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زمینشناسی و معدن::
لیتوسفر اقیانوسی
The greatest quantities are produced at divergent plate boundaries, in association with seafloor spreading, with lesser amounts forming at subduction zones, where oceanic lithosphere descends into the mantle.
The introduction of water to generate magma occurs mainly at convergent plate boundaries, where cool slabs of oceanic lithosphere descend into the mantle (Figure 4.20).
A balance is maintained because older, denser portions of oceanic lithosphere descend into the mantle at a rate equal to seafloor production.
In general, old oceanic lithosphere is about 2 percent more dense than the underlying asthenosphere, which causes it to subduct.
As a consequence, only oceanic lithosphere will subduct to great depths.
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