DANS LE NORD-EST DU MASSIF CENTRAL, LES SERIES DEVONO-DINANTIENNES MONTRENT UNE GRANDE DIVERSITE LITHOLOGIQUE ET STRUCTURALE. DANS LE MORVAN, LA SERIE DEVONIENNE VOLCANIQUE ET SEDIMENTAIRE, DE LA SOMME, CORRESPOND A UN ARC MAGMATIQUE INSTALLE A L'APLOMB DE LA ZONE DE SUBDUCTION DE L'OCEAN RHEIQUE. DANS LA REGION DE LA LOIRE, LA PRESENCE D'UN MAGMATISME BIMODAL THOLEITIQUE, PERMET DE RELIER LA GENESE DES FORMATIONS VOLCANIQUES, VOLCANO-SEDIMENTAIRES ET PLUTONIQUES DE L'ENSEMBLE BREVENNE-VIOLAY-BEAUJOLAIS A L'EXISTENCE D'UNE ZONE DE RIFTING, LOCALEMENT OCEANIQUE. LE BASSIN BREVENNE-VIOLAY-BEAUJOLAIS, FORME AU DEVONIEN SUPERIEUR, A CONNU ENSUITE UNE EVOLUTION TECTONO-METAMORPHIQUE COMPLEXE, AYANT CONDUIT A SA FERMETURE AVANT LE VISEEN MOYEN. L'ANALYSE STRUCTURALE DES FORMATIONS ANTE-VISEEN MOYEN DE LA REGION DE LA LOIRE MONTRE UNE EVOLUTION TECTONIQUE POLYPHASEE, ASSOCIEE A UN METAMORPHISME PROGRADE DE FACIES SCHISTE-VERT A AMPHIBOLITE. LE PREMIER EVENEMENT TECTONIQUE, D1, D'AGE PROBABLE FINI-DEVONIEN A TOURNAISIEN, SE TRADUIT PAR UNE FOLIATION REGIONALE SUB-HORIZONTALE ET UNE LINEATION D'ETIREMENT ORIENTEE NW-SE A N-S. PARTICULIEREMENT BIEN MARQUEE DANS LE GROUPE DE VIOLAY, ELLE CORRESPOND AU CHEVAUCHEMENT DES UNITES DEVONIENNES SUR LE SOCLE GNEISSIQUE D'AFFOUX. LE SECOND EVENEMENT, D2, FINI-TOURNAISIEN A VISEEN INFERIEUR, REPREND LA FOLIATION S1 ET EST RESPONSABLE D'UNE LINEATION D'ETIREMENT ORIENTEE NE-SW A E-W. LES CRITERES CINEMATIQUES ASSOCIES A CETTE DEFORMATION INDIQUENT DES SENS DE CISAILLEMENTS DIFFERENTS SUIVANT LES SECTEURS. LOCALEMENT, D2 S'AVERE MEME ETRE COAXIALE. LA SIGNIFICATION EXACTE DE CETTE DEFORMATION RESTE A DEFINIR. LA MISE EN EVIDENCE DANS CETTE PARTIE DU MASSIF CENTRAL D'UN EPISODE COMPRESSIF A VERGENCE NW, FINI-DEVONIEN A TOURNAISIEN, FAISANT SUITE A UNE PERIODE DE DISTENSION, A L'ORIGINE DE LA FORMATION DU RIFT DE LA BREVENNE, AU DEVONIEN SUPERIEUR, CONSTITUE UN ARGUMENT EN FAVEUR D'UNE EVOLUTION POLYCYCLIQUE DE LA CHAINE HERCYNIENNE.

Les reconstitutions paléobathymetriques des domaines océaniques permettent d'examiner non seulement la profondeur du plancher mais aussi la géometrie et l'évolution des chenaux de communication entre les différents bassins océaniques. Connaitre la bathymétrie est indispensable pour comprendre l'organisation et la distribution des corps sédimentaires et les répartitions des micro-organismes. L'étude des circulations océaniques et des concentrations de matières minérales associées suppose que soit établie une carte bathymétrique. La carte bathymétrique obtenue par la méthode exposée donne une profondeur génèrale préliminaire. Elle peut servir de base à des études de la sédimentation et des courants. Appliquée a la Téthys toute entière, cette méthode permet de caractériser au mieux la morphologie des seuils caraibes, méditerraneen, et indonésien et les circulations entre les bassins océaniques qu'ils séparent. L'utilisation d'un modèle numérique de circulations océaniques permet notamment de mettre en évidence l'influence de la topographie sur la distribution et la vitesse des courants. Un modèle de circulations océaniques au Tithonique supérieur est proposé et permet de localiser les zones potentielles d'upwellings

Gneiss domes are structural features associated with orogens worldwide. This study provides a structural analysis of the domes of the Harvey Cardiff Domain, associated with the Grenville Orogeny. Structural data and oriented samples were collected during field work in the summer of 2012. These were used in combination with published and unpublished foliation and lineation data to analyze structural patterns and determine a mechanism of formation for the domes. The end member scenarios for dome formation were taken from the gneiss dome classification scheme devised by Yin (2004). Most of these mechanisms were eliminated based on a lack of necessary large scale geologic features in the region of the study area. An analysis of the foliation pattern of the Cheddar and Cardiff domes was most consistent with formation by diapirism. However, the foliation patterns of the domes differ from the expected diapiric pattern, and seems to represent a non-horizontal slice through a diapir, cutting through a diapir neck in the north and a diapir hat in the south. This pattern can also be explained by rotation of diapiric foliation due to strain induced by the main orogenic event. This hypothesis was tested using COMSOL, a finite elastic strain model, and found to be realistic. With the methods used in this study it is not possible to tell whether this rotation occurred after or during dome emplacement.

The earth was shown in the last century to have a surface layer composed of large plates. Plate tectonics is the study of the movement and stresses in the individual plates that make up the complete surface of the world's sphere. Two types of earthquakes are observed in the surface plates, interplate and intraplate earthquakes, which are classified, based on the location of the origin of an earthquake either between two plates or within the plate respectively. Limited work has been completed on the definition of the boundary region between the plates from which interplate earthquakes originate, other than the recent work on the Mid Atlantic Ridge, defined at two degrees and the subsequent work to look at the applicability of this degree based definition. Others suggested an alternative view of a constant width for the interplate region in recent work at Texas A&M University. The objective of the paper is to determine whether the assumption of a linear width of the region along the tectonic plate boundaries to classify earthquakes as interplate and intraplate earthquakes using accepted statistical criteria provides a better fit to the data than the constant degree definition. There are three types of interplate boundaries defined by the relative movement of the two plates to each other, which further complicates this study. The study used a nonrandom analysis of regions of the different types of boundary to compare the rate and decay of the intraplate earthquakes from a notional centerline for the known boundaries. The study used GIS software and EXCEL for the statistical analysis component of the research work. The results show that a constant width definition provides a number of advantages in determining the relative definition of interplate and intraplate earthquakes when compared to the constant degree definition developed for work on the Mid Atlantic Ridge. Further research is suggested on a randomly selected set of study sites to improve the reliability and quality of the statistical work for each type of the boundary of the tectonic plates.

Le massif de Sixt constitue la couverture sedimentaire de la retombée Ouest du massif cristallin des Aiguilles Rouges . A ce titre, il occupe dans la zone externe des Alpes, la même place que le Vercors, la Chartreuse , les Bauges ou les Aravis. Pourtant, en se déplaçant du Sud au nord dans la zone subalpine, on constate une complication des structures et une tendance à la tectonique souple . Insensiblement la couverture décollée et plissée des environs de Grenoble va passer à des structures d 'amplitude plus forte pour aboutir aux nappes helvétiques . Par sa position, le massif de Sixt semble , alors , devoir prendre un caractère propre : celui de zone de transition . Les travaux de J.ROSSET sur la chaîne des Aravis (1957) ont montré que la tectonique de cette région s 'expliquait t r è s bien sans faire intervenir la notion de nappe : or , et nous l e verrons par la suite , j 'ai pu faire de nombreuses constatations analogues à celles de J .ROSSET . Pour l ' ensemble du massif de Sixt , plusieurs problèmes se sont posés : fallait - il toujours considérer les plis du Jurassique supérieur du Fond de la Combe comme eprésentant le flanc inverse d ' une nappe, et la "fenêtre du Pelly" comme un témoin de l'autochtone? Mon collègue X.PIERRE travaillant plus au Sud, s'est heurté aux mêmes difficultés: son étude s'est orientée sur l a "fenêtre des Fonts" et sur la présence d 'un éventuel Jurassique au contact du Cristallin des Aiguilles Rouges près des chalets de Moëde,

The Gull Rapids area, Manitoba, lies on the Superior craton margin and forms part of the Superior Boundary Zone (SBZ), a major collisional zone between the Archean Superior craton and the adjacent Paleoproterozoic Trans-Hudson Orogen. There are two main rock assemblages at Gull Rapids: orthogneisses (of possible Split Lake Block origin) and supracrustal rocks (metavolcanic and metasedimentary). Late, crosscutting felsic and mafic intrusive bodies (mostly dykes and sills) are used to constrain the relative and absolute timing of deformation and metamorphism. <br /><br /> The Gull Rapids area records a complex tectonic history. The area experienced four generations of Neoarchean ductile and brittle deformation (G1 ? G4) and one of Paleoproterozoic ductile-brittle deformation (G5). G1 deformation produced the main foliation in the map area, as well as local isoclinal folding which may be related to an early shearing event. M1a prograde mid-amphibolite facies metamorphism is contemporaneous with the early stages of G1. Widespread, tight to isoclinal sheath folding during G2 was recorded in the supracrustal assemblage, and is the result of southwest-side-up, dextral shearing during the early shearing event. A ca. 2. 68 Ga widespread phase of granitoid intrusion was emplaced late-G1 to early-G2, and is rich in metamorphic minerals that record conditions of M1b upper-amphibolite facies peak metamorphism. M1b metamorphism, late-G1 to early-G2 deformation, and intrusion of this felsic phase are contemporaneous. M2 retrograde metamorphism to mid-amphibolite facies was recorded sometime after M1b. G1 and G2 structures were re-folded during G3, which was then followed by G4 southwest-side-up, dextral and sinistral shearing, contemporaneous with late pegmatite intrusion at ca. 2. 61 Ga. This was followed by mafic dyke emplacement at ca. 2. 10 Ga, and then by G5 sinistral and dextral shearing and M3 greenschist facies metamorphism or hydrothermal alteration at ca. 1. 80 Ga. <br /><br /> Deformation and metamorphism at Gull Rapids post-dates emplacement and deposition of gneissic and supracrustal rocks, respectively. This deformation and metamorphism, except for G5 and M3, is Neoarchean (ca. 2. 68?2. 61 Ga), and represents a significant movement of crustal blocks: km-scale shearing of the supracrustal assemblage and consequent uplift of the Split Lake Block. Late deformation and metamorphism (G5, M3) may be related to the Paleoproterozoic Trans-Hudson orogeny. The Neoarchean and Paleoproterozoic zircon populations in the geochronological data suggest that the Gull Rapids area largely experienced Neoarchean deformation and metamorphism with a weak Paleoproterozoic overprint. All of the evidence presented above suggests that the Gull Rapids area lies in a part of the Superior Boundary Zone, yet does not lie at the exact margin of the Superior craton, and therefore does not mark the Archean-Proterozoic boundary proper in northeastern Manitoba.

The Gull Rapids area, Manitoba, lies on the Superior craton margin and forms part of the Superior Boundary Zone (SBZ), a major collisional zone between the Archean Superior craton and the adjacent Paleoproterozoic Trans-Hudson Orogen. There are two main rock assemblages at Gull Rapids: orthogneisses (of possible Split Lake Block origin) and supracrustal rocks (metavolcanic and metasedimentary). Late, crosscutting felsic and mafic intrusive bodies (mostly dykes and sills) are used to constrain the relative and absolute timing of deformation and metamorphism. <br /><br /> The Gull Rapids area records a complex tectonic history. The area experienced four generations of Neoarchean ductile and brittle deformation (G1 ? G4) and one of Paleoproterozoic ductile-brittle deformation (G5). G1 deformation produced the main foliation in the map area, as well as local isoclinal folding which may be related to an early shearing event. M1a prograde mid-amphibolite facies metamorphism is contemporaneous with the early stages of G1. Widespread, tight to isoclinal sheath folding during G2 was recorded in the supracrustal assemblage, and is the result of southwest-side-up, dextral shearing during the early shearing event. A ca. 2. 68 Ga widespread phase of granitoid intrusion was emplaced late-G1 to early-G2, and is rich in metamorphic minerals that record conditions of M1b upper-amphibolite facies peak metamorphism. M1b metamorphism, late-G1 to early-G2 deformation, and intrusion of this felsic phase are contemporaneous. M2 retrograde metamorphism to mid-amphibolite facies was recorded sometime after M1b. G1 and G2 structures were re-folded during G3, which was then followed by G4 southwest-side-up, dextral and sinistral shearing, contemporaneous with late pegmatite intrusion at ca. 2. 61 Ga. This was followed by mafic dyke emplacement at ca. 2. 10 Ga, and then by G5 sinistral and dextral shearing and M3 greenschist facies metamorphism or hydrothermal alteration at ca. 1. 80 Ga. <br /><br /> Deformation and metamorphism at Gull Rapids post-dates emplacement and deposition of gneissic and supracrustal rocks, respectively. This deformation and metamorphism, except for G5 and M3, is Neoarchean (ca. 2. 68?2. 61 Ga), and represents a significant movement of crustal blocks: km-scale shearing of the supracrustal assemblage and consequent uplift of the Split Lake Block. Late deformation and metamorphism (G5, M3) may be related to the Paleoproterozoic Trans-Hudson orogeny. The Neoarchean and Paleoproterozoic zircon populations in the geochronological data suggest that the Gull Rapids area largely experienced Neoarchean deformation and metamorphism with a weak Paleoproterozoic overprint. All of the evidence presented above suggests that the Gull Rapids area lies in a part of the Superior Boundary Zone, yet does not lie at the exact margin of the Superior craton, and therefore does not mark the Archean-Proterozoic boundary proper in northeastern Manitoba.

No description available.

Approximately 720 square miles of digital 3-dimensional seismic data covering the eastern Mississippi Canyon area, Gulf of Mexico, continental shelf was used to examine the structural and stratigraphic evolution of the geology in the study area. The analysis focused on salt tectonics and sequence stratigraphy to develop a geologic model for the study area and its potential impact on engineering and geologic hazards. Salt in the study area was found to be established structural end-members derived from shallow-emplaced salt sheets. The transition from regional to local salt tectonics was identified through structural deformation of the stratigraphic section on the seismic data and occurred no later than ~450,000 years ago. From ~450,000 years to present, slope depositional processes have become the dominant geologic process in the study area. Six stratigraphic sequences (I-VI) were identified in the study area and found to correlate with sequences previously defined for the Eastern Mississippi Fan. Condensed sections were the key to the correlation. The sequence stratigraphy for the Eastern Mississippi Fan can be extended ~28 miles west, adding another ~720 square miles to the interpreted Fan. A previously defined channel within the Eastern Fan was identified in the study area and extended the channel ~28 miles west. Previous work on the Eastern Fan identified the source of the Fan to be the Mobile River; however, extending the channel west suggests the sediment source to be from the Mississippi River, not the Mobile River. Further evidence for this was found in ponded turbidites whose source has been previously established as the Mississippi River. Ages of the stratigraphic sequences were compared to changes in eustatic sea level. The formation stratigraphic sequences appear decoupled from sea level change with ?pseudo-highstands? forming condensed sections during pronounced Pleistocene sea level lowstands. Miocene and Pleistocene depositional analogues suggest the location of the shifting Mississippi River Pleistocene depocenter is a more dominant influence on sequence formation. Thus, the application of traditional sequence interpretation with respect to sea level change should be reconsidered to also account for the shifting depocenter for both the study area as well as the broader Eastern Mississippi Fan.

Ce travail de thèse a pour objectifs d'analyser la tectonique active et son héritage structural<br />dans l'Alborz Central - chaîne de montagne active située au Nord de l'Iran et bordant le bassin Sud-<br />Caspien - et de caractériser l'aléa sismique dans la région de Téhéran, située sur le front Sud de<br />cette chaîne, où vivent quinze millions d'habitants. Les méthodes d'analyse misent en oeuvre sont<br />celles de l'étude morphotectonique et de la paléosismologie (images satellitaires, photos aériennes,<br />Modèles Numériques de terrains, géomorphologie, géologie du quaternaire, tranchées). Après un<br />rappel du cadre géologique et structural, une nouvelle synthèse paléogéographique à l'échelle de<br />l'Alborz – resitué dans le contexte de convergence entre l'Arabie et l'Eurasie - est proposée à partir de<br />l'analyse des structures et de leur réactivation au cours du temps. L'analyse de la cinématique des<br />failles actives, en particulier dans la zone interne de l'Alborz Central, permet de proposer un nouveau<br />modèle géodynamique de la région Sud-Caspienne. Un premier bilan de l'alea sismique (source,<br />vitesse, magnitude, intervalle de récurrence) est dressé pour la région de Téhéran.