Igneous Rocks

Sedimentary Systems

Generally cool. Rarely above 150o C

Metamorphic Systems

Hot. Low grade metamorphism can occur at 150oC. High grade metamorphism can take place at 800oC

Igneous System

Melting and remelting take place at 700oC to 1400oC.

Igneous Rocks

Rock that “freezes” (solidifies) from molten magma or lava.

Magma

Molten Rock Beneath the Surface.

Lava

Molten rock that reaches the surface. “freezes” at 650°C (1200F) to 1,100°C

(2000F).

Intrusive igneous rocks (plutonic)

Rocks formed from the solidification of magma below the Earth’s surface.

Extrusive igneous rocks (volcanic)

Rocks formed by the solidification of lava at the Earth’s surface as either

cooled lava or pyroclastic debris.

Extrusive Igneous Rocks

Small crystals (can’t really “see” them), Crystals are small because there is less time for them to form and expand.

Example of Extrusive Rocks

Basalt

- Common rock at volcanoes and on the

ocean bed (oceanic crust!!)

-Magma flows from a vent onto the Earth’s

surface (lava) and rapidly cools

Small Grains

Extrusive Rocks Grains are what size?

Big Grains

Intrusive Rock Grains are what size?

Rhyolite, Andesite, Basalt

Give me Examples of Extrusive Rocks

Granite, Diorite, Gabbro

Give me Examples of Intrusive Rocks

Magma Solid

Solidified mineral crystals are carried by the melt

Magma Liquid

The melt itself is comprised of mobile ions.

Magmas

Different mixes of elements yield different ______.

Solid, Liquid and Gas

Magma is made of three things?

Gas

Magmas contain abundant dissolved volatile _____.

Dry Magma

Scarce volatiles (dissolved gas).

Wet Magma

Up to 15% volatiles.

H20, CO2, SO2, N2, H2

Wet Magmas chemicals are what?

UltraMafic

Darkest

Mafaic

Meidum Dark

Intermediate

Medium

Felisic

Light

Rhyolite

This rock is felsic, has small crystals, melts at 600-800 C, and its main minerals that it has in it are:

-Na-plagioclase

-K-feldspar

-Quartz

-Mica

Granite

This rock is felsic, has large crystals, melts at 600-800 C, and its main minerals that it has in it are:

-Na-plagioclase

-K-feldspar

-Quartz

-Mica

Andesite

This rock is intermediate, has small crystals, melts at 800-1000 and its main minerals are:

Na+Ca-Plagioclase Amphibole

-Quartz

Diorite

This rock is intermediate, has large crystals, melts at 800-1000 and its main minerals are:

Na+Ca-Plagioclase Amphibole

-Quartz

Basalt

This rock is Mafic, small crystals, melts at 1000-1300, and its main minerals are:

-Ca-plagioclase

-Pyroxene

-Olivine

Gabbro

This rock is Mafic, large crystals, melts at 1000-1300, and its main minerals are:

-Ca-plagioclase

-Pyroxene

-Olivine

Komatiite

This rock is Ultramafic, small crystals, melts at 1400+, and its main minerals are:

-Olivine

-Pyroxene

Peridotite

This rock is Ultramafic, large crystals, melts at 1400+, and its main minerals are:

-Olivine

-Pyroxene

Ultra Mafic

Silcia Content ≤ 45% SiO2 (very silica-poor)

Very Silica Poor

Ultra Mafic is ….

Mafic

Silica content between 45% to 55% SiO2 (silica-poor)

Intermediate

Silica content 55% to 65% SiO2

Felsic

Silica content ≥ 65% SiO2 (silica-rich)

Silica Rich

Felsic is….

Ultra Mafic

What compotsion is the first to crystalize?

Felsic

What compostion is the last to crystalize?

Ultramafic vs. Felsic

High temp vs Low Temp

Bowens Reaction Series

The succession of mineral crystallization in a cooling magma.

Discontinues Series

Olivine, Pyroxene, Amphibole, Biotite, K-Feldspar, and Muscovite

Continuous Series

Ca-Rich, Plagioclase, and Na-Rich

Magma Chamber

A large volume of magma that has risen and accumulated within the crust.

Country Rock

(Wall rock) any crustal rock that was older than and intruded by an igneous body

Intrusive Contact

Boundary between the igneous inclusion and the surrounding country rock.

Xenolilth

Fragment of rock (usually a relic of country rock) distinct from the igneous rock in which it is enclosed.

Source of heat for Magma formation

Earth’s core and decay of radioactive elements.

Geothermal gradient

Rate at which temperature increases with increasing depth (crust: ̴ 30ºC/km).

Aggregates

Rocks melt over a range of temperatures because they are _______ of

minerals

Zone of Partial Melting

Rocks are partly molten and partly solid.

Mantle

Not molten, but solid rock (peridiole).

Magma Formation

For ____ _______ conditions must change so that the geothermal gradient can intersect the zone of partial melting.

Geothermal Gradiant, the Zone of Partial Melting

Decompression melting, flux melting and heat-transfer melting are ways that the _________ _________ intersection with ____ _____ _ ____ ____ can occur.

Decompression Melting

Occurs when a body of hot mantle rock moves upward and the pressure is reduced – lowering the temperature at which rocks melt.

Decrease in pressure

Decompression melting

Decompression Melting

A rift zone, mid-ocean ridge –→ divergent boundary, and mantle plume –→ hot-spot are examples of _______.

Silicon-Oxygen

Water under high pressure will break the ________ bonds in

minerals and the rocks will begin to melt

Flux Melting

Occurs when the addition of volatiles significantly decreases the melting

temperature of a rock.

Volatiles

Any substance (such as H2O, CO2, N2, H2, SO2) that evaporates relatively easily.

Heat-Transfer Melting

Occurs if the increase in temperature from a rising body of magma is sufficient to cause the surrounding crustal rock to melt.

Heat Transfer Melting

When magma from the mantle rises into the crust, the heat it carries raises the temperature of the surrounding crustal rock.

The Composition of a Melt

This depends on:

-Partial Melting

-Composition of the source-rock (mantle vs crustal source)

-Assimilation

-Magma mixing

-Fractional Crystallization

Assimilation

The process of magma ‘contamination’ in which blocks of wall rock fall into a magma chamber and dissolve.

Partial Melting

The process by which only part of an original rock melts to form magma (minerals with the lowest melting temperatures melt first, while minerals with higher melting temperatures remain solid).

Magma Mixing

Different magmas may blend in a magma chamber. The result combines the characteristics of the two magmas.

Magma Mixing

A way to change a melt is by…..

Magma Mixing

Often incomplete, resulting in blobs of one rock type suspended within the other like oil and vinegar

Fractional Crystallization

As magma cools, early crystals settle by gravity. Melt composition changes as a result.

-Fe, Mg, and Ca are removed in early settled solids.

-Si, Al, Na, and K remain in melt and increase in abundance.

Viscosity

Resistance to flow

• Affects the speed at which molten rock (magma or lava) flows

• Viscosity of a melt is dependent on:

-temperature

-volatile content

-silica (SiO2) content

-Crystal conten

Intrusive Igneous Structures

DIke, Sill, Laccolith

Dike

A tabular, discordant intrusive structure

Discordant

The Dike is the body is NOT parallel to any layering in the country rock. Which means it is what?

Sill

A tabular, concordant intrusive structure

Concordant

The Sill means the body is parallel to layering in the country rock. Which means it is what?

Laccolith

A concordant intrusive structure, similar to a sill, but the central portion is thicker and domed upward

Pluton

A blob-shaped’ body of magma that crystallized at a considerable depth within the crust

Plutons

Stock and Batholith are names of what?

Batholith

A large, discordant pluton – extent > 100 km2. It is formed of numerous coalesced plutons

Stock

A small, discordant pluton – extent < 100 km2.

Diapirs

Some plutons orgianted as what?

Diapir

A buoyant, light-bulb- shaped ‘blob’ of geologic material that rises upward

through the crust, deforming the overlying rock.

Texture

How quickly the magma or lava cooled intrusive (plutonic) or extrusive (volcanic).

Chemical Composition

Origin and evolution of magma prior to cooling and solidification.

Texture

These descrtiopns are types of what?

• crystalline

• porphyritic

• glassy

• fragmental

• vesicular

Crystal Size

Grain Size = _________

Crystal size

Rate of cooling and viscosity determine what?

Extrusive

Volcanic

Intrusive

Plutonic

Aphanitic texture

Extrusive (volcanic) grains are less than (<) 1 mm.

Aphanitic texture

FIne Grained

Phaneritic texture

• intrusive (plutonic)

• grains are greater than (>) 1 mm

Phaneritic texture

Coarse Grained

Pegmatite

-intrusive (plutonic) – magma enriched in volatiles

-grains are greater than (>) 1 cm, can be greater than (>)

Porphyritic texture

Two different rates of cooling and Phenocrysts.

Phenocrysts

Coarse-grained crystals enclosed in a groundmass of finer-grained crystals

Glassy Texture

Extremely rapid (almost instantaneous) cooling.