Re: ALL the oceanic crust is recycled in 180 My: unrealistic

brad <lbjohnson1949@xxxxxxxxx> wrote:

Please tell me how you can get Si rich magma by adding water.

Addition of volatile (like water) leads to partial melting => fractional
crystallization => silica rich magma.

This is the primary mechanism of andesite formation at "subduction
zones".


See subduction.

See Santa.


What don't you understand in "The big difference is in the scale."
If there is only a few thousand square km that are recycled, then almost
all the floor produced by ridges is extra surface.

So why is nothing older ? Some seafloor ( somewhere ) should be very
old.

Why is nothing older in the modern ocenic basins?
Nothing is older because the current large oceans did not exist 200 My
ago. There were only narrow basins in between cratons, about the width
of the Red Sea. Yep, the Red Sea *is* an ocean despite its name.


--
Florian
"Toute vérité franchit trois étapes. D'abord elle est ridiculisée.
Ensuite, elle subit une forte opposition. Puis, elle est considérée
comme ayant toujours été une évidence." - Arthur Schopenhauer
.

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