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Earth Science 10.3 Intrusive Igneous Activity

Earth Science 10.3 Intrusive Igneous Activity . Intrusive Igneous Activity . Classifying Plutons :. Volcanic rock that cools and hardens covers much of Earth’s surface. Most magma, however, cools and hardens deep within the Earth.

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Earth Science 10.3 Intrusive Igneous Activity

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  1. Earth Science 10.3 Intrusive Igneous Activity Intrusive Igneous Activity

  2. Classifying Plutons: • Volcanic rock that cools and hardens covers much of Earth’s surface. • Most magma, however, cools and hardens deep within the Earth. • This magma forms the roots of mountain ranges and a variety of landscape features.

  3. Classifying Plutons: • Recall that magma rises through the crust toward the surface. • As it rises, it may rise through fractures in the rock or force it’s way between layers of rock. • The magma may form thin sheets a few centimeters thick or collect in vast pools that can be kilometers wide. • All these formations have various names; dikes, sills, laccoliths and batholiths.

  4. Classifying Plutons: • Structures resulting from the cooling and hardening of magma beneath Earth’s surface are called plutons. • The word pluton is derived from Pluto, the Roman god of the underworld. • Plutons form in continental crust wherever magma slowly crystallizes and forms intrusive igneous rock. • Intrusive igneous rock = rock that forms as magma cools deep within the Earth. • Extrusive igneous rock = forms once magma emerges as lava and cools above earth’s surface.

  5. Classifying Plutons: • Over millions of years, uplift and erosion can expose plutons to the world above the surface. • There are several types of plutons: • Sills • Laccoliths • Dikes • Batholiths

  6. Sills and Laccoliths: • Sillsandlaccolithsare plutons that form when magma intrudes between rock layers close to the surface. • Sills and laccoliths differ in shape and often differ in composition. • Asillis a pluton that forms when magma flows between parallel layers of sedimentary rock. • Horizontal sills are the most common to be found.

  7. Sills and Laccoliths: • Sills form only at shallow depths, where the pressure from the weight of the overlying rock is low. • For a sill to form, the magma must lift the overhead rock to a height equal to the thickness of the sill. • While this takes energy; forcing the magma between rock layers requires less energy than forcing the magma all the way up to the surface. Exposed Sill

  8. Sills and Laccoliths: • A laccolith is a lens-shaped pluton that has pushed the overlying rock layers upward. • Like sills, laccolithsform when magma intrudes between sedimentary rock layers close to the surface. • The magma that forms laccoliths has a higher viscosity (thickness) than the magma that forms sills. • For this reason, the magma that collects bulges upward instead of spreading out in a thin layer. Exposed laccoliths

  9. Dikes: • Some plutons form when magma from a large magma chamber moves into fractures in the surrounding rocks. • Adike is a pluton that forms when magma moves into fractures that cut across rock layers. • Dikesare sheet-like structures that can range in thickness from less than a centimeter to more than a kilometer. • Most dikes are a few meters thick and extend for no more than a few kilometers. Two examples of dikes

  10. Batholiths: • Batholiths are very large bodies of intrusive igneous rock. • Abatholithis a body of intrusive igneous rock that has a surface exposure of more than 100 square kilometers. • Much larger than a pluton, a batholith can be hundreds of kilometers long and tens of kilometers across.

  11. Batholiths: • Gravity studies and seismic evidence indicate that batholiths are very thick, sometimes extending tens of kilometers downward into the crust. • A body of igneous rock similar to a batholith but having an area less than 100 kilometers is called a stock.

  12. How are Batholiths formed? • Batholiths form from many individual plutons that begin as blobs of magma deep beneath the surface. • The plutons slowly rise through the crust in the form of hot magma. • They clump together forming a huge irregular mass of underground magma, molten rock.

  13. How are Batholiths formed? • This magma never works it’s way to the surface. Instead, it cools and hardens underground forming granitic rock. • Over millions of years, uplift and erosion gradually expose the batholith at the surface. • Batholiths form the core of the Earth’s great mountain ranges; from the Northern Rockies to the Sierra Nevada Mountains in southern California.

  14. How are Batholiths formed? • Examples of batholiths that have been exposed by erosion Batholiths can be huge, extending hundreds of miles Half Dome Yosemite Sierra Nevada batholith

  15. Computer Lab Assignment: • Use the internet to research and write 3 paragraphs about one of the following geological formations. Describe how it was formed. DO NOT COPY CUT OR PASTE: each paragraph must be a minimum of 4 sentences. • The Giants Causeway in Northern Ireland • The Northern Canadian Rocky Mountains • Devil’s Tower, Wyoming • Mount Shasta, California • Crater Lake, Oregon

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