What was the Cordilleran orogeny? Briefly describe the four ...

[jwb375]

What was the Cordilleran orogeny? Briefly describe the four phases of the orogeny. What will be an ideal response?

Question 2

What was the tectonic evolution of western North America beginning with the Permian and through
  the Mesozoic? What will be an ideal response?

[Amiracle]

Answer to Question 1

The Cordilleran orogeny is the mountain-building activity that began during the Jurassic and continued
into the Cenozoic and is related to the westward movement of the North American plate as it overrode
the Pacific plate. During the Nevadan orogeny, the first phase, subduction of the Pacific plate beneath
North America generated large volumes of granitic magma at depths that were uplifted to become the
Sierra Nevada and other batholiths. During the second phase, the Sevier orogeny, older rocks were
thrust eastward on top of younger rocks in numerous overlapping, low-angle thrust faults producing
north-south-trending mountain ranges. The final pulse was the Laramide orogeny in which most of the
features of the present day Rocky Mountains began.

Answer to Question 2

During the Permian, an island arc and ocean basin formed off western North America, and then an
oceanic plate subducted beneath the island arc. Oceanic and island arc rocks were thrust eastward
against the craton during the Permian-Triassic boundary. In the Early Mesozoic, western North
America became an oceanic-continental convergent plate boundary, with a steeply dipping subduction
zone as North America moved over the Pacific plate.