Question

How did the location of the Laramide orogeny differ from that of the Cretaceous Sevier orogeny? What might explain this change?

Short answer

The location of the Laramide orogeny was more inland, while the Cretaceous Sevier orogeny occurred closer to the coastline. The primary factor explaining this change in location is the difference in angle of subduction. The Cretaceous Sevier orogeny had a steeper angle of subduction, leading to a more coastal location, whereas a shallower angle during the Laramide orogeny allowed the subducting plate to travel further inland before causing mountain building.

Step-by-step solution

Introduction to Laramide and Sevier orogenies

The Laramide orogeny and the Cretaceous Sevier orogeny are two mountain-building events that took place in the western part of North America. Both the events occurred during the Cretaceous period but had different geological characteristics and resulted in the formation of different mountain ranges. Understanding their differences in location is crucial for gaining insights into the geology and tectonic history of the region.

Location of Laramide orogeny

The Laramide orogeny took place from approximately 80 to 55 million years ago. The event resulted in the uplift of several mountain ranges, including the Rocky Mountains in the United States, the Sierra Madre Occidental in Mexico, and parts of the Andes in South America. The Laramide orogeny is characterized by its more inland location, which means the mountain building occurred relatively far from the coastline.

Location of Cretaceous Sevier orogeny

On the other hand, the Cretaceous Sevier orogeny lasted from approximately 140 to 50 million years ago and primarily affected the western regions of what is now the United States. The Sevier orogeny is characterized by a more coastal location, as the thrusting and folding that led to the formation of the Sevier mountain ranges occurred closer to the coastline, mainly in the present-day Nevada, Utah, Idaho, Montana, and Wyoming.

Comparing the locations of Laramide and Sevier orogenies

As we can observe, the Laramide orogeny occurred further inland, while the Sevier orogeny took place closer to the coastline. This difference in location gives each orogeny its distinct geological traits and results in the formation of different mountain ranges within the region.

Explaining the change in location

The main factor that could explain the change in location of these two orogenies is the angle of subduction. During the Cretaceous Sevier orogeny, oceanic plates were subducted beneath the North American continent at a relatively steep angle, leading to a more coastal location of the mountain-building processes. On the other hand, during the Laramide orogeny, a more shallow angle of subduction is believed to have occurred, which allowed the subducting plate to travel further inland beneath the continent before causing mountain building. This process, known as "flat-slab subduction," eventually resulted in the more inland location of the Laramide mountain ranges. In conclusion, the Laramide orogeny and the Cretaceous Sevier orogeny had different locations, with Laramide being more inland and Sevier being more coastal. The difference in location can be explained by the variation in the angle of subduction, with a shallower angle causing the Laramide orogeny to occur further inland than the Sevier orogeny.