Geog - tectonic topic 1

How do convection currents lead to tectonic plate movement?

The heat from the earth’s core causes the mantle material to become less dense and rise towards the surface. The rising mantle material then spreads beneath the plates and drag them apart, causing divergent plate movement. The mantle material loses heat snd sinks towards the core. Convergent plate movement occurs where the convection currents collide. The mantle material gets heated up again and the process repeats

How does slab-pull force contribute to tectonic plate movement?

When two plates converge, the denser oceanic crust is pulled down by gravity as it subducts beneath the less dense crust. The denser oceanic crust sinks deeper into the mantle under its own weight, pulling the rest of the plate with it, contributing to further convergence.

What is seafloor spreading?

Seafloor spreading is a process that occurs at mid-oceanic ridges where two oceanic plates are moving away from each other. Magma from deep within the earth then rises through mid-ocean ridges, cools and solidifies, constructing new oceanic crust.

How does the ages of rocks support the plate tectonic theory?

At the crest of the mid-ocean ridge is a spreading centre, where magma rising from the mantle cools and solidifies, forming new seafloor. The continuous formation of new seafloor at the crest of the ridge pushes the older seafloor further from the crest of the ridge. The ages of the rocks nearer to the crest of the ridge are younger than the rocks further away.

Why does magnetic stripping occur?

Magnetic stripping occurs due to the normal and reverse polarity of earth’s magnetic fields, which leads to stripes of rock on the seafloor with alternating magnetic properties

Define normal polarity.

When the magnetic north is pointing roughly towards the geographic north

Define reverse polarity.

When the magnetic north is pointing roughly towards the geographic south

What is magnetic stripping?

Magnetic stripping is the pattern where there are strips of normal polarity rock alternating alongside strips of reversed polarity rock

What are basaltic rocks, and how do they provide evidence to support plate tectonic theory?

Basaltic rocks contain magnetic minerals. Hence, when the iron-rich lava erupts from the centre of the mid-ocean ridge, cools, and solidifies, the magnetic field of the minerals in the lava will point towards Earth’s magnetic North, recording evidence of Earth’s polarity at that time.

What happens at divergent plate boundaries?

Two tectonic plates are moving away from each other, resulting in mid-oceanic ridges, volcanoes, rift systems and earthquakes

What happens at the oceanic-oceanic divergent plate boundary?

When two oceanic plates move apart, the decrease in overlying pressure causes parts of the underlying mantle to melt, forming magma. Magma rises through weak areas in the crust to the Earth’s surface, and fills gaps caused by the spreading plates. The lava cools and solidifies to form basaltic rocks, which make up new oceanic crust. A mid-oceanic ridge then forms at this plate boundary. At the centre of the ridge is a deep rift valley with steep sides. This linear depression marks the most active zone where magma rises to the surface and new basaltic rocks are formed. Magma from the asthenosphere rises to reach the Earth’s surface, filling the gaps caused by the spreading plates along the central rift valley, forming submarine volcanoes. After many eruptions, the volcanoes may break the surface of the ocean to form islands.

How do earthquakes form at divergent plate boundaries?

The stress and tension released when plates move causes earthquakes.

What happens at continental-continental divergent plate boundaries?

When two continental plates move apart, the rock fractures and forms parallel faults. The rock between these faults collapses to form a deep rift valley with steep sides. These rift valleys are areas where earthquakes occur as stress and tension are released when plates move. As the plates move apart, the decrease in overlying pressure causes parts of the underlying mantle to melt, forming magma. Magma rises through weak areas in the crust to the Earth’s surface, forming volcanoes.

What happens at convergent plate boundaries?

Two plates are moving towards each other, resulting in fold mountains, volcanoes, oceanic trenches and earthquakes.

Define subduction.

Subduction is the process where two oceanic plates collide, and the denser plate sinks beneath the less dense plate.

What happens at the oceanic-oceanic convergent plate boundaries?

When two oceanic plates move towards each other, the denser oceanic crust subducts beneath the less dense oceanic crust. This forms a deep depression known as an oceanic trench in the subduction zone. As the subducting plate sinks into the mantle, the high pressure forces water out of its oceanic crust. Water lowers the melting point of the overlying mantle, causing it to melt, forming magma. Magma from the asthenosphere rises to reach the Earth’s surface, forming a crescent chain of volcanoes.

How do earthquakes occur at the convergent plate boundary?

Friction along the subducting oceanic plate causes earthquakes to occur.

What happens at the continental - continental convergent plate boundary?

When two continental plates collide, subduction foes not take place as continental plates are too buoyant to subduct. Instead, the enormous pressure causes the rocks on the plates to be uplifted and buckled to form fold mountains. Earthquakes are very common here and can be violent due to the enormous build-up of pressure. Here, magma does not rise to the surface, hence no volcanoes are formed. 

What happens at the oceanic-continental convergent plate boundary?

The denser oceanic plate subducts beneath the continental plate. This forms an oceanic trench in the subduction zone. As the subducting plate sinks into the mantle, the high pressure forces water out of its oceanic crust. Water lowers the melting point of the overlying mantle, causing it to melt, forming magma. Magma rises through weak areas in the crust to the Earth’s surface, forming volcanoes on the continental plate. Friction along the subducting oceanic plate causes earthquakes to occur. The enormous pressure at this plate boundary causes the rocks on the continental plate to be uplifted and buckled, leading to the formation of fold mountains.

What happens at a transform plate boundary?

At transform boundaries, two plates slides past each other, and no crust is created or destroyed. However, the stress caused by the plate movement produces a fault. Earthquakes occur here as one block of rock suddenly slips past another. However, as magma does not rise to the Earth’s surface, there are no volcanoes at transform plate boundaries.