Understanding Magma

Introduction to Magma

• Definition: Super hot mixture of molten and semi-molten rocks beneath the Earth's surface.
• Purpose of the Lecture: To explain what magma is, its types, how it's formed, and the difference between magma and lava.

Composition of Magma

• Magma consists of:
  • Inorganic components (minerals and rocks)
  • Dissolved gases
  • Melt (hot liquid base)
• Composition varies based on magma type.

Types of Magma

1. Basaltic Magma

   • Silica concentration: 45-55 weight %
   • High in: Iron, magnesium, calcium
   • Low in: Potassium, sodium
   • Characteristics: Lowest gas content, lowest viscosity, highest temperatures.

2. Andesitic Magma

   • Silica concentration: 55-65 weight %
   • Moderate amounts of: Iron, magnesium, calcium, potassium, sodium, and gases.
   • Characteristics: Lower temperature and higher viscosity than basaltic magma.

3. Rhyolitic Magma

   • Silica concentration: 65-75 weight %
   • Low in: Iron, magnesium, calcium
   • High in: Potassium, sodium, and gas content.
   • Characteristics: Lowest temperature and highest viscosity of the three types.

Viscosity and Fluidity of Magma

• Viscosity: A property that describes a fluid's resistance to flow.
• Magma remains fluid due to high temperatures and pressures in the Earth's lower crust and upper mantle.

Origin of Magma

• Location: Deep beneath the Earth's surface in the lower crust and upper mantle.
• Conditions: High pressures and temperatures contribute to magma's fluid state.

Mechanisms of Magma Formation

1. Partial Melting

   • Heat-induced melting of rocks in the upper mantle/crust.
   • Only some minerals melt due to varying melting temperatures.
   • Upward movement of magma can melt surrounding rocks with lower melting points.

2. Decompression Melting

   • Requires a reduction in pressure for melting to occur without temperature increase.
   • Rocks can move upward to lower pressure zones (e.g., rift zones).

3. Flux-Induced Melting

   • Presence of fluids (like water) lowers the melting temperature of rocks near their melting point.
   • Initiates partial melting process once melting begins.

Phase Diagrams

• Definition: Graphical representation of a material's physical state based on temperature and pressure.
• Example: Shows how temperature and pressure affect the state (solid, liquid, gas) of a material.

Difference Between Magma and Lava

• Magma that breaks through the Earth's surface (during a volcanic eruption) is referred to as lava.
• Once lava cools, it forms volcanic rocks and volcanic glass.

Conclusion

• Summary: Magma formation mechanisms include partial melting, decompression melting, and flux-induced melting.
• Encouragement to check out further resources on volcanic rocks and diamond transport by magma.