GEOL-LAB chapter 5 outline

GEOL-LAB chapter 5 outline - Lab#5 Chapter 5 Using Igneous...

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February 14, 2012: Lab #5 Chapter 5 – Using Igneous Rocks to Interpret Earth History Formation of igneous rock: when rock in lower crust or upper mantle melts to form molten material called magma (rises up through crust. Some magma flows or spatters outs of surface as lava . Some magma explodes into the air as tiny particles of volcanic ash Extrusive igneous rock : igneous rock that forms from solidified lava or ash Intrusive igneous rock : magma never reaches the surface and solidifies underground – called so because it squeezes into (intrudes) the surrounding rocks. Massive blobs are called plutons – largest of these is called batholiths . Dikes : other intrusions that form thin sheets cutting across layering in the wall rock Sills : intrusions that form thin sheets parallel to the layers of wall rock Interpreting the Cooling Histories of Igneous Rock The key to understanding the cooling history of an igneous rock is its texture – the size, shape, and arrangement of its grains. Crystalline rocks: specimens composed of interlocking grains Glasses: those that are shiny and contain no grains Porous: sponge-like masses Fragmental: those that appear to be cemented together Determine the conditions under which igneous rocks form by examining their textures. Grain Size in Crystalline Igneous Rock When magma or lava begins to cool, small crystal seeds form – NUCLEATION – and crystals grow outward from the seeds until they interfere with one another. Crystals grow as ions migrate through magma to the crystal weeds, so anything that ssists ionic migration increases grain size in igneous rock. Cooling rate is the MOST IMPORTANT factor in controlling grain size –
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This note was uploaded on 02/23/2012 for the course GEOL 101 taught by Professor Mapes during the Summer '07 term at UNC.

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GEOL-LAB chapter 5 outline - Lab#5 Chapter 5 Using Igneous...

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