New version page

UA GEO 101 - Igneous Rocks

Type: Lecture Note
Pages: 6

This preview shows page 1-2 out of 6 pages.

View Full Document
View Full Document

End of preview. Want to read all 6 pages?

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

View Full Document
Unformatted text preview:

GEO 101 1st Edition Lecture 6 Outline of Last Lecture 1. Divergent Plate Boundaries 2. Divergent Plate Boundaries: Rifting 3. Driving Mechanisms 4. Testing the Theory: Evidence 5. Importance 6. The Rock Cycle Outline of Current Lecture 1. Igneous rocks 2. Igneous Rocks & Plate Tectonics 3. 2 components of magma 4. Evolution of magma 5. Changing Magma’s Composition 6. Textures7. Textures of Igneous Rocks a. Aphanitic b. Phaneriticc. Porphyritic Texture d. Glassy Texture 8. Competition of Igneous Rocks 9. Viscosity 10. Mafic Magma 11. Felsic Magma These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.12. Naming Igneous rocks a. Felsic b. Intermediatec. Mafic 13. Bowen’s Reaction Series 14. Intrusive Igneous Rock Current LectureCh.4 Igneous RocksIgneous Rocks • From rock that was once a melt• Magma:• Melt at depth = magma • If magma solidifies = intrusive/plutonic rocks• Magma at surface = lava• Lava = extrusive/volcanic rocksIgneous Rocks & Plate Tectonics • Convergent Boundaries• Divergent Boundaries• Hot Spots2 Components of Magma- Liquid portion = melt- Maybe solids - Volatiles = dissolved gases in melt e.g. H2O, CO2Evolution of Magmas • Over time, a volcano may have lavas of different compositionsChanging Magma’s Composition - Crystallization & Settling (differentiation)- Assimilation- Magma mixingTextures: • Texture: size, shape, & arrangement of minerals• Rate of cooling most important factor in crystal size• Slow rate = fewer but larger crystals• Fast rate = many small crystalsWe name igneous rocks based on textures and compositionTextures of Igneous Rocks (4 types) 1. Aphanitic (fine-grained) texturea. Rapid rate of coolingb. Microscopic crystals2. Phaneritic (coarse-grained) texturea. Slow coolingb. Large crystals3. Porphyritic texturea. Indicates 2 stages of coolingb. Large crystals (phenocrysts) in matrix of smaller crystals (groundmass)4. Glassy texturea. Very rapid coolingb. ObsidianComposition of Igneous Rocks • 4 categories of igneous rocks based on composition.• In other words, each igneous rock has a set of minerals that combine to make it. It is the percentage of each of these minerals that makes the categories. Compositions - Felsic:o Nonferromagnesian silicateso Feldspar and silicao Silica rich (SiO2) (>65%)o Continental crust- Intermediate:o Contain >25% ferromagnesian mineralso 53-65% silicaCompositions- Mafic:o Ferromagnesian silicates & Ca-rich feldsparo Silica poor (45-52%)o Oceanic crust & volcanic islands- Ultramafic:o Rareo Entirely ferromagnesian silicateso <45% silica Silica content indicates composition 45% to 70% Si range in crustViscosity (m): Resistance to flow• μ - flows slowly• ¯ μ - flows easilyViscosity (μ)- Resistance to flowo Low μ - flow easily, e.g. ?o High μ - flow slowly, e.g. ?- Silica content influences magma μ- Mafic magma - low μ, low o Si contento E.g. Hawaii- Felsic magma – high μ, higho Si contento E.g. CascadesViscosity (m): Resistance to flow• μ - flows slowly• ¯ μ - flows easilyMafic magma- ¯ μ- ¯ Si content- E.g. HawaiiFelsic magma- μ- Si content- E.g. CascadesNaming Igneous Rocks Felsic 1. Rhyolitea. Volcanic (extrusive), felsicb. Aphanitic texture2. Granitea. Intrusive equivalent of Rhyoliteb. Phaneritic texture Intermediate3. Andesitea. Volcanic (extrusive), intermediate comp.b. Aphanitic texture4. Dioritea. Intrusive equivalent of andesiteb. Phaneritic textureMafic5. 5. Basalta. Volcanic (extrusive), mafic b. Aphanitic texture6. Gabbroa. Intrusive equivalent of basaltb. Phaneritic texturec. Most of oceanic crust7. Obsidian a. Dark colored b. Glassy texture 8. Pumice a. Volcanic (extrusive b. Glassy texture c. Frothy 9. Pyroclastic Rocksa. Ejected during eruptions b. Varieties i. Tuff = ash-sized fragments ii. Volcanic breccia = particles > ashBowen’s Reaction Series • All magmas derived from parent mafic magma• As temperature decreases, mineral crystallization occurs• Minerals do not crystallize simultaneously from cooling magma, instead, crystallize in predictablesequenceIntrusive Igneous Rock - Magma emplaced at depth: cools & solidifies, called pluton o Duke – tabular, discordant pluton o Still – tabular, concordant pluton o Laccolith  Lens or mushroom-shaped pluton  Arches overlying strata upward o Batholith  Largest pluton, > 100 + km2 (smaller bodies termed


View Full Document
Loading Unlocking...
Login

Join to view Igneous Rocks 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 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?