Geological_Sciences_1100[2]

Geological_Sciences_1100[2] - 28/10/201014:33:00...

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28/10/2010 14:33:00
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Igneous ROcks 28/10/2010 14:33:00 Igneous Rocks Origin—crystallization from magma/lava Earth is differentiated into layers of material that increase in density towards  the core Pressure increases with depth, so melting temperature must also increase o At a depth of 10 km, a certain rock melts when the temperature  reaches 450.   What happens if that rock sits at 20 km depth? o Increase pressure, increase temperature Intrusive—form underground, cool slowly, big crystals Extrusive—form above ground, cool quickly, tiny crystals Types of Volcanoes  Cinder cone—typical volcano o Pyroclasic deposits—explosive  Shield volcano—like Hawaii, very gentle and broad Composite—pyroclastic, has a lot of ash, layered lava flows Igneous rocks classified by Texture o Rate at which minerals crystallize o Phaneritic (big crystals), aphanitic (little crystals, extrusive), porphyritic  (mix, started deep but then gets pushed out) o More viscous—finer texture Mineral composition o Kinds and amount of minerals present o Initial composition (what forms first), partial crystallization
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28/10/2010 14:33:00 Obsidian rock—igneous rock, very glassy Pyroclastic—popped fragments Pegmatitic texture Very large mineral grain,  Very slow cooling of the magma High abundance of water in the presence of the magma Bowen’s reaction series A model for the successive precipitation of minerals from a magma Different minerals crystallize from a melt at different temperatures
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28/10/2010 14:33:00 Example of Calderas:  Crater Lake, OR Formed when a magma body collapses  In Missouri Two large Precambrian calderas exposed in SE Missouri o Elephant rocks State Park o Johnson’s Shut-Ins State Park lots of different geographies, terrain crusts were glued together over time to form a larger craton other igneous features volcanic pipes and necks dikes—thin arm of magma connected to the main probe? o Tabular intrusive igneous feature that cuts through the surrounding  rock o Usually vertical  sills and laccoliths o sills—form parallel to the bedding, tabular igneous body that is intruded  parallel to layering,  must form at shallow levels of the earth mafic uniform thickness of sills magma must be able to flow easily o laccoliths—special case of a sill in which the magma collects as a len- shaped mass and causes the overlying rock to be arched over it form from magmas that are more viscous than those that form  sills
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Geological_Sciences_1100[2] - 28/10/201014:33:00...

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