Maps 1-4 are inserts within the thesis back cover / The Cambro-Ordovician sequence at St. Simon, Québec, was divided informally into ten horizons by Mathey (1970). The most prominent lithologies within the horizons are pelites, feldspathic sandstones and petromict conglomerates. One horizon 50 metres thick of feldspathic sandstones and conglomerates, described in this study, consists of three large fining upward sequences·. The fining upward sequences are defined by the occurrence of five facies. These facies are: poorly sorted coarse conglomerates, well sorted coarse conglomerates, medium conglomerates with scattered pebbles and boulders, fine conglomerate with scattered pebbles and boulders and coarse sandstones. The base of each sequence is characterized by the occurrence of coarse conglomerates; the top is characterized by the occurrence of fine conglomerates and coarse sandstones. Rarely do the coarse conglomerates grade into thick developments of medium and fine conglomerates. The fine conglomerates grade in places into coarse sandstones, although generally the coarse sandstones have sharp bases. The conglomerates display sharp bases, normal and inverse grading, grain imbrication and orientation. The long axes of the grains, which define the orientation are parallel to, and not transverse to the flow direction suggested by the imbrication. To produce these features it is suggested that turbulence and dispersive pressures were operative within the flow. If the pebbles had moved as bed load material, they would have come to rest with their long axes transverse and not parallel to the flow direction suggested by the imbrication. The term "fluxoturbidite" (Dzulynski et al., 1959) has been applied to some coarse grained deposits in geosynclinal sequences. The characteristic features of "fluxoturbidites" are their unusually coarse grain size, thick irregular bedding with associated slump structures and poorly developed grading. The differences between the conglomerates described in this study and the typical "fluxoturbidite" preclude the use of this term to describe the deposits described by the author. It is suggested that the conglomerates were deposited upon a submarine fan complex by currents which flowed parallel to the present tectonic axes. / Thesis / Master of Science (MSc)

Coronitic metagabbros occur as small isolated bodies along the contact between the Mariánské Lázně and the Teplá crystalline complexesin the NW of the Bohemian Massif. Metagabbros show variable metamorphic and textural characteristics with respect to their magmatic mineral assemblage and degree of metamorphism. The aim of this study is to characterize mineralogical, chemical, and microstructural changes related to metamorphic changes in selected representative samples. In addition, the associated calculation of P-T conditions can help to clarify the evolution of the boundary of both units as well as to provide constraints on formation of corona microstructures. Magmatic mineral assemblages in the metagabbros formed by plagiocase, orthopyroxene, clinopyroxene, amphibole, biotite and ilmenite occasionally olivine,spinel or quartz are generally well preserved. Metamorphism is mainly reflected by formation of single or multiple coronas at the contact of plagioclase with other primary minerals, the most common constuents are amphibole, garnet and orthopyroxene. Progressive breakdown of the magmatic plagioklase is reflected by formation of mixture An40 and An90 plagioclase associated with spinel,corundum and occasionally kyanite. According to chemical composition metagabbros follow tholeiitic trend and...

Ce travail de thèse est essentiellement consacré à l'investigation des populations de zircons et de l'âge des protolithes des formations varisques grâce à une datation U-Pb in situ systématique par le couplage Laser/MC-ICPMS, dans des formations orthodérivées, métasédimentaires et magmatiques tardi-orogéniques du Massif Central français et du domaine Sud armoricain. Cette étude a montré que les populations de zircons sont largement héritées, s'étalant de l'Archéen au Paléozoïque inférieur. L'ensemble des pics d'âges obtenus, ainsi que l'absence d'âge mésoprotérozoïque (1.7-1.1 Ga) accréditent l'affinité gondwanienne de ces formations. Des âges maximum de dépôt sont proposés pour les métasédiments des principales unités définies dans le Massif Central. Ces âges maximum de dépôt sont décroissants suivant l'empilement lithotectonique reconnu. En marge de ce travail, nous avons pu déterminer que les âges de mise en place des granitoïdes du Sillon Houiller (Massif Central) et du golfe du Morbihan se situent aux alentours de 300 Ma. Des âges plus anciens, principalement obtenus sur monazite lors d'études antérieures, ont été réinterprétés comme des âges hérités. L'abondance de zircons hérités d'âge ordovicien et néoprotérozoïque met en évidence la large contribution des métagranites et métasédiments fertiles de ces périodes dans la source des granites tardi-orogéniques varisques. Le granite de Sarzeau expose de plus les traces d'un protolithe silurien. Le recyclage de la croûte continentale est caractérisé par une évolution polycyclique au cours de l'orogénèse varisque, avec tout d'abord l'érosion de formations du craton africain, majoritairement d'âge néoprotérozoïque, puis la superposition des événements magmatiques cambro-ordoviciens et syn-orogéniques varisques.