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

Major Subdivisions of the Earth

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.

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

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

Composition of the Earth Element Weight Percent Atom percent Volume percent O 46.60 62.55 ≈ 94 Si 26.72 21.22┐ Al 8.13 6.47│ Fe 5.00 1.92│ Ca 3.63 1.94├ ≈ 6 Na 2.83 2.64│ K 2.59 1.42│ Mg 2.09 1.84┘ Ti 0.44 H 0.14 P 0.10

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.

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

Abundance of Elements .

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

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

Meteorite Categories Irons Stones Stony-irons Collection problems

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

Heat Loss Radiation Conduction Convection Advection

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

Geotherms Figure 1.11 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).

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

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

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

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