Read Books Online and Download eBooks, EPub, PDF, Mobi, Kindle, Text Full Free.
Evolution Tectono Metamorphique Dun Segment De Croute Continentale Archeenne
Download Evolution Tectono Metamorphique Dun Segment De Croute Continentale Archeenne full books in PDF, epub, and Kindle. Read online Evolution Tectono Metamorphique Dun Segment De Croute Continentale Archeenne ebook anywhere anytime directly on your device. Fast Download speed and no annoying ads. We cannot guarantee that every ebooks is available!
Book Synopsis Behaviour of the Sm-Nd Isotopic System During Metamorphism by : Valérie Chavagnac
Download or read book Behaviour of the Sm-Nd Isotopic System During Metamorphism written by Valérie Chavagnac and published by . This book was released on 1999 with total page 450 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aims of this Ph.D. Thesis were to decipher whether the use of Nd model ages are reliable constraints for the crustal evolution on Proterozoic migmatized terrane (example of the Limpopo Belt in South Africa) and to examine the consistency between Sm-Nd gamet and V-Pb zircon ages on eclogites (example of the VHPM Dabieshan in Central China). The Central Zone of the Limpopo Belt which is mainly composed of orthogneisses and paragneisses underwent granulite facies metamorphism followed by decompression metamorphic conditions (clockwise P-T loop) at 2.0 Ga. We have performed Sm-Nd and U-Pb work associated with major and trace element analyses on three examples of migmatites generated at 2.0 Ga to study the chemical and isotopic fractionation which may occur during migmatization. Partial melting following the Bt dehydration reaction did lead to different behaviour of Sm-Nd systematics for metagreywacke and metapelite. ln the first case, chemical equilibrium and full Nd isotope exchanges were not reached due to the incrongruent Pl melting and to the effect of accessory mineraIs (Mnz and Ap) on the compositions of the partial melt. Monazite entered the melt in prefarence to apatite, either by dissolution or by entrainment, and its unradiogenic Nd isotope signature dominates the leucosome. The Nd model ages on partial melt are up to 400 Ma older than those on paleosomes. The Nd model ages of these rocks cannot be used in a simple way to cons train the evolution of Southern Africa. ln the second case, incongruent Pl melting influenced the distribution of major, LILE and also REE between the partial melts and the paleosomes. Full Nd isotope exchange was nearly achieved while Pb-Pb systematics were not fully resetted. Incomplete exchange for both Nd and Pb for two leucosomes is also argued. It appears that the accessory minerals were chemically and isotopically equilibrated with the partial melt and the paleosome. The Nd model ages can be used to constrain the crustal growth of the Limpopo Central Zone. Finally, in migmatites formed by metamorphic segregation at subsolidus conditions on orthogneiss, chemical equilibrium and Nd isotope exchange were not reached during migmatization. The distributions of the elements are related to the proportional amounts of each mineraI in the migmatitic components. However, full Pb isotope exchange is reached here as highlighted by a Pb-Pb WR isochron yielding 2.0 Ga. ln addition, the geochemical characteristics combined with REE modelling provided arguments for closed system behaviour of the whole rock during migmatization. The isotopic compositions of the protolith obtained via mass balance calculations can be used to cons train crustal evolution. The UHPM Dabieshan is characterized by the occurrence of coesite and its quartz pseudomorph as inclusions in eclogites of basaltic composition but also of undoubted metasedimentary origin. Sm.-Nd garnet-omphacite-whole rock isochrons on the coesite-bearing eclogites of the Bixiling Complex gave ages at 210 ± 9 to 218 ± 4 Ma which are similar to 218.4 ± 1.8 Ma and 218.4 ± 2.5 Ma ages obtained by V-Pb zircon data. At the Shuanghe locality, Sm-Nd gamet-kyanite-whole rock isochron on a retrogressed eclogite gave an age at 231 ± 35 Ma in line with the U-Pb zircon data at 233 ± 21 Ma (lower intercept in the concordia diagram). ln addition, Ar-Ar and Rb-Sr phengite ages performed on the eclogite host gneisses (Bixilingg locality) yield 198 ± 4 Ma to 212 ± 2 Ma ages, overlapping the previous Sm-Nd and V-Pb zircon ages on the coesite-bearing eclogites. Consequently, the Sm-Nd garnet dating provide ages in agreement with V-Pb zircon ages and the quartzo-feldspathic gneisses underwent an event coeval to VHP on eclogites. Nd isotope equilibration at the VHP metamorphism appears to have been complete
Book Synopsis Mineralization and Sustainable Development in the West African Craton by : T. Aïfa
Download or read book Mineralization and Sustainable Development in the West African Craton written by T. Aïfa and published by Geological Society of London. This book was released on 2021-07-22 with total page 357 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Special Publication combines results obtained by interdisciplinary groups from numerous academic institutions working on Paleoproterozoic formations to decipher the origins of the main mineralization resources in the West African Craton (WAC) and their impacts on African economic development. Structural, geophysical, sedimentological, stratigraphical, geochemical, petrophysical and mineralogical analyses have been used to highlight the complexities involved in mineralization emplacement and its origin and evolution within the WAC. Fourteen articles contribute to new knowledge in mineral research. They show that the geodynamic evolution of the WAC is complex from one area to another: it involves subduction, collision and obduction during several deformation phases ranging from Birimian (2.3–2.0 Ga) to Pan-African (650–450 Ma) events. Various modelling techniques, when integrated, help in understanding the mechanisms of mineralization emplacement, some of which are still a matter of debate. The challenge for further studies is mitigation for sustainable development that can be appropriately used to minimize such damage.
Book Synopsis Evolution cénozoïque du bassin de Magellan et tectonique des Andes australes by : Marc Diraison
Download or read book Evolution cénozoïque du bassin de Magellan et tectonique des Andes australes written by Marc Diraison and published by . This book was released on 1998 with total page 382 pages. Available in PDF, EPUB and Kindle. Book excerpt: L'extrémité australe de l'Amérique du Sud se situe actuellement dans un contexte cinématique complexe impliquant les plaques Nazca, Antarctique et Scotia. Dans ce secteur, l'histoire compressive andine débute au Crétacé supérieur avec pour conséquences le soulèvement de la cordillère et le développement du bassin, d'avant-pays de Magellan. L'arcature actuelle des Andes australes résulte du développement progressif de l'orocline patagonien associé au fonctionnement d'un décrochement senestre le long de la bordure sud du continent depuis le Crétacé supérieur. A partir de 30 Ma, l'ouverture du passage de Drake entre le continent Sud-américain et la Péninsule Antarctique conduit à la croissance de la plaque Scotia. La subduction de la dorsale du Chili débute à 14 Ma au niveau de la Terre de Feu. Le point triple migre progressivement jusqu'à sa position actuelle à 46°30'S. L'étude structurale et cinématique de la région (analyse de populations de failles) a été réalisée principalement à la transition cordillère/bassin. Elle est complétée par l'analyse de l'imagerie satellitaire et de la topographie numérique, l'interprétation de données de sismique réflexion pétrolière, une étude paléomagnétique, et de la modélisation analogique. Cette étude met en évidence (1) des directions principales de raccourcissement subperpendiculaires à la cordillère tout le long de l'orocline, (2) des composantes décrochantes dextres et senestres le long des secteurs de la cordillère orientés respectivement N-S et E-O, et (3) des rifts néogènes disposés radialement affectant principalement la zone axiale du bassin de Magellan. Ce champ de déformation, compatible avec le contexte actuel, a été comparé à celui obtenu par modélisation analogique d'un orocline simple. Le passage progressif entre la zone de subduction à l'ouest et le décrochement au sud du continent (appelé effet de coin) semble être une condition suffisante au développement de l'essentiel des structures observées
Book Synopsis The Boundaries of the West African Craton by : Nasser Ennih
Download or read book The Boundaries of the West African Craton written by Nasser Ennih and published by Geological Society of London. This book was released on 2008 with total page 552 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Dynamique de l'érosion continentale aux grandes échelles de temps et d'espace by : Dimitri Lague
Download or read book Dynamique de l'érosion continentale aux grandes échelles de temps et d'espace written by Dimitri Lague and published by . This book was released on 2003 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: L'évolution à long terme des reliefs continentaux résulte de couplages complexes entre processus d'érosion et mouvements tectoniques qui tendent à s'équilibrer pour atteindre éventuellement un état stationnaire. La partie érosion de ces couplages est gouvernée par l'interaction entre des processus élémentaires de versant et de rivière, étroitement couplés, qui contrôlent l'organisation spatiale du réseau de drainage. Ces processus sont caractérisés par des vitesses d'érosion et de transport lentes sur les versants et très rapides dans les rivières, et dépendent souvent non-linéairement de la pente topographique et du flux d'eau. Il en résulte une dynamique complexe à l'échelle locale dont les conséquences à l'échelle continentale sur la vitesse et les volumes de matière transportés ne sont pas encore comprises. L'objectif de cette thèse a été de comprendre et modéliser cette dynamique à l'échelle des temps géologiques, dans le cadre de perturbations tectoniques simples, et pour des conditions climatiques constantes. Nous utilisons un modèle numérique permettant de simuler l'interaction de différents processus d'érosion de versant et de transport fluvial. Les solutions hors équilibre prédites par ce modèle ne pouvant être validées analytiquement ou à partir de données naturelles, une approche expérimentale inédite a été développée. Elle permet d'étudier précisément l'évolution d'une topographie soumise à l'action simultanée d'une surrection simple et de processus d'érosion et de transport par ruissellement. Au cours d'une expérience, la surface s'auto organise d'abord en une série de bassins versants de géométrie similaire aux systèmes naturels, puis l'altitude moyenne du système s'approche quasi-exponentiellement d'une valeur constante, traduisant un état d'équilibre macroscopique. L'analyse couplée des expériences et des simulations numériques montre que cette dynamique dépend fortement de la présence de zones de drainage internes non-connectées aux conditions limites du système, du degré de non-linéarité entre érosion et pente topographique et de l'existence d'un seuil d'érosion. A partir de l'analyse de systèmes naturels, via le formalisme de la relation pente-aire drainée, nous mettons en évidence l'existence d'un tel seuil dans les systèmes naturels. Pour ce faire nous avons développé un nouveau critère morphologique permettant de caractériser l'état dynamique des reliefs naturels. L'hypothèse d'équilibre dynamique entre érosion et tectonique, nécessaire à l'interprétation correcte des relations entre formes topographiques et processus d'érosion, peut être ainsi (in)validée. Ces résultats suggèrent que le seuil d'érosion habituellement négligé dans le calibrage des lois d'érosion élémentaires doit être explicitement pris en compte pour prédire correctement les formes topographiques naturelles, la dynamique de la croissance des réseaux de drainage et les relations à l'échelle continentale entre taux de dénudation et paramètres topographiques.
Book Synopsis Cristallochimie des éléments traces dans les phases du manteau terrestre by : Gilles Quérel
Download or read book Cristallochimie des éléments traces dans les phases du manteau terrestre written by Gilles Quérel and published by . This book was released on 1998 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt: La connaissance des coefficients de partage des éléments traces à haute pression et haute température est aujourd'hui requise afin de tester les différents modèles géochimiques d'évolution du manteau terrestre. Etant données les difficultés inhérentes à l'évaluation de ces coefficients de partage lors d'expériences d'équilibre dans différentes conditions (pression, température, composition chimique, ... ), la modélisation de la distribution de ces éléments traces est nécessaire. Cependant, celle-ci passe par la compréhension des phénomènes microscopiques qui contrôlent l'incorporation de l'élément. Ce travail a porté sur la détermination des différents sites d'accueil du chrome trivalent dans des minéraux du manteau à partir de l'étude de sa luminescence. Cette spectroscopie de luminescence, mise en oeuvre à haute pression en cellule à enclumes de diamant, permet de suivre l'évolution des niveaux d'énergie du cr3+ en fonction de la pression. Nous avons ainsi acquis des données de luminescence sur plusieurs phases cristallines de basse pression (spinelles, pyroxènes, forstérite), de haute pression (grenats, ilménite, pérovskites), et sur des verres silicatés de composition chimique simple. Les résultats obtenus sur les minéraux montrent que le Cr3+ s'incorporent majoritairement dans les sites octaédriques, nécessitant, dans certains cas, une compensation locale des charges. Les mécanismes de substitution, mais aussi l'énergie de stabilisation de l'élément trace dans la structure, dépendent alors fortement de la nature des cations disponibles pour assurer l'équilibre électrostatique. Dans les verres, nous mettons en évidence des variations importantes de la distribution de sites d'accueil en fonction de la composition chimique. La modélisation des paramètres thermodynamiques qui participent au partage du chrome à partir de nos données de haute pression est alors discutée
Book Synopsis Evolution tectono-métamorphique d'un segment de croûte continentale archéenne by : Alain Potrel
Download or read book Evolution tectono-métamorphique d'un segment de croûte continentale archéenne written by Alain Potrel and published by . This book was released on 1994 with total page 359 pages. Available in PDF, EPUB and Kindle. Book excerpt: LE BUT DE CETTE THESE EST DE DETERMINER L'EVOLUTION D'UN SEGMENT DE CROUTE CONTINENTALE ARCHEENNE, AINSI QUE L'INFLUENCE DE L'HISTOIRE PROTEROZOIQUE SUR LES CARACTERISTIQUES ORIGINELLES DE LA REGION. LA REGION CHOISIE EST L'AMSAGA (DORSALE REGUIBAT, CRATON OUEST AFRICAIN). L'APPROCHE EMPLOYEE EST PLURIDISCIPLINAIRE. LE PREMIER CHAPITRE CONSTITUE UN RAPPEL DU CONTEXTE GEOLOGIQUE REGIONAL. LE DEUXIEME CHAPITRE MET EN EVIDENCE LES GRANDS TRAITS STRUCTURAUX ET METAMORPHIQUES DE LA REGION. LA CARACTERISATION GEOCHIMIQUE DES PROTOLITHES MAGMATIQUES EST EFFECTUEE AU COURS DU TROISIEME CHAPITRE. LES GRANDES ETAPES GEOCHRONOLOGIQUES SONT DEFINIES AU COURS DU QUATRIEME CHAPITRE. ENFIN, LA SYNTHESE DES RESULTATS OBTENUS EST EFFECTUEE AU COURS DU DERNIER CHAPITRE. UN MODELE GEODYNAMIQUE TENANT COMPTE DE CES RESULTATS ET DES DIFFERENTS MODELES ACTUELLEMENT DEBATTUS SUR L'ARCHEEN EST PROPOSE DANS CETTE CINQUIEME PARTIE
Book Synopsis Evolution structurale et métamorphique de la croûte continentale archéenne (Craton de Dharwar, Inde du Sud) by : Hugues Bouhallier
Download or read book Evolution structurale et métamorphique de la croûte continentale archéenne (Craton de Dharwar, Inde du Sud) written by Hugues Bouhallier and published by . This book was released on 1995 with total page 227 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this thesis is to characterize the tectonie and metamorphie evolution of an Archaean continental segment (>2.5 Ga). The studied area is the Dharwar craton (South lndia) where deeper and deeper structural levels outcrop from North to South. This area has not been affected by post-Archaean deformation. We show that the disclosed strain field is the result of interfering gravitational diapirie bodies and regional shortening. At crustal scale, structures (diapirs and transcurrent shear zones) were developed within a single event that can be dated at around 2.5 Ga. They are synchronous with (i) an episode of juvenile continental crust formation (Closepet batholith) and (ii) regional metamorphism (migmatisation, granulitisation). Strain fields are not consistent with thrusts and stacking structures as usually observed in modern collision belts. The petrographie study reveals that sorne specifie diapiric zones, which underwent fast burial, have recorded a metamorphic prograde history associated with a pressure increase (from 3 to 7-8 kbar). Furthermore, these areas display sorne differences in the fluid phase that seem to be linked with the variations of permeability resulting from the type and the geometry of the metamorphic fabrics. ln summary, the Archaean continental crust of Dharwar craton does not display any structure that could be responsible for the thiekening of the crust. The regional strain results from body forces (diapirism) associated with boundary forces (transcurrent shear zones). The gravitational diapiric instabilities which concern large volumes of crust cannot be the result of crustal thickening and constitute a distinctive feature of Archaean tectonics
Download or read book Geodinamica acta written by and published by . This book was released on 1994 with total page 760 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Geology of the Arab World---An Overview by : Abderrahmane Bendaoud
Download or read book The Geology of the Arab World---An Overview written by Abderrahmane Bendaoud and published by Springer. This book was released on 2018-09-21 with total page 552 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is the result of the work of the first international congress of the ArabGU (Arabian Geosciences Union) which took place in Algiers (Algeria) in February 2016. It presents research articles and review papers on geology of the North Africa and Arabian Middle East . It provides information to the public on various fields of earth sciences and encourages further research in this field in order to attract an international audience.
Book Synopsis GAC Special Paper by : Geological Association of Canada
Download or read book GAC Special Paper written by Geological Association of Canada and published by . This book was released on 1956 with total page 520 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Migmatites and the Origin of Granitic Rocks by : Karl Richard Mehnert
Download or read book Migmatites and the Origin of Granitic Rocks written by Karl Richard Mehnert and published by . This book was released on 1968 with total page 420 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis São Francisco Craton, Eastern Brazil by : Monica Heilbron
Download or read book São Francisco Craton, Eastern Brazil written by Monica Heilbron and published by Springer. This book was released on 2016-12-05 with total page 326 pages. Available in PDF, EPUB and Kindle. Book excerpt: The region of the São Francisco river valley in eastern Brazil encompasses two main components of the geologic framework of the South American continent: the São Francisco craton and its marginal orogenic belts. Cratons, as the oldest, differentiated and relatively stable pieces of the continental lithosphere, preserve a substantial part of the Earth's memory. Orogenic belts, on the other hand, record collisional processes that occurred during a limited time span. Because of their topographic relief, mountain belts developed along craton margins provide however access to rock successions not exposed in the low lands of the adjacent cratons. The combination of geologic information obtained in cratonic domains and their marginal orogenic belts thus form the basis for deciphering substantial periods of Earth’s history. Corresponding to the most intensively studied portion of the Precambrian nucleus of the South American plate, the São Francisco craton and its margins host a rock record that spans from the Paleoarchean to the Cenozoic. Precambrian sedimentary successions that witness ancient Earth processes - many of them of global significance - are especially well preserved and exposed in this region. With all these attributes the São Francisco craton together with its fringing orogenic belts can be viewed as a ‘continent within a continent’ or a ‘continent in miniature’.
Book Synopsis Granulites and Crustal Evolution by : D. Vielzeuf
Download or read book Granulites and Crustal Evolution written by D. Vielzeuf and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 587 pages. Available in PDF, EPUB and Kindle. Book excerpt: Proceedings of the NATO Advanced Research Workshop on Petrology and Geochemistry of Granulites, Clermont-Ferrand, France, September 5-9, 1988
Book Synopsis Forum 1989 by : Geological Survey of Canada. Current Activities Forum
Download or read book Forum 1989 written by Geological Survey of Canada. Current Activities Forum and published by . This book was released on 1989 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis RTMAP Regolith Database Field Book and Users Guide by :
Download or read book RTMAP Regolith Database Field Book and Users Guide written by and published by . This book was released on 2007 with total page 184 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Canadian Journal of Earth Sciences by :
Download or read book Canadian Journal of Earth Sciences written by and published by . This book was released on 1989 with total page 836 pages. Available in PDF, EPUB and Kindle. Book excerpt:
