Sept 9 Lecture (Cont Drift, Plate tectonics)

Question 1

magnetic north has changed throughout geological time via ___ ___

Answer 1

magnetic reversal

Question 2

define normally magnetized rocks

Answer 2

rocks crystallizing at times when earth’s magnetic field was in the same orientation as today

Question 3

define reversely magnetized rocks

Answer 3

rocks crystallizing when the field was oriented the opposite direction as it is today

Question 4

___ ___ explains magnetic patterns on the seafloor

Answer 4

seafloor spreading

Question 5

explain the magnetic patterns on the seafloor and how it happened

Answer 5

1. newly formed basalts contain ferromagnesian minerals, so attain magnetism when cooled. the basalt is continuously extruded at mid-ocean ridges
2. as the seafloor splits/ moves away from the ridge, half of the newly magnetized material moves to 1 side and half to another: 2 symmetrical magnetized bands formed
3. new material fills in the crack, continuing the process
4. so, the ocean floor has developed an alternating pattern of normal and reversely magnetized rocks

Question 6

topographic maps of the seafloor have shown:

3

Answer 6

1. there are ridges running N-S in both Atlantic and pacific oceans
2. along the margins of some continents there are trenches several km deep
3. the other continents are bounded by shallow water shelves

Question 7

define lithosphere

- what do stresses cause?

Answer 7

earth’s crust and uppermost mantle (solid)

- stresses cause brittle and elastic deformation

Question 8

asthenosphere

Answer 8

plastic layer beneath the lithosphere

- lithosphere plates can move over this plastic layer; plates carry the continents

Question 9

some plates are moving towards each other = ___ ___ ___

• some plates are separating = ___ ___ ___
• to have this happen on a spherical planet, plates must be able to slide past one another (___ ____)

Answer 9

convergent plate boundary

divergent plate boundary

transform boundary

Question 10

at transform- fault boundaries:

Answer 10

plates slide horizontally past each other

Question 11

at divergent boundaries:

Answer 11

plates move apart and create new lithosphere

Question 12

at convergent boundaries:

Answer 12

plates collide and one is pulled into the mantle and recycled

Question 13

define black smokers

Answer 13

(occur at divergent boundaries- mid-ocean ridges)

- hot springs; sites of large biological communities that live off the volcanic heat/ gases (not sunlight)

Question 14

how is a new lithosphere formed at divergent boundaries?

Answer 14

at mid-ocean ridges, the release of pressure as the plates move apart allows hot basalt magma from the asthenosphere to reach the ocean floor. It cools & crystallizes to form a new lithosphere

Question 15

explain continental rifting at divergent boundaries

Answer 15

• plate separation can also occur on continents- characterized by long rift valleys w/ basalt eruptions
• sometimes, continental rifting allows a new ocean basin to open up

Question 16

continental lithosphere is (more/ less) dense than the asthenosphere (mantle)

Answer 16

less

Question 17

oceanic lithosphere is more similar in density to asthenosphere, so it’s easily forced under continental material when the plates converge. this is called ___

Answer 17

subduction

Question 18

at convergent boundaries, the subducted plate is heated/ melted, and reincorporated into the ___
- this applies to ___/___ convergent boundaries

Answer 18

asthenosphere

ocean/ continent

Question 19

how do andesite volcanoes form at ocean/ continent convergent boundaries?

Answer 19

they form where the melted material rises up through overlying plate to the surface

Question 20

why do mountains form at ocean/ continent convergent boundaries?

Answer 20

the continental crust is compressed, folded, and faulted. This deformation= mountains form

Question 21

in a continent/ continent collision, the 2 landmasses come together to form a ____
why?

Answer 21

mountain

- b/c both plates too buoyant to sink into mantle

Question 22

explain transform boundaries

Answer 22

b/c of spherical shape of earth, the spreading ridges cannot be long/ continuous. They’re in numerous short segments (2 opposite plates scrape past each other).
- lots of stress here, leads to eq

Question 23

explain hot spots

Answer 23

• unusual volcanic eruptions
• arise when isolated plumes of magma rise from deep within the asthenosphere to the surface
• plumes are fixed in the mantle, so as the plates move over it, there becomes a progressive trail of volcanoes at earth’s surface