Granitoid RocksPowerPoint PresentationSlide 3Slide 4Slide 5Slide 6Granitoid RocksGranitoid RocksA few broad generalizations:A few broad generalizations:1) Most granitoids of significant volume occur in areas 1) Most granitoids of significant volume occur in areas where the continental crust has been thickened by where the continental crust has been thickened by orogeny, either continental arc subduction or collision orogeny, either continental arc subduction or collision of sialic masses. Many granites, however, may post-of sialic masses. Many granites, however, may post-date the thickening event by tens of millions of years.date the thickening event by tens of millions of years.2) Because the crust is solid in its normal state, some 2) Because the crust is solid in its normal state, some thermal disturbance is required to form granitoidsthermal disturbance is required to form granitoids3) Most workers are of the opinion that the majority of 3) Most workers are of the opinion that the majority of granitoids are derived by crustal anatexis, but that the granitoids are derived by crustal anatexis, but that the mantle may also be involved. The mantle contribution mantle may also be involved. The mantle contribution may range from that of a source of heat for crustal may range from that of a source of heat for crustal anatexis, or it may be the source of material as wellanatexis, or it may be the source of material as wellGranitoid Rocks Granitoid Rocks Figure 18-7. Schematic cross section of the Himalayas showing the dehydration and partial melting zones that produced the leucogranites. After France-Lanord and Le Fort (1988) Trans. Roy. Soc. Edinburgh, 79, 183-195. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Granitoid Rocks Granitoid Rocks Table 18-4. A Classification of Granitoid Rocks Based on Tectonic Setting. After Pitcher (1983) in K. J. Hsü (ed.), Mountain Building Processes, Academic Press, London; Pitcher (1993), The Nature and Origin of Granite, Blackie, London; and Barbarin (1990) Geol. Journal, 25, 227-238. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Table 18-4. A Classification of Granitoid Rocks Based on Tectonic Setting. After Pitcher (1983) in K. J. Hsü (ed.), Mountain Building Processes, Academic Press, London; Pitcher (1993), The Nature and Origin of Granite, Blackie, London; and Barbarin (1990) Geol. Journal, 25, 227-238. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Figure 9-8.Figure 9-8. (a)(a) after Pearce and Cann (1973), after Pearce and Cann (1973), Earth Planet, Sci. Lett., Earth Planet, Sci. Lett., 1919, 290-300, 290-300. . (b)(b) after Pearce (1982) after Pearce (1982) in Thorpe (ed.), in Thorpe (ed.), Andesites: Orogenic andesites and related rocks. Wiley. Chichester. pp. 525-548Andesites: Orogenic andesites and related rocks. Wiley. Chichester. pp. 525-548, Coish et al. (1986), , Coish et al. (1986), Amer. J. Sci., Amer. J. Sci., 286286, 1-28, 1-28.. (c)(c) after Mullen (1983), after Mullen (1983), Earth Planet. Sci. Lett., Earth Planet. Sci. Lett., 6262, 53-62., 53-62.Granitoid Rocks Granitoid Rocks Table 18-3. The S-I-A-M Classification of GranitoidsTypeSiO2K2O/Na2OCa, Sr A/(C+N+K)*Fe3+/Fe2+Cr, Niδ18O87Sr/86SrMisc PetrogenesisM46-70% low high low low low < 9‰ < 0.705 Low Rb, Th, U Subduction zoneLow LIL and HFS or ocean-intraplateMantle-derivedI53-76% low high in low: metal- moderate low < 9‰ < 0.705 high LIL/HFS Subduction zonemafic uminous to med. Rb, Th, U Infracrustalrocks peraluminous hornblende Mafic to intermed.magnetite igneous sourceS65-74% high low high low high > 9‰ > 0.707 variable LIL/HFS Subduction zonehigh Rb, Th, Umetaluminous biotite, cordierite Supracrustal Als, Grt, Ilmenite sedimentary sourceAhighNa2Olow var var low var var low LIL/HFS Anorogenic→ 77% high peralkaline high Fe/Mg Stable craton high Ga/Al Rift zoneHigh REE, ZrHigh F, Cl* molar Al2O3/(CaO+Na2O+K2O)Data from White and Chappell (1983), Clarke (1992), Whalen