NORTHERN CORDILLERA TECTONIC MODEL

A series of maps spanning the past 700 million years tracks arc, accretionary complex and displaced craton margin terranes relative to the North American craton (NAC) and margin, and after accretion, tectonic activity on the new margin. Most terranes in Canada, southern and east-central Alaska originated near the western NAC; those in western and northern Alaska from the circum-Arctic region and northeast Russia.

The Rodina Supercontinent began to break up in the Neoproterozoic (~700 Ma). By the Cambrian (540 Ma) Laurentia (NAC + Greenland) was isolated and surrounded by passive margins. Convergence initiated in the Devonian (390 Ma) along its west and northwest margins (present coordinates) evolved by the Carboniferous (360 Ma) into an island arc chain containing Quesnellia, Stikinia + Yukon-Tanana Terrane, and by ~350 Ma, Wrangellia + Alexander Terrane, that extended from the coalescing Pangea Supercontinent into the ancestral Pacific Ocean. It was separated from the NAC by a back-arc basin (Slide Mountain Terrane) and the Angayucham Ocean that lay between the NAC and Siberian craton.

In Canada, the arc segments were juxtaposed with one another and the outer NAC margin between 185-174 Ma, following initial break up of Pangea as the central Atlantic Ocean began to open ~190 Ma. By the Middle Jurassic (~170 Ma) arc magmatism across the collage of accreted terranes was concurrent with tectonic uplift/erosion and deposition in local internal basins. By 160 Ma, detritus from the emerging Cordillera was shed over the craton margin; by 100 Ma, all but marginal parts of the Cordillera were above sea-level; and by 55 Ma, the NAC margin was thrust over the craton edge.

In Alaska, Angayucham Ocean remained open into the Late Jurassic when the Jurassic-Cretaceous north-facing (present coordinates) Koyokuk Arc overrode and deeply buried Arctic Alaska-Chukotka Terrane; both were in their current positions relative to the NAC by 100 Ma. In the later Cretaceous-Cenozoic, oblique convergence acting on weak upper plate arc lithosphere moved rocks in westerly parts of the Cordillera northward into east-central and southern Alaska along strike-slip faults whose cumulative displacement exceeds 1,000 km. Today, the Pacific Plate carries Yakutat Terrane into and under Southern Alaska and raises the highest mountains on the continent.