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Earth History GEOL 2110

Earth History GEOL 2110. The Mesozoic Era Geologic and Tectonic History of the North American Cordilleran. Major Concepts.

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Earth History GEOL 2110

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  1. Earth History GEOL 2110 The Mesozoic Era Geologic and Tectonic History of the North American Cordilleran

  2. Major Concepts • The geologic history of Cordilleran Orogen of North America during the Mesozoic Era was dominated compressional tectonics that accreted exotic terranes in the early Mesozoic (Triassic and early Jurassic periods) and then became Andean-type volcanic arc in the mid- to late Mesozoic (Jurassic and Cretaceous periods). • A flattening out of subduction in the Cretaceous is thought to squelch volcanism in the central part of the western US and bring about a basin and range type tectonism called the Laramideorogeny • A major transgression in the Cretaceous created a Great Interior Seaway where great accumulation of marine and non-marine sediment were deposited in the Great Plains

  3. Events of the Mesozoic Era

  4. Accumulation of Thick Cambrian Sediments on the Rifted Western Margin of Laurentia Belt Supergroup sediments preserved in rift grabens (aulocogens)

  5. Late Devonian-Mississippian Antler OrogenyAccretion of a Volcanic Island Arc

  6. The Ancestral Rocky MountainsPennsylvanian-Permian Cratonic Warping

  7. Penn-Perm OuchitaOrogenExtension of the AppalacianOrogen

  8. Tectonic Grain of Vergence shifts in the Mesozoic Paleozoic Vergence Mesozoic Vergence

  9. Triassic Accretion of Suspect TerranesCollage Tectonics Six Major Suspect Terranes 2 mostly Paleozoic 3 Late Paleozoic- Early Mesozoic 1 mostly Mesozoic Wrangellia – oceanic ridge system Sonoma/Stikinia – volcanic arcs

  10. Evidence for Suspect TerranesPaleomagnetic Latitudes Reconstructions and Tethyan Fossil Assemblages Many terranes contain fossils that suggest a source from the Tethys Sea

  11. Timing of Suspect TerranesVergence Cont, TerA and TerB all have unique paleopoleorienations Cover Sed I contains pebbles from Cont and Ter B only Cover Sed II contains pebbles from all terranes and late intrusions Age of granites sets upper age of vergence of TerA and TerB

  12. Late Triassic Transition to Andean-type Margin Antler Orogeny SonomanOrogeny Navajo Sandstone SierranOrogeny

  13. Continental Volcanic Arc

  14. Forearc Environment Accretionary Wedge - material scraped off descending slab Melange – complex mix of rock types – ophiolites and deep water sediments Forearc basin – filled with immature graywacketurbidites

  15. Forearc Rock Types Blueschist(Hi-P metamorphic rx) Franciscan Melange Pillowed Basalts Great Valley Greywackes

  16. Magmatic Arc EnvironmentGranite Batholiths – Feeders to Stratovolcanoes Mt Jefferson

  17. Foreland Basin EnvironmentClastic Wedge Sedimentation Alluvial Fan Conglomerates

  18. Sevier OrogenyIntense Compression in the Late Cretaceous (~80 Ma) Devonian Thrust Fault SentinalMtns, British Columbia Triassic

  19. LaramideOrogenyUplifted Blocks of Precambrian Crust Latest Cretaceous – Eocene (65-35 Ma)

  20. LaramideOrogenyMagmatic Null Zone – Shallow Slab Subduction

  21. Magmatic Nulls in the Andean Continental Arc • Gaps in volcanic activity • shallow subduction • overthickened slab Winter (2011)

  22. Next Lecture • Cretaceous Trangression • And Mesozoic Life

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