Geochemistry of the Knight Island Ophiolite and Chenega Island Volcanics, Prince William Sound, Alaska

The tectonic evolution of southern Alaska is defined by a long history of subduction, accretion, and coastwise transport of terranes along the North American margin (e.g. Plafker et al., 1994). Cowen (1982, 2003) and Haeussler et al. (2003) propose two competing hypotheses for the formation and transport history of the Mesozoic-Tertiary Chugach-Prince William terrane that extends for at least 2000 kilometers along the margin from Sanak Island in the west to Baranof Island in the East (Fig. 1 in Garver and Davidson, this volume). Paleomagnetic and geologic data suggest that the Chugach-Prince William terrane has experienced major coast-parallel northward transport along strike slip faults and thus there are critical questions about the timing and location of terrane accretion (Cowan, 2003; Haeussler et al., 2003; Sisson et al., 2003; Plafker et al., 1994). Near-trench intrusions of the Chugach-Prince William terrane by the Paleogene Sanak-Baranof magmatic belt are strong evidence for ridge subduction and these plutons show a distinct west-east age progression from 61 Ma on Sanak Island to 50 Ma on Baranof Island (Bradley et al., 2003; Haeussler et al., 2003). Cowen (1982, 2003) suggests that ridge subduction (Kula-Farallon) took place near the latitude of Washington State but Haeussler et al. (2003) introduced the Resurrection plate to explain a more northerly option for this plutonic belt.