#Subduction & Ocean Basin
19 messages in this thread
Hi, Kamron–
>> Same thing isn't it? If the material is malleable it has exceeded the
threshold and is not a solid anymore. >> I don't believe soothing that can
change its shape is a true solid.
So a paper clip is "liquefying" every time you bend it? Bending warms it, but
not _that_ hot! Why does it not fall apart as soon as it starts bending if it
liquefies? Your notion of "solid" fits neither the dictionary nor the
scientific definition. The crystal structure does not disappear during these
solid-state deformations, only a few bonds break and reform, not all of them at
once.
>> Keep looking at the Mid Ocean Ridge it is the single most compelling
evidence of the One Event Plate Motion Theory.
The mid-oceanic ridge strikes me as a problem for your theory – it is missing
in too many places where it should be. Besides the previously mentioned
surprises, the shape of the eastern U.S. coast should send a wave that would
meet one from N. Brazil to form an E-W extension of the ridge toward the
Caribbean. Beating the continents back and forth does not help that I can see;
either the previous motion was too early to make a difference in the final
result, or the extra waves would create interference patterns that would bust
up even your meet-in-the-middle scenario.
Put model continent shapes into a thick liquid and try to generate anything
wave patterns remotely resembling the existing ridge, taking pictures at any
point in time you like; I am confident you will not be able to.
In plate tectonics the shape of the ridge in the internal (new) oceans (the
Atlantic and Indian) is easily derived from the simple first principles of the
theory. Find the pairs of points at the continental shelf edges that were
together in the supercontinent of Pangaea, connect each pair and find the
midpoint; the collection of midpoints is a rather good approximation of the
ridge (I assume it will look better on a globe than on flat maps). That this
works as well as it does is a preposterous coincidence from the viewpoint of
your theory; that your theory needs lots of surprising crosscurrents and extra
assumptions to come close to explaining the precise shape of the ridge makes it
a weakness for your theory relative to plate tectonics.
–Doug
Hey Doug
>> The crystal structure does not disappear during these solid-state
deformations, only a few bonds break and reform, not all of them at once. <<
This is tough, the structure is so interlocking. The crystals have faces and
these are all packed together like a 3 d puzzle. How can they rearrange without
some melting going on. On a large area it is easier to allow this happening but
looking close at the structure there isn't alot of space for these toothy
crystals to rearrange themselves in a slow process without melting going on.
And melting would not occur at the temperatures at the water crust interface.
>>The mid-oceanic ridge strikes me as a problem for your theory – it is
missing in too many places where it should be.<<
The only place there is no ridge is in the area between S. America and the
Antarctica and here we have a very unique formation unlike any other in the
basins because of the motions that occurred there.
The ridge formed perpendicular to the sum of the force/direction of the flows.
The central part of the ridge formed while the continents were still in close
proximity. Also there is the wider faster motion at the bottom of the atlantic
split and the southward motion of S. America.
>>Put model continent shapes into a thick liquid and try to generate anything
wave patterns remotely resembling the existing ridge, taking pictures at any
point in time you like; I am confident you will not be able to.<< I have been
planning it….the material needs to be magma like…like cooling fudge but
needs to be more brittle as it skins over like wax. I think it will create the
same features if the materials used have the right properties.
>>In plate tectonics the shape of the ridge in the internal (new) oceans (the
Atlantic and Indian) is easily derived from the simple first principles of the
theory. Find the pairs of points at the continental shelf edges that were
together in the supercontinent of Pangaea, connect each pair and find the
midpoint; the collection of midpoints is a rather good approximation of the
ridge (I assume it will look better on a globe than on flat maps).<< true for
both theories
>> That this works as well as it does is a preposterous coincidence from the
viewpoint of your theory; that your theory needs lots of surprising
crosscurrents and extra assumptions to come close to explaining the precise
shape of the ridge makes it a weakness for your theory relative to plate
tectonics.<<
There is not a lot of difference in the connection points between the two
theories. They both have to deal with what is and work backwards.
The unbroken continuity of the ridge and the similarity of its components
makes it's creation in a single event almost obvious.
You mentioned waves again. If I started the wave idea it wasn't quite how I
see it. Its more like a tide motion. I see the central ridges forming in
succession as the continents moved in a slow back and forth motion as they
moved apart. After a while the back and forth motion subsided causing the
ridges to become smaller and smaller and then finally there was just smooth
motion in the final stages.
It is puzzling how the ridge runs into North America almost as if the
continent over ran the ridge after it formed.
Kamron
Hi, Kamron–
When a solid flows without liquefying, the crystal grains themselves can
distort; this is how you get the layered look of a gneiss or schist which
started as a granite or something similar. At least that is one way a grainy
solid can flow; there may be other mechanisms I am not aware of (perhaps in
some cases grains split and separate, perhaps material from one grain joins
another, perhaps they slide past along grain boundaries, and mixing of these
modes would not be a surprise, etc.).
I would not expect to see any such detectable trace of flows in the ocean-floor
basalts unless one is prepared to examine every microscopic grain for many
square meters with some method of distinguishing original features from later
flow features; as I noted, any shifts in direction of plate flow must be _very_
gradual compared to what happened to gneisses or glaciers.
>> The ridge formed perpendicular to the sum of the force/direction of the
flows.
I cannot see how this could be derived from your waves of lava. Every ripple
tank experiment I am aware of shows waves moving away perpendicularly from any
straight-line or similar generator. Such waves would meet in different places
than the observed ridges in many cases; the line along which wavefronts meet
would only be occasionally perpendicular to their travel. When they met in
non-parallel directions, your principle _as stated_ would require a ridge
perpendicular to the line of meeting, which is both unexpected and
contradictory to the ridge shape.
>> true for both theories
How can your theory expect the ridge position to be connected to past
juxtapositions of coastlines as plate tectonics does? This is a nastier
question if you have continents sloshing back and forth repeatedly, which helps
destroy any last traces remaining in the seafloors of the original positions of
the continents. The points where coasts once met are the same in both
theories, but I see no way this would be relevant to ridge positions in your
theory. Only the shapes of continents and their positions when your lava waves
were generated should have any bearing on ridge positions. This is the same
whether they are sharp waves or gentle swells (a better term than "tides"
unless you mean to imply gravitational cause).
>> It is puzzling how the ridge runs into North America almost as if the
continent over ran the ridge after it formed.
That is precisely what happened as I understand it. The Gorda/Juan de Fuca
plate off the Pacific Northwest coast is the tag end of the plate that North
America drove under, and it will soon be gone. I suppose it and the Cocos
plate off the Pacific coast of Mexico may have once been part of the same plate
until N. America overrode the connecting portion.
–Doug
>> How can your theory expect the ridge position to be connected to past
juxtapositions of coastlines as plate tectonics does?<<
I see the Americas both separating at the same time and moving away form
europe and Africa. The central part of the ridge is first exposed and begins
solidification as the waters pour into the huge split. The gap is only hundreds
of miles wide say when there is a slow slosh back forcing the center section to
break and crack in two directions. The drift resumes and gets say 600 miles
apart then a slosh back forcing the second ridge to ride up on the first. This
happens many time more each time a the cycle is less forceful as the earth
becomes more stable.
The latter ridges would be smaller than the first and the last part of the
drift went smoothly producing relatively smoother ocean basin.
The smooth continuous Atlantic ocean basin ridge shows no signs that N.
America split apart 35 million years before S. America.
It also doesn't have any markings to show the northward drift of S. America to
meet the N. Why would there be the deep trenches in the carribean if their was
a recent compression in the area?
And where did the ocean basin between N&S americas go?
I have modeled the current continents and they fit together very well right
now in the shape and condition they are in. The current theory has them
deforming and becoming other shapes completley before arriving in the positions
they are in now.
Why would they fit together so well if they have been deformed over and over?
Kamron
I think one problem you have is with scaling laws . For objects the size we
are talking about, the shear forces of the solid exist but are small compared
to the gravitational forces and convective forces (proportional to the small
temperature gradient) in these objects. That is why you can't build somet a
house the size of the empire state building out of stone. It would break
apart, crack, etc., but it's fall would probably be vaguely liquid like.
For a approximate mathematical model of the process, plus direct GPS evidence
of tectonic movement in Iceland, get a copy of the thesis: A Study of Crustal
Deformation in Iceland Using Boundry Element Modeling and the Global
Positioning System by Mary Christine Hackman, University of Colorado (1991)
(PhD thesis). I don't know where to get more convincing evidence of oceanic
subduction.
By the way, is the point you are making that one can NEVER trust indirect
measurements because interpretation requires assumptions? Son of Sam hears
voices in his head telling him to kill people. I don't think he lied. Voices
in head are a direct measurement. The police use indirect, forensic science.
Do I have to believe Son of Sam? Please state the type of evidence that YOU
would find compelling. Maybe it's out there, maybe it's not, but then we could
develope a real argument.
>> By the way, is the point you are making that one can NEVER trust indirect
measurements because interpretation requires assumptions? <<
My point on GPS was that it was not accurate enough to measure a few inches
over many thousands of miles at least initially.
There are too many variables that can distort the crust and the orbits to
resolve to the inch. LIke blowing up a digital picture. You are eventually
looking a squares of solid color that approximate the boundaries of the image.
As to the behavior of the ocean basin and if it is malleable under pressure I
have been expressing observations like how brittle the crust appears at the Mid
Ocean Ridge where it is supposed to be fresher and softer than the older harder
denser basin away from the ridge that seam to conflict with the theory.
The Ocean basin crust, if you plot all the motions that the current plate
tectonic theory proposes, is moving in many directions at once.
Plates in places are converging or moving all in toward the same area reducing
a frontal area by 1/3 without distortions. Plates are diverging and becoming
twice as wide without significant slumping sinking or splitting? That is what
the theory appears to be saying.
This is happening in areas where the basalt is cold and therefore brittle.
We have bold evidence of cracking all over the basins so the crust is brittle
enough to produce these thousands of mile long faults.
But I don't see the cracks and bunching or folding where the converging and
diverging is supposed to be occuring.
Kamron
I am no geophysicist. However, I know solid state physics fairly well. }iSome
of your reasoning is based, it appears, on the presumption that straight line
cracks and defaults only occur it rapid, catastrophic events. Not true. The
reason straight line defects occur is because they relieve stress most
efficiently, whether or not the motion is fast or slow. When mud dries, the
cracks are straight even though that is a slow process. Experiment, try to
attach an adhesive label to a small ball whose diameter is about the size of
the adhesive label. Try to attach it so that every little bit of area on the
label is in contact with the ball. You will see wrinkles, straight line folds,
and other shapes you say are impossible for a solid. Try to flatten these
folds with a hammer. That is analogous to the catastrophic event you feel took
place. Doesn't solve the problem, does it? In the region of the subduction
zone, the stress is relieved. Cracks, straight line cracks, do that. Of course
that region is almost crack free other than the big one. The two models you
claim contradict don't. One is an approximation of the other. If you have a
region with many pieces moving around, the average motion can be simple. Just
a scaling proble,m. The region areas move without cracking is because material
is sinking, and the big crack (the subduction zone) relieves the stress. What
do you mean britle? Do you mean the shear strength of the material is greater
than all the other forces? Not on this distance scale. Even the empire state
building needed steel girders because stone wasn't "brittle" or strong enough
to support it. These plates are much larger. I don't know GPS itself, but
workers claim it can have a resolution in centimeters under the right
conditions. My knowledge of optical interferometry, a small scale version of
the same thing, suggests that is plausible. Optical interferometry can measure
a 1 micron displacement between two object 1 meter away. Or more. On what do
you base the "fact" that GPS "can't." The GPS method is improving, so you may
not be able to make that claim forever, it is questionable now. Furthermore,
the forces for subduction are qualitatively known. What is the energy source
for your great catastrophe? From previous discussions, I think your answer
could be very interesting but not what I would call science. Anyway, thank
y~rou for making me }iresearch these things. I find tha{_t thesis particularly
good reading.
David
Good to hear from you.
>>The reason straight line defects occur is because they relieve stress most
efficiently, whether or not the motion is fast or slow.<<
I agree ….. the shift faults are very straight some for thousands of miles.
Some are slightly curved and usually in a consistent arc some for thousands of
miles usually centered across the Mid ocean rise. (There are the exceptions in
the north east pacific and a few other minor areas.)
This is unique to the earth and only in the ocean basins as far as we can see.
This brings up these questions.
Why is the stress releaved along such a long line or arc.
Why is the stress relieved in a balanced fashion on two separate plates having
only the most feeble of connections across the Mid Ocean Rise?( this is the
tough one)
Why is the stress that causes the stress relief only along the softer weaker
areas of the basin where there is a minimum of stress now compared ….and not
in the areas of greater stress where the plate is diverging or converging(do
you know what I mean here?) or subducting?
>>Experiment, try to attach an adhesive label to a small ball whose diameter
is about the size of the adhesive label. Try to attach it so that every little
bit of area on the label is in contact with the ball. You will see wrinkles,
straight line folds, and other shapes you say are impossible for a solid. Try
to flatten these folds with a hammer.<<
Yes paper can fold but try to bend a silicon chip around a ball.
>>In the region of the subduction zone, the stress is relieved. Cracks,
straight line cracks, do that. Of course that region is almost crack free other
than the big one.<<
Exactly ..the only crack is the one between the continent and the basin. How
can a 5 or 10 mile thick babasaltlate bend downward without cracking….
before it heats up. Bending would heat it but we need the bending force first
and there is no mechanism to do this. The thin ocean crust would also ride up
onto the continental plate in places much easier than diving downward, this
would happen at least sometimes.
>> The two models you claim contradict don't. One is an approximation of the
other. If you have a region with many pieces moving around, the average motion
can be simple. Just a scaling problem,m.<< I don't understand exactly what you
are referring to here.
>> The region areas move without cracking is because material is sinking,<<
sinking? I don't understand what you mean here either. It is said to be bending
at the zone. You know materials…. how can it bend?
>> and the big crack (the subduction zone) relieves the stress.<< This is a
crack between the continent and the basin plate isn't it?
But there is a lot of stress between the mid ocean ridge and the diverging and
converging that different plates have to go through on their way to the
subduction zones where are the cracks?
>>I don't understand What do you mean brittle?<<
Basalt is the one of the most brittle materials we have isn't it. By brittle I
mean it cracks before bending. It will easily crack and can't be bent. Like a
ceramic plate. Try and bend it & it will crack.
>>These plates are much larger.<< Even more brittle and crackable isn't it?
>>The GPS method is improving, so you may not be able to make that claim
forever, it is questionable now.<< I agree that GPS will be able to prove if
the motions are there and maybe already have seen some motion. I also agree
that GPS will eventually be able to resolve a cm between any two points.
>>What is the energy source for your great catastrophe e?<<
I prefer at this point to postulate a stellar interloper say 10 times larger
than the sun passing by the sun at 100 to 200 million miles away. It approached
the earth close enough to tear off more than half the earths crust. The balance
of the crust broke into the existing continents that still fit together
remarkably well.
>>I find tha{_t thesis particularly good reading. <<
I also find it all very fascinating. The record of the events are recorded in
the hardened basin of the oceans. As I look it all over and learn more it seams
to prove out better and better. I have seen so little of the earth but what I
have seen all fits. I welcome any observations or opinions or rebuttles.
Kamron
Hi, Kamron–
>> Still the planes run in all directions so it still is tough to see it
sliding smoothly in any direction.
Planes in many directions just mean there are more options for sliding in more
directions.
Actually, I have been talking "bonds" when we are mainly dealing with ionic
substances. Imagine two boards, studded with magnets at constant intervals
(all the magnets in one board are pointed the same way). Put the boards
parallel together turned so the magnets on one board attract those in the other
board, and bring the boards close. They will snap together, with each magnet
touching its counterpart in the other board. Now push along the length of one
board. It resists. Push harder – the boards may slip one
magnet-separation-distance so the magnets are paired again, but each with a new
"partner" on the other board. Make them into planar boards with magnets in a
regular two dimensional array, and you see what happens at a cleavage plane in
a solid – notice there are now two directions where you can push the boards so
the magnets all switch partners at once. Array this in three dimensions (now
you need "boards" that can pass through each other), and you have solid flow.
Pushing the boards really hard so the attraction is totally overcome and they
fly apart would be like breaking the solid. Pulling the magnets out of the
boards and jumbling them together in a pliable mass would be the equivalent of
liquefying the solid.
>> It is obvious that the ocean basin faults in true lines straight and slight
to moderate large curves. Some of the faults are thousands of miles long. So we
know that it breaks like a brittle solid.
All this proves is that it breaks like a brittle solid under _some_ conditions
– sharper stress in shorter time, and there is no time for bonds to be
rearranged. Hit old silly putty sharply with a hammer and it breaks –
does that mean it cannot be shaped without cracking?
>> The smooth continuous Atlantic ocean basin ridge shows no signs that N.
America split apart 35 million years before S. America.
Why the ^#$$%! should the _ridge_ show any such signs? It is brand new at
every point, exactly as plate tectonics says it must be. If you meant
seafloor, well aside from paleomagnetic, radioisotope, and fossil dating, I
cannot think of much evidence of the earlier separation of N.America from
Pangaea. I suspect there are ocean fossils from the N. American eastern
seaboard and/or the W. African facing coast that pre-date the
Cretaceous/Tertiary boundary, which would be a toughie for your theory but
predictable from plate tectonics.
>> And where did the ocean basin between N&S americas go?
If they did move together, it went into the mantle, of course. I think they
moved more apart than together – in Pangaea, S. America (Colombia) was up
against what is now the _west_ coast of Mexico and C. America, which were
folded up so there was no Caribbean separating them from N.America. Room had
to open up between them for C. America to straighten up in; I believe it arose
because N. America headed somewhat northwest while S. America went a little
more west or southwest.
I cannot imagine fitting the continents together without that folding of C.
America; at the very least you would have to disregard the common formations
connecting the continents where standard theory puts them, which is the chief
evidence they ever were connected.
>> Why would they fit together so well if they have been deformed over and
over?
They have not been deformed much since the breakup of Pangaea (when the
spreading zones sliced them apart into brand new shapes with little regard for
any _past_ deformations).
–Doug
Doug
Good visual on the magnets. Still tough to image one of the planets densest
most brittle materials deforming without the temperature threshold being
crossed. The shearing and rehealing process occuring on the microscopic level
would be hard pressed to redistribute materials over hundreds of miles.
The diverging and converging directions in the current theory require massive
redistributions of materials. This would require accelerations of materials to
accomplish the redistribution. It would surely result in visible cracks as the
plates went through these material redistributions.
We discussed how the ridge continues to telescope previous conditions into
existing like the shift faults being maintained well after the shifting
occurred. I expect to see this stitched into the area where the ridge sections
stitched together. You could call into play the highly shifted section
between Brazil and Africa, IT may have the history recorded there.
>> I think they moved more apart than together – in Pangaea, S. America
(Colombia) was up against what is now the _west_ coast of Mexico and C.
America, which were folded up so there was no Caribbean separating them from
N.America. Room had to open up between them for C. America to straighten up
in; I believe it arose because N. America headed somewhat northwest while S.
America went a little more west or southwest. <<
They were together in Pangaea. In the models I am looking at N. America &
eurasia separated quite a bit from Gondwana(S. America & Africa) looks like
more than a few thousands of miles 135 meg ago. This continued to separate to 5
or 6 thousand miles apart as late as 45 meg ago and only recently they are
moving back together.
I agree they were moved more together on the west side but the slight rotation
(clockwise) that S. America pulled the carribean apart while compressing the
pacific rim.
If N. America got a 100 million year head start on moving away from europe
then how did S. America not only catch up but pass N. America in the distance
of spreading race in the Atlantic spreading?
Kamron
Hi, Kamron–
>> We discussed how the ridge continues to telescope previous conditions into
existing like the shift faults being maintained well after the shifting
occurred. I expect to see this stitched into the area where the ridge sections
stitched together. You could call into play the highly shifted section
between Brazil and Africa, IT may have the history recorded there.
I am lost as to what you are talking about here.
>> They were together in Pangaea. In the models I am looking at N. America &
eurasia separated quite a bit from Gondwana(S. America & Africa) looks like
more than a few thousands of miles 135 meg ago. This continued to separate to 5
or 6 thousand miles apart as late as 45 meg ago and only recently they are
moving back together.
N. America is moving back toward Africa?!? That is not plate tectonics as I
know it. If you are talking about Africa and India striking Eurasia, that is
not moving "back together", since they were never so close going back to
Pangaea.
>> If N. America got a 100 million year head start on moving away from europe
then how did S. America not only catch up but pass N. America in the distance
of spreading race in the Atlantic spreading?
Why not? There is no reason to expect all spreading ridges to build seafloor
at the same rate; indeed every reference that I have which mentions the matter
has them varying all the way from 0 to 16 cm/year in spreading rate. The head
start was more like 50-60 million years; the N. Atlantic opened between
N.America (still part of Laurasia then) and W. Africa in the mid-Triassic and
the S. Atlantic opened between S. America and Africa at the end of the
Jurassic.
–Doug
>> I am lost as to what you are talking about here.
The area between the most eastern part of Brazil & Africa does have crimping
that could also be a crunching of S. America moving upward.
The Central American area looks like it is the product of a back forth action,
the curved fold of Panama with the matching curve of the lower antilles. These
are compression folds or arcs from pivoting.
>>N. America is moving back toward Africa?!?<< No I talking about N & S
America. In the current theory they are just recently moved back together.
>>There is no reason to expect all spreading ridges to build seafloor at the
same rate; indeed every reference that I have which mentions the matter has
them varying all the way from 0 to 16 cm/year in spread rate.<<
This would be quite a bit of a different rate all along what appears to be a
single mid ocean rise. How could the plate have a variable rate of expansion
along the Mid Section and not display this in its basins.
Are you saying the individual shift faults are where the stress of this
variable rate is being released?
>> The head start was more like 50-60 million years; the N. Atlantic opened
between N.America (still part of Laurasia then) and W. Africa in the
mid-Triassic and the S. Atlantic opened between S. America and Africa at the
end of the Jurassic.<<
It seams if this were the case the Mid Ocean ridge and associated shift faults
would display these motions by the angles of the shift faults.
The shift faults are not showing shifting in those directions. Where is the
plate being subducted to allow this motion?
Kamron
It, the subducted material, melts or breaks up (yes, as a "britttle" solid)
deep underground. Also, if the rate of expansion in one area changes, the rate
of subduction can change or stay the same in another. How stay the same? New
subduction zones open up somewhere else.
David
The plate bending along a straight front is very difficult. There being no
cracks at all in the plate no folds to take up the stress.
When you look at curved fronts both concave and convex the bending of the
plate takes on an even more unbelievable characteristics.
If the plate is moving towards an area where there is a curve ..say an arc
with the center closer to the middle of the area… then the plate is bending
downward here in the middle but it needs to stay flat and move hundreds of
miles further at each side . This would produce warping even in malleable
materials.
Get a regular 8.5 x 11 paper and trace an arc on it from two corners to a
place a two or more inches in from the long side. Now try and bend it all at
a 45 degree angle. The bending part must split regularly to accomplish the
bending and the paper wants to warp and deform if it doesn't split. Try an
outside curve same problems. Think what would happen to a very brittle thick
substance. It would warp and buckle and split.
This is very dense very brittle basalt, even millions of years would not hide
the warping and splitting.
Kamron
Hi, Kamron–
>> …N & S America. In the current theory they are just recently moved back
together
Maybe a little, but not much (I saw a subduction zone on the N. coast of S.
America in one map, but most maps deem this not worth showing, or maybe it is a
dead idea). It seems clear the bulk of the motions came from the spreading of
the Atlantic.
>> This would be quite a bit of a different rate all along what appears to be
a single mid ocean rise.
Just because a ridge appears as a single entity today does not mean it always
was, and there is no reason to expect the same spreading rate even at different
parts of the "same" ridge – that is what transform faults are for.
The southern part of the North Atlantic was created by a spreading zone that
drove into Pangaea first between the Americas, then between N. America and
Africa, then between N. America and Europe (it separated Greenland from N.
America, but stopped that and sent a new branch between Greenland and Norway,
which remained active much longer as the familiar Mid-Atlantic Ridge.
A different spreading zone drove from the south between S. America and Africa
before the northernmost Atlantic was created, apparently an offshoot or
redirection of the one separating Antarctica from Africa.
The ridges were not so much like a single entity until the transform fault
betwen N.Brazil and W.Africa mostly closed up, apparently due to the faster
spreading of the S. Atlantic ridge. There is still that jog in the fault we
have discussed as a relic of the non-identity of the ridges.
It looks like a single ridge because all this branching and redirecting
activity gets obscured as time passes – only the most recent and most active
spreading is as obvious as the Mid-Atlantic Ridge.
>> How could the plate have a variable rate of expansion along the Mid Section
and not display this in its basins. >> Are you saying the individual shift
faults are where the stress of this variable rate is being released?
The transform faults are the primary (I do not know about only) mechanism for
handling differential spreading rates. I take each transform fault to indicate
there was or is a difference in spreading rate at the ridge on either side of
the fault, though I may be assuming too much.
>> It seams if this were the case the Mid Ocean ridge and associated shift
faults would display these motions by the angles of the shift faults. The shift
faults are not showing shifting in those directions.
The ridge transform faults between the bulge of W. Africa and N. America (U.S.
eastern seaboard) seem to point from one to the other in a NW-SE direction.
The faults between Africa and S. America again appear to connect the two, as
far as I can see, in a more E-W direction. When I connect two continental
shelf edge points that are across an internal ocean, but that were adjacent in
Pangaea, I not only expect the ridge to be at the midpoint, I expect to see the
nearest transform faults lining up parallel to that line, and that is about
what I see. The connection should be a shortest-distance great circle arc,
which will seem to be an arc on an ordinary flat map – if anything, the
connections seem _too_ good on my flat map.
>>Where is the plate being subducted to allow this motion?
Somewhere out in the Pacific for most of these motions, much of it likely near
the west coasts of the Americas (thus the Cascade Mts.). Some subduction in
the Caribbean (creating a lot of the islands bounding it) appears to have
helped let the Americas connect up; I am a little fuzzy on what goes on in that
area.
–Doug
>> The ridges were not so much like a single entity until the transform fault
between N.Brazil and W.Africa mostly closed up,<<
What do you mean on closed up?
>> apparently due to the faster spreading of the S. Atlantic ridge. There is
still that jog in the fault we have discussed as a relic of the non-identity of
the ridges.<< Yea there is something in the ridge at that area but to me I can
see the long and short versions similarly.
>>It looks like a single ridge because all this branching and redirecting
activity gets obscured as time passes – only the most recent and most active
spreading is as obvious as the Mid-Atlantic Ridge.<<
I see where you are coming from here but there is big difference on what will
happen to the ridge depending on what the actual formation process is.
>>The transform faults are the primary (I do not know about only) mechanism
for handling differential spreading rates. I take each transform fault to
indicate there was or is a difference in spreading rate at the ridge on either
side of the fault, though I may be assuming too much.<< They definitely
adjusted stress.
This is the crux of the whole discussion. The plate motions.
However they are propelled are as you have discussed they could be dragged by
flows under the surface. They could be pushed by moving continents. They could
be pushed by each other. They are somewhat solid except for the mid ocean ridge
where one plate interfaces another.
Why would the transform faults still all line up across the Mid OCean Ridge
after millions of years of moving in all directions why are they mostly lined
up still?
>>The ridge transform faults between the bulge of W. Africa and N. America
(U.S. eastern seaboard) seem to point from one to the other in a NW-SE
direction. The faults between Africa and S. America again appear to connect the
two, as far as I can see, in a more E-W direction. When I connect two
continental shelf edge points that are across an internal ocean, but that were
adjacent in Pangaea, I not only expect the ridge to be at the midpoint, I
expect to see the nearest transform faults lining up parallel to that line, and
that is about what I see. The connection should be a shortest-distance great
circle arc, which will seem to be an arc on an ordinary flat map – if anything,
the connections seem _too_ good on my flat map.<<
I agree totally.
The shift faults by connecting up opposite points that connect show the motion
of the continents, still to this day.
… even though supposedly they have moved in complicated reforming methods
over time the shift faults still line up the exact motion in many areas. See
what i mean?
Why are the faults cutting across both plates when the motions of each are
separate. .. relatively unconnected?
Why are the shift faults still lined up across the mid rise if the plate
motions are in different directions and tangents?
Kamron
PS I owe working this out to you Thanks for the rich and rewarding
conversation.
Kamron,
>> Why would the transform faults still all line up across the Mid OCean Ridge
after millions of years of moving in all directions why are they mostly lined
up still? <<
There's no "why," because if I understand you right, this isn't what's
happening. The plates and the faults don't move "in all directions". The
faults move in directions dictated by plate motion. The plates move in
directions dictated by seafloor spreading.
Jon W.
Hi, Kamron–
>> >> The ridges were not so much like a single entity until the transform
fault between N.Brazil and W.Africa mostly closed up,<<
>> What do you mean on closed up?
Remember that jog in the Mid-Atlantic Ridge near the coast of N. Brazil? It
was once a far longer jog – after the N. Atlantic opened, S. America started
away from Africa, with a _long_ transform fault making the then-long connection
between the S. Atlantic ridge and the N.Atlantic ridge. As S. America caught
up with N. America, the ridges slid together along the transform fault, so the
connection shrank down to the jog we see today, making the two ridges seem near
continuous.
>> Why would the transform faults still all line up across the Mid OCean Ridge
after millions of years of moving in all directions why are they mostly lined
up still?
The motion has not been "in all directions"; the simple motion away from the
ridge at right angles to it has been by far the bulk of all motions. Having
seen a mention just today (new Earth mag) that N. America is now moving a bit
south of west (instead of its north of west motions during most of the
Atlantic's spreading), I am a little readier to accept that some convergence of
N. and S. America is part of orthodox theory – but notice it is not like they
have stopped all west motion while closing on each other, it is more like two
cars running almost parallel while slowly drifting into each other's lanes
(bang, ouch!). The major motion is all I am going to see within the flat-map
error.
My rules of thumb about connecting the originally-juxtaposed continental
margins and finding the ridge at the midpoint, with transform faults
paralleling the connection, were a gross overall picture, and assumed no
spreading or subduction that moved one continent without also moving the ridge
and the other continent. Any subduction between the Americas is a very modest
violation of that assumption, and the main internal oceans would not be so wide
without following the assumption much more than not.
This conversation has indeed been interesting; it has forced me to notice
weaknesses in my understanding of plate tectonics and fill them.
–Doug
Doug,
>>Some subduction in the Caribbean (creating a lot of the islands bounding it)
appears to have helped let the Americas connect up; I am a little fuzzy on what
goes on in that area.
Everyone is fuzzy about the Carib. There are at least 5 "microplates" in the
area, mostly being moved around with slight subduction on most of them. This
is why Mexico and Central America are so seismicly active. As for figuring out
the movement, there are lots of theories, and no sure answers.
There is a major subduction zone on the west coast off of Oregon and
Washington. It's called the Jaun deFucha plate. I saw a recent article that
suggests that the area is prime for a mag 9+ earthquake due to unrelieved
VERTICAL stress. (Unlike the horizontal movewment on the San Andreas to the
south)
Jim