Explanations for Pangea

Discussion in 'Earth Science' started by esoterik appeal, Jul 4, 2006.

  1. Walter L. Wagner Cosmic Truth Seeker Valued Senior Member

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    I've seen lots of interesting 2-d views of the spherical surface of the Earth, with the continental plates jostling around. It'd be great to see representations of the "keel"s that keep them 'anchored', since the pulling-tugging of plate tectonics also works on the "keels", if they are relatively solid rock, I would imagine, helping to move those plates around.
     
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  3. valich Registered Senior Member

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    Cratons are land masses with deep keels as opposed to their inclusive overlying shields and the sedimentary blanket, or the shields that are overlapping and contiguous with other cratons, as opposed to the tectonic plates of the lithosphere. Blocks are also components of the cratons. Cratons are anchored in the subcontinental mantle and may extend to depths of 200 km (oceanic lithosphere is about 70 km thick: continental lithosphere ~150 km). This is why we can trace the cratons to early supercontinents such as Pangea (290-180 mya) and the much early Kenorland (~2.7 bya) and Vaalbara (~3.3 to 2.8 bya, possibly even 3.6 bya). Cratons do not subduct because they are firmly anchored in place, making them much more stable. At least this is how I see it.

    I focus a lot on the consistancy of finding granite deposits, Archaean metamorphic gneiss, komatiites (diamond deposits/kimberlite), the greenstone belts, and the tonalite-trondhjemite-granodiorite (TTG) suites, granite-monzogranite-syenitegranite (GMS) suites and granite-monzogranite-syenitegranite (GMS) suites in all the Archaean cratons. U/Pb dating and Hf isotopic studies of detrital zircons date all these cratons to 3.8 to 4.2 ga. See articles on the Isua greenstone belt, Greenland; Yilgarn craton and Pilbara craton, Western Australia; Kaapval craton, South Africa; Slave craton, Northern Canada:
    http://en.wikipedia.org/wiki/Isua_greenstone_belt
    http://en.wikipedia.org/wiki/Yilgarn_craton
    http://en.wikipedia.org/wiki/Pilbara_craton
    http://en.wikipedia.org/wiki/Kaapval_craton
    http://en.wikipedia.org/wiki/Slave_craton

    I'm trying to tie some of the above together. Also, related to origins of life and ancient archaea, I'm researching the isoprenoid residues (biological signatures of archaea outer membranes) reported from the Messel oil shale of Germany and now in the Isua greenstone belt. For a brief overview of residue isoprene from the phospholipid outer membranes of archaea see: http://www.ucmp.berkeley.edu/archaea/archaeamm.html#isoprene

    In geology you can either use a geomorphological formula (cratons and the shields) or a tectonic formula (mobile plates) to describe continental land masses.

    You can see from the 3-D view below that cratons have an integrated mineral structure as opposed to the surrounding more transient layered areas:

    [

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    ]Cutaway to the Craton: Throughout much of the central United States, younger sedimentary rocks conceal the craton. But in Michigan, Wisconsin, and Minnesota — as well as throughout much of Canada — it is well-exposed. Source: http://www.mnh.si.edu/earth/text/4_1_3_1.html (good overview of the formation of the North American craton)

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    The equilibrium line between diamond and graphite intersects the oceanic geothermal gradient at depths of greater than 200 kilometres. This depth is considered to be unsuitable for the production of diamonds, likely due to the inability of fractures to propagate to that depth in an oceanic envirnment (too hot). However, recent discoveries of diamond-bearing 'Lamproite-like' rocks have been identified in Archean volcanic terrane (Michipecoten Greenstone Belt).
    Source: http://hosting.soonet.ca/eliris/geoforum/diamonds.htm
     
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  5. valich Registered Senior Member

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    Cutaway to the Craton: Throughout much of the central United States, younger sedimentary rocks conceal the craton. But in Michigan, Wisconsin, and Minnesota — as well as throughout much of Canada — it is well-exposed. Source: http://www.mnh.si.edu/earth/text/4_1_3_1.html (good overview of the formation of the North American craton)

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    The equilibrium line between diamond and graphite intersects the oceanic geothermal gradient at depths of greater than 200 kilometres. This depth is considered to be unsuitable for the production of diamonds, likely due to the inability of fractures to propagate to that depth in an oceanic envirnment (too hot). However, recent discoveries of diamond-bearing 'Lamproite-like' rocks have been identified in Archean volcanic terrane (Michipecoten Greenstone Belt).
    Source: http://hosting.soonet.ca/eliris/geoforum/diamonds.htm
     
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  7. valich Registered Senior Member

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  8. Laika Space Bitch Registered Senior Member

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    Valich, I don't know what you're doing. Would you explain the relevance of your most recent posts?
     
  9. valich Registered Senior Member

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    3,501
    This is an excellent image of the Dhawar Craton, obtained by P-wave data, that shows how it is firmly anchored into the asthenosphere. The Dharwar cratonic keel extends to a depth of 250 km or more.

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    P-wave data from the Indian subcontinent showing crustal thickness in the range of 35-40 km, with the biggest exception being the Himalayas which are known to have thicknesses of up to 80 km. Crustal thickening under the Himalayas is attributed to convergence and collision of continents during Cenozoic and Archean–Proterozoic. I believe the Bhandara Craton is part of the Southern Thrust Belt (MFT) of the Himalayas:

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    MT: Marwar Terrain NSL: Narmada Son Lineament
    DFB: Delhi Fold Belt BHC: Bhandara Craton
    AFB: Avavalli Fold Belt EGMB: Eastern Gnat Mobile Belt
    BUC: Buckelkhand Craton 6.2 velocity (km/s)
    SMB: Salpura Mobile Belt
    \ Fault
    Cross-section through Indian Shield at 26°N 72°E to 18°N 86°E
    Source: http://quake.wr.usgs.gov/research/structure/CrustalStructure/india/

    The Dharwar Craton is in southwest India and the Bhandara Craton is in the northeast.
     
  10. valich Registered Senior Member

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    3,501
    Are you following the posts? Walter asked:

    In answer to this, I posted a 3-D image of the "keels" that keep the continental plates - more accurately called "continental cratons" - "anchored," and this is what prevents them from "jostling around." This also serves as an explanation to the original posting asking for an explanation of Pangea, and all other supercontinents that have formed, and reformed, and reformed. These cratons remain in place anchored to the underlying asthenosphere but are sometimes split and reaccreted by rifting, magma plumes, and the mantle's convection currents. These cratons do not get subducted. They form the cores of the continents. Questions?
     
  11. valich Registered Senior Member

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    Anchoring "keels" of the Kaapvaal and Zimbabwe Cratons, South Africa; originally part of Pangea 200 million years ago; part of Gondwana 500 million years ago; part of the supercontinent of Rodinia 1 billion years ago; part of the supercontinent of Columbia (or Nuna, Hudsonland) 1.8-1.5 billion years ago; part of the supercontinent of Kenorland 2.7 billion years ago; and before that, part of the original supercontinent Vaalbara 3.6-2.8 billion years ago:

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  12. Laika Space Bitch Registered Senior Member

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    638
    Yes, Valich, I was following the posts, and I applaud your enthusiasm. But I'm perplexed by your shotgun approach to referencing. I see a couple of interesting tidbits pertaining to Walter's comment, and a good bit more of tenuously related clutter presented with no context or explanation.
     
  13. valich Registered Senior Member

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    3,501
    And what do you want an explanation for or of? I believe I thoroughly answered Walter's question. The above posts show how firmly cratons are rooted below the lithosphere in multiple aspects of discriptive analyses. You are free to explore the presentations for yourself as you see fit, but I think I've covered all the bases: 2-D, 3-D, p-waves, stratigraphic. Do you have any specific questions of interest that I can help you with, or useful comments that you would like to add to the thread?
     
  14. Walter L. Wagner Cosmic Truth Seeker Valued Senior Member

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    Valich:

    Thanks for the 3-d views. Your overkill approach does take some reading through, but it covers the topic. Wouldn't it be great to see it all on a globe, showing the cratons moving over time, forming continents, breaking up, reforming, getting buried by sediments, etc.!?

    Walter
     
  15. Laika Space Bitch Registered Senior Member

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    638
    Of course you covered all the bases - you answered Walter's question in the same way you would have if you'd dropped a bloody encyclopaedia in his lap! I'm sure your indiscriminate copy-and-pasting answered all his questions and more.
     
  16. valich Registered Senior Member

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    As I said, this also served to answer the initial question about the origins of Pangea and all the other supercontinents that came before. Why do you suddenly have an attitude about this? Objectivity? Anything productive to add to the thread?
     
  17. Laika Space Bitch Registered Senior Member

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    638
    My attitude is as it ever was. I have nothing to say right now about Pangea or the Earth's deep structure. I was merely reinforcing my initial comment about the irrelevance of some of your posts, which I stand by. You sometimes seem to me more of a free-association 'bot than an actual, thinking human. Harsh, but I hope you'll forgive me for it because I do actually value your contributions (some of them at least).
     
  18. valich Registered Senior Member

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    3,501
    Your attitude sucks! And you freely and openly admit that you have nothing to say about the post. So why are you even on it? Your comments about the comments are irrelevalent because they comment about nothing on this post. So what the hell are you talking about? It is beyond me?

    As you go through life you will find out that it is not only virtuous but also obligatorily necessary to be thorough; for example, when presenting course research papers, a thesis, dissertation, or journal articles. Accordingly, I appreciate your compliment that I was "encyclopaedic," but if you are criticizing this in any way, than that is condemnatory, and then I would suggest that you might find a happier home on MySpace.com to exchange your immature idle chit-chat criticism with the kids there.

    Although you may find "some" socalled "relevance to some of my posts" - what the hell does that mean? - "which I stand by you" - don't do think you're doing me any favors! - "You sometimes see to me more of a free-association" - again, I thank you for this compliment as I try to be more "free-association" in that I look at all sides without a stuborn one-sided bias. And you? Who are you? Just who do yo think you are?

    I come from a Liberal Arts and Humanitarian background - although I studied physics, calc, and science for two years - and am now studying Geology again, after two years of that, and now Biology (Palaeontology, Microbiology, Genetics, and some Veterinary Medicine), trying to peice together relationships between geology and the Origin of Life - what the hell are you doing except playing armchair criticism? And that's just what Walter's doing too. And is why I told him that he has a good mind and that he aught to apply it by going back to a school where he can have his ideas peer-reviewed by associates before posting wild unscientific ideas without using the scientific method.

    Everything I posted above are from researched journal articles. If you have a problem with that, then you should not be on thids forum.

    Again, Do you or do you not have anything constructive to post that is relavent to the constructive issues of this forum? If not, then I guess it is closed.
     
  19. Walter L. Wagner Cosmic Truth Seeker Valued Senior Member

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    2,518
    Don:

    While you come from a "liberal arts and humanitarian" background, but studied "physics, calc and science" for two years, I have a little more science background than that. I majored in science (1967-1972) initially as a mathematics and physics major, but switching my senior year to obtain my degree in biology. Thereafter, I engaged in cosmic radiation physics research for an additional two years, and then worked as a nuclear physicist for five more years in a medical physics setting, and have taught science and mathematics at various institutions during the 1980s-1990s. Currently I'm working at advancing PET/CT imaging capabilities at medical facilities. You might gleen some of that from some of my other posts.

    As you know, I am also broadly read in many other scientific fields. I do not post "wild, unscientific ideas".

    I suppose what Laika is getting at is that at times you 'thrash' at people, as above, and throw in far more information in a thread than most people have the time or inclination to wade through. Personally, I appreciate the in-depth additional material, though I suspect that most do not.

    Also, if you want to appear more professional, I would suggest you do a spell-check before posting. Relevant, not relavent. Ought, not aught. Irrelevant, not irrelevalent. Then, not than. Piece, not peice.

    Regards,


    Walter L. Wagner (Dr.)
     
  20. Laika Space Bitch Registered Senior Member

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    638
    Valich, I did not call you encyclopaedic. I was being condemnatory. I was condemning the way you linked to or copy-and-pasted large quantities of tenuously related material. For example: archaea, the history of the North American continent, diamonds and kimberlites, Canada’s mineral deposits – all with little or no explanation or justification. Your background doesn’t enter into this, and neither does mine.
     
  21. Ophiolite Valued Senior Member

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    9,232
    Advice that you should have taken from the moment you set foot on this forum. I don't kmow which of your many inane contributions cause me the most amusement, or frustration. I especially liked your persistent claim that there was no ice on Mars, but really there have been so many I've lost track.
    What many of us have a problem with is that any idiot can post articles from peer reviewed journals. You have proven this repeatedly. Big ****ing deal. (Oh, my profuse apologies. I forgot. You are the one who objects to bad language, yet believes it is acceptable to permeate entire threads with a stinking attitude.) What is required, expected, obligatory, and all the rest, is that you draw something of relevance from those peer reviewed articles and not just spout them in a wave of ersatz erudition.
    You will be entitled to make a complaint like that when you learn how to do that yourself.
    You patronising little prick.
     
  22. invert_nexus Ze do caixao Valued Senior Member

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    9,686
    Heh.
    I see your scholastic history has been rewritten once again.
    I suspect that you've finally settled on something closer to the truth this time.
    Glad to see that you've begun to realize that honesty isn't a bad route to take.

    I bet you have really hairy balls.

    I bet you wish you were a moderator.
     
  23. valich Registered Senior Member

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    3,501
    Hi Invert! Welcome back. Haven't heard from you for a while but it's always a pleasure to read "some" - not all - of your postings. Did I say something in the past that contradicts what I stated above? I have attended so many universities that I've taught and studied at - over 15 now - that I do openly admit that I lose track of the exact dates and times and numbers and years of this and that. If you really want me to list my autobiography in minute details, I hope you are willing to offer me compensation to spend the time to pay for it, as I really don't have the time.

    Again, as I have been consistently posting above. Does anyone have anything productive or constructive to add to this thread? Or is it for all practical reasons now closed?
     

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