6 Conclusion
We document ca. 100 million years of magmatic arc spatial localization along the ARZS of the mobile southern Alaska Wrangellia composite terrane by compiling 6485 total bedrock and single grain detrital ages, in the framework of a trench that moves outboard through successive accretion events (Figures 5 and 7). For example, repeated periods of arc magmatism in the Central Alaska Range Arc, located at times >500 km from the trench, highlights a first-order upper-plate control on magmatic spatial patterns. By deduction, inherited features of the upper-plate must be controlling both the geometry (e.g., dip) of the underlying slab and potentially focuses melt transport. Arc localization since ca. 100 Ma has been in part controlled by inferred upper-plate related hydrodynamic (viscous) mantle wedge “suction” forces driven by trenchward motion of plates inboard of the Wrangellia composite terrane with thick-cold lithosphere (>100 km and up to 200 km thick) (Figure 8).
There has been a justified geoscience community focus on trench-perpendicular magmatic arc migration (e.g., Gianni and Luján, 2021) due to the dynamic nature of convergent margins and the important processes related to slab rollback and advance that arc migrations reflect. Conversely, magmatic arc localization may be an underappreciated geodynamic process with implications for first-order upper-plate control on slab geometry and magma ascent processes. Hence, we recommend time-dependent numerical modeling to further evaluate the influence of these hydrodynamic “suction” forces on the shallow subduction geometry of the Yakutat oceanic plateau. Additionally, matching gaps in arc magmatism along North America’s western margin with the magmatic record of the Wrangellia composite terrane may provide further buttressing for the established “Baja-Alaska” paradigm (e.g., Tikoff et al., 2022; Boivin et al., 2022).