why there is no granite under seas ?

Answer 1

Granite is indeed found under seas. It is found at about the same ratio as at "above water" locations.

This must have been true for some time because there are locations (such as the state of Illinois) which have almost no granite at the surface, but do have considerable deposits of granite under limestone and sandstone which are considered sedimentary deposits from ancient oceans and large inland lakes.

Answer 2

There is granite under the seas. Most of the sea floor is made up of igneous granite and (more dense) basalt rock. They are just covered up. Most of the continental crust that is at the "bottom"of the plate is also granite or basalt. there are just other rock types and "stuff" on top.

Answer 3

Because you need continental crust and/or subduction to produce granites.

There are to basic ways to produce granites:
1) Partial melting of lower crust sedimentary/metamorphic rocks.
2) By Crystal fractionation. A big magma chamber crystallizes and the residual magma evolves to produce a smaller granite.

In order to melt significant amount of crust you need, heat, but more importantly, water. The oceans are full of water, yet, their magmas are pretty dry. When you have subduction, water is incorporated into the mantle melting it and producing water-rich magmas. So this water and heat will help melt the crust producing large amounts granitic magmas.

In the oceans you don't have this process and you can generate only very minor granites or not at all, only by crystal fractionation.

But in the continents you have subduction, delamination of the crust. Accumulation of basaltic magma at the base, etc. that will lead to the production of granites.

Answer 4

The seafloors are composed of basalt, plus other layers like sheeted gabbros, mafic dikes and other mafic rocks. Granite is light (2.8 g/cc) compared to basalt (3.3 g/cc). Granite "floats" on basalt. I have never heard of granite under the seas, but that doesn't mean there isn't any down there. Oh, and to correct a previous point, the seafloor is not composed of "Igneous Granite". And it is rudundant to refer to "igneous granite", since the definition of granite is "An igneous rock that..."

Answer 5

because of sea floor spreading it never stay the same, new rock is always formed at cretain time in the lava flow that comes up to the surface of the sea bed.

Answer 6

there is.. only most of the time it's covered in silt and other mineral deposits. it also depends on where on the ocean floor you look.. there are areas that have underwater canyons and mountains that have lots of granite and basalt, and there are areas where it's almost non-existant