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Kimberlite-borne granulite xenoliths provide rare insights into the age, chemical composition and tectonothermal evolution of the otherwise largely inaccessible deep cratonic crust. The formation and transformation of the lower continental crust (LCC) beneath the central Slave craton (Canada) is here illuminated using whole-rock trace-element and Sr-Nd isotope compositions of nine metabasaltic (MBG), one gabbroic (MGG) and two metasedimentary/hybrid (MSG) granulite xenoliths. On the one hand, published sulphide Re-Os and a few zircon U-Pb data indicate that at least a portion of the LCC beneath the central Slave craton has a Palaeoarchaean origin (∼3.3 Ga), which apparently coincides with a period of juvenile crust and deep lithospheric mantle formation during plume impingement beneath the pre-existing cratonic nucleus. On the other hand, enrichment in Li, Sr, LREE, Pb and Th, but relative depletion in Ti, Hf and HREE, suggest formation of (picro)basaltic protoliths by partial melting of a subduction-modified garnet-bearing source, Crystallisation in the crust after fractionation of plagioclase is inidicated by their Sr and Eu negative anomalies, which are complementary to the positive anomalies in the MGG. Samarium-Nd isotopes in MBG and MGG show large scatter, but fall on Neo- or Mesoarchaean age arrays. These elemental systematics are suggested to fingerprint deserpentinisation fluids plus small amounts of sedimentary melt as the main contaminants of the mantle source, supporting the operation of at least regional and transient subduction at 3.3 Ga. Evidence for quasi-coeval plume impingement and subduction beneath the central Slave craton in the Mesoarchaean is reconcilable in a dynamic regime where vertical tectonics, though waning, was still active and plate interactions became increasingly important. Unradiogenic 87Sr/86Sr (down to 0.7017) is consistent with significant loss of Rb and probably other heat-producing elements (K, Th, U) plus H 2 O during Neoarchaean metamorphism, which helped to enhance LCC viscosity and stabilise the cratonic lithosphere. [ABSTRACT FROM AUTHOR]

The Proterozoic evolution of Laurentia involved intermittent orogens and arc-related crustal growth along a modern-style convergent margin, termed the Great Proterozoic Accretionary Orogen (GPAO). The major lithotectonic provinces of the GPAO in the United States are exposed as telescoped equivalents within the thrust stack of the Grenville Province in Canada. We report zircon U Pb and Lu Hf isotope analyses for two orthogneisses and one quartzite from Archean and Paleoproterozoic domains in the gneiss belt of the SW Grenville Province, Canada. The data constrains Paleoproterozoic crustal growth and sedimentation for this part of the Laurentian margin. The orthogneisses have similar zircon U Pb and Lu Hf isotope systematics that reflect igneous reworking (ca. 1700–1660 Ma) of a Penokean aged (ca. 1.9 Ga) depleted mantle derived source, along with metamorphic reactivation at both ca. 1.45 Ga and during the Grenville Orogeny (1.2–1.0 Ga). The quartzite has a bimodal Paleoproterozoic (2.1–1.8 Ga) and Archean (> 2.5 Ga) detrital zircon age spectrum. The Paleoproterozoic detrital zircon grains have a wide range of Hf(t) compositions (εHf(t) = −12.5 to 10) reflecting co-eval interaction of Archean and depleted Paleoproterozoic sources, contrasted by a more restricted range for the Archean population (εHf(t) = −7 to 4). The new data support the presence of reworked ca. 1.9 Ga depleted mantle sources in the Paleoproterozoic Parautochthon, which extend further east than previously thought. They also identify correlations amongst detrital zircon age spectra and Hf isotope compositions in quartzites from different locations of the Archean Parautochthon. • Juvenile Penokean sources (∼1.9 Ga) extend into the SW Grenville Province. • Penokean (∼1.9 Ga) crust-mantle mixing recorded by detrital zircon Lu Hf isotopes. • Erosion and redeposition of sedimentary sinks can mask orogen detrital systematics. [ABSTRACT FROM AUTHOR]

Canada is one of the most important diamonds producers in the world despite the first diamond mine opening relatively recently in 1998 in the Slave craton. Given the increasing economic and scientific interest towards Canadian diamonds, an investigation of their geochemical and petrological properties was needed to better understand their genesis. A detailed review is given of all available petrological and geochemical data from >3000 Canadian diamonds and their silicate, oxide and sulfide inclusions from published literature and unpublished datasets, compared with data from worldwide datasets. Based on the available published data, different abundances of peridotites and eclogites in the lithosphere of the Canadian cratons are indicated by mineral inclusions, with the Slave craton exhibiting a high amount of eclogitic diamonds, and the Superior craton exhibiting a strong prevalence of peridotitic diamonds. Diamond formation from extremely 13C-depleted subducted organic matter is necessary to explain the extremely low δ13C observed in some samples from the Canadian lithosphere, which, as of today, are the lowest values ever recorded in mantle diamonds. Core-to-rim δ13C analyses revealed progressive rimward enrichment in 13C for some of the samples, a behavior which is associated to the crystallization of diamonds from oxidized C species (e.g., CO 2). Using the available data geothermobarometric calculations were performed on both single inclusions and inclusion pairs and provide a formation window for Canadian lithospheric diamonds from ∼140 to ∼210 km, with temperatures ranging from 900 to 1400 °C, which are generally higher than mantle residence temperature given by N aggregation geothermometry. Sub-lithospheric diamonds are sampled from ∼240 km to >660 km based on geobarometry on majoritic garnets and observations of inclusion assemblages. The age range of Canadian diamonds suggest numerous diamond-forming events that took place from the Paleo-Archean to the Neoproterozoic. • Petrological and geochemical differences exist among Canadian cratons. • Diamonds formed in different pulses from the Paleo-Archean to the Neoproterozoic. • Oxidizing fluids are involved in the formation of Canadian diamonds. • Lithospheric diamond stability field extends from ∼5 to ∼7 GPa. [ABSTRACT FROM AUTHOR]

Positive δ13C carb excursions are correlated through an upper Turinian to lower Chatfieldian carbonate-platform succession along the axis of the Ottawa Embayment and into outliers of the northern Ottawa-Bonnechere graben in central Canada. Successive Turinian excursions (E1 and E2) are lithostratigraphically constrained by erosional surfaces and hosted within the Watertown and overlying L'Orignal formations, respectively, the latter coeval with the Selby Formation in the adjacent northern Appalachian Basin. The excursions coincide with periods of regional transgression, but geographic patterns of 13C depletion versus enrichment coincide with structurally defined areas of stratigraphically condensed and preferentially thickened formation successions, respectively. Differential subsidence is interpreted to have created bathymetric variation resulting in intrabasinal restriction of seawater exchange between these areas, with preferential C org recycling with stratigraphic condensation. By early Chatfieldian time, segmentation of the once regional carbonate platform (L'Orignal Formation) produced a regional mosaic of low-energy muddy carbonate banks (Rockland Formation) and a deeper water platform (lower Hull Formation) settings subject to fluctuating high to low energy current flow. Excursion E3 occurs in both successions, but 13C enrichment is associated only with the bank-top muddy facies. This may identify preferential photosynthetic drawdown of 12C across the bank tops due to limited seawater exchange across the bank-deeper platform boundaries. Excursions E1 to E3, and a younger excursion (E4) in the Hull Formation, are correlated with varying confidence with excursions across southern Laurentia, excursion E3 being the local expression of the Guttenberg δ13C excursion. Our study supports local modulation of regional, if not global, δ13C excursions arising from structurally controlled changes in oceanography and productivity. • Turinian and early Chatfieldian δ13C excursions occur in the Ottawa Embayment. • Lithostratigraphic constraints reveal local excursion truncation, notably the GICE. • Lateral variation in excursion magnitude reflects local syndepositional controls. • Local controls modulate regional to global isotopic signals. [ABSTRACT FROM AUTHOR]

• Extensive new Ba isotopic survey of modern barites. • First Proterozoic Ba isotopic results. • Provides genetic model for enigmatic post-Marinoan barite formation. • Provides evidence for stratified post-Marinoan ocean. • Provides arguments for why barite horizons are confined to Marinoan and not Sturtian or Paleoproterozoic strata. Measurements of triple oxygen isotope ratios in barite horizons within post-Marinoan cap carbonates have provided some of the most compelling evidence that the Marinoan glaciation was a Snowball Earth event. However, the origin of these barite horizons remains unresolved. To constrain the Ba sources, and thus formation mechanisms of these horizons, we analyzed the Ba isotope composition of post-Marinoan barite deposits from Northwest Canada, Northern Norway, Brazil and South China. We augment these analyses with a Ba isotope survey of almost 100 modern and ancient additional barite measurements, including samples from pelagic (or 'marine'), hydrothermal, terrestrial, Proterozoic stratiform and cold seep environments. Unlike modern cold seep or terrestrial barites, we find that globally-distributed post-Marinoan barites exhibit a relatively narrow isotopic range, suggesting a well-mixed, effectively limitless Ba source. Moreover, post-Marinoan deposits exhibit a similar mean Ba isotope composition to modern marine barites, which we interpret as evidence of a marine Ba source. Considered alongside existing geochemical, geological, and new Ba isotope survey data, we conclude that Ba in barite horizons was sourced from a well-mixed, Ba-replete but SO 4 -poor reservoir that accumulated during the Marinoan Snowball Earth interval. This deep Ba reservoir was then transported upward—either by ocean circulation or dolomitization of underlying cap carbonates—and was brought into contact with continental weathering-derived sulfate in a post-glacial meltwater surface layer. Thus, in addition to providing a plausible mechanism for generating globally-synchronous deposition of post-Marinoan barite horizons that reconciles all existing geochemical and geological data, our results demonstrate the utility of Ba isotopes to interrogate the origin of enigmatic barite deposits throughout the sedimentary record. [ABSTRACT FROM AUTHOR]

Highlights • Thioaromatic concentrations of Peace River oils decreased with biodegradation. • Alkyl thioaromatic isomers showed different susceptibilities to biodegradation. • First detailed investigation of S isotope fractionation of OSCs in biodegraded oils. • Alkyl BTs were 34S-enriched in more biodegraded oils. • The δ34S values of alkyl DBTs showed no 34S fractionation in biodegraded oils. Abstract The heavy sulfur-rich oils of the Peace River oil sands were formed by severe anaerobic biodegradation. To investigate the impacts of biodegradation on organic sulfur compounds (OSCs) we have measured the distribution and δ34S values of alkylated thioaromatics detected in four oils from each of two Peace River wells (A and B). The fluid composition of the Peace River oil sands can be highly complex due to the variable contributions of sources, thermal maturity and secondary alteration. Nevertheless, a previous multi-molecular investigation of samples from well B oils (PR2 oil-leg of Marcano et al., 2013, Organic Geochemistry 59, 114–132) indicated that the oils had biodegradation levels (BLs) of 5–6, with biodegradation increasing down the oil column. The hydrocarbon composition of oils isolated from well A were biodegraded to a lesser degree than well B (i.e., the presence of isoprenoids and high molecular weight [MW] n -alkanes suggests BLs of ∼3–4). The concentrations of C 1 –C 3 alkylated benzothiophenes (BTs) and C 1 –C 3 alkylated dibenzothiophenes (DBTs) declined sharply through both wells consistent with increased biodegradation, although other alteration impacts (e.g., water washing) might also contribute. The rates of decrease recorded for selected isomers showed variable responses (e.g., 3&4-mBT > 2-mBT; 4-eDBT > 1,3-dmDBT) which implies different susceptibilities to biodegradation and which may contribute additional useful molecular parameters for evaluating the BL of biodegraded S-rich petroleum. The S-isotopic measurements showed a 34S enrichment in several alkyl BTs down the oil leg in well B, with their δ34S values increasing by up to 6‰, consistent with the microbial utilisation of 32S (n.b., the δ34S values of alkyl BTs were not measured in well A oils because of low aromatic sub-fraction concentrations). In contrast, there was little variation in the δ34S values of alkyl DBTs down both wells indicating negligible S-isotopic fractionation of these OSCs in the deeper more biodegraded oils, possibly because of their higher MW and resistance to biodegradation. The δ34S DBT (and bulk δ34S) values of the well B oils were generally slightly enriched than the well A oils probably due to differences in the relative contribution of the major Devonian and Jurassic source rocks. [ABSTRACT FROM AUTHOR]

• Calibration to both flow and isotope tracers produced the most robust results. • Tracer-aided modelling improves flow path identifiability. • Inclusion of isotope tracers can improve flow simulation performance. • Isotope metrics that include timing error are most helpful in calibration. Standard hydrologic model evaluation and calibration approaches focus on the accurate simulation of streamflow, disregarding internal process simulations. Stable isotope tracers can provide additional information on water sources, and process flux and storage, which can be used to inform model calibration. This study assesses the added value of isotope data in comparison to current best-practice flow-only calibration methods and evaluates the merits and limitations of isotope simulation performance metrics for the purposes of hydrological model calibration. Following several years of regular isotope sampling and measurement, an isotope-enabled process-based hydrologic model was tested on a large watershed in western Canada (Athabasca River), which allowed model calibration using global sensitivity analyses, Monte Carlo simulations, and multi-objective optimizations. Isotope tracer data were found to improve both process and streamflow component identifiability and produced some minor improvement in individual parameter value identifiability. Calibrating to optimize both flow and isotope simulation performance produced better flow simulation ensembles, with improved observation capture and validation performance, relative to calibrating to optimize flow simulations alone. Using an isotope simulation performance metric which includes timing error as a secondary optimization objective led to more robust streamflow modeling, even in mesoscale watersheds with limited isotope observation datasets. [ABSTRACT FROM AUTHOR]

The Silurian bedrock aquifer constitutes a major aquifer system for groundwater supply across the Ontario province in Canada. The application of natural and industrial fertilizers near urban centers has led to groundwater NO 3 − -N concentrations that sometimes have exceeded the drinking water limit, posing a threat to the usage of groundwater for the human consumption. Therefore, there is a growing interest and concern about how nitrate is being leached, transported and potentially attenuated in bedrock aquifers. This study assesses the local distribution of groundwater NO 3 − in the up-gradient area of two historically impacted municipal wells, called Carter Wells, in the City of Guelph, Canada, in order to evaluate the potential nitrate attenuation mechanisms, using both groundwater geochemical and isotopic analysis ( 3 H, δ 15 N-NO 3 , δ 18 O-NO 3 , δ 18 O-SO 4 , δ 34 S-SO 4 ) and a detailed vertical hydrogeological and geochemical bedrock characterization. The results indicate that probably the main source of nitrate to the Carter Wells is the up-gradient Arkell Research Station (ARS), an agricultural research facility where manure has been historically applied. The overburden and bedrock groundwater with high NO 3 concentrations at the ARS exhibits a manure-related δ 15 N and δ 18 O signature, isotopically similar to the high nitrate in the down-gradient groundwater from domestic wells and from the Carter Wells. The nitrate spatial distribution appears to be influenced and controlled by the geology, in which more permeable rock is found in the Guelph Formation which in turn is related to most of the high NO 3 − groundwater. The presence of an underlying low permeability Eramosa Formation favors the development of oxygen-depleted conditions, a key factor for the occurrence of denitrification. Groundwater with low NO 3 − -N concentrations associated with more oxygen-limited conditions and coincident with high SO 4 2− concentrations are related to more enriched δ 15 N and δ 18 O values in NO 3 − and to more depleted δ 34 S and δ 18 O values in SO 4 2− , suggesting that denitrification coupled with pyrite oxidation is taking place. The presence of macro crystalized and disseminated pyrite especially in the Eramosa Formation, can support the occurrence of this attenuation process. Moreover, based on tritium analysis, some denitrification can occur in shallow bedrock and within relatively short residence times, associated with less permeable conditions in depth which facilitates oxygen consumption through sulfide oxidation. The role of denitrification mediated by organic carbon cannot be discarded at the study site. This study suggests that the geological configuration and particularly the presence of low permeability Eramosa Formation can play an important role on nitrate natural attenuation, which may serve as a decision factor on defining the bedrock water supply system for both domestic and municipal purposes. [ABSTRACT FROM AUTHOR]

• The Nulliak supracrustal assemblage confirmed to be Eoarchean. • Zircon Hf isotope results indicate the presence of depleted mantle domains underneath the Saglek Block during the Eoarchean. • O-isotope signatures of Eoarchean metamorphic zircon indicate the reworking of material that experienced alteration at low temperature. The Archean Saglek Block, North Atlantic craton, is one of the oldest crustal segments preserved on Earth. This area records two granulite facies metamorphic events: one in the late-Eoarchean at ca. 3.7 Ga and one in the Neoarchean, at ca. 2.75 Ga. Here, we report the results of combined U–Pb/Hf/O in-situ isotope analyses of detrital and metamorphic zircon domains from two meta -sedimentary samples, one psammitic, and one pelitic. Both samples are components of the oldest supracrustal assemblage of the Saglek Block: the Eoarchean Nulliak supracrustal assemblage. The isotopic data presented in this study: (i) confirm deposition age of the Nulliak supracrustal assemblage before ca. 3.65 Ga, (ii) indicate local provenance of the detrital zircon, (iii) suggest deposition of the sedimentary protoliths in a convergent setting, such as an arc, (iv) crystallization of the oldest zircon during the early Eoarchean in a protolith derived from a depleted mantle component, (v) involvement of material that experienced prolonged low temperature alteration during the late Eoarchean granulite facies metamorphism and (vi) selective metamorphic overprinting during the Neoarchean granulite facies metamorphism. The new zircon U–Pb/Hf/O isotope data presented here in conjunction with previously published analyses suggest that a depleted mantle domain existed in the early Archean, as reflected in the positive εHf signature of zircon from the Saglek Block. Yet, such positive Hf isotope deviations are not the norm, but rather the exception in the preserved early Earth zircon record. In addition, mildly elevated zircon δ18O values, i.e. those ≥ 5.9 ‰, are as common in the early Archean as they are in the late-Archean zircon record, implying that crustal reworking was an active and efficient process all through the Archean. Hence, no significant variation in the nature of the reworking and broader geodynamic processes occurred during this period of time. [ABSTRACT FROM AUTHOR]

The Rock Canyon Creek REE–F–Ba deposit is a carbonate-hosted REE deposit located in the Alkaline Province of British Columbia, Canada, which hosts most REE mineralization. It shares tectonic, stratigraphic and structural similarities with nearby Mississippi Valley-type deposits. To constrain the dolomitization and mineralization processes, the δ26Mg, 87Sr/86Sr, and elemental compositions of dolomite, calcite, and fluorite were determined. The δ26Mg values of dolomite from the unmineralized zone (−1.83 ‰ and −1.67 ‰) are consistent with marine evaporative dolomite, but those from the mineralized zone (−0.97 ‰ to −0.17 ‰) are higher and more variable. The linear 87Sr/86Sr–Sr/Mg relationships, both in the dolomite and calcite from the unmineralized zone, suggest dolomitization in an evaporative marine environment. The high δ26Mg values with large variation and the non-stoichiometric Ca/Mg ratios in the dolomite from the mineralized zone suggest that this dolomite interacted with a relatively low-temperature hydrothermal fluid (<200 °C). Considering the Na, Ca, Sr, Ba, and LREE-enrichment and low 87Sr/86Sr signature in the dolomite from the mineralized zone as well as mineral paragenesis in the deposit, the most plausible scenario for the formation of the deposit is that marine-evaporitic dolomite re-equilibrated with basinal fluids along permeable zones, and at a later stage, carbohydrothermal REE-bearing fluids infiltrated into the Rock Canyon Creek brecciated zone and deposited the REE mineralization. Late-stage, post-mineralization calcite veins and iron oxides formed in the upper part of the deposit under supergene conditions, as suggested by combination of textural observations, REE patterns, and differences in isotopic compositions between dolomite and calcite from the mineralized zone. This study demonstrates that δ26Mg, 87Sr/86Sr, and element/Mg ratios in carbonate minerals are useful for characterizing mineralizing fluids in carbonate-hosted deposits, and discriminating mineralization-related dolomite from marine evaporative dolomite and unmineralized hydrothermal dolomite. • Mg and Sr isotopes of carbonates from carbonate-hosted REE–F–Ba deposit were determined. • Mg and Sr isotopes from the unmineralized zone suggested evaporative marine dolomitization. • Hydrothermal dolomite formed by a relatively low-temperature (<~200 °C) hydrothermal fluid. • REE mineralization caused by carbohydrothermal fluid after hydrothermal dolomite formation. • Mineralization-related and unmineralized dolomite can be discriminated by Mg isotopes. [ABSTRACT FROM AUTHOR]

• δ98Mo data of 0.85Ga microbial carbonate, lime mudstone and black shale fill temporal gap in Proterozoic Mo isotope record. • Carbonates and black shales are compared as suitable seawater δ98Mo archives. • Significant δ98Mo variation in carbonate samples likely related to porewater redox conditions. • 0.4‰ discrepancy between heaviest δ98Mo value of carbonate and shale indicates shale is unsuitable as seawater estimate. • Possible archive-dependent bias in δ98Mo interpretation may lead to underestimation of extent of Proterozoic oxic Mo sink. This study addresses marine palaeoredox conditions of the mid-Neoproterozoic by analysing the Mo isotope, trace element, and U-Th-Pb isotope compositions of shallow water microbial carbonate, deep water pelagic carbonate, and shale from the Stone Knife Formation (SKF) in NW Canada. The U-Th-Pb isotope SKF systematics of reef microbialite carbonates, and the moderately expressed negative Ce anomalies are consistent with the presence of dissolved O 2 in the surface waters. Thirteen of 14 analysed samples yield a depositional 206Pb/238U regression age of 0.850 ± 0.028 Ga. The Mo isotope data (δ98Mo) are distinct for the microbial and pelagic carbonates and the deeper water shales, with the isotopically heaviest black shales 0.4 ‰ lighter than the heaviest carbonate. The bulk digestion carbonate δ98Mo data scatter widely, ranging up to 1.64 ‰, and are not reproducible between repeat digestions. The spread in shallow-water carbonate δ98Mo cannot be attributed to a single origin (e.g., admixture of silicate-hosted Mo) and probably reflects a combination of factors, including the complex pathway of Mo into microbial carbonates. Regardless, we propose a minimum δ98Mo of 1.64 ‰ for the 0.85 Ga ocean, similar to other Neo- and Mesoproterozoic estimates from studies of proxies other than black shale. Our new black shale δ98Mo data agree with most previous results from 1.8 to 0.7 Ga shales. If interpreted as reflecting seawater, this would mean a minimum oceanic δ98Mo composition of only 1.29 ‰, implying a limited oxic reservoir compared to the modern Mo budget in agreement with previous studies. This study's results suggest that the discrepancy could also be explained by a systematic offset between δ98Mo compositions of black shales and the overlying water columns, regardless of depositional environment, akin to the relative depth distribution of δ98Mo in modern euxinic water columns such as the Black Sea. If valid, an implied heavier seawater δ98Mo throughout the Proterozoic would indicate that the magnitude of the Mo oxic sink remained relatively stable throughout the Proterozoic, shifting the apparent expansion of oxygen towards the younger boundary of the interpreted onset of the NOE (ca. 1.0–0.54 Ga). [ABSTRACT FROM AUTHOR]

Unique deposits that formed in the Precambrian oceans are the Banded Iron-Formations (BIFs) which are chemical sediments comprised of alternating layers of iron- and silica-dominated precipitates. The origin of this enigmatic banding is still debated, with most favoring a primary sedimentary and a few others arguing for a secondary diagenetic origin. We here use a high-resolution integrated multi-proxy approach and report on the Ge-Si-Fe and Th-U systematics and on the isotopic composition of Cr in exceptionally pure adjacent magnetite and metachert bands from the ∼2.7 billion years old Temagami BIF, Ontario, Canada. While each of the geochemical proxies alone may be controversial, our multi-proxy approach sheds new light on their applicability, as the two types of adjacent BIF bands are each characterised by a distinct geochemical signature. The magnetite bands show super-crustal (i.e. fractionated) Ge/Si ratios approaching those of modern marine high-temperature hydrothermal fluids, unfractionated Th/U ratios similar to those of crustal rocks, and unfractionated Cr isotope ratios similar to "Bulk Silicate Earth". Adjacent metachert bands, however, show lower (i.e. unfractionated) Ge/Si ratios close to those of modern seawater, sub-crustal (i.e. fractionated) Th/U ratios, and fractionated Cr isotope ratios above those of Bulk Silicate Earth. The composition of the magnetite bands suggests that the original iron-oxyhydroxide precipitated during periods when the dissolved Ge, Th, U, and Cr inventory of ambient seawater was dominated by input from mafic crust via anoxic high-temperature hydrothermal fluids. In contrast, the composition of the metachert bands indicates that these formed during times when ambient seawater was dominated by low-temperature riverine input from an evolved landmass that despite its Neoarchean age had provided environments for oxidative Cr and U mobilization during terrestrial weathering. This suggests that habitats with oxygenic photosynthesis existed on land at least 200 million years before the Great Oxidation Event. The systematic and internally consistent difference between the geochemical signatures shown by the two types of adjacent BIF bands also demonstrates that the prominent banding of BIFs is a primary depositional feature reflecting precipitation from different watermasses and is not the result of post-depositional separation of an initially homogeneous chemical sediment. • Metachert bands in Temagami BIF provide information about Neoarchean landmasses. • Temagami BIF's metacherts show unfractionated Ge/Si and fractionated δ 53 Cr and Th/U. • Fractionated δ 53 Cr and Th/U reveal oxidative weathering on land 200 my before the GOE. • Temagami magnetite bands show fractionated Ge/Si and unfractionated δ 53 Cr and Th/U. • Internally consistent signals from various proxies show primary origin of BIF banding. [ABSTRACT FROM AUTHOR]

Highlights: [•] We investigated the molecular and isotopic compositions of biodegraded oils from the Alberta Basin. [•] Alberta heavy oils show increasing biodegradation from top to bottom of the oil columns. [•] The level of oil biodegradation varies regionally in the basin, ranging from PM2 to PM10+. [•] S and N isotopic compositions of the heavy oils are not affected by severe biodegradation. [•] The S and N isotopic compositions of biodegraded oils are indicative of the primary oil charge. [Copyright &y& Elsevier]

Abstract: The aging of “new” mercury (Hg) was investigated in Experimental Lake 658 as part of the Mercury Experiment To Assess Atmospheric Loading In Canada and the United States (METAALICUS). Mercury enriched in 202Hg was added to the epilimnion over a three-year period to simulate direct atmospheric deposition. We evaluated the aging of newly added mercury (HgLake) in the water column using chemical methods and experiments to examine differences in phase partitioning and transport compared to the ambient pool, HgAmb. Aging was sufficiently slow to observe differences in the partitioning characteristics of HgLake and HgAmb. Amended HgLake initially partitioned to a greater extent to epilimnetic particulate matter (log Kd of HgLake =5.08; log Kd of HgAmb =4.9). HgLake was transported rapidly to the hypolimnion by settling particulate matter. Partitioning became more similar after amended Hg was recycled within the hypolimnion through redox processes. Experiments showed the removal of Hg from the aqueous phase by Fe and/or Mn oxyhydroxide–organic matter complexes. Separations using the anion exchange resin DEAE indicated that both HgLake and HgAmb were associated mainly with dissolved organic matter (DOM) and with partial association with sulfide in anoxic waters, but the degree of association of HgLake with DOM was higher in oxic (epilimnetic) waters. In the solid phase, chemical fractionation indicated greater association of HgLake with organic matter, while HgAmb showed greater association with oxyhydroxide and inert phases. Overall, the results suggest that “new” Hg added from the atmosphere is initially more particle-reactive than ambient Hg in the epilimnion, where initial sorption/partitioning occurs mainly to plankton and detrital particles. Once Hg has been deposited at the sediment–water interface, extended equilibration time in combination with microbial and chemical redox processes “age” the “new” Hg, and particle partitioning becomes similar for the added isotope and ambient pools. [Copyright &y& Elsevier]

Abstract: The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) was flown from Lynn Lake, Manitoba, Canada in August, 2000, during the maximum solar modulation period, with an average residual atmospheric overburden of 4.3g/cm2. Precise spectral measurements of cosmic ray hydrogen isotopes from 0.178GeV/n to 1.334GeV/n were made during the 28.7h of flight. This paper presents the measured energy spectra and their ratio, 2H/1H. The results are also compared with previous measurements and theoretical predictions. [Copyright &y& Elsevier]

Background: Leucine has been suggested to improve athletic performance. Therefore, the branched-chain amino acids (BCAAs), especially leucine, are popular as dietary supplements in strength- training athletes; however, the intake of leucine in excess of requirements raises concerns regarding adverse effects. Currently, the tolerable upper intake level (UL) for leucine is unknown. Objective: The objective of the current study was to determine the UL for leucine in adult men under acute dietary conditions. Design: Five healthy adults (20-35 y) each received graded step- wise increases in leucine intakes of 50, 150, 250, 500, 750, 1000, and 1250 mg • kg-1 d-1, which corresponded to the Estimated Average Requirement (EAR) and the EAR X3, X5, X10, X15, X20, and X25 in a total of 29 studies. The UL of leucine was identified by the measurement of plasma and urinary biochemical variables and changes in leucine oxidation by using L-[l-l3C]-leucine. Results: A significant increase in blood ammonia concentrations above normal values, plasma leucine concentrations, and urinary leucine excretion were observed with leucine intakes >500 mg •-1 d-1. The oxidation of L-[l-13C]-leucine expressed as label tracer oxidation in breath (F13CO2), leucine oxidation, and a-ketoisocaproic acid (KIC) oxidation led to different results: a plateau in (F13CO2) observed after 500 mg • kg-1 d-1, no clear plateau observed in leucine oxidation, and KIC oxidation appearing to plateau after 750 mg • kg-1 d-1. Conclusion: On the basis of plasma and urinary variables, the UL for leucine in healthy adult men can be suggested at 500 mg • kg-1 d-1' or ~35 g/d as a cautious estimate under acute dietary conditions. This trial was registered at clinicaltrials.gov as NCT00972582. [ABSTRACT FROM AUTHOR]

Background: Plant sterol (PS) supplementation is increasingly ac-cepted as a dietary strategy to lower plasma cholesterol concentra-tions. However, information is scarce about the effect of increased PS intake in potentially vulnerable groups, such as phytosterolemia heterozygotes (HET). Objective: This study assessed the responsiveness of circulating PS and lipid concentrations and cholesterol kinetics (absorption and synthesis) to daily PS supplementation in HET (ABCG8 S107X mutation) compared with a healthy control cohort. Design: A double-blind, randomized, crossover, placebo-controlled study was conducted in 10 HET and 15 control subjects. The par-ticipants had a mean (±SEM) age of 34 ± 2 y and a BM1 (in kg/m2) of 29.9 ±1.1 and consumed ∼ 1.6 g PS or placebo capsules daily with supper for 4 wk. Cholesterol absorption and synthesis were assessed by using [13C]cholesterol and deuterium oxide, respec-tively. Results: Plasma LDL-cholesterol concentrations decreased (P = 0.006) in both groups after PS supplementation (HET: 2.73 ± 0.19 mmol/L; control: 3.11 ± 0.19 mmol/L) compared with placebo (HET: 3.12 ± 0.20 mmol/L; control: 3.50 ± 0.21 mmol/L), whereas PS concentrations (campesterol+ß-sitosterol) increased (P = 0.03) in both groups after PS supplementation (HET: 39.72 ± 6.05 /¡mol/L; control: 24.03 ± 1.65 /¡mol/L) compared with placebo (HET: 27.32 ± 3.80 /&um;mol/L; control: 21.12 ± 2.05 /(mol/L). Cho-lesterol absorption efficiency decreased (P = 0.010) by ∼22% and ∼17% and synthesis rates increased (P = 0.040) by ∼20% and ∼24% in the HET and control groups, respectively, in response to PS consumption compared with placebo. Conclusion: These data suggest that heterozygosity for the ABCG8 S107X mutation does not influence the action of dietary PS on circu-lating cholesterol concentrations but may affect sterol absorption. This trial was registered at clinicaltrials.gov as NCT01102647. [ABSTRACT FROM AUTHOR]

Abstract: Tree-ring analyses have contributed significantly to investigations of past climate. Stable isotope climate proxies (δ18O, δD and δ13C values) enhance traditional ring-width data, although poor preservation of ancient wood has tended to limit development of stable isotope proxy records to the Holocene and the Late Pleistocene. Here we apply stable isotope techniques to wood that represent the remains of Mixed-Coniferous Boreal Vegetation preserved in Early Pliocene (4–5Ma) deposits at Strathcona Fiord, Ellesmere Island, Canada (ca. 78°N). Four well-preserved tree trunks, identified through wood anatomical characteristics as Larix (larch), from this high Arctic site provide annually resolved sequences of up to 250years from which we developed a high-resolution record of Pliocene climate. Stable oxygen isotope values, in conjunction with ring-width measurements were used to derive annually resolved temperature records for this site. Our ring-width and isotope-based reconstructions provide an annually resolved record, up to 250years, of temperature and indicate growing season (JJ) temperatures (15.8±5.0°C) 11.8±5.1°C, and mean annual temperatures (MAT) (−1.4±4.0°C) 18.3±4.1°C warmer than present. Estimated isotope values of precipitation of −16.3±2‰ (δ18O) and −150.1±8.9‰ (δD) were calculated from the isotopic values of wood cellulose. Relative humidity estimated from both δ13C and δD records ranged from 60 to 80%. Paleotemperature, source water and humidity estimates are comparable to those of a modern Boreal Forest growing ca. 15–20° south of modern Ellesmere Island. [Copyright &y& Elsevier]

Abstract: Brines in Cambrian sandstones and Ordovician dolostones of the St-Lawrence Lowlands at Bécancour, Québec, Canada were sampled for analysis of all stable noble gases in order to trace their origin and migration path, in addition to quantifying their residence time. Major ion chemistry indicates that the brines are of Na–Ca–Cl type, possibly derived from halite dissolution. 87Sr/86Sr ratios and Ca excess indicate prolonged interactions with silicate rocks of the Proterozoic Grenville basement or the Cambrian Potsdam sandstone. The brines constrain a 2–3% contribution of mantle 3He and large amounts of nucleogenic 21Ne∗ and 38Ar∗ and radiogenic 4He and 40Ar∗. 4He/40Ar∗ and 21Ne∗/40Ar∗ ratios, corrected for mass fractionation during incomplete brine degassing, are identical to their production ratios in rocks. The source of salinity (halite dissolution), plus the occurrence of large amounts of 40Ar∗ in brines constrain the residence time of Bécancour brines as being older than the Cretaceous. Evaporites in the St-Lawrence Lowlands likely existed only during Devonian–Silurian time. Brines might result from infiltration of Devonian water leaching halite, penetrating into or below the deeper Cambrian–Ordovician aquifers. During the Devonian, the basin reached temperatures higher than 250°C, allowing for thermal maturation of local gas-prone source rocks (Utica shales) and possibly facilitating the release of radiogenic 40Ar∗ into the brines. The last thermal event that could have facilitated the liberation of 40Ar∗ into fluids and contributed to mantle 3He is the Cretaceous Monteregian Hills magmatic episode. For residence times younger than the Cretaceous, it is difficult to find an appropriate source of salinity and of nucleogenic/radiogenic gases to the Bécancour brines. [Copyright &y& Elsevier]

Abstract: Geochemical and isotopic monitoring allows determination of CO2 presence in the subsurface through the sampling of produced fluids and gases at production and/or monitoring wells. This is demonstrated by data from 22 months of monitoring at the Pembina Cardium CO2 Monitoring Pilot in central Alberta, Canada. Eight wells centered around two CO2 injectors were sampled monthly between February 2005 and February 2007. Stable isotope analyses of the samples revealed that changes in the δ13CCO2 values in produced gas as well as changes in the δ18O values of the produced fluids indicate CO2 presence and identify trapping mechanisms at select production wells. Using equilibrium isotope exchange relationships and CO2 solubility calculations, fluid and gas saturations in the pore space in excess of that occupied by oil were calculated. We demonstrate that stable isotope measurements on produced fluids and gases at the Pembina Cardium CO2 storage site can be used to determine both qualitatively and quantitatively the presence of CO2 around the observation well, given that the injected CO2 is isotopically distinct. [Copyright &y& Elsevier]

Abstract: Elevated nitrate concentrations in streams and groundwater are frequently observed following forest harvest. In addition to depleting nutrients available for forest regeneration, elevated nitrate export following harvest can have deleterious effects on downstream aquatic ecosystems. As part of a forest harvest experiment conducted at the Turkey Lakes Watershed, Ontario, Canada, stable isotope techniques were employed to investigate nitrate attenuation in a natural wetland receiving high concentrations of nitrate as a result of clear-cutting in the catchment. Isotopic analysis of nitrate (δ18O, δ15N) and vegetation (δ15N) demonstrated that both denitrification and plant uptake of nitrate resulted in significantly lower nitrate concentrations in wetland outflow compared to incoming stream water. Although the 0.2-ha forested swamp (4% of catchment by area) was too small to be featured on standard topographic maps, the wetland remove 65–100% of surface water nitrate inputs, thereby protecting downstream aquatic habitats from the full effect of N release from forest harvest. The δ15N enrichment factor associated with nitrate attenuation in wetland surface water was lower than typically observed during denitrification in groundwaters, suggesting that nitrate removal is complete in some areas of the wetland. Plant assimilation of nitrate was also partially responsible for the low observed enrichment factor. Wetland plants recorded the high δ15N associated with denitrification activity in portions of the wetland. Apportionment of nitrate sources using δ18O–NO3 − at the outlet weir was unaffected by the wetland nitrate attenuation under pre- and post-harvest conditions due to the mid-catchment position of the wetland. Future forest management practices designed to recognize and preserve small wetlands could reduce the potentially detrimental effects of forest harvest on aquatic systems. [Copyright &y& Elsevier]

Although lead isotope ratios have been used to identify lead ammunition (lead shotshell pellets and bullets) as a source of exposure for First Nations people of Canada, the actual source of lead exposure needs to be further clarified. Whole blood samples for First Nations people of Ontario, Canada, were collected from participants prior to the traditional spring harvest of water birds, as well as post-harvest. Blood-lead levels and stable lead isotope ratios prior to, and after the harvest were determined by ICP-MS. Data were analyzed by paired t-tests and Wilcoxon Signed-Ranks tests. All participants consumed water birds harvested with lead shotshell during the period of study. For the group excluding six males who were potentially exposed to other sources of lead (as revealed through a questionnaire), paired t-tests and Wilcoxon Signed-Ranks tests showed consistent results: significant (p <0.05) increases in blood-lead concentrations and blood levels of 206Pb/204Pb and 206Pb/207Pb towards the mean values we previously reported for lead shotshell pellets; and a significant decrease in 208Pb/206Pb values towards the mean for lead shotshell pellets. However, when we categorized the group further into a group that did not use firearms and did not eat any other traditional foods harvested with lead ammunition other than waterfowl, our predictions for 206Pb/204Pb, 206Pb/207Pb and 208Pb/206Pb hold true, but there was not a significant increase in blood-lead level after the hunt. It appears that the activity of hunting (i.e., use of a shotgun) was also an important route of lead exposure. The banning of lead shotshell for all game hunting would eliminate a source of environmental lead for all people who use firearms and/or eat wild game. [Copyright &y& Elsevier]

Abstract: Three curves delineating δ 13C variations across the Early Cambrian Sekwi Formation carbonate ramp, Mackenzie Mountains, Northwest Territories, Canada, are incorporated into a biostratigraphic and sequence stratigraphic framework that provides a higher resolution temporal and spatial framework for the Sekwi Formation. The three δ 13C curves were correlated across a range of depositional environments, from tidal flat to deep subtidal on the Sekwi carbonate ramp. Eight δ 13C “cycles” in the curves (A–H) were correlated across the basin, complimenting the sequence stratigraphic framework. The most complete δ 13C curve from the Sekwi Formation correlates well with a composite Early Cambrian δ 13C curve from the Siberian Platform. However, the differing magnitude and absolute timing of some of the correlative isotopic excursions records the influence of regional tectonism, sea level changes, and diagenesis on the Sekwi ramp. Additionally, the Sekwi Formation δ 13C curve has more high-frequency variations than the Siberian curve, due in part to the higher sample density used to construct the Sekwi curve. The Early–Middle Cambrian boundary was not sampled in this study, but a large negative isotopic excursion in the very latest Early Cambrian coincides with a regional drowning that may be correlative throughout western Laurentia, but recognizing this event globally is problematic. [Copyright &y& Elsevier]

Abstract: Lu–Hf, Sm–Nd and in-situ clinopyroxene Sr and Pb isotope systematics, and mineral major and in-situ trace element compositions were obtained for a suite of non-diamond and diamond-bearing eclogites from the Diavik kimberlites (A154; 55 Ma old), Slave craton (Canada). Temperature estimates of last equilibration in the lithosphere for the non-diamond-bearing Diavik eclogites define two groups; low-temperature (800–1050 °C) and high-temperature eclogites (1100–1300 °C). Most diamond–eclogites indicate temperatures similar to those of the high-temperature eclogites. Isotopic and major and trace element systematics for the non-diamond- and diamond-bearing eclogites indicate overlapping chemical compositions suggesting similar rock formational histories. Calculated whole rock major and trace element abundances using chemical and modal abundances for constituent minerals exhibit broad similarities with mafic cumulates from ophiolite sequences. Most importantly the calculated whole rock eclogite compositions display positive Sr and Eu anomalies, typically interpreted as the result of plagioclase accumulation in cumulate rocks of oceanic crust sequences. Initial whole rock Hf isotopic values and in-situ Sr isotope data from clinopyroxene grains provide evidence that the eclogites were derived from precursor rocks with depleted mantle isotope characteristics. These combined results support the interpretation that the eclogites from Diavik represent remnants of subducted oceanic crust. Lu–Hf isotope systematics indicate that the oceanic protolith for the eclogites formed in the Paleoproterozoic at ∼2.1 Ga, which is in agreement with the in-situ Pb isotope data from clinopyroxene. This result also corroborates the ∼2.1 Ga Lu–Hf model ages recorded by mantle zircons from eclogite found within the Jericho kimberlite in the northern Slave Province (∼200 km northwest of Diavik). The results from both studies indicate a link between eclogite formation and Paleoproterozoic subduction of oceanic lithosphere along the present-day western margin of the Archean Slave craton. [Copyright &y& Elsevier]

Abstract: Surface water samples were collected from 55 sites in the Great Lakes Basin and analyzed for the presence of perchlorate using HPLC/MS/MS with an isotopically enriched internal standard. Sites included areas impacted by heavy industry, urbanization, agriculture and atmospheric deposition. Perchlorate was detected at several of the sites at concentrations close to the method detection limit (0.2μg/l). Despite these low concentrations, its presence was confirmed by sample concentration and determination of the isotopic ratio of perchlorate. The presence of perchlorate at two of the sites was related to a fireworks display which had occurred prior to sampling. The other detections of perchlorate were in rivers/creeks draining watersheds which had high density livestock and crop farming activity. We suspect the two are related. To our knowledge, these are the first reported concentrations of perchlorate in Canadian surface waters. [Copyright &y& Elsevier]

Abstract: Beluga (Delphinapterus leucas) continues to be an important food species for Arctic communities, despite concerns about its high mercury (Hg) content. We investigated whether Hg and cadmium (Cd) concentrations had changed during the 20th century in beluga near Somerset Island in the central Canadian Arctic, using well-preserved teeth collected from historical sites (dating to the late 19th century and 1926–1947) and during subsistence hunts in the late 1990s. Mercury concentrations in both historical and modern teeth were correlated with animal age, but 1990s beluga exhibited a significantly more rapid accumulation with age than late 19th century animals, indicating that Hg concentrations or bioavailability in their food chain had increased during the last century. The geometric mean tooth Hg concentration in modern 30 year old animals was 7.7 times higher than in the late 19th century, which corresponds to threefold higher concentrations in muktuk and muscle. Teeth from 1926 to 1947 were similar in Hg content to the late 19th century, suggesting that the increase had occurred sometime after the 1940s. In contrast, tooth Cd was not correlated with animal age and decreased during the last 100 years, indicating that anthropogenic Cd was negligible in this population. Late 19th century beluga displayed a greater range of prey selection (tooth δ 15N values: 15.6–20.5‰) than modern animals (δ 15N: 17.2–21.1‰). To prevent this difference from confounding the temporal Hg comparison, the Hg–age relationships discussed above were based on historical animals, which overlapped isotopically with the modern group. Tooth δ 13C also changed to isotopically more depleted values in modern animals, with the most likely explanation being a significant shift to more pelagic-based feeding. Industrial Hg pollution is a plausible explanation for the recent Hg increase. However, without further investigation of the relationship between the range exploitation of modern beluga and their possible exposure to regional marine food chains with (naturally) higher Hg contents than their historical counterparts, we cannot unequivocally conclude that the increase was anthropogenically driven. [Copyright &y& Elsevier]

Investigations on the distribution of thorium isotopes in the water column have been utilized as powerful tracers to investigate the geochemical pathways of particle-reactive material in the ocean. We measured Th (228Th, 230Th, 232Th and 234Th) isotopes in samples collected along a horizontal profile from Barrow, AK to the Canada Basin as well as two vertical profiles in the Canada Basin. The suspended particle concentrations were also measured to investigate the role of suspended particulate matter (SPM) in Th scavenging.The SPM inventory is more than an order of magnitude higher than that reported for the Alpha Ridge ice station, indicating that the SPM inventories vary over an order of magnitude in the deep Arctic Basins. The conditional partition coefficient of Th isotopes between suspended particulate matter and dissolved phase generally appears to be higher than those in non-polar regions, and this is attributed to more reactive suspended particulate matter. The residence times of total 230Th are significantly lower than those calculated for the Alpha Ridge station, while higher than those found in the Eurasian Basin and Beaufort Sea in the Canadian Basin. The calculated residence time in all the deep basins of the Arctic Ocean varied between 13±1 and 45±1 years. A reversible scavenging model applied to the distribution of Th isotopes (230Th–228Th in the deep waters and 234Th–228Th in the upper 100 m) indicates that the forward removal rate constant is higher than the value reported for the Alpha Ridge while the reverse rate constant is comparable to the Alpha Ridge station suggesting faster removal onto particulate matter and slower desorption of Th from the particulate matter. [Copyright &y& Elsevier]

Gas composition and stable isotope data were integrated to constrain the controls on the occurrence of H2S and CO2 in the subsurface Triassic of the west central Alberta Basin in Canada. Compositional data reveal that the wettest gases occur in the central part of the study area and are flanked by gases of increasing dryness to the east and west. H2S production in the Triassic system is attributed to sulfate reduction. Present temperatures in the subsurface are approximately 60 to 80 °C in the interval of interest. These temperatures are 50 to 55 °C less than the minimum threshold for thermal sulfate reduction (TSR), suggesting that bacterial sulfate reduction (BSR) is the probable mechanism of active H2S generation. Higher temperatures present during previous stages of burial were within the range of thermal sulfate reduction (TSR). Variability in the measured δ34S values of gases in Lower and Middle Triassic strata appears be controlled by dissolved sulfate fluxes from two sulfate sources having disparate δ34S signatures, as well as by the admixing of H2S generated by TSR at previous stages of deeper burial. [Copyright &y& Elsevier]

Lead concentrations and Pb isotope ratios were measured in the forest floor, mineral soil and vegetation at a white pine and a sugar maple stand in a woodland in south central Ontario. Lead concentrations decreased and 206Pb/207Pb ratios increased with mineral soil depth reflecting the mixing of pollution and natural Pb sources. Lead concentrations and 206Pb/207Pb ratios at 20–30 cm depth were ∼6–7 mg/kg and 1.31–1.32, respectively. Assuming an integrated 206Pb/207Pb ratio in deposition over time of 1.18, estimated from lichen measurements and published data for the region, approximately 65% of Pb in the surface (0–1 cm) mineral soil is from anthropogenic sources. Approximately 90% of pollution Pb is found in the 0–10 cm soil layer (Ah) and less than 3% of the pollution Pb is present in the forest biomass and mull-type forest floor combined. Despite low Pb concentrations in vegetation (<2.5 mg/kg), we estimate that between 65 and 100% of the Pb in vegetation and ∼75% of the Pb in the forest floor is from pollution sources. In total, the pollution Pb burdens at the pine and maple stands are estimated to be 860 and 750 mg/m2, respectively. [Copyright &y& Elsevier]

Potassic silica-undersaturated mafic volcanic rocks form a minor portion of the predominantly calc–alkaline Eocene Challis–Kamloops volcanic belt, which extends from the northwestern United States into central British Columbia (Canada). Their major occurrence is in the Penticton Group in south central British Columbia, where they reach a thickness of up to 500 m and form the northwestern edge of the Montana alkaline province. These analcime-bearing rocks (∼53–52 Ma old) are typically rhomb porphyries of ternary feldspar (An28Ab52Or20). Additional phenocryst phases include clinopyroxene, analcime, phlogopite and rare olivine. The rocks are characterized by high total alkalis, particularly K2O (>4.5 wt%) as well as by a distinct enrichment of large-ion lithophile elements versus heavy rare-earth elements and high-field-strength elements. They have unusual isotopic compositions compared to most other rocks of the Challis–Kamloops belt, particularly high negative ∊Nd values and elevated but relatively uniform initial 87Sr/86Sr ratios (∼0.7065). The potassic silica-undersaturated rocks overlie Precambrian crust and lithosphere and were at least in part derived from ancient metasomatized subcontinental mantle lithosphere, which was modified in a Precambrian subduction setting. The alkaline rocks of the Challis–Kamloops belt are related to a slab-window environment. In particular, they were formed above the southern edge of the Kula plate adjacent to the Kula–Farallon slab window, whereas the Montana alkaline province situated well to the southeast was formed directly above the Kula–Farallon slab window. Upwelling of the hotter asthenospheric mantle may have been the thermal trigger necessary to induce melting of fertile and metasomatized lithospheric mantle. [Copyright &y& Elsevier]

An isotope-based approach for water balance assessment is presented and applied to estimate throughflow, residence time and catchment runoff to 70 headwater lakes on the Boreal plain and uplands of northern and north-central Alberta, Canada. The survey reveals a complex hydrologic regime with systematic variability in water balance due to local site characteristics. On average, runoff to lakes in wetland-dominated catchments is found to be significantly higher than runoff to upland-dominated lakes, with generally higher contributions from catchments with low bog/fen ratios. The isotope method, which relies primarily on water sampling and isotopic analysis, can be easily integrated in routine water quality surveys and is shown to be a practical alternative to conventional hydrological modelling for comparative analysis of water balance controls on hydrochemistry and aquatic ecology of lakes, particularly in low-relief wetland-rich terrain. [Copyright &y& Elsevier]

The basement-hosted Bong uranium deposit in the Kiggavik region is associated with a broad hydrothermal alteration halo characterized by an inner illite-rich zone and an outer chlorite-rich zone. The uranium-bearing zones characterized by intense illite alteration yield high δ56Fe and δ26Mg values relative to the host rocks, with average whole-rock values of δ56Fe = 0.58 ± 0.15‰ and δ26Mg = 0.61 ± 0.29‰, and clay-size fraction values of δ56Fe = 0.51 ± 0.20‰ and δ26Mg = 0.82 ± 0.09‰. These isotopic values correlate with a decrease in average Fe2+ concentrations (0.47 versus 2.30 mol% Fe2+ in least-altered hosts). The high δ26Mg values reflect intense illite alteration, which preferentially incorporated heavier magnesium isotopes during alteration of both the ore zones and an upper hematite-altered horizon. Although the clay alteration with high δ56Fe and δ26Mg values coincides with the main uranium-bearing zone, the δ56Fe signatures reflect multiple stages of alteration and mineralization. The high δ56Fe values and lower Fe2+ contents of the uranium-bearing zones support leaching of Fe2+ (aq) enriched in lighter iron isotopes. Sequential leach δ56Fe experiments also indicate that formation of fine-grained iron oxides/hydroxides with positive δ56Fe values (+0.23 to +0.60‰) in late chemical fronts enhanced the primary positive δ56Fe signatures recorded in ore zones. Near surface samples with similar isotopic signatures provide clues to buried mineralization and support structural disruption of the systems after primary mineralization. Distal geochemical expressions of this system may include enrichment in iron contents with negative δ56Fe values and/or negative δ26Mg whole-rock or clay-size fractions values, reflecting precipitation of the isotopically light iron and magnesium leached during hydrothermal alteration. Although more costly to process, sequential leach δ26Mg or δ56Fe analyses produced greater variance in the ore zones relative to background values and removed anomalous values from carbonate minerals. Isotopic analyses of the clay-size fraction produced results comparable to the final digestion in the sequential leach process but this method in particular requires greater understanding the mineralogical controls on the isotopic signatures. [Display omitted] • Application of iron and magnesium isotope methods to hydrothermal uranium deposits • Complex hydrothermal fluid history revealed through iron and magnesium isotopes • Quantifying fluid-rock and redox reactions in the formation of unconformity-related uranium deposits [ABSTRACT FROM AUTHOR]

• Geochemistry, geochronology and zircon Hf isotopic compositions of the Eoarchean to Neoarchean crust from the Saglek-Hebron Complex (SHC). • The SHC felsic crust formed over one billion years through six distinct magmatic events. • Newly identified Paleoarchean Iluilik magmatic event. • Hadean to Eoarchean mafic crustal source for the SHC TTG. • Reworking of Eoarchean TTG producing granite over one billion years. • Distinct shift to more juvenile Hf isotopic composition at ∼3.2 Ga. • Implications for Earth's early crust evolution. The Saglek-Hebron Complex (SHC) located in Northern Labrador, Canada, includes some of the oldest crustal rocks on Earth. This granite-greenstone terrain is dominated by trondhjemite, Mg-rich tonalite, granite, with subordinate granodiorite, and recorded over one billion years of early magmatic history between ∼3900 Ma and ∼2700 Ma. New in-situ U-Pb analyses on zircons from eighteen rock samples, suggest that six distinct magmatic events formed the felsic crust of the SHC, during the Archean Eon. Age deconvolution analysis constrains these magmatic episodes at ca. 3857 Ma, 3744 Ma, 3575 Ma, 3330 Ma, 3224 Ma and 2750 Ma, respectively defined as the Iqaluk, the Uivak I, the Uivak II, the Iluilik, the Lister and the late granite events. The 3330 Ma Iluilik represents a newly defined magmatic event, distinct from the Lister event previously recognized at ∼3200 Ma. Uranium-Pb geochronology, combined with in-situ Hf isotopic data on zircons and geochemistry of the host rocks, reveal a complex and protracted crustal history of the SHC marked by the reworking of mafic and felsic crust over one billion years. Zircons from the oldest Iqaluk and Uivak I samples yield slightly suprachondritic initial εHf values (up to ∼+4), consistent with the involvement of a long-term depleted source in the Eoarchean. The 3330 Ma Iluilik granodiorite exhibits a low initial εHf value of −6, clearly diverging from the near-chondritic Hf isotopic composition of the 3224 Ma Lister tonalites. Considering a mafic crustal precursor (with a 176Lu/177Hf ratio of ∼0.02) for trondhjemite-tonalite-granodiorite (TTG) samples, the initial Hf isotopic compositions of the SHC Eoarchean to Paleoarchean zircons would be consistent with the reworking of Hadean mafic crust. The zircon εHf vs. time trend for granite samples corresponds to a 176Lu/177Hf ratio of ∼0.01, suggesting that the granitic crust was mainly produced by crustal reworking of the oldest TTG. Similarly to the felsic crust of the Itsaq Gneiss Complex of SW Greenland, the SHC granitoids appear to record a shift to more juvenile compositions at the end of the Paleoarchean. However, contrary to what is observed in SW Greenland, almost no input of juvenile material has been recorded by the SHC Neoarchean felsic crust. [ABSTRACT FROM AUTHOR]

Hinchey (2021) uses new Nd isotope data for metavolcanic and plutonic rocks from the Aillik Domain of the Makkovik Province to propose a reinterpretation of the Makkovik Province, arguing that the Aillik and Cape Harrison domains of the orogen should be combined into a single new domain. However, Hinchey reaches this conclusion by re-plotting the locations of the analysed samples to give the impression that Makkovikian rocks of the Aillik and Cape Harrison domains had similar ranges of (initial) Nd isotope composition. I will show in this comment that Hinchey's claim of largely overlapping Nd isotope signatures in the Aillik and Cape Harrison domains is incorrect, and that multiple lines of isotopic evidence do not support her tectonic model. [ABSTRACT FROM AUTHOR]

The tempo and magnitude of ocean oxygenation during the rise of animals in the Ediacaran Period (635 to 539 million years ago, or Ma) is debated. Reconciling this debate is key to understanding what role, if any, oxygen played in the rise of large morphologically complex life on Earth. We reconstruct a portion of Ediacaran ocean oxygenation history using thallium isotope records (reported as ε205Tl) captured in shales from South China (Wuhe section) and northwestern Canada (Goz A and Sekwi Brook sections). At first blush, our ε205Tl data from these two locations are very different. South China shales reveal two pronounced and extremely negative Tl isotope excursions, in mid-members II and III of the Doushantuo Formation (where ε205Tl authigenic reach nadirs of −10.4 ± 0.2; 2SD and − 9.1 ± 0.2; 2SD, respectively). In contrast, northwestern Canada shales reveal fairly invariant values (average ε205Tl authigenic = −2.1 ± 1.6; 2SD, n = 75). These disparate records are in much better agreement, however, if we cull from our dataset shales that were inferred in previous work to have been deposited in restricted settings. By comparison to analogous modern settings (e.g., the Black Sea), ε205Tl data in these shales most likely fingerprint local-scale processes. On the other hand, and also by comparison to modern settings (e.g., Cariaco and Santa Barbara basins), shales deposited in an open ocean setting probably captured a globally homogenous seawater ε205Tl (ε205Tl SW). Moving forward with this assumption, we find that Ediacaran open ocean ε205Tl SW values were predominantly comparable to bulk upper continental crust (ε205Tl = ~−2). These relatively heavy open ocean ε205Tl SW imply limited Mn oxide burial in global marine sediments for large periods of time during the Ediacaran, and by inference also limited accumulation of O 2 in global marine bottom waters. Only for what appear to be very brief episodes of time (≪5–10 million years) at ~635 Ma and ~580 Ma did open ocean ε205Tl SW reach values considerably lighter than bulk upper continental crust (for example, ε205Tl SW as low as −4.4 ± 0.2; 2SD at ~635 Ma and − 5.3 ± 0.3: 2SD at ~580 Ma). These much rarer negative ε205Tl SW values require short-lived episodes of globally enhanced Mn oxide burial in marine sediments, and by implication also brief episodes of enhanced accumulation of O 2 in global marine bottom waters. When interpreting geochemical data, it is important to make global-scale inferences only after identifying and accounting for local-scale overprints. Applying this strategy ourselves, we find compelling evidence for an Ediacaran global ocean that only very briefly experienced widespread bottom water oxygenation during the rise of animals. [ABSTRACT FROM AUTHOR]

Little is known about how forests adjust their gas-exchange mode while atmospheric CO 2 rises globally and air quality changes regionally. The present study aims at addressing this research gap for boreal spruce trees growing in three different regions of Canada, submitted to distinct levels of atmospheric emissions, by examining the amount of carbon gained per unit of water lost in trees, i.e., the intrinsic water use efficiency (iWUE). Under pristine air quality conditions, middle-to long-term trends passed from no-reaction mode to passive strategies due to atmospheric CO 2 , and short-term iWUE variations mostly ensue from year-to-year climatic conditions. In contrast, in trees exposed to pollutants from a copper smelter and an oil-sands mining region, air quality deterioration generated swift, long-term iWUE rises immediately at the onset of operations. In this case, the very active foliar strategy sharply reduced the intra-foliar CO 2 (Ci) pressure. Statistical modeling allowed identifying emissions as the main trigger for the iWUE swift shifts; subsequent combined effects of emissions and rising CO 2 led to passive foliar modes in the recent decades, and short-term variations due to climatic conditions appeared all along the series. Overall, boreal trees under different regional conditions modified their foliar strategies mostly without changing their stem growth. These findings underline the potential of acidifying emissions for prompting major iWUE increases due to lowering the stomatal apertures in leaves, and the combined influence of rising CO 2 in modulating other foliar responses. A fallout of this research is that degrading air quality may create true divergences in the relationship between tree-ring isotopes and climatic conditions, an impact to consider prior to using isotopic series for paleo-climatic modeling. Image 1 • IWUE was determined for boreal trees submitted to distinct levels of atmospheric emissions. • Trees from remote stands rise iWUE proportionally with atmospheric pCO 2. • IWUE trends of exposed stands depart from regular pCO 2 -induced reactions. • Trees modified their foliar strategies without changing their stem growth. • Modeling underlines the individual and combined influences of pCO 2 and acidifying pollutants. Gas exchange strategies of forests exposed to acidifying emissions create major divergences from responses to pCO 2 and climatic conditions, a concern for modeling global C and water cycles. [ABSTRACT FROM AUTHOR]

• We present LASS U–Pb and Sm–Nd isotope data from the Acasta Gneiss Complex, Canada. • Sm–Nd redistribution occurred at 3.3 Ga and again during the 1.89 Ga Wopmay orogen. • Sm–Nd redistribution is a common feature of ancient poly-metamorphic terranes. • Sm–Nd mobility may compromise the initial Nd isotope composition of ancient rocks. • Analysis of Nd-rich minerals proves useful for assessing bulk-rock Nd isotope data. The whole rock 143Nd isotope record of the Acasta Gneiss Complex (AGC) has been used to argue for the development of both depleted mantle and enriched crustal reservoirs during the Hadean. The 147Sm–143Nd isotope compositions of rocks from AGC, however, fall on an array with an errorchron date of ∼3.3 Ga, despite the majority of samples yielding substantially older zircon U–Pb ages. This has led to the suggestion of a major Sm–Nd "resetting" event at this time in the AGC. To better understand the Sm–Nd bulk-rock systematics of the AGC, we investigate the U–Pb age and Sm–Nd isotope compositions of apatite and titanite from the AGC, using the laser ablation split stream (LASS) method. Apatite from all samples yield broadly similar U–Pb dates of ∼1.89 to 1.83 Ga, in agreement with resetting during the 1.9 Ga Wopmay orogen. The Sm–Nd isotope compositions of the apatite, however, lie off the WR errorchron and show a high degree of initial Nd isotope heterogeneity. Conversely, titanite Sm–Nd systematics are consistent with the ∼3.3 Ga whole rock errorchron further supporting Sm–Nd modification at ∼3.3 Ga. Taken together, these show that the oldest rocks in the AGC underwent at least two post-crystallization events (at 3.3 and 1.9 Ga) that modified the Sm–Nd isotope system. These results also demonstrate the relative mobility of the Sm–Nd isotope system during orogenic events, which may compromise the ability to determine robust bulk-rock 143Nd isotope signatures. [ABSTRACT FROM AUTHOR]

The fourteenth International Conference on Electromagnetic Isotope Separators and Techniques related to their Applications, EMIS-14, held in Victoria, Canada, was attended by more than 130 participants. As compared to earlier EMIS conferences, EMIS-14 reflected the increasing importance of experimental developments applicable to unstable nuclei. Reports on efficient isotope separation, beam manipulation such as cooling, trapping and acceleration were presented. The theoretical basis for research with exotic beams was put by W. Nazarewicz. He clearly underlined the importance of neutron rich nuclei which cover a large and unexplored region of the nuclear chart. New phenomena such as the separation of proton and neutron matter in nuclei or disappearance and formation of new nuclear shells are expected. The investigation of the rich field of nuclei far-off stability will shed light on the in-medium nucleon–nucleon interaction and finally help to understand the structure of elementary matter. [Copyright &y& Elsevier]

• Quebecia terrane (Grenville Province) consists of over 95% juvenile 1.5 Ga oceanic arcs. • Slivers of crust with 1.8 Ga Nd ages divide Quebecia into a composite arc belt of terranes. • 1.5 Ga oceanic arcs were accreted to Laurentia after the 1.5 Ga Pinwarian orogenic event. • Some Quebecia terranes were rifted from the active margin and re-accreted further east. • Oblique tectonics may explain Pinwarian arc accretion without a major collisional orogen. There continues to be confusion in the geological community concerning the ages of crustal formation and crustal accretion within the central Grenville Province of Quebec. To clarify the geological history of crustal growth in the eastern part of the Quebecia terrane, sixty new Nd isotope analyses are presented from a 60,000 km2 area northwest of Baie Comeau. Most samples yield Pinwarian Nd model ages that suggest them to be derived from juvenile oceanic arc terranes. However, two large slivers with Paleoproterozoic TDM ages attest to the existence of hidden blocks of old crust, which divide the area of juvenile Pinwarian crust into a composite arc belt of smaller accreted terranes. The old crustal blocks probably do not reach the present surface, but represent an igneous crustal protolith of younger I-type magmatism. By comparison with a Mesozoic tectonic analogue, it is proposed that accreted juvenile arc crust with attached slivers of older crust were rifted away from an active margin to the west, and translated eastwards until blocked by the previously accreted Labradoria terrane. Although the Quebecia composite arc belt consists of over 95% of Pinwarian juvenile arc crust, the age of arc accretion was post-Pinwarian. The proposed oblique nature of the accretion process may explain the lack of a major collisional orogen at that time. This paper shows the usefulness of large-scale Nd isotope mapping of Precambrian crustal terranes to clarify complex processes of crustal formation and arc accretion. [ABSTRACT FROM AUTHOR]