LONG-LIVED DEXTRAL STRIKE-SLIP MOVEMENTS IN THE CABOT FAULT ZONE: ITS SIGNIFICANCE FOR THE EARLY PALEOZOIC TECTONIC HISTORY OF THE NEWFOUNDLAND APPALACHIANS

The Dashwoods block in the Newfoundland Appalachians has been affected by an Ordovician dynamo-thermal event (Taconic orogeny) and an associated magmatic phase (Notre Dame continental arc). Post-collisional Early Silurian magmatism in this block is accompanied by localized deformation and rapid uplift. In contrast, the presently juxtaposed Corner Brook Lake block of the internal Humber Zone is characterized by Early Silurian (Salinic) west-vergent deformation and associated metamorphism. An Ordovician dynamo-thermal event is absent and Taconic deformation appears to be restricted to a high-crustal level. Given these discrepancies, it is highly unlikely that these two segments were juxtaposed before the Late Silurian.

The Cabot Fault Zone (CFZ) separates the Dashwoods and Corner Brook Lake blocks. Field and petrographic observations, as well as U-Pb geochronology demonstrate that this crustal-scale tectonic zone has recorded Late Ordovician to Carboniferous – progressive or intermittent – ductile to brittle, oblique-dextral movement.

Dextral movement along the CFZ means that during the Early Silurian the Corner Brook Lake block was juxtaposed with a tectonic entity that currently should be present to the south. Palinspastic reconstruction along the CFZ may help identifying this tectonic entity, however, in absence of quantitative constraints on the dextral movement, such a reconstruction can only be very simplistic. One possible scenario is that, after subtracting ca. 300-400 km of dextral deformation, the peri-Gondwanan Aspy terrane (Cape Breton Island) is juxtaposed with the Corner Brook Lake block. By having translated the Dashwoods block away to the north, this scenario may explain the absence of a significant Taconic dynamo-thermal event in the Corner Brook Lake block. If this comparison holds any truth, incorporating such large strike-slip amounts would require re-examination of most tectonic models, which are mainly based on orthogonal convergence with minor strike-slip.