1. Fundamental Concepts GLY 4310 Spring, 2013
Petrology Lecture 1
Fundamental Concepts
GLY 4310
Spring, 2013

2. Major Subdivisions of the Earth

3. Seismic Wave Velocities versus Depth
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.

4. Origin of the Solar System
Solar Nebula
Rotational Flattening
Gravitational Collapse
Initiation of nuclear reactions
Planetesimal formation

5. Processes within the Disc
Strong gradients
Escape of volatiles
Retention of refractory compounds

6. Composition of the Earth
Element Weight Percent Atom percent Volume percent
O ≈ 94
Si ┐
Al │
Fe │
Ca ├ ≈ 6
Na │
K │
Mg ┘ Ti H P

7. Goldschmidt Classification
Lithophile: Literally, "stone-loving". Elements which incorporate into silicate phases, generally of low density.
Chalcophile: Literally, "copper-loving". However, since copper often forms sulfide phases, this really means elements which form sulfide phases, typically of intermediate density.
Siderophile: Literally, "Iron-loving". Elements, typically iron and alloying elements, which form a dense sulfide phase.
Atomphile: Light, gaseous elements. Some may have been retained during initial accretion, but most were lost to space. These substances, which form the atmosphere and oceans, probably accumulated slowly later in the earth's history.

8. Density Calculations Whole earth density = 5.52 g/cm3
Crustal rocks is around 3.0 g/cm3
Infer that there is a region of much higher density within the earth

9. Abundance of Elements .

10. Additional Constraints
Laboratory studies of seismic wave velocities
Natural samples of the mantle

11. Meteorites
Pieces of extra-terrestrial solid material that survive the plunge through the earth's atmosphere
Geological concentration of meteorites

12. Meteorite Categories
Irons
Stones
Stony-irons
Collection problems

13. Gradients
Both temperature and pressure increase with increasing depth below the surface
Geothermal gradient
Geobarometric gradient

14. Heat Loss
Radiation
Conduction
Convection
Advection

15. Importance of Heat Loss
Processes controlled by heat loss:
Metamorphism
Melting
Crystaliization

16. Geotherms
Figure Estimates of oceanic (blue curves) and continental shield (red curves) geotherms to a depth of 300 km. The thickness of mature (> 100Ma) oceanic lithosphere is hatched and that of continental shield lithosphere is yellow. Data from Green and Falloon ((1998), Green & Ringwood (1963), Jaupart and Mareschal (1999), McKenzie et al. (2005 and personal communication), Ringwood (1966), Rudnick and Nyblade (1999), Turcotte and Schubert (2002).

17. Pressure at the Base of the Crust
Putting units into the equation, we get:
~ 30 MPa/km
» 1 GPa at base of average crust

18. Units of Pressure
Traditionally, pressure was expressed in units of bars or kilobars
1 bar = 105 Pa (0.1MPa), so this is about 300 bars or 0.3 kbars/km
For the upper mantle, ρ ≈3.35 g/cm3. This gives a pressure gradient of about 35 Mpa/km
Remember that these numbers are good only near the earth’s surface
Core: ρ increases more rapidly since alloy more dense

19. Geobarometric Gradient
P increases = ρgh
Nearly linear through mantle
Figure shows the PREM (Preliminary Reference Earth Model) of Dziewonski and Anderson, which is a better reference to consult for pressures at depth within the earth

20. Tectonics and Magma Generation
5. Back-arc Basins
6. Ocean Island Basalts
7. Miscellaneous Intra Continental Activity
Kimberlites, Carbonatites, Anorthosites...
1. Mid-ocean Ridges
2. Intracontinental Rifts
3. Island Arcs
4. Active Continental Margins