Igneous and Metamorphic Petrology Quiz

Course Information

• Course number: Geol. 402
• Course title: Igneous and Metamorphic Petrology
• Instructor: Dr. Adnan Khan, Assistant Professor, Department of Geology
• Recommended textbook: Petrology: Igneous, Sedimentary, and Metamorphic by Harvey Blatt and Robert J. Tracy

Petrology Overview

• Petrology is the study of rocks, encompassing igneous, sedimentary, and metamorphic rocks.
• This includes their genetic distribution, classification, and formation processes.

Igneous Petrology

• The scientific study of igneous rocks
• Two key components:
  • Petrogenesis: The processes of rock formation
  • Petrography: The description of rocks, including their classification

Nature of Magma

• Magma is a naturally occurring, hot fluid within the Earth.
• It's a molten substance at high temperatures.
• It is called magma until it erupts on the surface, at which point it is called lava.

Magma Composition

• Magma is chemically complex, containing molecular building blocks for minerals.
• Mostly composed of silicates, along with oxides and sulfides of metals.
• Always contains water and other gases held in solution by pressure, with heat as the principle factor.

Magma Generation

• Magma forms when temperatures at depth in the Earth exceed the melting temperatures of rocks.
• This can occur through three primary processes, or a combination of them.

Sources of Heat for Melting Rocks

• Solar radiation: Minor heat source (50,000 times less potent than other sources)
• Core movement: Significantly contributes to melting by heat transfer
• Radioactive decay (U, U, Th, K, and Rb): A substantial heat source, contributing up to 50-100% of the Earth's internal heat.

Factors Generating Magma

• Increase of heat: Raises melting temperature, causing rocks to melt and form magma.
• Decrease of pressure: Causes phase change in rock, generating magma.

Processes Generating Magma

• Radiation: Emission of EM energy from hot bodies into surrounding bodies. Increasingly important at very high temperatures (>1200°C).
• Conduction: Transfer of kinetic energy via atomic vibrations. More efficient if the surface area of the enclosure is larger.
• Convection: Movement of material with contrasting temperatures, due to different densities. Crucial in magma generation.

Magma Evolution

• Differentiation: Separation of substances with different chemical compositions within a magma body.
• Partial Melting: Different minerals melt at different temperatures, resulting in magmas with different compositions depending on what minerals are present and the conditions.
• Assimilation: Incorporation of surrounding country rock into a magma body, altering its chemical composition.
• Mixing of Magmas: The mixing of two or more magmas with different compositions, which can create a new, intermediate composition.

Bowen's Reaction Series (diagram illustrated)

• This series describes the order in which minerals crystallize from a cooling magma.

Global Heat Flow Models (diagram illustrated)

• Global heat flow patterns are shown with warmer areas over spreading ridges and colder areas over cratons.