THE POPELOGAN-VICTORIA ARC — TETAGOUCHE-EXPLOITS BACKARC BASIN AND SALINIC OROGENESIS

Many advances have been made during the last 15 years concerning the tectonic setting and evolution of the various Ganderian elements involved in the Salinic orogenic system. In particular a combination of structure and geochronology of key-rock units has enhanced/modified existing models. New results from northern New Brunswick, Canada are presented and discussed herein. 1. Zircon inheritance confirms that the west-facing Popelogan-Victoria arc (PVA) and correlatives in New England are built upon Ganderian basement and hence represents its leading edge; 2. A voluminous Darriwilian-Sandbian pulse of E-MORB to alkalic mafic to ultramafic magmatism suggest subduction of a Iapetus ridge beneath the PVA and Tetagouche-Exploits backarc basin (TEB) between 464 and 458 Ma, immediately prior to accretion of the PVA to composite Laurentia at ca. 455 Ma; 3. oceanic elements of the TEB (~ 600-800 km wide) record deposition of ca. 463 Ma arc volcanic rocks such as ash and tuff and Late Ordovician (≤ 459 Ma) island arc basalt suggesting they formed close to the PVA and probably record migration of the PVA arc magmatic axis towards its rear due to shallowing of the subduction zone; 4. Upper Ordovician-Lower Silurian syntectonic clastic sediments were deposited unconformably to (dis)conformably above Sandbian-Katian pelagic sediments (chert and black shale) following initiation of west-directed Salinic subduction at ca. 450 Ma in the TEB; 5. The Matapedia successor basin is an accretionary forearc basin progressively expanding towards the southeast between 445 and 435 Ma due to accretion of the various TEB terranes and concomitant stepping back of the subduction zone. Salinic deformation is complex, polyphase and diachronous. Early Salinic tectonometamorphism generated Late Ordovician-Early Silurian (445-435 Ma) blueschist and HP-greenschist facies metamorphic rocks and was also responsible for the Belledune River mélange (which contains several large slices of mantle) and thrusting and folding in the arc-trench gap. Salinic collision of the Gander margin with composite Laurentia took place during the Middle to Late Silurian and caused widespread deformation, metamorphism, magmatism, inversion of the Matapedia and Fredericton basins and a widespread Middle to Late Silurian erosional hiatus.