Oceanic lithosphere thickens as it moves away from mid-ocean ridges primarily because of
A) the addition of new crust due to hot-spot volcanism.
B) the addition of new crust due to sedimentation.
C) the addition of new lithospheric mantle as a result of cooling.
D) reasons that geologists cannot determine at present.

Question

Quizplus · Accepted Answer

As oceanic lithosphere forms at mid-ocean ridges, it is hot and buoyant. As it moves away from these ridges, it cools and contracts, causing its density to increase. This increased density causes more lithospheric mantle material to be added to the bottom of the lithosphere, thickening it. Sedimentation and hot-spot volcanism can also contribute to thickening, but they are secondary factors compared to cooling and the addition of new lithospheric mantle material. Therefore, choice C is the best answer.

Oceanic Lithosphere Thickens as It Moves Away from Mid-Ocean Ridges