Atmospheric CO2 levels and global climate are regulated on geological timescales by the silicate weathering feedback. However, this thermostat has failed multiple times in Earth's history, most ...spectacularly during the Cryogenian (c. 720–635 Ma) Snowball Earth episodes. The unique middle Neoproterozoic paleogeography of a rifting, low-latitude, supercontinent likely favored a globally cool climate due to the influence of the silicate weathering feedback and planetary albedo. Under these primed conditions, the emplacement and weathering of extensive continental flood basalt provinces may have provided the final trigger for runaway global glaciation. Weathering of continental flood basalts may have also contributed to the characteristically high carbon isotope ratios (δ13C) of Neoproterozoic seawater due to their elevated P contents. In order to test these hypotheses, we have compiled new and previously published Neoproterozoic Nd isotope data from mudstones in northern Rodinia (North America, Australia, Svalbard, and South China) and Sr isotope data from carbonate rocks. The Nd isotope data are used to model the mafic detrital input into sedimentary basins in northern Rodinia. The results reveal a dominant contribution from continental flood basalt weathering during the ca. 130 m.y. preceding the onset of Cryogenian glaciation, followed by a precipitous decline afterwards. These data are mirrored by the Sr isotope record, which reflects the importance of chemical weathering of continental flood basalts on solute fluxes to the early–middle Neoproterozoic ocean, including a pulse of unradiogenic Sr input into the oceans just prior to the onset of Cyrogenian glaciation. Hence, our new data support the hypotheses that elevated rates of flood basalt weathering contributed to both the high average δ13C of seawater in the Neoproterozoic and to the initiation of the first (Sturtian) Snowball Earth.
•Dominant contribution from flood basalt weathering preceding the onset of Cryogenian glaciation.•High rates of flood basalt weathering contributed to high average δ13C through P fertilization.•Weathering of flood basalt provinces provided the final trigger for Snowball glaciation.
Neodymium-142 Evidence for Hadean Mafic Crust O'Neil, Jonathan; Carlson, Richard W; Francis, Don ...
Science (American Association for the Advancement of Science),
09/2008, Letnik:
321, Številka:
5897
Journal Article
Recenzirano
Neodymium-142 data for rocks from the Nuvvuagittuq greenstone belt in northern Quebec, Canada, show that some rock types have lower ¹⁴²Nd/¹⁴⁴Nd ratios than the terrestrial standard (ε¹⁴²Nd = -0.07 to ...-0.15). Within a mafic amphibolite unit, ¹⁴²Nd/¹⁴⁴Nd ratios correlate positively with Sm/Nd ratios and produce a ¹⁴⁶Sm-¹⁴²Nd isochron with an age of Formula: see text million years. These rocks thus sample incompatible-element-enriched material formed shortly after Earth formation and may represent the oldest preserved crustal section on Earth.
Radiogenic (87Sr/86Sr) and stable (δ88/86Sr) strontium isotope compositions spanning a calendar year are reported for rivers from across subarctic Canada that drain contrasting lithologies ranging ...from Precambrian bedrock (Koksoak, Great Whale and La Grande rivers of Northern Quebec) to carbonate and clastic Phanerozoic sedimentary rocks of the Western Interior Platform (Nelson River, of central and western Canada). The 87Sr/86Sr isotopic compositions of the river waters reflect the underlying geology, with rivers draining the Precambrian Shield having higher 87Sr/86Sr ratios (0.727–0.734) than the Phanerozoic dominated Nelson River (0.713). The stable strontium isotope values (δ88/86Sr) range from 0.26 to 0.39‰, with the values for the Nelson River overlapping those of the other three. Rivers that have not been developed for hydroelectric power show a seasonal variation in the 87Sr/86Sr ratios, whereas those that have been diverted or dammed show little or no seasonal variation due to increased residence time of their water in hydroelectric reservoirs. The three rivers from Northern Quebec show discrete ranges in their 87Sr/86Sr and δ88/86Sr isotope compositions that correlate with the Ca/Sr and Na/Sr ratios of the river water. These correlations are interpreted to reflect differential chemical weathering of felsic versus mafic source rocks and/or of surficial sediment vs bedrock sources.
•River impoundment (damming) alters the Sr isotope composition of rivers.•Spring meltwater plumes alter the Sr isotope composition of the rivers.•Stable Sr isotope compositions and river chemistry reflect the bedrock geology.•Stable Sr isotope compositions of boreal rivers reflect silicate vs carbonate weathering.
Plutonic rocks from the Mineiro Belt, Brazil record a delayed onset of the transition from TTG to sanukitoid-type magmatism (high Ba-Sr), starting during the Siderian magmatic lull when little ...juvenile magma was added to the continental crust. Rocks mostly belong to the calc-alkaline series, meta- to peraluminous and originally “I-type”, meaning that oxidized magmas were formed by partial melting of subducted material. The temporal distribution and apparent secular changes of the magmas are consistent with the onset of subduction-driven plate tectonics due to an increase of the subduction angle and opening of the mantle wedge. New isotopic analyses (Sm-Nd whole rock and Lu-Hf in zircon) corroborate the restricted juvenile nature of the Mineiro Belt and confirm the genetic link between the Lagoa Dourada Suite, a rare ca. 2350 Ma high-Al tonalite-trondhjemite magmatic event, and the sanukitoid-type ca. 2130 Ma Alto Maranhão Suite. U-Pb dating of zircon and titanite constrain the crystallisation history of plutonic bodies; coupled with major and trace element analyses of the host rocks, they distinguish evolutionary trends in the Mineiro Belt. Several plutons in the region have ages close to 2130 Ma but are distinguished by the lower concentration of compatible elements in the juvenile high Ba-Sr suite.
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•Latest juvenile TTG to sanukitoid transition in the Palaeoproterozoic starting during the Siderian lull.•Magmatic evolution of high Ba-Sr suite in the Mineiro Belt of Brazil.•Geochemistry and U-Pb analysis of zircon and titanite of several plutons within the Mineiro Belt.•Lu–Hf zircon and Sm–Nd whole rock isotope constraints on the short-lived Palaeoproterozoic crust.•Evolution of the Mineiro belt was driven by mantle extractions with minor crustal assimilation.
•Strong relationships exist between the 87Sr/86Sr of the wine, of the grape and of the labile fraction of the soil.•Vinification process does not alter the overall Sr budget.•Plants may be able to ...also extract strontium from the bulk fraction of the soil.
The 87Sr/86Sr isotope ratios were measured on grape, wine and soil samples collected in 13 commercial vineyards located in three major wine producing areas of Quebec (Canada). The soils yield Sr isotope ratios that are intimately related to the local geology and unambiguously discriminate the different producing areas. A strong relationship exists between the 87Sr/86Sr isotope ratios of the wine and the grapes. This suggests that the vinification process does not alter the overall Sr budget. Although the Sr isotope ratios of the grapes do not show a strong correlation with the bulk Sr isotope composition of the soil, they do correlate strongly with the Sr isotope composition contained in the labile fraction of the soil. This indicates that the labile fraction of the soil represents the Sr reservoir available to the plant during its growth. This study demonstrates that the Sr isotope approach can be used as a viable tool in forensic science for investigating the provenance of commercial wines.
We present new major element and isotopic (Nd-Sr-Hf-Pb) data and modelling from alkaline rocks of the Monteregian Igneous Province of southern Quebec (Canada) that constrain the mantle source and the ...magmatic origin of these rocks. The whole-rock chemical composition of the intrusions is consistent with fractional crystallization of an assemblage of olivine ± clinopyroxene (± plagioclase) derived from ocean island basalts (OIB)-like magmas, and variations in the Sr and Nd isotope compositions suggest as much as 20% crustal contamination. The bulk of the Nd-Sr-Hf and Pb isotopic data form a tight cluster between a depleted mantle end-member (HIMU, high-U/Pb mantle) and an enriched mantle (EMI) end-member and are thought to reflect a sub-continental lithospheric mantle that was metasomatized by a convecting asthenospheric plume. Variations in these isotopic compositions along the west-east axis of the Monteregian Province (from the Oka carbonatite to the Mount Shefford intrusion) may reflect various degrees of mixing between HIMU and EMI enriched mantle reservoirs. Anomalously low 207Pb/204Pb and 208Pb/204Pb isotopic ratios from some of the intrusions likely indicate incorporation of an Archean component within the lithospheric mantle. We propose a model in which Monteregian magmatism formed from melting of a predominantly Proterozoic metasomatized lithospheric mantle in response to lithospheric extension during the opening of the North Atlantic Ocean at ca. 124 Ma.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Manual interpretation of variants remains rate limiting in precision oncology. The increasing scale and complexity of molecular data generated from comprehensive sequencing of cancer samples requires ...advanced interpretative platforms as precision oncology expands beyond individual patients to entire populations. To address this unmet need, we introduce a Platform for Oncogenomic Reporting and Interpretation (PORI), comprising an analytic framework that facilitates the interpretation and reporting of somatic variants in cancer. PORI integrates reporting and graph knowledge base tools combined with support for manual curation at the reporting stage. PORI represents an open-source platform alternative to commercial reporting solutions suitable for comprehensive genomic data sets in precision oncology. We demonstrate the utility of PORI by matching 9,961 pan-cancer genome atlas tumours to the graph knowledge base, calculating therapeutically informative alterations, and making available reports describing select individual samples.
The anatomically simple plants that first colonized land must have acquired molecular and biochemical adaptations to drought stress. Abscisic acid (ABA) coordinates responses leading to desiccation ...tolerance in all land plants. We identified ABA nonresponsive mutants in the model bryophyte Physcomitrella patens and genotyped a segregating population to map and identify the ABA NON-RESPONSIVE (ANR) gene encoding a modular protein kinase comprising an N-terminal PAS domain, a central EDR domain, and a C-terminal MAPKKK-like domain. anr mutants fail to accumulate dehydration tolerance-associated gene products in response to drought, ABA, or osmotic stress and do not acquire ABA-dependent desiccation tolerance. The crystal structure of the PAS domain, determined to 1.7-Å resolution, shows a conserved PAS-fold that dimerizes through a weak dimerization interface. Targeted mutagenesis of a conserved tryptophan residue within the PAS domain generates plants with ABA nonresponsive growth and strongly attenuated ABA-responsive gene expression, whereas deleting this domain retains a fully ABA-responsive phenotype. ANR orthologs are found in early-diverging land plant lineages and aquatic algae but are absent from more recently diverged vascular plants. We propose that ANR genes represent an ancestral adaptation that enabled drought stress survival of the first terrestrial colonizers but were lost during land plant evolution.
Nitrogen, argon and helium isotopic compositions were measured by vacuum crushing in pyroxenes and amphiboles from mafic rocks belonging to the Monteregian Hills (Québec, Canada). For comparison, ...lead isotopic compositions were measured in plagioclase in the same samples. The goal of this study was to constrain the mantle sources of this igneous province, resolving a controversial issue that has persisted for more than 30years. The measured He and Ar show solubility-controlled elemental fractionation while N is affected by kinetic isotopic fractionation during melt degassing. In contrast, the 40Ar/36Ar ratio seems not to be affected by kinetic fractionation, but likely reflects mantle sources. The 40Ar/36Ar and 208Pb/206Pb ratios are meaningfully correlated, suggesting the mixing between a plume source showing high 208Pb/206Pb (≤2.06) and low 40Ar/36Ar ratios (~1200) and a recycled source such as HIMU showing low 208Pb/206Pb (≤1.95) and near-atmospheric 40Ar/36Ar ratios (~300). The N2/36Ar and 206Pb/204Pb ratios are inversely correlated. Although the N2/36Ar ratios are diluted by an atmospheric-like component, this relationship can be interpreted as the mixing between a recycled component (HIMU) and a mantle source that ambiguously could be either a plume source or the depleted mantle. The samples showing less radiogenic 206Pb/204Pb ratios show δ15N values of −7.6 to −7.4‰, which points to a MORB-type mantle source (δ15N=−5±2‰) rather than a plume source (δ15N=+3‰). Thus, there is contrasting evidence arguing for either a plume or a depleted mantle component. This ambiguity could be resolved by assuming that the plume source provided heat to melt a sub-continental mantle source. Thus, part of the volatile budget might be issued from this distinct mantle source. This study demonstrates the great potential of coupling radiogenic isotopes together with Ar and N isotopes. Nitrogen and argon are efficiently recycled in the mantle and thus can be helpful in tracing the crustal sources that affect the Sr–Nd–Pb isotopic systems in oceanic and continental volcanism.
► N, Ar and He isotopes are measured in magmatic pyroxenes and amphiboles, and Pb isotopes in plagioclases. ► The 40Ar/36Ar and 208Pb/206Pb ratios show a mixing between two mantle components. ► The mixing is between a recycled mantle (HIMU) and a depleted mantle (MORB) or plume mantle. ► This study shows the great potential of coupling Pb isotopes with Ar and N isotopes.
•Study describes the first R-IRG deposit in North-Africa to our knowledge.•Detailed mineralogical, isotopic (Pb, Sr–Nd), chronological and fluid inclusions data are given.•Original structural context ...with pre-granitic corridors explained the shape of the deposits.•3D model is proposed, discarding a genetic relationship of Pb–Ag veins with gold deposits.
Gold have been recently recognized in the Tighza (formerly Jebel Aouam) district, in the Hercynian belt of central Morocco. This district has long been known for its W mineralization, as well as major Pb–Ag–Zn, and minor Sb–Ba deposits, all geographically associated with late-Hercynian calc-alkaline magmatism. Gold mineralization in the district is mainly hosted by thick W–Au quartz veins located around the “Mine granite” small granitic plug. Within the veins, gold grade is highest (up to 70g/t) close to the granite but rapidly decreases going outward from the granite, defining a perigranitic zoning. Anomalous gold grades have also been measured in hydrothermal skarn layers close to two other granitic plugs (Kaolin granite and Mispickel granite), associated with disseminated As–Fe sulfides. The paragenetic sequence for the W–Au quartz veins shows three stages: (1) an early oxidized stage with wolframite-scheelite associated with early quartz (Q1), (2) an intermediate Bi–As–Te–Mo–Au sulfide stage with loellingite, bismuth minerals and native gold with a later quartz (Q2), restricted to a narrow distance from the granite, and (3) a late lower temperature As–Cu–Zn–(Pb) stage with abundant massive pyrrhotite, arsenopyrite and sphalerite, locally forming independent veins (“pyrrhotite vein”). Both Q1 hyaline and Q2 saccharoidal gold-bearing quartz display aqua-carbonic fluids with minor H2S and Cu and an homogeneous composition (81mole% H2O, 18mole% CO2 and about 1mole% NaCl). The trapping pressure is estimated to 1.5–2kbar with temperature ranging from 300 to 350°C. Q1 inclusions have exploded indicating an uplift of the Tighza block, that lead to saccharoidal Q2 quartz deposition with multiphase NaCl-saturated fluid inclusions. 40Ar/39Ar dating demonstrates that the “Mine granite”, tungsten skarnoid, scheelite-molybdenite veins, and very likely gold-bearing veins are coeval, emplaced at 286±1Ma. Multiple and widespread metal sources are indicated by radiogenic isotope studies. Nd and Sr isotope compositions of scheelite and granites suggest the participation of a juvenile component while lead isotopes demonstrate a major participation of the basement.
Both gold mineralization and zoning suggest that the system developed at the end of the magmatic activity, accompanying a major transition in magmatic fluid composition. The morphology of the gold-bearing mineralization is dependent of the permeability and the reactivity of host-rocks: focus circulation of fluids through pre-existing tectonic corridors, reactivated by late-Hercynian intrusions favor the formation of large W-type gold veins, while infiltration of fluid within reactive stratigraphic layers gives rise to skarn mineralization. A 40Ar/39Ar date (W1 north vein: 291.8±0.3Ma) indicates that hydrothermal circulation predates gold and tungsten deposition in open fractures as well as Mine granite emplacement.
The W–Au mineralization preceded the onset of a large convective hydrothermal cell around the intrusion that led to the formation of the Pb–Ag–Zn mined veins. The Tighza polymetallic district displays numerous similarities with the R-IRG model that was defined in the American Cordillera, such as thermal and zonation patterns, carbonic hydrothermal fluids and chronology of intrusion and related deposits, but also provides new insight to the R-IRG model such as wide Au-quartz veins instead of sheeted Au-veins, oxidation state of the magma, and Sr–Nd isotopic data. These results establish a major magmatic contribution and discard a direct genetic relationship between gold mineralization and major neighboring Pb–Ag–Zn veins. A large number of classic Pb–Zn district of the Western Hercynides belong to the same clan.
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