ALBERT

Description: This paper synthesizes the framework and geological evolution of the Arctic Alaska–Chukotka microplate (AACM), from its origin as part of the continental platform fringing Baltica and Laurentia to its southward motion during the formation of the Amerasia Basin (Arctic Ocean) and its progressive modification as part of the dynamic northern palaeo-Pacific margin. A synthesis of the available data refines the crustal identity, limits and history of the AACM and, together with regional geological constraints, provides a tectonic framework to aid in its pre-Cretaceous restoration. Recently published seismic reflection data and interpretations, integrated with regional geological constraints, provide the basis for a new crustal transect (the Circum-Arctic Lithosphere Evolution (‘CALE’) Transect C) linking the Amerasia Basin and the Pacific margin along two paths that span 5100 km from the Lomonosov Ridge (near the North Pole), across the Amerasia Basin, Chukchi Sea and Bering Sea, and ending at the subducting Pacific plate margin in the Aleutian Islands. We propose a new plate tectonic model in which the AACM originated as part of a re-entrant in the palaeo-Pacific margin and moved to its present position during slab-related magmatism and the southward retreat of palaeo-Pacific subduction, largely coeval with the rifting and formation of the Amerasia Basin in its wake. Supplementary material: Supplementary material Plate 1 (herein referred to as Sup. Pl. 1) comprises Plate 1 and its included figures, which are an integral part of this paper. Plate 1 contains regional reflection-seismic-based cross sections and supporting material that collectively constitute CALE Transects C1 and C2 and form an important part of our contribution. Plate 1 is referred to in the text as Sup. Pl. 1, Transects C1 and C2 as Plate 1A and 1B, and plate figures as fig. P1.1, fig. P1.2, etc.). Supplementary material 2 contains previously unpublished geochronologic data on detrital zircon suites and igneous rocks. Supplementary material are available at https://doi.org/10.6084/m9.figshare.c.3826813