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Thread: Mid Ocean Rift System

  1. #31
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    I know we are not discussing disintegration but that is what the Roche limit is about and what makes it irrelevant to this thread. Likewise the unsupported idea that gravitation from other bodies such as the Sun is irrelevant to this thread.
    The geology in Mid Ocean Rift System and Valles Marineris are relevant to this thread.

  2. #32
    Quote Originally Posted by grapes View Post
    The possible connections between volcanism and rifts appear in a lot of the literature--but also in the introductory textbooks. What part of that is not sensible?
    Although I have already replied to the above in another post, I had an additional thought last night about this issue.

    The three large volcanoes on Mars are reasonably close together in the one hemisphere in the same direction away from the rift, not too far away from the rift. Yes, that might suggest a connection between the two - the rift and the volcanoes - however the rift itself shows no distortion towards the direction of the volcanoes. It is fairly symmetrical. If the volcanoes were stretching the "skin" of Mars to make the rift, you'd expect to observe a distortion towards the volcanoes. It is not present. I think in this case, Occam's Razor applies - the simple and well known explanation for volcano formation is the best one, one which does not result in the stretching of a planet's surface. Any explanation for the rift using "volcano stretch" appears to be a complicated unknown process, but I would welcome correction as always.

  3. #33
    Quote Originally Posted by Reality Check View Post
    I know we are not discussing disintegration but that is what the Roche limit is about and what makes it irrelevant to this thread. Likewise the unsupported idea that gravitation from other bodies such as the Sun is irrelevant to this thread.
    The geology in Mid Ocean Rift System and Valles Marineris are relevant to this thread.
    Agreed. The idea in bold is best left alone in this thread.

  4. #34
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    Quote Originally Posted by Canis Lupus View Post
    The three large volcanoes on Mars are reasonably close together in the one hemisphere in the same direction away from the rift, not too far away from the rift. Yes, that might suggest a connection between the two - the rift and the volcanoes -....
    This is not quite what the proposed mechanism for Valles Marineris seems to be, It is not that the volcanoes cause the rift system. It is more that they have a common cause.
    The formation of Valles Marineris is thought to be closely tied with the formation of the Tharsis Bulge. The Tharsis Bulge was formed from the Noachian to Late Hesperian period of Mars, in three stages. The first stage consisted of a combination of volcanism and isostatic uplift; soon, however, the volcanism loaded the crust to a point at which the crust could no longer support the added weight of Tharsis, leading to widespread graben formation in the elevated regions of Tharsis. Stage two consisted of more volcanism and a loss of isostatic equilibrium; the source regions of the volcanism no longer resided underneath Tharsis, creating a very large load. Finally, the crust failed to hold up Tharsis and radial fractures formed, including at Valles Marineris. Stage three mainly consisted of more volcanism and asteroid impacts. The crust, having already reached its failure point, just stayed in place and younger volcanoes formed. Tharsis volcanism involved very low viscosity magma, forming shield volcanoes similar to those of the Hawaiian Island chain, but, because there is minor or no current active plate tectonics on Mars, the hotspot activity led to very long histories of repeated volcanic eruptions at the same spots, creating some of the largest volcanoes in the solar system, including the biggest, Olympus Mons.[8]
    Mars has no current tectonic movement. If a hot spot like the one under the Hawaiian Islands forms on Mars then it stays in one place. That allowed the formation of the Tharsis Bulge. Failures of the crust of the bulge formed rifts such as Valles Marineris.

    I suppose an analogy would be baking bread - it starts as a smooth dough blob but as it expands it can form fissures, rifts and peaks.
    Last edited by Reality Check; 2017-Jan-31 at 09:59 PM.

  5. #35
    Quote Originally Posted by Reality Check View Post
    This is not quite what the proposed mechanism for Valles Marineris seems to be, It is not that the volcanoes cause the rift system. It is more that they have a common cause.

    Mars has no current tectonic movement. If a hot spot like the one under the Hawaiian Islands forms on Mars then it stays in one place. That allowed the formation of the Tharsis Bulge. Failures of the crust of the bulge formed rifts such as Valles Marineris.

    I suppose an analogy would be baking bread - it starts as a smooth dough blob but as it expands it can form fissures, rifts and peaks.
    Thanks, that is a more thorough and fuller explanation than the one I had read about which had mentioned "stretching". Although I can't say using any reason one way or another if it seems correct to me, on the surface (so to speak) it appears to make more sense.

  6. #36
    The formation of Valles Marineris is thought to be closely tied with the formation of the Tharsis Bulge. The Tharsis Bulge was formed from the Noachian to Late Hesperian period of Mars, in three stages. The first stage consisted of a combination of volcanism and isostatic uplift; soon, however, the volcanism loaded the crust to a point at which the crust could no longer support the added weight of Tharsis, leading to widespread graben formation in the elevated regions of Tharsis. Stage two consisted of more volcanism and a loss of isostatic equilibrium; the source regions of the volcanism no longer resided underneath Tharsis, creating a very large load. Finally, the crust failed to hold up Tharsis and radial fractures formed, including at Valles Marineris. Stage three mainly consisted of more volcanism and asteroid impacts. The crust, having already reached its failure point, just stayed in place and younger volcanoes formed. Tharsis volcanism involved very low viscosity magma, forming shield volcanoes similar to those of the Hawaiian Island chain, but, because there is minor or no current active plate tectonics on Mars, the hotspot activity led to very long histories of repeated volcanic eruptions at the same spots, creating some of the largest volcanoes in the solar system, including the biggest, Olympus Mons.[8]
    Two problems here:

    1. The rift should be circular around the collapse. Not a line along an equator.
    2. The rift still should show signs of distortion towards the collapsed area. If anything there are signs of distortion away in all the wrong places.
    Last edited by Canis Lupus; 2017-Feb-01 at 10:11 PM.

  7. #37
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    Geologists are content with the proposed mechanism. As what you quoted states - Finally, the crust failed to hold up Tharsis and radial fractures formed, including at Valles Marineris.
    Where did you get that idea of a collapse producing a circular rift?
    Last edited by Reality Check; 2017-Feb-01 at 10:09 PM.

  8. #38
    Quote Originally Posted by Reality Check View Post
    Geologists are content with the proposed mechanism. As what you quoted states - Finally, the crust failed to hold up Tharsis and radial fractures formed, including at Valles Marineris.
    Where did you get that idea of a collapse producing a circular rift?
    By looking at where one would expect the collapses to be greatest - around the largest volcanoes.
    Last edited by Canis Lupus; 2017-Feb-01 at 10:16 PM.

  9. #39
    ... is thought to be closely tied ....
    Any geologist content with the above needs to be reeducated. Apologies for the bluntness, but it's one thing for a geologist to think the above is best theory, it is a big step further to be content with it.
    Last edited by Canis Lupus; 2017-Feb-01 at 10:27 PM.

  10. #40
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    Quote Originally Posted by Canis Lupus View Post
    By looking at where one would expect the collapses to be greatest - around the largest volcanoes.
    Read what you quote again - those "largest volcanoes" formed after Valles Marineris!

  11. #41
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    Quote Originally Posted by Canis Lupus View Post
    Any geologist content with the above needs to be reeducated.
    Rather than insulting geologists you should learn the likely mechanism for the formation of Valles Marineris
    1. "a combination of volcanism and isostatic uplift" creates the Tharsis bulge. The first "rifts" appear - grabens.
    2. More volcanism causes a loss of isostasy, i.e. denser material on the surface is no longer buoyed up by subsurface rocks. Thus:
      "Finally, the crust failed to hold up Tharsis and radial fractures formed, including at Valles Marineris."
    3. More volcanism including the formation of the largest volcanoes in the Solar System.


    ETA: Maybe the "bulge" term is confusing you. Tharsis is a volcanic plateau. It "bulges" above the surrounding terrain but is not a mound like a volcano. It is not even that circular - more of a peanut shape.
    Last edited by Reality Check; 2017-Feb-01 at 10:37 PM.

  12. #42
    Quote Originally Posted by Reality Check View Post
    Rather than insulting geologists you should learn geology ...
    Please don't misinterpret my post in such a negative fashion.

    For one thing, there are good geologists and ordinary ones, just like there are good lawyers and tradesman called craftsmen. To suggest that some of the part needs to adjust its thinking is no slur on the remainder of the whole. In fact, it is a tribute to their standard.

    The quote doesn't actually state geologists are content. That was your assertion. I was being polite towards you in pointing away from you but towards geologists who need reform.

    Don't worry about my level of geological understanding. Ever since I touched Susan's hand in the snowy mountains when we were the tender age of 16, it is has been of intense interest to me. It's funny what can inspire a person to take an almost life long interest in certain things. Sorry, but you have to appreciate that Susan had perfect wavy blonde hair, blue eyes, slim and most of all glaringly intelligent. Now chief surgeon at this country's finest children hospital.
    Last edited by Canis Lupus; 2017-Feb-01 at 10:46 PM.

  13. #43
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    Quote Originally Posted by Canis Lupus View Post
    Please don't misinterpret my post in such a negative fashion.
    A comment that geologists content with "most agreed upon theory today" need to be reeducated is negative in any interpretation. It is geologists who proposed and support the mechanism you quoted.
    My main point was that you seem to not understand what you quoted so:
    You should learn the likely mechanism for the formation of Valles Marineris
    1. "a combination of volcanism and isostatic uplift" creates the Tharsis bulge. The first "rifts" appear - grabens.
    2. More volcanism causes a loss of isostasy, i.e. denser material on the surface is no longer buoyed up by subsurface rocks. Thus:
      "Finally, the crust failed to hold up Tharsis and radial fractures formed, including at Valles Marineris."
    3. More volcanism including the formation of the largest volcanoes in the Solar System.

    Maybe the "bulge" term is confusing you. Tharsis is a volcanic plateau. It "bulges" above the surrounding terrain but is not a mound like a volcano. It is not even that circular - more of a peanut shape.

    Do you understand now that the big volcanos formed after Valles Marineris?
    Last edited by Reality Check; 2017-Feb-01 at 10:45 PM.

  14. #44
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    Quote Originally Posted by Canis Lupus View Post
    Ever since I touched Susan's hand in the snowy mountains when we were the tender age of 16, it is has been of intense interest to me. It's funny what can inspire a person to take an almost life long interest in certain things.
    As it was for me (without the touching Susan bit). Have you considered getting a degree in geology? I did and it was not only eye-opening, but a great experience.

  15. #45
    Quote Originally Posted by Reality Check View Post
    A comment that geologists content with "most agreed upon theory today" need to be reeducated is negative in any interpretation.
    Couldn't disagree more with the above assertion. Although I can see how an argument could be maintained in its favour. It is trumped by science's relentless curiosity to refine and better understand everything.


    It is geologists who proposed and support the mechanism you quoted.
    Nothing controversial here though! It is as you would expect, but it says little about much.

    Do you understand now that the big volcanos formed after Valles Marineris?
    Yes, I saw that the text suggested that, but considered carefully that it might not be stating as much as well. It is Wiki after all - very helpful yes, but ...

    I am quite happy for it to be correct. If it is, then the volcanoes have no relevance on the original formation of the rift. The point of this discussion is otherwise. I never brought them up as being relevant for the cause of the rift. It was someone else.
    Last edited by Canis Lupus; 2017-Feb-01 at 11:28 PM.

  16. #46
    Quote Originally Posted by geonuc View Post
    As it was for me (without the touching Susan bit). Have you considered getting a degree in geology? I did and it was not only eye-opening, but a great experience.
    No, my preference would be for physics, but at 54 and with my lifestyle in remote areas, I regard academia as over for me.

    Physics runs into everything and everything to me must dovetail.

    BTW I only touched her hand, telling her how beautiful it was. I'm sure that heart felt tribute to the delicacy of her hand served as no discouragement to her long climb to one of this country's finest surgeons. Gee, if I was conceited, I'd think it might serve as an inspiration to her. Such thinking is fanciful.
    Last edited by Canis Lupus; 2017-Feb-01 at 11:55 PM.

  17. #47
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    My interest in geology stemmed more from getting up close and personal with hills and mountains in my tramping (hiking) and skiing days. Plus living in NZ with fairly frequent earthquakes.

  18. #48
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    Quote Originally Posted by Canis Lupus View Post
    Yes, I saw that the text suggested that, but considered carefully that it might not be stating as much as well.
    The text is quite explicit - the volcanoes formed after Valles Marineris. Thus any suggestion that the volcanoes created Valles Marineris needs evidence that they existed before Valles Marineris.
    I suspect that the relative dating is derived from impact craters, maybe fewer craters on the volcanoes than in the canyon.

  19. #49
    Quote Originally Posted by Reality Check View Post
    My interest in geology stemmed more from getting up close and personal with hills and mountains in my tramping (hiking) and skiing days. Plus living in NZ with fairly frequent earthquakes.
    I think anyone who was watched the All Blacks play with mountains for men would be drawn to geology. I love the Blacks and I'm not even Kiwi - more than the Wallabies.

  20. #50
    Quote Originally Posted by Reality Check View Post
    The text is quite explicit - the volcanoes formed after Valles Marineris. Thus any suggestion that the volcanoes created Valles Marineris needs evidence that they existed before Valles Marineris.
    I suspect that the relative dating is derived from impact craters, maybe fewer craters on the volcanoes than in the canyon.
    Ok, we are in complete agreement. Probably also agree that it will be a long time before the Wallabies beat the All Blacks again.

  21. #51
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    A nitpick - the first mention of volcanoes in this thread came from you: It is speculated that the rift on Mars has been caused by the immense volcanoes... but you obviously know the current theory correctly now.

  22. #52
    Quote Originally Posted by Reality Check View Post
    My interest in geology stemmed more from getting up close and personal with hills and mountains in my tramping (hiking) and skiing days. Plus living in NZ with fairly frequent earthquakes.
    Did a fair bit of this, still do, along the great dividing range of Australia. We have decent mountains here too. They just aren't in your face all the time like NZ.

  23. #53
    Quote Originally Posted by Reality Check View Post
    A nitpick - the first mention of volcanoes in this thread came from you: It is speculated that the rift on Mars has been caused by the immense volcanoes... but you obviously know the current theory correctly now.
    That is a nitpick

    I brought it up to dismiss - the exact opposite as a cause. Ok?

    This is the quote you are looking for

    Quote Originally Posted by grapes View Post
    The possible connections between volcanism and rifts appear in a lot of the literature--but also in the introductory textbooks. What part of that is not sensible?
    Last edited by Canis Lupus; 2017-Feb-01 at 11:48 PM.

  24. #54
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    Quote Originally Posted by Canis Lupus View Post
    This is the quote you are looking for
    You stated: I never brought them up as being relevant for the cause of the rift.
    You were the first to bring up volcanoes as relevant to the cause of the rift: It is speculated that the rift on Mars has been caused by the immense volcanoes, however, I've never read anything sensible supporting that idea.
    grapes replied with a general comment about the possible connections between volcanism and rifts in the literature.
    You go onto an explanation that is wrong (and uncited): The only explanation I've read is that the volcanoes on Mars stretch the surface of the planet making the rift.
    Last edited by Reality Check; 2017-Feb-02 at 12:27 AM.

  25. #55
    Quote Originally Posted by Reality Check View Post
    You stated: I never brought them up as being relevant for the cause of the rift.
    You were the first to bring up volcanoes as relevant to the cause of the rift: It is speculated that the rift on Mars has been caused by the immense volcanoes...
    grapes replied with a general comment about the possible connections between volcanism and rifts in the literature.

    Ok, the thread speaks for itself. I'm very happy to let it speak for itself. Intelligent people will see for themselves what the thread says. I will not engage in discussion on this point any further

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