Abstract

The Lushs Bight Group in the Pilleys Island area of central Newfoundland consists of basaltic pyroclastic rocks, pillow lavas, and sheeted diabase dikes, cut by plugs of gabbro and quartz diorite which have produced local amphibolitization. The Lushs Bight rocks are commonly gently folded but locally strongly schistose along shear belts and fault zones and around the intrusive bodies. The sheeted diabase has been metamorphosed to the upper greenschist (actinolite) facies, while in the flows, chlorite is dominant over actinolite, indicating a lower grade of metamorphism.

The Roberts Arm Group consists of basaltic pillow lava locally overlain by dacite representing volcanic centers. This group has a strong bimodal chemistry; it differs from the Lushs Bight Group in the presence of dacite, in a lack of actinolite-grade metamorphism, and in that the basalt of the Roberts Arm Group is richer in K2O, Na2O, TiO2, Ba, Rb, and Zr, and poorer in CaO.

These data are taken as evidence that the Roberts Arm volcanic rocks possibly represent an island-arc suite which was deposited upon oceanic crust now represented by the Lushs Bight Group.

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