Lesson 3

1. Composition of Magma

  • Magma Composition:

    • Composed mainly of silicate minerals.

    • Contains gases (volatiles), crystals, and liquid rock.

2. Formation of Magma

  • Formation Process:

    • Magma forms through partial melting deep in the crust or the upper mantle.

  • Circumstances for Magma Formation:

    1. Decrease in pressure.

    2. Addition of volatiles to hot rocks.

    3. Transfer of heat from rising magma in the mantle to the crust.

3. Partial Melting

  • Partial Melting Explanation:

    • Occurs when only a portion of a solid rock melts as different minerals have different melting points.

    • Melting point is influenced by pressure; higher pressure increases melting points.

4. Mechanisms of Rock Melting

  • Main Mechanisms:

    1. Decompression Melting:

    • Takes place when rock is held at constant temperature but pressure is reduced.

    1. Flux Melting:

    • Occurs when water or carbon dioxide is added to a rock nearing its melting point, lowering the melting temperature.

5. Post-Formation of Magma

  • Magma Movement:

    1. Intrusion:

    • Magma moves upward into a volcano without erupting (Plutonism).

    • Plutonites: Igneous rock formations formed when magma solidifies below the Earth's crust.

    1. Extrusion:

    • An eruption of magmatic materials, leading to land formation on the surface (Volcanism).

  • Volcanism Definition:

    • All geological activities related to the flow and transportation of igneous material from the Earth's interior to the surface.

    • Volcanites: Rock formations created by the crystallization of molten lava on the surface.

6. Magma Chamber Dynamics

  • Magma Chamber:

    • A reservoir where magma occupies within the lithosphere; deeper chambers generally lead to more explosive eruptions.

7. Rising of Magma

  • Factors Influencing Magma Rise:

    • Density Contrast: Magma with a greater density difference compared to surrounding rock rises faster.

    • Magma may stop rising if its density equals the surrounding rock, leading to accumulation and slow solidification.

8.1 Viscosity of Magma

  • Viscosity Explanation:

    • Magmas of low viscosity flow more easily than those with high viscosity.

  • Controlling Factors:

    • Temperature, silica content, and volatile content directly affect viscosity.

9. Effects on Viscosity

  • Factors Influencing Viscosity:

    • Increased temperature leads to decreased viscosity.

    • Increased silica content (SiO2SiO_2) leads to increased viscosity.

    • Addition of water (H2OH_2O) leads to decreased viscosity.