Plate tectonics and magma genesis

1. PLATE TECTONICS AND MAGMA GENESIS

2.  Introduction
 Magma
 Plate tectonics
 World plates
 Plate movement
 Plate boundaries
1. Divergent
2. Convergent
3. Transform
 Conclusion
 Reference

3.  The Earth’s crust is divided into 12 major
plates which are moved in various directions.
 This plate motion causes them to collide, pull
apart, or scrape against each other.
 In the essentially soiled silicate mantle and
crust, magma can only be created where there
are significant local perturbations in pressure
and temperature or crystallization.
 It is source of the worlds voluminous basaltic
magmas.

4. Magma is mixture of molten or semi molten rock, volatiles and
solid that found beneath the surface of earth.
Magma is a complex high temperature fluid substance.
Temperature of most magmas are the range 700 c to 1300 c.
WHAT IS MAGMA

5. The Earth’s crust is divided into 12 major plates which are
moved in various directions.
This plate motion causes them to collide, pull apart, or scrape
against each other.
Each type of interaction causes a characteristic set of Earth
structures or “tectonic” features.
The word, tectonic, refers to the deformation of the crust as a
consequence of plate interaction.
WHAT IS PLATE TECTONIC

7. • “Plates” of lithosphere are moved around by
the underlying hot mantle convection cells

8.  Due to tremendous heat, rock in the
asthenosphere is like hot taffy.
 This allows plates to ride on top of hot, flowing
rick.
 Plates move because heat is being released
from deep inside the earth.
 Conversion currents causes hot material to rise
and expand (Plates diverge) and cooler
material to sink and contract (Plates converge).

9. Plate boundaries
•Plate boundaries can be categorized in three
fundamental type

10. • Oceanic lithosphere subducts underneath the continental
lithosphere.
• Oceanic lithosphere heats and dehydrates as it subsides.
• Felsic magma will produce by partial melting of basalt
• E.g. The Andes

11. When two oceanic plates collide, one runs over the other
which causes it to sink into the mantle forming a subduction
zone.

12.  During subduction the cold crust is progressively
heated by conduction of heat from the surrounding
mantle and also possibly by fictional heating at the
surface of the slab.
 With increasing pressure and temperature ,
prograde metamorphic reactions take place and the
basaltic components of the oceanic crust are converted
through greenschist and amphibolites facies
mineralogies to eclogite.
 The net effect of this metamorphism is to
dehydrate an originally hydrous mineral assemblage,
releasing H2 O as a separate fluid phase.

13. In general, we can consider that island-arc magmas
could be generated by partial melting of any of the
following sources.
1) Amphibolites, with or without aqueous fluid;
2) Eclogite, with or without aqueous fluid;
3) Iherzolite with aqueous fluid;
4) Iherzolite modified by reaction with hydrous
siliceous magma derived by partial melting of the
slab.

14.  Where plates separate and move in opposite directions,
allowing new lithosphere to form from upwelling magma.
This either occurs at mid-ocean ridges (the so-called
seafloor spreading) or at rifted continental margins.
 In response to partial melting of mantle lherzolite
undergoing adiabatic decompression in a narrow zone of
upwelling .
 Partial melting results in the formation of basaltic
magma which is injected through tensional fissures into a
narrow zone only a few kilometers wide at the ridge axis.
 Surface volcanism, sometimes in the form of pillow lava,
occurs but most of the magma solidifies within dykes and
layered intrusive at greater depths.

16. • Where plates slide past each other.
Transform Boundaries

17. • Transform boundaries plates move by each
other in the horizontal plane along
transform and transcurrent fault systems.
• The major process that occurs at transform
boundaries is transcurrent and transform
faulting with the accompanying dynamic
metamorphism.
• Transform boundaries are often characte-
rised by some of the highest magnitude
earthquakes recorded throughout history.
•

18.  The Earth’s crust is divided into 12 major plates
which are moved in various directions.
 Oceanic lithosphere heats and dehydrates as it
subsides , Felsic magma will produce by partial
melting of basalt.
 Where plates separate and move in opposite
directions, allowing new lithosphere to form from
upwelling magma.
 Surface volcanism, sometimes in the form of pillow
lava, occurs but most of the magma solidifies within
dykes and layered intrusive at greater depths.
 Transform boundaries are often characterised by
some of the highest magnitude earthquakes recorded
throughout history.

19.  Best, Myron G. Igneous and Metamorphic
Petrology. New Delhi: CBS Publishers &
Distributors Pvt. Ltd., 1986
 Francies J. Turner, 1960, John Verhoogen,
Igneous and Metamorphic Petrology.
 http://earthds.info/pdfs/EDS_19.PDF
 www.science.marshall.edu/elshazly/Igme.doc

20. THANK YOU

21. HAPPY
EARTH
DAY