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Author Topic: Why don't the mountains of the mid-atlantic ridge reach the coast either side?  (Read 365 times)

Offline dirtyape

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I am reading a book series that has elements of deep sea geology like the juan de fuca subduction zone and the mid atlantic ridge.  while i was reading i was struck by the idea that since the americas and europe/africa were once joined at the mid atlantic, and the spreading zone has huge mountain ranges, why arent there mt ranges all the way from the ridge to the continental shelfs?

mts on land get eroded by freeze/thaw, rain, wind, life, etc.  do ocean currents erode rock?
why are there great plains of mud in crustal material that was once montains on the ridge?
where did the mts go?
« Last Edit: 02/10/2016 16:03:57 by chris »


 

Online evan_au

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The undersea map on this page shows a lot of east-west cracks, in addition to the north-south mid-ocean ridge.

Perhaps the sea floor builds up a layer of dust from windstorms, meteorites, and algae shells that covers up the mountains, as it slowly spreads farther away from the mid-ocean ridge?
I guess we could test this hypothesis by looking at the depth of soft sediments on top of rock cores from various points in the Atlantic ocean.   

The basaltic ocean floor is subducted under the American and European/African continental plates, so you wouldn't expect it to extend all the way to the continental shelf.
 

Offline dirtyape

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Aiui, there are subduction zones in the southern Caribbean and near the mouth of the Med. They are very small in relation to the entire N Atlantic ocean. None off the continental shelf of N Am and W Eur. Between the continental shelf and the mid atlantic ridge, there are very deep abyssal plains.  If these were mts that were covered by mud, wouldn't the Atlantic be much shallower?  Since filling up mt valleys to their tops with mud would raise the level of the sea bottom to the tops of these mts.

The abyssal plains in the Atlantic, continental shelf-plains-mid Atlantic ridge, look like the great plains in the middle of the US.  Rockies-great plains-Appalachians. No mts in the great plains because there were no mt building events in that location.  But, if the Rockies and Appalachians were once side by side and then spread apart by a upwelling ridge of lava, say at the Mississippi, the great plains would be filled with mt ranges, right?

Why isn't the entire Atlantic basin from the ridge to the US/Eur continental shelf covered by mt ranges since the east coast of the US/west coast of Eur used to be ON the mid Atlantic ridge.   
 

Online evan_au

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Quote from: dirtyape
mid Atlantic ridge, look like the great plains in the middle of the US.  Rockies-great plains-Appalachians
There is a fundamental difference between the US continental mountain ranges, which are made of SIAL (Aluminosilicates), compared to the SIMA (Magnesium silicates) of the ocean basins. SIAL rocks tend to float on top of the denser SIMA rocks - or, in the case of the Atlantic basin, the SIAL continental crust is being pushed apart by the extrusion of SIMA at the mid-Atlantic ridge.

The continental mountain-building events rely on the continental crust floating on top of the underlying rocks.

As you observe, the decreasing heights of the mountains towards the Atlantic coasts is intriguing...
 

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