UNIVERSITY OF SOUTH ALABAMA Last Time GY 111 Physical Geology 1 The chemical composition of the crust 2 Crystallization of molten rock 3 Bowen s Reaction Series Lecture 9 Extrusive Igneous Rocks Bowen s Reaction Series Chemical Composition of the Crust Wt of atoms Oxygen 46 6 60 5 Silicon Element 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 Source http www ltcconline net julian Igneous Rock Composition Igneous Rock Texture 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 low Intermediate Medium Na Plagioclase amphibole biotite moderate Felsic Medium low Orthoclase quartz muscovite biotite high 65 Pause 1 Pyroclastic Igneous Rocks 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 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 Igneous Rocks Pyroclastic Pyro means fire Clastic means particles both are of Greek origin 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 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 The eruptions that produce pyroclastic rocks include phreatic plinian and ultraplinian These rocks cool extremely rapidly Textures are glassy to aphanitic 2 Pyroclastic Igneous Rocks Pyroclastic Igneous Rocks Volcanic ash Pyroclastic Igneous Rocks Volcanic ash Pyroclastic Igneous Rocks Volcanic ash Pumice Pyroclastic Igneous Rocks Nuee ardents and pyroclastic flows may deposit volcanic breccias or ignimbrites http ougseurope org trips santorini santorini Picture04 jpg Ignimbrite Obsidian Pyroclastic Igneous Rocks During pyroclastic eruptions volcanic gas is produced in copious quantities more so than ash and rock water vapor H20 carbon dioxide CO2 hydrogen chloride HCl sulfur dioxide SO2 nitrogen oxide N2O Hydrogen cyanide HCN argon Ar helium He 3 Felsic Intermediate Extrusive Igneous Rocks Other pyroclastic rocks Volcanic Bombs Tuff Rhyolite Chalk board Felsic Intermediate Extrusive Igneous Rocks Mafic Extrusive Igneous Rocks Rhyolite Mt St Helens Lava dome Felsic and intermediate rocks are classified by the amount of SiO2 in their bulk chemistry We can distinguish them on the basis of mineral composition and color Andesite Mafic Extrusive Igneous Rocks Mafic Extrusive Igneous Rocks Basalt http z about com d geology 1 0 F W scoria jpg Mafic extrusive igneous rocks have relatively low SiO2 contents in their bulk chemistry No ultramafic extrusive igneous rocks occur today Mafic extrusive igneous rocks erupted under water produce a unique structure called pillows Pillow basalt forms at divergent plate boundaries like the MidAtlantic Ridge Scoria 4 Today s Homework 1 Study Lecture test 1 next Tuesday Next Time Quiz 5 last one Intrusive igneous rocks 1 2 5
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