Download LECTURE W1-L2 - Earth Structure

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Transcript
Structure of the Earth
The upper part of the solid Earth
Crust
•Oceanic
•Continental
Mantle
•Lithosphere
•Astenosphere
Plates and plate boundaries
Geological activity is concentrated on plate boundaries
Types of plate boundaries
Mid-Atlantic ridge
Chile subduction
Himalayan collision
San Andreas fault
Rifting of continental crust to form a new ocean basin
Subducting oceanic
lithosphere deforms
sediment at edge of
continental plate
Collision – welding
together of continental
crust
Post-collision: two
continental plates are
welded together, mountain
stands where once was
ocean
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. Winter, From Dziewonski and Anderson (1981).
Phys. Earth Planet. Int., 25, 297-356. © Elsevier Science.
The
Geothermal
Gradient
Pattern of global heat flux variations compiled from
observations at over 20,000 sites and modeled on a
spherical harmonic expansion to degree 12. From Pollack,
Hurter and Johnson. (1993) Rev. Geophys. 31, 267-280.
Cross-section of the mantle based on a seismic tomography model. Arrows
represent plate motions and large-scale mantle flow and subduction zones
represented by dipping line segments. EPR =- East pacific Rise, MAR = MidAtlantic Ridge, CBR = Carlsberg Ridge. Plates: EA = Eurasian, IN = Indian, PA =
Pacific, NA = North American, SA = South American, AF = African, CO = Cocos.
From Li and Romanowicz (1996). J. Geophys. Research, 101, 22,245-72.
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 1-11. Winter, 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).
How to melt?
• Increase T
• Decrease P
• Move the solidus
Plate Tectonic - Igneous
Genesis
1. Mid-ocean Ridges
2. Intracontinental
Rifts
3. Island Arcs
4. Active Continental
Margins
5. Back-arc Basins
6. Ocean Island Basalts
7. Miscellaneous IntraContinental Activity

kimberlites, carbonatites,
anorthosites...