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Petrologi 3-difinisi


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Petrologi 3-difinisi

  1. 1. Igneous rocks: Some definitions Molten rock in the Earth is magma Magma is buoyant, rises to surface, & sometimes breaks through when magma reaches Earth’s surface it is called lava An igneous rock is formed when magma or lava cools and solidifies
  2. 2. Why should we care? Igneous rocks make up bulk of Earth’s crust Earth’s mantle is basically one huge igneous rock Important rocks economically Striking landscape features
  3. 3. Igneous rocks that form - at the surface are volcanic (extrusive) Igneous rocks that form - deep down are plutonic (intrusive)
  4. 4. Plutonic rocks To see them, they must be uplifted to surface And softer surrounding rock eroded away Magma body
  5. 5. Plutonic rocks For us to ever see them, they must be uplifted to the surface And softer surrounding rock eroded away
  6. 6. Plutonic igneous rock example: El Capitan Yosemite Nat. Park, California
  7. 7. As magma cools, atoms arrange in an orderly crystal structure crystallization
  8. 8. Note: different crystal sizes
  9. 9. Coarse-grained igneous rock Close up of crystals Note the variety of crystal sizes
  10. 10. TYPES OF MAGMA 1. granite ------ rhyolite “coarse” “fine” phaneritic aphanitic silica (SiO2) rich feldspar and quartz
  11. 11. 2. basalt---------gabbro “fine” “coarse” aphanitic phaneritic iron – magnesium (Fe – Mg) rich ferromagnesian minerals, plagioclase (Ca, Na feldspar)
  12. 12. Minerals to Rocks: Major Rock Groups IGNEOUS SEDIMENTARY METAMORPHIC
  13. 13. Igneous Rock - Molten rock that has cooled and crystallized into sold rock. • Crystal size determined by how fast the rock cooled. Due to how crystals grow. – Long time = large crystals – short time = small crystals • Course grain - crystals are easily seen with naked eye. • Fine grain - crystals < 1mm, but can still be seen without magnification. • Glassy - no crystals can be seen without magnification.
  14. 14. Forms and Structures of Igneous Rocks Intrusive Structures Extrusive Structures Lens-shaped Cone-sheet, Subjacent Sheet Ring Dikes Plutons Intrusions Intrusions Laccolith Batholith Phacolith Stock Dikes Sills Lopolith Diapirs Lava Plateau Volcanic Cone Vesicula Columnar r Jointing structure Pillow lava Amygdaloidal Block lava structure Ropy lava
  15. 15. Igneous Rocks Intrusives and Extrusives
  16. 16. Igneous Rock Structures
  17. 17. Intrusive Granite (large crystals)
  18. 18. Intrusive Igneous Rocks • Also called Plutonic • Rocks form inside the earth. Granite is the most common. • Cools slowly - Large crystals (course grain) • Magma - molten rock inside the earth.
  19. 19. Intrusive Igneous Rocks Exposed Shiprock California Granite Outcrop, Yosemite
  20. 20. Subjacent Plutons  Bathoilth  Large, irregular, major deep seated intrusive masses of very large size, elongated parallel to major tectonic regime.They have an outcrop areas greater than100km2  Stock  Is similar to batholiths, with surface area less than 100 km2. They have steeply plunging contact with no visible floor. Boss is a term applied to stocks of circular section  Diapirs  are bodies of rock and/or magma that are buoyant and moves upwards, piercing rocks above them.They appear as ballon like bodies intruded and displaced the country.
  21. 21. Extrusive Basalt (small crystals + glass)
  22. 22. The Structures of Lavas  Block Lava (subareial lava flows, result when volatile in the magma are boiled off in the vent before eruption  Ropy Lava (lava flows with less loss of volatiles show contorted snaky folds)  Pillow Lava (Submarine lava flows, exhibit a pillow structure that consists of isolated pillowed shaped masses piled one upon another  Vesicular Lava (Lava flows with gas cavities or vesicles which are trapped during solidification, eg. Scoria, Pumice,…)  Amygdaloidal structure (W hen vesilcles are later filled with secondary minerals such as Calcite, chlorite, chalcedony,..)  Columnar Jointing (fractures that separate polygonal, pencil-like cooling structures Several centimeters across.)
  23. 23. Extrusive Igneous Rocks • Also called volcanic • Rocks form at the earth’s surface. Known as Basalt • Cools rapidly - small crystals (glassy) • Lava - molten rock at the earth’s surface
  24. 24. Extrusive Igneous Rocks form near volcanoes Mt. Pinatubo Hawaii
  25. 25. Lava flow at Volcanoes National Park, Hawaii
  26. 26. Fig. 4.16
  27. 27. Fig. 4.17
  28. 28. Vesicular structure
  29. 29. Obsidian - extrusive Glassy texture (no defined crystals)
  30. 30. Fig. 4.12
  31. 31. Pumice extrusive with vesicles
  32. 32. Fig. 4.28
  33. 33. Fig. 4.30
  34. 34. Pillow Structure
  35. 35. Fig. 4.29