Geol 2311 – Mineralogy/Petrology I Fall 2001Lecture 1 - Magmas, lavas and igneous rocks – chemistry, mineralogy and rock classificationIgneous Petrology – the study of rocks formed from the solidification of magmaMagma – a chemically complex, high-temperature, viscous liquidMinor elements (2.0 – 0.1 wt%) e.g., Ti, Mn, Na, PMagma →into →RockMineral Assemblage - ƒ (magma composition, temperature, (pressure))Partitioning of elements among igneous mineralsMagmaPlagioclaseGeol 2311 – Mineralogy/Petrology I Fall 2001Lecture 1 - Magmas, lavas and igneous rocks – chemistry, mineralogy and rock classificationIgneous Petrology – the study of rocks formed from the solidification of magmaAttempts to:- determine the physical and chemical conditions of magma formation, transport and crystallization- explain the compositional diversity of igneous rocks and their parent magma- understand the tectonomagmatic history of the earth Magma – a chemically complex, high-temperature, viscous liquid Composition: variable, very generally classified as Ultramafic, Mafic, Intermediate, or Felsic Major elements (>2 wt. %) e.g., Si, Al, Fe, Mg, Ca, Minor elements (2.0 – 0.1 wt%) e.g., Ti, Mn, Na, PTrace elements (< 0.1 wt.%; measured in ppm or ppb)Temperature - ƒ (environment of magma formation, composition of source material)Viscosity (stickiness) - ƒ (temperature, composition (esp.silica content))Gas (Volatile) Content - ƒ (composition, pressure)General Magma Type: Ultramafic Mafic Intermediate FelsicTemperature: 1550º to 1600º 1250º to 1050º 1150º to 950º 1050º to 800ºViscosity: Low Low Intermediate HighGas Content: Very Low (<<1%) Low (<1%) Intermediate (1-3%) High (2-5%)Composition (wt. %)SiO246.5 50.0 57.7 70.5TiO20.3 1.9 1.0 0.3Al2O33.1 15.9 16.6 14.1FeO 11.2 10.3 7.2 2.8MnO 0.2 0.2 0.1 < 0.1MgO 32.9 7.0 3.7 0.7CaO 4.8 9.7 6.5 1.7Na2O .1 2.9 3.4 3.6K2O .01 1.1 1.8 3.9P2O5n.a. 0.3 0.3 0.1Total 99.0 99.3 98.3 97.8Trace Elements (ppm)Cr 3000 200 10 2Ni 1000 150 15 2Ba 20 40 300 350Zr 10 35 200 170Magma → into →Rock Mineral Assemblage - ƒ (magma composition, temperature, (pressure))Partitioning of elements among igneous mineralsElements1235ºMagma1235ºOlivine1225ºPlagioclase1180ºCa Pyroxene1160ºFe-Ti Oxide- LiquidusTemperatureSiO250 X X XAl2O316 X (X)FeO 10 X X XMgO 9 X XCaO 9 X XNa2O 2.3 XK2O 0.5 XTiO22 (X) XOH 0.2100% 12% 55% 27% 6% = GABBRO /BASALTRock Classification Schemes- Modal Classifications (for plutonic rocks) Granitic and Intermediate Rocks – QAPF (Figure 3-2, B&T)Mafic Rocks – variety of schemes, most based on proportions of Ol, Pyx, Pl, Ox (see next page)Ultramafic Rocks – based on Ol, Opx, Cpx (See Fig 3-4, B&T)- Cumulate Classifications (Texture-based)- Normative Classifications (for volcanic rocks)CIPW norm compositions plotted on modal classifications (e.g., Fig. 3-5, B&T)- Chemical Classifications (for volcanic rocks)AFM, Alkali-Lime, Alkali-Silica, Harker
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