Figure 1.

Cordilleran Archipelago in Early Cretaceous times, and its modern-day analogue. (A) Reconstruction of the intra-oceanic Archipelago that was overridden and accreted by North America (NAm) between ca. 150 Ma to ca. 50 Ma. Figure is corrected from Figure 1C in Pavlis et al. (2019), who attempted to render the model of Sigloch and Mihalynuk (2017) but omitted all eastward (Farallon) subduction. Present-day location of North America (NAm) is shaded gray; location in early Cretaceous times (ca. 140 Ma) is shaded yellow. Barbed lines are paleo-trench lines inferred from the presence of massive slab walls in the lower mantle; colored patches are associated arc terranes. Green—Farallon trenches and arcs; orange—Mezcalera trenches and arcs, including Insular Superterrane (INS) and Guerrero Superterrane (GUS); red—Angayucham (Ang) trenches and arcs (future Central Alaska). The Mezcalera (Mez.) [Angayucham] Ocean occupies the space between NAm and the Mezcalera [Angayucham] trench. NAm has started to override the archipelago, flipping orange, intra-oceanic, westward subduction to green, “Andean-style,” eastward subduction. Intermontane Superterrane (IMS) is a pre-accreted part of the NAm margin. (B) The modern-day southwest Pacific represents a closely analogous archipelago (after Sigloch and Mihalynuk, 2017). Base map was obtained by rotating and mirroring the present-day geography; see compass rose and compare to panel (C). Tectonic elements are colored and labeled to match their Cordilleran counterparts in (A). Dashed purple line, filled pale yellow, delineates Australian continental lithosphere. Its position relative to the archipelago is most analogous to NAm’s position ca. 120 Ma, shortly after starting to override the archipelago. Subduction polarity has started to flip from orange to green along Australia’s New Guinea trench segment (NGT). (C) Present-day southwest Pacific. Modern oceans and trenches are colored analogous to panels (A) and (B).