Convergent, Divergent, and Transform Boundaries

movement of magma in Upper Mantle found in Asthenosphere

what causes the movement of plates?

Theory of Plate Tectonics

states that the Earth's crust and upper mantle are broken into plates, which are huge rock slabs that move in different directions and at different rates over Earth's surfaces

continental rifting

splitting of a continent at a divergent plate boundary that create new ocean basins

mid-ocean ridge

an elevated area in the seafloor that form a mountain chain; a divergent plate boundary.

convection cells

areas in the mantle where rising of hot magma near the core towards the surface, while cooler magma sinks, setting up a current that causes plate activities

seafloor spreading

the continuous process occuring in mid-oceanic ridges in which both sides of the ridge move apart, causing decompression melting and widening (i.e spreading) of seafloor

the seafloor spreads apart along both sides of mid-oceanic ridgr as new crust is added. as a result, ocean floors carry the continents along with them

plate boundaries are compared to conveyor belts because of what reason

rift valley

a deep valley that forms where two continental plates move apart

1. Hot mantle rock rises
2. Melt forms under lithosphere
3. Magma rises into magma chamber in crust and is injected as dikes, forming a new crust
4. Lava erupts onto ocean floor adding to crust
5. Plates diverge / move apart, cool, and thicken

mid-ocean ridge process

constructive margins

the other term for divergent boundaries

mid-oceanic ridges

these are formed when earth's crust are spreading apart

seafloor spreading

what occurs along mid-oceanic ridges?

mid-ocean ridges

where do most divergent boundaries lie in?

molten magma

where do new materials found in crust came from when plates are separated?

2 to 20 cm per year

average spread rate of mid-oceanic ridges

2 - 2.5 cm per year

average spread rate of Mid-Atlantic ocean ridge

subduction

a process by which one plate slides beneath into mantle due to differences in lithospheric density

subduction zone

convergent boundary area wherein 2 lithospheric plates come together and one sinks beneath other

trench

results in seafloor depression produced by subduction

arcs

long, sublinear chains of volcanoes following the orientation of ocean trenches

oceanic-oceanic, oceanic-continental, continental-continental

types of convergent boundaries

oceanic-oceanic convergence

happens where 2 oceanic plates push against one another, causing the colder, denser, older plate to buckle up and sink into the mantle

oceanic-continental convergence

happens when oceanic lithosphere subducts below the continental lithosphere

continental-continental convergence

happens where 2 continental plates collide and push up. subduction in thus type of convergence is very minimal and has no trench

oceanic crust

everytime they diverge, a new seafloor is formed

the nearer the rock is to the ridge, the younger it is.

relationship of ridges and the age of rocks in the oceanic ridge

constructive margins

where are convection cells located?

30 degrees

subduction angle from the Earth's surface

it descends in the subduction zone

why is the lithosphere always destroyed ay convergent boundaries?

transform boundaries

a boundary where two plates slide past one another without creating or destroying lithosphere

San Andreas Fault

a major geological fault in California formed by a sliding transform boundary.

North American Plate and Pacific Plate

major plate boundaries present in San Andreas Fault

Juan de Fuca Plate

a minor plate near the San Andreas Fault

North American Plate goes south, Pacific Plate goes north

what is the direction of the major plates present in San Andreas Fault?

hanging wall

the block of rock that lies above an inclined fault or an ore body.

footwall

the rock that lies below the fault

normal fault

a fault in which the hanging wall moves down relative to the footwall; caused by tension stress

reverse fault

a type of fault where the hanging wall slides upward; caused by compression in the crust

strike-slip fault

the rocks on either side of the fault slip past each other sideways, with little up or down motion; formed due to shear stress

compression stress

stress that squeezes rock until it folds or breaks

shear stress

stress that pushes rocks in parallel but opposite directions

tension stress

pulls on the crust and stretches rocks and make it thinner; occurs where two plate are moving apart