1. The Olympic Mountains A Wedge of Fun

2. Olympic Mountains, Wilapa Hills & Oregon Coast Range E-1

3. Geology Map

4. Major Rock Units E-4 1.Peripheral Rocks 2.Core Rocks Separated by reverse faults

5. Peripheral Rocks: Mostly the Crescent Fm E-4 Age: Mostly Eocene (60-50 Myrs) Rocks Pillow Basalts Some Vesicular Basalts 15-30 km thick Limestone(Red) w/deep water forams

6. Crescent Formation Basalt of the Crescent Formation on Klahhane Ridge above Port Angeles (USGS).

7. Core Rocks E-4 Age: Eocene-Miocene (40-20 Myrs) Metamorphosed 14-12 Myrs Rocks Sandstones w/graded beds Shale Metamorphism East - Low Grade (11 km burial) West - Not Met. Youngest Oldest

8. Core Rocks Sandstone beds with thin shale interbeds on Windfall Peak. (USGS) Complexly disrupted sandstone and shale beds of Olympic Core on north ridge of Mount Fitzhenry. (USGS)

9. Olympic Structures E-3 Peripheral RocksCore Rocks Note faults place older rock over younger rock

10. Interpretation: Peripheral Rocks E-4 Hot Spot Island Terrane (fault bounded) Basalt Chemistry = Hot Spot & Divergent Zone

11. Modern Analogy - Iceland

12. Possible Eocene Reconstruction E-1 55 Myrs 35 Myrs

13. Plate Reconstruction: 55 Myrs D-2

14. Supporting Evidence: Rock Age E-3

15. Interpretation: Core Rocks E-4 Trench Sediments Accretionary Wedge

16. What is an Accretionary Wedge?

17. Olympic Accretionary Wedge

18. Olympic History E-4 Western Core rocks accreted first & were buried deepest (explains why they are oldest and most metamorphosed)

19. But Why is the North “Wedge” (Olympics) so much larger than the South “Wedge” (Wilipa Hills/Oregan Coast Range)? 1. Shoved in the Corner Insular ST Washington Olympics Coast Range Oregon

20. But Why is the North “Wedge” (Olympics) so much larger than the South “Wedge” (Wilipa Hills/Oregan Coast Range)? 2. There is a bend in the Juan de Fuca Plate under the Olympics N. America Cross Section North ------ South Juan de Fuca Olympics

21. Evidence for the Bend 1. NW Volcanoes 100 Depth Steep Subduction Shallow Subduction

22. Evidence for the Bend 2. NW Earthquakes Quakes occur in the subducting plate

23. Why is there a Bend at all? Basin & Range Extention to the South