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Author Topic:   Mid-ocean Ridges and Age of Formation
RAZD
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Message 1 of 45 (713889)
12-17-2013 12:30 PM


I may not be the best source to initiate this, as my knowledge of geology is weak.

That said I come to this topic as a side issue from Geology and the Great Flood, Why the Flood Never Happened, Message 290 where Faith is asking questions about Tectonics.

It occurs to me that a basic discussion of the mid-ocean ridges would help in

  1. showing the basic source of tectonic plate movement in a clear and unambiguous way, and

  2. showing how the age of the sides increase as you move away from the ridge, thus

  3. showing the basic rate of movement of the plate on each side and

  4. how constant that rate is

  5. that this process is going on today

  6. the time it takes for this to happen

It occurs to me that these ridge patterns are like tree rings and varves ...

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

http://www.ucmp.berkeley.edu/geology/tecmech.html

quote:
Plate Tectonics: The Mechanism

The main features of plate tectonics are:

  • The Earth's surface is covered by a series of crustal plates.
  • The ocean floors are continually moving, spreading from the center, sinking at the edges, and being regenerated.
  • Convection currents beneath the plates move the crustal plates in different directions.
  • The source of heat driving the convection currents is radioactivity deep in the Earths mantle.

Mid-Oceanic Ridges

The mid-oceanic ridges rise 3000 meters from the ocean floor and are more than 2000 kilometers wide surpassing the Himalayas in size. The mapping of the seafloor also revealed that these huge underwater mountain ranges have a deep trench which bisects the length of the ridges and in places is more than 2000 meters deep. Research into the heat flow from the ocean floor during the early 1960s revealed that the greatest heat flow was centered at the crests of these mid-oceanic ridges. Seismic studies show that the mid-oceanic ridges experience an elevated number of earthquakes. All these observations indicate intense geological activity at the mid-oceanic ridges.

Geomagnetic Anomalies

Occasionally, at random intervals, the Earth's magnetic field reverses. New rock formed from magma records the orientation of Earth's magnetic field at the time the magma cools. Study of the sea floor with magnometers revealed "stripes" of alternating magnetization parallel to the mid-oceanic ridges. This is evidence for continuous formation of new rock at the ridges. As more rock forms, older rock is pushed farther away from the ridge, producing symmetrical stripes to either side of the ridge. In the diagram to the right, the dark stripes represent ocean floor generated during "reversed" polar orientation and the lighter stripes represent the polar orientation we have today. Notice that the patterns on either side of the line representing the mid-oceanic ridge are mirror images of one another. The shaded stripes also represent older and older rock as they move away from the mid-oceanic ridge. Geologists have determined that rocks found in different parts of the planet with similar ages have the same magnetic characteristics.


Presumably the ridges are date-able by radiometric means, and there should be a number of different techniques to use so they can be checked for consilient dates.

Enjoy

Edited by RAZD, : image added


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AdminNosy
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(1)
Message 2 of 45 (713891)
12-17-2013 1:37 PM


Thread Copied from Proposed New Topics Forum
Thread copied here from the Mid-ocean Ridges and Age of Formation thread in the Proposed New Topics forum.
  
RAZD
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From: the other end of the sidewalk
Joined: 03-14-2004
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Message 3 of 45 (713892)
12-17-2013 2:44 PM
Reply to: Message 1 by RAZD
12-17-2013 12:30 PM


Some radiometric dates
Just a quick search gets me these two articles

(1) Steven J. Goldstein, Michael T. Murrell, Ross W. Williams, 231Pa and230Th chronology of mid-ocean ridge basalts, Earth and Planetary Science Letters, Volume 115, Issues 1–4, March 1993, Pages 151–159, http://dx.doi.org/10.1016/0012-821X(93)90219-Y

quote:
(Abstract): ... 231Pa and 230Th model ages were determined by estimating initial 231Pa/235U and 230Th/232Th ratios from axial samples and by assuming constancy of these ratios over time. All 231Pa and 230Th ages agree to +/-0-7 ka for samples with ages of 0-130 ka. These concordant ages validate the model assumptions of the two dating methods and suggest that mantle sources and melt generation processes have been uniform for these areas during the past 130 ka. Consequently, 231Pa and 230Th age-dates can be used to quantify the temporal and spatial dependence of volcanism at oceanic spreading centers during the past 375 ka

and

(2) R. A. Duncan, L. G. Hogan, Radiometric dating of young MORB using the 40Ar-39Ar incremental heating method, Geophysical Research Letters, Volume 21, Issue 18, pages 1927–1930, 1 September 1994, Article first published online: 7 DEC 2012, DOI: 10.1029/94GL01375 http://onlinelibrary.wiley.com/...4BF9EB7CAF0F071B9B4.f01t02

quote:
(abstract): Determination of reliable crystallization ages by K-Ar methods for young (<1 Ma), fresh basalts from the seafloor has been frustrated by several effects. The small amounts of radiogenic 40Ar developed over these timescales in such low-K rocks are difficult to resolve from predominantly atmospheric 40Ar. An additional concern is that mantle-derived 40Ar may not be totally outgassed when magmas quench at seafloor hydrostatic pressures. We have developed a successful strategy for partially separating atmospheric from radiogenic 40Ar in 40Ar-39Ar incremental heating experiments on mid-ocean ridge basalts, from the East Pacific Rise near the Clipperton Fracture Zone. Pre-heating samples to 400°C removes surficial atmospheric 40Ar, while subsequent heating at 600°–1000°C produces favorable proportions of radiogenic 40Ar. Experiments using “zero-age” glassy and holocrystalline samples show that mantle-derived 40Ar is retained only in the outermost few cm of rapidly cooled pillow basalts.

Seems to be more about method than results.

MORB is mid ocean ridge basalt.

Enjoy.

Edited by RAZD, : ..


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This message is a reply to:
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RAZD
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Posts: 18241
From: the other end of the sidewalk
Joined: 03-14-2004
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Message 4 of 45 (713894)
12-17-2013 3:26 PM
Reply to: Message 3 by RAZD
12-17-2013 2:44 PM


fun geology exercise
From NOAA

http://oceanexplorer.noaa.gov/...g/player/lesson02/l2la1.htm

quote:
Mid-Ocean Ridge Activity

This activity consists of naming the continents, identifying mid-ocean ridges, and determining the age of the ocean floor. Once you have labeled each map correctly, you should be able to answer the series of questions that follow the exercise.

The final map will allow you to explore all of the maps using a slide scale located above each tab. Navigating with the slide will provide different views of the maps, which will help with understanding the relationship between the continents, mid-ocean ridges and the age of the ocean floor.


Looks like the ocean floor age varies from 0 at the ridges to 180 million years at the furthest subduction zone.

This map is similar:

http://geology.about.com/...cmaps/ss/World-Seafloor-Ages.htm

quote:

... And the youngest seafloor ages very closely match the ongoing plate movements today that are measured in real time using the GPS system.


The oldest shown here is ~280 million years between Africa and Italy/Greece/Turkey.

Enjoy


we are limited in our ability to understand
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Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
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Stile
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Message 5 of 45 (713895)
12-17-2013 3:38 PM
Reply to: Message 4 by RAZD
12-17-2013 3:26 PM


Re: fun geology exercise
RAZD writes:

The oldest shown here is ~280 million years between Africa and Italy/Greece/Turkey.

Probably because the Mediterranean sea is so protected from the rest of the ocean formation?

Everywhere else has newer stuff being created and eventually flowing overtop... but here, it is sort of "locked off" and doesn't get backfilled.

Something like that?


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RAZD
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Posts: 18241
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Joined: 03-14-2004
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Message 6 of 45 (713897)
12-17-2013 5:07 PM
Reply to: Message 5 by Stile
12-17-2013 3:38 PM


Re: fun geology exercise
Probably because the Mediterranean sea is so protected from the rest of the ocean formation?

More likely that it is the last remnant of ocean floor being pushed under as the gap between narrows.

Everywhere else has newer stuff being created and eventually flowing overtop... but here, it is sort of "locked off" and doesn't get backfilled.

The floors are part of the plates moving away from the ridge, which causes the crack for new stuff to well up, solidify and start traveling with one or the other plate. The further away the older they are, having moved away from the center gap in the intervening years.

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

Something like that?

Not quite ...


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Pollux
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Message 7 of 45 (714139)
12-20-2013 5:07 AM


Sea mounts
Associated with plate tectonics are the many chains of islands and underwater mountains, formed as the plates moved over a hot spot of magma. This created volcanoes that built the mounts, and that died as the plate moved further away. The Hawaiian-Emperor chain is the best known one. Most of these show a linear increase in radiometric age as you move away from the hot spot, consistent with currently observed rates of movement of the plates, thus being a check on the accuracy of RM dating.
Fitting in all the tectonic movement during or post-Flood is a major problem for YEC. (With all the earthquakes Noah would not have been able to stand up, let alone plant a vineyard!) Adding the consistency of RM dates must be a killer!
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RAZD
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Posts: 18241
From: the other end of the sidewalk
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Message 8 of 45 (714149)
12-20-2013 9:15 AM
Reply to: Message 7 by Pollux
12-20-2013 5:07 AM


Re: Sea mounts
... This created volcanoes that built the mounts, and that died as the plate moved further away. ...

And they should have recorded the magnetic field orientation that was current at that time, so should correlate with bottom age and magnetic field.

Can you imagine all those magnetic field inversions occurring in a YEC model world?

Enjoy.


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Pollux
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(2)
Message 9 of 45 (714233)
12-20-2013 5:55 PM
Reply to: Message 8 by RAZD
12-20-2013 9:15 AM


Re: Sea mounts
Well of course all those magnetic reversals have to occur in a YEC model. Usually the tectonic movements are at the end and /or soon after the flood. So you have the plates whizzing around at miles per day, stupendous vulcanism to build the seamounts, oceanic crust, Deccan traps etc, radiogenic decay rates hyperaccelerated without heat problems, then you need an ice age afterward, to finish in time to build the pyramids. So much to do, so little time!
But wait. The evidence of the direction of the movement of ice in Southern Africa, South America, and Australia did not make sense until Weggener proposed continental drift, and it was realised the ice was there BEFORE the continents broke up.
Oh dear. As Fagin said in Oliver, I think I'd better think it out again!
It must have been easier being a Flood "geologist" before so many inconvenient facts were discovered.
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RAZD
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Posts: 18241
From: the other end of the sidewalk
Joined: 03-14-2004
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Message 10 of 45 (714238)
12-20-2013 6:21 PM
Reply to: Message 7 by Pollux
12-20-2013 5:07 AM


Re: Sea mounts
Associated with plate tectonics are the many chains of islands and underwater mountains, formed as the plates moved over a hot spot of magma. This created volcanoes that built the mounts, and that died as the plate moved further away. The Hawaiian-Emperor chain is the best known one. Most of these show a linear increase in radiometric age as you move away from the hot spot, consistent with currently observed rates of movement of the plates, thus being a check on the accuracy of RM dating.

And I was able to find this

http://www.geog.fu-berlin.de/...KIV/hawaii/introduction.html

quote:
The island chain of Hawaii - 3000 kilometers north west of the main island - is changing its direction to the north. This bend in the direction is to trace back for the fact that pacific ocean bed is changing its direction. This theory is based of magnetic minerals inside of basalt. The basalt was arised from magma, that was descended from the Hot-Spot. Inside of the liquid magma the minerals were aligned in the direction of the magnetic field of the earth. The alignment of the minerals inside the rock was changing over and over.

Doesn't appear to include a magnetic reversal.

Against that "standard" Hawaii Island theory is this:

http://www.mantleplumes.org/Hawaii.html

quote:
1. The “bend” did not result from a change in direction of Pacific plate motion: The Emperor and Hawaiian chains differ in trend by about 60°. The two trends intersect at about 30°N, near the Mendocino fracture zone (Figures 3 & 4). It is often assumed that this resulted from a change in direction of motion of the Pacific plate at ~ 50 Ma. However, such a change in plate direction did not occur, as is shown by magnetic lineations, fracture zone orientations and plate motion reconstructions [e.g., Raymond et al., 2000]. ...

2. The Emperor chain began near a ridge: 86Sr/87Sr is uniform along most of the volcanic chain, but decreases to MORB-like values on approaching the ~ 80 Ma Detroit seamount, the oldest (and largest) of the dated Emperor seamounts. ...


It seems that there is some dispute here, and that magnetic alignment with ridge spreading lines of magnetic orientations is part of the discussion.

Enjoy


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


• • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

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Pollux
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Message 11 of 45 (714246)
12-20-2013 8:19 PM
Reply to: Message 10 by RAZD
12-20-2013 6:21 PM


Re: Sea mounts
I read in recent months that the bend in the chain is due to migration south of the hot spot, while the plate was moving NW. This was indicated by magnetic evidence of the more distant mounts being formed at higher latitudes. This seems much more likely than the previous idea that the plate rotated. I guess there is still a great deal to learn about the inner Earth.
There are other sea mount chains that show the same increase in age as you go along them. Also there are old volcanoes in the Australian Great Dividing Range that also increase in age consistent with the rate of movement of the plate. The hot spot is thought to be in Bass Strait and weaker than previously.
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Faith
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Message 12 of 45 (714247)
12-20-2013 8:22 PM
Reply to: Message 9 by Pollux
12-20-2013 5:55 PM


Re: Sea mounts
Usually the tectonic movements are at the end and /or soon after the flood. So you have the plates whizzing around at miles per day,

No, not miles per day, not even miles per year. Some time ago I calculated the speed at which the tectonic plates would be separating based on their having begun to separate at the time of the Flood, and came up with 20 FEET per day as the starting speed -- or one and a half miles or 7920 feet per YEAR, or 600 feet per month or 20 feet per day. The average speed would have been 11 feet per day. All bringing us to the current two to four inches per year as estimated by evolution writer Jerry Coyne.

Is 20 feet per day such an outlandishly fast rate? That's ten feet of separation on either side of the mid-Atlantic ridge being generated daily or less than 6 inches hourly. Again, at the beginning of the movement.


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Coyote
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Message 13 of 45 (714250)
12-20-2013 8:43 PM
Reply to: Message 12 by Faith
12-20-2013 8:22 PM


Re: Sea mounts
Is 20 feet per day such an outlandishly fast rate? That's ten feet of separation on either side of the mid-Atlantic ridge being generated daily or less than 6 inches hourly.

Yes.

"Ranges of Spreading throughout the world's oceans: 1 cm/yr to 10 cm/yr."

http://www.science.smith.edu/...lab_pages/seafloorspread.htm

When the rates vary between 1 and 10 cm per year, your rate of ca. 600 cm per day is pretty silly.

And the funniest part is you don't have any evidence to support it. You're just making it all up as you go.


Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.

Belief gets in the way of learning--Robert A. Heinlein

How can I possibly put a new idea into your heads, if I do not first remove your delusions?--Robert A. Heinlein

It's not what we don't know that hurts, it's what we know that ain't so--Will Rogers

If I am entitled to something, someone else is obliged to pay--Jerry Pournelle

If a religion's teachings are true, then it should have nothing to fear from science...--dwise1


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Faith
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Message 14 of 45 (714255)
12-20-2013 9:10 PM
Reply to: Message 13 by Coyote
12-20-2013 8:43 PM


Re: Sea mounts
I figured a distance of 3000 miles (roughly that between Europe and North America) that had to be covered in 4300 years ending at a speed of two to four inches per year. That is what gave me the 20 feet per day starting speed.

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.


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Tanypteryx
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From: Oregon, USA
Joined: 08-27-2006
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Message 15 of 45 (714257)
12-20-2013 9:33 PM
Reply to: Message 14 by Faith
12-20-2013 9:10 PM


Re: Sea mounts
Faith writes:

I figured a distance of 3000 miles (roughly that between Europe and North America) that had to be covered in 4300 years ending at a speed of two to four inches per year. That is what gave me the 20 feet per day starting speed.

When did it slow down to the rate we have now? Would Ben Franklin have noticed it? Did anyone notice it and write about it?


What if Eleanor Roosevelt had wings? -- Monty Python

One important characteristic of a theory is that is has survived repeated attempts to falsify it. Contrary to your understanding, all available evidence confirms it. --Subbie

If evolution is shown to be false, it will be at the hands of things that are true, not made up. --percy


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