Brief overview of North American Cordilleran geology by Cin Ty Lee
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Brief overview of North American Cordilleran geology by Cin‐Ty Lee Note: make sure to take notes as I will talk or sketch on the board many things that are not presented explicitly in these slides Topography map of North America
Transcript of Brief overview of North American Cordilleran geology by Cin Ty Lee
Brief overview of North American Cordilleran geologyby Cin‐Ty Lee
Note: make sure to take notes as I will talk or sketch on the board many things that are not presented y g pexplicitly in these slides
Topography map of North America
Topography mapTopography map
H d th N th A i C dill fit i t l b l t t?How does the North American Cordillera fit into a global context?
Dickinson 2004
P‐wave tomography: Seismic structure beneath western USA
Burdick et al. 2008
Crustal provinces of North America (Laurentia)‐Proterozoic and Archean terranes were already assembled by 1.6 Ga
Hoffman, 1988
Crustal provinces in southwestern USA
Hoffman, 1988Bennett and DePaolo, 1987
Some examples of tectonic margins for your referencemargins for your reference
Dickinson and Snyder, 1978
1.1 Ga = Rodinia Super‐continent (Grenvillian age)Neo‐Proterozoic = Rodinia breaks up
“western” margin of Laurentia represents a passive margin due to opening ofwestern margin of Laurentia represents a passive margin due to opening ofthe Panthalassan ocean
700‐400 Ma
Western margin of Laurentiarepresents a passive margin
Dickinson and Snyder, 1978
400‐250 Ma
Passive margin is interrupted in Devonian times by the accretion of island arcs
Antler and Sonoma orogeniesAntler and Sonoma orogenies
Accretion of allochthonousterranes to the western margin f h N h A iof the North American craton
Antler/Sonoma orogenies result in the accretion of Paleozoic island arc terranes to western North America
PermianFormation of Pangea“ ” i f N h A i d i d b bd i“western” margin of North America now dominated by subduction zone
250‐50 Ma250 50 Ma
Subduction results in continued accretion of fringing island arcs and the generation of continental magmatic arcs
Sierra Nevada batholith
Sevier and Laramide Orogenies
150‐70 Ma
Sevier orogeny and ti t l ticontinental arc magmatism
Thin‐skinned deformation‐ thrust sheets
One view of convergent gmargin of western North America between 180‐50 My
DeCelles, 2004
Late Cretaceous
Present‐day geologic map y g g pof western North America, showing salient Cretaceous and younger tectonic featurestectonic features
DeCelles, 2004
Cretaceous (Turonian)
Generation of deep basins behind the arc
aka Cretaceous Inland Seaaka Cretaceous Inland Sea
‐high organic content (black shales, coal)b t it ( l f d f h)‐bentonite (clays formed from ash)
DeCelles, 2004
Cretaceous (Maastrichtian)
Isopach mapp p
back arc basins
DeCelles, 2004
Back arc basins may be related to dynamic topography and flexureBack arc basins may be related to dynamic topography and flexure
DeCelles, 2004Taken after Gurnis
Migration of arc magmatic front eastward~70 Ma Sierran arc magmatism cuts off and then sweeps eastward~70 Ma, Sierran arc magmatism cuts off, and then sweeps eastward
Eastward migration of arc front is thought to be related to flat subduction beginning at ~74 Ma and continuing until ~40 Ma~74 Ma and continuing until ~40 Ma
Dickinson and Snyder, 1978
Flat subduction results in thick‐skinned compressional deformationLARAMIDE OROGENY‐ LARAMIDE OROGENY
‐ basement‐core uplifts‐ examples of Laramide uplifts include the Rocky Mountains, Colorado Plateau, Wind River Range, Tetons
End result of Laramide orogeny is a thickened crust
Magmatism associated with the Laramide orogeny‐ Andesitic volcanoes near Yellowstone (the Absaroka Range) are associated with Laramide magmatismg
At ~30 Ma, compressionalforces along the edge of and beneath North America begin to decrease as the Pacific‐Farallon ridgeas the Pacific Farallon ridge approaches the margin.
Flat‐subducting Farallonl t “ ll ” b kplate “rolls” back or
collapses
Laramide orogeny endsg y
Thickened North American Cordillera begins to collapse gravitationallycollapse gravitationally
Collision of Pacific‐Farallon Ridge with North American trench, terminates subduction and generates a transform fault (the Sangenerates a transform fault (the San Andreas).
A “slabless” window opens up beneath western USA.
Basin and Range style extension kicks inkicks in
Late Cenozoic lithosphere extension results in the generation of decompression magmatism in the underlying asthenosphere
Yellowstone hotspot appears (not obviously related to extension; thought to be a plume)
DeCelles, 2004
Geologic summary
Dickinson, 2004
Useful Websites
Lava and magma database for western USAwww.navdata.org
Global supercontinent cycles www.scotese.com
San Andreas Fault plate reconstructions (Tanya Atwater)San Andreas Fault plate reconstructions (Tanya Atwater)http://emvc.geol.ucsb.edu/downloads.php
