Tectonics Gateway 1 Flashcards
What is the core
Composed mostly of iron and nickel, divided into a solid inner core (1200km thick) and a liquid outer core (2100km thick). Temperature of core is between 3000-5000 degrees Celsius
What is the mantle
Mostly solid rock but flows under high temperatures and pressure. 2900km thick. Divided into upper mantle and lower mantle. Upper mantle is a layer of solid rock and asthenosphere where rocks are close to melting point and easily deformed. Temperature between 800-3000 degrees Celsius
What is the crust
Outermost layer on which we live. Two types of crusts, oceanic and continental. Oceanic crust found beneath oceans, very thin at 5-8km thick. Continental crust found beneath continents, very thick around 30-70km. Oceanic crusts are more dense than continental crusts.
Oceanic crust made up of basalt
Continental crust made up of granite
Why do tectonic plates move (convection currents)
Tectonic plates move due to convection currents within the mantle. The core heats material in the mantle. This causes convection currents in the mantle material. Mantle expands, rises and spreads out beneath the plates. Plates are dragged along and move away from each other. Subsequently, the mantle cools and sinks. The sinking mantel material heats up again as it nears the core and the whole process repeats.
Why do tectonic plates move (slab-pull force)
Tectonic plates also move due to slab-pull force. This occurs when an oceanic plate subducts under a less dense plate and pulls the rest of the plate along.
Divergent plate boundaries (Oceanic-Oceanic)
Magma rises from the mantle at the zone of divergence to fill in the gap between the plates as they move apart. This cools and solidifies to form a ridge of new ocean floor called a mid-oceanic ridge. This process is called sea-floor spreading. At various points along the ridge, magma builds up above the ocean to form volcanic islands.
Examples of plates involved: North American and Eurasian plate
Features and phenomena: Mid-oceanic ridge, volcanoes, volcanic islands
Examples: Mid-Atlantic ridge, Askja volcano, Iceland
Divergent plate boundaries (Continental-Continental)
Fractures form at the divergent plate boundary. The land between the continental plates sink forming a linear depression called a rift valley.
Examples of plates involved: Somalian boundary of African plate and Nubian boundary of African plate
Features and phenomena: Rift valley and block mountains, volcanoes, earthquakes
Examples: Great East African Rift Valley, Mt. Kilimanjaro, Tanzania
Convergent Plate boundaries (Oceanic-Oceanic)
Two oceanic plates converge, the denser plate will subduct beneath the other plate. A deep ocean trench is formed at the subduction zone. The mantle above the subducted plate melts forming magma. The magma rises through faults in the crust forming undersea volcanoes. Eventually, the volcanoes may rise above sea level to form volcanic islands. Earthquakes may also occur at the boundary between the plates
Examples of plates involved: Pacific plate and Philippine plate
Features and phenomena: Oceanic trench, Island arcs, volcanoes, earthquakes
Examples: Marianas Trench, Marianas Islands
Convergent plate boundaries (Continental-Continental)
Plates made largely of continental crust may collide with other plates made large of continental crust. However, both plates have similar densities and hence, resist subduction. Instead, the plates break, slide along fractures in the crust and fold, forming fold mountains and causing earthquakes.
Examples of plates involved: Indian plate and Eurasian plate
Features and phenomena: Fold mountains, earthquakes
Examples: Himalayan mountains
Convergent plate boundaries (Oceanic-Continental)
The denser oceanic plate subducts beneath the continental plate. A deep ocean trench is formed at the subduction zone. The mantle above the subducted plate melts forming magma. The magma rises through the crust forming volcanoes. The crust of the continental plate is compressed and folds upwards or sideways. This forms fold mountains. Earthquakes may also occur at the boundary between the plates.
Example of plates involved: Nazca plate and South American plate
Features and phenomena: Oceanic trench, volcanoes, earthquakes, fold mountains
Examples: Atacama Trench, Andes Mountains
Transform plate boundaries (Continental-Continental or Oceanic-Oceanic)
Plates slide past each other. As they do so, tremendous stress builds up which is eventually released, often as a violent earthquake.
Example of plates involved: Pacific plate and North American plate
Features and phenomena: Earthquakes
Examples: Earthquakes along the San Andreas Fault, California, USA
