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The Growth of Western North America - Part
IIThe Insular Superterrane, North Cascades & San Juan
Islands
Our Story So Far…
C-3
Arrival of the Insular Superterrane
IntermontaineSuperterrane
InsularSuperterrane
MethowBasin
C-3
C-3
IntermontaineSuperterrane
InsularSuperterrane
MethowBasin
NorthCascades
After Accretion
Subduction zone relocates
North Cascades at 100 Myrs
Insular Superterane: Wrangellia Terrane
Rocks:Basalts
top: vesiclesbottom: pillows
Limestone
Age:Triassic/Jurassic
Source:Fossil clams and forams
western PacificPaleomagnetics
±15° N/S
Type of Terrane:Hot Spot Islands
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Photo: Dr. ML.Bevier
ObliqueCollision Continent
Terrane
ObliqueCollision Continent
ObliqueCollision Continent
ObliqueCollision Continent
Terrane is “smeared out” along coast
Insular Superterra
ne:Wrangellia
C-2
Wrangellia & the North Cascades
C-6
IntermontaineSuperterrane
InsularSuperterrane
MethowBasin
“Microterranes”
Modern Day
Analogy for
North Cascade Rocks
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Cont.
C-6IntermontaineSuperterrane
InsularSuperterrane
North Cascades &San Juan Islands
Time
Many Microterranes of the North Cascades & San Juan Is.
(See list on C-9)
C-4
• Skagit• Chelan Mountains• Nason• Shuksan• Nooksak River• Chilliwack• Haro• Turtleback• Deadman Bay• Garrison• Decatur• Western Melange• Eastern Melange• …and the rest…
Major Terrane Groupings
• Skagit• Chelan Mountains• Nason• Shuksan• Nooksak River• Chilliwack• Haro• Turtleback• Deadman Bay• Garrison• Decatur• Western Melange• Eastern Melange• …and the rest…
Skagit Crystalline Core
NW Cascades andSan Juan Thrust System
Melanges
Major Terrane Groupings
C-4
Skagit Crystalline Core
NW Cascades andSan Juan Thrust System
Melanges
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Skagit Crystalline Core
Skagit Gneiss
Cascade River Schist
HighGrade
NW Cascades ThrustsDarrington Phyllite
Shuksan Blueschist
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Protolith:Shale
Protolith:Basalt
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-- Subducted Ocean Crust --
Low to MediumGrade
Twin Sisters Dunite
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Major Terrane Groupings
Skagit Crystalline Core
NW Cascades andSan Juan Thrust System
Melanges
High Grade Met.
Medium Grade Met.
Low Grade Met.
C-4
Skagit Crystalline Core
NW Cascades & San Juan Islands Thrusts
Separated by thrust faults
C-5 & 6
San Juan Islands
C-7
San Juan Islands
C-7
Decatur TerraneJurassic
ChertBasaltGabbroSerpentinite
Ocean Crust
Similar to Terrane rocks in Northern California
San Juan Islands
C-7
Deadman Bay TerranePermian to Jurassic
ChertLimestoneW/Tethyan ForamsBasalt
Ocean Crust
Similar to Cache Creek Terrane in Intermontaine Superterrane
San Juan
Thrust Sheets
C-7
San Juan Island Thrust Sheets
C-8
NW Cascades/San Juan Islands
C-5
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Nanaimo Formation:Overlap Sequence
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Mt. Stuart - Stitching Pluton
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90 Myrs
Timing of the North CascadesCollision
C-1
Age of theMicroterranes
Age of Accretion115-90 Myrs
C-10
Meanwhile in Oregon…
Terranes of the
Wallowa Mountai
ns
C-11
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