GSCI 1050 Lecture Notes PDF

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GSCI 1050 Lecture Notes...

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GSCI 1050.002 2/9/2016 Page 1 of 2 (lecture topic continued from last lecture) Rock Cycle and Igneous Rocks Igneous Rocks – Magma – molten material below the surface o Intrusive – rocks formed from magma – Lava – molten rock above the surface o Extrusive – rocks formed from lava – Where does the heat come from? o Bombardment by asteroids on earth changed kinetic energy into heat o Differentiation generated more heat through friction o Heat is lost to space but it is slowed down by the new rock barrier and keeps the heat in o New heat is constantly created below the crust by radioactive decay – Magma formation o Decompression – as a rock rises, the pressure decreases, so that the heat is able to break the bonds and the rock melts  Mantle plumes  Divergent boundaries  Continental rifts (crust thins, decreases pressure)  Mid ocean ridges o Flux melting – addition of volatiles  Water and carbon dioxide break molecular bonds causing rocks to melt  Occurs during subduction o Heat transfer melting – heat transferred from mantle magma may be enough to melt crustal rocks – Magma composition 1) Felsic (feldspar and silica) - light colored rocks; 66-76% silica a. High viscosity, explosive 2) Intermediate – salt and peppery colored rocks; 52-65% silica a. High viscosity, explosive 3) Mafic (magnesium and iron) – dark colored rocks; 45-51% silica a. Low viscosity, runny 4) Ultramafic – often green color due to high olivine; 38-45% silica o Source rock composition  When mafic rocks are melted, they make mafic (runny) magma o Partial melting – different minerals melt at different temperatures, with silicates generally melting at lower temperatures o Assimilation – partial melting of rock surrounding the magma will change its compostion  Magma mixing – Magma movement o Rate of movement

GSCI 1050.002 2/9/2016 Page 2 of 2 1) Temperature  Hotter – low viscosity, fast flow  Colder – high viscosity, slow flow 2) Volatile Content  Higher content – low viscosity, fast flow  Lower content – high viscosity, slow flow 3) Silica content  Mafic – low viscosity, fast flow  Felsic – high viscosity, slow flow o Cooling Rate 1) Depth  Shallow – rapid cool  Deep – slow cool 2) Shape and Size of Mamga  High surface area – rapid cool  Low surface area – slow cool 3) Water amount  Much water – rapid cool  Little water – slow cool – Igneous rock composition o Intrusive  Pegmatitic – huge crystals, from cooling in water; grain size- 10mm+  Phaneritic – large crystals (diorite); grain size- 1-10mm o Porphoritic – both large and small crystals; start forming below ground, and finish above ground o Extrusive  Glassy – cools very rapidly  Aphanetic – small crystals (rhyolite); less than 1mm grain size  Vesicular – air bubbles  Pyroclastic – solidified flows (pumice)...