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The Olympic Mountains

The Olympic Mountains. A Wedge of Fun. Olympic Mountains, Willapa Hills & Oregon Coast Range. E-1. Geology Map. Major Rock Units. E-4. Peripheral Rocks Core Rocks. Separated by reverse faults. Peripheral Rocks: Mostly the Crescent Fm. E-4. Age: Mostly Eocene (60-50 Myrs). Rocks

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The Olympic Mountains

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  1. The Olympic Mountains A Wedge of Fun

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

  3. Geology Map

  4. Major Rock Units E-4 Peripheral Rocks 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 Complexly disrupted sandstone and shale beds of Olympic Core on north ridge of Mount Fitzhenry. (USGS) Sandstone beds with thin shale interbeds on Windfall Peak. (USGS)

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

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

  11. Modern Analogy - Iceland

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

  13. Plate Reconstruction: 55 Myrs D-2

  14. Supporting Evidence: Rock Age E-3

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

  16. What is an Accretionary Wedge?

  17. Olympic Accretionary Wedge

  18. Olympic History E-4 Notice: Sedimentary layers (Blakeley Fm, etc.) are folded/tilted Eastern 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” (Willipa Hills/Oregan Coast Range)? Insular ST 1. Shoved in the Corner Washington Olympics Coast Range Oregon

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

  21. Evidence for the Bend1. NW Volcanoes Steep Subduction Shallow Subduction 100 Depth

  22. Evidence for the Bend2. NW Earthquakes Quakes occur in the subducting plate

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

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