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THE LANGUAGE OF THE EARTH – PART I

THE LANGUAGE OF THE EARTH – PART I. IGNEOUS ROCKS. Average composition of the Earth’s Crust (by weight, elements, and volume). Layers of the Earth. OCEANIC CONTINENTAL CRUST CRUST SiO 2 47% 56% Al 2 O 3 16% 18% FeO 13% 9% MgO 10% 3% CaO 10% 4% Na 2 O 2% 5.5%

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THE LANGUAGE OF THE EARTH – PART I

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  1. THE LANGUAGE OF THE EARTH – PART I IGNEOUS ROCKS

  2. Average composition of the Earth’s Crust(by weight, elements, and volume)

  3. Layers of the Earth OCEANIC CONTINENTAL CRUST CRUST SiO2 47% 56% Al2O3 16% 18% FeO 13% 9% MgO 10% 3% CaO 10% 4% Na2O 2% 5.5% K2O 0.7% 2.5% TiO2 1.1% 1.3% P2O5 0.2% 0.7% Compositional Layers MANTLE SiO2 – 45% MgO – 37% FeO – 8% Al2O3 – 4% CaO – 3% others – 3% CORE Fe – 86% S – 10% Ni – 4% Structural Layers

  4. THE ROCK CYCLE

  5. Plate Tectonics The Engine Behind the Rock Cycle

  6. Definition IGNEOUS ROCK - An aggregate of minerals crystallized from molten rock (magma). Major distinctions in rock type are based on two criteria: • the chemical composition of the magma (mafic to felsic) and • the environmentof magma emplacement (plutonic or intrusive vs. volcanic or extrusive)

  7. Igneous Environments Fine-grained = Volcanic Coarse-grained = Plutonic

  8. IGNEOUS ROCK TEXTURES f (rate of cooling = crustal environment) Plutonic---Volcanic 1 mm Degree of Undercooling 1 mm

  9. Porphyritic Texture Indicative of two-stage cooling

  10. Magma Composition Related to Partial Melting of Source Melting the mantle makes MAFIC Magma Melting the crust makes FELSIC Magma Igneous rocks crystallize over a range of temperatures

  11. Igneous Rock-forming Minerals crystallized from Various Magma Compositions Magnesium-rich Iron-rich

  12. Generation of Diverse Magma Compositions in Various Geologic (Tectonic) Settings

  13. Volcanism and Earth’s Systems • Atmosphere – originally created from gases released from volcanic eruption • Hydrosphere – produced by condensation of volcanic water vapor • Biosphere both positively and negatively influenced by volcanism • lava flows and ash weather to produce fertile soils • violent eruptions can destroy nearly all life in their paths • large amounts of ash and volcanic gases in atmosphere can trigger rapid climate changes and contribute tomass extinctions

  14. Properties of Magmas Basalt Lobe Cinder Cone Pahoehoe Crust Fissure Eruption Mt Pinatubo Mt Fuji Mt St Helens New Zealand

  15. Effusive Eruptions Mafic magma Relatively low gas content (<1%) Fountaining followed by flow as gas content diminishes Creates vesicular to massive lava flows Photos from USGS

  16. Explosive Eruptions • Mostly involves intermediate to felsic magmas • Driven by degassing of magma as it rises up the neck of the volcanic vent • The dramatic increase of volume resulting from degassing causes the magma to be violently thrust out the neck and shattered into fine fragments – VOLCANIC ASH • Creates pyroclastic deposits http://www.geology.sdsu.edu/how_volcanoes_work/ Water solubility (carrying capacity) in rhyolite as function of pressure; from Yamashita (1999)

  17. Eruptive Styles and Volcanic Landforms • Effusive - magma fountains or oozes from vents • Fissure eruptions (flood or plateau basalts) • Shield Volcanoes • Submarine Eruptions (pillowed basalts) • Explosive – violent eruptions of gas-rich magmas • Stratovolcanoes (composite) • Pyroclastic eruptions – ash and fragments • Calderas – self-destruction of stratovolcanoes

  18. FLOOD BASALTS Basaltic Volcanism in Continental Settings

  19. NORTH SHORE Flood Basalts of the Midcontinent Rift

  20. Shield Volcanoes Basaltic Volcanism in Oceanic Settings Mauna Loa

  21. Cinder Cones –sputtering basalt eruptions

  22. StratovolcanoSteep, conical volcanoes built by the eruption of viscous lava flows, tephra, and pyroclastic flows, are called stratovolcanoes. Usually constructed over a period of tens to hundreds of thousands of years, stratovolcanoes may erupt a variety of magma types, including basalt, andesite, dacite, and rhyolite. All but basalt commonly generate highly explosive eruptions. Mt. St. Helens

  23. Explosive (pyroclastic) Eruptions Costa Rica Phillipines Mt St. Helens

  24. Mt. St. Helen’s

  25. Caldera Formation: The Fate of all Stratovolcanoes

  26. Pillowed Basalts Submarine Eruptions

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