1Chapter 4IGNEOUS ROCKSHow do oceans and continents differ?How do oceans and continents differ?Ocean crust is thin, dense and young.ygContinent crust is thick, old, and lightCrust and MantleLithosphere and AsthenospherePolymerization of Silica•Each Si atom is surrounded by 4 oxygens.•Polymerization is the degree to which the oxygens are shared with other Si atoms.•Polymerization is the number of Si-O-Si bonds per tetrahedron.–Olivine has none: isolated SiO4groups–Pyroxene has 50% shared: SiO3chains–Mica has has 75% shared: Si4O10sheets–Quartz and feldspar have 100% (Si,Al)O2framework.Polymerization of SilicaTetrahedron2Polymerization of SilicaTetrahedronOlivine (Mg2SiO4)PyroxeneMgSiO3Polymerization of SilicaMica (Sheet)Quartz (Framework)MAGMA•Magma is the term for any molten silicate material, whether below the surface or on top.•Volcanic rocks are erupted on the surface.–Volcanic rocks are fine-grained (<1 mm)•Intrusive igneous rocks crystallize from magma below the surface.–Intrusive igneous rocks are coarse-grained (> 1mm)–Pegmatites are very coarse-grained (> 1cm) Clicker Question 1•The term for any molten silicate material on or below the Earth’s surface is:A G it–A. Granite–B. Basalt –C. Magma–D. Pegmatite–E. LavaClicker Question 1•The term for any molten silicate material on or below the Earth’s surface is:A G it–A. Granite–B. Basalt –C. Magma–D. Pegmatite–E. LavaClicker Question 2•The most abundant element in the Earth is:–A. HydrogenB O –B. Oxygen –C. Magnesium–D. Silicon–E. Iron3Clicker Question 2•The most abundant element in the Earth is:–A. Hydrogen–B. Oxygen –C. Magnesium–D. Silicon–E. IronIgneous Rocks:Learning Goals•What does igneous mean?•Composition•Mineralogy–Mantle–Oceanic Crust–Continental Crust•Igneous Fractionation–How the chemistry evolvesIntrusive Igneous Rocks•Composition•Mineralogy•Geologic Setting–Mantle–Oceanic Crust–Continental Crust•Igneous Fractionation–How the chemistry evolvesIgneous Rock Compositions•Rock compositions are described in weight percents of oxides:•SiO2, MgO, FeO, Al2O3, etcTh iil iti i i •The principal variation in igneous rock compositions is silica (SiO2) content.•The degree of polymerization of silica increases with silica content. (in both crystals and melt).Igneous Rock Compositions•Igneous rocks vary in composition from –ultramafic (~40 wt%) (peridotite)mafic (4555%) (gabbro / basalt) –mafic (45-55%) (gabbro / basalt) –intermediate (55-65%) (diorite)–silicic (65-75 wt %) (granite)•The mantle is peridotite (ultramafic).•The ocean basins gabbro (mafic). •The continents are granite (silicic)Clicker Question 3•The composition of the mantle is said to be:–A. UltramaficB M fi–B. Mafic–C. Intermediate–D. Silicic–E. Sedimentary4Clicker Question 3•The composition of the mantle is said to be:–A. Ultramafic–B. Mafic–C. Intermediate–D. Silicic–E. SedimentaryIgneous Rock Names and Compositions• Intrusive Rock Name• Composition NameUlt fi• Volcanic Rock Name• Peridotite• Gabbro• Diorite• Granite•Ultramafic•Mafic• Intermediate• Silicic (felsic)• (Komatiite)• Basalt• Andesite• RhyoliteIgneous Rock Mineralogy• Peridotite (Ultramafic)– Olivine ((Mg,Fe)2SiO4)–Pyroxene• Gabbro (Mafic)– Feldspar (CaAl2Si2O8)Pyroxene ((Mg,Fe,Ca)SiO3)– Garnet (Mg3Al2Si3O12) or– Spinel (MgAl2O4)()– Pyroxene ((Mg,Fe,Ca)SiO3)– Olivine ((Mg,Fe)2SiO4)• Diorite (Intermediate)– Feldspar (CaAl2Si2O8) – Feldspar (NaAlSi3O8)Igneous Rock Mineralogy• Granite (Silicic)– Quartz (SiO2)– Feldspar (NaAlSi3O8) – Pyroxene ((Mg,Fe,Ca)SiO3)– Mica K(Mg,Fe,)3(Si,Al)2O10(OH)2– Feldspar (KAlSi3O8)– Mica (biotite) (K(Mg,Fe,)3(Si,Al)4O10(OH)2– Mica (muscovite)– (KAl2(Si,Al)4O10(OH)2Geologic Settings••Where?Where?•Mantle•Compositions•Ultramafic•Oceanic•Subduction Zones•Continental Mass•Mafic•Intermediate•Silicic (felsic)Geologic Settings:MantleMid-ocean ridges Oceanic IslandsIsland arcs Continental5There appear to be 13 major plates that cover the globe. Igneous Fractionation:Peridotite-basalt-granite •Partial Melting–Rocks have a melting interval of several hundred degrees C.g–First melt is rich in silica, water and trace elements.•Fractional Crystallization–First-formed crystals low in silica settle to the bottom. Igneous Fractionation:6Layered Mafic IntrusionIntrusive forms•Pluton: Any large discordant intrusion at depth–Batholith: large > 100 km2g–Stock: small < 100 km2•Dike: Tabular non-conformable•Sill: Tabular conformableDikes:Tabular discordantDikes:Tabular discordantSills:Tabular conformableSills: Tabular conformable7Clicker Question•Any small or large discordant intrusion at depth is known as a–A. Pluton–B. Batholith–C. Stock: –D. Dike–E. SillHow do oceans and continents differ?How do oceans and continents differ?•Oceanic crust is:–Thin (~7 km), –Dense (~3.1g/cm3) –Mafic (45-50% SiO2)(%2)–Young (< 200 my)•Continental Crust is:–Thick (>30 km),–Light (~2.7 g/cm3)–Silicic (> 60% SiO2)–Old (> 1000 my)Terms•Polymerization•Magma•Pegmatitie•Igneous Fractionation•Silicic•Peridotite•Gabbro•Diorite•Granite•Partial melting•Fractional Crystallization•Ultramafic•Mafic•IntermediateGranite•Pluton•Stock•Batholith•Dike•SillAssignment•Grotzinger Chapter 5•Sedimentary Rocks8Clicker Question•What is the most likely geologic setting in which conglomerate was deposited?deposited?–A. Continental alluvial fans–B. Continental deserts and beaches –C. Shallow-water marine–D. Deep-water marine –E. ReefsClicker Question•What is the most likely geologic setting in which sandstone was deposited?A Continental alluvial fans–A. Continental alluvial fans–B. Continental deserts and beaches –C. Shallow-water marine–D. Deep-water marine –E. ReefsClicker Question•What is the most likely geologic setting in which shale was deposited?A Continental alluvial fans–A. Continental alluvial fans–B. Continental deserts and beaches –C. Shallow-water marine–D. Deep-water marine –E. Reefs(Tropical Shallow
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