|
Contents
Laramide orogeny
The Laramide orogeny was a 30 million year period of mountain building[?] in western North America that started in the Late Cretaceous 70 million years ago and ended in the Late Paleogene 40 million years ago. The major feature that was created by this orogeny was the Rocky Mountains.
This period started when the angle of subduction occurring off the west coast of North America became so shallow that no volcanics occurred in the central west and the underlying oceanic lithosphere actually caused drag on the root of the overlying continental lithosphere. Geologists call such a lack of volcanic activity near a subduction zone a magmatic null. This particular null was created because the 300 kilometer depth needed to turn a subducting oceanic plate into a magma-generating machine occurred well under an already very think part of North America's continental crust and this area was also spread out over a long distance. Therefore there was never enough magma generated at any one place to make it possible for it the travel anywhere near the surface and feed volcanos. But the main result of shallow angle of subduction and the drag which it caused was a broad belt of mountains that were the progenitors of the Rocky Mountains.
Part of the proto-Rocky Mountains would be later modified by extention to become the Basin and Range Province.
| Elsewhere |  | |
Search engine
Web directory
|
CONTENTS:
|
