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

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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