AS Plate Tectonics

Question 1

Tillites

Answer 1

ancient glacial deposits preserved within a rock sequence.

Question 2

Evaporites

Answer 2

minerals formed by the evaporation of hypersaline water, for example halite (rock salt), gypsum and anhydrite.

Question 3

Apparent polar wandering curve

Answer 3

a line on a map which joins up the apparent positions of the magnetic north pole over time.

Question 4

Orogeny

Answer 4

a period of mountain building.

Question 5

Transform fault

Answer 5

a strike-slip fault which:

a) ends at the junction of another plate boundary or fault;

B) shows the same amount of deformation across the fault zone;

c) can form a tectonic plate boundary.

Question 6

Tear fault

Answer 6

a strike-slip fault which:

a) dies out without a junction with another fault;

b) has more displacement in the middle of the fault zone;

c) cannot form a tectonic plate boundary.

Question 7

Transform plate boundary

Answer 7

a fault where no crust is created or destroyed.

Question 8

Sheeted dykes

Answer 8

form from magma which usually does not reach the surface, and usually composed of dolerite.

Question 9

Pillow lava

Answer 9

form when lava erupts underwater, and cools rapidly in cold sea water, usually composed of basalt. The rounded masses formed are called pillows.

Question 10

Island arc

Answer 10

a curved line of andesitic volcanic islands. As the subducting plate heats up, partial melting occurs along the top surface of the descending oceanic crust, producing basaltic magma. As this wet, less dense, hot (1200°C) magma rises it may melt and differentiate into intermediate, andesite lavas.

Question 11

Deep-ocean trench

Answer 11

a long, narrow, linear submarine depression with relatively steep sides; the deepest example is over 10000 m deep. Trenches occur alongside island arcs or fold mountain belts and indicate where a plate is beginning to descend along a subduction zone.

Question 12

Benioff zone

Answer 12

(named after the scientist who identified it) a zone of earthquake foci sloping down at an angle of about 45° from the deep- ocean trench. The zone descends beneath oceanic island arcs or continental fold mountains, marking the boundary where one plate subducts beneath another. At higher levels, where the subduction is beginning, the earthquakes are generated along the boundary itself partly due to friction. Further down, the foci occur within
the plate as the interior part of the plate remains colder and more rigid, while the edges of the plate heat up.

Question 13

Migmatite

Answer 13

a metamorphic rock, such as gneiss, that melts to form an igneous rock.

Question 14

Guyot

Answer 14

flat-topped seamount, usually eroded by wave action.

Question 15

Seamount

Answer 15

a submarine mountain, often an extinct volcano.

Question 16

Diapir

Answer 16

a low density, buoyant material rising upwards in the same way as hot wax does in a lava lamp.

Question 17

Ridge push

Answer 17

a process where two sections of lithosphere are pushed apart by rising magma at the MOR.

Question 18

Slab pull

Answer 18

a process where a cold, dense section of lithosphere descends into the mantle at a subduction zone.

Question 19

Pangaea

Answer 19

(= all the Earth) a supercontinent that formed at the end of the Permian.