Jeff Apple Benowitz¹, Michael Everett Mann²

¹ GeoSep Services, 1521 Pine Cone Road, Moscow, ID, USA

² Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, USA

Corresponding author: Jeff Apple Benowitz (jeffapplebenowitz@gmail.com)

Abstract

Long-lived magmatic arcs theoretically should migrate large trench perpendicular distances as convergent margin configurations and slab geometry vary over time, however many arc-magmatic belts are spatially localized over 10’s of millions of years. We document, by compiling published crystallization geochronology data for southern Alaska (6485 total bedrock and single grain detrital ages combined), that since ca. 100 Ma, arc magmatism has been localized along the Alaska Range suture zone, at times over 500-km inboard. However, since ca. 100 Ma incoming subducting slab characteristics, beneath mobile southern Alaska and convergent margin configurations, varied greatly and include both normal oceanic plate and oceanic plateau subduction, plate vector changes, oroclinal bending and reconfiguration of trench shape, terrane accretion, long distance translation and a Paleocene slab break off/slab window event. Therefore, it is inferred that inherited upper-plate lithospheric shape and heterogeneity must control in part the geometry of the subducting slab below a mobile southern Alaskan margin through hydrodynamic (viscous) mantle wedge “suction” forces. Additionally, crustal thickness heterogeneity may preferentially focus magma ascent through melt ponding along Moho offsets, and upper-plate lithospheric-scale strike-slip faults may be acting as passive and active conduits for arc magmatism. Inherited upper-plate controls on slab geometry could be a factor localizing arc magmatism along other long-lived convergent margin settings.