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 Laramide Orogeny
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 Orogeny Accretion of a Volcanic Island Arc
Sediments Shed off the Antler Orogen

6. The Ancestral Rocky Mountains Pennsylvanian-Permian Cratonic Warping

7. Penn-Perm Ouchita Orogen Extension of the Appalacian Orogen

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

9. Triassic Accretion of Suspect Terranes Collage 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 Terranes Paleomagnetic Latitudes Reconstructions and Tethyan Fossil Assemblages
Many terranes contain fossils that suggest a source from the Tethys Sea

11. Timing of Suspect Terranes Vergence
Cont, TerA and TerB all have unique paleopole orienations
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
Accretion of Suspect/Exotic Terranes and Volcanic Arcs
Sonoman Orogeny
Navajo Sandstone
Sierran Orogeny

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 graywacke turbidites

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

16. Magmatic Arc Environment Granite Batholiths – Feeders to Stratovolcanoes
Mt Jefferson

17. Foreland Basin Environment Clastic Wedge Sedimentation
Alluvial Fan Conglomerates
= Molasse
Deep water muds
= Flysche

18. Sevier Orogeny Intense Compression in the Late Cretaceous (~80 Ma) results in Crustal Thickening by Overthrusting
Devonian
Thrust
Fault
Sentinal Mtns,
British Columbia
Triassic

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

20. Laramide Orogeny Magmatic Null Zone – Shallow Slab Subduction

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

22. Cretaceous Trangression
Next Lecture
Cretaceous Trangression
And Mesozoic Life