The Dog Bay Line: a major Silurian tectonic boundary in northeast Newfoundland

Abstract

The Dog Bay Line separates different Silurian rock groups in northeast Newfoundland. West of the line, terrestrial volcanic rocks and sandstones (Botwood Group) overlie marine greywackes and conglomerates (Badger Group). East of the line, red sandstones overlie shallow marine shales and limestones (Indian Islands Group). Throughout Dog Bay, the line is marked by a disrupted zone of dark grey to black shales, volcanic rocks, and gabbros. Pervasive dextral, transpressive ductile deformation followed by successively more brittle extension with renewed dextral movements mark the northwest side of the line on the coast.The Dog Bay Line is traceable for 100 km and it is open-ended. Dextral offset is deduced to be many tens of kilometres. The line trends northeast, parallel to outcrop belts, and both the line and outcrop belts are curved eastward at the coast. The Mount Peyton Batholith, dated at 420 ± 8 Ma, apparently cuts the line.The Dog Bay Line occurs within the Dunnage Zone whose Cambrian–Ordovician rocks represent vestiges of the Iapetus Ocean. Northwest of the line, the Silurian rocks were deposited on Ordovician rocks already accreted to Laurentia. Southeast of the line, the Silurian rocks were deposited on Ordovician rocks already amalgamated with the continental Gander Zone. Timing of major movement and a Silurian marine to terrestrial depositional change recorded on both sides of the line agree within error with isotopic ages for the onset of plutonism, regional deformation, and metamorphism in central Newfoundland. The Dog Bay Line may mark the terminal Iapetus Ocean.

Crustal Evolution of the Northeast Laurentian Margin and the Peri-Gondwanan Microcontinent Ganderia Prior to and During Closure of the Iapetus Ocean: Detrital Zircon U–Pb and Hf Isotope Evidence from Newfoundland

“…The Tetagouche -Exploits back-arc basin was closed during Early Silurian time, once again bringing the various fragments of Ganderia back together (440 -430 Ma;van Staal 1994;van Staal et al 2003;Pollock et al 2007). The associated principal suture in Newfoundland is the Dog Bay Line (Williams et al 1993;van Staal et al 2009van Staal et al , 2014.…”

Time-Transgressive Salinic and Acadian Orogenesis, Magmatism and Old Red Sandstone Sedimentation in Newfoundland

“…1) are underlain by Paleozoic and older rocks of the Dunnage and Gander tectonostratigraphic zones (Williams 1978). Tectonostratigraphic zones and subzones were principally defined on their pre-Silurian geological characteristics, although it was later shown that geological contrasts locally continued into the Silurian (Williams et al 1988(Williams et al , 1993Reusch and van Staal 2012). The Dunnage zone mainly comprises Cambro-Ordovician arc terranes and associated slivers of supra-subduction zone ophiolites, which were divided into the Notre Dame subzone (periLaurentian realm) and the Exploits subzone (peri-Gondwanan realm), separated by the Red Indian Line (Williams et al 1988;Williams 1993b;Hibbard et al 2006Hibbard et al , 2007.…”

“…2;Dunning and O'Brien 1989;van Staal 1994;Fyffe et al 2009; (van Staal 1994;van Staal et al 1998). Contrasts in the Ordovician-Silurian geology led to an additional subdivision of the Exploits subzone by Williams et al (1993), and introduction of the Dog Bay Line (Fig. 1).…”

“…His highly insightful stratigraphic and structural studies of the superbly exposed Silurian rocks in the Notre Dame Bay of north-central Newfoundland (Williams 1972(Williams , 1993a, led him to conclude that the Exploits subzone must have been internally divided into two parts separated by a significantly wide Middle Ordovician to Silurian marine seaway that is now sutured along the Dog Bay Line (Williams et al 1993). Williams considered the closure of this vestige of the Iapetus Ocean to be the tectonic cause of the Silurian deformation, although the responsible tectonic processes (i.e.…”

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

“…19B). van Staal et al (1998van Staal et al ( , 2009 interpreted this margin as the back-arc side, and thought that opening of the Tetagouche ocean, splitting the older (now inactive) Penobscot Arc into two parts, starting ~475 Ma, requires this margin not to have become the site of subduction until late Ordovician-early Silurian time, and that subduction ended in the later Silurian by collision of the Exploits subzone with the Ganderia margin (van Staal et al 1998(van Staal et al , 2009, the suture represented now (Williams et al 1993;S.H. Williams et al 1995) by the Dog Bay Line.…”