How are they alike? Different?

Question

How is oceanic crust and continental crust different? HOw are they alike?

Answer 1

Oceanic crust is primarily basalt (solidified volcanic lava) produced at ocean ridge spreading centers. In general terms, Basalt is a relatively dense iron-magnesium silicate.

On the crust, partial remelting of the original basaltic material has resulted in the formation of granitic materials, which are less dense and contain more silica and other granite-loving elements like potassium and sodium. This stuff rises up toward the surface (above the original basalt source). Parts near the surface then eventually erode and low density sediments accumulate on top of the crust, which also eventually recycle through partial melting blah blah blah.

So what exists now are vast low plains of oceanic crust (iron rich dense stuff) that is relatively thin, say 10 kilometers thick over the mantle, with "islands" of thicker (say 70 km thick) low density crust bobbing around as continents. Continents supposedly consist of an upper part that is generally granitic in composition with a lower basalt-like lower layer that is the residue of partial melting and crustal recycling and so forth.

Material is also added to crust when the continents ride over the ocean plates, which are then forced downward into the mantle. This material also partly melts producing less dense (more silica rich and iron poor) magma that also rises up.

Somewhere in that explanation is part of your answer I guess!

Answer 2

Ah... the simple joys of plate tectonics.

The crust is alike because it's all crust, i.e. solid rock floating on liquid rock.

And it's pretty straight forward that the stuff below sea level is thinner that the stuff above, right?

There's also the general principal that places where the crust is being stretched, tend to be thin & hence underwater, and the converse that regions of compression get thicker and are often mountainous.

Many details. Just a few basics.

Have fun.

Answer 3

Going back a long way in memory, but I think continental crust is thicker and mainly basalt in nature. It's usually the result of volcanic activity. Oceanic crust is predominantly sedimentary. Oceanic tectonics usually involve subduction zones which give rise to surrounding continents/islands as the subducted magma rises again.