IGNEOUS ROCKS/Carbonatites 217 particular composition will begin to melt; also the temperature at which a magma or lava of given composition will be completely crystallized See Also Earth: Mantle Igneous Rocks: Granite; Komatiite Large Igneous Provinces Mantle Plumes and Hot Spots Mining Geology: Magmatic Ores Pyroclastics Tectonics: Convergent Plate Boundaries and Accretionary Wedges; Mid-Ocean Ridges Volcanoes Further Reading Asimow PD, Hirschmann MM, and Stolper EM (1997) An analysis of variations in isentropic melt productivity Philosophical Transactions of the Royal Society of London, Series A 355: 255 281 Basaltic Volcanism Study Project (1981) Basaltic Volcanism on the Terrestrial Planets New York: Pergamon DePaolo DJ (1981) Trace element and isotopic effects of combined wallrock assimilation and fractional crystal lization Earth and Planetary Science Letters 53(2): 189 202 Grove TL, Kinzler RJ, and Bryan WB (1992) Fractionation of mid ocean ridge basalt (MORB) In: Morgan JP, Blackman DK, and Sinton JM (eds.) Mantle Flow and Melt Generation at Mid Ocean Ridges, pp 281 310 American Geophysical Monograph 71 Washington DC: American Geophysical Union Hirschmann MM (2000) Mantle solidus: experimental constraints and the effects of peridotite composition Geochemistry Geophysics Geosystems 1: 70 Kelemen PB, Hirth G, Shimizu N, Spiegelman M, and Dick HJB (1997) A review of melt migration processes in the adiabatically upwelling mantle beneath oceanic spread ing ridges Philosophical Transactions of the Royal Soci ety of London, Series A 355: 283 318 Langmuir CH, Klein EM, and Plank T (1992) Petrological systematics of mid ocean ridge basalts: constraints on melt generation beneath ocean ridges In: Morgan JP, Blackman DK, and Sinton JM (eds.) Mantle Flow and Melt Generation at Mid Ocean Ridges, pp 183 280 American Geophysical Monograph 71 Washington DC: American Geophysical Union Sigurdsson H, Houghton B, McNutt SR, Rymer H, and Stix J (eds.) (2000) Encyclopedia of Volcanoes San Diego, CA: Academic Press Wickham SM (1987) The segregation and emplacement of granitic magmas Journal of the Geological Society 144: 281 297 Yoder HS (1979) The evolution of the igneous rocks: fif tieth anniversary perspectives Princeton, NJ: Princeton University Press IGNEOUS ROCKS Contents Carbonatites Granite Kimberlite Komatiite Obsidian Carbonatites K Bell, Carleton University, Ottawa, ON, Canada ß 2005, Elsevier Ltd All Rights Reserved Introduction Few other igneous rocks are as intriguing and as fascinating as carbonatites Made up of at least 50% carbonate minerals, carbonatites have distinctive trace element chemistries, many contain unusual, accessory minerals and some are even associated with economic mineral deposits Because carbonated melts can be produced by very low degrees of partial melting (