UNIVERSITY OF SOUTH ALABAMA GY 111: Physical Geology Lecture 9: Extrusive Igneous Rocks Instructor: Dr. Douglas W. Haywick
Last Time 1) The chemical composition of the crust 2) Crystallization of molten rock 3) Bowen's Reaction Series Web notes 8
Chemical Composition of the Crust Element Wt% % of atoms Oxygen 46.6 60.5 Silicon 27.7 20.5 Aluminum 8.1 6.2 Iron 5.0 1.9 Calcium 3.6 1.9 Sodium 2.8 2.5 Potassium 2.6 1.8 Magnesium 2.1 1.4 All other elements 1.5 3.3
Crystallization of Magma http://myweb.cwpost.liu.edu/vdivener/notes/igneous.htm
Bowen s Reaction Series Source http://www.ltcconline.net/julian
Igneous Rock Composition Source: http://hyperphysics.phy-astr.gsu.edu Composition Formation Temperature Dominant Minerals Silica content Ultramafic Very high Olivine, pyroxene Very low (<45%) Mafic High Olivine, pyroxene, Ca-plagioclase Intermediate Medium Na-Plagioclase, amphibole, biotite Felsic Medium-low Orthoclase, quartz, muscovite, biotite low moderate high (>65%)
Igneous Rock Texture Extrusive Rocks (Rapid Cooling; non visible* crystals) Intrusive Rocks (slow cooling; 100 % visible crystals) *with a hand lens
Igneous Rock Texture
Igneous Rock Texture
Today s Agenda 1) Pyro-what? (air fall volcanic rocks) 2) Felsic and Intermediate Extrusive Rocks 3) Mafic Extrusive Rocks Web notes 9
Pyroclastic Igneous Rocks
Pyroclastic Igneous Rocks Pyroclastic: Pyro means fire. Clastic means particles; both are of Greek origin.
Pyroclastic Igneous Rocks Pyroclastic: Pyro means fire. Clastic means particles; both are of Greek origin. Pyroclastic rocks are usually erupted from composite volcanoes (e.g., they are produced via explosive eruptions from viscous, cool lavas)
Pyroclastic Igneous Rocks Pyroclastic: Pyro means fire. Clastic means particles; both are of Greek origin. Pyroclastic rocks are usually erupted from composite volcanoes (e.g., they are produced via explosive eruptions from viscous, cool lavas) The eruptions that produce pyroclastic rocks include phreatic, plinian and ultraplinian.
Pyroclastic Igneous Rocks Pyroclastic: Pyro means fire. Clastic means particles; both are of Greek origin. Pyroclastic rocks are usually erupted from composite volcanoes (e.g., they are produced via explosive eruptions from viscous, cool lavas) The eruptions that produce pyroclastic rocks include phreatic, plinian and ultraplinian. These rocks cool extremely rapidly. Textures are glassy to aphanitic.
Pyroclastic Igneous Rocks
Pyroclastic Igneous Rocks Volcanic ash
Pyroclastic Igneous Rocks Volcanic ash Pumice
Pyroclastic Igneous Rocks Volcanic ash Obsidian
Pyroclastic Igneous Rocks Nuee ardents and pyroclastic flows may deposit volcanic breccias or ignimbrites http://ougseurope.org/trips/santorini/santorini/picture04.jpg Ignimbrite
Pyroclastic Igneous Rocks During pyroclastic eruptions, volcanic gas is produced in copious quantities (more so than ash and rock). water vapor (H 2 0) carbon dioxide (CO 2 ) hydrogen chloride (HCl) sulfur dioxide (SO 2 ) nitrogen oxide (N 2 O) Hydrogen cyanide (HCN) argon (Ar) helium (He)
Other pyroclastic rocks Volcanic Bombs Tuff Rhyolite Chalk board
Felsic/Intermediate Extrusive Igneous Rocks
Felsic/Intermediate Extrusive Igneous Rocks Mt. St. Helens Lava dome Felsic and intermediate rocks are classified by the amount of SiO 2 in their bulk chemistry (they have relatively high SiO 2 content). We can distinguish them on the basis of mineral composition and color. Rhyolite Andesite
Mafic Extrusive Igneous Rocks
Mafic Extrusive Igneous Rocks Basalt Mafic extrusive igneous rocks have relatively low SiO 2 contents in their bulk chemistry. Ultramafic extrusive igneous rocks are relatively rare today. http://z.about.com/d/geology/1/0/f/w/scoria.jpg Scoria
Mafic Extrusive Igneous Rocks Mafic extrusive igneous rocks erupted under water produce a unique structure called pillows. Pillow basalt forms at divergent plate boundaries like the Mid- Atlantic Ridge Pillow Basalt
Today s Homework 1. Study; Lecture test 1 next Tuesday Next Time 1. Quiz 5; fill in the blanks 2. Intrusive igneous rocks
GY 111: Physical Geology Lecture 9: Extrusive Igneous Rocks Instructor: Dr. Doug Haywick dhaywick@southalabama.edu This is a free open access lecture, but not for commercial purposes. For personal use only.