Wingman Arrows

La Douleur Est Temporaire, La Victoire Est Toujours

01. Intro – Igneous Petrology

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The Earth’s Interior

Crust:

  • Oceanic crust: Thin: 10 km, Relatively uniform stratigraphy. ophiolite suite: Sediments, pillow basalt, sheeted dikes, more massive gabbro, ultramafic (mantle)
  • Continental Crust: Thicker: 20-90 km average ~35 km, Highly variable composition, Average ~ granodiorite

image Mantle: Peridotite (ultramafic)

  • Upper to 410 km (olivine ® spinel), Low Velocity Layer 60-220 km
  • Transition Zone as velocity increases ~ rapidly, 660 spinel -> perovskite-type SiIV –> SiVI
  • Lower Mantle has more gradual velocity increase

Core: Fe-Ni metallic alloy

  • Outer Core is liquid, No S-waves
  • Inner Core is solid

image image

Figure 1-2. Major subdivisions of the Earth. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

image 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.

image

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 Gradient

  • P increases = rgh
  • Nearly linear through mantle
  • ~ 30 MPa/km
  • » 1 GPa at base of ave crust
  • Core: r incr. more rapidly since alloy more dense

image

Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25, 297-356. © Elsevier Science.

Heat Sources in the Earth

1. Heat from the early accretion and differentiation of the Earth

  • still slowly reaching surface

2. Heat released by the radioactive breakdown of unstable nuclides

Heat Transfer

  1. Radiation
  2. Conduction
  3. Convection

The Geothermal Gradient

image

Figure 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

image

  1. Mid-ocean Ridges
  2. Intracontinental Rifts
  3. Island Arcs
  4. Active Continental Margins
  5. Back-arc Basins
  6. Ocean Island Basalts
  7. Miscellaneous Intra- Continental Activity
    1. kimberlites, carbonatites, anorthosites…

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John Winter

Author: MualMaul

leaving as a legend!!!

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