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Download Brief overview of North American Cordilleran geology by Cin
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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 y g p explicitly in these slides Topography map of North America Topography map Topography map H d How does the North American Cordillera fit into a global context? th N th A i C dill fit i t l b l t t? 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 margins for your reference Dickinson and Snyder, 1978 1.1 Ga = Rodinia Super‐continent (Grenvillian age) Neo‐Proterozoic = Rodinia breaks up “western” western margin of Laurentia margin of Laurentia represents a passive margin due to opening of represents a passive margin due to opening of the Panthalassan ocean 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 orogenies Antler and Sonoma orogenies Accretion of allochthonous terranes to the western margin of the North American craton f h N hA i Antler/Sonoma orogenies result in the accretion of Paleozoic island arc terranes to western North America Permian Formation of Pangea “ “western” margin of North America now dominated by subduction ” i fN hA i d i db bd i zone 250‐50 250 50 Ma 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 continental arc magmatism ti t l ti Thin‐skinned deformation ‐ thrust sheets One view of convergent g margin of western North America between 180‐50 My DeCelles, 2004 Late Cretaceous Present‐day geologic map yg g p of western North America, showing salient Cretaceous and younger tectonic features tectonic features DeCelles, 2004 Cretaceous (Turonian) Generation of deep basins behind the arc aka Cretaceous Inland Sea aka Cretaceous Inland Sea ‐high organic content (black shales, coal) ‐bentonite b t it (clays formed from ash) ( l f df h) DeCelles, 2004 Cretaceous (Maastrichtian) Isopach p map p back arc basins DeCelles, 2004 Back arc basins may be related to dynamic topography and flexure 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 ~70 Ma, Sierran arc magmatism cuts off, and then sweeps eastward 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 deformation ‐ LARAMIDE 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 magmatism g At ~30 Ma, compressional forces along the edge of and beneath North America begin to decrease as the Pacific‐Farallon as the Pacific Farallon ridge ridge approaches the margin. Flat‐subducting Farallon plate “rolls” back or l t “ ll ” b k collapses Laramide orogeny g y ends Thickened North American Cordillera begins to collapse gravitationally collapse gravitationally Collision of Pacific‐Farallon Ridge with North American trench, terminates subduction and generates a transform fault (the San generates a transform fault (the San Andreas). A “slabless” window opens up beneath western USA. Basin and Range style extension kicks in kicks 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 USA www.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
