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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.