Petrologi 2-genesis magma

Production of Igneous Production of Igneous Rocks:Rocks:Convergent Plate Convergent Plate BoundariesBoundaries

SubductionSubduction at at convergent plate convergent plate boundaries causes boundaries causes partial melting to partial melting to form magma and form magma and resulting igneous resulting igneous rocks.rocks.

Production of Igneous Production of Igneous Rocks:Rocks:Convergent Plate Convergent Plate BoundariesBoundaries

Magma rises from Magma rises from the mantle at the mantle at divergent plate divergent plate boundaries.boundaries.

Production of Igneous Production of Igneous Rocks:Rocks: Divergent Plate Boundaries Divergent Plate Boundaries

Origin of MagmaOrigin of Magma

Where does the Where does the heat come from heat come from that melts rocks?that melts rocks? Formation of EarthFormation of Earth Heat from the Heat from the

decay of decay of radioactive radioactive elementselements

Factors that Affect Magma Factors that Affect Magma FormationFormation

TemperatureTemperature Increases with depthIncreases with depth

PressurePressure Increases with depthIncreases with depth

Water ContentWater Content Decreases melting Decreases melting

pointpoint

Mineral CompositionMineral Composition Different minerals, Different minerals,

different melting points different melting points

Characteristics of MagmaCharacteristics of Magma

Slushy Mix of molten Slushy Mix of molten rock, gases, and rock, gases, and mineral crystalsmineral crystals

Common ElementsCommon Elements

Oxygen (O)Oxygen (O) Silicon (Si)Silicon (Si) Aluminum (Al)Aluminum (Al) Iron (Fe)Iron (Fe) Magnesium (Mg)Magnesium (Mg) Calcium (Ca)Calcium (Ca) Potassium (K)Potassium (K) Sodium (Na)Sodium (Na)

Compounds in MagmaCompounds in Magma Silica ( Si0Silica ( Si022))

Most abundantMost abundant Greatest effect on Greatest effect on

Magma CharacteristicsMagma Characteristics Effects melting tempEffects melting temp Viscosity of MagmaViscosity of Magma

Types of MagmaTypes of Magma Based on amount of SilicaBased on amount of Silica

BasalticBasaltic AndesiticAndesitic RhyoliticRhyolitic

Type of MagmaType of Magma SiOSiO2 2 ContentContent

RhyoliticRhyolitic 70%70%

AndesiticAndesitic 60%60%

BasalticBasaltic 50%50%

FLUIDITY OF MAGMA

Fluidity or Viscosity of magma depends on content (%) of Silica

Silica Rich-known as Acidic magma-More viscous, so do not spreads and piles up at one place

Silica poor-Known as Basic magma-Less viscous, moves faster and occupies larger area

However, the viscosity of magma is considerably influenced by temperature too. When temperature is less-more viscous and whenHigh temperature- less viscous.

Four main groups of igneous rocks Four main groups of igneous rocks based on magma type/mineral based on magma type/mineral compositioncomposition

Felsic: Felsic: high silica content, light colored, from thick & slow moving high silica content, light colored, from thick & slow moving magma, contains low amounts of Ca, Fe, and Mg dominant magma, contains low amounts of Ca, Fe, and Mg dominant minerals quartz, potassium rich feldsparminerals quartz, potassium rich feldspar Ex: granite, pumice, rhyoliteEx: granite, pumice, rhyolite Magma Type:Magma Type:

Intermediate: Intermediate: moderate amount of silica, mixture of colors moderate amount of silica, mixture of colors dominant minerals: sodium and calcium rich feldspardominant minerals: sodium and calcium rich feldspar Ex: andesite, dioriteEx: andesite, diorite Magma Type:Magma Type:

Mafic: Mafic: low silica content, dark colored, high levels of Fe & Mg low silica content, dark colored, high levels of Fe & Mg formed from thinner, more fluid, & hotter magma than Felsic formed from thinner, more fluid, & hotter magma than Felsic rocks dominant minerals hornblende, calcium rich feldsparrocks dominant minerals hornblende, calcium rich feldspar Ex: basalt, gabbroEx: basalt, gabbro Magma Type:Magma Type:

Ultramafic: Ultramafic: very low silica content, dark colors, high levels of Fe & very low silica content, dark colors, high levels of Fe & Mg dominant minerals: olivine, pyroxeneMg dominant minerals: olivine, pyroxene Ex: peridotite, duniteEx: peridotite, dunite Magma Type:Magma Type:

Scheme For Igneous RocksScheme For Igneous Rocks

Characteristics of magmaCharacteristics of magma

Igneous rocks form as molten rock cools Igneous rocks form as molten rock cools and solidifiesand solidifies

General Characteristic of General Characteristic of magmamagma Parent material of igneous rocksParent material of igneous rocks Forms from partial melting of rocks inside Forms from partial melting of rocks inside

the Earththe Earth Magma that reaches the surface is called Magma that reaches the surface is called

lavalava


General Characteristic of magmaGeneral Characteristic of magma Rocks formed from lava at the surface are Rocks formed from lava at the surface are

classified as classified as extrusive,extrusive, or or volcanicvolcanic rocks rocks Rocks formed from magma that crystallizes Rocks formed from magma that crystallizes

at depth are termed at depth are termed intrusiveintrusive, or , or plutonicplutonic rocksrocks


The nature of magmaThe nature of magma Consists of three components:Consists of three components:

A liquid portion, called A liquid portion, called meltmelt, that is composed , that is composed of mobile ionsof mobile ions

SolidsSolids, if any, are silicate minerals that have , if any, are silicate minerals that have already crystallized from the meltalready crystallized from the melt

VolatilesVolatiles, which are gases dissolved in the melt, , which are gases dissolved in the melt, including water vapor (Hincluding water vapor (H22O), carbon dioxide O), carbon dioxide

(CO(CO22), and sulfur dioxide (SO), and sulfur dioxide (SO22))


Crystallization of magmaCrystallization of magma Texture in igneous rocks is determined by Texture in igneous rocks is determined by

the size and arrangement of mineral grainsthe size and arrangement of mineral grains Igneous rocks are typically classified byIgneous rocks are typically classified by

TextureTexture Mineral compositionMineral composition


Highly debated topicHighly debated topic Generating magma from solid rockGenerating magma from solid rock

Produced from partial melting of rocks in Produced from partial melting of rocks in the crust and upper mantlethe crust and upper mantle

Role of heatRole of heat Temperature increases within Earth’s upper Temperature increases within Earth’s upper

crust (called the crust (called the geothermal gradientgeothermal gradient) average ) average between 20between 20ooC to 30C to 30ooC per kilometerC per kilometer

Estimated temperatures in Estimated temperatures in the the crust and mantlecrust and mantle


Role of heatRole of heat Rocks in the lower crust and upper mantle are Rocks in the lower crust and upper mantle are

near their melting pointsnear their melting points Any additional heat (from rocks descending Any additional heat (from rocks descending

into the mantle or rising heat from the mantle) into the mantle or rising heat from the mantle) may induce melting may induce melting


Role of pressureRole of pressure An increase in confining pressure causes an An increase in confining pressure causes an

increase in a rock’s melting temperature or increase in a rock’s melting temperature or conversely, reducing the pressure lowers the conversely, reducing the pressure lowers the melting temperaturemelting temperature

When confining pressures drop, decom-When confining pressures drop, decom-pression melting occurspression melting occurs

Decompression meltingDecompression melting


Role of volatilesRole of volatiles Volatiles (primarily water) cause rocks to melt Volatiles (primarily water) cause rocks to melt

at lower temperaturesat lower temperatures This is particularly important where oceanic This is particularly important where oceanic

lithosphere descends into the mantlelithosphere descends into the mantle

Evolution of magmasEvolution of magmas

A single volcano may extrude lavas A single volcano may extrude lavas exhibiting very different compositionsexhibiting very different compositions

Bowen’s reaction seriesBowen’s reaction series and the and the composition of igneous rockscomposition of igneous rocks

N.L. Bowen demonstrated that as a magma N.L. Bowen demonstrated that as a magma cools, minerals crystallize in a systematic cools, minerals crystallize in a systematic fashion based on their melting pointsfashion based on their melting points


Bowen’s reaction seriesBowen’s reaction series During crystallization, the composition of During crystallization, the composition of

the liquid portion of the magma continually the liquid portion of the magma continually changeschanges Composition changes due to removal of Composition changes due to removal of

elements by earlier-forming mineralselements by earlier-forming minerals The silica component of the melt becomes The silica component of the melt becomes

enriched as crystallization proceedsenriched as crystallization proceeds Minerals in the melt can chemically react and Minerals in the melt can chemically react and

changechange


Processes responsible for changing a Processes responsible for changing a magma’s compositionmagma’s composition

Magmatic differentiationMagmatic differentiation Separation of a melt from earlier formed Separation of a melt from earlier formed

crystals to form a different composition of crystals to form a different composition of magmamagma

AssimilationAssimilation Changing a magma’s composition by the Changing a magma’s composition by the

incorporation of foreign matter (surrounding incorporation of foreign matter (surrounding rock bodies) into a magmarock bodies) into a magma

Assimilation and magmatic Assimilation and magmatic differentiationdifferentiation


Processes responsible for changing a Processes responsible for changing a magma’s compositionmagma’s composition

Magma mixingMagma mixing Involves two bodies of magma intruding one Involves two bodies of magma intruding one

anotheranother Two chemically distinct magmas may produce Two chemically distinct magmas may produce

a composition quite different from either a composition quite different from either original magmaoriginal magma


Partial melting and magma formationPartial melting and magma formation Incomplete melting of rocks is known as Incomplete melting of rocks is known as

partial meltingpartial melting Formation of basaltic magmasFormation of basaltic magmas

Most originate from partial melting of Most originate from partial melting of ultramafic rock in the mantleultramafic rock in the mantle

Basaltic magmas form at mid-ocean ridges by Basaltic magmas form at mid-ocean ridges by decompression melting or at subduction zonesdecompression melting or at subduction zones


Partial melting and magma formationPartial melting and magma formation Formation of basaltic magmasFormation of basaltic magmas

As basaltic magmas migrate upward, confining As basaltic magmas migrate upward, confining pressure decreases which reduces the melting pressure decreases which reduces the melting temperaturetemperature

Large outpourings of basaltic magma are Large outpourings of basaltic magma are common at Earth’s surfacecommon at Earth’s surface


Partial melting and magma formationPartial melting and magma formation Formation of andesitic magmasFormation of andesitic magmas

Interactions between mantle-derived basaltic Interactions between mantle-derived basaltic magmas and more silica-rich rocks in the crust magmas and more silica-rich rocks in the crust generate magma of andesitic compositiongenerate magma of andesitic composition

Andesitic magma may also evolve by magmatic Andesitic magma may also evolve by magmatic differentiationdifferentiation


Partial melting and magma formationPartial melting and magma formation Formation of granitic magmasFormation of granitic magmas

Most likely form as the end product of Most likely form as the end product of crystallization of andesitic magmacrystallization of andesitic magma

Granitic magmas are higher in silica and Granitic magmas are higher in silica and therefore more viscous than other magmastherefore more viscous than other magmas

Because of their viscosity, they lose their Because of their viscosity, they lose their mobility before reaching the surfacemobility before reaching the surface

Tend to produce large plutonic structuresTend to produce large plutonic structures

Petrologi 2-genesis magma

Technology

magma cools

earth magma

hotter magma

basic magma

acidic magma

nature of magma

volcanic rocks rocks

magma silica si02