GEOCHEMISTRY OF THE EARLY EOCENE COAST RANGE VOLCANIC PROVINCE, PACIFIC NORTHWEST, AND EVIDENCE FOR PLUME-RIDGE INTERACTION

The Coast Range Volcanic Province (CRVP) is an early Eocene Large Igneous Province that outcrops in Oregon, Washington, and southern British Columbia. Despite its size, the tectonic origins of the province remain unclear. This paper presents new petrographic and geochemical data for the Siletz River Volcanics, a subunit of the CRVP, and combines them with preexisting data from other CRVP subunits to model the chemical evolution of the province. The models show progressive enrichment in incompatible elements towards the geographic center of the CRVP, which is consistent with the distribution of radiometric and biostratigraphic dates that McCrory and Wilson (2013) compiled. This symmetrical trend in age and enrichment suggests that the CRVP was erupted as the Kula-Farallon or Farallon-Resurrection Ridge overrode the Yellowstone hotspot, and was rifted laterally from the ridge into its present linear configuration before accretion to North America. Isotopic, structural, and metamorphic evidence from the literature provide further support for this hypothesis.