EARTH’S INTERNAL STRUCTURE AND MAGMA FORMATION PROCESSES.
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Transcript of EARTH’S INTERNAL STRUCTURE AND MAGMA FORMATION PROCESSES.
![Page 1: EARTH’S INTERNAL STRUCTURE AND MAGMA FORMATION PROCESSES.](https://reader038.fdocuments.net/reader038/viewer/2022103005/56649d215503460f949f70b0/html5/thumbnails/1.jpg)
EARTH’S INTERNAL STRUCTURE AND MAGMA FORMATION
PROCESSES
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Continental crust
Oceanic crust
Crust-mantle boundary (MOHO)
Upper mantle (down to 660-670 km)
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Mantle is subdivided mainly based on seismic wave velocities
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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
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Nature
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Red = Slow seismic velocityBlue = Fast seismic velocity
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Seismic tomography shows that some parts of the mantle are hotter than others
Would result in heat transfer
Conduction in lithosphere
Convection in asthenosphere
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Fig. 2.13, page 31
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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
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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
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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)
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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
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Melting caused by decreasing pressure is called DECOMPRESSION MELTING
Example: Hawaii (hot spot)Mid-Atlantic Ridge (divergent boundary)
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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)
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LINK TO: http://karel.troja.mff.cuni.cz/staff/HANKA_CIZKOVA/Anim/animace.htm
Dr. Hana Cizkova (Kyvalova)
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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)
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Increasing temperature:
When magma passes through and melts other solid rocks
Not a major process of magma formation