Geo11 - Rock Cycle and Igneous Rocks

• Rocks


  Naturally-occurring aggregate of two or more minerals, may or may not contain mineraloids, natural glass, organic matter, and pre-existing rocks or sediment
• Types of rocks vary based on composition, color, textures, structures, etc.
• Petrology


  The study of rocks; its genesis, composition, distribution and structure of rocks
• Petrography


  Branch of petrology that deals with the description and classification of rocks; their constituent minerals and texture
• Rock Cycle

  1. Explains the processes underwent by rocks on and under the earth's surface

  2. Allows us to view many of the interrelationships among different parts of the earth's system
• Classifications of Rocks


  • Igneous Rocks
  • Sedimentary Rocks
  • Metamorphic Rocks
• Magma


  Molten or partially molten rock composed of varying amounts of liquid (silicates, sometimes carbonate, sulfides, or oxides and ions of Al, Fe, Ca, Na, K, Mg), solids (mineral or rock fragments), and dissolved gas or volatiles (H2O, CO2, SO2)
• Classification of Magma


  • Silica Content: Felsic, Intermediate, Mafic, Ultramafic
  • Viscosity
  • Density
  • Temperature
• Common Types of Magma

  • Basaltic Magma
  • Granitic/Rhyolitic Magma
• Sources of Heat


  • Original heat of the earth at the time of formation
  • Radioactive decay of elements
  • Heat transfer from nearby magmatic body
  • Hot mantle plumes
  • Frictional heat
• Generation of Magma


  Melting in the upper mantle/lower crust due to heat, pressure, or addition of volatiles
• Locations of Magma Generation

  • Mid-oceanic ridges
  • Subduction zones
  • Hot spots
• Processes of Magmatic Differentiation

  • Fractional Differentiation
  • Partial Melting
  • Country Rock Assimilation
  • Magma Mixing
• Igneous Rocks


  Rocks formed from solidification of molten material called magma (intrusive) or lava which flows out from the depths (extrusive)
• Bowen's Reaction Series


  As magma cools, certain minerals crystallize first at relatively high temperature, in successively lower temperature, other minerals begins to crystallize
• Two Kinds of Igneous Rocks

  • Intrusives (Plutonic)
  • Extrusives (Volcanic)
• Types of Intrusive Igneous Activity

  • Batholith
  • Stock
  • Dike
  • Sill
  • Laccolith
  • Volcanic Neck
• Crystalline Textures of Igneous Rocks

  • Aphanitic
  • Phaneritic
  • Porphyritic
  • Pegmatitic
• Noncrystalline Textures of Igneous Rocks

  • Vesicular
  • Glassy
  • Pyroclastic
• Texture of Volcanic Ejecta

  • Ash
  • Lapilli
  • Block/Bomb
• Classification of Igneous Rocks by Crystal Shape

  • Euhedral
  • Subhedral
  • Anhedral
• Classification of Igneous Rocks by Mineral Composition

  • Presence/absence of quartz
  • Composition of feldspar
  • Amount of ferromagnesian minerals
• Metallic Resources from Igneous Rocks

  • Gold, silver, platinum, copper
  • Chromite, nickel, PGM
• Igneous rocks


  Rocks formed from the solidification of magma (intrusive) or lava which flows out from depths (extrusive) and/or through volcanic eruptions
• Magma


  Hot (600-1200°C) partially molten rock beneath the surface of the earth, composed of liquid silicates, solid minerals/rock fragments, and dissolved gases
• Lava


  Magma that has reached the surface of the earth through a vent
• Components of magma


  • Liquid silicates
  • Solid minerals/rock fragments
  • Dissolved gases (water vapor, CO2, SO2, HCl, HF)
• Classification of magma based on silica content

  • Felsic/Silicic/Acidic (>63% SiO2)
  • Intermediate (52-63% SiO2)
  • Mafic/Basic (45-52% SiO2)
  • Ultramafic/Ultrabasic (<45% SiO2)
• Viscosity


  The property of substances to resist flow
• Factors affecting magma viscosity

  Higher temperature → lower viscosity

  Higher SiO2 content → higher viscosity

  More H2O → lower viscosity
• Properties of different magma types

  • Ultramafic - hottest, densest

  Felsic - least dense
• Formation of magma


  Melting of upper mantle and/or lower crust

  Aided by: 1) Increase in temperature, 2) Decrease in pressure, 3) Addition of volatiles
• Increase in temperature


  Enables rock melting by crossing the solid-liquid boundary
• Decrease in pressure


  Causes adiabatic or decompression melting, commonly seen in divergent zones
• Addition of volatiles


  Causes flux-induced melting, lowers melting temperature of rocks
• Magmatic differentiation


  Processes that change the chemical composition of magma, including fractional crystallization, partial melting, assimilation, and magma mixing
• Fractional crystallization


  Formation and removal of crystals from magma, leading to relative enrichment of remaining magma
• Fractional crystallization


  Ferromagnesian minerals form first and settle, leaving magma more silica-rich and felsic
• Partial melting


  Only certain parts of the rock melt, typically silica-rich minerals first, resulting in more felsic magma
• Partial Melting


  Only certain parts of the rock will melt. Rocks do not melt at a single temperature, but instead melt over a range of temperatures depending on their mineral composition