The Corner Brook Lake block in the Newfoundland Appalachians: A suspect terrane along the Laurentian margin and evidence for large-scale orogen-parallel motion

Abstract

Available geochronological (U-Pb and Ar/Ar) and geological data indicate that the Corner Brook Lake block of the Humber zone in the western Newfoundland Appalachians has unique characteristics. Grenvillian ages (ca. 1.0 Ga), which are typical for the Laurentian Appalachian margin, are absent in the crystalline basement to the Corner Brook Lake block. This makes it unlikely that the block is underlain by true parautochthonous Humber margin basement. However, the lithological makeup of its late Neoproterozoic–Early Cambrian sedimentary cover and detrital zircon populations indicate a Laurentian-type provenance. In addition, there is no geochronological or other geological evidence for a Middle Ordovician tectono-thermal event in the Corner Brook Lake block, suggesting that it escaped the penetrative tectono-thermal effects of the Taconic collision present elsewhere in the Laurentian realm. Instead, the block underwent strong regional deformation and associated peak metamorphism during the Silurian Salinic orogeny. Combined evidence, including the absence of Grenvillian ages, the presence of late Neoproterozoic ca. 600 Ma granitoid plutons, the regionally distinct early Paleozoic tectonic history of the Corner Brook Lake block, and its fault-bounded nature, implies that the block represents an allochthonous terrane. Available data indicate that significant orogen-parallel movement of the block (possibly 400 km or more) could have taken place during the Appalachian orogeny. The possibility of large-scale strike-slip tectonics, in addition to the well-documented convergent motions, has significant implications for the tectonic interpretation of the early Paleozoic evolution of the Newfoundland Appalachians.