2 Ocean Basins and Seafloor Geology Free Online FlashCards

How does a mid-ocean ridge create new oceanic crust?

At a divergent boundary, plates pull apart; rising mantle material melts and forms new oceanic crust at a mid-ocean ridge.

What can happen when oceanic lithosphere is subducted?

At a convergent boundary, denser oceanic lithosphere can sink beneath another plate. This subduction forms a deep-ocean trench and may cause earthquakes and volcanic arcs.

How does oceanic crust age change with distance from a ridge?

Oceanic crust is youngest near ridge crests and becomes older farther away. Most present-day oceanic crust is less than about 200 million years old.

What is the continental shelf?

The continental shelf is the shallow, gently sloping, submerged edge of a continent.

What is the continental slope?

The continental slope is the steeper descent from the continental shelf toward the deep-ocean floor.

What is the continental rise, and where may it be less distinct?

The continental rise is a gentler, sediment-covered area at the base of many continental slopes. It may be absent or less distinct near a trench.

How can an abyssal plain become relatively flat?

An abyssal plain is a broad, deep region of seafloor that can be relatively flat where sediment has buried much of its underlying relief.

How do passive and active continental margins differ?

A passive margin lies away from an active plate boundary and can accumulate thick sediment. An active margin borders a plate boundary and may have trenches, earthquakes, and volcanism.

What do matching magnetic bands on either side of a ridge support?

Matching bands of alternating magnetic patterns on either side of many ridge segments support the idea that new crust spreads outward from the ridge.

What role do transform faults play at ridge segments?

Transform faults offset ridge segments and accommodate horizontal motion where plates slide past one another.

What is the source of lithogenous sediment?

Lithogenous, or terrigenous, sediment comes from weathered rock, often carried from land by rivers, wind, or glaciers.

What forms biogenous sediment, and what is such deep-sea sediment called?

Biogenous sediment comes from the remains of marine organisms, including shells and microscopic skeletons. Deep-sea sediment rich in these remains is called ooze.