This document discusses mechanisms of magma diversification, including partial melting, crystal fractionation, thermogravitational diffusion, liquid immiscibility, vapor transport, magma mixing, and assimilation. Partial melting refers to processes where a magmatic melt is created from a portion of solid rock. Crystal fractionation involves the separation of crystals from melt through settling, filtering, or flow. Thermogravitational diffusion causes components to separate due to temperature and density gradients. Liquid immiscibility can cause magma to split into immiscible liquid fractions. Vapor transport involves volatile release upon pressure reduction. Magma mixing combines magmas of different compositions. Assimilation incorporates country rock into magma through reaction.

1. SEMINAR ON
diversification of magma

2. CONTENTS
I N T R O D U C T I O N
M A G M A T I C D I F F E R E N T I AT I O N
M E C H A N I S M S O F M A G M A D I V E R S I F I C AT I O N
P A R T I A L M E L T I N G
C R Y S T A L F R A C T I O N AT I O N
T H E R M O G R A V I T AT I O N A L D I F F U S I O N
L I Q U I D I M M I S C I B I L I T Y
V A P O R T R A N S P O R T
M A G M A M I X I N G
A S S I M I L AT I O N
C O N T E N T S
R E F E R E N C E S

3. INTRODUCTION
 Magma is a hot viscous, siliceous melt containing water
vapour and gases. it comes from great depth below the
earth surface. It is composed of mainly O,Si,Al,Fe,Ca,Mg,Na
and K.When magma comes out upon the earth’s surface,
such magma is called lava.
There are two types of magma existed and all types of
igneous rocks were derived from them.
 These magmas are acidic magma and basic magma.

4. MAGMATIC DIFFERENTIATION
Magmatic differentiation is a complex
process whereby a single melt can produce a
wide variety of different igneous rocks.
Or it is the process by which magmas evolve
to give rise to a variety of magmas and rock
types (that have different compositions).
Therefore, certain physical processes are
required to cause the chemical diversification
of a magma (i.e. its differentiation).

5. MECHANISMS OF MAGMA DIVERSIFICATION
(DIFFERENTIATION)
1-Partial melting
2-Crystal fractionation
3-Thermogravitational diffusion
4-Liquid immiscibility
5-Vapor transport
6-Magma mixing
7-Assimilation

6. The term "partial melting," refer to processes
that create a magmatic melt from a portion
of a solid rock less than the whole. Because
most crystalline, or igneous, rocks in the
earth's crust are composed of a number of
silicate minerals that melt at different
temperatures, and of minerals with
heterogeneous crystal lattices, almost all
magmas are generated by partial melting.
PARTIAL MELTING

7. SEGREGATION
Separation of a partially melted liquid
from the solid residue

8. INCONGRUENT MELTING
Many minerals do not melt uniformly. Instead they
decompose as they melt, becoming melt plus a new solid
mineral species. One example is solid Forsterite
(Mg2SiO4), which decomposes to solid Enstatite (MgSiO3)
plus liquid silica (SiO2) in the melt.
Forsterite is chemically incompatible with quartz,
because the reaction ensures Enstatite forms from Olivine
and silica. Forsterite reacts with Quartz as follows:
Forsterite (Mg2SiO4) (s) + Quartz (SiO2) (l) = 2 Enstatite (MgSiO3) (s)

9. CRYSTAL FRACTIONATION
Crystal fractionation is the separation of crystals
from the melt, either during or after their
crystallization. Crystal fractionation is occur mainly
three ways
CRYSTAL SETTLING
CRYSTAL FRACTIONATION

10. CRYSTAL SETTLING
The differential motion of crystals and liquid
under the influence of gravity due to their
differences in density

11. CRYSTAL FRACTIONATION
Crystal fractionation is the separation of crystals
from the melt, either during or after their
crystallization. Crystal fractionation is occur mainly
three ways
FILTER PRESSING
CRYSTAL FRACTIONATION

12. Filter pressing, or
compaction, in
which a crystal
mush is squeezed
like a sponge by
weight of crystals
above.
F I LT E R P R E S S I N G

13. CRYSTAL FRACTIONATION
Crystal fractionation is the separation of crystals
from the melt, either during or after their
crystallization. Crystal fractionation is occur mainly
three ways
FLOW SEGREGATION
CRYSTAL FRACTIONATION

14. FLOW SEGREGATION

15. THERMOGRAVITATIONAL
DIFFUSION
A phenomenon in which a temperature gradient in a
mixture of fluids gives rise to a flow of one
constituent relative to the mixture as a whole. Also
known as thermo diffusion.
Stable and persistent stagnant boundary layers have
been shown to occur near the top and sides of
magma chambers

16. MODEL
Figure 11-11. Schematic section through a rhyolitic magma chamber undergoing convection-aided in-situ
differentiation. After Hildreth (1979). Geol. Soc. Amer. Special Paper, 180, 43-75.

17. LIQUID IMMISCIBILIT Y
 The acceptance of liquid immiscibility as a viable petrogenetic
process for the diversification of magmas has varied over the years
(Roedder 1979).
 Experimental studies have demonstrated that it can occur in
two types of silicate melt:
1. In highly Fe-rich basaltic melts, where one liquid is rich in Fe and
P and poor in Si, and the other is rich in Si but poor in Fe and P.
2. In highly alkaline melt.

18. Continued…..
 A magma may split up in two immiscible
liquid fractions of different composition like
oil and water as a result of cooling.
 Subsequent crystallization of these
immiscible parts give rise to different types
of rocks.

19. S O M E E X A M P L E S
Silicate-silicate immiscibility.
Late silica-rich immiscible droplets in Fe-rich tholeiitic basalts.
Sulfide-silicate immiscibility (massive sulfide deposits).
Carbonatite-nephelinite systems

20. As a volatile-bearing magma rises and
pressure is reduced, the magma may
eventually become saturated in the vapor,
and a free vapor phase will be released
VOLATILE TRANSPORT

21. MAGMA MIXING
Magma mixing is the mixing of two or more magmas
or magma batches to form a hybrid magma. The
resulting magma commonly inherits intermediate
properties of the two parent magmas.
Mixing two magmas that are compositionally
different will produce a magma of intermediate
composition.
For magma mixing to occur, both magmas have to
overcome their density contrasts, which will work at
separating them into two distinct layers.
Magma mixing is more common at the sites of mid-
oceanic ridges, where pulses of less differentiated
magmas are frequently injected into a fractionated
magma in the chamber beneath the ridge.

24. Assimilation is the reaction of the magma with the
country rocks, whereby these country rocks are
incorporated in the magma and eventually melt.
For this process to become an efficient mechanism
of differentiation, relatively large amounts of the
country rocks have to be assimilated by the
magma, and/or the compositions of these country
rocks have to be drastically different from that of
the magma.
ASSIMILATION

25. Criteria for recognition of assimilation:
1- The occurrence of xenoliths in the igneous
rocks, which are of similar composition to the
intruded country rocks.
2- Resorbed xenocrysts

26. CONCLUSION
Differentiation is the process by which magmas evolve to give rise
to a variety of magmas and rock types (that have different
compositions).
Therefore, certain physical processes are required to cause the
chemical diversification of a magma.
Liquid immiscibility is where liquids do not mix with each other like
oil and water as rate of cooling
Most melts develop in the lower crust or in the asthenosphere (upper
mantle), so, such melts have a primitive mafic or basaltic composition,
whereas melts developing in the upper crust have a higher initial silica
content.
. The main processes involved in differentiation are assimilation,
exchange of volatiles, fractional crystallization, and magmatic mixing.

27. REFERENCES
 2003,Myron.g.best,igneous and metamorphic petrology,blackwell
publishing, page no:316-324
 1989,M.Wilson,Igneous petrogenesis,springer,page no:82-97
 2004,El-shazly.a.k, igneous and metamorphic petrology, page no:1-6
 http://www.tulane.edu/~sanelson/eens211/magmadiff.ht
 http://en.wikipedia.org/wiki/liquid immiscibility

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