chapter 3 Flashcards
(16 cards)
What is plate tectonics?
It’s a theory that refers to the movement and interaction of the Earth’s lithosphere and explains the global distribution of geological phenomena. Includes formation, movement, collision and destruction of plates and the resulting geological events as seismicity (earthquakes), volcanism, continental drift, sea-floor spreading and mountain building
Explain continental drift
Supercontinent called pangaea broke up 225 million years ago and drifted away into present continents. Pangaea broke up into Laurasia and Gondwana then 65 Ma India collided with Asia, Australia separated from Antarctica and the final shape of the modern world formed
What is a tectonic plate?
It’s the lithosphere, which is 100 km thick (formed from the crust and part of the upper mantle)
How do plates move?
By convection currents in Earth’s mantle. The mechanical transfer of heat energy that occurs as heated material expands, rises, and displaces cooler material, which itself is heated. They occur below the lithosphere and asthenosphere.
Explain how a new oceanic crust is created.
By seafloor spreading, plates diverge and mantle plumes rise causing upwelling and fracturing (rifting). New materials are introduced forming Mid-Oceanic Ridge. Explorations in the Atlantic show that the seafloor is formed of young basalt.
What is the evidence supporting plate-tectonic theory? Describe and explain.
- Distribution of volcanic activity along plate boundaries. Volcanoes are especially active along destructive or convergent plate boundaries active along destructive or convergent plate boundaries at which an oceanic plate is subducted under the older but less dense continental plate
- Distribution of earthquakes along plate boundaries. Shallow, intermediate, and deep focus earthquakes depend upon the descending plate position
- The remarkable fit between South America and Africa, and North America and Europe
- Paleontological similarities: presence of the same fossils - ancient flora (plant fossils) and fauna (animal fossils)- in continents at both sides of the ocean (fossil evidence)
- Tectonic and stratigraphic similarities explain the presence of the same ancient fold belts (orogeny) at certain age that form mountains and rocks of the same age and type within these continents at both sides of the ocean
- Paleomagnetic evidence: same ancient magnetic pole position of both North America and Europe, South America and Africa. Suggesting that these were joined together in the past.
- Paleoclimatological evidence: the presence of glacial deposits at both sides of oceans (as former Gondwana)
- Age of oceanic crust at both sides of mid-oceanic ridge which increases away from mid-ocean ridge, with oldest basaltic rocks ~180 Ma.
List the tectonic and stratigraphic similarities on opposite sides of the Atlantic.
- Rock ages
- Fossils and climatic date
- Trends in geological structures
How does the age of oceanic crust support plate tectonics theory?
Age of oceanic crust on both sides of Mid Oceanic Ridge (young basaltic rocks) increases away from MOR, with the oldest basaltic rocks ~180 Ma old farthest away from the ridge.
How many plates occur on Earth?
N-American plate, S-American, African, Eurasian, Pacific, Antarctic, and Australian plate
List all eight smaller sub-plates occurring on Earth’s surface.
Arabian, Indian, Philippine Sea, Juan de Fuca, Cocos, Caribbean, Nazca, Scotia sub-plate
Define the asthenosphere.
Ductile part of the Earth is just below the lithosphere, including the lower mantle. It is about 180 km thick.
Difference between lithosphere and asthenosphere.
Lithosphere is cold, rigid, brittle and it breaks.
Asthenosphere is hot, ductile, and behaves plastically
What are the types of plate boundaries?
- Divergence: plates move away from each other, and tensional forces break up the solid lithosphere, allowing new material (magma and lava) to travel along these fractures reaching the Earth’s surface; new materials are being generated forming new ocean floors.
Example: mid-Atlantic ridge - Convergence: plates move towards each other; ancient crust being consumed. Forming trenches and subduction zones.
- Transform Fault: when plates slip past each other with destruction of the crust. It connects divergent and convergent plate boundaries
Example: San Andreas Fault, Yammouneh fault in Bekaa valley, Dead Sea transform
No volcanic activity associated with it, but can cause earthquakes
What are the types of transform faults?
a) Oceanic: two oceanic plates slide horizontally past each other
Example: MOR transform fault
b) Continental transform:
Example: San Andreas fault
List the types of convergence along with examples.
- Oceanic-oceanic: one plate is subducted, dehydrates, and melts, the melt rises causing seismic and volcanic activity.
Example: Japanese trench, Peru-Chile trench, Marianas Trench2. Oceanic-Continental: dinser and thinner oceanic plates slide under continental crust, reaching into the hot asthenosphere where it dehydrates and melts.
Example: Andes Mountains, Siera Nevada Batholith - Continental -Continental (Collision): when the continental plates converge (collide) causing extensive deformation and earthquakes.
Example: Himalaya mountains where Indian plate is colliding with Eurasian plate
What is a locked fault?
A fault that is not slipping because of friction is greater than shear stress across the fault. May store strain for a long time and eventually release it in an earthquake
