geo - techtonic plates

whats the difference between oceanic and continental plates

Oceanic Plates:

Made primarily of dense basaltic rock.

Thinner (about 5–10 km thick) but denser than continental plates.

Continental Plates:

Made of less dense granitic rock.

Thicker (up to 70 km thick) but less dense than oceanic plates.

what is the convection current theory

• Heat from the core heats the mantle, causing hot, less-dense material to rise.

• As it reaches the upper mantle, it spreads out, cools and becomes denser.

• The cooler, denser material sinks back down towards the core.

• This creates a circular movement called a convection current.

Impact on plate movement:

• Convection currents act like a conveyor belt, moving tectonic plates above them.

what is the dragging theory

Occurs at subduction zones, where an older, denser oceanic plate sinks

into the mantle under its own weight.

▪ As the plate sinks, it "pulls" the rest of the plate along with it.

▪ This is considered the strongest driving force behind plate movement.

what are the three plate boundaries

convergent (destructive)

constructive (divergent)

conservative (transform)

what is subduction

Subduction is a geological process where one of Earth's tectonic plates slides beneath another plate and sinks into the mantle.

what is the process at a convergent (divergent) boundary with two oceanic plates

The two plates collide as they move towards each other

• One of the plates bends and sinks underneath the other plate, The plate that sinks is denser because it is older and had more time to cool down

o As the plate bends and then sinks, rubbing against the other plate, earthquakes take place as the rock layers are not flexible, accumulating stress

• The plate that sinks in the asthenosphere breaks and melts, turning into magma

• The magma rises through the crust as it is less dense than the surrounding rock

o As magma moves through the crust, it picks up other rocks and becomes viscous(thick)

• The magma eventually reaches the surface and causes volcanic eruptions. These are violent eruptions because the magma is viscous (thick)

what are the land forms at an oceanic-oceanic convergent boundary

ocean trenches and volcanic island arcs

what is an ocean trench

a long and deep depression at the bottom of the ocean

located where the two plates meet, marking the plate boundary

what are volcanic island arcs

a long line of volcanoes

paralell to the plate boundary

located on the plate that doesnt sink

what is the case study for oceanic oceanic convergent plate boundaries

mariana islands and mariana trench

collision between the pacific and phillipine plate, the Pacific subducts underneath

• mariana trench is 11,000m deep

• mariana islands are 200km west of the trench

how did the mariana trench form?

1. The older Pacific Plate (PP) moves westward towards the less dense Philippine Plate (PHIP)

• 2. The PP subducts under the Philippine Plate.

• 3. The PP bends as it goes underneath, creating a large, deep V-shape at the point it descends.

• 4. Over time, an accretionary wedge builds up against the PHIP.

how did the mariana volcanic island arc form?

1. As the subducting Pacific Plate moves deeper, it encounters higher temperatures.

2. The mantle partially melts, creating magma.

3. The magma is less dense than the surrounding rock, causing it to rise toward the surface.

4. As the magma rises, it collects in magma chambers beneath the seafloor.

5. When enough pressure builds up, volcanic eruptions occur, creating underwater volcanoes.

6. Over time, repeated eruptions and the accumulation of volcanic material form volcanic

islands.

7. These islands emerge above sea level, forming a curved chain of volcanic islands parallel to

the trench.

at an oceanic- continental convergent (destructive) boundary what is the process

• The two plates collide as they move towards each other

• The oceanic plate bends and sinks underneath the continental plate

o The oceanic plate sinks because is denser (3 g/cm3 compared to 2.6 g/cm3)

o As the oceanic plate bends and then sinks, rubbing against the continental plate,

earthquakes take place as the rock layers are not flexible, accumulating stress

• The oceanic plate that sinks in the asthenosphere breaks and melts, turning into magma

• The magma rises through the crust

o As magma moves through the crust, it picks up other rocks and becomes viscous

(thick)

• The magma eventually reaches the surface and causes volcanic eruptions

o These are violent eruptions because the magma is viscous (thick)

what is the case study for fold mountain building

the andes mountains collision of the nazca and south american plates

how was the andes mountains formed? (fold mountain building)

Compression and Convergence: The ongoing collision between the Nazca and South

American plates causes thrust faulting, where the crust is compressed, thickened, and

pushed upward.

• Crustal Shortening and Thickening: The continent is compressed, causing crustal shortening

and thickening, which results in the vertical uplift of the Andes.

• Volcanic Activity: Volcanic eruptions build up the mountain range, contributing to both height

and volume.

• Isostatic Rebound: As mass is removed (e.g., erosion), the Earth's crust can "rebound" or rise

more easily, adding to the uplift.

• Active Uplift: The Andes continue to rise as the subduction process remains active.

at oceanic ocean divergent boundaries what is the landforms

seafloor spreading

what is the process of seafloor spreading

The two plates move apart

o The plates move apart because of the convection currents

• As the plates move apart, magma rises to the surface through the gap between the two plates

• Magma cools down and hardens along the plate boundary, creating new crust

o These type of plate boundaries are also known as constructive as new crust forms

here

• Meanwhile, more magma ascends, putting pressure on the boundary and forcing the plates to

move apart

• The new crust is oceanic and the process is called sea-floor spreading because more and

more oceanic crust is formed and the seas or oceans extend as the plates move apart

at continental constructive (divergent) plate boundaries what is the landform

rift valleys

how are rift valleys formed

1. Plates move apart → tension causes the crust to stretch and crack.

2. Faults form → large cracks develop in the crust.

3. The block of land between the faults drops down due to gravity.

4. This creates a long, steep-sided depression called a rift valley.

5. Magma rises through the cracks and may form new crust and volcanoes.

at oceanic plate constructive boundaries what landform is formed

mid ocean ridge

how are mid ocean ridges formed

1. Two oceanic plates move apart.

2. Magma rises from the mantle to fill the gap.

3. The magma cools and solidifies, forming new oceanic crust.

4. Continued magma rising and plate movement causes the new crust to build up into a long underwater mountain range called a mid-ocean ridge.

what is an example of a rift valley?

the Great rift valley in East Africa which is 6000km long

what is an example of a mid-ocean ridge

mid atlantic ridge separating the african and SA plates, spreading at 2.5cm/year