Subduction

[Rich_A12]

Why doesn't it take place in the middle of the oceans if there are no rules governing how plates move?

[Keenidiot]

They don't appear in the middle of the ocean, they appear on the edges of tectonic plates, when one plates is forced down by another plate. The other plate is also pushed up slightly.

[Rich_A12]

I know, my question is why doesn't subduction occur in the middle of oceans? What rules govern this?

 

Well that's not my question exactly. There are no rules governing what a plate does, each plate is apparently able to do what it wants, slip, slide under, slide over, go up, down, left, right. There are no patterns or rules. OK so that begs the question, what are the chances of subduction never taking place in the middle of oceans or even near to the middle of oceans and let's remember that the oceanic plates take up far more space than continental plates.

 

The chances are low to zero of subduction not taking place in the oceans i.e. there is a good chance, in fact it's more likely that subduction should take place in the oceans. However there are no signs of subductions taking place near or at the middle of oceans. This is a purely mathematic argument and it should puzzle anyone who cannot find an answer as to why!

[Moontanman]

I know, my question is why doesn't subduction occur in the middle of oceans? What rules govern this?

 

Well that's not my question exactly. There are no rules governing what a plate does, each plate is apparently able to do what it wants, slip, slide under, slide over, go up, down, left, right. There are no patterns or rules. OK so that begs the question, what are the chances of subduction never taking place in the middle of oceans or even near to the middle of oceans and let's remember that the oceanic plates take up far more space than continental plates.

 

The chances are low to zero of subduction not taking place in the oceans i.e. there is a good chance, in fact it's more likely that subduction should take place in the oceans. However there are no signs of subductions taking place near or at the middle of oceans. This is a purely mathematic argument and it should puzzle anyone who cannot find an answer as to why!

 

 

The "middle" of most oceans is where the crust is spreading out from magma being extruded under the ocean. The plates that collide are "floating" on the more dense basalt that underlies the oceans and the tectonic plates...

 

http://en.wikipedia.org/wiki/Mid-oceanic_ridge

 

http://en.wikipedia.org/wiki/Plate_tectonics

[Rich_A12]

Why are the continental plates so much harder, so much thicker, so much older and why are there huge vertical drops from continental plates to oceanic plates? The huge vertical drops aren't caused by errosion. Also the thickness of continental plates is fairly uniform and level, how can this uniform thickness be counted for?

[D H]

Well that's not my question exactly. There are no rules governing what a plate does, each plate is apparently able to do what it wants, slip, slide under, slide over, go up, down, left, right. There are no patterns or rules.

Of course there are.

 

Oceanic crust is considerably denser than continental crust. The continental crust float, the oceanic crust sinks. It's simple physics.

 

You appear to be on the verge of creating a fallacious argument. If that is truly your intent, please read the rules you agreed to abide by when you joined the site. If on the other hand you are just a bit confused about modern geology, ask away.

 

 

The chances are low to zero of subduction not taking place in the oceans

You are assuming here that "there are no rules", that "each plate is apparently able to do what it wants, slip, slide under, slide over, go up, down, left, right." That's just wrong. The motion is not (completely) random. There are "rules".

 

You are ignoring that oceanic crust is (a) much denser and (b) much, much younger than continental crust. The two go hand in hand. Subduction is oceanic crust sliding underneath continental crust. The opposite process, continental crust sliding beneath oceanic crust, occurs but rarely because of the huge disparity in density. This subduction pulls oceans apart but also pulls the continent across the ocean toward the subducting ocean crust.

 

However there are no signs of subductions taking place near or at the middle of oceans.

Well of course not. You are assuming there are no rules, that the process is purely random. This is falsified by your own statement. It's not random. There are "rules."

[Rich_A12]

I thought this was a forum for science, not a forum for adhering to scientific beliefs? The later is not science by the way!

[questionposter]

I thought this was a forum for science, not a forum for adhering to scientific beliefs? The later is not science by the way!

 

Subduction zones don't often occur in the middle of the ocean because subduction zones only occur at the boundaries between oceanic and continental plates simultaneously, and there are very little continental plate boundaries in the middle of the ocean.

 

http://www.learner.o...arth/plate.html

 

As you can see, there are some boundaries in the middle of the ocean, but most of those are continental-continental collisions, not continental-oceanic plate collisions.

 

S

Edited January 26, 2012 by questionposter

[Acme]

Why doesn't it take place in the middle of the oceans if there are no rules governing how plates move?

 

 

subduction does occur in the [middle of] oceans.

 

Plate Tectonics: Island Arcs

...Examples of island arcs created in this way are the Aleutians, the Kuriles, Japan, the Ryukyus, and the Philippines, found clustered around the northern and western borders of the Pacific Plate like a necklace. There are other island arcs to the south (Indonesia and the Solomon's), and although scientists are still puzzled by the exact origin of these southern island arcs, plate subduction is the suspected architect.

...

[Moontanman]

The thing to remember is that continental plates are like icebergs floating in the sea... granite bergs floating in a sea of basalt... the molten basalt wells up in the middle of oceans along the mid oceanic ridge, this basalt spreads out and then subducts under the lighter granite continents...

Edited January 26, 2012 by Moontanman

[Acme]

The thing to remember is that continental plates are like icebergs floating in the sea... granite bergs floating in a sea of basalt... the molten basalt wells up in the middle of oceans along the mid oceanic ridge, this basalt spreads out and then subducts under the lighter granite continents...

 

Again, not all subduction zones involve continental plates. For example, the Mariana islands are ocean volcanoes along a line where the Pacific Plate is subducting under the Mariana plate. Neither of these plates is continental.

 

Mariana Plate

The Mariana Plate is a small tectonic plate located west of the Mariana Trench and forms the basement of the Mariana Islands. It is separated from the Philippine Sea Plate by a long divergent boundary with numerous transform fault offsets. The boundary between the Mariana and the Pacific Plate to the east is a subduction zone with the Pacific Plate subducting beneath the Mariana....

 

 

 

 

 

[Moontanman]

I understand there are exceptions but for the most part my model is a good description of reality... Just like sea ice, a huge ice berg can ride up over sea ice and sea ice can ride up over layers of it's self... In the ocean this process is driven by under water currents on the earth it is driven by moving molten basalt deep in the earth.

Edited January 26, 2012 by Moontanman

[Acme]

I understand there are exceptions but for the most part my model is a good description of reality... Just like sea ice, a huge ice berg can ride up over sea ice and sea ice can ride up over layers of it's self... In the ocean this process is driven by under water currents on the earth it is driven by moving molten basalt deep in the earth.

 

In my opinion, the ice analogy is a poor model for plate tectonics. The OP is quite specific and i found all the replies lacking so I gave specific examples of subduction under oceans. Then too, not all spreading centers are oceanic, e.g. the East African Rift and the molten basalt is a result of the hot asthensophere rising and decompressing so the basalt is not the driver. The production of any igneous rock is more of a chemical matter than it is mechanical.

[D H]

The OP is quite specific and i found all the replies lacking so I gave specific examples of subduction under oceans.

THe OP is anything but specific. Keep in mind that this poster apparently believes in the ultra-crackpot nonsense of the expanding earth "theory": http://www.scienceforums.net/topic/63469-expanding-earth-theory-missing-mass-resolved.

[Rich_A12]

So there is virtually no subduction taking place in the oceans, more than 90% occurs between oceanic and continental plates? From a mathematical point of view what are the chances of this happening if there are no rules governing how plates moves? Someone said there are rules, please explain what rules govern how a plate moves and remember it has to be a pretty coherent pattern to produce an almost 0% chance of subduction taking place in the oceans.

 

They said the same thing to those who thought the Earth was round. Thankfully I cannot be hung, drawn and quartered for thinking things aren't as they seem.

 

http://www.thescienc...ass-energy.html

Edited January 26, 2012 by Rich_A12

[Moontanman]

So there is virtually no subduction taking place in the oceans, more than 90% occurs between oceanic and continental plates? From a mathematical point of view what are the chances of this happening if there are no rules governing how plates moves? Someone said there are rules, please explain what rules govern how a plate moves and remember it has to be a pretty coherent pattern to produce an almost 0% chance of subduction taking place in the oceans.

 

They said the same thing to those who thought the Earth was round. Thankfully I cannot be hung, drawn and quartered for thinking things aren't as they seem.

 

http://www.thescienc...ass-energy.html

 

 

Rich, did you not bother to read the posts people have spent their time posting to answer your questions? Continents are granite, it is lighter than the basalt of the ocean floors, this basalt is not only under the oceans it is under the continents as well. basalt wells up along mid ocean ridges and spread out as this basalt come to a continent is goes under the granite because it is heavier, this tends to move the continents around. What part of this specifically do you not understand? If you look at a map of the ocean floors you can see the mid oceanic rides where the ocean floor spreads out. As was indicated sometimes the ocean floors do subduct under another part of the ocean floor but most subduction occurs at continental margins mostly due to granite floating on the sea of basalt below. It is not a random process, a map of the sea floor shows this.

 

http://en.wikipedia.org/wiki/Mid-ocean_ridge

 

 

 

Formation processes

 

Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches.

There are two processes, ridge-push and slab pull, thought to be responsible for the spreading seen at mid-ocean ridges, and there is some uncertainty as to which is dominant. Ridge-push occurs when the growing bulk of the ridge pushes the rest of the tectonic plate away from the ridge, often towards a subduction zone. At the subduction zone, "slab-pull" comes into effect. This is simply the weight of the tectonic plate being subducted (pulled) below the overlying plate dragging the rest of the plate along behind it.

The other process proposed to contribute to the formation of new oceanic crust at mid-ocean ridges is the "mantle conveyor" (see image). However, there have been some studies which have shown that the upper mantle (asthenosphere) is too plastic (flexible) to generate enough friction to pull the tectonic plate along. Moreover, unlike in the image above, mantle upwelling that causes magma to form beneath the ocean ridges appears to involve only its upper 400 km (250 mi), as deduced from seismic tomography and from studies of the seismic discontinuity at about 400 km (250 mi). The relatively shallow depths from which the upwelling mantle rises below ridges are more consistent with the "slab-pull" process. On the other hand, some of the world's largest tectonic plates such as the North American Plate are in motion, yet are nowhere being subducted.

The rate at which the mid-ocean ridge creates new material is known as the spreading rate, and is generally measured in mm/yr. The common subdivisions of spreading rate are fast, medium, and slow with values generally being >100 mm/yr, 100–55 mm/yr, and 55–20 mm/yr, respectively. The spreading rate of the north Atlantic Ocean is ~ 25 mm/yr, while in the Pacific region, it is 80–120 mm/yr. Ridges that spread at rates <20 mm/yr are referred to as ultraslow spreading ridges (e.g., the Gakkel ridge in the Arctic Ocean and the Southwest Indian Ridge) and they provide a much different perspective on crustal formation than their faster spreading brethren.

The mid-ocean ridge systems form new oceanic crust. As crystallized basalt extruded at a ridge axis cools below Curie points of appropriate iron-titanium oxides, magnetic field directions parallel to the Earth's magnetic field are recorded in those oxides. The orientations of the field in the oceanic crust record preserve a record of directions of the Earth's magnetic field with time. Because the field has reversed directions at irregular intervals throughout its history, the pattern of reversals in the ocean crust can be used as an indicator of age. Likewise, the pattern of reversals together with age measurements of the crust is used to help establish the history of the Earth's magnetic field.

 

see also

 

http://en.wikipedia.org/wiki/Plate_tectonics

[Rich_A12]

“The greatest enemy of knowledge is not ignorance, but illusion of knowledge.” — Stephen Hawking

 

From your sig, subduction is an illusion - it doesn't happen. It is a solution to a problem that doesn't exist i.e. how can we make room for this mass that is appearing out of the oceans, I know let's make it disappear under the continental plates. This assumes that the Earth does not change size which is a false assumption. Subduction is nothing more than a slight bulge, it gives the impression of sinking beneath another plate but in fact it's just a bulge. Much like when a cake doesn't rise too well and bulges at the edges. There are no fault lines between oceanic and continental plates, the only fault lines lie in the middle of oceans which were created when Earth first fractured due to outward pressure caused by loss of energy through cracks and volcanoes which in turn leads to loss of gravity.

 

 

[Moontanman]

“The greatest enemy of knowledge is not ignorance, but illusion of knowledge.” — Stephen Hawking

 

From your sig, subduction is an illusion - it doesn't happen. It is a solution to a problem that doesn't exist i.e. how can we make room for this mass that is appearing out of the oceans, I know let's make it disappear under the continental plates. This assumes that the Earth does not change size which is a false assumption. Subduction is nothing more than a slight bulge, it gives the impression of sinking beneath another plate but in fact it's just a bulge. Much like when a cake doesn't rise too well and bulges at the edges. There are no fault lines between oceanic and continental plates, the only fault lines lie in the middle of oceans which were created when Earth first fractured due to outward pressure caused by loss of energy through cracks and volcanoes which in turn leads to loss of gravity.

 

 

 

Rich, you are absolutely wrong, taking energy away from anything makes it shrink not expand your analogy fails from the very start, everything that follows is false as well.

 

Watch this video for clarification or don't and remain ignorant...

 

http://www.youtube.com/user/potholer54#p/u/37/epwg6Od49e8

Edited January 26, 2012 by Moontanman

[Rich_A12]

I am not ignorant, I have a read a tonne of stuff already. This is like a hobby to me though so I'm no expert.

 

If energy affects gravity then taking away energy will reduce gravity and on a massive scale this would increase the space in which the massive body occupies. Sure decreasing the energy might make the atoms take up less space but in relation to the amount of gravity lost it's insignificant.

[D H]

From your sig, subduction is an illusion - it doesn't happen.

Baloney.

 

It is a solution to a problem that doesn't exist i.e. how can we make room for this mass that is appearing out of the oceans, I know let's make it disappear under the continental plates.

More baloney.

 

This assumes that the Earth does not change size which is a false assumption.

And even more baloney.

 

Just because you said this is the case does not mean it is true. You are making a bald assertion here; please read the rules of this forum.

 

There is absolutely no scientific evidence in favor of an expanding earth. None, zero, zip, nada.

 

There is overwhelming scientific evidence that subduction has occurred and continues to occur.

 

There is overwhelming scientific evidence that the Earth is more or less the same mass, and more or less the same size that it was shortly after its formation.

 

There is overwhelming scientific evidence that the physical constants have indeed been constant over the last 4.5 billion years (the age of the Earth).

[Rich_A12]

I think this is true but whether it actually is true is another matter - but what does it matter what I think, we're all only interested in what is true. This is merely a hypothesis, a thought, an idea - for that I need nothing more than words and a brain. Do scientists only consider proven science? Isn't hypothesis part of science?

[Klaynos]

I think this is true but whether it actually is true is another matter - but what does it matter what I think, we're all only interested in what is true. This is merely a hypothesis, a thought, an idea - for that I need nothing more than words and a brain. Do scientists only consider proven science? Isn't hypothesis part of science?

 

!

Moderator Note

Evidence wins. I strongly suggest you go read about the scientific method as applied to modern science. Then bother to learn some science before claiming it's all wrong.

 

Moving to speculations.

[Moontanman]

I think this is true but whether it actually is true is another matter - but what does it matter what I think, we're all only interested in what is true. This is merely a hypothesis, a thought, an idea - for that I need nothing more than words and a brain. Do scientists only consider proven science? Isn't hypothesis part of science?

 

 

Not if your hypothesis is shown to be false, even if you don't get that removing energy from the earth would make it shrink not expand it can be absolutely shown the earth is not expanding, we can measure the size of the earth to very small tolerances and there is no sign of expansion. other testable theories can and do explain the way the continents move and plate tectonics is real and happens, your "idea" cannot be supported by any evidence and is easily shown to be false, in fact as i have pointed out you proceed from an absolutely false notion then build up ever higher piles of false notions to support the original false notion, it's an epic fail....

[Klaynos]

!

Moderator Note

I'd also suggest actually reading peoples posts. If you don't understand something, there's no shame in that, just ask.

Also, please no one reply to my modnotes.

[Rich_A12]

Not if your hypothesis is shown to be false, even if you don't get that removing energy from the earth would make it shrink not expand it can be absolutely shown the earth is not expanding, we can measure the size of the earth to very small tolerances and there is no sign of expansion. other testable theories can and do explain the way the continents move and plate tectonics is real and happens, your "idea" cannot be supported by any evidence and is easily shown to be false, in fact as i have pointed out you proceed from an absolutely false notion then build up ever higher piles of false notions to support the original false notion, it's an epic fail....

 

Well my hypothesis suggests that equilibrium is attained eventually, perhaps Earth is already at that equilibrium therefore there would be no signs of further expansion. We do not have records of Earth's size dating back any more than a hundred years which is a totally insignificant amount of time. You would have to go back hundreds of thousands of years, even before we as a species existed to make a valid comparison. Therefore you cannot prove if this notion is true or false and there is no harm in making furhter notions or hypothesis based on the original hypothesis being true, in fact that is a form of validating or invalidating on unknown, also know as reverse engineering.