Structural and metamorphic relationships of pre-Fleur de Lys and Fleur de Lys rocks of the Baie Verte Peninsula, Newfoundland

Abstract

A variable assemblage of remobilized and recrystaltized granites and supracrustal rocks, formerly regarded as metasediments within the stratigraphic succession of the Eocambrian – Early Paleozoic western division of the Fleur de Lys Supergroup, have been recognized to constitute a basement to the Fleur de Lys metasediments. The basement rocks are exposed in (1} a central domal complex and (2) tectonic inliers within the Fleur de Lys metasediments (the cover) as modified isoclinal anticlines. Both the basement and the cover have undergone intense Lower Paleozoic deformation and lower-amphibolite faciès metamorphism.There is a marked petrographic distinction between rocks from the basement and those from the cover. Textures from the latter tend to conform with generally accepted equilibrium textures. Porphyroblastic habit of index minerals is a rule. In contrast, textures from the recrystallized basement rocks are of disequilibrium type, manifested by poikiloblasts and symplectites which have relatively large surface areas. Dendritic, myrmititic, and widmanstatten-like textures are common. Only where fully reconstituted to schists within zones of intense deformation do textures in the basement rocks resemble those in the cover.Tholeiitic dykes, that cut both cover and basement prior to the tectono-metamorphic events, have recrystallized to eclogite – garnet amphibolite assemblages in the basement. These also display the disequilibrium textures. In the cover, the dykes recrystallized to plagiociase amphibolites with equilibrium and porphyroblastic textures. From this it is argued that progressive metamorphism of the cover rocks and retrogressive metamorphism of the basement rocks occurred under similar P–T conditions and that the variable petrography of the basement and cover rock assemblages merely reflects different nucleation and growth kinetics related to relative "dry" and "wet" conditions respectively. The formation of textures within the "dry" basement was kinetically controlled and their morphologies are compatible with those formed by exsolution reaction mechanisms in alloys.