How did the Rockies form?

[jaymz]

I thought this was an interesting video, challenging the prevailing model that at least I've always seen as a layperson. Disclaimer: I am as much of a geologist as I am a rocket scientist (not at all), so I'm not qualified to take any sort of 'position' on this. But I know there are some experts in the field here, so I thought others might either find this interesting, or say "this is nothing new," or brush it off as unscientific quackery. I'll leave that to the pros.

I would summarize it, but I'm sure I would misrepresent it.

[geojed]

I’m a geologist, hence my screen name, and thanks for sharing this video. It’s a fun and thought provoking watch. I’ll have to check out some of his other videos.

One thing that I always have to remind myself is that the Rocky Mountains we see today are only 10-20 million years old. The older (100-60MYa) Sevier/Laramide structures were all eroded down to rolling hills. It wasn’t until the uplift of the Colorado Plateau that the CO Rockies as we know & see them today really formed.

Rocks Above The Clouds is a fun, concise read about CO Geology. Amazon link: https://a.co/d/5l6jGT2

[ECF55]

I dabbled in hard rock geology a while back. Thanks for the post.

There’s so much complexity in the Western Cordillera. Clearly, there have been many terrane accretions since the breakup of Pangea along that western margin. Isotopic dating of the intrusive granitic plutons can definitely help nail down when subduction and accretion occurred, but subsequent tectonic imprinting can obscure the story.

The main thing I struggle with out West is that the western margin of our continent has really been stretched out and (separately but relatedly) deformed along giant strike-slip faults. Colorado used to be closer to the ocean, but the interaction of the North American plate with the Pacific Plate has caused all kinds of stresses that have transported crustal units northward and simultaneously extended the crust within what became the Great Basin. As the video highlights, this also happened well before our current San Andreas fault paradigm along different faults. Piecing all of it back through history remains a rich topic of research (and one that I sadly do not contribute to).

[peter303]

The gist is can the theory of plate tectonics explain all mountains in the world? The answer is at least 80%-90%. Most mountains are at colliding or subducting oceanic tectonic plates, like the Andes, Sierra Nevada, Alps, Zagros, Himalayas. The US Rockies are a problem, being rather far inland from a plate boundary and dont easily fit this model. Some geologists construct contorted elaborations of plate tectonics to explain the Rockies. Like they were closer to the plate edge before Nevada stretched wider. Or the subducting ocean plate can stay shallow and go a good deal inland before dropping as may be the case in the Himalayas.

The talk refers to a big seismic data survey conducted 2004-2016 called the US Array. It blanked the US with 2000 seismometers covering 20% of the US for two years, gradually moving a 1000 of them eastward 300 miles each year. Until then seismometer coverage in the Rockies was pretty sparse, except for areas with large quakes like Salt Lake City or Yellowstone. Seismologists could finally get more detailed geologic images below the Rockies.

The data delineated areas of more firm, colder rock and others of softer, warmer rock. Some geologists, as in this talk, try to interpret these features in terms of plate tectonics. The cold hard parts could be a fossil subducting plate under the Rockies.

Science purists dislike adding more elaborations to a theory. At some point the theory can explain anything. Then loses its ability to predict novel observations. The Rockies may be one of these problems.

[two lunches]

these are some of my favorite threads. thanks OP

also would like to recommend Roadside Geology of Colorado for killing time at trailheads: https://www.amazon.com/Roadside-Geology ... 921&sr=8-1

[onebyone]

Are the Rockies getting bigger or smaller. I read bigger. I guess at such a small rate it will take thousands of years to rise several feet? IDK

[Scott P]

Are the Rockies getting bigger or smaller. I read bigger. I guess at such a small rate it will take thousands of years to rise several feet? IDK

The Colorado Rockies are mostly getting smaller, even though they are still rising. This is because they usually aren't rising fast enough to counteract erosion. The Colorado Rockies are older than the Rockies farther west, which is where the main areas are that are rising faster overall than erosion. The Wasatch Range, Tetons, Idaho Rockies, and Western Montana Rockies are rising faster than and are mostly newer than the Colorado Rockies. You can tell which areas of the Rockies are rising faster than others due to the frequency of earthquakes. In 1983, the Borah Peak quake cause a the peak to rise and additional 1-7 feet above the valleys and some of the surrounding areas rose 16 feet. You can go see the escarpment, which is very distinct and visible.

[LURE]

from what i understand, generally speaking, geologists don't have a firm agreement on exactly how the colorado rockies were uplifted.

i believe the low angle subduction slab theory remains the best one, i could be wrong. it's what they were still saying is the likely cause when i was in school less than 10 years ago

Geology Underfoot Along Colorado's Front Range is another good read whether or not you do the self guided field trips it intends to send you on

[justiner]

It's really simple - obvious really:

The Rocky Mountains Aren't Real.

[Dave B]

It's really simple - obvious really:

The Rocky Mountains Aren't Real.

Great, another wacko. Every one knows the Rocky Mountains are real, Justin. They're where the lizard people live, in underground tunnels.

[GuiGirard]

I’m a geologist, hence my screen name, and thanks for sharing this video. It’s a fun and thought provoking watch. I’ll have to check out some of his other videos.

One thing that I always have to remind myself is that the Rocky Mountains we see today are only 10-20 million years old. The older (100-60MYa) Sevier/Laramide structures were all eroded down to rolling hills. It wasn’t until the uplift of the Colorado Plateau that the CO Rockies as we know & see them today really formed.

Rocks Above The Clouds is a fun, concise read about CO Geology. Amazon link: https://a.co/d/5l6jGT2

Agree with you on all points.

Likewise, as a geologist I'll also have to dig into more academic papers to get a more educated opinion. His hypothesis is entirely plausible, if based only on the data that he presents. What I'm not aware of is how much it has been tested by other independent evidence and/or how much evidence there is against it.

But as you and others have mentioned, it's worth reiterating that not much is left in the modern CO landscape of the object of this presentation, the Laramide orogeny. A lot has happened since then, among which the subduction-driven Southern Rocky Mountain Volcanic Field (~38-22 million years old) that encompasses most of the San Juan, the (vastly eroded) Thirtynine-mile volcanic field, the eroded volcanic fields in N CO, and the intrusions and volcanic rocks in the Sawatch, Elks, West Elks (eg, the Mount Aetna intrusive complex, Mt Princeton granite, Grizzly Peak caldera, the Snowmass granite) and elsewhere.
In other words, no matter what caused the Sevier/Laramide orogeny, subduction of an eastbound oceanic plate under the westbound N American continent had resumed at that time.

The highly dissected nature of intrusive complexes from that period (as seen for instance in the Sawatch) is evidence for younger tectonic events. The most recent one being the opening of the Rio Grande rift and its northern extensions across Colorado, namely the San Luis and upper Arkansas valleys (grabens) and reactivated uplift of the Sangre de Cristo and Sawatch ranges, respectively.

[peter303]

Earthscope/UNAVCO is a university consortium based in Boulder that maintains hundreds of continuous GPS stations around the United states. There are about two dozen in Colorado. They can measure tectonic velocities as slow as one millimeter a year. Their data from the past decade shows the Colorado Rockies sinking about one millimeter a year. In the figure below the light blue triangles are the GPS (GNSS) station locations. Light blue means one millimeter or less downward per year. At this rate, the Rockies would drop a foot in three centuries.



The GPS velocity viewer is at this link if you want tweak display parameters

https://www.unavco.org/software/visuali ... iewer.html