Tectonic implications of early silurian thrust imbrication of the northern exploits subzone, Central Newfoundland

Central Newfoundland's Dunnage Zone contains a composite assemblage of island arc and oceanic rocks formed in the Paleozoic Iapetus Ocean. Two different and perhaps unrelated Late Cambrian-Middle Ordovician volcanic belts (Lush's Bight and Robert's Arm belts, and their correlatives) are preserved in the Notre Dame Subzone, and are interpreted to represent arc and back-arc basin sequences developed; (1) adjacent to the Laurentian margin of Iapetus and (2) in the intraoceanic realm of the 4000 km wide Paleozoic ocean. Paleozoic paleogeographic reconstructions suggest that the Exploits Subzone contains volcanic and sedimentary rocks originally deposited in a third arc located between the intraoceanic arc (Robert's Arm Belt) and the Peruvian promontory of Gondwana. The New Bay Pond area is located within the northern Exploits Subzone, and preserves an imbricate thrust stack formed during Late Ordovician/Early Silurian southeastward-directed thrusting. Thrust-load related subsidence led to deposition of cherts and argillites overlain by a southeastward-prograding wedge of orogenic flysch and molasse in a foreland trough. Late Ordovician-Early Silurian structural disruption of the flysch/molasse sequence and older strata of the northern Exploits Subzone, by a series of thrust faults, place Middle Ordovician rocks over the younger flysch, and formed a new, southeast-vergent accretionary wedge. This event records the emplacement of the Exploits Subzone over Gondwanan continental margin rocks of the Gander Zone, soon after the Notre Dame Subzone collided with the Appalachian margin of Laurentia. Continued closure of Iapetus brought together the collisionally modified margins of Gondwana and Laurentia. The Exploits Subzone is cut by numerous Silurian-mid Devonian predominantly dextral strike-slip faults, suggesting that this convergence involved a significant component of dextral transpression. Several pull-apart basins are located along these strike-slip faults, and are filled by Silurian volcano-sedimentary sequences. These faults formed in response to the counter-clockwise rotation of Gondwana, juxtaposing the Avolonian margin of Gondwana with the Appalachian margin of Laurentia by the Carboniferous.