Geology Reference
In-Depth Information
boundary where the dense oceanic crust is pushed under a plate of continental crust
and into the mantle.
While they may disagree on the particulars, scientists these days generally
agree that mantle materials move by convection and that cool, dense
lithosphere
(the crust and uppermost mantle) enters the mantle at subduction zone boundar-
ies. They have some good evidence to provide support to these ideas, as you see
in the next section.
Using Convection to Explain Magma, Vol-
canoes, and Underwater Mountains
In Chapter 8, I note that the theory of plate tectonics is a
unifying
theory for geology.
This means that the description of plate tectonics incorporates scientists' understand-
ing of many other geologic phenomena that have been observed. In this section, for ex-
ample, I explain how the subduction of crustal plates (courtesy of mantle convection) is
related to volcanoes.
When you're reading this section, keep in mind that the earth's mantle is sol-
id, not liquid. A common misconception is that the mantle of the earth is made en-
tirely of
magma
: melted, liquid rock.
It isn't!
Magma forms only under the right
conditions of heat.
In this section, I describe three places on the earth where magma-forming conditions ex-
ist:
In subduction zones where plates collide and one plate (the oceanic) subducts be-
neath the other (the continental)
Under oceanic crust at mantle plume hotspots (such as the Hawaiian volcanoes)
Along the boundary where two plates are moving apart (mid-ocean ridges)
