Sum11.208Olympics

Sum11.208Olympics - E-1 The Olympic Mountains Olympic...

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Unformatted text preview: E-1 The Olympic Mountains Olympic Mountains, Willapa Hills & Oregon Coast Range A Wedge of Fun E-2 Geology Map Major Rock Units 1. Peripheral Rocks 2. Core Rocks Separated by reverse faults E-2 Crescent Formation Peripheral Rocks: Mostly the Crescent Fm Age: Mostly Eocene (60-50 Myrs) Rocks Pillow Basalts Some Vesicular Basalts 15-30 km thick Limestone(Red) w/deep water forams Basalt of the Crescent Formation on Klahhane Ridge above Port Angeles (USGS). E-2 Core Rocks Core Rocks Age: Eocene-Miocene (40-20 Myrs) Metamorphosed 14-12 Myrs Rocks Sandstones w/graded beds Shale Complexly disrupted sandstone and shale beds of Olympic Core on north ridge of Mount Fitzhenry. (USGS) Metamorphism East - Low Grade (11 km burial) West - Not Met. Youngest Oldest Sandstone beds with thin shale interbeds on Windfall Peak. (USGS) E-2 Olympic Structures Core Rocks E-2 Interpretation: Peripheral Rocks Terrane (fault bounded) Peripheral Rocks Hot Spot Island Note faults place older rock over younger rock Basalt Chemistry = Hot Spot & Divergent Zone E-4 Modern Analogy - Iceland Possible Eocene Reconstruction 35 Myrs 55 Myrs D-2 Plate Reconstruction: 55 Myrs Supporting Evidence: Rock Age E-4 E-2 Interpretation: Core Rocks Accretionary Wedge Trench Sediments What is an Accretionary Wedge? E-1 E-3 Olympic Accretionary Wedge Olympic History 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) But Why is the North “Wedge” (Olympics) so much larger than the South “Wedge” (Willipa Hills/ Oregon Coast Range)? But Why is the North “Wedge” (Olympics) so much larger than the South “Wedge” (Willipa Hills/ Oregon Coast Range)? Insular ST 1. Shoved in the Corner Olympics Coast Range Olympics Washington Oregon 2. There is a bend in the Juan de Fuca Plate under the Olympics Cross Section North ------ South N. America Juan de Fuca Evidence for the Bend 1. NW Volcanoes Steep Subduction Shallow Subduction Evidence for the Bend 2. NW Earthquakes Quakes occur in the subducting plate 100 km Depth Why is there a Bend at all? Basin & Range Extension to the South Why is there a Bend at all? Basin & Range Extension to the South Cross Section of the Basin and Range ...
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