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.