The geology of the Western Arm Group, Green Bay, Newfoundland

Marten, B. (Brian Ernest) (1971) The geology of the Western Arm Group, Green Bay, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Western Arm area is underlain by mafic volcanic rocks of early Ordovician age, comprising the Lush's Bight Group succeeded conformably by the Western Arm Group. The Lush's Bight Group is composed of monotonous altered pillow basalts of great but unknown thickness. The study shows that the alteration, which dies out at the top of the Group, is an early event probably related to inherrent heat in the volcanic pile. The Western Arm Group, defined in this study, consists of a lower tuff formation, a middle pillow basalt formation and an upper formation comprising a lower tuff, and an upper agglomerate member. The tuffs are waterlain and include basic, intermediate and dacitic varieties with interbedded slump-breccias and minor chert and argillite horizons. -- Intrusion of gabbroic sills and a small quartz diorite pluton pre-dated a regional deformation. Evidence suggests that the intrusive rocks form a suite genetically related to the volcanism. -- A sub-vertical penetrative cleavage is zonally developed in the lower part of the succession but dies out below the middle of the Western Arm Group. A series of sinistral faults are sub-parallel to the cleavage and are believed to have developed during the folding. Folds are on a large scale, and the Western Arm Group is inferred to lie on the south limb of a major ENE-trending syncline. Metamorphism related to the folding was mainly limited to growth of chlorite and fibrous amphibole on the cleavage planes. -- Two major dextral wrench faults post-date the folding, and may be related to the Birchy Lake fault and the Cabot fault system. -- Comparison with other areas suggests that the Western Arm Group may be correlated with the Cutwell Group and with the Snooks Arm Group.

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