Midterm: Earth's Interior/Tectonics Flashcards
What is the evidence for the structure?
- Africa/South America have complementary shapes
- Common fossils across continents
- Evidence of past glaciation in now warm places
- Alternating magnetic anomalies on the seafloor (clinched it). The anomalies were also reflected in the age of the ocean floor, providing direct evidence of seafloor spreading.
Major Divisions
- Pacific Plate: The largest tectonic plate, encompassing most of the Pacific Ocean and known for its high seismic activity due to interactions with surrounding plates.
- North American Plate: Covers most of North America, including the continental United States and parts of Canada.
- Eurasian Plate: Includes most of Europe and Asia.
African Plate: Covers most of the African continent. - Antarctic Plate: Underlies the Antarctic continent.
- Indo-Australian Plate: Consists of the Indian subcontinent and Australia.
- South American Plate: Covers the majority of South America.
What is heat transfer?
Driving tectonic plate movement is convection within the Earth’s mantle, where hot, less dense rock rises from the deep interior, cools near the surface, and then sinks back down, creating a continuous cycle that moves the plates above it; this process is often described as “mantle convection.
What are the two types of crust
- Oceanic: Thinner (~10 km) and composed of dense, mafic rock. This is what makes up the ocean floor!
- Continental: Thicker (~40 km, but can range from 20 to 80 km) and composed of less dense, felsic rock. This is what we live on!
What do plate boundaries depend on?
(1) relative motion; and (2) types of crust involved.
What is a divergent (or constructive) boundary? And examples?
- Two plates moving apart from one another with magma from decompression melting of the mantle rising to fill the void. This causes seafloor spreading.
- Oceanic examples: Mid-Atlantic Ridge, East Pacific Rise, Iceland
- Continental examples: East African Rift Valley, Rio Grande Rift
What is a convergent (or destructive) boundary?
Two plates coming together. Their behavior depends on the type of crust on the two plates and their relative buoyancy.
What are the types of convergent boundaries?
Oceanic-Continent: Dense oceanic plate subducts beneath the less dense continental plate. Results in mountain-building and causes flux melting and volcanism (e.g., volcanic arcs).
Examples: Cascades, Andes
Oceanic-Oceanic: One plate (generally the older, colder, and thus denser one) subducts beneath the other. Causes flux melting and volcanism (e.g., island arcs).
Examples: Japan, Philippines
Continental-Continental: Collision. Both are buoyant and neither subducts beneath the other. Results in mountain-building.
Example: The Indian subcontinent has been colliding with the Eurasian plate for ~50 million, producing the Himalayas and Tibetan plateau.
What is a transform (or conservative) boundary?
Two plates slide past one another
Examples: San Andreas; Mid-ocean Ridge offsets
What are the three types of plate boundaries?
- Divergent (constructive) boundary
- Convergent (destructive) boundary
- Transform (conservative) boundary
Why do tectonic plates move?
- Ridge push
- Slab pull
- Convection traction
What is ridge push?
A plate slides under its own weight down the hot, raised asthenosphere at mid-ocean ridges
What is slab pull?
The cold, dense subducting slab, as it plunges into the mantle under its own weight, pulls the rest of the plate along.
What is convection traction?
Horizontal movements of mantle convection cells drag the plates along with them.
What kind of topography do plate boundaries have? What kind of events do they experience?
- Mountainous
- Earthquakes
What are hot spots?
Hot spots are volcanic locales fed by a plume, which is a hot, buoyant mass of material in the mantle that quickly rises to the base of the crust. The plume head melts due to decompression, resulting in volcanism. Examples of hot spots include Hawaii, Yellowstone, and Iceland.
Do hot spots move? What kind of activity do they form?
While tectonic plates move, hot spots are stationary. This results in long chains of past and current volcanic activity as the plate moves over the plume, which is what produced the Hawaiian Islands
