Tectono-magmatic evolution of peri-Laurentian and peri-Gondwanan arc-back arc complexes along the Red Indian Line, central Newfoundland Appalachians

Abstract

The Appalachian-Caledonian Orogen is a classic example of a Paleozoic accretionary orogen which turned into a collisional orogen. The Newfoundland Appalachians represent a critical element of the Appalachian-Caledonian Orogen to evaluate terrane linkages and tectonic models between the North American and European segments, especially those formed during the closure of lapetus. This thesis presents new geochemical, geochronological, Sm/Nd isotope, structural and P/T data and proposes informal tectonostratigraphic framework for the central Newfoundland Appalachians. The data presented in this thesis are used to test tectonic models for closure of the lapetus and thus have important implications for the interpretation of tectonic relationships in other parts of the northern Appalachians (e.g. New England) and the British Caledonides. Central Newfoundland is underlain by the peri-Laurentian Annieopsquotch Accretionary Tract and peri-Gondwanan Victoria Lake Supergroup, separated by the Red Indian Line, the main lapetan suture zone. Subduction in the Annieopsquotch Accretionary Tract initiated at c. 480 Ma. Subsequently two distinct continental arc-backarc terranes (c. 473 Ma Buchans and 465-460 Ma Red Indian Lake arcs) were formed over an approximately 15 Ma period. A refined tectonic model is proposed for the Annieopsquotch Accretionary Tract involving both thrust and strike-slip displacements. The data require rapid accretion of arc-backarc complexes to the Laurentian margin less than 10 Ma after their formation. This accretion forms part of the Taconic Orogeny and is associated with development of D1 shear zones as early as c. 470 Ma. The subduction in the Victoria Lake Supergroup initiated prior to 513 Ma. Subsequently two distinct arc complexes were formed (513-485 Ma Penobscot arc and 473-453 Victoria arc). The Penobscot arc has been previously interpreted as an intraoceanic arc, however Sm/Nd isotopes, zircon inheritance data and stratigraphic relationships indicate formation of the Penobscot arc on continental crust. This crust is similar to Ganderia, which is a postulated peri-Gondwanan microcontinent. The gap in arc magmatism between the Penobscot and Victoria arcs coincides with the obduction of ophiolites onto Ganderia (Penobscot Orogeny). The data presented herein support a new model for the tectonic evolution of the Penobscot arc above an east dipping subduction zone. In this model the Penobscot ophiolites are obducted as a result of backarc basin inversion, possibly due to accretion of a seamount (Summerford Group) or ridge subduction. Following the Penobscot Orogeny, arc volcanism recommenced as the Victoria arc which rifted from the Ganderia margin opening a wide Exploits-Tetagouche backarc in its wake. (Abstract shortened by UMI.)