brief overview of north american cordilleran geology by...
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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
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Topography mapTopography map
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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
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P‐wave tomography: Seismic structure beneath western USA
Burdick et al. 2008
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Crustal provinces of North America (Laurentia)‐Proterozoic and Archean terranes were already assembled by 1.6 Ga
Hoffman, 1988
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Crustal provinces in southwestern USA
Hoffman, 1988Bennett and DePaolo, 1987
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Some examples of tectonic margins for your referencemargins for your reference
Dickinson and Snyder, 1978
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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
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700‐400 Ma
Western margin of Laurentiarepresents a passive margin
Dickinson and Snyder, 1978
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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
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Antler/Sonoma orogenies result in the accretion of Paleozoic island arc terranes to western North America
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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
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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
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150‐70 Ma
Sevier orogeny and ti t l ticontinental arc magmatism
Thin‐skinned deformation‐ thrust sheets
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One view of convergent gmargin of western North America between 180‐50 My
DeCelles, 2004
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Late Cretaceous
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Present‐day geologic map y g g pof western North America, showing salient Cretaceous and younger tectonic featurestectonic features
DeCelles, 2004
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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
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Cretaceous (Maastrichtian)
Isopach mapp p
back arc basins
DeCelles, 2004
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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
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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
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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
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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
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Magmatism associated with the Laramide orogeny‐ Andesitic volcanoes near Yellowstone (the Absaroka Range) are associated with Laramide magmatismg
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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
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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
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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)
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DeCelles, 2004
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Geologic summary
Dickinson, 2004
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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