6. Rock Cycle and Plate Tectonics

Question 1

Porphyritic

Answer 1

a volcanic rock with a few large crystals

Question 2

Petrology

Answer 2

the chemical/ physical origin of rocks

Question 3

Name examples of metamorphic rocks

Answer 3

gneiss, mudstone, slate, marble

Question 4

What is continental drift theory?

Answer 4

• Alfred Wegener, 1926
• originally one supercontinent Pangea that split apart
• wasn’t believed: how could continents plow through ocean crust? Later discovered spreading ridge that pushed continents apart

Question 5

What is the plate tectonic theory? Give dates

Answer 5

• process of generating new crust and recycling old crust
• created at spreading ridge, cool and form ocean floor, subducted beneath continent or other oceanic crustal plate
• constant movement of tectonic plates- the rigid pieces of Earth’s surface (lithosphere)
• theory created in 1960s after Mary Tharp discovered giant mountain range under Pacific Ocean, stolen by boss
• process takes 200 Ma

Question 6

Talk about tectonic plates

Answer 6

• Rigid pieces of Earth’s surface (lithosphere)
• they can be big (Pacific plate) and small (Juan de Fuca)
• plates interact in 3 ways: convergent, divergent, transform
• plates don’t move fast (mm maybe cm/ year); subduction rate is faster (3-5 cm)
• movement by convection

Question 7

What is the spreading ridge?

Answer 7

• births new ocean crust

Question 8

What is convection?

Answer 8

• process that moves plate tectonics

- transfer of mass from hotter regions to cooler regions

Question 9

What are the three types of rock?

Answer 9

1. Igneous- extrusive/ intrusive, SiO2 content
2. Sedimentary- environment, degree of sorting
3. Metamorphic- their protolith

Question 10

Do metamorphic rocks ever melt to form?

Answer 10

No.

Only involves pressure and heat.

Question 11

How do metamorphic rocks form?

Answer 11

Sedimentary and igneous rocks pressurize and heat (don’t melt) to become metamorphic rocks

Question 12

How do sedimentary rocks form?

Answer 12

1. rocks weather to form sediments

2. Sediments lithify to form sedimentary rocks

Question 13

Give examples of metamorphic rocks.

Answer 13

• granite and silica-rich sediment metamorphose to gneiss
• carbonate-rich sediments lithify to limestone, metamorphose to marble
• mudstones metamorphose to slate

Question 14

How are sedimentary rocks classified? In what different ways are they deposited?

Answer 14

• classified based on environment and degree of sorting
• alluvial- fan, poorly sorted
• fleuvial- river
• aeolian- wind, well sorted. Cross bedding is a signature
• marine sediments- vary from beach to beach

Question 15

What’s a signature of aeolian sorting of sediments?

Answer 15

cross bedding

Question 16

Explain marine sediment sorting. The marine sequence.

Answer 16

sand/ silt lithifies to sandstone
mud lithifies to mudstone/ shale
carbonate lithifies to limestone

Question 17

Describe plate tectonics and heat flow.

Answer 17

• heat is trying to escape from core-mantle boundary
• produced by radioactive elements in mantle and core
• heat can’t flow via conduction or radiation because the mantle is made of silicate and oxides, which are insulators
• so heat has to be moved by convection

Question 18

What are convergent plate boundaries?

Answer 18

• where 2 or more tectonic plates collide
• subduction and thrust fault

1. Oceanic lithosphere vs. continental = volcanic mountain chains
2. Oceanic lithosphere vs oceanic = underwater earthquakes + tsunamis. Volcanic chain
3. continental vs continental lithosphere= mountains

Question 19

What happens when the oceanic lithosphere converges with the continental lithosphere? Give example

Answer 19

• oceanic lithosphere subducted under mantle
• oceanic lithosphere descends, water released because of high P + T, causing fluids to form, melting mantle further. Mantle rises and erupts to form volcanic mountain chain.
• Andes = W coast of South America

Question 20

What happens when the oceanic lithosphere converges with another oceanic lithosphere? Give example

Answer 20

• oceanic crust subducted
• Can form volcanic arc of islands- Aleutian islands of Alaska, Japan
• can cause underwater earthquakes and tsunamis

Question 21

What happens when the continental lithosphere converges with the continental lithosphere? Give example

Answer 21

• mountain building

- what brought sea sediments up to top of Everst

Question 22

What is divergent plate boundaries?

Answer 22

• normal faulting
• when plates are pulled apart, molten mantle fills gap to form new oceanic lithosphere, spreading ridge created, pushing apart
• forming basins and new oceans
• passive margin created when plates fail to pull apart, oceanic crust and continental crust not active
• failure = mid-continent rift

Question 23

What are transform boundaries?

Answer 23

• strike slip fault
• no subduction zone
• Ex- San Andreas Fault

Question 24

When were the last two supercontinents?

Answer 24

Pangea 300 Ma

Rodinia 1.2 Ga

Question 25

How are ocean islands like Hawaii created?

Answer 25

• Hawaii is in the middle of ocean plates

- plumes or hotspot create new crust

Question 26

Mid-Ocean Ridge

Answer 26

• 70,000 km long
• continuous ridge around earth
• a spreading ridge

Question 27

Which subduction zone has a trench?

Answer 27

subduction zone (convergent) between oceanic and continental lithosphere

Question 28

Match plate boundaries with forces and faults.

Answer 28

1. Convergent = compresssional = reverse/ thrust fault
2. Divergent = extensional = normal fault
3. Transform = strike/ slip

Question 29

What type of boundary does San Andreas have?

Answer 29

Strike/ Slip