Igneous Petrology - Geol. 402 Quiz

Course Information

• Course Number: Geol. 402
• Course Title: Igneous and Metamorphic Petrology
• Instructor: Dr. Adnan Khan
• Assistant Professor
• Department of Geology
• University of Karachi
• Recommended Textbook: Petrology: Igneous, Sedimentary, and Metamorphic by Harvey Blatt and Robert J. Tracy
• Selected chapters are available on Physics Photoshop

Petrology Branches

• Petrology is the study of rocks
• Genetic Distribution of the branches
  • Igneous
  • Sedimentary
  • Metamorphic

Igneous Petrology

• Scientific study of igneous rocks
• Includes two main areas:
  • Petrogenesis: The processes of rock formation
  • Petrography: Describing and classifying rocks

Petrography

• Rocks' description and classification

Petrogenesis

• Conditions under which rocks were formed

Igneous Rocks

• Derived from the Latin word "ignis" meaning fire or magmatic rock
• Formed by the cooling and solidification of magma or lava

Magma

• Term first introduced into geologic literature in 1825 by Scope
• Described as a “compound liquid” consisting of solid particles suspended in a liquid, resembling mud
• Natural fluid occurring in the Earth
• Generally very hot and found as a molten substance at high temperature
• Called magma until it reaches the surface, where it is called lava

Magma Composition

• Chemically complex, containing the molecular building blocks of minerals
• Largely consists of a solution of silicates with some oxides/sulfides of metals
• Always contains water and other gases held in solution by pressure; heat is the main factor in its liquidity

Magma Generation

• Magma is produced when the temperature at depth in the Earth exceeds the melting temperature of rocks
• Can be produced by three processes or a combination of them

Melting Temperatures of Rocks

• A table provides melting temperatures of granite and basalt at various depths within Earth

Processes of Magma Generation/Melting

• Radiation: EM energy emission from the surface of a hot body into cooler surroundings. Increasingly important at 1200°C
• Conduction: transfer of kinetic energy by atomic vibrations. Conducts faster if surface area is larger. Cannot occur in a vacuum.
• Convection: movement of materials with contrasting temperatures; density differences in gravitational fields

Sources of Heat for Melting Rocks

• Solar Radiation: 50,000x greater than other energy sources, but mainly affects the atmosphere and oceans. Causes changes in the solid earth through momentum transfer from the outer fluid envelope to the interior
• Core Movement: Exponential movement of heat caused by movement of material around the Earth's core

Radioactive Decay

• 238U, 235U, 232Th, 40K, and 87Rb have half-lives greater than 10⁹ years and thus continue to produce significant heat within the interior
• Can equal 50 to 100% of the Earth's total heat production

Core Formation

• Initial heating from short-lived radioisotopes and accretionary heat caused widespread interior melting (Magma Ocean)
• Additional heat was released when Fe sank toward the center and formed the core

Factors Generating Magma

• Increase in heat: causes rocks to reach a melting point where magma is formed
• Decrease in pressure: causes phase change, generating magma
• Change in composition/addition of water: decreases melting temperature of the rock

Crustal Geothermal Gradients

• Depictions of temperature and pressure gradients within the Earth's crust

Global Heat Flow Models

• Depictions of convection models and associated heat flow in the Earth's mantle

Bowen's Reaction Series

• Illustrates the sequence of mineral crystallization during magma cooling

Evolution in Magmas

• Differentiation
• Partial Melting
• Assimilation
• Mixing of Magmas

Magmatic Differentiation: Crystal Settling

• Describes how crystals settle in magma

Partial Melting

• Describes how hot, solid mantle rises from the base of the mantle, leading to the formation of a large head of a newly arrived mantle plume causing partial melting

Assimilation

• Illustrates how country rock melts into magma with a higher melting point

Mixing of Magmas

• Explains how silicic magma moving upward mixes with mafic magma moving rapidly, generating intermediate magma

Conclusions

• Magma generation on Earth is complex due to dynamic conditions.
• Magma generation processes in the Earth and Moon differ significantly.

Test your knowledge on Igneous and Metamorphic Petrology as covered in Geol. 402. This quiz focuses on key concepts such as petrogenesis, petrography, and the formation of igneous rocks. Perfect for students studying petrology in an advanced geology course.