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Main Idea Magma Eruption • 1. Does all magma erupt at the surface? Main Idea Magma Eruption • 2. Why does it matter where magma erupts or where it cools? Main Idea Magma Eruption • 3. How could you tell if there were an active magma intrusion below the surface? 18.3 – Intrusive Activity http://3dparks.wr.usgs.gov/2005/lakemead/images/volcanic.gif Plutons http://www.geo.hunter.cuny.edu/bight/images/pluton.jpg • Intrusive igneous rock body, including batholiths, stocks,sills & dikes • Formed through mountain-building processes and oceanic-oceanic collisions • Can be exposed at Earth’s surface to uplift and erosion Batholiths & Stocks • The largest plutons are called Batholiths. • Batholiths are coarse-grained, irregularly shaped, igneous rock mass that covers at least 100 km2 • Stocks are irregularly shaped plutons but smaller in size. • Both generally form 5-30 km below Earth’s surface and are common in the interior of major mountain chains Laccoliths • Relatively small • Mushroom-shaped pluton that forms when magma intrudes into parallel rock layers close to Earth’s surface • Laccoliths have flat bottoms and curved tops. http://www.indiana.edu/~geol105/images/gaia_chapter_5/dike&sill.jpg Sills • Pluton that forms when magma intrudes parallel rock layers http://www.austmus.gov.au/geoscience/images/earth_diagrams/volcano_structure.gif Dikes • Pluton that cuts across preexisting rocks and often forms when magma invades cracks in surrounding rock bodies http://www.waipahums.k12.hi.us/eportfolio05-06/wisportfolio05-06/team8d_portfolios/y_kenneth_e_portfolio/volcano_files/image002.png Plutons & Tectonics • Many plutons form as the result of mountain-building processes. • Plutons are thought to form as a result of continental-continental and oceaniccontinental convergence. Reinforcement • T/F • Batholiths are common in the interiors of mountain chains. • Laccoliths have curved bottoms and flat tops. • Sills form when magma is forced between rock layers. • Most igneous activity occurs deep within earth.