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Articles de revues sur le sujet "Hf-Nd-Pb isotopic compositions"
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Vezinet, Adrien, Emilie Thomassot, Yan Luo, Chiranjeeb Sarkar et D. Graham Pearson. « Diachronous Redistribution of Hf and Nd Isotopes at the Crystal Scale—Consequences for the Isotopic Evolution of a Poly-Metamorphic Crustal Terrane ». Geosciences 12, no 1 (12 janvier 2022) : 36. http://dx.doi.org/10.3390/geosciences12010036.
Texte intégralRésumé :
In metamorphic rocks, mineral species react over a range of pressure–temperature conditions that do not necessarily overlap. Mineral equilibration can occur at varied points along the metamorphic pressure–temperature (PT) path, and thus at different times. The sole or dominant use of zircon isotopic compositions to constrain the evolution of metamorphic rocks might then inadvertently skew geological interpretations towards one aspect or one moment of a rock’s history. Here, we present in-situ U–Pb/Sm–Nd isotope analyses of the apatite crystals extracted from two meta-igneous rocks exposed in the Saglek Block (North Atlantic craton, Canada), an Archean metamorphic terrane, with the aim of examining the various signatures and events that they record. The data are combined with published U–Pb/Hf/O isotope compositions of zircon extracted from the same hand-specimens. We found an offset of nearly ca. 1.5 Gyr between U-Pb ages derived from the oldest zircon cores and apatite U–Pb/Sm–Nd isotopic ages, and an offset of ca. 200 Ma between the youngest zircon metamorphic overgrowths and apatite. These differences in metamorphic ages recorded by zircon and apatite mean that the redistribution of Hf isotopes (largely hosted in zircon) and Nd isotopes (largely hosted in apatite within these rocks), were not synchronous at the hand-specimen scale (≤~0.001 m3). We propose that the diachronous redistribution of Hf and Nd isotopes and their parent isotopes was caused by the different PT conditions of growth equilibration between zircon and apatite during metamorphism. These findings document the latest metamorphic evolution of the Saglek Block, highlighting the role played by intra-crustal reworking during the late-Archean regional metamorphic event.
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Tong, Jie, Haibo Zou, Zipei Guo, Liwen Chang, Lizhu Wang et Yongwei Zhao. « Geochronology and Origin of Quaternary Dacites from the Daliuchong Volcano in the Tengchong Volcanic Field (TVF), SE Tibetan Plateau ». Minerals 14, no 10 (30 septembre 2024) : 990. http://dx.doi.org/10.3390/min14100990.
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Quaternary volcanoes from the southeastern Tibetan Plateau occur at the Tengchong volcanic field (TVF). The Daliuchong volcano is the largest volcano in the TVF, which has the most felsic compositions with explosive eruptions. The eruption history and origin of the Daliuchong volcano are a matter of debate. In the present paper, we report the groundmass K-Ar ages, whole-rock Sr-Nd-Pb-Hf isotopes, zircon U-Pb ages, and Hf-O isotopic compositions for the Daliuchong volcano to constrain its eruption history and petrogenesis. The groundmass K-Ar ages and zircon U-Pb ages indicate mid-Pleistocene (0.6 Ma to 0.3 Ma) eruptions. The presence of zircon phenocrysts with enriched mantle-like O-Hf isotopes (δ18O < 6‰, and εHf about −2) suggests the involvement of mantle-derived basaltic magmas. The whole-rock Pb isotope compositions and Sr-Nd isotope modeling reveal the involvement of magma from the lower crust. The zircon xenocrysts reveal previously unrecognized 20-Ma magmatic activity at the TVF and contamination of late Cretaceous (66–80 Ma) S-type granites during the formation of the Daliuchong dacites. The dacite magma at Daliuchong was formed by mixing of the mantle-derived magma and lower-crust-derived magma and subsequently contaminated by upper crustal materials, including late Cretaceous S-type granitic rocks.
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Linghu, Miaomiao, Zimu Li, Jinfeng Sun et Jiheng Zhang. « Magma Source and Petrogenesis of the Early Cretaceous Granites in The Liaodong Peninsula : Evidence from In Situ Apatite Sr-Nd and Zircon Hf-O Isotopes ». Minerals 13, no 4 (12 avril 2023) : 545. http://dx.doi.org/10.3390/min13040545.
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Apatite Sr-Nd and zircon Hf-O isotopes are broadly used to trace magma sources and constrain magma evolution processes, further improving our understanding of the origin of granitoids. We present zircon U-Pb ages, whole-rock major and trace elements, and whole-rock Sr-Nd-Hf, zircon Hf-O, and apatite Sr-Nd isotopic data for the coarse-grained quartz monzonite, biotite monzogranite, and granite porphyry in the Yushulinzi pluton in the Liaodong Peninsula, the eastern North China Craton, to establish their magma sources and petrogenesis. The coarse-grained quartz monzonite, biotite monzogranite, and granite porphyry were formed contemporaneously, with zircon U-Pb ages of 123–119 Ma. They share enriched whole-rock Sr-Nd-Hf and zircon Hf isotopic compositions, and the coarse-grained quartz monzonite has crust-like δ18O values (5.7–6.7‰). The coarse-grained quartz monzonite and biotite monzogranite have variable apatite (87Sr/86Sr)i ratios and negative apatite εNd(t) values. These isotopic characteristics indicate that the different rock types in the Yushulinzi pluton were derived from the partial melting of ancient crustal material in the North China Craton. Their geochemical and petrographic characteristics indicate that the crystal-melt segregation model can be employed to elucidate the genetic links among different rock types, with the coarse-grained quartz monzonite representing crystal accumulation and the biotite monzogranite and granite porphyry representing interstitial melts extracted from a crystal-rich magma chamber. Furthermore, the variable apatite Sr isotopic compositions and subtle differences in the peak zircon εHf(t) values of the studied rock samples confirm the possibility of a contribution from shallow crustal components and materials with high εHf(t) values during magma evolution, which is not readily revealed by their whole-rock Sr-Nd-Hf isotopic compositions. These results demonstrate that in situ apatite Sr-Nd and zircon Hf-O isotopic analyses have the potential to provide distinctive insights into the magma sources and evolution of magmatic systems.
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Roulleau, Emilie, et Ross Stevenson. « Geochemical and isotopic (Nd–Sr–Hf–Pb) evidence for a lithospheric mantle source in the formation of the alkaline Monteregian Province (Quebec) ». Canadian Journal of Earth Sciences 50, no 6 (juin 2013) : 650–66. http://dx.doi.org/10.1139/cjes-2012-0145.
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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.
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Bogina, Maria, Boris Belyatsky, Evgenii Sharkov, Alexey Chistyakov et Robert Krymsky. « Origin of the Middle Paleoproterozoic Tiksheozero Ultramafic-Alkaline-Carbonatite Complex, NE Fennoscandian Shield : Evidence from Geochemical and Isotope Sr-Nd-Hf-Pb-Os Data ». Minerals 11, no 6 (27 mai 2021) : 570. http://dx.doi.org/10.3390/min11060570.
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This article reports new geochemical, Sr-Nd-Hf-Pb and Re-Os data on the rocks of the Middle Paleoproterozoic (1.99 Ga) Tiksheozero ultramafic-alkaline-carbonatite complex confined to the northeastern margin of the Karelian Craton. We focus on the poorly studied silicate rocks. Based on petrographic and geochemical research, the silicate rocks are subdivided into two groups: an ultramafic-mafic series depleted in REE, and other incompatible elements and an alkaline series enriched in these elements. Isotope studies showed that all rocks have juvenile isotope signatures and were likely derived from a primitive OIB-type mantle source with possible contributions of the subcontinental lithospheric mantle (SCLM). Insignificant crustal contamination is recorded by Pb and Os isotopic compositions. The incompatible element enrichment in the alkaline rocks and depletion in ultramafic-mafic rocks of the mildly alkaline series with allowance for insignificant crustal contamination confirm their derivation from different primary melts. However, a narrow range of Sr, Nd, Hf, and Pb isotope compositions and compact clusters in 207Pb/204Pb-206Pb/204Pb, Nd-87Sr/86Sr and Hf-Nd isotope diagrams indicate their origination from a common mantle source. A model of subsequent two-stage melting is being most consistent with the geochemical data for this complex.
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Bell, K., A. N. Zaitsev, J. Spratt, S. Fröjdö et A. S. Rukhlov. « Elemental, lead and sulfur isotopic compositions of galena from Kola carbonatites, Russia – implications for melt and mantle evolution ». Mineralogical Magazine 79, no 2 (avril 2015) : 219–41. http://dx.doi.org/10.1180/minmag.2015.079.2.01.
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AbstractGalena from four REE-rich (Khibina, Sallanlatvi, Seblyavr, Vuoriyarvi) and REE-poor (Kovdor) carbonatites, as well as hydrothermal veins (Khibina) all from the Devonian Kola Alkaline Province of northwestern Russia was analysed for trace elements and Pb and S isotope compositions. Microprobe analyses show that the only detectable elements in galena are Bi and Ag and these vary from not detectable to 2.23 and not detectable to 0.43 wt.% respectively. Three distinct galena groups can be recognized using Bi and Ag contents, which differ from groupings based on Pb isotope data. The Pb isotope ratios show significant spread with 206Pb/204Pb ratios (16.79 to 18.99), 207Pb/204Pb (15.22 to 15.58) and 208Pb/204Pb ratios (36.75 to 38.62). A near-linear array in a 207Pb/204Pb vs.206Pb/204Pb ratio diagram is consistent with mixing between distinct mantle sources, one of which formed during a major differentiation event in the late Archaean or earlier. The S isotopic composition (δ34S) of galena from carbonatites is significantly lighter (–6.7 to –10.3% Canyon Diablo Troilite (CDT) from REE-rich Khibina, Seblyavr and Vuoriyarvi carbonatites, and – 3.2% CDT from REE-poor Kovdor carbonatites) than the mantle value of 0%. Although there is no correlation between S and any of the Pb isotope ratios, Bi and Ag abundances correlate negatively with δ34S values. The variations in the isotopic composition of Pb are attributed to partial melting of an isotopically heterogeneous mantle source, while those of δ34S (together with Bi and Ag abundances) are considered to be process driven. Although variation in Pb isotope values between complexes might reflect different degrees of interaction between carbonatitic melts and continental crust or metasomatized lithosphere, the published noble gas and C, O, Sr, Nd and Hf isotopic data suggest that the variable Pb isotope ratios are best attributed to isotopic differences preserved within a sub-lithospheric mantle source. Different Pb isotopic compositions of galena from the same complex are consistent with a model of magma replenishment by carbonatitic melts/fluids each marked by quite different Pb isotopic compositions.
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CINTRON FRANQUI, NADJA OMARA, SUNG HI CHOI et DER-CHUEN LEE. « Peridotites and basaltic rocks within an ophiolitic mélange from the SW igneous province of Puerto Rico : relation to the evolution of the Caribbean Plate ». Geological Magazine 154, no 1 (2 février 2016) : 96–118. http://dx.doi.org/10.1017/s001675681500093x.
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AbstractThe geology of Puerto Rico is divided into three regions: the north, central and SW igneous provinces. Characterized by its Jurassic ophiolitic mélange basement, lithology of the SW Igneous Province (SIP) is not related to either of the other two provinces. The ophiolitic mélange is exposed in three peridotite belts: Monte del Estado, Rio Guanajibo and Sierra Bermeja. We present geochemical data to identify the tectonic setting of the SIP peridotite formation and its relation to the evolution of the Caribbean Plate. Comparisons of spinel Cr no. (13–21), Mg no. (63.3–69.6) and TiO2suggest an abyssal peridotite origin; however, only Sierra Bermeja presents high TiO2characteristics of a mid-ocean-ridge-basalt- (MORB-) like melt reaction. Temperatures determined with two-pyroxene geothermometers indicated a cold thermal regime ofc. 800–1050°C, with characteristics of large-offset transform fault abyssal peridotites. The geochemistry and Sr–Nd–Hf–Pb isotopic compositions of basalts within the mélange were also analysed. Las Palmas amphibolites exhibited normal-MORB-like rare earth element (REE) and trace-element patterns, whereas metabasalts and Lower Cajul basalts exhibited island-arc tholeiitic-like patterns. Highly radiogenic Sr isotopes (0.70339–0.70562) of the basalts suggest seawater alteration; however, Pb–Pb and Nd–Hf isotope correlations represent the primary compositions of a Pacific/Atlantic MORB source for the amphibolites, metabasalts and Lower Cajul basalts. We propose that the SIP ophiolitic mélange was formed along a large-offset transform fault, which initiated subduction and preserved both proto-Pacific and proto-Caribbean lithospheric mantle. Younger Upper Cajul basalts exhibited enriched-MORB-like geochemical and isotopic signatures, which can be attributed to a tectonized Caribbean ocean plateau.
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Xu, Wang-Chun, Hong-Fei Zhang, Li-Ran Chen, Bi-Ji Luo, Liang Guo et Jing-Liang Guo. « Transition from the lithospheric to asthenospheric mantle-derived magmatism in the Early Jurassic along eastern Bangong–Nujiang Suture, Tibet : Evidence for continental arc extension induced by slab rollback ». GSA Bulletin 133, no 1-2 (2 juin 2020) : 134–48. http://dx.doi.org/10.1130/b35554.1.
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Abstract The transition of the geochemical signature in mafic rocks along the eastern Bangong–Nujiang suture in Tibet contains important information about geodynamic processes in the upper mantle. This study recognized two episodes of Early Jurassic gabbros from the Kaqiong terrane, a microblock within the Bangong–Nujiang suture zone. Early gabbros (ca. 197–191 Ma) appear as lenses in the basement complex and were overprinted by amphibolite/granulite-facies metamorphism at ca. 180 Ma. Later undeformed hornblende gabbros (ca. 177–175 Ma) occur as dikes intruding into the basement complex. The early metagabbros are characterized by arc-like geochemical features and enriched Nd-Hf isotopic compositions (whole rock ∑Nd(t) = –0.7 to +0.3; zircon ∑Hf(t) = –5.7 to –2.2), which suggests formation by partial melting of an enriched lithospheric mantle source. In contrast, the later hornblende gabbros have depleted Nd-Hf isotopic compositions (whole rock ∑Nd(t) = +6.1 to +7.1; zircon ∑Hf(t) = +10.7 to +16.8) and normal mid–oceanic–ridge basalt (N–MORB)-type rare earth element (REE) features. They also show variable enrichments of fluid mobile elements (e.g., Rb, U, Pb), indicative of the input of slab-derived fluids in their mantle source. Thus, the hornblende gabbros were most likely originated from the asthenospheric mantle metasomatized by subducted oceanic slab-derived fluids. The transition in geochemical and isotopic compositions of these mantle-derived magmas reveals a long-lasting lithosphere extension and thinning along the southern margin of the Qiangtang terrane in the Early Jurassic. Combined with geological observations, we propose that this transition has resulted from the southward rollback of the subducting Bangong–Nujiang Tethyan oceanic slab. The slab rollback could have initiated the overriding plate extension and the asthenosphere upwelling. Wider implications of this study are that an onset of slab rollback could be an important trigger for the transition of magmatic geochemistry in subduction zones.
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Garçon, Marion, Catherine Chauvel, Christian France-Lanord, Mara Limonta et Eduardo Garzanti. « Which minerals control the Nd–Hf–Sr–Pb isotopic compositions of river sediments ? » Chemical Geology 364 (janvier 2014) : 42–55. http://dx.doi.org/10.1016/j.chemgeo.2013.11.018.
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Xu, Wen-Liang, Jia-Hui Chen, Ai-Hua Weng, Jie Tang, Feng Wang, Chun-Guang Wang, Peng Guo, Yi-Ni Wang, Hao Yang et Andrey A. Sorokin. « Stagnant slab front within the mantle transition zone controls the formation of Cenozoic intracontinental high-Mg andesites in northeast Asia ». Geology 49, no 1 (25 août 2020) : 19–24. http://dx.doi.org/10.1130/g47917.1.
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Abstract The geochemistry of Cenozoic intracontinental high-Mg andesites (HMAs) in northeast Asia, together with regional geophysical data, offers an opportunity to explore the genetic relationship between the formation of intracontinental HMAs and subduction of the Pacific plate. Compared with primary HMAs in arcs, Cenozoic intracontinental HMAs in northeast Asia have lower Mg# [100 × Mg/(Mg + Fe2+)] values (53–56) and CaO contents (5.8–6.6 wt%), higher alkali (Na2O + K2O) contents (5.15–6.45 wt%), and enriched Sr-Nd-Hf isotopic compositions (87Sr/86Sr = 0.7056–0.7059; εNd = −4.9 to −3.4; εHf = −4.7 to −2.6) as well as lower Pb isotope ratios (206Pb/204Pb = 16.76–19.19; 207Pb/204Pb = 15.42–15.45; 208Pb/204Pb = 36.71–37.11). These Cenozoic intracontinental HMAs are similar to Cenozoic potassic basalts in northeast China with respect to their Sr-Nd-Pb-Hf isotopic compositions but have higher SiO2 and Al2O3 contents and lower K2O, MgO, and light rare earth element contents. These features indicate that these Cenozoic intracontinental HMAs originated from the mantle, where recycled ancient sediments and water contributed to partial melting of peridotite. Combined with the presence of a large low-resistivity anomaly derived from the mantle transition zone (MTZ) near these intracontinental HMAs, and their occurrence above the stagnant slab front within the MTZ (at 600 km depth) in northeast Asia, we conclude that the stagnant slab front, with high contents of recycled ancient sediments and water, has controlled the formation of Cenozoic intracontinental HMAs in northeast Asia.
Thèses sur le sujet "Hf-Nd-Pb isotopic compositions"
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Aquila, Quentin. « Explorer la géochimie des océans archéens avec les Formations de fer rubanées (BIF) : apport des compositions isotopiques Hf-Nd-Pb ». Electronic Thesis or Diss., Université Clermont Auvergne (2021-...), 2024. http://www.theses.fr/2024UCFA0054.
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Les Formations de fer Rubanées (BIF) sont des archives sédimentaires uniques pour étudier les océans primitifs de l'Archéen. Cependant, l'environnement de formation et les mécanismes en jeu dans la formation de ces sédiments chimiques riches en fer et en silicium sont peu contraints. Les BIF ont été très peu étudiés pour leurs compositions isotopiques en Nd-Hf alors qu'elles pourraient permettre d'apporter de nouvelles contraintes sur les sources hydrothermales et continentales alimentant les anciens océans. Pour mieux contraindre l'environnement de formation des BIF, j'ai combiné des aspects de terrains et une étude pétro-géochimique sur une succession sédimentaire de la ceinture de Barberton (3,25 Ga, Afrique du Sud). Le modèle de dépôt des BIF de Barberton implique un milieu de dépôt profond, au bas d'une pente et distal du continent. Cet environnement est perturbé ponctuellement par des dépôts gravitaires terrigènes (mafiques) caractéristiques d'un système sédimentaire d'éventail sous-marin profond. J'ai évalué si la signature géochimique de l'eau de mer (REE+Y, faibles HFSE) permettait d'indiquer la préservation des compositions isotopiques Hf-Nd-Pb primaires sur un BIF de la ceinture de Isua (3,7 Ga, Groenland). Le BIF de Isua montre des perturbations post-dépôts des compositions isotopiques Hf-Nd attribués à la présence d'apatites secondaires. Il a cependant préservé un âge 207Pb-206Pb de 3810 ± 7 Ma hérité de zircons détritiques. Le spectre REE+Y typique de l'eau de mer ne garantit donc ni la préservation des compositions isotopiques Hf-Nd primaires de l'eau de mer, ni de l'absence de toute contamination terrigène. Enfin, j'ai exploré l'origine et la source du Nd et de l'Hf dans les BIF à l'échelle des bandes sur des échantillons provenant de la ceinture de Témagami (2,7 Ga, Canada). Les compositions isotopiques initiales en Nd-Hf des bandes de BIF de Témagami riches en Si montrent un découplage des deux systèmes isotopiques. A l'inverse, celles des bandes riches en Fe demeurent couplées en Nd-Hf. Les bandes riches en Si enregistrent une composition isotopique en Hf radiogénique provenant des eaux d'altérations des continents felsiques. A l'inverse, l'Hf et le Nd des bandes riches en Fe pourrait provenir principalement de l'hydrothermalisme sous-marinThe Banded Iron Formations (BIF) are unique sedimentary archives for studying the primitive oceans of the Archean. However, the environment of formation and the mechanisms involved in the formation of these iron- and silicon-rich chemical sediments are poorly constrained. The BIFs have been little studied for their Nd-Hf isotopic compositions, although they could provide new constraints on the hydrothermal and continental sources feeding the ancient oceans. To better constrain the BIFs environment of formation, I combined field observations with a petro-geochemical study on a sedimentary succession from the Barberton belt (3.25 Ga, South Africa). The deposition model of the Barberton BIFs involves a deep depositional environment, at the base of a slope and distal from the continent. This environment is occasionally disturbed by gravity-driven terrigenous deposits (mafic) characteristics of a deep-sea fan system. I evaluated whether the seawater geochemical signature (REE+Y, low HFSE) indicated the preservation of the primary Hf-Nd-Pb isotopic compositions in a BIF from the Isua belt (3.7 Ga, Greenland). The Isua BIF shows post-depositional disturbances in the Hf-Nd isotopic compositions attributed to the presence of secondary apatites. However, it preserved a 207Pb-206Pb age of 3810 ± 7 Ma inherited from detrital zircons. Therefore, the REE+Y spectrum typical of seawater does not guarantee the preservation of the primary Hf-Nd isotopic compositions of seawater, nor the absence of any terrigenous contamination. Finally, I explored the origin and source of Nd and Hf in the BIFs at the scale of the bands on samples from the Témagami belt (2.7 Ga, Canada). The initial Nd-Hf isotopic compositions of the Si-rich bands of the Témagami BIFs show a decoupling of the two isotopic systems. Conversely, those of the Fe-rich bands remain coupled in Nd-Hf. The Si-rich bands record a radiogenic Hf isotopic composition originating from the weathering waters of felsic continents. Conversely, the Hf and Nd in the Fe-rich bands could mainly originate from submarine hydrothermalism
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Schmidberger, Stefanie. « Hf, Sr, Nd and Pb isotope systematics and major and trace element compositions of the Archean subcratonic lithosphere beneath Somerset Island, Arctic Canada ». Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=37656.
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Hf, Sr, Nd and Pb isotopes, and major, trace and rare earth elements (REE) were determined for a suite of peridotite and pyroxenite xenoliths, constituent garnet and clinopyroxene and the host Nikos kimberlite (100 Ma) from Somerset Island, in order to constrain the chemical and isotopic composition of the lithosphere beneath the northern Canadian craton. The refractory Nikos peridotites are characterized by high olivine forsterite contents (avg. Fo = 92.3) and depletions in incompatible major elements (Fe, Al, Ca), but are enriched in incompatible trace elements, such as large ion lithophile elements (LILE) and light rare earth elements (LREE), while having approximately chondritic heavy rare earth element (HREE) contents. Mass balance calculations using REE contents of clinopyroxene and garnet indicate that calculated LREE abundances for the Nikos xenoliths are significantly lower (e.g. Nd ~50%) than those of the analyzed whole-rocks. These results suggest the presence of small amounts of a kimberlite-related LREE-rich interstitial component (i.e. ~1% kimberlite liquid and/or ~0.01% apatite) to account for the excess LREE abundances, with little effect on the HREE budgets of the xenoliths.The 143Nd/144Nd(0.1Ga) (0.51249--0.51276) isotopic compositions of the Nikos peridotites are little variable and overlap those of the Nikos kimberlite at the time of sample transport. The low-temperature peridotites (<1100°C) that sample the shallow lithosphere are characterized by more radiogenic 176Hf/177Hf(0.1Ga) (0.28296--0.28419) and Pb (206Pb/204Pb (0.1Ga) = 17.82--19.03), but lower 87Sr/ 86Sr(0.1Ga) (0.7047--0.7066) isotopic ratios than those of the high-temperature peridotites (>1100°C; 0.28265--0.28333; 17.18--18.30; 0.7064--0.7085, respectively). Incompatible trace element compositions of the xenoliths confirm this depth stratification indicating that shallow and deep (>160 km) Somerset lithosphere are characterized by distinct chemical and isotopic characteristics.
The Lu-Hf isotope compositions of the low-temperature peridotites plot along a 2.8 Ga reference isochron, which is consistent with an interpretation that the shallow Somerset lithosphere stabilized in the Archean to depth of ~150 km. The deep lithospheric mantle, which is probably younger, does not share the same petrogenetic history and may contain recycled material (altered oceanic crust and sedimentary component?). The Hf isotope compositions for the shallow low-temperature peridotites indicate that part of the lithosphere beneath the Canadian craton is characterized by more radiogenic Hf isotope signatures than estimates for "depleted" mantle.
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Carpentier, Marion. « Composition chimique des sédiments entrant dans la zone de subduction des Petites Antilles ». Phd thesis, Universite Libre de Bruxelles, 2007. http://tel.archives-ouvertes.fr/tel-00187335.
Texte intégralRésumé :
Les laves provenant de l'arc des Petites Antilles sont caractérisées par une grande variabilité chimique et leurs compositions isotopiques suggèrent une contribution variable de matériel crustal ancien dans leur genèse. L'arc des Petites Antilles est également caractérisé par une zonation chimique nord-sud, les laves des îles du sud présentant généralement des signatures isotopiques crustales plus fortes que celles des îles du nord. Nous avons tenté dans cette étude d'établir s'il existe des variations de la composition chimique des sédiments entrant en subduction le long de l'arc, et si d'éventuels changements de leur composition peuvent expliquer les variations chimiques observées au sein des laves. Pour ce faire, nous avons réalisé une étude géochimique approfondie (majeurs, traces, isotopes du Sr, du Nd, de l'Hf et du Pb) du flux sédimentaire potentiellement entrant dans la zone de subduction à différentes latitudes. L'échantillonnage comprend des sédiments forés au niveau des sites 543 (nord de l'arc) et 144 (extrême sud de l'arc) lors des campagnes DSDP 78A et 14 respectivement, et des sédiments provenant de l'île de la Barbade (sud de l'arc). Les échantillons présentent une grande hétérogénéité lithologique correspondant globalement à un mélange en proportion variable entre une composante détritique et une composante biogénique (siliceuse ou carbonatée). De plus, au niveau du site 144, des niveaux très riches en matière organique (black shales) datant du Cénomanien supérieur au Santonien (~ 95 à 84 Ma) ont été forés. Ces formations correspondent à l'enregistrement des Oceanic Anoxic Events 2 et 3. Nous avons montré que la « dilution » variable de la fraction détritique par la composante biogénique est le facteur qui contrôle largement les variations de concentrations en éléments traces observées. De plus, nous avons révélé un enrichissement en U extrêmement important au sein des black shales du site 144. Les signatures isotopiques de l'Hf, du Nd et du Pb sont dominées par la composante détritique, alors que celle du Sr, dans le cas d'échantillons riches en carbonates est dominée par celle de l'eau de mer. Les sédiments des trois sites présentent des compositions isotopiques du Pb fortement radiogéniques par rapports aux sédiments océaniques « classiques », que nous avons associées à une forte contribution de matériel issu de l'altération des cratons guyanais et brésilien dans la composante détritique. De plus, la décroissance radioactive de l'U dans les black shales du site 144 a généré des rapports 206-207Pb/204Pb extrêmement radiogéniques.
Un mélange entre le manteau appauvri et les sédiments du site 543 reproduit les compositions isotopiques des laves de la partie nord de l'arc. Pour la partie sud de l'arc un mélange entre les sédiments les plus radiogéniques en Pb du site 144 et le manteau appauvri explique les compositions des laves des îles de la Martinique à Grenade. Une contribution croissante des black shales du nord vers le sud est nécessaire, et est de plus en accord avec l'augmentation du nord vers le sud de l'âge du plancher océanique subduit. Enfin, quelques sédiments de l'île de la Barbade présentent certaines caractéristiques compatibles avec leur implication dans la genèse des laves de la partie sud de l'arc.
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Carpentier, Marion. « Composition chimique des sédiments entrant dans la zone de subduction des Petites Antilles ». Phd thesis, Grenoble 1, 2007. http://www.theses.fr/2007GRE10153.
Texte intégralRésumé :
Les laves provenant de l’arc des Petites Antilles sont caractérisées par une grande variabilité chimique et leurs compositions isotopiques suggèrent une contribution variable de matériel crustal ancien dans leur genèse. L’arc des Petites Antilles est également caractérisé par une zonation chimique nord-sud, les laves des îles du sud présentant généralement des signatures isotopiques crustales plus fortes que celles des îles du nord. Nous avons tenté dans cette étude d’établir s’il existe des variations de la composition chimique des sédiments entrant en subduction le long de l’arc, et si d’éventuels changements de leur composition peuvent expliquer les variations chimiques observées au sein des laves. Pour ce faire, nous avons réalisé une étude géochimique approfondie (majeurs, traces, isotopes du Sr, du Nd, de l’Hf et du Pb) du flux sédimentaire potentiellement entrant dans la zone de subduction à différentes latitudes. L’échantillonnage comprend des sédiments forés au niveau des sites 543 (nord de l’arc) et 144 (extrême sud de l’arc) lors des campagnes DSDP 78A et 14 respectivement, et des sédiments provenant de l’île de la Barbade (sud de l’arc). Les échantillons présentent une grande hétérogénéité lithologique correspondant globalement à un mélange en proportion variable entre une composante détritique et une composante biogénique (siliceuse ou carbonatée). De plus, au niveau du site 144, des niveaux très riches en matière organique (black shales) datant du Cénomanien supérieur au Santonien (~ 95 à 84 Ma) ont été forés. Ces formations correspondent à l’enregistrement des Oceanic Anoxic Events 2 et 3. Nous avons montré que la « dilution » variable de la fraction détritique par la composante biogénique est le facteur qui contrôle largement les variations de concentrations en éléments traces observées. De plus, nous avons révélé un enrichissement en U extrêmement important au sein des black shales du site 144. Les signatures isotopiques de l’Hf, du Nd et du Pb sont dominées par la composante détritique, alors que celle du Sr, dans le cas d’échantillons riches en carbonates est dominée par celle de l’eau de mer. Les sédiments des trois sites présentent des compositions isotopiques du Pb fortement radiogéniques par rapports aux sédiments océaniques « classiques », que nous avons associées à une forte contribution de matériel issu de l’altération des cratons guyanais et brésilien dans la composante détritique. De plus, la décroissance radioactive de l’U dans les black shales du site 144 a généré des rapports 206-207Pb/204Pb extrêmement radiogéniques. Un mélange entre le manteau appauvri et les sédiments du site 543 reproduit les compositions isotopiques des laves de la partie nord de l’arc. Pour la partie sud de l’arc un mélange entre les sédiments les plus radiogéniques en Pb du site 144 et le manteau appauvri explique les compositions des laves des îles de la Martinique à Grenade. Une contribution croissante des black shales du nord vers le sud est nécessaire, et est de plus en accord avec l’augmentation du nord vers le sud de l’âge du plancher océanique subduit. Enfin, quelques sédiments de l’île de la Barbade présentent certaines caractéristiques compatibles avec leur implication dans la genèse des laves de la partie sud de l’arcLesser Antilles lavas display large chemical variability and their isotopic compositions suggest variable incorporation of old crustal material during their genesis. The Lesser Antilles arc is also characterized by a chemical zoning from north to south along the arc, and lavas from the southern islands generally display a more pronounced crustal fingerprint than northern lavas. The aim of the study is to determine whether a north-south chemical variation exists within the subducting sediment cover, and if potential change in the sediment compositions can explain the chemical variations observed in the lavas. We have undertaken a detailed geochemical study (major and trace elements, Sr-Nd-Hf-Pb isotopes) of sedimentary flux potentially entering the subduction zones at different latitudes. Sampling includes sediments drilled at sites 543 (northern forearc) and 144 (extreme southern forearc) during DSDP Legs 78A and 14 respectively, and sediments from Barbados island (southern forearc). Samples display large lithological heterogeneity which can globally be explained by mixing in variable proportion of a detrital component and a biogenic one (carbonated or siliceous). Moreover, at site 144, some organic rich deposits (black shales) of upper Cenomanian to Santonian (~ 95 to 84 Ma) were drilled and correspond to sedimentary records of Cretaceous Oceanic Anoxic Events 2 and 3. We have shown that variable dilution of detrital component by biogenic one is the main factor controlling the observed variations of trace element concentrations. Moreover, we have revealed an extremely important enrichment of U in site 144 black shales. Nd-Hf-Pb isotopic compositions of studied sediments mainly represent those of the detrital component, whereas Sr isotope ratios, in the case of carbonate rich sediments, are dominated by the seawater signature. Sediments from the three sites exhibit highly radiogenic Pb isotopic compositions if compared with other sediments localized in front of the other major subduction zones, due in part to the important input of detrital material derived from the Guyana and Brazilian Shields. Moreover, Cretaceous black shales from site 144, U-enriched, are characterized by extremely high Pb isotopes ratios due to radioactive decay of U. Mixing of depleted mantle with northern sediments (site 543) produce the isotopic compositions of lavas from the northern part of the arc. For the southern part of the arc, mixing of the depleted mantle and sediments from site 144 explain the compositions of lavas from the islands of Martinique to Grenada. An increase of black shales contribution from north to south is necessary and in agreement with the increasing age of subducting Atlantic crust from north to south along the Lesser Antilles trench. Finally, some sediments of Barbados island associated with sediments like those from site 543 may represent the appropriated sedimentary end member to explain isotopic composition of southern island lavas
Livres sur le sujet "Hf-Nd-Pb isotopic compositions"
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Flierdt, Tina Van de. The ND, HF, and PB isotopic composition of ferromanganese crusts and their paleoceanographic implications. 2003.
Trouver le texte intégralChapitres de livres sur le sujet "Hf-Nd-Pb isotopic compositions"
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Thompson, M. D., S. M. Barr et J. C. Pollock. « Evolving views of West Avalonia : Perspectives from southeastern New England, USA ». Dans New Developments in the Appalachian-Caledonian- Variscan Orogen. Geological Society of America, 2022. http://dx.doi.org/10.1130/2022.2554(03).
Texte intégralRésumé :
ABSTRACT Southeastern New England is largely composed of Ediacaran granitoid and related volcanic rocks formed during the main phase of arc-related magmatism recorded in West Avalonian lithotectonic assemblages extending through Atlantic Canada to eastern Newfoundland. In situ Lu-Hf analyses presented here for zircons from the Dedham, Milford, and Esmond Granites and from the Lynn-Mattapan volcanic complex show a restricted range of εHf values (+2 to +5) and associated Hf-TDM model ages of 1.3–0.9 Ga, assuming felsic crustal sources. The most evolved granites within this suite lie in a belt north and west of the Boston Basin, whereas upfaulted granites on the south, as well as the slightly younger volcanic units, show more juvenile Hf isotopic compositions. Similar inferences have been drawn from previously published Sm-Nd isotopic signatures for several of the same plutons. Collectively, the isotopic compositions and high-precision U-Pb geochronological constraints now available for southeastern New England differ in important respects from patterns in the Mira terrane of Cape Breton Island or the Newfoundland Avalon zone, but they closely resemble those documented in the Cobequid and Antigonish Highlands of mainland Nova Scotia and New Brunswick’s Caledonia terrane. Particularly significant features are similarities between the younger than 912 Ma Westboro Formation in New England and the younger than 945 Ma Gamble Brook Formation in the Cobequid Highlands, both of which yield detrital zircon age spectra consistent with sources on the Timanide margin of Baltica. This relationship provides the starting point for a recent model in which episodic West Avalonian arc magmatism began along the Tonian margin of Baltica and terminated during diachronous late Ediacaran arc-arc collision with the Ganderian margin of Gondwana.
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Konopelko, Dmitry L. « Chapter 3. Postcollisional intrusions of the Alai Segment of South Tien Shan ». Dans PALEOZOIC GRANITOID MAGMATISM OF WESTERN TIEN SHAN, 70–101. St. Petersburg State University, 2020. http://dx.doi.org/10.21638/11701/9785288060250.04.
Texte intégralRésumé :
The early Permian intrusions of the Alai Segment of the South Tien Shan comprise four geochemically contrasting intrusive series, including (1) I-type and (2) shoshonitic granitoids, (3) peraluminous granitoids including S-type leucogranites and (4) alkaline rocks and carbonatites, closely associated in space and time. New geochronological data indicate that diverse magmatic series of the Alai segment formed virtually coevally in a post-collisional setting. Five U-Pb zircon rock ages in the range 287 – 281 Ma, in combination with published ages, define the main post-collisional magmatic pulse at 290 - 280, which is similar to ages of post-collisional intrusions elsewhere in the South Tien Shan. The Sr-Nd-Pb-Hf isotopic compositions of the studied intrusions are consistent with the reworking of crustal material with 1.6 – 1.1 Ga average crustal residence times indicating the formation of the Alai segment of the South Tien Shan on a continental basement with Mesoproterozoic or older crust. It is suggested that position of the Alai microcontinent between two major sutures enabled delamination of its lithospheric mantle, which triggered the diverse post-collisional magmatism as a result of interaction of ascending asthenospheric material with lithospheric mantle and various crustal protoliths.
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Straub, S. M., S. Mallick, A. Gomez-Tuena et M. J. Dorais. « Data report : major and trace element and Nd-Pb-Hf isotope composition of the Site U1504 metamorphic basement in the South China Sea (IODP Expedition 367/368/368X) ». Dans Volume 367/368 : South China Sea Rifted Margin. International Ocean Discovery Program, 2022. http://dx.doi.org/10.14379/iodp.proc.367368.203.2022.
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Straub, S. M., A. Gomez-Tuena et M. J. Dorais. « Data report : major and trace element and Sr-Nd-Pb-Hf isotope composition of three granite clasts from Hole U1501D in the South China Sea (IODP Expedition 367/368/368X) ». Dans Volume 367/368 : South China Sea Rifted Margin. International Ocean Discovery Program, 2022. http://dx.doi.org/10.14379/iodp.proc.367368.202.2022.
Texte intégralActes de conférences sur le sujet "Hf-Nd-Pb isotopic compositions"
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Ramamurty, Prabala, Neethu Sukumaran, Teeda Kumar et Gugulothu Balu. « Radiogenic Sr-Nd-Hf-Pb isotopic compositions of submarine volcanic rocks of a Seamount from the Andaman Sea ». Dans Goldschmidt2023. France : European Association of Geochemistry, 2023. http://dx.doi.org/10.7185/gold2023.18359.
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Grabarczyk-Gurba, Anna, Ewa Krzemińska, Leonid Shumlyanskyy et Dominik Gurba. « A tentative model for the origin of anorthosite-gabbronorite Sejny Massif, NE Poland – Geochemistry, U–Pb ages, Sr–Nd and Hf–O isotopic composition ». Dans Goldschmidt2023. France : European Association of Geochemistry, 2023. http://dx.doi.org/10.7185/gold2023.16416.
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Yang, Yue-Heng. « High-Precision Sr-Nd-Hf-Pb Isotopic Composition of CGSG-1, CGSG-2, CGSG-4 and CGSG-5 Reference Materials by MC-ICP-MS and TIMS ». Dans Goldschmidt2020. Geochemical Society, 2020. http://dx.doi.org/10.46427/gold2020.3011.
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Ayers, John C., Xiaomei Wang, Nathan J. Katsiaficas et Xiaoming Liu. « USE OF ZIRCON U-PB AGES AND BULK TRACE ELEMENT AND ND AND HF ISOTOPE COMPOSITIONS TO DETERMINE SOIL PROVENANCE IN A LIMESTONE TERRANE, MIDDLE TN, USA ». Dans GSA Annual Meeting in Seattle, Washington, USA - 2017. Geological Society of America, 2017. http://dx.doi.org/10.1130/abs/2017am-299145.
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