Chapter 2: Plate Tectonics Slide Set 6 Flashcards
Who is Marie Tharp?
was an American geologist and oceanographic cartographer who, in partnership with Bruce Heezen, created the first scientific map of the Atlantic Ocean floor. Tharp’s work revealed the presence of the Mid-Atlantic Ridge, causing a paradigm shift in earth science that led to acceptance of the theories of plate tectonics and continental drift.
How does continental lithosphere break apart?
- Lithosphere stretches and thins.
- Brittle upper crust faults.
- Ductile lower crust flows.
- Asthenosphere rises and melts.
- Magma erupts.
What happens when the lithosphere if it keeps breaking?
- Continuation can create a new mid-ocean ridge.
- This process led to the breakup of Pangaea.
The continental rifting arises from _____
tensional forces that break the crust along a complex jumble of normal faults.
Explain how did The Colorado Plateau developed
- Western U.S. Basin and Range Province is a rift.
- Narrow north-south mountains separated by basins.
- Rifting tilted blocks of crust to form mountains.
- Sediment eroded from blocks, filling adjacent basins
Explain the early stage of Divergent Boundaries
- Rifting has progressed to mid-ocean ridge formation.
- Before substantial widening of the ocean.
- Forms a long, thin ocean basin with young oceanic crust
Give an example of an early stage divergent boundary
The Red Sea
Explain the East African Rift
- The Arabian plate is rifting from the African plate.
- Rifting has progressed to sea-floor spreading in:
- The Red Sea.
- The Gulf of Aden.
- Stretching continues along the East African Rift.
- Elongate trough bordered by faulted high cliff
- Volcanoes – Mt. Kilimanjaro
- The rift and two spreading ridges comprise a triple junction.
Explain the mid stage of Divergent Boundaries
- Ocean begins to widen.
- New sea-floor is added at the mid-ocean ridge.
- Continents move farther apart.
Give an example of an mid stage divergent boundary
Greenland and the North Atlantic
Explain the late stage of Divergent Boundaries
- Mature, wide ocean basin.
- Linear increase in age with distance from central ridge.
- Edge of ocean basin—oldest; ridge proximal—youngest
Give an example of an late stage divergent boundary
The Atlantic Ocean
The hot asthenosphere is at the base of the ___
mid-ocean ridges
What happens to the aging ocean crust?
Aging ocean crust moves away from this heat source:
- Cooling, increasing in density and sinking.
- Older, thicker lithosphere sinks deeper into mantle.
How did the Red Sea form?
- Rifting has progressed to mid-ocean ridge formation.
- Before substantial widening of the ocean.
- Forms a long, thin ocean basin with young oceanic crust.
The Red Sea and the Gulf of Aden were formed as the Arabian plate separated from Nubia, as Nubia obliquely collided with the Eurasian plate
Using concepts from Plate Tectonics, explain how the Red Sea formed.
A clear example of continental rifting is found in the Rift Valley in East Africa. As you can see on the map on the left, the continental rift is at a divergent plate boundary. When the plates move apart, magma rises up through the fractures as lava, pushing the continental lithosphere on either side further apart. If the process of rifting continues, this continent will end up splitting in two.
This is what has happened in the Red Sea. The Red Sea Rift separates the Arabian Peninsula from Africa. It once was a continental rift, but now it is an oceanic rift, generating oceanic lithosphere.
Where is the youngest ocean floor located?
Youngest rock on the ocean floor can be seen in divergent plate boundaries and hot spots.
Where is the oldest ocean floor located?
It is found in the Mediterranean Sea and is a remnant of an ancient ocean that is disappearing between Africa and Europe.
What are “black smokers” and where are they found?
Black smokers are found at some Mid-ocean ridges.
- Water entering fractured rock is heated by magma.
- Hot water dissolves minerals and cycles back out of rock.
- When water reaches the sea, minerals precipitate quickly
Subduction is balanced by ______
sea-floor spreading
Explain the concept of convergent boundaries/subduction zones
- Lithospheric plates move toward one another.
- One plate sinks back into the mantle (subduction).
- The subducting plate is always oceanic lithosphere.
- Continental crust cannot be subducted—too buoyant.
- Subduction recycles oceanic lithosphere.
Teeth/arrows on convergent plate margins on maps point towards the ______
overriding plate
Explain subduction
The downgoing plate slowly sinks down into the asthenosphere
What land features does subduction lead to?
- Deep-ocean trenches.
- Accretionary prisms.
- Volcanic arcs.
- Forearc basins.
What is Accretionary prism?
wedge-shaped mass of sediment scraped off the subducting oceanic plate
Give an example for an oceanic-continental convergent margin
The Andes volcanic mountain chain
Give an example for an oceanic-oceanic convergent margin
Japanese Island Arc
Give an example for an continental-continental convergent margin
The Himalayas formed by collision of the Indian plate with the Eurasian plate
Explain the concept of an continental-continental convergent margin
Because continental crust is less dense than oceanic crust and cannot subduct, colliding continental lithospheric plates will ram each other. Since the rocks cannot readily be pushed down, they have nowhere to go but up!
What is an orogeny?
mountain building, as continents ram into each other
How Did the European Alps form?
A. Volcanic Arc from a continental – oceanic convergent
margin
B. Continent – continent collision
C. Continental expression of a divergent plate boundary
B
Explain the concept of transform boundaries
- Lithosphere fractures and slides laterally
- No new plate forms; none consumed.
- Many transforms offset spreading ridge segments.
- Some transforms cut through continental crust.
Transform boundaries are characterized by
- Earthquakes
- Absence of volcanism
Transform faults connect ______
connect convergent or divergent plate boundaries
What is a fracture zone?
a transform fault that offsets the oceanic ridge and connects two divergent boundaries.
What are contienental transforms? Give an example
cut across continental crust
Example: The San Andreas Fault, California
Haiti and the Dominican Republic are on a ______ boundary with about ______ mm per year of relative motion.
transform
20 mm
How are plate velocities determined?
- Plate motion is now determined by GPS measurements.
- Global Positioning System (GPS) uses satellites.
- Knowledge of plate motion is now accurate and precise.
What are triple junctions?
- Point where three plate boundaries intersect.
- Multiple boundary combinations occur.
How do hot spots move and what is the significance in terms of their age?
- Hot-spot seamounts age away from originating hot spot.
- Age trend defines rate of plate motion.
- Line of seamounts indicates direction of plate motion
What did Tuzo Wilson proposed in terms of hot spots in 1963?
1963 - Tuzo Wilson proposed that hot-spot volcanoes develop over a long-lived magma source originating deep within the mantle.
Chain of extinct volcanoes called a _______.
hot-spot track
What do hot spots lead to?
- Hot spots perforate overriding plates.
- Volcanoes build above sea level.
- Plate motion pulls volcano off plume.
- Volcano goes extinct and erodes.
- Hot spots reinforce sea-floor spreading.
What is the name of the new Hawaiian Island that is forming?
Loihi
What is the name of the volcano island in Hawaii
Kauai
What are the two forces that drive plate motions?
- Ridge-push—elevated MOR pushes lithosphere away.
- Slab-pull—denser subducting plate is pulled downward.
Convection in the asthenosphere speeds or slows motion
