SETTING THE STAGE IN NW PANGEA – EARLY TO MID-PALEOZOIC TRANSLATION OF TERRANES AND ONSET OF THE CORDILLERAN CONVERGENT MARGIN (Invited Presentation)

The amalgamation of Pangea was the result of convergence of the Paleozoic continents (e.g., Laurentia, Baltica, Siberia, Gondwana) and successive closure of intervening ocean basins (e.g., Iapetus, Rheic, Uralian). The progressive loss of subduction zones in the interior of Pangea apparently led to propagation of subduction along its outer edges. The Silurian-Devonian closure of the Iapetus Ocean, and development of the Caledonides, are particularly relevant to the Paleozoic development of the NW margin of Pangea (today’s Cordilleran and Arctic margins of North America).

The convergence between Baltica and Laurentia, and the final closure of the Iapetus Ocean, are interpreted to have led to propagation of a Scotia-style subduction system that entrained terranes of Siberian, Baltican and NE Laurentian (Caledonian) affinities westward along northern Laurentia – the Paleozoic Northwest Passage. The Pearya and Arctic Alaska terranes were stranded first along the northern Laurentian margin in the Silurian-Devonian; both are bound by sinistral shear zones interpreted as the southern transform margin of the Northwest Passage. Other terranes (e.g., Alexander, Farewell, Northern Sierra, Eastern Klamath) were translated further west into Panthalassa and later accreted to the Cordilleran margin. Carboniferous closure of the Rheic Ocean, and convergence with Gondwana in the south, caused northward drift of Laurussia, development of the Ellesmerian and Antler orogens, southward translation of terranes and propagation of subduction along the Cordilleran margin in the Late Devonian-Early Mississippian. Subsequent development of the western peri-Laurentian arcs (e.g., Yukon-Tanana, Paleozoic Stikinia-Quesnellia, McCloud) was accompanied by the Mississippian-Permian opening of the Slide Mountain-Golconda back-arc basin along the Cordilleran margin; and subsidence of Sverdrup basin in the Arctic. Closure of the Slide Mountain-Golconda Ocean is recorded by the Permo-Triassic Klondike and Sonoma orogenies; which were closely followed by re-establishment of subduction along NW Pangea in the Middle Triassic, and development of Early Mesozoic arcs (e.g., Stikinia, Quesnellia, Wrangellia, Peninsular).