Regional Geology
Columbia Plateau
Willamette Valley
Justin
Filiberto
LPI
Some questions to ponder…
• Is this process constructional or
destructional?
– How? Why? What ways?
• What is the time scale of this processes?
– Catastrophic?
– Long term?
• How will I recognize it in the field?
• Does this processes have implications for
other planetary bodies?
Blue Mountains
• Accreted huge blocks of 5 terranes
– Olds Ferry: island arc and sediments
– Layered rocks from the forearc basin
– Baker terrane: deep ocean crust
– Grindstone terrane: shallow ocean basin
– Wallowa: volcanic arc
• Oldest rocks in Oregon
– Triassic
Coastal Range
and Willamette Valley
Coastal Range
and Willamette Valley
• Accreted volcanic seamounts
– Undersea mountains
– Small volcanic islands
• Accreted coastal marine sediments
– Later altered by glacial events
Klamath Mountains
Klamath Mountains
• Accreted exotic terranes
– Oceanic crust (Josephine Ophiolite)
– Ocean floor sediments
– Island arc volcanoes
• Numerous terranes added together like
fallen dominoes
Cascades
Cascades
• Subduction related volcanism
– Dehydration of subducting slab
– Fluid induced melting of overlying mantle
– Volatile-rich, silica-rich magma
– Explosive eruptions
– Stratovolcanoes
Basin and Range
Basin and Range
High Lava Plains
High Lava Plains
• “Young” eruptions (< 10 million years)
• Magma rose though cracks in the crust
– Brothers fault zone
• Bimodal lava compositions
– Basalts from “deep”
– Rholites produced from shallow hydrous melting
• Thin crust due to stretching (basin and range)
• Examples:
– Lava Butte
– Newberry Crater
– Fort Rock
Columbia River
Columbia River
• Huge out pouring of basaltic lava
• Release of lava from emplacement of
mantle plume
• Details and interaction with subduction are
still debated.
Subduction Factory
Explains all volcanism except Columbia River Basalts