Matthew Polacek
Web Summary
September 22nd web summary
Diagram of the earth (corrected), convection equation, s waves do not reach the core
because the outer core is liquid, “The inner workings of the earth” – in intro course
Convection Movies/ models: D double prime layer, plumes are born here boundary
between the core and mantle, subduction occurs because we have mechanisms
cooling or dripping down
Rising plumes results in volcanism this means that the outside of the planet is a
function of this mechanism of convection  or getting rid of its heat.
Pie slice, mechanism of cooling is convection which works well, hits lithosphere,
lithosphere cools by conduction. In some planets the lithosphere is made from a
solid lithosphere. “One Plate Planets” …. Earth is the only planet that we know of
thus far that has a “mobile lid planet”, our lithosphere is broken into plates
Asthenosphere: part of the upper mantle, slightly ductile because it mixes wit water
are results in a more ductile material, low velocity and low viscosity zone, slows
because of liquid, makes it slippery and allows lithosphere to move above.
Manifestation of hot planet volcanism, the result of this is a function of the
lithosphere
Hotspots, core mantle boundary, has nothing to do with the surface but rather whats
going on in in the depths
Venus and large shield volcanoes, ‘stability of the plumes’
On mars they are all in the same locations, only 2 major hotspots,
You don’t need plate tectonics to have volcanism, tectism anytime you move heat
you will break up lithosphere radially
We know the composition of the mantle, and what come out of the melt are basalts
Another consequence of convection: heat energy results in expansion and inversely
cooling results in reduction,  temperature of conduction mantle change in
temperature with depth is equal to .3 kelvin per Km or 1.0 K per kilobar
Mantle is adiabatic, this equation determines the adiabat
Lithosphere is solid, so there is a linear gradient of temperature change between the
mantle and lithosphere boundary this heat is transferred through conduction not
convection
Magnesium in your basalts, the amount of Mg in your basalt is a function of the
temperature of your melt, hotter temperature=more magnesium, this is how we
know the earth used to be hotter, the magnesium content of older basalts is higher
Melts can only occur at lower pressures regardless of temperature, this change
occurs at the solidus,
Figure at the end of class
Temperature and depth: solidus crosses the adiabate, then the solid becomes a
liquid, the intersection can occur at greater depths, greater depths have different
composition in addition to more of a melt, the reason for melting is different in each
case. Hot spots can cause shifts in the adiabat, results in enhanced melting. At
subduction zones you change the composition of the mantle making it easier to melt.