EARTH’S INTERNAL STRUCTURE AND MAGMA FORMATION PROCESSES

EARTH’S INTERNAL STRUCTURE AND MAGMA FORMATION

PROCESSES

Continental crust

Oceanic crust

Crust-mantle boundary (MOHO)

Upper mantle (down to 660-670 km)

Mantle is subdivided mainly based on seismic wave velocities

Nature

Information from seismic waves

“CAT-scan” of the mantle, using SEISMIC TOMOGRAPHY

Faster seismic velocity

Colder and stronger rocks

Slower seismic velocity

Warmer and weaker rocks

Nature

Red = Slow seismic velocityBlue = Fast seismic velocity

Seismic tomography shows that some parts of the mantle are hotter than others

Would result in heat transfer

Conduction in lithosphere

Convection in asthenosphere

Fig. 2.13, page 31

CONVECTION

• Heat transfer that results when warmer, less dense material rises, and cooler, denser material sinks

http://www.columbia.edu/itc/ldeo/mutter/jcm/Topic3/Topic3.html

CONVECTION

• Convection within the mantle used to be considered by some to be a major driving mechanism of plate tectonics (“ridge push” mechanism, page 30)

http://www.columbia.edu/itc/ldeo/mutter/jcm/Topic3/Topic3.html

http://anquetil.colorado.edu/szhong/

Melting by lowering pressure Melting temperature of a solid goes

UP under high pressure (becomes difficult to melt)

Melting temperature of a solid goes DOWN under low pressure (becomes easier to melt)

Is the major process of magma generation at divergent boundaries and hot spots (pages 30-31)

At divergent boundaries and hot spots, lithosphere becomes thinner

due to pulling from subducting slabs

Pressure is reduced and hot rocks from asthenosphere move upward (convection)

Rocks start to melt

Melting caused by decreasing pressure is called DECOMPRESSION MELTING

Example: Hawaii (hot spot)Mid-Atlantic Ridge (divergent boundary)

A little note on hot spots …

• Hot spot volcanoes are NOT associated with any plate boundary (example: Hawaii, Yellowstone, Galapagos island etc.)

• They develop over columns of very hot, plastic rock called MANTLE PLUMES (pages 39-44)

LINK TO: http://karel.troja.mff.cuni.cz/staff/HANKA_CIZKOVA/Anim/animace.htm

Dr. Hana Cizkova (Kyvalova)

Adding water under pressure

Melting temperature of a solid goes DOWN when water is added (wet rocks melt more easily than dry rocks)

Is the major process of magma generation at subduction zones (page 37, figure 2.18)

Increasing temperature:

When magma passes through and melts other solid rocks

Not a major process of magma formation

EARTH’S INTERNAL STRUCTURE AND MAGMA FORMATION PROCESSES

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