The Olympic Mountains A Wedge of Fun. Olympic Mountains, Wilapa Hills & Oregon Coast Range E-1.

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Presentation transcript:

The Olympic Mountains A Wedge of Fun

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

Geology Map

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

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

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

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

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)

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

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

Modern Analogy - Iceland

Possible Eocene Reconstruction E-1 55 Myrs 35 Myrs

Plate Reconstruction: 55 Myrs D-2

Supporting Evidence: Rock Age E-3

Interpretation: Core Rocks E-4 Trench Sediments Accretionary Wedge

What is an Accretionary Wedge?

Olympic Accretionary Wedge

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

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

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

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

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

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