Late Middle Ordovician olistostrome formation and magmatism along the Red Indian Line, the Laurentian arc – Gondwanan arc boundary, at Sops Head, Newfoundland

Abstract

The Sops Head Complex of Badger Bay, central Newfoundland, includes olistostromal and tectonized mélanges and marks the Red Indian Line, the boundary between the peri-Gondwanan Exploits and peri-Laurentian Notre Dame subzones of the oceanic Dunnage Zone. Basalts in the olistostromal mélange preserve peperitic contacts with mudstone and limestone within slumped sedimentary units, demonstrating that magmatism was coeval with olistostrome formation. Conodonts from the limestones date these events as late Darriwilian ("Llandeilian," Middle Ordovician) in age. The conodont fauna consists entirely of North Atlantic Faunal Realm elements, suggesting a peri-Gondwanan or mid-Iapetan provenance for limestone of the Sops Head Complex. Basalt geochemistry suggests magmatism in a mature volcanic-arc to back-arc setting. The Sops Head Complex shows similarities in age, provenance, and stratigraphic setting to the Dunnage Mélange, suggesting that the two units are correlative.