Register | Sign In


Understanding through Discussion


EvC Forum active members: 65 (9162 total)
5 online now:
Newest Member: popoi
Post Volume: Total: 915,821 Year: 3,078/9,624 Month: 923/1,588 Week: 106/223 Day: 4/13 Hour: 0/2


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Mid-ocean Ridges and Age of Formation
RAZD
Member (Idle past 1406 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


(2)
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 ...
Mid-ocean ridge - Wikipedia
The mechanism behind Plate Tectonics
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

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)

Replies to this message:
 Message 3 by RAZD, posted 12-17-2013 2:44 PM RAZD has replied

  
RAZD
Member (Idle past 1406 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


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, Error: DOI Not Found(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 Just a moment...
quote:
(abstract): Determination of reliable crystallization ages by K-Ar methods for young (<1 basalts.
Seems to be more about method than results.
MORB is mid ocean ridge basalt.
Enjoy.
Edited by RAZD, : ..

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)

This message is a reply to:
 Message 1 by RAZD, posted 12-17-2013 12:30 PM RAZD has replied

Replies to this message:
 Message 4 by RAZD, posted 12-17-2013 3:26 PM RAZD has seen this message but not replied

  
RAZD
Member (Idle past 1406 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


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
Mid-Ocean Ridge Activity
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
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)

This message is a reply to:
 Message 3 by RAZD, posted 12-17-2013 2:44 PM RAZD has seen this message but not replied

Replies to this message:
 Message 5 by Stile, posted 12-17-2013 3:38 PM RAZD has replied

  
RAZD
Member (Idle past 1406 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


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.
Mid-ocean ridge - Wikipedia
Something like that?
Not quite ...

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)

This message is a reply to:
 Message 5 by Stile, posted 12-17-2013 3:38 PM Stile has seen this message but not replied

  
RAZD
Member (Idle past 1406 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


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.

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)

This message is a reply to:
 Message 7 by Pollux, posted 12-20-2013 5:07 AM Pollux has replied

Replies to this message:
 Message 9 by Pollux, posted 12-20-2013 5:55 PM RAZD has seen this message but not replied

  
RAZD
Member (Idle past 1406 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


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:
The Emperor and Hawaiian chains
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 30N, 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)

This message is a reply to:
 Message 7 by Pollux, posted 12-20-2013 5:07 AM Pollux has replied

Replies to this message:
 Message 11 by Pollux, posted 12-20-2013 8:19 PM RAZD has seen this message but not replied

  
RAZD
Member (Idle past 1406 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


(1)
Message 27 of 45 (714311)
12-21-2013 11:18 AM
Reply to: Message 26 by Pollux
12-21-2013 5:26 AM


Getting back to the Mid-Ocean Ridges
If you mean 100 BC for 11 feet per day and it is not a misprint, this is still a 10,000 fold increase in rate of movement with its attendant quakes AND do not forget the vulcanism. Krakatoa cooled the earth for months due to its dust. You need maybe thousands of Krakatoas a year for centuries. The Romans probably would have noticed. ...
And all of this fantasy fast movement would leave the Mid-Ocean Ridge gap open more, the rock in the ridges would still be cooling and all the heat that would have been dispersed over hundreds of years would be concentrated into a few days. The water would boil over the ridges, filling the air with steam in addition to all that dust, and the sun would not be visible for many many years -- something even ol Noah would notice.
There would be many years of climate change that just is not recorded ...
To say nothing about all those magnetic reversals flipping the magnetic field all over the place and affecting it's ability to protect the earth from radiation from the sun ... also not recorded ...
Enjoy
Edited by RAZD, : ...

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)

This message is a reply to:
 Message 26 by Pollux, posted 12-21-2013 5:26 AM Pollux has replied

Replies to this message:
 Message 28 by Pollux, posted 12-21-2013 3:22 PM RAZD has seen this message but not replied

  
RAZD
Member (Idle past 1406 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


(1)
Message 43 of 45 (714833)
12-28-2013 10:32 AM
Reply to: Message 41 by Faith
12-28-2013 8:39 AM


moving plates and freezing lakes
I don't understand how anyone can get miles a day out of the simple problem of three thousand miles of distance covered in 4300 years.
Which doesn't account for all the other movements of the plates
http://pubs.usgs.gov/gip/dynamic/understanding.html
quote:
Scientists now have a fairly good understanding of how the plates move and how such movements relate to earthquake activity. Most movement occurs along narrow zones between plates where the results of plate-tectonic forces are most evident.
There are four types of plate boundaries:
  • Divergent boundaries -- where new crust is generated as the plates pull away from each other.
  • Convergent boundaries -- where crust is destroyed as one plate dives under another.
  • Transform boundaries -- where crust is neither produced nor destroyed as the plates slide horizontally past each other.
  • Plate boundary zones -- broad belts in which boundaries are not well defined and the effects of plate interaction are unclear.

The divergent boundaries are the mid-ocean ridges and the rift valley in Africa.
quote:
Divergent boundaries
Divergent boundaries occur along spreading centers where plates are moving apart and new crust is created by magma pushing up from the mantle. Picture two giant conveyor belts, facing each other but slowly moving in opposite directions as they transport newly formed oceanic crust away from the ridge crest.
Perhaps the best known of the divergent boundaries is the Mid-Atlantic Ridge. This submerged mountain range, which extends from the Arctic Ocean to beyond the southern tip of Africa, is but one segment of the global mid-ocean ridge system that encircles the Earth. The rate of spreading along the Mid-Atlantic Ridge averages about 2.5 centimeters per year (cm/yr), or 25 km in a million years. This rate may seem slow by human standards, but because this process has been going on for millions of years, it has resulted in plate movement of thousands of kilometers. Seafloor spreading over the past 100 to 200 million years has caused the Atlantic Ocean to grow from a tiny inlet of water between the continents of Europe, Africa, and the Americas into the vast ocean that exists today.
2.5 cm is 1 inch. per year.
quote:
Rates of motion
We can measure how fast tectonic plates are moving today, but how do scientists know what the rates of plate movement have been over geologic time? The oceans hold one of the key pieces to the puzzle. Because the ocean-floor magnetic striping records the flip-flops in the Earth's magnetic field, scientists, knowing the approximate duration of the reversal, can calculate the average rate of plate movement during a given time span. These average rates of plate separations can range widely. The Arctic Ridge has the slowest rate (less than 2.5 cm/yr), and the East Pacific Rise near Easter Island, in the South Pacific about 3,400 km west of Chile, has the fastest rate (more than 15 cm/yr).
So the movement you calculated relates to the slow end of the rates of motion, and the fastest is 6 times faster (6 inches per year).
quote:
Evidence of past rates of plate movement also can be obtained from geologic mapping studies. If a rock formation of known age -- with distinctive composition, structure, or fossils -- mapped on one side of a plate boundary can be matched with the same formation on the other side of the boundary, then measuring the distance that the formation has been offset can give an estimate of the average rate of plate motion. This simple but effective technique has been used to determine the rates of plate motion at divergent boundaries, for example the Mid-Atlantic Ridge, and transform boundaries, such as the San Andreas Fault.
Thus there is a wide range of information about time and rates of movement that are consistent around the world. This includes age of formation of the rock and ages of magnetic reversals.
Etewitness acciounts are certainly a lot more reliable than conjurings about the past from the present could possibly be. If he was there and died of the heat then we'd know he was right about the heaty.
And that is probably a good reason why trained observers who are knowledgeable about geology and physics end up with results that are certainly a lot more reliable than your conjurings about the past based on fantasy.
Message 37: ... No, there has to have been a cooling factor you aren't taking into account. ...
That is you hoping for a miracle again ... as you do for every piece of contrary evidence that is so inconvenient for your fantasy.
Now you want thermodynamics to change on your whim. If you change the thermodynamics so that water doesn't boil then you change the thermodynamics of everything else ... fresh water lakes and rivers would freeze solid by the same process of miraculous heat removal. Hilarious.
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)

This message is a reply to:
 Message 41 by Faith, posted 12-28-2013 8:39 AM Faith has not replied

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2023 by EvC Forum, All Rights Reserved

™ Version 4.2
Innovative software from Qwixotic © 2024