Sevier Laramide Orogenies The North rican Ame illera

Sevier & Laramide Orogenies

The North rican Ame illera Cord

Cordilleran Structure

Orogenic Sequence

The Orogenic Belt

Propagation of Thrust Belts

“Decollement”

Foreland Basins

Foreland Orogen Basin

Sevier Orogeny 170 to 80 Million years ago

Sevier: horribly complex

Middle Jurassic: 170 – 160 Million years ago

Late Jurassic: 160 – 155 Million years ago • Western Plate Margin Consolidates, accretion of Coast Range Ophiolite • Farallon Plate Subduction Begins

Latest Jurassic: 155 – 142 Million years ago • Voluminous Arc Magmatism • Crustal Shortening

Early Cretaceous: 142 – 110 Million years ago • Emplacement of “Mega-Thrust Sheet”

Middle Cretaceous: 110 – 85 Million years ago • Onset of rapid shortening and Sevier Orogeny

Sevier: oversimplified

Sediments in the Foreland Basin The diagram shows two diferent kinds of sediments in the foreland basin: • Sediment from the west is clastic sandstone and mudstone, eroded from the mountains of the thrust belt. • Sediments from the east are shales and marine sediments which developed in a shallow sea. The dotted line shows the migration of sea level back and forth as sediments were deposited.

Laramide Orogeny 80 to 40 Million years ago

Sevier: another look

Laramide to the east

Laramide Involves Basement!

Follow this link for a neat movie! http: //element. ess. ucla. edu/publications/1998_Laramide/RMF_velocity_movie. gif