BREAKING UP IS HARD TO DO: EVOLUTION OF THE NORTH AMERICAN CORDILLERAN MARGIN IN THE CONTEXT OF THE SIBERIAN CONNECTION

A tectonic plate reconstruction that connects the eastern margin of the Siberian craton to the Cordilleran margin of western NA satisfies 4 essential criteria: 1) a coherent pre-rift geological map with an interpretable geologic history; 2) correlative breakup and thermal subsidence of proposed conjugate margins; 3) viable continental drift paths for daughter continents; and 4) compatible paleomagnetic poles for daughter continents. Detailed examination of the reconstruction from both the North American and Siberian perspectives suggests a complex start-and-stop history of break up and separation of the two cratons. Siberia may have moved clockwise relative to NA about a pole of rotation in Greenland on transform faults that paralleled the Rocky Mountain trench. A broad region of low-angle detachment faulting occurred in the Great Basin and its Verkhoyansk counterpart in Siberia between transform faults. The earliest rifting began in Mesoproterozoic time with opening of the NA Belt-Purcell and Siberian Udzha continental rifts. Neoproterozoic continental rifting opened the NA Windermere rift basin and produced correlative breakup angular unconformities in Siberia and NA. Likely NA-sourced detrital zircons appear below but not above the breakup unconformity in Siberia. It appears that by Early Cambrian time separation was sufficient to isolate NA-derived detrital zircons from Siberia, and thick siliciclastics were trapped on the NA side, while clean carbonates accumulated on the Siberian side. However, trilobites and archeocyathans could migrate between the conjugate shelves at adjacent promontories. Both margins thermally subsided and accumulated shelf sediments at comparable rates during the Early Paleozoic. Both margins then experienced significant tectonism and igneous activity in the Middle and Late Devonian, as if the relative pole of rotation had shifted. Clockwise rotation of Siberia may have triggered a sequence of Paleozoic transpressional orogenies along the Cordilleran and Arctic margins of NA as it moved to its terminal collision with the Ural Mountains in Permian time.