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Petrology Lecture 1
Fundamental Concepts
GLY 4310
Spring, 2012
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
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
4
Abundance of Elements
5
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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Geobarometric
Gradient
• P increases = ρgh
• Nearly linear through
mantle
• ~ 30 MPa/km
• » 1 GPa at base of
average crust
• Core: ρ increases more
rapidly since alloy more
dense
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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...
8