Petrochemical and geochronological constraints on the origin of the Sops Arm group, the most westerly Silurian volcano-sedimentary extensional basin on the western Newfoundland composite Laurentian margin

• Published in: Canadian Journal of Earth Sciences
• Main Authors: Sandeman, H.A.I., Honsberger, I.W., Peddle, C., Kamo, S.L., Dunning, G.R.
• Other Authors: Targeted Geoscience Initiative 6, Department of Natural Resources, Government of Newfoundland and Labrador
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2024
• Subjects: Long Steady; Sops Arm; Sops Island; Newfoundland
• Online Access: http://dx.doi.org/10.1139/cjes-2024-0032; https://cdnsciencepub.com/doi/full-xml/10.1139/cjes-2024-0032; https://cdnsciencepub.com/doi/pdf/10.1139/cjes-2024-0032

The Sops Arm group of western Newfoundland, a sequence of subaerial to shallow marine mainly bimodal volcanic rocks and coarse- to fine-grained clastic sedimentary rocks, forms the only known Silurian overstep volcano-sedimentary basin in the Humber Zone of Newfoundland and the northern Appalachians. The group is divided into Western and Eastern sequences, separated by the Long Steady reverse fault, an arcuate, east-dipping, high-strain zone. Mafic volcanic rocks of both sequences are tholeiitic, transitional to calc-alkaline continental basalts derived from an enriched mid-ocean ridge basalt-like source contaminated by older Grenvillian lithosphere. Eastern sequence basalts are more primitive and exhibit less lithospheric contamination. Silicic volcanic rocks are dominantly ferroan, alkaline to strongly peralkaline, within-plate (A2-type) rhyolitic, upper crustal fractionates. Silicic rocks of the Western sequence are Telychian (ca. 434 Ma), whereas rhyolite from the Sops Island volcanic member of the Eastern sequence gave a new high-precision U–Pb zircon age of 429.39 ± 0.57 Ma (Homerian). Telychian and Homerian magmatism and associated sedimentation reflect episodic extension and/or transtension within an intracontinental basin of the eastern Humber Zone. Folding and imbrication of the group is constrained between ca. 401 Ma, the age of a deformed silicic dyke in the Eastern sequence and ca. 374 Ma, a muscovite cooling age from rocks in the Long Steady Fault. The Siluro-Devonian evolution of the group is consistent with widespread post-Salinic extension, far-field Acadian and Neoacadian deformation, and the emplacement of gold mineralization across the Dunnage Zone of Newfoundland.