Rocks and Weathering: Plate tectonics

Question 1

Three main theories about movement of plates

Answer 1

The convection current theory…
The dragging theory…
Hotspot…

Question 2

Sea-floor spreading

Answer 2

A process whereby new oceanic crust is formed through oceanic activity, as two oceanic plates diverge, and then gradually move away from the ridge.

Question 3

Subduction zone

Answer 3

Where an oceanic lithospheric plate collides with another plate.

Question 4

Benioff zone

Answer 4

A narrow zone of earthquakes dipping away from the deep-sea trench

Question 5

Evidence for subduction (3)

Answer 5

Existence of certain landforms, Benioff zone, distribution of temperature at depth

Question 6

Deep-sea trenches

Answer 6

Long, narrow depressions in the ocean floor with depths from 6km to 11km.

Question 7

Fold-mountains

Answer 7

When two plates converge and are forced to fold and buckle and orogeny occurs. (Where an oceanic plate meets a continental plate, the lighter, less dense continental plate may be folded and buckled into fold mountains like the Andes. Where two continental plates meet, both may be folded and buckled in the case of the Himalayas).

Question 8

Ocean ridges

Answer 8

Gian submarine mountain chains with a total length of more than 60,000km, between 1,000-4,000km wide and up to 2-3km above the surrounding sea bed.

Question 9

Volcanic island arcs

Answer 9

When oceanic lithosphere is subducted beneath oceanic lithosphere. Note the trench outer rise (due to the bending of the plate), the outer slope and the island arc.