Abstracts
Abstract
This paper is concerned with two aspects of folding and cleavage development in the "Carmanvllle Ophlolitic MSlange" of Newfoundland. First it is concerned with the problem of the timing of deformation relative to llthification and metamorphism, and second it is concerned with development of the cleavage.
According to previous interpretation the cleavage and associated folds are a product of soft-sediment deformation. The cleavage however, Is a second generation axial-plane structure and microstructural observations, presented here, show it to be later than the peak of metamorphism. Further, F2 folds occur in quartz veins where they are associated with a strong crystallographic fabric. The second generation structures are thus a product of hard-rock deformation. The origin of the F] folds however, remains equivocal.
Dyke-like structures previously attributed to migration of thixotroplc melange units are also post llthification and are a product of faulting and metamorphic differentiation. The S2 cleavage Is largely a product of rotation. In the coarser sediments whole clasts are rotated into the cleavage plane. Within shale clasts and in shale beds the cleavage has developed principally as a result of transposition by mlcrofolding. Folding fabrics have been modi-fled by grain growth.
RESUME
La presente etude traite de deux questions reli£es au dgvelopperaent du plissement et du clivage dans le "melange ophlolitique de Carmanvllle" (Terre-Neuve): 1) de la chronologic respective de la llthification et du mStamorphisme par rapport a la deformation et 2) du dgveloppement du clivage.
Auparavant, on attribuait le clivage et les plis a la deformation de sediments non-consolidSs. II appert cependant que le clivage correspond a un plan axial de deuxiSme generation et les elements structuraux microscopiques indlquent que ce clivage est posterleur a la phase maximal du mStamorphisme. De plus, les plis F2 se retrouvent dans des velnes de quartz ou lis sont assocles a une trame cristsllographique tres bien deflnie. Les structures de deuxiSme generation provlennent done d'une deformation llthlque. L'origine des plis Fj demeure toutefois incertaine. Dea structures en forme de dykes que l'on attribuait jadis a des phenomenes de thixotropie au sein du melange sont en fait le resultat de failles et de differentiation metamorphique survenues apres la llthification des sediments.
Le clivage Sz est principalement dO a un mouvement de rotation et dans les sediments grosslers, des fragments entiers ont ete reorientes selon le plan de clivage. Le clivage qui affecte les lits et les fragments de schlste argileux est surtout le resultat d'une transposition par micro-pllssement. Les trames de plissement ont ete modiflees par la croissance des grains.
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