Felsic Eocene Volcanic Rocks On The Olympic Peninsula And Their Implications For Ridge Subduction
Abstracts With Programs - Geological Society Of America
Recent work (Haeussler et al., 2003) attributes adakites and felsic near trench magmatism from Oregon to Alaska to the subduction of two spreading ridges: the Kula-Resurrection and the Kula-Farallon. This model implies that both ridges should have been subducted in the vicinity of the Olympic Peninsula/southern Vancouver Island at approximately 50 Ma. We present data on four felsic volcanic deposits of Eocene age on the Olympic Peninsula that may help to constrain the timing and geometry of one or both of these ridge subduction events. Adakites have been identified at three of these volcanic centers: Bremerton Hills (BH; Tepper et al., 2002), Chimacum (CR; Hahn et al., 2004), and most recently at Mt. Zion (MZ). MZ adakites occur as one or more porphyritic lava flows interbedded within Lyre Formation conglomerates and also as clasts within this unit. MZ lavas share many attributes of BH and CR adakites (e.g., Sr/Y > 20, Yb 400 km (super 2) area of the NE Olympic Peninsula. Felsic volcanic rocks at Striped Peak (SP) are approximately 50 km west of the adakite localities and include water-lain crystal-vitric tuff with pumice clasts up to 3 cm in size and tuffaceous sandstones. These rocks are interbedded within Crescent Formation basalts (>48 Ma), implying that they are older than the adakites (46-48 Ma at BH). Based on their inferred age and proximity to southern Vancouver Island, we suggest the SP volcanics may be associated with approximately 50 Ma magmatism in the Leech River Complex or the approximately 51 Ma Flores volcanics. Ongoing geochemical and geochronological work will further examine this possibility.
Wolfe, Melissa R., and Jeffrey H. Tepper. 2004. "Felsic Eocene volcanic rocks on the Olympic Peninsula and their implications for ridge subduction." Abstracts With Programs - Geological Society Of America 36(5; 5): 223-223.