma magmatic charnockites in the adjacent Salem Block, while the metamorphic age is synchronous with the regional metamorphic event. The geochemical data suggest that the rocks were derived from a depleted mantle source. Sub-arc mantle metasomatism of slab derived fluids and subsequent partial melting produced hydrous, aluminous basalt magma. The magma fractionated at depth to produce a variety of high-alumina basalt compositions, from which the anorthositic complex with its chromite-rich and amphibole-rich layers formed as cumulates within the magma chamber of a supra-subduction zone arc. The coherent initial176Hf/177Hf ratios and positive eHf values (1.7 – 4.5) of the magmatic zircons in the anorthosite are consistent with derivation of a rather homogeneous juvenile parent magma from a depleted mantle source. Our study further confirms that the southern part of the Dharwar Craton was an active convergent margin during the Neoarchean with the generation and emplacement of suprasubduction zone arc magmas which played a significant role in continental growth.

U–Pb zircon SHRIMP geochronology and Lu–Hf zircon LA–MC–ICPMS isotope geochemistry are used to constrain the ages of Paleoproterozoic felsic magmatism and their crustal sources in the Aillik Group, Makkovik Province of Labrador. This information is important for understanding the extent of crustal reworking vs. juvenile crustal growth in subduction-related magmatism during the Paleoproterozoic and improves framework knowledge for uranium exploration in the Central Mineral Belt of Labrador. U–Pb SHRIMP zircon geochronology from four felsic tuff samples collected from two different areas of the Aillik Group yield magmatic 207Pb/206Pb ages of 1852 ± 7 Ma (2σ), 1854 ± 7 Ma (2σ), 1861 ± 7 Ma (2σ), and 1862 ± 7 Ma (2σ). The ages fall within the range of previous U–Pb zircon dates reported for felsic volcanic rocks of the Aillik Group. Altogether these dates indicate that felsic volcanism spanned at least 30 m.y. and was perhaps most intense during the last 10 m.y. of that interval. A foliated syn-deformational monzogranite in the Aillik Group (Cross Lake granite) yields a 207Pb/206Pb zircon date of 1805 ± 6 Ma (2σ), which indicates that development of a pervasive planar fabric associated with northwestward thrusting of the Aillik Group continued after this time. Initial e H f s t values for magmatic zircons from the four felsic tuffs (−4.8 to −1.9, −1.7 to +2.2, −11.8 to +3.8, −9.0 to −4.6) and monzogranite (−4.8 to −1.5) exhibit significant variability, which indicates heterogeneous sources. Most of the zircon grains have negative initial e H f s t values and calculated crust formation Hf-isotope TDM model ages point to substantial contributions from melts of ancient crust, ranging in age from ca. 2200 to 2900 m.y. and clustering at ca. 2500 m.y. Inherited zircon grains in the felsic tuffs and monzogranite, mainly have U–Pb ages of ca. 1880–1920 Ma, though others are older, up to ca. 2743 Ma. Hf-isotope TDM model ages for the inherited zircons are similar to those of the magmatic zircons. The Hf-isotope results indicate that subduction-related felsic magmatism in the Makkovik Orogen involved significant crustal reworking (∼80%) during formation of the Aillik Group.

Fil: Varela, Maria Eugenia. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - San Juan. Instituto de Ciencias Astronomicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronomicas, de la Tierra y del Espacio; Argentina

Isotopic analyses of ancient mantle-derived magmatic rocks are used to trace the geochemical evolution of the Earth’s mantle, but it is often difficult to determine their primary, initial isotope ratios due to the detrimental effects of metamorphism and secondary alteration. We present in situ analyses by LA-MC-ICPMS for the Pb isotopic compositions of igneous plagioclase (An75–89) megacrysts and the Hf isotopic compositions of BSE-imaged domains of zircon grains from two mantle-derived anorthosite complexes from south West Greenland, Fiskenaesset and Nunataarsuk, which represent two of the best-preserved Archean anorthosites in the world. In situ LA-ICPMS U–Pb geochronology of the zircon grains suggests that the minimum crystallization age of the Fiskenaesset complex is 2,936 ± 13 Ma (2σ, MSWD = 1.5) and the Nunataarsuk complex is 2,914 ± 6.9 Ma (2σ, MSWD = 2.0). Initial Hf isotopic compositions of zircon grains from both anorthosite complexes fall between depleted mantle and a less radiogenic crustal source with a total range up to 5 eHf units. In terms of Pb isotopic compositions of plagioclase, both anorthosite complexes share a depleted mantle end member yet their Pb isotopic compositions diverge in opposite directions from this point: Fiskenaesset toward a high-μ, more radiogenic Pb, crustal composition and Nunataarsuk toward low-μ, less radiogenic Pb, crustal composition. By using Hf isotopes in zircon in conjunction with Pb isotopes in plagioclase, we are able to constrain both the timing of mantle extraction of the crustal end member and its composition. At Fiskenaesset, the depleted mantle melt interacted with an Eoarchean (~3,700 Ma) mafic crust with a maximum 176Lu/177Hf ~0.028. At Nunataarsuk, the depleted mantle melt interacted with a Hadean (~4,200 Ma) mafic crust with a maximum 176Lu/177Hf ~0.0315. Evidence from both anorthosite complexes provides support for the long-term survival of ancient mafic crusts that, although unidentified at the surface to date, could still be present within the Fiskenaesset and Nunataarsuk regions.

The Voisey’s Bay Ovoid Ni–Cu–Co magmatic sulfide deposit, Labrador, is generally poor in precious metals (Pt, Pd, Ag, Au), but unusual occurrences with elevated levels (Pt + Pd > 0.5 ppm) are present. We present a quantitative description of the precious-metal mineralogy of four such occurrences within massive sulfides. The four samples, all from near the center of the Ovoid, were examined by SEM-based Mineral Liberation Analysis for characterization of precious-metal minerals. Distributions of precious metals among the major sulfide minerals were estimated using mass-balance calculations based on bulk assays of the samples and the proportions and compositions of the minerals. The results indicate that the majority of precious metals are present as discrete mineral phases including sperrylite, froodite, michenerite, Au–Ag alloy, volynskite, stutzite and acanthite, whereas minor to moderate amounts of Pt, Pd, Ag and Au are found in solid solution in pyrrhotite, pentlandite, chalcopyrite and galena. The precious-metal minerals are normally associated with pentlandite, galena, chalcopyrite, pyrrhotite and magnetite, and rarely with breithauptite (NiSb), altaite (PbTe), other precious-metal minerals and native bismuth. With the exception of sperrylite, which is coarse grained and liberated easily by electric pulse disaggregation, the precious-metal minerals are most commonly found as fine inclusions in pentlandite and galena, and less so as larger attachments. The associations are consistent with previously reported precious-metal mineral data from a hornblende gabbro dyke of the Southeast Extension Zone at Voisey’s Bay, demonstrating similar modes of crystallization, which are likely related to crystallization of a highly differentiated sulfide magma in both areas. Processing of Pt from sperrylite and perhaps Pd from froodite could be achieved in ores with a mineralogy similar to the samples described here by grinding, and gravity or flotation methods, but the Au–Ag alloy, volynskite and stutzite would likely be too fine to recover as discrete grains for Ag and Au concentration. Instead, the Ag and Au could be recovered as a by-product of Ni–Cu–Co processing of the pentlandite and chalcopyrite, which are the major hosts of the Ag and Au minerals.

Upper Jurassic to Lower Cretaceous synrift sandstones from two industry exploratory wells in the Flemish Pass Basin were studied for provenance using heavy mineral proxies. These sandstones were deposited during the North Atlantic rifting stage, at which time rifting intensified between Iberia and the Grand Banks. Several heavy mineral methods were used, including in-situ U-Pb geochronology and morphological and chemical analysis of detrital zircons, chemical discrimination of detrital tourmalines, and heavy mineral ratios.Clastic bed-load material entering the northern Flemish Pass Basin during the Tithonian to Berriasian was connected to transport systems reaching west, as far as 400 to 500 km (249–311 mi). Source areas to the west included igneous rocks and associated cover sequences of the Avalon zone, as well as the magmatic rocks, metasedimentary rocks, and associated cover sequences present in the Central mobile belt. The eastward-directed input of bed-load material into the basin is considered to have resulted in the concentration of sandstone units along its western margin, with deteriorating reservoir grade toward the east. Given the regional extent of drainage systems, it is likely that similar constraints apply to equivalent sandstones in the adjacent East Orphan Basin.By the Valanginian–Barremian, paleodrainage orientations had switched and bed-load material began to enter the Flemish Pass Basin from more proximal areas to the southeast with the Avalon zone basement.Overall, no evidence exists to support sediment sourcing from the Iberian margin or the Flemish Cap-Galicia Bank continental fragment to the east, and material from these areas is instead interpreted to have been shed into the incipient Atlantic Ocean or Bay of Biscay. Also, no evidence exists to support sourcing from Grenville basement farther to the west, implying that a drainage divide may have existed somewhere between central and western Newfoundland, west of which material was presumably being transported to the south or southwest.

An improved method for precise and accurate in situ determination of Sm–Nd isotopes, with high spatial resolution, and high sample throughput, in light rare earth element enriched accessory minerals by laser ablation-multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) is discussed. The accuracy of the method is demonstrated by comparison of LA-MC-ICPMS analyses of several natural minerals (Durango apatite, Hondo Canyon titanite, Daibosatsu allanite, Mae Klang monazite, and Trebilcock monazite) to isotope dilution-thermal ionization mass spectrometry (ID-TIMS) analyses of the same minerals. The TIMS analyses demonstrate that each of these minerals, with the possible exception of Durango apatite, is more homogeneous in Nd isotopic composition than can be measured based upon the internal precision of the LA-MC-ICPMS analyses in this study. Thus, these natural minerals may be considered as isotopically homogeneous reference materials for Nd isotopic determinations. In addition two synthetic glasses produced specifically for in situ Sm–Nd isotopic determination and external calibration are presented here. The three main obstacles in obtaining accurate and precise Sm–Nd isotopic measurements by LA-MC-ICPMS are the isobaric interference correction of 144Sm on 144Nd, determination of the Sm mass bias, and accurately measuring the 147Sm/144Nd which is imperative for producing robust initial Nd isotopic compositions. The 144Sm interference correction was calculated using the measured 149Sm and recently published Sm isotopic abundances. The Sm mass bias was determined using an exponential law and the 147Sm/149Sm measured in the sample. Determination of 147Sm/144Nd was done by calibration to an external glass reference material synthesized specifically for this purpose. This approach produced 147Sm/144Nd that is in agreement with ID-TIMS analysis. The MC-ICPMS instrument configuration used in this study also allows for the determination of Eu and Gd, thereby permitting simultaneous determination of Eu anomalies along with Sm–Nd isotopic composition. The high spatial resolution and sample throughput at a geologically useful level of accuracy and precision possible with LA-MC-ICPMS offers numerous potential geochemical applications including provenance tracing, terrane reconstruction, crustal growth studies, fluid composition and evolution, metamorphic reaction pathways, and silicic magma generation and evolution.

The Sigma REE and shale-normalized (PAAS) REESN values of modern brachiopods (biogenic low-Mg calcite: bLMC) represented by several species from high- to low latitudes, from shallow- to deep waters and from warm- and cold-water environments, define three distinct average 'seawater' trends. The warm- and cold-water brachiopods define two indistinguishable (p

Apatite is a common U- and Th-bearing accessory mineral in igneous and metamorphic rocks, and a minor but widespread detrital component in clastic sedimentary rocks. U–Pb and Th–Pb dating of apatite has potential application in sedimentary provenance studies, as it likely represents first cycle detritus compared to the polycyclic behavior of zircon. However, low U, Th and radiogenic Pb concentrations, elevated common Pb and the lack of a U–Th–Pb apatite standard remain significant challenges in dating apatite by LA-ICPMS, and consequently in developing the chronometer as a provenance tool. This study has determined U–Pb and Th–Pb ages for seven well known apatite occurrences (Durango, Emerald Lake, Kovdor, Mineville, Mud Tank, Otter Lake and Slyudyanka) by LA-ICPMS. Analytical procedures involved rastering a 10 μm spot over a 40 × 40 μm square to a depth of 10 μm using a Geolas 193 nm ArF excimer laser coupled to a Thermo ElementXR single-collector ICPMS. These raster conditions minimized laser-induced inter-element fractionation, which was corrected for using the back-calculated intercept of the time-resolved signal. A Tl–U–Bi–Np tracer solution was aspirated with the sample into the plasma to correct for instrument mass bias. External standards (Plesovice and 91500 zircon, NIST SRM 610 and 612 silicate glasses and STDP5 phosphate glass) along with Kovdor apatite were analyzed to monitor U–Pb, Th–Pb, U–Th and Pb–Pb ratios Common Pb correction employed the 207Pb method, and also a 208Pb correction method for samples with low Th/U. The 207Pb and 208Pb corrections employed either the initial Pb isotopic composition or the Stacey and Kramers model and propagated conservative uncertainties in the initial Pb isotopic composition. Common Pb correction using the Stacey and Kramers (1975) model employed an initial Pb isotopic composition calculated from either the estimated U–Pb age of the sample or an iterative approach. The age difference between these two methods is typically less than 2%, suggesting that the iterative approach works well for samples where there are no constraints on the initial Pb composition, such as a detrital sample. No 204Pb correction was undertaken because of low 204Pb counts on single collector instruments and 204Pb interference by 204Hg in the argon gas supply. Age calculations employed between 11 and 33 analyses per sample and used a weighted average of the common Pb-corrected ages, a Tera–Wasserburg Concordia intercept age and a Tera–Wasserburg Concordia intercept age anchored through common Pb. The samples in general yield ages consistent (at the 2σ level) with independent estimates of the U–Pb apatite age, which demonstrates the suitability of the analytical protocol employed. Weighted mean age uncertainties are as low as 1–2% for U- and/or Th-rich Palaeozoic–Neoproterozoic samples; the uncertainty on the youngest sample, the Cenozoic (31.44 Ma) Durango apatite, ranges from 3.7–7.6% according to the common Pb correction method employed. The accurate and relatively precise common Pb-corrected ages demonstrate the U–Pb and Th–Pb apatite chronometers are suitable as sedimentary provenance tools. The Kovdor carbonatite apatite is recommended as a potential U–Pb and Th–Pb apatite standard as it yields precise and reproducible 207Pb-corrected, 232Th–208Pb, and common Pb-anchored Tera–Wasserburg Concordia intercept ages.

In order to improve our understanding of HSE geochemistry, we evaluate the effect of Fe on the solubility of Pd in silicate melts. To date, experimentally determined Pd solubilities in silicate melt are only available for Fe-free anorthite-diopside eutectic compositions. Here we report experiments to study the solubility of Pd in a natural picritic melt as a function of pO2 at 1300 °C in a one atm furnace. Palladium concentrations in the run products were determined by laser-ablation-ICP-MS. Palladium increases from 1.07 ± 0.26 ppm at FMQ-2, to 306 ± 19 ppm at FMQ+6.6. At a relative pO2 of FMQ the slope in log Pd concentration vs. log pO2 space increases considerably, and Pd concentrations are elevated over those established for AnDi melt compositions. In the same pO2 range, ferric iron significantly increases relative to ferrous iron. Furthermore, at constant pO2 (FMQ+0.5) Pd concentrations significantly increase with increasing XFeO-total in the melt. Therefore, we consider ferric Fe to promote the formation of Pd2+ enhancing the solubility of Pd in the picrite melt significantly. The presence of FeO in the silicate melt has proven to be an important melt compositional parameter, and should be included and systematically investigated in future experimental studies, since most natural compositions have substantial FeO contents.

Residential soil and house dust were collected in St John's to assess the levels of lead exposure and potential human health risk. Although St John's does not have an identified, major point source for lead, nor is it a heavily industrialized or populated city, 51% of all analysed soil samples (n = 1231) exceeded the Canadian Council of Ministers of the Environment (CCME) residential soil lead guideline of 140 ppm, 26% exceeded the 400 ppm United States Environmental Protection Agency (US EPA) guideline for soil in children's play areas, and 9% exceeded the 1200 ppm US EPA guideline for soil outside of play areas. High soil lead concentrations, particularly those above 1200 ppm, are clustered in the older downtown core. Samples located along exterior house walls (dripline) have the highest mean soil lead concentrations, followed by open spaces in yards (ambient) and then roadside sites. Lead in dripline soil samples from older housing stock is sourced to lead-bearing paint. Lead from both dripline and amb...

Anorthositic impact melt rocks, their target rocks (principally anorthosite, mangerite, granodiorite) and zircon clasts from the ∼36-Ma-old, 28-km-wide Mistastin Lake crater of northern Labrador (55°53′N; 63°18′W) have been examined in order to evaluate the scale and origin of compositional heterogeneities in impact melts produced in craters of moderate size. In particular we assess whether and, if so, how the initial composition of the impact melt was modified as it entrained mineral clasts derived from the underlying rocks over which it flowed when it moved away from the shock-induced, central melting zone. A secondary goal was to determine if zircon clasts in the impact melts are present in the proportions of their target rock sources and/or the substrate lithologies over which they flowed. Chemical compositions of bulk samples of 33 melt rocks and 14 target rocks were measured by XRF and SN-ICPMS. Matrix compositions of nine samples of impact melt rocks were determined by EPMA and LA-ICPMS. Zircon grains from four samples of target rock and zircon clasts from three samples of impact melt rock were measured for multi-element composition, U–Pb age and Hf-isotopic composition by LA-(MC)-ICPMS. The data reveal compositional heterogeneities in the impact melts on the scales of both bulk samples and matrices. Bulk samples can be divided into compositions with high and low concentrations of high-field-strength elements (HFSE; Ti, Zr, Nb) and Fe, Ba, Ce and Y. High HFSE-type melt rocks formed when impact melt entrained large quantities of clasts from mangerite, which is rich in HFSE. Matrix compositions of bulk samples do not show the HFSE distinction but are affected by the introduction of low-temperature melts from the clasts to form dispersed, micron-scale silica-rich heterogeneities. The best estimate of sources of the initial impact melt is ∼73% anorthosite, ∼7% mangerite and ∼20% granodiorite, based on least-squares modeling of major-element compositions of the matrices of thinner flows. Zircon derived from anorthosite can be distinguished from zircon from mangerite and granodiorite by higher Nb/Ta and Eu/Eu* ratios and more negative initial e Hf values. Zircon clasts >40 mm in size in the impact melt rocks are dominantly or exclusively derived from mangerite and granodiorite rather than from anorthosite. Because anorthosite was the principal source of impact melt at Mistastin, zircon may be a poor provenance indicator for anorthosite contributions to impact melts, particularly where grains smaller than 40 microns are not analyzed.

Avalonia is the largest accreted crustal block in the Appalachian orogen and comprises a collection of late Neoproterozoic volcano-sedimentary sequences that are overlain by a Palaeozoic platformal sedimentary succession. Detrital zircons from the Conception Group are dominated by 570–620 Ma ages and contain a significant component generated by erosion of coeval igneous arc-volcanic rocks. Overlying samples from the Cuckold and Crown Hill formations are dominated by Neoproterozoic populations with ages between 600 and 650 Ma and are interpreted to be derived from the underlying calc-alkaline arc-plutonic rocks. Early Palaeozoic platform units are dominated by c . 620 Ma zircons with lesser Mesoproterozoic and Palaeoproterozoic zircons. The range of detrital zircon ages is inconsistent with a West African provenance and suggests that Avalonia originated along the Gondwanan margin of the Amazon craton. The influx of Mesoproterozoic and Palaeoproterozoic detritus in the Avalonian platform suggests a major change in tectonic regime. The prominent change in provenance is interpreted to be related to separation of Avalonia from Gondwana during the Early Ordovician opening of the Rheic Ocean. The Redmans Formation is interpreted to represent the rift–drift transition of the Rheic Ocean, which imposes important constraints on the palaeotectonic evolution of Avalonia. Supplementary material: U–Pb isotopic data of LA-ICP-MS analysis of detrital zircons are available at http://www.geolsoc.org.uk/SUP18346.

The Vazante Group consists of a late Mesoproterozoic (∼1.0–1.1 Ga) carbonate-dominated marine platform sequence in east-central Brazil. The upper part of the sequence consists of a glaciomarine diamictite unit overlain by a cap carbonate. The δ13C profile of the upper Vazante shows significant negative plunges, one preglacial (drop of ∼5.5‰ VPDB) and two postglacial (drops of ∼9 and 5‰VPDB, respectively). The C-isotope plunge in the preglacial carbonates is correlated with low Th/U ratios (0.1–1.4) and a negative Ce/Ce* shift (∼0.4), suggesting deposition under relative reducing conditions. In contrast, the C-isotope plunges in the postglacial carbonates are associated with high Th/U ratios (>2) and positive Ce/Ce* shifts (up to ∼1.5), thus reflecting oxidizing conditions. Variations in the redox conditions of the late Mesoproterozoic ocean, reflected by changes in the Th/U and Ce/Ce* ratios, are likely attributable to a combination of both global and local climatic and oceanographic changes, similar to what has been inferred for the Neoproterozoic oceans.

In situ LA-ICPMS U-Pb, trace element, and Hf isotope data in zircon demonstrate a Carboniferous age for eclogite-facies metamorphism in Siluro-Devonian protoliths in the Huwan shear zone, Dabie Mountains, Central China. This age contrasts with the more prevailing Triassic age for high- to ultrahigh pressure (HP to UHP) metamorphism in the Qinling-Dabie-Sulu orogen. Metamorphic zircon in two eclogite samples from Sujiahe is characterized by low Th/U ratios, small negative Eu anomalies, flat HREE patterns, and low 176Lu/177Hf ratios. These geochemical signatures suggest that the zircon crystallized in the presence of garnet and in the absence of plagioclase feldspar. Furthermore, temperatures of ~ 655 and ~ 638 °C, calculated using the Ti content of zircon, are consistent with their formation during eclogite-facies metamorphism. The weighted mean 206Pb/238U age of 309 ± 4 Ma (2δ) for this zircon improves previous age estimates for eclogite-facies metamorphism in the Huwan shear zone, ranging from 420 to 220 Ma. Metamorphic zircon from one eclogite sample from Hujiawan, most likely formed during prograde metamorphism, yields an equivalent age estimate of 312 ± 11 Ma. Magmatic zircon cores in the three samples yield ages for the magmatic protoliths of the eclogites ranging from 420 ± 7 to 406 ± 5 Ma, and post-dating the middle Paleozoic collision of the North China and the Qinling terrain. The zircon crystals in the three eclogite samples display a large variation of eHf (t) values of − 4.9 to 21.3. The metamorphic zircon overgrowths show the same range of eHf (t) values as those of the inherited magmatic crystal interiors. This suggests that the metamorphic zircon overgrowths may have formed by dissolution-reprecipitation of pre-existing magmatic zircon thereby preserving their original Hf isotopic composition. The high eHf (t) values suggest that the protoliths were derived from depleted mantle sources, most likely Paleotethyan oceanic crust; while the low eHf (t) values are attributed to crustal contamination. Some eclogites in the Huwan shear zone have a distinctive signature of continental crust most probably derived from the Yangtze Craton. The coexistence of Paleozoic oceanic crust and Neoproterozoic continental crust with similar metamorphic ages in the Huwan shear zone implies that Paleozoic Paleotethyan oceanic crust was produced within a marginal basin of the northern Yangtze Craton. The opening of the Paleo-Tethyan ocean was slightly younger than the collision of the North China Craton and the Qinling terrain during the Late Paleozoic in the Qinling-Dabie-Sulu orogen. Subduction of the Paleo-Tethyan oceanic crust and associated continental basement resulted in the 309 ± 2 Ma (2σ) eclogite-facies metamorphism in the Huwan shear zone. The subsequent Triassic continent-continent collision led to the final coalescence of the Yangtze and Sino-Korean cratons. Amalgamation of the Yangtze and North China cratons was, therefore, a multistage process extending over at least 200 Ma.

Research in 2006 and 2007 dealing with laser ablation-(multicollector)-inductively coupled plasma-mass spectrometry, LA-(MC)-ICP-MS, involved studies concerned with optimising the technique itself, as well as applying the method to a variety of problems in the Earth sciences. The causes of elemental and isotopic fractionation produced during laser ablation continues to be of considerable interest, with evidence mounting that processes occurring both at the ablation site and in the argon plasma of the ICP are culpable. There is growing excitement in the use of femtosecond lasers for LA-(MC)-ICP-MS, with the hope that they reduce or eliminate melting and non-congruent volatilisation at the ablation site and thus approach stoichiometric sampling. Ablation chamber design emerged as a serious concern, particularly with respect to achieving the rapid washout needed for fine-scale compositional mapping of geological objects. LA-MC-ICP-MS provided data for a wide range of isotopic systems, especially hafnium, but also B, S, Mg, Cu, Fe, Sr, Nd, Pb and U. Measurement uncertainties in LA-ICP-MS were discussed by several researchers, and are critically reviewed here - total uncertainties for trace element concentration measurements of silicates including errors on the calibration values of common reference materials are ∼10% (95% confidence limits), though the precision of individual spot measurements (50 to 100 μm) is much better, ∼1% RSD, using a 193 nm laser and a sector field-ICP-MS. LA-ICP-MS U-Pb ages for zircon and other U-rich accessory phases are claimed by most geoanalysts to have 2s uncertainties of ∼0.7 and 1.3% respectively but the actual accuracy of the method is probably only as good as ∼2% (2s), when uncertainties associated with laser-induced Pb/U fractionation are included.

Solubilities for a wide range of siderophile elements (SE: Ni, W, Re, Ir, Os, Pt, Rh) have been determined in a haplobasaltic melt composition (An42Di58) using the mechanically assisted equilibration (MAE) technique. Here we present a review of the data obtained and the experience gained over the past decade using this approach. In particular, the major experimental and analytical challenges encountered (and inferred to result from so-called “nanonugget” formation) are described. After a general background overview of siderophile element solubility experiments, the experimental (MAE) and analytical techniques are described. Major element composition was routinely determined by electron microprobe analyses (EMP), whereas trace elements were determined using a wide variety of analytical techniques (Ni, W: INAA, EMP, ICP-AES; Re, Ir, Pt, Rh and Os: INAA, SIMS, dissolution- (diss-ICPMS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS)). The last technique, in particular, has demonstrated its powerful capabilities for micro-analyses, supplying information on both absolute trace element concentrations and on small scale heterogeneities in run products. All investigated SEs exhibit solubilities whose systematic variation with oxygen fugacity (fO2) is consistent with their presence as stoichiometrically dissolved oxide species in the melt phase. There is no indication of zero-valence species dissolved at any fO2 condition. In the case of highly-SE (HSE: Pt, Rh, Re, Os, Ir), INAA results appear to indicate a decrease of HSE solubility with decreasing fO2 down to a fO2 limit which depends on the investigated HSE. Below this limit, bulk HSE concentrations remain either constant with large variations or increase with further fO2 decrease. Duplicate analyses of samples by LA-ICPMS reveal increasing amounts of so-called nanonuggets with decreasing fO2, which lead to high HSE concentrations in the glass samples obtained by bulk analytical methods such as INAA. The formation of HSE (and potentially some SE) nanonuggets in low fO2 samples raises the question of whether nanonuggets are formed either during the quench by precipitation from precursor species dissolved homogeneously in the melts, or are precipitated in situ at high temperature due to true thermodynamic oversaturation. The combination of the MAE technique with LA-ICPMS micro-analytical methods has enabled us to extend our knowledge of the solubility behaviour of HSE to unprecedentedly low fO2 values. Clarification of the solubility mechanism for SE as well as the nanonugget issue, however, will undoubtedly require further novel experimental designs.

A total of 56 non-porphyritic pyroxene and pyroxene/olivine micro-objects from different unequilibrated ordinary chondrites were selected for detailed studies to test the existing formation models. Our studies imply that the non-porphyritic objects represent quickly quenched liquids with each object reflecting a very complex and unique evolutionary history. Bulk major element analyses, obtained with EMPA and ASEM, as well as bulk lithophile trace element analyses, determined by LA-ICP-MS, resulted in unfractionated (solar-like) ratios of CaO/Al2O3, Yb/Ce as well as Sc/Yb in many of the studied objects and mostly unfractionated refractory lithophile trace element (RLTE) abundance patterns. These features support an origin by direct condensation from a gas of solar nebula composition. Full equilibrium condensation calculations show that it is theoretically possible that pyroxene-dominated non-porphyritic chondrules with flat REE patterns could have been formed as droplet liquid condensates directly from a nebular gas strongly depleted in olivine. Thus, it is possible to have enstatite as the stable liquidus phase in a 800 × Cl dust-enriched nebular gas at a p tot of 10−3 atm, if about 72% of the original Mg is removed (as forsterite?) from the system. Condensation of liquids from vapor (primary liquid condensation) could be considered as a possible formation process of the pyroxene-dominated non-porphyritic objects. This process can produce a large spectrum of chemical compositions, which always have unfractionated RLTE abundances. Late stage and subsolidus metasomatic events appear to have furthered the compositional diversity of chondrules and related objects by addition of moderately volatile and volatile elements to these objects by exchange reactions with the chondritic reservoir (e.g., V, Cr, Mn, FeO as well as K and Na). The strong fractionation displayed by the volatile lithophile elements could be indicative of a variable efficiency of metasomatic processes occurring during and/or after chondrule formation. Histories of individual objects differ in detail from each other and clearly indicate individual formation and subsequent processing.

This study reports the first documented occurrence of platinum group-minerals (PGM) in the vicinity of the Voisey’s Bay magmatic sulfide ore deposit. The PGM are present in a sulfide poor, hornblende gabbro dyke in the Southeast Extension Zone of the massive sulfide Ovoid deposit. The dyke has somewhat elevated concentrations of platinum-group elements (PGE) and gold (up to 1.95 g/t Pt, 1.41 g/t Pd, and 6.59 g/t Au), as well as Cu, Pb, Ag, Sn, Te, Bi and Sb. The PGM formed by magmatic processes and were little disturbed by subsequent infiltration of an externally-supplied hydrothermal fluid. To date, no similar PGM occurrences have been discovered in the Ovoid deposit itself.

Several types of granites including alkaline granites and alkali feldspar granites are distributed in the Karamaili tectonic belt of East Junggar, Xinjiang, China. Some medium-small tin deposits are located within or near the contact zones of the granitic intrusions. The alkaline granites share all the features commonly observed in peralkaline A-type granites. They contain alkalic mafic minerals such as riebeckite and aegirine; have high contents of SiO2, alkalis, Rb, Th, Zr, Hf, REE (except Eu), and high ratios of FeO*/MgO and Ga/Al; and show strong depletions in Ba, Sr, Eu in the spidergrams. Laser ablation-ICPMS U-Pb zircon geochronology indicates a crystallization age of ca. 305 Ma for the granites; TIMS analyses of the granites found high eNd(T) values of +5.9 to +6.5. Considering their geochemical features, alkaline granites most likely formed by fractional crystallization of granodioritic magmas, which were probably produced by partial melting of lower crustal basaltic to andesitic rocks formed from oceanic crustal materials that were deeply buried during late Paleozoic subduction and accretion. Six molybdenite samples from the Sareshike tin deposit in East Junggar yielded an isochron age of 307 ± 11 Ma (2σ) and a weighted mean model age of 306.5 ± 3.4 Ma, consistent with zircon U-Pb ages of the alkaline granites. Low Re contents (0.323-0.961 ppm) in the molybdenite suggest that they originated from crustal sources related to the alkaline granites. Considering their identical ages, close spatial distribution, and similar sources, we argue that the A-type granites have a genetic relationship with the tin mineralization, and that the same association may be important elsewhere.

This review of laser ablation-inductively coupled plasma-mass spectrometry includes research that employed quadrupole instruments, and single-collector and multicollector magnetic sector field instruments. The most important trend in 2004–2005 was the growing appreciation that small matrix effects in LA-(MC)-ICP-MS need to be addressed in order to produce highly precise and accurate data by the method. The issue is most acute for isotope ratio measurements that require standard-sample-standard bracketing but can also be important for certain elemental analysis. Matrix-dependent elemental and isotopic fractionations were studied from the standpoint of laser-sample interactions and the behaviour of laser-generated particles in the ablation cell, transfer tubing and ICP torch. Innovations in LA-(MC)-ICP-MS involved signal smoothing, in torch laser ablation, on-line isotope dilution and molecular oxide monitoring. Other important research was carried out on the calibration and homogeneity of various reference materials; and the exploration of mature (in situ U-Pb geochronology) and emerging (apatite fission-track chronometry, U-Th/He thermochronology, boron/strontium/uranium-series isotopic microanalysis) applications in the Earth sciences.

The abundance of gold and selected trace elements in magmatic sulfide and rock-forming minerals from Silurian–Devonian granitoids in southwestern New Brunswick were quantitatively analyzed by laser-ablation inductively coupled plasma mass-spectrometry. Gold is mainly hosted in sulfide minerals (i.e., chalcopyrite, pyrrhotite, and pyrite), in some cases perhaps as submicron inclusions (nanonuggets). Gold is below detection (

We determined the solubility limit of Pt in molten haplo-basalt (1 atm anorthite-diopside eutectic composition) in piston-cylinder and multi-anvil experiments at pressures between 0.5 and 14 GPa and temperatures from 1698 to 2223 K. Experiments were internally buffered at ∼IW + 1. Pt concentrations in quenched-glass samples were measured by laser-ablation inductively coupled-plasma mass spectrometry (LA-ICPMS). This technique allows detection of small-scale heterogeneities in the run products while supplying three-dimensional information about the distribution of Pt in the glass samples. Analytical variations in 195Pt indicate that all experiments contain Pt nanonuggets after quenching. Averages of multiple, time-integrated spot analyses (corresponding to bulk analyses) typically have large standard deviations, and calculated Pt solubilities in silicate melt exhibit no statistically significant covariance with temperature or pressure. In contrast, averages of minimum 195Pt signal levels show less inter-spot variation, and solubility shows significant covariance with pressure and temperature. We interpret these results to mean that nanonuggets are not quench particles, that is, they were not dissolved in the silicate melt, but were part of the equilibrium metal assemblage at run conditions. We assume that the average of minimum measured Pt abundances in multiple probe spots is representative of the actual solubility. The metal/silicate partition coefficients (Dmet/sil) is the inverse of solubility, and we parameterize Dmet/sil in the data set by multivariate regression. The statistically robust regression shows that increasing both pressure and temperature causes Dmet/silto decrease, that is, Pt becomes more soluble in silicate melt. Dmet/sil decreases by less than an order of magnitude at constant temperature from 1 to 14 GPa, whereas isobaric increase in temperature produces a more dramatic effect, with Dmet/sil decreasing by more than one order of magnitude between 1623 and 2223 K. The Pt abundance in the Earth’s mantle requires that Dmet/sil is ∼1000 assuming core-mantle equilibration. Geochemical models for core formation in Earth based on moderately and slightly siderophile elements are generally consistent with equilibrium metal segregation at conditions generally in the range of 20–60 GPa and 2000–4000 K. Model extrapolations to these conditions show that the Pt abundance of the mantle can only be matched if oxygen fugacity is high (∼IW) and if Pt mixes ideally in molten iron, both very unlikely conditions. For more realistic values of oxygen fugacity (∼IW − 2) and experimentally-based constraints on non-ideal mixing, models show that Dmet/sil would be several orders of magnitude too high even at the most favorable conditions of pressure and temperature. These results suggest that the mantle Pt budget, and by implication other highly siderophile elements, was added by late addition of a ‘late veneer’ phase to the accreting proto-Earth.

A new method has been developed for the accurate and precise measurement of sulfur isotopes (32S, 33S, 34S) in solids on a scale down to 80–100 μm by laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The method was developed independently on two different sets of instrumentation, both of which give equivalent results with comparable accuracy and precision. The first instrumental set-up utilizes Xe gas in a hexapole collision and reaction cell for interference attenuation coupled with a mass discrimination correction by external normalization using a nebulised vapour of 37Cl/35Cl standard solution. The second employs high mass resolution by sector field mass spectrometry to avoid the interfering O2+ isobars with a 30Si/29Si standard aerosol for external normalization. The external isotope mass discrimination correction was applied using the exponential law and was further calibrated for both sets of instrumentation by linear interpolation in a sample–standard bracketing method. Mean δ34SV-CDT and δ33SV-CDT show excellent agreement (within analytical error, typically 0.6 and 1.5‰, respectively) with compiled data for IAEA-S series AgS standard reference materials. Results for NIST SRM 127 (sulfate) were less accurate when calibrated against the IAEA-S series sulfides, whilst significant and consistent deviations in accuracy of up to 3‰ were observed in both sets of instrumentation for Soufre de Lacq SRM sulfur. Such generic matrix effects may be widespread in LA-ICP-MS due to differential ablation rates, particle formation, particle transport efficiency and ionization efficiency in an argon plasma.

A mineralogical mass balance has been calculated for the fraction of platinum group elements (PGE) incorporated as solid solution in sulfides and sulfarsenides and the fraction that occurs as major constituents in platinum group minerals (PGM) in the Kelly Lake Ni-Cu-PGE sulfide deposit in the Copper Cliff offset, Sudbury. Low levels of PGE in sulfides were determined quantitatively for the first time in Sudbury ores by laser ablation microprobe-inductively coupled plasma-mass spectrometry (LAM-ICP-MS), providing significantly more accurate data on the inventory and mineralogical distribution of the PGE than in previous studies. The majority of the Pt (98%), Rh (97%), and Ir (86–91%), and lesser but still large fractions of Pd (77–87%) and Ru (67–71%), occur as discrete PGM with the remainder occurring (in decreasing abundance) in solid solution in gersdorffite (1,700 ppm ∑PGE), pentlandite (1.35 ppm), chalcopyrite (0.5 ppm), and pyrrhotite (0.3 ppm). Although the PGE are present in low concentrations in sulfides, the abundances of these phases can be high enough to constitute a significant fraction of the total PGE. In particular, significant proportions of the Pd (14–23%) and Ru (~30%) in the Kelly Lake samples are hosted by sulfides and sulfarsenides. This has important implications for the genesis of the PGE, for the redistribution of the PGE during cooling and hydrothermal alteration, and for metal recovery during ore beneficiation.

We have performed six experiments in which we equilibrated monosulfide solid solution (mss) with sulfide melt in evacuated silica capsules containing solid buffers to fix oxygen and sulfur fugacity, at temperatures of 950°C, 1000°C and 1050°C at bulk concentrations of ∼50 ppm for each of the PGE and Au, 5% Ni, and 7% Cu. Concentrations of O, S, Fe, Ni and Cu were determined by electron microprobe, whereas precious metal concentrations were determined by laser-ablation inductively-coupled mass spectrometry. Partition coefficients of all elements studied show minimal dependences on oxygen fugacity from the IW to the QFM buffers when sulfur fugacity is fixed at the Pt-PtS buffer. Cu, Pt, Pd and Au are strongly incompatible and Ru remains moderately to strongly compatible under all conditions studied. At all oxygen fugacities, at the Pt-PtS sulfur buffer, Ir and Rh remain highly compatible in mss. In the single run at both low oxygen and low sulfur fugacity Ir and Rh were found to be strongly incompatible in mss. At QFM and Pt-PtS the partition coefficient for Ni shows weak temperature dependence, ranging from 0.66 at 1050°C to 0.94 at 950°C. At lower oxygen and sulfur fugacity Ni showed much more incompatible behavior. Comparison with the compositions of sulfide ores from the Lindsley deposit of Sudbury suggests that the sulfide magma evolved under conditions close to the QFM and Pt-PtS buffers. The compatible behavior observed for Ni, Ir and Rh at Lindsley and most other magmatic sulfide deposits hosted by mafic rocks requires equilibration of mss and sulfide liquid at moderately high sulfur fugacity and low temperatures near to the solidus of the sulfide magma. We argue that this constraint requires that the sulfide magma must have evolved by equilibrium crystallization, rather than fractional segregation of mss as is commonly supposed.

Subduction of oceanic lithosphere is thought to be responsible for producing heterogeneity in Earth's mantle; the heterogeneity is most clearly preserved in the compositions of ocean island basalts (OIB). The variation of trace element and isotopic ratios in OIB is commonly explained by recycling of ancient oceanic crust associated with terrigenous or pelagic sediment. However a variety of chemical and physical arguments seem to indicate that subducted oceanic crust is not the source of OIB. In particular, experimental petrologic studies indicate that the most plausible source for OIB is the partial melting of peridotite in the presence of CO2 or silica-deficient pyroxenites. Alternative hypotheses for the source of OIB are subducted oceanic basal lithosphere enriched by metasomatic liquids and delaminated metasomatised continental lithosphere. Lithospheric metasomatism is common to both hypotheses and could produce silica-deficient pyroxenite; however, the exact chemical and physical nature of the process and how it leads to chemical variations in recycled lherzolite that produce the various OIB isotopic end-member “signatures” is unclear. Chemical variations observed in the Cantal basalt (France) are interpreted as the result of a lithospheric metasomatic mechanism and provide important new constraints on the nature of this metasomatic process. The Cantal basalts, similar to OIB in composition, show unusual variations in Nb / Th, Nb / U, La / Nb and Ce / Pb ratios from the first (13–9 Ma) to the last (9–3 Ma) emitted basalt. The basalts are homogeneous with respect to their Sr, Nd, and Pb isotopic composition, ruling out variable sediment contamination of their mantle sources. We postulate that these trace element variations result from an evolution of metasomatic vein compositions present in a vein plus enclosing lithospheric mantle source. Cantal basalt compositions may be used to constrain the trace element variation generated by the evolution of a metasomatic agent within the lithosphere. Reconstruction of compositions in different parts of the lithosphere indicates significant heterogeneities in Th / Pb, U / Pb and Sm / Nd resulting from the metasomatic process. Subduction and isolation of this metasomatic lithosphere generates over 1–1.8 Ga, Nd and Pb isotopic variations similar to those observed in oceanic island basalts. Moreover, these isotopic variations are correlated with variations in trace element ratios commonly interpreted as the product of mixing between different end-member mantle components (HIMU and EM). The model calculations suggest that isotopic and trace element variations observed in OIB may more likely be the result of melting metasomatised subducted oceanic lithosphere rather than a mixture of chemically distinct mantle sources that formed and evolved independently from one another.

Geochronological, geochemical, and morphological analysis of detrital zircon in the Jack Hills and Mount Narryer metasedimentary belts, Western Australia, indicates the grains were derived from diverse rocks, including >4000 Ma sources that predate the oldest known terrestrial rock. In three metaconglomerate layers in the western part of the Jack Hills, 4200–3800 Ma zircon makes up 14% of the population, 3800–3600 Ma grains form only 2%, and 3550–3250 Ma zircon is dominant with a significant peak at 3380 Ma (U‐Pb ages and trace element concentrations were obtained by laser‐ablation microprobe inductively coupled plasma mass spectrometry). These grains are interpreted as being derived from similar rock types because they are indistinguishable in U concentration (50–200 ppm), internal zoning (both oscillatory and sector zoning within the same grain), and morphology (subequant fragments of grains). We conclude that a previously proposed evolved granitic source is unlikely because the zircon differs ...