Plate Tectonics Flashcards
the edges where two plates meet. Most geologic activities, including volcanoes,
earthquakes, and mountain building, take place at plate boundaries.
Plate boundaries
the two plates move away from each other.
Divergent plate boundary
the two plates move toward each other.
Convergent plate boundary
the two plates slip past each other.
Transform plate boundary
Divergent (constructive) plate boundary
A divergent plate boundary is located between two plates that are moving apart. In this type of plate boundary, the underlying magma rises to the surface (then called lava) filling the gap between the separating plates and forming a chain of underwater mountains called mid-ocean ridges. The pulling apart of plates and the insertion of lava through the gaps may result in the formation of volcanic islands.
Most of the divergent boundaries are found on the seafloor where they form ocean ridges. An example is the Mid-Atlantic ridge.
The seafloor spreading begins in the central rift. The process of seafloor spreading along divergent boundary may cause an ocean basin to grow wider, which takes over millions of years. Some divergent boundaries can form on continents. A long and narrow depression called a rift valley when the continental crust begins to stretch and separate. This rifting may eventually lead to the formation of a new ocean basin. An example of this is the East African rift.
Since the crust along divergent boundaries are stretched, normal faults are associated with these areas. Earthquakes with shallow focus (0-70 km deep) and a magnitude of less than 7 occur in these regions.
Convergent(destructive) plate boundary
At a convergent plate boundary, two tectonic plates move toward each other. These two plates are of different densities. When they converge, the denser plate sinks in to the mantle beneath the less dense plate. This sinking process is called subduction.
an oceanic plate beneath a continental plate causes earthquakes and forms a line of
volcanoes known as a continental arc.
Subduction
Types of Convergent Boundary
When a continental crust collides with an oceanic crust, the oceanic
plate goes beneath the continental plate because oceanic plate is denser.
Oceanic – Continental boundary
Types of Convergent Boundary
where one oceanic plate subducted under another oceanic plate
Oceanic –oceanic boundary
Types of Convergent Boundary
where a continental plate collides with a second continental plate
Continental –continental boundary
Transform plate boundary
At a transform plate boundary, two plates slide horizontally past each other as they move in opposite directions. They could happen in both oceans and continents. California’s San Andreas Fault is an example of this type.
At transform boundaries, the two tectonic plates grind past each other in a horizontal direction. This movement results in a crack or fracture in the Earth’s crust called fault. Thus, transform boundaries are responsible for earthquakes.
Processes and Landforms along Plate Boundaries
Convergent Boundaries
a boundary where neither of the plates are subducted
because the continental rock is too light to be carried very far into the dense mantle.
Continent – Continent Convergent Zone
the process when an oceanic tectonic plate slides under a continental plate or
another oceanic plate. The plates crumple upon crashing into each other exposing deep seated
granite and gneisses.
Subduction
The continental crust may also be cracked in pieces and shoved aside. As a result, the
continental crust folds upward creating a chain of ??
folded mountains or mountain ranges.
The Himalayas were formed in this way as India crashed into Eurasia around 50 million years ago. Again, the process in known as ??
The upfold is the anticline while the downfold is the syncline. This is what happened to rocks when they are compressed.
folding.
