How do oceans and continents differ Chapter 4 IGNEOUS ROCKS How do oceans and continents differ Crust and Mantle Lithosphere and Asthenosphere Ocean crust is thin dense and y young g Continent crust is thick old and light Polymerization 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 Polymerization of Silica Tetrahedron Olivine has none isolated SiO4 groups Pyroxene has 50 shared SiO3 chains Mica has has 75 shared Si4O10 sheets Quartz and feldspar have 100 Si Al O2 framework 1 Polymerization of Silica Pyroxene Tetrahedron Olivine Mg2SiO4 MgSiO3 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 Polymerization of Silica Mica Sheet Quartz Framework Clicker Question 1 The term for any molten silicate material on or below the Earth s surface is A Granite A G it B Basalt C Magma D Pegmatite E Lava 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 A Granite G it B Basalt C Magma D Pegmatite E Lava Clicker Question 2 The most abundant element in the Earth is A Hydrogen B Oxygen B O C Magnesium D Silicon E Iron 2 Clicker Question 2 Igneous Rocks Learning Goals The most abundant element in What does igneous mean Composition Mineralogy the Earth is A Hydrogen B Oxygen Mantle Oceanic Crust Continental Crust C Magnesium D Silicon E Iron Intrusive Igneous Rocks Composition Mineralogy Geologic Setting Mantle Oceanic Crust Continental Crust Igneous Fractionation How the chemistry evolves Igneous Rock Compositions Igneous rocks vary in composition from ultramafic 40 wt peridotite mafic 45 55 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 Igneous Fractionation How the chemistry evolves Igneous Rock Compositions Rock compositions are described in weight percents of oxides SiO2 MgO FeO Al2O3 etc The Th principal i i l variation i ti iin iigneous rock compositions is silica SiO2 content The degree of polymerization of silica increases with silica content in both crystals and melt Clicker Question 3 The composition of the mantle is said to be A Ultramafic B Mafic B M fi C Intermediate D Silicic E Sedimentary 3 Clicker Question 3 Igneous Rock Names and Compositions The composition of the mantle is said to be Volcanic Composition Intrusive Name Rock Name Rock Name A Ultramafic B Mafic C Intermediate D Silicic E Sedimentary Igneous Rock Mineralogy Peridotite Ultramafic Gabbro Mafic Olivine Mg Fe 2SiO4 Pyroxene Mg Fe Ca SiO3 Feldspar CaAl2Si2O8 Pyroxene Mg Fe Ca SiO3 Olivine Mg Fe 2SiO4 Garnet Mg3Al2Si3O12 or Spinel MgAl2O4 Geologic Settings Compositions Where Ultramafic Mafic Intermediate Silicic felsic Ult Ultramafic fi Mafic Intermediate Silicic felsic Peridotite Gabbro Diorite Granite Komatiite Basalt Andesite Rhyolite Igneous Rock Mineralogy Diorite Intermediate Granite Silicic Feldspar CaAl2Si2O8 Feldspar NaAlSi3O8 Pyroxene Mg Fe Ca SiO3 Mica K Mg Fe 3 Si Al 2O10 OH 2 Quartz SiO2 Feldspar NaAlSi3O8 Feldspar KAlSi3O8 Mica biotite K Mg Fe 3 Si Al 4O10 OH 2 Mica muscovite KAl2 Si Al 4O10 OH 2 Geologic Settings Mantle Mid ocean ridges Oceanic Islands Island arcs Continental Mantle Oceanic Subduction Zones Continental Mass 4 There 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 g C First melt is rich in silica water and trace elements Fractional Crystallization First formed crystals low in silica settle to the bottom Igneous Fractionation 5 Layered Mafic Intrusion Intrusive forms Pluton Any large discordant intrusion at depth Batholith large g 100 km2 Stock small 100 km2 Dike Tabular non conformable Sill Tabular conformable Dikes Tabular discordant Dikes Tabular discordant Sills Tabular conformable Sills Tabular conformable 6 Clicker Question Any small or large discordant intrusion at depth is known as a A Pluton B Batholith C Stock D Dike E Sill How 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 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 Partial melting Fractional Crystallization Ultramafic Mafic Intermediate Silicic Peridotite Gabbro Diorite Granite Pluton Stock Batholith Dike Sill Assignment Grotzinger Chapter 5 Sedimentary Rocks 7 Clicker Question What is the most likely geologic setting in which conglomerate was deposited A Continental alluvial fans B Continental deserts and beaches C Shallow water marine D Deep water marine E Reefs Clicker Question What is the most likely geologic setting in which sandstone was deposited A Continental alluvial fans B Continental deserts and beaches C Shallow water marine D Deep water marine E Reefs Clicker Question What is the most likely geologic setting in which shale was deposited A Continental alluvial fans B Continental deserts and beaches C Shallow water marine D Deep water marine E Reefs Tropical Shallow Marine 8
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