transcript
- Slide 1
- GEOL- 103 Lab 2: Igneous/Metamorphic Rocks
- Slide 2
- Slide 3
- Igneous Rocks Form as molten rock cools and solidifies General
characteristics of magma Parent material of igneous rocks Forms
from partial melting of rocks Magma at surface is called lava
Environments Extrusive: rocks formed from lava (volcanic rocks)
Intrusive: rocks formed from magma (plutonic rocks) Can also have
both stages
- Slide 4
- Igneous Textures Used to describe overall appearance of rock
based on: Crystal size Arrangement of minerals Factors affecting
crystal size Rate of cooling Slow rate: fewer, large crystals Fast
rate: abundant, small crystals Very fast rate: no crystals % of
silica present Dissolved gases
- Slide 5
- Igneous Rock Textures Aphanitic texture Fine-grained Rapid
cooling rate Microscopic crystals Phaneritic texture Coarse-grained
Slow cooling rate Large, visible crystals
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- Igneous Rock Textures Porphyritic texture Mineral forms at
different depths and temperatures Large crystals (phenocrysts) are
embedded in matrix of smaller crystals (groundmass) Glassy texture
No crystals Very rapid cooling
- Slide 7
- Igneous Rock Textures Pyroclastic texture Formed from
collisions due to volcanic eruptions Many different sized particles
Vesicular texture Formed during volcanic eruptions Contains holes
formed by captured gases
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- Mineral Compositions Felsic Light-colored silicate minerals
(quartz, feldspar, muscovite) High amounts of silica; high
viscosity; high gas content Common in continental crust Mafic
Dark-colored silicate minerals (olivine, pyroxene, amphibole,
biotite, plagioclase) More dense than felsic rocks Low amounts of
silica; low viscosity Common in oceanic crust and volcanic
islands
- Slide 9
- Mineral Compositions Intermediate Contain 25% or more dark
silicate minerals Associated with explosive volcanic activity Mix
of mafic and felsic compositions Ultramafic Rare composition common
in mantle High in magnesium and iron Composed mostly of olivine
(green tint)
- Slide 10
- Bowens Reaction Series
- Slide 11
- Slide 12
- Metamorphic Rocks Formed through process of metamorphism
Transition of one rock into another by increasing temperature
and/or pressure conditions Produced from: Igneous rocks Sedimentary
rocks Other metamorphic rocks Progresses incrementally from
low-grade to high-grade During metamorphism, rock must remain
essentially solid
- Slide 13
- Metamorphic Settings Contact metamorphism Body of magma comes
into contact with country rock Chemical alterations from hot,
ion-rich water Localized event Regional metamorphism Occurs during
large-scale regional mountain building events Produces greatest
volume of metamorphic rock Rocks usually display zones of contact
and/or hydrothermal metamorphism
- Slide 14
- Metamorphic Agents Heat Most important agent Recrystallization
results in new, stable minerals Heat sources: contact metamorphism
and/or geothermal gradient (25C/km) Pressure Increases with depth
Realigns mineral crystals
- Slide 15
- Metamorphic Agents Hydrothermal fluids Water containing other
volatile compounds Enhances migration of ions to affect
recrystallization of existing minerals Fluid sources: pore spaces,
fractures, and hydrated minerals Parent rocks Rock with same
overall composition of metamorphic rock Mineral make-up of parent
rock influences degree of metamorphism that may occur
- Slide 16
- Metamorphic Textures Refers to size, shape, and arrangement of
mineral grains Foliation Any planar arrangement of mineral grains
or structural features within a rock Formation Rotation of platy
and/or elongated minerals Recrystallization of minerals in
direction of preferred orientation Changing shape of
equidimensional grains into aligned, elongated shapes
- Slide 17
- Metamorphic Textures Types of foliation Slaty: rocks can be
easily split into thin, tabular sheets Schistosity: platy minerals
visible and exhibit a layered structure Gneissic: distinctive
banded appearance Nonfoliation Develop in low deformation
environments Composed of minerals with equidimensional
crystals
- Slide 18
- Samples Igneous Rocks Basalt Diorite Gabbro Granite (x2)
Obsidian Peridotite Porphyritic Andesite Pumice Rhyolite Scoria
Volcanic Tuff Metamorphic Rocks Anthracite Gneiss Marble Phyllite
Quartzite Schist (x2) Slate