'nother fun site

continental drift
are the continents being pushed by the midocean ridges
or
are the continents being dragged into the deep trenches by gravity
(much like covers falling off a bed)
or
both ?
.........................
North America(where I live) seems to have been pulled apart at least twice in the last 400 million years
The last time (@50 million years ago)it seems to have left a series of fault zones up the Mississippi valley
and then, North America seems to have been pushed back together again by the spreading Atlantic sea floor?
These movements have torn fragments off the appalacians leaving one in texas, and another in missouri.
fig-6-3-appalachain-ouachita-marathon-chain-new-10x.jpg

While in the Basin and Range of the western US, the crust has been stretched by up to 100% of its original width. As a result of this extension, the average crustal thickness of the Basin and Range region is 30 - 35 kilometers (19 - 22 miles), compared to a worldwide average of around 40 kilometers (25 miles).
Indicating the continent being pulled into the deep trenches along the pacific shore
so
Both?
At different times?
or by varying degrees over time?
 
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