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Geo101.05.IgneousRxs[1] - Igneous Rocks rocks formed by the...

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1 Igneous Rocks … rocks formed by the solidification (cooling or freezing) of melt or molten rock Igneous Rocks … melt or molten rock is commonly referred to as magma … much like ice forms by the freezing of water at 0° (32°F) …igneous rocks form by the cooling / freezing of magma, only at much higher temperatures, …between 650° and 1100°C Magma that cool at or near Earth’s surface are termed Extrusive or Volcanic rocks Magma that cool beneath Earth’s surface are termed Intrusive or Igneous rocks What is magma made of? The composition of the magma depends on: Original Composition of the melt Partial melting (fractionation) of source rock Contamination of “country rock” and/or Fractional crystallization What is magma made of? All magmas contain Si and O Magmas also contain varying proportions of elements such as Al, Ca, Na, K, Fe, Mg Water and Volatiles Wet magmas include up to 15% volatiles such as CO 2 , N 2 , H 2 , SO 2
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2 How / where do igneous rocks originate ? Melting and extruding of molten rock Heat transfer… Addition of volatiles… Decompression… Melting Partial Melting / Fractionation Decompression Melting Partial Melting / Fractionation Fractional (partial) melting since materials melt at different temperatures, raising temperatures high enough to melt silicates can result in those materials with higher melting temperatures to fall out of solution..thus the melt is now fractionated or different in compostion from the total composition of the orignal rock When this melt cools, it will form a rock of different
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