Petrologi 3-difinisi
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Petrologi 3-difinisi






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Petrologi 3-difinisi Petrologi 3-difinisi Presentation Transcript

  • 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
  • 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
  • Igneous rocks that form - at the surface are volcanic (extrusive) Igneous rocks that form - deep down are plutonic (intrusive)
  • Plutonic rocks To see them, they must be uplifted to surface And softer surrounding rock eroded away Magma body
  • Plutonic rocks For us to ever see them, they must be uplifted to the surface And softer surrounding rock eroded away
  • Plutonic igneous rock example: El Capitan Yosemite Nat. Park, California
  • As magma cools, atoms arrange in an orderly crystal structure crystallization
  • Note: different crystal sizes
  • Coarse-grained igneous rock Close up of crystals Note the variety of crystal sizes
  • TYPES OF MAGMA 1. granite ------ rhyolite “coarse” “fine” phaneritic aphanitic silica (SiO2) rich feldspar and quartz
  • 2. basalt---------gabbro “fine” “coarse” aphanitic phaneritic iron – magnesium (Fe – Mg) rich ferromagnesian minerals, plagioclase (Ca, Na feldspar)
  • Minerals to Rocks: Major Rock Groups IGNEOUS SEDIMENTARY METAMORPHIC
  • 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.
  • 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
  • Igneous Rocks Intrusives and Extrusives
  • Igneous Rock Structures
  • Intrusive Granite (large crystals)
  • 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.
  • Intrusive Igneous Rocks Exposed Shiprock California Granite Outcrop, Yosemite
  • 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.
  • Extrusive Basalt (small crystals + glass)
  • 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.)
  • 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
  • Extrusive Igneous Rocks form near volcanoes Mt. Pinatubo Hawaii
  • Lava flow at Volcanoes National Park, Hawaii
  • Fig. 4.16
  • Fig. 4.17
  • Vesicular structure
  • Obsidian - extrusive Glassy texture (no defined crystals)
  • Fig. 4.12
  • Pumice extrusive with vesicles
  • Fig. 4.28
  • Fig. 4.30
  • Pillow Structure
  • Fig. 4.29