Ch 01 Intro.ppt

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  • Igneous PetrologyJohn Winter

  • The Earths InteriorCrust:Oceanic crustThin: 10 kmRelatively uniform stratigraphy = ophiolite suite: Sedimentspillow basaltsheeted dikesmore massive gabbroultramafic (mantle)Continental CrustThicker: 20-90 km average ~35 kmHighly variable compositionAverage ~ granodiorite

  • The Earths InteriorMantle:Peridotite (ultramafic)Upper to 410 km (olivine spinel) Low Velocity Layer 60-220 kmTransition Zone as velocity increases ~ rapidly660 spinel perovskite-type SiIV SiVILower Mantle has more gradual velocity increaseFigure 1-2. Major subdivisions of the Earth. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

  • The Earths InteriorCore: Fe-Ni metallic alloyOuter Core is liquidNo S-wavesInner Core is solidFigure 1-2. Major subdivisions of the Earth. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

  • Figure 1-3. Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left, rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. Blackwell Scientific. Oxford.

  • Figure 1-5. Relative atomic abundances of the seven most common elements that comprise 97% of the Earth's mass. An Introduction to Igneous and Metamorphic Petrology, by John Winter , Prentice Hall.

  • The Pressure GradientP increases = rghNearly linear through mantle~ 30 MPa/km 1 GPa at base of ave crustCore: r incr. more rapidly since alloy more denseFigure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25, 297-356. Elsevier Science.

  • Heat Sources in the Earth1. Heat from the early accretion and differentiation of the Earthstill slowly reaching surface

  • Heat Sources in the Earth1. Heat from the early accretion and differentiation of the Earthstill slowly reaching surface2. Heat released by the radioactive breakdown of unstable nuclides

  • Heat Transfer1. Radiation2. Conduction3. Convection

  • The Geothermal GradientFigure 1-9. Estimated ranges of oceanic and continental steady-state geotherms to a depth of 100 km using upper and lower limits based on heat flows measured near the surface. After Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311.

  • Plate Tectonic - Igneous Genesis 1. Mid-ocean Ridges2. Intracontinental Rifts3. Island Arcs4. Active ContinentalMargins 5. Back-arc Basins6. Ocean Island Basalts7. Miscellaneous Intra-Continental Activitykimberlites, carbonatites, anorthosites...

    1. RadiationRequires transparent mediumRocks arent (except perhaps at great depth)2. ConductionRocks are poor conductorsVery slow3. ConvectionMaterial movement (requires ductility)Heat-induced expansion and buoyancyMuch more efficient than conduction

    Continental Gradient higher than Oceanic GradientRange for bothHighest at Surfacewater and cold surfaceIn the future we will often use average values rather than the ranges