The Olympic Mountains

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The Olympic Mountains

• A Wedge of Fun

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Olympic Mountains, Wilapa Hills Oregon Coast
Range
E-1
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Geology Map
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Major Rock Units
E-4

1. Peripheral Rocks
2. Core Rocks

Separated by reverse faults
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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
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Crescent Formation
Basalt of the Crescent Formation on Klahhane
Ridge above Port Angeles (USGS).
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Core Rocks
E-4
Age Eocene-Miocene (40-20 Myrs) Metamorphosed
14-12 Myrs
Rocks Sandstones w/graded beds Shale Metamorphis
m East - Low Grade (11 km burial) West - Not Met.
Youngest
Oldest
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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)
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Olympic Structures
E-3
Peripheral Rocks
Core Rocks
Note faults place older rock over younger rock
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Interpretation Peripheral Rocks
E-4
Terrane (fault bounded)
Hot Spot Island

• Basalt Chemistry Hot Spot Divergent Zone

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Modern Analogy - Iceland
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Possible Eocene Reconstruction
E-1
35 Myrs
55 Myrs
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Plate Reconstruction 55 Myrs
D-2
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Supporting Evidence Rock Age
E-3
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Interpretation Core Rocks
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Accretionary Wedge
Trench Sediments
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What is an Accretionary Wedge?
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Olympic Accretionary Wedge
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Olympic History
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Western Core rocks accreted first were buried
deepest (explains why they are oldest and most
metamorphosed)
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But Why is the North Wedge (Olympics) so much
larger than the South Wedge (Wilipa
Hills/Oregan Coast Range)?
Insular ST
1. Shoved in the Corner
Washington
Olympics
Coast Range
Oregon
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But Why is the North Wedge (Olympics) so much
larger than the South Wedge (Wilipa
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
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Evidence for the Bend1. NW Volcanoes
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Evidence for the Bend2. NW Earthquakes
Quakes occur in the subducting plate
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Why is there a Bend at all?
Basin Range Extention to the South
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