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Author Topic: Plate Tectonics  (Read 12889 times)

Offline JimBob

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Plate Tectonics
« on: 09/03/2006 16:39:07 »
For all interested, as DoctorBeaver is, I do not want to write all this again so here is a link that is rather comprehensive.

(Eth, sorry I couldn't find the thread where you aked for this)

http://www.uwgb.edu/dutchs/EarthSC202Notes/platetec.htm

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Offline Ophiolite

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Re: Plate Tectonics
« Reply #1 on: 09/03/2006 17:34:18 »
The discovery of plate tectonics was a moving experience.

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Offline JimBob

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Re: Plate Tectonics
« Reply #2 on: 10/03/2006 16:47:27 »
Especailly if one happened to be using Mr. Crapper's invention when the event occured!

Im on the Ubuntu. It is a bit slower but acceptable.

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Offline DoctorBeaver

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Re: Plate Tectonics
« Reply #3 on: 11/03/2006 00:49:49 »
Thank you, JimBob

Brand new forum
http://beaverland.forumup.us/
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Offline Ophiolite

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Re: Plate Tectonics
« Reply #4 on: 11/03/2006 11:44:37 »
An interesting aspect of plate tectonics is that the revolution it brought to the Earth sciences, comparable with the impact of evolution on biology, was delayed by four decades because geologists in general, and geophysicists in particular, rejected Wegner's hypothesis of Continental Drift.

This rejection was base upon two things:
a) No plausible mechanism was proposed.
b) Wegner was not a geologist, but a meterologist. Therefore, what could he possibly know about geology.

I am certain that the second of these reasons was the more potent in ignoring the concept.

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Offline JDG8R

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Re: Plate Tectonics
« Reply #5 on: 20/03/2006 02:48:28 »
Never understood how those young interior mountain ranges like the rockies got there.  Yeah, I can see the Andes or the San Bernardino's,for example, happening, so close to the coast and what-not, but please update the latest on the Rockies again?

« Last Edit: 20/03/2006 03:00:05 by JDG8R »
 

Offline JimBob

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Re: Plate Tectonics
« Reply #6 on: 20/03/2006 04:36:36 »
JDG - you'll get as many explinatrions as there are people. But I just turned on the TV and I am going to get of-line. BAD storms with two tornados aimed roght at me. Tomorrw, if I don't find Dorthey in OZ.


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Offline Ophiolite

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Re: Plate Tectonics
« Reply #7 on: 20/03/2006 13:08:08 »
JDC -
The growth of the Rocky Mountains has been one of the most perplexing of geologic puzzles. Normally, mountain building is focused between 200 to 400 miles inland from a subduction zone boundary, yet the Rockies are hundreds of miles farther inland. What geologic processes raise mountains at this scale? Although geologists continue to gather evidence to explain the rise of the Rockies, the answer most likely lies with an unusual subducting slab.
At a 'typical' subduction zone, an oceanic plate typically sinks at a fairly high angle (see above). A volcanic arc grows above the subducting plate. During the growth of the Rocky Mountains, the angle of the subducting plate may have been significantly flattened, moving the focus of melting and mountain building much farther inland than is normally expected.
It is postulated that the shallow angle of the subducting plate greatly increased the friction and other interactions with the thick continental mass above it. Tremendous thrusts piled sheets of crust on top of each other, building the extraordinarily broad, high Rocky Mountain range.


Source:http://wrgis.wr.usgs.gov/parks/province/rockymtn.html


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Offline JimBob

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Re: Plate Tectonics
« Reply #8 on: 21/03/2006 00:49:10 »
Hi Jim, able to get back to you this evening; must keep other people happy, esp. since they have the part-time work for me.

As I said, there are many theories but what is evident to most geologist is the different tectonic styles from province to province. One of the reasons is the different lithosphere elementnts below the western part of the NA continent. (see http://www.colorado.edu/GeolSci/faculty/pdf/karlstrom_et_al_0302.pdf esp. the N-S crossections)

An example of the problem of multiple mechanisms is seen in the existence of the Colorado Plateau and what role it played in the Laramide Orogeny and subsequent movement. Many geologist, myself included, find the most convincing explination to be the deissaperance of the Farallon plate beneath the continent and it NOT being subducted  into the mantel until it reach the middle of the continent. This would explain in my mind the very young (~5 Ma) age of the Colorado River and the extremly fast uplift of the Plateau. (see http://www.uwgb.edu/dutchs/platetec/kula.htm )

Yet others refuse to even consider this possibility, because of the crustal thinning and resultant structurally higher MOHO under the Great Basin. This was domonstrated by Podhil (? cannot remeber the name, USGS employee, rebuilding a bibliography lost in a reformat) in the late 80's or early 90's.

Bring this question up with a room full of geologist in Denver and the discusion will be spirited.

A majority, however, will now lean toward the idea I think best suits all the data.

Yet this doesn't fully address the evolution of the Cordilleras in southern New Mexico or most of Wyoming and all of Montana and Idaho. In Colorado the range is only a little over 100 miles wide. In New Mexico, they thin to almost nothing which cannot adequately be accounted for.  North of Colorado the mountains are three to four times as wide. No generally acceptable mechanism for these problems has been put forward to date.

The USGS page does account for the anomolies mentioned since the lithosphere is thinner to the west of the Rockies from southern Washington to Mexico and vulcanism is very pronounce in the same area of thining. No one seems to be able to yet come up with a full blown explination. It seems to be analogus to the yet unreached Unified Field Theory!  

I have my own ideas but they are from personal observations only. None have been published but I am discussing them with several friends who are retired now, all have their doctorate, and one is a former state geologist. We are onto the road to publishing so until that time I'll let it lie.

Jim

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Offline JDG8R

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Re: Plate Tectonics
« Reply #9 on: 21/03/2006 01:30:43 »
Thank you so much for these thoughtful answers guys. On this and other posts.  You mention research that I'm not aware of (I am very out of touch) and if I still lived close to a good library, might be inclined to go there and read and understand the details and form my own opinion.

But I do understand what you describe.

How about this (warning: armchair question coming):

For this topic, and a myriad of others, what is your general feeling toward catastrophism?  

I am convinced (by watching tv on the subject I am not ashamed to admit) that  certain very large (1000's of square mile)erosion features  happen relatively quickly (The one on tv was one  probably known to you, somewhere in Montana I think).  A simple model, using sediment for the plain and water plus glacial till as the released material,  showed that storing water above that plain and releasing it (like a glacial lake periodically unplugged) would create a landscape very similar to what this certain canyon or basin actually looks like today.  Deep cut ravines.  Angular features. And large boulders stuck up out of the ground out in the middle of flatlands.  The time scale there I think was in the 1,000s of years.

Anyway, I try to apply this to tectonics in my feeble mind. Seems to me that a meteor impact in the right place is going to release some major stresses that have built up in the crust. Have we recorded a major stress relief yet?

Suppose a shallow SiAlic subducted plate below Utah has spent 10 million years moving east.  Along the way it throws up the mountains around Park City.  Then whack, the meteor hits and that baby slides all the way to Snowmass and provides us with another excellent place to ski.

There are probably a million different scenarios.

What is the greatest elevation change of any mountian range that has been observed in the last 500 years?  Does that extrapolate to anywhere near the 14,000 feet in elevation over what ever the age of the rockies are or to the 29,000 feet over the age of the Himalyayas?

No specific question here, just fun thoughts, I guess.  Reply if inclined.  I hope you do.

I'm thinking meteors are THE driver in the "gross" geology of the earth.  Just look at that pockmarked moon for heaven's sake.

Here's some food for thought:
newbielink:http://antwrp.gsfc.nasa.gov/apod/ap060319.html [nonactive]



Has catastrophism been given any study or serious thought when it comes to plate tectonics?



Fun stuff!
Jim

And now, for something completely different, here is a sample of the best music to ever have been played in our solar system:

  newbielink:http://music.ibiblio.org/pub/multimedia/jamz/movies/abb1970-09-23.mpgf/ [nonactive]
« Last Edit: 21/03/2006 02:59:33 by JDG8R »
 

Offline JimBob

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Re: Plate Tectonics
« Reply #10 on: 21/03/2006 03:34:29 »
quote:
Originally posted by JDG8R

 (snip)

For this topic, and a myriad of others, what is your general feel toward catastrophism?  

I am convinced (by watching tv on the subject I am not ashamed to admit--well sort of) that  certain very large (1000's of square mile)erosion features happen relatively quickly (The one on tv was one  probably famous to you, somewhere in Montana I think).  




This is the Washington-0regon scab lands you are thinking of. They were formed by Lake Agassiz, a ice-plugged lake of huge area on the  Columbia River. The ice would melt every 100-1000 years and the dam would break, scouring out huge erosional features and moving huge boulders in some places but also laying down a turbidite-like layer of sediment in others (fineing upward). There are literaly thoushands of these layers stacked one upon another so they are very varve-like. This is indeed a  catastophic terrain. A friend of mine did his doctorate on catastophic features in Laguna Madre, a highly saline lagoon behing the South Texas barrier islands. Catastrophies happen. But usually only in "small" areas.

The excetions are there but they are the exception, not ther rule.
10's of thousand of feet of deep sea marine shales that are seen in many places are not the result of catastrophic events.

I agree that the earth has been hit as many times as the moon has by comets and asteroids. BUT, the lack of visual aireal photographic evidence of this is the precise argument for a slow, gradualy evolving earth. If catastorphies were the reason for orogonies and other large scale phenomina, then you would not have any reason for the craters being removed. The earth's surface would look like them moon.  

quote:

What is the greatest elevation change of any mountian range that has been observed in the last 500 years?  Does that extrapolate to anywhere near the 14,000 feet in elevation over what ever the age of the rockies are or to the 29,000 feet over the age of the Himalyayas?




Oh yes, there are more than enough rate of uplif studies that allow more than enough time.


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Offline Bass

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Re: Plate Tectonics
« Reply #11 on: 21/03/2006 04:21:10 »
quote:
Originally posted by JimBob
This is the Washington-0regon scab lands you are thinking of. They were formed by Lake Agassiz, a ice-plugged lake of huge area on the  Columbia River.


Not to nit-pick, but Lake Agassiz was not located on the Columbia River drainage.  Lake Missoula is regarded as the likely source of floodwaters for the scablands in Washington-Oregon.

Subduction causes orogeny.
 

Offline JimBob

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Re: Plate Tectonics
« Reply #12 on: 21/03/2006 05:27:57 »
Thank you for the correction, Bass. I can still learn things and I somehow I had poor wiring in my memory circuits. Altzheimer's starting?

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Offline JDG8R

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Re: Plate Tectonics
« Reply #13 on: 25/03/2006 02:00:43 »
"If catastorphies were the reason for orogonies and other large scale phenomina, then you would not have any reason for the craters being removed."

JimBob, how about weathering which occurs here but not on the moon?

Not being a wise-ass, just trying to keep this thread alive...

Jim Bob, I ran across this which you posted elswhere.  Since this was just found, maybe there are way more out there?

newbielink:http://www.sciencedaily.com/releases/2006/03/060303204735.htm [nonactive]

At least it makes you wonder????

JimD

P.S.  I don't claim to know jack shi*, just asking questions and offering blunt thoughts. Please don't be offended.
« Last Edit: 25/03/2006 02:16:27 by JDG8R »
 

Offline Ophiolite

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Re: Plate Tectonics
« Reply #14 on: 25/03/2006 02:16:14 »
There are around one hundred impact craters identified on the Earth. There is a neat site I used to have the url for which had photographs of mearly all of them. I shall try to find it. Some of them are way old.

Remember though that 2/3 of impacts are over the ocean, and many are simply airbursts, so there is only superficial surface damage.

You might also want to amuse yourself with a comparison of the energy required to raise the Himalayas with the energy released by say the KT boundary bolide. I think you will find a couple of orders of magnitude shortfall of required energy.

Edited for typo.

Observe; collate; conjecture; analyse; hypothesise; test; validate; theorise. Repeat until complete.
« Last Edit: 25/03/2006 12:07:25 by Ophiolite »
 

Offline JDG8R

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Re: Plate Tectonics
« Reply #15 on: 25/03/2006 02:25:57 »
Thanks for the good info Ophi, I am just throwing it out there.

I'm not saying that the impacts raise the mountains, but that the tectonics which we all agree exist, are accelerated, or their pressure released violently, and suddenly at impact.  More abruptly than would otherwise slowly happen, and that we have experience with, as with minor, terrestrial driven earthquakes.

And maybe that raises mountains higher than they otherwise would have risen or in places that buckle where we wouldn't have expected them to.

This is amusing. I'd hate to have a job or avocation or hobby that wasn't.

W/B

Oooh, another thought:  100 impacts identified, how many mass extinctions identified?
« Last Edit: 25/03/2006 02:32:02 by JDG8R »
 

Offline Ophiolite

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Re: Plate Tectonics
« Reply #16 on: 25/03/2006 12:11:45 »
Five mass extinctions. Most of the impacts are quite small, comparatively speaking.

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Offline Amergin

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Re: Plate Tectonics
« Reply #17 on: 04/04/2006 02:13:29 »
quote:
Originally posted by Ophiolite

JDC -
The growth of the Rocky Mountains has been one of the most perplexing of geologic puzzles. Normally, mountain building is focused between 200 to 400 miles inland from a subduction zone boundary, yet the Rockies are hundreds of miles farther inland. What geologic processes raise mountains at this scale? Although geologists continue to gather evidence to explain the rise of the Rockies, the answer most likely lies with an unusual subducting slab.
At a 'typical' subduction zone, an oceanic plate typically sinks at a fairly high angle (see above). A volcanic arc grows above the subducting plate. During the growth of the Rocky Mountains, the angle of the subducting plate may have been significantly flattened, moving the focus of melting and mountain building much farther inland than is normally expected.
It is postulated that the shallow angle of the subducting plate greatly increased the friction and other interactions with the thick continental mass above it. Tremendous thrusts piled sheets of crust on top of each other, building the extraordinarily broad, high Rocky Mountain range.


Source: newbielink:http://wrgis.wr.usgs.gov/parks/province/rockymtn.html [nonactive]


Observe; collate; conjecture; analyse; hypothesise; test; validate; theorise. Repeat until complete.



As India moved north on it plate approaching Asia, sediments in the ocean floor were pushed up to become the Himalaya Mountains. Similarly, North Amerca as its plate drifted westward, rode over the Plate spreading east from the Pacific Ridge. We call the plate to the west the Pacific Plate but are unsettled on what to call the one diving under North America. Sediments not only piled up on the old North American coast about where the Rockies are today, but a series of microcontinents riding on the east Pacific Plate became attached like India to Asia. Many of these were added in the area between the Rockies, Cascade-Sierras, and the more recent coastal mountains of California, Oregon, Washington, British Columbia (and Baja California.)

I think that one can see this scale of orogeny down into Mexico in the almost parallel Sierra Madre Oriental and Sierra Madre Occidental where they converge is in the narrow neck of Mexico.



More pressing issues are not the hugc magma cauldron under Yellowstone and the strangely active New Madrid Fault (future rift zone?) up the Mississippi valley in Missouri.

Amergin


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Re: Plate Tectonics
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