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Crystallization of

Magma

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Magma Generation

 Magma: is a hot, naturally occurring mobilerock-forming material of complex silicatesand oxides.

Most magmas are a combination of liquid,

gases, solids(crystals). t is generated in theupper parts of mantle (asthenosphere) andlo!er crust.

Magma is generated mainly at "#$%% places:

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a- Along mid-ocean ridges: (diverging plates) asoceanic crust is thinned producing pressure off the

mantle which then melts.

 b- Near  subduction  zone:(Converging plates). Meltingmay occur in upper mantle because water and

sediment introduced by subducting slab causes partial

melting of the upper mantle

C -  At hot spots: where hot mantle material rises andmelts as pressure is released.

Magma Generation

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 A- Primitive Magmas: are unmodified magmas that formthrough anateis (melting) of Mantle roc!s that have not beenchanged in composition since they formed

 "- Primary Magmas: are any chemically unchanged meltderived from any !ind of #re-eisting roc!. All primitivemagmas are primary$ but most primary magmas that yieldmodern roc! is not primitive.

 C - Parental Magmas:are magmas that have given rise to other

magmas  %- Derivitive  Magmas&are magmas derived directly from a

 preeisting magma

Types of Magma (origin)

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 A- Mafic (Basic) magma:

 temperature ranges between ' to * C  less than ++, i* 

cools to include mafic minerals/ olivine$ pyroene$ and Ca- plagioclase.

 "- Intermediate magma:  temperature ranges between 0+ to ' C 

 i* between ++, and 1+,

cools to include minerals pyroene$ Ca-plagioclase$ Na- plagioclase$ amphibole$ and mica.

 C - Felsic magma:  temperature ranges between 0+ to 1 C$

 i* between 1+ - 22,$ cools

cools to form felsic minerals such as 3-feldspar$ 4uartz$ mica$

amphibole$ and Na- amphibole.

Types of Magma (SiO)

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 A- Temperat!re: T"e temperat!re ranges #et$een %&& 

'to && 

'

 "- Density: T"e val!es of density meas!red at roomtemperat!re for nat!ral an"ydro!s glasses (o#sidians)ranges from a#o!t * gm+cm, for acid li-!ids to a#o!t .

gm+cm, for #asic glasses

C - /iscosity:/iscosity of magma depends !pon: SiO content 0t"e more SiO t"e more visco!s

Temperat!re  0 lo$ temperat!re magma is "ig"er viscosityt"an "ig"  temperat!re magma

/olatiles content (1O and 'O2): t"e more 1O and 'O t"e lessvisco!s

 

P"ysical properties of magma