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.

Lawrence Head Volcanics and Dunnage Mélange, Newfoundland Appalachians: Origin by Ordovician Ridge Subduction or in Back-Arc Rift?

“…It seems possible as an alternative that the disrupted materials on Camel and Knight Islands, located near or at the northwestern margin of the western Dunnage Mélange, were generated separately from, and formed at a later time than the bulk of the western Dunnage, which is not elsewhere reported to contain materials of such a young inferred age. In this context, we reject the hypothesis of McConnell et al (2002) that the Dunnage Mélange is laterally equivalent to the Boones Point-Sops Head Mélange, because it is clear, as reported by Nelson (1979Nelson ( , 1981, that a significant part of the matrix and many of the blocks in the Boones Point-Sops Head are quartzrich arenite and associated argillite identical to those in the late Ordovician-early Silurian Point Leamington and Gull Island Formations. The Boones Point-Sops Head mélange must be of that age or younger, even though it contains blocks, or olistostromic remnants, containing older Ordovician fossils also reported by Nelson (1981).…”

Evidence for seamount accretion to a peri-Laurentian arc during closure of Iapetus 1This article is one of a series of papers published in CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.2 Geological Survey of Canada Contribution 20100465.

“…These are interpreted as large knockers in the mélange, although it should be noted that some mafic rocks form basalt-shale pepperites along strike to the northeast (McConnell et al 2002) and, as such, form part of the stratigraphy. The mafic rocks (Fig.…”

“…2) and is characterized by tholeiitic mafic volcanic rocks, minor felsic volcanic rocks, and locally abundant sedimentary and epiclastic rocks (Bostock 1988). It lies immediately west of the Sop's HeadBoones Point Complex, which is a tectonic mélange characterized by highly deformed dark grey to black shale with basaltic knockers (O'Brien 2001(O'Brien , 2003McConnell et al 2002). The Crescent Lake terrane is separated from the calc-alkaline rocks of the Mud Pond terrane by the Crescent Lake thrust (Kerr 1996), which appears to be an early mylonite zone that is overprinted by late brittle deformation (Kerr 1996).…”

“…To the southeast of the Red Indian Line, the Wild Bight Group comprises arcderived epiclastic and sedimentary rocks, as well as minor volcanic and plutonic rocks (O'Brien 2001). Adjacent to the Red Indian Line, these rocks occur as broken formation and mél-ange (i.e., Sop's Head -Boones Point Complex) overlain by syn-collisional, transgressive Katian black shale (McConnell et al 2002). To the northwest of the Red Indian Line, the periLaurentian Robert's Arm Group (Bostock 1988) is characterized by Late Dapingian to Darriwilian (i.e., Arenig to Llanvirn of McKerrow and van Staal 2000) mafic and felsic volcanic arc rocks with interlayered sedimentary rocks.…”

From Large Zones to Small Terranes to Detailed Reconstruction of an Early to Middle Ordovician Arc–Backarc System Preserved Along the Iapetus Suture Zone: A Legacy of Hank Williams

“…Abundant late Middle to Late Ordovician sedimentary rocks and mélange occur along the Red Indian Line; however, these rocks were mainly deposited in syn-collisonal basins and became imbricated during the subsequent increments of arc-arc collision (McConnell et al 2002;Waldron et al 2012). Hence, in general, these rocks do not represent remnants of the oceanic accretionary complexes.…”