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INTRUSIVE ROCK STRUCTURES

INTRUSIVE ROCK STRUCTURES. Pages 43 to 46 in your textbook. Country Rock or Wall rock. The surrounding rock (Grey) around the intruding magma (Black). Pluton. Any igneous rock mass crystallized below the earth’s surface. It can be any geometric shape.

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INTRUSIVE ROCK STRUCTURES

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  1. INTRUSIVE ROCK STRUCTURES Pages 43 to 46 in your textbook

  2. Country Rock or Wall rock • The surrounding rock (Grey) around the intruding magma (Black)

  3. Pluton • Any igneous rock mass crystallized below the earth’s surface. It can be any geometric shape. • This is why internal igneous rocks are also referred to as Plutonic Rocks • We can observe plutons after the intrusive rock mass has been tectonically uplifted above the earth’s surface.

  4. Sill • Sheet like, 2D plutons • Concordant = parallel to bedding • Low viscosity • Under great pressure • Ability to separate the weakness in the country rock

  5. A sill in the Salt River Canyon, AZ

  6. Dike • Sheet like, 2D plutons • Squeezes into zones of weakness • Discordant = crosses to bedding

  7. Spanish Peaks and Radiating Dikes (southern CO)

  8. Spanish Peaks Dike Outcrop

  9. Laccolith • Laccolith – beginning of a sill but pressure caused doming of the rocks above them. • Over time erosion has stripped off the overlying sedimentary rocks, leaving the remains of the laccolith and dike exposed at the surface • Is often fed by a dyke from underneath.

  10. Laccolith • Crown Butte • Concordant and silicic magma

  11. Batholith • Large pluton of igneous rock spanning 10’s of km to mountain ranges of 1000’s of km’s. • B.C.’s Coast Mountains are from a large Batholith • Roots of these mountains can extend for 5km into the ground.

  12. After the overlying rocks get eroded… You could be left with a mountain range such as this in Vancouver

  13. Stock • Same idea as a Batholith just on a smaller scale. • A few km’s rather than 100’s of km’s.

  14. Stock vs Batholith • Both are discordant equidimensional pluton • Batholith is very large • Stock is very small

  15. Volcanic landforms • Volcanic pipes and necks • Pipes are short conduits that connect a magma chamber to the surface • Volcanic necks are resistant vents left standing after erosion has removed volcanic cone

  16. Pipe or Neck • Cylindrical, elongated in 1 dimension • Remains of a volcano • Discordant Black Tusk – Garibaldi Park B.C.

  17. Formation of a volcanic neck

  18. Devil’s Tower – Wyoming, U.S.A.

  19. Xenoliths • Pieces of country rock incorporated into the melt but not melted • “Foreign Rock”

  20. Light colored dike with dark colored Xenoliths

  21. This process can often bring up samples of uncommon rocks from deep in Earth’s crust. • Basalt with peridotite xenolith.

  22. Can also help in relative dating. Which rock is older, the gabbro or the granite?

  23. Chilled Margin Chilled margin of pegmatite dike in grandodiorite. • Note the coarse-grained nature of the dike near its center. • And the fine-grained nature near the margin.

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