2 Introduction3 Introduction4 Igneous Rocks5 Igneous Rocks6 Why Does Magma Form?7 Causes of Melting8 Causes of Melting9 Causes of Melting10 Causes of Melting11 What Is Magma Made Of?12 What Is Magma Made Of?13 Major Types of Magma14 Magma Movement15 Magma Movement16 Magma Movement17 Magma Movement18 Making Igneous Rock19 Bowen’s Reaction Series20 Igneous Environments21 Extrusive Settings22 Extrusive Settings23 Intrusive Settings24 Intrusive Settings25 Intrusive and Extrusive26 Influence on Landscape27 Where Does Igneous Activity Occur?28 Volcanic Arcs29 Hot Spots30 Large Igneous Province31 Continental Rifts32 Mid-Ocean RidgesEssentials of Geology, 4th editionby Stephen MarshakChapter 4Up from the Inferno:PowerPoint slides prepared by Rick Oches, Professor of Geology & Environmental Sciences, Bentley University, Waltham, Massachusetts1.Magma and Igneous Rocks2 IntroductionEssentials of Geology, 4th editionby Stephen MarshakChapter 4Up from the Inferno:PowerPoint slides prepared by Rick Oches, Professor of Geology & Environmental Sciences, Bentley University, Waltham, Massachusetts2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 eruption5 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 columnsEssentials of Geology, 4th editionby Stephen Marshak© 2013 W.W. Norton & CompanyChapter 4Up from the Inferno:Magma and Igneous Rocks6 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. Meltingis 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 carriedto shallower depths.Mantle plumesBeneath riftsBeneath mid-ocean ridges8 Causes of MeltingP drops when hot rock is carried to shallower depths.Mantle plumesBeneath riftsUnder mid-ocean ridges9 Causes of MeltingAddition of volatiles (flux melting)Volatiles lower the melting T of a hot rock.Common volatiles include H2O and CO2.Subduction carries water into the mantle, melting rock.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)13 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Mafic (Mg- and Fe-rich) 45–52% SiO2Ultramafic 38–45% SiO214 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 ocean15 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.17 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:Less SiO2 (mafic)—lower viscosity.More SiO2 (felsic)—higher viscosity.Essentials of Geology, 4th editionby Stephen Marshak© 2013 W.W. Norton & CompanyChapter 4Up from the Inferno:Magma and Igneous Rocks18 Making Igneous RockFractional crystallization—settling early formed crystals. Felsic magma can evolve from mafic magma. Modeled by Bowen’s reaction seriesExperimental results of mineral growth in magmasA mineral succession proceeds from cooling.19 Bowen’s Reaction SeriesN. L. Bowen—devised experiments cooling melts (1920s). Early crystals settled out, removing Fe, Mg, and Ca. Remaining melt progressively enriched in Si, Al, and Na.He discovered that minerals solidify in a specific series. Continuous—plagioclase changed from Ca-rich to Na-rich. Discontinuous—mineralsstart and stop crystallizing.OlivinePyroxeneAmphiboleBiotite20 Igneous EnvironmentsTwo major categories—based on cooling locale.Extrusive settings—cool at or near the surface.Cool rapidly.Chill too fast to grow big crystals.Intrusive