Sea Floor Spreading & Plate Tectonics

Ch.2 The Sea Floor

A.Types of Plate Boundaries1.Divergent boundaries, where plates move away

from each other.2.Convergent boundaries, where plates move

towards each other.3.Transform boundaries, where plates slide along

next to each other.

I. Sea Floor Spreading & Plate Tectonics

B. The lithosphere, about 100 km (60 miles) thick, is rigid and composed of the crust and the upper mantle.

C. The lithosphere floats on the more plastic upper mantle, or asthenosphere.

I. Sea Floor Spreading & Plate Tectonics

D. At convergent boundaries, two plates collide with each other. Three types of convergence:

1. Oceanic plate and a continental plate.2. Between two oceanic plates.3.Between two continental plates.

I. Sea Floor Spreading & Plate Tectonics

E. Oceanic / Continental Convergence1.Oceanic crust (basalt) is more dense, it tends to

dive down where it meets continental crust (granite), called subduction.

2.Forms submarine trenches, or subduction zones, as well as volcanoes and earthquakes.

3.Can pull an entire continent (Denver).

I. Sea Floor Spreading & Plate Tectonics

F. Oceanic / Oceanic Convergence1.Both sink – one deeper than the other

a. Mariana Trench is deepest place (~36,000 feet deep)2.Subduction melts ocean sediment, creating a

source of magma, which is released in volcanoes forming volcanoes and islands arcs.

3.Aleutian Islands

I. Sea Floor Spreading & Plate Tectonics

G. Continental / Continental Convergence1. Push each other up like rams butting heads,

forming mountain ranges.2.Himalaya Mountains3.Cascade Mountains

I. Sea Floor Spreading & Plate Tectonics

H. Transform Plate Boundaries1. Two plates that slide

past each other.2.San Andreas fault - 5

centimeters per year for the past 10 million years.

I. Sea Floor Spreading & Plate Tectonics

I. Hot Spots1. Place where magma

forces its way up through the lithosphere.

2. Can form volcanoes (Hawaiian islands), geysers, and bubbling mud pools (Yellowstone)

3. Can lift an entire continent (African Plateau), known as a superplume.

I. Sea Floor Spreading & Plate Tectonics