MAGMATISM AND DEFORMATION ALONG THE NORTHERN CIRCUM-PACIFIC MARGIN FROM NE RUSSIA TO THE CORDILLERA
Contrasts in deformational history date back to the Permo-Triassic where eruption of Siberian Traps and rifting in NE Russia contrast to shortening in the Canadian Cordillera (closure of Slide Mountain Basin). The main Mesozoic shortening event in NE Russia and Alaska occurred ~ 150- 130 Ma, during a “lull” in both magmatism and deformation in the Cordillera. Magmatism in NE Russia and Alaska was voluminous in the timespan 120- 65 Ma but took place in neutral to extensional tectonic settings compared to the history of near continued convergence in the Cordillera. Geologically, these changes in the tectonic setting of magmatism (occurring near the Canadian- Alaskan border) resulted in a relatively narrow zone of magmatism and parallel zones of shortening and strike-slip in the Cordillera compared to broad and complex patterns of magmatism as subduction migrated Pacific-ward, culminating in subduction zone step-outs to Kamchatka (~65 Ma) and the Aleutians ~45 Ma.
The near coincidence in timing of events (albeit of differing nature) suggests that the absolute motions of the continental plates involved are coupled in a global plate framework and that their motion towards or away from subduction zones are important in dictating the origin of their associated magmatic belts and the tectonic settings for magmatism.