The Earth’s Interior
- 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
- 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
Figure 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 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
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
The Geothermal Gradient
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
- Mid-ocean Ridges
- Intracontinental Rifts
- Island Arcs
- Active Continental Margins
- Back-arc Basins
- Ocean Island Basalts
- Miscellaneous Intra- Continental Activity
- kimberlites, carbonatites, anorthosites…