Plate Tectonics: A Paradigm Under Threat?

silylene old · Dec 1, 2004

There are NO volcanos in Tibet or Nepal. There is no subduction going on there. Actually Tibet does have volcanoes. The Kunlun Volcano group in NW Tibet (over 70 pyroclastic cones) had its last recorded eruption in 1951 (Ashi Shan Volcano). The "unnamed Caldera" in Tibet had an eruption in 1973 http://users.bendnet.com/bjensen/volcano/asia/tibet-unnamed1.html <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center">- - - - - - - - - - - - - - - - - - - - - - </div><div class="Discussion_UserSignature" align="center">I really, really, really miss the "first unread post" function. </div> </div>

Saiph · Dec 1, 2004

so he had a poor choice of words for a title. And it's occasionally in his posts too. His descriptions, and his overall points make it clear, however, that he's talking about the mechanism behind plate tectonics, not their existence in general. So, earthseed: To help clear things up, make sure you're clear about the distinction between plate tectonics (earth's crust is made of plates), their motion (subduction, rifts, etc), and the cause of the motion (gravity, lubrication, convection etc). When you say plate tectonics, it's a little vague which aspect you're talking about. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

Saiph · Dec 1, 2004

steve: Btw, congrats on your promotion to solar system. If only I could get back to that...grrr I was almost a cluster...ah well. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

Saiph · Dec 1, 2004

We certainly seem to be disagreeing more lately, or at least at odds. But that's what makes this all rather enjoyable. If I came here and everybody agreed, frankly, I'd be bored stiff. And I'm not to bothered by losing my status. Gave me a chance to use a different moniker. Besides, its quality that counts, as you've said. On the other hand, that was ~4000 quality posts....grrr. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

earthseed · Dec 1, 2004

The title of this thread is from the web page that inspired it, except I added a question mark. The intention was to get help in countering its arguments. I did not get much of that, but there has been some other interesting discussion. I am frustrated that there is this coherent (to me) argument against a theory I accept, and I cannot answer it. It does not help that the one area I investigated in some depth (deep continental roots) the author appears to be right. I think that paper is a hatchet job, collecting every bit of evidence that does not fit plate tectonic theory and presenting it as balanced analysis. It is done well enough that it might take even a well informed geologist quite a while to pick it apart, and such a person could consider it wasted time. What I can't tell is just how many weaknesses and holes there are in the theory as it stands today.

earthseed · Dec 1, 2004

From the conclusion of the paper discussing the subduction of water: <blockquote>The old water cycle that researchers once envisioned is being replaced by a new one: some subducted water quickly goes back to the surface through volcanoes, but some flows down to reservoirs 250 miles underground. Mantle plumes that pass through them force the water out and gradually back up to the surface.</blockquote>There is a lot more area with subduction going on to remove water from the ocean than there are mantle plumes to return it. The net loss of water should have started a long time ago. But the oceans are still there. I can't envision any process that would transport an entire ocean into the mantle (the author claims the mantle has the same amount of water as the oceans) without an equally efficient process to return it, and mantle plumes are not up to the job. I suspect the mantle has a lot less water than that, and long term loss from subduction is an exceptional event that does not occur in normal subduction.

Maddad · Dec 1, 2004

JonClarke I am curious about something you touched on. You said that some oldtimer geologists would probably take a mistrust of plate tectonics to the grave. Why is that? Is it that they do not accept some of the evidence for PT, or is it that they feel we are not giving enough weight to an alternative explanation? Rest of the Forum Jon's got a doctorate in geology, he's been a corporate geologist for 25 years, he's taught geology in two different universities, he's currently a geological research scientist, and lastly is creating and testing the technology that the first astronauts will use on Mars. When Jon talks about geology, I listen.

Maddad · Dec 1, 2004

earthseed ""Established fact" is a bit strong for something we can't directly see and has mostly occured in the distant past. Except that we can directly see (measure) it, and it is happening right now, not just in the past. bobvanx "I wonder what swh33 does during an earthquake. Explains why they can't happen.

earthseed · Dec 1, 2004

I started this thread in the hope of listening to him.

Saiph · Dec 2, 2004

simple, that's the way science advances! in general the "old guard" i.e those eyeing retirement, are the stodgy buggers who resist change (which is an essential element in science actually). The reason is they've spent most of their careers thinking about a problem a certain way, and giving certain answers. Heck, they've built careers on what they've said. To change their mind now, even with strong evidence, is to admit they are wrong. The most you'll get out of them tends to be: We'll see, but here's what I think.... That's what I've seen anyway. They take small inovations in stride, but major shake ups are heavily resisted by them. On the other hand, young scientists tend to take a new idea and run with it. If they do it right, and it pans out, it pays off big time. If they do it right, and it doesn't work out (science wise) they've got time to take care of it, have earned experience, and haven't really lost any face (they don't have any to begin with). Now, if they go about it wrong, it can ruin their careers right out of the gate. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

earthseed · Dec 2, 2004

I am reading a book (Plate Tectonics - An Insider's History of the Modern Theory of the Earth, edited by Naomi Oreskes) containing accounts of the development of plate tectonics written by the scientists who were involved. Most of these, of course, are by the young scientists referred to by Saiph. The essay I found most interesting was by Gordon J. MacDonald, who does not quite fit the mold. He believed in continental drift in the 1940's, then came to reject it in the 1950's as he learned more about the interior of the Earth. His argument is that continents have a very different structure from the ocean floor, including deep roots (I have mentioned this above), so they cannot move around on top of ocean plates. And the structure of the mantle precludes large scale convection. On the other hand, he states the view (which he still holds)<blockquote>In the 1960's I found the contradiction between the geophysical evidence for a strong earth [no mantle convection] and the mobility required by some geologic observations deeply troubling.</blockquote> In his paper, Pratt claims geologists accepted plate tectonics because of a herd mentality. I scoffed at this, thinking about the resistance of the old geologists that Jon is refering to. Yet several of the essays admitted that following the plate tectonics "revolution" in the 1960's, there followed a "reign of terror" in the 1970's when geologists were pressured to frame their work with plate tectonics, even if the scale of that work made it irrelevant. MacDonald also refers to a herd mentality, concluding his essay with<blockquote>Long ago, the geologic herd overcame the physicist herd in the battle about the age of the earth. They now have a comfortable confidence that the have found truth in plate tectonics, even if there are a few troublesome details yet to be dealt with.</blockquote> The "troublesome details" are where the next advances are to be made. Constructive skepticism about

JonClarke · Dec 2, 2004

Earthseed: One inaccuracy in that artcile is that mantle plumes (if they exist) do not recycle water subducted into the mantle. Much of water in subducted slab is released by heating and returns to the upper crust via island arc igenous activities. Maddad: earthseed and Saiph have summed but the cutural aspects why some people continue to find it hard to accept. It is also worth noting that many earth scientists become more sceptical, if not cynical with age. After all, they have seen a lot of theories come in with a bang and exit with a whimper. Other factors is that some people like being iconoclasts, and that the grand picture of plate tectonics is very remote from the day to day work and experience of most geologists. It is worth noting that opposite to contiental drift was only really strong in North America, especially the US, where holding it was a career-limiting move. In the rest of the scientfic world is was an accepted, if minority, perspective. A number of leading figures publically advocated it - Holmes in the UK, Du Toit and King in South Africa, Carey in Australia, and of course Wegner in Germany, it caused (and still causes) much cynical assumement when the US geological establishment finally caught up with the rest of the world and even tried to appropirate it (Not to denigrate the achievements of Hess, Wilson, et al.). Cheers Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

earthseed · Dec 2, 2004

Jon: The author of the subduction of water paper claims that water can be carried deep into the mantle, and that there is evidence of it being there. Do you accept that part? Yet there is no credible way for the water to return to the surface. It does not add up, unless Louis Frank is right about the rain of small ice comets. I have not heard much about this one for a while, so I suppose it is just another interesting notion with little merit.

JonClarke · Dec 3, 2004

Hi earthseed Erk, I am getting well and truly out of by depths with the lower mantle. The problem is we know so little about, and have almost no samples, except from a few unusual rocks. Virtually everything people say is based on theoretcial models and simulations, all assumption ridden, added by seismic tomography. We don't know for sure that plumes exist, for example (although they are not unreasonable). Sunducting slaps can go quite deep, several hundred km certainly, perhaps down to a thousand. I think the mantle is thought, for the most part, to be anhydrous. However obvious local wet spots exist, especially above subducting slabs. Most supposed plume rocks are "dry". However there are a few odd types of rocks like lamprophyres that are thought to come from the lower mantle, these contain hydrous minerals, so there is some what down there. But don't take my word for it. It is a long time since I have had to think that deeply (as it were) about the mantle <img src="/images/icons/smile.gif" /> Hope this helps Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

nexium · Dec 3, 2004

Extreme views are useful as they help identify the middle which is typically closer to the truth. Assuming subduction does occur (I think there is little doubt) some of the material contains chemically combined water that is not released until the temperature reaches 1000 degrees c = 1832 f. It is possible that this material could be subducted to a depth of 1000 kilometers and that conciderable chemically combined water is found thoughout the outer mantal. The typical mantal temperature may be well below 1000 degrees c as we have not accually measured it. Numerious assumptions are made to arrive at guestimated temperatures, and large local variations are possible, if not probable. Neil

alkalin · Dec 3, 2004

Jon Clarke, I have a question for someone such as yourself. It has to do with the possibility that the moon might play a roll in the forces necessary for PT. I understand that this has been proposed before but was rejected, and I would like to know why. I have been toying with the idea off and on, mostly off, for close to ten years, and doing some of the force calculations that convinced me there might be something to it. Anyway, I got somewhat into doing a research paper again after the Pratt thing was mentioned. My field though is ooptical engineering, and I’m still a weak PT. Sometimes I write this way so I hope you don’t take me too seriously.

earthseed · Dec 3, 2004

I assume you mean the moon's tidal forces. They move water in the ocean. Could they giggle the plates enough to provide lubrication to encourage movement? Interesting question.

earthseed · Dec 5, 2004

Let me float a few ideas as to how the moon could affect plate tectonics. I think the moon's gravitational attraction is too weak to have a direct effect on the interior of the Earth, so we need an amplifier. The moon does affect water, which creates tides. This means the depth of the ocean is continually changing. The weight of the water presses down on the plate below it, which rests on the elastic mantle. So there is a constant change in pressure, which could increase the lubrication between the ocean plate and the mantle layer below it. A regular cycle of tidal changes could possibly cause harmonic interference, and act as a second amplifier. The tide will change the ocean depth by less than 1%, and that rests on a plate that is 3-10 km thick, so this motion does not amount to that much.

alkalin · Dec 5, 2004

ES, yes , I agree. I think we may be thinking along the same lines. There is a more robust mechanism necessary, and might even be available, and that is what might provide the necessary force. Tides only trigger it. But I’m not sure I would call it resonance or harmonic, but maybe there is something to this as well.

JonClarke · Dec 5, 2004

Hi alkalin I don't think I have ever seen the moon invoked as a cause of plate tectonics, except possibly, in saying that formation of the moon resulted in a thinner crust which may have made it possible in the first place. All the plate tectonic processes - mantle convection, seafloor spreading, subduction, island arc formation etc. aredriven by internal processes and made possible by internal states. Cheers Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

silylene old · Dec 5, 2004

stevehw33: yup! I know, I was just correcting the statement about whether there were any volcanoes in Tibet. I believe the unnamed volcano in western Quinghai was originally within the border of old Tibet, before the Chinese conquested it. The Kunlun field is in Tibet, and as you point out, and thought to be a hot spot magma plume (which is very interesting, since hot spot locations mid-continent are rather unusual! - which is why I was aware of this). For the record, there are no recently active volcanoes in Nepal, Bhutan, Sikkim, Bangladesh, eastern Pakistan or mainland India. India does have a couple of offshore volcanoes. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center">- - - - - - - - - - - - - - - - - - - - - - </div><div class="Discussion_UserSignature" align="center">I really, really, really miss the "first unread post" function. </div> </div>

alkalin · Dec 6, 2004

JC, thanks very much for an answer at least. Not the one I wanted, but what do I know. Is there a source I could go to for more research on this subject. And hopefully one I do not have to register and pay dues for? Certainly convection is important in many ways, just that actual measurements of it do not pan out so far as the only prime mover. Or am I wrong. Some of Pratt’s remarks seem to indicate compression going on in the mid Atlantic ridge area---this does not indicate convection, in my view. That’s why another mechanism that supplies compression needs to be thought about.

centsworth_II · Dec 6, 2004

"All the plate tectonic processes.... are driven by internal processes... I just opened my latest issue of Science News to find this article: "Some temblors probably were triggered by tides" http://www.sciencenews.org/articles/20041204/note12ref.asp I don't know if the type of earthquakes involved are associated with plate tectonics, but if tides can affect faults, causing earthquakes, perhaps they do also have a effect on plate tectonics. <div class="Discussion_UserSignature"> </div>

JonClarke · Dec 6, 2004

It would surprising if there is no localised compression on the MAR. But as a whole to MAR. like all grabens is clearly an extensional feature. I can't think of any site that specifically discusses the the moon and the earth. I suggest you search for sites that discuss the formation of the moon, and tidal influences. Also look for informatrion about the drivers of mantle convection and plate tectonics. Sorry I could not be more helpful. Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

Maddad · Dec 6, 2004

earthseed The Moon's gravity does cause tides in the Earth's crust of up to about a foot. It's not a cause of plate tecktonics, as you said, but it should produce a small amount of heating from the flexing of rock. Perhaps JonClarke might know some specifics.

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