Origin of the Late Eocene Eshamy Suite Granitoids in Western Prince William Sound, Alaska

The Eshamy suite plutons (ESP) are in the midst of the Sanak-Baranof (SB) belt, a series of neartrench, Paleocene to Eocene granitic intrusions into the Chugach-Prince William (CPW) terrane flysch along the southern margin of Alaska (Fig.1, Garver and Davidson, this volume and references therein). Intruded from 62-48 Ma, west-to-east migration of a subducting north-south-striking mid-ocean ridge is the widely accepted model for the emplacement of the SB plutons (Bradley et al., 2003; Cole et al., 2006; Cowan, 2003; Haeussler et al., 2003; Madsen et al., 2006). However, Cowan (2003) suggested that the same pattern of intrusion of the SB plutons can be explained by the coast-parallel migration of the CPW terrane over a stable trench-ridge-trench (TRT) intersection at the latitude of Washington State (4849°N). Regardless of the tectonic geometry of the TRT interactions, these authors propose that as the ridge subducted, the adjacent oceanic plates diverged creating a slab window that exposed the continental margin to hot sub-oceanic asthenosphere and its associated basaltic melts. Near the trench, advective heat would drive melting of water-rich, poorly-consolidated sedimentary rocks. Intrusions formed through this process would be a mixture of mid-ocean ridge basalt (MORB) and accretionary prism sediments (Bradley et al., 2003; Kusky et al., 2003 and citations therein).