Geology of the Annieopsquotch Complex, southwest Newfoundland

• Published in: Canadian Journal of Earth Sciences
• Main Author: Dunning, G. R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1987
• Subjects: Newfoundland
• Online Access: http://dx.doi.org/10.1139/e87-112; http://www.nrcresearchpress.com/doi/pdf/10.1139/e87-112

The Annieopsquotch Complex is an ophiolite that forms the Annieopsquotch Mountains of southwest Newfoundland. It contains rocks of the critical zone, gabbro zone (2.3 km thick), sheeted dyke zone (1.5 km thick), and pillow lava zone of a typical ophiolite. The zones trend northeast, face and dip southeast at approximately 50–70°, and are offset by faults.Cumulate rocks of the critical zone preserve graded layers, trough structures, and slump folds and locally are metamorphosed and deformed. The gabbro zone contains many textural varieties of gabbro, pegmatitic pods, layering, trondhjemite pods, and amphibolite near the base. It passes through a transition zone to a sheeted dyke zone that extends the full strike length of the ophiolite. Dykes trend northwest and are aphyric or plagioclase-phyric diabase. The pillow lava zone, besides pillow basalt, contains minor pillow breccia, hyaloclastite, and chert.The Annieopsquotch Complex is faulted against an Ordovician tonalite terrane to the northwest across the Lloyds River Fault and against the Victoria Lake Group to the southeast. It is cut by dykes and sills correlated with both these units. The complex is cut by two Late Ordovician gabbro–diorite intrusions and a granite of presumed Devonian age and is unconformably overlain by Early Silurian terrestrial sedimentary and volcanic rocks.Major-, trace-element, and clinopyroxene chemistry of the complex and other ophiolitic fragments between Buchans and King George IV Lake is typical of N-type MORB. These likely constituted one allochthon of Iapetus Ocean or marginal basin crust emplaced over the Ordovician continental margin of North America during the Taconic Orogeny.