GSCI 1050 Lecture 6: 02.02.2017

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GSCI 1050
Jennifer Cooper Boemmels

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GSCI1050-002 02.02.17 9:30-10:15 lecture 10:20 Quiz for Tuesday (sessions 1-5) - bring notes, book don’t have to identify minerals, just know their essential properties (know the connection between physical and internal crystal structure) prep material is still due on Tuesday Today’s course: Igneous rocks and Volcanoes -Minerals and questions -Lecture -Prep materials Muddiest Point - continental drift vs. seafloor spreading? what is plate tectonics? lithosphere broken into pieces 1) continental drift - idea of Pangaea by Wegener 2) seafloor spreading - idea of Hess/Dietz 3) (Final product) plate tectonics Flux melting vs decompression melting? Clicker Questions • Silicates are most common class of minerals within Earth’s crust
 • Which condition ill allow a crystal to display distinct crystal faces? A mineral that has grown uninhibited, potentially filling an open void (ex: geode) ◦ We call a crystal with well-defined set of faces euhedral ◦ anhedral crystals don’t show their true crystal faces ◦ orbicular granite - a mineral that has formed within a cooling magma and is beginning to be dissolved back into the magma Igneous Rocks and Volcanoes • Magmas and igneous rocks
 • Intrusive vs. Extrusive features
 • Volcanic shape and activity
 • Volcanic Eruptions and Material
 Magmas and igneous rocks • Igneous textures result mainly from the cooling history of a magma, which ranges from glassy to pegmatitic ◦ it all boils down to texture and composition • texture for a rock is the size, shape and arrangement of grains present in a rock (nothing to do with the feel) • Examples of igneous textures: ◦ ex: crystalline - coarse (visible grains to naked eye) or fine (grains not visible to naked eye) ◦ ex: fragmental (associated with volcanoes) ◦ ex: glassy - pyroclastic or glass (note that glass refers to rock that cooled so quickly that it didn’t have time to form atomic arrangements; same starting material, but no mineral grains formed)
 • Magma compositions change due to partial melting, fractional crystallization and host- rock effects ◦ based on ▪ silica content ▪ Fe/Mg content • Examples of igneous compositions: ◦ felsic (high silica) ◦ intermediate (medium silica) ◦ mafic (low silica) ◦ ultramafic (really low silica) • What controls magma composition? Well, it comes from the mantle ◦ partial melting of the mantle ▪ whole area that’s undergoing melting is not me
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