PLATE TECTONICS, VOLCANISM AND IGNEOUS ROCKS

PLATE TECTONICS, VOLCANISM AND IGNEOUS ROCKS PLATE TECTONICS TO IGNEOUS ROCKS Internal Heat Seafloor Spreading/Plate Tectonics Volcanism Plate Boundary Intra-plate (hot spot) Divergent Convergent Igneous Rocks Igneous rocks will be different based on where/how they are formed relative to plate tectonic activity ROCK TYPES METHOD OF FORMATION Igneous formed by crystallization (freezing) of molten rocks Sedimentary formed cementing eroded fragments of igneous, sedimentary or metamorphic rocks Metamorphic formed by changing existing sedimentary or igneous rocks by heat and/or pressure 1

ROCK TYPES CAN CHANGE Rock Cycle Rock formation is related to plate tectonics Heat, pressure, melting, cooling are all caused by plate tectonic processes ROCKS COMPOSITION OF THE EARTH S CRUST Elements Basic structure of all matter Minerals Inorganic Compounds Combination of elements Rocks Combinations of minerals Igneous, sedimentary, metamorphic ELEMENTS IN EARTH S CRUST 98% of Earth s crust is made of 8 elements Silicon (Si) Oxygen (O 2 ) Aluminum (Al) Magnesium (Mg) Calcium (Ca) Sodium (Na) Potassium (K) Iron (Fe) 2

MINERALS IN EARTH S CRUST u Elements combine in predictable ways to form minerals u Minerals combine in predictable ways to form rocks MINERALS TO IGNEOUS ROCKS q Igneous rocks form when combinations of melted minerals freeze/solidify/ crystallize q Different minerals have different melting/freezing points and crystallize at different temperature q Therefore, temperature has an effect on igneous rock formation Bowen s Reaction Series IGNEOUS ROCK FORMATION Ø Important factors in the formation of igneous rock types Ø Source + chemistry of parent magma Ø Interaction between chemistry of magma and existing rocks of crust Ø Rate of cooling + crystallization temperature of minerals Ø Each of these factors has a connection to plate tectonics 3

IGNEOUS ROCK CHARACTERISTICS ü We classify igneous rocks based on color, crystal type and crystal size ü Color ü Indicates difference in chemical composition ü Lighter colors = higher levels of Si and Al ü Darker colors = higher levels of Mg and Fe ü Crystal type ü Indicates magma chemistry and temperature of formation ü Crystal Size ü Indicates rate of cooling ü Smaller = faster cooling ü Larger = slower cooling IGNEOUS ROCK TYPES v Intrusive Igneous Rock v Formed beneath surface from solidified magma v Deep formation = slow cooling = large v Shallow formation = faster cooling = small v Extrusive Igneous Rock v Formed on surface from solidified lava v Rapid cooling rate = fine or non-existent IGNEOUS ROCK TYPES - FELSIC ² Chemistry = High levels of Si and Al ² Minerals = High levels of quartz, K + Na feldspar, biotite ² Color = Light colored mineral ² Viscosity = High ² Melting Temp = Low ² Gas Level = High ² Relative Density = Low ² Volcanic Source = continental volcanoes 4

IGNEOUS ROCK TYPES - MAFIC ² Chemistry = High levels of Fe, Ca and Mg ² Minerals = High levels of Ca Feldspar, pyroxene, olivine ² Color = Dark colored minerals ² Viscosity = Low ² Melting Temp = High ² Gas Level = Low ² Relative Density = High ² Volcanic Source = Mid-ocean ridge + hot spot volcanoes IGNEOUS ROCK TYPES ANDESITIC ² Chemistry = Intermediate levels of Si, Fe, Ca and Mg ² Minerals = High levels of Ca + Na Feldspar, pyroxene, amphibole ² Color = Intermediate colored minerals ² Viscosity = Intermediate ² Melting Temp = Intermediate ² Gas Level = Intermediate ² Relative Density = Intermediate ² Volcanic Source = Ocean arc + continental volcanoes MAGMA TYPE + VOLCANIC ERUPTION Felsic Magma Mafic Magma High Viscosity Low Viscosity High Dissolved Gas Low Dissolved Gas Explosive Eruptions Non-Explosive Eruptions 5

IGNEOUS ROCK CLASSIFICATION There are a variety of ways to classify igneous rocks We use the observable characteristics of color + texture Color is determined by magma/lava chemistry Texture is determined by crystal size Crystal size is determined by cooling rate Cooling rate is determined by depth of formation We infer chemistry + depth of formation from observations IGNEOUS ROCK CLASSIFICATION Lighter colored rocks Darker colored rocks Large Small No/Fine Intrusive Extrusive IGNEOUS ROCK CLASSIFICATION Felsic Fine Andesitic Mafic Small Large 6

IGNEOUS ROCKS + PLATE TECTONICS 7