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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 Topography map How does the NthNorth AiAmerican Cor dillera fit itinto a gllblobal contt?text?

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, 1988 Bennett and DePaolo, 1987 Some examples of tectonic margins for your reference

Dickinson and Snyder, 1978 1.1 Ga = Rodinia Super‐ (Grenvillian age) Neo‐Proterozoic = Rodinia breaks up “western” margin of Laurentia represents a passive margin due to opening of the Panthalassan 700‐400 Ma

Western margin of Laurentia represents 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

Accretion of allochthonous terranes to the western margin of the NNhorth AAimerican craton Antler/Sonoma orogenies result in the accretion of island arc terranes to western North America Permian Formation of Pangea “”“western” margin of NNhorth AAimerica now ddiominate d by subduct ion zone 250‐50 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 and continen ta l arc

Thin‐skinned deformation ‐ thrust sheets One view of convergent margin of western North America between 180‐50 My

DeCelles, 2004 Late Present‐day gggeologic map of western North America, showing salient Cretaceous and younger tectonic features

DeCelles, 2004 Cretaceous (Turonian)

Generation of deep basins behind the arc aka Cretaceous Inland

‐high organic content (black shales, coal) ‐btitbentonite (l(clays ffdormed from ash)

DeCelles, 2004 Cretaceous (Maastrichtian)

Isopach map

back arc basins

DeCelles, 2004 Back arc basins may be related to dynamic topography and flexure

DeCelles, 2004 Taken after Gurnis Migration of arc magmatic front eastward ~70 Ma, Sierran arc magmatism cuts off, and then sweeps eastward Eastward migration of arc front is thought to be related to flat beginning at ~74 Ma and continuing until ~40 Ma

Dickinson and Snyder, 1978 Flat subduction results in thick‐skinned compressional deformation ‐ LARAMIDE OROGENY ‐ basement‐core uplifts ‐ examples of Laramide uplifts include the Rocky , , 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 magmatism At ~30 Ma, compressional forces along the edge of and beneath North America begin to decrease as the Pacific‐Farallon ridge approaches the margin.

Flat‐subducting Farallon pltlate “ll”“rolls” bbkack or collapses

Laramide oroggyeny ends

Thickened North American begins to collapse gravitationally Collision of Pacific‐Farallon Ridge with North American trench, terminates subduction and generates a transform (the San Andreas).

A “slabless” window opens up beneath western USA.

Basin and Range style extension kicks in

Late lithosphere extension results in the generation of decompression magmatism in the underlying

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 USA www.navdata.org

Global supercontinent cycles www.scotese.com

San Andreas Fault plate reconstructions (Tanya Atwater) http://emvc.geol.ucsb.edu/downloads.php