Abstract

Granitoid plutons of similar (Silurian–Devonian) age intrude four of the tectono-stratigraphic zones of northeastern Newfoundland, and show systematic petrographic and chemical differences corresponding to the tectonic zone in which they occur. Those intruding the dominantly mafic volcanic and sedimentary rocks of the Botwood and Exploits Zones are dominated by calc-alkaline hornblende–biotite bearing granodiorite, quartz diorite and granite. Those intruding the metamorphic rocks of the Gander Zone are two-mica garnet-bearing 'leucogranites' mainly in metasedimentary rocks, and microcline – megacrystic biotite granites and quartz monzonites, mainly in gneissic terrains. The Gander Zone plutons are more silicic and have lower Na/(Na + K) and K/Rb ratios than those of the Botwood and Exploits Zones, although the Rocky Bay pluton, close to the boundary between them, shows some transitional features. This close correspondence between granitoid plutons and crustal rocks of different tectonic settings is taken as evidence for their formation by partial melting of the crustal rocks.

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