New version page

ECU GEOL 1500 - Igneous Rocks - Fall 2014

This preview shows page 1-2-3-4 out of 12 pages.

View Full Document
View Full Document

End of preview. Want to read all 12 pages?

Upload your study docs or become a GradeBuddy member to access this document.

View Full Document
Unformatted text preview:

B. Other Important Constituents“Color-Texture Identification Key” <http://csmres.jmu.edu/geollab/Fichter/IgnRx/keyc-t.html>DISTRIBUTION OF INTRUSIVE IGNEOUS ROCKCLASSIFICATION OF PLUTONSPrincipal Types of Intrusions3 DISTINCT COMPOSITIONAL TYPES OF MAGMA (Review)Magma Types and Bowen’s Reaction SeriesIGNEOUS ROCKS A. The Rock Cycle is the cyclic movement of Earth materials, during the course of which rocks are created, destroyed, and altered by both internal and external processes. B. The processes in the Rock Cycle are driven by Heat Energy from Radioactivity and by Solar Energy and by Gravitational Energy.The Rock CycleI. Igneous Rocks are rocks that cool and crystallize from magma or molten rock either inside the Earth’s crust or on its surface.II. Magma is molten rock, together with suspended crystals and dissolved gases, that form when temperatures rise sufficiently high for melting to occur in the crust and upper mantle. Most magma is a mixture of liquid (melt) and crystals and a small percentage of dissolved gases. “Magma” <http://volcanoes.usgs.gov/about/pglossary/magma.php>MagmaIII. Lava is magma that is erupted at the Earth’s surface from a volcanic cone or fissure. “Lava” <http://volcanoes.usgs.gov/about/pglossary/lava.php>Lava FlowIV. Depth of Melting - 50-250 km (mostly in the Asthenosphere) Convergent Boundary Divergent Boundary A. Geothermal Gradient = Rate at which temperature increases with increasing depth below the Earth’s surface. The average Geothermal Gradient for the Earth is about: 2.5oC/100 meters or 25oC/kilometer. So, the depth at which melting occurs (50-250 km) is the depth at which the balance between temperature and pressure favors melting.V. Composition of Magma (and Igneous Rocks)“Magma” <http://volcanoes.usgs.gov/about/pglossary/magma.php> A. Silicate (SiO2) [~50 to 70%] Melt with Oxides of Al, Ca, Na, K, Fe, and Mg2Classification and Major Oxide Compounds of Igneous Rocks B. Other Important Constituents1. Gases - Water Vapor (H2O), Carbon Dioxide (CO2), Sulfur Dioxide (SO2), and other gases 2. Xenoliths (Rock Fragments broken off from surrounding country rock)VI. Properties of MagmaA. High Temperatures (700 to 1400oC)B. Relatively high Viscosity. Viscosity is the internal resistance to flow in liquids or gases so the more viscous a liquid is, the less fluid it is. Viscosity depends on Temperature and Composition.1. Higher the Temperature, the Lower the Viscosity (Inversely Proportional)2. Higher the Silica Content, the Higher the Viscosity (Directly Proportional)Classification and Flow Characteristics of Magma and LavaVII. Characteristic Feature of Igneous RocksA. They are composed of an interlocking mosaic of crystals of different silicate minerals.Note the Interlocking Mineral Crystals in this Granite3VIII. Classification of Igneous Rocks is Based on:A. Chemical and Mineral Composition 1. Felsic/Rhyolitic/Granitic = High Silica Content (65 to 70%); White, light gray, pink, red, or purple in colour); High Potassium (K), Sodium (Na), and Aluminum (Al) Content; Low Fe-Mg content.2. Intermediate/Andesitic = Intermed. Silica Content (~60%); Intermediate Fe-Mg Content; Medium-dark gray, dark green, purple in colour.3. Mafic/Basaltic = Low Silica Content (~50%); High Fe-Mg Content; Dark Gray to Black in Colour.4. Ultramafic = Very Low Silica Content (~40%); Very High Fe-Mg Content; Black in Colour, Green-Brown if Olivine only.Print this Chart and Bring It to Class4Note the increasingly darker colour in the Igneous rocks below from Felsic to Ultra-mafic Granite Diorite Gabbro Peridotite Rhyolite Andesite BasaltB. Texture (Grain Size of the Crystals), which is controlled by the rate of cooling at different depthsSee Textural Terms in Igneous Rock Classification Diagrams1. Slow Cooling at Depth within the Earth’s Crust results in Coarse-grained/Phaneritic Textures [Intrusive or Plutonic in Origin]2. Rapid Cooling on the Earth’s surface results in Fine-grained/Aphanitic Textures [Extrusive or Volcanic in Origin]3. Extremely Rapid Cooling on the Earth’s surface results in Glassy Textures [Extrusive or Volcanic in Origin] – Note the Classic Conchoidal Fracture5Black Obsidian Red and Black Mottled Obsidian4. Extremely Rapid Cooling on the Earth’s surface with trapped gases results in Vesicular Textures [Extrusive or Volcanic in Origin] Pumice Scoria5. Two stages of Cooling at 2 Different Depths within/on the Earth results in Porphyritic Textures [Can be Extrusive/volcanic in Origin or Intrusive/Plutonic in Origin] Porphyritic Granite Porphyritic Basalt (Very Coarse-grained Phenocrysts) (Coarse-grained Phenocrysts in In coarse-grained Groundmass) fine-grained Groundmass)6. A Pegmatite is a very coarse-grained, crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as Pegmatitic. Crystal sizeis the most striking feature of Pegmatites, with crystals usually over 5 cm in size. Individual crystals over 10 meters across have been found, and the world's largest crystal was found within a Pegmatite. The mineralogy of a Pegmatite is in all cases dominated by some form of Feldspar, often with Mica and usually with Quartz, being altogether "Granitic" in character. Pegmatites represent exsolved granitic material which crystallizes in the country rock.Very coarse-grained with all crystals being 2.5 cm or larger [Intrusive or Plutonic in Origin]6Granitic PegmatitesIgneous Rock Classification Chart“Simple Igneous Rock Classification” <http://csmres.jmu.edu/geollab/Fichter/IgnRx/simpclass.html>“Color-Texture Identification Key” <http://csmres.jmu.edu/geollab/Fichter/IgnRx/keyc-t.html> “Composition Key Phaneritic Igneous Rocks” <http://csmres.jmu.edu/geollab/Fichter/IgnRx/keycomp.html> C. Know how to read Mineral Percentages from “Igneous Rock Classification” DiagramView the following Igneous Rocks and the “Rock Forming Minerals” at the sites below:Andesite Porphyry, Basalt, Basalt Porphyry, Vesicular Basalt, Diorite, Dunite, Gabbro, Alkali Granite, Obsidian, Pumice, Rhyolite, Scoria“Igneous Rock Index”


View Full Document
Loading Unlocking...
Login

Join to view Igneous Rocks - Fall 2014 and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Igneous Rocks - Fall 2014 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?