How did the Rocky Mountains Form?
Nick Zentner・42 minutes read
The lecture delves into the controversial formation of the Rocky Mountains, challenging conventional models of the past 50 million years, proposing continental collision instead of subduction. Geologists suggest North America collided with a fixed island arc, different from the old Farallon plate theory, causing unique geological features like thrust faults and magma generation in the Rockies.
Insights
- The traditional model of Rocky Mountain formation involving the Farallon plate subducting beneath California is challenged by new evidence, suggesting a continent versus continent collision similar to the Himalayas, with North America moving towards fixed island arcs, contrary to previous beliefs of the Farallon plate moving towards North America.
- The intricate geological processes forming the Rockies include North America colliding with a fixed island arc, resulting in the continental crust being pulled into the trench, leading to slab failure, magma generation, and complex interactions between multiple subduction zones, showcasing thrust faults, reverse faults, and stacked sedimentary rocks in regions like the Canadian Rockies and Northern Montana Rockies.
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Recent questions
How did the Rocky Mountains form?
Through continent collision and complex geological processes.
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Summary
00:00
Rocky Mountains Formation Controversy Explained
- Lecture on how the Rocky Mountains formed, focusing on controversial content.
- Instructor's background in geology and teaching experience for 35 years.
- Teaching approach in geology 101, starting with passive topics and transitioning to plate tectonics.
- Explanation of plate boundaries and mountain formation globally.
- Mention of the Himalayas as an example of convergent continent collision.
- Different types of major mountain ranges worldwide, including volcanoes and underwater ranges.
- Introduction to the controversy surrounding the formation of the Rocky Mountains.
- Discussion of old and new evidence challenging the conventional model of Rocky Mountain formation.
- Description of the old model explaining the Rocky Mountains' formation involving the Farallon plate subducting beneath California.
- Explanation of the geology of the Rocky Mountains, including block uplifts and thrust faults, between 100 and 50 million years ago.
16:57
"Rockies Formed by Pacific Collision, Slab Wall"
- 85 million years ago, Sierra Nevada rocks solidified, shutting off volcanic activity in Yosemite.
- The Fairlawn plate model shifts activity eastward between 85 and 50 million years ago.
- By changing the angle of the Fairlawn plate 85 million years ago, thrust faults in Colorado, Wyoming, Utah, and Montana were created.
- The entire system shuts down 50 million years ago, particularly in Idaho and Montana.
- Seismic tomography reveals ocean plates still present in the lower mantle, contradicting past beliefs.
- The old Fairlawn plate is not found in the mantle, challenging previous models.
- A vertical slab wall, five times thicker than normal, is discovered beneath the East Coast of North America.
- The sinking rate of this slab wall is determined to be 10 millimeters per year.
- The slab wall is interpreted as a fixed oceanic trench, impacting the formation of the Rocky Mountains.
- North America's collision with a fixed microcontinent in the Pacific, not the Fairlawn plate, led to the formation of the Rockies.
36:03
Rockies' Formation: Continent Collision and Thrust Faults
- The Rocky Mountains' formation differs from the California story due to the Laramide orogeny, a result of the North American continent colliding with a fixed island arc.
- The geology of the Rocky Mountains involves uplifted blocks, such as those in Colorado and Utah, extending up to the Canadian Rockies, with the Snake River plain and other features.
- Traditional explanations of the Rockies involved the Farallon plate subducting eastward, creating the Sierra Nevada and eventually the Rockies by altering the subduction angle.
- The new model suggests a continent versus continent collision, akin to the Himalayas, with North America drifting towards fixed island arcs, contrary to the previous belief of the Farallon plate moving towards North America.
- The formation of the Rockies includes the shortening of the crust, thrust faults, and reverse faults, with North America's continental crust being pulled into the trench, leading to slab failure and magma generation.
- The Rockies' construction involves multiple subduction zones, with North America encroaching on fixed island arcs, causing complex geometries and interactions.
- The Canadian Rockies and Northern Montana Rockies exhibit thrust faults and stacked sedimentary rocks, showcasing the effects of the collision between North America and the fixed island arc.
- The Burgess Shale and other sedimentary layers within the Rockies may hold crucial details for understanding the region's formation, particularly when studying paleomagnetism.
- The animation illustrates North America's approach towards the fixed island arc, with the continent's leading edge being pulled into the trench, leading to slab failure and the initiation of complex geological processes.
- The process of North America colliding with the fixed island arc, causing the continental crust to be pulled into the trench, highlights the intricate mechanisms behind the formation of the Rockies, including slab failure and magma generation.
54:32
Sierra Nevada Purple Line: Suture Zone Discovery
- Leading geophysicists and Canadian field geologists suggest that the purple line in the Sierra Nevada foothills may be the suture zone between the fixed island arc and North America, sparking a hunt to pinpoint the exact location for potential Westward subduction models in the lower 48 states, with considerations for both Westward and Eastward subduction occurring simultaneously to satisfy California geologists' California Triad theory. Additionally, a new perspective on the formation of the Rocky Mountains is proposed, requiring adjustments from Eastward to Westward movements and the removal of India from the geological picture.
