Igneous Petrology and Volcanology - UPSC Success

156 Pages·2013·4.57 MB·English

by  Hetu Sheth

Igneous Petrology and Volcanology
Lectures, H. C. Sheth, Dept. of Earth Sciences, IIT Bombay
Lava springs, Kilauea volcano, Hawaii
• Earth is a planet ~4.5 billion years old and has an
average radius of 6,371 km.
• Earth has three
main divisions or
shells:
1. The core (mostly
metallic iron and
nickel).
2. The mantle (mostly
Fe-Mg silicate
rocks).
3. The crust (various
silicates, oxides,
carbonates, etc.)
Granite
Seven elements that make up ~97% of the Earth by
mass, and which make up various minerals and rocks
The main elements that make up the Earth’s Crust
(by mass and by volume)
The Earth’s interior
Divisions of the Core and the Mantle
are:
• The Inner Core (5150 km-6371 km)
– Pressures are so great that iron is
solid, despite its high temperature.
• The Outer Core (2900 km-5150 km):
Iron is molten.
• The Lower Mantle (670 km-2900
km): Dense silicate rocks
• The Upper Mantle (base of the crust
to 670 km): Dense silicate rocks
– The temperature at the core-mantle
boundary is ~ 5000oC.
Heat sources in the Earth:
1. Heat from the early accretion and differentiation of the
Earth
2. Heat released by radioactive decay
Heat transfer is by:
1. Radiation (heat from distant source via an intervening
medium)
2. Conduction (hotter and colder bodies in physical
contact)
3. Convection (hotter regions of a fluid upwell, colder
regions sink)
• Igneous rocks are formed through the cooling and
solidification of magma.
• Magma is molten, mobile rock material existing within a
planet, generated by natural processes.
• No magmas are made up of metallic Fe-Ni; liquid Outer
Core cannot be the source.
• Most magmas are silicates, indicating silicate sources
(Mantle, crust, or both).
• The unusual “carbonatites” are carbonates of Ca, Mg, Fe,
etc., and also come from the Mantle.
• The science of igneous rocks is called igneous petrology
(Latin “ignis” = fire, compare Sanskrit “agni”; Greek
“petra” = rock, “logia” = discourse).
Textbooks
• Best, M. G. Igneous and Metamorphic Petrology, 2nd
Edn., Blackwell, 2003.
• Cox, K. G., Bell, J. D. and Pankhurst, R. J. The
Interpretation of Igneous Rocks. Unwin Hyman, 1979.
• Hall, A. Igneous Petrology, 2nd Edn., Longman, 1996.
• McBirney, A. R. Igneous Petrology, 3rd Edn., Jones &
Bartlett, 2006.
• Middlemost, E. A. K. Magmas and Magmatic Rocks.
Longman, 1985.
• Parfitt, E. and Wilson, L. Fundamentals of Physical
Volcanology. Wiley-Blackwell, 2008.
• Winter, J. D. Introduction to Igneous and Metamorphic
Petrology. Prentice-Hall, 2001.