Within the Ruker Province of East Antarctica, there is evidence for several key geological events that have occurred coincidently with periods of dynamic earth evolution. A detailed evaluation of the tectonic history of the region is therefore required. This research focuses on the tectonic development of the Ruker Province. The main aspects of this research can be summarised as follows: (1) an evaluation of the gross crustal architecture of the region through the development of a new stratigraphic and structural framework; (2) new U-Th-Pb (LA-ICPMS) age data from detrital zircon grains extracted from thick metasedimentary units that comprise a major component of the Ruker Province; (3) new 40Ar/39Ar data from metamorphic minerals to determine the cooling history of the province; (4) mineral equilibria modelling of metamorphic mineral assemblages to constrain pressure-temperature (P-T) conditions during key orogenic events; (5) a kinematic analysis of brittle/ductile deformation features. Ideas developed from these new data provide inferences on the assembly and dispersion of the late Proterozoic super-continents Rodinia (c. 1000 Ma) and Gondwana (c. 500 Ma).

In the Grenville age basement rocks of Virginia and North Carolina, nearly thirty Cryogenian volcanic/plutonic complexes have been recognized. A-type granites and rhyolites dominate the igneous complexes within the Cryogenian Magmatic Province (CMP), but compositional variations range from gabbro through syenites. The mineralogy, chemical composition and field data including microstructural emphasis suggests emplacement of these igneous complexes in an extensional setting. In this study U/Pb zircon ages of several plutons were determined using secondary ion mass spectrometry. The ages suggest two episodes of magmatism. An older episode (739 to 745 Ma) of magmatism includes White Oak Creek, Suck Mountain, and Amisville plutons. The younger episode (613 to 694 Ma) includes Dillons Mill, Stewartsville, Mobley Mountain, Rockfish River, and Fine Creek Mills plutons. These two age groups also display differences in geochemistry. In contrast to the older group of plutons, the younger plutons are characteristically more metaluminous, lower in silica, higher in aluminum and phosphate, lower agpatic index, less REE enrichment, minimal K-feldspar and accessory mineral fractionation. The distribution of the older group of plutons over a distance of nearly 600km requires the development of a crustal scale zone of extension. A space-time analysis suggests that these plutons represent a continental plume track similar to the White Mountain Magma Series. Plume head arrival ages of 765 to 754 Ma in the southern part of the region are measurably older than 735 to 705 Ma observed in the north, and yield a plate motion rate of ~2 cm/year. / Master of Science

Made available in DSpace on 2014-06-11T19:32:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-12-22Bitstream added on 2014-06-13T20:43:22Z : No. of bitstreams: 1 ruiz_as_dr_rcla.pdf: 6913065 bytes, checksum: cbe25a84910e7cbf831069db789ad4e8 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O propósito deste trabalho é caracterizar o arcabouço e história tectônica do SW do Cráton Amazônico em Mato Grosso, com base no acervo de dados geológicos inéditos, obtidos no mapeamento geológico nas escalas 1:250.000 e 1:100.000 e dos resultados litogeoquímicos e geocronológicos (U-Pb, Sm-Nd e Ar-Ar). As informações geocronológicas e geoquímicas prévias foram integradas e interpretadas com base no quadro geológico definido pelos novos dados de campo. Longa e complexa evolução geológica, que se estende do Paleoproterozóico ao Neoproterozóico, resultou na formação do Supercontinente Rodínia e consolidação do Cráton Amazônico. Em Mato Grosso, produziu um arranjo tectono-estratigráfico em cinco segmentos crustais, aqui denominados Domínios Tectônicos, os quais registram desde a quebra do Supercontinente Atlântica à ruptura do Supercontinente Rodínia e formação dos cinturões brasilianos/pan-africanos (Faixa de Dobramento Paraguai). Associa-se à deformação o metamorfismo regional na fácies xisto verde que é claramente mais intenso na porção oriental-central do cinturão orogênico. À fase compreesiva, segue-se um estágio de colapso extensional do orógeno, assinalado pelo desenvolvimento de zonas de cisalhamento dúcteis, com cinemática normal (Zona de Cisalhamento Piratininga, Indiavai-Lucialva e Corredor), magmatismo granítico tarde a pós-cinemático, de derivação crustal, (eNd(t) negativo), da suíte Guapé e magmatismo máfico toleítico sub-alcalino, do enxame de diques máficos da Suíte Rancho de Prata e alcalino, das soleiras máficas das Suítes Intrusivas Salto do Céu e Huanchaca. Ao final da Orogenia Sunsás, em torno de 900 Ma, consolida-se o Supercontinente Rodínia e, por conseqüência, o SW do Cráton Amazônico, reativado no Criogeniano para a instalação da Faixa de Dobramentos Paraguai. / The purpose of this thesis is to characterize the framework and the tectonic history of the Southwest Amazonian Craton in Mato Grosso based on collecting new geological data obtained from mapping in the 1:250.000 and 1:100.000 scales and lithogeochemical and geochronological results (U-Pb, Sm-Nd e Ar-Ar). Preexistent geochemical and geocronological data were reevaluated and reinterpreted based on the geological picture depicted by new field data. Long and complex geological evolution starting since Paleoproterozoic to Neoproterozoic times resulted in the Rodinia Supercontinent formation and the Amazonian Craton consolidation and produced a tectono-stratigraphic array of five crustal segments, named Tectonic Domains that record data since the break-up of the Atlantica Supercontinent until the rupture of the Rodinia Supercontinente and the formation of the Brasiliano / Panafrican belts (Paraguai Fold Belt). Regional metamorphism of grenschist facies is associated to the deformation and it is clearly more intense in the central-east portion of the orogenic belt. Compressive phase is followed by a stage of extensional collapse of the orogen marked by the developing of ductile shear zones with normal kinematics (Piratininga, Indiavai-Lucialva and Corredor Shear Zone), late- to post-kinematic granitic magmatism of crustal derivation (negative eNd(t)) of the Guapé suite and mafic tholeiitic sub-alkaline magmatism of the mafic dyke swarm Rancho de Prata and alkaline of the mafic sills of the Salto do Céu and Huachanca suites. At the end of the Sunsás Orogeny, around 900 Ma, consolidate the Rodinia Supercontinente and in consequence the SW Amazonian Craton that was reactivated in the Cryogenian Period for the installation of the Paraguai Fold Belt.

There exist various glacial units in the Neoproterozoic strata of southern Namibia (Kalahari Craton). They were recognised and discussed in the scientific literature for at nearly 100 years (e.g. Coleman, 1926; Gevers, 1931; Schwellnuss, 1941; Martin, 1965). The Snowball Earth theory (Hoffman et al., 1998) had an huge impact on Neoproterozoic geosciences and especially outcrops of the Otavi Group in northern Namibia helped to strengthen and support this idea. Nevertheless, the Neoproterozoic glacial horizons in southern Namibia were difficult to interpret and even more difficult to correlate, due to their tectonic overprint and their scarce outcrops. In order to correlate and differentiate the various Neoproterozoic glacial units of southern Namibia (western rim of Kalahari Craton) a multi‐method approach based on isotopic analyses on zircon grains, whole rock geochemistry, grain size measurements combined with extensive field work, mapping and sampling was applied. In total, ten sections were mapped and measured from which 33 samples were chosen for further analyses. Two of these samples represent local basement rocks, 19 the siliciclastic Neoproterozoic sedimentary cover including glacial diamictites, and twelve carbonate samples. 3474 single zircon grains were picked and measured for their dimensions (width and length). Of those, 2404 zircons were analysed with LA‐ICP‐MS techniques for their U‐Pb and Th‐U ratios in order to calculate detrital zircon ages and to obtain information about the source magma. 1535 of those gave concordant ages (90‐110 % of concordance). Further, selected zircon grains (in total 346) with concordant U‐Pb ages were analyses for their εHf(t) values. To gather more information and to be able to provide absolute ages for the Neoproterozoic glacial units the new technique of LAICP‐MS U‐Pb dating on carbonate samples was tested and gave reliable results for ten out of twelve samples (representing seven different sample locations). Field work revealed two sections containing the Sturtian as well as the Marinoan glacial diamictites in relatively undisturbed succession that qualified as reference profiles for Neoproterozoic strata in southern Namibia: the Dreigratberg and the Namuskluft section in the Gariep Belt close to the Orange River. All analysed samples contain a very similar detrital zircon isotopic record and the whole rock geochemical analyses confirm this interpretation. All siliciclastic samples show a general felsic provenance, with zircon ages mainly divided into two age groups (Mesoproterozoic 1.0 – 105 Ga and Palaeoproterozoic 1.7 – 2.1 Ga), reflecting four different growth and recycling events of Mesoproterozoic to Archaean crustal units. The samples have a geochemical signature of continental island arc and the zircon grain dimensions (width vs. length) are also very similar for all samples. Direct age dating of the samples based on detrital zircons was not possible caused by the lack of ages reflecting deposition times. Nevertheless, the most important differences between the various glacial horizons were found in petrographic features (diamictite pebble contents) and the age peak shift of detrital zircon U‐Pb ages (P/M ratio). Based on these and the two reference profiles correlations to other sections were achievable and the differentiation of four distinct Neoproterozoic glacial horizons for southern Namibia was possible. Furthermore, these new results provide new insights into the Neoproterozoic Gariep Belt formation comprising Tonian rifting events, Cryogenian formation of the Arachania Terrane and final Ediacaran collision of the Rio de la Plata and Kalahari cratons. The combination of all results reflects a continuous sedimentary recycling on the western Kalahari Craton. Comparison and statistical similarity tests based on zircon age data bases for possible source areas defined the Namaqua Natal and Gariep belts as the most likely sedimentary source areas, providing the rock material that got recycled for at least 200 Ma from Kaigas glaciation at ca. 750 Ma to Vingerbreek glaciation at ca. 550 Ma. In addition, the lack of exotic detrital zircon ages within the two Snowball Earth events of this study suggests the interpretation of none or only very minor glacial movement confirming the idea of a completely ice‐covered Earth. The assumed Sturtian and Marinoan ages of Numees Fm and Namaskluft Mbr diamictites were confirmed by the results of U‐Pb cap carbonate dating. Based on these, a minimum duration of ca. 8 Ma for the Sturtian and of ca. 14 Ma for the Marinoan glaciation can be assumed.:Abstract Kurzfassung Contents List of Figures List of Tables List of abbreviations Scientific question and thesis structure 1 Introduction 1.1 The Neoproterozoic era: Supercontinent dispersal and global glaciations 1.1.1 Rodinia supercontinent: Formation, dispersal, and location of Kalahari Craton 1.1.2 Glacial events during the Neoproterozoic era 1.1.2.1 A brief history on the discovery of Snowball Earth events 1.1.2.2 Formation and termination of a Snowball Earth event: The Snowball Earth flow chart 1.1.2.3 Hypotheses for cap carbonate formation 1.1.2.4 Survival of life during a Snowball Earth event 1.2 The Kalahari Craton 1.2.1 Evolution of the Kalahari Craton 1.3 Overview over the Geology of Namibia under special consideration of southern Namibia (Kalahari Craton) 2 Characteristics of southern Namibian Neoproterozoic glacial samples and sides 3 The problematic correlations of Neoproterozoic glacial deposits of the Kalahari Craton (southern Namibia) 4 Methods 4.1 Field work 4.2 Whole Rock geochemical analyses 4.3 Heavy mineral separation and SEM analyses on zircon grains of siliciclastic samples 4.4 Zircon grain size analyses 4.5 LA‐ICP‐MS analyses on zircon grains 4.5.1 U‐Pb analyses with LA‐SF‐ICP‐MS 4.5.2 Th‐U ratio determination on zircon grains 4.5.3 Hf‐isotope measurements with LA‐MS‐ICP‐MS 4.6 LA‐ICP‐MS U‐Pb dating on carbonates 4.7 Provenance interpretations and likeness tests based on zircon U‐Pb age data bases 5 Study I: “The Namuskluft and Dreigratberg sections in southern Namibia (Kalahari Craton, Gariep Belt): a geological history of Neoproterozoic rifting and recycling of cratonic crust during the dispersal of Rodinia until the amalgamation of Gondwana” 5.1 Introduction and geological setting 5.2 Samples and methods 5.3 Results 5.4 Discussion and interpretation 5.5 Summary 6 Study II: “The four Neoproterozoic glaciations of southern Namibia and their detrital zircon record: The fingerprints of four crustal growth events during two supercontinent cycles” 6.1 Introduction 6.2 The samples 6.3 Methods 6.4 Results 6.5 Interpretation and discussion 6.6 Conclusion/Summary 7 Study III: “Correlation of Neoproterozoic diamictites in southern Namibia” 7.1 Introduction 7.2 Sample sites 7.2.1. The Kaigas and Sturtian Numees diamictites at the Orange River section 2.1.1. Outcrops of the Kaigas Fm diamictites 7.2.1.2 Outcrop of the Numees Fm diamictites (Sturtian) 7.2.2 The Sturtian diamcitite of the Blaubeker Fm (Witvlei Grp) at the farmgrounds Blaubeker and Tahiti 7.2.2.1 The Blaubeker diamictite at Blaubeker Farm (type locality) 7.2.2.2 The Blaubeker diamictite at Tahiti Farm (Gobabis‐syncline) 7.2.2.3 Correlation of Blaubeker diamictite at Blaubeker and Tahiti farms 7.2.3 The Sturtian diamictite at the Trekpoort Farm section 7.2.4 The Sturtian and Marinoan diamictites at Namuskluft section (reference profile) 7.2.5 The Sturtian and Marinoan diamictites at Dreigratberg section 7.2.6 Sturtian diamictite and Marinoan‐type cap carbonate at Dreigratberg North section 7.2.7 The Marinoan diamictite at the Witputs Farm section 7.2.8 The post‐Gaskiers Vingerbreek diamictite 7.2.8.1 The Vingerbreek diamictite along the Orange River 7.2.8.2 The Vingerbreek diamictite at Tierkloof Farm (Klein Karas Mountains) 7.3 Methods 7.4 Data and Results 7.4.1 Results of the U‐Pb detrital zircon data 7.4.2 Results of the U‐Pb carbonate dating 7.4.3 Results of zircon grain width and length measurements 7.4.4 Results of the Th‐U zircon ratios 7.4.5 Results of Lu‐Hf isotopic measurements 7.4.6 Geochemical results of the siliciclastic and basement samples 7.4.7 Geochemical results of the carbonate samples 7.5 Discussion and Conclusion 8 Sediment provenance and Snowball Earth ice dynamics 9 Implications on the evolution of the Gariep Belt 10 Conclusions and outlook 11 References Supplementary Material / Die neoproterozoischen Einheiten des südlichen Namibias (Kalahari Kraton) umfassen verschiedene glaziale Einheiten, die schon seit fast 100 Jahren bekannt sind und wissenschaftlich beschrieben wurden (z.B. Coleman, 1926; Gevers, 1931; Schwellnuss, 1941; Martin, 1965). Die Schneeball Erde Theorie (Hoffman et al., 1998) hatte einen enormen Einfluss auf die geologischen Studien des Neoproterozoikums, wobei besonders Aufschlüsse der Otavi Gruppe Nordnamibias die Theorie stärken und bestätigen. Im Gegensatz dazu sind neoproterozoische glaziale Horizonte Südnamibias aufgrund ihrer tektonischen Überprägung und der wenigen Aufschlüsse schwer zu interpretieren und zu korrelieren. Mit dem Ziel, die neoproterozoischen glazialen Einheiten Südnamibias zu unterscheiden und zu korrelieren, wurde ein Multimethodenansatz basierend auf Isotopenanalysen an Zirkonmineralen, Gesamtgesteinsgeochemie, Mineralkorngrößenmessungen und intensiver Feldarbeit angewandt. Insgesamt wurden zehn Profile kartiert und vermessen, von denen 33 Proben zur weiteren Analyse ausgewählt wurden. Zwei dieser Proben stammen vom lokalen Grundgebirge, 19 aus den sedimentären Einheiten darüber (inklusive der glazialen Ablagerungen) und zwölf repräsentieren Karbonatgesteinsproben. 3474 Einzelzirkone wurden hinsichtlich ihrer Breite und Länge vermessen, wovon 2404 Minerale mittels LA‐ICP‐MS nach ihren U‐Pb und Th‐U‐Gehalten analysiert wurden. 1535 dieser Minerale ergaben konkordante Alter (90 – 110% Konkordanz). Darüber hinaus wurden von 346 ausgewählten konkordanten Zirkonen die εHf(t) Werte bestimmt. Um das Datenset zu vervollständigen wurden LA‐ICP‐MS U‐Pb Analysen an Karbonatgesteinen an zehn von zwölf Proben erfolgreich getestet. Im Zuge der Feldarbeiten kristallisierten sich zwei Profile nahe des Oranje heraus, welche die Sturtian und die Marinoan Vereisung in nahezu ungestörter Lagerung enthalten und sich deshalb als Referenzprofile qualifizieren. Alle analysierten Proben zeichnen sich durch sehr ähnliche Zirkonisotopenwerte aus, was durch die Gesamtgesteinsgeochemieanalysen weiterhin bestätigt wird. Alle siliziklastischen Proben zeigen eine generelle felsische Provenienz mit Zirkonaltern welche sich hauptsächlich in zwei Altersgruppen unterteilen lassen (mesoproterozoisch 1.0 – 1.5 Mrd Jahre, paläoproterozoisch 1.7 – 2.1 Mrd Jahre). Diese reflektieren vier verschiedene krustale Entwicklungsstadien vom Mesoproterozoikum bis Archaikum. Die geochemische Signatur aller Proben deutet auf einen kontinentalen Inselbogen hin und auch die Zirkonmineralgrößen sind für alle Proben ähnlich. Eine direkte Altersdatierung auf Grundlage der detritischen Zirkone war aufgrund fehlender junger Alter nicht möglich. Dennoch ist eine Unterscheidung der glazialen Schichten Südnamibias basierend auf den petrographischen Eigenschaften und dem sich verschiebenden Alterstrend der detritischen Zirkone möglich (P/M Verhältnis). In Kombination mit den zwei Referenzprofilen ist eine umfassende Korrelation aller untersuchten Profile möglich und die Unterscheidung von vier Neoproterozoischen glazialen Schichten in Namibia gelungen. Die Ergebnisse geben weitere Einblicke in die neoproterozoische Entwicklung des Gariep Gürtels, welcher durch Riftvorgänge im Tonium, die Bildung des Arachania Terranes während des Cryogeniums und die ediakarische finale Kollision zwischen den Rio de la Plata und Kalahari Kratonen geprägt ist. Die Kombination aller Ergebnisse zeigt ein kontinuierliches Sedimentrecycling auf dem westlichen Kalahari Kraton. Vergleiche und statistische Ähnlichkeitsanalysen basierend auf U‐Pb Zirkonalterdatenbanken ergaben, dass der Namaqua Natal und der Gariep Gürtel die wahrscheinlichsten Liefergebiete sind. Das Recycling fand für mindestens 200 Millionen Jahre zwischen der Kaigas Vereisung (etwa vor 750 Millionen Jahren) und der Vingerbreek Vereisung (etwa vor 550 Millionen Jahren) statt. Darüber hinaus zeigt das Fehlen fremder Zirkonalter für die Schneeball Erde Proben, dass sich die Eispanzer kaum oder nur sehr wenig bewegt haben können, was die Theorie einer komplett zugefrorenen Erde unterstützt. Die Ergebnisse der U‐Pb Karbonatgesteinsdatierungen bestätigen des angenommene Sturtian und Marinoan Alter der Numees Fm und des Namaskluft Mbr. Basierend auf diesen Analysen kann eine Mindestlänge von etwa 8 Millionen Jahren für das Sturtian und etwa 14 Millionen Jahren für das Marinoan Schneeball Erde Ereignis angenommen werden.:Abstract Kurzfassung Contents List of Figures List of Tables List of abbreviations Scientific question and thesis structure 1 Introduction 1.1 The Neoproterozoic era: Supercontinent dispersal and global glaciations 1.1.1 Rodinia supercontinent: Formation, dispersal, and location of Kalahari Craton 1.1.2 Glacial events during the Neoproterozoic era 1.1.2.1 A brief history on the discovery of Snowball Earth events 1.1.2.2 Formation and termination of a Snowball Earth event: The Snowball Earth flow chart 1.1.2.3 Hypotheses for cap carbonate formation 1.1.2.4 Survival of life during a Snowball Earth event 1.2 The Kalahari Craton 1.2.1 Evolution of the Kalahari Craton 1.3 Overview over the Geology of Namibia under special consideration of southern Namibia (Kalahari Craton) 2 Characteristics of southern Namibian Neoproterozoic glacial samples and sides 3 The problematic correlations of Neoproterozoic glacial deposits of the Kalahari Craton (southern Namibia) 4 Methods 4.1 Field work 4.2 Whole Rock geochemical analyses 4.3 Heavy mineral separation and SEM analyses on zircon grains of siliciclastic samples 4.4 Zircon grain size analyses 4.5 LA‐ICP‐MS analyses on zircon grains 4.5.1 U‐Pb analyses with LA‐SF‐ICP‐MS 4.5.2 Th‐U ratio determination on zircon grains 4.5.3 Hf‐isotope measurements with LA‐MS‐ICP‐MS 4.6 LA‐ICP‐MS U‐Pb dating on carbonates 4.7 Provenance interpretations and likeness tests based on zircon U‐Pb age data bases 5 Study I: “The Namuskluft and Dreigratberg sections in southern Namibia (Kalahari Craton, Gariep Belt): a geological history of Neoproterozoic rifting and recycling of cratonic crust during the dispersal of Rodinia until the amalgamation of Gondwana” 5.1 Introduction and geological setting 5.2 Samples and methods 5.3 Results 5.4 Discussion and interpretation 5.5 Summary 6 Study II: “The four Neoproterozoic glaciations of southern Namibia and their detrital zircon record: The fingerprints of four crustal growth events during two supercontinent cycles” 6.1 Introduction 6.2 The samples 6.3 Methods 6.4 Results 6.5 Interpretation and discussion 6.6 Conclusion/Summary 7 Study III: “Correlation of Neoproterozoic diamictites in southern Namibia” 7.1 Introduction 7.2 Sample sites 7.2.1. The Kaigas and Sturtian Numees diamictites at the Orange River section 2.1.1. Outcrops of the Kaigas Fm diamictites 7.2.1.2 Outcrop of the Numees Fm diamictites (Sturtian) 7.2.2 The Sturtian diamcitite of the Blaubeker Fm (Witvlei Grp) at the farmgrounds Blaubeker and Tahiti 7.2.2.1 The Blaubeker diamictite at Blaubeker Farm (type locality) 7.2.2.2 The Blaubeker diamictite at Tahiti Farm (Gobabis‐syncline) 7.2.2.3 Correlation of Blaubeker diamictite at Blaubeker and Tahiti farms 7.2.3 The Sturtian diamictite at the Trekpoort Farm section 7.2.4 The Sturtian and Marinoan diamictites at Namuskluft section (reference profile) 7.2.5 The Sturtian and Marinoan diamictites at Dreigratberg section 7.2.6 Sturtian diamictite and Marinoan‐type cap carbonate at Dreigratberg North section 7.2.7 The Marinoan diamictite at the Witputs Farm section 7.2.8 The post‐Gaskiers Vingerbreek diamictite 7.2.8.1 The Vingerbreek diamictite along the Orange River 7.2.8.2 The Vingerbreek diamictite at Tierkloof Farm (Klein Karas Mountains) 7.3 Methods 7.4 Data and Results 7.4.1 Results of the U‐Pb detrital zircon data 7.4.2 Results of the U‐Pb carbonate dating 7.4.3 Results of zircon grain width and length measurements 7.4.4 Results of the Th‐U zircon ratios 7.4.5 Results of Lu‐Hf isotopic measurements 7.4.6 Geochemical results of the siliciclastic and basement samples 7.4.7 Geochemical results of the carbonate samples 7.5 Discussion and Conclusion 8 Sediment provenance and Snowball Earth ice dynamics 9 Implications on the evolution of the Gariep Belt 10 Conclusions and outlook 11 References Supplementary Material

Cette thèse de doctorat se focalise sur la fin du Précambrien, le Néoprotérozoïque, une période charnière dans lhistoire de la Terre, par létude dunités ophiolitiques datées entre 800 et 700 Ma. Les travaux présentés ici portent sur létude pétrographique, géochimique et magnétique des serpentinites de ces ophiolites. Associées à des sutures panafricaines en bordure des cratons ouest africain et amazonien, ces ophiolites sont les témoins des subductions et de la lithosphère océanique associées à la dislocation du supercontinent Rodinia. Létude de ces ophiolites permet de proposer des contextes de formation pour ces sections de lithosphère océanique. Une autre question à lorigine de ce travail était : Létude de la serpentinisation et de lhydrothermalisme associé permet-elle dapporter des contraintes sur le paléoenvironnement océanique ? Les travaux sur les serpentinites et les roches mafiques associées des unités ophiolitiques de lAraguaia belt (757 ± 49 Ma1, Brésil) constituent la première étude géochimique réalisée sur ces unités. La chimie des spinelles couplée à des travaux de modélisation géochimique, portant essentiellement sur les concentrations en REE, attestent dun protolithe hautement réfractaire, ayant enduré entre 14 et 24 % de fusion partielle. Ces travaux témoignent aussi de laffinité abyssale de ces serpentinites, confirmée par les signatures N-MORB et E-MORB des basaltes associés. Il apparait que la serpentinisation de ces unités sest probablement opérée en deux temps, en domaine océanique, puis par interaction avec des fluides dérivés des sédiments encaissants, aboutissant à de forts enrichissements en LILE, en B et en Li dans ces serpentinites. Finalement, nous proposons que ces sections de lithosphère océanique, ainsi que les métasédiments les abritant (Tocantins group), soient les reliques dune transition océan-continent (TOC) en bordure est du craton amazonien. Les études de terrain, pétrographiques et géochimiques sur les sections ophiolitiques de Khzama (762 ± 2 Ma2) et dAït Ahmane (Anti-Atlas, Maroc) ont dans un premier temps permis de confirmer le lien supposé entre ces deux ophiolites. Les spinelles des serpentinites de ces unités sont caractérisés par des Cr# très élevés et des Mg# bas témoignant dun protolithe ayant enduré des taux de fusion supérieurs à 25 %, confirmant leur affinité avec la zone de subduction anti-atlasique. Ceci est corroboré par de très faibles concentrations en éléments incompatibles comme Al, Ti, HREE et HFSE. Le contexte le plus probable concernant la genèse de ces sections de lithosphère est ainsi un même centre daccrétion arrière-arc intra-océanique, à la marge du supercontinent Rodinia. Létude comparative des serpentinites de ces ophiolites a aussi permis de mettre en évidence en évidence lintérêt des mesures magnétiques pour tracer le degré daltération des spinelles chromifères dans les serpentinites, approche pouvant être étendue à dautres types de roches. Notamment, nous montrons que la Cr-magnétite et la ferritchromite peuvent être identifiées à laide des mesures de susceptibilité magnétique en chauffe. Enfin, lassociation des méthodes magnétiques, pétrographiques et géochimiques nous permet de proposer un modèle concernant la formation des veines de magnétite massives de lunité dAït Ahmane Nord. Nous montrons que le triptyque : serpentinites et spinelles altérés et veines de magnétite centimétriques, constitue un système hydrothermal abyssal fossile, de type fumeur noir. Dans ce contexte, les compositions isotopiques en oxygène des veines de magnétite permettent de proposer une valeur du 18O des océans néoprotérozoïques profonds de -1.33 ± 0.98 (VSMOW), soit une valeur très similaire à lactuel (entre -1 et +1 VSMOW). Elle tranche aussi le débat sur lévolution du 18O des océans au cours des temps géologiques en attestant dune constance de celui-ci, au moins depuis le Néoprotérozoïque. / This Doctoral thesis focus on the end of the Precambrian, the Neoproterozoic, a pivotal period in the Earth history, by the study of ophiolitic units dated between 800 and 700 Ma. This work essentially deals with the petrography, geochemistry and magnetism of serpentinites from these ophiolites. They are associated with Panafrican orogenic belts along the West African and the Amazonian cratons and witnesses the subductions and the oceanic lithosphere associated to the break-up of the supercontinent Rodinia. The study of these neoproterozoic ophiolites allowed us to propose the formation settings for these sections of oceanic lithosphere. Another question behind this work is: Does the study of serpentinization and associated hydrothermalism allows one to provide constraints on the oceanic paleoenvironment? Work on the serpentinites and associated mafic rocks from the Araguaia belt ophiolitic units (757 ± 49 Ma1, Brazil) constitute the first geochemical study realized on these units. The Cr-spinel chemistry coupled with geochemical modeling, concerning essentially the REE concentrations, attest to a highly refractory protolith that endured between 14 and 24% of partial melting. This work also indicate an abyssal affinity (i.e. MOR rather than SSZ) of these serpentinites, which is confirmed by the N-MORB and E-MORB geochemical signature of the associated basalts. It appears that the serpentinization of these units probably took place in two steps, first in oceanic domain and then by interaction with fluids derived from the surrounding sediments after obduction, leading to strong LILE, B and Li enrichments in the serpentinites. Finally, we propose two potential settings concerning the origin of the sections of oceanic lithosphere presently found in the Araguaia belt: (1) an ocean-continent transition or (2) slices of a more mature lithosphere trapped into an accretionary wedge. Fieldwork, petrography and geochemical analysis on serpentinites from the Khzama (762± 2 Ma²) and Aït Ahmane ophiolitic sections (Anti-Atlas, Morocco) firstly allowed to confirm the supposed link between these two ophiolites. Cr-spinels in serpentinites from these units are characterized by very high Cr# and low Mg# testifying of a protolith having endured partial melting greater the 25%, confirming their affinity with the anti-atlasic subduction zone. This is corroborated by very low incompatible element concentrations such as Al, Ti, HREE and HFSE. Thus, the most likely setting for the genesis of these sections of lithosphere is a same intra-oceanic back-arc spreading center at the margin of the Rodinia supercontinent. The comparative study of all studied serpentinites from Neoproterozoic ophiolites in different settings also demonstrates the ability of magnetic measurements in monitoring the Cr-spinel alteration degree, a method which can be extended to other types of rocks. In particular, we show that Cr-magnetite and ferritchromite can be identified using thermomagnetic curves. Finally, the association of magnetic, petrographic and geochemical methods allows us to propose a model concerning the formation of the massive magnetite veins of the North Aït Ahmane unit. We show that the triptych consisting in: altered serpentinites, spinels and centimetric magnetite veins, results from a fossil, black smoker type, abyssal hydrothermal system. In this context, the oxygen isotopic compositions of the magnetite veins provide a 18O value of the deep Neoproterozoic oceans of -1.33 ± 0.98 (VSMOW), a value that is very similar to the current one (between -1 and +1 VSMOW). It also settles the debate on the evolution of the 18O of the oceans during geological time, attesting of its consistency, at least since the Neoproterozoic.

Cette thèse de doctorat se focalise sur la fin du Précambrien, le Néoprotérozoïque, une période charnière dans l'histoire de la Terre, par l'étude d'unités ophiolitiques datées entre 800 et 700 Ma. Les travaux présentés ici portent sur l'étude pétrographique, géochimique et magnétique des serpentinites de ces ophiolites. Associées à des sutures panafricaines en bordure des cratons ouest africain et amazonien, ces ophiolites sont des vestiges des subductions et de la lithosphère océanique associées à la dislocation du supercontinent Rodinia. L'étude de ces ophiolites permet de proposer des contextes de formation pour ces sections de lithosphère océanique. Une autre question à l'origine de ce travail était : L'étude de la serpentinisation et de l'hydrothermalisme associé permet-elle d'apporter des contraintes sur le paléoenvironnement océanique ? / This Doctoral thesis focus on the end of the Precambrian, the Neoproterozoic, a pivotal period in the Earth history, by the study of ophiolitic units dated between 800 and 700 Ma. This work essentially deals with the petrography, geochemistry and magnetism of serpentinites from these ophiolites. They are associated with Panafrican orogenic belts along the West African and the Amazonian cratons and witnesses the subductions and the oceanic lithosphere associated to the break-up of the supercontinent Rodinia. The study of these neoproterozoic ophiolites allowed us to propose the formation settings for these sections of oceanic lithosphere. Another question behind this work is: Does the study of serpentinization and associated hydrothermalism allows one to provide constraints on the oceanic paleoenvironment?

Cette thèse de doctorat se focalise sur la fin du Précambrien, le Néoprotérozoïque, une période charnière dans lhistoire de la Terre, par létude dunités ophiolitiques datées entre 800 et 700 Ma. Les travaux présentés ici portent sur létude pétrographique, géochimique et magnétique des serpentinites de ces ophiolites. Associées à des sutures panafricaines en bordure des cratons ouest africain et amazonien, ces ophiolites sont les témoins des subductions et de la lithosphère océanique associées à la dislocation du supercontinent Rodinia. Létude de ces ophiolites permet de proposer des contextes de formation pour ces sections de lithosphère océanique. Une autre question à lorigine de ce travail était : Létude de la serpentinisation et de lhydrothermalisme associé permet-elle dapporter des contraintes sur le paléoenvironnement océanique ? Les travaux sur les serpentinites et les roches mafiques associées des unités ophiolitiques de lAraguaia belt (757 ± 49 Ma1, Brésil) constituent la première étude géochimique réalisée sur ces unités. La chimie des spinelles couplée à des travaux de modélisation géochimique, portant essentiellement sur les concentrations en REE, attestent dun protolithe hautement réfractaire, ayant enduré entre 14 et 24 % de fusion partielle. Ces travaux témoignent aussi de laffinité abyssale de ces serpentinites, confirmée par les signatures N-MORB et E-MORB des basaltes associés. Il apparait que la serpentinisation de ces unités sest probablement opérée en deux temps, en domaine océanique, puis par interaction avec des fluides dérivés des sédiments encaissants, aboutissant à de forts enrichissements en LILE, en B et en Li dans ces serpentinites. Finalement, nous proposons que ces sections de lithosphère océanique, ainsi que les métasédiments les abritant (Tocantins group), soient les reliques dune transition océan-continent (TOC) en bordure est du craton amazonien. Les études de terrain, pétrographiques et géochimiques sur les sections ophiolitiques de Khzama (762 ± 2 Ma2) et dAït Ahmane (Anti-Atlas, Maroc) ont dans un premier temps permis de confirmer le lien supposé entre ces deux ophiolites. Les spinelles des serpentinites de ces unités sont caractérisés par des Cr# très élevés et des Mg# bas témoignant dun protolithe ayant enduré des taux de fusion supérieurs à 25 %, confirmant leur affinité avec la zone de subduction anti-atlasique. Ceci est corroboré par de très faibles concentrations en éléments incompatibles comme Al, Ti, HREE et HFSE. Le contexte le plus probable concernant la genèse de ces sections de lithosphère est ainsi un même centre daccrétion arrière-arc intra-océanique, à la marge du supercontinent Rodinia. Létude comparative des serpentinites de ces ophiolites a aussi permis de mettre en évidence en évidence lintérêt des mesures magnétiques pour tracer le degré daltération des spinelles chromifères dans les serpentinites, approche pouvant être étendue à dautres types de roches. Notamment, nous montrons que la Cr-magnétite et la ferritchromite peuvent être identifiées à laide des mesures de susceptibilité magnétique en chauffe. Enfin, lassociation des méthodes magnétiques, pétrographiques et géochimiques nous permet de proposer un modèle concernant la formation des veines de magnétite massives de lunité dAït Ahmane Nord. Nous montrons que le triptyque : serpentinites et spinelles altérés et veines de magnétite centimétriques, constitue un système hydrothermal abyssal fossile, de type fumeur noir. Dans ce contexte, les compositions isotopiques en oxygène des veines de magnétite permettent de proposer une valeur du 18O des océans néoprotérozoïques profonds de -1.33 ± 0.98 (VSMOW), soit une valeur très similaire à lactuel (entre -1 et +1 VSMOW). Elle tranche aussi le débat sur lévolution du 18O des océans au cours des temps géologiques en attestant dune constance de celui-ci, au moins depuis le Néoprotérozoïque. / This Doctoral thesis focus on the end of the Precambrian, the Neoproterozoic, a pivotal period in the Earth history, by the study of ophiolitic units dated between 800 and 700 Ma. This work essentially deals with the petrography, geochemistry and magnetism of serpentinites from these ophiolites. They are associated with Panafrican orogenic belts along the West African and the Amazonian cratons and witnesses the subductions and the oceanic lithosphere associated to the break-up of the supercontinent Rodinia. The study of these neoproterozoic ophiolites allowed us to propose the formation settings for these sections of oceanic lithosphere. Another question behind this work is: Does the study of serpentinization and associated hydrothermalism allows one to provide constraints on the oceanic paleoenvironment? Work on the serpentinites and associated mafic rocks from the Araguaia belt ophiolitic units (757 ± 49 Ma1, Brazil) constitute the first geochemical study realized on these units. The Cr-spinel chemistry coupled with geochemical modeling, concerning essentially the REE concentrations, attest to a highly refractory protolith that endured between 14 and 24% of partial melting. This work also indicate an abyssal affinity (i.e. MOR rather than SSZ) of these serpentinites, which is confirmed by the N-MORB and E-MORB geochemical signature of the associated basalts. It appears that the serpentinization of these units probably took place in two steps, first in oceanic domain and then by interaction with fluids derived from the surrounding sediments after obduction, leading to strong LILE, B and Li enrichments in the serpentinites. Finally, we propose two potential settings concerning the origin of the sections of oceanic lithosphere presently found in the Araguaia belt: (1) an ocean-continent transition or (2) slices of a more mature lithosphere trapped into an accretionary wedge. Fieldwork, petrography and geochemical analysis on serpentinites from the Khzama (762± 2 Ma²) and Aït Ahmane ophiolitic sections (Anti-Atlas, Morocco) firstly allowed to confirm the supposed link between these two ophiolites. Cr-spinels in serpentinites from these units are characterized by very high Cr# and low Mg# testifying of a protolith having endured partial melting greater the 25%, confirming their affinity with the anti-atlasic subduction zone. This is corroborated by very low incompatible element concentrations such as Al, Ti, HREE and HFSE. Thus, the most likely setting for the genesis of these sections of lithosphere is a same intra-oceanic back-arc spreading center at the margin of the Rodinia supercontinent. The comparative study of all studied serpentinites from Neoproterozoic ophiolites in different settings also demonstrates the ability of magnetic measurements in monitoring the Cr-spinel alteration degree, a method which can be extended to other types of rocks. In particular, we show that Cr-magnetite and ferritchromite can be identified using thermomagnetic curves. Finally, the association of magnetic, petrographic and geochemical methods allows us to propose a model concerning the formation of the massive magnetite veins of the North Aït Ahmane unit. We show that the triptych consisting in: altered serpentinites, spinels and centimetric magnetite veins, results from a fossil, black smoker type, abyssal hydrothermal system. In this context, the oxygen isotopic compositions of the magnetite veins provide a 18O value of the deep Neoproterozoic oceans of -1.33 ± 0.98 (VSMOW), a value that is very similar to the current one (between -1 and +1 VSMOW). It also settles the debate on the evolution of the 18O of the oceans during geological time, attesting of its consistency, at least since the Neoproterozoic.

Svalbard represents the uplifted and exhumed northwest corner of the Barents Sea Shelf. Pre-Carboniferous rocks of Svalbard are divided into the Eastern, Northwestern and Southwestern Terranes, were amalgamated during the Caledonian Orogen and are separated by north-south-trending strike-slip faults. Even though our knowledge of Svalbard’s pre-Carboniferous history has increased dramatically during the last two decades, a major issue remains: Where did the different tectonostratigraphic terranes of Svalbard originate? The answer to this question has profound significance for the entire eastern Laurentian margin, which spans two supercontinent cycles, from the amalgamation and breakup of Rodinia to the amalgamation of Pangea. This thesis constrains the tectonothermal evolution of Svalbard’s Northwestern Terrane (NWT) using ion microprobe and LA-ICP-MS U-Pb zircon geochronology and electron microprobe thermobarometry on metasediments, clastic rocks and granitoids. Detrital zircon age populations of metasediments from the NWT suggests that they (e.g. the Krossfjorden Group) were deposited at c. 1000 Ma in a remnant ocean basin setting outboard the Eastern Grenville Province and were subsequently deformed and intruded by Late Grenvillian granitoids during the final suturing of Rodinia. Thus, a northern branch of the Grenvillian/Sveconorwegian orogeny is not present. This older history of the NWT is extensively overprinted by Late Caledonian deformation and metamorphism, with peak metamorphic conditions of 850 °C at >6 kbars, and subsequent migmatization of the Krossfjorden Group at c. 420 Ma. Based on these data, together with the detrital zircon age population from overlying Late Silurian-Early Devonian clastic rocks, a unifying model is proposed involving fragments from the Grampian orogen and Avalonian crust originally accreted to the Laurentian margin, subsequently transported northwards along sinistral strike-slip faults during Scandian deformation. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 4: In press.

No description available.

Global paleogeography exerts a first order control on both the deep and surficial components of the Earth system. Temporal and spatial constraints on the Mozambique Belt of Eastern Africa are needed to understand its crustal evolution and its role in assembly of Gondwana. This thesis provides detailed data on the timing, sources and nature of tectono-thermal events responsible for magmatism in the Mozambique Belt in southern Malawi. An integrated approach of petrography, geochemistry, radiogenic isotopes, and single zircon geochronology has been used to determine spatial and temporal constraints and to better constrain models of the assembly of East and West Gondwana, which occurred along the Mozambique Belt. In particular the thesis attempts to address key unresolved questions about the number and timing of accretionary pulses within the orogen. LA-ICP-MS single zircon U-Pb results show tectono-thermal events in four periods: Mesoproterozoic from 1128 ± 30 Ma to 1033 ± 20 Ma; Neoproterozoic (956 ± 12 Ma – 594 ± 65 Ma); Cambrian (530 ± 3 Ma – 515 ± 12 Ma); and Cretaceous (118 ± 2 Ma). Metamorphism is dated from a charnockitic gneiss that yielded a lower intercept age of 515 ± 18 Ma. The granitoids are intermediate to acidic with relative enrichment in LILEs and depletion in HFSEs with moderately negative anomalies in Th, Nb, P, Zr and Ti. REE spider plots show enrichment in LREEs and depleted HREEs with negative Eu anomalies. The meta-granites are largely metaluminous with a few peraluminous, I-type granites belonging to the calc-alkaline series. Radiogenic isotope data reveals slight differences with older, Mesoproterozoic rocks showing positive ɛNd and ɛHf values signifying derivation from depleted mantle material, whilst the younger rocks display negative epsilon values suggestive of crustal material recycling and mixing for their source and origins. Granitoids of southern Malawi display characteristics consistent with derivation in a continental Andean type arc with some aspects of the chemistry resembling tonalite-trondhjemite-granite (TTG) suites mapped in the Mozambique Belt in Kenya, Tanzania, Mozambique, and Antarctica although the data are not sufficiently compelling to assign the Malawi rocks to classic TTGs.