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•Eoarchean zircon grains are preserved in the sediments of the Carajás Basin.•The Carajás Domain contains relicts of a Paleo- to early Mesoarchean basin.•The Carajás Domain hosts the ...Neoarchean Parauapebas Large Igneous Province.•The LIP immediately preceded a period of continental extension that formed a rift.•The Carajás Basin evolved to a Transamazonian back-bulge basin.
Despite representing one of the largest cratons on Earth, the early geological evolution of the Amazonia Craton remains poorly known due to relatively poor exposure and because younger metamorphic and tectonic events have obscured initial information. In this study, we investigated the sedimentary archives of the Carajás Basin to unravel the early geological evolution of the southeastern Amazonia Craton. The Carajás Basin contains sedimentary rocks that were deposited throughout a long period spanning more than one billion years from the Mesoarchean to the Paleoproterozoic. The oldest archives preserved in this basin consist of a few ca. 3.6 Ga detrital zircon grains showing that the geological roots of the Amazonia Craton were already formed by the Eoarchean. During the Paleoarchean or the early Mesoarchean (<3.1 Ga), the Carajás Basin was large and rigid enough to sustain the formation and preservation of the Rio Novo Group greenstone belt. Later, during the Neoarchean, at ca. 2.7 Ga, the southeastern Amazonia Craton witnessed the emplacement of the Parauapebas Large Igneous Province (LIP) that probably covered a large part of the craton and was associated with the deposition of some of the world largest iron formations. The emplacement of this LIP immediately preceded a period of continental extension that formed a rift infilled first by iron formations followed by terrigenous sediments. This major change of sedimentary regime might have been controlled by the regional tectonic evolution of the Amazonia Craton and its emergence above sea-level. During the Paleoproterozoic, at ca. 2.1 Ga, the Rio Fresco Group, consisting of terrigenous sediments from the interior of the Amazonia Craton, was deposited in the Carajás Basin. At that time, the Amazonian lithosphere could have either underwent thermal subsidence forming a large intracratonic basin or could have been deformed by long wavelength flexures that induced the formation of basins and swells throughout the craton under the influence of the growing Transamazonian mountain belt.
•Nd-isotope systematics of Fortescue, Hamersley and Turee Creek sediments and volcanics.•Role of LIPs weathering to riverine fluxes during the Archean-Proterozoic transition.•Major change of ...continentally-sourced material at the onset of the GOE.•Elevated rates of weathering stimulated the GOE and first global glaciation.
An ongoing debate concerns what initiated the Great Oxidation Event (GOE) and associated glaciation between ~ 2.45 and 2.2 Ga. One possibility is the emergence of continental landmasses and the increase of subaerial igneous province weathering during the Late Archean. We test this hypothesis in the Hamersley Basin by reporting Nd-isotope data from a succession of iron formations (IFs), mudstone/siltstones and glacial diamictites from the Boolgeeda Iron Formation and overlying Turee Creek Group deposited during the GOE. In a 147Sm/144Nd - ɛNd(t) diagram, the data define a negative trend indicating the contribution of a high ɛNd(t) ~ +3 hydrothermal component and a strongly negative ɛNd(t) ~ -9 crustal component, which is compatible with the Nd-isotope composition of the upper continental crust but also of the underlying felsic volcanics of the Woongarra Rhyolite and crustally-contaminated mafic volcanics of the Fortescue Group. A less pronounced negative trend originating from the same hydrothermal source but correlated with non-contaminated ultramafic Fortescue volcanics (ɛNd(t) ~ -2) is observed for the older Joffre, Dales Gorge and Marra Mamba IFs. As Nd-isotopes are not sensitive to redox conditions, the major shift of Nd-isotopic compositions at ~ 2.45 Ga cannot be linked to a change in the weathering regime, rather to a change in the nature of the continental surface exposed to weathering. One explanation is that the Sm-Nd sources for sediments deposited before and during the GOE were locally derived from the underlying subaerial LIPs, reflecting a change in the geodynamic context of deposition and/or hydrographic network and catchment areas. Another explanation could be a significant change in the nature of fluid–rock interactions due to the increase role of weathering processes associated with the emergence of continental landmasses. Additional Nd isotope data from different cratons worldwide are needed, however, to infer as to whether or not the marked shift in Nd isotope compositions recorded in the Turee Creek Group reflect a change in the global hydrological cycle. Our data support the role of large subaerial magmatic provinces as triggers of the rise of atmospheric oxygen and the onset of glaciations at the beginning of the Proterozoic.
The Araçuaí orogen of SE Brazil exposes numerous amounts of magnesian, metaluminous, calc-alkaline, and medium- to high-K granitoid batholiths that were emplaced during early convergence between the ...São Francisco and Congo cratons during West Gondwana assembly in the late Neoproterozoic. Previously proposed sources for these pre-collisional granitoids include the Paleoproterozoic basement and mantle-derived magma based on isotopic signatures, abundant microgranular enclaves and contemporaneous mafic intrusions. Zircons from migmatitic basement gneiss, a noritic intrusion and five granitoid intrusions were analysed for U–Pb–Hf isotopes to evaluate their magma source. Paleoproterozoic migmatites represent addition of juvenile crust in an accretionary orogenic setting at ca. 2.2–2.0 Ga evidenced by their positive zircon εHf values. The Hf isotopic composition of zircon from pre-collisional granitoids has a large range of negative εHf values between −28.8 and −1.7 indicating crustal protoliths. This range of unradiogenic Hf isotopic compositions is explained by inefficient mixing of magmas derived from felsic and mafic Paleoproterozoic sources that hybridised during incremental growth of the plutons. Zircon grains of contemporaneous mafic intrusions display slightly higher, yet enriched, Hf isotopic compositions consistent with crustal contamination of mantle magmas. The new Hf isotope data, integrated with other chemical and isotopic evidence, suggest derivation of the pre-collisional granitoids from lower crustal sources of the Paleoproterozoic basement, with only minor contributions from mantle-derived magmas. Thus, magmatism of the Araçuaí orogen related to the assembly of West Gondwana was dominantly a crustal-reworking event.
•In situ zircon U-Pb-Hf isotope data of Araçuaí orogen granitoids and basement gneiss.•Zircon U-Pb age dispersion consistent with incremental pluton growth from 630 to 580 Ma.•Final emplacement and solidification of granitoids occurred at 590–580 Ma.•Large range of negative εHf values consistent with mixing of basement melt sources.
We investigated olivine minette dykes from the Rio Colan Valley of the Julian Alps (NE Italy) to provide new constraints on the mantle geochemistry underneath this extreme sector of the Italian ...Southern Alps. Petrographic observations, high Mg#s, high Cr and Ni contents, low Dy/YbCN ratios and flat heavy rare earth element (REE) profiles imply these are primary magmas derived from a depleted peridotite with olivine and garnet as possible residual phases. However, high K2O and incompatible trace element contents, coupled with superchondritic Nb/Ta ratios, suggest that the source was modified into a rutile–phlogopite-bearing carbonated peridotite by multiple metasomatic events such as recycling of crustal material and carbonatitic metasomatism related to an old orogenic event and rutile-rich metasomatism linked to the Pangaea break-up. Laser ablation – multi-collector – inductively coupled plasma – mass spectrometer (LA-MC-ICP-MS) U–Pb geochronology of apatites from two dykes yielded differences between unforced and forced discordia ages up to ∼45 Ma, likely due to the initial 207Pb/206Pb correction adopted. Nonetheless, because forced discordia and 206Pb/238U weighted mean ages are overall similar within the uncertainty, our preferred interpretation is that olivine minettes intruded and crystallized at ∼67 Ma. The age and anorogenic signature of these magmas are consistent with the regional extensional tectonics in the Julian Alps due to the advance of the external Dinaric front following Adria plate eastward subduction. Eventually, we show also that Rio Colan magmas are geochemically hybrid products between lamprophyres and lamproites compared with similar Italian and Western Mediterranean volcanics.
The emplacement of Large Igneous Provinces (LIPs) during the Neoarchean is thought to have influenced the Earth's surface by modulating global climate and the supply of nutrients to the oceans. ...However, the links between Neoarchean LIPs and Earth's surface changes are complex and not fully understood due to a lack of sedimentological constraints documenting the relationships between magmatic activity and concomitant depositional environments. At ca. 2.75 Ga, the Amazonia Craton witnessed the emplacement of the Parauapebas LIP, which is mainly composed of vesicular basalts and associated volcaniclastic rocks. The Carajás Formation conformably overlies the basalts of the Parauapebas LIP. It comprises extensive iron formations (IFs) interbedded with minor carbonate and volcaniclastic horizons, which were deposited in various shallow to deep-water settings. Zircon U–Pb dating of volcaniclastic layers yielded ages between 2732 ± 5 Ma and 2720 ± 6 Ma, which indicates that the volcanic activity continued 30–40 Myrs after the main peak in magmatic activity of the Parauapebas LIP. Above the Carajás Formation, the Igarapé Bahia Group consists mainly of terrigenous sediments that are interleaved at their base with minor IFs. This group does not preserve evidence of contemporaneous volcanic activity and comprises detrital zircon populations with ages between ca. 3.0 and 2.7 Ga. The few IFs horizons at the base of the Igarapé Bahia Group could reflect a long-lasting hydrothermal activity linked with the emplacement of the Parauapebas LIP. This LIP thus exerted a major control on depositional environments both in space and time by favoring the deposition of IFs (e.g., in shallow to deep-water settings) during a period that exceeded 30 Myrs.
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•The Carajás Formation comprises diversified iron-rich sedimentary facies•The Carajás Formation was deposited between ca. 2750 Ma and ca. 2710 Ma•Iron-rich facies were favored by the Parauapebas LIP activity•No evidence of volcanic activity was observed in the Igarapé Bahia Group
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•The Serra Sul Formation corresponds to subaqueous depositional environments.•There is no evidence of glacial environments for the Serra Sul diamictite.•The Serra Sul Formation has a ...maximum depositional age of 2684 ± 10 Ma.
The Carajás Basin, Amazonian Craton, hosts extensive Neoarchean to Paleoproterozoic sedimentary archives, which are still poorly constrained regarding their depositional settings, ages, and type of basin in which they have been deposited. In this study, we performed detailed sedimentological investigations and U-Pb dating of detrital zircon in four drill cores intercepting the recently defined Serra Sul Formation. Our data show that this formation corresponds to various shallow to deep subaqueous environments. Shallow water environments are characterized by local occurrences of microbially-mediated structures, while deep water environments are characterized by polymictic conglomerates resulting from the mixing of materials of different origins during downslope debris flow. Both sedimentary facies and common occurrence of syn-sedimentary deformations attest for recurrent slope instabilities. Geochronological investigations allow to define a maximum depositional age of 2684 ± 10 Ma, that is several tens million years younger than other Neoarchean sedimentary units of the Carajás Basin. Major peaks in age distribution indicate that the Serra Sul Formation derives from local sources that constitute the basement of the Carajás Basin. The infilling of the Carajás Basin by local sources, together with sedimentary facies and depositional environments attesting for slope instabilities, suggest that the Serra Sul Formation was deposited during an active extensional tectonic phase. Such Neoarchean to early Paleoproterozoic tectonic setting compares with those documented in many other cratons worldwide and suggests that it could correspond to the break-up of one of the first documented supercontinent.
Despite representing one of the largest cratons on Earth,the early geological evolution of the Amazonia Craton remains poorly known due to relatively poor exposure and because younger metamorphic and ...tectonic events have obscured initial information.In this study,we investigated the sedimentary archives of the Carajás Basin to unravel the early geological evolution of the southeastern Amazonia Craton.The Carajás Basin contains sedimentary rocks that were deposited throughout a long period spanning more than one billion years from the Mesoarchean to the Paleoproterozoic.The oldest archives preserved in this basin consist of a few ca.3.6 Ga detrital zircon grains showing that the geological roots of the Amazonia Craton were already formed by the Eoarchean.During the Paleoarchean or the early Mesoarchean(＜3.1 Ga),the Carajás Basin was large and rigid enough to sustain the formation and preser-vation of the Rio Novo Group greenstone belt.Later,during the Neoarchean,at ca.2.7 Ga,the southeast-ern Amazonia Craton witnessed the emplacement of the Parauapebas Large Igneous Province(LIP)that probably covered a large part of the craton and was associated with the deposition of some of the world largest iron formations.The emplacement of this LIP immediately preceded a period of continental exten-sion that formed a rift infilled first by iron formations followed by terrigenous sediments.This major change of sedimentary regime might have been controlled by the regional tectonic evolution of the Amazonia Craton and its emergence above sea-level.During the Paleoproterozoic,at ca.2.1 Ga,the Rio Fresco Group,consisting of terrigenous sediments from the interior of the Amazonia Craton,was depos-ited in the Carajás Basin.At that time,the Amazonian lithosphere could have either underwent thermal subsidence forming a large intracratonic basin or could have been deformed by long wavelength flexures that induced the formation of basins and swells throughout the craton under the influence of the growing Transamazonian mountain belt.
BACKGROUND:Early life exposure to air pollution has been linked with cognitive impairment in children, but the results have not been conclusive. We analyzed the association between traffic-related ...air pollution and cognitive function in a prospective birth cohort in Rome.
METHODS:A cohort of 719 newborns was enrolled in 2003–2004 as part of the GASPII project. At age 7 years, 474 children took the Wechsler Intelligence Scale for Children-III to assess their cognitive development in terms of IQ composite scores. Exposure to air pollutants (NO2, PMcoarse, PM2.5, PM2.5 absorbance) at birth was assessed using land use regression models. We also considered variables indicating traffic intensity. The effect of environmental pollution on IQ was evaluated performing a linear regression model for each outcome, adjusting for gender, child age at cognitive test, maternal age at delivery, parental educational level, siblings, socio-economic status, maternal smoking during pregnancy, and tester. To account for selection bias at enrollment and during follow-up, the regression models were weighted for the inverse probabilities of participation and follow-up.
RESULTS:A 10 μg/m higher NO2 exposure during pregnancy was associated with 1.4 fewer points (95% confidence interval = −2.6, −0.20) of verbal IQ, and 1.4 fewer points (95% confidence interval = −2.7, −0.20) of verbal comprehension IQ. Similar associations were found for traffic intensity in a 100 m buffer around home. Other pollutants showed negative associations with larger confidence intervals.
CONCLUSIONS:Consistent with previous evidence, this study suggests an association of exposure to NO2 and traffic intensity with the verbal area of cognitive development.See Video Abstract at http://links.lww.com/EDE/B12.
A precise measurement of optical power, forward voltage, and junction temperature of light-emitting diodes (LEDs) is the key for characterization and health monitoring of these devices. In many ...cases, LED characterization is carried out with relatively long (10 ms and longer) pulses, that is, in conditions in which self-heating can significantly impact measurement results. To overcome this limitation, this article proposes a fast and versatile measurement approach based on a specifically designed current source, with a maximum current of about 1 A, high stability (variations under 0.1%) and settling time <inline-formula> <tex-math notation="LaTeX">\boldsymbol {\lt }20 </tex-math></inline-formula><inline-formula> <tex-math notation="LaTeX">\boldsymbol {\mu } </tex-math></inline-formula> s, and demonstrates its applicability to pulsed and transient characterization of power LEDs. The proposed system has the inherent advantages of 1) permitting a fast pulsed characterization of the devices, which-as we demonstrate-is much more accurate than quasipulsed or dc analysis; 2) allowing isothermal characterization of LEDs without requiring long settling times, with beneficial impact on the throughput of LED characterization; 3) allowing characterization of the voltage heating transient (during constant current operation), which is the key for junction temperature and thermal resistance extraction, as well as for the development of compact models; 4) monitoring the optical power during the self-heating transient; and 5) the spectrum of the device providing additional information, such as the peak-shift or the phosphor behavior. The efficacy of the proposed approach has been demonstrated by testing commercial LEDs: the results clearly indicate that a fast (<inline-formula> <tex-math notation="LaTeX">\boldsymbol {\lt }20 </tex-math></inline-formula><inline-formula> <tex-math notation="LaTeX">\boldsymbol {\mu } </tex-math></inline-formula> s) LED characterization is necessary for a proper extraction of the main spectral parameters and of the related temperature dependence.
the Inverse probability weighting (IPW) is a methodology developed to account for missingness and selection bias caused by non-randomselection of observations, or non-random lack of some information ...in a subgroup of the population.
to provide an overview of IPW methodology and an application in a cohort study of the association between exposure to traffic air pollution (nitrogen dioxide, NO₂) and 7-year children IQ.
this methodology allows to correct the analysis by weighting the observations with the probability of being selected. The IPW is based on the assumption that individual information that can predict the probability of inclusion (non-missingness) are available for the entire study population, so that, after taking account of them, we can make inferences about the entire target population starting from the nonmissing observations alone.The procedure for the calculation is the following: firstly, we consider the entire population at study and calculate the probability of non-missing information using a logistic regression model, where the response is the nonmissingness and the covariates are its possible predictors.The weight of each subject is given by the inverse of the predicted probability. Then the analysis is performed only on the non-missing observations using a weighted model.
IPW is a technique that allows to embed the selection process in the analysis of the estimates, but its effectiveness in "correcting" the selection bias depends on the availability of enough information, for the entire population, to predict the non-missingness probability. In the example proposed, the IPW application showed that the effect of exposure to NO2 on the area of verbal intelligence quotient of children is stronger than the effect showed from the analysis performed without regard to the selection processes.
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