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Download Introduction to Earth Science Ch. 01
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Intrusive Igneous Activity • Plutons result from the cooling and hardening of magma within the earth • Exposed at surface after uplift and erosion • Pluton refers to Pluto, the Roman god of the underworld Origin of Magma • Magma is rock melted by earth’s internal heat • Magma results from melting of the crust and upper mantle • Earth’s internal temperature increases with depth from 2030°C per kilometer • Known as geothermal gradient Where is Magma Produced? • Subduction zones, friction between two tectonic plates • Water decreases melting temp at subduction zones • Subduction creates continental and marine volcanic arcs • Hot spots, rising material melts due to lessening of pressure (decompression melting) Earth’s Geothermal Gradient Temperature increases with depth within the earth Pluton Classification • Plutons classified by size, shape, and relationship to surrounding rock layers • Types of Plutons: • • • • • Sills Laccoliths Dikes Batholiths Stocks Sills & Laccoliths • A sill forms when magma is injected between sedimentary layers • Sills resemble buried lava flows • A laccolith is a type of sill that pushes the overlying rock layers into an arch shape Sill A sill results from molten magma injected into sedimentary layers Sill Sills are parallel to the layers http://www.psrd.hawaii.edu/WebImg/Sill.gif Sedimentary layers Perfect Sill Sedimentary layers are visible above and below the sill Sill http://z.about.com/d/geology/1/0/J/S/sill.jpg Laccolith Bear Butte, a laccolith near the Black Hills in Wyoming, has been exposed by weathering http://www.tulane.edu/~sanelson/images/laccolith.gif Ship Rock, NM Dike Dikes • Dikes are plutons that form when magma is injected into fractures that cut across existing rock layers • Dikes can radiate like spokes on a wheel from a volcanic neck http://www.rosssea.info/geology.html Dike in Sedimentary Layers Notice how the igneous intrusion (dike) has cut across existing sedimentary layers Dike Batholith Batholiths can form the cores of mountains • Largest plutons, often form mountain ranges • Surface exposure > 100 square kilometers (km2) • Stocks are < than 100 km2 Batholiths Idaho features some large batholiths Half Dome at Yosemite, CA is part of a batholith complex Igneous Stock •Devil’s Post Pile in California is an igneous stock •Note the 6sided columnar jointing of the basalt http://www.anthroarcheart.org/tblt7.htm Summary of Igneous Bodies
