A SYNTHESIS OF NORTHERN CIRCUM-PACIFIC MAGMATISM AND TECTONISM ASSOCIATED WITH CIRCUM-ARCTIC LITHOSPHERE EVOLUTION (CALE) TRANSECT C

A recently completed lithospheric transect across the Arctic spanning 5100 km from the Lomonosov Ridge to the Aleutians includes a time-space synthesis of the magmatic and deformational history of Alaska and Russia, allowing comparisons of the timing and nature of events along strike of the margin, including the northern Cordillera. Within this broader framework, the geology of the Arctic-Alaska–Chukotka microplate (AACM) suggests it originated as part of the continental shelves of Laurentia and Baltica (joined by the Caledonian orogen) and was translated southward during Cretaceous rifting of the Amerasia Basin (Arctic Ocean). During this time it formed part of the dynamic northern Pacific margin, its lithosphere progressively modified by extension and intrusion of subduction related magmas. During the time-span 120 to 50 Ma, magmatism along the Russia-Alaska sector of the margin occurred in an extensional to neutral tectonic environment, differing from the Canadian Cordillera where it is mostly syn-shortening. A possible plate tectonic model that could explain these differences is one where the Arctic began as a Triassic re-entrant in the paleo-Pacific margin and moved to its present position during slab-related magmatism and southward retreat of paleo-Pacific subduction, coeval in part with formation of the Amerasia Basin in its wake beginning in the Aptian-Albian.