GSU GEOL 1122K - Study Guide Chapter 4 (9 pages)

Essentials of Geology 4th edition by Stephen Marshak 2013 W W Norton Company Up from the Inferno 1 Chapter 4 Up from the Inferno Magma and Igneous Rocks Magma and Igneous Rocks 2 Introduction Volcano a vent where molten rock comes out of Earth Example Kilauea Volcano Hawaii Hot 1 200oC lava pools around the volcanic vent Hot syrupy lava runs downhill as a lava flow The lava flow slows loses heat and crusts over Finally the flow stops and cools forming an igneous rock 3 Introduction Igneous rock is formed by cooling from a melt Magma melted rock below ground Lava melted rock once it has reached the surface Igneous rock freezes at high temperatures T 1 100 C 650 C depending on composition There are many types of igneous rock 4 Igneous Rocks Melted rock can cool above or below ground Extrusive igneous rocks cool quickly at the surface Lava flows streams or mounds of cooled melt Pyroclastic debris cooled fragments Volcanic ash fine particles of volcanic glass Volcanic rock fragmented by eruption 5 Igneous Rocks Melted rock can cool above or below ground Intrusive igneous rocks cool out of sight underground Much greater volume than extrusive igneous rocks Cooling rate is slower than for extrusives Large volume magma chambers Smaller volume tabular bodies or columns PowerPoint slides prepared by Rick Oches Professor of Geology Environmental Sciences Bentley University Waltham Massachusetts 6 Why Does Magma Form Magma is not everywhere below Earth s crust Magma only forms in special tectonic settings Partial melting occurs in the crust and upper mantle Melting is caused by 1 Melted rock can cool above or below ground Intrusive igneous rocks cool out of sight underground Much greater volume than extrusive igneous rocks Cooling rate is slower than for extrusives th edition 4Large volume magma chambers Chapter 4 Essentials of Geology by Stephen Marshak Smaller volume tabular bodies or columnsUp from the Inferno Magma and Igneous Rocks 2013 W W Norton Company Why Does Magma 6 Form Magma is not everywhere below Earth s crust Magma only forms in special tectonic settings Partial melting occurs in the crust and upper mantle Melting is caused by pressure release volatile addition heat transfer 7 Causes of Melting Decrease in pressure P decompression The base of the crust is hot enough to melt mantle rock But due to high P the rock doesn t melt Melting will occur if P is decreased P drops when hot rock is carried to shallower depths Mantle plumes Beneath rifts Beneath mid ocean ridges 8 Causes of Melting P drops when hot rock is carried to shallower depths Mantle plumes Beneath rifts Under mid ocean ridges Causes of Melting Addition of volatiles flux melting Volatiles lower the melting T of a hot rock PowerPoint slides prepared Rick Oches Professor of Geology Environmental byCommon volatiles includeSciences H2O Bentley andUniversity CO2 Waltham Massachusetts Subduction carries water into the mantle melting rock 9 10 Causes of Melting 2 Causes of Melting Addition of volatiles flux melting Chapter 4 Essentials of Geology 4th edition Up from the Inferno by Stephen Marshak Volatiles lower the melting T of a hot rock Magma and Igneous Rocks 2013 W W Norton Company Common volatiles include H2O and CO2 Subduction carries water into the mantle melting rock 9 10 Causes of Melting Heat transfer melting Rising magma carries mantle heat with it This raises the T in nearby crustal rock which then melts 11 What Is Magma Made Of Magmas have three components solid liquid and gas Solid solidified mineral crystals are carried in the melt Liquid the melt itself is composed of mobile ions Dominantly Si and O lesser Al Ca Fe Mg Na and K Other ions to a lesser extent Different mixes of elements yield different magmas 12 What Is Magma Made Of Gas variable amounts of dissolved gas occur in magma Dry magma scarce volatiles Wet magma up to 15 volatiles Water vapor H2O Carbon dioxide CO2 Sulfur dioxide SO2 Nitrogen N2 Hydrogen H2 Major Types of Magma There are four major magma types based on silica SiO2 Felsic feldspar and silica 66 76 SiO2 Intermediate 52 66 SiO2 PowerPoint slides prepared Rick Oches MgProfessorand of Geology Environmental Sciences Bentley University Massachusetts byMafic Fe rich 45 52 SiOWaltham 2 Ultramafic 38 45 SiO2 13 14 Magma Movement Magma doesn t stay put it tends to rise upward Magma may move upward in the crust 3 2 Hydrogen H2 Major Types of Magma There are four major magma types based on silica SiO2 Felsic feldspar and silica 66 76 SiO2 Chapter 4 Essentials of Geology 4th edition Up from the Inferno by Stephen Marshak Intermediate 52 66 SiO 2 and Igneous Rocks Magma 2013 W W Norton Company Mafic Mg and Fe rich 45 52 SiO2 Ultramafic 38 45 SiO2 13 14 Magma Movement Magma doesn t stay put it tends to rise upward Magma may move upward in the crust Magma may breach the surface a volcano This transfers mass from deep to shallow parts of Earth A crucial process in the Earth System Provides the raw material for soil atmosphere and ocean 15 Magma Movement Why does magma rise It is less dense than surrounding rocks Magma is more buoyant Buoyancy lifts magma upward Weight of overlying rock creates pressure Pressure squeezes magma upward It is like mud squeezed between your toes 16 Magma Movement Speed of magma flow governed by viscosity Lower viscosity eases movement Lower viscosity is generated by higher T lower SiO2 content higher volatile content Magma Movement Viscosity depends on temperature volatiles and silica Temperature hot lower viscosity cooler higher viscosity Volatile content More volatiles lower viscosity Less volatiles higher viscosity Silica SiO2 content PowerPoint slides prepared by RickLess Oches Professor Geology Environmental Sciences Bentley University Waltham Massachusetts SiO2of mafic lower viscosity More SiO2 felsic higher viscosity 17 18 Making Igneous Rock Fractional crystallization settling early formed crystals Felsic magma can evolve from mafic magma 4 Temperature hot lower viscosity cooler higher viscosity Volatile content More volatiles lower viscosity th edition 4Less volatiles higher viscosity Chapter 4 Essentials of Geology Up from the Inferno by Stephen Marshak Silica SiO2 content Magma and Igneous Rocks 2013 W W Norton Company Less SiO2 mafic lower viscosity More SiO2 felsic higher viscosity 18 Making Igneous Rock Fractional crystallization settling early formed crystals Felsic magma can evolve from mafic magma Modeled by Bowen s reaction series Experimental results