Dunnage Melange and Subduction of the Protacadic Ocean Northeast Newfoundland

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Abstract
The Dunnage melange outcrop, 10 km wide between the Dildo and Holmes Point faults on the north and south, is truncated eastward by the northeast-trending Reach fault. The matrix of laminated black and greenish argillite has interbeds of graded graywacke, tuff, and lava. A limestone layer has Middle Cambrian fossils. Olistostromes are interbedded. Boulders are mainly graywacke and pillow lava, with less abundant plutonic and volcanic rocks, chert and dolomite; spheroidal masses exceed diameters of 10 m; facings are rather random. Southeast-dipping cleavage is isoclinally folded; primary structures (including bedding) rarely are apparent. Northward on New World Island between the Dildo and Lukes Arm faults lie several sequences of Ordovician volcanic and sedimentary rocks and Silurian sedimentary rocks, separated northward by angular unconformity. Beyond is the complex Lushs Bight terrane. South of the Holmes Point fault are volcanic and sedimentary rocks of the Campbellton sequence. The Lukes Arm and Reach faults, transcurrent, may have displacements of scores or hundreds of kilometres. Ordovician and Devonian stocks intrude the melange. Faults cut Devonian instrusions; Jurassic dikes cut the Dildo fault. The Campbellton sequence may have oceanic crust; the New World Island sequences contain island arc associated volcanic rocks. The Dunnage is interpreted as forming in a northwest-dipping subduction zone margining the Ordovician Protacadic Ocean. The melange was formed near the surface of a submarine trench into which olistostromes and olistoliths moved from the island arc terrane to the northwest. The melange was not made chaotic within the subduction zone. Relations to isolated segments of Protacadic Ocean crust elsewhere depend on palinspastic restorations of fault-displaced structural blocks.

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