Transcript Petrology - FAU-Department of Geosciences

Petrology Lecture 1
Fundamental Concepts
GLY 4310
Spring, 2013
1
Major
Subdivisions of
the Earth
2
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.
3
Origin of the Solar System
•
•
•
•
•
Solar Nebula
Rotational Flattening
Gravitational Collapse
Initiation of nuclear reactions
Planetesimal formation
4
Processes within the Disc
• Strong gradients
• Escape of volatiles
• Retention of refractory compounds
5
Composition of the Earth
• Element
Weight Percent Atom percent
•
•
•
•
•
•
•
•
•
•
•
46.60
26.72
8.13
5.00
3.63
2.83
2.59
2.09
0.44
0.14
0.10
O
Si
Al
Fe
Ca
Na
K
Mg
Ti
H
P
62.55
21.22┐
6.47│
1.92│
1.94├
2.64│
1.42│
1.84┘
Volume percent
≈ 94
≈ 6
6
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.
7
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
8
Abundance of Elements
9
Additional Constraints
• Laboratory studies of seismic wave
velocities
• Natural samples of the mantle
10
Meteorites
• Pieces of extra-terrestrial solid material that
survive the plunge through the earth's
atmosphere
• Geological concentration of meteorites
11
Meteorite Categories
•
•
•
•
Irons
Stones
Stony-irons
Collection problems
12
Gradients
• Both temperature and pressure increase with
increasing depth below the surface
 Geothermal gradient
 Geobarometric gradient
13
Heat Loss
•
•
•
•
Radiation
Conduction
Convection
Advection
14
Importance of Heat Loss
• Processes controlled by heat loss:
 Metamorphism
 Melting
 Crystaliization
15
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).
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Pressure at the Base of the Crust
• Putting units into the equation, we get:
P  2800kg m  9.8m s  35,000m 
3
2
9.6  10 kg ms  9.6  10 Pa  1GPa
8
2
8
• ~ 30 MPa/km
• » 1 GPa at base of average crust
17
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
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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
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Tectonics and Magma Generation
•
•
•
•
• 5. Back-arc Basins
1. Mid-ocean Ridges
2. Intracontinental Rifts • 6. Ocean Island Basalts
• 7. Miscellaneous Intra3. Island Arcs
Continental Activity
4. Active Continental
 Kimberlites, Carbonatites,
Margins
Anorthosites...
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