View Full Version : Types of Mountains


kingwinner
10-01-05, 05:40 PM
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?
http://myweb.cwpost.liu.edu/vdivener/notes/basin_range_profile.gif

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!

Laika
10-01-05, 06:13 PM
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.

kingwinner
10-02-05, 03:50 PM
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?

kingwinner
10-09-05, 09:24 PM
Can someone clarify? (especailly Q3, I don't get how rock layers of dome mountains are considered undeformed and unfolded...)

valich
10-21-05, 12:40 PM
"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?
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.

Ophiolite
10-21-05, 03:26 PM
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.

valich
10-21-05, 06:23 PM
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.
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:

"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?

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.

Ophiolite
10-22-05, 05:50 AM
I was taught in my geology class 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.

valich
10-22-05, 05:15 PM
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.

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.

Xylene
10-22-05, 05:34 PM
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.

valich
10-22-05, 06:36 PM
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.

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

protostar
10-22-05, 07:38 PM
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.

valich
10-22-05, 11:03 PM
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

Ophiolite
10-23-05, 07:14 AM
You definitely do have a mental problem. .....you constantly belittle other people that you deem to be trying to be more intelligent than you, .I belittle assholes like yourself who persistently refuse to listen to multiple posters of quality.


I gave a correct basic very clear and understandable answer to a simple question. .No. Your answer was wrong. W R O N G. Wrong. I corrected it. Get that through your thick skull.


Actually, metamorphic rock can fold to, but not in the orogenosis.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.

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..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.

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. 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.

kingwinner
10-23-05, 08:00 PM
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! :)


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.
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?

valich
10-24-05, 04:14 AM
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.

valich
10-24-05, 04:25 AM
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.

kingwinner
10-24-05, 10:18 PM
Folding refers to rocks that fold in upon themselves without breaking

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...

Xylene
10-24-05, 10:34 PM
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.

valich
10-24-05, 11:17 PM
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

valich
10-24-05, 11:34 PM
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.
Yes, but what I do not know - totally because of my ignorance of the New Zealand geographic region - is, is this considered a mountain? Or is it a geological land mass build up? Where erosion has just filled in the low-lying areas? New Zealand is a fascinating geological and biodiverse region that I can only hope to someday explore in my lifetime.

Laika
10-25-05, 03:19 AM
I have a couple of small nit-picks with what you've said here Valich:


Most mountains are formed through volcanic or molten lava activities in plate tectonic divergences or convergences

While some mountains certainly are constructed from gradually accumulating deposits of volcanic rock (the Hawaiian Islands providing a prime example), I don't think you're justified in saying that this is the origin of most mountains.

I'm not sure if you meant magmatic instead of volcanic. If you did, I'd take issue with that too. I will present the Alps as a lovely example of a mountain range formed by tectonic convergence. This range was formed not by magmatic processes, but by the accommodation of crustal shortening via folding and thrust stacking. There are igneous rocks exposed in some areas, though in my ignorance I don't know whether they were intruded during orogenesis or if they simply represent basement rock involved in the deformation. Either way, the Alps consist largely of sedimentary and metasedimentary rock-types, and I believe a similar thing can be said of the Himalayas.

About the Andes I know practically nothing, but I imagine that magmatism and volcanism has played a larger role in their formation. Even so, I expect that thrusting and folding will still have provided the main cause for crustal thickening.

You also say:


The rock folding is there, but it is almost always underneath the thin surface of sedimentary deposits and not visually apparent

One key point about mountains is that erosion begins as soon as they rise above the depositional level, so while unconsolidated sediment may accumulate locally, in general it will be rapidly stripped away. Beautiful folds can most certainly be very visually apparent.

valich
10-25-05, 06:31 PM
I have a couple of small nit-picks with what you've said here Valich:
While some mountains certainly are constructed from gradually accumulating deposits of volcanic rock (the Hawaiian Islands providing a prime example), I don't think you're justified in saying that this is the origin of most mountains.

I'm not sure if you meant magmatic instead of volcanic. If you did, I'd take issue with that too. I will present the Alps as a lovely example of a mountain range formed by tectonic convergence. This range was formed not by magmatic processes, but by the accommodation of crustal shortening via folding and thrust stacking. There are igneous rocks exposed in some areas, though in my ignorance I don't know whether they were intruded during orogenesis or if they simply represent basement rock involved in the deformation. Either way, the Alps consist largely of sedimentary and metasedimentary rock-types, and I believe a similar thing can be said of the Himalayas.

About the Andes I know practically nothing, but I imagine that magmatism and volcanism has played a larger role in their formation. Even so, I expect that thrusting and folding will still have provided the main cause for crustal thickening.

One key point about mountains is that erosion begins as soon as they rise above the depositional level, so while unconsolidated sediment may accumulate locally, in general it will be rapidly stripped away. Beautiful folds can most certainly be very visually apparent.

Dear Nit Bitch: I have no time for senseless nitpicking. In any case, the Hawaii islands are formed from volcanic rifts in mid-ocean tectonic plate ridges that resulted in the accumulation of magma being built up and the result are the active and inactive volcanoes that make up the Hawaiin Islands today. Read my above posts specifically regarding the Hawaiin Island volcanoe system above. Thanks.

I have never made any mention of the Alps. You are certainly welcome to share with us your intelligent explanations and views. Please do. Thank you.

Magma consolidates within the crust to form igneous rock. Magma that extrudes onto the Eath's surface is then called lava. There's really not much of a big difference to worth arguing about. Both magma and lava have various compositional components of mineral makeup.

Your last point is a bit obscure. Certainly erosion begins as soon as Nature's forces act on the deposition. What do you consider as a "depositional level"? Of course igneous rock will not erode as fast as sedimentary rock, and sedimentary rock may take hold as plant life starts to grow. This then adds to further sedimentary deposits. I don't see the point of what you're trying to say. Yes, of course, erosion is always a factor in our environment? And?

Laika
10-26-05, 03:23 AM
I'm sorry if you think that what I wrote was senseless, but you said a few things that I thought were erroneous. Now there's one more:


the Hawaii islands are formed from volcanic rifts in mid-ocean tectonic plate ridges

The Hawaiian Islands do not lie on a mid-ocean ridge, but sit atop a hot spot. Plate tectonics has carried the plate over this relatively static point, causing a mountain chain which youngs to the south east.

The reason I differentiated between magma and lava is that you claimed that:


Most mountains are formed through volcanic or molten lava activities in plate tectonic divergences or convergences

Granted, the Hawaiian chain has been formed through such processes (though in an intraplate setting). But I still do not think your claim is justified. Some mountains, surely... but most?

I brought up the Alps because it is a range about which I am not wholly ignorant, and because I believe they provide an example of a range in which magmatic and volcanic processes are largely irrelevant.

I brought up erosion because of your claim that:


The rock folding is there, but it is almost always underneath the thin surface of sedimentary deposits and not visually apparent

Erosion will ensure that the "thin surface of sedimentary deposits" will be a fleeting feature of a mountain.

valich
10-26-05, 05:44 PM
Plate tectonics has carried the plate over this relatively static point, causing a mountain chain which youngs to the south east.

The reason I differentiated between magma and lava is that you claimed that:
Granted, the Hawaiian chain has been formed through such processes (though in an intraplate setting). But I still do not think your claim is justified. Some mountains, surely... but most?

I brought up the Alps because it is a range about which I am not wholly ignorant, and because I believe they provide an example of a range in which magmatic and volcanic processes are largely irrelevant.

I brought up erosion because of your claim that:
Erosion will ensure that the "thin surface of sedimentary deposits" will be a fleeting feature of a mountain.
Well, I certainly never claimed that "the thin surface of sedimenary deposits is a "fleeting feature of a mountain"". But the Hawaiin Islands are a serious of volcanoes.

"The Hawaiian Islands do not lie on a mid-ocean ridge, but sit atop a hot spot. Plate tectonics has carried the plate over this relatively static point, causing a mountain chain which youngs to the south east."

This is absolutely correct, but, as I said, it is due to plate tectonic activity. I don't believe that I said convergence, subduction, or abduction. Nevertheless, without a rift, how can you account for magma immerging outward to form volcanic uplift?

"A hot spot is a stationary activity relative to the moving tectonic plate above it, so a chain of islands results as the plate drifts. Over long periods of time, this type of island is eventually eroded down and "drowned" by isostatic adjustment, becoming a seamount. Plate movement across a hot-spot produces a line of islands oriented in the direction of the plate movement. An example is the Hawaiian Islands"
http://en.wikipedia.org/wiki/IslandS

Without sometype of a rift or a crack between the tectonic plates, how can you account for magma uplift that now produces the active lava-flowing volcanic islands of Hawaii today? I have no other explanation. Do you?

The Aplines or Alpides consist of both the Alps in Europe and the Himalayas in Asia. This is because their mutually folding both began together during the Tertiary (1.7 mya).

invert_nexus
10-26-05, 07:11 PM
Oh Christ.
I don't have time to lambast you as you deserve, but just give it up, Valich.
You very clearly stated that " the Hawaii islands are formed from volcanic rifts in mid-ocean tectonic plate ridges". It doesn't matter if you mentioned "convergence, subduction, or abduction" in regards to said activity. You very clearly stated 'tectonic plate ridges'.

So. Just give it up and admit that you said a stupid thing. This is why people hate you, you know.

And yes. Hawaii has formed as a series of islands because of plate tectonics, but the hot spot itself has nothing to do with tectonics.

Arrrgh.
You're such a fucking dick. I shit you not.

valich
10-26-05, 07:50 PM
Regarding the Hawaiin Island volcanoes, I think that what is most confusing is: "What differentiates "hot spots" from cracks or ridges in a plate?" There seems to be a few other Sciforums that are now addressing this issue ("Earth Science" category). Basically, though, hot spots are similar to cracks in tectonic plates, but these socalled "hot spots" occur within, rather than on the edges of lithospheric tectonic plates. I think that this is where the confusion lies: hot magma rises from movement of tectonic plates to create volcanic activity.

"Hawaii is a classic example of a "hot-spot trail", created by a giant plume of magma that rises from the core of the Earth to the surface. As the Pacific plate passes over the plume....Such mantle plumes are deeply entrenched in the geological "standard model", going hand-in-hand with plate tectonics."
http://www.mantleplumes.org/VolcanicBombs.html

"Geologists believe that a huge column of upwelling lava, known as a “plume,” lies at a fixed position under the Pacific Plate. As the ocean floor moves over this “hot spot” at about five inches a year, the upwelling lava creates a steady succession of new volcanoes that migrate along with the plate - a conveyor belt of volcanic islands"
http://www.platetectonics.com/book/page_17.asp

In general: "The magma rises through the Pacific Plate to supply the active volcanoes."
http://volcano.und.nodak.edu/vwdocs/vwlessons/hot_spots/introduction.html

The United State Geological Service (USGS) refers to this area as a "ridge":
"Over the past 70 million years, the combined processes of magma formation, volcano eruption and growth, and continued movement of the Pacific Plate over the stationary Hawaiian "hot-spot" have left a long trail of volcanoes across the Pacific Ocean floor. The Hawaiian Ridge-Emperor Seamounts chain extends some 6,000 km from the "Big Island" of Hawaii to the Aleutian Trench off Alaska. The Hawaiian Islands themselves are a very small part of the chain and are the youngest islands in the immense, mostly submarine mountain chain composed of more than 80 volcanoes. The length of the Hawaiian Ridge segment alone, from the Big Island northwest to Midway Island, is about equal to the distance from Washington, D.C. to Denver, Colorado (2,600 km)...A sharp bend in the chain indicates that the motion of the Pacific Plate abruptly changed about 43 million years ago, as it took a more westerly turn from its earlier northerly direction. Why the Pacific Plate changed direction is not known, but the change may be related in some way to the collision of India into the Asian continent, which began about the same time. As the Pacific Plate continues to move west-northwest, the Island of Hawaii will be carried beyond the hotspot by plate motion."
http://pubs.usgs.gov/publications/text/Hawaiian.html

"The prevailing theory among geophysicists is that the Hawaii-Emperor Seamounts formed as the Pacific Plate moved over a fixed hot spot that today is located beneath the island of Hawaii and is responsible for the world's most active volcano, Kilauea. The segment known as the Hawaiian Ridge, which includes the main Hawaiian Islands and a chain of islands, atolls, and seamounts known collectively as the Northwestern Hawaiian Islands, extends some 1,800 miles (3,000 kilometers) northwest across the Pacific. At the end of the Northwestern Hawaiian Islands, the chain turns sharply northward and becomes the Emperor Seamoun. According to most researchers, this sharp bend represents a rapid change in direction of the Pacific Plate as it passed over the fixed hot spot 47 million years ago."
http://news.nationalgeographic.com/news/2003/08/0814_030814_hotspot.html

"Hot spot volcanoes often have long rift zones that radiate from a summit caldera, along which smaller vents and fissures occur. HAWAII, MAUI, NI'IHAU - High-resolution bathymetric maps show that submarine flat-topped volcanic cones are common on the submarine rift zones of Kilauea, Kohala, Mahukona, and Haleakala volcanoes. Samples show these cones are tholeiitic basalt erupted during the shield-building stage. These flat-topped cones appear to have formed during effusive eruptions lasting years to decades, and apparently form as continuously overflowing submarine lava ponds.
http://www.mbari.org/volcanism/Hawaii/HR-VolcProc.htm

"Two forms of Hawaiian volcanism are poorly understood: post-erosional eruptions and the Hawaiian Arch flows. Various hypotheses have been forwarded to explain these magmatic events; one such mechanism that is relatively undeveloped associates volcanism with the topographic uplift caused by lithospheric flexure. We propose a model in which melt is generated as a direct consequence of the flexural uplift, which surrounds new volcanic shields as they grow. This uplift causes upward flow and decompression of the underlying asthenosphere. We assume that a thick (100 km), heterogeneous layer of asthenosphere is near its solidus, a condition resulting from mantle plume material that first melted partially beneath the shield, but has since flowed laterally away from the shield. One prediction of our model is similar geochemical characteristics between the two types of volcanism, and this is consistent with results of recent geochemical studies. Another prediction is volcanism occurs where the lithosphere is actively rising, during the loading of a volcanic shield."
http://www.agu.org/meetings/wp04/wp04-sessions/wp04_V43B.html

"The concept of a hot spot envisions a small source of heat fixed deep in the Earth, below the lithospheric plates. Molten rock from the heat source rises rapidly, melting its way through the overlying lithospheric plate and emerging on the surface to form a volcano. But because the plate is moving, the volcano is soon carried away from the point over the heat source, and becomes dormant. The hot spot burns its way through the lithosphere directly above it and begins to construct a new volcano. The result is an ever-lengthening line of volcanoes whose abrupt beginning at an active vent marks the location of the hot spot itself."
http://mac01.eps.pitt.edu/harbbook/c_iii/chapter_3b.htm

"Mantle Hot Spots: where magma burns a hole through the crust in the middle of a tectonic plate. While this type of volcano may occur in the middle of continental crust, the best and most abundant examples of hot spots are to be found in the middle of oceanic plates. Because this magma is not “recently” recycled crustal material, it tends to be lower in SiO2 content, producing the quiet type of volcanic eruption that is characterized by gentle lava flows of black basalt."
http://www.ontariogeoscience.net/lessonplans/hot-spots.html

"A major puzzle for proponents of the theory of plate tectonics, and a key complaint of those who resisted this theory, was the formation of island chains like the Hawaiian Islands. How could a trail of islands form in the middle of a plate away from its boundaries if the centers of volcanic activity were oceanic ridges?

The answer was provided by a famous Canadian geologist, J. Tuzo Wilson, who hypothesized in 1963 that the plates did indeed move, but that certain regions of the crust are characterized by "hot spots." These hot spots represent regions where magma continuously breaks through the lithosphere, i.e. they represent stationary magma sources in the asthenosphere. As the plates move across these hot spots, volcanic islands are formed"
http://www.oceansonline.com/hotspots.htm

Also see: http://www.emporia.edu/earthsci/student/sedlacek2/mantle.htm

valich
10-26-05, 07:54 PM
Oh Christ.
I don't have time to lambast you as you deserve, but just give it up, Valich.
You very clearly stated that " the Hawaii islands are formed from volcanic rifts in mid-ocean tectonic plate ridges". It doesn't matter if you mentioned "convergence, subduction, or abduction" in regards to said activity. You very clearly stated 'tectonic plate ridges'.

So. Just give it up and admit that you said a stupid thing. This is why people hate you, you know.

And yes. Hawaii has formed as a series of islands because of plate tectonics, but the hot spot itself has nothing to do with tectonics.

Arrrgh.
You're such a fucking dick. I shit you not.
GET A LIFE!!!

valich
10-26-05, 09:09 PM
I think that this is the key:

"The concept of a hot spot envisions a small source of heat fixed deep in the Earth, below the lithospheric plates. Molten rock from the heat source rises rapidly, melting its way through the overlying lithospheric plate and emerging on the surface to form a volcano."

The lithospere is about 60 miles thick, while a tectonic plate is only a small segment of that area of the lithosphere. So where plate teconic explanations stop - although how can they totaly stop: they have to provide an opening? - the underlying magma uplifting the lithosphere explains that origin source.

Xylene
10-26-05, 11:39 PM
Yes, but what I do not know - totally because of my ignorance of the New Zealand geographic region - is, is this considered a mountain? Or is it a geological land mass build up? Where erosion has just filled in the low-lying areas? New Zealand is a fascinating geological and biodiverse region that I can only hope to someday explore in my lifetime.

The Northland region is mostly plain, fairly low-set by New Zealand standards, i.e. below 600 ft a.s.l. The trench into which the sediment fell was quite deep, several thousand feet, so there's a long sedimentary column. The scene is complicated by comparitively recent volcanism, which occurred between about 20 million (west coast) and 3 millon years ago (east coast). Apart from that volcanic activity, everything else is sedimentary. It's a mountain in reverse, if you like--an upside down mountain range.

invert_nexus
10-27-05, 07:18 AM
GET A LIFE!!!

Get some integrity.

valich
10-27-05, 04:22 PM
The Northland region is mostly plain, fairly low-set by New Zealand standards, i.e. below 600 ft a.s.l. The trench into which the sediment fell was quite deep, several thousand feet, so there's a long sedimentary column. The scene is complicated by comparitively recent volcanism, which occurred between about 20 million (west coast) and 3 millon years ago (east coast). Apart from that volcanic activity, everything else is sedimentary. It's a mountain in reverse, if you like--an upside down mountain range.
Wow! Complicated indeed, but thanks a lot for the clarification! Now I know exactly what you mean when you were referring to a reverse layering. And your more thorough explanation now deeply motivates me to look into this fascinating scenario of simultaneous trench-filling and volcanic activity in the Northland region. Thanks!

valich
10-27-05, 07:03 PM
While some mountains certainly are constructed from gradually accumulating deposits of volcanic rock (the Hawaiian Islands providing a prime example), I don't think you're justified in saying that this is the origin of most mountains.
The Wikipedia gives an explanation of the stages of the volcanic buildups in the Hawaiian fissure or ridge, but there seems to be a debate that has been going on now for about thirty years as to whether this socalled "hot spot" is due to thermal convection currents and circulation within the mantle below the lithosphere, or whether it is due to a direct upwelling of a mantle plume originating at the mantle-core boundary. To make matters even worse, to arrive at a more accurate explanation, nowadays the word "hotspot" and "mantle plume" are being used interchangeably. In any case, this hotspot is quite large and remains stationary below the lithosphere while the Pacific plate and the above volcanoes move west northwest above it.

"The assembly line that forms the volcanoes is driven by a "hot spot," or plume of hot material, deep within the Earth that partially melts to produce magma as it rises beneath the Pacific Plate. As the plate moves west-northwest, each volcano moves with it from its place of origin above the hot spot. The age and orientation of the volcanic chain records the direction and rate of movement of the Pacific Plate. The pronounced 43-million-year-old bend between the Hawaiian Ridge and the Emperor Seamount Chain marks a dramatic change in plate direction."
http://hvo.wr.usgs.gov/volcanowatch/1995/95_09_08.html

Among other factors, it is this pronounced bend leading to two seperate fissure zones that is the most challenging aspect to finding a precise and accurate working hypothesis for the formation of the volcanoes of Hawaii:

"The Hawaiian chain apparently consists of two strands of volcanoes located along distinct but parallel curving pathways. Multiple volcanoes line up to form each strand....The alignment of the Hawaiian Islands reflected localized volcanic activity along segments of a major fissure zone on the ocean floor. This “great fissure” origin for the islands served as a working hypothesis for subsequent studies until the mid-20th century....Then it was pointed out that the time-progressive volcanism along the Hawaiian chain could be explained by the lithosphere moving across a stationary hot spot in the mantle. This led to the theory of deep mantle plumes when Morgan [1971; 1972] proposed that a) this hot spot was continually supplied by a plume from the deep mantle, and b) there are approximately 20 such plumes in the mantle. Fixity relative to one-another, time-progressive volcanic tracks, and a high rate of volcanism were considered to be the primary characteristics of volcanic regions fuelled by deep-mantle plumes.

The Hawaiian - Emperor system appears superficially to fit the fixed deep mantle plume hypothesis well....The most compelling and widely quoted evidence today is still geometric considerations such as fixity, perceived parallelism with other volcanic chains and the regular time progression of volcanism, along with the high melt productivity. Lnear time-progression of volcanism and high magmatic productivity can be explained by other mechanisms such as propagating cracks and high mantle fertility. Nevertheless, for about 20 years there has been no serious challenge to the fluid-dynamic, deep thermal mantle plume hypothesis for the origin of the Emperor and Hawaiian islands and seamounts. There are, however, a substantial number of aspects of the chains that are not predicted by the plume hypothesis and fit it poorly. These must give clues to alternative genesis models.....

Aspects of the Emperor and Hawaiian chains unpredicted by the plume hypothesis:
1) The “bend” did not result from a change in direction of Pacific plate motion....In addition to the change in trend, the locus of volcanism moved south by ~ 800 km relative to the geomagnetic and biofacies reference frames while the Emperor Seamount chain formed.
2) The Emperor chain began near a ridge.
3) There is no Emperor/Hawaiian “plume head."
4) The magmatic rate is highly variable.
5) There is no heatflow anomaly: Lithosphere underlain by a thermal plume is expected to be thinner and to have higher heat flow than the average for lithosphere of the same age elsewhere. Heatflow across the Hawaiian swell, however, shows no significant anomaly.
6) Mantle temperature is elevated by up to ~ 200°C: Petrology can be used to infer the temperature where surface-erupted melts were last in equilibrium with the mantle source, and Tp, the mantle potential temperature. The results for Hawaii are variable, and whether or not a high temperature anomaly is inferred depends on what “average” mantle temperature is considered to be. “Average” mantle temperature is mostly studied at mid-ocean ridges (MORs), since this is where magma of mantle origin is mostly erupted. The temperatures required for plumes to rise are debated. Peridotic plumes from the core-mantle boundary would require temperature anomalies of the order of 600 K.... [However] Combinations of geophysical and geochemical arguments (e.g., “garnet signature” in rare-Earth elements, olivine-liquid geothermometers have been used to infer temperatures beneath Hawaii of [only] 150 - 200 K higher than MORs.
7) The melt originates from the shallow asthenosphere [upper ~200km region of the 2,900 km mantle].
8) The basalt geochemistry [of the Hawaiian volcanoes] does not require a mantle plume, or a deep or hot source.
9) Seismology has not detected a plume.

Any satisfactory theory for Hawaiian volcanism must explain (or rationalize) the:
- change in migration direction of the melting locus at the bend,
association of the great bend with the Mendocino fracture zone,
- change in migration rate at the bend,
- apparent commencement of the volcanic chain near a ridge,
- absence of a “plume head”,
- large variations in magmatic production, and a current magmatic rate about 3 times greater than the next most productive hotspots,
- absence of a significant heat flow anomaly,
- absence of lithospheric thinning,
- absence of a strong high-temperature signal in the erupted basalts,
- production of very large volumes of magma even though the depth to the top of the melting column is exceptionally large compared with MORs,
- spatial and temporal variation in the composition of erupted lavas on a variety of scales, remote location of Hawaii, near the center of a very large plate,
- seismic whole-mantle mantle structure that is apparently normal compared with the Pacific ocean elsewhere,
- occurrence of a bathymetric swell (a moat and “arch”) along the eastern two-thirds of the Hawaiian chain and wrapping around its southeastern end, with alkalic basaltic volcanism occurring at some places along it."

"The Emperor and Hawaiian Volcanic Chains: How well do they fit the plume hypothesis?," by G. R. Foulger1 & Don L. Anderson.
http://www.mantleplumes.org/Hawaii.html

Laika
10-28-05, 05:54 AM
Well, I certainly never claimed that "the thin surface of sedimenary deposits is a "fleeting feature of a mountain"

Indeed, this is what I said. You said:


The rock folding is there, but it is almost always underneath the thin surface of sedimentary deposits and not visually apparent

And it is that claim which I disagree with.

Also, remember that this is the Earth Science section of a scientific forum. In this context certain terms carry specific meanings, which may not correspond to their usage in common parlance. You have to be careful, therefore, that when you say "volcanic rifts in mid-ocean tectonic plate ridges", that's really what you mean.

Anyway, this thread's gone quite far off the topic. The main issue I had with what you posted was that you claimed


Most mountains are formed through volcanic or molten lava activities in plate tectonic divergences or convergences

which I think is just plain inaccurate.

Ophiolite
10-28-05, 12:57 PM
Anyway, this thread's gone quite far off the topic. The main issue I had with what you posted was that you claimed


Most mountains are formed through volcanic or molten lava activities in plate tectonic divergences or convergences

which I think is just plain inaccurate.Indeed Laika, as with many (and it may be most) of what Vallich posts he is wholly, totally, irrevocably, absolutely, incontrovertibly incorrect. He has raised flawed thinking to an artform and he must surely be its supreme master.

[I can actually 'prove' Vallich's statement is correct, but it does require taking some liberties with facts, and some fluid use of definitions. That's what makes his posts dangerous to those trying to learn: he gives the appearance of authenticity, yet supplies severe distortions. A Government Health Warning may be appropriate for all his posts.]

valich
10-28-05, 08:50 PM
Indeed Laika, as with many (and it may be most) of what Vallich posts he is wholly, totally, irrevocably, absolutely, incontrovertibly incorrect. He has raised flawed thinking to an artform and he must surely be its supreme master.

[I can actually 'prove' Vallich's statement is correct, but it does require taking some liberties with facts, and some fluid use of definitions. That's what makes his posts dangerous to those trying to learn: he gives the appearance of authenticity, yet supplies severe distortions. A Government Health Warning may be appropriate for all his posts.]
What the hell's your mental problem? Your posts just distract from the educational content of these forums. You profess to be the expert here - challengingly stating: "you're in my area now" - yet you're only posting another condescending obnoxious belittling reply. What's the purpose: simpleminded kicks and jollies?

From what I learned through my geology curriculum of courses, including one on "plate tectonics," hot spots are not the same as magma plumes. Today, however, most articles seem to use the two terms interchangeably.

What I was taught - and at the time it was still speculation - and what I continuosly keep learning today, and for the rest of my life for that matter, are the most recent facts. I was taught that there are basically three hypotheses:

1) That hot spots are created by a plume of magma that rises directly from the mantle/core boundary of the Earth to the lithosphere, or to above it.
2) That hot spots are due to thermal convection currents and circulation within the mantle below the lithosphere originating from the mantle/core boundary.
3) Or, that there are two - or possibly more - levels of circulation of magma and solid rock slowly taking place within the mantle: one being within the upper asthenosphere, the others being below it.

I have not read of any seismographic evidence that proves that any one of the above three are now theories or not. If you know of any more updated information, then please post it. Thanks.

valich
10-28-05, 09:05 PM
You said:

And it is that claim which I disagree with.

Also, remember that this is the Earth Science section of a scientific forum. In this context certain terms carry specific meanings, which may not correspond to their usage in common parlance. You have to be careful, therefore, that when you say "volcanic rifts in mid-ocean tectonic plate ridges", that's really what you mean.

The main issue I had with what you posted was that you claimed:

which I think is just plain inaccurate.
Unfortunately the posts within posts don't post. I don't know how to do that but it doesn't matter, right? Anyways, so what is your counter-theory of the way that the majority of mountains on Earth have formed?

Also, in reference to a "volcanic rifts in mid-ocean tectonic plate ridges," that is what they are saying that adds to the still unexplained theory and dilemma behind the formation of the Hawaiian volcanoes: that one fissure formed next to a ridge? From what I have been reading, this is one reason why the debate has been going on for thirty years now. The other reasons: refer to what I quoted from citations posted above.

Please reply. I am eager to learn more and would accept your views as contributing to the world base of knowledge. We all learn and in this way arrive at the facts, or it may lead to more questions, but in any case it leads to progress in scientific knowledge.

Ophiolite
10-29-05, 04:04 AM
Vallich your post on hot spots is a complete strawman. I am objecting, as Laika did, to your statement that most mountains are formed through volcanic or molten lava activities. This is incorrect. I am belittling you and your posts because they are consistently misleading. I object to you misleading others with your own misunderstanding. Such unscientific behavour deserves to be put down at every opportunity. I shall continue to do so. The only mental problem on display here is your own overtly sociopathic behaviour.

Laika
10-29-05, 07:02 AM
Well it's not really a counter-theory, but it is quite clear that continental mountain ranges are formed by crustal shortening. This horizontal contraction is accommodated by vertical thickening. The thickening is accomplished by folding and reverse faulting. Although igneous activity (I think generally intrusions of felsic magma) may occur during this process, they are not responsible for the orogeny, but are merely a consequence of it.

As I say, this is not controversial and, having done no original research of my own, I'm afraid that I'm not "contributing to the world base of knowledge". I wish I could.

valich
10-29-05, 02:59 PM
Continental mountain ranges, like the Rockies, Appalachians and Alpine-Himalayas, that we covered above, were formed by subduction, abduction, or convergence of plates. The convergence of two plates, as in the case of the Northern Rockies, leads to buckling up and folding. The Cascade Range is much more complex and involves a circulatory uplifting and deformation of the crust, but is ultimately caused from the San Juan Tectonic Plate moving east underneath the North American Plate.

Yesterday we posted two replies to a new thread called "Volcano Experts:

The Eurasian-Melanesian mountain belt is one of two of the Earth's major mountain building systems. The other major active belt is the Circum-Pacific belt system. The Eurasian-Melanesian mountain belt system, sometimes called the Alpino-Mediterranean belt, stretches from Western Europe to New Zealand and includes the Alpine-Himalayan Mountains that were both caused - and are still forming - by the collision and subduction of the African plate and the Indian Plate moving under the European Plate. The Circum-Pacific belt system circles the Pacific Ocean and includes the socalled "pacific Ring of Fire" (producing countless eathquakes and volcanoes) and the Pacific Plate. The subduction of the Pacific Plate under the Asia has produced the mountains in Japan, China, and Borneo. These two huge belt systems pretty much cover all the major mountain ranges in the world. I think the only other major mountain range is the one under the mid-Atlantic Ocean produced by the Mid-Atlantic Ridge, where two plates are diverging and spreading apart.

You are right though: "mountain ranges are formed by crustal shortening. This horizontal contraction is accommodated by vertical thickening. The thickening is accomplished by folding and reverse faulting." The outermost layer of the Earth is the crust - part of the lithosphere - but underneath this thin chemical crust are the underlying tectonic plates that produce these crustal shortings and vertical tickenings through uplifts, buckling, and folding: the outermost crust is normally only a few miles thick, but the underlying plates can be 50 miles thick.

About 1/4 of the Earth consists of mountains, but in general, mountains are over 2,000 ft. tall, or else they would be hills.

Ophiolite
10-29-05, 03:20 PM
So you concede that your original statement that "most mountains are formed through volcanic or molten lava activities" was incorrect. Excellent. At last we are making progress.

valich
10-30-05, 10:29 PM
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 [dome mountains]. 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.
Did my incorrect statement that "a hot pool of lava underneath" cause the confusion? Apparently this was a big error on my part to say, but I later posted that it was a trivial argument: magma is called lava only when it is on the surface, but minerolagically there is basically no big difference to argue over.

All mountains are produced by convergent, divergent, or transform boundaries of tectonic plates OR by volcanoes that erupt within plates that form volcanic arcs or small mountains. All of these processes involve the transformation of igneous rock into molten magma that deforms the tectonic plates to create mountains. Am I stating anything incorrect here?

Laika
10-31-05, 03:08 AM
No, your statement that "most mountains are formed through volcanic or molten lava activities in plate tectonic divergences or convergences" caused the confusion. I maintain that this is not correct.


All mountains are produced by convergent, divergent, or transform boundaries of tectonic plates OR by volcanoes that erupt within plates that form volcanic arcs or small mountains. I think that's basically fair to say, except that volcanic arcs are a consequence of subduction rather than intraplate volcanism.


All of these processes involve the transformation of igneous rock into molten magma that deforms the tectonic plates to create mountains

It is this that I have an issue with. I assume you meant that the igneous rocks are formed by the magma? Or did you mean that magma is formed by the melting of pre-existing igneous rock? Either way, to say that magmatic activity occurs during orogeny is not the same as saying that magmatic activity is responsible for the orogeny. The mountain building is accomplished through folding and reverse faulting.

valich
10-31-05, 06:38 PM
So you concede that your original statement that "most mountains are formed through volcanic or molten lava activities" was incorrect. Excellent. At last we are making progress.
Lava is molten magma extruded through volcanic activity and igneous rock is made from solidified molten magma. Ninety-five percent of the Earth's crust and lithosphere are composed of igneous rock down far below 200 km.; therefore, 95% of the Earth's crust came fom molten magma (and some impurities).

Every major mountain chain in the world was made through tectonic plate activities, magma plumes, or a hot spot - like in dome mountains - AND are composed of volcanoes, and have been partially or entirely built by volcanoes, or the magma underneath moving the tectonic plates. The Andes, Appalachians, Alpides, Cascades, Himalayas, Rockies, the Mid-Atlantic Mountain Range, and every orogeny range formed throughout the history of the Earth are or were composed of volcanoes. Molten magma formed all these mountains both from below through tectonic plate convergence, subduction, divergence, or transform faults, and from above by volcanic activity. The only exception that I can think of are dome mountains: they are short and wide and formed by uplifts due to a plume or a hot spot. Heck, even a volcano itself is a mountain formed entirely by its own volcanic activity.

valich
10-31-05, 06:43 PM
The mountain building is accomplished through folding and reverse faulting.Not volcanoes and dome mountains. Volcanoes are mountains formed entirely by layering: dome mountains can be uplifted without folding.

Laika
10-31-05, 07:56 PM
Every major mountain chain in the world was made through tectonic plate activities, magma plumes, or a hot spot - like in dome mountains - AND are composed of volcanoes, and have been partially or entirely built by volcanoes, or the magma underneath moving the tectonic plates

Valich, surely you don't mean to extend your use of the terms "volcanic or molten lava activities" to include the mantle convection responsible for plate tectonics? I wouldn't have expected somebody who has "been teaching for over ten years after twenty years of higher education" to fall prey to one the most common misconceptions about the mantle.

Magma is molten rock.

The mantle is not molten rock.

Plate tectonics is not a volcanic or molten lava activity.

valich
10-31-05, 10:27 PM
Valich, surely you don't mean to extend your use of the terms "volcanic or molten lava activities" to include the mantle convection responsible for plate tectonics? I wouldn't have expected somebody who has "been teaching for over ten years after twenty years of higher education" to fall prey to one the most common misconceptions about the mantle.

Magma is molten rock.

The mantle is not molten rock.

Plate tectonics is not a volcanic or molten lava activity.
Please do not requote my term "molten lava activities" again as I have corrected that very trivial mistake three times already! Get it? It was an extremely "trivial" error written in haste. I am not submitting a scientific paper for publication in a journal here: this is a "forum."

I quote from three dictionaries:
"Magma is molten rock material from which igneous rocks is formed."
McGraw-Hill Dictionary of Earth Science
"Magma: Naturally occurring molten rock material"
Dictionary of Geological Terms, prepared by The American Geological Institute.
"Magma: A molten fluid, formed within the crust or upper mantle of the Earth."
Dictionary of Geology, D.G.A. Whitten, Penguin Reference.

Do you know what causes plate tectonic movements? Tectonics revolutionized the geographic stratum of the Earth into a smaller outer crust, a tectonic plate within the lithosphere, and an underlying asthenosphere (a portion in the upper mantle that is even more fluid than the upper lying lithosphere). The lower you go, the more plastic and fluid it gets with convection currents that recirculate the upper crust that is subducted through plate tectonics. Finally when you reach the outer core of the Earth it is a completely liquid structure, with a center solid core made up mostly of iron and a bit of nickel. This outer core circulating around the Earth's solid inner core is what gives the Earth's its magnetic field, including the North-South pole magnetism.

The lower you go down into the Earth, the hotter it gets, until you reach the solid iron center core which cannot be melted any further than the liquid magma igneous rock chemical compositions above it: basalts, dolerite, gabbro, granite, pyrclastic rocks, rhyolie, serpentine, trachyte, and pneumatolysed liquified rocks.

valich
10-31-05, 11:25 PM
So you concede that your original statement that "most mountains are formed through volcanic or molten lava activities" was incorrect. Excellent. At last we are making progress.
As usual, you misquote my original posting to satisfy your egotistic self-satisfying needs, right? Truth in kowledge has no place for this. Now that I look back, I see that I originally posted: "Most mountains are formed through volcanic or molten lava activities in plate tectonic divergences or convergences." And I corrected my trivial error. Damn! Please contribute to the educational advancement of this forum: it is called "Sciforum: the intellegent comunity."

Laika
11-01-05, 03:18 AM
Most mountains are formed through volcanic or molten lava activities in plate tectonic divergences or convergences

Valich, I am not picking at your substitution of lava with magma. In truth, I read it as "most mountains are formed through volcanic or molten magma activities" anyway. But this still doesn't make it correct.

I said:
Magma is molten rock

You said:
Magma is molten rock material from which igneous rocks is formed
Magma: Naturally occurring molten rock material
Magma: A molten fluid, formed within the crust or upper mantle of the Earth
Great. No arguments there.
However, you still claim something which I don't think is just a trivial mistake. You said (with my boldface):
Every major mountain chain in the world was made through tectonic plate activities, magma plumes, or a hot spot - like in dome mountains - AND are composed of volcanoes, and have been partially or entirely built by volcanoes, or the magma underneath moving the tectonic plates

If you mean to extend 'molten lava/magma activities' to incorporate mantle circulation, and thus tenuously support your claim that "most mountains are formed through volcanic or molten lava activities in plate tectonic divergences or convergences", then you are in error. The mantle is solid (a plastic solid - granted). Even at ocean ridge axes there is only partial melting of mantle material. This is why the ocean crust is basaltic in composition compared to the mantle, which is peridotite.
The magma produced behind subduction zones is a result of water being introduced into the mantle by the subducting plate. This lowers the melting point of the rock, causing partial melting to occur in a process called anatexis.

Ophiolite, correct me if I'm wrong. With that moniker I'm sure you know it in far greater detail than myself!

Valich, please understand that although I have quoted you several times in this post, I am not focussing on your magma/lava typo. I just think there's a more fundamental error within your posts.

Ophiolite
11-01-05, 10:05 AM
Laika, you are correct in your summary and in your concerns over his fundamental errors. I have given up on Vallich several times. I do not know whether he is thick, mentally compromised, deliberately provocative or what. Frankly I would stop posting anything in response to his posts except that he is so often so wrong that I worry that casual readers are going to be misled by his misinformation and misinterpretations.

My degree is in geology and though I only worked as a geologist for a brief period I have retained a close association with aspects of geology through my work (specifically drilling technology, wherein the mechanical properties of rock are of prime importance) and through reading. I get quite emotional when I see facts and theories being distorted as vallich has done. Several posters of long standing have taken him to task on several threads for the same kind of thing. He simply refuses to acknowledge his errors, attacks the individual, pours out a mass of jargon and multiple references that have relevance only because they contain some of the same words, sewing confusion in his wake.
The best thing might be just to ignore him. (Alternatively, I am considering using it as an opportunity to see if their is anything in the use of voodoo dolls to extract vengance at a distance. You will recognise that as a joke, Vallich will see it as evidence of my mental problems.)

valich
11-02-05, 10:12 PM
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.
But they do not alway fold!

valich
11-02-05, 10:22 PM
The mantle is solid (a plastic solid - granted). Even at ocean ridge axes there is only partial melting of mantle material. This is why the ocean crust is basaltic in composition compared to the mantle, which is peridotite.
The magma produced behind subduction zones is a result of water being introduced into the mantle by the subducting plate. This lowers the melting point of the rock, causing partial melting to occur in a process called anatexis.
The mantle is solid? And then you say it is "plastic"? Basalt is the Earth's crust's (lithosphere) most uncompassing solidified magma.

"Water being introduced into the mantle by the subducting plate"? Cite your sources please! Fluidity is not equivallent to water, let alone magma or metamorphism. You're implying that the ocean crust is basaltic because it is in the ocean, under water? And that this is not part of the Earth's mantle?

valich
11-02-05, 10:34 PM
My degree is in geology and though I only worked as a geologist for a brief period I have retained a close association with aspects of geology through my work (specifically drilling technology, wherein the mechanical properties of rock are of prime importance) and through reading. I get quite emotional when I see facts and theories being distorted as vallich has done. Several posters of long standing have taken him to task on several threads for the same kind of thing. He simply refuses to acknowledge his errors, attacks the individual, pours out a mass of jargon and multiple references that have relevance only because they contain some of the same words, sewing confusion in his wake.
The best thing might be just to ignore him. (Alternatively, I am considering using it as an opportunity to see if their is anything in the use of voodoo dolls to extract vengance at a distance. You will recognise that as a joke, Vallich will see it as evidence of my mental problems.)
Always this, "and my degree in geology...blah, blah,blah" as if this means jack. You've been so wrong so many times in your posts, espectially regarding "dome mountains" that you by all ethical standards should render your degree back to whatever institute granted it to you!

You, and whoever you are referring to, have continuously refused to acknowledge any and all of my factual scientific citations, instead relying on your own subjective interpretations without ANY facts.

Laika
11-03-05, 02:44 AM
The mantle is solid? And then you say it is "plastic"?

Yes, these two terms are not mutually exclusive. To say that the rocks in the mantle are plastic is to say that they undergo plastic (permanent) deformation when stressed. All solids undergo varying degrees of elastic, plastic and brittle deformation, depending on the type of solid, confining pressure, temperature and strain rate. The mantle is a plastic solid.


Basalt is the Earth's crust's (lithosphere) most uncompassing solidified magma

I'm not sure what you mean by this. The term lithosphere refers to a structural rather than compositional unit. The Earth's lithosphere is the rigid outer part of the Earth. It is composed not only of ocean floor basalt, but also more felsic continental rocks, and even incorporates huge thicknesses (up to dozens of kilometres) of ultramafic mantle rocks that have been underplated.


You're implying that the ocean crust is basaltic because it is in the ocean, under water? And that this is not part of the Earth's mantle?

The mantle consists mostly of peridotite (magnesium and iron silicate). This has a very high melting point. Therefore, when partial melting occurs due to rifting or a hot spot plume, the resulting melt contains a disproportionate volume of minerals with lower melting points, that are more easily included in the magma. This is why rocks of basaltic composition do not reflect the composition of the mantle, but are relatively enriched in pyroxenes and feldspars. This is why the ocean crust is basaltic.


"Water being introduced into the mantle by the subducting plate"? Cite your sources please! Fluidity is not equivallent to water, let alone magma or metamorphism

Between being formed at a spreading axis, and being subducted some millions of years later, the ocean lithosphere has plenty of time for hydrothermal alteration. Water is incorporated into the structures of some minerals, hydrating and changing them. When these are subducted the volatiles released lower the melting point of the surrounding rocks. If the melting point is lowered to below that of their current temperature, partial melting will occur. This is called ANATEXIS, and will be in one of your many books on the subject. The composition of the melt can be further modified by the process of fractionation and differential crystallisation as the molten material accumulates. This is why intrusions and eruptions in a continental setting generally involve more silica-rich material. Quartz has a low melting point compared to the other components which may have started in the melt, but which then crystallised out in an unexposed chamber.

The ocean crust is derived from, but is not part of, the Earth's mantle.

valich
11-03-05, 08:21 PM
No, your statement that "most mountains are formed through volcanic or molten lava activities in plate tectonic divergences or convergences" caused the confusion. I maintain that this is not correct.

I think that's basically fair to say, except that volcanic arcs are a consequence of subduction rather than intraplate volcanism.
Excellent. Volcanic arcs are definitely formed by subduction and not "intraplate" volcanism. Plate tectonic convergences can lead to subduction, transformation boundies, or a direct confrontation of the converging plates.

valich
11-03-05, 08:54 PM
Yes, these two terms are not mutually exclusive. To say that the rocks in the mantle are plastic is to say that they undergo plastic (permanent) deformation when stressed. All solids undergo varying degrees of elastic, plastic and brittle deformation, depending on the type of solid, confining pressure, temperature and strain rate. The mantle is a plastic solid.I never said that the mantle was solid? When a plate is subducted it is a subducted solid plate. Current theory is that there are circulating convection currents in the mantle that circulate parts of subducted plates within the mantle.


I'm not sure what you mean by this. The term lithosphere refers to a structural rather than compositional unit. The Earth's lithosphere is the rigid outer part of the Earth. It is composed not only of ocean floor basalt, but also more felsic continental rocks, and even incorporates huge thicknesses (up to dozens of kilometres) of ultramafic mantle rocks that have been underplated.The lithosphere is composed of both the plates, countless compositional minerals, "mantle rock that has been underplated," and the magma that moves them.


The mantle consists mostly of peridotite (magnesium and iron silicate). This has a very high melting point. Therefore, when partial melting occurs due to rifting or a hot spot plume, the resulting melt contains a disproportionate volume of minerals with lower melting points, that are more easily included in the magma. This is why rocks of basaltic composition do not reflect the composition of the mantle, but are relatively enriched in pyroxenes and feldspars. This is why the ocean crust is basaltic.Again, as you yourself know, are you referring to what is considered the physical or chemical composition categorizing of the mantle? The ocean crust is mostly basaltic. The crust is much thinner in the ocean than the much larger crust on the continents that consist of much much more sedimentary rock. The majority of the upper crust on continents is not basaltic.


Between being formed at a spreading axis, and being subducted some millions of years later, the ocean lithosphere has plenty of time for hydrothermal alteration. Water is incorporated into the structures of some minerals, hydrating and changing them. When these are subducted the volatiles released lower the melting point of the surrounding rocks. If the melting point is lowered to below that of their current temperature, partial melting will occur. This is called ANATEXIS, and will be in one of your many books on the subject. The composition of the melt can be further modified by the process of fractionation and differential crystallisation as the molten material accumulates. This is why intrusions and eruptions in a continental setting generally involve more silica-rich material. Quartz has a low melting point compared to the other components which may have started in the melt, but which then crystallised out in an unexposed chamber.
Yes! Yes! Yes! Not all plate boundaries, subductions, and intraplate fissure have a straight axis. This is one problem why the creation of the Hawaiian Island volcanic region is still not fully explained. There is a dual-degree intraplate fissure that developed alongside a pre-existing ridge that is yet unexplained. The Pacific Plate moves over an underlying hotspot here.

The ocean crust is derived from, but is not part of, the Earth's mantle.Keep up your research. When are you going to write a book?

Xylene
11-04-05, 12:52 AM
As for other types of mountains--and again using New Zealand as an example because I know it so well--here's the current state of play so far as geological knowledge about NZ.

The Pacific Plate is pivoting anti-clockwise, with the axis of rotation centred at about 60 degrees southern latitude and on the International dateline. That means that the full force of the plate's rotation is swinging due west (ie at a 90 degree angle) directly at the Australian Plate, on which the western part of the North Island sits. This collision affects the southern half of the east coast of the North Island. This creates successive ranges of hills by compression, because as the Pacific Plate is subducted under the North Island, sea-floor material is scraped off, piled up and hardened into rock by compression. Inland of the coastal ranges, the descent of the plate into the mantle is creating tension, which is stretching and thinning the crust. This has created the Taupo Volcanic Zone (TVZ) where all of New Zealand's largest volcanos ore situated presently. This is the current geological axis of New Zealand, i.e. where the most intense volcanic activity is going on.

Further down, in the South Island, the angle where the Australian Plate meets the Pacific Plate is much more oblique; the action is a sliding motion rather than a head-to-head impact as further north. The result is a slip-strike earthquake zone, the Great Alpine Fault, which runs all the way down through the South Island. Occasionally (periodicity being 250-400 years) there are vast earthquakes on this faultline. 30mm of strain builds up in a year on this fault, and the last time there was a major tremor there was about 1720 AD. So the 250-year danger-zone was entered in about 1970. Any time from now on, going by past geological evidence at least, we can expect another major earthquake on the Alpine Fault.

The Southern Alps, along the western edge of the South Island, are caused by the compressive forces of the Australian Plate's impact with the Pacific Plate. New Zealand was once attached to Australia, but broke away millions of years ago (how many slips my mind just now--I think about 55 mya). Anyway, New Zealand was once much larger than it is presently--at the time it broke away it was a continent about half the size of Australia. As the Tasman Sea widened between NZ and Oz, the continental crust of New Zealand was stretched and thinned. Plus of course erosion did its work. The result is that now New Zealand's former continent is mostly underwater.

valich
11-06-05, 10:54 PM
I know you have been following this thread, so you must of read what I replied to Xylenes's post, to which HE replied:

"The Northland region is mostly plain, fairly low-set by New Zealand standards, i.e. below 600 ft a.s.l. The trench into which the sediment fell was quite deep, several thousand feet, so there's a long sedimentary column. The scene is complicated by comparitively recent volcanism, which occurred between about 20 million (west coast) and 3 millon years ago (east coast). Apart from that volcanic activity, everything else is sedimentary. It's a mountain in reverse, if you like--an upside down mountain range."

I thanked him graciously for this revelation and told him that I am anxious to learn more, but do not have the time to research it right now. Can you combine your explanation with his to make the two more understandable together?

The Cascade Mountain Region is similarly confusing to me. The simplest explanation only refers to the subduction of the Juan de Fuca Plate but the formation of the entire range includes climatic shifts, the surrounding basalt ranges, the Columbian Basin, and the consequent "circular activity" in the upper crust?

Ophiolite
11-07-05, 05:40 AM
Always this, "and my degree in geology...blah, blah,blah" as if this means jack. Well, it means a fucking lot to me weasel, since I adore geology and the concepts and the theories and the paradigms. I am delighted to have such limited understanding as I do have on the subject and it offends me when a cretin such as you[rself distorts, misinterprets and plain lies. I mentioned my degree on this occasion because it was a relevant reply to Laika's post.


You've been so wrong so many times in your posts, espectially regarding "dome mountains" Cite a single example.



You, and whoever you are referring to, have continuously refused to acknowledge any and all of my factual scientific citations, instead relying on your own subjective interpretations without ANY facts.Your factual citations are consistently either irrelevant, misinterpreted or misapplied. You have revealed consistently that you have no understanding of the material you are quoting. Please piss off.

valich
11-07-05, 07:33 PM
Typical words from the "toilet mouth." As I said to your elementary associates:

I have posted the most excepted explanations within the scientific community as they are writen in almost all - maybe all - biology textbooks, and as they are supported in most scientific journals. Who are you guys? Paleontologists? Geologists? Scientists? No! You guys are Sciforum fanatics who browse the web like pinball wizards and excell in condemning other people who proclaim to know more knowledge than you then just cut them down (do I detect jealousy?).

How immature and unscientific. This forum is called "Sciforum - the Intelligent Community." The first step to be part of it should be to use the scientific method, but instead your first step is to condemn others and resort to being a "toilet mouth," rather than responding to ideas in a respectable scientific way. GET A LIFE!

Laika
11-08-05, 03:02 PM
As I said to your elementary associates

Do you mean to group me in this category? If so, I am far from offended by the association. However, I do object to this:


Who are you guys? Paleontologists? Geologists? Scientists? No! You guys are Sciforum fanatics who browse the web like pinball wizards and excell in condemning other people who proclaim to know more knowledge than you then just cut them down (do I detect jealousy?)

Yes, I am trained in geology. I am not a "Sciforum fanatic", though I do find it an exceptionally effective work avoidance strategy right now. I am far from jealous of you.

If your post did not refer to me, then please ignore it.

valich
11-08-05, 10:23 PM
Laika, I respect your posts and am very happy to read your intelligent comments: they are scientific, logical, and well-worded. Rest assured, I am not referring to you.

Invert_Nexus, Ophiolite, and (occasionally - but not very often) Spurious actually "stalk" me throughout sciforum threads and then post vulgar, condemning, belittling, condescending posts. There is no place for this type of obnoxious distracting behavior in the advancement of science - nline or off. In fact, Invert just posted another reply on another thread trying to justify the use of vulgarity in scientific forums. Throughout my thirty year academic career I have never heard of or been subjected to this type of abuse and vulgarity. This is amusing to say the least. But in no way are you part of their belligerent postings.

Ophiolite
11-09-05, 12:09 PM
Invert_Nexus, Ophiolite, and (occasionally - but not very often) Spurious actually "stalk" me throughout sciforum threads and then post vulgar, condemning, belittling, condescending posts. .Get real. I have better things to do with my time than follow you around. However, each time I see your self righteous drivel I shall attack it.

I am pleased to note that you understood my posts to be vulgar, condemning, belittling, condescending . At least you are getting the message. I shall be happy (you can't begin to realise how happy) to post positive, affirming, embracing posts in response to yours, when you conduct yourself in a manner that demonstrates you do indeed have a thirty year academic career, and not merely a one year academic career repeated thirty times.

By the way, a simple statistical analysis of the timing of your posts, my posts and Invert Nexus's posts, reveals that you are the stalker. Interesting that you chose to make the accusation before one of us pointed that out.

valich
11-09-05, 02:04 PM
Stop stalking me. Stop wasting mine and other people's time who sincerely are trying to learn by posting useless nonsense, like the above post, and PLEASE GET A LIFE!

Ophiolite
11-09-05, 05:46 PM
I have reported you for your false accusation of stalking. Please do not repeat it.

valich
11-09-05, 06:03 PM
I can prove that you are stalking me on these posts just like you are doing again right now and just like you did to me again two minutes ago on the thread "Volcano Experts." You gave an unsolicited degrading responce: that's called stalking. Stop stalking me and get a life. I've also reported you to the administrator and if you don't stop harassing and stalking me I'll get a court order for the adminstrator to give me your email address and real name and take you to court! The administrator has already posted a thread that user's reframe from using vul;garity and stop degrading and belittling people on the forums. Evidently his post is falling on deaf ears. Stop stalking me by posting a rude, vulgar, irrelevant, and belittling reply everytime I post!

Ophiolite
11-09-05, 06:18 PM
Fuck off vallich. If I was stalking you I would be pursuing you in every thread in which you post. A cursory examination of these fora will reveal that there are several threads in which I leave it to others to counter your noxious drivel.
In those threads in which I have an interest I shall continue to berate and condemn you for as long as I draw breath, or until you clean up your act. Learn to live with it or get the hell out of here.
Oh, you could just use the ignore button - so much cheaper than lawyers. But if that's the route you want to go down, let me know. I'll show you mine, if you show me yours. I can't wait till we get to the part where the character witnesses are called. That should be a hoot.

valich
11-09-05, 10:23 PM
Now this is a unique form of mountain building just reported on CNN caused by radiation and wind that caused mountains to be formed on newly created stars:

"Radiation and winds from these massive stars forced material outward, leaving the dense pillar-shaped clumps. Many astronomers think our Sun was formed in a similar setup, then later migrated away from the clump."
"Telescope sees 'Mountains of Creation," by Robert Roy Britt, Nov. 9, 2005. http://www.cnn.com/2005/TECH/space/11/09/dust.clouds/index.html

Xylene
11-10-05, 12:07 AM
Here's another way to form mountains, valich--you take the moon of one of the larger worlds, you cool it down (as it does when it loses radioactive heat) and you end up with a range of mountains where the tidal effect of the parent planet has been frozen into the icy crust.

Of course, these mountains would be racked by earthquakes all the time because of the ongoing interaction with the parent world. Also, they'd be moving up and down on a sort of slushy under-ice layer, because the entire body of the moon would still be flexed and heated by tidal effects during each rotation.

Ophiolite
11-10-05, 01:58 PM
Staying with your extraterrestrial origins, Xylene, just consider the mountains generated by impact on any of the terrestrial worlds.

Xylene
11-10-05, 07:54 PM
Staying with your extraterrestrial origins, Xylene, just consider the mountains generated by impact on any of the terrestrial worlds.

I know--I've seen Gosse's Bluff in Australia--it's rather humbling to think of the power involved, and that it happened in a fraction of a second.