SYN-KINEMATIC MAGMATISM IN CENTRAL NEWFOUNDLAND: CONSTRAINTS ON THE TACONIC AND SALINIC OROGENIES

The central Newfoundland Appalachians comprise a well-developed south-southeast verging accretionary tract developed during the Ordovician to Silurian oblique closure of the Iapetus Ocean. Structural analysis has revealed multiple deformation events (D1-D7). The complexity and timing of the deformation is in part resolved by syn-tectonic intrusions. The oldest syn-kinematic plutons intrude into Ordovician shear zones and stitch Lower Ordovician ophiolites to the adjacent Dashwoods microcontinent. The stitching plutons belong to the Otter Pond Complex (468±2 Ma: U/Pb zircon), Portage Lake and Pierre's Pond suites (464±2, 462±2, 459±3 Ma: U/Pb zircon). These intrusions constrain the earliest Taconic tectonism (D1). The position, orientation, kinematics and associated metamorphism of the D1 shear zones, suggest that they formed in response to the Ordovican closure of the Iapetus Ocean's main tract. Voluminous Silurian plutonic suites in central Newfoundland also have syn-kinematic and stitching relationships with reactivated D1 shear zones. Syn-tectonic igneous rocks include porphyritic felsic dykes in the Victoria Delta Fault (431±1 Ma) and plutons of the Puddle Pond Suite (431±4: Ar/Ar hornblende; 427±1: U/Pb zircon; 426±1: U/Pb titanite). Stitching and syn-tectonic relationships indicate that the initially Ordovician shear zones in several places were reactivated during the Silurian (D2). D2 was accompanied by lower pressure metamorphism (2.5-3.5 kbar). The Silurian orogenesis (D2) in central Newfoundland thus started by 432 Ma and lasted until at least 426 Ma. The age and style of D2 is consistent with the Silurian Salinic Orogeny which resulted from the closure of the Tetagouche-Exploits backarc basin and arrival of Ganderia at the Laurentian margin.