Types of Mountains

Discussion in 'Earth Science' started by kingwinner, Oct 1, 2005.

  1. kingwinner Registered Senior Member

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    796
    1) Graben and fault-block mountain are created by a faulted block moving up or down. But from definition grabens are flat horizontal valleys but fault-block mountains are not flat horizontal plateaus? (I think a block moving up should simply create flat plateaus...) This following figure is what I mean. Why the fault-block mountains are not flat while the grabens are flat?
    [​IMG]

    2) How does a fold mountain look like and how does a fault-block mountain look like, in terms of appearance? I mean, how can I distinguish a folded mountain from a fault-block mountain? (I have seen pictures of both types of mountains, but honestly, I can't tell a single difference)

    I hope someone can explain to me! Thank you!
     
  2. Laika Space Bitch Registered Senior Member

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    638
    With regard to your first question, the horsts in such a scenario will be exposed and will be preferentially weathered, as all mountains are. Even a beautifully regular fault block will quickly (geologically speaking) become eroded and irregular. The downthrown fault blocks, in contrast, may subside below the depositional level, and will therefore become infilled by mountain-derived sediment.

    As to your second question, I myself know of no way by which you could distinguish one mountain's origin from that of another simply from photographs. The broader picture will provide clues in the geometry of the subsiding and uplifting areas however, as rift zones are often composed of two staggered lines of crescent-shaped normal faults (concave towards the middle) bounding the subsiding area. Fold mountains, on the other hand, follow no such pattern. The best way to distinguish them would be to get close up to the rocks. The folds and reverse faults present in rocks that have been compressed can be differentiated from the normal faults in areas which have undergone extension.
     
  3. kingwinner Registered Senior Member

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    796
    1) I see, fault-block mountains are perferentially eroded, thus they are not flat. On the other hand, grabens are lower so much less erosion occurs, so there are quite flat! But why plateaus (ie high land formed beside folded mountains instead of a fault block dropping) like the Colorado and Tibetan Plateaus are flat-topped? How is a plateau different from a fault-block mountain?

    2) So fold mountains and fault-block mountains look similar that it is hard to distinguish...so how do people identify which mountains are fold mountains (e.g. Himalayas) and which are fault-block mountains (e.g. Sierra Nevada mountains in the US)? How do they know that? By examining rock layers?

    3) "Dome mountains are the result of a great amount of melted rock pushing its way up under the earth without folding or faulting resulting in a rounded dome" (quote from web sites)
    How can this "without folding" be possible? When magma pushes rock layers upward, the rock layers above are deformed by bending, or in other words, folding...or else dome mountains can't be formed...can someone please explain why dome mountains are formed without folding?
     
  4. kingwinner Registered Senior Member

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    796
    Can someone clarify? (especailly Q3, I don't get how rock layers of dome mountains are considered undeformed and unfolded...)
     
    Last edited: Oct 10, 2005
  5. valich Registered Senior Member

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    3,501
    Dome mountains are formed where a region of flat-lying sedimentary rocks is warped or bowed upward making a structural dome. Why would you expect any of the rock and soil to fold? To prove this to yourself, take a piece of paper and cover it with small rocks and soil mixed with water to form a muddy compacted layer. Then push up on it from underneath with your fist. What happens? It forms a dome with ripples, like runoff streams, and some of the soil and rocks roll down the side of the paper, but there is no folding. Maybe a better example would be to use something more elastic like a balloon. Pretend the air that you blow into it is the hot magma. It forces a curved dome to form on the top. If there were rock and mud on the top, it would expand, then crack, then roll down the dome formation, then form runoffs of erosion, like when it rains.

    Folding occurs when plates of rock underneath are forced against another tectonic plate. The pressure produced has to cause one of the plates to give way - either one plate goes on top of the other one, or one goes underneath it, or one starts to fold, or buckle up, under the pressure and heat. This is completely different from just having a hot pool of lava underneath the earth's crust pushing upward. Since it just pushes the Earth's crust up, there is no counter force acting against it to cause any folding. The hot magma is a fluid so it cannot fold, and the Earth's surface is just being pushed up.
     
  6. Ophiolite Valued Senior Member

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    8,321
    Kingwinner: vallich is superficially correct - for superficial deposits. In all other regards he is incorrect. So, for surface sediments that have not been consolidated and have experienced only the very early stages of lithification and diagenisis, then generally we would see behaviour as vallich describes.
    For all other sediments the intrinsic strength of the rock is more than sufficient to provide resistance to the upwelling so that folding readily occurs (or faulting if the uplift is rapid). There are several other circumstances in which folding can occur which vallich seems blissfully unaware of. Let me know if you would like some examples.

    Vallich, don't even think of challenging me on this. You're in my territory now. I'm the expert on rock deformation. I make my living from it. So play it smart, read and learn, and keep your mouth shut, unless you want to say thanks.
     
  7. valich Registered Senior Member

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    3,501
    I don't "challenge": I learn. If you have something that you'd like to contribute to further explain the question then by all means do so. What is your mental problem that drives you to always belittle other people and be so condescendingly obnoxious and impolite.

    The question was:
    I was taught in my geology class that "Dome mountains are formed where a region of flat-lying sedimentary rocks is warped or bowed upward making a structural dome." Mountain building (oregeny) can be categorized in different ways. Of course volcanic dome mountains undergo a great deal of lava building and folding, as do mountains that form as a result of plate tectonics. We are talking about mountains being formed from sedimentary rocks and soil, as I stated: not older metamorphic or igneous rock mountains.
     
  8. Ophiolite Valued Senior Member

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    8,321
    And I was taught in a multiplicity of classes whilst obtaining my geology degree, followed by a lifetime of maintaining an interest in the topic by reading research papers, and more recently fifteen years where the geo-mechanical properties of rocks were central to the work that I do.
    I was belittling you vallich because you claim you want to learn, but it has to be on your terms, from the individuals you deem to be suitable teachers. I don't give a flying Aardvark whether you learn a damn thing or not, nor how you view my comments. What I am now determined to do is that you do not screw up the understanding of others.
    Kingwinner has asked a variety of interesting questions in this and several other forums. I have made an effort to answer some of them, especially, as was the case here, when the answer he has been given is simple or simplistic. It was a simple answer you were given in your geology class.
    I repeat, your argument (and the useful experimental analogy you gave) are a simplification that applies to unconsolidated sediments. Once the processes of diageneisis have set in (which begins frankly, even with sediments a foot below the depositional interface) the rock begins to acquire cohesion. How that rock reacts to stress will depend upon its composition (clays will behave quite differently from sandstones, for example), internal structure (bedding planes; extent and character of interlaminations; etc), texture (grain size and angularity, for instance) and so forth.
    But generally once a rock has been lithified to an in situ compressive strength of say 10,000 psi, then it will have no problem being folded. The majority of sedimentary rocks have compressive strengths greater than 10,000 psi. The notable exceptions are those of Tertiary age.
    However, even here, if we consider as an example the salt domes in the Gulf of Mexico (were these on land they would produce a nice little mountain), we get complex folds on the flanks of the rising salt diapers.
    In short, despite what you were told in your simplified geology class, there is plenty of folding associated with dome mountains.
     
  9. valich Registered Senior Member

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    3,501
    You definitely do have a mental problem. You do realize that,. don't you? As I stated, you constantly belittle other people that you deem to be trying to be more intelligent than you, you constant resort to condescding criticism, and your use of vulgarity is uncivilized. Now your resorting to pulling rank to explain a point - resorting to supporting your explanations by flaunting your diploma.

    I gave a correct basic very clear and understandable answer to a simple question. But I guess you have a problem with that? Actually, metamorphic rock can fold to, but not in the orogenosis. A beautiful example of this is a cut-away surface structure on the Icefield Parkway between Banff and Jasper in Alberta. But this was due to surface folding from plate tectonic pressure acting against the already metamorphisized rock: not mountain building.

    Did I say I had just one socalled "simplified geology class"? How rude and direspectful. I've been teaching for over ten years after twenty years of higher education.

    Salt crystallizes in a competely different way then sedimentary rock, and when you talk about diagenesis your talking about sediment near the Earth's surface at low temp and pressure: the loose sediment is not metamorphisized yet into solid massive rock formation. We're talking about direct uplifting of loose sedimentary deposits on the surface of the Earth. This would be phase one: the pre-burial changes in diagenesis. I think it's very helpful to understand this by using the illustration I gave above by mixing a rock and soil solution with water and spreading it over a sheet of paper. This is the type of mountain building that we are talking about: not salt domes.

    You are just so immature, stubborn, and pig-headed, it's just a joke to me. You're never objective, as half your posting reflects on that, and you just go around wasting other people/s time through your continuous trolling condescending remarks.
     
  10. Xylene Valued Senior Member

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    1,398
    Horst-and-graben landscapes, such as the Basin and Range province of the western USA, are formed when the tectonic plate is being pulled apart, and therefore stretched and thinned. So far as I know (not being an expert in the field, so forgive my errors if I'm wrong) that's the only way horst and graben landscapes can be formed.

    For example, the Great Rift Valley in East Africa is formed in that manner, being the result of a vast upwelling of hot material underneath the African Plate.

    The valley of Whangarei in New Zealand has the same formation, i.e. graben, though the geological history of Northland is a lot more complex than simple thinning. There, the geological picture is complicated by events which were happening off the east coast of Northland. The layering is younger lower down, and older higher up towards the surface i.e. in total reverse of the usual. This is because there was a landmass off the Northland coast, (when the area of Northland which is now above sea-level was a submarine trough). The erosion-materials from this eastern landmass filled the depression, and hence you have the reverse-situation of younger-to-older sediment layers.
     
  11. valich Registered Senior Member

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    3,501
    That's very interesting and I think you are under-estimating your knowledge by implying that you're not an expert in the field. One does not have to have a degree in, nor a PhD in, geology to know so much.

    What you're presenting are examples of mountain building through plate seperation. In this case the lava that emerges would be younger on top. However, in dome mountains there is an uplift of fresh magma from underneath so the older rock would be on top while the younger rock solidifies below. If I am following you correctly, you're saying that the erosion material filled in the depression, but this erosion material would be older than the younger lava material below. How would it be a reverse situation? Except in relation to mountains that are formed by volcanic eruptions or plate convergences? Which are the most prominent way they are formed.

    Excellent examples of
     
  12. protostar Registered Senior Member

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    98
    This is my first post. I am happy to see this topic. I have a question and
    this website is by far the best for informatiion that I have seen so far.
    I need some info on under ocean mountains and volcano's.
    Val,Xy and O, I would like your opinion on the Gakkel ridge.
    I know that it is a gigantic volcanic mountain chain stretching beneath the Arctic Ocean. With deep valleys 5,500 meters beneath the sea surface and 5,000 meter- high summits,
    I would like to know of the recent activity there now and what your opinion is to the events taking place.
    Thank you for any information you may share.
     
  13. valich Registered Senior Member

    Messages:
    3,501
    Ophiolite would definitely know more than I on this, as I wasn't even aware that we had an active volcanic ridge beneath the Arctic Ocean? It appears to be the Northern edge of the Pacific plate that seperates North America form Europe consisting of a massive chain of volcanoes. It is the world's slowest-spreading, and the deepest, ocean ridge on our Earth! "The Gakkel Ridge lies deep in the ocean (5000 meter; 16,000 feet). It is located at the north end of the Atlantic Ocean, above the Arctic Circle."

    According to a quick search on the online encyclopedia Wikipidea, apparently it is a very recent discovery (1999):
    "The Gakkel Ridge, about 1800 kilometers long, is the slowest spreading ridge on earth. Until 1999, when scientists, operating from a nuclear submarine, discovered active volcanos along this ridge, the Gakkel Ridge was believed to be non-volcanic. In 2001 two research icebreakers, the German Polarstern and the US Healy, with several groups of scientists, were sent to the Gakkel Ridge to explore the ridge and to collect petrological samples. Among other discoveries, many hydrothermal vents ("black smokers") were found during this expedition. This came as a surprise; the finding is difficult to explain with current models for sea floor spreading."

    Also: "It is the slowest example of seafloor spreading at a mid-ocean ridge, its basalt crust is extremely thin, and it has an exceptionally deep and straight rift axis. Mantle rocks might be widely exposed at the surface. There is recent volcanic activity at 90°E on Gakkel Ridge, and there may be hydrothermal vents there. With all of these unique features, it is quite a special place in the global spectrum of mid-ocean ridges! It remains the last geologically unsampled mid-ocean ridge only because it is so difficult to get there."
    source: "Fire + Ice: Exploring for Volcanoes Beneath the Arctic," The Arctic Mid-Ocean Ridge Expedition, July 31 - October 3, 2001.
    http://www.earthscape.org/r1/hea01/hea01e.html

    Also the following, but very technical article. Ophiolite would have to decipher some of the technical contents?:
    "The Gakkel Ridge (GR) basalts are fairly primitive, with high MgO and Ni (i.e., mg > 70, MgO > 9 wt%, Ni > 165 ppm). According to these geochemical and to petrographic results, i.e. spinifex textures, the volcanics are termed komatiitic basalts. The concentrations of the mantle-incompatible elements correspond to E-MORB. Dark spherical droplets of basanitic composition within the basalts are believed to be relicts of an incomplete magma-mixing whose basanitic end-member could well account for the enriched character of the GR basalts in terms of rare earth elements, Ti and incompatible trace elements. Isotopically, the GR samples (KAL 11-370-5-1 and 3) are characterized by Sr-Nd ratios which place them above the MORB array on a Sr-Nd isotope diagram. The positive D 8/4 values of the GR basalts show their source region to possess traces of an enrichment similar to the DUPAL signature. This is remarkable since so far the DUPAL signature is believed to be present only in Indian but not in Atlantic or Pacific MORB. These results also argue against a model of whole mantle convection (Hart, 1988) in which upwelling of enriched material at the equator is balanced by downwelling of depleted material at the Poles."
    http://www.palmod.uni-bremen.de/FB5/Ozeankruste/DeRidge/Gakkel.html
     
  14. Ophiolite Valued Senior Member

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    I belittle assholes like yourself who persistently refuse to listen to multiple posters of quality.

    No. Your answer was wrong. W R O N G. Wrong. I corrected it. Get that through your thick skull.

    That's orogenisis by the way. And of course it can fold. And it does fold - during orogenisis. We study the orientations of the schistosity and of the fold axes in order to distinguish between different periods of orogenisis and different phases within an orogenesis. But once again you get it wrong, stating that folding does not occur in the orogenisis. At least you are consistent. We can disregard most of what you say.
    Here are your words: "I was taught in my geology class." Not, "I was taught in my geology course", or, "I was taught in my extensive range of education in geology."
    However, it is obvious to any geologist reading this thread that your grasp of geology is basic, distorted and wrong. I don't know what you have been teaching, or what your twenty years of higher education was in, but neither involved geology. Accept your ignorance in this area. I think everyone else has.
    Let's set aside the fact that most sedimentary rocks don't crystalise. The rest is just wrong. Do you understand that valich? Your grasp of these simple geological concepts is wholly flawed. The loose sediment pretty rapidly becomes lithified to an extent that gives it an internal strength (as I have already explained to you) that makes it fully capable of being folded.
     
  15. kingwinner Registered Senior Member

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    796
    I hope valich and Ophiolite can stop arguing, no matter what, you two are both good in science and explaning things to others! Just calm down! :)

    Hello,

    Folding means rocks permanently deform with breaking, or simply means bending, right? So if the rocks are pushed up, the rock layers are upcurved, that means the rocks are bent, or folded, or deformed without breaking, right? Unfolded rock layers mean that they are completely or close to completely flat, right?
     
    Last edited: Oct 24, 2005
  16. valich Registered Senior Member

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    3,501
    The problem with Ophiolite, as I see it, is his continuous abusive and senseless bickering - the trivial nitpicking, the continuous postings of condescending obnoxious criticisms, and his immature emotional outbursts that degrade the educational value of the forums for all of us. He needs to somehow learn to challenge his knowledge into a productive rational and nonobtrusive polite way. To me his posts are an interesting and entertaining distractment from my work - as bizarre and abnormal as they may be, they are nonetheless amusing. I would describe the last post as "cut-paste-copy" comic strip-like, slapstick joke. That's how look at it. It's a waste of everyone's time. What he needs to do is to challenge his knowledge into rational thoughts and premises without cutting down other people and making such a mockery out of himself, and in the process, destroying the educational content of these forums for those of us that have a SINCERE desire to learn: so sad.

    Folding refers to rocks that fold in upon themselves without breaking, else it is just composite layering. The other answers to your questions depends on the composition of the rock - or rock and soil, as in what we were originally referring to in to the process of dome mountains formed out of sedimentary rocks and loose soil.

    In general there are three basic types of rocks: sedimentary, metamorphic, and igneous. Igneous rocks are formed when hot molten lava magma solidifies from volcanoes, hot spots, and mid-ocean rifts where plates diverge or converge. Igneous rock form most of the underlying basis of most all mountain builds and consist of about 95% of the earth's crust but are normally hidden between the thinner layers of sedimentary and metamporphic rock above. Igneous rock are also the most likely to fold as they solidify because of their initial fluidity and the great amount of pathways that they can take while solidifying.

    Metamorphic rock are formed through high temperatures and pressures applied usually to igneous rock, but these temps and pressures can metamporphize sedemenatary rock as well. This change/formation process is called metamporhism and results in beautifu foliage formations that are sometimes visible, such as when an earthquake reveals the side of a cliff. When lava pushes againsts existing igneous or sedimentsary rock and changes ists structure or composition, this is an example of metamorphism in action. So it too often results in a lot of folding.

    Most of the surface of the Earth is covered with less compacted sdimentary rock such as chalk, limestone, sandstone, and shale. If you've ever picked up chalk or sandstone, them you can easily see how it justs crumbles into small particles, or how we use chalk to write on a blackboard. Shale also easily crumbles but you've probably noticed the more compacted layering of shale as composed to igneous or metamporphic rock. Although both igneous and metamorphic rock are subjected to erosiom, sedimentary rock are by far the most easily eroded type of rock resulting in small particlem silt, sand, and sometimes clay. In fact, some sedimentary rock are formed from the compaction of the decay of biological organisms (carbon is formed from the compaction of dead plants under pressure over millions of years), such as mollusc shells and corals.

    This is really an extremely simplified explanation of basic rock formations and within these three major classifications you need to consider the chemical compositions within each one: types of minerals being compacted, types of compaction mechanisms, crystallization structure, fluidity, pH factors, pressure, temperature, depth within the Earth, and a host of other physical forces, to say the least.

    This is what I learned in my many geology courses (plural) that were in the curriculum towards a geology degree. but the above is what is always taught in beginning geolgy.
     
  17. valich Registered Senior Member

    Messages:
    3,501
    Correction: When I was referring to some of the beautiful meatamorphic rock foldings, I meant to write "foilation," not "foliage." I'm reading biology and thinking about geology and its oh sooo late already.
     
  18. kingwinner Registered Senior Member

    Messages:
    796
    So the rock layers forming dome mountains are definitely folded, deformed, and bent...like an upside-down U shape...because the rock layers are upcurved and not longer flat and horizontal again...right?

    This is an unfolded rock layer: (flat, not bent)
    ===================

    That's basically what I understand! What I get from the definition of "folding" is that as soon as there is bending, it is considered to be folded...
     
    Last edited: Oct 25, 2005
  19. Xylene Valued Senior Member

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    1,398
    Valich, the Northland area of New Zealand is interesting because of the way it was formed by deposition from a different land-mass to the east. Land rose to the east of present-day Northland, which was at that time a sea-floor depression. The land was as you would expect, youngest sediments on top, oldest below, as with normal stratigraphy. The erosion therefore placed the youngest sediment into the trench first, then the older, then the older ad infinitum until the eastern landmass was destroyed. (Check out the book New Zealand Adrift by Graham Stephens)The resulting stratigraphy of Northland is youngest at the bottom, oldest at the top.
     
  20. valich Registered Senior Member

    Messages:
    3,501
    Most mountains are formed through volcanic or molten lava activities in plate tectonic divergences or convergences. Convergences can result in one igneous rock slab going over or under the other, or a direct confrontation that has to lead to buckling and folding of one or the other tectonic plate. This is the most pervasive way in which mountains are formed. This folding then protrudes upward toward the surface and uplifts the thin layer of sedimenary rock. The rock folding is there, but it is almost always underneath the thin surface of sedimentary deposits and not visually apparent. However, the definition of a "dome mountain" seems to be deviant and different from what we have been taught in the past, and it exemplifies the multiple patterns of orogeny (mountain forming):

    "There are five basic kinds of mountains: dome, fold, fault-block, volcanic, and dome mountains. These different types of mountain names not only distinguish the physical characteristics of the mountains, but also how they were formed.

    Dome mountains are the result of a great amount of melted rock pushing its way up under the earth [hot spots] without folding or faulting resulting in a rounded dome. As the dome is raised above its surroundings, erosion occurs, and as a result of erosion, peaks and valleys are formed."
    http://www.woodlands-junior.kent.sch.uk/Homework/mountains/types.htm

    I would suspect that these socalled "dome mountains" are not extremely tall in height and would not constitute a long chain of a mountain ranges: certainly not the Appalachians or the Rockies (definitely not!). But may account for the numerous smaller mountains scattered throughout the world.

    For example, "There are cases where viscous magma has intruded from depth but not made it to the surface. Instead it domes up the uppermost layers of the surface - kind of like a blister. The most famous case is Showa-shinzan, in Japan. It isn't anything really special - the magma just doesn't quite have enough push to make it to the surface."
    http://volcano.und.edu/vwdocs/frequent_questions/grp12/question4499.html

    "Dome mountains are formed where a region of flat-lying sedimentary rocks is warped or bowed upward making a structural dome. Their topography is characterized by a relatively flat, dissected surface sloping gradually toward the surrounding lowlands, or basins. The diameters of the bases of dome mountains range up to hundreds of kilometers."
    "Encyclopadia Brittanica" http://www.britannica.com/ebi/article-204985

    "Mountains are made in several ways:

    Dome Mountains - These mountains are the result of a great amount of melted rock pushing its way up under the earth. Over thousands of years the dome mountains form in the place where the earth is pushed up.

    Fault Block Mountains - These mountains form when faults or cracks in the earth's crush force some materials or blocks of rock up and others down.

    Fold Mountains - These are formed as layers of the earth react to forces pushing in on either side, much as a piece of paper folds when pushed together.

    Volcanic Mountains - These are formed from the vast amounts of lava that have hardened after spurting out of a volcano.

    Residual Mountains - These are mountains that are really plateaus that have worn down from erosion."
    http://www.mcwdn.org/MAPS&GLOBES/Mountains.html
     

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