9.3 – Actions at Plate Boundaries – Part I

Do Now What is seafloor spreading?

Do Now What is seafloor spreading? The process by which plate tectonics produces new oceanic lithosphere.

Key Words Segment

Vocab Words Oceanic Ridge Rift Valley Seafloor Spreading

Divergent Boundaries Most divergent boundaries are located along the crests of oceanic ridges. Divergent boundaries is where new oceanic lithosphere is created. When the plates move away from each other, fractures are created, and hot molten magma wells up from the hot mantle below, cools and forms new seafloor.

Oceanic Ridges Along well-developed divergent plate boundaries, the seafloor is elevated, forming the oceanic ridge. The system of oceanic ridges is the longest physical feature on Earth’s surface, stretching more than 70,000 kilometers in length. Deep faulted structures called rift valleys are found along the axes of some segments.

Seafloor Spreading Seafloor spreading is the process by which plate tectonics produces new oceanic lithosphere. Typical spreading rates = 5 cm/year Slow on a human time scale But this is still fast in terms of geologic time. All of the current ocean basins could have been generated within the last 200 million years; none of the ocean floor has been dated older than 180 million years old.

Seafloor Spreading

Continental Rifts When the spreading centers develop within a continent, the landmass may split into two or more smaller segments. EX: East African Rift Valley May represent the beginning stages of the break up of the African continent. Rift valleys show us the what possibly happened with the continental breakup idea.

Group Activity On page 259, Figure 9; copy the picture and label all the parts, put them in your folder when you complete it.