Review of Cordilleran Tectonics Antler Orogeny ~380 Ma

Review of Cordilleran Tectonics
• Future Parks: Death
Valley and Yosemite
• To understand these parks
we need to remember the
three events that formed
the Cordillera
– Sevier Orogeny
– Laramide Orogeny
– Basin and Range Extension
(and San Andreas Faulting)
Antler Orogeny ~380 Ma
• This is not part of
Cordilleran Tectonics
• Rather, it builds the crust
that is later involved in
Cordilleran Mountain
Building
• Subduction of Laurentian
plate Stops and reverses
subduction when
continent hits subduction
zone
– Antler Arc is accreted to
Laurentia
– New, Klamath Arc begins
• More Accreted Terrains…
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Accreted Terrain comprise western NA crust
• This process continued
through-out the
Paleozoic-Mesozoic
building the western
portion of NA
Sevier Orogeny 165-80 Ma
• Beginning of Cordilleran mountain
building
• Typical Andean-Type subduction
• 165 Ma, Subduction of Farallon Plate
begins
• Notice the following ‘Parts’:
Accretionary Prism, Forearc Basin,
Volcanic Arc, Fold-thurst Belt
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Parts of the Sevier Orogeny
• Accretionary Prism
– Sediments scraped from subducting slab
– This old accretionary prism now composes the
bedrock of the California coastal mountain ranges
Parts of the Sevier Orogeny
• Forearc Basin
– Sediments derived
from volcanic arc
– Sevier forearc basin is
now preserved as the
Great Valley of
California
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Parts of the Sevier Orogeny
• Sierra Nevada Batholith
• This is the magmatic system
that fed the now eroded
volcanic arc
• Yosemite is in this region
Parts of the Sevier Orogeny
• Sevier Fold-Thrust Belt
• These rocks were ‘plowed’ up to the east
of the arc
• We say these faults at Glacier
• This belt continues through Canada into
Alaska
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Laramide Orogeny 80-40 Ma
• Shallow subduction angle of Farallon Slab becomes
• Younger, thinner, hotter more buoyant slab
• Volcanic Arc jumps East (e.g. San Juan, Absoroka, Devil’s
Tower)
• ‘Pops-up’ thick basement uplifts along reverse, re-activate
Precambrian normal faults.
• Distinctive rocky mountain uplift of RM NP, and Colorado
Plateau
Laramide Basement Uplifts
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Basin and Range Extension
• Subduction ceases on western margin of
NA
• Supper thick Cordillera (after Sevier and
Laramide events)
– Deep under the Cordillera, rocks are hot
and can flow
– Shallow, cold crust breaks
• The whole region then extends as deep
crust flows away (e.g. silly putty) under
‘gravitational collapse’
San Andreas Faulting
• Transform boundary
developed when PacificFarallon mid-ocean ridge
subducted beneath NA
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San Andreas Fault System
• Series of ‘parallel’ faults
– San Andreas, Hayward etc.
– Most activity is in the coastal
ranges
• Total Displacement is ~600
km at ~6 cm/year
• Bends in the strike-slip fauts
cause compression
(restraining bend) and
extension (releasing bend)
depending on orientation of
bend relative to plate motion.
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