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1
De, Assunção Rodrigues Mariana. "Analyse de la provenance sédimentaire des bassins du Crétacé du système Andes-Amazonie-marge équatoriale et des relations avec la paléogéographie et la tectonique". Electronic Thesis or Diss., Toulouse 3, 2023. http://www.theses.fr/2023TOU30363.
Abstract (sommario):
Le Crétacé est caractérisé par d'importants changements paléogéographiques, géodynamiques et climatiques, incluant notamment la formation de nouveaux océans dont l'Océan Atlantique équatorial, la fragmentation continue du Gondwana et des périodes à effet de serre. Tous ces changements sont potentiellement contenus dans les enregistrements sédimentaires des bassins. Le système Andes-Amazonie-Marge équatoriale est un vaste système sédimentaire dont l'évolution géodynamique et paléoenvironnementale est enregistrée dans les bassins d'avant-pays retroarc amazonien, les bassins intracratoniques brésiliens et ceux de la marge équatoriale. Dans la partie occidentale (région andine), des études récentes suggèrent que le début de l'orogenèse andine s'est produit au cours du Crétacé supérieur, mais le développement des systèmes de drainage et la source des sédiments déposés au cours du Crétacé restent encore peu connus. Le Crétacé inférieur est enregistré dans des bassins brésiliens intracratoniques et équatoriaux et témoigne des phases de rifting crustal suivant la fragmentation du Gondwana. Le bassin d'Araripe est un bon exemple de ces bassins puis qu'il contient un registre sédimentaire complet et particulièrement bien étudié. Cependant, l'origine des sédiments issus des différentes étapes tectoniques de la formation de bassin ainsi que la provenance crétacée des incursions marines l'ayant affecté restent à préciser. Cette thèse vise à proposer une reconstruction paléogéographique du système Andes-Amazonie-Marge équatoriale pendant le Crétacé et à analyser les changements géodynamiques et tectoniques qu'ont affecté. Pour ce faire, nous avons utilisé les méthodes de la provenance et en particulier la géochimie des éléments majeurs et traces, la composition isotopique en Sm et Nd, les âges U-Pb sur zircons. Les résultats obtenus ont permis d'identifier les zones sources du bassin d'Araripe pendent les phases pré, syn et post-rift et ainsi de mieux comprendre la configuration paléogéographique de la région nord-est du Brésil au début du Crétacé. Les sédiments du bassin d'Araripe proviennent principalement des terrains Paléoprotérozoïque (2,3-1,6 Ga) de la province de Borborema et des plutons granitiques du cycle Brasiliano (720-541Ma). Le bassin possède une histoire sédimentaire liée aux phases de rupture de l'Atlantique Sud et équatorial. Pendant la phase pré-rift (~152-135 Ma), le bassin faisait partie de la dépression Afro-Brésilienne et recevait des sédiments en provenance du N-NO. Lors la phase rift (~135-125Ma), il y a eu un changement de source due à rupture continentale et à la formation de l'Atlantique Sud, avec un apport de sédiments en provenance de la partie orientale de la province de Borborema. Pendant la phase post-rift (121-113 Ma), le bassin a cessé d'être alimenté par la partie orientale et les incursions marines ont dominé l'environnement de sédimentation. Enfin, au cours de la phase post-rift II (113-100 Ma) un dernier changement de sources a été observée, avec des sources au NE qui reflètent le moment final de la fragmentation du Gondwana. L'étude de la provenance des sédiments des bassins de l'Amazonie occidentale (Acre et Madre de Dios) indique que les sources sont cratoniques, provenant principalement des terrains Ventuari-Tapajos (2,0 - 1,82 Ga) et Rio Negro - Juruena (1,82 - 1,54 Ga). Ces résultats indiquent qu'un vaste réseau de drainage intracontinental ("Sanozama") qu'a émergé en réponse au soulèvement de l'Arche de Purus et des régions cratoniques du Brésil et des Guyanes pendant l'ouverture de l'océan Atlantique équatorial. L'intégration des résultats obtenue compilée avec les données de la littérature a permis de proposer quatre cartes paléogéographiques de la partie septentrionale de la plate-forme sud-américaine. Ils mettent en évidence comment les mécanismes géodynamiques liées à l'ouverture des océans atlantiques sud et équatoriaux ont contrôlé et façonné la paléogéographie de cette régionThe Cretaceous is characterized by major paleogeographic, geodynamic, and climatic changes, including the formation of new oceans such as the equatorial Atlantic Ocean, the continued fragmentation of Gondwana, and greenhouse effect periods. All these changes are potentially contained in the sedimentary records of the basins. The Andes-Amazonia-Equatorial Margin system is a vast sedimentary system whose geodynamic and palaeoenvironmental evolution is recorded in the Amazonian retroarc foreland basins, the Brazilian intracratonic basins, and those of the equatorial margin. In the western part (Andean region), recent studies suggest that the onset of the Andean orogeny occurred during the Late Cretaceous, but the development of drainage systems and the source of sediments deposited during the Cretaceous are still poorly understood. The Lower Cretaceous is recorded in Brazilian intracratonic and equatorial basins and bears witness to crustal rifting phases following Gondwana's break-up. The Araripe Basin is a good example of these basins since it contains a complete and particularly well-studied sedimentary record. However, the origin of the sediments from the various tectonic stages of basin formation and the Cretaceous origin of the marine incursions that affected it remain to be determined. The aim of this thesis is to propose a palaeogeographic reconstruction of the Andes-Amazonia-Equatorial Margin system during the Cretaceous and to analyze the geodynamic and tectonic changes that affected it. To do this, we used provenance methods, in particular major and trace element geochemistry, Sm and Nd isotopic composition, and U-Pb ages on zircons. The results obtained have enabled us to identify the source zones of the Araripe Basin during the pre-, syn- and post-rift phases and thus to gain a better understanding of the palaeogeographic configuration of the north-eastern region of Brazil at the beginning of the Cretaceous. The sediments in the Araripe basin come mainly from the Palaeoproterozoic (2.3-1.6 Ga) terrains of the Borborema province and the granitic plutons of the Brasiliano cycle (720-541Ma). The basin has a sedimentary history linked to the South Atlantic and equatorial break-up phases. During the pre-rift phase (~152-135 Ma), the basin was part of the Afro-Brazilian depression and received sediments from the N-NW. During the rift phase (~135-125Ma), there was a change in source due to continental break-up and the formation of the South Atlantic, with an influx of sediments from the eastern part of the Borborema province. During the post-rift phase (121-113 Ma), the basin ceased to be fed by the eastern part and marine incursions dominated the sedimentation environment. Finally, during the post-rift II phase (113-100 Ma) a last change in sources was observed, with sources to the NE reflecting the final moment of the fragmentation of Gondwana. A study of the provenance of sediments from the basins of western Amazonia (Acre and Madre de Dios) indicates that the sources are cratonic, originating mainly from the Ventuari-Tapajos (2.0 - 1.82 Ga) and Rio Negro - Juruena (1.82 - 1.54 Ga) terrains. These results indicate that a vast intracontinental drainage network ('Sanozama') emerged in response to the uplift of the Purus Arch and the cratonic regions of Brazil and the Guianas during the opening of the equatorial Atlantic Ocean. The integration of the results obtained compiled with data from the literature has made it possible to propose four palaeogeographic maps of the northern part of the South American platform. They highlight how geodynamic mechanisms linked to the opening of the South Atlantic and equatorial oceans controlled and shaped the paleogeography of this region
2
Chavagnac, Valérie. "Behaviour of the Sm-Nd isotopie system during metamorphism : Examples from the HT-LP metamorphic terrane of the Limpopo Belt, South Africa and the UHP metamorphic terrane of Dabieshan, Central China". Phd thesis, Université Rennes 1, 1998. http://tel.archives-ouvertes.fr/tel-00620022.
Abstract (sommario):
Les buts de cette thèse sont (1) de déterminer si les âges modèles en Nd obtenus sur des terrains protérozoïques migmatisés correspondent réellement à l'âge d'extraction du magma de sa source mantellique (exemple du Limpopo Belt en Afrique du Sud) et (2) de comparer les âges Sm-Nd sur grenat et les âges U-Pb sur zircon déterminés sur des éclogites (exemple du Dabieshan en Chine Centrale). La Zone Centrale du Limpopo Belt est constituée principalement d'orthogneiss et de paragneiss. Elle a subi un métamorphisme granulitique suivi par des conditions métamorphiques de décompression à 2.0 Ga (trajectoire pression et température dans le sens horaire). Nous avons effectué des analyses isotopiques en Sm-Nd et U-Pb combinées aux analyses en éléments majeurs et traces sur trois examples de migmatites formées à 2.0 Ga afin d'étudier le fractionnement chimique et isotopique qui pourrait avoir lieu au cours de la migmatisation. La fusion partielle selon la réaction de déhydratation de la biotite met en exergue des comportements différents du système isotopique Sm-Nd dans les métagreywackes et dans les métapélites. Dans le premier cas, l'équilibre chimique et l'homogénéisation isotopique en Nd n'ont pas été achevés à cause de la fusion incongruente du plagioclase et de l'influence des minéraux accessoires sur la composition chimique des liquides. Il est démontré que la monazite est préférentiellement entraînée dans les leucosomes plutôt que l'apatite, provoquant ainsi la domination de la composition chimique de la monazite sur celles des liquides. De plus, la composition isotopique en Nd non-radiogénique de ce minéral accessoire domine celle du leucosome. Ainsi, les âges modèles en Nd des leucosomes sont jusqu'à 400 Ma plus vieux que ceux obtenus sur les paléosomes. Les âges modèles en Nd obtenus sur ces roches ne peuvent donc pas être uti lisés comme âge de formation de la croûte continentale en Afrique du Sud. Dans le cas des métapelites, la fusion incongruente du plagioclase a influencé la distribution des éléments majeurs, des Larges Ion Lithophi le Element ainsi que des Rare Earth Efement entre les paléosomes et les leucosomes. L'échange isotopique -en Nd entre les différents composants migmatitiques a été pratiquement atteint, au contraire des isotopes du Pb qui ne montrent qu'une homogénéisation partielle. Cependant, deux leucosomes à grenat présentent des compositions isotopiques en Sm-Nd et U-Pb supérieures aux autres composants migmatitiques. Ceci suggère qu'en règle générale les minéraux accessoires ont été chimiquement et isotopiquement équilibrés avec les leucosomes et les paléosomes. De ce fait, les âges modèles en Nd calculés sur les paléosomes et les leucosomes représentent des âges significatifs pour la formation de la croûte continentale dans la Zone Centrale du Limpopo Belt. Le dernier exemple est un orthogneiss migmatitique qui s'est formé par ségrégation métamorphique à des conditions subsolidus. La distribution des éléments majeurs et traces est directement proportionnelle à la quantité de chaque minéraux formant les composants migmatitiques. L'échange __ _ ___ _ isotopique en Pb a été achevé comme le montre l'isochrone en Pb-Pb sur les roches -:_~~ totales à 2.0 Ga. De plus, les caractéristiques géochimiques associées à une modélisation de la distribution des REE indiquent que le système est resté clos à - -----l'échelle de la roche totale durant le processus de migmatisation .. Ainsi, la composition isotopique en Nd du protolithe a pu être déterminée grâce à l'équation de conservation de masse et peut être utilisée pour défini~ l'âge de la formation de la croûte continentale. Le terrain Métamorphique de Ultra-Haute Pression (UHPM) du Dabieshan ______ est caractérisé par la présence de coésite et de quartz pseudomorphe dans les éclogites de composition basaltique mais aussi dans les roches d'origine sédimentaire. Les Isochrones en Sm-Nd sur grenat-omphacite-roche totale des éclogites à coésite du Massif de Bixiling donnent des âges variant entre 210 ± 9 Ma et 218 ± 4 Ma, très similaires aux âges U-Pb sur zircon à 218.4 ± 1.8 Ma et 218.4 ± 2.5 Ma (Ames et al., 1995). De plus, une isochrone Sm-Nd sur grenat-disthène-roche totale d'une éclogite rétromorphosée donne un âge à 231 ± 35 Ma en accord avec un âge à 233 ± 21 Ma (intercepte bas dans le diagramme concordia). Nous avons (:lffectué des datations par les méthodes Rb-Sr et Ar-Ar sur des phengites et des biotites de l'encaissant des éclogites à coésite de Bixiling. Les âges varient entre 198 ± 4 Ma et 212 ± 2 Ma recouvrant les âges précedemment obtenus par Sm-Nd sur les éclogites à coésite. Par conséquent, les âges Sm-Nd sur grenat sont en accord avec les âges U-Pb sur zircon et montrent que les gneiss quartzo-feldspathiques ont subi un événement métamorphique à -210 Ma comme les éclogites. L'homogénéisation isotopique en Nd entre les différents minéraux semblent être atteinte à l'âge du métamorphisme.
3
Nowicki, G. [Verfasser]. "Kernspektroskopische Untersuchungen der Isotone ¹³⁷Nd und ¹³⁹Sm / G. Nowicki". Karlsruhe : KIT-Bibliothek, 2010. http://d-nb.info/118725276X/34.
4
Thorogood, E. J. "Provenance of the pre-Devonian sediments of England and Wales : Sm-Nd isotopic evidence". Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293429.
5
Anglin, Carolyn Diane Carleton University Dissertation Geology. "Sm-Nd and Sr isotopic studies of scheelite from some Superior Province gold deposits". Ottawa, 1992.
6
Goodwin-Bell, Jo-Anne Stafford. "A geochemical and Sm-Nd isotopic study of Cordilleran eclogites from the Yukon-Tanana terrane". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0007/MQ28939.pdf.
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Kay, Andrew. "Sm-Nd isotope, major element, and trace element geochemistry of the Nashoba terrane, eastern Massachusetts". Thesis, Boston College, 2012. http://hdl.handle.net/2345/bc-ir:107672.
Abstract (sommario):
Thesis advisor: Christopher J. HepburnThe Nashoba terrane in eastern Massachusetts comprises Cambrian-Ordovician mafic to felsic metavolcanic rocks and interlayered sediments metamorphosed during the mid-Paleozoic and intruded by a series of dioritic to granitic plutons during the Silurian to earliest Carboniferous. This work comprises two parts discussing the Sm-Nd isotope characteristics and major and trace element geochemistry of the Nashoba terrane: the first discusses the Cambrian-Ordovician metamorphosed units, the second discusses the Silurian-Carboniferous plutons. Part I: The Nashoba terrane in eastern Massachusetts lies between rocks of Ganderian affinity to the northwest and Avalonian affinity to the southeast. Its relationship to either domain was unclear and has been investigated. Major and trace element geochemical data indicate a mix of arc, MORB, and alkaline rift related signatures consistent with an origin of the terrane as a primitive volcanic arc-backarc complex built on thinned continental crust. Newly determined Sm-Nd isotopic data clarifies the original tectonic setting. Amphibolites of the Marlboro and Nashoba Formations have high εNd values (+4 to +7.5) consistent with formation in a primitive volcanic arc with minimal interaction between arc magmas and crust. Intermediate and felsic gneisses have moderate εNd values between +1.2 and –0.75 indicating a mixture of juvenile arc magmas and an evolved (likely basement) source. Depleted mantle model ages of 1.2 to 1.6 Ga indicate a Mesoproterozoic or older age for this source. Metasedimentary rocks have negative εNd values between –6 and –8.3 indicating derivation primarily from an isotopically evolved source (or sources). The model ages of these metasedimentary rocks (1.6 to 1.8 Ga) indicate a source area of Paleoproterozoic or older age. The εNd values and model ages of the intermediate and felsic rocks and metasedimentary rocks indicates that the basement to the Nashoba terrane is Ganderian rather than Avalonian. The Nashoba terrane therefore represents a southward continuation of Ganderian arc-backarc activity as typified by the Penobscot and/or Popelogan-Victoria arc systems and the Tetagouche-Exploits backarc basin in the northern Appalachians. Part II: Between 430 and 350 Ma the Nashoba terrane experienced episodic dioritic and granitic plutonism. Previous workers have suggested a supra-subduction zone setting for this magmatism based on the calc-alkaline nature of the diorites. Previously determined major and trace element geochemical data along with newly determined Sm-Nd isotopic data indicate that a subduction zone was active beneath the Nashoba terrane during the majority of the 430 to ca. 350 Ma magmatism (and likely throughout). Trace element geochemistry indicates a strong arc component in all magmas and suggests that the various Silurian to Carboniferous plutonic rocks of the Nashoba terrane could all have been derived by modification of a slightly enriched NMORB-type source via subduction zone input and crustal contamination. Most of the rocks from this period have intermediate εNd values consistent with contamination of juvenile magmas by an evolved source. The late Proterozoic model ages for most of these rocks suggest the Ganderian basement of the Nashoba terrane as the source of evolved material. One rhyolite from the nearby Newbury Volcanic Complex (of unknown affinity) has a moderately negative εNd value consistent with derivation by partial melting of Cambrian-Ordovician metasedimentary rocks of the Nashoba terrane. This suggests that the Newbury Volcanic Complex formed as the surface expression of mid-Paleozoic Nashoba terrane plutonism. Geochemical and isotopic similarities between the plutonic rocks of the Nashoba terrane and widespread contemporary Ganderian plutonism suggest that the Nashoba terrane remained a part of Ganderia during its transit and accretion to the Laurentian margin. Significantly younger model ages in the youngest granitic rocks indicate that Avalonian crust may have underthrust the Nashoba terrane after 400 Ma and contributed to the generation of these granites
Thesis (MS) — Boston College, 2012
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Earth and Environmental Sciences
8
Flageole, Janick. "Sm-Nd Isotopic Composition of Mantle-Derived Rocks from the Saglek-Hebron Gneiss Complex, Northern Labrador". Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39208.
Abstract (sommario):
The Saglek-Hebron Gneiss Complex (SHC) is located in Northern Labrador within the Nain Province. It has recorded multiple magmatic events over more than 1 billion years, making it ideal to study the evolution of mantle-derived rocks through time. Here we present a 147Sm-143Nd isotopic study focussing on the different generations of mantle-derived rocks in the SHC. A total of 83 samples have been analysed, including: 1) mafic metavolcanic rocks; 2) ultramafic rocks divided into two distinct groups (a Fe-rich group enriched in incompatible elements and more depleted ultramafic rocks with lower Fe contents); 3) mafic metamorphosed dikes called the Saglek dikes; and 4) undeformed mafic dikes. Some samples exhibit evidence of post-magmatic geochemical and isotopic disturbance but only the least disturbed samples have been considered to constrain the timing of formation of the different lithologies and the isotopic composition of their mantle source. The mafic metavolcanic rocks combined with the co-genetic low-Fe ultramafic rocks yield an isochron age of 3819 ± 190 Ma (MSWD=34, n=25) with an initial εNd value of +2.3 ± 0.6. The high-Fe enriched ultramafic rocks yield a younger age of 3433 ± 220 Ma (MSWD=10.4, n=10) with an initial εNd= +1.8 ± 0.5. The two generations of mafic dikes appear to have been emplaced in the Mesoarchean and the Neoarchean. The Saglek dikes yield an isochron age of 3565 ±120 Ma (MSWD=1.17, n=10) with an initial εNd value of +1.7 ± 0.1, while the Sm-Nd isochron age for the undeformed mafic dikes is 2694 ±79 Ma (MSWD=3.2, n=21) with an initial εNd value of +1.7 ± 0.1. All generations of mantle-derived rocks yield positive initial εNd values, where only the Eoarchean rocks display an initial Nd isotopic composition similar to the depleted mantle. The Mesoarchean ultramafic rocks, Saglek dikes and Neoarchean mafic dikes display almost identical initial εNd values, despite an age difference of ~800 Ma. This could suggest the contribution of distinct mantle sources or, if all generations of mantle-derived rocks in the SHC were produced from the same mantle source, it implies that this source evolved with a nearly chondritic Sm/Nd ratio for almost the whole Archean Eon. The fact that the initial isotopic compositions of the mantle-derived rocks appear to deviate from the depleted mantle with time, could also suggest an increasing interaction with older evolved crust.
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Linkermann, Sean Aaron. "Emplacement of the 2.44 Ga ultramafic layered Kemi intrusion, Finland PGE, geochemical and Sm-Nd isotopic implications". Thesis, Rhodes University, 2011. http://hdl.handle.net/10962/d1005552.
Abstract (sommario):
Europe’s largest chrome deposit is hosted by the 2.44 Ga Kemi ultramafic layered intrusion. The lower half of the intrusion consists of peridotites, pyroxenites and chromitite layers while the upper half consists of websterites, gabbronorites and leucogabbros. The mafic minerals of the lower and upper parts of the intrusion are altered to serpentine, chlorite, talc, amphiboles and carbonates. However, the original mineralogy is still preserved in the middle part of the intrusion. Earlier work on the Kemi intrusion concentrated mainly on the economically important chromitite layers and suggested that these layers were formed through contamination of a single pulse of primitive magma by underlying Archaean basement crustal material. The broad variations of the major element concentrations reflect variations in the mode of the Kemi rocks. The petrology, which shows olivine- and orthopyroxene-dominated rocks in the lower portion of the intrusion to plagioclase- and clinopyroxene-dominated rocks in the upper portion, shows a gross consistency with a fractional crystallization process.The incompatible elements are relatively enriched in the lower portion of the intrusion which is not consistent with a broad fractional crystallization process. These variations suggest that the ultramafic portion of the KemiIntrusion is relatively enriched in trapped liquid compared to the mafic portion.ε2.44 Nd values ranges from +4 (consistent with depleted mantle source) to -10 (indicating a contribution from Archaean crust). The lower peridotites, pyroxenites and websterites have ε2.44 Nd values ranging between depleted mantle signatures and -2, whereas the gabbroic cumulates have ε2.44 Nd values which cover a range from around -5 to -10. Nd isotopic variation in the lower part of the profile is punctuated by distinct spikes to lower ε2.44 Nd corresponding to the chromitite horizons. Both the lower and upper portions of the Kemi Intrusion show enrichment of LREEC1 relative to HREEC1. The LREEC1 enriched values start to increase markedly from about the 1000 meter mark and continue to increase in value towards the roof of the intrusion.The main enrichment of PGE (ΣPPGE = 55 to 148 ppb) occurs approximately 90 to 160 m above the basal contact, beginning within andcontinuing above the main chromitite ore horizon. The mantle-normalized PGE abundances of the main chromitite horizon and the peridotites and pyroxenites below it show enrichment of IPGEPM (Os + Ir + Ru) relative to PPGEPM (Rh + Pd + Pt). In contrast, the overlying rocks are characterised by enrichment of PPGEPM relative to IPGEPM. These PGE-patterns suggest the influence of two distinct controlling processes above and below the main chromitite reef.The isotopic data are consistent with the initial introduction of multiple pulses of depleted mantle-derived magma crystallising olivine and pyroxene. Before the parent magma was fed into the Kemi magma chamber, it underwent crustal contamination and assimilation in a staging chamber within the lower crust. Some of these pulses were “critically crustally contaminated”, inducing chromite saturation and precipitation. The modelling also predicts minor in-situ contamination of the parent magma in the Kemi chamber with its wall and roof rocks. Above the main chromitite layer (about 160 m above the basal contact), the chromite content decreases and the PPGEPM/IPGEPM values increase which is consistent with scavenging of the IPGE into the lowermost layers and/or evolving magma compositions. Above 1000 m, the isotopic and REE data indicate a new magma pulse which has also been extensively contaminated in the staging magma chamber before emplacement into the Kemi magma chamber. The contamination in the staging magma chamber increased which is reflected in a progressively larger crustal component towards the top of the Kemi Intrusion
10
Schmitt, Wolfgang. "Application of the Sm-Nd Isotope System to the Late Quaternary Paleoceanography of the Yermak Plateau (Arctic Ocean)". Diss., lmu, 2007. http://nbn-resolving.de/urn:nbn:de:bvb:19-71834.
11
Kondo, Nozomi. "Major element composition of the Hadean crust: constraints from Sm-Nd isotope systematics and high-pressure melting experiments". Kyoto University, 2018. http://hdl.handle.net/2433/232387.
Abstract (sommario):
Kyoto University (京都大学)0048
新制・課程博士
博士(人間・環境学)
甲第21186号
人博第858号
新制||人||204(附属図書館)
29||人博||858(吉田南総合図書館)
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 小木曽 哲, 教授 石川 尚人, 教授 酒井 敏, 准教授 飯塚 毅
学位規則第4条第1項該当
12
Farrell, Thomas. "Investigating the Tectonic Significance of Spiral Garnets from the Betic-Rif Arc of Southern Spain and Northern Morocco Using Sm-Nd Garnet Geochronology:". Thesis, Boston College, 2019. http://hdl.handle.net/2345/bc-ir:108592.
Abstract (sommario):
Thesis advisor: Ethan F. BaxterSpiral garnets are well-documented metamorphic microstructures that have been observed in orogens throughout the world. The preferred orientation of spiral garnet axes has been proposed (Bell and Johnson, 1989) to record and preserve information about the timing, rate, and orientation of the tectonic-scale processes. Using the model of Be Spiral garnets are well-documented metamorphic microstructures that have been observed in orogens throughout the world. The preferred orientation of spiral garnet axes has been proposed (Bell and Johnson, 1989) to record and preserve information about the timing, rate, and orientation of the tectonic-scale processes. Using the model of Bell and Johnson (1989), Aerden et al. (2013) proposed a link between the preferred orientation of spiral garnets and changes in relative plate motion between Iberia and Africa. The goal of this thesis is to this relationship by absolutely dating, eight samples from the Betic-Rif arc with measurable spiral axis orientations were chosen for Sm-Nd garnet geochronology. Chapter one is a detailed literature review of prior work on the formation and interpretation of spiral garnets. In chapter two we present 11 bulk Sm-Nd garnet ages from eight samples, these ages range from 35.6 ± 2.8 to 13.62 ± 0.69 Ma. The results from the obtained bulk garnet ages reveal a more complex relationship between FIA orientations and plate motion that originally hypothesized in Aerden et al. (2013). Large-scale rigid block rotations that postdate garnet growth may have influenced the current orientation of FIA from the western Betic-Rif. In chapter three, zoned geochronology was conducted on a single sample from the Nevado-Filabride Complex. This study revealed spiral garnet formation occurring on a rapid timescale, just 〖0.45〗_(-0.32)^(+0.51) Myr. While other zoned garnet studies have shown similar rapid growth in subduction zone setting (Dragovic et al., 2012), this is the first such documentation of such rapid growth from a garnet hosting spiral inclusion trails in a regional metamorphic setting. We calculated strain rates considering different genetic models for the spiral inclusion trails either by garnet rotation in simple shear, or by episodic overgrowth of suborthogonal crenulation cleavages due to switching stress axes. In both cases a similar fast strain rate of ca. 10-13 s-1 was obtained, which is an order of magnitude faster than typical regional strain rates and faster than previous spiral garnet studies regardless of the method used to calculate strain-rate
Thesis (MS) — Boston College, 2019
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Earth and Environmental Sciences
13
BROS, REGIS. "Geochimie isotopique (sm-nd, rb-sr, k-ar, u) des argiles du bassin proterozoique de franceville et des reacteurs d'oklo (gabon)". Université Louis Pasteur (Strasbourg) (1971-2008), 1993. http://www.theses.fr/1993STR13059.
Abstract (sommario):
Le francevillien est une serie sedimentaire proterozoique non affectee par des evenements metamorphiques en depit de son age. Ses sediments detritiques sont utilisables pour etudier l'evolution temporelle des mineraux argileux et l'histoire de la migration d'hydrocarbures pendant la diagenese d'enfouissement. Le systeme isotopique sm-nd a ete utilise pour dater des fractions argileuses extraites d'ampelites; deux isochrones sm-nd ont ete obtenues, donnant des ages similaires de 2099+/-115 ma et 2036+/-79 ma. Les donnees mineralogiques, chimiques et la composition isotopique du nd indiquent qu'une homogeneisation isotopique a eu lieu entre les argiles authigenes, les eaux de formation et les hydrocarbures pendant la diagenese. Un modele est propose qui implique la decarboxylation de la matiere organique, la formation d'acides organiques permettant la dissolution de feldspaths potassiques detritiques et leur remplacement in situ par des mineraux argileux. Les ages isochrones correspondent donc a l'age de la formation des argiles qui a eu lieu lors d'un evenement diagenetique precoce, au niveau de la production d'hydrocarbures. L'originalite du bassin de franceville est la presence de reacteurs nucleaires fossiles dans le gisement d'u d'oklo. La decouverte des nouveaux reacteurs 10 et 13 preserves de l'alteration meteorique a suscite un vif interet parmi les chercheurs qui travaillent dans le cadre de la gestion de dechets de haute activite. Une etude mineralogique et isotopique de l'environnement argileux du reacteur 10 a ete effectuee afin de mieux comprendre le comportement de quelques actinides et produits de fission generes dans le cur du reacteur. Les resultats indiquent qu'une fraction de l'u, du pu et des terres rares a ete remobilisee lors du lessivage du reacteur par les solutions hydrothermales, a migre vers la bordure argileuse du reacteur et a ete piegee par la chlorite. Les principales implications de ce travail concernent la capacite de retention de materiaux argileux vis-a-vis des radioelements dans un milieu geologique
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WAKAKI, Shigeyuki. "Estimation of optimal isotopic compositions of Sr, Ba, Nd and Sm spikes for double spike thermal ionization mass spectrometry by error propagation simulation". Dept. of Earth and Planetary Sciences, Nagoya University, 2012. http://hdl.handle.net/2237/20538.
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Maruoka, Miriam Tyoka da Silva. "Is?topos de Nd na proveni?ncia de rochas e sedimentos da Bacia Potiguar, NE do Brasil". Universidade Federal do Rio Grande do Norte, 2007. http://repositorio.ufrn.br:8080/jspui/handle/123456789/18804.
Abstract (sommario):
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Previous issue date: 2007-05-04Nd ISOTOPES IN THE PROVENANCE OF TERRIGENOUS AND CARBONATE ROCKS AND SEDIMENTS OF THE POTIGUAR BASIN, NORTHEASTERN BRAZIL. Mesozoic and Cenozoic rocks from the Potiguar Basin, including terrigenous and carbonate sediments have been investigated to identify their isotopic signature and source areas. Additionally, this study aims to determine the provenance of terrigenous and carbonate sediments on the Brazilian Continental shelf adjacent to Potiguar Basin. The Sm-Nd isotopic signatures of the rocks yielded model ages (TDM) in the range of 2,19- 2,88 Ga, indicating archean to paleoproterozoic sources from the basement. The terrigenous sediments yielded model ages (TDM) in the range of 2,31-2,26 Ga, from 17,5 to 0 cm depth. Despite the small number of samples, limited variations of provenance ages indicates the homogenization of the sediments, probably due to the strong influence of the basement, as the main source of sediments to the shelf. The Sm-Nd isotopic signatures of the carbonate sediments yielded model ages (TDM) in the range of 2,09-2,61 Ga, indicating archean to paleoproterozoic sources from the basement. The results also indicate that the shelf sediments are mainly derived from the A?u River or other small rivers from the Setentrional Sector of Rio Grande do Norte State. The littoral drift doesn?t seem to contribute with sediments from the Oriental Sector since isotopic signatures from this sector were not detected.
An?lises isot?picas Sm-Nd em rochas mesoz?icas e cenoz?icas da Bacia Potiguar, incluindo sedimentos terr?genos e carbon?ticos que aportam do Rio Piranhas-A?u, foram realizadas objetivando a caracteriza??o de suas assinaturas isot?picas e identifica??o de suas ?reas fonte. As assinaturas isot?picas Sm-Nd das rochas apresentaram idades modelo (TDM) variando de 2,88 a 2,19 Ga, indicando fontes, principalmente, paleoproteroz?icas e arquenas do embasamento. Os sedimentos terr?genos plataformais apresentaram idades modelo (TDM) de 2,31 Ga e 2,26 Ga, coletados, respectivamente, nas profundidades de 10-17,5 cm e 0-5 cm. Apesar do n?mero pequeno de amostras, a pequena varia??o na idade indica homogeneiza??o dos sedimentos, talvez devido a forte influ?ncia do embasamento como fonte de material para a plataforma. As assinaturas isot?picas Sm-Nd dos sedimentos carbon?ticos plataformais apresentaram idades modelo (TDM) variando de 2,61 a 2,09 Ga, indicando fontes do embasamento arqueano a paleoproteroz?ico. Estes resultados indicam ainda que os sedimentos terr?genos presentes na plataforma em estudo s?o ou foram trazidos principalmente pelo rio A?u, ou outros rios menores da por??o setentrional do Rio Grande do Norte. A deriva litor?nea aparentemente n?o tem compet?ncia para arrastar sedimentos da por??o oriental para a setentrional, tendo em vista que os valores ?Nd registrados n?o s?o compat?veis com as rochas da por??o oriental.
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Santos, Gustavo Macedo de Paula. "Quimioestratigrafia isotópica (C, O, Sr) e geocronologia (U-Pb, Sm-Nd) das rochas da Formação Sete Lagoas, Grupo Bambuí". Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/44/44141/tde-10022014-110652/.
Abstract (sommario):
Idades radiométricas absolutas recentemente publicadas levantaram questões sobre a evolução deposicional da Formação Sete Lagoas (FSL). Esta unidade é composta predominantemente por carbonatos com rochas siliciclásticas subordinadas e constitui a unidade basal do Grupo Bambuí, sobreposta aos depósitos glaciogênicos da Formação Jequitaí no Cráton São Francisco (CSF). Este estudo combina quimioestratigrafia isotópica (C, O e Sr) e geocronologia (U-Pb e Hf em zircão detrítico e Sm-Nd em rocha total) em amostras de cinco seções da FSL na região de Lagoa Santa, MG, sul do CSF, com a finalidade de responder a tais questionamentos. As seções Vespasiano (VS) e Ana Paula (AP) são constituídas por calcários cinzas e dolomitos beges, com altos teores de sedimentos terrígenos e pobres em matéria orgânica. Os valores de \'delta\'\'POT.13C\' mais representativos do ambiente deposicional oscilam em uma estreita faixa ao redor de 0%o. Estes dados permitem posicionar estas seções na primeira sequência deposicional da FSL, acima dos carbonatos de capa Sturtianos (~740 Ma) da base desta unidade. As seções Bairro da Lapinha (BL), Pedra do Baú (BAU) e Parque da Gruta da Lapinha (PGL) são compostas por calcários de coloração cinza escura a negra, pobres em sedimentos detríticos e ricos em matéria orgânica. São caracterizados por valores de \'delta\'\'POT.13\' C bastante positivos (> 6%o) e razões \'87 ANTPOT.Sr\'/\'86 ANTPOT.Sr\' próximas de 0,7075. Estas seções estão posicionadas na segunda sequência deposicional da FSL. Zircões detríticos foram separados de três amostras de marga das seções VS, AP e PGL e datados pelo método U-Pb. Os resultados indicam que os sedimentos siliciclásticos da FSL na área de estudo provêm de fontes de longa residência crustal do Orógeno Araçuaí-Oeste Congo. A população expressiva mais jovem tem 557 Ma e determina a idade máxima de deposição para a segunda sequência da unidade e para a maior parte do Grupo Bambuí. Além disso, grãos de zircão concordantes mais jovens com idades de 537 ± 4 Ma e 506 ± 7 Ma para a primeira e segunda sequência, respectivamente, refutam a existência de um hiato deposicional expressivo entre as duas sequências, como recentemente proposto, e endossam uma idade deposicional do limite Ediacarano/Cambriano para a FSL. Se existe uma discordância, esta está posicionada entre os carbonatos de capa Sturtianos e as seções com valores de \'delta\'\'POT.13\'C\' ao redor de 0%o. Estas idades indicam que grande parte do Grupo Bambuí foi depositada em uma bacia de foreland, após o fechamento do Oceano Adamastor que culminou com a edificação da Faixa Araçuaí a leste do CSF. As razões \'87 ANTPOT.Sr\'/\'86 ANTPOT.Sr\' obtidas nos carbonatos da FSL contrastam com as recentes curvas de evolução de Sr para os oceanos, especialmente no Cambriano, quando razões maiores que 0,7085 são esperadas. É provável que esta unidade tenha sido depositada em um mar epicontinental restrito e a correlação global por meio de isótopos de Sr não é confiável nestes casos.Recently published geochronological data has arisen questions on the Sete Lagoas Formation (SLF) depositional evolution. This unit is mainly composed by carbonate rocks with subordinated pelitic intercalations and represents the basal unit of the Bambuí Group, which overlies the glacial deposits of the Jequitaí Formation in the São Francisco Craton (SFC). This study combines isotope chemostratigraphy (C, O, Sr) and geochronology (U -Pb and Hf on detrital zircons and Sm-Nd on whole rock samples) in five sections of the SLF in the Lagoa Santa (MG) region, southern part of SFC, in order to answer such questions. Vespasiano (VS) and Ana Paula (AP) sections are composed by gray limestones and beige dolostones, with high contents of detrital sediments and poor in organic matter. The most representative \'delta\'\'POT.13C\' values obtained oscillate within a narrow range around 0%o. These data allow positioning these sections in the first depositional sequence of the SLF, above the basal Sturtian cap carbonates (~740 Ma) of this unit. Bairro da Lapinha (BL), Pedra do Baú (BAU) and Parque da Gruta da Lapinha (PGL) sections comprises dark gray to black limestones, with low detrital sediments contents and rich in organic matter. They are characterized by very positive \'delta\'\'POT.13\'C values (> 6%o) and \'87 ANTPOT.Sr\'/ \'86 ANTPOT.Sr\' ratios close to 0.7075. These sections belong to the second sequence of the SLF. Detrital zircons were retrieved from three marl samples from sections VS, AP and PGL and dated by the U-Pb method. The results indicate that the siliciclastic sediments of the SLF come from sources of long crustal residence time located in the Araçuaí-West Congo Orogen. The youngest population is 557 Ma aged and sets the maximum depositional age for the second sequence of SLF and most of the Bambuí Group. Furthermore, younger concordant zircon grains with ages of 537 ± 4 Ma and 506 ± 7 Ma for the first and second sequence, respectively, refute the hypothesis of a major sedimentation gap between the sequences, as recently proposed, and endorse an Ediacaran/Cambrian age for the SLF. If such gap does exist, it lies between the Sturtian cap carbonates and the sections with \'delta\'\'POT.13\' C around 0%o. These ages also indicate that the deposition of most of the Bambuí Group took place in a foreland basin, after the closure of the Adamastor Ocean which led to the edification of the Araçuaí Belt to the east of the SFC. The \'87 ANTPOT.Sr\'/ \'86 ANTPOT.Sr\' ratios obtained on the SLF carbonates contrast with the recently proposed Sr evolution curves, especially for the Cambrian, from where ratios higher than 0.7085 would be expected. It is possible that the SLF was deposited on a restricted eipiric sea and global correlations based on Sr isotopes are not reliable in such cases.
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Hepple, Robert Alexander. "The effects of low degree alteration on Sm-Nd and U-Pb isotope systematics in Eoarchean basalts from the Doolena Gap and Warralong Greenstone belts, Pilbara Craton, Western Australia". Thesis, Queensland University of Technology, 2014. https://eprints.qut.edu.au/74860/1/Robert_Hepple_Thesis.pdf.
Abstract (sommario):
This research led to the discovery of one of the best preserved remnants of the Earth's surficial environment 3.47 billion years ago. These ancient volcanic and sedimentary rocks contain original minerals and textures that are rare in rocks of this age. The research concentrated on chemical analysis of volcanic rocks to differentiate secondary alteration from the primary magmatic signature. This study contributes to our understanding of melting processes and geochemical reservoirs in the early Earth, which is vital for forward modelling of Earth's geodynamic evolution.
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Paquette, Jean-Louis. "Comportement des systèmes isotopiques U-Pb et Sm-Nd dans le métamorphisme éclogitique. Chaîne Hercynienne et chaîne Alpine". Phd thesis, Université Rennes 1, 1987. http://tel.archives-ouvertes.fr/tel-00675107.
Abstract (sommario):
Les éclogites témoignent, pour la plupart d'entre elles, de l'existence de lambeaux de paléocroûtes océaniques affectées par des conditions tectonométamorphiques très intenses. Ces roches représentent généralement les premiers épisodes de la formation des chaînes de montagne, avant les phénomènes de collision continentale. L'étude géochronologique et géochimique des éclogites est fondamentale car elle apporte d'une part de nombreuses contraintes à la géologie des massifs cristallins étudiés, et permet d'autre part de caractériser le comportement des systèmes isotopiques \ lors d'un métamorphisme de haute grade. - L'ensemble des résultats géochimiques et isotopiques montre que la maiorité des * protolithes des éclogites étudiées provenant du Massif Armoricain (Champtoceaux-Léon) et des massifs externes alpins (Aiguilles Rouges-Belledonne- Argentera) sont comparables aux basaltes de rides' médio-océaniques actuels. - L'étude géochronologique U-Pb sur zircons a révélé une large gamme d'âges de magr:natisme initial de ces métabasites. Les résultats sont divisés - en d eux groupes : les âges précambriens et les âges paléozoiques. Un modèle de faible contamination, ion géochronoches qui propose qu'une très faible contribution crustale introduise une informat logique erronnée sans perturber les caractères géochimiques des roches étudiées, permet d'interpréter la diversité des âges précambriens obtenus. Dans les deux domaines étudiés, le magmatisme océanique d'âge paléozoique a été daté en deux époques distinctes :460-500 Ma et 350-380 Ma. - Le métamorphisme éclogitique est lui -même constitué de plusieurs époques : (1) précoce : 480 Ma, (2) majeur 400-440 Ma et (3) tardif à 350-370 Ma. Ceci permet de proposer la fermeture de plusieurs domaines océaniques et une évolution non-synchrone de l'ensemble de la chaîne Hercynienne. - Dans la chaîne Alpine, les âges obtenus par U-Pb * sur zircons 286 Ma (magmatisme) pour le métagranite éclogitique du Mont Mucrone et 117 Ma (métamorphi ~ me) sur une métaquartzite éclogitique du massif de Dora-Maïra permettent de corréler les âges obtenus avec les conditions P-T du métamorphisme le système U-Pb du granite n'a pas été modifié par le métamorphisme PH-BT, au contraire l'événement HP-HT a été enregistré par les zircons d'un sédiment.
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Santos, Gustavo Macedo de Paula. "Quimioestratigrafia isotópica (C, O, Sr, Li, Mg) e proveniência sedimentar (U-Pb, Hf, Sm-Nd) do grupo Bambuí no sul da bacia do São Francisco". Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/44/44141/tde-26042018-092122/.
Abstract (sommario):
Neste trabalho são apresentados novos dados isotópicos de C, O, Sr, Mg e Li e elementares de Elementos Terras Raras (ETR) para as rochas carbonáticas do Grupo Bambuí, no sul da Bacia do São Francisco. Também são apresentadas idades U-Pb e isótopos de Hf em zircão detrítico e dados isotópicos de Sm-Nd em amostras de rocha total de rochas siliciclásticas no mesmo setor da bacia. Os dados quimioestratigráficos permitem dividir as três formações basais do Grupo Bambuí em três intervalos quimioestratigráficos (chemostratigraphic intervals - CI), cada qual registrando um estágio evolutivo da bacia. O CI-1 corresponde à capa carbonática da Formação Sete Lagoas que apresenta excursão isotópica negativa de C, valores de \'delta\'¹³C negativos e razões 87Sr/86Sr crescentes de 0,7074 a 0,7082. Este intervalo marca o início da transgressão marinha que inundou o Cráton do São Francisco onde a bacia estava sujeita a controles locais na química marinha, gerando carbonatos com padrões planares de distribuição normalizada de ETR e com variações acopladas de \'delta\'7Li e \'delta\'26Mg dependentes das fácies sedimentares. O intervalo CI-2 corresponde à porção intermediária da Formação Sete Lagoas na qual foi reportada a ocorrência de Cloudina sp. (550-542 Ma). As rochas carbonáticas deste intervalo apresentam valores de \'delta\'¹³C ao redor de 0%o, \'delta\'7Li ao redor de 16%o, \'delta\'26Mg de aproximadamente -3,5%o e razões 87Sr/86Sr entre 0,7080 e 0,7087, dentro do padrão esperado para o limite Ediacarano-Cambriano. Neste estágio, a transgressão marinha culminou com a conexão da Bacia do São Francisco com outras bacias gondwânicas, permitindo migração de fauna e homogeneização isotópica. Apesar de alguns sinais geoquímicos de caráter global, o cenário intracontinental da bacia a mantinha sujeita a controles locais, observados no enriquecimento de ETR leves em relação aos pesados e por duas excursões negativas nos valores de \'delta\'7Li perfeitamente acopladas a excursões positivas de\'delta\'26Mg. O intervalo CI-3 engloba as formações Sete Lagoas superior, Serra de Santa Helena e Lagoa do Jacaré e seus calcários com valores de \'delta\'¹³C bastante positivos (acima de +3%o) e razões 87Sr/86Sr ao redor de 0,7075, abaixo das esperadas para o limite Ediacarano-Cambriano. O CI-3 marca a restrição da bacia em relação ao reservatório geoquímico e isotópico global, provavelmente pelo soerguimento dos orógenos marginais ao cráton. Tal soerguimento provocou aumento da taxa de denudação e consequente decréscimo da intensidade de intemperismo nas áreas fontes, reduzindo o fluxo dissolvido para a bacia, observado no desacoplamento dos sistemas isotópicos de Mg e Li, e ciclos de decréscimo das razões Sr/Ca e 26Mg removidos pela precipitação carbonática. A diminuição da intensidade de intemperismo e a declividade das áreas fontes tornaram o fluxo dissolvido oriundo de carbonatos mais importantes que os de silicatos, resultando em diminuição das razões 87Sr/86Sr, no aparecimento de distribuições normalizadas de ETR com padrão \"água do mar\", na restrição do suprimento de sulfato na bacia e consequente metanogênese. Os dados geocronológicos mostram que não houve uma reorganização significativa nas áreas de fontes para a bacia desde a deposição das fácies mais finas da Formação Carrancas e Laminito Moema até a deposição da Lagoa do Jacaré. Embora não resolva as principais questões de idade e geotectônicas da bacia, esta constatação é mais um argumento a favor da ausência de uma discordância na base da Formação Sete Lagoas, o que sugere que a glaciação na base da Bacia do São Francisco é provavelmente do Ediacarano Médio / Superior. Se existir esta discordância, a única idade absoluta disponível para a capa carbonática sugere que a glaciação seria Sturtiana (~720 Ma).This work presents new C, O, Sr, Mg and Li isotope data and Rare Earth Element (REE) concentrations for the carbonate rocks of the Bambuí Group, in the southern São Francisco Basin. U-Pb and Hf geochronology in detrital zircon grains and whole rock Sm-Nd ages in siliciclastic rocks in the same area are also presented. The chemostratigraphic data allow subdividing the three lower units of the Bambuí Group in three Chemostratigraphic Intervals (CI), each one recording a different evolution stage of the basin. The CI-1 comprises the Sete Lagoas Formation cap carbonates that display C isotope negative excursion, very negative \'delta\'¹³C values and 87Sr/86Sr ratios increasing upwards from 0.7074 to 0.7082. This intervals marks the start of the marine transgression over the São Francisco Craton in which the basin was subject to local controls over seawater, as shown by the flat type shale normalized REE distributions and coupled facies dependent \'delta\'Li and \'delta\'26Mg values variations. The CI-2 corresponds to the middle portion of the Sete Lagoas Formation where the Cloudina sp. (550-542 Ma) occurrence was described. The carbonate rocks of this interval display \'delta\'¹³C values around 0%o, \'delta\'7Li values around 16%o, \'delta\'26Mg around -3.5%o and 87Sr/86Sr between 0.7080 and 0.7087 that are expected for the Ediacaran-Cambrian limit. During this stage, the marine transgression provided connection of the São Francisco basin to other West Gondwana basins, allowing fauna migration and isotope homogenization. In spite of the global geochemical signals observed, the intracontinental scenario kept the basin subject to local controls, as shown by the enrichment in light REE and two perfectly coupled \'delta\'7Li and \'delta\'26Mg negative excursions. The CI-3 comprises the limestones of the upper Sete Lagoas, Serra de Santa Helena and Lagoa do Jacaré formations and with very positive \'delta\'¹³C values (> +3%o) and 87Sr/86Sr ratios around 0.7075, lower than those expected for the Ediacaran-Cambrian limit. The CI-3 records the restriction of the basin in relation to the global ocean geochemical and isotope reservoir, probably by the uplift of the craton\"s marginal orogens. Such uplift caused higher denudation rates and consequent decrease in the weathering intensity of the source areas, diminishing the dissolved influx to the basin that is observed in the Mg and Li isotope systems decouplement and in cycles of Sr/Ca ratios and 26Mg decrease by carbonate precipitation removal. The weathering intensity decrease caused the dissolved influx from carbonates to be more important than the one from silicates, resulting in the drop down of the 87Sr/86Sr ratios, the appearance of the \"seawater\" REE shale normalized distributions, and sulphate supply restriction driving methanogenesis. The geochronological data show that no significant reorganization of the basin source areas occurred from the deposition of the Carrancas Formation and Moema Laminites finer facies to the Lagoa do Jacaré Formation. Although the data do not solve the age and geotectonic questions, they add another argument against the existence of an unconformity at the base of the Sete Lagoas Formation, suggesting that the glaciation of the São Francisco Basin is likely Middle to Late Ediacaran in age. If there is an unconformity, the only available absolute age suggests it is a Sturtian Glaciation (~720 Ma).
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Schneider, Julie. "COMPORTEMENT DES RADIOCHRONOMETRES Rb/Sr, Ar/Ar ET Sm/Nd AU COURS DU METAMORPHISME : CAS DES ECLOGITES DE L'ARC DE BERGEN (NORVEGE)". Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2004. http://tel.archives-ouvertes.fr/tel-00463535.
Abstract (sommario):
Une bonne compréhension du comportement des radiochronomètres est essentielle pour mener des études de thermochronologie visant à contraindre des processus géodynamiques. Cependant, le comportement des radiochronomètres est complexe car dicté par un grand nombre de facteurs intrinsèques et extrinsèques au système étudié. Au cours de cette thèse, nous avons cherché à déterminer quels étaient les facteurs critiques lors des processus de rééquilibrage isotopique survenant durant un événement métamorphique de haut grade. Ainsi, nous avons étudié le comportement des systèmes isotopiques Rb/Sr, Ar/Ar et Sm/Nd lors de l'éclogitisation partielle (contrôlée par la déformation et la circulation de fluides) au Calédonien de roches granulitiques grenvilliennes dans l'Arc de Bergen en Norvège. Nous montrons, grâce à une étude géochronologique fine associée à différentes observations (pétrologiques, géochimiques in situ et sur fractions minérales, diffraction X et isotopes de l'oxygène) permettant de contraindre avec précision le flux des éléments d'un site textural vers un autre au cours des réactions d'éclogitisation, que le facteur principal garantissant un rééquilibrage isotopique complet pour les systèmes Rb/Sr et Sm/Nd lors d'un événement métamorphique de haut grade est la redistribution homogène des éléments à l'échelle de l'échantillon. Cependant, la circulation de fluides et la déformation qui peuvent être associées aux processus de recristallisation ne sont pas nécessairement suffisant pour garantir une telle réhomogénéisation. La mise en solution des éléments d'un système ou la fusion partielle apparaissent comme deux mécanismes de réhomogénéisation bien plus efficaces. Pour le système Ar/Ar, le facteur critique est l'évacuation totale de l'argon radiogénique précédemment accumulé dans le système. Cette évacuation est favorisée, mais non garantie, par la circulation de fluides en raison de la plus forte solubilité de l'argon dans les fluides. Cependant un grand nombre de facteurs vont contrôler ce processus : quantité d'argon radiogénique initialement présente (fonction de la composition chimique de la roche et de son âge), composition chimique du fluide, et circulation en système ouvert ou fermé.
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Canile, Fernanda Maciel. "Geologia isotópica em zircões detríticos (U-Pb, Hf e O) e em rocha total (Sm-Nd e Pb-Pb) das rochas da Bacia do Paraná em Santa Catarina". Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/44/44141/tde-24022016-140417/.
Abstract (sommario):
Dados isotópicos U-Pb, Hf e de O foram obtidos em zircões detríticos das unidades do final do Paleozoico e início do Mesozoico da Bacia do Paraná, sudeste do Brasil, com o objetivo de determinar a proveniência dos sedimentos, assim como contribuir para o entendimento da evolução tectônica da bacia. Assinaturas isotópicas Sm-Nd e Pb-Pb em amostras de rocha-total também foram obtidas com o intuito de auxiliar na interpretação sobre as áreas fontes. A seção estudada, Coluna White em Santa Catarina, inclui rochas de 11 unidades estratigráficas (da base para o topo): Formação Rio do Sul, Formação Rio Bonito, incluindo os membros Triunfo, Paraguaçu e Siderópolis, Formação Palermo, Formação Irati, Formação Serra Alta, Formação Teresina, Formação Rio do Rasto, subdividida nos membros Serrinha e Morro Pelado, e Formação Botucatu, Idades U-Pb foram obtidas em 1941 grãos de zircão detrítico e variam de 242 Ma a 3,4 Ga. Todas as unidades sedimentares apresentam quatro grupos principais de zircões detríticos, Neoarqueano (2,7-2.5 Ga), Paleoproterozoico Médio (2,0-1,8 Ga), Grenviliano (1,1-0,9 Ga) e Brasiliano (850-490 Ma), refletindo a importância do embasamento Pr-e-Cambriano que bordeja a parte leste da bacia como áreas fontes, tais como as Faixas Dom Feliciano, Kaoko e Namaqua-Natal, incluindo o embasamento local datado em 584 Ma. O Membro Siderópolis apresenta uma importante mudança nas fontes dos sedimentos que preencheram a Bacia do Paraná, pois é a partir dessa unidade que o pico de idade permiana (266 a 290 Ma) é observado. Esse pico persiste até o topo da seção, a Formação Botucatu. As assinaturas isotópicas de O e Hf dos zircões detríticos mostram que parte dos grãos do Paleoproterozoico Médio é provavelmente de rochas do embasamento atualmente recoberto, que estava exposto até a deposição da Formação Rio Bonito. Os isotópos de Hf e O também mostram que parte dos zircões com idade grenviliana é proveniente de rochas argentinas, o que implica em longas distâncias de transporte. As assinaturas isotópicas de parte dos grãos permianos os ligam a fontes da Argentina e Chile, sendo que parte desses grãos possui forma mais arredondada, o que sugere que eles alcançaram a bacia pelo transporte em ambientes subaquáticos e não somente pelo ar (quedas de cinzas vulcânicas) como é comumente apontado. Outros picos de idade mais jovens (Ordoviciano ao Carbonífero), observados a partir da Formação Palermo e nas unidades superiores, também são provenientes de fontes argentinas e chilenas, mostrando a importância dos detritos de fontes distantes durante o preenchimento da bacia. Os dados Sm-Nd e Pb-Pb em rocha total mostram que os sedimentos da Bacia do Paraná apresentam predominância de fontes de origem crustal. As assinaturas são semelhantes aos granitoides de Santa Catarina, rochas da Faixa Ribeira, do Escufo Brasileiro, das Faixas Namaqua-Natal e Kaoko, Terreno Arequipa-Antofalla (embasamento dos Andes) e granitoides do Norte da Patagônia. Esses dados corroboram os padrões de zircões detríticos observados, que apontam para áreas fontes tanto proximais quanto distais. Além disso, as idades modelo Sm-Nd (\'T IND. DM\') obtidas são mais antigas que 1,4 Ga e mais negativas (-10 a -15) nas unidades inferiores (Formação Rio do Sul até o Membro Paraguaçu), enquanto que as unidades superiores apresentam valores de \'\'épsilon\' IND.Nd(0) entre -6 a -12 e idades modelo \'T IND.DM\' mais jovens que 1,5 Ga, sugerindo a participação de uma fonte mais jovem a partir da deposição do Membro Siderópolis, conforme foi observado pelos dados de zircão detrítico (pico de idade permiana)U-Pb, Hf and O isotope data were obtained from detrital zircons from late Paleozoic-early Mesozoic units from Paraná Basin, southeastern Brazil, in order to constain the provenance of the sediments, as well as to contribute to the understanding of the tectonic evolution of the basin. Whole rock Sm-Nd and Pb-Pb isotopic signatures were also taken in order to help the interpretation. The studied section, White Column in Santa Catarina state, includes rocks from 11 stratigraphic units (from base to top): Rio do Sul Formation, Rio Bonito Formation (Triunfo, Paraguaçu and Siderópolis members), Palermo Formation, Irati Formation, Serra Alta Formation, Teresina Formation, and Rio do Rasto Formation (Serrinha and Morro Pelado members) and Botucatu Formation. U-Pb ages were obtained on 1941 detrital zircons and range from 242 Ma to 3400 Ma. All sedimentary units show four main detrital age groups, Neoarchean (2700-2500 Ma), mid-Paleoproterozoic (2000-1800 Ma), Grenvillian (1100-900 Ma) and Brasiliano (850-490 Ma), reflecting the importance of the Precambrian basement bordering the east side of the basin, such as Dom Feliciano, Kaoko and Namaque-Natal Belts as source areas, including the local basement that was dated at 584 Ma. The Siderópolis Member shows an important change in the source of sediments with a Permian age-peak (266 to 290 Ma). This age-peak persists towards the top of the section until the Botucatu Formation. O and Hf isotopic signatures from the detrital zircons show that a portion of the mid-Paleoproterozoic grains is probably from rocks of the presently covered basement, which was exposed until the deposition of the Rio Bonito Formation. O and Hf isotopes also show that some Grenvillian aged zircons are from Argentinian rocks, which implies a long transport distance. Isotopic signatures of part of the Permian grains also link them to sources from Argentina and Chile, and part of these grains has more rounded shapes, suggesting that they reached the basin after long distance traveling on subaquatic environment and nor only through the air (ash falls) as it is commonly accepted. Other younger age peaks (Ordovician to Carboniferous) found from Palermo Formation upsection are also linked to Argentinian and Chilean sources, showing the importance of distant sources during the filling of the basin. The Sm-Nd and Pb-Pb data on whole rocks show that the sediments from the Paraná Basin present predominance of sources with crustal origin. Osotopic signatures are similar to granitoid rocks from Santa Catarina, Ribeira Belt, Brazilian Shield, Namaqua-Natal and Kaoko Belts, as well as the Arequipa-Antofalla terranes (Andes basement) and granitoids from North Patagonia. These data corroborate the observed detrital zircon patterns thar point to both proximal and distal source areas. \'T IND.DM\' model ages older than 1.4 Ga and more negative (-10 to -15) epsilon values were observed in the lower units (Rio do Sul Formation to Paraguaçu Member), while the upper units show \'\'épsilos\' IND.Nd(0)\' values ranging from -6 to -12 and \'T IND. DM\' model ages younger than 1.5 Ga, corroborating the addition of a younger source starting from the Siderópolis Member deposition upwards, as noted by detrital zircon data (Permian age-peak).
22
Li, Yuting. "Investigating sediment size distributions and size-specific Sm-Nd isotopes as paleoceanographic proxy in the North Atlantic Ocean : reconstructing past deep-sea current speeds since Last Glacial Maximum". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/273776.
Abstract (sommario):
To explore whether the dispersion of sediments in the North Atlantic can be related to modern and past Atlantic Meridional Overturning Circulation (AMOC) flow speed, particle size distributions (weight%, Sortable Silt mean grain size) and grain-size separated (0–4, 4–10, 10–20, 20–30, 30–40 and 40–63 μm) Sm-Nd isotopes and trace element concentrations are measured on 12 cores along the flow-path of Western Boundary Undercurrent and in the central North Atlantic since the Last glacial Maximum (LGM). North Atlantic is a useful place to explore how size-specific sediment provenance is related to sedimentary inputs and deep-current advection because mantle-derived materials in Iceland is a unique sedimentary source compared to crustal-derived terranes in Europe, Greenland and North America. The four main processes transporting sediments from continents to the North Atlantic (bottom currents, turbidity currents, ice-rafting events, airborne inputs) can be well distinguished through the size-specific physical and geochemical records. When primarily advected by the bottom currents, Holocene sediments show that the finer-sized fractions (0–4, 4–10, 10–20 μm) were transported further, and the coarser size fraction (40–63 μm) matched local inputs. In the deep coretops (> 2700 m) proximal to southern Greenland, fine-slit size fraction (10–20 μm) instead of clay size fraction (0–4 μm) observed more Icelandic-material contribution. In the past, the 20–30, 30–40 and 40–63 μm particles in the shallower Iceland-proximal core (1249 m) reflect Icelandic composition variation due to the abrupt volcanic eruption around 13–9 ka; while in the deeper Iceland-proximal core (2303 m) they were sensitive to the changing bottom flow speed. Downstream in cores proximal to southern Greenland (> 2272 m) and eastern North America (3555 m), composition of the 20–63 μm sediments could be used as an indicator for the retreating of the Greenland and Laurentide Ice Sheets which affect the sediment accessibility of the covered geological terranes; while the 0–4, 4–10 and 10–20 μm particles were more sensitive towards the changing direction (northern-sourced or southern-sourced) and velocity of the bottom current. In the open North Atlantic, the composition of the 0–10 μm particles were less variable between the cold and warm climate intervals compared to the 10–63 μm particles, and the 30–40 and 40–63 μm size fractions were sensitive towards both ice-rafting events and bottom flow direction. During LGM, shallower and vigorous northern-sourced water (NSW) was observed overlaying the deeper southern-sourced water (SSW), with the boundary between 2133 to 2303 m in southern Iceland, and ~ 2272 m in southern Greenland. Reduced NSW occurred during Heinrich Stadial 1, until AMOC above ~ 3500 m recovered to vigorous modern-like version no later than ~ 13.5 ka. Sluggish overflow was observed in North Atlantic between 12.2–11.7 ka above ~ 3500 m. Reduction of Iceland-Scotland Overflow Water occurred around 9.7 ka, and started recovering to its modern vigorous no later than ~ 8.6 ka. These relative past AMOC strength variations (vigorous/sluggish) are firstly converted to actual bottom-current speed (in cm/s) using laminar advection model in this work: vertical settling velocity of particle having the most Icelandic contribution is calculated by Stokes’ Law, and the lateral deep-sea current speed is calculated when the vertical settling depth and the lateral advection distance of the particle traveled before settling are constrained. Primary modelling errors originating from temperature/salinity variations in past deep seawater, winnowing process in fine particles, basaltic-signature dilution by crustal input, and lateral advection pathways of Icelandic-material are further discussed, indicating relatively low modelling error (< ~ 10–20 %). The modelling results agree well with modern deep-sea current speed measurements and backtrack-trajectory eddy resolving model (Ocean model for the Earth Simulator, OFES18), indicating reasonable quantifications of past AMOC flow speeds.
23
Chavagnac, Valérie. "Behaviour of the Sm-Nd isotopic system during metamorphism : examples from HT-LP metamorphic terrane of the Limpopo Belt, South Africa and the UHP metamorphic terrane of Dabieshan, Central China". Rennes 1, 1998. http://www.theses.fr/1998REN10101.
Abstract (sommario):
Les objectifs de cette these sont (1) de determiner si les ages modeles en nd obtenus sur des terrains proterozoiques migmatises correspondent reellement a l'age d'extraction du magma de sa source mantellique (exemple du limpopo belt en afrique du sud) et (2) de comparer les ages sm-nd sur grenat et les ages u-pb sur zircon determines sur des eclogites (exemple du dabieshan en chine centrale). La zone centrale du limpopo belt est constituee principalement d'orthogneiss et de paragneiss. Elle a subi un metamorphisme granulitique a 2. 0 ga (trajectoire pression et temperature dans le sens horaire). Nous avons effectue des analyses isotopiques en sm-nd et u-pb combinees aux analyses en elements majeurs et traces sur trois exemples de migmatites formees a 2. 0 ga afin d'etudier le fractionnement chimique et isotopique qui pourrait avoir lieu au cours de la migmatisation. La fusion partielle selon la reaction de deshydratation de la biotite met en exergue des comportements differents du systeme isotopique sm-nd dans les metagrauwackes et dans les metapelites.
24
Schneider, Julie. "Comportement des radiochronomètres Rb/Sr, Ar/Ar et Sm/Nd au cours du métamorphisme : Cas des éclogites de l'arc de Bergen (Norvège)". Phd thesis, Montpellier 2, 2004. http://tel.archives-ouvertes.fr/tel-00440768.
Abstract (sommario):
Une bonne compréhension du comportement des radiochronomètres est essentielle pour mener des études de thermochronologie visant à contraindre des processus géodynamiques. Cependant, le comportement des radiochronomètres est complexe car dicté par un grand nombre de facteurs intrinsèques et extrinsèques au système étudié. Au cours de cette thèse, nous avons cherché à déterminer quels étaient les facteurs critiques lors des processus de rééquilibrage isotopique survenant durant un événement métamorphique de haut grade. Ainsi, nous avons étudié le comportement des systèmes isotopiques Rb/Sr, Ar/Ar et Sm/Nd lors de l'éclogitisation partielle (contrôlée par la déformation et la circulation de fluides) au Calédonien de roches granulitiques grenvilliennes dans l'Arc de Bergen en Norvège. Nous montrons, grâce à une étude géochronologique fine associée à différentes observations (pétrologiques, géochimiques in situ et sur fractions minérales, diffraction X et isotopes de l'oxygène) permettant de contraindre avec précision le flux des éléments d'un site textural vers un autre au cours des réactions d'éclogitisation, que le facteur principal garantissant un rééquilibrage isotopique complet pour les systèmes Rb/Sr et Sm/Nd lors d'un événement métamorphique de haut grade est la redistribution homogène des éléments à l'échelle de l'échantillon. Cependant, la circulation de fluides et la déformation qui peuvent être associées aux processus de recristallisation ne sont pas nécessairement suffisant pour garantir une telle réhomogénéisation. La mise en solution des éléments d'un système ou la fusion partielle apparaissent comme deux mécanismes de réhomogénéisation bien plus efficaces. Pour le système Ar/Ar, le facteur critique est l'évacuation totale de l'argon radiogénique précédemment accumulé dans le système. Cette évacuation est favorisée, mais non garantie, par la circulation de fluides en raison de la plus forte solubilité de l'argon dans les fluides. Cependant un grand nombre de facteurs vont contrôler ce processus : quantité d'argon radiogénique initialement présente (fonction de la composition chimique de la roche et de son âge), composition chimique du fluide, et circulation en système ouvert ou fermé.
25
Chavagnac, Valérie. "Behaviour of the Sm-Nd isotopic system during metamorphism : examples from the HT-LP metamorphic terrane of the Limpopo Belt, South Africa and the UHP metamorphic terrane of Dabieshan, Central China /". Rennes : Géosciences, Université de Rennes I, 1999. http://catalogue.bnf.fr/ark:/12148/cb370399598.
26
Campos, Roberto Sacks de. "Petrologia, caracterização geológica, geoquímica e geocronológica do magmatismo pré, sin e pós-colisional presente no Complexo Metamórfico Brusque nas regiões de Itapema e Botuverá, Santa Catarina, Brasil". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/32594.
Abstract (sommario):
Este trabalho objetiva a caracterização petrológica, geoquímica, geocronológica e metamórfica das rochas ortoderivadas pertencentes ao Complexo Metamórfico Brusque em duas regiões: Itapema e Botuverá, Santa Catarina, Brasil. Dos litotipos, destacam-se as exposições de rochas metamáficas e metaultramáficas, ocorrentes em ambas regiões. Em Itapema também foram investigados corpos de leucogranitos peraluminosos e na região da cidade de Botuverá foram investigados diques de diabásio e lamprófiro espessartítico. A análise das condições de geração e das fontes dos eventos magmáticos responsáveis pela geração destas rochas foi fundamental para a caracterização e avaliação do significado tectônico destas unidades no CMB, que foram posicionadas durante os períodos pré, sin e pós colisionais de evolução deste. A foliação regional do complexo é representada por uma S2 de baixo ângulo na região de Itapema e por uma superfície de mais alto ângulo na região de Botuverá, basculada por atuação da fase D3. Dados de geotermometria Hb-Pl indicam que a foliação principal dos xistos máficos foi gerada em condições da transição entre as fácies xistos verdes e anfibolito inferior. O magmatismo pré-orogênico do Complexo Metamórfico Brusque é constituído por lentes de rochas máficas-ultramáficas, produtos do metamorfismo de basaltos, gabros, rochas cumuláticas relacionadas e sedimentos vulcanogênicos. Estas rochas possuem afinidade toleítica e um elevado teor de ETR leves e elementos LILE. A análise de razões de elementos incompatíveis, a disposição dos corpos ígneos intercalados aos metassedimentos e a ausência de crosta oceânica sugerem que foram posicionados em ambiente tipo intra-placa continental, síncronos a sedimentação da bacia. Os valores iniciais de εNd entre -2.96 e 5.05 das rochas metavulcânicas de Itapema e entre -0.14 e -6.97 das rochas de Botuverá indicam a participação de crosta paleoproterozóica na gênese destes magmas. Os valores em geral elevados de 87Sr/86Sr justificam o envolvimento da crosta continental, e os valores mais altos encontrados em Botuverá, destacam o maior envolvimento deste componente na região. O magmatismo sin tectônico está representado por corpos de leucogranitos peraluminosos que mostram posicionamento concordante com a foliação S2. Os parâmetros composicionais destas rochas caracterizados pelas baixas razões K2O/Na2O, CaO/Na2O e LaN/YbN, os baixos teores de Rb, Sr, Zr, Y, Yb e Lu, são consistentes com uma evolução associada com magmas gerados a partir da fusão parcial de rochas crustais de composição pelíticas ricas em quartzo, com participação restrita de processos de diferenciação. Na região de Botuverá a ocorrência de diques de lamprófiros e diabásios que cortam as unidades metamórficas indica que seu posicionamento é pós-colisional. Geoquimicamente possuem afinidade entre as séries toleítica e shonshonítica. O padrão de distribuição dos elementos traços e as razões Th/Yb e Ta/Yb indicam que a extração dos diabásios ocorreu a partir de uma fonte mantélica enriquecida, com presença de rutilo e granada no resíduo e fortemente contaminada por crosta. Estas características são semelhantes às encontradas em rochas vulcânicas básicas pós-colisionais no sul do Brasil. Os dispersos valores de єNd(618) para os termos básicos, variando entre -13.74 e +5.52 destacam a heterogeneidade da fonte e reforçam a importância do componente crustal na geração destas rochas. Foi obtida uma idade concordante de 618 ±8.7 Ma (LA-ICP-MS) pelo método U-Pb em zircão, balizando a idade dos primeiros processos magmáticos pós-colisionais da orogênese brasiliana para a região de Botuverá.This work objective the characterization of the petrology, geochemistry, geochronology and metamorphism of ortoderivate rocks that belong to Brusque Metamorphic Complex BMC) in two regions: Itapema and Botuverá, Santa Catarina, Brazil. Within these, good expositions of mafic and metaultramafic rocks occur in both regions. In Itapema, bodies of peraluminous leucogranites were also investigated. Around Botuverá were investigated diabase dikes and lamprophyres. The analysis of the conditions of generation and sources of magmatic events responsible for the development of these rocks was essential for the characterization and assessment of the significance of these tectonic units in the BMC, and it were placed during the pre-, syn-and post-collisional period of it’s evolution. The regional foliation of the complex is represented by a low angle S2 surface in Itapema region and a higher angle foliation in the region of Botuverá, folded by actuation of the D3 event. Petrography and Hb-Pl geothermometry data indicate that the main foliation of the mafic schists was generated in conditions between the transition of greenschist and lower amphibolite facies. The pre-orogenic magmatism of the Brusque Metamorphic Complex consists of lenses of mafic-ultramafic, products from the metamorphism of basalts, gabbros, related cumulate rocks and volcanogenic sediments. These rocks have a tholeiitic affinity and high contents of LREE and LILE elements. The analysis of incompatible elements ratios, the position of igneous bodies intercalated with the metasediments and the absence of oceanic crust suggest that the basalts were placed in an intra-continental plate environment, synchronous with sedimentation of the basin. The initial εNd values between -2.96 and 5.05 for the metavolcanics of Itapema and between -0.14 and -6.97 for the rocks of Botuverá indicate the involvement of Paleoproterozoic crust on the genesis of these magmas. The generally high 87Sr/86Sr values justify the involvement of crust, and the highest values found in Botuverá, highlight the greater involvement of this component in the region. Syn tectonic magmatism is represented by bodies of peraluminous leucogranite showing emplacement concordant to S2 foliation. Compositional parameters of these rocks characterized by low ratios K2O/Na2O, CaO/Na2O and LaN / YbN, low levels of Rb, Sr, Zr, Y, Yb and Lu, are consistent with magmas generated from partial melting of pelitic rocks, with limited participation of differentiation processes. In the region of Botuverá the occurrence of diabase dykes and lamprophyres cutting the regional metamorphic units indicates that its position is post-collisional. Geochemically show affinity between the tholeiitic and shonshonitic series. The distribution pattern of trace elements and the Th/Yb for Ta/Yb ratios indicate that extraction of diabase occur from an enriched mantle source, with the presence of rutile and garnet in the residue and heavily contaminated by crust. These characteristics are similar to those found in rocks post-collisional basaltic volcanic in south Brazil. The scattered values of єNd (618) in basic terms, ranging between -13.74 and +5.52 highlight the heterogeneity of mantle supply and reinforce the importance of crustal component in the generation of these rocks. A concordant age of 618 ± 8.7 Ma by U-Pb (LA-ICP-MS) zircon method were obtained, marking a early magmatic processes of post-collisional Brasiliano orogeny in the region of Botuverá.
27
Harper, Charles L. "On the nature of time in cosmological perspective : a comparative study of the weak and strong interaction chronometries via an analysis of high resolution ⁸⁷Rb-β-̄⁸⁷Sr, ²³⁵/²³⁸U-α-²⁰⁷/⁷⁰⁶Pb and ¹⁴²Sm-α-¹⁴³Nd isotopic age determinations of meteoritic, lunar and geological samples". Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670359.
28
Lahaye, Yann. "L'altération des komatiites". Phd thesis, Université Rennes 1, 1995. http://tel.archives-ouvertes.fr/tel-00655890.
Abstract (sommario):
Dans le but de tester la capacité des komatiites à préserver leur composition géochimique et isotopique (Sr,Nd, 0) primaire, caractéristique du manteau archéen, les coulées basaltiques et komatiitiques des ceintures de roches vertes de l'Abitibi et de Barberton ont été étudiées. . Les komatiites peu altérées ont des compositions géochimiques compatibles avec le fractionnement de l'olivine; seuls les éléments alcalins sont mobilisés. Dans les komatiites plus altérées, les concentrations en High Field Strength Element (HFSE) par rapport aux Terres Rares (REE) produisent des anomalies variables à l'intérieur des coulées. Ces anomalies sont produites par le fractionnement des phases mantelliques de haute pression eVou la mobilité de ces éléments par les fluides hydrothermaux. ' Les mobilités géochimiques et les perturbations tardives des systèmes isotopiques (Sr, Nd, 0) à l'échelle de la roche totale sont expliquées par des processus d'échange isotopique et par le fractionnement tardif des éléments en traces. Afin de déterminer la composition isotopique initiale de ces coulées * komatiitiques, les compositions isotopiques en Néodyme et Oxygène ont été * mesurées sur des minéraux primaires. A partir de ces données, il apparait que la source des komatiites d'Alexo (Abitibi) à une valeur ENd(T) supérieure à celle obtenue sur les basaltes. Ces différences isotopiques en neodyme s'intègrent dans un modèle de plume mantellique pour la genèse des komatiites. De même, les pyroxènes de Barberton de la formation de Weltevreden ont une valeur ENd (T) systématiquement supérieure ou égale aux valeurs obtenues sur roche totale dans les autres formations. Les principaux facteurs qui contrôlent les mobilités géochimiques dans les komatiites altérées sont (1) la* composition du fluide, (2) leurs faibles concentrations initiales en éléments en traces, (3) la nature des phases secondaires qui concentrent les éléments en traces et (4) leur texture.
29
David, Marta Edith Velásquez. "Composição isotópica de Pb-Sr e Nd da mineralização de ouro do depósito Córrego do Sítio, Quadrilátero Ferrífero (MG): implicações na modelagem conceitual". Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/44/44141/tde-19042007-142433/.
Abstract (sommario):
O Quadrilátero Ferrífero (MG) é uma importante unidade geotectônica do Cráton do São Francisco que alberga jazidas de ferro e ouro hospedadas na seqüência greenstone belt Rio das Velhas e cuja evolução geodinâmica esteve regida por vários eventos tectonometamórficos. Depósitos de ouro gerados por fluidos epitermais e remobilizações orogênicas proterozóicas se associam intimamente com camadas bandas de ferro e raramente disseminados em metapelitos no topo do greenstone. Nas mineralizações é comum uma paragênese que cristalizou mediante diversos processos e em distintos estágios com predomínio de sulfetos de ferro. Em geral os minérios possuem forte controle estrutural por dobras, falhas e cisalhamentos transcorrentes, desenvolvidos durante vários eventos deformacionais de diversa índole e estreita relação com processos de alteração hidrotermal como sericitização, carbonatação, cloritização, entre outros de menor incidência. O depósito de ouro Córrego do Sítio hospeda-se na seqüência silisiclástica de origem turbidítica metamorfisada em fácies xisto verde denominada Associação de Litofácies Ressedimentada que faz parte do Grupo Nova Lima, se apresenta disseminado em metapelitos e em veios de quartzo com carbonato. A mineralização que acompanha o ouro cristalizou em vários estágios principais nos que predominaram (i) pirita + pirrotita, (ii) arsenopirita + pirrotita + pirita com texturas finas e orientadas, (iii) arsenopirita com pirrotita e sulfosais em veios de quartzo, (iv) pirita grossa pervasiva em todas as rochas hospedeiras. O estudo da composição isotópica Pb, Sr e Nd, permitiu identificar que as fontes dos fluidos mineralizantes foram as rochas hospedeiras, que na evolução policíclica da mineralização participaram eventos metamórficos e hidrotermais a 2.2, 2.0 Ga. e sobreimpostos a ~600 Ma. os quais induziram os processos de circulação hidrotermal na área de estudo. Mediante comparativa com outros depósitos da região, sugere-se que os metais formadores do minério depositaram-se em Córrego do Sítio à idade de 2.2 Ga. originados a partir da BIF tipo São Bento e remobilizados por fluidos através de falhas inversas. Análises geocronológicas U-Pb (SHRIMP) e K-Ar embora não decisivos em quanto à determinação da idade da mineralização, revelaram a idade de ~2.7 Ga. como o limite temporal para a deposição das rochas hospedeiras. No contexto geológico aplicado se estabelece a potencialidade para a prospecção aurífera que apresentam as rochas metapelíticas do topo do Greenstone Belt Rio das Velas associadas a camadas bandadas de ferro com ouro, e que os alvos mais relevantes seriam zonas com falhas inversas e cisalhamentos transcorrentes.The Quadrilátero Ferrífero is an important geotectonic unit of the São Francisco Craton that host iron and gold deposits within the vulcanosedimentary rocks of the greenstone belt Rio das Velhas. The geodynamic evolution of this greenstone includes several tectonometamorphic events. Gold deposits were formed by epithermal fluids, remobilized during the Proterozoic orogenic processes, are associated whit the banded iron formations and are sporadically disseminate in metapelitic rocks within the top of the greenstone sequence. In the ores is common the crystallization of iron sulfide minerals during diverse stages. Gold deposits have an important structural control by folds, reverse faults and strike-slip shearing zones, and are commons several hydrothermal alteration processes like sericitization, chloritization and carbonate usually related to the deformation. The Córrego do Sítio gold deposit is hosted in turbiditic siliciclastic rocks that are metamorphosed in the greenschist facies. The gold is associated with the iron sulfide arsenopyrite and pyrite, which are disseminated in metapelitic rocks and quartz-carbonate veins. The mineralization includes vary stages of crystallization, (1) pyrite and pyrrotite (2) arsenopyrite, pyrrotite and fine pyrite, (3) arsenopyrite whit pyrrotite and sulphosalts in quartz vein, and (4) pervasive pyrite. An integrated Pb, Sr e Nd, isotopic study of the Córrego do Sítio deposit allowed to identify that sources of the mineralizing fluids was the host rocks, that in the policiclic evolution the gold mineralizaton had participation events of metamorphism and hidrothermalism to age 2.2, 2.0 and 0.6 Ga. respectively the wich induced the hydrothermal circulation processes in the study area. The isotopic character of this deposit and its comparison with similar ones, suggest that the gold and its metals associated it is deposited in Córrego do Sítio to age 2.2 Ga. and that metals were derived from the banded iron formations, and remobilized by hidrothermal fluids across reverse faults. Although U-Pb (SHRIMP) and K-Ar geochronologic data were not conclusive to constrain the age of the mineralization, they provide to age ~2.7 Ga. that a good limit for the sedimentation of the host rock. It is suggest that there is a potential for gold prospection within the metapellitic rocks associated with banded iron formation of the Greenstone Rio das Velhas, and that the more relevant targets include areas with inverse and strike-slip fault.
30
Boulay, Sébastien. "Enregistrements sédimentaires des variations de la mousson sud-est asiatique au cours des 2 derniers millions d'années". Phd thesis, Université Paris Sud - Paris XI, 2003. http://tel.archives-ouvertes.fr/tel-00006427.
Abstract (sommario):
L'objectif principal de cette thèse est l'étude de l'impact des variations de la mousson sud-est asiatique sur l'enregistrement sédimentaire en mer de Chine du Sud (MCS) au cours des 2 derniers Ma. La fraction terrigène de 3 sites ODP (Leg 184, sites 1144, 1145 et 1146) localisés dans la partie nord de la MCS, a servi de base à une approche pluridisciplinaire alliant sédimentologie, minéralogie et géochimie. L'utilisation combinée de la diffraction des rayons X et de la géochimie isotopique (systèmes Rb/Sr et Sm/Nd) a permis d'identifier les sources du sédiment. Le matériel fin (<2µm), provient majoritairement de la rivière des Perles avec toutefois, lorsque l'intensité de la mousson d'été augmente (cycles de 23ka), des apports importants de smectite se faisant depuis l'arc volcanique de Luzon (3 à 15% de la fraction <2µm). L'étude granulométrique a permis de caractériser la dynamique sédimentaire en individualisant 3 populations granulométriques évoluant différemment au cours du temps et en montrant des augmentations de tailles de grains nettes lors des épisodes glaciaires. Ces variations sont attribuées au remaniement de la plate-forme lors des changements du niveau marin, remettant en question les précédentes hypothèses associant ces variations à des apports éoliens plus important lors de l'augmentation de la mousson d'hiver. Au cours des 2 derniers Ma, l'intensité de la mousson d'été présente trois grandes phases de variations : 2-1,2 Ma : oscillation de faible amplitude en relation avec l'insolation aux hautes latitudes (41ka). 1,2-0,9 Ma : intensification liée au ralentissement de la circulation océanique mondiale et à la fermeture des seuils indonésiens. 0,9-0 Ma : diminution progressive associée au refroidissement global.
31
Feneyrol, Julien. "Pétrologie, géochimie et genèse des gisements de tsavorite associés aux gneiss et roches calco-silicatées graphiteux de Lemshuku et Namalulu, Tanzanie". Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0348/document.
Abstract (sommario):
La tsavorite, grossulaire vert à V-Cr-Mn, est contenue dans des gneiss et roches calco-silicatées graphiteux, souvent associés à des marbres dolomitiques, et appartenant à la ceinture métamorphique néoprotérozoïque mozambicaine. La tsavorite se trouve soit dans des nodules ou des veines de quartz (gisements primaires), soit dans des placers (gisements secondaires). L'étude minéralogique des tsavorites propose un nouveau protocole de certification de leur origine géographique, à partir du rapport V/Cr, de la teneur en Mn et du [delta]18 O. L'étude des gisements de Lemshuku et Namalulu en Tanzanie montre que le métamorphisme des protolithes sédimentaires riches en matière organique et évaporites s'est effectué à P = 7,0 ± 0,4 kbar et T = 677 ± 14°C, à 634 ± 22 Ma (datation U-Th-Pb sur monazite). Le bâti métamorphique s'est refroidi vers 500 Ma (datation 40Ar-39Ar sur muscovite). Deux stades de métasomatose sont reliés à la formation de la tsavorite : (i) une métasomatose de diffusion formant les nodules à P = 5,0-7,4 kbar et T = 580-691°C; (ii) une métasomatose calcique d'infiltration contemporaine de la formation des veines de quartz à P = 3,6-4,9 kbar et T = 505-587°C. Ces dernières sont datées in situ par la méthode Sm-Nd à 606 ± 36 Ma. Les évaporites continentales, déposées dans une sabkha de côte marine avec des sédiments silico-calcaires, sont transformées en tsavorite dans le cas des nodules, alors que les sels fondus sont associés à la formation des veines de quartz. Les minéralisations sont contrôlées par la lithostratigraphie et la tectoniqueTsavorite, a (V, Cr, Mn)-bearing green grossular, is hosted by graphitic gneisses or calc-silicates, often asssociated with dolomitic marbles, and belonging to the Metamorphic Neoproterozoic Mozambique Belt. Tsavorite is found either as nodules or in quartz veins (primary deposits), or in placers (secondary deposits). The mineralogical study of tsavorites suggests a new protocol to certificate their geographical origin, based on the V/Cr ratio, Mn content and delta18O. The study of the Lemshuku and Namalulu deposits in Tanzania has shown that the metamorphism of organic matter-rich and evaporites-rich sedimentary protoliths occurred at P = 7.0 ± 0.4 kbar and T = 677 ± 14°C, at 634 ± 22 Ma (U-Th-Pb dating on monazite). The metamorphic series cooled down at around 500 Ma (40Ar-39Ar dating on muscovite). Two metasomatic stages are linked to the formation of tsavorite : (i) diffusion metasomatism forming nodules at P = 5.0-7.4 kbar and T = 580-691°C; (ii) calcitic infiltration metasomatism forming quartz veins at P = 3.6-4.9 kbar and T = 505-587°C. These last have been dated in situ with Sm-Nd dating at 606 ± 36 Ma. Continental evaporites, deposited in a coastal marine sabkha with (Si, Ca)-bearing sediments, transformed into tsavorite in the case of the nodules, while the molten salts are associated with the formation of the quartz veins. The mineralisations are controlled by lithostratigraphy and structure
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Romano, Antônio Wilson. "Évolution tectonique de la région nord-ouest du quadrilatère ferrifère : Minas Gerais-Brésil (Géochronologie du socle, aspects géochimiques et pétrographiques des supergroupes Rio Das Velhas et Minas)". Nancy 1, 1989. http://www.theses.fr/1989NAN10364.
Abstract (sommario):
Étude de la lithostratigraphie et des déformations de la région situé au nord-ouest du quadrilatère ferrifère de Minas Gerais. Elle présente deux séries supracrustales d'âge archeen et protérozoïque inférieur. Ce socle a été affecté par la mise en place de granitoïdes. Deux évènements de déformation majeurs sont relevés. Une étude isotopique permet de dater la différenciation crustale et l'orogénèse minas, les conditions pression-température du métamorphisme sont déterminées. Deux hypothèses sont envisagées pour expliquer une altération métasomatique remarquable dans le supergroupe de Rio Das Velhas
33
Pin, Christian. "Essai sur la chronologie et l'évolution géodynamique de la chaîne hercynienne d'Europe". Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 1989. http://tel.archives-ouvertes.fr/tel-01001861.
Abstract (sommario):
Ce travail utilise les propriétés des géochronomètres et de traceur pétrogénétique des systèmes isotopiques Sm-Nd, Rb-Sr et U-Pb, pour apporter une contribution à l'interprétation géodynamique de la Chaîne Hercynienne d'Europe. Dans ce but, on a étudié des formations d'origine magmatique diverses, choisies pour leur signification vis-à-vis des reconstitutions paléo-tectoniques. Les résultats obtenus sur certaines suites bimodales (par ex. groupes leptyno-amphiboliques), et des associations basiques-ultrabasiques de nature ophiolitique (Chamrousse, Sudètes) suggèrent l'existence d'au-moins deux épisodes de distension majeurs, accompagnés de formation de croûte océanique, au Cambro-Ordovicien et au Dévonien. La caractérisation de paléo-magmatismes d'arc et/ou de marge active montre que des phénomènes de subduction ont également marqué, à plusieurs reprises, l'évolution hercynienne (par ex. Dévonien sup. du N du Massif Central). Par ailleurs, l'étude des granulites s.l. de la chaîne met en évidence leur dualité d'âge et d'origine. Aux éclogites et granulites de haute pression, formées dans un contexte de subduction au Paléozoïque moyen, s'opposent des granulites de pression plus faible, d'âge tardi-hercynien, qui constituent la croûte inférieure de l'Europe moyenne (par ex. Zone d'Ivrée, Zone Nord-Pyrénéenne). La croûte supérieure est caractérisée par des granitoïdes carbonifères, dont l'abondance inhabituelle souligne, non seulement l'ampleur du phénomène thermique hercynien s.s., mais aussi la très large prépondérance des matériaux "fertiles", surtout métasédimentaires, sur d'éventuels fragments de socle Précambrien repris. D'une façon générale, le rôle essentiel des processus de la Tectonique des Plaques est confirmé. Le schéma d'évolution historique proposé met l'accent sur l'existence de deux événements tectono-métamorphiques majeurs, séparés par une période de régime distensif. Le premier, d'âge Silurien, est important au plan métamorphique, mais mineur du point de vue orogénique. Il ne peut donc pas correspondre à une collision continent-continent, mais pourrait plutôt être interprété en termes d'obduction, ou de collision arc-continent. Le second événement, éo-Carbonifère, correspond à la fermeture des domaines océaniques. Il marque le début d'une évolution intra-crustale complexe, dominée d'abord par une tectonique tangentielle de grande ampleur, à double déversement, puis par un régime général de cisaillements décrochants. Une culmination thermique, d'origine probablement mantellique, accompagne cette dernière période, et semble responsable de la différenciation intra-crustale du segment médio-européen. A de nombreux égards, ce schéma de développement de l'Europe Varisque peut trouver un analogue plus récent dans le système alpin et méditerranéen. Les deux chaînes paraissent en effet résulter de processus voisins sinon identiques, impliquant la fermeture d'océans successifs, et ne différer que par la nature, immature (Hercynides) ou cratonisée (Alpes), des domaines engagés dans les phénomènes de collision.
34
Maas, Roland. "The application of Sm-Nd and Rb-Sr isotopic systematics to ore deposits". Phd thesis, 1987. http://hdl.handle.net/1885/140154.
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Mkaza, Masizole. "Sm-Nd isotopic disequilibrium between minerals in Merenskycyclic units of the Bushveld Complex, South Africa". Thesis, 2009. http://hdl.handle.net/10210/1964.
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Lau, W. K. "Geochemical and Sm-Nd isotopic composition of Palaeoproterozoic eclogite and associated rocks in the Usagaran Orogenic Belt, Tanzania". Thesis, 2009. http://hdl.handle.net/2440/129279.
Abstract (sommario):
This item is only available electronically.Eclogites from the Usagaran Orogenic Belt of Tanzania have been reliably dated at 2.0 Ga and are the oldest reported subduction-related eclogites within a well-preserved orogenic belt. Based on limited geochemistry from two samples of eclogite from the Usagaran Belt, Möller et al. (1995) concluded that the protoliths were similar to MORB. This study analyzed a larger number of eclogitic samples and a suite of structurally intercalated mafic and pelitic rocks to establish the tectonic setting of the Usagaran Orogenic Belt rocks. Eclogitic rocks from the Usagaran Orogenic Belt display LILE and LREE enrichment relative to present-day MORB. Variations in εNd values from depleted mantel at 2.0 Ga supported this interpretation. The mantle-derived mafic rocks show strong Nb depletions, indicating that they are subduction-related. Enrichment of mafic rocks in LILE and LREE are likely caused by dehydration of the subducting slab with some contamination from crustally derived materials perhaps via subducted sediment. The intercalated pelites are mainly derived from the Tanzanian Craton, with a significant mafic input evidenced by high Cr & Ni values. Based on the geochemical isotopic compositions and field relationships, the eclogites, mafic rocks and pelites all formed in a subduction setting that operated around 2.0 Ga. Despite the fact that the Earth was hotter in its early history, modern plate tectonics, (i. e., subduction of cold oceanic crust into a warm mantle resulting in high-pressure low-temperature metamorphism), occurred and was recorded in the Usagaran Belt during the Palaeoproterozoic. Thus modern-style plate tectonics have operated since at least 2.0 Ga.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2009
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Trestrail, J. L. "U-Pb detrital zircon, geochemical and Nd isotope constraints on sedimentary provenance of the Chewings Range Quartzite, Warumpi Province, Arunta Region, NT". Thesis, 2010. http://hdl.handle.net/2440/106279.
Abstract (sommario):
This item is only available electronically.The Chewings Range Quartzite is a meta-sedimentary cover sequence located in the Warumpi Province of the Arunta Region. U-Pb detrital Zircon analysis of the Chewings Range Quartzite indicates a minimum depositional age of ~ 1640Ma, with the main population of zircons residing within a range of 1700 – 1800Ma. Evidence from Sm-Nd isotopic data suggests that a series of Staurolite Garnet Schists, often grouped with the Chewings Range Quartzite, has a significantly more juvenile character. This suggests that it may represent a new unit with a significantly differing provenance to that of the Chewings Range Quartzite. Combined REE, geochemistry and detrital zircon dating suggests that the Chewings Range Quartzite was derived primarily off the Arunta Region and North Australian Craton, while the Stauralite Garnet Schists holds more affinity with juvenile Musgrave Province to the south.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2010
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Chaumba, Jefferson B. "The Russell Lake Allochthon, southern Appalachians structure, petrography, bulk-rock and mineral chemistry, O, H, and Sm-Nd isotope geochemistry /". 2009. http://purl.galileo.usg.edu/uga%5Fetd/chaumba%5Fjefferson%5Fb%5F200908%5Fphd.
Abstract (sommario):
Thesis (Ph. D.)--University of Georgia, 2009.Directed by Michael Roden. For abstract see https://getd.libs.uga.edu/pdfs/chaumba%5Fjefferson%5Fb%5F200908%5Fphd.pdf. Includes bibliographical references (leaves 246-279).
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Schmitt, Wolfgang [Verfasser]. "Application of the Sm-Nd isotope system to the late quaternary paleoceanography of the Yermak Plateau (Arctic Ocean) / vorgelegt von Wolfgang Schmitt". 2007. http://d-nb.info/985282169/34.
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Gomwe, Tafadzwa Euphrasia Sharon. "A geochemical profile through the Uitkomst Complex on the farm Slaaihoek, with special reference to the platinum-group elements and Sm-Nd isotopes". Diss., 2002. http://hdl.handle.net/2263/28469.
Abstract (sommario):
The Uitkomst Complex is a mineralized, layered basic to ultrabasic intrusion, hosted by sedimentary rocks of the lower part of the Transvaal Supergroup. It is situated on the farms Uitkomst 541JT and Slaaihoek 540JT, about 25 km north of Badplaas and 50 km east of the eastern limb of the Bushveld Complex in the Mpumalanga province of South Africa. The intrusion plunges between 8 to 10º to the northwest with an established length of 12 km and a total thickness of 850 m. It is divided into seven lithological Units (from base to top), the Basal Gabbro (BGAB), Lower Harzburgite (LHZBG), Chromitiferous Harzburgite (PCR), Main Harzburgite (MHZBG), Pyroxenite (PXT), Gabbronorite (GN) and Upper Gabbro units (UGAB). A detailed petrographic and geochemical investigation of borehole core SH176, which provided a complete intersection of the Uitkomst Complex was carried out. The study shows that the Complex may have crystallized in a dynamic magma conduit setting. The whole rock geochemical trends indicate that there is a reversed fractionation in the basal portion of the Complex and a lack of fractionation in much of the MHZBG. Trace and REE variations show a decrease in concentration with height, contrary to what is expected of a progressively differentiating magma in a close system. Further, the platinum-group element concentration of the four basal units show no depletion with increasing height, suggesting that the individual units are not related to each other by means of in situ fractionation. Instead, a model whereby the individual units crystallized from distinct pulses of magma best explains the data. By comparing Nd isotopes and ratios of highly incompatible trace elements like [Th/La]n and [Sm/Ta]n from the Uitkomst Complex and Bushveld Complex it is seen that the Uitkomst magmas are of a similar lineage as the B1 magma of the Bushveld Complex, supporting a genetic link between the two complexes. The upper portion of the Uitkomst Complex shows values more akin to B3 magmas indicating the possible presence of more than one type of magma. Based on the available S isotope and trace element data, the sulphides of the Complex appear to have formed within the Complex, probably in response to contamination of the magma with dolomite. Entrainment of sulphides from depth is considered unlikely. The relatively low Cu/Ni ratios of the sulphides in the LHZBG, PCR and MHZBG (Cu/Ni 0.03 to 0.8) may be modelled by sulphide segregation from B1 magma and not from fractionation of sulphides that were later entrained in the streaming magma.Dissertation (MSc)--University of Pretoria, 2006.
Geography, Geoinformatics and Meteorology
Unrestricted
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Higgie, D. R. "Tectonic provenance of the Palaeoproterozoic Plum Tree Volcanics: implications for the initiation of the McArthur Basin". Thesis, 2018. http://hdl.handle.net/2440/130627.
Abstract (sommario):
This item is only available electronically.The Palaeoproterozoic (1825 ±4Ma) Plum Tree Volcanics are a bimodal suite of basalt and rhyolite lavas forming part of the fluvial conglomerate-sandstone sequence of the upper Edith River Group. They are preserved in remnants unconformably overlying the Pine Creek Orogen north of Katherine in the Edith River, Mt Callanan and Birdie Creek Basins. These sequences directly post-date the convergent deformation of the Pine Creek Orogen and mark the beginning of the extensional regime that initiated the McArthur Basin. The tectonic setting of the Plum Tree volcanism, whether divergent intraplate rift or mantle hotspot, may suggest how the formation of the McArthur Basin began and provide insight into how the Pine Creek Orogen compression ceased. In this paper, geochemical methods were used to determine the tectonic setting of the Plum Tree Volcanics. Whole rock geochemical data were collected via XRF, ICP-MS and ICP-OES. Nd-Sm and Sr isotopic data were collected via column chromatography and TIMS. Petrographic data were collected via optical petrography. Radiogenic Sr (87Sr/86Sr= ~0.708) and non-radiogenic Nd (εNd(i)= -6 to -8) isotopes suggest a crustal component in melt evolution. Modelling of melt evolution by pure fractional crystallisation presents well-fitting liquid lines of descent, suggesting a fractional crystallisation driven melt evolution. Tholeiitic basalts and trace element geochemistry suggests a mantle derived melt driven by a mantle plume and intraplate continental rifting. Modelling of AFC processes suggest a lower crust sourced assimilant. Ambiguous basalt geochemistry supports a continental rift derived melt and an oxygen fugacity of FMQ -1 suggests a primitive, reduced melt reflecting a mantle parent. Optical petrography presents a plagioclase and clinopyroxene rich mineral assemblage reflecting a mantle parent.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2018
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Larbi, Youcef. "Caractérisation géochimique (éléments majeurs et éléments en traces), traçage isotopique (Sm-Nd, Lu-Hf) et géochronologie (Pb-Pb, U-Pb) du groupe de Wakeham, N.E. Québec : bassin sédimentaire prétérozoïque dans la province de Grenville". Thèse, 2003. http://constellation.uqac.ca/745/1/17773537.pdf.
Abstract (sommario):
Le Groupe de Wakeham, situé dans le segment oriental de la Province de Grenville, est principalement composé d'arénites, d'arkoses, de shales et d'un petit volume de roches volcaniques felsiques et mafiques. Les roches sédimentaires sont recoupées par des gabbros et des granites peralumineux, post-tectonique et syn-tectonique tardif. Le Groupe de Wakeham se distingue de la plupart des unités lithotectoniques de la Province de Grenville par une déformation peu prononcée et par la présence de roches métamorphisées au faciès des schistes verts. Afin de caractériser les roches sédimentaires du Groupe de Wakeham et leurs sources, de déterminer leurs provenances et de connaître l'âge de ces sources ainsi que d'évaluer l'âge de dépôt des matériaux sédimentaires, nous avons entrepris une étude géochimique, isotopique (Sm-Nd et Lu-Hf) et géochronologique (Pb-Pb et U-Pb).
La géochimie des éléments majeurs indique que le bassin sédimentaire du Groupe de Wakeham renferme à la fois des sédiments très matures (SiC>2 élevé et MgO faible) et des sédiments immatures (S1O2 faible et MgO élevé). Ces roches sont potassiques et de nature essentiellement arénitique à arkosique ce qui reflète la composition de la roche mère qui varie de roche sédimentaire quartzitique à granitique. Les profils de terre rares montrent généralement une grande similarité avec ceux des shales nord américains (NASC). Ceci suggère que la majorité des sédiments du Groupe de Wakeham ont des caractéristiques de roches sédimentaires protérozoïques.
Les analyses Sm-Nd sur des arénites, des arkoses et des shales provenant de la partie est du Groupe de Wakeham révèlent des valeurs eNd (1,6 Ga) variant entre -5 et +6. Les âges modèles calculés définissent quatre pics d'âges à 1800, 1900, 2300 et 2700 Ma. Ceci suggère que ces grès sont composés d'un mélange de matériaux provenant de source essentiellement protérozoïque avec une contribution archéenne de moindre importance. Leurs âges modèles font ressortir deux régions-sources majeure: 1) une source à 1900-1800 Ma qui est similaire à ceux de l'orogène trans-labradorien ; 2) une autre source d'âge 2700-2600 Ma qui est semblable aux âges des cratons archéens (provinces du Supérieur, de Rae et de Nain). Les granites intrusifs dans les sédiments du Groupe de Wakeham ont des âges U-Pb qui varient entre 1495 Ma et 1510 Ma et des valeurs eNd (1,5 Ga) entre +1 et +3. Ces données indiquent que les granites ont probablement été contaminés par des sédiments d'une croûte protérozoïque ou ont été le résultat de la fusion d'une croûte protérozoïque. Les données isotopiques du Hf sur des zircons prélevés à partir d'échantillons provenant des parties est et ouest du Groupe de Wakeham sont en accord avec les isotopes du Nd et supportent aussi la présence de sources protérozoïques et archéennes.
Des zircons des mêmes échantillons analysés pour les isotopes du Hf ont été datés par la méthode Pb-Pb. Ces âges sont ceux des sources des sédiments du Groupe de Wakeham qui sont semblables aux âges des batholites trans-labradoriens ainsi qu'à ceux trouvés dans les provinces du Supérieur, de Nain et de Rae. Enfin, dans le but de déterminer l'âge d'un événement magmatique affectant le bassin sédimentaire du Groupe de Wakeham, nous avons analysé des zircons de l'échantillon de granite du Lac au 22eme mille qui révèlent un âge U-Pb elzévirien (l,3±0,l Ga). Cet âge dans la partie ouest du Groupe de Wakeham et ceux connues dans la partie est montrent que l'ensemble du bassin sédimentaire du Groupe Wakeham a été affecté par le même événement tectonomagmatique elzévirien.
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Van, Wyck Nicholas. "Oxygen and carbon isotopic constraints on the development of eclogites, Holsn/oy, Norway and major and trace element, common Pb, Sm-Nd, and zircon geochronology constraints on petrogenesis and tectonic setting of pre- and early proterozoic rocks in Wisconsin". 1995. http://catalog.hathitrust.org/api/volumes/oclc/32642090.html.
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Robinson, Frank Alexander. "Geochronological and geochemical constraints on the lithospheric evolution of the Arabian shield, Saudi Arabia: understanding plutonic rock petrogenesis in an accretionary orogen". Thesis, 2014. http://hdl.handle.net/2440/84674.
Abstract (sommario):
The Arabian-Nubian shield reflects the complex interplay between juvenile oceanic and continental arc fragments accreted during the final stages of Gondwanian super continental assembly. To date, much of the geochronological and geochemical data from the Arabian Shield, Saudi Arabia, is absent or poorly constrained and extrapolated from neighbouring Middle Eastern and African countries. Little attention has been paid to the petrogenesis and tectonic significance of the plutonic rocks pursuant to lithospheric orogenesis. A total of 137 samples from 26 geological units were collected from the Midyan, Hijaz, Asir, Tathlith, Afif, Ad Dawadimi and Ha’il terranes with particular emphasis on accretionary suture zone and within plate setting relationships. Extensive data bases are constructed using zircon U-Pb geochronology and Hf isotopes to evaluate Gondwanian significance and whole rock major and trace element geochemistry, Nd, Sm, Sr isotopes and zircon geochemistry to determine their petrogenetic properties. These parameters provide new insight into changing mantle conditions beneath collisional sutures (Yanbu, Nabitah and Halaban) and within plate asthenospheric upwelling. 19 granitic units are subdivided into metaluminous, peraluminous and peralkaline groups that possess distinguished island arc (~950-730Ma), syncollisional (~<730-636Ma), post tectonic (~<636-600Ma) and anorogenic (<600Ma) U-Pb geochronology. These magmatic phases represent accretionary cycles initiating from the dismantlement of Rodinia, closure of the Mozambique Ocean and final Gondwana amalgamation. Evidence for final assembly is recorded at ~525Ma (Najd fault reactivation) which is now the youngest dated magmatism in the Arabian-Nubian Shield and warrants repositioning of the regional unconformity at ~542Ma. Emplacement of sampled Arabian Shield classic A-type post-tectonic and anorogenic granitoids falls into three categories: 1) Intrude sutures immediately following collision which contain extensive mafic cumulate fractionation and N-MORB affiliation. 2) Plate boundary juxtaposed suites without obvious mafic cumulates, but posses contaminated N-MORB geochemistry. 3) Within plate granitoids isolated from plate boundaries and also without obvious mafic cumulates, but with a distinctive enriched (OIB) like asthenospheric mantle source. All categories produce similar felsic endmembers, but contain isotopically distinct mantle source. These are differentiated using a newly developed geochemical scheme (contaminated and enriched mantle granitoids) that is successfully applied to regional Arabian-Nubian examples. The diachronous Nabitah Orogenic Belt symbolises collision and subduction between western oceanic and eastern continental terranes that was terminated by the appearance of category 1 post-tectonic granitoids. This long lived (~50Ma) granitic magmatism contains mingling textures, discrete crystallisation ages, distinguished zircon morphologies and isotopically less juvenile mafics that geochronologically and geochemically reflect magmatic pulsing from a contaminated lower crustal MASH zone. The transition from N-MORB like mafics to isotopically enriched granitoids (isotopically similar to category 3 suites) reflects subduction magmatism followed by slab tear and asthenospheric influx. Conversely, the appearance of category 3 anorogenic plutons is characterised by widespread, tightly constrained (<10Ma) magmatism that is geochemically enriched, economic and symbolic of lithospheric delamination and asthenospheric (OIB like) upwelling. Differences between category 1, 2 and 3 zircon geochemistry constrain further contaminated and enriched mantle source behaviour that produces similar felsic products from distinguished petrogenetic processes. In summary, the work presented in this thesis establishes clear distinctions between accretionary syncollisional suites and anorogenic suites, but more significantly, post-orogenic plutons confined to suture zones from those confined to within plate settings. This allows new petrogenetic insights into changing juvenile mantle beneath the Arabian Shield.Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2014