Palaeozoic granitoid plutonism of southern Newfoundland: contrasts in timing, tectonic setting and level of emplacement

• Published in: Transactions of the Royal Society of Edinburgh: Earth Sciences
• Main Authors: Elias, Peter, Strong, D. F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1982
• Subjects: Paleontology; Earth and Planetary Sciences (miscellaneous); Newfoundland
• Online Access: http://dx.doi.org/10.1017/s0263593300009603; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0263593300009603

ABSTRACT Fourteen granitoid plutons studied in the Baie d'Espoir area of southern Newfoundland are divisible into a northern group of eight and a southern group of six. The former tend to be undeformed, have thermal aureoles, and intrude greenschist facies Ordovician and Silurian rocks of the Dunnage zone following a period of folding and thrusting towards the SE. Four Rb-Sr whole-rock isochrons yield similar ages around 430 Ma for these plutons, fixing the deformation within early Silurian times. The latter plutons syntectonically intruded without aureole effects, and are all foliated and elongate parallel to the regional fabric of amphibolite facies gneisses and migmatites of the Gander zone. Whole-rock Rb-Sr isochrons around 350 Ma for both syntectonic and post-tectonic plutons indicate a rapid metamorphism, deformation, intrusion and uplift of the Gander zone in this area. There appear to be no systematic relationships between petrological and geochemical characteristics of the plutons and their tectono-stratigraphic setting. This study conclusively invalidates earlier hypotheses that deformed granitoid rocks of the Gander zone are older than the undeformed granitoids of the Dunnage zone; indeed, just the reverse is true.