Post on 06-Jan-2016
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transcript
Announcements:
Final Exam
Monday, Dec. 16, 11-1
this room
TODAY:
Structural Evolution of W. North America:
From Proterozoic to Present
Goals:
(1) Appreciation of "local" geology
(2) Interplay between plate tectonics and deformation
(3) Long and dynamic history of growth and deformation of continents
Archean – Middle
Proterozoic growth of
North America
Good old "Yankee" basement
Youngs from N to S
Middle Proterozoic to
Cambrian rifting of W.
U.S.
What rifted away???
Sedimentary evidence for a rifted continental margin: Late Proterozoic - Cambrian
Thermal subsidence following rifting
The margin of W. North America 500 Myr ago
All the crust to the west is either younger or was
torn off of some other continent and
subsequently attached to N.A.
Paleozoic passive margin sedimentation
along continental margin- beautifully preserved in
the Grand Canyon
But!: There was action going on to the west
during some of this time- Antler Orogen
(Devonian-Mississippian)
Cross section of the middle Paleozoic Antler Orogen
Growth of an outboard arc and disruption (by thrusting) of the passive margin
There was also action to the
east during late Paleozoic time
Collision between S.
America / Africa with SE U.S. to form ancestral
Rocky Mountains
The Permo-Triassic Sonoma orogeny:
"retro-arc" thrusting
The Sevier orogeny:
E-directed thrusting behind a magmatic
arc–
"retro-arc" fold-thrust belt and associated
foreland basin system
What's going on at this time (~60 myr ago?)
Eastward sweep in magmatism
Basement-involved deformation
"Laramide" orogeny
Magmatism starts sweeping back to west
– 45 Myr ago
More "Laramide" deformation
More westward sweep in magmatism-
Major change in style of deformation!
Rifting and development of
Cordilleran metamorphic core
complexes related to major crustal extension
Basin and Range Extension
Eruption of Columbia River basalts
Magmatism back to west
Growth of Basin and Range Province
Today!
Relating plate tectonics to continental deformation
Bigger picture: formation of the Cordilleras due to long-lived oceanic subduction
Concept of "Suspect" terranes- possibly far-traveled and torn off of other continents, rafted across large tracts of
oceans and finally accreted to W. N.A.
Crustal "immigration"
Reminder!:
Final Exam
Monday, Dec. 16, 11-1
this room
Next Lecture:
Review for final