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The Late Eocene Eshamy Suite plutons (ESP) intrude turbidites of the Chugach-Prince William (CPW) terrane in western Prince William Sound. The Prince William Sound region of South-Central Alaska consists of the Chugach-Prince William Terrance (CPW), containing the Valdez and Orca Group separated by the Contact fault. The Valdez Group is Late Cretaceous in age and is characterized by a thick sequence of interbedded siltstone, greywacke, and pebble conglomerate likely deposited as turbidites on submarine fans (Tysdal and Plafker, 1978). South of the Valdez is the Orca Group of Paleocene to Eocene age, characterized by folded and faulted rocks that have been intruded by younger plutons (Davidson and Garver, 2017). The CPW has been traditionally interpreted as a Late Cretaceous to Paleocene accretionary wedge complex that was either formed in situ or was deposited farther south and subsequently transported a significant distance along the continental margin (cf. Cowan, 2003; Haeussler et al., 2003). The ESP is a bimodal suite of granites dominated by biotite granites and leucogranites with subordinate gabbro. Questions for the ESP include the crystallization ages for the plutons, their relationship to igneous rocks found farther inboard, and the nature of the tectonic setting. For this study, we examined a set of granites from Miners Bay and Cedar Bay to compare with the rocks from the Nellie Juan and Eshamy Bay plutons to the southwest (Fig. 1), and the Caribou Creek volcanics (CCV) that occur 200 km inland. Our results show that the Miners and Cedar Bay plutons fall within the age range of the CCV and are marginally older than the Nellie Juan (NJP) and Eshamy Bay plutons (EBP) (Cole et al., 2006; Johnson, 2012). However, preliminary geochemical data suggest that the ESP may not be directly related to the CCV and therefore may have formed in a different tectonic setting.
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Crystallization ages and geochemistry of the Miners Bay and Cedar Bay Plutons, Prince William Sound, Alaska
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