This lesson introduces seafloor spreading, how the idea developed, and the forces that move tectonic plates. It matters because the movement of the seafloor helps explain how ocean basins and continents change over time.
Seafloor spreading is the formation of new oceanic crust at mid-ocean ridges followed by its movement away from the ridge. At these underwater mountain chains, plates move apart and magma rises through fractures. The magma cools and solidifies, adding new crust to the seafloor.
All flashcards
What is seafloor spreading?
The formation of new oceanic crust at a mid-ocean ridge and its gradual movement away from the ridge.
How did Hess and Dietz's proposal change the explanation of continental drift?
They proposed that the seafloor itself moves outward from a ridge, carrying continents on moving plates instead of continents plowing through fixed ocean floor.
What is slab pull?
A force produced when cold, dense oceanic lithosphere sinks at a subduction zone and pulls the rest of its tectonic plate along.
What is ridge push?
The tendency of rigid lithosphere to slide away from the elevated mid-ocean ridge over the hot asthenosphere below.
Why is magma pressure not usually considered the main driver of spreading?
Plate motion is mainly associated with forces such as slab pull and ridge push; magma commonly rises passively into fractures as plates are pulled apart.
Quiz questions
What does the spreading half-rate measure?Answer: The rate at which new oceanic lithosphere is added to one plate on one side of a ridge.
What is the crustal accretion zone at a spreading center?Answer: The zone where new oceanic crust is added and the youngest crust is found.
Why do magnetic anomalies commonly form mirror-image stripes on opposite sides of a ridge?Answer: Crust formed at the ridge records magnetic polarity and moves outward on both sides.
Which spreading-rate category applies to rates greater than 90 mm per year?Answer: Fast spreading.
Which cooling model explains why old seafloor approaches a nearly constant depth?Answer: The cooling-plate model, which limits cooling above a roughly constant-temperature base.
Based on the Wikipedia article Seafloor spreading, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.