Low-Potash Lush's Bight Tholeiites: Ancient Oceanic Crust in Newfoundland?

Abstract

The Lush's Bight Group of north-central Newfoundland consists mainly of regionally metamorphosed pillowed basalts. Mafic dikes and sills, comagmatic with the basalts, are abundant and dioritic stocks and silicic igneous rocks constitute a small portion of the group. Most rocks belong to a tholeiitic suite derived from low-K tholeiite that has a trace element content similar to oceanic tholeiite. A few rocks are slightly alkaline, implying that alkali basalt may have contributed to the volcanic pile. The thickness, chemical composition, and lithology of the group suggest it represents the upper (dominantly volcanic) part of layer two of oceanic crust. Alternatively, formation as a tholeiitic shield beneath a mid-ocean volcanic island is suggested by the alkaline affinities of some rocks and by a thick pyroclastic sequence that conformably overlies the group.The Lush's Bight Group contains many volcanogenic iron-copper sulfide occurrences.Mid-ocean ridges are recognized as magmatically dominated environments in which hydrothermal fluids of plutonic and volcanic origin might constitute ore fluids.