Week 3 Flashcards
Igneous Rocks
formed from hot material
Magma is composed of…
- A liquid component (called “melt” ).
- Gases (called “volatiles” ), including water vapor and carbon dioxide.
Where does magma come from?
Most magma is generated by the partial mantle. Temperature and pressure increase with depth in Earth’s lithosphere
Increased temperature acts to melt rock, increased pressure acts to drive the material toward a solid state.
Decompression Melting
In places where hot, near-liquid, material of the asthenosphere is allowed to rise toward the surface, the pressure acting on this material is lowered.
Reduction of pressure on allows the material to be completely molten into magma.
Occurs in places where lithospheric plates are moving apart.
Hydration-Related Melting
Subduction: in some places on Earth, one lithospheric plate is pushed under another.
As the plate descends, it is heated, and releases the water in the form of vapour.
The vapour therefore hydrates the rock in the asthenosphere
Water vapour lowers the melting point of rock, allowing it to melt into magma
In this way, “wet” rocks tend to melt at LOWER temperatures than “dry” rocks
Plutonic/Intrusive Igneous Rocks
Rocks that form from the cooling of magma below the surface are commonly called plutonic igneous rocks
Because they are formed from magma intruded into pre-existing rocks of the crust, they are also called intrusive igneous rocks
Igneous Intrusions
The magma in a magma chamber and smaller offshoots intruded into pre-existing layered rocks through fractures and contacts between sedimentary rock layers.
Batholith
Very large mass of igneous rock formed from cooling of a major magma chamber
Dyke
A tabular-shaped igneous body oriented at a significant ANGLE to layers of pre-existing rocks.
Sill
A tabular-shaped igneous body intruded PARALLEL to layers of preexisting rocks.
Laccolith
A blister-like igneous body intruded parallel to layers of pre-existing rocks (but involving some upwarping of overlying layers)
Volcanic Neck
The remnant of igneous material that once occupied the vent of a volcano.
Phaneritic texture of plutonic/intrusive igneous rocks
mineral crystals of intrusive igneous rocks are large enough to be observed with the unaided eye
Extrusive Igneous Rocks
Rocks that form from the cooling of magma ABOVE the surface. Formed from magma EXTRUDED from the ground
Lava
Magma that escapes a magma chamber and reaches Earth’s surface can erupt from a volcanic centre
How is lava extruded
From a volcanic vent due to the expansion of volatiles (gases) as they escape to the surface in response to a decrease in pressure
Aphanitic
Because extrusive igneous rocks cool above Earth’s surface, mineral crystals have little time to grow. As a result, the mineral crystals of extrusive igneous rocks are TOO SMALL to be observed with the unaided eye.
Porphyritic
When a magma cools slowly underground in its early stages, then travels rapidly toward the surface where it can cool at a faster rate. This two-stage cooling can result in a rock that is essentially aphanitic (from quick cooling phase), but contains a few large crystals called phenocrysts (from slow cooling phase)
Glassy
When lava solidifies too quickly for any significant crystallization to occur. Unordered ions remain essentially “frozen” before they can unite to form crystals. Obsidian is a common rock exhibiting such a texture.
Pyroclastic
Eruptions that are exceptionally violent can eject particles containing blobs of molten material and pulverized bits of rock.
Ferromagnesian Minerals
Those silicate minerals containing iron and magnesium.
Due to their iron/magnesium content, they are dark in colour (green, brown or black).
EX. Olivine, Pyroxene, Amphibole, Biotite Mica
Feldspar Minerals
most common mineral group, forming under a very wide range of temperatures and pressures.
Like quartz, the structure of feldspar minerals is a three dimensional framework of silica, but also contains very light metals
Bonds are less uniform in strength than in quartz.
Bowen’s Reaction Series
describes the order in which minerals crystallize from cooling magma
Mafic Rocks
Igneous rocks containing a high concentrations of dark minerals (especially ferromagnesian minerals). Generally very dark in colour.
Felsic Rocks
Igneous rocks that contain small amounts of dark minerals. Generally light in colour
Intermediate Rocks
These are rocks that have a colour in-between mafic and felsic.
Sedimentary Rocks
formed by the accumulation and hardening of sediment.
Classic Sediment
consisting of particles derived from pre-existing rocks (e.g. sand)
Chemical Sediment
consisting of mineral matter precipitated from a solution (e.g. salt)
Biochemical Sediment
consisting of materials produced by organisms (e.g. shells, bone, teeth, leaves, wood, etc.)
Mechanical/Physical Weathering
physical breakup of rocks and minerals without changes in their composition
Chemical Weathering
breakdown of minerals due to chemical reaction of minerals with water or gases in the air.
Classic Sediment Transportation
Sedimentary particles can be transported away from their source by:
- wind or water (lighter particles), sorted well
- mudflows end up poorly sorted
Evaporites
Dissolved ions can become too concentrated for the water to hold, so positive and negative ions join together and precipitate as minerals
Evaporite deposits accumulate in basins isolated from main sea seawater flows, becomes concentrated in dissolved ions and sinks
EX. Gypsum and Halite
Biogenic/Biochemical Sediment
Chemical sediment formed through biological activities
EX. bones, shells, teeth, plant remains
Metamorphism
Formed by the transformation of pre-existing rocks under the influence of high temperatures and pressures and chemically active fluids
Three types of metamorphism
1) Contact metamorphism
2) Regional metamorphism
3) Metasomatism
Contact Metamorphism
Pre-existing rock is “baked” under relatively low pressures.
Commonly occurs when rock is heated by igneous intrusion, forming a metamorphic halo in the adjacent rock.
Mineral grains recrystallize in random orientations (due to uniform pressure). Overall composition of the rock basically remains the same.
Regional Metamorphism
Pre-existing rock subjected to heat and pressure on a regional scale.
Commonly associated with mountain building events in which rocks are lowered to great depths and squeezed by compressive forces
Metasomatism
Occurs when fluids (generally water or carbon dioxide) react with a pre-existing rock and alter the chemical composition of minerals within the rock
Foliation
Regional metamorphism generally occurs in areas where two lithospheric plates are pressing against one another, and rocks are subjected to differential stress
In response to this stress, platy/elongate minerals line up to produce a foliated texture
Jade
Formed by metasomatism… Due to its extreme toughness, jade can be carved into intricate designs
