Talk:Basin and range

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Basin and Range

I always thought this was called the "Basin and Range Province" because it was more-or-less unique, but this description makes it sound like there are more. What are the others?? Stan 13:40 14 Jun 2003 (UTC)

I'm only really familiar with North American geology but I'm sure some other basin and range systems exist elsewhere (esp. back in geologic time). Basins and ranges (or horsts and grabens) are common on the earth anywhere where there are extentional forces at work. Perphaps a general article at horst and graben and a specific one at Basin and Range Province would be best. --mav

There is also some controversy about the origin of the Basin and Range province. mav listed a common one, but I've heard three others. I've been meaning to research this, since I don't know how accepted each hypothesis actually is.

My (non-expert) opinion is that Basin and Range applies to the province, and is unique. -- hike395 03:58 21 Jun 2003 (UTC)

The Rocky Mountains were created first during the Laramide Orogeny during the Cordilleran mountain building episode. After the mountains were raised nearly as high as the Himalayas then part of western North America started to stretch and much of the high mountain plateau started to get broken up into ranges with grabens in between them. There are a couple major reasons hypothesized to explain this; movement of the Pacific Plate relative to the North American Plate. I've also read many times that there may be a very large hot spot under that part of North America and that the crust there is a lot thinner than in other parts. To explain this some geologists hypothesize that much of the root of the very high mountain plateau formed by the Laramide orogeny broke off. All pretty darn interesting. Oh, and upon further re-reading a couple of my geology books dealing with this subject I've noted that this province is most often called Basin and Range Province or Basin and Range province. Which capitalization do you think is best? --mav 04:34 21 Jun 2003 (UTC)

I would recommend Province over province... The explanations I've seen are

1. After the Laramide orogeny, the crust under the Rockies got overthickened and the Great Basin spread out in response.
2. As the East Pacific spreading center subducted beneath the North American plate, it formed a "slab gap", which causes heat from the mantle to thin out the crust and cause the spreading.
3. As you've said above, traction from the Pacific Plate stretches the North American plate towards the West.
4. The upwelling zone in the mantle (under Yellowstone) stretched and fractured the crust. (A variant I saw: the upwelling caused by an asteroid impact)

Should we include this in the main article, in some suitable NPOV way? -- hike395 07:35 21 Jun 2003 (UTC)

Thanks for jogging my memory. Number 4 is new to me and I suspect is wrong simply because the Yellowstone hot spot is too small and too far north to have any effect over such a huge area of the south western proto-Rockies. The Yellowstone hotspot has, however, created the Snake River Plain. There seem to be two competing ideas about how the crust responded to the great deal of campaction it went through with the Laramide orogeny. I hadn't heard of number 1 before but it does seem to be more believable than what I was taught about the root of the Rockies at that point falling away (both should be mentioned though). Number 2 is interesting since I recall that the "slab gap hypothesis" was also one of the explanation for the extension and flood basalts seen in southern Washington, Oregon and northern California about 17 million years ago.

I also now recall one of my professors lecturing about a similar thing happening to explain the Basin and Range but there was no mention in any of my textbooks about it. The way she explained it is that the Laramide orogeny resulted from a fast and very shallow angle of subduction - so shallow that the were no volcanics associated with it in the central West ; the zone where super-critically-heated steam (comming off the subducting oceanic crust) melted rock was spread out over too large of an area to concentrate enough magma in one place to punch through. So when the spreading zone finally was subducted, that gap and its underlying magmatic plume continued to travel east under North America at a shallow angle (sic. close to the root of the continental lithosphere). This heat and pressure had the opposite effect that the shallow subduction had and extension was the result. Thanks again for reminding me about that - its been a few years. I'll see about bringing all this together and placing it in the article tomorrow. --mav

Hey, great articles on Basin and Range Province and Laramide orogeny! Also, wanted to share a little more research: [1][2] .. Looks like people are starting to believe that deep-seated mantle plumes are bogus, anyway. So, instead of Yellowstone causing the Basin and Range, it may be that the Basin and Range caused Yellowstone! -- hike395 12:29 22 Jun 2003 (UTC)

Thanks! You had me going there a bit by saying "Looks like people are starting to believe that deep-seated mantle plumes are bogus..." since that would mean a very important part of plate tectonic theory was being disproved. Don't scare me like that! :-) I think you intended to say "Looks like people are starting to believe that deep-seated hot spots fed by mantle plumes are bogus..." Interesting links BTW - but I never really bought the deap-seated hot spot idea anyway. Just the thought of such a narrow chimney of convention managing to move heat and magma all the way from deep in the mantle always seemed preposterous when HUGE convention currents are operating in the same mantle and are driving plate tectonics. --mav

Oops, sorry for the imprecision. I meant hot spots, as you inferred. Shouldn't type things at 4AM local time... I find mantle convection hard to thinking about --- we're talking viscosity of piano wire and time scales of tens of millions of years, so it's really hard (for me) to get a good intuition.

Hm. I think I'll update the hot spot article. -- hike395 16:46 22 Jun 2003 (UTC)