Igneous rocks and plate tectonics

Summary

This video explains how magma is created and how it forms igneous rocks with varying compositions. Magma originates from heat within Earth's interior, melting the lithosphere and being forced to the surface, often resulting in volcanic eruptions. The composition of magma can be mafic (rich in iron and magnesium) or felsic (rich in silicon), depending on its source. Magma forms at mid-ocean ridges, volcanic arcs, and hotspots, each creating different types of rocks based on the composition of the surrounding materials. Examples of locations where magma forms include mid-ocean ridges, island arcs, and hotspots like Hawaii.

Takeaways

• 😀 Magma is created when heat from the Earth's interior melts the upper lithosphere, leading to the formation of volcanoes.
• 😀 Initially, magma is rich in iron and magnesium, but as it travels to the surface and cools, it forms various types of igneous rocks.
• 😀 Igneous rocks can be classified into two categories: mafic (rich in iron and magnesium) and felsic (rich in silicon).
• 😀 Magma can form in three primary areas: mid-ocean ridges, volcanic arcs, and hotspots.
• 😀 The majority of Earth's magma forms at plate boundaries, especially at mid-ocean ridges and subduction zones.
• 😀 Mid-ocean ridges involve oceanic plates being pulled apart, leading to partial melting and the formation of basaltic rocks.
• 😀 Oceanic magma is typically mafic due to rapid rise through thin oceanic crust, replenishing magma chambers, and low contamination from crust.
• 😀 Volcanic arcs form above subduction zones, and the resulting magma can range from intermediate to felsic, depending on the environment.
• 😀 Island arcs are formed when an oceanic plate is subducted under another oceanic plate, creating intermediate mafic magma.
• 😀 Continental arcs are formed when an oceanic plate is subducted under a continental plate, resulting in intermediate felsic magma due to contamination from the continental crust.
• 😀 Hotspots are caused by thermal upwelling from deep in the Earth's core, creating magma that can be mafic (under oceanic crust) or felsic (under continental crust).

Q & A

How is magma created?

Magma is created when heat from the Earth's interior melts the upper lithosphere, causing solid rock to become molten.

What are the main components of magma when it is initially created?

Initially, magma is rich in iron and magnesium but low in silicon, giving it a mafic composition.

Why does magma cool as it moves toward the surface?

Magma cools as it rises towards the surface because the surrounding environment is cooler than the molten rock, leading to the formation of solid igneous rocks.

What are igneous rocks, and how are they formed?

Igneous rocks are formed when magma cools and solidifies. Their composition depends on the type of magma and the cooling process.

What are the three primary areas where magma is created?

Magma is created at mid-ocean ridges, volcanic arcs, and hotspots.

How do mid-ocean ridges contribute to magma formation?

At mid-ocean ridges, oceanic plates are being pulled apart, allowing heat from the mantle to melt the rock below, forming magma that rises through the crust.

What is partial melting, and how does it affect magma composition?

Partial melting is a process where only a fraction of the material in the mantle melts. This creates magma that is less dense than the solid rock, allowing it to travel up toward the surface.

Why is oceanic magma typically more mafic than continental magma?

Oceanic magma is more mafic because the magma chambers are continuously replenished with heat, the oceanic crust is thin, and there is minimal contamination from surrounding materials.

What makes volcanic arcs different from mid-ocean ridges in terms of magma composition?

Volcanic arcs, formed at subduction zones, produce magma with more intermediate to felsic compositions compared to mid-ocean ridges, which produce more mafic magma.

How do hotspots create magma, and what is unique about them?

Hotspots are created by thermal upwelling from deep within the mantle. The rising mantle plumes melt the overlying lithosphere, producing magma. Hotspots are unique because they occur randomly, not at plate boundaries.