6. Rock Cycle and Plate Tectonics Flashcards
Porphyritic
a volcanic rock with a few large crystals
Petrology
the chemical/ physical origin of rocks
Name examples of metamorphic rocks
gneiss, mudstone, slate, marble
What is continental drift theory?
- 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
What is the plate tectonic theory? Give dates
- 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
Talk about tectonic plates
- 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
What is the spreading ridge?
- births new ocean crust
What is convection?
- process that moves plate tectonics
- transfer of mass from hotter regions to cooler regions
What are the three types of rock?
- Igneous- extrusive/ intrusive, SiO2 content
- Sedimentary- environment, degree of sorting
- Metamorphic- their protolith
Do metamorphic rocks ever melt to form?
No.
Only involves pressure and heat.
How do metamorphic rocks form?
Sedimentary and igneous rocks pressurize and heat (don’t melt) to become metamorphic rocks
How do sedimentary rocks form?
- rocks weather to form sediments
2. Sediments lithify to form sedimentary rocks
Give examples of metamorphic rocks.
- granite and silica-rich sediment metamorphose to gneiss
- carbonate-rich sediments lithify to limestone, metamorphose to marble
- mudstones metamorphose to slate
How are sedimentary rocks classified? In what different ways are they deposited?
- 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
What’s a signature of aeolian sorting of sediments?
cross bedding
Explain marine sediment sorting. The marine sequence.
sand/ silt lithifies to sandstone
mud lithifies to mudstone/ shale
carbonate lithifies to limestone
Describe plate tectonics and heat flow.
- 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
What are convergent plate boundaries?
- where 2 or more tectonic plates collide
- subduction and thrust fault
- Oceanic lithosphere vs. continental = volcanic mountain chains
- Oceanic lithosphere vs oceanic = underwater earthquakes + tsunamis. Volcanic chain
- continental vs continental lithosphere= mountains
What happens when the oceanic lithosphere converges with the continental lithosphere? Give example
- 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
What happens when the oceanic lithosphere converges with another oceanic lithosphere? Give example
- oceanic crust subducted
- Can form volcanic arc of islands- Aleutian islands of Alaska, Japan
- can cause underwater earthquakes and tsunamis
What happens when the continental lithosphere converges with the continental lithosphere? Give example
- mountain building
- what brought sea sediments up to top of Everst
What is divergent plate boundaries?
- 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
What are transform boundaries?
- strike slip fault
- no subduction zone
- Ex- San Andreas Fault
When were the last two supercontinents?
Pangea 300 Ma
Rodinia 1.2 Ga
How are ocean islands like Hawaii created?
- Hawaii is in the middle of ocean plates
- plumes or hotspot create new crust
Mid-Ocean Ridge
- 70,000 km long
- continuous ridge around earth
- a spreading ridge
Which subduction zone has a trench?
subduction zone (convergent) between oceanic and continental lithosphere
Match plate boundaries with forces and faults.
- Convergent = compresssional = reverse/ thrust fault
- Divergent = extensional = normal fault
- Transform = strike/ slip
What type of boundary does San Andreas have?
Strike/ Slip
