Igneous Petrology Part 2

IGNEOUS ROCK

Any crystalline or glassy rock that formed from the cooling and solidification of magma

Magma

Consists mostly of igneous rock matter but may contain various minerals, gas phase that may dissolved in a liquid or may be present as a separate gas phase

Intrusive IGNX RX

when magma cools down beneath the surface of the earth

magma crystallizes

Extrusive IGNX RX

When magma cools down on the surface of the earth

TYPES OF MAGMA
(RECITE THE TABLE)

CHERT

100 % SiO2

Andesitic Magma
(SR: Andesite)

Intermediate Fe, Mg, Ca, K, Na

800-1000 deg celsius

Intermediate Viscocity and Gas content

Basaltic Magma
(SR: Basalt)

High Fe, Mg, Ca
Low in K, Na

1000-1200 deg celsius

LOW Viscocity and Gas content

Rhyolitic Magma
(SR: Rhyolite)

Low Fe, Mg, Ca
High K, Na

650-800 deg celsius

HIGH Viscocity and Gas content

Mantle generated by partial melting

Where do magmas came from?

Core
Right

_____ is not likely to be source of magma because it does not have the ______ chemical composition

Core

The layer of the earth that is mostly iron

SILICATE

Magmas are _____ liquids
Main Composition of Magma

Magmas DO NOT come from the molten outer core of the earth

MANTLE

Magma is generated from the earth's_____

PARTIAL MELTING

Magma is generated from the earth's mantle due to what process

Earth's Surface
Earth's Subsurface

Heat Sources

Heat from the sun

Heat Source based on the surface of the earth

Earth's Accretion
Radioactive Decay

Heat Sources based on the subsurface of the earth

Radiation, Conduction, Convection

What are the three types of heat transfer?

The three types of heat transfer can participate in the formation of magma.

Radiation: pluton is included
Conduction: if there are Intrusions
Convection: Through the Mantle

25 degrees celsius per km depth

What is the Value of Geothermal Gradient?

Rocks melt over a RANGE of temperatures

Range

Rocks melt at a _______ temperature.
Minerals melt at a _______ temperature


Single
Variety
Range

Single

Minerals melt at a _______ temperature


Single
Variety
Range

As you go down towards the center of the earth, the geothermal gradient increases 25 degrees celsius per km depth

Geothermal Gradient

Heating of wet and dry rocks

The meting of dry rocks is similar to the melting of dry minerals only that it has a range of temperatures where partial melting exist.

P increases with T
(directly proportional)

The meting of rocks containing water or CO2 (wet rocks) is similar to the melting of wet minerals only that it has a range of temperatures where partial melting exist.

P increases while T decreases
(inversely proportional)

0 to 100 degrees Celsius

The degree of partial melting ranges from _______ deg celsius

Decompression Melting

Upwelling hot material with the drop of pressure (decrease in pressure)

Hot Spots
Ocean Ridge
Rift Valley
Subduction Zones

Environments where melting occurs

Flux Melting

melting due to the addition of volatiles

Lowering the melting temperature can be achieved by adding water or carbon dioxide

Flux Melting

Lowering the melting temperature can be achieved by adding water or carbon dioxide

To generate magma, geothermal gradient must be raised or melting temp of rx must be lowered.

Wet rocks are easier to melt than dry rocks because wet rocks already contain moisture/water.

Primitive Magma

Is one that is close to its original composition and therefore in theory not undergone cryystal fractionation

Evolved Magma

Magma that is different from the starting composition and Crystal Fractionation has taken place

Magmatic Differentiation

a process whereby an originally homogeneous magma changes it's composition or becomes heterogeneous.

Fractional Crystallization
Magmatic Mixing
Magmatic Assimilation

Mechanisms in Magmatic Differentiation

Fractional Crystallization

the crystallization and removal of different minerals from the cooling magma

there are minerals that tend to crystallize first compared to some. Those with high melting point will melt while those with a low melting point remain solid

Magma Mixing

If two magma with different compositions come in contact to one another (mixed).

Magmatic Assimilation

changing a magma's composition (altered) by the incorporation (inclusion) of surrounding rock bodies into a magma

the composition of magma is dependent to the assimilated/contaminated country rock.

Magmatic Assimilation

reaction between the magma and the host rock

Assimilation

magma reacts with the country rock

Increase in Temp
Decompression (dec in pressure)
Flux Melting
Partial Melting

Ways on how to GENERATE magma

Magmatic Assimilation

Contamination of magma by crustal rx
reaction of magma and the host rock

Liquid Immiscibility

2 liquid with different composition coexist at equilibrium